PFManual 14 1 en Ed1 Vol II PDF

DIgSILENT PowerFactoryVersion 14.1

User’s ManualVolume II

Edition 1

DIgSILENT GmbH

Gomaringen, Germany

May 2011

Publisher:

DIgSILENT GmbH

Heinrich-Hertz-Straße 9

72810 Gomaringen / Germany

Tel.: +49 (0) 7072 - 9168-0

Fax: +49 (0) 7072 - 9168-88

Please visit our homepage at:

http://www.digsilent.de

Copyright DIgSILENT GmbHAll rights reserved. No part of this publication may be reproduced or distributed in any form without per-mission of the publisher.

May 2011

DIgSILENT PowerFactory User’s Manual

Contents of Volume I

General InformationAbout this Guide 1-11.1 Contents of the User’s Manual . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1-11.2 Used Conventions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1-2Contact 2-1Documentation and Help System 3-1PowerFactory Overview 4-14.1 General Concept . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-24.2 PowerFactory Simulation Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-34.3 General Design of PowerFactory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-44.4 Data Arrangement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-64.5 User Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-8

4.5.1 Menu Bar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-114.5.2 Main Toolbar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-114.5.3 The Output Window. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-15

4.6 Getting Help . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-19The PowerFactory Data Model 5-15.1 Database, Objects and Classes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-15.2 PowerFactory Project Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-2

5.2.1 The Library . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-35.2.2 The Network Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-55.2.3 Operation Scenarios. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-55.2.4 Study Cases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-65.2.5 Changed Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-6

5.3 The Network Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-75.3.1 Network Diagrams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-85.3.2 Network Topology Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-105.3.3 Network Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-125.3.4 Variations and Expansion Stages . . . . . . . . . . . . . . . . . . . . . . . . . . .5-175.3.5 Switching Rules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-19

5.4 The Equipment Type Library . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-215.5 The Operational Library . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-22

5.5.1 Circuit Breaker Ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-235.5.2 Demand Transfer. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-245.5.3 Faults . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-255.5.4 Capability Curves for Generators . . . . . . . . . . . . . . . . . . . . . . . . . . .5-29

i


5.5.5 Outages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-295.5.6 Running Arrangements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-315.5.7 Thermal Ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-32

5.6 Parameter Characteristics and Parametric Studies. . . . . . . . . . . . . . . . . . . . 5-335.7 DIgSILENT Programming Language (DPL) Scripts . . . . . . . . . . . . . . . . . . . . 5-33

AdministrationProgram Administration 6-16.1 Program Installation and Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-16.2 The Log-on Dialogue . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-1

6.2.1 Log On Configuration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-26.2.2 License Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-36.2.3 Network Settings. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-46.2.4 Database Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-56.2.5 Advanced Settings. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-56.2.6 Appearance Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-5

User Accounts and User Groups 7-17.1 PowerFactory Database Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-17.2 The Database Administrator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-27.3 Creating and Managing User Accounts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-27.4 Creating User Groups. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-37.5 The Demo Account . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-4User Settings 8-18.1 General Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-18.2 Graphic Windows Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-28.3 Data Manager Settings. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-48.4 Output Window Settings. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-58.5 Functions Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-58.6 Directories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-68.7 Editor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-68.8 StationWare . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-7

HandlingExecuting Power System Analyses 9-19.1 Defining or Activating a Project . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-19.2 Creating of a Network Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-19.3 Calculation Commands in PowerFactory . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-19.4 Edit relevant Objects for Calculation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-39.5 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-3Basic Project Definition 10-110.1 Defining and Configuring a Project . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-1

ii


10.1.1 The Project Edit Dialogue . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-310.1.2 Project Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-410.1.3 Activating and Deactivating Projects . . . . . . . . . . . . . . . . . . . . . . .10-510.1.4 Exporting and Importing of Projects . . . . . . . . . . . . . . . . . . . . . . .10-6

10.2 Creating New Grids. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-6Network Graphics (Single Line Diagrams) 11-111.1 Defining Network Models with the Graphical Editor . . . . . . . . . . . . . . . . . .11-1

11.1.1 Adding New Power System Elements . . . . . . . . . . . . . . . . . . . . . . .11-111.1.2 Drawing Nodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11-311.1.3 Drawing Branch Elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11-411.1.4 Marking and Editing Power System Elements . . . . . . . . . . . . . . . . .11-511.1.5 Interconnecting Power Subsystems . . . . . . . . . . . . . . . . . . . . . . . .11-611.1.6 Working with Substations in the Graphical Editor . . . . . . . . . . . . . .11-911.1.7 Working with Branches in the Graphical Editor . . . . . . . . . . . . . . . 11-1011.1.8 Working with Templates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-1011.1.9 Defining and Working with Transmission Lines . . . . . . . . . . . . . . . 11-1211.1.10 Working with Single Phase Elements . . . . . . . . . . . . . . . . . . . . . 11-15

11.2 Graphic Windows and Database Objects . . . . . . . . . . . . . . . . . . . . . . . . . 11-1511.2.1 Network Diagrams and Graphical Pages . . . . . . . . . . . . . . . . . . . . 11-1611.2.2 Active Graphics, Graphics Board and Study Cases . . . . . . . . . . . . . 11-1611.2.3 Single Line Graphics and Data Objects . . . . . . . . . . . . . . . . . . . . . 11-1811.2.4 Editing and Selecting Objects . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-1811.2.5 Creating New Graphic Windows. . . . . . . . . . . . . . . . . . . . . . . . . . 11-21

11.3 Basic Functionality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-2211.3.1 The Page Tab . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-2211.3.2 The Drawing Toolboxes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-2311.3.3 The Active Grid Folder (Target Folder) . . . . . . . . . . . . . . . . . . . . . 11-23

11.4 Drawing Diagrams with already existing Network Elements . . . . . . . . . . . 11-2411.4.1 Drawing Existing Terminals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-2411.4.2 Drawing Existing Lines, Switch Gears and Transformers. . . . . . . . . 11-2511.4.3 Building Single line Diagram from Imported Data . . . . . . . . . . . . . 11-2511.4.4 Creating a new substation in an Overview Diagram. . . . . . . . . . . . 11-2811.4.5 Show Detailed Substation Graphic . . . . . . . . . . . . . . . . . . . . . . . . 11-29

11.5 Drawing of Network Components from Templates or Predefined Objects . . 11-2911.6 Graphic Commands, Options and Settings. . . . . . . . . . . . . . . . . . . . . . . . 11-30

11.6.1 General Commands and Settings . . . . . . . . . . . . . . . . . . . . . . . . . 11-3011.6.2 Commands and Settings for Block Diagrams and Single Line Graphics11-3711.6.3 Commands and Settings for Single Line Graphics . . . . . . . . . . . . . 11-3811.6.4 Graphic Layers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-4111.6.5 Diagram Colouring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-4511.6.6 Colour Legend Block On/Off . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-4611.6.7 The Title Block. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-4611.6.8 The Legend Block . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-4711.6.9 Editing and Changing Symbols of Elements . . . . . . . . . . . . . . . . . 11-47

11.7 Result Boxes, Text Boxes and Labels . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-4711.7.1 General Concept . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-4711.7.2 Editing Result Boxes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-4911.7.3 Formatting Result Boxes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-5111.7.4 Text Boxes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-5111.7.5 Labels. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-52

iii


Data Manager 12-112.1 Using the Data Manager . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-1

12.1.1 Moving Around in the Database Tree. . . . . . . . . . . . . . . . . . . . . . . 12-312.1.2 Adding New Items. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-412.1.3 Deleting an Item . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-612.1.4 Cut, Copy, Paste and Move Objects. . . . . . . . . . . . . . . . . . . . . . . . 12-612.1.5 The Data Manager Message Bar . . . . . . . . . . . . . . . . . . . . . . . . . . 12-712.1.6 Additional Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-7

12.2 Defining Network Models with the Data Manager . . . . . . . . . . . . . . . . . . . 12-812.2.1 Defining New Network Components in the Data Manager . . . . . . . . 12-912.2.2 Connecting Network Components in the Data Manager . . . . . . . . . . 12-912.2.3 Defining Substations in the Data Manager . . . . . . . . . . . . . . . . . . . 12-912.2.4 Defining Branches in the Data Manager . . . . . . . . . . . . . . . . . . . . 12-1012.2.5 Defining Sites in the Data Manager . . . . . . . . . . . . . . . . . . . . . . . 12-1112.2.6 Editing Network Components using the Data Manager . . . . . . . . . 12-11

12.3 Searching for Objects in the Data Manager. . . . . . . . . . . . . . . . . . . . . . . 12-1212.3.1 Sorting Objects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-1212.3.2 Searching by Name . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-1312.3.3 Using Filters for Search . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-13

12.4 Editing Data Objects in the Data Manager . . . . . . . . . . . . . . . . . . . . . . . 12-1612.4.1 Editing in Object Mode. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-1712.4.2 Editing in "Detail'' Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-1712.4.3 Copy and Paste while Editing . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-19

12.5 The Flexible Data Page Tab in the Data Manager . . . . . . . . . . . . . . . . . . 12-2012.5.1 Customizing the Flexible Data Page. . . . . . . . . . . . . . . . . . . . . . . 12-21

12.6 The Input Window in the Data Manager. . . . . . . . . . . . . . . . . . . . . . . . . 12-2212.6.1 Input Window Commands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-22

12.7 Save and Restore Parts of the Database. . . . . . . . . . . . . . . . . . . . . . . . . 12-2312.7.1 Notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-24

12.8 Spreadsheet Format Data Import/Export . . . . . . . . . . . . . . . . . . . . . . . . 12-2512.8.1 Export to Spreadsheet Programs (e. g. MS EXCEL) . . . . . . . . . . . . 12-2512.8.2 Import from Spreadsheet Programs (e. g. MS EXCEL) . . . . . . . . . . 12-26

Study Cases 13-113.1 Creating and Using Study Cases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-213.2 Summary Grid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-313.3 Study Time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-313.4 The Study Case Edit Dialogue . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-413.5 Variation Configuration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-613.6 Operation Scenarios . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-613.7 Commands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-613.8 Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-7

13.8.1 Switch Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-813.8.2 Set Parameter Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-813.8.3 Short-Circuit Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-813.8.4 Intercircuit Fault Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-813.8.5 Events of Synchronous Machines . . . . . . . . . . . . . . . . . . . . . . . . . 13-813.8.6 Events of Loads. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-913.8.7 Outage of Element . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-913.8.8 Save Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-9

13.9 Results Objects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-913.10 Variable Sets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-11

iv


13.11 Triggers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-1213.12 Graphic Board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-12Project Library 14-114.1 Equipment Type Library . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-114.2 Operational Library. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14-2

14.2.1 Circuit Breaker Ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14-314.2.2 Demand Transfers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14-414.2.3 Fault Cases and Fault Groups . . . . . . . . . . . . . . . . . . . . . . . . . . . .14-514.2.4 Capability Curves (MVAr Limit Curves) for Generators . . . . . . . . . . .14-614.2.5 Element Outages and Generator Deratings . . . . . . . . . . . . . . . . . . .14-714.2.6 Running Arrangements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14-914.2.7 Thermal Ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-12

14.3 Templates Library. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-1314.4 Global Template Library . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-14Grouping Objects 15-115.1 Areas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15-115.2 Virtual Power Plants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15-1

15.2.1 Defining and Editing a New Virtual Power Plant. . . . . . . . . . . . . . . .15-215.2.2 Applying a Virtual Power Plant. . . . . . . . . . . . . . . . . . . . . . . . . . . .15-315.2.3 Inserting a Generator into a Virtual Power Plant and Defining its Virtual Power

Plant Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15-315.3 Boundaries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15-415.4 Circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15-615.5 Feeders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15-615.6 Network Operators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15-915.7 Network Owners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15-915.8 Paths . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-1015.9 Zones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-10Operation Scenarios 16-116.1 Operation Scenarios’ Background. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16-116.2 How to use Operation Scenarios . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16-3

16.2.1 How to create an Operation Scenario. . . . . . . . . . . . . . . . . . . . . . .16-316.2.2 How to save an Operation Scenario . . . . . . . . . . . . . . . . . . . . . . . .16-416.2.3 How to activate an existing Operation Scenario. . . . . . . . . . . . . . . .16-516.2.4 How to deactivate an Operation Scenario . . . . . . . . . . . . . . . . . . . .16-516.2.5 How to identify operational data parameters . . . . . . . . . . . . . . . . .16-6

16.3 Administering Operation Scenarios . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16-716.3.1 How to view objects missing from the Operation Scenario data . . . .16-716.3.2 How to compare the data in two operation scenarios . . . . . . . . . . .16-816.3.3 How to view the non-default Running Arrangements . . . . . . . . . . . .16-816.3.4 How to transfer data from one Operation Scenario to another . . . . .16-816.3.5 How to update the default data with operation scenario data . . . . . .16-916.3.6 How exclude a grid from the Operation Scenario data . . . . . . . . . . .16-916.3.7 How to create a time based Operation Scenario . . . . . . . . . . . . . . 16-10

16.4 Advanced Configuration of Operation Scenarios. . . . . . . . . . . . . . . . . . . . 16-1216.4.1 How to change the automatic save settings for Operation Scenarios16-1216.4.2 How to modify the data stored in Operation Scenarios. . . . . . . . . . 16-12

v


Network Variations and Expansion Stages 17-117.1 Basic Functionality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-117.2 Creating New Variations and Expansion Stages. . . . . . . . . . . . . . . . . . . . . 17-217.3 Activating Variations and Expansion Stages . . . . . . . . . . . . . . . . . . . . . . . 17-317.4 Conflicts During Activation of Variations . . . . . . . . . . . . . . . . . . . . . . . . . . 17-417.5 Deleting an Expansion Stage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-517.6 Displaying the Activation Times of Expansion Stages . . . . . . . . . . . . . . . . . 17-517.7 Editing the Activation Times of Expansion Stages . . . . . . . . . . . . . . . . . . . 17-517.8 The Recording Expansion Stage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-517.9 Setting a Expansion Stage as the Recording Stage . . . . . . . . . . . . . . . . . . 17-617.10 Displaying the Recording Expansion Stage in the Status Bar. . . . . . . . . . . 17-617.11 Checking/Editing the Study Time (Date/Time of the Calculation Case). . . . 17-617.12 The Variation Scheduler . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-617.13 Comparing Variations and Expansion Stages . . . . . . . . . . . . . . . . . . . . . . 17-817.14 Splitting Expansion Stages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-917.15 Applying Expansion Stages Changes . . . . . . . . . . . . . . . . . . . . . . . . . . 17-1017.16 Consolidation of Variations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-1017.17 Colouring Variations and their Changes from within the Single Line Graphic17-1017.18 Converting System Stages into Variations . . . . . . . . . . . . . . . . . . . . . . . 17-11Parameter Characteristics 18-118.1 Defining Scalar Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-118.2 Defining Discrete Time Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-218.3 Defining Discrete Parameter Characteristics . . . . . . . . . . . . . . . . . . . . . . . 18-318.4 Defining Continuous Parameter Characteristics . . . . . . . . . . . . . . . . . . . . . 18-518.5 Defining Frequency Parameter Characteristics . . . . . . . . . . . . . . . . . . . . . 18-718.6 Defining Time Parameter Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . 18-718.7 Defining Two-dimensional Parameter Characteristics . . . . . . . . . . . . . . . . . 18-818.8 Importing Parameter Characteristics from Files . . . . . . . . . . . . . . . . . . . . 18-1018.9 Handling Scales and Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-11Reporting and Visualizing Results 19-119.1 Results, Graphs and Documentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-1

19.1.1 Editing Result Boxes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-119.1.2 Output of Device Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-419.1.3 Output of Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-719.1.4 Result Objects. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-8

19.2 Comparisons Between Calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-1219.2.1 Editing a Set Of Comparison Cases . . . . . . . . . . . . . . . . . . . . . . . 19-1219.2.2 Update Database. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-13

19.3 Variable Sets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-1419.3.1 The Variable Set Monitor Dialogue . . . . . . . . . . . . . . . . . . . . . . . 19-1419.3.2 Searching the Variables to Monitor . . . . . . . . . . . . . . . . . . . . . . . 19-1619.3.3 Examples of Variable Selection . . . . . . . . . . . . . . . . . . . . . . . . . . 19-1719.3.4 Selecting the Bus to be Monitored. . . . . . . . . . . . . . . . . . . . . . . . 19-23

19.4 Virtual Instruments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-2319.4.1 Virtual Instrument Panels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-2519.4.2 Plots . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-3119.4.3 The Vector Diagram. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-4119.4.4 The Voltage Profile Plot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-4419.4.5 Schematic Visualization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-48

vi


19.4.6 The Waveform Plot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-4919.4.7 The Curve-Input Command. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-5119.4.8 Embedded Graphic Windows. . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-5419.4.9 Tools for Virtual Instruments. . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-5619.4.10 User-Defined Styles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-66

Data Management 20-120.1 Project Versions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20-1

20.1.1 What is a Version? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20-120.1.2 How to Create a Version. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20-220.1.3 How to Rollback a Project . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20-320.1.4 How to Check if a Version is the base for a derived Project . . . . . . .20-420.1.5 How to Delete a Version . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20-4

20.2 Derived Projects. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20-520.2.1 Derived Projects Background. . . . . . . . . . . . . . . . . . . . . . . . . . . . .20-520.2.2 How to Create a Derived Project . . . . . . . . . . . . . . . . . . . . . . . . . .20-8

20.3 Comparing and Merging Projects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20-920.3.1 Compare and Merge Tool Background . . . . . . . . . . . . . . . . . . . . . .20-920.3.2 How to Merge or Compare two projects using the Compare and Merge Tool

20-920.3.3 How to Merge or Compare three projects using the Compare and Merge Tool

20-1120.3.4 Compare and Merge Tool Advanced Options. . . . . . . . . . . . . . . . . 20-1220.3.5 Compare and Merge Tool 'diff browser' . . . . . . . . . . . . . . . . . . . . 20-14

20.4 How to update a Project . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20-2120.4.1 Updating a Derived Project from a new Version . . . . . . . . . . . . . . 20-2120.4.2 Updating a base project from a Derived Project . . . . . . . . . . . . . . 20-2220.4.3 Tips for working with the Compare and Merge Tool. . . . . . . . . . . . 20-22

20.5 Sharing Projects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20-24The DIgSILENT Programming Language - DPL 21-121.1 The Principle Structure of a DPL Command. . . . . . . . . . . . . . . . . . . . . . . .21-121.2 The DPL Command Object . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21-2

21.2.1 Creating a new DPL Command . . . . . . . . . . . . . . . . . . . . . . . . . . .21-321.2.2 Defining a DPL Commands Set . . . . . . . . . . . . . . . . . . . . . . . . . . .21-321.2.3 Executing a DPL Command . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21-421.2.4 DPL Advanced Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21-421.2.5 DPL Script Page . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21-5

21.3 The DPL Script Editor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21-521.4 The DPL Script Language . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21-6

21.4.1 Variable Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21-621.4.2 Constant parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21-721.4.3 Assignments and Expressions . . . . . . . . . . . . . . . . . . . . . . . . . . . .21-721.4.4 Standard Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21-721.4.5 Program Flow Instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21-921.4.6 Input and Output. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21-10

21.5 Access to Other Objects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21-1121.5.1 Object Variables and Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . 21-12

21.6 Access to Locally Stored Objects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21-1221.7 Accessing the General Selection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21-1321.8 Accessing External Objects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21-14

vii


21.9 Remote Scripts and DPL Command Libraries. . . . . . . . . . . . . . . . . . . . . . 21-1521.9.1 Subroutines and Calling Conventions . . . . . . . . . . . . . . . . . . . . . . 21-16

21.10 DPL Functions and Subroutines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21-17PowerFactory Interfaces 22-122.1 DGS Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-1

22.1.1 DGS Interface Typical Applications . . . . . . . . . . . . . . . . . . . . . . . . 22-222.1.2 DGS Structure (Database Schemas and File Formats) . . . . . . . . . . . 22-222.1.3 DGS Import . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-322.1.4 DGS Export. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-5

22.2 PSS/E File Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-622.2.1 Importing PSS/E Steady-State Data. . . . . . . . . . . . . . . . . . . . . . . . 22-622.2.2 Import of PSS/E file (Dynamic Data) . . . . . . . . . . . . . . . . . . . . . . 22-1122.2.3 Exporting a project to a PSS/E file. . . . . . . . . . . . . . . . . . . . . . . . 22-12

22.3 NEPLAN Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-1522.3.1 Importing NEPLAN Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-15

22.4 UCTE-DEF Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-1722.4.1 Importing UCTE-DEF Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-1722.4.2 Exporting UCTE-DEF Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-19

22.5 CIM Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-2022.5.1 Importing CIM Data. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-2022.5.2 Exporting CIM Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-22

22.6 MATLAB Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-2322.7 OPC Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-23

22.7.1 OPC Interface Typical Applications . . . . . . . . . . . . . . . . . . . . . . . 22-2422.7.2 OPC Server Setup and PowerFactory Configuration. . . . . . . . . . . . 22-24

22.8 StationWare Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-2422.8.1 About StationWare . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-2522.8.2 Component Architecture. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-2522.8.3 Fundamental Concepts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-2722.8.4 Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-3222.8.5 Getting Started . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-3322.8.6 Reference. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-4222.8.7 Technical Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-47

22.9 API (Application Programming Interface) . . . . . . . . . . . . . . . . . . . . . . . . 22-51

viii


Contents of Volume II

Power System Analysis FunctionsLoad Flow Analysis 23-123.1 Technical Background. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23-4

23.1.1 Network Representation and Calculation Methods . . . . . . . . . . . . . .23-523.1.2 Active and Reactive Power Control. . . . . . . . . . . . . . . . . . . . . . . . .23-823.1.3 Advanced Load Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23-1223.1.4 Temperature Dependency of Lines and Cables . . . . . . . . . . . . . . . 23-17

23.2 Executing Load Flow Calculations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23-1923.2.1 Basic Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23-1923.2.2 Active Power Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23-2123.2.3 Advanced Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23-2423.2.4 Iteration Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23-2623.2.5 Outputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23-2723.2.6 Low Voltage Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23-2823.2.7 Advanced Simulation Options . . . . . . . . . . . . . . . . . . . . . . . . . . . 23-29

23.3 Result Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23-3023.3.1 Viewing Results in the Single Line Diagram. . . . . . . . . . . . . . . . . . 23-3023.3.2 Flexible Data Page . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23-3123.3.3 Predefined Report Formats (ASCII Reports) . . . . . . . . . . . . . . . . . 23-3123.3.4 Diagram Colouring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23-3123.3.5 Load Flow Sign Convention . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23-32

23.4 Troubleshooting Load Flow Calculation Problems . . . . . . . . . . . . . . . . . . 23-3323.4.1 General Troubleshooting. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23-3423.4.2 Data Model Problem. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23-3523.4.3 Some Load Flow Calculation Messages. . . . . . . . . . . . . . . . . . . . . 23-3623.4.4 Too many Inner Loop Iterations . . . . . . . . . . . . . . . . . . . . . . . . . 23-3623.4.5 Too Many Outer Loop Iterations . . . . . . . . . . . . . . . . . . . . . . . . . 23-37

23.5 Load Flow Sensitivities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23-4023.5.1 Load Flow Sensitivities Options . . . . . . . . . . . . . . . . . . . . . . . . . . 23-4123.5.2 Load Flow Sensitivities Execution and Results . . . . . . . . . . . . . . . . 23-4223.5.3 Technical Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23-43

Short-Circuit Analysis 24-124.1 Technical Background. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24-2

24.1.1 The IEC 60909/VDE 0102 Method . . . . . . . . . . . . . . . . . . . . . . . . .24-424.1.2 The ANSI Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24-924.1.3 The Complete Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-1124.1.4 The IEC 61363 Method. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-13

24.2 Executing Short-Circuit Calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-1424.2.1 Toolbar/Main Menu Execution . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-1424.2.2 Context-Sensitive Menu Execution . . . . . . . . . . . . . . . . . . . . . . . . 24-15

ix


24.2.3 Faults on Busbars/Terminals. . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-1524.2.4 Faults on Lines and Branches . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-1624.2.5 Multiple Faults Calculation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-17

24.3 Short-Circuit Calculation Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-1924.3.1 Basic Options (All Methods) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-1924.3.2 Verification (Except for IEC 61363) . . . . . . . . . . . . . . . . . . . . . . . 24-2224.3.3 Basic Options (IEC 60909/VDE 0102 Method). . . . . . . . . . . . . . . . 24-2324.3.4 Advanced Options (IEC 60909/VDE 0102 Method) . . . . . . . . . . . . 24-2424.3.5 Basic Options (ANSI C37 Method) . . . . . . . . . . . . . . . . . . . . . . . . 24-2724.3.6 Advanced Options (ANSI C37 Method). . . . . . . . . . . . . . . . . . . . . 24-2924.3.7 Basic Options (Complete Method) . . . . . . . . . . . . . . . . . . . . . . . . 24-3124.3.8 Advanced Options (Complete Method). . . . . . . . . . . . . . . . . . . . . 24-3324.3.9 Basic Options (IEC 61363) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-3524.3.10 Advanced Options (IEC 61363) . . . . . . . . . . . . . . . . . . . . . . . . . 24-36

24.4 Result Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-3724.4.1 Viewing Results in the Single Line Diagram . . . . . . . . . . . . . . . . . 24-3724.4.2 Flexible Data Page. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-3824.4.3 Predefined Report Formats (ASCII Reports) . . . . . . . . . . . . . . . . . 24-3824.4.4 Diagram Colouring. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-38

Harmonics Analysis 25-125.1 Harmonic Load Flow. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25-2

25.1.1 Basic Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25-225.1.2 IEC 61000-3-6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25-425.1.3 Advanced Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25-4

25.2 Frequency Sweep . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25-525.2.1 Basic Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25-625.2.2 Advanced Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25-7

25.3 Filter Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25-725.4 Modelling Harmonic Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25-9

25.4.1 Definition of Harmonic Injections . . . . . . . . . . . . . . . . . . . . . . . . . 25-925.4.2 Assignment of Harmonic Injections . . . . . . . . . . . . . . . . . . . . . . . 25-1625.4.3 Harmonic Distortion Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25-1725.4.4 Frequency Dependent Parameters. . . . . . . . . . . . . . . . . . . . . . . . 25-1925.4.5 Waveform Plot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25-21

25.5 Flicker Analysis (IEC 61400-21) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25-2225.5.1 Continuous Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25-2225.5.2 Switching Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25-2325.5.3 Flicker Contribution of Wind Turbine Generator Models . . . . . . . . . 25-2525.5.4 Definition of Flicker Coefficients . . . . . . . . . . . . . . . . . . . . . . . . . 25-2525.5.5 Assignment of Flicker Coefficients . . . . . . . . . . . . . . . . . . . . . . . . 25-2625.5.6 Flicker Result Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25-27

25.6 Definition of Result Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25-2725.6.1 Definition of Variable Sets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25-2825.6.2 Selection of Result Variables within a Variable Set . . . . . . . . . . . . 25-29

25.7 Literature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25-30Flickermeter 26-126.1 Flickermeter (IEC 61000-4-15) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26-2

26.1.1 Calculation of Short-Term Flicker . . . . . . . . . . . . . . . . . . . . . . . . . 26-226.1.2 Calculation of Long-Term Flicker . . . . . . . . . . . . . . . . . . . . . . . . . . 26-2

x


26.2 Flickermeter Calculation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26-326.2.1 Flickermeter Command. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26-326.2.2 Data Source . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26-426.2.3 Signal Settings. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26-526.2.4 Advanced Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26-626.2.5 Input File Types. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26-8

26.3 Literature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26-12Stability and EMT Simulations 27-127.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27-227.2 Calculation Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27-3

27.2.1 Balanced RMS Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27-327.2.2 Three-Phase RMS Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . .27-327.2.3 Three-Phase EMT Simulation. . . . . . . . . . . . . . . . . . . . . . . . . . . . .27-4

27.3 Setting Up a Simulation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27-427.3.1 Basic Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27-627.3.2 Step Sizes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27-727.3.3 Step Size Adaptation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27-827.3.4 Advanced Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27-927.3.5 Noise Generation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27-1227.3.6 Advanced Simulation Options - Load Flow . . . . . . . . . . . . . . . . . . 27-12

27.4 Result Objects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27-1327.4.1 Saving Results from Previous Simulations. . . . . . . . . . . . . . . . . . . 27-14

27.5 Events. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27-1527.5.1 Switch Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27-1827.5.2 Parameter Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27-1827.5.3 Short-Circuit Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27-1827.5.4 Intercircuit Fault Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27-1927.5.5 Events of Synchronous Machines. . . . . . . . . . . . . . . . . . . . . . . . . 27-1927.5.6 Events of Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27-1927.5.7 Outage of Element . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27-1927.5.8 Save Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27-2027.5.9 Set Integration Step Size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27-2027.5.10 Tap Event . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27-20

27.6 Running a Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27-2027.7 Models for Stability Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27-21

27.7.1 System Modelling Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27-2127.7.2 The Composite Model. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27-2627.7.3 The Composite Frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27-2927.7.4 The Common Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27-3227.7.5 The Composite Block Definition . . . . . . . . . . . . . . . . . . . . . . . . . . 27-3627.7.6 Drawing Composite Block Diagrams and Composite Frames . . . . . . 27-37

27.8 User Defined (DSL) Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27-4327.8.1 Modeling and Simulation Tools . . . . . . . . . . . . . . . . . . . . . . . . . . 27-4627.8.2 DSL Implementation: an Introduction . . . . . . . . . . . . . . . . . . . . . 27-4627.8.3 Defining DSL Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27-50

27.9 The DIgSILENT Simulation Language (DSL) . . . . . . . . . . . . . . . . . . . . . . 27-5427.9.1 Terms and Abbreviations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27-5427.9.2 General DSL Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27-5527.9.3 DSL Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27-5627.9.4 DSL Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27-5627.9.5 Definition Code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27-57

xi


27.9.6 Initial Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27-5827.9.7 Equation Code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27-6127.9.8 Equation Statement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27-6127.9.9 DSL Macros. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27-6227.9.10 Events and Messages. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27-6327.9.11 Example of a Complete DSL Model . . . . . . . . . . . . . . . . . . . . . . 27-64

27.10 Matlab Integration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27-6527.10.1 Implementation of Voltage Controller - Example . . . . . . . . . . . . . 27-6527.10.2 Implementation with Built-In Model. . . . . . . . . . . . . . . . . . . . . . 27-6627.10.3 Implementation with Matlab Model . . . . . . . . . . . . . . . . . . . . . . 27-6727.10.4 The Matlab File . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27-7027.10.5 Additional notes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27-71

Modal Analysis / Eigenvalue Calculation 28-128.1 Theory of Modal Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28-128.2 How to Complete a Modal Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28-5

28.2.1 Completing a Modal Analysis with the Default Options . . . . . . . . . . 28-528.2.2 Explanation of Modal Analysis Command Basic Options (ComMod) . . 28-628.2.3 Advanced Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28-8

28.3 Viewing Modal Analysis Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28-928.3.1 Viewing Modal Analysis Reports in the Output Window . . . . . . . . . . 28-928.3.2 Viewing Modal Analysis Results using the built-in Plots . . . . . . . . . 28-1128.3.3 Viewing Modal Analysis Results using the Modal Data Browser. . . . 28-1828.3.4 Viewing Results in the Data Manager Window . . . . . . . . . . . . . . . 28-20

28.4 Troubleshooting Modal Analysis Calculation Problems . . . . . . . . . . . . . . . 28-2228.4.1 Models not supported by the QR method . . . . . . . . . . . . . . . . . . . 28-2328.4.2 The Arnoldi/Lanczos Method is slow . . . . . . . . . . . . . . . . . . . . . . 28-23

Model Parameter Identification 29-129.1 Target Functions and Composite Frames . . . . . . . . . . . . . . . . . . . . . . . . . 29-2

29.1.1 The Measurement File Slot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29-329.1.2 Power System Element Slot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29-329.1.3 Comparison Slot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29-4

29.2 Creating The Composite Identification Model . . . . . . . . . . . . . . . . . . . . . . 29-429.2.1 The Comparison Object . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29-5

29.3 Performing a Parameter Identification . . . . . . . . . . . . . . . . . . . . . . . . . . . 29-629.4 Identifying Primary Appliances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29-8Contingency Analysis 30-130.1 Technical Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30-1

30.1.1 Single Time Phase Contingency Analysis . . . . . . . . . . . . . . . . . . . . 30-430.1.2 Multiple Time Phases Contingency Analysis . . . . . . . . . . . . . . . . . . 30-430.1.3 Time Sweep Option (Single Time Phase) . . . . . . . . . . . . . . . . . . . . 30-530.1.4 Consideration of Predefined Switching Rules . . . . . . . . . . . . . . . . . 30-530.1.5 Parallel Computing Option (Single Time Phase) . . . . . . . . . . . . . . . 30-5

30.2 Executing Contingency Analyses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30-630.3 The Single Time Phase Contingency Analysis Command . . . . . . . . . . . . . . 30-7

30.3.1 Basic Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30-930.3.2 Effectiveness. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30-1130.3.3 Multiple Time Phases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30-1230.3.4 Time Sweep . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30-14

xii


30.3.5 Advanced Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30-1530.3.6 Parallel Computing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30-1630.3.7 Calculating an Individual Contingency . . . . . . . . . . . . . . . . . . . . . 30-1830.3.8 Representing Contingency Situations - Contingency Cases . . . . . . . 30-18

30.4 The Multiple Time Phases Contingency Analysis Command . . . . . . . . . . . . 30-2130.4.1 Basic Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30-2130.4.2 Effectiveness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30-2230.4.3 Multiple Time Phases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30-2230.4.4 Time Sweep . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30-2430.4.5 Advanced Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30-2430.4.6 Parallel Computing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30-2430.4.7 Defining Time Phases for Contingency Analyses . . . . . . . . . . . . . . 30-2430.4.8 Representing Contingency Situations with Post-Fault Actions . . . . . 30-26

30.5 Creating Contingency Cases Using Fault Cases and Groups. . . . . . . . . . . . 30-2830.5.1 Browsing Fault Cases and Fault Groups . . . . . . . . . . . . . . . . . . . . 30-2930.5.2 Defining a Fault Case . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30-3030.5.3 Defining a Fault Group . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30-31

30.6 Creating Contingency Cases Using the Contingency Definition Command . . 30-3230.7 Comparing Contingency Results. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30-3530.8 Result Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30-37

30.8.1 Predefined Report Formats (Tabular and ASCII Reports) . . . . . . . . 30-37Reliability Assessment 31-131.1 Probabilistic Reliability Assessment - Technical Background . . . . . . . . . . . .31-3

31.1.1 Reliability Assessment Procedure. . . . . . . . . . . . . . . . . . . . . . . . . .31-331.1.2 Stochastic Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31-431.1.3 Calculated Results for Reliability Assessment . . . . . . . . . . . . . . . . .31-631.1.4 System State Enumeration in Reliability Assessment . . . . . . . . . . . 31-1131.1.5 Failure Effect Analysis in Reliability Assessment . . . . . . . . . . . . . . 31-12

31.2 Setting up the Network Model for Reliability Assessment . . . . . . . . . . . . . 31-1731.2.1 How to Define Stochastic Failure and Repair models . . . . . . . . . . . 31-1831.2.2 How to Create Feeders for Reliability Calculation. . . . . . . . . . . . . . 31-2231.2.3 How to Configure Switches for the Reliability Calculation . . . . . . . . 31-2231.2.4 Load Modeling for Reliability Assessment . . . . . . . . . . . . . . . . . . . 31-2331.2.5 Fault Clearance Based on Protection Device Location. . . . . . . . . . . 31-2931.2.6 How to Consider Planned Maintenance. . . . . . . . . . . . . . . . . . . . . 31-2931.2.7 Specifying Individual Component Constraints . . . . . . . . . . . . . . . . 31-29

31.3 Running The Reliability Assessment Calculation . . . . . . . . . . . . . . . . . . . . 31-3031.3.1 How to run the Reliability Assessment . . . . . . . . . . . . . . . . . . . . . 31-3031.3.2 Viewing the FEA results for a Specific Contingency . . . . . . . . . . . . 31-3631.3.3 Viewing the Load Point Indices . . . . . . . . . . . . . . . . . . . . . . . . . . 31-3631.3.4 Viewing the System Reliability Indices (Spreadsheet format) . . . . . 31-3731.3.5 Printing ASCII Reliability Reports . . . . . . . . . . . . . . . . . . . . . . . . . 31-3831.3.6 Using the Colouring modes to aid Reliability Analysis . . . . . . . . . . . 31-3931.3.7 Using the Contribution to Reliability Indices Script. . . . . . . . . . . . . 31-40

31.4 Voltage Sag Analysis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31-4131.4.1 Calculation Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31-4131.4.2 Performing a Voltage Sag Table Assessment. . . . . . . . . . . . . . . . . 31-43

31.5 Compact Reliability Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31-47

xiii


Generation Adequacy Analysis 32-132.1 Technical Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32-132.2 Database Objects and Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32-4

32.2.1 Stochastic Model for Generation Object (StoGen) . . . . . . . . . . . . . . 32-432.2.2 Power Curve Type (TypPowercurve) . . . . . . . . . . . . . . . . . . . . . . . 32-532.2.3 Meteorological Station (ElmMeteostat). . . . . . . . . . . . . . . . . . . . . . 32-6

32.3 Assignment of Stochastic Model for Generation Object . . . . . . . . . . . . . . . 32-732.3.1 Definition of a Stochastic Multi-State Model . . . . . . . . . . . . . . . . . . 32-732.3.2 Stochastic Wind Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32-832.3.3 Time Series Characteristic for Wind Generation . . . . . . . . . . . . . . . 32-9

32.4 Demand definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32-1132.5 Generation Adequacy Analysis Toolbar. . . . . . . . . . . . . . . . . . . . . . . . . . 32-1132.6 Generation Adequacy Initialisation Command (ComGenrelinc) . . . . . . . . . 32-1232.7 Run Generation Adequacy Command (ComGenrel) . . . . . . . . . . . . . . . . . 32-1532.8 Generation Adequacy Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32-16

32.8.1 Draws (Iterations) Plots . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32-1632.8.2 Distribution (Cumulative Probability) Plots . . . . . . . . . . . . . . . . . . 32-1732.8.3 Convergence Plots . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32-1932.8.4 Summary of variables calculated during the Generation Adequacy Analysis

32-21Optimal Power Flow 33-133.1 AC Optimization (Interior Point Method). . . . . . . . . . . . . . . . . . . . . . . . . . 33-1

33.1.1 Basic Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33-133.1.2 Initialization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33-1433.1.3 Advanced Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33-1533.1.4 Iteration Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33-1533.1.5 Output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33-17

33.2 DC Optimization (Linear Programming) . . . . . . . . . . . . . . . . . . . . . . . . . 33-2033.2.1 Basic Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33-2133.2.2 Initialization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33-2633.2.3 Advanced Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33-2733.2.4 Iteration Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33-28

33.3 Contingency Constrained DC Optimization (LP Method) . . . . . . . . . . . . . . 33-3133.3.1 Basic Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33-3233.3.2 Initialization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33-3733.3.3 Advanced Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33-3733.3.4 Iteration Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33-3733.3.5 Output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33-37

Optimization Tools for Distribution Networks 34-134.1 Optimal Capacitor Placement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-1

34.1.1 OCP Objective Function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-234.1.2 OCP Optimization Procedure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-434.1.3 Basic Options Page . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-534.1.4 Available Capacitors Page. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-734.1.5 Load Characteristics Page. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-834.1.6 Advanced Options Page . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-1134.1.7 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-12

34.2 Tie Open Point Optimization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-1334.2.1 How to Access the Tie Open Point Optimization Tool . . . . . . . . . . 34-14

xiv


34.2.2 Tie Open Point Optimization Background . . . . . . . . . . . . . . . . . . . 34-1434.2.3 How to run a Tie Open Point Optimization . . . . . . . . . . . . . . . . . . 34-15

34.3 Cable Size Optimization. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-1734.3.1 Objective Function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-1734.3.2 Optimization Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-1834.3.3 Basic Options Page . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-1834.3.4 Advanced Options Page . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-21

Protection 35-135.1 Using Protection Devices. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-1

35.1.1 The Relay Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-235.1.2 The Fuse Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-3

35.2 Basic Protection Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-535.2.1 The Current Transformer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-535.2.2 The Voltage Transformer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-735.2.3 The Measurement Block . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-1135.2.4 The Frequency Measurement Block . . . . . . . . . . . . . . . . . . . . . . . 35-1235.2.5 The Directional and Polarizing Blocks . . . . . . . . . . . . . . . . . . . . . . 35-1235.2.6 The Starting Block . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-1535.2.7 The Instantaneous Overcurrent Block . . . . . . . . . . . . . . . . . . . . . 35-1535.2.8 The Time Overcurrent Block . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-1735.2.9 The Distance Polygon Block . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-1935.2.10 The Timer Block. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-2035.2.11 The Frequency Block . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-2135.2.12 The Under-/Overvoltage Block. . . . . . . . . . . . . . . . . . . . . . . . . . 35-2135.2.13 The Logic Block . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-22

35.3 Time-Overcurrent Plot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-2335.3.1 Changing Tripping Characteristics . . . . . . . . . . . . . . . . . . . . . . . . 35-24

35.4 The Time-Distance Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-3135.4.1 Path Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-3235.4.2 The Time-Distance Plot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-3335.4.3 Time-Distance Plot Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-3435.4.4 Other Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-37

35.5 Relay Plot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-3735.5.1 Modifying the Relay Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-39

35.6 Protection Analysis Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-4235.7 Modelling Protection Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-42

35.7.1 The Modelling Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-4235.7.2 The Relay Frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-4435.7.3 The Block Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-4435.7.4 The Block Element . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-45

Network Reduction 36-136.1 Technical Background. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .36-2

36.1.1 Network Reduction for Load Flow . . . . . . . . . . . . . . . . . . . . . . . . .36-236.1.2 Network Reduction for Short-Circuit. . . . . . . . . . . . . . . . . . . . . . . .36-2

36.2 How to Complete a Network Reduction. . . . . . . . . . . . . . . . . . . . . . . . . . .36-236.2.1 How to Backup the Project (optional). . . . . . . . . . . . . . . . . . . . . . .36-336.2.2 How to run the Network Reduction tool . . . . . . . . . . . . . . . . . . . . .36-336.2.3 Expected Output of the Network Reduction . . . . . . . . . . . . . . . . . .36-4

36.3 Network Reduction Command . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .36-5

xv


36.3.1 Basic Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36-636.3.2 Outputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36-736.3.3 Advanced Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36-936.3.4 Verification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36-10

36.4 Network Reduction Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36-1036.5 Tips for using the Network Reduction Tool . . . . . . . . . . . . . . . . . . . . . . . 36-13

36.5.1 Station Controller Busbar is Reduced. . . . . . . . . . . . . . . . . . . . . . 36-1336.5.2 Network Reduction doesn’t Reduce Isolated Areas . . . . . . . . . . . . 36-1336.5.3 The Reference Machine is not Reduced . . . . . . . . . . . . . . . . . . . . 36-13

State Estimation 37-137.1 Objective Function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37-237.2 Components of the PowerFactory State Estimator . . . . . . . . . . . . . . . . . . . 37-2

37.2.1 Plausibility Check. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37-437.2.2 Observability Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37-437.2.3 State Estimation (Non-Linear Optimization) . . . . . . . . . . . . . . . . . . 37-5

37.3 State Estimator Data Input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37-537.3.1 Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37-637.3.2 Activating the State Estimator Display Option. . . . . . . . . . . . . . . . 37-1137.3.3 Editing the Element Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37-12

37.4 Running SE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37-1437.4.1 Basic Setup Options. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37-1437.4.2 Advanced Setup Options for the Plausibility Check . . . . . . . . . . . . 37-1837.4.3 Advanced Setup Options for the Observability Check . . . . . . . . . . 37-1837.4.4 Advanced Setup Options for Bad Data Detection . . . . . . . . . . . . . 37-1837.4.5 Advanced Setup Options for Iteration Control . . . . . . . . . . . . . . . 37-19

37.5 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37-2137.5.1 Output Window Report . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37-2137.5.2 External Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37-2237.5.3 Estimated States . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37-2437.5.4 Colour Representation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37-25

AppendixGlossary A-1Hotkeys Reference B-1B.1 Graphic Windows Hotkeys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-1B.2 Data Manager Hotkeys. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .B-3B.3 Dialogue Hotkeys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .B-5B.4 Output Window Hotkeys. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .B-6B.5 Editor Hotkeys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-8The DIgSILENT Output Language C-1Element Symbol Definition D-1D.1 General Symbol Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .D-1D.2 Geometrical Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .D-2

xvi


D.3 Including Graphic Files as Symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . D-4Index E-1

xvii


xviii

DIgSILENT PowerFactory

Power System Analysis Functions

DIgSILENT PowerFactory Load Flow Analysis

Chapter 23Load Flow Analysis

Whenever evaluating the operation and control of power systems, the electrical engineer is typically encountered with questions such as:

• Are the voltages of every busbar in the power system acceptable?

• What is the loading of the different equipment in the power system? (transformers, transmission lines, generators, etc.)

• How can I achieve the best operation of the power system?

• Does the power system have a weakness (or weaknesses)? If so, where are they located and how can I countermeasure them?

Although we may consider that the above questioning would arise only when analyzing the behavior of ''existing'' power systems; the same interrogations can be formulated when the task relates to the analysis of "future" systems or "expansion stages" of an already existing power system; such as evaluating the impact of commissioning a trans-mission line or a power plant, or the impact of refurbishment or decommissioning of equipment (for example shutting down a power plant because it has reached its life expectancy).

Fig. 23.1: Power System Analysis: System Operation and System Planning

Taking into account these two aspects: 1) Present operation and 2) Future operation, is

23 - 1


how power should be analyzed. From one side, an operation or control engineer requires relevant information to be available to him almost immediately, meaning he must be able to obtain somehow the behavior of the power system under different configurations that can occur (for example by opening or closing breakers in a substation); on the other side, a planning engineer requires obtaining the behavior of the system reflecting reinforce-ments that have not yet been built while considering the corresponding yearly and/or monthly load increase. Regardless of the perspective, the engineer must be able to determine beforehand the behavior of the power system in order to establish, for example, the most suitable operation configuration or to detect possible weakness and suggest solutions and alternatives. Figures 23.2 and 23.3 illustrate the system operation and planning aspects.

Fig. 23.2: Power System Operation Example

Fig. 23.3: Power System Planning Example

Load flow calculations are used to analyze power systems under steady-state non-faulted (short-circuit-free) conditions. Where steady-state is defined as a condition in which all the variables and parameters are assumed to be constant during the period of obser-

23 - 2


vation. We can think of this as ''taking a picture'' of the power system at a given point in time. To achieve a better understanding let us refer to Figure 23.4. Here a 24 hour load demand profile is depicted. The user can imagine this varying demand to be the demand of a specific area or region, or the demand of a whole network. In this particular case the load is seen as increasing from early in the morning until it reaches it’s maximum at around 18:00 hrs. After this point in time, the total load then begins to decrease. A load flow calculation is stated to be a steady-state analysis because it reflects the system conditions for a certain point in time, such as for instance at 18:00 hrs (maximum demand). As an example, if we require determining the behavior of the system for every hour of the day, then 24 load flows need to be performed; if the behavior for every second is required then the number of load flow calculations needed would amount to 86 400. In PowerFactory, the active power (and/or reactive power) of the loads can be set with a Characteristic so they follow a certain profile (daily, weekly, monthly, etc.). By doing so, the active power will change automatically according to the date ant time specified. For more information please refer to Chapters 5 (5.6) and 18.

Fig. 23.4: Example of a Load Demand Curve

A load flow calculation will determine the active and reactive power flows for all branches, and the voltage magnitude and phase for all nodes.

The main areas for the application of load flow calculations can be divided in normal and abnormal (Contingency) system conditions as follows:

Normal System Conditions

• Calculation of branch loadings, system losses and voltage profiles.

• Optimization tasks, such as minimizing system losses, minimizing generation costs, open tie optimization in distributed networks, etc.

• Calculation of steady-state initial conditions for stability simulations or short-circuit calculations using the complete superposition method.

Abnormal System Conditions

• Calculation of branch loadings, system losses and voltage profiles.

• Contingency analysis, network security assessment.

• Optimization tasks, such as minimizing system losses, minimizing generation costs, open tie optimization in distributed networks, etc.

• Verification of system conditions during reliability calculations.

• Automatic determination of optimal system resupplying strategies.

23 - 3


• Optimization of load-shedding.

• Calculation of steady-state initial conditions for stability simulations or short-circuit calculations using the complete superposition method (special cases).

Regarding the above definitions of ''normal'' and ''abnormal'' system conditions, a distinction should be made in terms of the manner simulations should be performed:

Simulation of normal operating conditions: Here, the generators dispatch as well as the loads are known, and it is therefore sufficient for the load flow calculation to represent these generators dispatch and to provide the active and reactive power of all loads. The results of the load flow calculation should represent a system condition in which none of the branch or generator limits are exceeded.

Simulation of abnormal operating conditions: Here a higher degree of accuracy from the models is needed. It can no longer be assumed that the entire system is operating within limits. The models must be able to correctly simulate conditions which deviate from the normal operating point. Hence the reactive power limits of generators or the voltage dependency of loads must be modelled. Additionally, in many applications, the active power balance cannot be established with a single slack bus (or machine). Instead, a more realistic representation of the active and reactive power control mechanisms have to be considered to determine the correct sharing of the active and reactive power gener-ation.

Besides the considerations regarding abnormal conditions presented above, the assumption of balanced systems may be inappropriate for certain distribution networks. State of the art computational tools for power systems analysis must be therefore able to represent unbalanced networks for load flow calculations as well.

The calculation methods and the options provided by PowerFactory’s load flow analysis function allow the accurate representation of any combination of meshed 1-, 2-, and 3-phase AC and/or DC systems. The load flow tool accurately represents unbalanced loads, generation, grids with variable neutral potentials, HVDC systems, DC loads, adjustable speed drives, SVSs, and FACTS devices, etc., for all AC and DC voltage levels. With a more realistic representation of the active and reactive power balance mechanisms, the tradi-tional requirement of a slack generator is left optional to the user.

The most considerable effect of the resistance of transmission lines and cables is the generation of losses. The conductor resistance will at the same time depend on the conductor operating temperature, which is practically linear over the normal range of operation. In order to carry out such type of analysis, PowerFactory offers a Temper-ature Dependency option, so that the conductor resistance is corrected according to the specified temperature value.

For very fast and reliable analysis of complex transmission networks, where only the flow of active power through the branches is considered, PowerFactory offers an additional load flow method, namely ''DC load flow (linear)'', which determines the active power flows and the voltage angles within the network.

The following sections introduce the calculation methods and the options provided with PowerFactory’s load flow tool. This information is a guide to the configuration of the

PowerFactory load flow analysis command ( ).

23.1 Technical Background

This section presents the general aspects of the implementation of PowerFactory’s load

23 - 4


flow calculation tool. An understanding of the concepts introduced here should be suffi-cient background to manage the options presented in the load flow analysis command dialogue. Further technical details related to the models (Network Components) imple-mented in PowerFactory for load flow calculations are provided in the Technical Refer-ences.

23.1.1 Network Representation and Calculation Methods

A load flow calculation determines the voltage magnitude (V) and the voltage angle () of the nodes, as well as the active (P) and reactive (Q) power flow on branches. Usually, the network nodes are represented by specifying two of these four quantities. Depending on the quantities specified, nodes can be classified as:

• PV nodes: here the active power and voltage magnitude are specified. This type of node is used to represent generators and synchronous condensers whose active power and voltage magnitude are controlled (synchronous condensers P=0). In order to consider equipment limits under abnormal conditions (as mentioned in the previous section), reactive power limits for the corresponding network components are also used as input information.

• PQ nodes: here the active and reactive power are specified. This type of node is used to represent loads and machines with fixed values. Loads can also be set to change (from their original Po and Qo values at nominal voltage) as a function of the voltage of the node to which the load itself is connected. Elements specified as PQ (for example synchronous machines, static generator's PWM converters or SVS's) can be ''forced'' by the algorithm so that the P and Q resulting from the load flow are always within limits.

• Slack node: here the voltage magnitude and angle are fixed. In traditional load flow calculations the slack node (associated with a synchronous generator or an external network) carries out the balancing of power in the system.

• Device nodes: special nodes used to represent devices such as HVDC converters, SVSs, etc., with specific control conditions (for example the control of active power flow at a certain MW threshold in a HVDC converter, or the control of the voltage of a busbar by an SVS).

Note: In traditional load flow calculations, asynchronous machines are represented by PQ nodes, assuming that the machine operates at a certain power factor, independent of the busbar voltage. Besides this traditional representation, PowerFactory offers a more accu-rate " slip iteration" (AS) representation based on the model equiv-alent circuit diagrams. For further information please refer to the corresponding Technical Reference.

In contrast to other power system calculation programs, PowerFactory does not directly define the node characteristic of each busbar. Instead, more realistic control conditions for the network elements connected to these nodes are defined (see the Load Flow tab of each element’s dialogue). For example, synchronous machines are modelled by defining one of the following control characteristics:

• Controlled power factor (cos()), constant active and reactive power (PQ);

• Constant voltage, constant active power (PV) on the connected bus;

23 - 5


• Secondary (frequency) controller ('slack', SL).

It is also important to note that in PowerFactory the active and reactive power balance of the analyzed networks is not only possible through a slack generator (or external network). The load flow calculation tool allows the definition of more realistic mechanisms to control both active and reactive power. For further information please refer to Section 23.1.2.

AC Load Flow Method

In PowerFactory the nodal equations used to represent the analyzed networks are implemented using two different formulations:

• Newton-Raphson (Current Equations).

• Newton-Raphson (Power Equations, classical).

In both formulations, the resulting non-linear equation systems must be solved by an iterative method. PowerFactory uses the Newton-Raphson method as its non-linear equation solver. The selection of the method used to formulate the nodal equations is user-defined, and should be selected based on the type of network to be calculated. For large transmission systems, especially when heavily loaded, the standard Newton-Raphson algorithm using the "Power Equations" formulation usually converges best. Distribution systems, especially unbalanced distribution systems, usually converge better using the "Current Equations" formulation.

In addition to the Newton-Raphson iterations, which solve the network nodal equations, PowerFactory applies an outer loop when the control characteristic of automatic trans-former tap changers and/or switchable shunts is considered. Once the Newton-Raphson iterations converge to a solution within the defined tolerance (without considering the setpoint values of load flow quantities defined in the control characteristic of the tap changers/switchable shunts (see Figure 23.5)), the outer loop is applied in order to reach these target values. The actions taken by the outer iterative loop are:

• Increasing/decreasing discrete taps;

• Increasing/decreasing switchable shunts; and

• Limiting/releasing synchronous machines to/from max/min reactive power limits.

Once the above-listed actions are taken, a new Newton-Raphson load flow iteration takes place in order to determine the new network operating point.

23 - 6


Fig. 23.5: Setting of the Control Mode for an Automatic Tap Changer

In the classical load flow calculation approach, the unbalances between phases are neglected. For the analysis of transmission networks this assumption is generally admis-sible. In distribution networks this assumption may be inappropriate depending on the characteristics of the network. PowerFactory allows for the calculation of both balanced (AC Load Flow, balanced positive sequence) and unbalanced (AC Load Flow Unbalanced, 3-phase (ABC)) load flows according to the descriptions above.

DC Load Flow Method

In addition to the ''AC'' load flow calculations presented in this section, PowerFactoryoffers a so-called ''DC'' load flow calculation method. The DC load flow should not be inter-preted as a method to be used in case of DC systems given that it basically applies to AC systems.

Some occasions we may require performing fast analysis in complex transmission networks where only a reasonable approximation of the active power flow of the system is needed. For such situations the DC load flow can be used. Other applications of the DC load flow method include situations where the AC load flow has trouble converging (see Section 23.4: Troubleshooting Load Flow Calculation Problems).

In this particular method, the non-linear system resulting from the nodal equations is simplified due to the dominant relation that exists between voltage angle and active power flow in high voltage networks. By doing so a set of linear equations is thereby obtained, where the voltage angles of the buses are directly related to the active power flow through the reactances of the individual components. The DC load flow does not require an iterative process and the calculation speed is therefore considerably increased. Only active power flow without losses is considered. Summarizing, the DC load flow

Control Mode

Settings of the Control Mode

23 - 7


method has the following characteristics:

• The calculation requires the solving of a set of linear equations.

• No iterations required, therefore fast, and also no convergence problems.

• Approximate solution:

- All node voltage magnitudes fixed at 1.0 per unit.

- Only active power and voltage angles calculated.

- Losses are neglected.

23.1.2 Active and Reactive Power Control

Active Power Control

Besides the traditional approach of using a slack generator to establish the power balance within the system, PowerFactory’s load flow calculation tool provides other active power balancing mechanisms which more closely represent the reality of transmission networks (see selection in the Active Power Control tab of the load flow command). These mecha-nisms are implemented in the steady-state according to the control processes that follow the loss of large power stations:

• As Dispatched: As mentioned at the beginning of this section, the conventional approach in load flow calculations consists assigning a slack generator, which will establish the power balance within the system. Besides this traditional approach, PowerFactory offers the option of balancing by means of a single or a group of loads (Distributed Slack by Loads). Under such assumptions, the active power of the selected group of loads will be modified so that the power balance is once again met; while leaving the scheduled active power of each generator unchanged. Other methods of balancing include considering the participation of all synchronous generators according to their scheduled active power (Distributed Slack by Generation).

• According to Secondary Control: If an unbalance occurs between the scheduled active power values of each generation unit and the loads plus losses, primary control will adapt (increase/decrease) the active power production of each unit, leading to an over- or under-frequency situation. The secondary frequency control will then bring the frequency back to its nominal value, re-establishing cost-efficient generation delivered by each unit. Secondary control is represented in PowerFactory’s load flow calculations by network components called 'Power Frequency Controllers' (ElmSecctrl). If the Active Power Control option According to Secondary Control is selected, the generators considered by the Power Frequency Controllers establish the active power balance according to their assigned participation factors (for further information, please refer to the corresponding Technical Reference).

• According to Primary Control: Shortly following a disturbance, the governors of the units participating in primary control will increase/decrease their turbine power and drive the frequency close to its nominal value. The change in the generator power is proportional to the frequency deviation and is divided among participating units according to the gain (Kpf) of their primary controllers and which is depicted in Figure 23.6. If the Active Power Control option According to Primary Control is selected in PowerFactory’s load flow command, the power balance is established by all generators (synchronous generators, static generators and external grids) having a

23 - 8


primary controller gain value different than zero (parameter Prim. Frequency Bias in the Load Flow tab page - Figure 23.7). The modified active power of each generator is then calculated according to the following equation:

where,

is the modified active power of generator i,

is the initial active power dispatch of generator i and

is the active power change in generator i.

The active power change of each generator ( ) will be determined by its corresponding primary controller gain value (Kpf-i) and the total frequency deviation.

where,

Kpf-i is the primary controller gain parameter of generator i and

is the total frequency deviation.

The total frequency deviation ( ) can be obtained according to:

where corresponds to the active power change sum of every generator:

Fig. 23.6: Primary Frequency Bias

Pi Pi-dispatch Pi+=

Pi

Pi-dispatch

Pi

Pi

Pi Kpf-i f=

f

f

fPTot

Kpf---------------=

PTot

PTot Pj

j 1=

n

=

23 - 9


Fig. 23.7: Primary Frequency Bias (Kpf) Setting in the Load Flow Tab Page of the Synchronous Machine Element (ElmSym)

• According to Inertias: Immediately following a disturbance, the missing/excess power is delivered from the kinetic energy stored in the rotating mass of the turbines. This leads to a deceleration/acceleration and thus to a decrease/increase in the system frequency. The contribution of each individual generator towards the total additional power required is proportional to its inertia. If the Active Power Control option According to Inertias is selected in PowerFactory’s load flow command, the power balance is established by all generators. Individual contributions to the balance are proportional to the inertia/acceleration time constant of each generator (defined on the RMS-Simulation tab of the synchronous generator type’s dialogue and depicted in Figure 23.8). This relation can be mathematically described as follows:

where,

is the modified active power of generator i,

is the initial active power dispatch of generator i and

is the active power change in generator i.

The active power change of each generator ( ) will be determined by its corresponding inertia gain (Kpf-i) and the total frequency deviation, as follows:

Kpf

Pi Pi-dispatch Pi+=

Pi

Pi-dispatch

Pi

Pi

23 - 10


where,

is the total frequency deviation and

Kpf-i is the inertia gain parameter of generator i, which can be calculated as:

with

where,

is the moment of Inertia,

is the rated angular velocity,

is the generator nominal apparent power and

is the acceleration time constant rated to

Fig. 23.8: Inertia/Acceleration Time Constant Parameter of the Synchronous Machine Type (TypSym). RMS-Simulation Tab Page

Figure 23.9 illustrates the different type of active power control.

Pi Kpf-i f=

f

Kpf-i J n 2=

J Sn

Tags

n2

----------=

J

n

Sn

Tags Sn

Tags

23 - 11


Fig. 23.9: Frequency Deviation Following an Unbalance in Active Power

Note The Secondary Control option will take into account the participa-tion factors of the machines defined within a 'Power-Frequency Controller' (ElmSecctrl) in order to compensate for the frequency deviation. In such a case, the final steady state frequency is con-sidered to be the nominal value (number 1 in Figure 23.9). The Pri-mary Control option will take into account the frequency droop (MW/Hz) stated in every machine in order to determine the active power contribution. Depending on the power unbalance, the steady state frequency will deviate from the nominal value (num-ber 2 in Figure 23.9). The According to Inertias option will take into account the inertia/acceleration time constant stated in every ma-chine in order to determine its active power contribution. In this case, depending on the power unbalance, the steady state fre-quency will deviate from the nominal value (number 3 in Figure 23.9).

Reactive Power Control

The reactive power reserves of synchronous generators in transmission networks are used to control the voltages at specific nodes in the system and/or to control the reactive power exchange with neighboring network zones. In PowerFactory’s load flow calculation, the voltage regulator of the generators has a voltage setpoint which can be set manually (defining a PV bus type as introduced in Section 23.1.1), or from an Automatic Station Controller (ElmStactrl). This Automatic Station Controller combines several sources of reactive power to control the voltage at a given bus. In this case the relative contribution of each reactive power source (such as generators and SVSs) is defined in the Station Controller dialogue. For further details about the use and definition of Automatic Station Controllers please refer to Appendix C.4.4 (Station Controller (ElmStactrl)).

23.1.3 Advanced Load Options

Voltage Dependency of Loads

All non-motor loads, as well as groups of non-motor loads that conform a sub-system, for

23 - 12


example, a low-voltage system viewed from a medium voltage system, can be modelled as a "general load".

Under "normal conditions" it is permissible to represent such loads as constant PQ loads. However under "abnormal conditions", for example during voltage collapse situations the voltage-dependency of the loads should be taken into account.

Under such assumptions, PowerFactory uses a potential approach, as indicated by Equations (23.1) and (23.2). In these equations, the subscript 0 indicates the initial operating condition as defined in the input dialogue box of the Load Type.

Eqn 23.1:

where,

Eqn 23.2:

where,

By specifying the particular exponents (e_aP, e_bP, e_cP and e_aQ, e_bQ, e_cQ) the inherent load behavior can be modelled. For example, in order to consider a constant power, constant current or constant impedance behavior, the exponent value should be set to 0, 1 or 2 respectively. In addition, the relative proportion of each coefficient can be freely defined using the coefficients aP, bP, cP and aQ, bQ, cQ. For further information, please refer to the General Load technical reference.

Note These factors are only considered if the "Consider Voltage Depen-dency of Loads" is checked in the Load-flow Command window. If no Load Type (TypLod) is assigned to a load, and the load flow is performed considering voltage dependency then the load will be considered as Constant Impedance.

Feeder Load Scaling

In radially operated distribution systems the problem often arises that very little is known about the actual loading of the loads connected at each substation. The only information sometimes available is the total power flowing into a radial feeder. To be able to still estimate the voltage profile along the feeder a load scaling tool is used. In the simplest case the distribution loads are scaled according to the nominal power ratings of the trans-formers in the substations. Of course, more precise results are obtained by using an average daily, monthly or annual load.

The previous is explained in Figure 23.10. Here, the measured value at the beginning of the feeder is stated to be 50 MW. Throughout the feeder there are three loads defined, of which only for one of them the load is precisely known (20 MW). The other two loads

P P0 aPvv0-----

e_aPbP

vv0-----

e_bP1 aP– bP– v

v0-----

e_cP+ +

=

cP 1 aP– bP– =

Q Q0 aQvv0-----

e_aQbQ

vv0-----

e_bQ1 aQ– bQ– v

v0-----

e_cQ+ +

=

cQ 1 aQ– bQ– =

23 - 13


are estimated to be at around 10 MW each. PowerFactory’s load flow analysis tool offers a special Feeder Load Scaling option so that the selected groups of loads (scalable loads) are scaled accordingly in order to meet the measured value.

Fig. 23.10: Radial Feeder. Feeder Load Scaling Option

In PowerFactory the following options for Feeder Load Scaling are available:

• No scaling.

• Scaling to measured apparent power.

• Scaling to active power.

• Scaling to measured current.

• Scaling Manually.

• Scaling to measured reactive power.

• Scaling to measured power factor.

Furthermore, the previous options can be combined; for example, scaling a selected groups of loads in order to meet a measured active power and power factor.

Note Loads that are to be scaled must be marked as such (Adjusted by Load Scaling), also the load scaling must be enabled in the load flow command option (Feeder Load Scaling).

The feeder load scaling process also can take into account the different type of load behavior represented. Figure 23.11 illustrates just this. Here, a radial feeder consisting of three different type of loads is depicted (constant power, constant current and constant impedance). Under such assumptions, performing a load flow calculation with the option Consider Voltage Dependency of Loads (see previous Section), will result in calculated base quantities according to the type of load specified; for example, Ibase for the constant current load and Zbase for the constant impedance load. If in addition to the voltage dependency of loads, the Feeder Load Scaling option is enabled, the calculated scaling factor k is applied according to the type of load defined in the feeder.

23 - 14


Fig. 23.11: Feeder Load Scaling Factor Considering Different Behavior of Loads

In PowerFactory, the amount of Feeder definitions is not limited to the amount of radial paths represented in the model. This means that the user can define more than one feeder element (ElmFeeder) along the same radial path, as indicated in Figure 23.12. In this particular example, both Feeder 1 and 2 have the same specified orientation (-->Branch). While Feeder 1 is defined from the beginning of the radial path, Feeder 2 is defined after load L2. This particular type of feeder representation is termed as Nested Feeders. Since Feeder 1 is defined from the beginning of the radial path, every load (L1, L2, L3 and L4), as well as every feeder (Feeder 2) along this path will be considered as part of its definition. Since Feeder 2 is along the path defined for Feeder 1; Feeder 2 is nested in Feeder 1.

In such cases, executing the load flow (with the option Feeder Load Scaling) will treat the two feeders as independent. Although nested, Feeder 1 will only try to scale loads L1 and L2 according to its setting, while Feeder 2 will scale loads L3 and L4. If Feeder 2 is placed Out of Service, then Feeder 1 will scale all the loads along the radial path (L1, L2, L3 and L4).

Fig. 23.12: Nested Feeder Definition

For further information on Feeder definitions please refer to Chapter 15.5 (Feeders).

Load Scaling Factors

Loads can be scaled individually by adjusting the Scaling Factor parameter located in the

23 - 15


Load Flow tab page of the Load Element.Together with the scaling factor, the actual load is calculated as follows:

If voltage dependency of loads is considered then Equations (23.1) and (23.2) become;

Eqn 23.3:

Eqn 23.4:

Note: In order to consider a load in the feeder-load-scaling process, the option Adjusted by Load Scaling has to be enabled. In this case, the individual Scaling Factor of the load is not taken into account but overwritten by the feeder-scaling factor.

Additionally, loads can be grouped in zones, areas or boundaries so the scaling factor can be easily edited. In case of zones, there will be an additional Zone Scaling Factor.

Coincidence of Low Voltage Loads

In a low voltage system every load may consist of a fixed component with a deterministic amount of power demand plus a variable component comprising many different, small loads, such as lights, refrigerators, televisions, etc., whose power varies stochastically between zero and a maximum value. Under such conditions, PowerFactory uses a probabilistic load flow calculation, which is able to calculate both maximum and average currents as well as the average losses and maximum voltage drops. The probabilistic load flow calculation used by PowerFactory can be applied to any system topology, including meshed low-voltage systems.

PowerFactory’s probabilistic load flow calculation uses low voltage loads comprised of several customers with fixed and variable (stochastic) demand components. The maximum value of the variable component (which is dependent upon the number of customers, n) is described by the following formula:

Where Smax is the maximum variable load per connection (customer) and the function g(n) describes the maximum coincidence of loads, dependent upon the number of connections, n. If a Gaussian distribution is assumed, the coincidence function is:

P Scale P0=

Q Scale Q0=

P Scale P 0 aPvv0-----

e_aPbP

vv0-----

e_bP1 aP– bP– v

v0-----

e_cP+ +

=

Q Scale Q 0 aQvv0-----

e_aQbQ

vv0-----

e_bQ1 aQ– bQ– v

v0-----

e_cQ+ +

=

Smax n n g n Smax=

23 - 16


The average value of the variable component is:

Note: Low voltage loads can be represented in PowerFactory by Low Voltage Load (ElmLodlv) elements which can be directly connect-ed to terminals or by Partial Low Voltage Loads (ElmLodlvp) which are defined along transmission lines/cables (see the Defini-tion of Line Loads section on the Load Flow tab of transmission line/cable elements - ElmLne).

23.1.4 Temperature Dependency of Lines and Cables

The most important effect of the resistance of transmission line and cable conductors is the generation of losses (I²R). Resistance will also affect the voltage regulation of the line due to voltage drop (IR).

The resistance of a conductor is mainly affected by the operating temperature, and its variation can be considered practically linear over the normal range of operation (an increase in temperature causes an increase in resistance). In PowerFactory, the load flow calculation has two options for considering the Temperature Dependency of resis-tance for lines and cables:

• at 20°C: When this option is selected, the load flow calculation uses the resistances (lines and cables) stated in the Basic Data tab page of the corresponding component (TypLne, TypCon, TypCab).

Fig. 23.13: Specification of the Resistance at 20°C in the Basic Data tab page of the line type (TypLne)

• at Maximum Operational Temperature: When this option is selected, the load flow calculation uses the corrected value of resistance, which is obtained with the following equation:

g n g1 g–

n---------------+=

Sav g Smax=

Resistance

23 - 17


Eqn 23.5:

where,

R20 is the resistance at temperature 20°C (Basic Data tab of the corresponding type)

is the temperature coefficient in K-1

Tmax is the maximum operational temperature (Load Flow tab of the corresponding type)

Rmax is the resistance at temperature Tmax

Fig. 23.14: Temperature Dependency Option Setting in the Load Flow tab page of the line type (TypLne)

Additionally, the resistance temperature dependency can be defined by specifying either the resistance at maximum operational temperature, the temperature coefficient (1/K) or the conductor material (Aluminium, Copper or Aldrey).

Table 23.1 indicates the electrical resistivities and temperature coefficients of metals used in conductors and cables referred at 20°C/68°F (taken from IEC 60287-1 standard).

Table 23.1:Electrical Resistivities and Temperature coefficients of Aluminium and Copper

Material Resistivity (m)

Temperature

coefficient [K-1]

Aluminium 2.8264x10-8 4.03x10-3

Copper 1.7241x10-8 3.93x10-3

Rmax R20 1 Tmax 20oC– + =

Tmax

Specification of the Temperature dependency

23 - 18


23.2 Executing Load Flow Calculations

A load flow calculation may be initiated by:

• Pressing the icon on the main toolbar;

• Selecting the Calculation Load Flow ... option from the main menu.

An example of the load flow command dialogue is shown in Figure 23.15.

Fig. 23.15: Load Flow Command (ComLdf) Dialogue

The following pages explain the load flow command options. Following this, some hints are given regarding what to do if your load flow cannot be solved.

The following pages describe the different load flow command (ComLdf) options. for more detail technical background regarding the options presented here, please refer to Section 23.1.

23.2.1 Basic Options

Calculation Method

AC Load Flow, balanced, positive sequencePerforms load flow calculations for a single-phase, positive sequence network representation, valid for balanced symmetrical networks. A

23 - 19


balanced representation of unbalanced objects is used (for further details please refer to Section 23.1.1).

AC Load Flow, unbalanced, 3 Phase (ABC)Performs load flow calculations for a multi-phase network representation. It can be used for analyzing unbalances of 3-phase systems, e.g. introduced by unbalanced loads or non-transposed lines, or for analyzing all kinds of unbalanced system technologies, such as single-phase- or two-phase systems (with or without neutral return). For further details please refer to Section 23.1.1.

DC Load Flow (linear)Performs a DC load flow based on a set of linear equations, where the voltage angles of the buses are strongly related to the active power flow through the reactances of the individual components (for further details please refer to Section 23.1.1).

Reactive Power Control

This option is available only for AC load flow calculations.

Automatic Tap Adjust of TransformersAdjusts the taps of all transformers which have the option Automatic Tap Changing enabled on the Load Flow tab of their element dialogues. The tap adjustment is carried out according to the control settings defined in the transformer element's dialogue (for further information please refer to the corresponding Technical Reference ).

Automatic Shunt AdjustmentAdjusts the steps of all switchable shunts that have the option Switchable enabled on the Load Flow tab of the shunt’s element dialogue (for further information please refer to corresponding Technical Reference).

Consider Reactive Power LimitsConsiders the reactive power limits defined by generators and SVSs. If the load flow cannot be solved without exceeding the specified limits, a convergence error is generated. If this option is not enabled, PowerFactory will print a warning message if any of the specified limits are exceeded.

Consider Reactive Power Limits Scaling FactorThis option is only available if Consider Reactive Power Limits is enabled. If selected, the reactive power limits of generators are scaled by the relaxation factors: Scaling factor (min) and Scaling factor (max) which are set on the Load Flow tab of the generator element's dialogue. Note that the reactive power limits of generators are also defined on the Load Flow tab of the generator element's dialogue by one of the following: maximum/minimum values, 5.5.4, or according to the generator’s assigned type.

Load Options

Consider Voltage Dependency of LoadsThe voltage dependency of loads with defined voltage dependency

23 - 20


factors (Load Flow tab of the general- and complex load types) will be considered.

Feeder Load ScalingScales loads with the option Adjusted by Feeder Load Scaling enabled on the Load Flow tab of their element dialogue by the Scaling Factor specified in the Load Scaling section of the feeder element (for information about feeder elements please refer to Section 5.3.3 (Network Data)). In this case, the Scaling Factor specified on the Load Flow tab of load element dialogue is disregarded.

Consider Coincidence of Low-Voltage LoadsCalculates a 'low voltage load flow' as described in Sections 23.1.3 and 23.2.6, where load coincidence factors are considered (for C.2.6 and C.2.7 objects), so as to produce maximum branch currents and maximum voltage drops. Since coincidence factors are used, the result of low voltage analysis will not obey Kirchhoff's current law.After the load flow has been successfully executed, maximum currents (Imax), maximum voltage drops (dumax) and minimum voltages (umin, Umin) are displayed in every branch element and at every busbar. The usual currents and voltages represent here average values of voltages and currents. Losses are calculated based on average values, and maximum circuit loading is calculated using maximum currents.

Scaling Factor for Night Storage HeatersThis is the factor by which the night storage heater power (as found in Low Voltage Load elements) is multiplied for all low voltage loads.

Temperature Dependency: Line/Cable Resistances

...at 20°CThe resistance of each line, conductor and cable will be according to the value stated in the Basic Data tab page of their corresponding type (at 20°C).

...at Maximum Operational TemperatureThe resistance of each line, conductor and cable will be adjusted according to the equation (23.5) described in Section 23.1.4 and the Temperature Dependency option stated in its corresponding type (TypLne, TypCon, TypCab).

23.2.2 Active Power Control

Active Power Control

As explained in Section 23.1.2, PowerFactory’s load flow calculation offers several options for maintaining power balance within the system under analysis. These options are:

as Dispatched:If this option is selected and no busbar is assigned to the Reference Busbar (Reference Bus and Balancing section of the Active Power

23 - 21


Control tab), the total power balance is established by one reference generator/external grid ("slack"-generator). The slack generator can be directly defined by the user on the Load Flow tab of the target element. The program automatically sets a slack if one has not been already defined by the user.

according to Secondary Control:Power balance is established by all generators which are considered by a "Secondary Controller" as explained in Section 23.1.2. Active power contribution is according to the secondary controller participation factors.

according to Primary Control:Power balance is established by all generators having a Kpf-setting defined (on the Load Flow tab of a synchronous machine element dialogue), as explained in Section 23.1.2. Active power contribution is according to the droop of every generator.

according to Inertias:Power balance is established by all generators, and the contribution of each is according to the inertia (acceleration time constant) as explained in Section 23.1.2.

Consider Active Power Limits:Active power limits for generators (as defined on the element’s Load Flow tab) participating in active power balance, will be applied. If this option is disabled, the active power output limits may be violated, in which case a warning is issued. This option is not available when the Active Power Control option is set to either as Dispatched or according to Inertias.

Reference Bus and Balancing

If as Dispatched is selected in the Active Power Control section of the tab, further options regarding the location of the reference busbar and the power balancing method are available:

Balancing by Reference Machine:For each isolated area, the reference machine will balance the active power.

Balancing by Load at Reference Busbar:This option is valid only when the reference bus bar has been defined. The load with highest active power injection at the reference bus will be selected as the slack (such as to balance the losses).

Balancing by Static Generator at Reference Bus:As in the case of Balancing by Load, this option is valid only when the reference bus bar has been defined. The static generator with the highest nominal apparent power at the reference bus will be selected as the slack (i.e. to balance the losses).

Distributed Slack by Loads:When this option is selected, only the loads which have the option Adjusted by Load Scaling in the isolated area will contribute to the balancing. The distribution factor calculated for a load is determined by the following equation:

23 - 22


where,Pini is the initial active power of the load.

Fig. 23.16: Adjusted by Load Scaling option in the Load Flow tab page of the Load element (ElmLod)

Distributed Slack by Generation (Synchronous Generators):All the synchronous generators in the isolated area will contribute to the balancing. As in the Distributed Slack by Loads option, the distribution factor calculated for a generator is determined by the following equation:

where,Pini is the initial dispatched active power of the generator.

Interchange Schedule:This option is available only when the Distributed Slack by Loads or Distributed Slack by Generation is selected. It allows the loads or generation in a region to be scaled up or down to control the interchange of this region. The type of the region could be:

Grids: Available for both distributed load slack and distributed generation.

Zones: Available for both distributed load slack and distributed generation.

Boundaries: Only available for distributed load slack.

Ki

Pini i

Pini j,

j 1=

N

---------------------=

Ki

Pini i

Pini j,

j 1=

N

---------------------=

23 - 23


In the load flow page of the grid, zone or boundary elements, the following operational parameters are available:

Consider Interchange Schedule: Enables or disables the Interchange Schedule for this region. By default this option is not selected.

Scheduled active power interchange: States the expected interchange of the grid, zone or boundary.

Fig. 23.17: Consider Interchange Schedule option in the Load Flow tab page of the Grid element (ElmNet)

Reference Busbar:A different busbar to the one connecting the slack machine (or network) can be selected as a reference for the voltage angle. In this case the user must specify the value of the voltage angle at this selected reference bus, which will be remotely controlled by the assigned slack machine (or network).

Angle:User-defined voltage angle for the selected reference busbar. The value will be remotely controlled by the slack machine (external network). Only available if a Reference Busbar has been selected.

23.2.3 Advanced Options

Load Flow Method

As explained in Section 23.1.1, the nodal equations used to represent the analyzed networks are implemented using two different formulations:

• Newton-Raphson (Current Equations)

• Newton-Raphson (Power Equations, classical)

In both formulations, the resulting non-linear equation systems must be solved using an iterative method. PowerFactory uses the Newton-Raphson method as its non-linear equation solver. The selection of the method used to formulate the nodal equations is user-defined, and should be selected based on the type of network to be calculated. For large transmission systems, especially when heavily loaded, the classical Newton-Raphson algorithm using the Power Equations formulation usually converges best. Distri-bution systems, especially unbalanced distribution systems, usually converge better using the Current Equations formulation.

23 - 24


Load Flow Initialisation

No Topology RebuildWill speed up large sets of consecutive load flow calculations. Enabling this option means that the topology of the system will not be rebuilt when calculating the next load flow. If no topological changes will be made to the system between these consecutive load flow calculations, then this option may be enabled.

No Initialisation (no flat-start)Initializes a load flow from a previously convergent solution (no flat-start).

Consideration of transformer winding ratioSets the manner in which voltage initialisation takes place at nodes. Reducing the relaxation factor results in an increased number of iterations, but yields greater numerical robustness.

Tap Adjustment

MethodThe direct method will include the tap controller models in the load flow calculation (i.e. in the internal loop involving the Newton-Raphson iterations). The new tap positions will then be calculated directly as a variable and are therefore known following a single load flow calculation.The stepped method will calculate a load flow with fixed tap positions, after which the required tap changes are calculated from the observed voltage deviations and the tap controller time constants. The load flow calculation is then repeated with the new tap positions, until no further changes are required. These tap adjustments take place in the outer loop of the calculation.

Min. Controller Relaxation FactorThe tap controller time constants are used in the automatic tap changer calculations to determine the relative speed of the various tap controllers during the load flow iterations. The relaxation factor can be used to slow down the overall controller speeds (in case of convergence problems, set a factor of less than 1.0), or to speed them up (for a faster load flow, set a factor of greater than 1.0).

Station Controller

Available on the second page ( ) of the Advanced Options tab. The options presented in this field determine the reactive power flow from generators participating in station controllers (ElmStactrl). Please refer to Appendix C.4.4 (Station Controller (ElmStactrl)) for information on station controllers and their control modes.

23 - 25


Modeling Method of Towers

with in/output signalsThe equations of the lines are modelled in the tower. It should be noted that selecting this option will result in slower performance.

ignore couplingsInter-circuit couplings are ignored.

equations in linesThe constant impedance and admittance matrices are calculated by the tower and used to develop the equations of the lines. The equations involving coupling are modeled in the lines; consequently, using this option results in faster performance than using option with in/output signals.

Use this load flow for initialization of OPF

The results of this load flow calculation are used to initialize the OPF calculation.

23.2.4 Iteration Control

The options on this tab relate to the non-linear equation solver and are therefore only available for PowerFactory’s AC load flow calculation methods.

Max. Number of Iterations for

The load flow calculation comprises an inner loop involving the Newton-Raphson method (see Section 23.1.1), and an outer loop to determine changes to tap settings and to consider generator reactive power limits. Default values for the maximum number of iterations for these two loops are 25 iterations for the inner loop, and 20 iterations for the outer loop.

Newton-Raphson Iteration - itrlxThe inner loop of the load flow involves the Newton-Raphson iterations. This parameter defines the maximum number of iterations (typically 25).

Outer Loop - ictrlxThe outer loop of the load flow calculation will determine changes to the tap changer (depending on the tap adjustment method selected), and considers reactive power limits of generators, etc. These are adjusted in the outer loop and then a new iteration of the inner loop is started again (see Section 23.1.1). The maximum number of outer loop iterations (typically 20) is set by this parameter.

Number of Steps - nstepsProblematic load flows with slow convergence may be improved by starting a load flow calculation for a low load level, and then increasing the load level in a number of steps. This is achieved by setting the Number of Stairs to a value greater than one. For example, nsteps =3 begins a load flow at a load/generation level of 1/3 and the increases the power to 100% over two further steps.

23 - 26


Max. Acceptable Load Flow Error for

A higher precision or a faster calculation can be obtained by changing the maximum allowable error (i.e. tolerance). The values of the calculated absolute error for nodes, or the calculated relative errors in the model equations, e.g. voltage error of voltage controlled generators, are specified here.

Nodes - errlf Maximum Iteration Error of Nodal Equations (typical value: 1 kVA).

Model Equations - erreq Maximum Error of Model Equations (typical value: 0.1%).

Convergence Options

Relaxation FactorA Newton-Raphson relaxation factor smaller than 1.0 will slow down the convergence speed of the load flow calculation, but may result in an increased likelihood of convergence for systems which are otherwise difficult to solve.

Automatic Model Adaptation for ConvergencyThe PowerFactory load flow calculation will always first try to find a solution using non-linear mathematical power system models. If a solution cannot be found, and this option is enabled, an adaptive algorithm will change these models slightly to make them more linear, until a solution is found. Any model adaptations are reported in the output window.

23.2.5 Outputs

Show 'Outer Loop' messagesWill print a report concerning the outer loop iterations, which may be used to solve convergence problems.

Show Convergence Progress ReportWill print a detailed report throughout the load flow calculation. When enabling this option the Number of reported buses/models per iteration can be stated. As a result, the required number of buses and models with the largest error will be reported (e.g. by stating 3, the 3 buses and models with the largest error will be printed out in the output window). As in the case of 'Outer Loop' messages, this information can be useful in solving convergence problems.

Show Verification Report

Produces a table in the output window with a list of overloaded power system elements and voltage violations, according to the following values:

Max. Loading of Edge ElementReference value of the maximum loading used by the 'Verification Report'.

Lower Limit of Allowed VoltageReference value for the minimum allowed voltage used by the 'Verification Report'.

23 - 27


Upper Limit of Allowed VoltageReference value for the maximum allowed voltage used by the 'Verification Report'.

OutputDisplays the report format definition that will be used. The arrow

button ( ) can be pressed to edit or inspect the report settings. This option is only available if Show Verification Report is selected.

23.2.6 Low Voltage Analysis

As explained in Sections 23.1.3 and 23.2.1, low voltage loads (ElmLodlv and ElmLodvp) are modelled in PowerFactory with fixed and variable (stochastic) components. The parameters which define these fixed and variable components are set in both the load flow command dialogue (i.e. globally), and in the load types’ dialogues (i.e. locally) according to the settings defined below.

Definition of Fixed Load per Customer

The fixed load is the non-stochastic component of the load, which is not subject to coinci-dence factors. The active and reactive power defined in this field, multiplied by the number of customers (defined in the load element itself), are added to the fixed load component defined for each low voltage load (ElmLodlv and ElmLodvp). For further information about LV loads please refer to the corresponding technical references: C.2.6 and C.2.7.

Definition of Variable Load per Customer

The variable component of low voltage loads can be globally defined using the parameters in this section or by specifically defining LV load types for the target loads.

The Max. Power per Customer is the independent maximum kVA per customer. This value, multiplied by the Coincidence Factor (ginf) (see Section 23.1.3), gives the "Average Power" per customer, which is used in load flow calculations.

The 'total' maximum variable power per load is calculated using the Max. Power per Customer, the Coincidence Factor (ginf), and the number of customers (defined in the load element itself) as described in Section 23.1.3.

For further information about LV loads please refer to the corresponding technical refer-ences: C.2.6 and C.2.7.

Note The factors defined in the section 'Definition of Variable Load per Customer' are used as global data for the load flow calcula-tion. If specific LV load types are defined, the locally-defined data in the type is used by the corresponding loads. For all other LV loads with no type assigned, the global data from the load flow command is used.

23 - 28


Voltage Drop Analysis

For the consideration of the stochastic nature of loads, PowerFactory offers two calcu-lation methods:

• Stochastic Evaluation

• Maximum Current Estimation

The Stochastic Evaluation method is the more theoretical approach, and can also be applied to meshed network topologies. The Maximum Current Estimation method applies stochastic rules only for the estimation of maximum branch flows. Based on the maximum current flow in each branch element, maximum voltage drops are calculated and added along the feeder. Obviously, this method has its limitations in case of meshed LV networks.

23.2.7 Advanced Simulation Options

This page, as shown in Figure 23.18, is not only important for load flow but also for other calculation functions such as transient simulation. Utilizing the options on this page can result in improved performance; i.e. the speed of a transient simulation may improved when protection devices are neglected in the calculation.

Fig. 23.18: Advanced Simulation Options in the load flow command dialogue

Consider Protection DevicesCalculates the tripping times for all modeled relays and fuses. This will also show the load currents in the overcurrent plots and/or the measured impedance in the R-X diagrams. Disabling this option will speed up the calculations.

Ignore Composite ElementsDisables all controller models. The panes Models Considered and Models Ignored are used to disable specific groups of controller models. Model names can be moved between these panes by either

23 - 29


double-clicking on them or by selecting them and using the arrow buttons. Enabling this option may result in faster convergence, or an increased likelihood of convergence for systems which are otherwise difficult to solve.

23.3 Result Analysis

In PowerFactory the results can be displayed directly in the single line diagram, in tabular form or by using predefined report formats. Also available are several diagram colouring options in other to have a "quick" overview of the results.

23.3.1 Viewing Results in the Single Line Diagram

Once a load flow calculation has been successfully executed, the result boxes shown in the single-line diagram will be populated. There is a result box associated with each "side" of an element. So for example a load has one result box, a line two result boxes, and a three-winding transformer three result boxes. In PowerFactory these elements are collectively called edge elements. In addition, there are result boxes for nodes or buses.

The information shown inside a result box depends on the element to which it is associated. There are a few predefined formats for edge elements and a few predefined formats for buses. In order to see the selection, first perform a load flow, then, from the main menu, select Output Results for Edge Elements or Output Results for Buses. These menu options will show the list of available result box formats. Alternatively, you can select (click) inside a result box on the single-line diagram, then right-click and from the context sensitive menu choose Format for Edge Elements or in case of a node Format for Nodes. Figure 23.19 serves as an example.

Fig. 23.19: Selecting the Result Box from the Single Line Diagram.

Besides these predefined formats the result boxes can be formatted in order to display selected variables.

23 - 30


By right-clicking on one of the result boxes and selecting the option Edit Format for Edge Elements and afterwards pressing the "Input Mode" button three options will be available: "Predefined Variables", "User Selection" or "Text Editor". The "User Selection" option will allow the selection of any of the available variables.

23.3.2 Flexible Data Page

Once a load flow calculation has been successfully executed, pressing the "Edit Relevant

Objects for Calculation" button ( ) located on the main menu will prompt a submenu with icons for all classes that are currently used in the calculation. Clicking any of the class-icons will open a browser with all elements of that class that are currently used in the calculation. The left-most tab-page at the bottom of the browser is the "Flexible Data" tab page. Click on this tab page to show the flexible data. To change the columns in the

flexible page, press the "Define Flexible Data" button ( ). This will bring a selection window where the set of variables can be edited. In the left pane the available variables will be shown while the right pane will list the selected variables. Pressing the << or >> buttons will move the selected variable from the one pane to the other pane.

23.3.3 Predefined Report Formats (ASCII Reports)

In PowerFactory there are predefined report formats also called ASCII reports, available to the user. These ASCII reports can be created by pressing the "Output Calculation

Analysis" button ( ) located on the main menu (a load flow must be calculated first). This will bring a selection window in which the user can select a specific type of report. Some reports like the "Complete System Report" will have various options which the user can set. The report selection window also shows the report definition which will be used for the selected report. Pressing Execute will write the report to the output window. Although the reports are already predefined, the user has the possibility of modifying the reports if required (by clicking on the blue arrow pointing to the right of the "used format" definition).

A Verification Report can be also printed out automatically each time a load flow calcu-lation is executed (see Section 23.2.5).

23.3.4 Diagram Colouring

When performing load flow calculations, it is very useful to colour the single line-diagram in order to have a quick overview of the results, for example if elements have a loading above 90% or if the voltages of the busbars are outside the specified limits. In Power-Factory there is the option of selecting different colouring modes according to the calcu-lation performed. If a specific calculation is valid, then the selected colouring for this calculation is displayed. As an example, if the user selects the colouring mode "Zones" for "No Calculation" and "Low and High Voltage/Loadings" for the load flow calculation, then the initial colouring will be according to "Zones". However, as soon as the load flow is calculated, the diagram will be coloured according to "Low and High Voltage/Loadings". If the load flow calculation is reset or invalid, the colouring mode switches back to "Zones".

The Diagram Colouring has also a 3-priority level colouring scheme also implemented,

23 - 31


allowing colouring elements according to the following criteria: 1st Energizing status, 2nd

Alarm and 3rd "Normal" (Other) colouring.

Energizing StatusIf this check box is enabled "De-energized" or "Out of Calculation" elements are coloured according to the settings in the "Project Colour Settings". The settings of the "De-energized" or "Out of Calculation" mode can be edited by clicking on the "Colour Settings" button.

AlarmIf this check box is enabled a drop down list containing alarm modes will be available. It is important to note here that only alarm modes available for the current calculation page will be listed. If an alarm mode is selected, elements "exceeding" the corresponding a limit are coloured. Limits and colours can be defined by clicking on the "Colour Settings" button.

"Normal" (Other) ColouringHere, two lists are displayed. The first list will contains all available colouring modes. The second list will contain all sub modes of the selected colouring mode. The settings of the different colouring modes can be edited by clicking on the "Colour Settings" button.

Every element can be coloured by one of the three previous criteria. Also, every criterion is optional and will be skipped if disabled. Regarding the priority, if the user enables all three criterions, the hierarchy taken account will be the following:

- "Energizing Status" overrules the "Alarm" and "Normal Colouring" mode. The "Alarm" mode overrules the "Normal Colouring" mode.

23.3.5 Load Flow Sign Convention

By default, PowerFactory has the following load flow sign convention (Mixed Mode):

Branches:Power Flow going out of the Busbar is positive while going into the busbar is negative.

Loads: Power Flow going out of the Busbar is positive while going into the busbar is negative. Here, the term load considers "General Loads", "Low-Voltage Loads", "Motors", "Shunts/Filters" and "SVS". A synchronous machine stated as a "Motor" will have also this sign convention.

Generation:Power Flow going out of the Busbar is negative while going into the busbar is positive. Here, the term Generation considers "Generators", "External Grids", "Static Generators" and "Current and Voltage Sources". An asynchronous machine stated as a "Generator" will have also this sign convention.

In PowerFactory there is the option of choosing between the following sign conven-tions:

23 - 32


• Mixed Mode (Default).

• Load Oriented (all the flows directions will be according to the load definition).

• Generator Oriented (all the flows directions will be according to the generator definition).

In order to change the sign convention, select Edit Project... from the main menu. In the dialogue window that pops-up, go to the Basic Data tab page and click on the Project Settings button. In the Advanced Calculation Parameters tab page of the Project Settings window (Figure 23.20) click on the Flow Orientation drop down window and select the required option.

Fig. 23.20: Flow Orientation Setting

23.4 Troubleshooting Load Flow Calculation Problems

In general, if a solution can be found (in other words, the network is mathematically solvable), PowerFactory will find a solution. In some cases the user may have made an error which will not allow a solution to be found; such as a large load causing a voltage drop so large that a voltage collapse results. In a real-world power system the same problem would be found.

When creating a network for the first time it is best to enter the data for only a small part or 'path' of the network and solve the network by calculating a load flow. PowerFactoryhas a data verification process in which certain checks are performed, such as whether a line is connected between nodes of the same voltage; and the correct voltage orientation of transformers, etc.

Typical reasons for non-convergence in the load flow are:

• Data model problem.

• Too many inner loop iterations.

• Too many outer loop iterations.

• Excessive mismatch.

23 - 33


• Tap hunting.

Clearly this is not an exhaustive list of problems, but these are the main causes of non-convergence and that will be discussed in this section.

23.4.1 General Troubleshooting

The place to search for the causes of the non-convergence problem is in the Power-Factory output window. Here, there can be three different types of messages printed out, which are the following:

Info messages (green/blue):Information detailing the load flow convergence (inner and outer loop iterations).Information of generators with reactive power compensation at output limit.Information on the total number of isolated areas (see 23.4.3).

Warning messages (dark red):Warning messages do not need to be corrected for the load flow to solve, however they could give you an indication of where the problem is. Take note of the warning messages and evaluate them in terms of your system. Important warnings, such as ''Exceeding Mvar limit range'' may not be acceptable.''Unsupplied Areas'' messages indicate that an isolated area with ''Consumers'' (such as loads and motors) is without a generator, power source or external supply.

Error messages (red): Error messages must be corrected for a load flow to solve. Error messages could be generated by PowerFactory's data checking function, which include messages such as DIgSI/err - missing type! In most cases the messages have links to the data base and graphic. The following options can be performed in order to trace errors:

• Use the data-verification tool ( ).

• Once errors have been detected, open the problematic element dialogue window by double clicking on the name directely from the output window. Or alternatevely, right mouse button over the name and select 'edit', or 'edit and browse', or 'mark in graphic'.

The amount of information being printed to the PowerFactory output window can be changed by the user. Once error messages have been analyzed and corrected and the load flow still does not solve, the user may want to print more detailed information on the convergence progress.

Tick the Show Convergence Progress Report option found in the Outputs tab of the load flow dialogue (refer to Section 23.2.5).

This will print messages to the output window that can provide clues as to where the convergence problems may lie.

The single line graphic can also be colored to show low and high voltages and overloadings. This will also provide a good indication of possible problems. Look at the undervoltage nodes and overloaded elements and investigate why they are overloaded; look at load setpoints, line lengths and line type data (the impedances may be too high, for example).

Note As explained above, there are 3 different types of messages that

23 - 34


are printed to the output window: warning, error and information messages. Only error messages must be corrected for a load flow to solve. Take note of the warning messages and evaluate them in terms of your system, however these do not need to be corrected for the load flow to solve. "Unsupplied Areas" means that unsup-plied areas with ''Consumers'' is without a generator, power source or external supply.

If there is still no convergence then set the option Out of Service for most of the elements (see each elements Basic Data tab). Following this, bring these elements back into service, one at a time, from the source element 'downwards', performing a load flow calculation each time.

When experiencing large unbalances, such as when there are a number of single or dual phase elements, or when using power electronics elements, select the Newton-Raphson (Current Iteration) option on the Advanced tab of the load flow dialogue.

23.4.2 Data Model Problem

In PowerFactory, there are three different levels of data verification implemented:

Parameter Level:Checks the consistency of the parameter being inputted; for example, inputting a negative value in the length of the line will prompt an error message. Other verifications implemented include checking if the parameter inputted is within certain limits.

Object Level:Checks the consistency of the data being inputted from the component itself; for example, checking if the magnetizing losses of a transformers are less that the total magnetizing apparent power (i.e. magnetizing current), checking if the inputting of the manufacture’s data results in a feasible torque-slip characteristic, etc.

System Level:Checks the consistency of the data being inputted from a system point of view; for example, checking if lines/cables are connected between the same voltage levels, checking if the HV/MV/LV side of transformers is compatible with the voltage level of busbars, checking if there are missing types, etc.

Data model problems can normally be fixed easily as the output window message refers directly to the element causing the problem.

Typical cases of data model problems are:

DIgSI/err - missing type!: It indicates that input data (electrical data defined in types) is missing. In most cases the messages have links to the data base and graphic.

DIgSI/err - Check control conditions!: It normally appears when more than one controller (for example a station controller) is set to control the same element, such as the same busbar. PowerFactory will print the name of the controlled element to the output window. Starting from the controlled element, access the controllers to fix the problem.

DIgSI/err - Line connected between different voltage levels!

23 - 35


23.4.3 Some Load Flow Calculation Messages

DIgSI/info - Grid split into 182 isolated areasAn ''isolated area'' indicates that a busbar or a group of busbars are not connected to the slack busbar. An isolated generator or an isolated external grid forms an isolated area. An isolated area refers basically to nodes.Each isolated area is assigned an index (Parameter name b:ipat under ElmTerm\Basic) and needs a load flow reference (slack) of its own. These busbars can be found colouring the single line graphic according to isolated grids.

DIgSI/wrng - 2 area(s) are unsuppliedAn ''unsupplied area'' is an isolated area with ''Consumers'' (such as loads and motors) without a generator, power source or external supply. That is U=0 and I=0. Unsupplied areas belong to the group of isolated areas. The unsupplied areas can be identified by displaying the following parameter in the ''Consumers'' components (loads, synchronous/asynchronous motors):

• r:bus1b:ipat. Gives the Index of the isolated area

• r:bus1:b:imode= 0. Indicates there is no slack in the isolated area therefore indicating its unsupplied.

• r:bus1:b:imode> 0. Indicates the area is supplied.

DIgSI/err - Outer loop did not converge. Maximum number of iterations reachedFore some hints on this type of error please refer to Section 23.4.5.

23.4.4 Too many Inner Loop Iterations

Too many inner loop iterations are ''normally'' related to voltage stability (voltage collapse) problems. For example, a large load causing voltage drops so high that a voltage collapse results. Also very weak connections resulting from faults or outages may lead to voltage collapse during contingency analysis.

The problem will not only be found in the simulation but would be found in the real world as well!

The main causes leading to a voltage stability problem can be summarized as follows:

- Excessive active power demand leading to a high voltage drop.

- Lack of reactive power compensation.

Diagnosis and Solution:The main source of Information is the output window.Enable the ''Show Convergence Progress Report'' option found in the ''Outputs'' tab of the load-flow dialogue.Analyze the convergence of the inner loop iterations: check the progress in the load flow error for nodes and model equations:

• Are they increasing or decreasing?

• If the error is not continuously decreasing, it could be an indication of a voltage stability problem.

23 - 36


• Identify the element (load, generator) with high convergence error. Use the Mark in Graphic option to identify the zone of the network having the problem.

Several possible countermeasures can be undertaken to fix the problem:

• Use the Iteration Control options on the load flow command (increasing the number of stairs as the first option, typically to 3).

• Load shedding: disconnect the load identified as responsible for the high convergence error.

• Connect additional reactive power compensation.

• Using the flexible data page, check if there are any heavily loaded circuits, these indicate weak connections.

Once the load flow converges, check if there are areas with voltages with high deviation from operating voltages.

Excessive Mismatch

Where there is a large mismatch between demand and generation (>15%) the load flow is unlikely to converge. This is typified by a large number of iterations followed by warnings or errors such as:

No convergence in load flow!

Equation system could not be solved. Check Control Conditions!

Depending on the size of the mismatch, the failure might occur during the initial Newton-Raphson or during subsequent outer loop iteration. There may also be a large number of maximum/minimum reactive power reached and transformer tap statements.

Solution:

• Set the option Show Convergence Progress Report on the Outputs tab page and observe which elements are having the highest mismatches. These elements should be closely checked.

• Check the mismatch on the Reference machine by performing a DC load flow as Dispatched allowing for normal losses. Rebalancing the network might alleviate convergence problems.

23.4.5 Too Many Outer Loop Iterations

Outer loops iterations are required to calculate discrete tap positions of transformers, number of steps of switchable reactive power compensation, etc. in order to match the voltage profile or reactive power control specified by the user.

Too many outer loop iterations is referring to a solution that is too far away from the starting point (default tap positions) to converge in the allowed number of outer loop iterations.

Diagnosis and Solution:The outer-loop does the following:

23 - 37


• Increasing/Decreasing discrete taps.

• Increasing/Decreasing switchable shunts.

• Limiting/Releasing synchronous machines to/from max/min reactive power limits.

If the outer loop does not converge, it can have the following reasons:

• Tap upper and lower limits are too close, so that the voltage can never be kept in the desired range.

• The same with switchable shunts.

• Other toggling effects, for example synchronous machine limits and tap positions don't find a stable solution.

The main source of Information is the output window. Check first the following:

• Is the number of messages reducing with each outer loop iteration?

The following messages in the output window may indicate a problem and lead to a non-convergent solution.

Maximum/minimum tap position reached

DIgSI/pcl - --------------------------------

DIgSI/pcl - '\.... \Transformer.ElmTr2':

DIgSI/pcl - Maximum Tap Position reached

DIgSI/pcl - --------------------------------

The message indicates that more/less reactive power is required at this location (the tap is at maximum/minimum position). The message indicates therefore an area in the network where a lack/excess of reactive power is likely to happen.

Reactive power limit left

DIgSI/pcl - --------------------------------

DIgSI/pcl - '\.... \ Generator.ElmSym':

DIgSI/pcl - Reactive Power Limit left

DIgSI/pcl - --------------------------------

This will lead to a convergence error. A load flow calculation without considering reactive power limits may find a solution. Check then required reactive power at the generator.

Maximum/minimum reactive power reached.

DIgSI/pcl - --------------------------------

DIgSI/pcl - '\....\Generator.ElmSym':

DIgSI/pcl - Maximum Reactive Power Reached

DIgSI/pcl - --------------------------------

23 - 38


Basically means that there is no regulation margin in the specified generators.

In general the results from the last iteration should be available to view on the output window.

• Is the mismatch always in the same (or similar) location?

• How far away from the solution was the original starting point?

All actions (except for shunt switching) are displayed in the output window by blue messages. Observing these messages allows to conclude what the reason for the convergence problem was, for example if a synchronous machine toggles between limited/released, the problem is related to this particular machine.

• If no toggling can be observed, increasing the maximum number of outer iteration loops may help.

• If the load flow converges, improve the convergence of subsequent

calculations by saving the tap positions ( ).

If the load flow does not converge after a large number of iterations then other methods of improving convergence are:

• Use the direct method on the advanced options page of the load flow command.

• Set the maximum tap changes per iteration to be a small number, for example 1. This will result in PowerFactory not changing all tap changers at once by several steps but only by maximum of 1 step at once. In larger networks this is often improving the convergence.

• Perform a load flow without automatic taps and shunt adjustment. If the load flow does not converge in this case, it could be an indication that the load is exceeding the voltage stability limits, thus the load is too high.

Tap Hunting

Tap hunting can be easily recognised when one or more transformers oscillate between tap positions until the number of outer loop iterations is exhausted. This is normally due to the transformer (controller) target voltage dead band being smaller than the trans-former tap step size.

The messages below indicate an example of a single transformer Tap-Hunting:

23 - 39


This problem of no converging load-flow with the 'stepped' tap changing method is caused by a slightly different way of the iteration to reach the correct tap position and load-flow results. This might result in a non-convergence in the outer loop, when the controller range (Vmax-Vmin) of the tap changer is near to the value of the additional voltage per tap.

Solution:

• Change the minimum relaxation factor on the Advanced Options tab page of the load flow command to a smaller value. This might help the load flow to converge.

• Check if the dead bands of the target or control busbars of the corresponding transformers are correctly set. Also check if the tap changer data on the load flow page of the transformer type is correct.

• Disable the automatic tap changing of the transformers where tap hunting occur. Run the load flow (it should converge in this case!) and then check the sensitivity of the tap changer increasing and decreasing the tap position by one step. Verify the results against the dead band of the target busbar.

23.5 Load Flow Sensitivities

PowerFactory’s Load Flow Sensitivities (ComVstab) command is shown in Figure 23.21. This command performs a voltage sensitivity analysis based on the linearization of the system around the operational point resulting from a load flow calculation (as explained in Section 23.5.3).

The ComVstab command is accessible by the following means:

• selecting the 'Additional Tools' icon ( ) for the toolbar (in PowerFactory’s main

icon bar) and then clicking on the ComVstab icon ( ); or

• right-clicking on a busbar/terminal or transformer and selecting Calculate --> Load Flow Sensitivities... . In this case the command will be automatically set to calculate the sensitivity to power injections/tap changes on the selected busbar/transformer.

23 - 40


The selected terminal/transformer will be automatically set in the Busbar (or Transformer) reference.

Fig. 23.21: Load Flow Sensitivities Command (ComVstab) Dialogue

23.5.1 Load Flow Sensitivities Options

The options available for the Load Flow Sensitivities command (Figure 23.21) are:

Initialization

Load Flow:Displays which load flow command will be used to initialize the sensitivity analysis. If no load flow calculation has been executed before opening the Load Flow Sensitivities (ComVstab) command, or if the calculation has been reset, the Load Flow displays the most recently executed load flow command in the active study case.

Sensitivities

Diagonal Elements Only:The effect of the injections of P and Q at each busbar are evaluated for the busbar itself (effect on voltage magnitude ,

, and on voltage angle , for each busbar) and the corresponding adjacent branches. In this mode, the calculated sensitivities , , , and

in the branches (index n) always refer to derivations

and of the adjacent buses (index i). This means that the sensitivities are calculated for all busbars and for all branches, according to variations in power (P and Q) at the directly connected busbars.

Sensitivity to a Single Busbar:The effect of the injections of P and Q at the selected busbar are calculated for the whole network (i.e. for all buses and branches). The

target busbar can be selected using the Busbar button ( ) located at the bottom of the dialogue. Alternatively, the target bus can be

vi Pi

vi Qi i Pi i Pi

Pn Pi Qn Pi Pn Qi

Qn Qi

Pi Qi

23 - 41


selected in the single line graphic by right-clicking on it and selecting Calculate --> Load Flow Sensitivities from the context-sensitive menu. The sensitivities of all busbars and branches are calculated according to variations in power (P and Q) at the selected busbar.

Sensitivity to a Single Transformer Tap Position:This option evaluates the effect of changing the tap position of a selected transformer in the network. The sensitivities dP/dtap [MW/tap step], dQ/dtap [Mvar/tap step] for branches, and dphi/dtap [deg/tap step], dv/dtap [p.u./tap step] for buses are calculated. The target

transformer can be selected using the Transformer button ( ) located at the bottom of the dialogue. Alternatively, the target transformer can be selected in the single line graphic by right-clicking on it and selecting Calculate -> Load Flow Sensitivities from the context-sensitive menu.

Modal Analysis:This option performs an eigenvalue calculation on the sensitivity matrix as explained in Section 23.5.3. The number of eigenvalues to be calculated is defined in the Number of Eigenvalues field at the bottom of the dialogue. The eigenvalues are always calculated in order of their largest magnitude, so selecting n eigenvalues will display the n eigenvalues in descending order according to magnitude (note that the larger the number of desired eigenvalues, the longer the calculation will take).In the Display Results for Mode field, the user can specify the number of a specific eigenvalue, for which the stability behavior (i.e. the eigenvectors and participation factors) is to be analyzed. The algorithm then additionally calculates the , (branch sensitivities) and the , (bus sensitivities) which correspond to the mode specified (see Section 23.5.3 for further technical background).

23.5.2 Load Flow Sensitivities Execution and Results

When the ComVstab command has been configured and the Execute button has been pressed, the program calculates several sensitivity factors such as ,

, , etc., according to the selected options, for buses and branch elements.

Upon completion of the sensitivity factor calculation, the following message appears in the output window:

DIgSI/info - Load Flow Sensitivities calculated!

The calculated results can be displayed via the 'Flexible Data Page' (see Section 12.5) by selecting the sensitivities from the load flow variables (Variable Set: 'Current, Voltages and Powers'). The names of the variables correspond to the calculated derivations, i. e. the result of the expression is stored in the variable named dvdP; and likewise

the result of the expression is stored in the variable dphidQ.

P Q Q Q v Q Q

vi Pi

vi Qi i Pi i Qi

vi Pi

i Qi

23 - 42


When the Modal Analysis option is selected, the calculated eigenvalues are displayed (in descending order according to magnitude) in the output window. The eigenvectors and participation factors can be displayed using the 'Flexible Data Page'.

23.5.3 Technical Background

PowerFactory’s Load Flow Sensitivities function (ComVstab) performs a static voltage stability calculation as described below.

Linearizing the load flow equations around the actual operating point leads to the following equation system:

Eqn 23.6:

The equation system in (23.6) shows that changes in the voltage magnitude and angle due to small changes in the active and reactive power can be directly calculated from the load flow Jacobian matrix. For example if P is set to 0, the sensitivities of the type dv/dQ are calculated from (23.6) according to:

Eqn 23.7:

where:

Eqn 23.8:

As can be seen from (23.7), the variation of voltage magnitude at each busbar can be described by a linear combination of small reactive power variations according to:

Eqn 23.9:

In this case the diagonal elements Si1 of S represent the voltage variation at bus i due to a variation of reactive power at the same point. The non-diagonal elements Sij describe the voltage variation at busbar i due to the variation in reactive power at a different point on the network.

Positive dv/dQ sensitivity indicates stable operation. High sensitivity means that even small changes in reactive power cause large changes in the voltage magnitude; therefore the more stable the system, the lower the sensitivity (high voltage sensitivities are indic-ative of weak areas of the network).

Note: Recall that in HV networks branches are predominantly reactive.

JP JPv

JQ JPv

v

PQ

=

v JQv1–Q SvQQ= =

JQv JQJP1–

JPv– JQv+=

vi Si1Q1 SinQn+ +=

23 - 43


Voltage magnitudes depend primarily on reactive power flows and voltage angles depend on active power bus injections.

The sensitivity analysis can be extended in order to determine the active and reactive power variations on branches (in the PowerFactory network model all components carrying a flow, i.e. lines, transformers, generators are regarded as branches) due to variations in active and reactive power busbar injections. In this case the sensitivities are calculated using the branch-node Jacobian matrix.

By applying a modal transformation to (23.7) the dV/dQ sensitivity can be expressed as an uncoupled system of the form:

Eqn 23.10:

where:

Eqn 23.11:

In (23.10), is a diagonal matrix whose elements correspond to the eigenvalues of the sensitivity matrix, SvQ, from (23.7). Therefore, the voltage variation at each mode depends only on the reactive power variation at the same mode:

Eqn 23.12:

The eigenvalues i, which are real, provide the necessary information about the voltage stability of the system. If i is positive, the modal voltage increase and the modal reactive power variations are in the same direction and the system is therefore stable. The magnitude of the eigenvalue indicates how far/close one voltage mode is to instability.

In (23.10), T= [1...n] corresponds to the matrix of right eigenvectors of SvQ, while T-

1 corresponds to the left eigenvectors matrix:

Eqn 23.13:

The participation factor of bus k to mode i is defined by the product of the kth component of the left and right eigenvector of mode i:

v T1–SvQTQ SvQQ= =

v Tv and Q TQ= =

SvQ

vi iQi=

T1–

1T

nT

=

23 - 44


Eqn 23.14:

The sum of the participation factors of all nodes corresponds to the scalar product of the left and right eigenvector, and is therefore equal to one. In this sense, the participation factor gives an indication of the extent of the influence the variation of active power on a node has on a voltage mode.

pik ikik=

23 - 45


23 - 46

DIgSILENT PowerFactory Short-Circuit Analysis

Chapter 24Short-Circuit Analysis

Power systems as well as industrial systems are designed so that loads are supplied safely and reliably. One of the major aspects taken into account in the design and operation of electrical systems is the adequate handling of short-circuits. Although systems are de-signed to stay as free from short circuits as possible, they still can occur. A short-circuit condition generally causes large uncontrollable currents flows, which if not properly de-tected and handled can result in equipment damage, the interuption of large areas (in-stead of only the faulted section) as well as placing personnel at risk. A well-designed system should therefore isolate the short-circuit safely with minimal equipment damage and system interruption.Typical causes of short-circuits can be the following:

• Lightning discharge in exposed equipment such as transmission lines.

• Premature aging of the insulation due mainly to permanent overloadings, inappropriate ventilation, etc.

• Atmospheric or industrial salt ''Build-Up'' in isolators.

• Equipment failure.

• Inappropriate system operation.

One of the many applications of a short-circuit calculation would be to check the ratings of network equipment during the planning stage. In this case, the planner is interested in obtaining the maximum expected currents (in order to dimension equipment properly) and the minimum expected currents (to aid the design of the protection scheme). Short-circuit calculations performed at the planning stage commonly use calculation methods that require less detailed network modelling (such as methods which do not require load information) and which will apply extreme-case estimations. Examples of these methods include the IEC 60909/VDE 0102 method, the ANSI method and the IEC 61363 method. A different field of application is the precise evaluation of the fault current in a specific situation, such as to find out whether the malfunction of a protection device was due to a relay failure or due to the consequence of improper settings (for example an operational error). These are the typical applications of exact methods such as the superposition method (also known as the Complete Method), which is based on a specific network op-erating point.

The short-circuit calculation in PowerFactory is able to simulate single faults as well as multiple faults of almost unlimited complexity. As short-circuit calculations can be used for a variety of purposes, PowerFactory supports different representations and calculation methods for the analysis of short-circuit currents.

This chapter presents the handling of the short-circuit calculation methods as implement-ed in PowerFactory. Further background on this topic can be found in Section 24.1.

24 - 1



Beside load flow calculations, short-circuit is one of the most frequently performed calcu-lations when dealing with electrical networks. It is used both in system planning and sys-tem operation (see Figure 24.1, in special cases Methods 2.1 and 2.2 are also used for network planning). Calculation quantities which have been newly-introduced in Power-Factory Version 14 are shown in Figure 24.1, also a graphical representation of the short-circuit current time function is illustrated in Figure 24.2. The IEC 61363 standard which outlines the procedures for calculating short-circuit currents that may occur on a marine or off shore a.c. electrical installation is not shown in Figure 24.1.

Fig. 24.1: Areas of Application of Short-Circuit Calculations

According to IEC 60909 the definition of the currents and multiplication factors shown in Figure 24.1 are as follows:

• initial symmetrical short-circuit current (RMS),

• peak short-circuit current (instantaneous value),

• symmetrical short-circuit breaking current (RMS),

• thermal equivalent short-circuit current (RMS),

• factor for the calculation of the peak short-circuit current,

• factor for the calculation of the symmetrical short-circuit breaking current,

• factor for the heat effect of the d.c. component,

• factor for the heat effect of the a.c. component,

besides the above currents, the Complete Method introduces the following current defini-tion:

• peak short-circuit breaking current (instantaneous value).

Ikss

ip

Ib

Ith

m

n

ib

24 - 2


Fig. 24.2: Short-Circuit Current Time Function

Typical applications examples of short-circuit analysis in system planning include:

• Ensuring that the defined short-circuit capacity of equipment is not exceeded with system expansion and system strengthening.

• Co-ordination of protective equipment (fuses, over-current and distance relays).

• Dimensioning of earth grounding systems.

• Verification of sufficient fault level capacities at load points (e.g. uneven loads such as arc furnaces, thyristor-driven variable speed drives or dispersed generation).

• Verification of admissible thermal limits of cables and transmission lines.

Example applications of short-circuit analysis in system operation include:

• Ensuring that short-circuit limits are not exceeded with system reconfiguration.

• Determining protective relay settings as well as fuse sizing.

• Calculation of fault location for protective relays, which store fault disturbance recordings.

• Analysis of system faults, e.g. misoperation of protection equipment.

• Analysis of possible mutual interference of parallel lines during system faults.

The fundamental difference between the assumptions used by the calculation methods is that for system planning studies the system operating conditions are not yet known, and therefore estimations are necessary. To this end, the IEC 909 (VDE 0102) method which uses an equivalent voltage source at the fault location has become generally accepted in Western Europe. A revised version of this was published as IEC 60909 in July 2001. This method works independently of the load flow (operating point) of a system. It is based on the nominal and/or calculated dimensions of the operating point of a system and uses correction factors for voltages and impedances, to give conservative results. For the cal-culation of minimum and maximum short-circuit currents, different correction factors are applied. However, it should be mentioned that both IEC 60909 and VDE 0102 do not deal with single phase elements (expect single phase elements in the neutral conductor).

Another very similar method is the ANSI method, which is basically used in North America and is accepted in other countries as well. The ANSI method is based on the IEEE Stan-

24 - 3


dards C37.010(1979) which is for equipment applied in medium and high voltage systems (grater than 1000 Volts) and C37.13(1990) which is for power circuit breakers in low volt-age systems (less that 1000 Volts).

For short-circuit calculations in a system operation environment, the exact network oper-ating conditions are well-known. If the accuracy of the calculation according to IEC 60909 is not sufficient - or to verify the results of this method - the superposition method can be used. The superposition method calculates the expected short-circuit currents in the net-work based on the existing network operating condition. If the system models are correct, the results from this method are always more exact than the results of the IEC 60909 method. The system analyst is, however, responsible that she/he has chosen the most unfavourable conditions with respect to the sizing of plant. In some cases, this might re-sult in extensive studies required.

Also available in PowerFactory Version 14 is the IEC 62363 method which outlines the procedure for calculating short-circuit currents on marine or offshore electrical systems such like ships.

24.1.1 The IEC 60909/VDE 0102 Method

The IEC 60909/VDE 0102 method uses an equivalent voltage source at the faulted bus and is a simplification of the superposition method (Complete Method). It is illustrated in Figure 24.3.

The goal of this method is to accomplish a close-to-reality short-circuit calculation without the need for the preceding load-flow calculation and the associated definition of actual operating conditions. Figure 24.3 illustrates how the equivalent voltage source method can be derived from the superposition method. The main simplifications are as follows:

• Nominal conditions are assumed for the whole network, i.e. Ui = Un,i.

• Load currents are neglected, i.e. IOp = 0.

• A simplified simulation network is used, i.e. loads are not considered in the positive and negative sequence network.

• To ensure that the results are conservatively estimated, a correction factor, c, is applied to the voltage at the faulted busbar. This factor differs for the calculation of the maximum and the minimum short-circuit currents of a network.

The short-circuit calculation based on these simplifications may be insufficient for some practical applications. Therefore, additional impedance correction factors are applied to the physical impedances of the network elements. This method is described in detail in the following section.

Please note in addition that both IEC 60909 and VDE 0102 do not deal with single phase elements (expect single phase elements in the neutral conductor).

24 - 4


Fig. 24.3: Illustration of the IEC 60909/VDE 0102 Method

As illustrated in Figure 24.1, IEC requires the calculation of the initial symmetrical short circuit current in order to derive the rest of the physical quantities, each of which is a function of the following:

• R/X ratio,

• Machine characteristics

• Synchronous generator type of excitation system,

• Contact parting time,

• Type of network (if it’s radial or meshed),

• Determination if the contribution is "near to" or "far from" the short-circuit location,

Regarding the type of network, IEC describes three methods for the calculation of (peak short-circuit current) in meshed networks which are defined as follows:

Method A: Uniform Ratio R/XThe factor is determined based on the smallest ratio of R/X of all the branches contributing to the short-circuit current.

Ik

ip

24 - 5


Method B: Ratio R/X at the Short-Circuit LocationFor this method the factor is multiplied by 1.5 to cover inaccuracies caused by using the ratio R/X from a network reduction with complex impedances.

Method C: Equivalent FrequencyAn equivalent impedance Zc of the system as seen from the short-circuit location is calculated assuming a frequency (for a

nominal frequency ) or for a nominal frequency

). This is the recommended Method in meshed networks.

Note: In PowerFactory methods B and C are available to the user. Method C is the one recommended in meshed networks. For more information please refer to Section 24.3.4

IEC Impedance Correction Factors

The IEC method uses only the rated parameters of network elements. This is advanta-geous in that only little information is necessary to perform a short-circuit calculation. However, considering that, for example, the short-circuit contribution of a synchronous generator depends heavily on the excitation voltage and on the unit transformer tap changer position, the worst-case value of this impedance is considered by applying a cor-rection factor (< 1).

This idea is illustrated in Figure 24.4. The correction factor c should be determined so that I”k = I”k,IEC. The IEC standard defines an equation for the correction factor for each ele-ment type.

Fig. 24.4: Principle of Impedance Correction (IEC/VDE Method)

As the IEC standard includes a worst-case estimation for minimum and maximum short-circuit currents, some PowerFactory elements require additional data. These elements are:

LinesIn their type, the maximum admissible conductor temperature (for minimum short-circuit currents) must be stated (Figure 24.5). Line capacitances are not considered in the positive/negative sequence systems, but must be used in the zero-sequence system.

fc 20 Hz=

fc 50 Hz= fc 24 Hz=

fc 60 Hz=

24 - 6


Fig. 24.5: Maximum End Temperature Definition in the Line Type (TypLne)

TransformersRequire a flag indicating whether they are unit or network transformers as shown in Figure 24.6. Network transformers may be assigned additional information about operational limits which are used for a more precise calculation of the impedance correction factor. Unit transformers are treated differently depending on whether they have an on-load or a no-load tap changer (Figure 24.7).

Fig. 24.6: Unit Transformer Definition in the Transformer Element (ElmTr2)

Maximum End Tem-perature

Unit Transformer Definition

24 - 7


Fig. 24.7: On-Load Tap Changer Definition in the Transformer Type (TypTr2)

Synchronous MachinesSubtransient impedances are used. Additionally, information regarding the voltage range must be given as seen in Figure 24.8.

Fig. 24.8: Voltage Range Definition in the Synchronous Machine Element (ElmSym)

Asynchronous MachinesThe ratio of starting current to rated current is used to determine the short-circuit impedance (Figure 24.9).

On-Load Tap Chang-er Defini-tion

Syn. Machine Voltage Range

24 - 8


Fig. 24.9: Locked Rotor Current Definition in the Asynchronous Machine Type (ElmAsymo)

Please refer to the IEC 60909 standard to find detailed information regarding specific equipment models and correction factors for each element.

24.1.2 The ANSI Method

ANSI provides the procedures for calculating short-circuit currents in the following stan-dards:

ANSI/IEEE Standard C37.010 - 1979, IEEE Application Guide for AC High-Voltage Circuit Breakers Rated on a Symmetrical Current Basis.

ANSI/IEEE Standard C37.13 - 1990, IEEE Standard for Low-Voltage AC Power Circuit Breakers Used in Enclosures.

ANSI/IEEE Standard 141- 1993, IEEE Recommended Practice for Electric Power Dis-tribution of Industrial Plants (IEEE Red Book).

ANSI/IEEE Standard C37.5 - 1979, IEEE Application Guide for AC High-Voltage Circuit Breakers Rated on a Total Current Basis. (Standard withdrawn).

ANSI C37.010 details the procedure for equipment applied in medium and high voltage systems considering a classification of the generators as either "local" or "remote" de-pending on the location of the fault, as well as taking into account motor contribution. The procedure also covers first cycle and interrupting time currents, with emphasis on in-terrupting time currents.

ANSI C37.13 details the procedure for power circuit breakers applied in low voltage sys-tems (less than 1000 Volts), while mainly focusing on first-cycle currents, impedance of motors and the fault point X/R ratio. Typically, fuses and low voltage circuit breakers begin to interrupt in the first half cycle so no special treatment for interruptive current is given. It could be the case however, that nevertheless the equipment test include a dc compo-nent specification.

Due to the differences in the high and low voltage standards, it would be understandable to say that two first-cycle calculations are required. The first calculation would be for high voltage busbars and a second calculation would be for low-voltage busbars.

In IEEE/ANSI Standard 141-1993 (Red Book) a procedure for the combination of first cy-

Locked Ro-tor Current

24 - 9


cle network is detailed. There is stated that in order to simplify comprehensive industrial system calculations, a single combination first-cycle network is recommended to replace the two different networks (high/medium-voltage and low voltage). This resulting com-bined network is then based on the interpretation of the ANSI C37.010, ANSI C37.13 and ANSI C37.5 their given.

Total and Symmetrical Current Rating Basis of Circuit Breakers and Fuses according to ANSI Standards

Depending on the circuit breaker year of construction different ratings are specified. High-voltage circuit breakers designed before 1964 were rated on "Total" current rating while now a day's high-voltage circuit breakers are rated on a "Symmetrical" current basis. The difference between these two definitions is on how the asymmetry is taken into account. While a "Total" current basis takes into account the ac and dc decay, "Symmetrical" cur-rent basis takes into account only the ac decay. To explain further these definitions please refer to Figure 24.10.

Fig. 24.10: Asymmetrical Short-Circuit Current

The DC component "DC" is calculated according to the following equation:

Eqn 24.1:

The RMS value of the ac component (RMS) is then calculated as:

Eqn 24.2:

DCP1 P2–

2-------------------=

RMSP1 P2+

2.828-------------------=

24 - 10


The total interrupting current in RMS is then:

Eqn 24.3:

From the above, Equation (24.2) corresponds to the "Symmetrical" current calculation and Equation (24.3) to the "Total" current calculation.

Some of the main ANSI guidelines for the calculation of short-circuit currents are the fol-lowing:

• The pre-fault busbar voltage is assumed to be nominal (1.0 p.u.).

• The fault point X/R ratio is calculated based on a separate resistance network reduction which is latter used to calculate the peak and total asymmetrical fault current.

• Depending on the location of the fault, the generator currents being fed to the short circuit are classified as "local" or "remote". A remote source is treated as having only a dc decay, while a local source is treated as having a dc and ac decay. Depending on this classification, corresponding curves are used in order to obtain the multiplication factors.

According to ANSI standard, the following short-circuit currents are calculated:

• symmetrical momentary (first cycle) short-circuit current (RMS),

• symmetrical interrupting short-circuit current (RMS),

• asymmetrical momentary (Close and Latch - Duty) short-circuit current

(RMS). Obtained by applying a 1.6 factor to ,

• peak short-circuit current (instantaneous value). Obtained by applying a 2.7

factor to ,

• asymmetrical momentary (Close and Latch - Duty) short-circuit current

(RMS). Obtained by applying a factor to according to the calculated X/R ratio,

• peak short-circuit current (instantaneous value). Obtained by applying a

factor to , according to the calculated X/R ratio.

24.1.3 The Complete Method

The complete method (sometimes also known as the superposition method) is, in terms of system modelling, an accurate calculation method. The fault currents of the short-cir-cuit are determined by overlaying a healthy load-flow condition before short-circuit incep-tion with a condition where all voltage supplies are set to zero and the negative operating voltage is connected at the fault location. The procedure is shown in Figure 24.11.

The initial point is the operating condition of the system before short-circuit inception (see Figure 24.11a). This condition represents the excitation conditions of the generators, the tap positions of regulated transformers and the breaker/switching status reflecting the op-erational variation.

From these pre-fault conditions the pre-fault voltage of the faulted busbar can be calcu-

Tot DC2

RMS2

+=

Isym_m

Isym_i

I16asym_m

Isym_m

I27peak_m

Isym_m

Iasym_m

Isym_m

Ipeak_m

Isym_m

24 - 11


lated. For the pure fault condition the system condition is calculated for the situation where, the negative pre-fault busbar voltage for the faulted bus is connected at the fault location and all other sources/generators are set to zero (see Figure 24.11b).

Since network impedances are assumed to be linear, the system condition after fault in-ception can be determined by overlaying (complex adding) both the pre-fault and pure fault conditions (see Figure 24.11c).

Fig. 24.11: Illustration of the Complete Method

The Complete Method for calculating short-circuits has been improved in PowerFactory Version 14 as described below. Additionally, the quantities described below are shown in Figure 24.1.

• A more precise Peak Short-Circuit Current ip is calculated based on the accurate subtransient short-circuit current (which is calculated using the complete method) and the R/X ratio (which is based on the IEC 60909 standard);

24 - 12


• The Short-Circuit Breaking Current Ib (RMS value) is calculated based on the subtransient short-circuit current and the transient short-circuit current (both of which are calculated by the complete method);

• The Peak Short-Circuit Breaking Current ib is calculated from the RMS short-circuit breaking current Ib and the decaying d.c. component;

• The Thermal Equivalent Short-Circuit Current Ith is calculated based on the IEC standard, using the m and n factors (see Figure 24.1). The n-factor calculation uses the transient current instead of the steady-state current;

• Additionally, loads can have a contribution to the short-circuit current, which can be defined in the load element (Fault Contribution section of Complete Short-Circuit tab).

24.1.4 The IEC 61363 Method

The IEC 61363 standard describes procedures for calculating short-circuit currents in three-phase AC radial electrical installations on ships and on mobile and fixed offshore units.

The IEC 61363 standard defines only calculation methods for three phase (to earth) short circuits. Typically marine/offshore electrical systems are operated with the neutral point isolated from the hull or connected to it trough an impedance. In such systems, the high-est value of short-circuit current would correspond to a three phase short circuit. If the neutral point is directly connected to the hull, then the line-to-line, or line-to ship’s hull short-circuit may produce a higher current. Two basic system calculation approaches can be taken, "time dependent" and "non-time dependent".

According to the IEC 61363 standard, PowerFactory calculates an equivalent machine that feeds directly into the short circuit location. This machine summarizes all "active" and "non-active" components of the grid.

The shot-circuit procedure in IEC 61363 calculate the upper envelope (amplitude) of the maximum value of the time dependent short-circuit (see Figure 24.2). The envelope is cal-culated using particular machine characteristics parameters obtainable from equipment manufacturers using recognized testing methods, and applying the following assump-tions:

• All system capacitances are neglected.

• At the start of the short-circuit, the instantaneous value of voltage in one phase at the fault point is zero.

• During the short-circuit, there is no change in the short-circuit current path.

• The short-circuit arc impedance is neglected.

• Transformers are set at the main tap position.

• The short-circuit occurs simultaneously in all phases.

• For generator connected in parallel, all generators share their active and reactive load proportionally at the start of or during the short-circuit.

• During each discrete time interval, all circuits components react linearly.

The exact guidelines on how this is achieved is specified in the standard.

Because the standard considers specific system components and models ("active" and "non-active") some of the models that can be used in PowerFactory will have no de-

24 - 13


scription according to the standard (such as External Grids, Voltage Sources, Static Gen-erators, etc.). How these elements are considered and transformed to a replacement equivalent machine is described in the corresponding Technical Reference.

According to this method, the following short-circuit values are calculated:

• initial symmetrical short-circuit current,

• upper envelope of short-circuit current ,

• decaying (aperiodic) component of short-circuit current,

• peak short-circuit current,

• steady-state short-circuit current.

The calculating formulae and methods described produce sufficiently accurate results to calculate the short-circuit current during the first 100 ms of a fault condition. It is assumed in the standard that during that short time the control of the generators has no significant influence on the short circuit values. The method can be used also to calculate the short-circuit current for periods longer than 100 ms when calculating on a bus system to which the generators are directly connected. For time periods beyond 100 ms the controlling ef-fects of the system voltage regulators may be predominant. Calculations including the voltage regulator effects are not considered in this standard.

In PowerFactory besides the standard IEC 61363 method, an EMT simulation method is available which considers also the first 100 ms of a three phase short-circuit.

24.2 Executing Short-Circuit Calculations

There are different methods of initiating the short-circuit calculation command (ComShc) in PowerFactory, which may result in a different configuration of the command. These methods are described in Sections 24.2.1 and 24.2.2.

24.2.1 Toolbar/Main Menu Execution

The short-circuit command may be executed from the toolbar or main menu in Power-Factory as follows:

• By pressing the icon on the main toolbar; or

• By selecting the Calculation -> Short-Circuit ... option from the main menu.

If the user is performing the short-circuit for the first time (by using one of the above op-tions), the short-circuit command will be configured in a certain manner by default; that is the command will be set by default to execute a short-circuit calculation on all busbars/terminals in the network. If a short-circuit calculation has been already performed (the command exists in the study case) the settings displayed by the short-circuit command will be according to the most recent short-circuit calculation. As an example, if the user performs a short-circuit calculation according to ANSI for only one busbar in the system, the next time the user executes again the short-circuit, the command will have the most recent settings, that is, in this case according to ANSI and for the specified busbar.

I''k

Ik t

idc t

ip

Ik

24 - 14

http://www.digsilent.de/Company/Latest_News/files/IEC61363_TechnicalReference.pdf


24.2.2 Context-Sensitive Menu Execution

The short-circuit command may be executed from the context-sensitive menu in Power-Factory by selecting an element(s) in the single-line diagram, right-clicking and selecting one of the following options:

• Calculate... Short-Circuit: performs a short-circuit calculation for each element selected by the user. It should be noted that the short-circuit calculation for each element is carried out completely independently of the short-circuit calculation for each other element. For this calculation, only the following combinations of elements may be selected:

- Single or multiple terminals/busbars; or

- A single line; or

- A single branch.

If several terminals/busbars are selected for analysis, the results of each individual short-circuit calculation will be displayed together on the single-line graphic.

• Calculate... Multiple Faults: performs a short-circuit calculation according to the complete method, for the ‘simultaneous’ short-circuit of all elements selected by the user. Any combination of busbars, terminals, lines and branches can be selected for this calculation. Additionally, switch/circuit breaker open/close operations can also be included in the calculation. When this calculation is selected, the option Multiple Faults in the (ComShc) dialogue will be automatically ticked.

24.2.3 Faults on Busbars/Terminals

The short-circuit command should first be called using one of the methods described in Sections 24.2.1 and 24.2.2. The simplest way to calculate several busbar/terminal short-circuits individually and to then combine the results into one diagram is to select the op-tion All Busbars (or alternatively, Busbars and Junction/Internal Nodes) in the Fault Loca-tion section of the Short-Circuit Calculation (ComShc) dialogue, as displayed in Figure 24.12. Note that to access this option, Multiple Faults in the dialogue must be un-selected.

Fig. 24.12: Short-Circuit Calculation Command (ComShc) Dialogue: Faults at All Busbars

If the user would instead like to select from the single-line diagram a single busbar/ter-minal, or multi-select several busbars/terminals for calculation, the dialogue will be con-figured as follows:

• When only a single busbar/terminal is selected, and Calculate Short-Circuit is chosen from the context-sensitive menu, the Fault Location reference (bottom of dialogue) is set to the selected element.

• When two or more busbars/terminals are selected and Calculate Short-Circuit is chosen from the context-sensitive menu, the Fault Location reference (bottom of

24 - 15


dialogue) is set to a so-called "Selection Set'' (SetSelect) object, which contains a list of references to the selected busbars/terminals.

In either case, various options for the calculation can be modified. Please refer to Section 24.3 for a detailed description of the options available. It should be noted that selecting or deselecting the option Multiple Faults may change the selection of fault locations and may therefore lead to a calculation for locations other than the busbars/terminals selected in the single line graphic. After pressing the Execute button, the calculation is executed and, if successful, the results are displayed in the single line graphic. In addition, a result report is available and may be printed out.

Once a selection of fault locations is made and the short-circuit calculation is performed, it is simple to execute further calculations based on the same selection of elements. This can be done by the following alternative means of executing the short-circuit calculation command:

• By pressing the icon on the main toolbar; or

• By selecting the Calculation -> Short-Circuit ... option from the main menu.

The short-circuit setup dialogue then shows the previously selected busbars/terminals in the Fault Location section under User Selection.

24.2.4 Faults on Lines and Branches

It is not only possible to calculate short-circuits on busbars and terminals, but also on lines and branches. It should be noted, however, that only a single line or a single branch can be selected at a time, for each short-circuit calculation. It is not possible to select multiple lines and/or branches for calculation. To calculate a short-circuit on one of these types of elements, proceed as follows:

• From the single-line diagram, select a single line or a single branch where the fault should be calculated.

• Right-click on the element and select Calculation -> Short-Circuit ... . The short-circuit command (ComShc) dialogue opens and the user can then define the location of the fault relative to the element’s length (see Figure 24.13), including which terminal the fault distance should be calculated from. It should be noted that the Short-Circuit at Branch/Line section of this tab is only available when a line or branch has been selected for calculation.

• Clicking the button located in the Short-Circuit at Branch/Line section of the tab will enable the user to select whether the fault location is defined as a percentage or as an absolute value.

24 - 16


Fig. 24.13: Configuration of Line/Branch Faults in ComShc Dialogue

When a fault on a line/branch is calculated, a box containing the calculation results is dis-played next to the selected element.

24.2.5 Multiple Faults Calculation

Multiple faults involve the simultaneous occurrence of more than one fault condition in a network. This option is only available for the complete method. To calculate simultaneous multiple faults, proceed as follows:

• Select two or more elements (i.e. busbars/terminals, lines, ...) and right-click.

• Select the option Calculate -> Multiple Faults. The Short-Circuits dialogue pops up, displaying the short-circuit event list. A 3-phase fault is assumed by default at all locations in the event list. Click OK. The Short-Circuit command dialogue then pops up. In this dialogue, the Multiple Faults option is ticked in combination with the complete short-circuit method.

• Finally, press Execute to start the calculation.

In cases where the event list has to be adapted to reflect the intended fault conditions (that is, not necessarily the calculation of 3-phase faults), please proceed as follows:

• Open the short-circuit events object using one of the following methods:

- In the Fault Location section of the short-circuit (ComShc) dialogue, press the Show button (see Figure 24.14); or

- Press the icon located on the main tool bar (just besides the short-circuit command button); or

- In a Data Manager window, open the IntEvtshc object from the current study case, also denoted by the icon.

24 - 17


Fig. 24.14: Accessing the Short-Circuit Events List

• A window opens up which shows the list of events (that is short-circuits at the selected locations). When double-clicking on one entry in this list (double-clicking on the entire row), a window with a description of the event is opened.

• The short-circuit event settings can now be modified. The list of fault locations consists of a "Short-Circuit Event List'' (IntEvtshc) object, which holds one or more short-circuit events (EvtShc). Each of these events has a reference to a fault location (a busbar/terminal, line, etc.) and displays a short description of the fault type. An example is shown in Figure 24.15.

• The user could add more fault locations to the "Short-Circuit Event List'' (IntEvtshc) object by right clicking on addition elements in the single line diagram Add to.. -> Multiple Faults.

Fig. 24.15: A Short-Circuit Event (EvtShc)

Note To re-use the event list (IntEvtshc) later, this object can be copied to a user-defined folder in the Data Manager. This will prevent it from being modified during future calculations. When repeating the calculation with the same configuration, the reference in Cal-culate -> Multiple Faults can be set to this object. The other option would be to copy the events to the Fault Cases folder located in the ”Operational Library/Faults” folder of the project. The user would then need to press the From Library button (Figure 24.14).

24 - 18


24.3 Short-Circuit Calculation Options

The following sections describe the options available in PowerFactory’s short-circuit cal-culation command. Some of these options are dependent upon the selected calculation method, therefore separate sections dedicated to each method are presented.

24.3.1 Basic Options (All Methods)

The options presented in this section are common to all implemented calculation methods and are used to define the general settings of the short-circuit calculation. The specific options for each method are presented below in separate sections.

Fig. 24.16: IEC Calculation - Basic Options

An example of the short-circuit command dialogue is shown in Figure 24.16 (IEC calcula-tion in this case). The sections of the dialogue which are common to all calculation meth-ods are:

Method

PowerFactory provides the following calculation methods for short-circuit calculation:

• according to VDE 0102/0103 (the German VDE standard);

• according to IEC 60909 (the International IEC standard);

• according to ANSI (the American ANSI/IEEE C37 standard);

24 - 19


• complete (superposition method which considers the pre-fault load-flow results (see Section 24.1.3));

• according to IEC 61363.

The specific options for each of these methods are available on the Advanced Options tab of the short-circuit command (ComShc) dialogue.

Fault Type

The following fault types are available:

• 3-Phase Short-Circuit

• 2-Phase Short-Circuit

• Single Phase to Ground

• 2-Phase to Ground

• 1-Phase to Neutral

• 1-Phase Neutral to Ground





• 3-Phase Short-Circuit (unbalanced)

The fault types with a neutral conductor should only be used for systems which are mod-elled using neutral conductors.

Fault Impedance (Except for IEC 61363)

The fault impedance corresponds to the reactance and the resistance of the fault itself (such as the impedance of the arc or of the shortening path). This can be defined by means of an enhanced model, where line to line (Xf(L-L), Rf(L-L)) and line to earth (Xf(L-E), Rf(L-E)) impedances are regarded (note: requires option Enhanced Fault Impedance to be enabled). If the option Enhanced Fault Impedance is not enabled, fault impedances are defined by their equivalent values, Xf and Rf.

Figures 24.17 to 24.19 illustrate the differences between the enhanced and the simplified representation of fault impedances for the following fault types: (i) 3-phase short-circuits; (ii) 2-phase faults to ground; and (iii) 2-phase faults.

24 - 20


Fig. 24.17: Fault Impedance Definition: 3-Phase Short-Circuit

Fig. 24.18: Fault Impedance Definition: 2-Phase to Ground Fault

Fig. 24.19: Fault Impedance Definition: 2-Phase Fault

24 - 21


Show Output

A textual report is automatically written to PowerFactory’s output window when the Show Output option of the dialogue is enabled. The command which generates this report

is displayed in blue text next to the Command button . The user can click on this but-ton to select which type of report will be printed out. Just below the Command button, blue text informs the user of the currently-selected report type.

Fault Location

The fault location selection options are:

At User Selection:In this case a reference to a single terminal/busbar/line/branch or to a selection of busbars/terminals (SetSelect), as explained in Sections 24.2.3 and 24.2.4 must be given.

At Busbars and Junctions/Internal Nodes:For every terminal (ElmTerm) in the network, a short-circuit calculation is carried out, independently (one after the other).

At All Busbars:For every terminal (ElmTerm) in the network whose Usage is set to Busbar (see Section 5.3.2), a short-circuit calculation is carried out, independently (one after the other).

If the option Multiple Faults has been ticked when the Complete Method is being used, a reference to a set of fault objects (IntEvtshc), as explained in Section 24.2.5, must be set. This is done in the Fault Location section of the dialogue; using the Short Circuits ref-erence.

Note: Multiple faults will only be calculated for the 'Complete Method', when the option 'Multiple Faults' is enabled. When this option is en-abled, a short-circuit calculation is carried out for each individual fault location, simultaneously. When this option is disabled, cases where more than one fault location have been selected (i.e. several busbars/terminals), a sequence of short-circuit calculations is per-formed (i.e. each short-circuit calculation is carried out independ-ently of each other short-circuit calculation).

24.3.2 Verification (Except for IEC 61363)

When enabled (Verification Tab Page), the user can enter thresholds for peak, interrupting and thermal maximum loading. The Verification option will then write a loading report to the output window with all devices that have higher loadings than the defined max. val-ues. This report shows the various maximum and calculated currents for rated devices. Rated devices include, for instance:

• Lines which have a rated short-time current in their line type which is greater than zero; and

• Breakers or coupling switches which have a type with a valid rated current.

24 - 22


24.3.3 Basic Options (IEC 60909/VDE 0102 Method)

The Basic Options tab of the Short-Circuit Calculation dialogue is shown in the previous section in Figure 24.16.

In general, please note that the calculation according to IEC 60909 and VDE 0102 does not take into account line capacitances, parallel admittances (except those of the zero-sequence system) and non-rotating loads (e. g. ElmLod). Single phase elements are con-sidered only if they are located in the neutral conductor.

Published

This option offers a sub-selection for the selected Method, where the version of the stand-ard to be used can be selected according to the year in which it was issued. The most recent standard is 2001, however 1990 is still available for the verification of documented results.

Calculate

The drop-down list offers the choice between the minimal or maximal short-circuit cur-rent.

If external grids are defined, the corresponding maximum or minimum value will be se-lected automatically. For example if in the short circuit command you select "Calculate" according to "Maximum Short Circuit currents", the maximum short circuit value from the external grid is considered for the calculation.

The equivalent voltage source is based on the nominal system voltage and the voltage factor c. The voltage factor c will depend on the voltage level and on the selection of the "Calculate according to…" stated in the short-circuit command.

Max. Voltage tolerance for LV systems

In accordance with the IEC/VDE standard, this voltage tolerance is used to define the re-spective voltage correction factor, c. The voltage tolerance is not used when a user-de-fined correction factor is defined.

Short-Circuit Duration

The value for the Breaker Time is used to calculate the breaking current of a circuit break-er. The value for the Fault Clearing Time (Ith) is required for the equivalent thermal cur-rent.

Note: The fields 'Method', 'Fault Type', 'Fault Impedance', 'Output' and 'Fault Location' are described in Section 24.3.1.

24 - 23


24.3.4 Advanced Options (IEC 60909/VDE 0102 Method)

Fig. 24.20: IEC calculation - Advanced Options

Generally, the Advanced Options tab (shown in Figure 24.20) is used for settings to tune the various short-circuit calculation methods. Familiarization with the IEC/VDE standard before modifying these options is strongly recommended.

Grid Identification

The calculation of the factor kappa is different in the cases of meshed or radial feeding of the short-circuit. Normally PowerFactory will automatically find the appropriate setting. The option Always meshed will force a meshed grid approach.

c-Voltage Factor

The standard defines the voltage factor c to be used for the different voltage levels. In special cases the user may want to define the correction factor. In this case, activate the box User-Defined, then a specific c-factor can be entered.

Asynchronous Motors

Whether the calculation considers the influence of asynchronous motors on short-circuit currents depends on this setting, which may be Always Considered, Automatic Neglection,

24 - 24


or Confirmation of Neglection.

Conductor Temperature

When activating the User-Defined option, the initial (pre-fault) conductor temperature can be set manually. This will influence the calculated maximum temperature of the conduc-tors, as caused by the short-circuit currents.

Decaying Aperiodic Component

Allows for the calculation of the DC current component, for which the decay time must be given. According to the IEC/IEC standard, methods B, C and C' can be selected.

The following nomenclature is used:

Tb Breaker Time (see Short-Circuit command)

fn Nominal frequency

Ik" Initial short-circuit current

Method B: Uses the complex calculated equivalent impedance of the networkwith a security factor of 1.15:

Method C: Uses the R/X ratio calculated with the equivalent frequency method. The equivalent frequency is dependent on the breaking time (see Table 24.1). This method is recommended for maximum accuracy.

Table 24.1: Breaking Times

The ratio Rc/Xc is the equivalent impedance calculated at the frequency given by:

fn * Tb < 1 < 2.5 <5 < 12.5

fc / fn 0.27 0.15 0.092 0.055

iDC 2 Ik e– Tb

RX----

=

iDC 2 Ik e– Tb

Rf

Xf

----- =

Rf

Xf------

Rc

Xc------

fc

fnom-----------=

24 - 25


Method C': Uses the R/X ratio as for the peak short-circuit current, thus selecting the ratio fc/fn = 0.4. This option speeds up the calculation, as no additional equivalent impedance needs to be calculated.

Peak Short-Circuit Current (Meshed network)

In accordance with the IEC/VDE standard, the following methods for calculating kappa can be selected:

Method B':Uses the ratio R/X at the short-circuit location.

Method C(1):Uses the ratio R/X calculated at a virtual frequency of 40% of nominal frequency (20 Hz for fn = 50 Hz, or 24 Hz for fn=60 Hz), based on the short-circuit impedance in the positive sequence system.

Method (012):Like C(1), but uses the correct short-circuit impedance based on the positive-, negative- and zero-sequence system.

Calculate Ik

The steady-state short-circuit currents can be calculated using different means to consider asynchronous machines:

Without MotorsWill disconnect all asynchronous motors before calculating the current Ik.

DIgSILENT MethodConsiders all asynchronous motors according to their breaker current. The breaker opens after the maximum possible time.

Ignore Motor ContributionsConsiders asynchronous motor impedances during the calculation, but will reduce the calculated results for motor contributions.

Consider Protection Devices

This option will calculate measured currents for all protection devices and will evaluate tripping times. To increase the speed of the calculation, this option can be disabled when protection devices do not need to be analyzed.

Calculate max. Branch Currents = Busbar Currents

This option is used to check the rating of the circuit breakers against the system breaker currents. Normally the breaker currents are calculated as max{Ibus-Ibranch, Ibranch}. If

fc

fc

fnom----------- fnom=

24 - 26


this option is activated, the busbar short-circuit current is used as the breaker current, which is actually an over-estimation of the currents.

Automatic Power Station Unit detection

The IEC/VDE standard forces a different impedance correction factor to be applied to sep-arate generators and transformers than that applied to a unit/block (power station) con-sisting of a generator including its step-up transformer. PowerFactory tries to detect power stations. When this option is disabled, block transformers must be marked accord-ingly by setting the Unit Transformer option available in the VDE/IEC Short-Circuit tab of the transformer element dialogue (Figure 24.6).

24.3.5 Basic Options (ANSI C37 Method)

Fig. 24.21: ANSI calculation - Basic Options

Prefault Voltage

Value of the pre-fault voltage. In ANSI, the pre-fault voltage is the system rated voltage (1.0 p.u.). Although a higher or lower voltage can be used in the calculation if operation conditions show otherwise.

24 - 27


Consider Transformer Taps

The ANSI standard optionally allows the current tap positions of the transformers to be considered. This can be selected here.

NACD Mode

Depending on the location of the fault, ANSI classifies the different currents being fed to the short circuit as "local" or "remote". A remote source is treated as having only a dc decay, while a local source is treated as having a dc and ac decay. Depending on this clas-sification, corresponding curves are used in order to obtain the multiplication factors.

In PowerFactory the ANSI short-circuit method has the option of selecting the NACD (No AC Decay) mode.

The NACD factor is the ratio of remote current contribution to the total fault current: NACD = Iremote/Ifault. This NACD factor is used to calculate the breaker currents, including the DC component of the current. The remote current contribution required to evaluate the NACD factor is the sum of all remote generator contributions (induction generators, syn-chronous machines, and external grids).

The calculation of the NACD factor can be very time consuming, as the contribution of each generator is calculated individually. Therefore, different approximation methods can be selected, which represent the most common interpretations of the ANSI standard:

InterpolatedThe NACD factor is calculated, and the correction factor for the asymmetrical fault current is interpolated between the "dc decay only" and "AC/DC decay" curves with the following equation:MF = AC/DC factor + (DC factor - AC/DC factor)*NACDIf (NACD = 1) then only the DC factor is used; if (NACD = 0) then only the AC/DC factor is used.

PredominantThe the NACD factor is calculated. If the resulting factor is greater than or equal to 0.5, then the "dc decay only'' curve is used, which means that the remote generation is higher than the local generation.

All RemoteAll contributions are set to ‘remote’; the NACD factor is not calculated, but assumed equal to 1 and only the "dc decay only'' curve is used.

All LocalAll contributions are set to ‘local’; the NACD factor is not calculated, but assumed equal to 0 and only the "AC/DC decay" curve is used.

Current/Voltages for

The calculation mode for the currents and voltages to be evaluated:

LV/MomentaryEvaluates the subtransient short-circuit currents.

LV/InterruptingEvaluates the breaker currents.

24 - 28


30 CycleEvaluates the 30-cycle (steady-state) current.


24.3.6 Advanced Options (ANSI C37 Method)

Fig. 24.22: ANSI Calculation - Advanced Options

Calculate

This option is used to select the various currents (according to the ANSI standard) which are to be calculated. The options are as follows:

• Momentary Current (Close and Latch Duties)

• Interrupting Current

• 30 Cycle Current

• Low-Voltage Current

Bypass Series Capacitance

Series capacitances may be optionally bypassed for the ANSI short-circuit calculation. Al-ternatively, they may be not bypassed, always bypassed/neglected or this option may be

24 - 29


set depending on the type of short-circuit being calculated.

The options are as follows:

• No Bypassing

• All Currents

• LV & Interrupting & 30 Cycle Current

• 30 Cycle Currents

X/R Calculation

The user may select between a complex number X/R ratio calculation, or a calculation which considers R and X separately.

The fault point X/R will determine the system dc time constant and consequently the rate of decay of the transient dc current. Although in PowerFactory the X/R ration can be calculated from the complex network reduction, using this approach will not insure a con-servative result. In an attempt to provide a conservative approach, ANSI C31.010 requires that the X/R ratio be determined by a separate R network reduction.


This option will calculate measured currents for the selected protection devices and will evaluate tripping times. To increase the speed of the calculation, this option can be disa-bled when protection devices do not need to be analyzed.


This option is used to check the rating of the circuit breakers against the system breaker currents. Normally the breaker currents are calculated as max{Ibus-Ibranch, Ibranch}. If this option is activated, the busbar short-circuit current is used as the breaker current, which is actually an over-estimation of the currents.

24 - 30


24.3.7 Basic Options (Complete Method)

Fig. 24.23: Complete Method - Basic Options

As opposed to the calculation methods according to IEC/VDE and ANSI, which represent short-circuit currents by approximations, the complete method evaluates currents without using approximations. This accurate evaluation of the currents takes into account the sys-tem conditions immediately prior to the onset of the fault.

Load Flow

The pre-fault system condition used by the complete method can be determined either by the evaluation of a load flow, or by means of a simplified method, which initializes the internal voltages of all components that contribute to the short-circuit current with their nominal values, multiplied by a scaling factor, c.

The load flow command used to initialize the short-circuit calculation (when Load Flow Initialization on the Advanced Options tab is selected, see Section 24.3.8) is displayed

next to the button labelled Load Flow ( ). The load flow command can be accessed and

modified by pressing this button . The load flow command displayed here is initially taken from the currently active study case.

24 - 31


Short-Circuit Duration

The value for the Break Time (when set to “Global”) is used to calculate the breaking cur-rent of circuit breakers. Depending on the user selection, the value used for the break time within the calculation is:

globalWhen set to “Global”, the breaking current is calculated according to the Break Time specified in the short-circuit command.

min. of localWhen set to “min. of local”, the breaking current is calculated according to the shortest Break Time of all circuit breakers (defined in the Complete Short-Circuit tab of ElmCoup objects) connected to the busbars being studied.

localWhen set to “local” , the breaking current is calculated for each connected circuit-breaker according to its own Break Time (defined in the Complete Short-Circuit tab of ElmCoup objects), however, the busbar results will show the breaking current according to the shortest Break Time of all circuit breakers.


24 - 32


24.3.8 Advanced Options (Complete Method)

Fig. 24.24: Complete Method - Advanced Options

Initialisation

The user may select to initialize the complete method by one of the following options:

• the load flow calculation referred to in the Load Flow field of the Basic Options tab; or

• the nominal voltages with a user-defined correction factor (c-Factor). It should be noted that this option is only available in the dialogue when Load Flow Initialisation is not selected.

Peak, DC Currents, R/X ratio (ip, ib, idc)

This option allows the definition of the method used to determine the factor kappa () and the R/X_b ratio, required for the calculation of the peak and the DC component of the short-circuit current. The methods available correspond to those given in the IEC/VDE standard.

BUses the ratio R/X at the short-circuit location. In this case both ratios (R/X_p for the calculation of , and R/X_b) are equal.

24 - 33


C(1)For , the ratio R/X_p calculated at a virtual frequency of 40% (based on the short-circuit impedance in the positive sequence system) is used. The R/X_b ratio is calculated according to the equivalent frequency method, considering the breaking time and the positive sequence impedance (as for Method C from the IEC standard, however it should be noted that the IEC correction factors are not considered).

C(012)Like C(1) described directly above, but uses the correct short-circuit impedance based on the positive-, negative- and zero-sequence system.


This option will calculate measured currents for all protection devices and will evaluate tripping times. This option can be disabled to increase the calculation speed when protec-tion devices do not need to be analyzed.


This option is used to check the rating of the circuit breakers against the system breaker currents. Normally the breaker currents are calculated as max{Ibus-Ibranch, Ibranch}. If this

option is activated, the busbar short-circuit current is used as the breaker current, which is an over-estimation of the currents.

Overhead Line Modelling: Phase Matrices

For the unbalanced short-circuit calculation, PowerFactory always uses the phase com-ponent matrix. The following options define which phase matrix is used:

Untransposed: the short-circuit calculation uses the untransposed phase matrix.

Symmetrically Transposed: the short-circuit calculation uses the symmetrically trans-posed phase matrix for untransposed lines.

24 - 34


24.3.9 Basic Options (IEC 61363)

Fig. 24.25: IEC 61363 (EMT) - Basic Options

Calculate Using

In that section the user could select between the options:

• Standard IEC 61363 Method

• EMT Simulation Method

With the first option the short-circuit is calculated according to the IEC 61363 standard this is outlined in section 24.1.4. This short-circuit calculation method is only an approxi-mation and therefore the results are not exact.

When selecting the EMT method PowerFactory calculates for each fault case a three phase short-circuit with a fault impedance of 0 ohm on the selected locations. This addi-tional, high precision short-circuit calculation method provides further valuable informa-tion, and especially when power systems objects must be considered, which are not covered by the IEC 61363 standard.

The Break Time input parameter represents the contact separation time for circuit-break-ers. The default setting is 100 ms.

If the EMT Simulation Method option is active the configuration of the Simulation and also

24 - 35


the Simulation Results are available. The Simulation option displays the *.ComSim dia-logue that is described in more detail in Chapter 27.6 (Stability and EMT Simulations). The simulation time is set per default to 160 ms. This is necessary because the short circuit is started after phase A voltage crosses zero and because the first 100 ms after the short-circuit are displayed as results.

The Simulation Results pointer indicates where the results of the EMT short-circuit simu-lation will be stored (ElmRes). Typically no changes are required. In another note, this EMT simulation setup (Initial Conditions and Run Simulation command) is stored sepa-rately from the normal EMT simulation in order to avoid confusion.

Fault Impedance

The Fault Impedance option is disabled since the IEC 61363 standard considers the short-circuit impedance to be zero.

Create Plots

By enabling the Create Plots option, the user can select between the following:

• Show only short-circuit currents at faulted terminalWith this option selected, PowerFactory will create automatically a time domain plot of the short-circuit current at the selected terminal, which includes its upper envelope and DC component.

• Show all short-circuit current contributionsWith this option selected PowerFactory will create automatically a time domain plot of the short-circuit current at the selected terminal and a plot for all connected elements to the faulted terminal. Each created plot will consist of the short-circuit current, the upper envelope and the DC component.

24.3.10 Advanced Options (IEC 61363)

The settings available on the advanced options page of the IEC 61363 dialogue will de-pend on the selected calculation method.

Standard IEC 61363

With the standard calculation method the pre-load condition can be configured. The avail-able options are:

• use load flow initializationWith this option a load flow is calculated before the short circuit is calculated. If this option is selected a link to the used load flow is shown.

• use rated current/power factor

• With this option is no load flow calculated before the short circuit is calculated. The preload condition is obtained from the rated values of the grid elements.

• neglect preload conditionWith this option is no preload information used to calculate the short circuit.

Furthermore is the option ‚Consider Transformer Taps‘ available. According to the stand-ard are all transformers calculated with their main position so this options should normally

24 - 36


be disabled.

EMT Simulation Method

With ‚EMT simulation method‘ selected on the basic options page is only the choice for ‚Assume Inertia as infinite‘ available. If this option is selected the acceleration time con-stants of all rotating machines are set to 9999 s


In PowerFactory the results can be displayed directly in the single line diagram, in tab-ular form or by using predefined report formats. Also available are several diagram co-louring options in other to have a "quick" overview of the results.

24.4.1 Viewing Results in the Single Line Diagram

Once a load flow calculation has been successfully executed, the result boxes shown in the single-line diagram will be populated. There is a result box associated with each "side" of an element. So for example a load has one result box, a line two result boxes, and a three-winding transformer three result boxes. In PowerFactory these elements are collectively called edge elements. In addition, there are result boxes for nodes or buses.

The information shown inside a result box depends on the element to which it is associated. There are a few predefined formats for edge elements and a few predefined formats for buses. In order to see the selection, first perform a short-circuit, then, from the main menu, select Output Results for Edge Elements or Output Results for Short-Circuit Buses or Output Results for Short-Circuit Buses. These menu options will show the list of available result box formats. Alternatively, you can select (click) inside a result box on the single-line diagram, then right-click and from the context sensitive menu choose Format for Edge Elements or in case of a node Format for Nodes. Figure 24.26 serves as an example.

Fig. 24.26: Selecting the Result Box from the Single Line Diagram.

24 - 37


Besides these predefined formats the result boxes can be formatted in order to display selected variables.

By right-clicking on one of the result boxes and selecting the option Edit Format for Edge Elements and afterwards pressing the "Input Mode" button three options will be available: "Predefined Variables", "User Selection" or "Text Editor". The "User selection" option will allow the selection of any of the available variables.

24.4.2 Flexible Data Page

Once a short-circuit calculation has been successfully executed, pressing the "Edit

Relevant Objects for Calculation" button ( ) located on the main menu will prompt a submenu with icons for all classes that are currently used in the calculation. Clicking any of the class-icons will open a browser with all elements of that class that are currently used in the calculation. The left-most tab-page at the bottom of the browser is the "Flexible Data" tab page. Click on this tab page to show the flexible data. To change the

columns in the flexible page, press the "Define Flexible Data" button ( ). This will bring a selection window where the set of variables can be edited. In the left pane the available variables will be shown while the right pane will list the selected variables. Pressing the << or >> buttons will move the selected variable from the one pane to the other pane.

24.4.3 Predefined Report Formats (ASCII Reports)

In PowerFactory there are predefined report formats also called ASCII reports, available to the user. These ASCII reports can be created by pressing the "Output Calculation

Analysis" button ( ) located on the main menu (a short-circuit must be calculated first). This will bring a selection window in which the user can select a specific type of report. Some reports like the "Currents/Voltages" will have various options which the user can set. The report selection window also shows the report definition which will be used for the selected report. Pressing Execute will write the report to the output window. Although the reports are already predefined, the user has the possibility of modifying the reports if required (by clicking on the blue arrow pointing to the right of the "used format" definition).

A Show Output and Verification Report can be also printed out automatically each time a short-circuit calculation is executed (see Section 24.3.1 and 24.3.2).

24.4.4 Diagram Colouring

When performing short-circuit calculations, it is very useful to colour the single line-diagram in order to have a quick overview of the results, for example if elements have a loading above rated short-time current or if peak short-circuit currents are higher than the specified values. In PowerFactory there is the option of selecting different colouring modes according to the calculation performed. If a specific calculation is valid, then the selected colouring for this calculation is displayed. As an example, if the user selects the colouring mode "Areas" for "No Calculation" and "Loading of Thermal/Peak Short-Circuit Current" for the short-circuit calculation, then the initial colouring will be according to "Areas". However, as soon as the short-circuit is calculated, the diagram will be coloured according to "Loading of Thermal/Peak Short-Circuit Current". If the short-circuit calcu-

24 - 38


lation is reset or invalid, the colouring mode switches back to "Areas".

The Diagram Colouring has also a 3-priority level colouring scheme also implemented, allowing colouring elements according to the following criteria: 1st Energizing status, 2nd

Alarm and 3rd "Normal" (Other) colouring.

Energizing StatusIf this check box is enabled "De-energized" or "Out of Calculation" elements are coloured according to the settings in the "Project Colour Settings". The settings of the "De-energized" or "Out of Calculation" mode can be edited by clicking on the "Colour Settings" button.

AlarmIf this check box is enabled a drop down list containing alarm modes will be available. It is important to note here that only alarm modes available for the current calculation page will be listed. If an alarm mode is selected, elements "exceeding" the corresponding a limit are coloured. Limits and colours can be defined by clicking on the "Colour Settings" button.

"Normal" (Other) ColouringHere, two lists are displayed. The first list will contains all available colouring modes. The second list will contain all sub modes of the selected colouring mode. The settings of the different colouring modes can be edited by clicking on the "Colour Settings" button.

Every element can be coloured by one of the three previous criteria. Also, every criterion is optional and will be skipped if disabled. Regarding the priority, if the user enables all three criterions, the hierarchy taken account will be the following:

- "Energizing Status" overrules the "Alarm" and "Normal Colouring" mode. The "Alarm" mode overrules the "Normal Colouring" mode.

24 - 39


24 - 40

DIgSILENT PowerFactory Harmonics Analysis

Chapter 25Harmonics Analysis

One of the many aspects of power quality is the harmonic content of voltages and cur-rents. Harmonics can be analyzed in either the frequency domain, or in the time-domain with post-processing using Fourier Analysis. The PowerFactory harmonics functions al-low the analysis of harmonics in the frequency domain.

The following functions are provided by PowerFactory:

• Harmonic Load Flow (including harmonic load flow according to IEC 61000-3-6 and flicker analysis according to IEC 61400-21)

• Frequency Sweep

PowerFactory’s harmonic load flow calculates actual harmonic indices related to voltage or current distortion, and harmonic losses caused by harmonic sources (usually non-linear loads such as current converters). Harmonic sources can be defined by either a harmonic current spectrum or a harmonic voltage spectrum. In the harmonic load flow calculation, PowerFactory carries out a steady-state network analysis at each frequency at which harmonic sources are defined.

A special application of the harmonic load flow is the analysis of ripple-control signals. For this application, a harmonic load flow can be calculated at one specific frequency only.

The harmonic load flow command also offers the option of calculating long- and short-term flicker disturbance factors introduced by wind turbine generators. These factors are calculated according to IEC standard 61400-21, for wind turbines generators under con-tinuous and switching operations.

In contrast to the harmonic load flow, PowerFactory’s frequency sweep performs a con-tinuous frequency domain analysis. A typical application of the frequency sweep function calculates network impedances. The result of this calculation facilitates the identification of series and parallel resonances in the network.

These resonance points can identify the frequencies at which harmonic currents cause low or high harmonic voltages. Network impedances are of particular importance for applica-tions such as filter design.

PowerFactory provides a toolbar for accessing the different harmonic analysis com-mands. This toolbar can be displayed (if not already active) by selecting the 'Harmonics' icon ( ) on the main toolbar. The Harmonics toolbar provides two icons to open pre-configured command dialogues for the two different calculations:

• : Calculate Harmonic Load Flow

• : Calculate Impedance Frequency Characteristics (Frequency Sweep)

The command dialogues can be also accessed through the main menu by selecting:

25 - 1


• Calculation Harmonics Harmonic Load Flow...; or

• Calculation Harmonics Impedance Frequency Characteristic... .

Additionally, following the calculation of a harmonic load flow, a third icon on this toolbar

is activated. The icon is used to open the 'Filter Analysis' (ComSh) command dia-logue. The Filter Analysis command analyzes results from the most recent harmonic load flow calculation and outputs results to PowerFactory’s output window.

All functions and their usage are described in this chapter.

25.1 Harmonic Load Flow

To calculate a harmonic load flow, click on the icon to open the dialogue for the 'Har-monic Load Flow' (ComHldf) command as shown in Figure 25.1.

Fig. 25.1: Harmonic Load Flow Command (ComHldf)

For a detailed description of how harmonic injections are considered by PowerFactory, refer to Section 25.4 (Modelling Harmonic Sources), in which the analysis and the har-monic indices are described.

The following sections describe the options available in the harmonic load flow command.


Network Representation

Calculate Harmonic Load Flow

Nominal Frequency, Output Frequency, Harmonic Order

25 - 2


Calculate Flicker

Result Variables and Load Flow


BalancedIn the case of a symmetrical network and balanced harmonic sources, characteristic harmonics either appear in the negative sequence component (5th, 11th, 19th, etc.), or in the positive sequence component. Hence, at all frequencies a single-phase equivalent (positive or negative sequence) can be used for the analysis.

Unbalanced, 3-phase (ABC)For analyzing non-characteristic harmonics (3rd-order, even-order, inter-harmonics), or harmonics in non-symmetrical networks, the Unbalanced, 3-phase (ABC) option for modelling the network in the phase-domain should be selected.

Calculate Harmonic Load Flow

Single FrequencySelecting this option will perform a single harmonic load flow calculation at the given Output Frequency (parameter name: fshow) or at the given harmonic order (parameter name: ifshow). A common application for this input mode is the analysis of ripple control systems. The results of the analysis are shown in the single line diagram, in the same way as for a normal load flow at the fundamental frequency.

All FrequenciesSelecting this option will perform harmonic load flow calculations for all frequencies for which harmonic sources are defined. These frequencies are gathered automatically prior to the calculation. The results for all frequencies are stored in a result file, which can be used to create bar chart representations of harmonic indices (see also Section 19.4.2 (Plots)). The results of the analysis at the given Output Frequency are shown in the single line diagram.


Nominal FrequencyPowerFactory can only calculate harmonics of AC-systems with identical fundamental frequencies. The relevant nominal frequency must be entered here (usually 50Hz or 60Hz).

Output FrequencyThis is the frequency for which results are displayed in the single-line graphic. In the case of a Single Frequency calculation, this is the frequency for which a harmonic load flow is calculated. When option All Frequencies is selected, this parameter only affects the display of results in the single line diagram. It does not influence the calculation itself. In this case, the results displayed in the single line diagram are for the defined Output Frequency. A change made to the Output

25 - 3


Frequency will cause the Harmonic Order to be automatically changed accordingly.

Harmonic OrderThis is the same as the Output Frequency but input as the Harmonic Order (f/fn). The Harmonic Order multiplied by the Nominal Frequency always equals the Output Frequency. Both floating-point and integer values are valid as inputs. A change made to the Harmonic Order will cause the Output Frequency to be automatically changed accordingly.

Calculate Flicker

Calculate FlickerWhen selected, the long- and short-term flicker disturbance factors are calculated according to IEC standard 61400-21. See Section 25.5 (Flicker Analysis (IEC 61400-21)) for more detailed information.


Result VariablesThis option is available if Calculate Harmonic Load Flow option All Frequencies has been selected, and is used to select the target result object for storing the results of the harmonic load flow. See Section 25.6 (Definition of Result Variables) for more information regarding specifying and defining result variables.

Load FlowThis displays the load flow command used by the calculation. Click on

the arrow button ( ) to inspect and/or adjust the load flow command settings.

25.1.2 IEC 61000-3-6

Treatment of Harmonic SourcesThe alpha exponent values on this page will only be considered by the harmonic load flow (that is to say that the calculation will be carried out according to the IEC 61000-3-6 standard) if at least one harmonic source in the network is defined as IEC 61000 (see Section: IEC 61000 Harmonic Sources). On this page, if According to IEC 61000-3-6 is selected, these tables display the alpha exponent values as given in the IEC 61000-3-6 standard, as read-only values. If User Defined is selected, the definition of the alpha exponent values is user-definable in terms of integer and/or non-integer harmonic orders.


Based on Fundamental Frequency Values (IEEE)All values are based on fundamental frequency values, as defined by IEEE standards.

25 - 4


Based on Total RMS-Values (DIN)All values are based on "true RMS''-values, as defined by DIN standards.

Based on Rated Voltage/CurrentAll values are based on the rated voltage/current of the buses and branches in the network, respectively.

25.2 Frequency Sweep

To calculate frequency dependent impedances, the impedance characteristic can be com-puted for a given frequency range using the Frequency Sweep Command (ComFsweep).

This function is available by clicking on the icon available in the Harmonics toolbar.

The harmonic frequency sweep command is shown in Figure 25.2.

Fig. 25.2: Harmonic Frequency Sweep Command (ComFsweep)

Harmonic analysis by frequency sweep is normally used for analyzing self- and mutual- network impedances.

However, it should be noted that not only self- and mutual-impedances can be analyzed and shown. The voltage source models (ElmVac, ElmVacbi) available in PowerFactory allow the definition of any spectral density function. Hence, impulse or step responses of any variable can be calculated in the frequency domain. One common application is the analysis of series resonance problems.

The following sections describe the options available in the harmonic frequency sweep command.

25 - 5




Balanced, positive sequenceThis option uses a single-phase, positive sequence network representation, valid for balanced symmetrical networks. A balanced representation of unbalanced objects is used.

Unbalanced, 3 Phase (ABC)This option uses a full multiple-phase, unbalanced network representation.

Impedance Calculation

The frequency sweep will be performed for the frequency range defined by the Start Fre-quency and the Stop Frequency, using the given Step Size.

The Automatic Step Size Adaptation option allows an adaptive step size. Enabling this op-tion will normally speed up the calculation, and enhance the level of detail in the results by automatically using a smaller step size when required. The settings for step size adap-tation can be changed on the Advanced Options tab.


Nominal FrequencyThis is the fundamental frequency of the system, and the base frequency for the harmonic orders (usually 50Hz or 60Hz).

Output FrequencyThis is the frequency for which the results in the single line diagram are shown. This value has no effect on the actual calculation.

Harmonic OrderThis is the harmonic order equivalent of the Output Frequency. The Harmonic Order multiplied by the Nominal Frequency always equals the Output Frequency. Both floating-point and integer values are valid as inputs.


Result VariablesUsed to select the target result object which will store the results of the harmonic frequency sweep. See Section 25.6 (Definition of Result Variables) for more information regarding specifying result variables.

Load FlowThis displays the load flow command used by the calculation. Click on

the arrow button ( ) to inspect and/or adjust the load flow command settings.

The results of PowerFactory’s frequency sweep analysis are the characteristics of the impedances over the frequency range.

25 - 6



Selecting the option Automatic Step Size Adaptation on the Basic Data tab of the frequen-cy sweep command is one way to increase the speed of the calculation. This option en-ables the use of the step size adaptation algorithm for the frequency sweep.

With this algorithm, the frequency step between two calculations of all variables is not held constant, but is adapted according to the shape of the sweep. When no resonances in the impedance occur, the time step can be increased without compromising accuracy. If the impedance starts to change considerably with the next step, the step size will be reduced again. The frequency step is set such that the prediction error will conform to the two prediction error input parameters, as shown below:

errmaxMaximum Prediction Error (typical value: 0.01)

errincMinimum Prediction Error (typical value: 0.005)

nincStep Size Increase Delay (typically 10 frequency steps)

Calculate R, X at output frequency for all nodes

Normally, PowerFactory calculates the equivalent impedance only at selected nodes. When this option is selected, following the harmonic calculation, the equivalent imped-ance is calculated for all nodes.

25.3 Filter Analysis

The Filter Analysis command is a special form of the Output of Results command (ComSh), whose function is to generate a report. It analyzes the results from the previous harmonic load flow and outputs results to the PowerFactory output window. It outputs a summary of the harmonics for the terminals/busbars and branch elements at the fre-quency specified in the Output Frequency field of the harmonic load flow command. It also reports the parameters and different variables for the installed filters.

The filter analysis command can be activated using the icon or by using the Output

Calculation Analysis icon from the main menu (see also Section 19.1.3: Output of Re-sults). This will open the same dialogue as that used for the reporting of harmonic results, as displayed in Figure 25.3. This command can alternatively be launched from the single line graphic, after selecting one or more elements, and right-clicking and selecting Output Data... -> Results. Results will then be output for the selected elements. It should be not-ed that elements should be selected according to the type of report being generated. This means that for Busbars and Branches only terminals and branches should be selected, for Busbars/Terminals only terminals should be selected; and for Filter Layout and Filter Re-sults only shunts should be selected.

In the dialogue, the Output Frequency specified in the harmonic load flow command is displayed in red text (see top of dialogue in Figure 25.3). There are four different reports to choose from:

Busbars and BranchesThis displays the results of the harmonic load flow for all node and

25 - 7


branch elements in the network. The distortion for various electrical variables is printed and summarized.

Busbars/TerminalsFor the electrical nodes, the rated voltage, the voltage at the calculation frequency, as well as RMS values and distortion at the nodes are displayed.

Filter LayoutThe filter layout of all active filters in the network is calculated for the given frequency. The rated values and impedances of the filter as well as the type and vector group are printed to the output window. Additionally, the currents through the different components are shown, as are the losses.

Filter ResultsThe filter results show the main layout of all filters in the network for the calculation frequency. For a set of frequencies, the voltages and currents through the filter are tabulated.

Fig. 25.3: Filter Analysis Report Command (ComSh) Dialogue

The default format used for the report in the output window is defined in the Used Format section of the dialogue and can be set or changed by clicking on the Filter Layout button

( ).

Use SelectionResults will only be reported for elements defined in a selection. A selection of elements can be defined by selecting them either in the single line graphic or in the Data Manager, right-clicking and choosing Define...-> General Set. This General Set then exists in the Study Case and can be selected when the Use Selection option is activated.

25 - 8


25.4 Modelling Harmonic Sources

Every switched device produces harmonics and must therefore be modelled as a harmonic source. In PowerFactory, harmonic sources can be either current or voltage sources.

The following models can be used to generate harmonics (the PowerFactory element names are given in parentheses):

• General loads (ElmLod), if they are modelled as a current source (which can be defined on the Harmonics tab of the load’s assigned Type);

• Thyristor rectifiers (ElmRec, ElmRecmono);

• PWM-converters (ElmVsc, ElmVscmono), which are generally modelled as harmonic voltage sources;

• Voltage sources (ElmVac, ElmVacbi), which may also be used for ripple control applications;

• Current sources (ElmIac), with a user-defined spectrum of harmonic injections.

• Static generators (ElmGenstat);

• Static var systems (ElmSvs).

See Section 25.4.1 (Definition of Harmonic Injections) for information on how to define harmonic injections for these sources.

Note: Harmonic injections can be modelled in EMT simulations using the Fourier source object. For further details please refer to the Tech-nical References.

25.4.1 Definition of Harmonic Injections

For the following PowerFactory elements, the harmonic injections must first be defined using the Harmonic Sources type object (TypHmccur):



• PWM-converters (ElmVsc, ElmVscmono);

• Current sources (ElmIac);



When defining the spectrum via the Harmonic Sources type object, the harmonic infeeds can be entered according to one of three options: Balanced, Phase Correct or Unbalanced, Phase Correct (shown in Figures 25.4 and 25.5, respectively), or IEC 61000 (shown in Fig-ure 25.6). The Harmonic Sources object is a PowerFactory 'type' object, which means that it may be used by many elements who have the same basic type. Multiple current source loads may, for example, use the same Harmonic Sources object. Note that Pow-erFactory has no corresponding element for this type.

25 - 9


Phase Correct Harmonic Sources

For the Balanced, Phase Correct harmonic sources option, in both balanced and unbal-anced harmonic load flows, the magnitudes and phases of positive and negative sequence harmonic injections at integer harmonic orders can be defined, as shown in Figure 25.4.

Fig. 25.4: Balanced, Phase Correct Harmonic Sources Type (TypHmccur)

For the Unbalanced, Phase Correct harmonic sources option, the magnitudes and phases of positive and negative sequence harmonic injections at integer and non-integer har-monic orders can be defined, as shown in Figure 25.5. In the case of a balanced harmonic load flow, harmonic injections in the zero sequence are not considered, and harmonic in-jections at non-integer harmonic orders are considered in the positive sequence. In the case of an unbalanced harmonic load flow, harmonic injections in the zero sequence and at non-integer harmonic orders are considered appropriately. See Table 25.2 for a com-plete summary.

25 - 10


Fig. 25.5: Unbalanced, Phase Correct Harmonic Sources Type (TypHmccur)

IEC 61000 Harmonic Sources

The IEC 61000-3-6 standard [25.1] describes a “second summation law”, applicable to both voltage and current, which is described mathematically as [25.1]:

Eqn 25.1: (IEC 61000 Harmonic Voltage Magnitude)

where is the resultant harmonic voltage magnitude for the considered aggregation of

sources at order , and is the exponent as given in Table 25.1 [25.1].

Uh Uh m

m 0=

N

=

Uh

N h

25 - 11


The Harmonic Sources type set to option IEC 61000 (as shown in Figure 25.6) allows the definition of integer and non-integer harmonic current magnitude injections. In the case of balanced and unbalanced harmonic load flows, zero sequence order injections and non-integer harmonic injections are considered in the positive sequence. This is summarized in Table 25.2. It should be noted that in order to execute an harmonic load flow according to IEC 61000-3-6, at least one harmonic source in the network must be defined as IEC 61000 (i.e. as shown in Figure 25.6).

Fig. 25.6: IEC 61000 Harmonic Sources Type (TypHmccur)

The definition of the spectrum of harmonic injections for the voltage source (ElmVac, Elm-Vacbi) is done differently to other elements. The harmonic injections are directly input on the Harmonics tab of the voltage source element itself via the Harmonic Voltages table, as shown in Figure 25.7.

Additionally, the voltage source allows the following to be input for use in the Frequency Sweep calculation:

• Spectral density of voltage magnitude;

• Spectral density of voltage angle;

Table 25.1: IEC 61000-3-6 Summation Exponents According to Harmonic Order

Alpha Exponent Value

Harmonic Order

1 h<5

1.4 5<=h<=10

2 h>10

25 - 12


• Frequency dependencies (in the form of a Frequency Polynomial Characteristic). See Section 25.4.4 (Frequency Dependent Parameters) and Chapter 18: Parameter Characteristics for further details.

Fig. 25.7: Definition of Harmonic Voltages for Voltage Source Element

Selection of Type of Harmonic Sources

The Harmonic Sources object (TypHmccur) is independent of the whether the harmonic source is either a voltage source or a current source. The decision as to whether harmonic sources are fed into the system as harmonic voltages or as harmonic currents is made exclusively by the element to which the Harmonic Sources object is assigned. The consid-eration by the calculation of the sequence components of harmonic injections is given in Table 25.2.

Magnitudes and Phase Values

The quantities of the spectrum type are rated to current/voltage at the fundamental fre-quency in the balanced case. Hence, in the case of a harmonic current source, the actual

25 - 13


harmonic current at frequency fh is calculated by:

where

The values at the fundamental frequency, I1 and 1, are taken from a preceding load flow calculation. A normal load flow calculation is therefore required prior to a harmonic load flow calculation.

In case of balanced systems in which only characteristic harmonics of orders 5, 7, 11, 13, 17, etc. occur, the option Balanced, Phase Correct should be selected in the Balanced/Un-balanced Sources section (as shown in Figure 25.4). In this context, Balanced refers to characteristic harmonics. In the balanced case, the harmonic frequencies are determined by the program (note that in the unbalanced case, the harmonic frequencies can be free-ly-defined).

For harmonic sources which produce non-characteristic, unbalanced or inter-harmonics, the option Unbalanced, Phase Correct should be set in the Type of Harmonics Sources sec-tion. In the Unbalanced, Phase Correct case, the harmonic frequency, magnitude and phase angle of each phase can be chosen individually for each harmonic frequency. This mode therefore caters for every possible kind of harmonic source.

The problem commonly arises as to how one can represent the harmonic content in a sys-tem which differs to the native modal system (positive, negative or zero sequence sys-tem). The following example illustrates how to represent the 3rd harmonic in a positive or negative sequence system (as opposed to the native zero sequence system).

In the symmetrical case, the phase shift between the three phases is:A: 0°B: -120°C: +120° (-240°)

Ih kh eh

I1 e1 =

kh

Ih I1 if balanced

Iah Ia1 if unbalanced phase a

Ibh Ib1 if unbalanced phase b

Ich Ic1 if unbalanced phase c

=

h

h 1– if balanced

ah a1– if unbalanced phase a

bh b1– if unbalanced phase b

ch c1– if unbalanced phase c

=

25 - 14


For harmonics of order n:A: 0°B: -n*120°C: +n*120°

Taking the 3rd harmonic as an example:A: 0°B: -360°(= 0°)C: +360° (=0°)

Consequently, the 3rd harmonic in the ideally balanced case only in the zero sequence component, as their native modal system. For representing 3rd harmonics (and multiples thereof) in the positive sequence system, the following phase correction needs to be en-tered:

A: 0°B: +(n-1)*120°C: -(n-1)*120°

Again taking the 3rd harmonic as an example:A: 0°B: -360° + 240° = -120°C: +360° - 240° = 120°

25 - 15


25.4.2 Assignment of Harmonic Injections

The assignment of harmonic injections to the following elements is done via the individual element’s dialogue on the Harmonics page.



• PWM-converters (ElmVsc, ElmVscmono);

• Current sources (ElmIac);



This is illustrated in Figure 25.8 for the case of a general load.

Table 25.2: Consideration of Sequence Components of Harmonic Injections

Harmonic Load Flow Command Setting

Harmonic Current Source Type

Sequence Components of Harmonic Injections

Balanced Balanced, Phase Correct

Positive, negative; integer orders only.

Unbalanced, Phase Correct

Positive, negative; zero sequence orders are ignored and non-integer harmonics are in the positive sequence.

IEC 61000 Positive, negative; zero sequence orders and non-integer harmonics are in the positive sequence.

Unbalanced Balanced, Phase Correct

As for balanced harmonic load flow.

Unbalanced, Phase Correct

Positive, negative, zero; integer and non-integer harmonics.

IEC 61000 As for balanced harmonic load flow.

25 - 16


Fig. 25.8: Assignment of Harmonic Current Source to a Load Element (ElmLod)

Harmonic CurrentsUsed to select and display the assigned Harmonic Sources type (TypHmccur).

Type of Harmonic SourcesDisplays the type of harmonic source selected in the assigned Harmonic Sources type (TypHmccur).

Harmonic current referred toFor phase correct sources, the harmonic current may be referred to either the fundamental current or the rated current. If the harmonic current source type (TypHmccur) has been selected to be IEC 61000, the harmonic current is always referred to the rated current and this option is read-only.

Harmonic injections defined for voltage sources (ElmVac, ElmVacbi) are implicitly as-signed, as they are defined on the element’s Harmonics page. No further assignment is therefore necessary. See Section 25.4 (Modelling Harmonic Sources) for further informa-tion.

25.4.3 Harmonic Distortion Results

The harmonic loadflow calculation in PowerFactory provides a vast number of results for network elements. Some of the more prominent result variables are described in this section.

The harmonic distortion of a current or of a voltage can be quantified in terms of the Har-monic Distortion (HD), as described by (25.2). To describe the overall distortion, the Total Harmonic Distortion index THD (see (25.3)) has been introduced. An alternative, less common index is the Total Arithmetic Distortion TAD (see (25.4)). All distortion indices are described by their equations (below) for the current, but may be similarly described for voltage distortion.

25 - 17


Eqn 25.2:

Eqn 25.3: (Total Harmonic Distortion)

Eqn 25.4: (Total Arithmetic Distortion)

where

I(fi) Component of the current at frequency fi

Iref Reference value for the current

Eqn 25.5: (Total RMS value)

Eqn 25.6: (Arithmetic Sum value)

The reference value Iref depends on the standard used. The two possible options are the calculation according to DIN (25.7) and according to IEEE (25.8), as presented below:

Eqn 25.7: (DIN Standard)

Eqn 25.8: (IEEE Standard).

Another value which may be of importance is the Total Power (see (25.9)), which de-scribes the power absorbed over all frequency components:

Eqn 25.9: (Total Power)

It should be noted that for networks containing IEC 61000 harmonic current sources, re-sult variables for the voltage angle and current angle are not applicable (as the angles cannot be known). Additionally, the following result variables are available:

• ku, ki: Voltage and current diversity factors, respectively (always ‘1’ for networks containing only phase correct sources);

Eqn 25.10: (Voltage Diversity Factor)

HDI fi I fi

I f1 --------------=

THDI1

Iref-------- IRMS

2I2

f1 –=

TADI1

Iref-------- IA I f1 – =

IRMS I2

fi

i 1=

n

=

IAI fi

i 1=

n

=

Iref DIN IRMS=

Iref IEEE I f1 =

Ptot P fi

i 1=

n

=

kuUh

2

U 2

---------------------=

25 - 18


where is the IEC 61000 harmonic voltage magnitude as defined in (25.1) and is the voltage magnitude.

• HD, THD and TAD for non-integer harmonic orders.

25.4.4 Frequency Dependent Parameters

Due to the skin effect and variations in internal inductance, resistances and inductances are usually frequency dependent. This can be modeled in PowerFactory by associating a "frequency characteristic'' with these quantities. Two types of characteristic may be used: either a Frequency Polynomial Characteristic (ChaPol) as illustrated in Figure 25.9, or a user-defined frequency table (TriFreq and ChaVec). These kinds of characteristics are then assigned via the Harmonics tab of the correspoding element’s dialogue, as illustrated by the example in Figure 25.10 for a line element.

Fig. 25.9: The Frequency Polynomial Characteristic (ChaPol)

For the polynomial characteristic object shown in Figure 25.9, the following formula is used:

The parameters a and b are specified in the Frequency Polynomial Characteristic dialogue. Variable y is usually expressed as a percentage of the corresponding input parameters. For example, the resulting line resistance is obtained by:

An example of the use of the polynomial characteristic for a line type is shown in Figure 25.10.

Uh U

y fh 1 a– afh

f1---- b

+=

R fh R y fh =

25 - 19


Fig. 25.10: Frequency Dependencies in a Line Type

It also is possible to define frequency dependent characteristics using a vectorial param-eter characteristic (ChaVec). An example for a grid impedance defined with a vectorial pa-rameter characteristic is shown in Figure 25.11.

Fig. 25.11: Frequency Dependent Grid Impedance as Vectorial Characteristic (ChaVec)

The following objects can have frequency dependent parameters defined using a frequen-cy characteristic:

• Line type (TypLne)

• Asynchronous machine type (TypAsmo)

• Synchronous machine type (TypSym)

• Shunt/filter (ElmShnt)

• AC voltage source (ElmVac)

• AC voltage source - two terminals (ElmVacbi)

• AC current source (ElmIac)

• AC current source - two terminals (ElmIacbi)

25 - 20


• NEC/NER (ElmNec)

• Complex load (TypLodind)

• 2-W transformer (TypTr2)

• 3-W transformer (TypTr3)

Lines which are represented by a tower type (TypTow) are automatically assigned a har-monic characteristic. The same applies to cables using the detailed cable representation type (TypTow).

25.4.5 Waveform Plot

The waveform plot is used to display the waveform of a voltage or a current following a harmonic loadflow calculation. The harmonics are typically emitted by a harmonic voltage or current source, as described in Section 25.4 (Modelling Harmonic Sources).

In this plot, a waveform is generated using the magnitude and phase angle of the har-monic frequencies. With this diagram, a variable such as the voltage or current, which is defined in a harmonic source (i.e. a power electronic device or a load), can be easily shown as a time-dependent variable. This way the real shape of the voltage can be seen and analyzed. An example plot of harmonic distortion is shown in Figure 25.12.

Fig. 25.12: Use of the Waveform Plot to display Harmonic Distortion

For a more detailed description of this type of plot, see Section 19.4.6 (The Waveform

25 - 21


Plot).

For other types of plots, it should be noted that as the results of the discrete harmonic analysis are discrete, the plots generated from the result file should have the Bars option enabled. To do this, open the subplot dialogue by double-clicking on a subplot, going to the Advanced tab, and selecting Bars in the Presentation frame.

25.5 Flicker Analysis (IEC 61400-21)

The IEC standard 61400-21 [25.2] describes the measurement and assessment of power quality characteristics of grid connected wind turbine generators (WTGs). One of these power quality characteristic parameters pertains to voltage fluctuations. Voltage fluctua-tions can produce undesirable effects on the consumer side which may manifest as ‘flicker’ (visible flickering effects from light sources), and voltage changes (voltage magnitude be-ing too high or too low).

In the assessment of a WTG’s power quality in terms of voltage fluctuations, the operation of WTGs can be subdivided into two modes: continuous operation and switching opera-tions (see Sections 25.5.1 (Continuous Operation) and 25.5.2 (Switching Operations) for definitions). These modes of operation are considered by the PowerFactory flicker cal-culation, which calculates the short-term and long-term flicker disturbance factors. See Section 25.5.6 (Flicker Result Variables) for a list of the flicker result variables available. The calculation of flicker is performed optionally as part of the harmonic load flow com-mand. For a detailed description of how to configure and execute a harmonic load flow, including the calculation of flicker, refer to Section 25.1.1 (Basic Options).

25.5.1 Continuous Operation

Continuous operation is defined in IEC standard 61400-21 as the normal operation of the wind turbine generator (WTG) excluding start-up and shut-down operations. The short-term and long-term flicker disturbance factors during continuous operation are defined as [25.2]:

Eqn 25.11:

(Short-term and long-term flicker disturbance factors for continuous operation)

where is the short-term flicker disturbance factor; is the long-term flicker distur-

bance factor; is the flicker coefficient for continuous operation; is the network im-

pedance angle (degrees); is the average annual wind speed (m/s); is the rated

Pst Plt c k va Sn

Sk-----= =

Pst Plt

c k

va Sn

25 - 22


apparent power of the wind turbine (VA); and is the short-circuit apparent power of the grid (VA).

When more than one WTG exists at the point of common coupling (PCC), the following summation is required [25.2]:

Eqn 25.12:

(Summed short-term and long-term flicker disturbance factors for continuous operation)

where is the number of wind turbine generators at the PCC.

25.5.2 Switching Operations

Switching operations are defined in IEC standard 61400-21 as start-up or switching be-tween wind turbine generators (WTGs). In this mode of operation, the short-term and long-term flicker disturbance factors during switching operations are defined as [25.2]:

Eqn 25.13:

(Short-term flicker disturbance factor for switching operations)

where is the number of switching operations in a 10-minute period; is the flicker

step factor; is the network impedance angle (degrees); is the rated apparent pow-

er of the wind turbine (VA); and is the short-circuit apparent power of the grid (VA).

Eqn 25.14:

(Long-term flicker disturbance factor for switching operations)

where is the number of switching operations in a 120-minute period; is the flicker

step factor; is the network impedance angle (degrees); is the rated apparent pow-

er of the wind turbine (VA); and is the short-circuit apparent power of the grid (VA).

When more than one WTG exists at the PCC, the following summation is required [25.2]:

Eqn 25.15:

(Short-term flicker disturbance factor under switching operations)

Sk

Pst Plt1Sk----- c k va Sn i 2

i 1=

Nwt

= =

Nwt

Pst 18 N100 31

kf k Sn

Sk----- =

N10kf

k Sn

Sk

Plt 8 N1200 31

kf k Sn

Sk----- =

N120 kf

k Sn

Sk

Pst18Sk------ N10 i kf i k Sn i 3 2

i 1=

Nwt

0 31

=

25 - 23


Eqn 25.16:

(Long-term flicker disturbance factor under switching operations)

where is the number of WTGs at the PCC.

The relative voltage change due to the switching operation of a single WTG is computed as [25.2]:

Eqn 25.17:

(Relative Voltage Change (%))

Plt8Sk----- N120 i kf i k Sn i 3 2

i 1=

Nwt

0 31

=

Nwt

d 100 ku k Sn

Sk----- =

25 - 24


25.5.3 Flicker Contribution of Wind Turbine Generator Models

The calculation of flicker according to IEC standard 61400-21 in PowerFactory considers flicker contributions of the following generator models:

• Static generator (ElmGenstat)

• Asynchronous machine (ElmAsm)

• Doubly-fed asynchronous machine (ElmAsmsc)

In order that these models can contribute flicker, their flicker contributions must first be defined and assigned, as described in Sections 25.5.4 (Definition of Flicker Coefficients) and 25.5.5 (Assignment of Flicker Coefficients).

25.5.4 Definition of Flicker Coefficients

Flicker coefficients are defined in PowerFactory by means of the Flicker Coefficients type (TypFlicker), as illustrated in Figure 25.13. When created, this is stored by default in the Equipment Type Library folder in the project tree.

Fig. 25.13: Definition of Flicker Coefficients using the Flicker Coefficients Type (TypFlicker)

The Flicker Coefficients type allows the input of six parameters (all of which are defined in IEC standard 61400-21):

Network Angle, psi (degrees)

This is the network impedance angle and must be entered in either the range [-180,180]

25 - 25


(default), or [0,360]. Any mix of these ranges is not permitted. Network angles must be entered in ascending order.

Coefficient, c(psi)

The flicker coefficient as a function of the network impedance angle.

Step Factor, kf(psi)

The flicker step factor as a function of the network impedance angle.

Voltage Change Factor, ku(psi)

The voltage change factor as a function of the network impedance angle.

Maximum Switching Operations: N10

The maximum number of switching operations in a 10-minute period.

Maximum Switching Operations: N120

The maximum number of switching operations in a 120-minute period.

25.5.5 Assignment of Flicker Coefficients

The Harmonics page of these elements’ dialogues contains a Flicker Contribution section which allows the assignment of Flicker Coefficients. This is illustrated in Figure 25.14.

Fig. 25.14: Assignment of Flicker Coefficients in an Asynchronous Machine (ElmAsm)

If Flicker Coefficients is left assigned, the generator is then considered to be an ideal source for the flicker calculation, as illustrated in Figure 25.15.

25 - 26


Fig. 25.15: Asynchronous Generator (ElmAsm) Model as Ideal Source

25.5.6 Flicker Result Variables

Following the calculation of flicker according to IEC 61400-21, the following result vari-ables for every node in the network are available in the single line graphic:

• Pst_cont; Plt_cont: short-term and long-term flicker disturbance factors for continuous operation of the wind turbine generator/s;

• Pst_sw; Plt_sw: short-term and long-term flicker disturbance factors for switching operations of the wind turbine generator/s;

• d_sw: relative voltage change (as a percentage).

For the mathematical definitions of these result variables, refer to Sections 25.5.1 (Con-tinuous Operation) and 25.5.2 (Switching Operations).

25.6 Definition of Result Variables

In order to record the results of either the Harmonic Load Flow or Frequency Sweep cal-culation, the variables of interest must be defined. However, for each of these calcula-tions, a small selection of variables are recorded by default in the result object defined on each command’s Basic Data page by the Result Variables parameter.

For the Harmonic Load Flow the following variables are recorded by default:

• Harmonic order (-);

• Frequency (Hz);

• HD (%) (for terminals);

• Voltage across inductor (p.u.) (url) (for shunts/filters);

• Voltage across capacitor (p.u.) (uc) (for shunts/filters);

• Current through inductor (A) (IL) (for shunts/filters);

• Current through resistor Rp (A) (IRp) (for shunts/filters);

• Current through capacitor C (A) (IC) (for shunts/filters);

• Voltage across capacitor C1 (A) (uc1) (for shunts/filters);

• Voltage across capacitor C2 (A) (uc2) (for shunts/filters);

• Voltage across resistor Rp (p.u.) (urp) (for shunts/filters);

25 - 27


For the Frequency Sweep, the following variables are recorded by default:

• Harmonic order (-);

• Frequency in Hz (Hz);

In order to define additional variables to be recorded, a two-step process is required of firstly creating the desired Variable Set and then selecting the variables for recording with-in these sets. These steps are described in Sections 25.6.1 (Definition of Variable Sets) and 25.6.2 (Selection of Result Variables within a Variable Set), respectively.

25.6.1 Definition of Variable Sets

To define a Variable Set, right-click on a network component (or multi-select several net-work components and right-click), either in the single-line diagram or in the data manager, and select the option DefineVariable Set (Harmonic Load Flow); or DefineVariable Set (Frequency Sweep). This will add a new (but still empty) variable set for the selected object to the result object (referred to by parameter Result Variables on the Basic Options tab of the Harmonic Load Flow or Frequency Sweep command dialogue).

All results of harmonic analyses, with the exception of the harmonic load flow using option Single Frequency (for which no results are recorded), are stored in a normal result object (ElmRes). This result object stores the result variables against the frequency for which they were calculated. For more information about the result object, see Section 19.1.4 (Result Objects).

To access the variable sets, click on the Edit Result Variables icon ( ) on the main tool-bar. There are two instances of this button: one associated with the Harmonic Load Flow

. and one associated with the Frequency Sweep . Select the button associated with the relevant calculation. The variable set manager dialog will open which displays the list of all defined variable sets for that calculation. After the variable set has been created and its variables have been defined, each variable set contains the variables of interest for a single object. A window is opened automatically whenever a new variable set is defined, as shown in Figure 25.16, displaying the list of variable sets. In Figure 25.16, three vari-able sets have been defined for three different network elements: one for load element "General Load", one for line element "Line 1" and one for terminal element "Sym-Termi-nal".

A new variable set can also be defined by clicking on the New icon ( ), shown in the top left corner of Figure 25.16. By doing this, the Variable Set dialogue will appear as shown in Figure 25.17. To proceed with selecting the result variables for the variable set, see Section 25.6.2 (Selection of Result Variables within a Variable Set). For further infor-mation on variable sets, refer to Chapter 19: Reporting and Visualizing Results.

25 - 28


Fig. 25.16: Example of a List of Variable Sets

25.6.2 Selection of Result Variables within a Variable Set

The selection of result variables for a variable set can only proceed when the column la-belled Object for any defined variable set (as shown in Figure 25.16) is set. This can be done by either double-clicking the appropriate cell of the Object column, or by right-click-ing the cell and selecting Select Element.... This binds the variable set to a specific object or network element.

A single variable set from the variable sets list can be accessed (and the desired variables defined) by either double-clicking on the icon in the corresponding row (for example,

in the case of the "Sym-Terminal" in Figure 25.16), or by right-clicking on the icon and selecting the Edit menu option. The Variable Set object (IntMon) dialogue opens, as shown in Figure 25.17 for the example of the "Sym-Terminal". By selecting the Har-monics tab of this dialogue, a list of all result variables that are available for the selected object (applicable to harmonics analysis or frequency sweep) is then available for selec-tion. The Object field in the dialogue in Figure 25.17 shows that the variable set is defined for the network element "Sym-Terminal".

25 - 29


Fig. 25.17: Selection of Harmonics Analysis Result Variables for a Terminal

Result variables may be added or removed from the set of selected variables by highlight-

ing the desired variable and pressing the or buttons. Additionally, different vari-ables are available for selection depending on the selection made from the Variable Set drop-down list. This drop-down list is available in the Filter for section on the Harmonics tab of the Variable Set dialogue, as displayed in Figure 25.17. For further information on variable sets, refer to Chapter 19: Reporting and Visualizing Results.

25.7 Literature

[25.1] Technical Report IEC 1000-3-6, First Edition 1996-10, "Electromagnetic Compati-bility (EMC) - Part 3: Limits - Section 6: Assessment of emission limits for distorting loads in MV and HV power systems - Basic EMC publication"

[25.2] International Standard IEC 61400-21, Edition 2.0, 2008-08, "Wind turbines - Part 21: Measurement and assessment of power quality characteristics of grid connected wind turbines"

25 - 30


25 - 31


25 - 32

DIgSILENT PowerFactory Flickermeter

Chapter 26Flickermeter

In terms of power quality, the term "flicker" is used to describe the phenomenon of un-wanted, rapidly fluctuating light levels due to voltage fluctuations. The IEC 61000-4-15 standard specifies the function and design of apparatus for the measurement of flicker, termed the "Flickermeter". This Flickermeter comprises five functional blocks which, via the use of multipliers, weighting filters, and smoothing and squaring operations, perform the tasks of simulating the "lamp-eye-brain" chain response, and statistically evaluating the flicker signal [26.1]. PowerFactory provides a Flickermeter command for the calcu-lation of the short-term and long-term flicker according to IEC 61000-4-15.

The following sections explain the calculation of short- and long-term flicker by the Flick-ermeter command, as well as its configuration and handling.

26 - 1


26.1 Flickermeter (IEC 61000-4-15)

26.1.1 Calculation of Short-Term Flicker

The calculation of the short-term flicker value ( ) according to IEC 61000-4-15 is a mea-sure of the severity of the flicker based on an observation period of 10 minutes. It is de-fined mathematically as follows [26.1]:

where the percentiles , , , and are the flicker levels exceeded for 0.1; 1; 3; 10; and 50% of the time during the observation period. The subscript 's' used in the above formula indicates that smoothed values should be used, which are defined as fol-lows [26.1]:

26.1.2 Calculation of Long-Term Flicker

The calculation of the severity of long-term flicker, , considers the short-term flicker severity values over a longer period of time and is calculated according to the following equation [26.1]:

Eqn 26.1:

(Long-term flicker severity)

where are the consecutive values and is the number of obser-

vation periods. It can be seen from (26.1) that when , .

Pst

Pst 0 0314 P0 1 0 0525 P1s 0 0657 P3s 0 28 P10s 0 08 P50s + + + +=

P0 1 P1 P3 P10 P50

P50s P30 P50 P80+ + 3=

P10s P6 P8 P10 P13 P17+ + + + 5=

P3s P2 2 P3 P4+ + 3=

P1s P0 7 P1 P1 5+ + 3=

Plt

Plt

Psti3

i 1=

N

N

-----------------3

=

Psti i 1 2 3 = Pst N

N 1= Plt Pst=

26 - 2


26.2 Flickermeter Calculation

26.2.1 Flickermeter Command

This command is accessible via the Flickermeter icon in the Stability toolbar, which is accessible via the button. The PowerFactory Flickermeter command dialogue is shown in Figure 26.1.

Fig. 26.1: Data Source Page of Flickermeter (ComFlickermeter) Command

26 - 3


26 - 4

26.2.2 Data Source

File Input

Import data fromSpecifies the type of data file containing the input data. There are five file types available for selection.

FilenameThe name of the input data file.

Result FileThe name of the input PowerFactory result file.

Configuration FileRelevant to ComTrade input files only. The name of the corresponding configuration file.

InfoA summary of information read from the file.

Use System SeparatorsRelevant to comma-separated value (CSV) input files only. Tick the checkbox to use the same separators for parsing the file as those used by the operating system. When unchecked, separators are user-definable.

Separator for columnsIn the case of a PowerFactory Measurement File as the input file type, this indicates the character used as a separator for the columns in the file. In the case of a User Defined Text File as the input file type, the separator may be selected as one of Tab, Space or Other (user-defined).

Decimal SeparatorIndicates the separator used for decimal numbers. This is user-definable for a User Defined Text File as the input file type.

Selection of Data for Calculation

This table allows the selection of input file data to be analyzed. The leftmost column (with labels 'y1', …, 'y24 ') provides a naming convention for the output of results, indicating which time-series signals from the input file were analyzed.

ElementRelevant only to a Result File input file type. Used to specify the element from the result file for which a variable to analyze will be selected. This variable is then specified in the Variable column of the same table.

VariableRelevant only to a Result File input file type. Used to specify the variable for the Flickermeter command to analyze. This variable is associated with the selected Element (see above).


Column NumberRefers to the column/s in the input file which correspond to the time-series signal/s to be analyzed.

Variable NameFor ComTrade files, the variable name is automatically read from the input file and displayed in the Variable Name column. No variable name is provided for other file types.

Calculate PstAllows the user to select the signals in the input file for which to calculate the short-term flicker ( ). Valid for all input file types with the exception of result files.

26.2.3 Signal Settings

Signal Settings

Signal TypeSelection of either EMT or RMS input signal type.

Specify start timeUser-defined start time at which data should be read from file. This is an absolute time value that exists within the input file, from which data will be read. If this value cannot be found in the file, the next time point after the specified start time will be used instead.

Resample DataThe input data will be resampled by the user-defined New Sampling Rate. If the time step of the data within the input file is not constant, the Flickermeter calculation will automatically resample the data at the average sampling rate taken from the input file.

New Sampling RateUser-defined sampling rate at which data will be resampled if option Resample Data has been selected.

Pst

26 - 5


26 - 6

Calculation Settings

Observation PeriodThe time period over which the flicker will be analyzed.

Calculate PltPerform calculation of long-term flicker ( ). When this option is checked, a result file is written.

Observation PeriodsThe number of successive observation periods (or “time windows”) to analyze.


Input signals for Flickermeter can be either RMS or EMT signals. The algorithm treats both of these inputs the same, with the exception of the weight filter coefficients, scaling factor and the cut-off frequency used. The weight filter coefficients are preset (see Table 26.1), however the scaling factor and cut-off frequency are user-definable parameters and are described below.

Parameter Definitions

Cut-off FrequencyCut-off frequency of Butterworth filter (Hz). When using an RMS input signal, the cut-off frequency is set to 50Hz; when using an EMT input signal, its default value is 35Hz but can be user-defined.

Filter OffsetThe offset (in seconds) for the filters to stabilize. A positive, non-zero offset should always be entered. When using an RMS input signal, the filter offset is set to 5s; when using an EMT input signal its default value is 5s but can be user-defined.

Scaling FactorCalibration parameter. When using an RMS input signal, the scaling

Table 26.1:Flickermeter Weight Filter Coefficients

Variable EMT (from IEC 61000-4-15) RMS

1.74802 1,74

Plt

2 4 05981 2 4 1

1 2 9 15494 2 9 15

2 2 2 27979 2 2 27979

3 2 1 22535 2 1 22535

4 2 21 9 2 1000


factor is set to 300469,4835 (defined as 2 / (0.0025*0.0025) / 1.065). When using an EMT input signal, its default value is 303317,5 but can be user-defined.

Set to defaultResets the Cut-off Frequency, Filter Offset and Scaling Factor to default values.

Constant Sampling Rate

ToleranceTolerance for determining whether the sampling rate is constant or not. This tolerance is considered on the Data Source page in the Info frame when displaying the Constant Sampling Rate parameter.

Result Variables

This displays the location of the stored result variables. The result object can be directly accessed by clicking on the arrow button . It should be noted that the Result Variables parameter is only visible if the Calculate Plt checkbox on the Signal Settings page has been selected and the value entered for the Observation Periods on the Signal Settings page is greater than 1.

Report

Results of the Flickermeter calculation are displayed in PowerFactory’s output window provided that Report has been selected.

When executing the Flickermeter command within DPL, the command option 'Report' must be disabled.

CommandDisplays the command used to output results. The Flickermeter command will write results to a result file provided that option Calculate Plt on the Signal Settings page has been selected. The result file used can be accessed via the dialogue which opens when the Command button is pressed.

Additionally, results of the Flickermeter command can be viewed within the Data Manager as Flexible Data of the Flickermeter command itself. The relevant variable names for se-lection when defining the Flexible Data are "b:Pst_y1", … , "b:Pst_y24", for short-term flicker values; and "b:Plt_y1", … , "b:Plt_y24" for long-term flicker values). In this case, viewing the results of a Flickermeter calculation will appear similar to that illustrated in Figure 26.2. It should be noted that when multiple Observation Periods have been calcu-lated, only the Plt results will be displayed (Pst results are shown as '0.'); and for a single Observation Period the Pst results will be displayed. For further information on defining Flexible Data in the Data Manager in PowerFactory, refer to 12.5: The Flexible Data Page Tab in the Data Manager.

26 - 7


26 - 8

Fig. 26.2: Using Flexible Data to Access Flickermeter Results

26.2.5 Input File Types

The Flickermeter command can handle five different input file types. The configuration of the Flickermeter command for each file type differs slightly, and is therefore described for each case in this section.

ComTrade

If a ComTrade file has been selected as input to the Flickermeter command, the command dialogue will look similar to that shown in Figure 26.3. The Configuration File correspond-ing to the ComTrade data file is automatically displayed, as is the Sampling Rate as read from the ComTrade configuration file. The Selection of Data for Calculation table in Figure 26.3 shows the column number and corresponding variable name as read from the Com-Trade configuration file and also a user selection for which the short-term flicker value should be calculated (checkbox in the Calculate Pst column). In the example shown in Fig-ure 26.3, a single variable has been selected for analysis. It can be read from this table that this variable corresponds to column 1 of recorded data in the ComTrade input data file. See Section 26.2.2 (Data Source) for information on other Flickermeter command op-tions.


Fig. 26.3: Configuration of Flickermeter Command for ComTrade Input File

Comma Separated Values and User Defined Text Files

If a Comma Separated Values (CSV) file or a user defined text file has been selected as input to the Flickermeter command, the command dialogue will look similar to that shown in Figure 26.4. For a CSV file or user defined text file, the Selection of Data for Calculation table in Figure 26.4 shows that variables can be selected for analysis according to their corresponding column number in the input file. In the example illustrated, data from col-umn 1 has been selected for analysis. See Section 26.2.2 (Data Source) for information on other Flickermeter command options.

26 - 9


26 - 10

Fig. 26.4: Configuration of Flickermeter Command for CSV or User Defined Text Input File

PowerFactory Measurement File

If a PowerFactory Measurement File has been selected as input to the Flickermeter com-mand, the command dialogue will look similar to that shown in Figure 26.5. The Power-Factory measurement file is a simple ASCII file containing a column of data for each variable recorded in it. Hence, it can be seen from Figure 26.5 that the variable contained in column 5 of the file will be analyzed by the Flickermeter command. The PowerFactory measurement file can be used to record results from other PowerFactory calculations and then used as input to the Flickermeter command. For further information on the use of PowerFactory measurement files, please refer to annex C.8.2: File Object (ElmFile). See Section 26.2.2 (Data Source) for information on other Flickermeter command options.


Fig. 26.5: Configuration of Flickermeter Command for PowerFactory Measurement File

Result File

If a Result File has been selected as input to the Flickermeter command, the command dialogue will look similar to that shown in Figure 26.6. Using a PowerFactory result file as the input file type is practical when the user wants to first record results from, for ex-ample, an EMS/RMS simulation in a result file, and then analyze the flicker contribution of one or more variables from this file. In the example in Figure 26.6, the specified Element in the Selection of Data for Calculation table is a terminal element (named "LV Busbar") recorded in the result file, with its corresponding voltage selected as the Variable to ana-lyze. See Section 26.2.2 (Data Source) for information on other Flickermeter command options.

26 - 11


Fig. 26.6: Configuration of Flickermeter Command for Result File

26.3 Literature

[26.1] International Standard IEC 61000-4-15, Edition 1.1, 2003-02, "Electromagnetic Compatibility (EMC) - Part 4: Testing and measurement techniques - Section 15: Flicker-meter - Functional and design specifications

26 - 12


26 - 13


26 - 14

DIgSILENT PowerFactory Stability and EMT Simulations

Chapter 27Stability and EMT Simulations

The transient simulation functions available in DIgSILENT PowerFactory are able to analyze the dynamic behavior of small systems and large power systems in the time do-main. These functions therefore make it possible to model complex systems such as in-dustrial networks and large transmission grids in detail, taking into account electrical and mechanical parameters.

Transients, stability problems and control problems are important considerations during the planning, design and operation of modern power systems. Studies involving electro-magnetic transients and different aspects of stability may be conducted using time-do-main simulations for varying time periods, or dynamic or small-signal stability analysis tools using (for example) eigenvalue analysis.

A large range of AC and DC systems can be analyzed (i.e. transmission systems with de-tailed models of power plants, complex HVDC systems, motor start-up), as well as a com-bination of both. Applications such as wind power integration or power electronics constitute new challenges in the analysis of power systems, and as a result new models and techniques are provided in PowerFactory to meet these requirements.

For modelling a variety of machines and controller units, as well as the electrical and me-chanical components of power plants, etc., PowerFactory’s global library provides a large number of predefined models. This library includes models of generators, motors, controllers, motor driven machines, dynamic loads and passive network elements. As an example, this library contains the IEEE standard models of power plant controllers. Fur-thermore, the user can model specific controllers and develop block diagrams of power plants with a large degree of freedom.

A Stability simulation in PowerFactory is started by:

• Selecting the Stability toolbar by clicking on the Stability icon from the Select toolbar;

• Calculating the initial conditions for the simulation by either pressing the icon on the main toolbar, or by selecting Calculation Stability Initial Conditions... from the main menu;

• When the initial values have been calculated successfully, the icon on the main toolbar will be activated and can be pressed to start the simulation.

27 - 1


27.1 Introduction

The study of power system stability involves the analysis of the behavior of power systems under conditions before and after sudden changes in load or generation, during faults and outages. The robustness of a system is defined by the ability of the system to maintain stable operation under normal and perturbed conditions. It is therefore necessary to de-sign and operate a power system so that transient events (i.e. probable contingencies), can be withstood without the loss of load or loss of synchronism in the power system. Transients in electrical power systems can be classified according to three possible time-frames:

• short-term, or electromagnetic transients;

• mid-term, or electromechanical transients;

• long-term transients.

The multilevel modelling of power system elements and the use of advanced algorithms means that the functions in PowerFactory can analyse the complete range of transient phenomena in electrical power systems. Consequently, there are three different simula-tion functions available:

1 A basic function which uses a symmetrical steady-state (RMS) network model for mid-term and long-term transients under balanced network conditions;

2 A three-phase function which uses a steady-state (RMS) network model for mid-term and long-term transients under balanced and unbalanced network conditions, i.e. for analyzing dynamic behaviour after unsymmetrical faults;

3 An electromagnetic transient (EMT) simulation function using a dynamic network model for electromagnetic and electromechanical transients under balanced and unbalanced network conditions. This function is particularly suited to the analysis of short-term transients.

In addition to the time-domain calculations, two other analysis functions are available:

• Parameter Identification

• Modal Analysis or Eigenvalue Analysis

Time-domain simulations in PowerFactory are initialized by a valid load flow, and Pow-erFactory functions determine the initial conditions for all power system elements includ-ing all controller units and mechanical components. These initial conditions represent the steady-state operating point at the beginning of the simulation, fulfilling the requirements that the derivatives of all state variables of loads, machines, controllers, etc., are zero.

Before the start of the simulation process, it is also determined what type of network rep-resentation must be used for further analysis, what step sizes to use, which events to han-dle and where to store the results.

The simulation uses an iterative procedure to solve AC and DC load flows, and the dynam-ic model state variable integrals simultaneously. Highly accurate non-linear system models result in exact solutions, including during high-amplitude transients. Various numerical in-tegration routines are used for the electromechanical systems (including voltage regula-tors and power system stabilisers) and also for the hydro-mechanical or thermo-mechanical models.

The process of performing a transient simulation typically involves the following steps:

1 Calculation of initial values, including a load flow calculation;

2 Definition of result variables and/or simulation events;

27 - 2


3 Optional definition of result graphs and/or other virtual instruments;

4 Execution of simulation;

5 Creating additional result graphs or virtual instruments, or editing existing ones;

6 Changing settings, repeating calculations;

7 Printing results.

27.2 Calculation Methods

27.2.1 Balanced RMS Simulation

The balanced RMS simulation function considers dynamics in electromechanical, control and thermal devices. It uses a symmetrical, steady-state representation of the passive electrical network. Using this representation, only the fundamental components of volt-ages and currents are taken into account.

Depending on the models of generators, motors, controllers, power plants and motor driv-en machines used, the following studies may be carried out:

• transient stability (e.g. determination of critical fault clearing times);

• mid-term stability (e.g. optimization of spinning reserve and load shedding);

• oscillatory stability (e.g. optimization of control device to improve system damping);

• motor start-up (e.g. determination of start-up times and voltage drops);

Various events can be included in the simulation, including the following examples:

• start-up and/or loss of generators or motors;

• stepwise variation of loads;

• load-shedding;

• line and transformer switching/tripping;

• symmetrical short-circuit events;

• insertion of network elements;

• power plant shut down;

• variations of controller setpoint;

• change of any system parameter.

Because of the symmetrical network representation, the basic simulation function allows the insertion of symmetrical faults only.

27.2.2 Three-Phase RMS Simulation

If asymmetrical faults or unbalanced networks have to be analysed, the three phase RMS simulation function must be used. This simulation function uses a steady-state, three-phase representation of the passive electrical network and can therefore compute unbal-anced network conditions, either due to unbalanced network elements or due to asym-

27 - 3


metrical faults. Dynamics in electromechanical, control and thermal devices are represented in the same way as in the basic RMS simulation function.

Asymmetrical electromechanical devices can be modelled, and single-phase and two-phase networks can also be analysed using this analysis function.

In addition to the balanced RMS simulation events, unbalanced fault events can be sim-ulated, such as:

• single-phase and two-phase (to ground) short-circuits;

• phase to phase short-circuits;

• inter-circuit faults between different lines;

• single- and double-phase line interruptions.

All of these events can be modelled to occur simultaneously or separately, hence any com-bination of symmetrical and asymmetrical faults can be modelled.

27.2.3 Three-Phase EMT Simulation

Voltages and currents are represented in the EMT simulation by their instantaneous val-ues, so that the dynamic behavior of passive network elements is also taken into account. This is necessary for the following applications:

• DC and harmonic components of currents and voltages;

• Exact behavior of inverter-driven machines;

• Exact behavior of HVDC transmission systems;

• Non-linear behavior of passive network elements such as transformer saturation;

• Overvoltage phenomena in switching devices;

• Lightning strikes and travelling waves;

• Analysis of the exact behavior of protection devices during faults.

The high level of detail used to represent the modelled network means that all phases and all defined events (symmetrical and asymmetrical) can be simulated. The EMT function can also be used for the simulation of longer-term transients. However, due to the passive network elements being represented dynamically, the integration step size has to be sig-nificantly smaller than in the case of a steady-state representation and as a result, the calculation time increases.

27.3 Setting Up a Simulation

Based on the results of a load flow calculation, all internal variables and the internal op-erating status of connected machines, controllers and other transient models have to be determined. As a result of this calculation, the synchronous generator excitation voltages and load angles are calculated. Additionally, all state variables of controllers and power plant models, and any other device which is active and will affect the time-domain simu-lation, are also calculated.

The calculation of initial conditions is started by either:

• Selecting the icon from the icon toolbar, and then pressing the icon;

27 - 4


• Selecting Calculation Stability Initial Conditions... from the main menu.

In the Initial Conditions command (ComInc) dialogue all simulation settings can be de-fined, such as the simulation type (i.e. RMS or EMT, balanced or unbalanced) and simu-lation step size settings.

These settings include:

Basic OptionsThe simulation type is selected here (RMS, EMT; balanced, unbalanced), and the load flow command, the result object and the event list are defined.

Step SizesMaximum and minimum step size are specified for use by the step size algorithms.

Step Size AdaptationEnables the variable step size algorithm.

Advanced OptionsIncludes various error margins, iteration limits, damping factors, etc.

Noise GenerationDefines parameters of the noise generation for stochastic applications.

27 - 5


Fig. 27.1: The Initial Conditions Command (ComInc) Dialogue


The basic options are used to select the simulation type and the network representation. References to the result object, the event list and the load flow command are available

for inspecting or editing these objects, by clicking on the respective icon.

Verify Initial Conditions

If the initial conditions can be fulfilled, the power system will be in a steady-state condi-tion. When the Verify Initial Conditions options is enabled, then the condition dx/dt=0 is checked for all state variables. If one or more of the state variable derivatives does not equal zero, the power system may start 'moving' from the very beginning of the simula-tion, even without the application of an external event. In this case the user should anal-yse the relevant controller or model and its defined initial conditions carefully.

27 - 6


All warnings or error messages issued in the output window should be checked carefully. Typical problems are devices which are overloaded or operate above or below signal lim-itation from the beginning of the simulation.

The error message displayed in the output window might look as follows: DIgSI/err - Some models could not be initialized. DIgSI/err - Please check the following models: DIgSI/err - 'Simple Grid\AVR Common Model.ElmDsl': DIgSI/err - Initial conditions not valid !

Automatic Step Size Adaptation

This option enables the step size adaptation algorithm, and can be used to speed-up the simulation considerably. PowerFactory adjusts the step size to the actual course of each state variable at any moment in time. Based on the local discretisation error, Power-Factory calculates an optimal step size that keeps the numerical errors within the spec-ified limits. A step size controller adjusts the integration step size.

As a result, when fast transients have decayed, PowerFactory automatically increases the step size and speeds up the simulation process considerably. In the case of events (external or internal), the step size is always set back to the Minimum Step Size. This way, the behavior of the system during a transient event is represented with the best accuracy.

If this option is activated, two integration step sizes are available on the Step Size tab of the dialogue:

Electromagnetic Transients/Electromechanical TransientsMinimum step size for EMT and RMS simulations, respectively.

Maximum Step SizeMaximum step size for the simulation.

Further parameters to adapt this algorithm can be found on the Step Size Adaptation tab.

27.3.2 Step Sizes

Integration Step Sizes

When using a fixed step size for the simulation (deactivate Automatic Step Size Adaptation on the Basic Options tab), the integration step size for EMT or RMS has to be set.

It is often unnecessary to plot every single calculated time step, and this reduction in plot-ted data can also result in a reduced simulation time. For this purpose, the step size for the output graphs can be set, so that not every point in time throughout the simulation time will be drawn on the virtual instruments plot. By selecting a larger Output step size, the simulation process will speed up without influencing the calculation process. It should be noted, however, that fast changes may not be seen in the reported results.

The parameters which are available for the step size are:

dtemt Electromagnetic Transients (typical value: 0.0001 sec)

dtgrd Electromechanical Transients (sym, asm, vco, pss) (typical 0.01 sec)

dtout Output (typical equal to dtemt for EMT; and dtgrd for RMS simulation)

27 - 7


Start Time

The start time of the simulation. This is typically negative, allowing the first event to be analysed to take place at t=0s.

Note When setting up time-domain simulations, it is very important to use the correct time steps for simulations in order to observe the right phenomena in the results. For the RMS simulation the mini-mum time step should always be smaller then the time constants in the system. In controllers one must consider both the open-loop and the closed-loop time constants. For electromagnetic tran-sients, e.g. when analyzing travelling waves, the smallest travelling time would be the upper limit for the minimum time step.

In addition to the Newton-Raphson based algorithm for the solution of "weak'' non-linear-ities (i.e. saturation effects in synchronous and asynchronous machines), the EMT simu-lation function allows interrupts for the simulation of "strong'' non-linearities (i.e. switches, two-slope transformer saturation or thyristors). These interrupts can also occur between time steps.

In case of such an interrupt, all time dependent variables are interpolated to the instant of interrupt and the simulation restarts at that point. This prevents numerical oscillations and allows much a lower integration step size to cater for power electronics devices.

The dynamic model equations of the voltage-controllers (vco) and the power system sta-bilisers (pss) are solved simultaneously with the electrical generator and passive network equations (stepsize dtgrd).

27.3.3 Step Size Adaptation

If option Automatic Step Size Adaptation is enabled on the Basic Options tab, further step size options are available on the Step Size Adaptation tab. These options are:

errmaxMaximum Prediction Error (typical value: 0.01)

errincMinimum Prediction Error (typical value: 0.01)

nincDelay for Step Size Increase (typical value: 10 time steps)

fincSpeed Factor for increasing the time step (default value: 1.5)

fdecSpeed Factor for decreasing the time step (default value: 2)

ddtemt_maxMaximum increase of step size (typical values: 0.05 for RMS; 0.001 sec for EMT)

Note The simulation time can be very sensitive to some of the parame-ters. For example when you increase the maximum time step the duration of calculating transients may not always increase. If this

27 - 8


time step is increased over an "optimal'' time step the simulation time may increase as well. It is strongly recommended to critically observe the simulation time and the results for different simulation parameters.


The advanced options may be used to tune the performance of the simulation algorithm. Less experienced users are recommended to use the default values.

Event Control

Resolution Factor

The value entered here (parameter name: kres) determines the time interval used to syn-chronize events. Every time an internal or external event occurs (usually between two in-tegration time steps), PowerFactory interpolates all state variables up to the moment in time at which the event has occurred and restarts the simulation from there. In the case of large disturbances it is possible that a very large number of events occur almost simultaneously. As this would slow down the simulation considerably, PowerFactory ex-ecutes all events that occur within a time interval of duration kres*dtmin at the same time.

All system variables are then interpolated up to the point in time when the event takes place, and the simulation is started from there. A higher resolution factor decreases the minimum time interval between events. The default value of 0.001 is usually sufficient.

If an event occurs, there are two different options available:

Interpolation at user defined events

• Calculation of v(t) and v(t+h) as usual. PowerFactory uses special numerical methods to allow this without numerical oscillations.

Re-Initialize After Event

• Calculation of v(t) and v(t+h), hence two values at the same time, one before the occurrence of the event, and one after. The second method is applied if the option Re-initialize After Event is enabled.

Further parameters can be changed to control the simulation algorithm.

Integration Control

errseqMaximum Error of State Equations (typical value: 0.1%)

itrpxMaximum Number of Successive State Iterations (typical value: 10)

alpha_rmsDamping Factor (RMS) (typical value: 1)

27 - 9


alpha_emtDamping Factor (EMT) (typical value: 0.99)

Iteration Control

errsmMaximum Iteration Error of Nodal Equations (typical value: 10*errlf)The iteration error errsm depends on the nominal power of the machines and the voltage levels. As an adequate starting value, errsm should be set to:errsm = 10*errlf, where errlf is the Max. Allowable Load-Flow Error for each Bus. Checking is best done by plotting some voltages at generator busbars. If voltage steps are observed, the value of errsm should be reduced.

erreqMaximum Error of Model Equations (typical value: 1%)

itrlxMaximum Number of Iterations (typical value: 25)itrpx specifies the max. number of iterations at each integration step which are allowed to reach the max. tolerable bus-error errsm. During the transient simulation process, the typical number of iterations required is between 1 and 5. Under certain conditions - i.e. after switching operations - up to 25 iterations may be observed.

itrjxIteration Limit to Recompute Jacobian Matrix (typical value: 5)

Signal Buffer

Reference System

Local/Global Reference System

The PowerFactory stability analysis uses the angle of a reference machine and refers all other angles to this reference angle. This is a numerically very efficient approach. After running initial conditions, the reference machine is displayed in the output window. It is usually the "Slack''-machine of the load-flow calculation.

In case of several isolated islands, PowerFactory offers the option of using one refer-ence machine for the whole system (Global Reference System), or to use an individual reference machine for each island. The first case should be used if the islands are re-syn-chronised again later in the simulation. In all other cases the option (Local Reference Sys-tem) should be used because it leads to a higher numerical stability and to faster simulation times.

Calculate Maximum Rotor Angle Deviation

PowerFactory can also calculate the maximum deviation between the rotor angles be-tween the synchronous machines in the system. This variable is then called dfrotx and can be chosen and displayed from the variables of all synchronous generators in the sys-

27 - 10


tem. This variable can be used as an indicator for the synchronous operation of a large transmission system.

A-stable integration algorithm for all models

If you enable this option, PowerFactory uses an A-stable numerical integration algo-rithms for all models to solve the simulation. In this case dynamic model equations and network equations are solved simultaneously. This algorithm is (slightly) slower in case of small step sizes but converges much better in case of large step sizes. Typical applications are longer term simulations, in which the simulation step size is increased considerably after fast transients have decayed. Another typical application are systems with power electronics. Even if power electronics devices are usually equipped with very fast controls, the A-stable algorithm still allows reasonable step sizes, at which the relaxation method would fail.

When using a conventional, explicit numerical integration algorithm, such as Runge-Kutta (not an A-stable algorithm), the integration step size must be adjusted to the eigenvalues of a system. Such a method (Relaxation Method) means a mutual solution of dynamic model equations and network equations until convergence is reached: This algorithm is fast for small step sizes but fails to converge when the step size is increased. Best choice for classical transient stability applications. But if excessively large step sizes are used, the numerical solution becomes unstable, even if fast modes have fully decayed and are no longer apparent in the system.

With the PowerFactory A-stable algorithm, the step size can be adjusted to the actual course of all state variables without considering numerical stability. When fast transients have decayed, the step size can be adjusted to the speed of slower transients, etc.

If some very fast modes are not of interest, a large step size can be selected from the beginning, and the algorithm will automatically smooth fast variations. A typical applica-tion of this type of algorithm is the simulation of long-term phenomena - where it is nec-essary to increase the simulation step size to the range of minutes, even if fast modes are present in the system.

However, if power electronics are involved, characteristic time constants can be extremely short (i.e. 1ms), even if a stability model with steady-state equations for the electrical net-work is used. Hence, using a classical integration algorithm would require the use of step sizes significantly smaller than the smallest time constant of the system, otherwise it would be numerically instable.

Note A requirement for using the A-stable integration algorithm is that just "true" input and output signal variables are used for exchang-ing information between different models.

It should be mentioned, that it is also possible to choose the usage of an A-stable algo-rithm for some element models only (not for all models), so that it is possible to run just a part of the models with the A-stable algorithm (for example the power electronic con-verters or fast controllers). This option is available in the dialogues of the elements.

With the A-stable algorithm, these systems can be analysed with reasonable step sizes. Hence, the A-stable algorithm cannot be described as using simplified models but as a different type of numerical integration algorithm.

27 - 11


27.3.5 Noise Generation

The Noise Generator element (ElmNoise) can be used in a transient simulation to pro-duce a noise signal based on random numbers. On the Noise Generation page of the ComInc dialogue, the random number generation method can be selected. The random number generator can be selected to be automatic (by selecting option auto), which is the default value and the most commonly used.

Alternatively, the option renew may be selected, in which case the random seed of the noise generator can be selected manually from "A" to "K". Thus the noise signal will look the same in every simulation, i.e. the results of a former simulation can be reproduced exactly.

27.3.6 Advanced Simulation Options - Load Flow

There are further options which can influence the simulation process and its results. In the load flow command dialogue (ComLdf, see also Section 23.2) on the Advanced Sim-ulation Options tab, the influence of protection devices or various controller models can be neglected. Hence the chosen models or protection devices will be ignored during the simulation as well as in load flow and other calculations. This is illustrated in Figure 27.2.

Fig. 27.2: Advanced Simulation Options in the ComLdf Command Dialogue

The options available for the consideration of protection devices are:

none No protection devices are considered in the calculations

all All protection devices are considered

27 - 12


main Only the protection devices are in operation, which are defined as 'main' devices

backup Only the 'backup' protection devices are considered. According to the controller models, there is the possibility to ignore all controllers and mechanical elements with the option Ignore Composite Elements. If there are only some specific model types one would like to neglect in the simulation, they can be moved from the left window Considered Models to the right window, Ignored Models.

27.4 Result Objects

During an EMT or RMS simulation, a large number of signal variables are changing over time. To reduce the available data and to narrow down the number of variables to those necessary for the analysis of each particular case, a selection of these signals for later use has to be defined.

Therefore, one or more result objects containing the result variables can be configured. The simulation function needs the reference to a result object to store the results.

The command dialogues for calculation functions, that produce signals, have result object references, as depicted in Figure 27.3 for the Initial Conditions (ComInc) dialogue. See also Figure 27.1 for the complete dialogue.

Fig. 27.3: Result Object Reference

Such a result object reference refers to the currently used result object. The downward

arrow button ( ) is used to select or reset the reference, or to edit the contents of the referenced result object.

The right-arrow button ( ) is used to edit the result object itself. When editing the out-put variables press this Edit button and then Contents to get access to the list of vari-ables stored inside the result object. This will pop up the corresponding ElmRes edit dialogue.

An easier way to edit or inspect the result object is to press the icon on the main toolbar, or to select the Data Stability Result Variables option from the main menu. This will enable the user to edit the contents of the currently selected Result object in the Initial Conditions (ComInc) command dialogue. Result objects (ElmRes) are treated in detail in Chapter 19 (Reporting and Visualizing Results).

To add variables of different elements to the result object for RMS and EMT simulations, right-click on the desired element in the single-line graphic and select Define...--> Variable

27 - 13


Set (Sim)... as shown in Figure 27.4.

Fig. 27.4: Defining a Variable Set for a Line Element

This element will then be monitored during the simulation. A browser window is automat-ically opened, and by double-clicking on the variable set icon ( ) of the relevant row, the variables of interest to be recorded can then be selected. See also Section 19.1.4 (Re-sult Objects).

Note Most of the variables for RMS and EMT simulations are identical. Nevertheless there may exist variables that are valid for EMT but not for RMS calculations. It is advisable to only use variables for the calculation which is currently being performed.

27.4.1 Saving Results from Previous Simulations

The variables to be monitored are stored (by default) in the result object All calculations. The results of the variables in the current simulation are stored in this file also. If the re-sults of two different simulations are to be displayed, e.g. in one virtual instrument, there is the possibility to save the result object of a previous simulation simply by copying the result object All calculations and renaming it to something else.

This can be done easily in the data manager. The result object can be found in the cur-rently active study case. Copy the result object and paste it into the same study case. Following this, a second result object will be created with the name All calculations(1). If desired, the object can be renamed to something more appropriate.

In the following simulation, the default result object All calculations will be overwritten

27 - 14


with the new results, but the copied results will not be modified and can be displayed to-gether with the new simulation results in one plot. For further information see Section 19.4.2 (Plots).

27.5 Events

Besides the reference to a result object, the simulation function needs a reference to an event object to determine the simulation events. The default event object in Power-Factory is Simulation Events and, like the result object, is also stored inside the study case.

External events are used in steady-state calculations (e.g. short-circuit calculations) as well as for transient calculations (Simulations).

PowerFactory offers several kinds of events for time-domain simulations:

1 Switch events (EvtSwitch)

2 Parameter events (EvtParam)

3 Short-circuit events (EvtShc)

4 Intercircuit fault events (EvtShcll) 5 Synchronous machine events (EvtSym)

6 Load events (EvtLod)

7 Outage of element (EvtOutage)

8 Message events (EvtMessage)

9 Set integration step size event (EvtStep)

10 Tap event (EvtTap)

The different events are stored in the event object. The contents of the currently selected event object (labelled Events) can be found in the ComInc dialogue. This object can be

edited using the right-arrow ( ) button followed by the Contents button to access the event list stored inside the event object.

Alternatively, the event object can be easily accessed from the main toolbar by pressing

the Edit Simulation Events icon. A list of the currently defined events will be displayed including the set simulation time, when the event will occur, and the related object. Figure 27.5 shows an example set of events.

27 - 15


Fig. 27.5: The Event Object Including a Set of Events

When creating a new event, use the icon in the toolbar, as can be seen in the Simu-lation Events object dialogue in Figure 27.5. The event type can be chosen from the list in the element selection dialogue which pops up, as shown in Figure 27.6. The events can also be modified during a simulation by stopping the calculation, editing the events and continuing the simulation.

27 - 16


Fig. 27.6: Defining a New Simulation Event

An alternative means of defining events is as follows: upon calculation of the initial con-

ditions ( ), or when the simulation is already running, double-click on the desired cu-bicles to create switch events. Additionally, the user can right-click on an element and then select an element-related event such as Define... Switch Event, Define... Load Event or Define... Short-Circuit Event.

During a simulation all previous events (i.e. events which have already occurred), are dis-played in a grey font style and can no longer be edited or changed. When the simulation is finished or is stopped manually, the events which are still to come in the simulation can be altered and new events can be created.

Note At the end of a simulation the event list shows all events, which are now grey in color. They can no longer be modified for this simula-tion, because the simulation could be restarted from this point on. To change the events for a new simulation one must first initialise the calculation again ( ), so the simulation time is reset to the beginning.

27 - 17


27.5.1 Switch Events

Switch events are used only in transient simulations. To create a new switch event, press

the icon on the main menu (if this icon is available), which will open a browser con-

taining all defined simulation events. Click on the icon in this browser, which will show a IntNewobj dialogue which can be used to create a new switching event.

Fig. 27.7: Creation of a New Switch Event (IntNewobj)

After pressing OK, the reference to the switch (labelled Breaker or Element) must be man-ually set. Any switch in the power system may be selected, thus enabling the switching of lines, generators, motors, loads, etc. The user is free to select the switches/breakers of all phases or of only one or two phases.

It should be noted that more than one switching event must be created if, for instance, a line has to be opened at both ends. These switch events should then have the same ex-ecution time.

27.5.2 Parameter Events

With this type of event, an input parameter of any element or DSL model can be set or changed. First, a time specifying when the event will occur is inserted. Then an element

has to be to specified/selected using the down-arrow button . Then choose Select... from the context-sensitive menu. Afterwards insert the name and the new value of a valid element parameter.

27.5.3 Short-Circuit Events

This event applies a short-circuit on a busbar, terminal or on a specified point on a line. The fault type (three-phase, two-phase or single-phase fault) can be specified as well as the fault resistance and reactance and the phases which are affected.

27 - 18


The duration of the fault cannot be defined. Instead, to clear the fault, another short-cir-cuit event has to be defined, which will clear the fault at the same location. An example is shown in Figure 27.5.

27.5.4 Intercircuit Fault Events

This type of event is similar to the short-circuit event described in Section 27.5.3 (Short-Circuit Events). Two different elements and their respective phases are chosen, between which the fault occurs. As for the short-circuit event (EvtShc), four different elements can be chosen:

• Busbar (StaBar) • Terminal (ElmTerm)

• Overhead line or cable (ElmLne)

27.5.5 Events of Synchronous Machines

There is a special event for synchronous machines, which is used to easily change the mechanical torque of the machine. The user specifies the point in time in the simulation for the event to occur, and an active synchronous machine ElmSym. The user can then define the additional mechanical torque supplied to the generator. The torque can be pos-itive or negative and is entered in per unit values.

27.5.6 Events of Loads

The user specifies the point in time in the simulation for the event to occur, and a load element (ElmLod, ElmLodlv or ElmLodlvp). The value of the load can then be altered using the load event.

There are different ways to change the power of the selected load:

StepChanges the current value of the power (positive or negative) by the given value (in % of the nominal power of the load) at the time of the event.

RampChanges the current value of the power by the given value (in % of the nominal power of the load), over the time specified by the Ramp Duration (in seconds). The load ramping starts at the time of the event.

27.5.7 Outage of Element

This event can only be used during an RMS simulation, when an element is to be put out of service at a specific point in time. The option Take element out of service should be selected within the dialogue. It should be noted that it is not possible to bring the outaged elements back into service during the transient simulation. This is only possible in steady-state calculation functions, e.g. short-circuit calculation or reliability assessment. In time-domain simulation the following error message will occur in the output window:

27 - 19


DIgSI/err (t=000:000 ms) - Outage Event in Simulation not available.Use Switch-Event instead!

27.5.8 Save Results

This event is only used in the PowerFactory Monitor of the program. It cannot be used during time-domain simulations.

27.5.9 Set Integration Step Size

27.5.10 Tap Event

The user specifies the point in time in the simulation for the tap event to occur, and a shunt or transformer element (ElmShnt, ElmTr2, etc). The Tap Action can then be spec-ified.

27.6 Running a Simulation

Upon successful calculation of the initial conditions (i.e. execution of ComInc ), the

icon on the main toolbar will be activated and can be pressed to start the simulation.

The simulation is performed for the time interval between the start time defined in the initial conditions command ComInc, and the stop time (parameter name: tstop), which can be specified in the simulation (ComSim) dialogue. After a simulation has finished, it

may be continued by pressing the icon again, and entering a new stop time. In this case, the stop time may also be entered relative to the current simulation time.

A running simulation may be interrupted by pressing either the icon or the icon on the main toolbar. Additional events can be created and results may be viewed while

the simulation is paused. The simulation is then continued by pressing the icon again. Pausing and continuing the simulation may be done as often as required.

27 - 20


27.7 Models for Stability Analysis

Stability analysis calculations are typically based on predefined system models. In the ma-jority of cases the standard IEEE definitions for controllers, prime movers and other as-sociated devices and functions are used.

For planning purposes, this approach might be acceptable. The predefined sets of param-eters will allow a favorable and reasonable behavior of the analyzed system. This ap-proach is often also applied to operation analysis, and the system should show a response similar to a real system.

For systems and configurations for which no IEEE models exist, such as wind generators, HVDC-systems, etc., powerful tools for user defined modelling are required. For this pur-pose, highly specialised, exact models can be created in PowerFactory.

In cases when manufacturers are able to supply exact controller models including real pa-rameters, the system model can be improved by not using the IEEE standard models, but instead building a new block diagram of the individual controller/mechanical system to represent the device. This facilitates highly accurate system modelling.

Utilities and consultants often conduct system operation performance and optimization studies, and therefore have a clear need for accurate methods and tools for creating ac-curate transient models for stability analysis.

This includes complex operation analysis and special component planning problems. This demand led to the development of highly flexible and accurate DIgSILENT Power-Factory time-domain modelling features, which are introduced in this chapter.

27.7.1 System Modelling Approach

System modelling for stability analysis purposes is one of the most critical issues in the field of power system analysis. Depending on the accuracy of the implemented model, large-signal validity, available system parameters and applied faults or tests, nearly any result could be produced and arguments could be found for its justification.

This is one aspect of the complexity of a transient stability study. The other aspect results from the often large set of time-domain models that are required, each of which may be a combination of other models. All these time-domain models are ultimately wired togeth-er into one large, single transient model from which the basic set of system differential equations can be obtained.

Given this complexity of a transient analysis problem, the PowerFactory modelling phi-losophy is targeted towards a strictly hierarchical system modelling approach, which com-bines both graphical and script-based modelling methods.

The basis for the modelling approach is formed by the basic hierarchical levels of time-domain modelling:

• The DSL block definitions, based on the "DIgSILENT Simulation Language" (DSL), form the basic building blocks to represent transfer functions and differential equations for the more complex transient models.

• The built-in models and common models. The built-in models or elements are the transient PowerFactory models for standard power system equipment, i.e. for generators, motors, static VAr compensators, etc. The common models are based on the DSL block definitions and are the front-end of the user-defined transient models.

27 - 21


• The composite models are based on composite frames and are used to combine and interconnect several elements (built-in models) and/or common models. The composite frames enable the reuse of the basic structure of the composite model.

The relation between these models and the way that they are used is best described by the following example.

Suppose the frequency deviation due to the sudden loss of a fully-loaded 600 MW unit in a particular network is to be analyzed. Depending on the network and the required detail in the calculated results, such analysis may ask for a detailed modelling of the voltage controllers, prime movers and primary controllers, or any other important equipment for all large generators in the system.

Fig. 27.8: Example of a Composite Generator or Power Plant Model

Figure 27.8 shows a typical configuration of a synchronous generator with power system stabilizer, voltage controller, primary controller, and prime mover model. The primary con-troller and prime mover can be summarized as the primary controller unit model. To cre-ate this kind of model, the following actions are required:

1 Transient models for each required controller type or unit type have to be defined (Model/Block Definition).

2 For each generator, the transient models of the individual controller must be customized by setting the parameters to the correct values (Common Model).

3 A diagram has to be made defining the connections between the inputs and outputs of the various models (Composite Frame).

4 For each generator, the diagram and the customized transient models are to be grouped together to define an unique 'composite' generator model (Composite Model).

It may seem unnecessary to include steps 2 and 3: it would be possible to create custom-ized transient models for each generator directly, with 'burned-in' parameter settings, and to link these models to a generator without having to define a diagram first. This, how-ever, would mean that one would have to create a new voltage controller, e.g. for each generator in the system.

Often the design of many of these voltage controllers will be similar. To omit the need of creating copies of these controllers for each generator and to avoid redundant copies of controllers or also of whole generator models.

Here the same relationship as that between individual controller (Common Model) and

PSSPower System

Stabilizer

PCOPrimary Controller

PCUPrimary Controller Unit

PMUPrime Mover Unit

VCOVoltage Controller

VEXC

VPSS

AV

VGEN

PGEN

GENPT

SYMSynchronous

Machine

27 - 22


controller definition (Model Definition) is used; this time between the generic power plant diagram (Composite Frame) and the individual power plant (Composite Model). DIgSI-LENT PowerFactory uses two key objects in creating composite models, which can be compared to the element definition of the different elements:

• The Common Model (ElmDsl) combines general time-domain models or model equations (a block definition) with a set of parameter values and creates an integrated time-domain model.

• The Composite Model (ElmComp) connects a set of time-domain models inside a diagram (a composite frame) and creates a 'composite model'.

The following diagrams explain the relation between the Composite Model (which is using a Frame as type) and the Common Model (based on a block diagram as type) in detail.

• The Composite Model (ElmComp), see Figure 27.9, references the definition of a composite frame. This composite frame is basically a schematic diagram containing various empty slots, in which controller or elements can be assigned. These slots are then interconnected according to the diagram, see Section Composite Block Definitions (part of Section 27.8.3: Defining DSL Models). The slots in the composite frame are pre-configured for specific transient models.

• The schematic diagram in Figure 27.10 shows a Composite Frame (BlkDef) which has one slot for a synchronous machine, one for a primary controller unit (pcu slot), and one for a voltage controller (vco slot). The composite model, which uses this composite frame, shows a list of the available slots and the name of the slot. Now the specific synchronous generator, voltage controller or primary controller unit model can be inserted into these slots.

• The synchronous machine that is used in the Composite Model is called a Built-In Model, see Figure 27.11. This means that such elements are pre-configured elements which do not need a specific model definition. Any kind of element which is able to provide input or output variables, e.g. converters, busbars, etc, can be inserted into the slots.

• The voltage controller, and primary controller unit, however, are user-defined Common Models, see Figure 27.12. The 'front-end' of all user-defined transient models is always a common model (ElmDsl), which combines a model definition with specific parameter settings. There are predefined definitions as well, so that the user can create her/his own model definitions.

• The common model has a reference to the Model Definition (BlkDef), which looks similar to the composite frame (shown in Figure 27.13). Here different blocks are defined and connected together according to the diagram. The input and output variables have to fit with the slot definition of the slot that the model is defined for.

Not all slots of the composite model must necessarily be used. There can also be empty slots. In such cases, the input of this slot is unused and the output is assumed to be con-stant over the entire simulation. The usage of composite models with a composite frame, and the common model with its block definitions are described in the next sections.

The design and creation of user defined common models using the "DIgSILENT Simu-lation Language" (DSL) can be found in Section 27.8 (User Defined (DSL) Models).

27 - 23


Fig. 27.9: Example of a Composite Model Using the Frame “Frame_Generator”

Fig. 27.10: Composite Frame “Frame_Generator”

Fig. 27.11: Generator “G1” (Built-In Model)

u

upss

pt

ve

fe

vco slotElmVco*

0

1

pcu SlotElmPcu*

sym SlotElmSym*

0

1

0

1

pss slotElmPss*

L1

G~G1

27 - 24


Fig. 27.12: Example of a Common Model Using the Definition “vco_simple”

Fig. 27.13: Example of a Model Definition “vco_simple”

u o12

usetp

yi

o1

3

uerrs

upss

ve- _{K/(1+sT)}_Ke,Te

Emax

Emin

PID ControllerTa,Tb,K1

vco_Simple: Simplified Excitation System

2

3

1

0

27 - 25


27.7.2 The Composite Model

A composite model element (ElmComp) can created using the "New Object" ( ) icon, located in the toolbar of the data manager and selecting Composite Model from the avail-able options. The next step is to select the composite frame. The composite frame can be stored either in the global library or in the local library, and is conceptually similar to a type definition for an electrical element. The composite model then shows the list of slots in the composite frame as shown in Figure 27.14.

Existing controllers or models can be assigned to a slot manually by right-clicking the slot and selecting Select Element/Type, as depicted in Figure 27.14. A data manger window will pop up and the user can then browse the grid for the element to insert into the se-lected slot.

Fig. 27.14: Editing the Composite Model (ElmComp) Dialogue

When inserting controller models into a slot, it is often the case that the controller element has not yet been created. To create a new controller element select New Element/Type from the slot’s context-sensitive menu. PowerFactory will automatically jump to the project Library and show a list of available user defined models (ElmDsl).Selecting a model definition from the project library or the global library will open the el-ement dialogue of the newly-created common model, so that its parameters can be de-fined, similar to (for example) a transformer element. If no suitable model is found, a block definition has to be selected prior to setting the model parameters (see Section 27.7.3 (The Composite Frame) and Figure 27.13).

If an element is assigned to a slot, it is possible to edit the assigned element by simply right-clicking and selecting Edit Element/Type. The right-mouse button menu entry Reset Element/Type will reset the slot, so that it is empty again.

27 - 26


Note Depending on the settings of the individual slot, the menu entry Reset Element/Type will not only clear the marked slot but also de-lete the built-in or common model, if it is stored inside the compos-ite model in the data manager. These settings are explained in detail in Section 27.7.3 (The Composite Frame).

A faster method for defining standard composite models is to right-click on an object in the single line diagram and select Define... from the context menu of the element.

When a standard composite model is available for the selected object, a list of the avail-able controllers is shown. Selecting a controller will add it to the composite model, which is automatically created when no composite model yet exists for the selected object.

Standard composite models are available for:

• The synchronous motor and generator;

• The asynchronous motor and generator;

• The static VAr system.

Slot Update

The Slot Update button in the composite model (ElmComp) dialogue will re-read the slot definitions from the composite frame and will cancel all invalid slot assignments.

A slot assignment is invalid when a model has been assigned to a slot which is not suited to receive this kind of model, i.e. a voltage controller cannot be assigned to a slot defined for a primary controller model.

All built-in models and common models which have been created for a specific composite model are stored in that composite model itself. The contents of a composite model are shown in the data manager where the composite model is treated as a normal database folder. Basic power system equipment, such as synchronous machines or static VAr com-pensators, are normally not stored in the composite folder, but in the grid itself.

The slot update will try to re-assign each model found in its contents to the corresponding slot.The options defined for each slot are important, and are described in the paragraph Classification in Section 27.7.3 (The Composite Frame).

Step Response

The Step Response button in the composite model (ElmComp) dialogue will activate the Step Response command (ComStepres). The dialogue can be seen in Figure 27.15.

Next to the references to the composite model, the template and the target directory, the two step response tests, which will be created, can be specified. The study case to be activated can also be selected. When Execute is pressed, PowerFactory will create a new folder in the current project named Step Response Test. Figure 27.16 shows this fold-er in the data manager.

27 - 27


Fig. 27.15: Step Response Command (ComStepres) Dialogue

Fig. 27.16: Step Response Folder in the Data Manager

Inside the Step Response Test folder, a second folder is created, named according to the composite model which is to be tested. Here the simple test grid can be found including only the generator, the complete composite model and a load. Additionally there will be two new study cases in which a step response for the AVR and the PCU, respectively, of the composite model can be tested.

The user can switch between these two study cases and her/his previously-used study cases by activating and deactivating them.

Note There is now no longer any connection between the original ele-ments and the new elements of the composite model. Therefore, you can change any controller settings without changing your net-work.

After testing the controller, the folder Step Response Test can be deleted completely with-out loss of information in the original network.

27 - 28


27.7.3 The Composite Frame

A composite frame is a block diagram which defines two or more slots, their input and output signals, and the connections between them. A composite frame is defined graph-ically by drawing it.

Drawing a composite model frame is similar to drawing a normal block diagram. The main difference is that instead of common blocks, only slots may be used.

To create a new composite frame select the Insert New Graphic icon on the main tool-bar (in the graphics window) and then select Block/Frame Diagram and press Execute as shown in Figure 27.17. This new block definition will then be automatically created in the local library.

Fig. 27.17: Creating a New Composite Frame

An empty diagram of the frame will appear in the graphics window. A slot is then created

by selecting the icon in the graphics toolbox and positioning the slot on the drawing surface by clicking once at the desired location. This is similar to placing elements in the single-line diagram.

An empty slot will be drawn on the page. To define the slot’s input and output signals and different parameters, edit the slot by double-clicking it. The slot edit dialogue will pop up as shown in Figure 27.18.

27 - 29


Fig. 27.18: Slot Dialogue (BlkSlot)

Name and Sequence

The name of the slot will appear later in the composite model dialogue, and it is therefore recommended to name this element according to which slot it will be assigned (e.g. 'vco slot'). The Sequence parameter defines the order of the slots appearing in the composite model dialogue.

Classification

The classification options only effect the external behavior of the slot.

LinearThe slot representation in the frame diagram will be as a linear or non-linear model.

Automatic, model will be createdWhen this option is activated, the function 'Slot Update' (see Section 27.7.2: The Composite Model) will automatically create a DSL model and ask for a block definition from the library.

Local, Model must be stored insideThis option is activated by default. This means that when a Slot Update is executed in the composite model, PowerFactory will only search for elements which are stored inside the ElmComp. A reference to models which are stored outside, i.e. the synchronous generator in a plant model, will be removed from the slot.

27 - 30


Not all input or output signals of built-in elements or common models have to be used and defined in the slot. A slot may only have an input or an output signal.

For example, the voltage or frequency of an AC voltage source ElmVac may be controlled by an external function. Therefore, the slot for the source will only have two input signals u0 and f0. More information about drawing composite frame diagrams can be found in Section 27.7.6 (Drawing Composite Block Diagrams and Composite Frames).

Input and Output Signals

The input and/or output signal(s) have to be defined for each slot. The available signal names for the Built-In transient models (Elements) can be found in the corresponding Technical References.

The given input and output signal names in this slot dialogue have to match the input/output signals of the given transient model exactly, or the signals will not be connected properly and an error message will result.

Only after one or more input and output signals have been defined for a slot, is it possible to connect the slot with signal lines to other slots. It is therefore recommended to first position and edit all slots and to draw the signal connections thereafter.

Limiting Signals

There is also the possibility to enter 'limiting signals'. These signals are handled by Pow-erFactory exactly like normal input signals. The difference is only in the graphical repre-sentation in the block diagram. These signals will be shown as inputs on the top or bottom of the slot.

Class/Name Filter

There is also the possibility to specify a filter for the class name and/or for the model name to be inserted. This makes sense when (for example) only synchronous machines should be assigned to the slot. In this case, the class name ElmSym* would be entered. Pow-erFactory then will only allow the element class "synchronous machine'' to be inserted into the slot. A filter for a specific (part of an) element name can also be defined.

Assigning a Block Definition to a Slot

A block definition (BlkDef) can be assigned directly to a slot. This option will simplify the handling of the slot and prevent errors due to mis-matched signal names of slot and as-signed block.

To assign the external form of a block definition to the selected slot, edit the slot by dou-

ble-clicking it and choose the "select" button for the "Block Definition" in the dialogue. Now the block definition can be selected, e.g. the type of controller or built-in element, which should be assigned to this slot later.

As an example, if the newly-defined slot ought to represent a synchronous machine in the frame diagram, a predefined block definition can be chosen to insert the input and output signals to this slot available for the element ElmSym. A controller should, for example, only be assigned to a slot, when only this type of controller is to be inserted into this slot, and no other model can be.

27 - 31


Some predefined block definitions can be found in the global library in the path Library\ Models\Built-in.

When the block definition is selected (in our example the ElmSym.BlkDef), the input and output as well as limiting signals will disappear from the slot dialogue. The filter for the class name will automatically be entered. When clicking on the Ok button, the slot will then show the right inputs and outputs of the block definition.

Note When a block definition is assigned directly to a slot, only the input/output signals are set automatically. The internal equations/defini-tions of the block definition are not implemented in the slot and the slot itself remains empty. There is always the need to create a common model, which is the model inserted into the slot of the composite model. When the slot refers to an outside block defini-tion, beware that this reference is also inside your project. If the reference to the definition is invalid or changed, the slot may be changed as well. Therefore, assign a block very carefully.

27.7.4 The Common Model

The common model element (ElmDsl, ) is the front-end object for all user-defined block definitions. This means that user-defined transient models, but also the block dia-grams that are ready-shipped with the PowerFactory program, cannot be used other than through a common model. The common model combines a model or block definition with a specific set of parameter values. The common model shown in Figure 27.19 uses the block definition “vco_Simple”.

Typically the model definition is implemented as a block definition, such as that shown in Figure 27.20.

A model definition contains block references which may in turn either point to a primitive block definition (see Figure 27.21) or to a another composite block definition (see Figure 27.22). The structure of the block definition is thus recursive and the user should check that this recursive structure does not contain circular references to composite block defi-nitions.

A primitive block definition contains one or more DSL expressions and forms a basic block for more complex transient models. A description of how to use and create DSL models can be found in Section 27.8 (User Defined (DSL) Models).

It is also possible to implement the model definition not as a block definition, but directly as a primitive block definition (Figure 27.21), coded using DSL.

Each block definition generally has one or more parameters which can be changed to de-fine the model's behavior. Two kinds of parameters are supported:

• Scalar parameters, i.e. amplification factors, offsets, setpoints, etc.

• Two and three dimensional array parameters, which are used in the DSL lapprox()/lapprox2() and sapprox()/sapprox2() functions.

27 - 32


Fig. 27.19: Common Model for the VCO

Fig. 27.20: Block Definition of the VCO, Using a Sub-Definition

u o12

usetp

yi

o1

3

uerrs

upss

ve- _{K/(1+sT)}_Ke,Te

Emax

Emin

PID ControllerTa,Tb,K1

vco_Simple: Simplified Excitation System

2

3

1

0

27 - 33


Fig. 27.21: Implementation of the Limiter Block, Using a DSL Routine

Fig. 27.22: Implementation of the Controller, Defining a Sub-Block

To create a common model, use the "New Object" ( ) icon in the toolbar of the data manager and select Common Model. The block/model definition has to be selected first. Similar to the composite frame, this definition is either stored in the global library or in the local library.

The common model then displays the list of available parameters and arrays from the block diagram, as shown in Figure 27.23. All parameters are listed on the first page of the common model, and their values can be specified there.

y2 yo

o11(

1..

yo(1)

o11

yi1

o1yi

-

1/sTTb

KK1

K1/K2Ta,Tb

27 - 34


Fig. 27.23: Common Model with Parameter List

If the selected block definition uses one or more arrays in its definition, then these arrays are displayed on the second page (for simple characteristics) and third page (for two-di-mensional characteristics) of the ElmDsl object. In Figure 27.24 an example is shown for a 13x4 array definition.

Fig. 27.24: Common Model with Array List

The characteristics are defined as follows:

CharacteristicIn the row labelled 'Size', insert the number of rows in the first cell; the number of columns is set automatically. If the number of rows is

changed, jump to the previous page and back again to update the characteristic.

27 - 35


Two-Dimensional CharacteristicIn the row labelled 'Size', insert the number of rows in the first cell and the number of columns in the second cell. If one of these numbers is

changed, jump to the previous page and back again to update the characteristic.

27.7.5 The Composite Block Definition

A composite block diagram of the model definition is a graphical representation of a math-ematical transfer function, which produces one or more output signals as a function of one or more input signals. A block diagram may also have limits (minimal and maximal values) as input signals.

A block diagram may thus be described as:

(y_0, y_1, ...) = function(u_0, u_1, ...)

where y_0, y_1, ... represent output signals 0, 1, ... and u_0, u_1, ... represent for input signals 0, 1, .... These signals are all functions of time.

Block diagrams consist basically of the following elements:

Summation Pointswhich produce the single output y=(u_0+u_1+...)

Multiplierswhich produce the single output y=(u_0*u_1*...)

Divisorswhich produce the single output y=(u_0/u_1/...)

Switcheswhich produce the single output y=u_0 or y=u_1

Signal Lineswhich produce one or more outputs from one input: y_0=y_1=...=u

Block Referenceswhich are used to include other block definitions.

Block references can be looked upon as macros that insert a low-level block definition in-side a composite block diagram definition. A block reference may either point to another composite block definition or to a primitive block definition.

The PowerFactory program is shipped with a large set of primitive block diagrams for most common controller elements like PID-controllers, Dead Bands, Valve Characteristics, etc., and can be found in the PowerFactory tree under Database | Library | Models |Global_Macros. These predefined DSL primitives may be copied and altered for specific needs.

A block reference is created by using the icon in the graphics toolbox. This creates an empty square which can then refer to any existing block definition in the library.

Note The composite frame and the model definition are very similar and their usage is almost identical. When creating one or the other PowerFactory recognizes the class when you place the first slot

27 - 36


or block. If you place a block ( ) first, the icon for the slot will become inactive, so the user cannot inadvertently mix up slots and blocks in one diagram. See also Section 27.7.6 (Drawing Com-posite Block Diagrams and Composite Frames).

If the block type is selected, PowerFactory inserts all available parameters of the re-ferred block. The user may change the name of any parameter, however ensure that the order of the parameters is not changed. The order is important so that the right parameter is assigned to the parameters inside the block definition.

Signal lines are directed branches, connecting input and output signals. A single output line may be branched off and connected to more than one input terminal.

After the block reference has been edited, it will show the input, output and limiting signal connection points of the referenced block definition as one or more colored dots on the left and right side, respectively, on the upper and lower side of the box. Signal lines may then be connected to these points. It is allowed to refer to the block definition more than once in the same block diagram. This way, it is possible to use a particular PID-controller, for instance, twice or more in the same model definition.

An example of a simple block diagram, comprising a multiplier, a summation point and a standard PI block, is shown in Figure 27.25.

Fig. 27.25: Example of a Simple Block Diagram

When rebuilding a diagram (by pressing the icon), the DSL representation of the block diagram is written to the output window. For the example block diagram in Figure 27.25, this results in the following output:

model o1 = 'MyBlock'(i1,i2;x1;Kp,Ti;yi)s1 = '\System\Library\Models\DSL\PI.BlkDef'(xe;x1;Kp,Ti;yi)xe = i1*i2o1 = s1+i2+i1

This simple example shows the whole meaning of the block diagram graphics: it is a con-venient way to define specific controllers, based on standard components.

However, it would also be possible to define exactly the same block diagram by entering the above DSL script manually and thereby create a primitive block definition.

27.7.6 Drawing Composite Block Diagrams and Composite Frames

Although the composite block diagram and the composite frame diagram should be dis-

27 - 37


tinguished from one other, they are drawn in the same way.

The basic distinction between a block diagram and a frame diagram is that the latter con-tains only slots and signals, whilst the block diagram must not contain any slots.

A new block or frame diagram can be created in various ways:

• Selecting the main menu entry File New or Strg-N and then selecting the option Block/Frame Diagram from the "New" command dialogue (ComNew);

• By clicking on the Insert New Graphic icon on the toolbar of an open graphic, and selecting the option Block/Frame Diagram;

• By right-clicking on, or inside a (library) folder in the active project in the data manager and selecting New... Block/Frame - Diagram from the context-sensitive menu;

• By using the New Object icon in the database manager and selecting Block Definition (BlkDef).

Note The two later options only create a block definition object (BlkDef), but no graphic. This method is therefore not suitable for creating a composite block or frame diagram, but only for creating primitive block definitions by entering the DSL code.

In the first two methods, a graphic will be created and will appear in the open graphics board. A new graphics board will be created when no graphics board is open. The new block/frame diagram graphic will show a single rectangular block, which depicts the block or frame. The name of the new diagram will appear on top of the frame.

Inside this rectangle the following objects can be placed from the graphic toolbox for the block diagram:

Node objects: - block references

- summation points

- multipliers

- divisors

- switches

- different kinds of graphical objects

Branch objects: - signals lines

Inside a frame diagram only the following elements are allowed:

Node objects:- slots

- different kinds of graphical objects

Branch objects:- signals lines

These objects can be selected from the Drawing Toolbox. The toolbox also has buttons

27 - 38


for pure graphical add-on objects (lines, polygons, rectangles, texts, etc.) as shown in Figure 27.26. It should be noted that the availability of this toolbox is according to wheth-

er or not the graphic is ‘frozen’ ( ). When the graphic is not frozen, the toolbox is avail-able, and likewise, when the graphic is frozen for editing, the toolbox is hidden.

Fig. 27.26: Block/Frame Diagram Objects

Note When creating a frame or a block definition, PowerFactory rec-ognizes the type of definition when you place the first slot or block. Because a composite frame diagram may only contain slots and signal lines, creating a slot will disable all other node objects in the drawing toolbox. If you place a block ( ) first, the icon for the

slot will become inactive, so you can't mix up slot and block elements in one diagram.

Adding a Block Reference

Drawing the block objects and connecting them with signals is done in a similar way as is done with elements in the single line graphic. A block reference is first displayed as an empty square which has to be edited in order to assign a (low level) block diagram to it.

Because of lack of information about the number of inputs and outputs of the new block reference before a (lower level) block definition is assigned to it, it is not possible to con-nect signals to the empty block. It is therefore recommended to first draw all block refer-ences and to assign block definitions to them. The block references then show all available input and output signal connections.

A block reference is edited by right-clicking on it and selecting Edit from the context-sen-sitive menu, or simply by double-clicking on it. The dialogue as displayed in Figure 27.27 will pop up.

27 - 39


Fig. 27.27: Edit Dialogue of the Block Reference

Use the Select button ( in Figure 27.27) to select a model definition. Predefined stan-dard block diagrams for your usage are located in the folder Database\ Library\ Models.

It is also possible to create a block in the graphical Block Definition by dragging Macros from the global library or project library into the drawing area of the Block Definition, us-ing the Drag & Drop functionality.

Adding Calculation Blocks

Summation Point Every dot can be used as an input to the summation point. The sign of signals at summation points can be changed by editing the summation point object. The "edit" dialogue will pop up, where any connected input connection can be inverted. It should be noted that not all dots have to be used and only one dot can be defined as an output.

Multiplier Every grey dot of this block can be used as an input or output of the multiplier. An output of three input signals will thus be: out=(in_0*in_1*in_2). It should be noted that not all dots have to be used and only one dot can be defined as an output.

Divisor Every grey dot of this block can be used as an input or output for the divisor. The first input will be the numerator and thus will be divided by the second (and if existing, the third) input. The order of the signals will be clockwise beginning from the left. An output of three input signals will then be: out=(in_0/in_1/in_2). Mind that not all dots have to be used and only one dot can be defined as an output.

27 - 40


Switch Two input signals can be applied to this block, which will be connected to the output according to the position of the switch. Additionally a control signal has to be connected to the top, which will define the operation of the switch. If the control signal is 0.5 or less, the switch will stay in the displayed state, whereas a signal greater than 0.5 will cause the switch to change to the upper signal and the other way round. In the edit dialogue the zero position of the switch may be altered.

Connecting Signals

After drawing and defining the block references, slots or other node elements, they can

be connected with signal lines. After selecting the button from the graphical toolbox, a signal line is drawn by first clicking on a 'from' node (output of a block/slot), optionally clicking on the drawing surface to make a non-direct connection, and finally clicking on a 'to' node (input to a block/slot). The input and output terminals of common blocks and other node elements are depicted with colored dots (see Figure 27.28).

Fig. 27.28: Block Signal Connections

Green:Input

Red: Output

Blue:Min. Limitation

Pink:Max. Limitation

Gray:Every signal can be connected

The signal lines can also be edited in the corresponding dialogue, which provides the pos-sibility to change the name of the signal.

Multi-Signal Connections

Signals normally connect a single output parameter with a single input parameter. Espe-cially in the case of three phase signals, as is often the case for voltage or current signals, multi-signal connections may be used.

A multi-signal is defined by writing two or more signal names together, separated by semi-colons, e.g "I_A;I_B;I_C''. In Figures 27.29 and 27.30, the multi-signal output and input

27 - 41


of two block definitions are shown. Both blocks will show a single input or output connec-tion point. They can be connected to each other by a single signal line, as illustrated in Figure 27.31.

Fig. 27.29: Output Definition of Block 1

Fig. 27.30: Input Definition of Block 2

Fig. 27.31: Multi-Signal Connection

Note The number of variables and their order in the output signal must be equal to the number of signals in the input signal.

Block Diagram Input and Output Definitions

The composite block diagram normally has input, output and limiting signals of its own. Input signal points are defined by starting a new signal line on the left, top or bottom side of the frame enclosing block diagram. This will create a new input signal for the composite block definition.

New output signals are defined by ending a signal line by clicking on the right side of the enclosing rectangle frame.

Signals, which are thus connected to the rectangular frame, have the following meanings:

• connected to the left side: Input

• connected to the right side: Output

• connected to the bottom side: Minimum Limitation

• connected to the top side: Maximum Limitation

Note The names of the input and output signals must be the same as the names of the input and output signals defined in the slot or block to which it is intended to assign the definition.

27 - 42


Resize

If a marked symbol has small black squares at its corners, it can be resized by left clicking one of the squares, as can be seen in Figure 27.32. The cursor will change to a double diagonal arrow, and moving it (while holding down the left mouse button) resizes the ob-ject. Release the mouse when the new size is correct.

Fig. 27.32: Resizing an Object

It is also possible to make the object(s) have a new size by clicking on one side of the marking box. The marked object(s) will only resize in one direction in that case. This is not possible for all objects. Some objects may only be resized with a fixed X/Y- ratio; some other objects cannot be resized at all.

Additional Equations

After the internal structure of the block diagram has been defined graphically, the block diagram itself can be edited. This can be done without having to close the graphical rep-resentation of the block diagram. By left or double-clicking the enclosing rectangular frame, the block diagram edit dialogue will pop up. This dialogue will show all input, out-put and internal signals, as have been defined graphically.

On the second page of the dialogue, which can be accessed by pressing the button, information and equations for the initialisation of the block can/has to be entered. Addi-tionally, the name and the unit of the parameters to be defined in the common model can be specified (see also Section 27.8: User Defined (DSL) Models).

Additional DSL equations can be defined on the second page of the block diagram edit dialogue.

27.8 User Defined (DSL) Models

System modeling for stability analysis purposes is one of the most critical issues in the field of power system analysis. Depending on the accuracy of the implemented models, large signal validity, available system parameters and applied faults or tests, nearly any result could be produced and arguments could be found for its justification.

A simple example illustrates this. In a 10 GW power system the expected steady-state frequency deviation when losing a fully loaded 2000 MW unit depends highly on the frequency dependency, K_f, of loads. Assuming a total system droop of 7% and a K_f value of 0, the steady-state frequency deviation will be approximately 700 mHz.

Now with a more realistic coefficient of K_f = 5 %/Hz, the steady-state frequency

27 - 43


deviation is expected to be 596 mHz only. On the other hand, the frequency dependency might be slightly higher or lower, but the non-linear characteristics of hydro turbine efficiencies and steam valve non-linearities could be more relevant at a certain unit loading point. Consequently, as long as only one or two different loading scenarios are considered, average values with reasonable simple models may give acceptable results by tuning only some key parameters like the frequency dependency of loads or droop settings.

Thus system model structures and parameter settings are to be best evaluated against the following main criteria:

System sizeLarge and small systems have different "key parameters''. Referring to the above example, for a smaller power system the frequency dependency of loads is irrelevant, while in large systems such as UCTE or UPS/IPS, frequency dependency may cover the spinning reserve requirements totally.

Unit sizeSteady-state and transient behavior of large units is more decisive for the overall system response than smaller units which might have a very negligible effect on the total system.

System structureIndependent of system and unit size, the system structure may be more relevant than any other factor. This can be easily demonstrated when weak systems with a longitudinal geographical extension or appropriate substructures are analyzed.

System faultMost relevant to system modeling considerations are the applied faults and related problems which are to be analyzed. The analysis of system damping and PSS tuning will not necessarily require the boiler dynamics to be considered. On the other hand, load shedding optimization and frequency restoration would not give appropriate results if mid- and long-term characteristics of relevant system elements are neglected.

Study purposeIn general, for systems which are in the planning stage, typical models and parameters could be applied as long as there is no specific additional information available. However, a more detailed representation is necessary for system extensions, where a detailed model representation should form part of the performance specification. Special attention has to be paid to the analysis of operational problems and operation optimization. For these cases, detailed modeling of the relevant components is critically important.

As soon as a detailed analysis and representation of system models is required, the subse-quent questions to be asked are:

• How can the structures and parameters of the model be determined?

• Are IEEE models and additional manufacturers’ block diagrams adequate and accurate?

27 - 44


• How could the available information be used within the power system analysis software?

The approach which is presented here and successfully applied in various projects can be called the "Advanced System Modeling Approach (ASMA)''. Typical applications are:

• The analysis of controller problems and relevant malfunctions, especially under disturbance conditions;

• Optimization of control parameter settings;

• Modeling of unconventional system structures and control concepts often found in industrial systems;

• Study applications for the design and specification phase of components and systems (e.g. power system stabilizer, generator and HVDC controllers).

For the ASMA approach, the following steps are critically important:

Setup of system modelsBased on the fundamental equations of engineering and physics, the basic algebraic and differential equations are to be set up according to the required degree of accuracy. In addition, all parameters such as time constants and gains which could be also derived from these basics, are to be calculated with the same degree of accuracy.

Performance of system testsIn order to define all other parameters and, in particular, non-linear characteristics, system performance tests are the best method. In the majority of cases, frequency response tests will not permit the determination of any non-linear structure and its parameters. Special test procedures, which do not interfere with normal operation, have to be applied to focus on the steady-state characteristics, gains and time constants. These measurements are preferably executed with a highly accurate digital transient performance measurement system.

System IdentificationNon-linear, multi-input and multi-output system identification techniques are applied for system identification procedures. Typically, the mismatch between measured and identified data should be smaller than 2%.

Comparison of measurements and simulationsBesides the analysis of subsystems and components, overall system performance is to be compared with the theoretical model for all relevant operating modes.

Of course, very strict application of the ASMA approach is not necessary for modeling relays and less complex or digital control functions, as these are clearly defined by their appropriate general and acceptance test documentation. However, independently of the analyzed system, where the system representation cannot be matched to a classical IEEE or any other standard model, there is a substantial need for an easy to use and flexible method for the realization of individual models.

27 - 45


27.8.1 Modeling and Simulation Tools

As already indicated, the most critical and decisive factor for reliable simulation results is the accuracy and completeness of system model representation for identification and simulation purposes. Methods for solving this task range from the classical and traditional way of using software which allows interfacing of user-defined models at the FORTRAN/C level - typically via connection lists - to the block-oriented approach which is based on the provision of predefined low-level block macros being connected at the case definition level.

In addition, most modern commercially available general purpose simulation tools may be used for flexible and specific system representation. Unfortunately, this approach does not adequately cover the special electrical system load flow characteristics.

In order to provide a very flexible modeling and simulation tool, which forms part of a stability program, a control system based simulation language was developed. The following describes the main features of the DIgSILENT Simulation Language (DSL): • The simulation tool falls into the category of a Continuous System Simulation

Languages (CSSL);

• DSL includes a complete mathematical description of (time-) continuous linear and non-linear systems;

• The simulation tool is based upon common control and logic diagrams, leading to a non-procedural language, as the sequence of elements can be chosen arbitrarily. In other words, a DSL model can be converted into a graphical representation;

• Provision of flexible definition of macros, which could be: algebraic equations, basic control elements like PID, PTn or even complete physical subsystems like valve groups or excitation systems;

• Provision of various intrinsic functions such as: "select'', "lim'', "limits'', "lapprox'', "picdrop'' in order to provide a complete control of models;

• Provision of various formal procedures for error detection and testing purposes such as: algebraic loop detection, reporting of unused and undefined variables and missing initial conditions.

27.8.2 DSL Implementation: an Introduction

The "DIgSILENT Simulation Language" is used to define new dynamic controllers which receive input signals from the simulated power system and which react by changing some other signals.

DSL itself can be looked upon as an add-on to the transient analysis functionality of PowerFactory. During the simulation, the model equations of the DSL models are combined with those describing the dynamic behavior of the power system components. These equations are then evaluated together, leading to an integrated transient simulation of the combination of the power system and its controllers.

The DSL main interfacing functions are:

Signal input and output channels:Any variable defined within the kernel (currently more than 2500) and in a DSL model, can be accessed in a read-and-write mode. Main and sub-address features are implemented allowing the access of any signal existing in the system or to build up complex structures such as

27 - 46


hardware-based modules taking equipment "rack'' and "function card'' structures into account.

Events:Conditions evaluated by DSL models may cause events to be sent to the program kernel where they will be scheduled within the event queue.

Output and Monitoring:Conditions may trigger user-defined messages to be displayed in the output window.

Fig. 27.33: Structure of the PowerFactory DSL System

The structure of a DSL model is best explained by an example. This example considers a prime mover unit model of a simple hydro turbine. This DSL model has been defined graphically, and contains one embedded DSL macro. This embedded macro models a single integrator and is defined by programming it.

The basic method for designing new DSL models is as follows:

1 A set of basic DSL models is created. These models implement simple, 'primitive' controllers like a 'first order time lag' or a 'PID' controller. The PowerFactory program is shipped with a large number of these primitive controller models. New primitives are created by programming their differential equations and signal settings, using the DSL language.

2 The more complex controller is created graphically by drawing its block diagram. This kind of block diagram normally uses references other DSL models which are thus combined into a more complex controller. Controller references may be used to include DSL primitive models into the complex model, but may also refer to other graphically defined complex models. Highly complex controllers may thus be

27 - 47


designed in a hierarchical way, by designing sub-models and sub-sub-models, where the DSL primitives form the lowest level. Section 27.8.3 (Defining DSL Models) describes these procedures in detail.

Fig. 27.34: Diagram of a Simple Model of a Hydro Turbine

Figure 27.34 depicts the model definition that was used to define the hydro turbine model.

The resulting DSL code, as shown in the output window when a graphical Rebuild ( ) is performed is:

1. model Pt = 'pmu_hydro'(At,C;x1;Ti;)2. pt_x = 'I.BlkDef'(xe;x1;Ti;)3. i3 = i1/i24. i1 = At*At5. i2 = pt_x*pt_x6. i4 = xe*pt_x7. xe = i3-C8. Pt = pt_x-i4

The line numbers have been added for readability. The corresponding block definition shows:

Output Signals : Pt Input Signals : At, C State Variables : x1 Parameter : Ti Internal Variables :

The example describes a simple hydro turbine model with the input signals A_t and C and the output signal P_t.

Fig. 27.35: Graphical Representation of a DSL Model of an Integrator

Figure 27.35 depicts the graphical representation of the embedded primitive DSL model. This primitive model is included in the hydro turbine (in line 2 of the definition of the hydro). The DSL primitive implements a single integrator and is programmed as follows:

1. model y = 'I'(xe;x1;Ti;)

27 - 48


2. [Ti] = 's'3. limits(Ti) = (0,)4. inc(x1) = y5. inc(xe) = 06. x1. = xe/Ti7. y = x1

Line 1 is generated by clicking on the Equations button in the block diagram dialogue. Lines 2..7 were entered manually.

The block definition dialogue was used to set the following:

Output Signals : y Input Signals : xe State Variables : x1 Parameter : Ti Internal Variables

Parts of a DSL Model

Both example DSL models show the two basic parts of any DSL model, primitive or complex:

1 The interface definitions

2 The DSL model description

Interface description

The interface defines the model name, names of input and output signals, model param-eters and state variables. These are shown in the output window in the model heading.

Example (line 1 from the hydro turbine model): 1. model Pt = 'pmu_hydro'(At,C;x1;Ti;)

The block diagram dialogue further allows for the definition of limiting parameters and input signals, and the classification of the model as a linear model and/or as a DSL macro.

Model description

The model description describes the DSL model, based on the signals defined in the interface. The DSL description includes:

• Parameter descriptions: name and unit

• Allowed parameter ranges

• Initial conditions and functions which are used to calculate initial values.

• The algebraic relations which define the controller.

Example (the integrator):

2. [Ti] = 's' ! the unit of Ti is seconds3. limits(Ti) = (0,) ! Ti > 04. inc(x1) = y ! initially x1=y5. inc(xe) = 0 ! initially xe=0

27 - 49


6. x1. = xe/Ti ! equation 1: deltax1 / deltat = xe/Ti7. y = x1 ! equation 2: y=x1

Advanced Features

The numerical integration of DSL models, interrupt scheduling and input-output signal processing is handled automatically by the program kernel. In addition, if the output of a DSL model is an electric current being added to the appropriate total bus current - which is the case if a load or generator model is created - all Jacobian elements necessary for the iterative simulation procedure will be calculated automatically.

Another useful feature of DSL is the algorithm implemented for numerical setup of the system matrix for eigenvalue calculation purposes. Consequently, any model implemented at the DSL level will be automatically taken into consideration when calculating the system eigenvalues or when applying the modal network reduction approach (MRT). Of course, any signal limiting functions will be disabled automatically for this calculation procedure.

In addition, inputs and outputs of model parameters, its organization via windows menus etc. is also derived automatically from the DSL model.

27.8.3 Defining DSL Models

A new DSL model is created either by entering the DSL code in the equation part of a "Block Definition'' (BlkDef) object, or by creating a new Graphical Block Diagram (see also section Composite Block Definitions on how to create a new block definition). Both methods will result in a Block Definition Object which holds the definition of the DSL model.

The block definition objects thus serve two purposes in the process of constructing a DSL model:

• They hold the definitions and parts of a graphically constructed composite block definition, and the diagram graphic which was used to define the model;

• They provide the surrounding in which a new "DSL primitive '' or 'primitive block definition' can be defined.

Composite Block Definitions

To create a new composite block definition:

• Use the main menu entry File New or Strg-N and then select the option Block/Frame Diagram from the "New" command dialogue (ComNew).

• Use the Insert New Graphic icon on the toolbar (of the graphics window) and select the option Block/Frame Diagram.

To access the dialogue of the block definition (BlkDef), double-click on the frame box surrounding the diagram.

Complex block definition objects are conceptually similar to "Grid Folders'' in the Power-Factory database tree. They are defined by graphically defining a controller block diagram of which they will store the graphical information and all logic parts. These parts include signals, small standard components (adders, multipliers, etc.) or DSL primitives.

27 - 50


Although a complex block definition object is created graphically, it allows for additional DSL equations to define those aspects of the controller that would be otherwise difficult to enter in a graphical way.

The graphical environment in which a complex block diagram is constructed, is not treated here. Please refer to Chapter 11 (Network Graphics (Single Line Diagrams)) for more information.

Primitive Block Definitions

To create a primitive DSL block definition:

• Right-click on or inside a (library) folder in the active project in the data manager and select New... Block/Frame - Diagram from the context-sensitive menu;

• Use the "New Object" icon in the database manager and select Block Definition (BlkDef);

• Double-click an new/empty block reference in an open block diagram and then use

the button to select a block definition. Following this, use the icon to create a new block definition inside the local library.

DSL primitives are the building blocks from which the more complex controller diagrams are composed. A DSL primitive, for example, might implement a low pass filter, which may then be used to graphically construct more complex controllers which include this kind of filter.

Unlike transformers or other power system components, which may be looked upon as 'power system primitives', a DSL primitive is only referred to by a complex block diagram and may thus be used in more than one complex DSL model at the same time.

Block Definition Dialogue

When creating a primitive DSL model or by double-clicking on the frame of a composite block definition, a dialogue will appear, where input and output variables, parameters, state variables and limiting signals can be defined. Furthermore, additional equations, initial conditions of variables as well as names and units of parameters can be inserted.

Figure 27.36 shows an example dialogue of a PI controller including limiting parameters and a 'switch' signal.

27 - 51


Fig. 27.36: Dialogue of the Block Definition

• The Name and Title will appear in the library folder, where the model is stored.

• The Level of the model representation is only important when using or changing old models. For new created models "Level 3'' should always be used. For macros, this option does not have any impact, because the level of the highest block is important, i.e. the controller definition.

• "Automatic Calculation of Initial Conditions'': PowerFactory can calculate the initial conditions automatically. However, if no sequence is found (because of, for example, deadlock situations) there will be an error message.

• "Classification'': Linear

This option will only effect the graphical representation of the block in the diagram. If this option is enabled, the block will be represented as a linear block, otherwise as a non-linear block with two lines.

MacroThis option is used to identify the block definition as a macro inside the library.

27 - 52


MatlabEnabling the 'Matlab' tag will show an input dialogue, where a Matlab (*.m) file can be defined with which the block definition can communicate during a simulation. For more information about the Matlab interface see Section 27.10 (Matlab Integration).

• A constant Limiting Parameter may be defined, which are defined in the common model dialogue, as well as limiting signals, which are similar to input signals. The difference is the graphical representation in the block diagram.

• Input and output signals have to be defined for internal use inside the block definition. The number and their name will then appear in the graphical diagram when the block is used.

• State variables are needed when not only linear, but also differential, equations are used. Then for every first-order derivative one state variable must be specified.

• The Parameters will appear in the common model dialogue and can then be specified. The parameter defined in the block definition will automatically be inserted in the block reference. The names of the parameters can be different in the block reference and in the block definition. Only the order must be identical.

• Internal variables are only used inside the block definition but can not be set from outside.

There are several buttons on the right side of the dialogue:

ContentsThis button will display the (possible) contents of the block definition. This can be the graphically inserted objects, further block references or the packed macros. This may additionally include, for example, internally-defined events.

Equations The "Equations" button will print the DSL equations to the output window, regardless of whether they are defined graphically or on the "Additional Equations" page, as well as variable definitions.

Macro Equat. This button prints the current block definition DSL equations (including the equations in the used macros) to the output window.

Check "Check" will verify the model equations and output error messages if errors have occurred. Otherwise the following message will occur:

DIgSI/info - Check '\TestUser.IntUser\Windparks.IntPrj\Library \Block Definitions\DFIG\Voltage Control.BlkDef':DIgSI/info - Block is ok.

Check Inc.The initial conditions of the block definition will be printed and checked.

PackPack will copy all used DSL models (macros) of a composite model definition to the folder "Used Macros" inside the block definition. In this way there will now be references to other projects or libraries outside the model. Beware: any further changes in the macro library have no influence; the macros are copied and no longer linked to the library. So

27 - 53


if there is an error in a certain macro it has to be fixed separately in each packed block.

Pack-> MacroThis command will reduce the entire model including DSL blocks and additional equations and macros into one DSL model containing only equations. All graphical information will be lost. It should be noted that this command is irreversible.

EncryptThe "Encrypt" button is available when Pack-> Macro is activated before. This command encrypts all equations inside the model, so that the equations can not be seen or output anymore. In this way a model containing sensitive or restricted device equations can be delivered without showing the internal equations. It should be noted that this command is irreversible and a decrypt function is not available.

By clicking on the button the second page of the dialogue can be accessed. Here the (additional) equations of the DSL model can be defined. Also further information e.g. the initial conditions of state variables and the name and unit of parameters can be specified.

Figure 27.37 shows the additional equations of the DSL model of the PI controller.

Fig. 27.37: Dialogue of the block definition - Page 2

The next section describes the handling and usage of the DSL language.

27.9 The DIgSILENT Simulation Language (DSL)

The DSL language is used to program models for the electrical controllers and other components used in electrical power systems. As for any other simulation or programming language, a special syntax is provided for the model formulation.

This syntax is explained in the following order:

27.9.1 Terms and Abbreviations

The following terms and abbreviations are used to describe the DSL syntax:

expr- arithmetic expression, not to be terminated with a ';'

- arithmetic operators: +, -, *, /

- constants: all numbers are treated as real numbers

27 - 54


- standard functions: sin(x), cos(x), tan(x), asin(x), acos(x), atan(x), sinh(x), cosh(x), tanh(x), exp(x), ln(x), log(x) (basis 10), sqrt(x) (square root), sqr(x) (power of 2), pow(x,y), abs(x), min(x,y), max(x,y), modulo(x,y), trunc(x), frac(x), round(x), ceil(x), floor(x).These standard functions are described in detail in the last chapter.

- Parenthesis: (arithmetic expression)

All trigonometric functions are based on radians (RAD).

Example:A = x1+2.45*T1/sin(3.14*y)

boolexpr - logical expression, not to be terminated with a ';'

- Logical relations: <, >, <> (inequality), >=, <=, =.

- Unary operators: .not.

- Binary operators: .and. .or. .nand. .nor. .eor.

- Parentheses: {logical expression}

Example: A = {x1>0.and..not.x2 <= 0.7}.or.T1=0.0

string

anything within '...' (single quotation marks).

Example: A = 'this is a string'

27.9.2 General DSL Syntax

Line length:The maximal line length is 80 characters. Longer lines have to be broken by using the '&' sign in the first column of the continuing line. A '&' sign in the first column joins the current row and its preceding row.

Example: y = lapprox(x, 1.674, 7.367, 2.485, 12.479, 5.457, 18.578& 6.783, 15.54, 8.453, 12.589, 9,569, 6.478)

Line breaking cannot be used within names or strings.

Case sensitivityAll keywords, names, functions, variables, models, macros, etc. are case sensitive.

BlanksAll blanks are removed when the DSL code is processed. Exception: blanks in strings are kept.

CommentsThe '!' sign causes the remaining line to be interpreted as a comment. Comments are removed when the DSL code is processed.

27 - 55


Example: ! comments may start at the beginning of a linex1. = select(at<>0, ! comments may be used in broken lines& (1-sqr(x1)/sqr(at))/Tw, 0)

27.9.3 DSL Variables

A DSL model may use five different types of variables:

Output signalsOutput signal variables are available as input signals to more complex DSL models.

Input signalsInput variables may originate from other DSL models or from power system elements. In the latter case, currents and voltages, as well as any other signal available in the analyzed power system, become available to the DSL model.

State variablesState variables are time-dependent signals generated and used within the DSL model itself.

ParametersParameters are 'read only' numbers which are set to alter the behavior of the DSL model.

Internal variablesInternal variables are defined and used in the DSL model to ease the construction of a set of DSL equations.

The following rules may be helpful when interpreting warning and error messages:

• A state variable may not be simultaneously used as a state variable and an output variable; if required, the use of an assignment like y=x1 is recommended.

• All parameters are real numbers.

• A special parameter 'array_iiii' (with up to 4 digits i), with 2*iiii elements is provided to define characteristics (see procedure "lapprox'').

• Only the derivatives of state variables can be assigned an expression.

27.9.4 DSL Structure

DSL models are constructed of three parts:

• The interface part, which states the model name, title, classification and variable set. This part is set in the first page of the block diagram dialogue;

• Definition code;

• Equation code.

The definition and equation code form the actual controller network definition and are treated in the next sections.

27 - 56


27.9.5 Definition Code

Definition code in the equation part of a DSL model is used to define parameter properties and initial conditions.

Unit and Parameter Description

vardef(varnm) = unitstring;namestringUnit and name for variable varnm.

Examples:vardef(Ton) = 's';'Pick up time for restart' ! defines unit and namevardef(Ton) = ;'Pick up time for restart' ! only defines namevardef(Ton) = 's'; ! only defines unit

[varnm] = unitstringUnit for variable varnm, maximum 10 characters wide.Remark:A macro call causes error messages if the units of the substituted variables do not match the defined units.

Example:[Ton] = 's' ! defines unit

Valid Value Ranges

limits(varnm) = [/( minimum value, maximum value ]/)Defines the valid interval for variable varnm. Violations of the interval limits during simulation will be reported:

limits(yt)=(,1] is equivalent to output(yt>1,'Maximum exceeded: yt=yt>1')

The '(' and ')' braces exclude the minimum or maximum value from the interval; the '[' and ']' braces include them.

Examples:limits(x)=[min,max] ! min <= x <= maxlimits(x)=(min,max] ! min < x <= maxlimits(x)=(,max] ! x <= maxlimits(x)=(min,) ! min < x

If required and if possible, the program automatically determines the smallest interval under several intervals of the same variable.

Example:limits(x)=(1,3) and limits(x)=(2,4] results in 2<x<3.

Macro models often define limits for certain variables. The model which uses the macro might also define limits for the variables which are used in the macro calls. The 'smallest interval' method gives the calling model thus the freedom to redefine parameter limits without violating the internal macro limit definitions.

27 - 57


27.9.6 Initial Conditions

Direct Setting of Initial Conditions

inc(varnm) = exprDefinition of the initial condition of variable varnm. If inc(varnm) is not defined, the normal assignment expression will be evaluated (only possible if varnm is of the intern or input type). If inc(varnm) is defined, it will be evaluated when the model is reset.

inc0(varnm) = exprDefinition of the initial condition of variable varnm, for unconnected output or input variables. This variant of the inc() statement is used only when the variable varnm could not be initialized through the initial condition of the connected input or output signal. The inc0() statement is thus used to make open input or output terminals possible.

incfix(varnm) = exprThis variant of the inc() statement is valid only in connection with automatic initialization and is used to determine the initial values in ambivalent situations. With the incfix, one or more variables can be directly initialized so that other variables can be initialized automatically.

Example:An AVR model has two inputs, [upss , usetp ], and one output, [uerrs ]. Both inputs cannot both be initialized automatically by the single output value, which is determined by the connected machine. Therefore one of the inputs must be initialized as fixed, e.g. by incfix(upss)=0. The initial value of usetp is now automatically determined, using upss=0.

Iterative Setting of Initial Conditions

Three functions are available for determining initial values iteratively: looping, intervalinc, newtoninc.

These functions are used to find the initial value for one set of parameters if the initial values of another set of parameters, which are functions of the first set of parameters, are known.

The iterative functions are used to find the (approximated) values for the unknown parameters for which the known parameter take their initial value.

loopinc (varnm, min, max, step, eps)Performs a simple linear search for a single value for which the parameter varnm is closest to its known initial value.

varnm = target variable, whose initial value is knownmin = lower limitmax = upper limitstep = stepsizeeps = maximum error

Example:inc(a) = loopinc(b, -5, 5, 0.01, 0.001)

27 - 58


• The initial value of variable a is searched for by evaluating parameter b, beginning at a=-5, ending at a=5, with an increment of 0.01.

• Return value: the value of a for which the deviation of b from its known initial value, takes the smallest value. A warning is given if the smallest deviation is greater than eps.

• Restriction: Can only be used on the right side of an inc() statement

intervalinc(varnm, min, max, iter, eps)Performs an 'interval-division search' for a single value for which the parameter varnm is closest to its known initial value.varnm = target variable, whose initial value is knownmin = lower limit, max = upper limititer = maximum number of iterationss = maximum error

Exampleinc(a) = intervalinc(b, -5, 5, 40, 0.001)

Explanation:The initial value of the variable a is searched for, within the interval [-5,5] by suc-cessively dividing the interval as long as the deviation of the variable b from its initial value is less than eps. The iteration stops if the maximum number of iterations is reached, and a warning is given if the smallest deviation is greater than eps.

Restriction:May only be used on the right side of an inc() statement

newtoninc(initexpr, start, iter, eps)Performs a Newton iterative search for one or more parameters by minimising the errors in a set of coupled equations.

initexpr = the expression which must equal the parameters whose initial value is soughtstart = the starting value for the parameter whose initial value is soughtiter = the maximum allowed number of iterationseps = the maximum allowed absolute error between initexpr and the parameter whose initial value is sought.

Example:qt0 = 0.5eps = 0.000001maxiter = 100inc(hedr) = newtoninc(hw-sqr(qedr)*(Rds+Rdr), hw, maxiter, eps)inc(qt1) = newtoninc(Pt1/(4*dh*eta1), qt0, maxiter, eps)inc(qt2) = newtoninc(Pt2/(4*dh*eta2), qt0, maxiter, eps)inc(qt3) = newtoninc(Pt3/(4*dh*eta3), qt0, maxiter, eps)inc(qt4) = newtoninc(Pt4/(4*dh*eta4), qt0, maxiter, eps)

This example shows a part of the initial value definitions for a model where the initial values of 5 parameters (hedr ,qt1 ,..,qt4) are sought simultaneously by setting up a system of coupled equations and solving that system by the Newton method so that, eventually:

hedr hw qedr Rds Rdr+ –

qt1 Pt1 4 dh eta1

27 - 59


The following guidelines should be considered:

• Add the initial conditions to the complex block, as opposed to each primitive (like a first-order time lag).

• The general initialisation 'direction' is from right to left, i.e. the outputs are normally known and the inputs (or setpoints) have to be determined.

• If initial conditions are not defined for a certain variable, the simulation equations are used instead. It should be therefore enough to specify the initial conditions of the state variables and input variables.

• The option Automatic Calculation of Initial Conditions requires configuring, but does not require correct initial conditions for each state/input variable. The initial values are only used to initialize the iteration process. The incfix-function can be used to determine the initial values in ambiguous situations.

• Use the option Verify Initial Conditions to check if the initial conditions lead to the correct result.

qt2 Pt2 4 dh eta2

qt3 Pt3 4 dh eta3

qt4 Pt4 4 dh eta4

27 - 60


27.9.7 Equation Code

Within the equation code, all equations necessary to build up the simulation models are included. The set of equations defines a set of coupled differential equations which describe the transfer functions between the input and output signals. These transfer functions may range from simple linear, single-input single-output functions, to highly complex non-linear, non-continuous, multi-input, multi-output functions.

DSL is used to describe the direct relationships between signals and other variables. Expressions may be assigned to a variable, or to the first derivative of a state variable. Higher order differential equations have to be thus split up into a set of single order equations by the introduction of additional state variables.

27.9.8 Equation Statement

The equation statements are used to assign expressions to parameters, thus relating all parameters in a set of differential equations.

Syntax:

varnm = exprAssigns expression 'expr' to variable 'varnm'.

Examples:y = sin(a)+3*x1y = .not. x1>2 .or. a<=3

varnm. = exprAssigns expression expr to the first order derivative of the variable varnm.

Examples:x1. = (xe-x1)/T1x2. = x1

Remarks

• DSL assignments may occur in any sequence. The sequence does not influence the evaluation of the assignments.

• All variables are of type floating point, even if assigned to a boolean expression, in which case the value will be 0.0000 or 1.0000.

• When a variable z is used in a logical expression (i.e. y=.not.z), the logical 1 of z is tested by evaluating (z>0.5):y1 = .not.z is interpreted and equal to y1 = (z=<0.5)There is no warning against mixing logical and non-discrete variables in expressions.Consequently the following code will not cause a message to be emitted: depending on y, z will take the value x1 + 4.0, or just x1:

y = .not. x1>2 .or. a<=3z = 4.0*y + x1

• The assignment of a value to a variable takes place in an order which recognizes the connections between these variables. In the case of the following example, the second line will be evaluated first, then line 1:

1. a = b+52. b = x13. x1. = 1

27 - 61


• Algebraic loops are not supported. In the following example, an error message will be displayed:

a = b+5b = 2*a

• If there is no assignment to a variable varnm, varnm will keep its initial value. The right side expression may not contain derivatives. Derivatives may only appear on the left side of the equal sign. The first example is correct; the second is false.

x1. = asin(a) ! Correcta = sin(x1.) ! Not accepted

27.9.9 DSL Macros

A DSL macro is a predefined DSL model, complex or primitive, which is meant to be included in higher level DSL models. The block diagram edit dialogue offers a 'Macro' classification option which can be set to mark the model as a macro.

A DSL macro is included in a higher level DSL model either by creating a block reference in the block diagram graphics or by its explicit inclusion in a DSL equation.

Syntax:

varnm1, varnm2,... = macroname (i1,i2,... ; s1,s2,... ; p1,p2,... ; i1,i2,...)Assigns the output signals of the DSL macro macroname to the variables varnm1, varnm2 , ... Assigns the input signals of DSL macro to the variables i1, i2,... The macro uses the state variables s1, s2,... the parameters p1, p2,... and the internal variables i1, i2,...

Example:P1,P2 = '\User\I.BlkDef'(i1,i2;s1,s2;T1,T2)

This example assigns to P1 and P2 the output of DSL model \ User\ I.BlkDef .

Macro calls are not supported within expressions, even if they only have one output variable.

Correct example:y = my_macro(x1, s1, p1, i1) !

Incorrect example:y = 3 * my_macro(x1, s1, p1, i1) + 4

which should be replaced by:y1 = my_macro(x1, s1, p1, i1)y = 3 * y1 + 4

DSL Internal Macro Handling

A preparser substitutes each macro call with the equation code of the macro. The variables of the macro DSL model are then replaced by the variables used in the macro call. The local variable names of macros thus disappear after the preparation process.

DSL Models

In general, there are two basic types of DSL models possible:

1 Models of electrical devices such as generators, loads or HVDC systems. These models are characterized by their principal output signal "complex device current'',

27 - 62


which is injected to the electrical grid at a certain busbar. However, in addition to the electrical device currents, there may be any other variable defined as an output signal. A summary of the available variables of each element can be seen in the corresponding Technical References.

2 Models with output signals which are not directly injected to the electrical network (general devices). Among these types of models are prime mover units, voltage controllers, relays, calculation procedures, etc.

27.9.10 Events and Messages

The DSL language provides procedures for the generation of an interrupt event and for sending messages to the output window:

• The procedure fault(boolexpr, event_string) generates an event and is evaluated at the beginning of each time step

• The procedure output(boolexpr, message_string) outputs a message and is evaluated at the end of each time step.

The "fault" and "output" procedures are evaluated at each time step during the simulation of a model. The first time that boolexpr is found to be true, the string will be processed and a message will be sent to the output window, or an event will be added to the Power-Factory event queue. The '"fault" or "output" procedures will be disabled afterwards until the DSL model is reset, to prevent an avalanche of messages or events.

Both procedures are explained in detail in the following paragraphs.

output(boolexpr, message_string)

The message_string may contain variables and the special function num(boolexpr) or num(expr):

• Variable names which appear directly after an '=' sign will be substituted by their actual values; hence, the line of code below may generate the message:maximum exceeded: yt=1.2 > ymax=1.0:

output(yymax,'maximum exceeded: yt=yt > ymax=ymax')

• The num(expr) or num(boolexpr) will be substituted with the calculated value of the expression, e.g.:

value=num(a+b) may produce value=3.5000

fault(boolexpr, event_string)

Each DSL model can add events to the event list. A DSL model of a distance relay, for instance, can open the power switch of a line by adding the correct switch event. 'Adding an event' is done by executing an existing event object in the PowerFactory database.

Consequently, all events that may be used by the DSL model have to be created together with the DSL model. They must all be stored inside the common model (ElmDsl). These DSL events will thus form an integrated part of the DSL model.

The event_string in the fault expression must refer to the name of one of these events. At evaluation, the event will be thrown onto the event stack if boolexpr is true. As soon as the simulation reaches the event, it will execute it. Consequently, a delayed event may be thrown by the DSL model by setting the execution time ahead of the current time.

27 - 63


The parameters of the event can be modified in the fault string by assigning a new value. The mechanism is the same as described above in the output procedure.

Example: fault(u>1.1,'name=MySwitchEvent1 dtime=0.15')

If the variable u exceeds 1.1, the event named 'MySwitchEvent1' will be thrown onto the event stack and its variable dtime (relative event time) will be set to 15 milliseconds. The event will thus be delayed for that amount of time, which, in this case, mimics the time needed to open a switch. The actual switch that will open is defined in the event object 'MySwitchEvent1'.

Note The events are accessed or created by opening the edit dialogue of the common model (double-click on the DSL model in the Data Manager), and then pressing the button Events in the dia-logue. A list of events already defined inside this model is dis-played.The events are not added to the project’s global event list unless the event is 'activated' by the DSL model.

27.9.11 Example of a Complete DSL Model

Thermal Double Reheat Turbine with Steam Storage

Controller Model:model pt,ptmw ='pmu_1'(at,sgn,cosn,ngnum;x1,x2,x3,x4;Thp, Tip,Tlp,alflp,Tspi) [T1] = 's'limits(T1) = [0,)limits(alfhp) = [0,1]vardef(alfhp) = ;'High pressure turbine ratio';limits(alflp) = [0,1-alfhp]vardef(alflp) = ;'Low pressure turbine ratio';vardef(Tspi) = 's';'Boiler capacity time constant';limits(Tspi) = (0,)vardef(Thp) = 's';'High pressure turbine time constant';vardef(Tip) = 's';'First reheater time constant';vardef(Tlp) = 's';'Second reheater time constant';

inc(x1) = y/Kinc(xe) = y/Kinc(x4) = 1.0inc(at) = ptinc(steamflow0) = ptinc(ylp) = ptx1. = select(T1>0,(xe-x1)/T1,0)y = K*select(T1>0,x1,xe) ! if T1=0 => y=xesteamflow = at*x4x4. = (steamflow0 - steamflow)/Tspi ! boileryhp = PT1(steamflow;x1;Thp) ! high pressure partyip = PT1(yhp;x2;Tip) ! medium pressure partylp = PT1(yip;x3;Tlp) ! low pressure partpt = yhp*alfhp + ylp*alflp+ yip*(1.0-alfhp-alflp)ptmw = pt*sgn*cosn*ngnum ! only for output purposes

27 - 64


The used macro 'PT1' is defined as: model y = 'PT1'(xe;x1;K,T1;)x1. = select(T1>0,(xe-x1)/T1,0)y = K*select(T1>0,x1,xe) ! if T1=0 => y=xeinc(x1) = y/Kinc(xe) = y/K[T1] = 's' limits(T1) = [0,)

27.10 Matlab Integration

Additionally to designing controllers or various electrical and mechanical models using the DIgSILENT Simulation Language, there is also the possibility to use an interface to Matlab. This interface gives the opportunity to model controller or very complex transfer functions using the Matlab environment and insert them as a block definition into a frame in a PowerFactory transient simulation.

PowerFactory can correspond to the Matlab program during the simulation. It will transfer the input values of a block to Matlab for every time step, which will then simulate a specified *.m file in its own environment and gives back the results as the outputs of the block definition. Consequently this function needs a installation of the Matlab program including the Simulink package.

The implementation of a Matlab file is shown in the next sections. In this example a voltage controller is implemented first using a built-in model (ElmVco) and using a definition from Matlab. This example can also be found in the FAQ on the DIgSILENThome page.

27.10.1 Implementation of Voltage Controller - Example

In this example the grid consists of two generators, one load and one line, as shown in Figure 27.38.

Fig. 27.38: Matlab example grid

The simulation event is defined for the load, where the reactive power is increased after 0.5 seconds.

The complete example contains three files:

27 - 65


1 Matlab Example.dz is a PowerFactory file.

2 VCOtype16.m is a Matlab M-file.This file is an interface to the Simulink model, and it is used as a middle layer in the communication between PowerFactory and Simulink.

3 vcotype16mod.mdl is a Simulink model and contains Simulink implementation of VCO type 16.

27.10.2 Implementation with Built-In Model

In the base study case, the voltage controller models are represented by the built-in models VCO type 16 (ElmVco__16). The built-in VCO type 16 inside PowerFactory is one excitation control system with simplified exciter. Both composite models use the AVR inside the IEEE-frame from the global library. The generators have different VCO param-eters set.

In Figure 27.39 the edit dialogue of the ElmVco with the parameters of the AVR can be seen.

Fig. 27.39: Parameters dialogue of the voltage controller

The model representation of the ElmVco__16 is indicated in Figure 27.40.

27 - 66



The plots resulting from the simulation (Figure 27.45) show busbar voltages and excitation voltage for both generators. The results are stored in result files located under the “Results” folder of the relevant study case.

27.10.3 Implementation with Matlab Model

In the second study case "Matlab'' which is a modification of the base case, VCO type 16 is modelled inside the Simulink package, instead of using a built-in model. The Matlabconsole is started automatically when running the simulation.

To implement a Matlab model into a current project in PowerFactory it has to be included into a frame similar to a DSL model definition. This procedure is described in detail in the Section 27.10 (Matlab Integration). First a slot inside the frame has to be created, where the controller model should be inserted. This is done exactly like for imple-menting built-in models or common models. Then a block definition BlkDef has to be created inside the library. Instead of programming the transfer function using the DSL code, there can now the definition of the Matlab code be imported.

This can be done in the dialogue of the block definition. When creating a primitive DSL model in the library by

• right-clicking a or inside a (library) folder in the active project in the data manager and selecting New... Block/Frame - Diagram from the context menu.

• using the "New Object'' icon in the database manager and selecting Block Definition (BlkDef).

• double-clicking an new/empty block reference in an open block diagram and then use

the button to select a block definition. Then The icon can be used to create a new block definition inside the local library.

Now open the dialogue of the new BlkDef

• by double-clicking on the frame of a composite block definition

• by double-clicking the definition in side the library or on its icon

Here input and output variables, parameters, state variables and limiting signals have to be defined. Instead of inserting the equations to describe the different function blocks, a Matlab file *.m can be selected, when the option Matlab is activated.

The edit dialogue of the block definition including the parameter definition and the

27 - 67


selected file can be seen in Figure 27.41 for the mentioned example.

Fig. 27.41: Composite model using a special frame

The model representation of the ElmVco__16 in the Matlab Simulink package is shown in Figure 27.42.


When the block definition is specified, a DSL model has to be created first. As described in Section 27.7.4 (The Common Model), the common model element (ElmDsl, ) is the front-end object for all user-defined block definitions. This means that all user-defined transient models including built-in elements or Matlab models cannot be used other than through a common model.

The common model then combines a model or block definition with specific set of parameter values. The edit dialogue of the DSL element now looks different to the built-in ElmVco. From Figure 27.43 can be seen, that this dialogue is similar to the normal DSL models. All time constants and other parameters are the same as for the built-in VCO models.

27 - 68


Fig. 27.43: Parameters dialogue for the Matlab voltage controller

Figure 27.44 shows the composite model using the special frame with the generator 'G1' and the Matlab-AVR inserted into the slots.

Fig. 27.44: Composite Model using a special frame

These results from the simulation of the reactive power step using the built-in VCO model (dotted curves) and using the Matlab representation (solid curves) can be seen in Figure 27.45.

27 - 69


Fig. 27.45: Results of the transient simulation with the Built-In model

27.10.4 The Matlab File

The Matlab file VCOtype16.m is an interface configuration for the Simulink model, stored in the file vcotype16mod.mdl, and the PowerFactory DSL model. There the input and output signals, the parameters and the state variables are defined, as described below. The transfer function is specified.

The contents of this file is listed here:

function [t, x, y] = VCOtype16global U Tvm Usetp Upss Vska Tisp Ur1mx Ur1mn Vsex Efdmx Efdmn ve1 x1 x2options = simget('VCOtype16mod');options = simset('InitialState', [x1,x2]);[t, x, y] = sim('VCOtype16mod', [], options);

PowerFactory inserts the following variables into the Matlab workspace:

U, Tvm, Usetp, Upss, Vska, Tisp, Ur1mx, Ur1mn, Vsex, Efdmx, Efdmn, ve1, x1, x2

Those variables are necessary to successfully run the Simulink model. There are three input signals (U, Estop, Upss), one output signal Uerrs and two state variables x1 and x2.

In each step of the PowerFactory simulation the Simulink model is completely evaluated. State variables ('InitialState') are assigned to Simulink model in each step of the simulation. For PowerFactory it is a simple function call:

[t, x, y] = VCOtype16.

PowerFactory uses only one Simulink model for both generators. To avoid limitation of

27 - 70


Simulink, which allows only one instance of the model running at the same time, Power-Factory must send all parameters in the each step of the simulation.

To find appropriate equations for the initial conditions you need to understand the construction of the transfer function blocks in Simulink. To obtain this understanding you can replace the variables with actual numbers in the Matlab Simulink model, set the initial conditions, run it for a few seconds and monitor the outputs of all transfer functions to see whether the model initialized correctly.

The Matlab Simulink model (.mdl) and the interface file (.m) file may not have the same name.

The order of the state variables in the interface file's statement "options = simset('Initial-State', [x1, x2, …….])" is important; the order of the elements in the vector [x1, x2, …] must be the same as in the state variable vector constructed internally by Matlab. To determine the order of the Matlab state variable vector the user may use the command "[sizes,x0,xstring]= ModelName" in the Matlab workspace, where ModelName is the name of the Simulink model (without the .mdl extension and without inverted commas). The output of the string variable xstring contains the names of the dynamic blocks in the Simulink model in the desired order. In the case of the above example the first state variable is in the measurement block and the second state variable is in the integrator:

xstring =...'VCOtype16_model/Measure/State Space'...'VCOtype16_model/Integrator'

The names of the variables in the 'Initial conditions' fields in the masks of the Simulinkmodel dynamic blocks is irrelevant.

The initial conditions are set within PowerFactory. Also, for the purpose of Power-Factory’s model checking mechanisms, the state derivatives equal to zero

The Simulink solver parameters are set to integrate over one small time step, e.g. start time = 0, end time = 0.01, and step size = 0.01.

The y-matrix returned by MATLAB contains the output variables. If more than one output variable is defined in the DSL model, then those are sorted alphabetically before assigning the outputs from MATLAB. For example, if there are two outputs "uerrs" and "output", then the value from the first column of the y-matrix is assigned to "output" and the value from the second column is assigned to "uerrs".

27.10.5 Additional notes

DIgSILENT PowerFactory calls MATLAB using the programme identification keys "Matlab.Application" and "Matlab.Application.Single". PowerFactory will start that same MATLAB installation which was used last. Additional information on the calling of MATLAB is available on http://www.mathworks.com.

27 - 71

http://www.mathworks.com


27 - 72


27 - 73


27 - 74


27 - 75


27 - 76

DIgSILENT PowerFactory Modal Analysis / Eigenvalue Calculation

Chapter 28Modal Analysis / Eigenvalue Calculation

The Modal Analysis command calculates the eigenvalues and eigenvectors of a dynamic multi-machine system including all controllers and power plant models. This calculation can be completed at the beginning of a transient simulation and at every time step when the simulation is stopped. Note that sometimes in the literature Modal Analysis is referred to as 'Eigenvalue Calculation' or 'Small Signal Stability'. Throughout, this chapter the cal-culation will generally be referred to as Modal Analysis.

This chapter provides a brief background on the theory of Modal Analysis, followed by a detailed explanation of how to complete such an analysis in PowerFactory. The various methods of analyzing the results are also presented. Finally, a 'troubleshooting' section explains what to do when you receive common errors.

28.1 Theory of Modal Analysis

The calculation of eigenvalues and eigenvectors is the most powerful tool for oscillatory stability studies. When doing such a study, it is highly recommended to first compute the 'natural' system oscillation modes. These are the oscillation modes of the system when all controller and power plant models are deactivated so every synchronous machine will have constant turbine power and constant excitation voltage. After determining these 'natural' modes, the effects of controllers (structure, gain, time constants etc.) and other models can be investigated.

After the initial conditions have been calculated successfully, which means that all time-derivatives of the state variables should be zero (the system is in steady state), or the simulation has been stopped at a point in time, the modal analysis calculates the complete system A-matrix using numerical, iterative algorithms. The representation of the electro-dynamic network model is equivalent to the representation used for the balanced RMS simulation, except for the general load model, for which the frequency dependencies are neglected.

The computation time for the Modal Analysis is approximately proportional to the number of state space variables to the power of three. Considering, that most power system ob-jects and models will contain several (perhaps up to a dozen or more for some complex controllers), the calculation time can rapidly increase as the size of the system being con-sidered increases. For this reason, alternative methods for calculating the system eigen-values and eigenvectors must be used when the system grows very large. PowerFactory supports two types of analysis methods.

A multi-machine system exhibits oscillatory stability if all conjugate complex eigenvalues making up the rotor oscillations have negative real parts. This means that they lie in the

28 - 1


left complex half-plane. Electro--mechanical oscillations for each generator are then sta-ble.

More formally, assuming that one of the conjugate complex pair of eigenvalues is given by:

then the oscillatory mode will be stable, if the real part of the eigenvalue is negative

The period and damping of this mode are given by:

where An and An+1 are amplitudes of two consecutive swing maxima or minima respec-tively.

The oscillatory frequencies of local generator oscillations are typically in the range of 0.5 to 5 Hz. Higher frequency natural oscillations (those that are not normally regulated), are often damped to a greater extent than slower oscillations. The oscillatory frequency of the between areas (inter-area) oscillations is normally a factor of 5 to 20 times lower than that of the local generator oscillations.

The absolute contribution of an individual generator to the oscillation mode which has been excited as a result of a disturbance can be calculated by:

where

generator speed vector

i'th eigenvalue

i'th right eigenvector

magnitude of excitation of the i'th mode of the system (at t=0) (depending on the disturbance)

n number of conjugate complex eigenvalues(i.e. number of generators - 1)

In the following c is set to the unit vector, i.e. c = [1, ..., 1], which corresponds to a the-

i i ji=

i 0

Ti2 i

----------=

di i–1

Tp------

An

An 1+---------------

ln= =

t ci i ei t

i 1=

n

=

t

i

i

ci

28 - 2


oretical disturbance which would equally excite all generators with all natural resonance frequencies simultaneously.

The elements of the eigenvectors i then represents the mode shape of the eigenvalue i and shows the relative activity of a state variable, when a particular mode is excited. For example, the speed amplitudes of the generators when an eigenfrequency is excited, whereby those generators with opposite signs in i oscillate in opposite phase.

The right eigenvectors i can thus be termed the "observability vectors''. The left eigen-vectors i measures the activity of a state variable x in the i-th mode, thus the left eigen-vectors can be termed the "relative contribution vectors''.

Normalization is done by assigning the generator with the greatest amplitude contribution the relative contribution factor 1 or -1 respectively.

For a n-machine power system, n-1 generator oscillation modes will exist and n-1 conju-gate complex pairs of eigenvalues i will be found. The mechanical speed of the n gen-erators will then be described by:

The problem of using the right or left eigenvectors for analyzing the participation of a gen-erator in a particular mode i is the dependency on the scales and units of the vector ele-ments. Hence the eigenvectors i and i are combined to a matrix P of participation factor by:

The elements of the matrix pij are called the participation factors. They give a good indi-cation of the general system dynamic oscillation pattern. They can be used to determine the location of eventually needed stabilizing devices to influence the system damping ef-ficiently. Furthermore, the participation factor is normalized so that the sum for any mode is equal to 1.

The participation factors can be calculated not only for the generator speed variables, but for all variables listed in Table 28.1.

Name Unit Description

1

2

...

n

c1

11

12

...

1n

e1t

c2

21

22

...

2n

e2t

... c2

n1

n2

...

nn

ent

+ + +=

pi

p1i

p2i

...

pni

1i i1

2i i2

...

ni in

= =

28 - 3


Table 28.1: Variables accessible for eigenvalue calculation

When are modal analysis results valid?

A modal analysis can be started when a balanced steady-state condition is reached in a dynamic calculation. Normally, such a state is reached by a balanced load-flow calculation, followed by a calculation of initial conditions. However, it is also possible to do a balanced RMS simulation and start a modal analysis after the end of a simulation or during a sim-ulation when you have manually stopped it.

Although, the modal analysis can be executed at any time in a transient simulation it is not recommended that you do so when the system is not in a quasi-steady state. This is because each modal analysis is only valid for a unique system operating point. Further-more, the theory behind modal analysis shows that the results are only valid for 'small' perturbations of the system. So although you can complete a modal analysis during a large system transient, the results obtained would change significantly if the analysis was repeated a short time step later when the operating point of the system would be signif-icantly different.

s:speed p.u. Speed

s:phi rad Rotor-angle

s:psie p.u. Excitation-Flux

s:psiD p.u. Flux in D-winding

s:psix p.u. Flux in x-winding

s:psiQ p.u. Flux in Q-winding

28 - 4


28.2 How to Complete a Modal Analysis

This section explains the steps required to complete a 'Modal Analysis' in PowerFactory Completing an analysis using the default options is explained in the first sub-section. The second sub-section explains the various options available in the 'Modal Analysis' com-mand.

28.2.1 Completing a Modal Analysis with the Default Options

To complete a modal analysis in using the default options in PowerFactory, you must follow the steps below:

1 Use the toolbar selection button to choose the 'Modal Analysis' toolbar. The process is illustrated in Figure 28.1.

Fig. 28.1: How to select the 'Modal Analysis' toolbar

2 'Calculate Initial Conditions' using the button to open the command and then press Execute. Note that the calculation of initial conditions needs a converging load-flow. More information about the options in the 'Calculation of Initial Conditions' command can be found in Section 27.3.

3 Open the 'Modal Analysis ...' command using the button.

4 If you want to quickly complete the modal analysis and capture all eigenvalues using the default options, you can press Execute in the subsequent dialog box and the calculation will proceed. When the calculation is complete you can view the 'Modal Analysis' results. This is explained in detail in Section 28.3.

Internal Calculation Procedure

When executing the Modal Analysis command by pressing Execute, the initial conditions of all elements are calculated first (assuming that the calculation is initialised from a load-flow rather than during a RMS simulation). Then the modal analysis constructs a system matrix from the load-flow and the dynamic data. The eigenvalues and eigenvectors are

Open the toolbar selection window by clicking 'Select Toolbar' button.

Choose the 'Modal Analysis' toolbar.

The 'Modal Analysis' toolbar.

28 - 5


calculated directly from that matrix. PowerFactory automatically does the linearization of all relevant system elements because eigenvalue calculations need linearized models.

28.2.2 Explanation of Modal Analysis Command Basic Options (ComMod)

The 'Modal Analysis' command dialog is shown in Figure 28.2. This section explains the available command options.

Fig. 28.2: Modal Analysis command dialog

Calculation Method

There are two possible calculation methods for the Modal Analysis, they are:

• QR-Method; This method is the 'classical' method for calculating all of the system eigenvalues.

• Selective Modal Analysis (Arnoldi/Lanczos); This method only calculates a subset of the system eigenvalues around a particular reference point. Often this method is used in very large systems when using the QR-method could be very time consuming. It is especially useful if the user knows the target area of interest for the eigenvalues. This option needs more configuration as explained below.

Complex reference point (RP)

Here you must enter the reference point on the real-imaginary plain for the Selective Mod-al Analysis.

28 - 6


Which Eigenvalues

The selective eigenvalue calculation determines eigenvalues 'close' to the reference point using one of three different measures for 'closeness'. The options are:

• Smallest Magnitude w.r.t RP; If this option is selected, the selective eigenvalue calculation chooses eigenvalues that are closest to the reference point by magnitude of the eigenvalue.

• Smallest Imaginary Part w.r.t RP; If this option is selected, the selective eigenvalue calculation chooses eigenvalues that are closest to the reference point using only the imaginary part of the eigenvalue.

• Smallest Real Part w.r.t RP; If this option is selected, the selective eigenvalue calculation chooses eigenvalues that are closest to the reference point using only the real part of the eigenvalue.

This option can be further clarified using a diagram as shown in Figure 28.3. The three eigenvalue pairs are as follows:

• A; -0.8 +/- 1.4

• B; -0.7 +/- 1.5

• C; -0.5 +/- 2.0

Say the reference point was set to the origin (0,0). Then using the first method above, the closest eigenvalue pair would be A because this pair has the smallest magnitude. Us-ing method two, the closest pair would be C because this pair has the smallest real com-ponent. Finally, using the third method, the closest pair would also be A because this pair has the smallest imaginary component.

Fig. 28.3: Illustration of different eigenvalue selection methods

Number of Eigenvalues

This parameter limits the total number of eigenvalues calculated by the 'Selective Eigen-value' calculation method. An eigenvalue pair is defined as 'one' eigenvalue mode for this calculation.

28 - 7


Settings

The Settings button, is a reference (pointer) to the 'Calculation of Initial Conditions' command, also accessed through the button, that is used by the Modal Analysis com-mand. It is provided here so that you can easily inspect the selected calculation options.


The advanced options tab for the modal analysis is shown in Figure 28.4. This section ex-plains the options available on this page.

Fig. 28.4: Advanced Options tab of the Modal Analysis command dialogue

Calculate

There are three checkboxes here:

• Left Eigenvectors (Controllability); If this option is enabled, the Modal Analysis command will calculate the 'Left Eigenvectors'. It is enabled by default. The user can visualise the 'Controllability’ for any mode using the 'Mode Phasor Plot' or 'Mode Bar Plot' described in Section 28.3.2.

• Right Eigenvectors (Observability); If this option is enabled then the Modal Analysis command will calculate the 'Right Eigenvectors' (Observability) for each state variable. It is disabled by default. The user can visualise the 'Observability' for any mode in either the 'Mode Phasor Plot' or 'Mode Bar Plot' described in Section 28.3.2.

• Participation Factors; If this option is enabled then the Modal Analysis command will calculate Participation Factors for each state variable. It is disabled by default. The user can visualise the Participation Factors for any mode using the 'Mode Phasor Plot' or 'Mode Bar Plot' described in Section 28.3.2.

Results

This selection control provides a reference (pointer) to the results object that is used to store the calculation results of the Modal Analysis. After a completed calculation, these results can be exported to an external format such as a spreadsheet or text-file using the ASCII result exporter tool as described in Section 19.1.4.

By default the Modal Analysis captures results for all state variables from all models active in the calculation. The observability is also calculated by default for the variables shown in table 28.1. In addition, the Modal Analysis command can calculate the Controllability and Participation Factors for these variables.

28 - 8


28.3 Viewing Modal Analysis Results

There are several ways for the user to view the results of the Modal Analysis calculation, including through pre-defined reports to the Output Window, using the built-in plots with-in PowerFactory or using the spreadsheet like data browser. Additionally, the user can search individual objects within the database and view the Controllability, Observability, and Participation for a particular mode within the familiar data manager or object filters. This section describes how to get results using these four methods.

28.3.1 Viewing Modal Analysis Reports in the Output Window

This section describes how to view the Modal Analysis results in the PowerFactory Out-put Window To do this follow these steps:

1 Left-click the "Output Calculation Analysis" icon on the main toolbar. The 'Output of Results' dialog should be visible.

2 Select the eigenvalues radio button and the dialog should look as shown in Figure 28.5.

3 There are four options for the report. You must choose one of these options in the 'Output of Eigenvalues' section of the dialog:

- Eigenvalues; This option prints a report of all the calculated eigenvalues.

- Controllability/Observability/Participations; Selecting any of these options changes the dialog format to that shown in Figure 28.6. The various options are explained as follows:

Select EigenvalueTo print a report showing all eigenvalues and for each eigenvalue a filtered list of the state variables’ Controllability, Observability or Participation Factors, then choose the option 'Filtered' from this drop down menu. Adjust the filter settings in the box below to determine which eigenvalues will not be shown in the report. Alternatively, to display a report for a single eigenvalue, choose the eigenvalue index from this box. Note when choosing a single eigenvalue, the filter settings are not applied to the report.

Variable SelectionTo show all variables (for example, speed, phi, psiD), select 'Show all'. To filter the displayed variables according to Controllability, Observability or Participation Factor, choose 'Min. contribution' and enter the value for the minimum contribution. Alternatively, for greater control over which variables are displayed, select the 'User Defined States' option. The button Show shows the currently selected variables. More variables can be added using the Add button whereas all variables can be removed by using the Remove All button.

4 Press Execute. An example report for eigenvalues is shown in Figure 28.7. The results of the participation factors for a single mode in a small example power system are shown in Figure 28.8. Note the 'Detailed' check-box shows the bar chart in the report, whereas the normal report shows only numerical values.

28 - 9


Fig. 28.5: Output of eigenvalues only

Fig. 28.6: Output of Controllability, Observability or Participation Factors

28 - 10


Fig. 28.7: Output of system eigenvalues

Fig. 28.8: Output of participation factors for a single mode (detailed)

28.3.2 Viewing Modal Analysis Results using the built-in Plots

There are three special plot types in PowerFactory for visualising the results of a modal analysis calculation; the Eigenvalue Plot, the Mode Bar Plot and the Mode Phasor Plot.

Each type of plot can be automatically created by selecting the icon and clicking the desired plot icon. This section explains how to use each plot and also how these plots can be exported to external software.

How to use the The Eigenvalue Plot (VisEigen)

Creating the EigenValue Plot1 Using the plot selection toolbar as shown in Figure 28.9, choose the Eigenvalue Plot

by clicking the icon.

2 The Eigenvalue Plot will appear in a new window. Note, every time you select the EigenValue Plot icon from the drop-down menu, a new plot window will be created.

28 - 11


Fig. 28.9: Selection of the Modal Analysis plots

Interpreting the EigenValue Plot

An example EigenValue Plot is shown in Figure 28.10.

The Eigenvalue Plot displays the calculated eigenvalues in a two axis coordinate system. For the vertical axis, it is possible to select among the imaginary part, the period or the frequency of the eigenvalue. The horizontal axis shows the real part.

Stable eigenvalues are shown in green (default) and unstable eigenvalues in red (default). Each eigenvalue can be inspected in detail by double clicking it on the plot. This will bring up a pop-up dialog where the index, the complex representation, the polar representation and oscillation parameters of the mode can be inspected as illustrated in Figure 28.11.

Fig. 28.10: The Eigenvalue Plot

Create Eigenvalue Plot

Create Mode Bar Plot

Create Mode Phasor Plot

-3.1290-7.9335-12.738-17.542-22.347 Real Part [1/s]

14.792

8.8753

2.9584

-2.9584

-8.8753

-14.792

Imaginary Part [rad/s]

Stable EigenvaluesUnstable Eigenvalues

DIg

SIL

EN

T

28 - 12


Fig. 28.11: IntEigen dialogue

Changing the appearance of the EigenValue Plot

All settings that control the appearance of the Eigenvalue Plot can be accessed by double clicking a empty area of the plot. A dialog as shown in Figure 28.12 will appear. The op-tions available are explained as follows:

• Appearance; Here the color of the stable and unstable eigenvalues can be adjusted. You can also decide whether to display the plot legend and the stability borders. The so-called 'Stability Borders' option shades the area of the plot containing all the modes shown on the plot. It is not an 'area of stability' as such.

• Filter Options; Here you can choose to restrict the display of eigenvalues on the plot according to defined criteria. Eigenvalues can be restricted by range (independently in either the x or y axes) by selecting the 'Restrict Range' option. The 'Restrict Indexes' options allows the user to choose from the complete list of eigenvalues, a limited subset to display on the plot. Alternatively, just the 'Oscillatory Modes' can be displayed by choosing the 'Show Oscillatory Modes' option.

• Scale; Here the range of the plot (x and y axes limits) can be defined. Also by enabling the 'Adapt Scale' option, the x and y axes tick marks will be displayed as integer values, rather than floating point numbers. For example, the axis marks will be 10.0, 20.0 and 30.0 rather than 9.7988, 19.5976 and 29.3964.

28 - 13


Fig. 28.12: The Eigenvalue Plot settings

How to use The Mode Bar Plot (VisModbar)

Creating the Mode Bar Plot1 Using the plot selection toolbar as shown in Figure 28.9 choose the Mode Bar Plot by

clicking the icon.

2 The Mode Bar Plot will appear in a new window. Note, every time you select the Mode Bar Plot icon from the drop-down menu, a new plot window will be created.

Interpreting the Mode Bar Plot

An example Mode Bar Plot is shown in Figure 28.13. The Mode Bar Plot displays the con-trollability, observability or participation factors of variables for a user selected eigenvalue in bar chart form. This allows for easy visual interpretation of these parameters.

Double clicking any of the bars in the plots shows the detailed IntEigstate dialogue as shown in Figure 28.14. This dialogue displays the magnitude, phase and sign of the vari-ables for controllability, observability and participation in the selected mode. Note, the ob-servability and participation factors are only shown if these calculations were enabled in the Modal Analysis Command as described in Section 28.2.3.

28 - 14


Fig. 28.13: Example Mode Bar Plot

Fig. 28.14: Eigenvalue state dialogue

Changing the appearance of the Mode Bar Plot

All settings that control the appearance of the Eigenvalue Plot can be accessed by double clicking a empty area of the plot. A dialog as shown in Figure 28.15 will appear. The op-tions available are explained as follows:

• Mode Selection; Here you must choose the mode displayed on the plot. The observability, controllability or participation factors will then be displayed for this mode. Note, if you are interested in a mode near a particular value, but don’t know the index of the mode, you can enter the real and imaginary values in the boxes here, and PowerFactory will automatically select the closest mode.

1.000.500.00-0.50-1.00

Grid / 01_Sym; speed: -0.803 / +168.8 deg

Grid / 13_Sym; phi: +0.232 / +0.7 deg


Grid / 02_Sym; phi: +0.113 / -7.4 deg

Grid / 08_Sym; phi: +1.000 / +0.0 deg


Grid / 05_Sym; phi: +0.873 / -0.2 deg


Grid / 11_Sym; phi: +0.635 / +1.6 deg


Participation of mode: -1.119 -12.250*jMagnitude: 12.301 1/s, Angle: -95.220 degPeriod: 0.513 s, Frequency: 1.950 HzDamping: 1.119 1/s, Ratio of Amplitudes: 1.775 Min. contribution: 0.100

28 - 15


• Shown values; Here you can select to display either the Controllability, Observability or Participation Factors for the selected mode.

• Filter Options; Here you can choose to restrict the display of variables on the plot according to defined criteria. Displayed variables can be restricted to a minimum contribution by selecting the 'Min. Contribution' option, or for greater control the variables to display can be selected manually by selecting the 'User Defined States' option and manually choosing the variables to display.

• Appearance; Here you can adjust the color and style of the bars and choose to show the plot legend and also the annotation (value) for each bar.

Fig. 28.15: Mode Bar Plot Dialog

How to use the Mode Phasor Plot (VisModephasor)

Creating the Mode Phasor Plot1 Using the plot selection toolbar as shown in Figure 28.9 choose the Mode Phasor

Plot by clicking the icon.

2 The Mode Phasor Plot will appear in a new window. Note, every time you select the Mode Phasor Plot icon from the drop-down menu, a new plot window will be created.

Interpreting the Mode Phasor Plot

An example Mode Phasor Plot is shown in Figure 28.16. The Mode Phasor Plot displays the controllability, observability or participation factors of variables for a user selected ei-genvalue in polar form. Variables are grouped and colored identically if their angular sep-aration is less than a user defined parameter (default 3 degrees).

Double clicking any of the bars in the plots shows the detailed IntEigstate dialogue as

28 - 16


shown in Figure 28.14. This dialogue is identical to the dialog displayed when clicking on one of the bars in the Mode Bar Plot.

Fig. 28.16: The Mode Phasor plot

Changing the appearance of the Mode Phasor Plot

All settings that control the appearance of the Mode Phasor Plot can be accessed by dou-ble clicking a empty area of the plot. The dialog that appears is very similar to the dialog for the Mode Bar Plot and the Mode Selection, Filter Options and Appearance can be al-tered in the same way. In addition, there are three more options:

• Cluster; Enabling this option will 'cluster' variables with a angular separation less than the parameter entered. A cluster shares the same diagram color.

• Show only points; If this parameter is disabled, the vectors will appear as points on the diagram rather than arrows.

• Show unit circle; The unit circle can be removed from the plot by disabling this option.

Exporting a Modal Analysis Plot to External Software

Any of the Modal Analysis plots can be exported to a WMF or BMP file for use in an exter-nal software program such as a word processor. It is recommended to use the WMF for-mat where possible because this format is a vector based format (which means that the plot looks good regardless of scaling) and is compressed so uses much less disk space than the BMP file.

To export a Modal Analysis plot follow these steps:

1 From the main PowerFactory file menu, choose the Option File -> Export ... -> Windows Metafile (*.WMF). A 'Save As' dialog will appear.

2 Choose an appropriate File name and disk location and click 'Save'.

1.000.50-0.50-1.00

1.00

0.50

-0.50

-1.00

Participation of mode: -1.119 -12.250*jMagnitude: 12.301 1/s, Angle: -95.220 degPeriod: 0.513 s, Frequency: 1.950 HzDamping: 1.119 1/s, Ratio of Amplitudes: 1.775 Min. contribution: 0.100

Cluster 2: Grid / 01_Sym; psiD: 0.15 / -95.5 deg

Cluster 3: Grid / 11_Sym; phi: 0.64 / 1.6 deg Grid / 13_Sym; phi: 0.23 / 0.7 deg Grid / 08_Sym; phi: 1.00 / 0.0 deg Grid / 05_Sym; phi: 0.87 / -0.2 deg

Cluster 4: Grid / 02_Sym; phi: 0.11 / -7.4 deg

Cluster 1: Grid / 01_Sym; speed: 0.82 / 168.8 deg Grid / 13_Sym; speed: 0.16 / 170.2 deg Grid / 05_Sym; speed: 0.62 / 170.3 deg Grid / 11_Sym; speed: 0.49 / 170.3 deg Grid / 08_Sym; speed: 0.73 / 170.6 deg

DIg

SIL

EN

T

28 - 17


Note: The process of exporting multiple plots can be automated using a DPL script. See the DPL function WriteWMF() for more information.

28.3.3 Viewing Modal Analysis Results using the Modal Data Browser

The Modal Analysis results can be displayed in a convenient data browser specially de-signed for working with these results. To display the results in this data browser follow these steps:

1 Click the icon found in the Modal Analysis toolbar. The ComModres dialogue as shown Figure 28.17 will appear.

2 Optional: If you want to display the Modal Analysis results from another Study Case, you need to select user-defined for 'Shown Results' and select an alternative results object. Normally you should leave this value on 'Default'

3 The procedure now depends on if you want to view the calculated eigenvalues, or if you want to view the controllability, observability and participation factors for variables related to a particular eigenvalue.

- If you only want to display the eigenvalues, then leave the 'Shown Values' on 'Eigenvalues'.

- If you want to view the controllability, observability and participation factors for a particular eigenvalue then you must select 'States' and choose the 'Eigenvalue index'.

4 Press the Execute button. The data browser window will appear as shown in Figure 28.18 (for eigenvalues) or as shown in Figure 28.19 for a single eigenvalue and the controllability etc for each variable.

Fig. 28.17: Displaying modal analysis results in a data browser (ComModres

dialogue)

28 - 18


Fig. 28.18: Modal analysis results in a data browser (eigenvalues)

Fig. 28.19: Modal analysis results in a data browser (controllability etc)

Note: The results in the eigenvalue data browser can be sorted or grouped by clicking on the column heading. Clicking once sorts the column in descending order, a second time in ascending order.

Viewing the Mode Bar Plot or Mode Phasor Plot directly from the Modal Data Browser

When you view the Eigenvalues in the data browser as shown in Figure 28.18, you can quickly show the Mode Bar Plot or Mode Phasor plot of the eigenvalue. To do so follow these steps:

1 Right-click the mode icon on the left most side of the browser. The context sensitive menu will appear.

28 - 19


- For a Mode Phasor Plot choose the option 'Show -> Phasor Plot -> Controllability etc'.

- For a Mode Bar Plot choose the option 'Show -> Bar Plot -> Controllability etc'.

Exporting the results from the Modal Analysis Data Browser to external software

To export the results shown in the Modal Analysis Data Browser to an external software program (such as a spreadsheet tool) follow these steps:

1 In the browser window left click and drag a selection of data that you would like to export. To select all data press <CTRL-A>.

2 Right-click within the selection and choose the option 'Spread Sheet Format -> Copy (with column headers)'.

3 Open the external software and paste the data from the windows clipboard.

28.3.4 Viewing Results in the Data Manager Window

The data manager and object filter can be used to view the participation factors, control-lability or observability for power system elements such as synchronous machines after completing an Modal Analysis. There are three tasks that you might need to complete to show this information. Tasks one and two are compulsory, whereas task three is only nec-essary if you are viewing the eigenvalue results in the data manager or object filters for the first time.

Task 1: Choosing the Eigenvalue and variable to view

1 Firstly, make sure you have executed a Modal Analysis as described in Section 28.2.

2 From the Modal Analysis toolbar click the 'Set Eigenvalue' icon . The Set Eigenvalue dialog (ComSeteval) should appear as shown in Figure 28.20.

Fig. 28.20: The 'Set Eigenvalue' dialog

3 Typically, you should leave the 'Shown results' set to Default, unless you wish to view results from an alternative Study Case.

28 - 20


4 Choose the 'Eigenvalue index' to display results for by entering the number using the keyboard or by using the increment/decrement control.

5 Choose the 'State Variable' to view the results for by using the drop-down selection menu.

6 Press the Execute button. It will appear as if nothing has happened - this is normal.

Task 2: Viewing the results in the Object filter

1 Select the synchronous machine icon from the object filter menu as shown in Figure 28.21.

Fig. 28.21: Choosing the synchronous machine object filter

2 A list of all 'Relevant' synchronous machines will appear in a data manager style window. Select the Flexible Data tab from the bottom of the window. In Vista/Windows 7 this will be highlighted in blue.

3 Scroll across the window to view the columns containing the observability, controllability and participation factor date. If you don’t see these column headings as shown in Figure then you will need to define the 'Flexible data' as described in Task Three.

Fig. 28.22: Object filter for synchronous machines showing the

Task 3: Changing the Flexible Data Columns to show the participation factors

1 Click the 'Define Flexible Data' icon from the window toolbar. A Variable set browser selection window will appear.

2 Choose the 'RMS Simulation' tab from the top of this window.

3 In the 'Filter for' settings choose the Variable Set 'Calculation Parameter'.

4 In the 'Available Variables' window, scroll to near the bottom until you see the variables p_mag (Participation, Magnitude) etc. Holding <shift> select this variable and all eight other variables down to rEVec_mags (Observability, Magnitude signed).

28 - 21


5 Click the right arrows icon >> between the 'Available Variables' and 'Selected Variables' windows. The variables you selected in 4 should disappear from the left window and appear appended to the right window. The screen should look similar to Figure 28.23.

6 Press the OK button. Now you can scroll to the right in the flexible data page to view the values of these variables.

Note: The results can only be displayed for one eigenvalue and variable at a time. For instance, eigenvalue 3 and speed. To change the dis-played eigenvalue and/or variable, repeat task one above. You don’t need to repeat task three every time because after this has been done the first time in the project it will remain configured this way until you change the 'defined variables' in the flexible data page.

Fig. 28.23: Variable set selection of Controllability, Observability and Participation Factor variables for Synchronous Machines.

28.4 Troubleshooting Modal Analysis Calculation Problems

There are various things that can go wrong during an attempt at a Modal Analysis and PowerFactory usually provides error messages to indicate the nature of the problem when

28 - 22


it occurs. This chapter describes some of the common problems that can occur when at-tempting a Modal Analysis and the probable solutions.

28.4.1 Models not supported by the QR method

Sometimes the Modal analysis calculation will fail with an error like: ''The system contains models which cannot be supported by QR method. Please try Selective Modal Analysis (Ar-noldi/Lanczos)''. There are several PowerFactory models that are not supported by the QR method such as:

• The Asynchronous Machine (ElmAsm);

• The PWM converter (ElmVscmono, ElmVsc);

• DFIG (ElmAsmsc);

• DC machine (ElmDcm);

• DC line (ElmLne with type set to DC);

• Complex load;

• DC shunt;

• DC surge arrester;

• DC valve (ElmValve);

• DC series reactor;

If you get such a message, you have two options for resolving the problem:

1 Place all objects from your project as listed above out of service (you could possibly create a operation scenario for this purpose so that you can easily revert to the base model for load-flow, short circuit etc).

2 Use the Arnoldi/Lanczos method. In the majority of cases, this is probably the best option.

28.4.2 The Arnoldi/Lanczos Method is slow

The Arnoldi/Lanczos Method is a selective eigenvalue calculation and should not be used when you need to calculate all the system eigenvalues. When you need all the system eigenvalues, the QR method will generally be faster.

The Arnoldi/Lanczos method is generally fast when computing a selective number of ei-genvalues around a desired point. If you need to get a larger number of eigenvalues than the default, it is suggested that you increase the requested number of values slowly, say starting with 20 then 50 etc.

28 - 23


28 - 24

DIgSILENT PowerFactory Model Parameter Identification

Chapter 29Model Parameter Identification

The process of parameter estimation for power system elements for which certain mea-surements have been made is performed with the "Parameter Estimation" function using

the icon .

The ComIdent command object is a high performance non-linear optimization tool, which is capable of a multi parameter identification for one or more models, given a set of measured input and output signals. This identification is principally performed in the following way:

• A "Measurement File'' object (ElmFile) is created which maps the raw measured data onto one or more "measurement signals''. These signals may contain measured excitation and response signals.

• The measurement signals are used as inputs by the models of the power system elements for which one or more parameters have to be identified, or they may be used to control voltage or current sources.

• The output signals of the power system elements are fed into a comparator, just as the corresponding measured signals. The comparator is thus given the measured response on the excitation and the simulated response of the element models.

• The comparator calculates an objective function, which is the weighted sum of the differences between the measured and the simulated response, raised to a whole power (by default to the power of 2).

• The ComIdent command will collect all objective functions from all comparator objects in the currently active study case and will minimize the resulting overall objective function. To do this, the ComIdent command is given the list of parameters which are to be identified. The objective functions are minimized by altering these parameters.

This whole process is visualized in Figure 29.1.

29 - 1


Fig. 29.1: The identification Principle

Of course, Figure 29.1 only visualizes the principle of the identification. To connect mea-surement files, power system models and comparator objects to each other, a composite frame is used. This, and all other details of the PowerFactory identification functions, is described in the following sections.

29.1 Target Functions and Composite Frames

The parameter identification process is performed by minimizing objective functions. These objective functions are calculated by ElmCompare objects from the difference be-tween measured responses and calculated responses of one or more power system ele-ments.

To define an objective function, the measured excitation signals must be connected to the component models or to voltage or current sources, and the measured and calculated re-sponse signals must be connected to the compare object. All this is done graphically by drawing a Composite Frame, using a block definition (BlkDef) with slots.

A simple example of an identification block diagram, for the objective function for a volt-age controller, is visible in Figure 29.2.

29 - 2


Fig. 29.2: Simple identification block diagram

The block diagram uses slots which reserve space for the measurement files, the compar-ator and the element models.

29.1.1 The Measurement File Slot

The measurement file object (ElmFile) has the following signals available:

• Number of Input Signals: 0

• Number of Output Signals: 10

• Input Signals Names: -

• Output Signals Names: "y1,..,y10''

The measurement file slot in the example of Figure 29.2 has the following settings:

• Class Name Filter: "ElmFile'' • Output Signals: "y1,y2'' The fact that the signal is named "output'' signals in the case of the measurement file does not implicate that the parameter identification only regards measured response sig-nals ("measured outputs'') from power system elements. It only means that the measured excitation signals will be mapped onto ElmFile signals. The ElmFile will reproduce the measured excitation and response signals during the identification process.

29.1.2 Power System Element Slot

Power system element slots are used in the identification block diagram in the same way as they are used to define composite models.

As in the case of a composite model diagram, the element slots may use any of the avail-able parameters of the power system element model as input or output. The in- and out-put signals are defined by stating the exact variable name (see also Section Composite Block Definitions in Section 27.8 (User Defined (DSL) Models)).

In the case of the example in Figure 29.2, the "Vco1'' slot has the following parameters set:

• Class Name Filter: "ElmVco*'' • Output Signals: "uerrs''

29 - 3


• Input Signals: "u''

29.1.3 Comparison Slot

The comparison object ElmCompare has the following properties:

• Number of Input Signals: 21

• Number of Output Signals: 0

• Measured Response Signal Names: "in1mea,..,in10mea'' • Simulated Response Signal Names: "in1sim,..,in10sim'' • Weighting Factor: qzpf • Output Signals Names: -

The calculated value of the objective function will be multiplied by the weighting factor before it is put out. The weighting factor may be used, for instance, to connect a time-window to the comparison object which forces the objective function to zero for those mo-ments in time which are not to be used in the identification process.

In the case of the example in Figure 29.2, the Comparison slot has the following param-eters set:

• Class Name Filter: "ElmCompare'' • Input Signals: "in1meas,in1sim''

29.2 Creating The Composite Identification Model

The identification block diagram only defines a generalized 'workbench' that is needed for the identification process. Its function is similar to that of the "Composite Frame'' object. There is also the need to create a composite model, based on the block diagram, to iden-tify particular parameters of particular objects.

Suppose having a voltage controller model of which one wants to identify the parameters ka '' and ta. Measurements of the behavior of the physical appliance are available as mea-sured voltage-curves on the input and output of the controller during a disturbance.

Assuming the example identification block diagram of Figure 29.2, a composite model (ElmComp) has to be created in the active grid folder.

Note If the identification process only addresses secondary power sys-tem element, which are not directly connected to busbars, the identification process does not require a power system grid.However, all calculation functions like load-flow or EMT simulation require a calculation target in the form of an activated grid of sys-tem stage folder. Therefore, a grid folder with at least one 'DUM-MY' busbar has to be created when secondary element models are to be identified.

The composite model must be set to use the identification block. It will then show the slots that have been defined in that block. In the current example, the composite model dialogue will look like Figure 29.3.

29 - 4


Fig. 29.3: The example composite identification model

In this figure, the three slots have been assigned already. Visible is that the comparison object "Compare Signals'' is selected, as well as a measurement file and the voltage con-troller of which to find the best possible values for ka and ta.

29.2.1 The Comparison Object

The comparison object calculates the objective function from the connected measured and simulated responses. It allows for the use of weighting factors and for other powers to raise to. The example in Figure 29.4 shows the default settings.

29 - 5


Fig. 29.4: The comparison object dialogue

In this figure, the 10 difference signals are listed, with their weighting factor. By default, these are one, but they may be edited freely. The power factor equals 2 by default but may be set to any other positive whole number from 2 to 10.

The objective function calculated by the comparison object equals

where

• is the measured response (i.e. "in1mea'')

• the simulated response (i.e. "in1sim'')

• is the weighting factor (i.e. for the difference signal nr.1)

• p is the power

29.3 Performing a Parameter Identification

The identification process is executed by the ComIdent command. This command can

be opened by the icon on the main menu. This icon can be found on the "Stability''

toolbar which is be accessed by selecting the icon .

The Comident dialogue is depicted in Figurefigure 29.5.

Mi Si– wi p

i 1=

n

Mi

Si

wi

29 - 6


Fig. 29.5: The ComIdent dialogue

This dialogue shows references to the following objects:

Composite ModelThis reference is normally not needed. When left open, the identification process will automatically gather all composite identification models and will minimize all objective functions.When the composite model reference is set, then the identification will only minimize that model's objective function.

Load-Flow SettingsThis reference is automatically set to the load-flow command that will be used during the identification process.

Initial ConditionsThis reference is automatically set to the initial conditions command that will be used during the identification process.

SimulationThis reference is automatically set to the simulation command that will be used during the identification process.

The identification process allows for the use of load-flow calculations and/or dynamic sim-ulations.

The "Load-Flow'' and "Simulation'' pages shows the variables that are to be identified, in case of a load-flow or a dynamic identification. See for example Figure 29.6.

29 - 7


Fig. 29.6: Setting identification parameters

In this example, two parameters of the voltage controller element "vco IEEEX1'' from the Composite Identification Model are listed. The identification process will alter these pa-rameters in order to minimize the objective functions.

The "Mode'' field in the parameter list determines the parameter constraints:

0 means not to change the parameter, but to leave it at its initial conditions. This option may be used to temporarily exclude some parameters from the identification process.

1 mean to optimize the parameter without restrictions

2 means to optimize the parameter, given the constraint that the parameter value must always be greater than zero.

Although the object for which the parameters are optimized in this example is the same object as is used in the Composite Identification Model, it is allowed to enter any other parameter from any other element, as long as that element belongs to the active study case. Such may be used to optimize secondary appliance, where only the behavior of the primary appliance has been measured.

29.4 Identifying Primary Appliances

A primary appliance, such as a general load, an asynchronous machine or a static var sys-tem, do not have an input signal like a voltage controller or any other secondary appli-ance. It would therefore not be possible to connect a measured signal directly to a load model in order to simulate its response.

To identify a primary element model, a small grid model is used to which one or more controllable voltage sources may be connected. These voltage sources will translate the measured voltage signals from the measurement file into a normal busbar voltage which will be used in the load-flow or simulation calculations. The response of the primary ele-ment models connected to that busbar may then be compared to a measured response.

An example of this method is shown in the following figures.

29 - 8


Fig. 29.7: Identification diagram with primary element

In Figure 29.7, a simple Identification Block Diagram is shown in which the measurement file is no longer connected to the element slot, but to the voltage source slot. The voltage at the busbar at which the voltage source will be connected will thus be forced to the mea-sured values during the identification process.

Fig. 29.8: Primary element and voltage source

In Figure 29.8, a very simple grid is shown to which the load which is to be identified and a voltage source element are connected. As with the normal identification process, a Com-mon Identification Model has to be created which uses the Identification Diagram with Primary Element as shown in Figure 29.7. In the ComIdent command dialogue, the un-known parameters of the load may then be listed.

It is of course possible to mix the identification of both primary and secondary power sys-tem elements at the same time.

29 - 9


29 - 10

DIgSILENT PowerFactory Contingency Analysis

Chapter 30Contingency Analysis

In Chapter 23 the general aspects of load flow analysis and its main areas of application were presented. Additionally, two perspectives were discussed: that of planning and that of system operation (see Figure 23.1). There it was made evident that regardless of the perspective, the behavior of the system must be analyzed under both normal and abnormal conditions.

When referring to contingency analysis, we are essentially referring to the analysis of abnormal system conditions. In general, contingency analysis can be defined as: "the evaluation of the violations in system operating states (if any) that certain contingencies can pose to the electrical power system"; or put in other words, contingency analysis is the execution and evaluation (loading and voltage-wise) of post-fault load flows; each of which reflect the "outage" of a single or group of elements (such as transformers, busbars, transmission lines, etc.).

Contingency analyses can be therefore used to determine power transfer margins or for detecting the risk inherent in changed loading conditions. This chapter deals with deter-ministic contingency analysis.


The contingency analysis module available in PowerFactory offers two distinct contin-gency analysis methods:

Single Time Phase Contingency Analysis:The non-probabilistic (deterministic) assessment of failure effects under given contingencies, within a single time period.

Multiple Time Phase Contingency Analysis:The non-probabilistic (deterministic) assessment of failure effects under given contingencies, performed over different time periods, each of which defines a time elapsed after the contingency occurred. It allows the definition of user defined post-fault actions.

Figures 30.1 and 30.2 illustrate the general sequence of both methods. Here the results of both pre- and post-fault load flows are compared to the specified loading and voltage limits; based on this comparison contingency reports are generated.

In Figure 30.1 the term Single Time Phase is used because only one post-fault load flow

30 - 1


is analyzed per contingency case.

Figure 30.2 illustrates the multiple time phases contingency analysis method. Here, more than one post-fault load flow can be analyzed for the same contingency; hence the term Multiple Time Phase. Furthermore, if required, each time phase can have its own post-fault actions defined. The defined post-fault actions can be either a single event or a combination of the following events:

• Load shedding

• Generator re-dispatching

• Switching action (opening or closing)

• Tap changing

In PowerFactory, the term Fault Case (used in both Figures) is used to define a contin-gency.

Fig. 30.1: Single Time Phase Contingency Analysis Method

30 - 2


Fig. 30.2: Multiple Time Phase Contingency Analysis Method

Before describing in detail the contingency analysis itself, it is necessary to introduce two basic concepts which define the functionality of this tool:

• Contingencies: These are objects in PowerFactory of the class ComOutage

( ) which are used to represent contingencies. They are defined by a set of events which represent the occurrence of the originating fault(s) over time and the subsequent fault clearing and post-fault actions. It should be noted that depending on the method selected and the value assigned to the Post Contingency Time parameter (see Section 30.3.3: Multiple Time Phases), post-fault actions are carried out. For further information on the definition and use of contingencies please refer to Section 30.4.7 (Defining Time Phases for Contingency Analyses).

• Time Phases: These represent points in time at which the steady-state operational point of the network under analysis is calculated. Each time phase is defined via a user defined Post Contingency Time (see the Multiple Time Phases tab of the Contingency Analysis command). The Post Contingency Time defines the end of a phase; that is, the point in time at which the steady-state of the network is calculated. For further information regarding the definition of time phases refer to Section 30.4.7 (Defining Time Phases for Contingency Analyses).

30 - 3


30.1.1 Single Time Phase Contingency Analysis

The single time phase contingency analysis function first performs a pre-fault (base) load flow calculation. Following this, for each contingency (stored inside the command itself) it performs a corresponding post-contingency load flow (for a single time phase), which take one or more primary components out of service. The command calculates the initial consequences of the contingencies, but does not regard the operational measures taken to mitigate voltage band problems or supply interruptions.

It is important to mention here that if the contingency analysis command is set to consider Automatic Tap Adjust of Transformers and Shunt Adjustment, they will only be considered if their time constants are smaller than the current Post Contingency Time or if the Consider Specific Time Phase flag (Multiple Time Phases page) is not enabled. Additionally, the operational thermal ratings of branch elements during the contingency (if 'short term' thermal ratings (5.5.7) have been defined) will depend on the duration of the contingency i.e. the current Post Contingency Time.

The raw results of the single time phase contingency analysis correspond to the steady-state operational points of the network being studied, considering each one of the defined contingencies up to the given Post Contingency Time (see Section 30.3: The Single Time Phase Contingency Analysis Command for further information on this setting). The reporting facilities available in PowerFactory’s contingency analysis function allow the filtering of results of interest to the user, including maximum loading of branch elements, exceeded voltage limits, etc. Refer to Section 30.3 (The Single Time Phase Contingency Analysis Command) for further information on configuring the reporting settings, and Section 13.9 (Results Objects) for information on handling result objects (ElmRes) in PowerFactory.

Note: If the Fault Case contains post-fault actions such as load shedding, generator re-dispatch, tap changing and switching actions (clos-ing), these are ignored in the Single Time Phase mode, regardless of the specified Post Contingency Time.

30.1.2 Multiple Time Phases Contingency Analysis

As indicated previously, PowerFactory provides tools for the analysis of contingencies over multiple time phases, allowing the definition of post-fault actions that can lead to the mitigation of voltage band problems or supply interruptions which are caused by faults in the networks under analysis.

As in the single time phase contingency analysis, the multiple time phases contingency analysis function first performs a pre-fault (base) load flow calculation. The major difference here is that for each contingency (stored inside the command), it loops over the list of defined time phases (also stored inside the command itself), calculating the corresponding post-contingency load flows. For each load flow calculation, the events (faults and post-fault actions) whose time of occurrence are earlier than, or equal to, the corresponding Post Contingency Time, are considered.

Similar to single time phase contingency analysis, the effect of transformer tap changers and switchable shunts depends on these components’ corresponding time constants and the current Post Contingency Time. Controllers are only considered if their time constants are smaller than the current Post Contingency Time. Additionally, the operational thermal ratings of branch elements during the contingency (if 'short term' thermal ratings (5.5.7)

30 - 4


have been defined) will depend on the duration of the contingency i.e. the current Post Contingency Time.

The raw results of the contingency analysis with multiple time phases correspond to the steady-state operational point of the network being studied, at every Post Contingency Time for each of the defined contingencies. The reporting features included in the function allows the filtering of problematic contingencies, according to maximal loading of branch elements, exceeded voltage limits, etc.

30.1.3 Time Sweep Option (Single Time Phase)

PowerFactory provides a special Calculate Time Sweep option for the Single Time Phasemethod, and which can be found on theTime Sweep tab of the contingency analysis command. When enabled, the date and time of the active Study Case will be modified according to a list predefined by the user. The application of this option is in situations where the calculation of contingencies is required for a certain time span; for example, the automatic calculation of contingencies for every hour of the day.

Here it is important to note that in order for the Time Sweep to activate the corresponding scenarios automatically, a Scenario Scheduler (IntScensched) object needs to first be created and afterwards activated. Once the execution of the contingency analysis has finished, the Study Case date and time are restored to their original setting. For more information on the Scenario Scheduler please refer to Chapter 16.

In addition, the Time Sweep option can be used in combination with the Parallel Computing option (Section 30.1.5).

30.1.4 Consideration of Predefined Switching Rules

In PowerFactory, the contingency analysis can be setup to consider predefined switching rules of substations (refer to Chapter 5 for further information). The Switching Rule defines switching actions for different fault locations (arranged in a matrix) that can be reflected at a certain time. These switching actions will always be relative to the current switch position of every breaker.

30.1.5 Parallel Computing Option (Single Time Phase)

The computation time required to perform a contingency analysis largely depends on two factors:

• The size of the power system; and

• The number of contingencies considered.

Depending on these factors, the computation time could take from a couple of seconds (or less) up to several minutes.

With the development of multi-core machines and the existence of Ethernet network technology, the calculation of contingencies in parallel is now an option in Power-Factory. This feature facilitates the significant reduction of required computation time depending on the number of cores being used.

By default, the Parallel Computing option is enabled in each user account; however, the setting can be modified when the user has logged on as an Administrator.

30 - 5


The following sections provide detailed information regarding the execution and settings of the contingency analysis command in its single or multiple time phase configuration.

30.2 Executing Contingency Analyses

To access the various contingency analysis related functions within PowerFactory, click

on the icon on the "Select Toolbar" (shown in Figure 30.3).

To initiate the contingency analysis command, click on the icon, which should now be visible in the first row of icons at the top right of the screen.

Fig. 30.3: Contingency Analysis Selection from the Main Toolbar

Fig. 30.4: Contingency Analysis Related Functions

Both the Single Time Phase and Multiple Time Phases contingency analysis are carried out

using the Contingency Analysis command (ComSimoutage, ). When configured and executed, it performs a 'base' load flow calculation to determine the operational point of the network under no-fault conditions. The command contains Contingency Cases(ComOutage objects) which define one or more elements that are taken out of service simultaneously. Following the calculation of the base load flow, a contingency load flow

Contingency Definition

Contingency Analysis

Contingency Comparison

Show Contingencies

Show Fault Cases

Show Fault Groups

Edit Result Variables

Start, Next and Stop Tracing Buttons

Report Contingency Analysis Results

30 - 6


for each of these contingencies is calculated. This calculation considers the post-fault thermal ratings of branch elements (see Section 5.5.7), transformer tap changer controller time constants and automatic shunt compensators (for further information please refer to Section 30.3: The Single Time Phase Contingency Analysis Command).

In PowerFactory, contingency cases can be generated by two primary means:

• Via the definition and use of Fault Cases and Fault Groups; and/or

• Using the Contingency Definition (ComNmink) command, either via its toolbar icon

( ) or by selecting component(s) in the single-line graphic, right-clicking and selecting Calculate --> Contingency Analysis... .

In the first case, contingency cases can be created using references to user defined Fault Cases and Fault Groups (introduced in Section 5.5.3) from the Operational Library. By means of a topological search, PowerFactory determines which circuit breakers must be opened in order to clear the faults, and generates the corresponding contingency cases. Each contingency case is generated with its corresponding interrupted components for each fault case/group. Fault cases and groups reside in the Operational Library folder, and can be reused. Hence there is no need to manually redefine the same contingencies each time a contingency analysis is required. For further information on creating contin-gencies from fault cases/groups, please refer to Section 30.5 (Creating Contingency Cases Using Fault Cases and Groups).

In the second case, contingencies can be created using the Contingency Definition

command. This command is available either via the icon on the main toolbar, or by right-clicking on a selection of elements in the single line diagram, and selecting the option Calculate --> Contingency Analysis.... Either an n-1 or an n-2 outage simulation for the selected elements can then be prepared. Additional to these two options an n-k outage for mutually coupled lines/cables is available. The Contingency Definitioncommand optionally allows all lines/cables, transformers, series reactors, series capac-itors and/or generators to be selected to create contingencies. For further information on creating contingencies using the Contingency Definition command, please refer to Section 30.6 (Creating Contingency Cases Using the Contingency Definition Command).

The following sections provide detailed information regarding the settings and features of the contingency analysis command in its single time phase configuration.

30.3 The Single Time Phase Contingency Analysis Command

The settings of the Basic Options page of the contingency analysis command (ComSi-

moutage ) are illustrated in Figure 30.5.

30 - 7


Fig. 30.5: Basic Options settings of the Contingency Analysis (ComSimoutage) Command

When executing a contingency analysis, the general sequence of operations performed is as follows:

• Execution of a 'base' load flow in order to determine the initial operational point of the network. This 'base' (pre-fault) load flow is performed according to the settings stated in the load flow command and which is referenced on the Basic Options tab page of the contingency analysis command.

• Execution of the 'contingency' load flows. That is, for each of the stored contingency cases, it places the interrupted components (see Section 30.3.8: Representing Contingency Situations - Contingency Cases) on outage and performs a contingency (post-fault) load flow. Here, the settings of the post-fault load flows will depend on how the contingency command is configured. That is, if specified by the user, the pre-fault and post-fault load flows can be executed with different settings (only a difference in certain settings are allowed). For more information please refer to Section 30.3.3 (Multiple Time Phases).

The contingency load flow is characterized by the Post Contingency Time parameter (available on the Multiple Time Phases tab of the Contingency Analysis command if either the option Allow different settings has been enabled, or when the option Consider Specific Time Phase has been selected). This parameter determines the duration of the interval between the occurrence of the fault(s) which define the contingency, and the time when the load flow calculation of the network under the contingency situation is performed. The Post Contingency Time is a key parameter of the single time phase contingency analysis because:

1 The actions of transformer automatic tap changers and switchable shunt compensators on the faulted network are only regarded if the time constants of their

30 - 8


controllers are less than the defined Post Contingency Time (meaning that the controllers are fast enough to operate during the time phase); and

2 The operational thermal ratings of branch elements during the contingency (if 'short term' thermal ratings (see Section 5.5.7) have been defined) will depend on the duration of the contingency, i.e. the Post Contingency Time.

Note: The 'base' and the 'contingency' load flow calculations by default use the same load flow command (ComLdf object). However, the user can define different load flow commands for these two calcu-lations by selecting the option ‘Allow different settings’ on the Mul-tiple Time Phases tab of the contingency analysis command (ComSimoutage). The actions of automatic tap changers and switchable shunts are only possible if the corresponding options are selected in the 'Basic Options' tab of the load flow command(s).

The contingency analysis uses a result file object (ElmRes, see Section 13.9: Results Objects) to store the voltages at terminals and the loading of certain branch element classes (lines, transformers, series capacitances and series reactances). Recording the loadings for all branches and the voltages for all terminals for every contingency may lead to excessive data storage. Therefore, in order to minimise data storage, only significant results are recorded. In contingency analysis, a calculated parameter is considered to be significant if the threshold (Limits for Recording) of the corresponding component are out of the threshold. Limits can be set individually for each terminal and branch element (in the Load Flow tab of the element’s dialogue) or globally in the Limits for Recording field of the contingency analysis command. A calculated result is stored in the result file whenever one of the constraints (individual or global) is violated.

The settings of the contingency analysis command are entered using the dialogue shown in Figure 30.5. The following subsections explain each of the available options.


Calculation Method

AC Load Flow CalculationThe contingency analysis uses an iterative AC load flow method to calculate the power flow and voltages per contingency case.

DC Load Flow CalculationThe contingency analysis uses a linear DC load flow method to calculate the active power flow per contingency case.

DC Load Flow + AC Load Flow for Critical CasesThe contingency analysis will perform two runs (if required). First it will use a linear DC load flow method to calculate the active power flow per contingency case; if for certain contingencies loadings are detected to be outside a certain threshold, then for these cases the contingency

30 - 9


analysis will recalculate the post-fault load flow using the iterative AC load flow method. The criteria (threshold) used for the AC recalculation of critical DC cases is stated on the Advanced Options page.

Limits for Recording

The parameters in this section set the global threshold used to determine whether a calcu-lated result is recorded in the Results object (object pointed to by the Results for AC or Results for DC field located in the bottom section of the Basic Options page). Whenever one of the defined constraints is violated, the calculated result (for the corresponding contingency case and network component) is recorded.

Max. thermal loading of components (%)Maximum thermal loading in percent. Loadings exceeding this value will be recorded in the result file for the corresponding component.

Lower limit of allowed voltage (p.u.)Minimum admissible voltage in per unit. Voltages lower than this value will be recorded in the result file for the corresponding terminal.

Upper limit of allowed voltage (p.u.)Maximum admissible voltage in per unit. Voltages higher than this value will be recorded in the result file for the corresponding terminal.

Maximum voltage step change (%)Maximum (+/-) admissible voltage change in percent. Larger voltage changes (pre-fault vs. post-fault) will be recorded in the result file for the corresponding terminal.

Contingencies

The Contingencies section of the Basic Data tab, as shown in Figure 30.6, allows the display, creation and removal of contingencies. These are the contingencies that will be analyzed by the contingency analysis command.

Fig. 30.6: Contingencies Section of Contingency Analysis Dialogue

ShowDisplays a list of all defined contingencies.

Add Cases/GroupsThis button is used to create the contingency cases (ComOutage objects) based on fault cases and/or fault groups. A fault case contains events: one for the fault location, and (optionally) others specifying post-fault actions. Fault groups contain a set of references to fault cases. In order to use the Add Cases/Groups option, the fault cases and/or groups must have been previously defined in the Operational Library. If these have been defined, when the Add Cases/Groups

30 - 10


button is pressed, a data browser listing the available fault cases/groups pops up. The user can then select the desired fault cases/groups from this browser and press Ok. The corresponding contingencies are then created automatically by PowerFactory. One contingency is created for each selected fault case, and one contingency is created for each fault case referred to within each selected fault group. For further information on creating contingencies from fault cases/groups, please refer to Section 30.5 (Creating Contingency Cases Using Fault Cases and Groups).

Remove AllRemoves all contingency cases (ComOutage objects) stored in the contingency analysis command.

Results for AC/DC

Depending on the calculation method selected, the reference to the corresponding result file object (ElmRes) is defined. If, for example, the calculation method DC Load Flow + AC Load Flow for Critical Cases is selected, two result file objects will be referenced (one for AC calculations and another for DC calculations). The results stored in this file are filtered according to the global threshold set in the Limits for Recording section of the Basic Data tab, and also according to the individual limits defined within each component’s respective dialogue (such as on the Load Flowtab of the element’s own dialogue). For further information on result objects, please refer to Section 13.9: Results Objects.

30.3.2 Effectiveness

The Effectiveness tab of the contingency analysis command (Figure 30.7), allows the display, addition and removal of quad boosters and generators in order to calculate their effectiveness.

Fig. 30.7: Effectiveness Options Settings of the Contingency Analysis Command

30 - 11


Calculate Quad Booster Effectiveness

Show QBsShows a list of the transformers for which the effectiveness should be calculated.

Add QBsAdds references to transformers for which the effectiveness should be calculated. Only transformers where the additional voltage per tap is different to 0 and multiples of 180 degrees will be listed (Load Flow tab of the transformer type (TypTr2) Phase of du parameter).

Remove AllRemoves all references to transformers for which the effectiveness is currently calculated.

Calculate Generator Effectiveness

Show Gen.Shows a list of the generators for which the effectiveness should be calculated.

Add Gen.Adds references to transformers for which the effectiveness should be calculated.

Remove AllRemoves all references to generators for which the effectiveness is currently calculated.

30.3.3 Multiple Time Phases

The Multiple Time Phases tab, as shown in Figure 30.8, allows the selection of the contin-gency method to be performed as well as the corresponding settings.

30 - 12


Fig. 30.8: Multiple Time Phases Option Settings of the Contingency Analysis Command

Method

Single Time PhasePerforms the contingency analysis for a single time phase.

Multiple Time PhasePerforms the contingency analysis for multiple time phases, allowing the definition of post-fault actions.

Base Case versus Contingency Load Flow

Use same settingsUses the settings from the base case load flow for the contingency case load flow.

Allow different settingsAllows different settings for the base case load flow and the contingency case load flow.


Base Case Load FlowOnly available when option Allow different settings is selected in the Base Case versus Contingency Load Flow section of the Multiple Time Phases tab. This is a reference to the load flow command used to calculate the network operational point before the simulation of contingencies. The settings of this load flow command can be edited by

pressing the button.

Contingency Load FlowOnly available when option Allow different settings is selected in the

30 - 13


Base Case versus Contingency Load Flow section of the Advanced Options tab. This is a reference to the load flow command used to assess the network in contingency situations. It is characterized by the Post Contingency Time, which is defined in the Post Contingency Time field, also located in the Calculation Settings section of the dialogue. The contingency load flow command referred to by the Contingency Load Flow is always stored inside the contingency analysis command itself. The settings of this load flow command can be edited by pressing

the button. The Contingency Load Flow command settings can be set to those of the currently used by the Base Case Load Flow

command by pressing the button.

Note: If no 'Contingency Load Flow' command is defined, the 'Base Case Load Flow' command is used to asses the network under contin-gency situations. In this case the action of automatic transformer tap changers and switchable shunt compensators is directly con-sidered (provided that the corresponding options are selected in the 'Basic Options' tab of the assigned load flow command).

Consider Specific Time PhaseOnly available when option Use same settings is selected in the Base Case versus Contingency Load Flow section. This option must be enabled to define a post contingency time.

Post Contingency Time (End of Time Phase)This value defines the time phase of the contingencies. This means that all switch-open events with an event time less than or equal to this are considered in the contingency.

30.3.4 Time Sweep

The Time Sweep settings shown in Figure 30.9 allow the automatic modification of the date and time of the active Study Case according to a list predefined by the user. The advantage of this option is in situations where the contingency analysis needs to be automatically performed taking into account different system conditions such as consid-ering several load and generation profiles (according to the hour of the day).

30 - 14


Fig. 30.9: Time Sweep Option Setting of the Contingency Analysis Command

Note: When enabled, the Time Sweep will automatically change the Date and Time of the active Study Case. However, in order for the Study Case to activate the corresponding scenario automatically, a Sce-nario Scheduler (IntScensched) object needs to first be created and afterwards activated. Once the execution of the contingency analysis has finished, the Study Case date and time is restored to its original setting. For more information on the Scenario Scheduler please refer to Chapter 16.

To add study times to the list, first enable the Calculate Time Sweep option, then right-click anywhere in the table and select Insert Rows (alternatively select Append Rows or Append n Rows). To modify the date and time, double-click on the corresponding Study Time cell. Additionally, the user has the option to ignore previously defined Study Timesby enabling the Ignore flag. This ensures that the contingency analysis will not take into account the ignored Study Times in the calculation.


Restricted Recording of Contingencies Results

Do not record contingency result if base case is above... If in the pre-fault load flow elements have loadings above this value, then they are not recorded in the results.

Output per Contingency Case

ShortDisplays only the number of iterations required for each contingency case.

DetailedDisplays the full load flow output per contingency case.

30 - 15


Consider Predefined Switching Rules of SubstationsIf this option is selected, predefined switching rules which describe switching actions for different fault locations will be considered. For more information on Switching Rules, please refer to Chapter 5.

Criteria for AC Recalculation of Critical DC CasesIf the calculation method DC Load FLow + AC Load Flow for Critical Cases is selected, the recalculation of critical DC cases using the AC load flow method is performed whenever:

1 The maximum loading of a component is greater than or equal to the first value specified; for example 100% (parameter name: maxLoadAbs); or

2 The maximum loading of a component is greater than or equal to the second value specified; for example 80% (parameter name: maxLoad) and the maximum relative change of loading compared to the base case is equal to or greater than the value specified; for example 5% (parameter name: stepLoad).

In addition to these settings, if required, the user can define a set of components to be ignored in the AC recalculation or to ignore components if they are already overloaded in the base case. This set of components is assigned via the Components to be ignored field.

Fig. 30.10: Advanced Options Settings of the Contingency Analysis Command

30.3.6 Parallel Computing

There are two types of settings associated with the Parallel Computing option. The first and more general group of settings are the ones related to the management of the parallel computation function (computing method and the assignments of slaves). To access and modify these settings; log-on first as an administrator and afterwards open a Data

30 - 16


Manager window. Locate and edit the Parallel Computing Manager (\System\Configu-ration\Parallel Computation\) as indicated in Figure 30.11.

The users can however define their own settings by creating a system folder (with key "Parallel") under the folder "\\Configuration" and then creating the setting object "ComParalman". This can only be carried out when logged on as administrator.

The available options are:

Master Host Name or IPRefers to the machine name or IP address of the master host. If a local multi-core machine is used, the name "localhost" can be used.

Parallel Computing Method1) Local Machine with Multi Cores/Processors: All the slaves will be started in the local machine.2) Local Machine Plus Remote Machines: The slaves will be started in both the local and remote machines.

Number of SlavesDefines the number of slaves that will be started in the local machine. This number should not be greater than the number of cores available in the local machine.

Computer GroupSpecifies the link to a computer group (number of remote machines) which will be used for parallel computing.

Fig. 30.11: Parallel Computing Manager

The second group of settings are the ones related to the execution of the contingency analysis; and which are located in the Parallel Computing tab page of the contingency analysis command (Figure 30.12).

30 - 17


Enable Parallel Contingency Analysis for AC, DC or Time SweepIf the corresponding option is enabled, the contingencies will be calculated in parallel; otherwise the contingency analysis is executed in its default mode (i.e. sequential calculation).

Minimum Number of ContingenciesThe parallel contingency analysis will be started only if the number of contingencies is greater than this setting.

Package Size for Optimized Method and Package Size for Standard Method The master distributes the contingencies to slaves per package. The package size indicates how many contingencies will be calculated by a slave each time. The contingencies can be calculated using either optimized method or standard method. As the standard method is much slower than optimized method, the package size of the standard method should be smaller than that used for the optimized method to balance the calculation.

Fig. 30.12: Parallel Computing Settings of the Contingency Analysis Command

30.3.7 Calculating an Individual Contingency

To calculate an individual contingency, click on the Show button in the contingency analysis command dialogue (see Figure 30.6) to open the list of contingencies included in the analysis. From here the user can right-click on a contingency of interest, and select Execute from the context sensitive menu. Additionally, the corresponding element can be marked in the single line graphic by right-clicking on the contingency object in the list and selecting Mark in Graphic from the context sensitive menu.

30.3.8 Representing Contingency Situations - Contingency Cases

Contingency cases (ComOutage objects) are objects used in PowerFactory to define contingency situations within the analyzed networks. A contingency case determines which components are put on outage. When a contingency analysis (ComSimoutage) is executed, the contingency analysis command considers each of the contingency cases stored inside it, taking the corresponding components out of service and performing a

30 - 18


contingency load flow.

As mentioned previously, the contingency cases used by a specific contingency analysis command are stored inside the command itself. Contingency cases are created either by using Fault Cases and/or Fault Groups (see Section 30.5), or via the Contingency

Definition command ( , see Section 30.6). Once the contingencies have been defined in the contingency command, the cases can be viewed by using the Show button available in the dialogue (see Figure 30.6). Additionally, the contingency cases within the active study case’s contingency analysis command may be viewed by clicking on the Show

Contingencies icon ( ), located on the main toolbar (only available when the Contin-

gency Analysis toolbar is selected). In both cases a new data browser showing the defined contingencies is opened, with the contingencies listed inside. By double-clicking on a contingency from the list, the corresponding dialogue for that particular contingency is opened (as illustrated in Figure 30.13). The dialogue displayed in Figure 30.13 shows the following fields:

NameName of the contingency case.

Not AnalyzedIf enabled, the case is not considered by the contingency analysis command.

NumberAn identification number given to the contingency and which is stored in the results. This number can be used for reporting purposes.

Fault CaseReference to the fault case (if any) from where the contingency case originated.

Fault GroupReference to the fault group (if any) from where the contingency case originated. This field is only available if the contingency case has an associated fault group.

Events Used for this Contingency (Multiple Time Phase only)The user can specify wether to generate the events based on the fault case definition (automatically), or to use locally defined events. If the user chooses to use locally defined events, then the ComOutage object which defines the contingency (located in contingency command of the study case) can be modified independently.

Interrupted ComponentsThis is a table showing the components put on outage by the contingency case. The table, which is read-only, is automatically generated when the contingency case is created.

Fault TypeDisplays the fault type and the contingency order. See Figure 30.18.

Contingency AnalysisReference to the contingency analysis command where the contingency case is stored.

30 - 19


The Mark in Graphic button highlights the interrupted components in the single line diagram.

Fig. 30.13: Contingency Cases (ComOutage objects)

Normally, contingency cases (ComOutage objects) are analyzed by the contingency analysis command (ComSimoutage) in which they are stored. However, each contin-gency case provides the functionality of a command itself, and can be executed individ-ually using the Execute button at the top right of the ComOutage dialogue. In this case the actions taken by the circuit breakers, which must switch to clear the fault, are shown in the single line graphic (only if the contingency case was created using fault cases/groups).

Note: The 'Interrupted Components' table is updated by the program each time the contingency analysis is executed.

For further information on contingency cases generated using fault cases and/or fault groups, please refer to Section 30.5 (Creating Contingency Cases Using Fault Cases and Groups). For information on contingency cases created using the Contingency Definition(ComNmink) command, please refer to Section 30.6 (Creating Contingency Cases Using the Contingency Definition Command).

30 - 20


30.4 The Multiple Time Phases Contingency Analysis Command

As explained in Section 30.2 (Executing Contingency Analyses), the multiple time phases contingency analysis is executed with the same contingency analysis command (ComSi-moutage) as that used for the single time phases contingency analysis. In the multiple time phases configuration it determines the initial operational condition of the system via a 'base' load flow calculation. Following this, it loops over the defined time phases for each stored contingency (ComContingency object). Load flow calculations are performed which consider the contingency events whose time of occurrence is earlier than, or equal to, the Post Contingency Time, which is set in the corresponding load flow command.

As a result of the execution of the Contingency Analysis command, the steady-state operational point of the network at the Post Contingency Time, for every contingency, is obtained. The calculated results are filtered according to user defined criteria and recorded in the Results (ElmRes) object referred to by the Contingency Analysis command.

When configured to perform contingency analysis with multiple time phases, the Contin-gency Analysis command stores the contingencies to be analyzed within the command itself. If different settings for the contingency load flow are stated, a folder (named Time Phases) is also stored within the command; this folder contains the load flow commands that define the time phases. The user may define as many contingencies and time phases as required, following the procedures explained in this section.

The Contingency Analysis command can be accessed via the main toolbar by clicking on

the icon (provided that the Contingency Analysis toolbar has already been selected). The following subsections present the options available in the dialogue provided that the user has selected the Multiple Time Phases method in the contingency command (Multiple Time Phases tab).


Calculation Method

This setting is configured as described for Single Time Phase operation. Please refer to Section 30.3.1 (Basic Options). Only AC Load Flow Calculation and DC Load Flow Calcu-lation methods are available (no DC Load Flow + AC Load Flow for Critical Cases).


This setting is configured as described for Single Time Phase operation. Please refer to Section 30.3.1 (Basic Options).

Contingencies

This setting is configured as described for Single Time Phase operation. Please refer to

30 - 21


Section 30.3.1 (Basic Options).

Results for AC/DC

This setting is configured as described for Single Time Phase operation. Please refer to Section 30.3.1 (Basic Options).

30.4.2 Effectiveness

These options are only available for the Single Time Phase calculation. Please refer to Section 30.3.2 (Effectiveness).

30.4.3 Multiple Time Phases

The Multiple Time Phases tab, as shown in Figure 30.14, allows the selection of the contingency method as well as its corresponding settings. Although most of the setting descriptions are similar to those given for the Single Time Phase method, they are reviewed here.

Fig. 30.14: Multiple Time Phases Option Settings of the Contingency Analysis Command (Multiple Time Phases Method)

Method

Single Time PhasePerforms the contingency analysis for a single time phase.

Multiple Time PhasePerforms the contingency analysis for a multiple time phases, allowing the definition of post-fault actions.

30 - 22


Base Case versus Contingency Load Flow

Use same settingsUses the settings from the base case load flow for the contingency case load flow.

Allow different settingsAllows different settings for the base case load flow and the contingency case load flow.


Load Flow Only available when option Use same settings is selected in the Base Case versus Contingency Load Flow section of the Advanced Options tab. This is a reference to the load flow command used to calculate both the network operational point before the simulation of contingencies, and the contingency load flow(s). The settings of this

load flow command can be edited by pressing the button.

Base Case Load FlowOnly available when option Allow different settings is selected in the Base Case versus Contingency Load Flow section of the Advanced Options tab. This is a reference to the load flow command used to calculate the network operational point before the simulation of contingencies. The settings of this load flow command can be edited by

pressing the button.

Time Phase n

Lists the defined time phase(s). The button next to each time phase can be used to remove the corresponding time phase. If the option Allow different settings has been selected on the Advanced Options tab, the Time Phase will have its corresponding load

flow accessible by pressing the button next to the defined time phase.

Add Time PhaseOpens an input dialogue to define the new time phase by entering its Post Contingency Time. If the option Allow different settings has been selected on the Advanced Options tab, the previous load flow settings (i.e. those with the preceding occurrence in time) will be used for the new time phase. In the case that there is no previous time phase load flow, the base case settings will be used for the new time phase.

Use Base Case Settings for AllCopies the settings from the base case load flow to all time phase load flows.

30 - 23


Post contingency time for order identification

The order of the contingencies stored inside the command is calculated according to the time defined in this field. Only the events (actions) taking place before this point in time are considered when calculating the contingency order.

Note: In PowerFactory a region is defined as a set of topologically con-nected components. A region is interrupted if it is energized (topo-logically connected to a network reference bus) before a fault and de-energized afterwards. The order of a contingency corresponds to the number of interrupted regions at the time of its calculation (i.e. the 'Post contingency time for order identification').

30.4.4 Time Sweep

This option is only available for the Single Time Phase calculation. Please refer to Section 30.3.4 (Time Sweep).


This setting is configured as described for Single Time Phase operation. Please refer to Section 30.3.5 (Advanced Options).

30.4.6 Parallel Computing

This option is only available for the Single Time Phase calculation. Please refer to Section 30.3.6 (Parallel Computing).

30.4.7 Defining Time Phases for Contingency Analyses

The time phases of a contingency analysis are defined in the Calculation Settings section of the Multiple Time Phases tab of the Contingency Analysis command, by specifying a Post Contingency Time for each defined time phase. A specified Post Contingency Timedefines the end of a time phase and is used to determine which events (actions) from the analyzed contingency are considered. If the time of occurrence of an event from a contin-gency occurs earlier than or equal to the Post Contingency Time, the event will be considered in the corresponding load flow calculation.

Each defined time phase uses a corresponding load flow calculation, and by default, this is the same load flow calculation as that used for the base case load flow. In this case, the load flow used for the entire contingency analysis calculation is accessible via the Load

Flow field ( ), as shown in Figure 30.15. If the option Allow different settings in the Base Case versus Contingency Load Flow section of the Multiple Time Phases tab is selected, the user can define individual load flow commands for each time phase, as illus-

trated in Figure 30.16. Access to each load flow command and its settings is via the button.

30 - 24


Fig. 30.15: Same Settings for Base Case and Contingency Load Flows

Fig. 30.16: Different Settings for Base Case and Contingency Load Flows

Note: Transformer tap changer controllers and switchable shunts are only considered by a time phase if their time constants are smaller than the current Post Contingency Time. The operational thermal ratings of branch elements during a contingency (if 'short term' thermal ratings (see Section 5.5.7) have been defined) will also de-pend on the duration of the contingency (i.e. the current Post Con-tingency Time).

The Contingency Analysis time phases (which are essentially just load flow commands) are stored within a folder inside the ComSimoutage command and can be accessed in

several ways. One way is by clicking on the button next to each defined time phase in the Calculation Settings section of the Multiple Time Phases tab; by doing so, the edit dialogue of the corresponding load flow command pops up.

Another way is through the Data Manager. After performing a contingency analysis, a contingency command object (ComSimoutage) is created inside the current active Study Case. If the contingency analysis was performed using the Multiple Time Phasesmethod (with different load flow settings), then a Time Phases folder with the corre-sponding time phase load flow commands will be created inside the contingency analysis, as illustrated in Figure 30.17.

30 - 25


Fig. 30.17: Location of the Time Phases Folder

New time phases can be defined in the data browser by clicking on the Add Time Phase

button. Existing time phases can be deleted using the button. Note that after several time phases have been defined, this list is then scrollable using the up/down arrow

buttons ( ) available in the dialogue.

30.4.8 Representing Contingency Situations with Post-Fault Actions

Contingency situations which include post-fault actions are represented in Power-Factory via objects called 'contingencies' (ComOutage, ). The contingencies are defined by a set of events which represent:

• Faults on the selected components;

• The switching actions carried out to isolate the faulty components; and

• The post contingency actions taken in order to mitigate the subsequent voltage band problems and/or supply interruptions.

Load Flow Commands of the Time Phases

Time Phases FolderContingency Analysis Command

30 - 26


Contingencies are created based on fault cases defined in the Operational Library. These fault cases define the location of the fault events, and may also define post contingency actions taken to isolate the fault and mitigate the effects of the outage of the component(s). Whenever a new contingency is created, a link from the ComOutageobject to the fault case is set. New contingencies can be created in a Contingency Analysiscommand by clicking on the Add Cases/Groups button in the Configuration section of the Basic Data tab (see Section 30.3.1: Basic Options).

Besides the events which are transferred from the linked fault case during calculation of the contingency case, the user has the possibility of defining additional post contingency actions in the contingency by manually creating new events.

The contingencies calculated in a Contingency Analysis, are stored inside the command itself and can be accessed using the Show button (see Figure 30.6). Alternatively, the contingencies in the Contingency Analysis command contained in the active study case

can be viewed by clicking on the Show Contingencies icon ( ) on the main toolbar. In both cases a new data browser listing the defined contingencies is shown. By double-clicking on a selected item from the list, the edit dialogue of the corresponding contin-gency (Figure 30.13) pops up.

Normally, contingency cases are analyzed by the Contingency Analysis command in which they are stored. However, each case provides the functionality of a command and can be executed individually using the Execute button at the top right of the ComOutage dialogue (see Figure 30.13). In this case, all of the time phases are executed for the selected contingency considering its associated events. The results observed in the single line graphic correspond to those from the last time phase, including the final states of the network switches.

The events that define a contingency can be displayed in a list format in a new data browser by pressing the Events button in the fault case (IntEvt) dialogue (as shown in Figure 30.20). This data browser can be used to edit and/or delete the listed events. New

events can be created by using the New icon at the top of the opened browser window. Only four different types of events are allowed in the contingency analysis as post-fault actions, which are:

• Load Event (EvtLod)

• Dispatch Event (EvtGen)

• Switch Event (EvtSwitch)

• Tap Event (EvtTap)

It should be noted that events created locally in the contingency object are only considered if the ComOutage option Use locally defined events (User defined) is selected in the Events Used for this Contingency field.

The Start Trace button ( ) (available on the main toolbar) can be used to follow the behavior of the system over time. When this button is pressed, a dialogue opens allowing the user to select a contingency. Following the selection of a contingency by the user and pressing OK, the contingency dialogue is closed and the base case load flow is executed. The execution of the first event(s) and all subsequent event(s) is initiated by pressing the

Next Time Step button ( ) on the main toolbar. At each time step the load flow calcu-lation results and the state of the network circuit breakers are displayed in the single line

30 - 27


graphic. It should be noted that the Next Time Step evaluates events according to their time of occurrence, and not according to the time phases defined in the Contingency Analysis command. After the last time event(s) have been executed, the Next Time Step

button becomes inactive. The Stop Trace button ( ) can be pressed to clear the calcu-lation. Alternatively, the Trace button in each ComOutage dialogue can be used to initiate the Trace for that particular contingency.

Note: The 'Trace' functionality can be started directly from the main tool-

bar by pressing the 'Start Trace' button ( ). In this case a data browser listing all available contingencies (i.e. those stored inside the 'Contingency Analysis' command of the active study case) is displayed. After the user selects the desired contingency by dou-ble-clicking on it, the 'Base Case' load flow is executed. The subse-quent event(s) are then calculated using the 'Next Time Step' button.

30.5 Creating Contingency Cases Using Fault Cases and Groups

Contingency cases created from fault cases can be regarded as contingency situations produced in a network as a consequence of the clearing of a fault. Fault cases without switching events (created following the procedure described in Section 14.2.3: Fault Cases and Fault Groups) are used to automatically generate contingency cases in the contingency analysis command, by pressing the Add Cases button and selecting the desired objects from the data browser that pops up.

For every selected fault case, the calculation automatically detects which circuit breakers must open in order to clear the defined fault(s). All components which lose their connection to the network reference bus following the switching actions that clear the fault(s), are regarded as 'interrupted' and are subsequently added to the Interrupted Components table of the corresponding contingency case. In other words, these compo-nents are put on outage by the contingency case.

Depending on the fault defined in the fault case that generates a contingency, the Fault Type field in the contingency case dialogue (Figure 30.18) is set to:

• Busbar fault: If the contingency originates from a fault on a busbar

• n-k fault: With contingency order equal to k (where k >= 0). k corresponds to the number of network regions (sets of topologically connected components) which are disconnected during a fault, by the switching actions performed. It should be noted that the switching actions which are considered depend on the post contingency time used by the update (this time differs between single- and multiple time phase analyses).

30 - 28


Fig. 30.18: Fault Type Field in the Contingency Case (ComOutage) Dialogue

Note: In PowerFactory an interrupted component is a network primary element that is energized before a fault and de-energized after-wards. A component is considered to be energized if it is topolog-ically connected to a network reference bus. A region is defined as a set of topologically connected components. Like components, re-gions can have energized, de-energized and interrupted states, de-pending on their connection to a network reference bus.

Contingency cases can be created from fault cases/groups, which reside in the Opera-tional Library, by pressing the Add Cases/Groups button in the contingency analysis command (see Section 30.3.1 (Basic Options) and Figure 30.6). In the case of creating contingencies from fault group(s), a contingency case will be generated for each fault case referred to in the selected fault group(s).

Note: The 'topological search' algorithm used by the program to set con-tingency cases from fault cases requires the explicit definition of at least one reference bus in the analyzed system. A bus is explicitly set as a reference if it has connected to it either a synchronous generator (ElmSym), or an external network (ElmExtnet) with the option 'Reference Machine' enabled (available on the element’s 'Load Flow' tab).

30.5.1 Browsing Fault Cases and Fault Groups

There are two types of subfolder inside the Faults folder in the Operational Library: Fault Cases and Fault Groups.

30 - 29


Fig. 30.19: Contents of the Faults folder in the Operational Library

In order to make a new folder of either of these types, left-click on the Faults folder icon

( ) and then press the "New Object" button ( ) on the Data Manager toolbar. In the drop-down list, select whether a new Fault Cases or Fault Groups folder should be created.

The Fault Cases folder holds every contingency (n-1, n-2, or simultaneous) defined for the system, as described in Section 30.5.2 (Defining a Fault Case). Alternatively, several fault cases can be selected and stored in a Fault Group, as described in Section 30.5.3 (Defining a Fault Group).

30.5.2 Defining a Fault Case

To define a fault case for an element in the grid, select it in the single-line diagram. Then right-click and choose one of: Define … --> Fault Case --> Single Fault Case or Define ...--> Fault Case --> Multiple Fault Cases, n-1 (or Multiple Fault Cases, n-2) or Define ... --> Fault Case --> Mutually Coupled Lines/Cables, n-k.

If Multiple Fault Cases, n-2 is selected, fault cases will be created for the simultaneous outage of every unique combination of two elements in the selection. If the user selects Single Fault Case, a fault case will be created for the simultaneous outage of all elements in the selection.

If Mutually Coupled Lines/Cables, n-k is selected, then fault cases will be created for the simultaneous outage of each coupled line in the selection.

Alternatively, a filter can be used. This can be done (for example) with the help of the Edit

Relevant Objects for Calculation button ( ), to list all elements for which outages are to be defined. These elements can then be highlighted and the user can then right-click on the highlighted selection and choose (for example) Define … --> Fault Case.... The Simulation Events/Fault dialogue opens, as shown in Figure 30.20, where the user can enter the desired name of the fault case in the Name field.

On the second page of the Basic Data tab of the same dialogue, the user can create

30 - 30


the corresponding switch events, by clicking on the Create Switch Events button.

Fig. 30.20: Creation of Fault Case (IntEvt)

Fault cases can also be defined by the Contingency Definition command, as explained in Section 30.6 (Creating Contingency Cases Using the Contingency Definition Command).

For further background on fault cases, please refer to Section 5.5.3 (Faults).

30.5.3 Defining a Fault Group

To define a fault group, left-click on the Fault Groups folder. Then click on the 'New Object'

button ( ). A Fault Group dialogue pops up as shown in Figure 30.21. In this dialogue the user can specify the name of the fault group in the Name field, and add fault cases to this new group using the Add Cases button. Click the Cases button to view existing cases (if any) in the fault group.

Fig. 30.21: Creation of Fault Group (IntFaultgrp)

Note: When a fault group is defined and fault cases are added to it, a ref-erence is created to each of these fault cases. The fault case itself resides in the Fault Cases subfolder. This means that if an item in the fault group is deleted, only the reference to the fault case is deleted. The fault case itself is not deleted from the Fault Cases subfolder.

30 - 31


30.6 Creating Contingency Cases Using the Contingency Definition Command

The Contingency Definition command (ComNmink) is used to automatically generate contingency cases based on selected components. It is accessible via the Contingency

Analysis toolbar ( ) but using the button. The Contingency Definition command can be used to automatically generate contingency cases for either (i) a user-defined selection of elements; or (ii) pre-defined sets of elements. These two approaches are now described.

To generate contingency cases for a user-defined selection of elements:

Select the components to be put on outage either by multi-selecting them in the single line graphic or the Data Manager.

Right click on the selection and choose Calculate --> Contingency Analysis... from the context sensitive menu. This command will create a list with references to the selected objects inside the Contingency Definition command (ComNmink). The command dialogue shown in Figure 30.22 will pop up.

Select the required outage level.

Select the Creation of Contingencies option according to how the contingencies should be handled (see explanation of options below) and click on Execute.

To generate contingency cases for either the complete system or from pre-defined sets of elements:

Click on the icon on the main toolbar to open the command;

Select the option Whole System in the Create Cases for field;

Select the required pre-defined set of elements (for example transformers and lines);

Select the Creation of Contingencies option according to how the contingencies should be handled (see explanation of options below) and click on Execute.

30 - 32


Fig. 30.22: Contingency Definition Dialogue (option: Generate Contingencies for

Analysis)

Once the Contingency Definition command is executed, it generates the corresponding contingency cases according to the options and elements selected. The Contingency Analysis command, which is automatically created inside the current active Study Case is then automatically opened. The created contingencies can be analyzed by executing this already-opened Contingency Analysis command. Note that when a new list of contin-gencies is created using the Contingency Definition command, the previous content of the contingency analysis command is overwritten.

It is also possible to open the Contingency Definition command directly from the Contin-

gency Analysis toolbar ( ), without any previous selection, by clicking on the icon. In this case, contingencies for all elements within the network (selected according to their class, as described below), can be created.

The Contingency Definition command offers the following options to generate contin-gency cases from the selected objects:

Creation of Contingencies

Generate Fault Cases for LibraryGenerates fault cases which are stored in the Operational Library, in a folder named Faults.

Generate Contingencies for AnalysisGenerates contingencies which are stored in the contingency analysis command, and then opens the contingency analysis command (ComSimoutage) dialogue.

30 - 33


Outage Level

n-1Creates single contingency cases for each of the selected components.

n-2Creates contingency cases for every unique combination of two selected components.

n-k cases of mutually coupled lines/cablesCreates contingency cases for every set of mutually coupled lines/cables. If for example, three lines are modeled as having a mutual coupling, by selecting this option a fault case is created considering the simultaneous outage of the three coupled lines.

Lines/cables

Contingency cases according to the selected outage level will be generated for all lines and cables (ElmLne objects) in the system.

Transformers

Contingency cases according to the selected outage level will be generated for all trans-formers (ElmTr2, ElmTr3 objects) in the system.

Generators

Contingency cases according to the selected outage level will be generated for all synchronous generators (ElmSym objects) in the system.

Series Capacitors

Contingency cases according to the selected outage level will be generated for all series capacitors (ElmScap objects) in the system.

Series Reactors

Contingency cases according to the selected outage level will be generated for all series reactors (ElmSind objects) in the system.

The selection of elements to outage in the Contingency Definition command can also be created by the use of DPL scripts. Please refer to the ComNmink methods in the appendix DPL Reference.

Note: It is important to note the difference between contingency cases created from fault cases and contingency cases created with the Contingency Definition command. In the former, the cases are re-garded as the outage of certain network components as a conse-quence of fault clearing switching actions, with the fault(s) being defined by the fault case and the switching actions automatically

30 - 34


calculated by the program. In the latter, the cases are regarded as contingency situations generated by the outage of a selected group of components.

30.7 Comparing Contingency Results

In order to compare contingencies in a fast and easy way, PowerFactory provides a

Contingency Comparison function ( ). The Contingency Comparison function is only enabled if the user has previously defined the contingency cases in the Contingency Analysis command, as explained in Sections 30.5 (Creating Contingency Cases Using Fault Cases and Groups) and 30.6 (Creating Contingency Cases Using the Contingency Definition Command). The general handling of the Contingency Comparison function is as follows:

1 Define the contingency cases in the Contingency Analysis command (see Sections 30.5: Creating Contingency Cases Using Fault Cases and Groups and 30.6: Creating Contingency Cases Using the Contingency Definition Command).

2 Click on the Contingency Comparison button ( ). A window will pop up allowing the user to select the required contingency cases (Figure 30.23). The selection can correspond to one, several, or all contingency cases.

Fig. 30.23: Selection of Contingency Cases for Comparison

30 - 35


3 By clicking on the OK button, the Comparing of Results On/Off button (Figure 30.24) is enabled and the selected contingency cases are automatically executed.

Fig. 30.24: Comparing of Results Button

4 The single line graphic result boxes will display the results, based on the comparison mode and the two compared cases. By default, the comparison is made between the Base Case and the last selected contingency case in the list.

5 To change the comparison mode and/or the cases to be compared, click on the Edit Comparing of Results button (Figure 30.24). The Compare dialogue will pop up displaying the current settings. To change the cases to be compared, click on the

black arrow pointing down ( ) and select a different case (Figure 30.25).

Fig. 30.25: Selection of other Cases for Comparison

6 If the contingency analysis is defined with time phases, the compare dialogue will have the option of selecting the time phase.

7 Once the calculation is reset (for example by either making changes in the model or by clicking on the Reset Calculation button), the comparison mode will be disabled.

Comparing of Results Button

Edit Comparing of Results Button

30 - 36



30.8.1 Predefined Report Formats (Tabular and ASCII Reports)

In PowerFactory the Contingency Analysis function has a special set of predefined report formats that can be launched by clicking on the Report Contingency Analysis

Results button ( ), which is illustrated in Figure 30.4. The Report Contingency Analysis Results button will only be enabled if the user has previously executed the Contingency Analysis command, as explained in Section 30.2 (Executing Contingency Analyses). Once the reporting of results has been launched, the dialogue window illustrated in Figure 30.26 will be displayed.

Fig. 30.26: Contingency Analysis Reports Dialogue

The following types of report can be selected:

• Maximum Loadings:Only the maximum loaded component (according to the specified loading limit) for each contingency is displayed in a single list.

• Loading Violations:All overloaded components (according to the specified loading limit) for each contingency are displayed in a single list.

Additional Filter Settings

Type of Report

Output Format Selection: Tabular or ASCII

Study Time Definition for Reporting

30 - 37


• Voltage Steps: All voltage deviations of terminals (between the base case and the contingency case) for each contingency are displayed in a single list. Reports the highest voltage deviation of terminals (between the base case and the contingency case) considering all contingencies. Any such terminal is reported only once. Only terminals with the highest voltage deviation greater than the specified maximum voltage step are reported.

• Maximum Voltages: Reports the greatest voltage violation of a terminal (greater than or equal to the specified voltage limit) considering all contingencies. Any such terminal is reported only once (i.e. it is reported for the contingency causing this violation).

• Minimum Voltages:Reports the greatest voltage violation of a terminal (less than or equal to the specified voltage limit) considering all contingencies. Any such terminal is reported only once (i.e. it is reported for the contingency causing this violation).

• Maximum Voltage Violations: Reports all voltage violations of a terminal (greater than or equal to the specified upper voltage limit) considering all contingencies.

• Minimum Voltage Violations: Reports all voltage violations of a terminal (less than or equal to the specified lower voltage limit) considering all contingencies.

• Loading Violations per Case: All overloaded components (according to the specified loading limit) for each contingency are displayed in separate lists (i.e. one list per contingency case).

• Voltage Violations per Case: All busbars with exceeding voltage (maximum or minimum) are displayed in separate lists.

• Generator Effectiveness:Generators having an effectiveness greater than or equal to the specified value (%) are displayed in a single list.

• Quad-Booster Effectiveness:Quad-booster transformers having an effectiveness greater than or equal to the specified value (MW/Tap) are displayed in a single list.

• Non-convergent Cases:The non-convergent cases of the contingency analysis are displayed in a list.

30 - 38


Fig. 30.27: Tabular Report of Loading Violations

The tabular format (Figure 30.27) for reporting has the following sections:

• Header:Identifies the report and its data.

• Filter:Represented as drop-down lists, allowing the selection of one item at a time or as "Custom".

• Table:Matrix of rows and columns containing cells that can refer to an object and provide actions such as "Edit", "Edit and Browse" and "Mark in Graphic". It also supports copy and paste, scroll features, page up and down keys as well as Ctrl+Pos1, Ctrl+End and HTML view.

Although the tabular reports are already predefined, the user can modify them if required (by going to the second page of the Report Contingency Analysis Results dialogue and clicking on the blue arrow pointing to the right of the Used Format definition).

Column Header

Loading Limit Specification

Filter

30 - 39


30 - 40

DIgSILENT PowerFactory Reliability Assessment

Chapter 31Reliability Assessment

Reliability assessment involves determining, generally using statistical methods, the total electric interruptions for loads within a power system. The interruptions are described by several indices that consider aspects such as:

• the number of customers;

• the connected load;

• the duration of the interruptions;

• the amount of power interrupted; and

• the frequency of interruptions.

Other measures of reliability such as voltage sags and swells can also be considered as part of a reliability assessment.

The reliability assessment module of PowerFactory offers two calculation functions:

Network reliability assessment:The probabilistic assessment of power system interruptions during an operating period.

Voltage sag assessment:The probabilistic assessment of the frequency and severity of voltage sags during an operation period.

Both of these calculation methods have different applications. Network reliability assessment is used to calculate expected interruption frequencies and annual interrup-tions costs, or to compare alternative network designs. Voltage sag assessment is used to determine the expected number of equipment trips due to deep sags.

Reliability analysis is an automation and probabilistic extension of contingency evaluation. For such analysis, you are not required to pre-define outage events, instead the tool can automatically choose the outages to consider. The relevance of each outage is considered using statistical data about the expected frequency and duration of outages according to component type. The effect of each outage is analyzed automatically such that the software simulates the protection system and the network operator's actions to re-supply interrupted customers. Because statistical data regarding the frequency of such events is available, the results can be formulated in probabilistic terms.

This chapter deals with probabilistic Network Reliability Assessment. For information on PowerFactory’s deterministic Contingency Analysis, please refer to Chapter 30 (Contin-gency Analysis).

The reliability assessment functions can be accessed by activating the reliability toolbar

using the icon on the toolbar selection control as illustrated in Figure 31.1.

31 - 1


Fig. 31.1: Reliability Toolbar Selection

The basic user procedure for completing a reliability assessment consists of the following steps as shown in Figure 31.2. Steps on the left are compulsory, while steps on the right are optional and can be used to increase the detail of the calculation.

Fig. 31.2: Reliability Assessment User Procedure

Reliability toolbar selection

Reliability Assessment Calcu-

View Considered Contingencies

Create Load States

Start Fault Trace

31 - 2


These procedures are explained in detail in the following sections

31.1 Probabilistic Reliability Assessment - Technical Background

The Reliability Assessment procedure considers the network topology, protection systems, constraints and stochastic failure and repair models to generate reliability indices. The technical background of the procedure and Stochastic Models is described in this sub-chapter.

31.1.1 Reliability Assessment Procedure

The generation of reliability indices, using the Reliability Assessment tool also known as 'reliability analysis', consists of the following:

• Failure modeling;

• Load modeling;

• System state creation;

• Failure Effect Analysis (FEA);

• Statistical analysis; and

• Reporting

Fig. 31.3: Reliability Analysis: Basic Flow Diagram

The reliability analysis calculation flow diagram is depicted in Figure 31.3. The failure models describe how system components can fail, how often they might fail and how long it takes to repair them when they fail. The load models can consist of a few possible load demands, or can be based on a user-defined load forecast and growth scenarios.

The combination of one or more simultaneous faults and a specific load condition is called a 'system state'. Internally, PowerFactory’s system state generation engine uses the failure models and load models to build a list of relevant system states. Subsequently, the Failure Effect Analysis (FEA) module analyzes the faulted system states by simulating the

Electric System Model

System State Generation

Failure Effect Analysis

Statistical Evaluation

Failure ModelsLoad Models

31 - 3


system reactions to these faults. The FEA takes the power system through a number of post-fault operational states that can include:

• Fault clearance by tripping of protection breakers or fuses;

• Fault separation by opening separating switches;

• Power restoration by closing normally open switches;

• Overload alleviation by load transfer and load shedding.

• Voltage constraint alleviation by load shedding (distribution option only).

The objective of the FEA function is to determine if system faults will lead to load inter-ruptions and if so, which loads will be interrupted and for how long.

The results of the FEA are combined with the data that is provided by the system state generation module to create the reliability statistics including indices such as SAIFI, SAIDI and CAIFI. The system state data describes the expected frequency of occurrence of the system state and its expected duration. However, the duration of these system states should not be confused with the interruption duration. For example, a system state for a line outage, perhaps caused by a short-circuit on that line, will have a duration equal to the time needed to repair that line. However, if the line is one of two parallel lines then it is possible that no loads will be interrupted because the parallel line might be able to supply the full load current.

Even if the loads are interrupted by the outage, the power could be restored by network reconfiguration - by fault separation and closing a back-feed switch. The interruption duration will then equal the restoration time, and not the repair duration (equivalent to the system state duration).

31.1.2 Stochastic Models

A stochastic reliability model is a statistical representation of the failure rate and repair duration time for a power system component. For example, a line might suffer an outage due to a short-circuit. After the outage, repair will begin and the line will be put into service again after a successful repair. If two states for line A are defined as 'in service' and 'under repair', monitoring of the line could result in a time sequence of outages and repairs as depicted in Figure 31.4.

Fig. 31.4: Line availability states are described by the status of the line (in service or under repair). Each of these states lasts for a certain time.

Line A in this example fails at time T1 after which it is repaired and put back into service at T2. It fails again at T3, is repaired again, etc. The repair durations R1=T2-T1, R2=T4-T3, etc. are exaggerated in this example.

The repair durations are also called the 'Time To Repair' or 'TTR'. The service durations

AA

R1 R2 R3S2 S3 S4

tT1 T2 T3 T4 T5 T6

31 - 4


S1=T1, S2=T3-T2, etc. are called the 'life-time', 'Time To Failure' or 'TTF'.

Both the TTR and the TTF are stochastic quantities. By gathering failure data about a large group of similar components in the power system, statistical information about the TTR and TTF, such as the mean value and the standard deviation, can be calculated. The statistical information is then used to define a Stochastic Model.

There are many ways in which to define a Stochastic Model. The so-called 'homogenous Markov-model' is a highly simplified but generally used model. A homogenous Markov model with two states is defined by:

• A constant failure rate ; and

• A constant repair rate .

These two parameters can be used to calculate the following quantities:

• mean time to failure, TTF = 1/;

• mean time to repair, TTR = 1/;

• availability, P = TTF/(TTF+TTR);

• unavailability Q, = TTR/(TTF+TTR);

The availability is the fraction of time when the component is in service; the unavailability is the fraction of time when it is in repair; and P+Q = 1.0.

For example, if 7500 monitored transformers were to show 140 failures over 10 years, during which a total of 7360 hours was spent on repair, then:

These equations also introduce some of the units used in the reliability assessment:

• frequencies are normally expressed in [1/a] = 'per annum' = per year;

• lifetimes are normally expressed in [a] = 'annum';

• repair times are normally expressed in [h] = 'hours';

14010 7500---------------------- 1

a--- 0,00187

1a---= =

TTF1--- 536a= =

TTR7360140------------ h 52,6h 0,006a= = =

1TTR------------ 167

1a---= =

P536

536 0,006+---------------------------- 0,999989= =

Q0,006

536 0,006+---------------------------- 6

mina

----------= =

31 - 5


• probabilities or expectancies are expressed as a fraction or as time per year ([h/a], [min/a]).

A homogenous Markov model can also have more than two states. This kind of model can be used to distinguish between faults that are repaired quickly, and faults that take longer to repair. Two repair states are then defined, each with a different mean repair time.

The homogenous Markov model is memory-less. For instance, if preventive maintenance is performed to improve the reliability of a component, it does not make a difference if the last maintenance was completed one week or 5 years ago, or even if maintenance was performed at all. The probability that the component will fail in the next period will be equal in all cases. Therefore, the effect of changing preventive maintenance strategies cannot be calculated when using the homogenous Markov model.

Additionally, because of the memory-less quality, all repairs are similar, with the only difference the mean duration. Interruption costs, however, might be dependent on the fraction of repairs that take longer than a certain amount of time. For example, a repair might take 2 hours on average, but when compensation has to be paid for interruptions longer than 3 hours, and when such long repairs occur in 20% of all cases, using the mean duration alone will not produce correct results. Consequently, a realistic assessment of interruption costs is not possible when using the homogenous Markov model.

31.1.3 Calculated Results for Reliability Assessment

The network reliability assessment produces two types of indices:

• Load point indices

• System indices

These indices are separated into frequency/expectancy indices and energy indices. Furthermore, there are indices to describe the interruption costs.

Load point indices are calculated for each load (ElmLod), and are used in the calculation of many system indices. This section describes the simplified equations for the reliability indices. However, note that the PowerFactory reliability assessment calculations use more complex calculation methods. Nevertheless, the simplified equations shown here can be used for hand calculations or to gain insight into the reliability assessment results.

In the definitions for the reliability indices, the following parameters are used:

The number of customers supplied by load point i

The number of affected customers for an interruption at load point i

The frequency of occurrence of contingency k

The probability of occurrence of contingency k

C The number of customers

A The number of affected customers

The total connected kVA interrupted, for each interruption event, m

Duration of each interruption event, m

Ci

Ai

Frk

prk

Lm

rm

31 - 6


The total connected kVA supplied

Load Point Frequency and Expectancy Indices

ACIF: Average Customer Interruption Frequency ACIT: Average Customer Interruption Time LPIF: Load Point Interruption Frequency LPIT: Load Point Interruption Time AID: Average Interruption Duration

These indices are defined as follows:

, Unit: 1/a

, Unit: h/a

, Unit: 1/a

, Unit: h/a

wherei is the load point index, k is the contingency index, and frac_i,k is the fraction of the load which is lost at load point i, for contingency k. For unsupplied loads, or for loads that are shed completely, frac_i,k=1.0. For loads that are partially shed, 0.0 <= frac_i,k < 1.0.

System Indices

SAIFISystem Average Interruption Frequency Index, in units of [1/C/a], indicates how often the average customer experiences a sustained interruption during the period specified in the calculation.

CAIFICustomer Average Interruption Frequency Index, in units of [1/A/a], is the mean frequency of sustained interruptions for those customers

LT

ACIFi Frk fraci k

k=

ACITi Prk fraci k

k=

LPIFi ACIFi Ci=

LPITi ACITi Ci=

AIDi

ACITi

ACIFi----------------=

31 - 7


experiencing sustained interruptions. Each customer is counted once regardless of the number of times interrupted for this calculation.

ASIFIAverage System Interruption Frequency Index, in units of [1/a], The calculation of this index is based on load rather than customers affected. ASIFI can be used to measure distribution performance in areas that supply relatively few customers having relatively large concentrations of load, predominantly industrial/commercial customers.

SAIDISystem Average Interruption Duration Index, in units of [h/C/a], indicates the total duration of interruption for the average customer during the period in the calculation. It is commonly measured in customer minutes or customer hours of interruption.

CAIDICustomer Average Interruption Duration Index, in units of [h], is the mean time to restore service.

ASIDIAverage System Interruption Duration Index, in units of [h/a], is the equivalent of SAIDI but based on load, rather than customers affected.

ASAIAverage Service Availability Index, this represents the fraction of time that a customer is connected during the defined calculation period.

ASUIAverage Service Unavailability Index, is the probability of having all loads supplied.

MAIFIMomentary Average Interruption Frequency Index, in units of [1/Ca], evaluates the average frequency of momentary interruptions. The calculation is described in the IEEE Standard 1366 'IEEE Guide for Electric Power Distribution Reliability Indices'.

, Unit: 1/C/a

, Unit: 1/A/a

, Unit: h/C/a

, Unit: h

SAIFIACIFi Ci

Ci----------------------------------=

CAIFIACIFi Ci

Ai----------------------------------=

SAIDIACITi Ci

Ci----------------------------------=

CAIDISAIDISAIFI-----------------=

31 - 8


, Unit h/a

, Unit 1/a

Load Point Energy Indices

LPENS: Load Point Energy Not Supplied LPES: Load Point Energy Shed

These indices are defined as follows:

in MWh/a

in MWh/a

Where Pd_i is the weighted average amount of power disconnected Ps_i is the weighted average amount of power shed at load point i.

ASUIACITi Ci

8760 Ci----------------------------------=

ASAI 1 ASUI–=

ASIDIrm Lm LT

-------------------------------=

ASIFILm

LT---------------=

MAIFIIMi Nmi

Ni--------------------------------=

LPENSi ACITi Pdi Psi+ =

) )

LPESi ACITi Psi=

)

31 - 9


System Energy Indices

ENSEnergy Not Supplied, in units of [MWh/a], is the total amount of energy on average not delivered to the system loads.

SESSystem Energy Shed, in units of [MWh/a], is the total amount of energy on average expected to be shed in the system.

AENSAverage Energy Not Supplied, in units of [MWh/Ca], is the average amount of energy not supplied, for all customers.

ACCIAverage Customer Curtailment Index, in units of [MWh/Ca], is the average amount of energy not supplied, for all affected customers.

in MWh/a

in MWh/a

in MWh/Ca

in MWh/Ca

Load Point Interruption Cost

LPEIC is defined as

in $/a

whereLPEIC_i,k

is the average interruption cost for load point i and contingency case k, considering the load point interruption costs function and the assessed distribution of the durations of the interruptions at this load point for contingency case k. The interruption costs are calculated differently for different cost functions. All cost functions express the costs as a function of the interruption duration. For cost functions expressed in money per interrupted customer, the number of interrupted customers

ENS LPENSi=

SES LPESi=

AENSENS

Ci-------------=

ACCIENS

Ai-------------=

LPEICi LPEICi k=

31 - 10


is estimated for each interruption as the highest number of customers interrupted at any time during the whole interruption duration.

System Interruption Costs

EICExpected Interruption Cost, in units of [M$/y], is the total expected interruption cost.

IEARInterrupted Energy Assessment Rate, in units of [$/kWh], is the total expected interruption cost per not supplied kWh.

in M$/a

in $/kWh

Additional Calculated Indices for Load Points

AID: Average Interruption Duration [h]

Additional Calculated Indices for Busbars/Terminals

AID: Average Interruption Duration [h] AIF: Yearly Interruption Frequency [1/y] AIT: Yearly Interruption Time [h/y]

31.1.4 System State Enumeration in Reliability Assessment

In PowerFactory, Reliability Assessment uses a System State Enumeration to analyze all possible system states, one by one. A fast 'topological' method is used which ensures that each possible system state is only analyzed once. State frequencies (average occurrences per year) are calculated by considering only the transitions from a healthy situation to an unhealthy one and back again. This is important because the individual system states are analyzed one by one, and the (chronological) connection between them is therefore lost.

The enumerated calculation method is fast for quick investigation of large distribution networks, but does not compromise accuracy. Exact analytic averages are calculated. Distributions of reliability indices, however, cannot be calculated. For example, the average annual unavailability in hours/year can be calculated, but the probability that this unavailability is less than 15 minutes for a certain year cannot be calculated.

The state enumeration algorithm can include independent failures, simultaneous (n-2) failures, common mode failures, numerous load states and planned outages.

An overview flow diagram for the reliability assessment by state enumeration is shown in Figure 31.5.

EIC LPEICi=

IEAREICENS------------=

31 - 11


Fig. 31.5: Overview Flow Diagram for Reliability Assessment by State Enumeration

After the State Enumeration is complete, you can view each simulated system state using the 'tracing tool' on the Reliability Toolbar, see Section 31.3.2 for more information.

31.1.5 Failure Effect Analysis in Reliability Assessment

The simulation of the system response to specific contingencies is called 'Failure Effect Analysis' (FEA). The System State Enumeration algorithm uses the FEA engine to analyze the following steps after a contingency:

• Fault Clearance;

• Fault Isolation;

• Power Restoration;

• Overload Alleviation;

• Voltage Constraint Alleviation;

• Load Transfer;

• Load Shedding;

This section describes each of these steps in detail.

Pre-Processing- Load Curves- Load Growth- Statistics Initialization

Post-Processing- Load Point Indices- System State Indices- Reports

FirstContingency

NextContingency

Fault Clearance

Fault Separation

Power Restoration

Optimize Energy at Risk

OptimizeLoad Shedding

Update Statistics

Worst-Case AC Load-Flow

First Year of Load Growth

Next Year of Load Growth

Next Load Demand

First Load Demand

AdjustLoad-Flow

Overload ?N

More

More

More

Y

31 - 12


FEA analysis for the network assessment can consider or ignore constraints. For overload alleviation, the algorithm uses an AC load flow to search for overloaded branches and if any are identified then it attempts to resolve them, firstly by load transfer and secondly by load shedding. If constraints are not considered by the FEA, then a load-flow for each state is not required and consequently the simulation is much faster.

For every simulated failure, a contingency is created by the FEA algorithm. If the calcu-lation uses load characteristics, a contingency is created for every combination of failure and load state. Likewise, when maintenance (planned outages) is considered, there are more states for each outage and contingency combination.

Fault Clearance

The fault clearance step of the FEA assumes 100% selectivity of the protection. Therefore, it is assumed that the relays nearest to the failure will clear the fault. If protection/switching failures are considered in the FEA, it is assumed that the next closest protection device (after the failed device) has 100% selectivity. As described in (Protection/Switch Failures), PowerFactory does not consider separate switch and protection failures, instead these are lumped together. In the pre-processing phase of the reliability assessment, all breakers in the system that can be tripped by a relay, or fuse are marked as 'protection breakers'. Figure 31.6 shows a simple network containing four loads, several circuit breakers (CB) and disconnectors (DS) and a back-feed switch (BF). The possible load interruptions caused by a fault on 'Ln4' will now be investigated.

Fig. 31.6: Short-Circuit on Ln4

To clear the fault, the FEA starts a topological search from the faulted component/s to identify the closest protection breaker/s that can clear the fault. These breaker/s are then opened to end the fault clearance phase of the FEA. If it is not possible to isolate the fault because there are no appropriate protection breakers, then an error message will be printed and the reliability assessment will end.

The area isolated by the fault clearance procedure is called the 'protected area'. Figure 31.7 shows the example network after the fault clearance functions have opened the protection breaker 'CB1'. The protected area is the area containing all switches, lines and loads between 'CB1' and the back-feed switch, 'BF'. Therefore, during the clearance of this fault, loads 1, 2, and 3 are interrupted.

31 - 13


Fig. 31.7: Protected Area

Fault Separation

The next step of the FEA is to attempt to restore power to healthy network sections. It does this by separating the faulted section from the healthy section by opening section-alizing switches.

The fault separation procedure uses the same topological search for switches as the fault clearance phase. The fault separation phase starts a topological search from the faulted components to identify the closest switches that will isolate the fault. These switches are subsequently opened. Note, all closed switches can be used to separate the faulted area. The area that is enclosed by the identified fault separation switches is called the 'separated area'. The separated area is smaller than, or equal to, the 'protected area'. It will never extend beyond the 'protected area'.

The healthy section which is inside the 'protected area', but outside of the 'separated area' is called the 'restorable area' because power can be restored to this area. Figure 31.8 shows the example network with the separation switches, 'DS2' and 'DS4' open. The separated area now only contains the faulted line, Ln4.

There are now two restorable areas following the fault separation; the area which contains load 1, and the area which contains loads 2 and 3.

Fig. 31.8: Separated Area Highlighted

31 - 14


Power Restoration

The Power Restoration process of the FEA energizes the healthy areas of the system after the fault separation process has isolated the faulted area. Note that only open switches that are enabled for use in power restoration will be considered by PowerFactory as candidate switches for power restoration. Additionally, PowerFactory uses a 'smart power restoration' procedure that also considers the direction of the power restoration and the priority (stage) of the switch. The fastest candidate switch is always selected when there is more than one restoration alternative. Each restorable area that is recon-nected to the supplied network is called a 'restored' area. For more information about the switch configuration for smart power restoration, see Section 31.2.3.

If we consider the previous example after the fault separation phase is complete, the following switch actions are required to restore power to the two separate 'restorable' areas:

• Separation switch 'DS2' is 'remote-controlled' and has a switching time of 3 minutes. Power to load 1 is restored by (re)closing the protection breaker, 'CB1' which is also remote controlled. Load 1 is therefore restored in 3 minutes (=0.05 hours).

• Power to load 2 and 3 is restored by closing the back-feed switch, 'BF'. Because the back-feed switch has a actuation time of 30 minutes, loads 2 and 3 are restored in 0.5 hours. The network is now in the post-fault condition as illustrated in Figure 31.9.

Fig. 31.9: Power Restoration by Back-Feed Switch BF1 and CB1

All loads and terminals in a separated area are interrupted for the mean duration of the repair, which is normally several hours. All loads and terminals in a restored area are inter-rupted for the time needed to open all separators and to close all power restoration switches. You can analyze the effects of improved automation and remote control by lowering the actuation times for the remote controlled switches.

Overload Alleviation

If the power restoration does not cause any thermal overloads, then the FEA can proceed to calculate the statistics for that state and then analyze the next state. However, if thermal constraints are enabled, then PowerFactory will complete load-flows to check that all components are still within their thermal capability after the power restoration is complete. If necessary, load transferring, partial or full load shedding might be required to alleviate the thermal over-load. Note load transferring and partial load shedding are only considered by the transmission analysis option. The distribution option considers only

31 - 15


discrete switch actions. Therefore, loads must be fully shed or remain in service.

Figure 31.10 shows a line overload in the post-fault condition in the example network: line 'Ln1' is loaded to 113%.

Fig. 31.10: Overloaded Post-Fault Condition

Note: In the distribution reliability option, voltage constraints can be con-sidered in addition to thermal constraints. The voltage constraint alleviation process is similar to the thermal overload alleviation process, where loads will be shed if necessary to maintain all ter-minals on the feeder within the defined limits.

Load Transfer (Transmission Option only)

In some cases, load transfer switches and/or the alternative feeders are not included in the network model where reliability assessment is completed. In these cases, the automatic power restoration cannot switch an unsupplied load to an alternative supply. An example is when a (sub-)transmission network is analyzed and the connected distri-bution networks are modeled as single lumped loads. In this scenario, transfer switches that connect two distribution networks will not be visible. Therefore, the possibility of transferring parts of the lumped load model to other feeders can be modeled by entering a transfer percentage at each lumped load. This transfer percentage defines the portion of the lumped load that can be transferred 'away' from the analyzed network, without specifying to which feeder(s) the portion is transferred.

The use of the load transfer percentage (parameter name: Transferable on the load element’s Reliability tab) is only valid when load transfer is not expected to result in an overloading of the feeders which pick up the transferred loads.

Load transfer is used in the overload alleviation prior to the calculation of power at risk (see the following section for further information). The power at risk is considered to be zero if all overloads in the post-fault condition can be alleviated by load transfers alone.

Load Shedding

In the example network shown in Figure 31.11, loads 1, 2, 3 and 4 all contribute to the line overload. Consequently, some of these loads must be shed. There are three basic variations of shedding that can be used:

31 - 16


• Optimal load shedding

• Priority optimal load shedding

• Discrete optimal load shedding

Optimal load shedding presumes that all loads can be shed precisely (an infinite number of steps). PowerFactory attempts to find a solution that alleviates the overload with the lowest amount of load shed. In the example network it does not matter which load is shed, because a one MW reduction of any load will cause an equal reduction of the line loading. In more complex (meshed) networks, with more than one overloaded branch, the reduction of one particular load might have a greater impact on the total overloading than the reduction of another load.

PowerFactory uses linear sensitivity indices to first select those loads with any contri-bution to overloading. A linear optimization is then started to find the best shedding option. The resulting minimum amount of shed load is called the 'Power Shed', because it equals the minimum amount of load that must be shed to alleviate overloads after the power restoration. The power shed is multiplied by the duration of the system state to get the 'Energy Shed'. The total energy shed for all possible system states is reported after the reliability assessment is complete, and is referred to as the 'System Energy Shed' (SES).

Fig. 31.11: Ld1 is shed to alleviate the overload on Ln1

Loads are shed automatically based on their allocated priority, with PowerFactoryattempting to shed low priority loads, prior to high priority loads wherever possible. In the transmission reliability option, loads can be partially or fully shed, whereas in the distri-bution option, loads can only be fully shed.

31.2 Setting up the Network Model for Reliability Assessment

Prior to starting a Reliability Assessment Calculation, you must setup the Network Model with specific reliability data models. This chapter discusses the following procedures:

• How to Define Stochastic Failure and Repair Models;

• How to Create Feeders for Reliability Assessment;

• How to Configure Switches for the Reliability Assessment;

• Load Modelling for Reliability Assessment;

31 - 17


• Considering Multiple System Demand Levels;

• Defining Fault Clearance Based on Protection Device Location;

• How to Consider Planned Maintenance;

• Specifying Individual Component Constraints;

31.2.1 How to Define Stochastic Failure and Repair models

Stochastic Failure models define the probability that a component will fail and when it does fail, the mean time to repair the component. The following Stochastic failure models are supported by PowerFactory:

• Busbar/Terminal Stochastic Model

• Line/Cable Stochastic Model

• Transformer Stochastic Model

• Common Mode Stochastic Model

• Protection/Switch Failure Model

• Double Earth Fault Failure Model

This section describes each of these Stochastic Models and the procedure for defining them.

Busbar/Terminal Stochastic Model (StoTypbar)

It is possible to define a Stochastic Model for every busbar and terminal within the network. The Stochastic Model can be defined either through the object type or through the object element. If you want to use the same Stochastic Model for a number of different busbars/terminals then you should define it through the object type. Alterna-tively, if you want to use a Stochastic Model for only one element, then you should define it through the element reliability dialog.

You can use Stochastic Models defined through types and elements together as required - the element definition always overrides the type definition.

To define a Stochastic Model for a busbar type follow these steps:

1 Open the dialog for the busbar type and select the Reliability tab.

2 Using the 'Stochastic Model' selection control click the black triangle and select the option 'New project type'. The dialog for the 'Bar Type Failures' will appear.

3 Enter the failure data for the busbar and the failure data per connection. Note that the probability of the busbar failure is the sum of these two failure frequencies. For example a busbar with 3 connections, a failure frequency for the busbar of 0.002 and a failure frequency of 0.005 per connection will have a total probability of failure of 0.002 + 3 * 0.005 = 0.017.

4 Enter the mean repair duration.

5 Press OK twice to return to the element dialog.

To define a Stochastic Model for a busbar element follow these steps:

1 Open the dialog for the busbar element and navigate to the Reliability tab.

31 - 18


2 Using the 'Element model' selection control click the black triangle and select the option 'New project type'. The dialog for the 'Bar Type Failures' will appear.

3 Enter the failure data and repair time data as described above for the busbar type.

4 Press OK to close the element dialog.

Note: If you define a stochastic element model for a busbar/terminal that also has a stochastic type model within its corresponding type, the element model overrules the type model.

Line/Cable Stochastic Model (StoTyplne)

It is possible to define a Stochastic Model for every line or cable within the network. The Stochastic Model can be defined either through the object type or through the object element. If you want to use the same Stochastic Model for a number of different lines/cables then you should define it through the object type reliability page. Alternatively, if you want to use a Stochastic Model for only one element, then you should define it through the element reliability page.

To define a Stochastic Model for a line or cable type follow these steps:

1 Open the dialog for the line type and select the Reliability tab.

2 Using the 'Stochastic Model' selection control click the black triangle and select the option 'New project type'. The dialog for the 'Line Type Failures' will appear.

3 Enter the Sustained Failure Frequency. Note that the probability of the line failure is determined using this value and the length of the line. For example, a 12 km line with a Sustained failure frequency of 0.032 (1/(a*km)) will have a failure probability of 12 * 0.032 = 0.384 (1/(a*km)).

4 Enter the mean repair duration in hours.

5 Enter the Transient Fault Frequency. Note this parameter is used for the calculation of the MAIFI index.


To define a Stochastic Model for a line or cable element follow these steps:

1 Open the dialog for the line element and navigate to the Reliability tab.

2 Using the 'element model' selection control click the black triangle and select the option 'New project type'. The dialog for the 'Line Type Failures' will appear.

3 Enter the failure data and repair time data as described above for the line type.

4 Press OK to return to the element dialog.

Transformer Stochastic Model (StoTyptrf)

It is possible to define a Stochastic Model for every transformer within the network. The Stochastic Model can be defined either through the object type or through the object element. If you want to use the same Stochastic Model for a number of different trans-formers then you should define it through the object type reliability page. Alternatively, if you want to use a Stochastic Model for only one transformer element, then you should define it through the element reliability page.

31 - 19


To define a Stochastic Model for a transformer type follow these steps:

1 Open the dialog for the transformertype and select the Reliability tab.

2 Using the 'Stochastic Model' selection control click the black triangle and select the option 'New project type'. The dialog for the Transformer Type Failures' will appear.

3 Enter the failure frequency data (1/a).

4 Enter the mean repair duration in h.


To define a Stochastic Model for a transformer element follow these steps:

1 Open the dialog for the transformer element and select the Reliability tab.

2 Using the 'element model' selection control click the black triangle and select the option 'New project type'. The dialog for the 'Transformer Type Failures' will appear.

3 Enter the failure data and repair time data as described above for the transformer type.

4 Press OK to return to the element dialog.

Common Mode Stochastic Model (StoCommon)

A common mode failure involves the simultaneous failure of two or more power system components. An example is a distribution feeder where two lines with different voltages share the same poles. If one or more poles fail, for example a car hits a pole, then both lines will be interrupted simultaneously: these lines have a 'common failure mode'. Such a failure will usually be more likely than the probability of the two lines failing indepen-dently at the same time.

In PowerFactory, it is possible to define a common mode failure object to consider such failures in the reliability calculation. These Stochastic Models consider the common mode failure probability in addition to the independent failure mode of each component within the model.

To define a common mode failure Stochastic Model follow these steps:

1 Using the Data Manager, select the 'Common Mode' failures folder within the 'Operational Library'.

2 Click the 'New Object' button to create a Stochastic Common Mode failure object (StoCommon). The dialog for the object should appear.

3 Double click in the first empty cell of the 'Name' column, to open an object selection browser.

4 Use the browser to find the first object that is part of the Common Mode failure that you are trying to define.

5 Click OK to return to the Common Mode Failure dialog.

6 Add a cell below the last full cell by right-clicking within an empty area of the dialog and selecting the option 'Append Rows'.

7 Repeat steps 3-6 to add more objects to the Common Mode Failure.

8 Click the 'Failure Data' tab and enter the Sustained Failure Frequency, Mean Outage duration and Transient Fault Frequency data.

31 - 20


9 Click OK to save your changes.

Protection/Switch Failures

PowerFactory can consider the failure of the protection system to clear the fault as a stochastic probability within the reliability calculation. This is enabled by entering a 'Proba-bility of Failure' into the switch object. To enter this data:

1 Open the dialog for the switch object where you want to enter the switch failure probability. Normally switches are accessed by right clicking their containing cubicle and selecting the option 'Edit Devices'.

2 On the Reliability tab of the switch object, enter the 'Fault Clearance: circuit breaker fails to open probability' in percent. For example, a 5 % failure rate means that on average 1 out of 20 attempted fault clearance operations will fail.

Note: PowerFactory does not distinguish between a protection system failure and a switch failure. For example, the reason that a switch fails to open could be caused by a faulty relay, a protection mal-grading or a faulty circuit breaker. The cumulative probability of all these events should be entered into the switch failure probability.

Double Earth Faults

A double earth fault in PowerFactory is defined as follows: a single earth fault on a component followed by a second simultaneous earth fault on another component.

A double earth fault might occur after voltage rises on healthy phases on a feeder following a single phase to earth fault on the feeder, causes a second phase to earth fault on the same feeder.

Double earth faults occur on lines, transformers (2 Winding and 3 Winding transformers) and busbars, and PowerFactory supports adding the conditional probability data for double earth faults for Stochastic Models of these components. The reliability calculation automatically generates a contingency event for every double earth fault that meets the following conditions:

• Both objects are in the same part of the network (supplied by the same transformers).

• The star point of the transformers that supply that part of the network is isolated or compensated (star point grounded and Peterson Coil enabled).

• The frequency of single earth faults of the first object is > 0

• The probability of double earth fault of the second object is > 0.

The frequency for single earth faults and the probability of the second earth fault data can be entered on the 'Earth Fault' page of every Stochastic Model. Follow these steps to enter data for a Line Stochastic Model:

1 Open the Stochastic Failure Model for the line (either through the reliability page of the line type or the line elements).

2 Select the Earth Fault page.

3 Enable the option 'Model Earth Faults'

31 - 21


4 Enter the data for the frequency of single earth faults

5 Enter the data for the conditional probability of a second earth fault

6 Enter the Repair duration.

7 Close the Stochastic Model.

Note: The double earth fault is a conditional probability. Therefore, the probability of one occurring in the network is the probability of an earth fault on component A * probability of an double earth fault on component B

31.2.2 How to Create Feeders for Reliability Calculation

All loads that are to be considered for the reliability calculation must be incorporated within a feeder. Additionally, the feeders must be radial - mesh systems cannot be considered and will be ignored. PowerFactory automatically checks for parallel compo-nents within each feeder and if any are detected the following message will be printed to the output window:

DIgSI/wrng - The following feeders contain parallel components and are therefore ignored by the optimal power restoration:

The reliability calculation can proceed with other feeders in the system but all contin-gencies within the feeder with parallel components will be ignored. Therefore, it is recom-mended to first radialize all feeders before proceeding with the reliability calculation.

To create a feeder:

• Right click on the cubicle at the head of the feeder and select the option Define -> Feeder; or

• for fast creation of multiple feeders right click the bus the feeder/s are connected to and select the option Define -> Feeder. More information on feeders and feeder creation can be found in Chapter 15.5.

31.2.3 How to Configure Switches for the Reliability Calculation

A critical component of the Failure Effect Analysis (FEA), is the behavior of the switches in the network model. Switches in PowerFactory are classified into four different categories:

• Circuit Breakers; Typically these are automatic and controlled by relays and through remote communications. They are used for clearing faults and for closing back-feeds for power restoration.

• Disconnectors; Used for isolation and power restoration

• Load-Break-Switch; Used for isolation and power restoration

• Switch Disconnector; Used for isolation and power restoration

All switches in PowerFactory are modelled using the StaSwitch or ElmCoup objects. The switch category (CB, disconnector etc) is selected on the basic data page of the switch.

The actions that the FEA analysis takes depends on the configuration of these switches

31 - 22


and, optionally, the location of protection devices.

To configure a switch for reliability analysis follow these steps:

1 Open the dialog for the switch and select the reliability page. This can be done directly by editing switches modelled explicitly on the single line diagram, or for switches embedded within a cubicle, by right-clicking the cubicle and selecting the option 'edit devices', to access the switch.

2 Select the ‘Sectionalizing' option. The following choices are available:

- Remote controlled (Stage 1); This option means that the actuation time of this switch is taken from the global 'remote controlled' switch actuation time. The default time is 1 min but this can be adjusted within the reliability command, see Section 31.3.1: How to run the Reliability Assessment.•Typically remote controlled switches are circuit breakers controlled by relays or with communications from a control room.

- Indicator of Short Circuit (Stage 2); This option represents a switch that has an external indication of status on the outside of the switch enclosure. This allows the operator/technician to easily identify the switch status and actuate the switch.

- Manual (Stage 3); These switches need direct visual inspection to determine their status and therefore take longer to actuate than either stage 1 or stage 2 switches.

3 Select the ‘Power Restoration’ option. The following choices are available:

- Do not use for power restoration; If this option is selected the switch can only be used for isolation of equipment or load shedding. It will not be used by the FEA calculation to restore power.

- From terminal i to j; If this option is selected, the switch will only be used to restore power if the post restoration power flow is in the direction from terminal i to terminal j. The switch will not be used for power restoration in the opposite direction.

- From terminal j to i; If this option is selected, the switch will only be used to restore power if the post restoration power flow is in the direction from terminal j to terminal i. The switch will not be used for power restoration in the opposite direction.

- Independent of direction; If this option is selected the switch will be used to restore power flow regardless of the direction of the post restoration power flow.

4 Enter the time to actuate switch (Stage 2 and 3 switches only); This field specifies the time taken by the operator to actuate the switch. Note, this excludes the local access and access time if the switch is within a substation. The total actuation time of such a switch is therefore the switch actuation time + the substation access time + the local access time.

Note: The Sectionizing options are only considered in the 'Distribution' reliability analysis option. If the 'Transmission' mode is selected, then all switches are assumed to be remote controlled.

31.2.4 Load Modeling for Reliability Assessment

This section describes the load element parameters that are used by the reliability calcu-lation. The first sub-section describes how to input the number of customers that each

31 - 23


load represents and how to classify each load. The second sub-section describes the process of creating a load interruption cost characteristic. The third sub-section describes how to define load shedding and transfer parameters.

How to Specify the Number of Customers for a Load

Many of the reliability indices such as SAIFI and CAIFI are evaluated based on the number of customers interrupted. Therefore, for accurate calculation of these indices it is important to specify the number of customers that each load represents. To do this:

1 Open the dialog for the target load element.

2 Select the Reliability page.

3 In the 'Number of connected customers' field, enter the number of customers that this load represents.

4 Repeat this process for each load in the system you are modelling.

Load Classification

Every load can be optionally classified into agricultural, commercial, domestic or industrial load. This option does not affect the calculation of the reliability indices and is provided for categorisation purposes only.

How to model Load Interruption Costs

When supply to a load is interrupted, there is a cost associated with the loss of supply. In many cases, the cost for short duration interruptions, say less than one hour, could be less (on a per unit basis), than the cost of interruptions longer than one hour. An example interruption cost curve is shown in Figure 31.12.

Fig. 31.12: Example Load Interruption Cost Curve

PowerFactory supports the definition of such cost curves for load elements. They can be defined using the 'time dependent rate' characteristic on the reliability page of the load element. To define such a characteristic follow these steps:

31 - 24


1 Choose the 'Select' option from the 'time dependent rate selection control on the reliability page of the load element. A data manager browser should appear with the 'Equipment Type Library' selected.

2 Optional: If you have previously defined a 'time dependent rate' characteristic and want to re-use it, you can select it now. Press OK to return to the load element to reliability page.

3 Create a characteristic by pressing the 'New Object' button from the data browser toolbar. A type creation dialog should appear.

4 Press OK to create the 'Parameter Characteristic'. A 'Parameter Characteristic' dialog box will appear. You now need to create a scale the defines the 'x-axis' values of the characteristic. To do this:1 Using the 'Scale' selection control, choose the select option. A data browser will

appear.

2 Create a 'Scale' by pressing the 'New Object' button from the data browser toolbar. A Element selection dialog will appear.

3 Choose the 'Time Scale' (TriTime') option from the list box. A time scale object dialog will appear.

4 Choose the unit 'min'.

5 Enter the minute values you want to consider as part of your characteristic above. These are the x-axis values. You can append more rows by right-clicking within a cell and selecting the option 'Append Rows'.

6 Press OK twice to return the 'time dependent rate' characteristic you created earlier. The scale values you entered should appear in burgundy text in the left most column of the characteristic.

5 Enter the cost values for interruption duration.

6 Press OK to return to the load element reliability page.

7 Select the unit of the interruption cost function by choosing from the following options:

$/kW Cost per interrupted power in kW.

$/customer Cost per interrupted customer.

$ Absolute cost.

8 Optional: enter a scaling factor for the 'time dependent' rate characteristic.

Note that the interruption cost function is not interpolated. As an example, consider the following cost function:

This then means that for the following durations the cost is as follows:

30min $7.50

60min $20.00

180min $80.50

0min t 30min $0.00

31 - 25


Specifying Load Shedding and Transfer Parameters

Load transfer and load shedding are used to alleviate violated voltage or thermal constraints caused by the power restoration process. There is a distinction between load transfer for constraint alleviation, such as described in this section, and load transfer for power restoration. Load transfer by isolating a fault and closing a back-stop switch is considered automatically during the fault separation and power restoration phase of the failure effect analysis.

If a violated constraint is detected in the post-fault system condition, a search begins for the loads contributing to these overloads. The overloads are then alleviated by either:

• Transferring some of these loads, if possible; or

• Shedding some of these loads, starting with the lowest priority loads.

To define the load shedding parameters follow these steps:

1 Open the reliability page of the load element.

2 Enter the number of load shedding steps using the 'Shedding steps' list box. For example, four shedding steps means that the load can be shed to 25%, 50%, 75% or 100% of its base value. Infinite shedding steps means that the load can be shed to the exact value required to alleviate the constraint.

3 Enter the 'Load priority'. The reliability algorithm will always try to shed the loads with the lowest priority first. However, high priority loads can still be shed if the algorithm determines this is the only way to alleviate a constraint.

4 Enter the load transfer percentage in the 'Transferable' parameter. This defines the percentage of this load that can be transferred away from the current network. PowerFactory assumes that the transferred load is picked up by another network that is not modelled, hence load transferring in this way is equivalent to load shedding in terms of constraint alleviation. The difference is that transferred load is still considered as supplied load, whereas shed load is obviously not supplied.

5 Optional: Use the selection control next to 'Alternative Supply (Load)' to specify an alternative load that picks up all transferred load.

Note: There is a critical difference between the transmission reliability and distribution reliability functions. In distribution reliability all constraint alleviation is completed using switch actions, so loads can only be fully shed (switched out) or they remain in service. However, by contrast, the transmission reliability option can shed or transfer a percentage of the load.

Considering Multiple System Demand Levels (Optional)

If you have defined time-based characteristics for the feeder loads so that the demand

30min t 60min $7.50

60min t 180min $20.00

180min t $80.50

31 - 26


changes depending on the study case time, then you might want to also consider using these different demand patterns in the reliability analysis. Because the reliability analysis always analyses a discrete 'system state', it is normally not practical to consider every possible demand level because the number of discrete states in a practical system is usually very large. Instead, the load demand for a one year period is can be discretized and converted into several so-called 'load states', and a probability of occurrence for each state. For reference, the internal procedure that PowerFactory follows to create load states is described in Chapter 34.1.5.

The Reliability Command does not automatically generate the load states. Therefore, if you wish to consider multiple demand levels in your reliability analysis you must first get PowerFactory to generate the load states. This procedure is described in the next section.

To Create Load States

Pre-requisites:

Prior to creating load states you must have defined time based parameter characteristics for some loads within your network model. See Chapter 18 for more information on parameter characteristics.

Follow these steps to create the load characteristics:

1 Click the 'Create Load States' button on the reliability toolbar. The load states creation dialog will appear.

2 Optional: Use the Reliability Assessment selection control to inspect or alter the settings of the Reliability Calculation command. This selection control points to the default reliability command within the active Study Case.

3 Optional: Use the Load Flow selection button to inspect and alter the settings of the load flow command. This selection control points to the default load-flow command within the active Study Case.

4 Enter the year to generate the load states for.

5 Enter the Accuracy. More information about the accuracy is available in Chapter 34.1.5. Essentially, the lower accuracy percentage, the more load states that are generated.

6 Optional: Limit the number of load states to a user-defined value.

7 Optional: Change the threshold for ignoring load states with a low probability by altering the 'Minimum Probability'. You can also disable this feature by unchecking the 'Ignore load states with a small probability' flag.

8 Click Execute to generate the load states.

To View Existing Load States

After you have generated the load states as described above, or if you want to inspect previously generated load states follow these steps:

1 Using the data manager, select the Reliability Assessment Command within the Active Study Case.

31 - 27


2 Use the filter to select the 'characteristic load states' object . There should now be one object visible in the right panel of the data manager.

3 Double-click this object to view the load states. Figure 31.13 shows the dialog of the load states object.

Fig. 31.13: Load States (SetCluster) dialogue box

The load states object properties are as follows:

Basic Data

Year The Year used to create the load states.

• Loads: Table containing each load considered by the load states creation algorithm and their peak demand.

• Cluster: Table containing all load clusters. The first row in the table contains the probability of the corresponding cluster. The remaining rows contain the power values of the loads. Every column in the table contains a complete cluster of loads with the corresponding power.

• Number of loads: Number of loads considered in the load cluster object.

• Number of states: This equals the number of columns in the “Clusters” table.

Diagram Page

Displayed LoadUse the selection control to change the load displayed on the plot.

PlotThe plot shows the cluster values (P and Q) for the selected load where the width of each bar represents the probability of occurrence for that cluster in the given year.

31 - 28


31.2.5 Fault Clearance Based on Protection Device Location

The Reliability Calculation has two options for fault clearance:

• Use all circuit breakers; or

• Use only circuit breakers controlled by protection devices (fuses or relays).

The second option is the more realistic option, because only locations within the network that can automatically clear a fault will be used by the reliability calculation to clear the simulated faults. However, you must create protection devices to control each automatic switch for this option to work correctly.

31.2.6 How to Consider Planned Maintenance

The PowerFactory reliability calculation supports the definition and automatic inclusion of planned network maintenance. Maintenance is implemented with a planned outage object. These objects are found within the 'Outages' sub-folder within the project 'Opera-tional Library'. The following steps describe the procedure for creating a planned outage:

1 On the single line diagram (or within the data manager), select the object (or objects) that you would like to define an outage for.

2 Right-click the selected object/s and from the menu that appears choose the option 'Define -> Planned Outage'. The dialog box for the planned outage will appear.

3 Using the Start Time selection control '...', enter the time that the outage begins.

4 Using the End Time selection control '...', enter the time that the outage ends.

5 Optional: Adjust the Outage Type. Typically you would leave this on the default ‘Outage of Element' option, but if you wanted to model a generator derating, then you would choose the 'Generator Derating' option.

Note: When the reliability calculation considers outages it creates a unique contingency case for every contingency with the outage ap-plied and also without the outage. For example, for a network with two planned outages and six contingencies there will be a total of 6 * 3 = 18 contingency cases.

31.2.7 Specifying Individual Component Constraints

The reliability calculation can automatically consider voltage and thermal constraints for the power restoration process. There are two options for specifying the constraints:

• Global Constraints; All network constraints are based on the constraints specified on the constraints tab of the Reliability Command Dialog.

• Individual Component Constraints; For this option every branch and terminals object has constraints defined within these objects.

To Specify Individual Terminal Voltage Constraints

Follow these steps to specify voltage constraints for terminals:

1 Open the reliability page of the target terminal.

31 - 29


2 Enter the Max and Min Voltage limits in the fields near the bottom of this page.

3 Click OK to close the dialog and save the changes.

To Specify Individual Line/transformer Thermal Constraints

Follow these steps to specify thermal constraints for a line or transformer:

1 Open the reliability page of the target line/transformer.

2 Enter the Max Loading in the field near the bottom of this page.

3 Click OK to close the dialog and save the changes.

31.3 Running The Reliability Assessment Calculation

The procedure for using the PowerFactory Reliability Assessment tool and analyzing the results generated by the tool is described in this section.

31.3.1 How to run the Reliability Assessment

In PowerFactory the network Reliability Analysis is completed using the Reliability Assessment command (ComRel3 ). This command is found on the 'Reliability

Analysis' toolbar , see Figure 31.1. The options for the reliability command that are presented within its dialog are described in the following sub-sections.

Basic Options

The following options are available on the Basic Options page Reliability AssessmentCommand dialog.

Method Connectivity analysis

This option enables failure effect analysis without considering constraints. A load is assumed to be supplied if it is connected to a source of power before a contingency, and assumed to undergo a loss of supply if the process of fault clearance separates the load from all power sources. Because constraints are not considered, no load-flow is required for this option and hence the analysis will be faster than when using the alternative load-flow analysis option.

Load flow analysisThis option is the same as the connectivity analysis, except that constraints are considered by completing load-flows for each contingency. Loads might be disconnected to alleviate voltage or thermal constraints. For the transmission analysis option, Generator re-dispatch, load transfer and load shedding are used to alleviate overloads.

Calculation time periodComplete year

The reliability calculation is performed for the current year specified in

31 - 30


the 'Date/Time of the Calculation Case'. This can be accessed and the

date and time changed by clicking the button.

Single Point in TimeThe Reliability Calculation is completed for the network in its current state at the actual time specified by the 'Date/Time of the Calculation Case'.

Note: If load states or maintenance plans are not created and consid-ered, then these options make no difference because the reliability calculation is always completed at the single specified time.

Load Flow This button is a link to the load-flow calculation command used for the analysis. The load demand is calculated using this load-flow. In addition, its settings are used for the constraint evaluation load-flows.

NetworkDistribution

The reliability assessment will try to remove overloading at components and voltage violations (at terminals) by optimizing the switch positions in the radial system. If constraints occur in the power restoration process, loads will be shed by opening available switches. This option is the recommended analysis option for distribution and medium voltage networks.

TransmissionThermal overloads are removed by generator re-dispatch, load transfer and load shedding. First generator re-dispatch and load transfer is attempted. If these cannot be completed or do not remove the thermal overload, load shedding actions will occur. Generator re-dispatch and load transfer do not affect the reliability indices. However, by contrast, load shedding leads to unsupplied loads and therefore affects the reliability indices.

Automatic Contingency Definition

The 'Selection' list presents three possible options for the contingency definition. These are:

• Whole system: PowerFactory will automatically create a contingency event for every object that has a Stochastic Model defined.

• Single Grid: Selecting this option shows a selection control. Now you can select a single grid and only contingencies for objects in this grid will be created.

• User Defined: Selecting this option shows a selection control. Now you can select a set of objects (SetSelect), and contingencies will be created for each of these objects that has a Stochastic Model defined.

In addition to the above contingency definition options, the automatic contingency definition can be further controlled with the following checkboxes:

• Busbars/Terminals; You must enable this flag for PowerFactory to create Busbar and terminal contingencies.

31 - 31


• Lines/Cables; You must enable this flag for PowerFactory to create Line/Cable contingencies.

• Transformers; You must enable this flag for PowerFactory to create transformer contingencies.

• Common Mode; You must enable this flag for PowerFactory to create Common Mode contingencies. See Common Mode Stochastic Model (StoCommon) for more information.

• Independent second failures; You must enable this flag for PowerFactory to consider n-2 outages in addition to n-1 outages. Caution: n-2 outages for all combinations of n-1 outages are considered. This means that for a system of n contingencies there are (n * (n-1)) / 2) + n, contingencies to consider. This equation is quadratic, so for this reason, this option is disabled by default.

• Double-earth faults; You must enable this flag for PowerFactory to consider double-earth faults. See Double Earth Faults for more information.

• Protection/switching failures; You must enable this flag for PowerFactory to consider protection devices or circuit breakers’ failure to operate. See Protection/Switch Failures for more information.

Outputs

The following options are available on the Outputs tab of the Reliability command. Results

This option allows the selection of the result element (ElmRes) where the results of the reliability analysis will be stored. Normally, PowerFactory will create a result object within the active study case.

Perform Evaluation of Result FileThe Reliability Analysis automatically writes all simulation results to a result object specified above. After completing the Reliability Calculation, PowerFactory automatically evaluates the result object to compute the reliability indices. This button allows you to re-evaluate a results file that has previously been created by this or another reliability calculation command. The benefit of this is that you do not have to re-run the reliability calculation if you only want to recalculate the indices from an already completed calculation, which is typically much more time consuming than the result object evaluation.

OutputDisplays the form used for the output report. Report settings can be

inspected and the format selected by clicking on the button.

Recording LimitsThese options define when PowerFactory will record bus voltages and line loadings in the reliability assessment result object. For example, if the loading limit is specified as 80 %, then line loadings will only be recorded on lines where the calculated loading is greater than 80 %.

FEA

A failure effect analysis (FEA) is made for each system state that occurs during the state

31 - 32


enumeration. The configuration options are explained next.

Fault Clearance Breakers Use all circuit breakers

All switches in the system whose Usage is set to Circuit Breaker can be used for fault clearance.

Use only circuit breakers with protection deviceAll circuit breakers in the system which are controlled by a protection device (fuse or relay) can be used for fault clearance.

Fault Separation/Power Restoration

This option will only be enabled if Automatic Power Restoration is enabled on the Advanced Options Tab.

Concurrent Switch ActionsIt is assumed that the switching actions can be performed immediately following the specified switching time. However, a switch can be closed for power restoration only after the faulted element was disconnected. The analogy for this mode, is if there were a large number of operators in the field that were able to communicate with each other to coordinate the switching actions as quickly as possible. Therefore, this option gives an optimistic assessment of the 'smart power restoration'.

Sequential Switch ActionsIt is assumed that all switching actions are performed sequentially. The analogy for this mode, is if there is only a single operator in the field and they are required to complete all switching. The fault separation and power restoration is therefore slower when using this mode compared with the 'concurrent' mode.

Consider Sectionalizing (Distribution analysis only)

If enabled, the FEA considers the switch sectionalizing stage when attempting fault separation and power restoration. First sectionalizing is attempted using only stage 1 switches, if this is not successful then stage 1 and 2 switches are used. Finally, if this is not successful, then stage 1, 2 and 3 switches are used.

Time to open remote controlled switches

The time (in minutes) taken to open remote controlled switches.

Constraints

The settings for global constraints are defined within this page. The options are as follows:

Consider Thermal Constraints (Loading)

If this option is enabled, thermal constraints are considered by the FEA. Global constraints for all components

Constraints specified in 'Max thermal loading of components' apply to all components.

Individual constraint per component The maximum thermal loading limit is considered for each component separately. This loading limit can be found on the Reliability tab of each component.

31 - 33


Max thermal loading of components (Global constraints only)The maximum thermal loading of all components can be specified in percent value.

Consider Voltage Limits (Terminals)

If this option is enabled voltage limits are considered by the FEA.Global Constraint for all terminals

Constraints specified in Lower and Upper Limit of allowed voltage apply to all terminals

Individual Constraint per terminal Voltage constraints are considered for each terminal separately. These constraints can be found on the Reliability tab of each terminal.

Lower limit of allowed voltage (Global constraint only)You can specify the lower limit of allowed voltage in p.u that will apply to all terminals.

Upper limit of allowed voltage (Global constraint only) You can specify the upper limit of allowed voltage in pu that will apply to all terminals.

Ignore all constraints for

Constraints are ignored for all terminals and components below the entered voltage level.Nominal voltage below or equal to

The voltage level in kV is specified here if 'Ignore all constraints for...' is enabled.

Note: Voltage constraints are only available in the 'Distribution' analysis option. Thermal constraints are available in the 'Transmission' and 'Distribution' analysis.

Maintenance

This tab allows you to enable or disable the consideration of Maintenance based on the Planned Outages you have defined. See Section 31.2.7, for more information on defining planned outages. The following options are available on this page:

Consider Maintenance

If enabled, all maintenance that falls in the selected time period, whether it’s a year or a single point in time, is considered.

Show used planned outages When clicked, this button will show a list of all planned outages that will be considered by the calculation.

Show all planned outages When clicked, this button will show a list of all planned outages created in the project, including those not considered by the analysis because they fall outside of the selected time period.

Load Data

If the Reliability Calculation option 'Complete Year' is selected on the basic options page,

31 - 34


then the following options are available on the Load Data page.

Consider Load states

Enable this flag to consider the load states in the reliability calculation. The reliability calculation does not create load states automatically. If this flag is enabled but the states have not been created, then an error will be printed to the output window and the reliability calculation will stop. Otherwise the following two buttons are available.

Create Load States Launches the 'Load state creation' command after closing the reliability command. See (To Create Load States), for more information on load state creation.

Show all existing Load states Opens a list of all current load states.

Advanced Options

Failures, correction of forced outage rateThis option performs an automatic correction/normalization of the reliability indices to allow for the fact that not all unlikely but possible contingencies have been considered in the analysis. For instance, n-3 contingencies have a non-zero probability.

Fault Clearance/ Automatic Power RestorationDo not save corresponding switch events

Results of internal nodes of substations will not be written to the result file. This minimizes the amount of objects created in the database while performing calculations with many contingencies caused by big networks (e.g if independent second failures or double earth faults are enabled).

Save corresponding switch events Corresponding switch events will be saved in the database while performing calculations.

Automatic Power Restoration

If enabled, automatic power restoration will be considered.

Calculate Existing Contingencies (Do not create contingencies)

If enabled, the existing contingencies inside the reliability command will be used in the analysis. Note that the options for automatic contingency definition on the Basic Options tab disappears.

Switch/Load eventsDelete switch events

Removes all switch events associated with the contingencies stored inside the command.

Delete load eventsRemoves all load events associated with the contingencies stored inside the command.

Loadflow Analysis, OverloadingsConsider branch if loadings exceeds

If there are overloaded elements in the system, these overloadings should be removed through overload alleviation. Branches whose

31 - 35


loading exceeds this limit, are considered by the overload alleviation algorithm.

A reliability assessment will be started when the Execute button is pressed. The calcu-lation time required for a reliability assessment can range from a few seconds for a small network only considering n-1 contingencies, to several hours for a large network consid-ering n-2 contingencies. A reliability assessment calculation can be interrupted by clicking

on the Break icon ( ) on the main toolbar.

31.3.2 Viewing the FEA results for a Specific Contingency

After the Reliability Analysis has completed, it is possible to view the fault clearance, fault separation, power restoration and load shedding actions completed by the algorithm for each contingency. To do this:

1 Click the 'Fault Trace' button on the Reliability toolbar. A list of available contingencies will appear in a new window.

2 Select the contingency to consider and click OK. The network will be initialized to the state before the inception of the fault.

3 Click the 'Next Step' button to advance to the next system state. This will usually show the system state immediately after the protection has operated and cleared the fault.

4 Click the 'Next Step' button to advance through more steps, each click advances one time step.

5 To stop the fault trace, click the 'Stop Trace' button.

31.3.3 Viewing the Load Point Indices

You can view the Reliability Assessment Load Point Indices in two ways: in the load result boxes in single line graphic, or in the data browser (data manager or load filter). This sub-section describes both of these methods.

View the Load Point Indices in the Single Line Diagram

After you have executed the Reliability Assessment Calculation, all loads within the Network Single Line Graphic, will show the following load point indices:

• AID

• LPIF

• LPIT

• LPIC

As usual, with PowerFactory result boxes, you can hover the mouse pointer over the result box to show an enlarged popup of the results. This is demonstrated in Figure 31.14.

31 - 36


Fig. 31.14: Single Line Diagram Graphic Showing the Load Point Indices Results

Note: You can show any of the calculated load point indices in the load result boxes. To do this modify the displayed variables as described in Chapter 19.3.3.

View the Load Point Indices in the Data Browser

To view the load point indices in the Data Browser (as a selectable spreadsheet list), follow these steps:

1 Select the load element icon from the 'Edit Relevant Objects for Calculation

Selection' button . A list of all loads considered in the calculation will appear.

2 Choose the 'Flexible Data' tab. Calculated Load Point Indices for each load will appear in Green Font text. By default, not all available load point indices will be shown.

3 Optional: Click the 'Define Flexible Data' button , to show all available variables.

4 Optional: Add more variables to the 'Selected Variables' by double-clicking the variable in the 'Available Variables' window.

5 Optional: Click OK to view the result variables in the data browser.

31.3.4 Viewing the System Reliability Indices (Spreadsheet format)

The System Reliability Indices can be viewed for the whole system, individual grids, or for individual feeders. Viewing these results is described in this sub-section.

To View Complete System Reliability Indices

Follow these steps to view the complete system reliability indices:

31 - 37


1 Select the 'Grids' icon from the 'Edit Relevant Objects for Calculation' button

located on the main toolbar. A list of all grids in the network model and a summary grid will appear.

2 Click the “Flexible Data' tab.

3 Click the 'Define Flexible Data' button to show the variable selection dialog.

4 Click the Reliability tab (if not already selected).

5 Choose the variable set 'Calculation Parameter', from the list selection control in the 'Filter for' section. A list of available reliability indices will appear.

6 Select the indices that you wish to view, and double click them to move them to the 'Selected Variables' window.

7 Click OK to view the result variables in the data browser.

Note: Steps 3-7 are only required the first time you want to view the sys-tem reliability indices, or if you want to change the displayed vari-ables. PowerFactory 'remembers' these settings within each project.

To View Feeder Reliability Indices

Reliability indices can also be viewed for each Feeder. To do this:

1 Select the 'Feeder' icon from the 'Edit Relevant Objects for Calculation' button

located on the main toolbar. A dialog box with a list of all feeders in the network model will appear.

2 Click the 'Flexible Data' tab.

3 Click the 'Define Flexible Data' button to show the variable selection dialog.

4 Click the Reliability tab (if not already selected).

5 Choose the variable set 'Calculation Parameter', from the list selection control in the 'Filter for' section. A list of available reliability indices will appear.

6 Select the indices that you wish to view, and double click them to move them to the 'Selected Variables' window.

7 Click OK to view the result variables in the data browser.

Note: Steps 3-7 are only required the first time you want to view the Feeder reliability indices, or if you want to change the displayed variables. PowerFactory 'remembers' these settings within each project.

31.3.5 Printing ASCII Reliability Reports

PowerFactory has three built-in ASCII Reliability Reports that you can use to show

31 - 38


detailed print outs of the Reliability Calculation results. To do this, follow these steps:

1 Click the 'Output Calculation Analysis' icon on the main toolbar. A dialog box showing the available reports will appear.

2 Choose the report that you want to view.

3 Click Execute. The selected ASCII report will be printed to the PowerFactory Output Window.

Note: ASCII reports can be copied into a word processing tool directly from the Output Window. However, for a more professional look, try printing the report directly to PDF format from the Output Win-dow.

31.3.6 Using the Colouring modes to aid Reliability Analysis

There are several colouring modes that can aid you when using the reliability assessment functions. These are:

• Colouring according to 'Feeders'; Use this to identify each Feeder and to see which feeder picks up load when back-feed switches are closed.

• Colouring according to 'Connected Grid Components'; Use this to identify de-energized sections of the network during the fault isolation, separation and power restoration.

• Switches, type of usage. Use this mode to check the type of switches in the system when they are not modelled explicitly in the single line diagram.

To Colour According to Feeders

1 Click the 'Diagram Colouring' button . The Diagram colouring dialog will appear.

2 Select the tab for the function you want to show the colouring mode for. For example, if you want the feeder colouring to appear before a calculation, then select the 'Basic Data' tab. If you want the colouring to appear after a load-flow choose the load-flow tab.

3 Check the '3. Other' box and select 'Topology' from the drop down list.

4 Select 'Feeders' in the second drop down box.

5 Optional: To change the feeder colour settings click the 'colour settings' button. You can double click the displayed colours in the colour column and select a different colour for each feeder as desired.

6 Click OK to close the Diagram Colouring dialog and save your changes.

To Colour According to Connected Grid Components

The 'Connected Grid Components' colouring mode displays all the network components that are electrically connected together in the same colour. Other components are not coloured. To enable this mode:

31 - 39


1 Click the 'Diagram Colouring' button . The diagram colouring dialog will appear.

2 Select the load-flow tab.

3 Check the '3. Other' box and select 'Topology' from the drop down list.

4 Select 'Connected Grid Components' in the second drop down box.


To Colour According to Switch Type

The 'Switches: type of usage' colouring mode displays all switches in the network with a different colour depending on their 'switch type'. For instance circuit breakers will be displayed in a different colour to disconnectors. To enable this mode:

1 Click the 'Diagram Colouring' button . The diagram colouring dialog will appear.

2 Select the tab for the function you want to show the colouring mode for. For example, if you want the switch type colouring to appear before a calculation, then select the 'Basic Data' tab. If you want the colouring to appear after a load-flow choose the load-flow tab.

3 Check the '3. Other' box and select 'Secondary Equipment' from the drop down list.

4 Select 'Switches, Type of Usage' in the second drop down box.

5 Optional: To change the switch colour settings, click the 'colour settings' button. You can double click the displayed colours in the colour column and select a different colour for each switch type as desired.


31.3.7 Using the Contribution to Reliability Indices Script

It can be useful to analyze the influence of a particular component or group of compo-nents on the calculated reliability indices. This enables the identification of components that can be targeted for upgrade to improve reliability, or to examine the impact of improved switch automation for example. This sub-section describes the built-in DPL script that can be used for these purposes.

To Start the Contribution to Reliability Indices Script

1 Execute a Reliability Assessment Calculation (or ensure that you activate a study case where a reliability analysis has previously been completed).

2 Click the 'Edit Relevant Objects for Calculation' button from the main toolbar. Depending on whether you want to view the contributions by Feeder, Grids, Areas or Zone, choose one of the following icons from the list of icons that appears:

- For Grids choose the icon.

- For Feeders choose the icon.

- For Zones choose the icon.

31 - 40


- For Areas choose the icon.

3 In the window that appears, select the object/s that you want to show the reliability indices contributions.

4 Right-click one of the selected object icons. A menu will appear.

5 Choose 'Execute DPL scripts'. A window displaying a list of DPL scripts will appear.

6 Select the 'Contribution to Reliability Indices' Script and click OK. The script dialog box will appear. The available options are explained in the next section.

How to Configure and Run the Contribution to Reliability Indices Script

1 Enter '1' in the value column for 'calcSystemIndices' parameter to make the script print the system indices results. '0' suppresses the printing of the system indices.

2 Enter '1' in the value column for 'calcEnergyIndices' parameter to make the script print the Energy indices results. '0' suppresses the printing of the Energy indices.

3 Enter '1' in the value column for 'outputComponentClasses' to make the script display contributions from each class such as lines, cable, transformers. '0' supresses the printing of the class information.

4 Enter '1' in the value column for 'outputIndivComponents' parameter to make the script print the results indices for each object in the selected area. '0' suppresses the printing of the individual indices.

5 Optional: Enter '1' in the 'outputPercentages' column to display the results from the script in percent format.

6 Optional: Enter a percent threshold in the 'outputThreshold' column to limit the printed results to those above a specific threshold.

7 Click Execute to run the script. The results are printed to the PowerFactory output window.

31.4 Voltage Sag Analysis

Voltage Sag Analysis, is a calculation the assesses the expected frequency of voltage sags within a network. The PowerFactory Voltage Sag tool calculates a short-circuit at the selected load points within the system and uses the failure data of the system components to determine the voltage sag probabilities.

31.4.1 Calculation Options

Voltage sag analysis has a lot in common with probabilistic reliability analysis. Both use fault statistics to describe the frequency of faults and then use these statistics to weight the results of each event and to calculate the overall effects of failures.

Reliability analysis looks for sustained interruptions as one aspect of quality of supply, whereas voltage sag analysis calculates the voltage drop during the fault until the protection system has disconnected the defective component.

An assessment of voltage sag tables for a selection of load points can be started as follows:

31 - 41


• Select one or more busbars/terminals and/or loads in the single line diagram or the data manager, right-click the selection and select "Calculate... --> Voltage sag table..."; or

• Click on the icon on the main toolbar to activate the Additional Tools toolbar (if

not already visible), and then click the Voltage sag table assessment icon ( ).

In both cases, the voltage sag table command dialogue will open, as shown in Figures 31.15 and 31.16.

Fig. 31.15: Voltage Sag Table Assessment - Basic Options

Basic Options Load selection

Reference to the set of load points. A load point can be defined by a busbar, terminal or load.

Short-circuit commandDisplays the short-circuit command that is used. The options for the short-circuit type will be changed during the voltage sag calculation, depending on the Advanced Options specified in the ComVsag dialogue. However, other settings can be inspected or changed by

clicking on the button.

ResultsReference to the result file that is used for storage of results.

Exposed area limitThis defines the minimum remaining voltage for the voltage sag calculation to continue calculating short-circuits at busbars which are further away from the selected load points. If short-circuits at all busbars (at a certain distance away from all load points) result in voltages at the load points being higher than this limit, then no further short-circuit will be analyzed.

Advanced Options

The Advanced Options shows the various short-circuit types that can be analyzed by the voltage sag assessment command. All components for which a failure model has been defined use the same short-circuit frequency. It is not possible to define frequencies of occurrence for single phase, two-phase or three-phase short-circuits independently for each component. The relative frequency for each type of short-circuit is entered for all components in a uniform way.

31 - 42


Fig. 31.16: Voltage Sag Table Assessment - Advanced Options

The voltage sag analysis simulates various faults at all relevant busbars. It starts with the selected load points, and proceeds to neighboring busbars until the remaining voltage at all load points does not drop below the defined Exposed area limit. The remaining voltages and the short-circuit impedances for all load points are written to the result file specified by the Results parameter.

After all relevant busbars have been analyzed, the sag table assessment continues by analyzing short-circuits at the midpoint of all lines and cables that are connected between the relevant busbars. Again, the remaining voltages and short-circuit impedances for all load points are written to the result file.

After the complete exposed area has been analyzed in this way, the result file contains the values for Z_F1, Z_F2, Z_F0, Z_S1, Z_S2, Z_S0 and ura, uia, urb, uib, urc, uic for the two ends of all relevant lines and cables and at their midpoints.

The written impedances are interpolated between the ends of a line and the middle with a two-order polynomial. From them, and from the written remaining voltages, the various source impedances are estimated. These estimated impedances are also interpolated between the ends and the midpoint.

The interpolated impedances are then used to estimate the remaining voltages between the ends and the midpoints of the lines or cables. This quadratic interpolation gives good results also for longer lines, and also for long parallel or even triple parallel lines.

The main advantage is a substantial reduction in computation and an increase in the overall calculation speed.

31.4.2 Performing a Voltage Sag Table Assessment

A voltage sag table assessment is performed in two phases:

31 - 43


1 A result file with remaining voltages and short-circuit impedances is created by executing the ComVsag command. This can be done by selecting one or more nodes, right-clicking and executing the Calculate... --> Voltage sag table... option, or

by initiating the command directly from the main toolbar by clicking on the icon.

2 A voltage sag plot is created by selecting one or more of the nodes for which the ComVsag command was executed, right-clicking and executing the option Show --> Voltage Sag Plot...

Alternatively,

• The Load selection in the ComVsag dialogue can be filled manually with a set of objects. A load point is defined by a terminal, a busbar, or by a single-connection element (a load, motor, generator, etc.). These kinds of elements can be multi-selected from the single-line diagram or data manager. Once selected, right-click on them and select Define... --> General Set from the context-sensitive menu. This set can then be selected as the Load selection.

• A voltage sag plot can be created on a virtual instrument page manually, and the load points can then be selected from the list of analyzed load points.

If several objects are selected which are all connected to the same busbar, then that busbar will be added only once to the set of load points.

The Load selection parameter in the voltage sag assessment command should be set to use the SetSelect which has the Used for: Voltage sag table flag set. However, any other selection can be assigned to the Load selection.

The voltage sag tables are not calculated until a voltage sag plot is constructed. Upon reading the remaining voltages, short-circuit frequencies and short-circuit impedances from the result file, a voltage sag table is constructed for each selected load point. Figure 31.17 shows the voltage sag plot dialogue.

31 - 44


Fig. 31.17: Voltage Sag Plot Dialogue

Because there is no single definition of a voltage sag, the plot offers a selection of sag definitions:

• Minimum of Line-Neutral Voltages

• Minimum of Line-Line Voltages

• Minimum of Line-Line and Line-Neutral Voltage

• Positive Sequence Voltage

Secondly, the x-variable against which the sag frequency will be shown has to be selected. Possible x-variables are:

• Remaining Voltage

• Nom. Voltage at Shc-Busbar

• Fault Clearing Time

• Short-Circuit Type

Additionally, the x-variable can be sub-divided according to a split-variable (parameter

31 - 45


name: Split Bars in). Possible split variables are:

• no split

• any of the possible x-variables

the same parameter cannot be selected for the x-variable and the split-variable.

An example of the resulting voltage sag plot, in accordance with the settings shown in Figure 31.17 is shown in Figure 31.18.

Fig. 31.18: Example Voltage Sag Plot

The voltage sag plot always shows the annual frequency of occurrence on the y-axis.

The example plot shows a bar for each load point for each x-variable, which is the Remaining Voltage. All three loads can be seen to suffer either deep sags (remaining voltage less than 0.4 p.u.), or shallow sags, although the values at 0.8 p.u. are also signif-icant. Each bar is subdivided to the nominal voltage at SHC-Busbar. The shallow sags are caused by the low voltage network, as well as the deep sags. The high voltage network seems to cause moderate voltage sags. This is caused by the fact that the low voltage networks in this example are radially operated and the higher voltage networks are meshed. More detailed information about a specific value in the voltage sag plot can be obtained by placing the mouse over a bar or part of a bar (without clicking) and allowing the balloon help to pop up.

The voltage sag plot dialogue has a Report button, which outputs the voltage sag plot data to the output window. A table for each selected load point will be written in accor-dance to the selected Voltage Sag definition, x-Variable and Split Bars in selection. An example of a voltage sag table is shown below. The reported voltage sag tables also show the totals for each row and column.

DIgSI/info - 'Grid\TA2.ElmTerm'col : Remaining Voltage (Volt.Sag) [p.u.]row : Nom. Voltage at Shc-Busbar (Unom Shc) [kV]val : Frequency of Shc (Sag Freq.) [1/a]---------------------------------------------------------------------- | 0.20 0.50 0.60 0.80 0.85 0.90 0.95 1.00 |-------|-------------------------------------------------------|------ 10.0 | 1.56 0.94 0.00 0.00 0.00 0.00 2.25 6.75 | 11.50 50.0 | 1.45 1.52 0.00 0.83 0.09 0.12 1.08 5.57 | 10.66 150.0 | 3.50 2.32 1.67 0.00 0.00 0.00 0.00 0.00 | 7.50 380.0 | 0.00 1.25 0.00 1.25 0.00 0.00 0.00 0.00 | 2.50-------|-------------------------------------------------------|------ | 6.52 6.04 1.67 2.08 0.09 0.12 3.33 12.32 | 32.16----------------------------------------------------------------------

31 - 46


31.5 Compact Reliability Glossary

Lost load

A system load that is disconnected from the supply as a direct result of one or more system failures by intervention of automatic protection devices. A system load cannot be partly lost.

Shed load

A system load that is disconnected from the supply as a result of one or more system failures by intervention of a system operator. A system load can be shed up to a certain percentage.

Stochastic

A quantity is said to be stochastic when its value is random and therefore unknown. The range of possible values is known, however, as is the respective likelihood of these values. The number of eyes thrown with a dice is random, the possible outcomes are {1,2,3,4,5,6} and the likelihood is frac16 for each outcome. For a continuous range of possible outcomes, the likelihood is a continuous function, which is called the Probability Density Function or 'PDF'.

Statistic

Statistical calculation methods are used to analyze stochastic quantities. A simple example is the method for calculating a mean repair duration by dividing the total time spend repairing by the number of repairs performed.

Information obtained using statistical methods on measured data can be used to build Stochastic Models of the observed equipment.

Outage

The removal of a primary component from the system.

Forced Outage

The unplanned removal of a primary component from the system due to one or more failures in the system. A failure does not have lead to lead to an outage, for instance the failure of a transformer tap changer.

Scheduled Outage

The planned removal of a primary component from the system.

Maintenance

The planned removal of one or more primary components from the system.

31 - 47


Spare Unit

A reserve component, not connected to the system, which can be used as a replacement for a component on outage by switching or replacing.

Failure

The event in which a component does not operate as intended or stops operating as intended. An example of the former is a circuit breaker that fails to trip; an example of the latter is a transformer that is tripped by its Buchholz relay.

Hidden Failure

An undetected change in a component which will lead to the failure of the component the next time it is required to operate, unless it is inspected and repaired first.

Active Failure

The failure of a component which activates the automatic protection system. Active failures are always associated with short-circuits.

Passive Failure

The failure of a component which does not activate the automatic protection system.

Repair

The restoration of the functionality of a component, either by replacing the component or by repairing it.

Interruption

An unplanned zero-voltage situation at one or more load points due to outages in the system.

Contingency

The state of a system in which one or more primary components are on outage. The level of a contingency is determined by the number of primary components on outage. A "k-Level'' contingency is thus the state of a system in which exactly k primary components are on outage.

Adequacy

The ability of the electrical power system to meet the load demand under various steady state system conditions.

31 - 48


Security

The ability of the system to meet the load demand during and after a transient or dynamic disturbance of the system.

Availability

The fraction of time a component is able to operate as intended, either expressed as a real fraction or in hours per year.

Redundant Unit

A component whose outage will never lead to an interruption in the base state which cannot be restored by normal switching actions (i.e normal network reconfiguration) alone.

Base State

The state of the system where all components are able to operate as intended.

(n-1) system

A system for which all relevant components are redundant units.

(n-k) system

A system for which the outage of k or less components will never lead to an interruption which cannot be restored by normal switching actions (i.e normal network reconfigu-ration) alone.

Distribution Function

The distribution function for the stochastic quantity X equals the cumulative density function CDF(x).

CDF(x) = the probability of X to take a value smaller than x.

Probability Density Function

The function PDF(x), describing the probability of the stochastic quantity to take a value from an interval around x, divided by the length of that interval. The PDF(x) is the deriv-ative of the distribution function.

Hazard Rate Function

The function HRF(x) describes the probability of a stochastic quantity to be larger than x+dx, given the fact that it is larger than x, divided by dx. Therefore, the hazard rate can describe the probability of the failure of an element in the upcoming time period, given the fact that it is still functioning properly. The hazard rate is often used to describe equipment ageing and wear. A well-known example is the 'bath-tub' function which

31 - 49


describes the probability of a device failing in the next period during wear-in, normal service time and wear-out.

31 - 50

DIgSILENT PowerFactory Generation Adequacy Analysis

Chapter 32Generation Adequacy Analysis

The ability of the power system to be able to supply system load under all possible load conditions is known as 'System Adequacy'. Specifically this relates to the ability of the generation to meet the system demand while also considering typical system constraints such as:

• Generation unavailability due to fault or maintenance requirements;

• Variation in system load on an monthly, hourly and minute by minute basis;

• Variations in renewable output (notably wind generation output), which in turn affects the available generation capacity.

The PowerFactory 'Generation Adequacy' Tool is designed specifically for testing of 'System Adequacy'. Using this tool, it is possible to determine the contribution of wind generation to overall system capacity and to determine the probability of 'Loss of Load' (LOLP) and the 'Expected Demand Not Supplied' (EDNS).

Note: In PowerFactory V14.1, the Generation Adequacy Assessment is completed using the 'Monte Carlo Method' (probabilistic)


The analytical assessment of Generation Adequacy requires that each generator in the system is assigned a number of 'probabilistic states' which determine the likelihood of a generator operating at various output levels. Likewise, each of the system loads can be assigned a time based characteristic that determines the actual system load level for any point of time. A simplified general illustration of the Generation Adequacy assessment is shown in Figure 32.1.

In such a small example, it is possible to determine the Generation Adequacy analytically in a relatively short time. However, as the number of generators, generator states, loads and load states increases, the degrees of freedom for the analysis rapidly expands so that it becomes impossible to solve in a reasonable amount of time. Such a problem is ideally suited to Monte Carlo simulation.

32 - 1


Fig. 32.1: Generation Adequacy Assessment Illustration

Monte Carlo Method

In the Monte Carlo method, a sampling simulation is performed. Using uniform random number sequences, a random system state is generated. This system state consists of random generating operating states and of random time points. The generating operating states will have a corresponding generation power output, whereas the time points will have a corresponding power demand. The value of Demand Not Supplied (DNS) is then calculated for such state. This process is done for a specific number of draws (iterations). At the end of the simulation, the values of the Loss of Load Probability (LOLP), Loss of Load Expectancy (LOLE), Expected Demand Not Supplied (EDNS), and Loss of Energy Expectancy (LOEE) indices are calculated as average values from all the iterations performed.

Pseudo Random Number Generator

A Monte Carlo simulation relies on the generation of random numbers of 'high' quality. As all computers run deterministic code to generate random numbers, a software random number generator is known as a pseudo random number generator (PRNG). There are various PRNGs available, some of which do not display appropriate statistical qualities for use in Monte Carlo simulations, where very long sequences of independent random numbers are required.

PowerFactory uses an implementation of the 'RANROT' PRNG. This generator displays

32 - 2


excellent statistical qualities suitable for Monte Carlo simulations and is also relatively fast.

Example

To illustrate the process of a Monte Carlo simulation, an example is now presented using Figure 32.1 as the example network.

For each iteration, the operating state for each generator is randomly selected by gener-ating a uniform random number. For each of these states, the corresponding power output of the generator is calculated. The total generation power of the system is calculated by summing all the generator outputs.

For the same iteration, a time point in the system is randomly selected. For this time point, the power demand of each load is obtained. The total demand of the system is calculated by summing all the load demands. It is then possible to obtain the 'Demand Not Supplied' (DNS) value for this iteration, where DNS is defined as shown in Equation (32.1).

Eqn 32.1:

For example, in the first iteration, the generator states might be G1: 100%, G2: 100%, and G3: 75%. The corresponding outputs would be then G1: 100 MW, G2: 60 MW, and G3: 60 MW. The total generation output is the sum of all the three generator outputs; 220 MW. Also, a random time point yields Load A: 85 MW, Load B: 60 MW and Load C: 30 MW. The total system demand is the sum of all the load demands; 175 MW. Since the generation is greater than the demand, all the demand is supplied and the value of DNS is zero.

In a second iteration, the generator states might be G1: 0%, G2: 75%, and G3: 75%. The corresponding outputs would be then G1: 0 MW, G2: 45 MW, and G3: 60 MW. The total generation output is now 105 MW. A second random time point yields say Load A: 60 MW, Load B: 50 MW, and Load C: 20 MW. The total system demand is now 130 MW. In this case, the generation is smaller than the demand, so there is demand that cannot be supplied. The demand not supplied is defined as the difference between demand and generation - 25 MW in this iteration.

Continuing the analysis for a few subsequent iterations yields the results shown in Table 32.1:

Table 32.1: Example Monte Carlo Analysis

Iteration six yields a second case where demand is not supplied.

Once the analysis has continued in this way (usually for several tens of thousands of itera-tions) various indices of system adequacy can be calculated. The indices Loss of Load

DNS Demand= Generation–

32 - 3


Probability (LOLP) and Expected Demand Not Supplied (EDNS) are the critical measures. They are calculated as follows:

Eqn 32.2: %

Eqn 32.3:

where is the number of iterations where and is the total number of itera-tions.

Therefore, for the above example the indices are calculated as follows:

%

32.2 Database Objects and Models

There are several database objects in PowerFactory specifically related to the 'Generation Adequacy' Analysis, such as:

• Stochastic Model for Generation Object (StoGen);

• Power Curve Type (TypPowercurve); and

• Meteorological Station.

This section provides information about each of these objects.

32.2.1 Stochastic Model for Generation Object (StoGen)

This object is used for defining the availability states of a generator, an example of which is shown in Figure 32.2. An unlimited number of states is possible with each state divided into:

• Availability of Generation (in %)

• Probability of Occurrence (in %)

This means that for each state, the total available generation capacity in % of maximum output must be specified along with the probability that this availability occurs. Note that probability column is automatically constrained, so that the sum of the probability of all

LOLPNDNS

N-------------- 100=

EDNSDNSN

-------------------=

NDNS DNS 0 N

LOLP26--- 100 33,33= =

EDNS306------= 5MW=

32 - 4


states must equal 100 %.

Fig. 32.2: Stochastic Model for Generation Dialog Box

The Stochastic model for generation object should reside within the project library, 'Equipment Type Library'.

Note that the generator maximum output is calculated as where is the

nominal apparent power and is the nominal power factor.

32.2.2 Power Curve Type (TypPowercurve)

This object is used to specify the wind speed (in m/s) vs nominal power output (p.u or MW) for wind turbine generators. The dialog for the curve is shown in Figure 32.3.

Fig. 32.3: Power Curve Type (TypPowercurve)

For wind-speed values between specified curve values, PowerFactory interpolates using the method specified in the 'Approximation' drop down menu. Interpolation options include:

• constant

Generation Availability

Probability of Availability

Snom cos Snom

cos

'Approxima-tion' (curve interpolation method)

32 - 5


• linear

• polynomial

• spline and

• hermite.

To change the Power unit, go to the configuration tab and choose either p.u or MW by selecting the appropriate radio button.

32.2.3 Meteorological Station (ElmMeteostat)

It is often the case that 'groups' of wind generators have a wind speed characteristic that is correlated. PowerFactory can represent such a correlation through the 'Meteo Station' Object. This object is a 'grouping element' and is located within the project 'Network Data’ as shown in Figure 32.4.

Fig. 32.4: Project Data Structure showing the location of the 'Meteo Station' Object

Note that when two wind generators are correlated as members of the same 'Meteo Station', they may still have different average wind speeds defined within their Generation Adequacy dialog. During the Monte Carlo Analysis, a random wind speed is drawn for each 'Meteo Station'. This wind speed is then applied to every wind generator in that 'Meteo Station' using the Weibull Stochastic Model. Thus, the power is calculated according to the individual power curve of the generator.

When the generator is using time characteristics as a wind model, then the correlation is given by the Monte Carlo drawn time, which is the same for all the generators of the system.

Meteorological stations can be defined either via the element that is to be part of the meteorological station (from any of the generator elements described in Section 32.3), or via the single line diagram by right-clicking on an appropriate element and selecting 'Define… -> Meteo Station' (or 'Add to… -> Meteo Station') from the context-sensitive menu. Note that the ability to define a 'Meteo Station' is dependent upon whether at least

32 - 6


one of the 'member' generators has the options 'Generator' and 'Wind Generator' selected on its Basic Data page. If these options are not selected, the context menu entry is not visible.

Note: A graphical coloring mode exists for Meteorological Stations, so that they can be visualized in the single line graphic.

32.3 Assignment of Stochastic Model for Generation Object

For the Generation Adequacy Analysis, there is a distinction between 'Dispatchable (Conventional) Generation' and 'Non-dispatchable Generation'. Dispatchable generation refers to generation that can be controlled at a fixed output automatically, typically by varying the rate of fuel consumption. This includes generation technologies such as gas thermal, coal thermal, nuclear thermal and hydro.

Non-dispatchable generation refers to generation that cannot be automatically controlled because the output depends on some non controllable environmental condition such as solar radiation or the wind speed. Wind turbine and solar photovoltaic generators are examples of such 'environmentally dependent' generation technologies.

32.3.1 Definition of a Stochastic Multi-State Model

For both Dispatchable and Non-dispatchable generation it is possible to assign a Stochastic Multi-State model to define the availability of each unit. The availability is defined in a number of 'States' each with a certain probability as described in Section 32.2.1.

Definition of a Stochastic Model for Dispatchable (Conventional) Generation

The following 3-phase models are capable of utilising the Stochastic Model For Generation Object (see 32.2.1), provided they are defined as generators and not as motors within their respective element dialogs:

• Synchronous machine (ElmSym);

• Static generator (ElmGenstat) set as 'Fuel Cell', 'HVDC Terminal', 'Reactive Power Compensation', 'Storage', or other 'Static Generator';

• Asynchronous machine (ElmAsm); and

• Doubly-fed asynchronous machine (ElmAsmsc)

In all cases, the stochastic model object is assigned on the element’s 'Generation Adequacy' page, under 'Stochastic Multi-State Model'. This is illustrated in Figure 32.5.

32 - 7


Fig. 32.5: Generation Adequacy tab with a Stochastic Model for generation selected

Also, to consider the generation as 'dispatchable', the 'Wind Generation' option in the 'Basic Data' tab page of the synchronous, asynchronous, and doubly fed machine should be disabled.

Definition of a Stochastic Model for Non-Dispatchable (Wind and Renewable) Generation

As for the dispatchable generation, the following 3-phase models are capable of utilising the stochastic model for generation object, provided they are defined as generators and not as motors:

• Synchronous machine (ElmSym) set as 'Wind Generator';

• Static generator (ElmGenstat) set as 'Wind Generator', 'Photovoltaic' or 'Other Renewable'

• Asynchronous machine (ElmAsm) set as 'Wind Generator'; and

• Doubly-fed asynchronous machine (ElmAsmsc) set as 'Wind Generator'

In all cases, the stochastic model object is assigned on the element’s 'Generation Adequacy' tab page, under 'Stochastic Multi-State Model', as illustrated in Figure 32.5.

Objects not considered in Generation Adequacy Analysis

External Grids (ElmXnet), voltage and current sources (ElmVac, ElmIac) are ignored in the Generation Adequacy analysis.

32.3.2 Stochastic Wind Model

In addition to the stochastic multi-state model for generation described above, a stochastic wind model may be defined on the element’s Generation Adequacy page (provided that the type of generation is a wind generator). To enable this, navigate to the Generation Adequacy tab and check the option 'Wind Model'. The page will appear as shown in Figure 32.6.

32 - 8


Fig. 32.6: Stochastic Wind Model Definition

When the Stochastic Wind Model is selected, the wind generation characteristic is described using the Weibull Distribution. The mean wind speed, and shape factor (Beta) of the distribution can be adjusted to achieve the desired wind characteristic for each wind generator.

In addition to describing the Weibull distribution using Mean Wind Speed and Beta, the following alternate methods of data input can be used:

• Mean Wind Speed and Variance;

• Lambda and Variance;

• Lambda and Beta.

The input method can be changed by using the input selection arrow and choosing the desired method from the input window that appears.

32.3.3 Time Series Characteristic for Wind Generation

If detailed data of wind generation output over time or wind speed over time is available, then this can be used instead of a Stochastic Model. The data can be read by Power-Factory as either a ChaVec characteristic or from an external file using the ChaVecFile

Wind Power Curve definition

Meteo Station definition

Selection of Stochastic wind model

32 - 9


characteristic. In both cases the information required is one year of data in hourly intervals - although non integer values can also be specified in the referenced data.

If the option 'Time Series Characteristics of Wind Speed' is selected, then the actual wind generator power output for each iteration is calculated automatically from the Wind Power Curve. If the option, 'Time Series Characteristic of Active Power Contribution' is selected then no power curve is required.

Data for multiple years can also be used by referencing an additional characteristic for each year. The 'Generation Adequacy' algorithm then selects a random wind speed or power value from one of the input data years - essentially there is more data for the random Monte Carlo iteration to select from.

A screenshot showing a wind generator model with three years of data is shown in Figure 32.7.

Fig. 32.7: Wind Model using Wind Output Data

Other Renewable Generation

Static Generators (ElmGenstat) of category 'Photovoltaic' or 'Other Renewable' cannot have a Stochastic wind model definition. However, they may still have a 'Stochastic Multi-State model'. Their output is added to the aggregated non-dispatchable generation as described later in this chapter.

Consideration of Parallel Machines

The Generation Adequacy analysis automatically considers parallel machines defined in the basic data of the generator object using the variable 'ngnum', as shown in Figure 32.8. Each of the parallel machines is treated independently. For example, a random operational state is generated for each of the parallel machines. Effectively this is the same as if 'n' machines were modelled separately.

32 - 10


Fig. 32.8: Synchronous machine element with the parameter 'ngnum' (number of parallel machines highlighted).

32.4 Demand definition

Unless a time characteristic is assigned to either the Active Power (plini) or Scale factor (scale0) variables (highlighted in Figure 32.9) of the load element, then the load is treated as fixed demand. This means that the demand value does not change during the entire analysis. Both General Loads (ElmLod) and LV Loads (ElmLodlv) are considered for the analysis.

Fig. 32.9: ElmLod object dialog showing the variables that can have applied time Characteristics effecting the Generation Adequacy analysis.

More information about assigning time based characteristics to object variables can be found in Chapter 18: Parameter Characteristics.

32.5 Generation Adequacy Analysis Toolbar

The selection of the Generation Adequacy toolbar is shown in Figure 32.10.

32 - 11


Fig. 32.10: Generation Adequacy Toolbar selection

Once selected, the available buttons are shown in Figure 32.11.

Fig. 32.11: Generation Adequacy Analysis Toolbar

32.6 Generation Adequacy Initialisation Command (ComGenrelinc)

Before a Generation Adequacy Analysis can be completed, the simulation must be initialised. The Initialisation dialog box with the 'Basic Options' tab selected is shown in Figure 32.12. The available options are explained in this section.

Generation Adequacy Tool-

Initialise Generation Adequacy Analysis

Run Generation Adequacy Analysis

Stop Generation Adequacy Analysis

Create Distribution Plots

Create Draws Plots

Create Convergence Plots

32 - 12


Fig. 32.12: Generation Adequacy Initialisation Command

Network

• System Losses; Here a fixed percentage of losses can be entered. This value is subtracted from the total generation at each iteration.

• Load Flow Command; This is a reference to the load-flow command that will be used to obtain the network topology for the analysis. It must be set to 'AC load-flow balanced, positive sequence' or 'DC load-flow'. A converging load-flow is a requirement for the Generation Adequacy analysis.

Demand Consideration

• Fixed Demand Level; If this option is selected, all load time characteristics are ignored and the total demand is calculated at the initial iteration and used for all subsequent iterations.

• Consider Time Characteristics; If this option is selected, any time characteristics assigned to loads will be automatically considered in the calculation. Therefore, the total demand can vary at each iteration.

Consider Maintenance Plans

If this option is enabled then any maintenance plans (out of service or derating) in the

32 - 13


project will be automatically considered. Consequently, when an iteration draws a time that falls within a planned outage or derating, the outage (or derating) is applied to the target element resulting in a reduction in available generation capacity.

To define a maintenance plan, right-click the target object from the single line graphic or from the data manager and select the option 'Define... -> Planned Outage'. For more information on Planned Outages refer to Chapter 5.5.5 (Outages).

Time Dependent Data

• Year of Study; The period considered for the Generation Adequacy analysis is always one year. However, it is possible for load characteristics to contain information for many years. Therefore, the year considered by the calculation must be selected. Note that this variable does not influence the wind speed or wind power data if the wind model for the generator references time series data as described in Section 32.3.3 (Time Series Characteristic for Wind Generation). If more than one year’s data is available, this simply increases the 'pool' of available data for the analysis.

• Months, Days; These checkboxes allow the user to select the time period that will be considered for the analysis. For instance, if only 'January' is selected then the iteration time will be constrained to within this month.

Time Intervals

The user can specify up to three time intervals for the time window in which the analysis will be completed. The time interval starts at the 'From' hour (0 minutes, 0 seconds), and ends at the 'To' hour (0 minutes, 0 seconds) inclusive.

Output options

The output window of the 'Generation Adequacy Initialisation Command' is shown in Figure 32.13.

Fig. 32.13: Output options for the Generation Adequacy Initialisation

• Create Plots; If this option is checked, then PowerFactory will automatically create output plots after the simulation finishes. See Section 32.8 for details of the plots that are automatically created. Note this will generate a new set of plots for each run of the analysis. So, if you wish for an existing set of plots to be updated, then leave this option unchecked.

32 - 14


• Draws; If this option is checked, then the user can specify a location for the results of the simulation to be permanently stored within the database. This is the result of each iteration. If this option is unchecked, then the results are deleted after each simulation run.

• Distribution; Here the user can select the storage location for the distribution probabilities for the entire analysis. This information is always retained in the database.

Advanced Options

The Advanced Options screen is shown in Figure 32.14. Here the user can change the option for the generation of random numbers from 'auto' to 'renew'. If the 'renew' option is selected, then the simulation can use one of a number of pre-defined random seeds (A-K). As the software 'pseudo-random' number generator is deterministic, this allows for the exact sequence of random numbers to be repeated.

Fig. 32.14: Initialisation Command Advanced Options

32.7 Run Generation Adequacy Command (ComGenrel)

The 'Run Generation Adequacy Analysis Command' appears in two styles depending on the status of the calculation. If the calculation is being run for the first time, then it appears as shown in Figure 32.15. On the other hand, if some iterations are already complete, then the calculation can be continued and the dialog appears as shown in Figure 32.16.

Fig. 32.15: Run Generation Adequacy Command Dialog (new simulation)

32 - 15


Fig. 32.16: Run Generation Adequacy Command Dialog (post simulation)

Pressing Execute will run the Generation Adequacy Analysis. The button can be used to interrupt the analysis before the set number of iterations is complete, if desired. Later, the simulation can be resumed from the 'stop point' using the 'Run Generation Adequacy Analysis Command'.

Max Number of Iterations

This specifies the number of iterations to be completed by the Monte Carlo Analysis. The default setting is 100,000.

Additional Iterations

After one analysis is completed, the Generation Adequacy Analysis can be extended for a number of 'Additional Iterations'. Especially in very large systems, it may be useful to run the first simulation with a smaller number of initial iterations, say 20,000 and then run additional iterations as necessary using this option.

Generation Adequacy

This reference provides a link to the 'Generation Adequacy Initialisation Command', so that the calculation settings can be easily inspected.

32.8 Generation Adequacy Results

Result plots for the Generation Adequacy Analysis are automatically generated if the 'Create Plots' option is enabled in Initialisation Command output options. Alternatively, the plots can be manually created using the toolbar plot icons .

32.8.1 Draws (Iterations) Plots

This button draws by default four figures for the following result variables:

• Total Available Capacity in MW;

• Available Dispatchable Generation in MW;

• Total Demand in MW;

• Available Non-dispatchable capacity in MW;

32 - 16


• Total Reserve Generation Capacity in MW;

• Total Demand in MW;

• Residual Demand in MW

Each of the data points on the plots represents a single Monte Carlo iteration.

•

32.8.2 Distribution (Cumulative Probability) Plots

This button draws a distribution plot which is essentially the data from 'Draws' plots sorted in descending order. The data then becomes a cumulative probability distribution. An example is shown in Figure 32.17.

Fig. 32.17: Distribution (Cumulative Probability) Plots

Obtaining the LOLP from the Distribution Plots

The LOLP index can be obtained by inspection directly from the Distribution Plots if the demand is constant. The LOLP can be read directly from the intersection of the Total Generation curve and the Total Demand curve as demonstrated in Figure 32.18.

When the demand is variable, then the LOLP index cannot be inferred from the above diagram. Figure 32.19 shows such a case. There is no intersection point even though the calculated LOLP index in this case is 20 %. In such cases, the LOLP index must be inferred from the distribution plot of the Total Reserve Generation. As shown in Figure 32.20, the

32 - 17


intersection of this curve with the x-axis gives the LOLP index.

Fig. 32.18: Inferring the LOLP index directly from the intersection of the Total Generation and Total Demand

Fig. 32.19: Variable Demand - distribution of Total Generation and Total Demand

32 - 18


Fig. 32.20: Total Reserve Generation

32.8.3 Convergence Plots

This button creates the so-called convergence plots for the LOLP and EDNS. As the number of iterations becomes large the LOLP index will converge towards its final value, likewise for the EDNS. The convergence plots are a way of visualising this process. An example convergence plot is shown in Figure 32.21.

32 - 19


Fig. 32.21: Example Convergence Plot

Note: By default, the convergence plot is zoomed to the plot extents and due to the number of iterations it may be difficult to observe the upper and lower confidence limits. It is suggested that the 'Zoom Y-axis' and 'Zoom X-axis' buttons are used to observe the confidence limits in greater detail.

On both plots, the upper and lower confidence intervals are also drawn.

The sample variance is calculated as follows:

where is the number of samples, is the sample and is the sample mean. The 90 % confidence interval is calculated according to the following formula:

where z is the standard inverse probability for the 'Student’s t distribution' with a confi-dence interval of 90 %. Note z tends to 1.645 (inverse normal) as the number of iterations becomes large.

2 1n 1–------------ yi y– 2

i 1=

n

=

n yi y

CL yn

------- z=

32 - 20


32.8.4 Summary of variables calculated during the Generation Adequacy Analysis

Table 32.2: Generation Adequacy Calculated Variables

32 - 21


32 - 22

DIgSILENT PowerFactory Optimal Power Flow

Chapter 33Optimal Power Flow

The Optimal Power Flow (OPF) module in PowerFactory optimizes a certain objective function in a network whilst fulfilling equality constraints (the load flow equations) and inequality constraints (i.e. generator reactive power limits). The user can choose between interior point and linear optimization methods. In the case of linear optimization, contin-gency constraints can also be enforced within OPF.

An OPF calculation in PowerFactory can be initiated by one of the following means:

• By going to the main menu and selecting Calculation --> Optimal Power Flow...; or

• By clicking on the OPF icon on the main toolbar.

In both cases, the calculation is started by pressing the Execute button in the OPF command dialogue.

33.1 AC Optimization (Interior Point Method)

If the AC Optimization method is selected, the OPF performs a non-linear optimization based on a state-of-the-art interior point algorithm. The following sections explain the selection of objective function to be optimized, the selection of control variables, and the definition of inequality constraints. The OPF command in PowerFactory is accessible by going to the main menu and selecting Calculation --> Optimal Power Flow... , or via the

OPF icon on the main toolbar.


The Basic Options tab of the OPF dialogue (AC optimization method) is shown in Figure 33.1.

Fig. 33.1: Basic Options Tab of OPF Dialogue (AC Optimization Method)

33 - 1


Method

To perform an AC optimization OPF study, the Method must be set to AC Optimization (Interior Point Method) as shown in Figure 33.1.

Objective Function

The OPF command dialogue, configured for AC optimization, has a selection of three distinct objective functions, as shown in Figure 33.2. These are:

• Minimization of Losses

• Minimization of Costs

• Minimization of Load Shedding

Fig. 33.2: Objective Function Selection for OPF (AC Optimization Method)

Minimization of Losses

When this objective function is selected, the goal of the optimization is to find a power dispatch which minimizes the overall active power losses.

Minimization of Costs

When this objective function is selected, the goal of the optimization is to supply the system under optimal operating costs. More specifically, the aim is to minimize the cost of power dispatch based on non-linear operating cost functions for each generator and on tariff systems for each external grid.

For this purpose, the user needs to introduce for each generator, a cost function for its power dispatch; and for each external grid, a tariff system.

- Cost Functions for GeneratorsImposing an operating cost function on a generator element is done as follows: on the Optimization tab of each synchronous machine (ElmSym) element’s dialogue (see Figure 33.3), it is possible to specify the operating costs of the unit with the aid of the Operating Costs table (which relates active power produced (in MW) to the corresponding cost (in $/h)). This data is then represented graphically beneath the Operating Costs table, for verification purposes (see Figure 33.3). The number of rows that can be entered in to the table is unlimited. To add or delete table rows, right-click on a row number in the table and select the appropriate command (i.e.

33 - 2


'Copy', 'Paste', 'Select All'; 'Insert Rows', 'Append Rows', 'Append n Rows', 'Delete Rows', etc.). If there are more than two rows, spline interpolation is used.

- Tariff Systems for External GridsAn external grid contributes to the overall cost function by a predefined tariff system. On the Optimization tab of each external grid (ElmXnet) element’s dialogue (see Figure 33.4), the tariffs can be edited via the Incremental Costs table. This table relates the cost (in $/MWh) over a certain range of active power exchange. The input data is represented graphically beneath the Incremental Costs table. In addition, the user can enter a monthly no load cost (in $/month), which can be interpreted as a vertical shift of the cost function (see Figure 33.4).

In contrast to a synchronous machine, where the cost curve is directly expressed in $/h, the cost curve of an external grid is defined by means of a tariff which holds within certain intervals. Mathematically speaking, the cost curve of a synchronous machine is calculated as the interpolation of predefined cost points, whereas the cost curve of an external grid is a piecewise linear function with predefined slopes in each interval.

Fig. 33.3: Editing the Operating Costs of a Synchronous Machine (ElmSym)

33 - 3


Fig. 33.4: Editing the Incremental Costs of an External Net (ElmXnet)

Note that this piecewise linear function is not differentiable at the interval limits. Since non-differentiable functions might cause problems within the optimization routine, PowerFactory smooths the cost function slightly over a small range around the non-differentiable points. The width of this range can be defined by the user through the Smoothing of Cost Function factor (also shown in Figure 33.4). A value of 0% corresponds to no smoothing of the curve, whereas a value of 100% corresponds to full interpolation. The default value is 5%. It is recommended to leave this value at its default setting.

Minimization of Load Shedding

The goal of this objective function is to minimize the overall cost of load shedding, such that all constraints can be fulfilled. A typical application for this objective function is “Infeasibility Handling”. For the abovementioned objective functions, it may occur that the constraints imposed on the network are such that no feasible solution exists. This is evidenced by a lack of convergence of the optimization. In such cases, it is highly likely that not all loads can be supplied due to constraint restrictions. Hence it is recommended in these situations to firstly perform a Minimization of Load Shedding.

In this (and only this) optimization scenario, all load elements which have the option Allow load shedding enabled will act as controls. This option is enabled in the load (ElmLod) element’s dialogue on the Optimization tab in the Controls section. All loads without this option enabled will behave as they would in a conventional load flow calculation. In order to minimize the overall load shedding, for each individual load, the user must specify the

33 - 4


cost of shedding (in $ per shed MVA).

For each load that participates as a control in the optimization, the scaling factor will be optimized. The optimization is such that the overall cost of load shedding is minimized. Additionally, the user can specify the range over which the load may be scaled (options Min. load shedding and Max. load shedding), as shown in Figure 33.5.

Fig. 33.5: Editing a Load Element (ElmLod) for Minimization of Load Shedding

Controls

The global control parameters can be selected on the Basic Options tab of the OPF dialogue (see Figure 33.6). The user can specify which parameters might serve as poten-tial degrees of freedom for the OPF algorithm; i.e. which parameters will contribute as controls. The set of potential controls can be grouped into four categories:

1 Generator Active Power Dispatch (ElmSym)

2 Generator Reactive Power Dispatch (ElmSym)

3 Transformer Tap Positions (for 2- and 3-winding transformers):

- 2-Winding Transformer (ElmTr2):

• Tap Position (continuous or discrete)

- 3-Winding Transformer (ElmTr3):

• HV-Tap Position (continuous or discrete)

• LV-Tap Position (continuous or discrete)

• MV-Tap Position (continuous or discrete)

4 Switchable Shunts (ElmShnt):• Number of steps (continuous or discrete)

It should be noted that the load scaling factors will only be taken into account for the Mini-mization of Load Shedding objective function. In this case, all loads which allow load shedding are automatically used as controls.

These global controls determine which element controls will be considered in the optimi-zation. The general rule is as follows: a parameter will be considered as a control if the corresponding flag is set on the Optimization page of the element’s dialogue and if, in

33 - 5


addition, the corresponding global parameter is set on the Basic Options tab of the OPF command dialogue (see Figure 33.6).

For example, if the control parameter Tap Position HV-Side of a 3-winding transformer is enabled (as shown in Figure 33.9), it will only be included in the OPF as a control param-eter if the corresponding option Transformer Tap Positions is enabled in the OPF command dialogue (as shown in Figure 33.6).

If enabled, the abovementioned control parameters serve as variable setpoints during the OPF. However, if a parameter is not enabled as a control parameter, the OPF will treat this parameter according to the load flow settings.

Fig. 33.6: Global Controls for OPF (AC Optimization Method)

This could be a fixed position or a position found due to the option Automatic Tap Adjust of Transformers being selected in the load flow command. In this mode, the transformer tap position could be found in order to control the voltage of a certain node, or to be a slave that is externally controlled by some other transformer tap.

Setting Individual Model-Based Controls

Each control can be individually selected to take part in the optimization. Specifically, for each generator (ElmSym), each transformer (ElmTr2, ElmTr3), and each shunt (ElmShnt), the user can check the corresponding Controls flag on the optimization page of the element’s dialogue.

33 - 6


Synchronous Machines

A synchronous machine may contribute two possible setpoints, namely active and reactive power control (see Figure 33.7).

Fig. 33.7: Active and Reactive Power Controls of a Synchronous Machine (ElmSym)

2- and 3-Winding Transformers

If a transformer has the Tap Position option selected, the user can further select the asso-ciated Control Mode to be used. This determines whether the tap position will be treated as a continuous or a discrete control parameter in OPF. Note that a 3-winding transformer has up to three tap changers which may individually be used as either continuous or discrete control parameters in OPF.

Figure 33.8 shows the Controls section of the dialogue for a 2-winding transformer and Figure 33.9 shows the Controls section of the dialogue for a 3-winding transformer. It should be noted that the Optimize section with the selection of Pre- and post-fault position or Only pre-fault position are only considered by the DC OPF.

Fig. 33.8: Tap Position Control (and Loading Constraint) for a 2-Winding Transformer

33 - 7


Fig. 33.9: Tap Position Control for a 3-Winding Transformer

Shunts

In a similar fashion to transformers, the number of steps for a shunt may serve as either a continuous or a discrete optimization parameter (see Figure 33.10).

Fig. 33.10: Control Parameter for a Shunt (ElmShnt)

Constraints

The user can formulate various inequality constraints for certain system parameters, such that the OPF solution lies within these defined limits. Since all inequality constraints are considered as “hard constraints”, setting constraints may result in no feasible solution being found.

The handling of OPF constraints in PowerFactory is very flexible, and various categories of constraints exist. A constraint is considered in the OPF if and only if the individual constraint flag is checked in the element and the corresponding global flag is enabled in the OPF dialogue. Figure 33.11 shows the Constraints available for the AC optimization formulation of OPF in PowerFactory.

33 - 8


Fig. 33.11: Constraints Settings for OPF (AC Optimization Method)

The optimization uses further constraints that are automatically imposed as soon as the corresponding parameter is used as a control. Examples of such constraints are tap posi-tion limits and the number of steps for switchable shunts.

Network elements and their available constraints are listed below:

• Busbars and Terminals (ElmTerm):

- Minimum Voltage

- Maximum Voltage

• Lines (ElmLne):

- Maximum Loading

• 2- and 3-Winding Transformer (ElmTr2, ElmTr3):

- Maximum Loading

- Tap Position range (if corresponding tap is a designated control parameter)

• Shunts (ElmShnt): - Controller Steps range (if switchable steps are designated control parameters)

• Generator (ElmSym):

- Minimum Active Power

33 - 9


- Maximum Active Power

- Minimum Reactive Power

- Maximum Reactive Power

• Boundary (ElmBoundary):

- Minimum Active Boundary Flow

- Maximum Active Boundary Flow

- Minimum Reactive Boundary Flow

- Maximum Reactive Boundary Flow

Branch Flow Limits (max. loading)

Branch flow limits formulate an upper bound on the loading of any branch (ElmLne, ElmTr2, ElmTr3, etc). The user has to specify a maximum value for the loading on the element’s Optimization page (see Figure 33.12). If specified as shown in Figure 33.12, this constraint is only taken into consideration if the corresponding flag (Branch Flow Limits (max. loading)) in the OPF dialogue is also ticked. Loading limits are supported for lines and 2- and 3-winding transformers.

Fig. 33.12: Max. Loading Constraint of a Line Element (similar for 2- and 3-Winding

Transformers)

Active and Reactive Power Limits of Generators and External Grids

For each synchronous machine (ElmSym) and external grid (ElmXnet), the user may impose up to four inequality constraints: namely a minimum and maximum value for active power generation; and a minimum and maximum value for reactive power gener-ation (see Figure 33.13). Active power limits are specified as MW values; reactive power limits may be specified as either absolute values or as per unit values (i.e. referred to the type’s nominal apparent power). Alternatively, it is possible to directly use the reactive power limits specified in the synchronous machine’s type (TypSym). Again, the user is free to select any number and combination of the available constraints.

33 - 10


Fig. 33.13: Active and Reactive Power Constraints of a Synchronous Machine

(ElmSym)

Voltage Limits of Busbars/Terminals

The maximum and minimum allowable voltages for each terminal or busbar element (ElmTerm) can be specified in the corresponding element’s dialogue (see Figure 33.14). Therefore, each terminal or busbar may contribute at most two inequality constraints to the OPF. Maximum and minimum voltage limits may be imposed individually; i.e. it is possible to specify an upper limit without specifying a lower limit.

Fig. 33.14: Voltage Constraints for a Terminal/Busbar (ElmTerm)

Boundary Flow Limits

PowerFactory boundary elements (ElmBoundary, icon ) define topological regions in a power system by a user-specified topological cut through the network. Constraints

33 - 11


can be defined for the flow of active and reactive power in a network (over a defined boundary or between internal and external regions of a boundary), and this constraint can then be enforced in OPF. For detailed information on defining boundaries, please refer to Section 15.3.

Fig. 33.15: Defining Boundary Flow Limits (ElmBoundary)

Mathematical Background

The non-linear optimization is implemented using an iterative interior-point algorithm based on the Newton-Lagrange method. Recall that the goal of the optimization is to mini-mize an objective function f subject to the equality constraints imposed by the load flow equations and also to the inequality constraints defined for various power system elements. This is summarised mathematically as follows:

subject to:

where g represents the load flow equations and h is the set of inequality constraints. Introducing a slack variable for each inequality constraint, this can be reformulated as:

We then incorporate logarithmic penalties and minimize the function:

where µ is the penalty weighting factor. In order to change the contribution of the penalty function:

min f x =

g x 0=

h x 0

g x 0=

h x s+ 0=

s 0

min f x log si

i–=

33 - 12


to the overall minimization, the penalty weighting factor µ will be decreased from a user-defined initial value (µmax) to a user-defined target value (µmin).

The smaller the minimum penalty weighting factor, the less the applied penalty will be for a solution which is close to the constraint limits. This may result in a solution that is close to the limiting constraint bounds (if necessary). However, a smaller minimum penalty weighting factor will result in a higher number of iterations required.

Results

The presentation of OPF results is integrated into the user interface, in that the OPF solu-tion is available via the complete set of variables available for conventional load flow calculations. These can be viewed in the single line diagram or through a data browser. The inclusion of the following variables in the Flexible Data tab (for synchronous machines and grids) is suggested, as shown in Figure 33.16. The Variable Set must be set to 'Calcu-lation Parameter' as indicated below, and the actual variable names are given in paren-theses.

Synchronous machines:

• Active Power ('Calculation Parameter' P:bus1; this parameter is highlighted in Figure 33.16)

• Reactive Power ('Calculation Parameter' Q:bus1)

• Apparent Power ('Calculation Parameter' S:bus1)

• Voltage Magnitude ('Calculation Parameter' u:bus1)

Fig. 33.16: Definition of Flexible Data for Synchronous Machines (ElmSym)

Grids:

• Total Production Cost, including costs through external grids ('Calculation Parameter' c:cst_disp; see this parameter highlighted in Figure 33.17). It should be noted that the production costs are expressed in the same units utilized in the production cost tables of the individual generator elements.

• Active Power Losses ('Calculation Parameter' c:LossP)

• Reactive Power Losses ('Calculation Parameter' c:LossQ)

• Active Power Generation ('Calculation Parameter' c:GenP)

fpen log si

i=

33 - 13


• Reactive Power Generation ('Calculation Parameter' c:GenQ)

Fig. 33.17: Definition of Flexible Data for Grids (ElmNet)

In addition to these results, the complete set of variables from conventional load flow calculations is available. For further information on defining Flexible Data in PowerFac-tory, please refer to Section 12.5.

A text report is also available and can be generated by clicking on the Output Calculation

Analysis icon on the main toolbar. This offers various templates for detailed result documentation.

33.1.2 Initialization

The non-linear optimization requires initialization to generate an initial starting condition. The Iteration tab of the OPF dialogue as shown in Figure 33.18 allows the user to select the initialization method.

Fig. 33.18: Initialization Settings for OPF (AC Optimization Method)

Initialization of Non-Linear Optimization

Load Flow

Displays the load flow command which is used for initialization in the case that no flat start initialization is used.

Initialize by Flat-Start

The user may choose whether the initialization is performed by a load flow calcula-tion or by a flat start. If it is known in advance that the final solution of the optimi-

33 - 14


zation is close to a valid load flow solution, initialization using a load flow calculation results in faster convergence.

No Flat Initialization (Use Load Flow Result)

If this option is selected, the OPF checks whether an “OPF-initializing” load flow re-sult has been calculated prior to the OPF. Here, “OPF-initializing” means that the flag Use this load flow for initialization of OPF was enabled in the load flow command dialogue before execution. This flag can be found on the second page of the Ad-vanced Options tab in the load flow command dialogue. The result of this load flow is then used as a starting point for the iterative OPF interior-point algorithm. If no valid OPF-initializing load flow result is found, the OPF will recalculate a new load flow.


Penalty Weighting Factor

The penalty weighting factor determines the amount by which the penalty is applied. For example, the smaller the specified penalty weighting factor, the less the penalty will be applied for solutions which are close to constraint limits.

Initial ValueInitial value of the penalty weighting factor.Target ValueTarget value of the penalty weighting factor.Reduction FactorA factor by which the current penalty weighting factor will be divided by betweenthe iterations.

Fig. 33.19: Penalty Weighting Factor Settings for OPF (AC Optimization Method)


PowerFactory offers the user flexibility in configuring of the number of iterations and the convergence criteria for OPF. The available options on the Iteration Control tab of the

33 - 15


OPF dialogue are shown in Figure 33.20.

Fig. 33.20: Iteration Control Settings for OPF (AC Optimization Method)

The implementation of the Lagrange-Newton method means that the OPF will internally minimize the resulting Lagrange function:

with the Lagrange multipliers .

The following parameters can be used to alter the stopping criteria for this iterative process. The algorithm stops successfully if the following three criteria are fulfilled:

1 The maximum number of iterations has not yet been reached.

2 All load flow constraint equations g(x)=0 are fulfilled to a predefined degree of exactness (i.e. within an allowable tolerance), which means:

- all nodal equations are fulfilled

- all model equations are fulfilled

3 The Lagrange function L converges. This can be achieved if:

- either the objective function itself converges to a stationary point, or the gradient of the objective function converges to zero.

The following parameters are used to configure these stopping criteria. The alteration of the default values for these parameters is recommended only for advanced users.

Maximum Number of Iterations

Interior-Point Algorithm (Inner Loop)

L x s f x log si T

g x h x s+ + +

i–=

33 - 16


Maximum number of iterations for the interior-point algorithm.

Control Loop (Outer Loop)

Maximum number of iterations of the outer loop.

Convergence Criteria

Max. Acceptable Error for Nodes

The maximum allowable error for the nodal equations (in kVA).

Max. Acceptable Error for Model Equations

The maximum allowable error for the model equations (in %).

Max. Change of Objective Function

Used when Convergence of Objective Function option values of objective function become constant is selected. The user enters a value (in %), below which the La-grangian is considered to have converged.

Max. Value for Gradient of Objective Function

Used when Convergence of Objective Function option gradient of objective function converges to zero is selected. The user enters an absolute value, below which the Lagrangian is considered to have converged.

Convergence of Objective Function

Options relating to the convergence criteria for the Lagrangian function: either the value of the function itself is required to converge to a stationary point, or the gra-dient of the Lagrangian is required to converge, as described below.

values of objective function become constant

If this option is selected, the user is asked to enter a value for the Max. Change of Objective Function. If the change in value between two consecutive iterations falls below this value, the Lagrangian is considered to have converged.

gradient of objective function converges to zero

If this option is selected, the user is asked to enter a value for the Max. Value for Gradient of Objective Function. If the gradient falls below this value, the Lagrangian is considered to have converged.

For reasons of mathematical exactness, it is strongly recommended to select the latter option, gradient of objective function converges to zero. If the underlying Jacobian matrix is numerically instable, this often results in oscillatory behaviour in the last iterations. Therefore, the latter method provides assurance that the result is in fact a minimum.

33.1.5 Output

Prior to the non-linear optimization, the OPF informs the user (in the output window) of the total number of constraints and controls that will be considered in the subsequent calculation. This information is detailed such that the imposed constraints and the partic-ipating controls are counted for each constraint and control categories separately. Two

33 - 17


options are available to select the level of detail contained in output messages. These options are available in the Output tab of the OPF dialogue and are shown in Figure 33.21 and are described below.

Fig. 33.21: Output Settings for OPF (AC Optimization Method)

Show Convergence Progress Report

If this flag is checked on the Output page of the OPF dialogue, the user will get a detailed report on the convergence of the non-linear optimization. For each step of the iteration, the following figures are displayed in the output window (actual variable names are shown parenthesized in italics):

• The current error of the constraint nodal equations (in VA) (Err.Nodes);

• The current error of the constraint model equations (Err.ModelEqu);

• The current error of the inequality constraints (eInequ);

• The current value of the gradient of the Lagrangian function (gradLagFunc);

• The current value of the Lagrangian function (LagFunc);

• The current value of the objective function f to be minimized (ObjFunc);

• The current value of the penalty function fpen (PenFunc);

• The current values of the relaxation factors (Rlx1, Rlx2) for the primal and dual variables;

• The current value of the penalty factor µ (PenFac).

Show Max. Nodal and Model Equation Error Elements

If this flag is checked, the algorithm outputs per iteration, the components which have the largest error in the equality constraints (i.e. mismatch in the load flow equations).

33 - 18


An outer loop is wrapped around the central non-linear optimization algorithm. This outer loop is required to perform rounding and optimization of the evaluated tap and shunt posi-tions to discrete values (if desired by the user). The maximum number of outer loops is defined on the Iteration Control tab of the dialogue. However, if no convergence is reached with the defined number of outer loops, the user will be informed via a message in the output window that further outer loop iterations are required.

33 - 19


33.2 DC Optimization (Linear Programming)

The following describes the configuration of the DC optimization formulation of OPF in PowerFactory.

Internally, from the settings provided, a linear programming (LP) formulation of the problem is derived. The load flow is calculated using the linear DC load flow method. For general information regarding DC load flow, refer to Section 23 (Load Flow Analysis). PowerFactory uses a standard LP-solver (based on the simplex method and a branch-and-bound algorithm) which ascertains whether the solution is feasible. The result of the linear optimization tool includes calculated results for control variables, such that all imposed constraints are fulfilled and the objective function is optimized.

Provided that a feasible solution exists, the optimal solution will be available as a calcula-tion result. That is, the algorithm will provide a DC load flow solution where all generator injections and tap positions are set to optimal values. The DC load flow solution includes the following calculated parameters (parameter names are given in italics):

• For terminals:

- Voltage Angle (phiu [deg])

- Voltage Magnitude (u [p.u.]; assumed to be 1.0 p.u. in DC calculation)

- Voltage Magnitude (upc [%]; assumed to be 100 % in DC calculation)

- Line-Ground Voltage Magnitude (U [kV])

- Line-Line Voltage Magnitude (U1 [kV])

• For branches:

- Active Power Flow (P [MW])

- Active Power Losses (Ploss [MW]; assumed to be 0 MW in DC calculation)

- Reactive Power Flow (Q [Mvar]; assumed to be 0 MVAr in DC calculation)

- Reactive Power Losses (Qloss [Mvar]; assumed to be 0 MVAr in DC calculation)

- Loading (loading [%]; Loading with respect to continuous rating)

The following parameters are calculated in addition to the results found by the DC load flow:

• For generators:c:avgCosts

The fixed cost factor [$/MWh] used in the objective function (i.e. average cost considering the costs at the generator’s active power limits).

c:PdispOptimal power dispatch for generator.

c:cst_dispProduction costs in optimal solution:cst_disp = costs * Pdisp

• For Transformers:c:nntap

Optimal tap position.

• For loads:

33 - 20


c:PdispOptimal load shedding for load.


The Basic Options tab of the OPF dialogue (DC optimization method) is shown in Figure 33.22.

Fig. 33.22: Basic Options Tab of OPF Dialogue (DC Optimization Method)

Method

To perform a DC optimization OPF study, the Method must be set to DC Optimization ( Linear Programming LP) as shown in Figure 33.22.

Objective Function

The user can select a linear optimization objective function using the list box as shown in Figure 33.23. These objective functions are now described.

33 - 21


Fig. 33.23: Objective Function Selection for OPF (DC Optimization Method)

Feasibility CheckPerforms a feasibility check of the network considering the specified controls and constraints (i.e. performs a constrained load flow).

Minimization of CostsThe objective is to minimize generation costs. To perform a cost minimization calculation for each generator, a cost factor needs to be entered:Cost curve $/MWh per generator element (ElmSym, see Figure 33.3)The (linear) algorithm uses a fixed cost-factor [$/MWh] per generator. This cost factor is the average cost considering the costs at the generator’s active power limits. The selection of this objective function provides the option of calculating the Locational Marginal Prices (LMPs). For further information on this option refer to: Shadow Prices and Locational Marginal Prices (LMPs).

Min. Generator Dispatch ChangeMinimizes the change in generator dispatch from the generators’ initial value.

Controls

The Controls section of the OPF Basic Options tab is highlighted in Figure 33.24. The basic role of each control is as described for the AC optimization method in Section 33.1.1 (Basic Options).

33 - 22


Fig. 33.24: Controls Selection for OPF (DC Optimization Method)

The user can select from the following control variables (the names of the associated PowerFactory elements are provided in parentheses):

• Generator Active Power Dispatch (ElmSym)In generator optimization, for each selected generator a single control variable is introduced to the system. The total number of generator controls in this case equals the number of selected generators.

• Transformer Tap Positions (ElmTr2, ElmTr3)

In tap optimization, for each selected transformer a single control variable is introduced to the system. The total number of tap controls in this case equals the number of selected transformers.

• Allow Load Shedding (ElmLod)A separate control variable is introduced to the system for each selected load. The total number of load controls in this case equals the number of selected loads. This control variable can be selected in conjunction with any objective function.

Note At least one type of control variable in the Controls section of the OPF dialogue must be selected.

33 - 23


Constraints

The three constraints shown in Figure 33.25 are as described for the AC optimization method in Section 33.1.1 (Basic Options).

Fig. 33.25: Constraints Selection for OPF (DC Optimization Method)

For DC optimization the following constraint is also imposed:

Transformer Tap Constraints (implicitly imposed)Minimum and maximum tap positions (ElmTr2, ElmTr3) for transformers are considered. These constraints are implicitly imposed when transformer tap positions are specified as controls in the Controls section of the dialogue (see Figure 33.25). This means that two constraints are introduced to the LP for the base case tap position calculation.

Handling

Active power dispatch constraints can be chosen on an individual basis (via a checkbox) per generator. See Figure 33.13 for setting minimum and maximum constraints for gener-ators for optimization. It should be noted that generator constraints are not implicitly imposed when active power dispatch is selected as a control.

Tap position constraints will be implicitly imposed whenever the corresponding tap is a

33 - 24


designated control variable, as in Figure 33.8.

Loading constraints can be chosen on an individual basis (via a checkbox) per line element (ElmLne), as shown in Figure 33.12. If loading constraints are included, the maximum loading limits will be calculated with respect to the type of the element, or with respect to a thermal rating object (IntThrating, as shown in Figure 33.26). If a thermal rating object is selected, the limits will be calculated with respect to the Continuous Rating value.

Fig. 33.26: Thermal Rating Object (IntThrating) Ratings Tab for Setting Rating Values

Boundary flow constraints can be chosen on an individual basis per boundary element (ElmBoundary), as shown in Figure 33.15.

Shadow Prices and Locational Marginal Prices (LMPs)

If the option Calculate Locational Marginal Prices (LMPs) (displayed at bottom of the dialogue in Figure 33.25) is selected, the Locational Marginal Price (LMP) is calculated. The Shadow Price is always calculated. The LMP represents the change in the system’s total production costs based on a unit change of load at the bus. The calculation of LMP takes into account the network constraints.

The system lambda represents the change in the system’s total production costs based on a unit change of any load in the absence of network constraints.

With the Calculate Locational Marginal Prices (LMPs) option ticked, the execution of the OPF will (on the fly) calculate the LMP for each busbar. The following quantities (current, voltage and powers) are available for all busbars (i.e. ElmTerm elements with Usage set to 'Busbar'):

• LMP in $/MWh (Locational marginal price)

• SysLambda in $/MWh (System lambda)

33 - 25


In addition to the LMPs, the DC Optimization always computes the shadow prices. These quantities are available per component, which introduces a constraint to the system. The shadow price then represents the change in the objective function if the constraint is released by a unit change. The shadow prices are available as results for the PowerFac-tory elements listed below (result variable names are given followed by their corre-sponding unit). These result variable names are available as 'Calculation Parameters' when defining variable sets for each element. For more information on defining variable sets, refer to 13.10: Variable Sets.

• Line (ElmLne):

- ShadowPrice in $/MWh (Shadow price)

• 2-Winding Transformer (ElmTr2, ElmTr2n):

- ShadowPrice in $/MWh Shadow price (loading constraint))

- ShadTapMax in $/MWh Shadow price (Maximum Tap constraint))

- ShadTapMin in $/MWh Shadow price (Minimum Tap constraint))

• 3-Winding Transformer (ElmTr3):

- ShadowPrice in $/MWh (Shadow price (loading constraint)))

- ShadTapMaxLV in $/MWh (Shadow price (Maximum Tap constraint (LV)))

- ShadTapMinLV in $/MWh (Shadow price (Minimum Tap constraint (LV)))

- ShadTapMaxMV in $/MWh (Shadow price (Maximum Tap constraint (MV)))

- ShadTapMinMV in $/MWh (Shadow price (Minimum Tap constraint (MV)))

- ShadTapMaxHV in $/MWh (Shadow price (Maximum Tap constraint (HV)))

- ShadTapMinHV in $/MWh (Shadow price (Minimum Tap constraint (HV)))

• Boundary (ElmBoundary):

- ShadowMaxP in $/MWh (Shadow price (max. total active power constraint)))

- ShadowMinP in $/MWh (Shadow price (min. total active power constraint)))

• Synchronous Machine (ElmSym):

- ShadowMaxP in $/MWh (Shadow price (upper limit active power)))

- ShadowMinP in $/MWh (Shadow price (lower limit active power)))

• External Grid (ElmXnet):- ShadowMaxP in $/MWh (Shadow price (upper limit active power)))

- ShadowMinP in $/MWh (Shadow price (lower limit active power)))

• General Load (ElmLod):

- ShadowMaxP in $/MWh (Shadow price (max. load shedding)))

- ShadowMinP in $/MWh (Shadow price (min. load shedding)))


The OPF calculation is initialized by a load flow, which is displayed by the Load Flowparameter on the Initialization tab of the OPF dialogue. The user can inspect the load flow settings by clicking on the button, as illustrated in Figure 33.27. The load flow command contained in the current study case is set here automatically. Within the load

33 - 26


flow command, the Calculation Method will be automatically set to DC Load Flow (linear) for use by OPF (when Method is set to one of the LP variants).

Fig. 33.27: Initialization Settings for OPF (DC Optimization Method)


The Advanced Options tab of the OPF dialogue is shown in Figure 33.28.

Fig. 33.28: Advanced Options for OPF (DC Optimization Method)

Load Shedding Options

If Allow Load Shedding is among the selected Controls (see Section 33.2.1: Basic Options) on the Basic Options tab, an additional term will be added to the objective function. The weight of this term can be controlled using the Penalty Factor in the Load Shedding Options section of the OPF dialogue.

The following term will be added to the objective function, where is the specified Penalty Factor, and is the cost factor of load :ci i

33 - 27


Transformer Tap Deviation Control

If tap positions are to be optimized, different solutions can yield the same optimal value for the objective function. One can therefore impose a term to the objective function, which forces the solution to be as close as possible to the initial transformer tap positions.

Use Penalty Factor for Tap DeviationIf enabled, the following additional term is added to the objective function:

Penalty FactorSpecifies the weighting factor for the additional objective function term above.

Calculation of Transformer Tap Positions

Discrete controls (Using direct method)

This method calculates discrete tap position values within the LP (known as the “di-rect method”). This method may provide better accuracy, however will yield fewer solutions.

Continuous controls (Using outer loop rounding)

This method calculates continuous tap position values and then rounds these values to discrete values in the outer loop of the calculation. This method may be faster but the values may not be optimal.

Additional Settings

Check for Constraint Violations after Optimization

If selected, the calculated solution of the Simplex method will be checked (for over-loadings) by means of a contingency analysis (contingency constrained OPF) or a DC load flow. If an optimized result file is written this check will automatically be executed.

Use Presolve procedure

If selected, the LP is checked for linear dependencies of constraints. They will be eliminated and only the corresponding (smaller) system is solved.


Two outer loop settings are available: (i) control of the number of iterations of the algo-rithm; and (ii) definition of a constraint tolerance. These settings are shown in Figure

ci Loadij

Loadicurr

–

i 1=

nLoad

j 1=

nCo

tapi0

tapicurr

–

i 1=

nTr

33 - 28


33.29 and are described below.

Fig. 33.29: Iteration Control Settings for OPF (DC Optimization Method)

Outer Loop

Following the solution of the LP problem, it may be the case that loading constraints are not within their boundaries. The reason is that for taps, the algorithm uses tap sensitivities which assume a linear change in MW flow per tap step. Since these tap sensitivities depend on the initial tap position, the result becomes inaccurate if the optimal tap position is far from the initial tap position. This inaccuracy can be remedied by an additional outer loop. At each iteration, this outer loop starts with the optimized tap positions which were calculated in the previous loop. The following Outer Loop settings can be entered on this tab:

Max. Number of IterationsMaximum number of outer loop iterations until all constraints are fulfilled (within a defined tolerance).

Max. Acceptable Error for ConstraintsMaximum relative error (in %) by which a constraint can be violated while still being considered a feasible solution.

It should be noted that when Max. Number of Iterations is set to ‘1’, the LP is solved without outer loops.

Limitation of Branch Flow Constraints

This option is useful for avoiding long calculation times for large systems. If selected, the LP is solved via an iterative procedure which iterates until no further constraint violations are found (with respect to the Max. Acceptable Error for Constraints parameter). It should be noted that the option Check for Constraint Violations after Optimization on the Advanced Options page must be selected in order to utilise this iterative procedure. An initial set of branch flow constraints must be selected by the user, as described below.

33 - 29


Initial Set of Branch Flow Constraints

The set of branch flow constraints to be considered can either be the set of N most highly loaded components or a user-defined set. In the case of the set of N most highly loaded components, the program finds these automatically either by using a contingency analysis calculation (in the case of a contingency constrained DC OPF) or by using the initial load-flow (for the other OPF methods). In the case of a user-defined set, the user must define and assign a set of components. A set of components can be defined either via the single line graphic or data manager, by multi-selecting the desired components, right-clicking and selecting Define...-> General Set.... This set can then be selected and assigned via the button.

Max. number of additional constraints per iteration

After solving the LP with an initial set of constraints, the solution is checked against all loading constraints and overloaded components are added to the LP. The parameter Max. number of additional constraints per iteration specifies the maximal number of added components.

33 - 30


33.3 Contingency Constrained DC Optimization (LP Method)

The Contingency Constrained DC Optimization performs an OPF using DC optimization (as described in Section 33.2: DC Optimization (Linear Programming)), subject to various user defined constraints and subject also to the constraints imposed by a set of selected contingencies.

The Contingency Constrained DC Optimization also considers user-defined post-fault actions. That is, the optimization can be carried out using contingency cases that include any specified post-fault action. These actions include switch events, generator redispatch events, load shedding events and tap change events.

In order for the OPF to consider post-fault actions, the contingency analysis command that is assigned to the OPF must be set to “Multiple Time Phases”. The contingency cases can then be defined to contain post-fault actions. For further information on defining contingency cases with post-fault actions, see 30.4: The Multiple Time Phases Contin-gency Analysis Command.

In addition to the result variables available for DC optimization, the contingency constrained OPF offers the following result variables (as well as those provided by the DC load flow, as described in Section 33.2: DC Optimization (Linear Programming)):

• For generators:c:Pdisp Optimal generation for each contingency case.

The optimum generation for each contingency case is stored as a parameter event object in the corresponding contingency object (ComOutage).Thus, each contingency object will hold parameter events for each selected generator (the name of the parameter event is the name of the generator). The parameter event reflects the optimal generation for that generator in the given contingency case.

• For Transformers:c:nntap Optimal tap positions for each contingency case.

The optimum tap positions for each contingency case are stored as a parameter event object in the corresponding contingency case object (ComOutage).Thus, each contingency object (ComOutage) will hold parameter events for each selected transformer (the name of the parameter event is the name of the transformer). The parameter event reflects the optimal tap position for that transformer in the given contingency case.

c:mxTpChng (_l, _m, _h)mxTapChng is the maximum tap change deviation between the optimal base case tap position and the optimal tap position considering all contingencies.For 3-winding transformers, HV-, MV- and LV-side tap changes are calculated individually.

• For loads:c:Pdisp Optimal load shedding for each contingency case.

The optimum load shedding for each contingency case is stored as a parameter event object in the corresponding contingency case object (ComOutage).

33 - 31


Thus, each contingency object will hold parameter events for each selected load (the name of the parameter event is the name of the load). The parameter event reflects the optimal load shedding for that load in the given contingency case.


The Basic Options tab of the OPF dialogue (contingency constrained DC optimization method) is shown in Figure 33.30.

Fig. 33.30: Basic Options Tab of OPF Dialogue (Contingency Constrained DC Optimization Method)

33 - 32


Method

To perform a contingency constrained OPF study, the Method must be set to Contingency Constrained DC Optimization (LP) as shown in Figure 33.30.

Contingency Analysis

This is a reference to the Contingency Analysis (ComSimoutage) command to be used during the contingency constrained OPF. The user can select and set this contingency analysis command via the button, and view or edit the contingency analysis command settings using the arrow button . If the user would like the contingency cases to use post-fault actions, the Method used by the contingency analysis command must be set to Multiple Time Phases. See 30.4: The Multiple Time Phases Contingency Analysis Command for further information on configuring the contingency analysis command.

Objective Function

The selection of objective function for Contingency Constrained DC Optimization includes the same objective functions as those provided for DC Optimization (see Section 33.2.1: Basic Options). Two additional objective functions are provided, which are shown in Figure 33.31 and described below.

Fig. 33.31: Objective Function Selection for OPF (Contingency Constrained DC Optimization Method)

Min. Generator Dispatch Change (Pre-to-Postfault) Minimizes the sum of the generator dispatch changes between the base case and each contingency case.

Min. Transformer Tap Change (Pre-to-Postfault) Minimizes the sum of the tap position changes between the base case and each contingency case.

33 - 33


Controls

The definition of control variables for the contingency constrained DC optimization method differs slightly from the DC optimization method, however the basic fundamental role of each control is as described for the AC optimization method in Section 33.1.1 (Basic Options). The Controls section of the OPF dialogue is highlighted in Figure 33.32.

Fig. 33.32: Controls Selection for OPF (Contingency Constrained DC Optimization Method)

The user can select from the following control variables:

• Generator Active Power Dispatch (ElmSym, ElmXnet)Dispatch in Contingencies

- Use base case dispatch: For all contingency cases, use the generator dispatch from the base case. Using this setting, a single control variable is introduced to the system for each selected generator. The total number of generator controls in this case equals the number of selected generators and/or external networks.

- Allow different dispatch: For each contingency case, allow a generator dispatch different to that used in the base case. Using this setting, for each selected generator, a control variable is introduced for the base case and for each contingency case. This option must be

33 - 34


selected from the drop-down box when the objective function Min. Generator Dispatch Change (Pre-to-Postfault) has been selected. The total number of generator controls in this case equals:(number of selected generators) * (1 + number of selected contingencies)

• Transformer Tap Positions (ElmTr2, ElmTr3)Tap Positions in Contingencies

- Use base case tap positions: For all contingency cases, use the transformer tap positions from the base case. Using this setting, a single control variable is introduced to the system for each selected transformer. The total number of tap controls in this case equals the number of selected transformers.

- Allow different tap positions: For each contingency case, allow tap positions different to those used in the base case. Using this setting, for each selected transformer, a control variable is introduced for the base case and for each contingency case. This option must be selected from the drop-down box when the objective function Min. Transformer Tap Change (Pre-to-Postfault) has been selected. The total number of tap controls in this case equals:(number of selected transformers) * (1 + number of selected contingencies)

• Allow Load Shedding (ElmLod)A separate control variable is introduced to the system for the base case and for each contingency case. This control variable can be selected in conjunction with any objective function. The total number of load controls equals:(number of selected loads)*(1 + number of selected contingencies)

Constraints

The Constraints section of the OPF dialogue for the contingency constrained DC optimi-zation method is shown in Figure 33.33.

This formulation of OPF performs a contingency analysis for a predefined set of contin-gencies (ComOutage objects; i.e. a set of interrupted components per contingency case). The Max. Loading (parameter name: maxload) for lines and transformers (ElmLne, ElmTr2, ElmTr3; (one constraint per bus)) for each contingency case is considered in the calculation. For each loading constraint, the number of constraints added to the LP will be: 2*(number of contingencies).

In addition to the constraints provided for DC optimization (for further information see Section 33.2.1: Basic Options), the contingency constrained DC optimization method offers additional constraints:

Maximum Number of Tap Changes per ContingencyIf this checkbox is ticked, then for each contingency, no more than the maximum tap posi-tion change steps from the base case to the contingency case are allowed over all trans-formers (i.e. for a given contingency, a constraint is enforced on the sum of all maximum difference of base case to contingency case taps, over all transformers).

Transformer Tap Constraints (implicitly imposed)Minimum and maximum tap positions for transformers(ElmTr2, ElmTr3) are considered. These constraints are implicitly imposed when transformer tap positions are specified as

33 - 35


controls in the Controls section of the OPF command dialogue (see Figure 33.33). This leads to two constraints in LP formulation for the base case tap position calculation, and to: 2 x (1 + number of contingencies) constraints for contingency case calculations.

Fig. 33.33: Constraints Selection for OPF (Contingency Constrained DC Optimization Method)

Handling

Active power dispatch constraints can be chosen on an individual basis (via a checkbox) per generator. See Figure 33.13 for setting minimum and maximum constraints for gener-ators for optimization.

Tap position constraints will be implicitly imposed whenever the corresponding tap is a designated control variable, as illustrated in Figure 33.8. The tap position limits are defined in the transformer’s assigned Type.

Loading constraints can be chosen on an individual basis (via a checkbox) per line element (ElmLne) and per transformer element (ElmTr2, ElmTr3), as shown in Figure 33.12. Once a loading constraint for a specific line or transformer is imposed, it will be considered by all contingencies contained in the contingency list. If loading constraints are included, the maximum loading limits will be calculated with respect to the type of the element, or with respect to a thermal rating object (IntThrating, as shown in Figure 33.26). If a thermal rating object is selected, the limits will be calculated with respect to the Contin-

33 - 36


uous Rating value.

Boundary flow constraints can be chosen on an individual basis per boundary (ElmBoundary), as shown in Figure 33.15. Once a boundary constraint for either the maximum total active power limit or minimum total active power limit is imposed, it will be considered by all contingencies in the contingency list.

The list of contingencies to be considered by the OPF is selected by choosing a specific contingency analysis command (parameter Contingency Analysis in the OPF dialogue,Basic Options tab), which contains in its folder the contingency objects (ComOutage) to be considered.


As described for DC optimization. Please refer to Section 33.2.2 (Initialization).


As described for DC optimization. Please refer to Section 33.2.3 (Advanced Options).


As described for DC optimization. Please refer to Section 33.2.4 (Iteration Control).

33.3.5 Output

For contingency constrained DC OPF, results can be optionally recorded for those branches which exceed a selected limit value. This can be done for both the non-optimized results and the optimized results. For each recording of results (i.e. with optimized or non-optimized values) a separate result file must be chosen.

33 - 37


Fig. 33.34: Output Settings for OPF (Contingency Constrained DC Optimization Method)

Contingency Analysis Results

Allows the selection of result files for the contingency analysis results with and/or without optimized controls.

Results (before optimization)The result file in which to store the non-optimized results.

Results (after optimization)The result file in which to store the calculated (optimized) results.


The limits displayed here are set in the selected Contingency Analysis command on the Basic Options tab of the contingency analysis command dialogue. They define the limits outside of which results will be written to the result file(s). See Section 30.3.1 for further information.

Reports

Following a contingency constrained DC OPF calculation, the Output of Results command button on the main toolbar becomes active. This command allows the printing of various reports, as illustrated in Figure 33.35. The following reports are offered:

Optimal Solution Prints a detailed report to the output window, showing all optimal settings (including component-wise) against the relevant contingency.

Optimal Solution (per Contingency)Prints a detailed report to the output window, showing all optimal settings, on a per-contingency basis.

33 - 38


Maximum LoadingsPrints a detailed report to the output window showing the maximum loadings of compo-nents against the relevant contingency. The user may define the loading limit for which to report violations, and may select whether to report only the highest loadings for branch components.

Loading Violations Prints a report to the output window showing components with loading violations, against the relevant contingency. The user may define the loading limit for which to report viola-tions, and may select whether to report only the highest loadings for branch components. Additionally, the reporting of violations in contingency cases may be suppressed if viola-tions already exist in the base case.

Violations per CasePrints a report to the output window showing components with loading violations, on a per-contingency case basis. The user may define the loading limit for which to report violations, and may select whether to report only the highest loadings for branch compo-nents. Additionally, the reporting of violations in contingency cases may be suppressed if violations already exist in the base case.

Fig. 33.35: Output of Results Command for Contingency Constrained DC OPF

33 - 39


33 - 40

DIgSILENT PowerFactory Optimization Tools for Distribution Networks

Chapter 34Optimization Tools for Distribution Networks

The objective of this chapter is to present the PowerFactory tools for the optimization of distribution networks. By means of simple command edit dialogues it is possible to cal-culate the optimal placement, type and size of capacitors in radial distribution networks; the optimal separation points of meshed networks and the optimal type of reinforcement cables and overhead lines. Each section introduces a different tool, presenting a general description, the objective function, the optimization procedure and the command dia-logues.

34.1 Optimal Capacitor Placement

Optimal Capacitor Placement (OCP) is an automatic algorithm that minimizes the cost of losses and voltage constraints in a radial distribution network by proposing the installation of new capacitors at nodes (terminals) within the network. The optimal size and type of capacitor is selected from a list entered by the user. The algorithm also considers the an-nual cost of such capacitors and only proposes new capacitors for installation when the reduction of energy loss and voltage constraint costs exceeds the annual cost of the ca-pacitor (investment, maintenance, insurance etc).

To access the OCP tool, select the OCP toolbar from the toolbar selection window as illus-trated in Figure 34.1.

Fig. 34.1: How to select the Optimal Capacitor Placement Tools

The buttons in the OCP toolbar are as follows:

• The main Optimal Capacitor Placement command is started with this button: . The command and the various user-defined options are described in detail in Sections 34.1.3 to 34.1.6).

• This button: deletes the results (removes all placed capacitors) from a previous OCP routine.

The button for activating the Optimal Capacitor Place-ment toolbar.

Optimal Capacitor Place-ment toolbar.

34 - 1


• After a successful optimisation, the list of nodes (terminals) where capacitors are

proposed for installation can be accessed using this button: .

• Following a successful OCP, the list of proposed capacitors can be accessed using this

button: .

• To list all results from the OCP in a ASCII text report printed to the output window use

the following button: . The report also displays the original system losses and voltage constraint costs and such costs after the installation of the proposed capacitors.

The sections in this sub-chapter are as follows:

34.1.1 OCP Objective Function

The OCP optimization algorithm minimizes the total annual network cost (which is a sum of three parts: cost of grid losses, cost of all installed capacitors and fictitious penalty cost of voltage violations) according to:

where:

• CLosses is the annual cost of grid losses. Essentially, this is the I2R loss of all elements in the network.

• CCapi is the annual cost of a capacitor (investment, maintenance, insurance), as entered by the user in the list of possible capacitors. m is the total number of installed capacitors.

• CVoltVioli corresponds to a fictitious cost used to penalize a bus (terminal) voltage violation. n is the total number of feeder terminals.

Evaluating the Voltage Violation Cost

As there is no 'real' cost for a voltage violation, if the user wants to consider voltage vio-lations as part of the OCP algorithm, they must assign a 'fictitious' cost for such violations. The voltage violation cost is calculated based on the user specified voltage limits and pen-alty factors. The voltage limits are defined in the 'Basic Options' tab of the OCP command dialogue ('vmin' and 'vmax' parameters, see Section 34.1.3: Basic Options Page). The penalty factors are defined in the 'Advanced Options' tab of the same command ('weight' and 'weight2' fields, see Section 34.1.6: Advanced Options Page). The penalty values are applied for voltages inside the admissible voltage band (parameter 'weight': Penalty Fac-tor 1) and for voltages outside the admissible band (parameter 'weight2': Penalty Factor 2).

There are two possible situations for a terminal voltage and the calculation for the ficti-tious voltage violation cost is slightly different for each situation. The two situations are explained as follows:

TotalCosts CLosses CCapi CVoltVioli

i 1=

n

+

i 1=

m

+=

34 - 2


1 In situation one, the voltage U of a terminal is within the allowed voltage band (between vmax and vmin) but deviates from the nominal voltage of 1 p.u. The penalty cost is calculated as:

where:

U is the absolute deviation from the nominal voltage in p.u. ( ).w1 is the penalty factor (parameter 'weight') inside the admissible voltage band in $/% from the 'Advanced Options' tab.

2 For situation two, the voltage U is outside the allowed voltage band (greater than vmax or less than vmin) and the penalty cost is calculated as:

, if voltage is higher than max. limit:

or

, if voltage is lower than min. limit:

where:U is the absolute deviation from the nominal voltage Un in p.u.

Un+ Umax is the higher voltage limit in p.u.

Un - Umin is the lower voltage limit in p.u.

w1 is the penalty factor (parameter 'weight') for voltage inside the admissiblevoltage band in $/% from the 'Advanced Options' tab.w2 is the penalty factor (parameter 'weight2') for voltage outside the admissiblevoltage band in $/% from the 'Advanced Options' tab.

The algorithm can be summarized in two sentences:

• If the voltages are inside the admissible band the penalty cost applied is equal to

• If the voltages are outside the admissible band the penalty cost applied is equal to

the penalty inside the band ( ) plus the factor , with being either the maximum or the minimum limit value of the admissible band.

Figure 34.2 illustrates the concept of the voltage band violation cost.

CVoltViol w1 U=

U U Un–=

U Un Umax+

CVoltViol w2 U Umax– w1 U+=

U Un Umin–

CVoltViol w2 U Umin– w1 U+=

w1 U

w1 U w2 U Ulim– Ulim

34 - 3


Fig. 34.2: Fictitious cost assigned by voltage band violations

34.1.2 OCP Optimization Procedure

To find the optimal configuration of capacitors, PowerFactory applies the following steps:

• First a sensitivity analysis determines the 'best' candidate terminal; This involves evaluating the impact on the total cost (Losses + Voltage Violations) by connecting the largest available capacitor from the user-defined list of capacitors to each target feeder terminal. At this stage the cost of the largest capacitor is excluded.

• Terminals are ranked in descending order of total cost reduction. The terminal that provides the largest cost reduction becomes the 'best' candidate terminal for a 'new' capacitor.

• The optimisation routine then evaluates the cost reduction at the candidate terminal using each available capacitor from the user-defined list including the cost of each capacitor. The 'best' capacitor is the one that reduces the cost the most when also considering the annual cost of that capacitor.

• Repeat step one but any terminals that have previously been selected as candidates for capacitor installation are not included in the ranking of candidate terminals. The algorithm stops when all terminals have had capacitors installed, or the installation of capacitors cannot reduce costs any further.

Note: If Load Characteristics are considered, then the above algorithm will be completed for every independent load state. See Section 34.1.5 for how the load states are determined.

34 - 4


34.1.3 Basic Options Page

Fig. 34.3: Basic Options page

Feeder

Here the target feeder for the optimum capacitor placement is selected. The feeder is a special PowerFactory element that must be created by the user before it can be selected in this dialogue (for information about feeders refer to 5.3.3 (Network Data)).

Method

• Optimization; This option calculates the optimal placement for capacitors using the methodology described in Section 34.1.2. The output of the analysis is printed to the output window and any new capacitors are connected to the target terminal/s if the 'Solution Action' - 'Install capacitors' is selected.

• Sensitivity Analysis; Performs the sensitivity analysis that ranks the candidate terminals according to their impact on the total loss cost excluding the capacitor cost. The output is presented in the Output Window. This option provides a quick indication of the most effective place for a single capacitor. No capacitors are installed if this option is selected.


Here either a 'Balanced, positive sequence' or a 'Unbalanced' network representation can be selected. The Load-flow command referenced below these radio buttons is automati-

34 - 5


cally adjusted to the correct calculation method based on this selection.

Constraints

Here the voltage constraint limits (upper and lower) can be entered, along with a limita-tion for the 'Total Reactive Power of all Capacitors' that can be added by the Optimal Ca-pacitor Placement tool. The total reactive power of all capacitors includes all existing capacitors along the feeder plus any more capacitors proposed by the optimization tool.

Note: The voltage constraints are meaningless if penalty factors for de-viations outside of the nominal range are not entered as discussed in detail in Section 34.1.1: OCP Objective Function.

Energy Costs

The energy cost ($/kWh) can be entered manually or taken from an External Grid. Note, if more than one External Grid exists in the network, the algorithm takes the first External Grid by database ID. The calculation of the cost of the network losses is as follows:

where:TC is the total cost per annum in $; MC is the energy cost of losses in $/kWh; andL is the total losses in kW.

Note that if characteristics are applied to the loads and the analysis uses the option 'Con-sider Load Characteristics' (see Section 34.1.5), then the losses calculation becomes a summation over each time state considered.

Note: The default energy cost units are $/kWh. However, this can be changed to Euro or Sterling (£) via the project settings from the main menu bar. 'Edit -> Project... Project Settings -> Input Vari-ables tab -> Currency Unit'.

Solution Action

• Report only (do not modify network); The result of the optimisation is a report to the Output Window only, no modifications are made to the network model.

• Install capacitors (modify network). If this option is chosen, the capacitors that the optimization proposes for the network will be automatically installed. However, note that the single line diagram is not automatically updated, only the network model database. Therefore, if you want to visualize the placement of the capacitors, the 'Draw Existing Net Elements' button must be used and the capacitors placed manually - see Section 11.4 (Drawing Diagrams with already existing Network Elements). Alternatively, the placed capacitors can be visualized on the Voltage Profile Plot of the Feeder, see (Viewing results on the Voltage Profile Plot).

TC MC 8760 L=

34 - 6


34.1.4 Available Capacitors Page

Fig. 34.4: Optimal Capacitor Placement - Available Capacitors Page

On this page, the user defines the available capacitors for the OCP command. One capac-itor is entered per row. To add a new capacitor, right-click within any cell and select the option 'Insert Rows', 'Append Rows' or 'Append n Rows'. The following fields are manda-tory for each row:

• Ignored; If this option is checked, then the capacitor specified in this row will be ignored by the OCP command.

• Q per Step Mvar; Here the nominal reactive power of the capacitor in Mvar per step is specified.

• Switchable; If this option is enabled then the algorithm can use a capacitor with multiple steps.

• Max. Step; If the 'Switchable' option is enabled, then this option specifies the maximum number of steps available to the optimisation algorithm. The maximum available reactive power is therefore Max. Step * Q per Step Mvar.

• Technology; Specifies whether the capacitor is Three-phase or Single-phase.

• Cost; Important. This is the total cost of the capacitor bank per annum. This is a critical parameter for the OCP command as the capacitor will only be installed if the losses offset by its installation are greater than the annual cost of the capacitor.

Available Capacitors

• Allow use of each capacitor multiple times; This is the default option and it means that every capacitor in the list can be used at more than one feeder terminal (multiple times).

Only visible if the Network Representation is set to 'Unbalanced' within the 'Basic Options' page.

34 - 7


• Use each capacitor only once; If this option is enabled then each capacitor can only be placed at one terminal along the target feeder.

Treatment of 3-phase capacitors

This option allows the specification of the 'technology' type for 3-phase capacitors. This option is only available when the 'Network Representation' is set to 'Unbalanced' in the basic options page.

34.1.5 Load Characteristics Page

Fig. 34.5: Load Characteristics Page

If load characteristics should be considered by the optimization algorithm, then the option 'Consider Load Characteristics' should be enabled on this page. For more information on creating load characteristics please refer to Chapter 18 (Parameter Characteristics).

Load States

Two options are available:

1 'Use existing Load States'; If this option is selected then the system load state that is active in the system (the load state observed as a result of a single load-flow at the current point in time) will be used as the load state for the optimization algorithm. For example, if there is a 1 MW load with a active characteristic that gives the current load value of 0.6 MW, then the load used for the optimization will be 0.6 MW, not 1 MW.

2 'Create Load States'; If this option is selected then PowerFactory automatically discretises all load characteristics into a number of 'states' using a special algorithm. Basically, the algorithm iterates through every hour of the selected time period to determine the number of unique operating load states that exist. Every operating state is assigned a probability based on the number of times that it occurs and this

34 - 8


probability is used to determine the losses cost for each state. An example of how the algorithm works is explained below.

Start and End Time

This option allows the user to define the time period that the algorithm uses for the de-termining the discrete load states. The time period is only relevant if 'Load States' option 2 is selected. The time period is inclusive of the start time but exclusive of the end time.

Accuracy

This parameter affects the load discretisation algorithm. The accuracy parameter is only relevant if 'Load States' option 2 is selected.

Limit number of load states

Limits the total number of load states. This limit is only relevant if 'Load States' option 2 is selected. If the total number of calculated load states exceeds this parameter then ei-ther the time period of the sweep or the accuracy must be reduced.

Ignore load states with a small probability

This parameter affects the load discretisation algorithm. States with a probability less than this parameter are excluded from the discretisation algorithm. This option is only relevant if 'Load States' option 2 is selected.

Show Load States

This button can be used after a completed optimisation to show the calculated load states used for the previous calculation. This button is only relevant if 'Load States' option 2 is selected.

Example of Load Discretisation Algorithm

Consider a network of two loads with time based characteristics determining the load val-ues shown in columns two and three of Table .

Table 34.1:Load discretisation example

34 - 9


The load discretisation process works as follows:

1 Determine the maximum value of each load for the time interval considered. In the example table above the Load 1 peak is 5 MW and the Load 2 peak is 10 MW.

2 Determine the 'load interval size' for each load. The interval size . Where 'Acc' is the accuracy parameter entered by the user. For the

example above using an accuracy of 10 %, the Load 1 interval size is 0.5 MW and the Load 2 interval size is 1 MW.

3 For each hour of the time sweep and for each load determine the Load Interval:

where is the load value at hour 'i'. Load interval values for each

load are displayed in columns four and five in Table .

4 Identify all intervals that are common to both loads and group these as independent states.

5 Calculate the probability of each state based on its frequency of occurrence. The independent states (grouped by color in Table ) are listed along with their probability in Table 34.2.

Table 34.2: Independent States and their Probability

Lp

Int

Int Lp Acc=

LInt CeilLi

Int------- = Li

34 - 10


34.1.6 Advanced Options Page

Fig. 34.6: Advanced Options page

Candidate Buses

• All terminals in feeder; If this option is selected, every terminal in the feeder is considered as a possible candidate for a 'new' capacitor.

• Percentage of terminals in feeder; Selecting this option and entering 'x' percent for the parameter means the optimization algorithm will only consider 'x' percent of the feeder terminals as targets (candidates) for 'new' capacitors. The ranking of terminals is according to the Sensitivity Analysis as described in Section 34.1.2.

Max. Number of Iterations

This parameter determines the maximum number of iterations of the optimisation algo-rithm before it automatically stops. As a maximum of one capacitor is placed per iteration, this effectively limits the total number of capacitors that can be placed by the optimisation routine.

Max. Execution Time

This parameter specifies the maximum time the optimisation routine can run before it is automatically interrupted.

Penalty Factors for Voltage Deviation

• Factor for Deviation from 1 p.u (weight); This parameter is used to determine the total 'fictitious cost' for terminals deviating from 1 p.u. The cost is applied to each phase of the terminal. For example, if a three phase terminal voltage is measured at 0.95 p.u for each phase and the 'fictitious cost rate' is $10,000/% then the total cost of this deviation is $150,000 (5% * $10,000 * 3).

34 - 11


Note If no penalty costs are to be applied within the admissible band, this factor should be set to zero. If this value is greater than zero, the program will add additional costs to all terminals with voltage different than 1.0 p.u.

• Additional Factor outside range [vmin, vmax] (weight2); This parameter can be used to apply an additional weighting factor to the first deviation factor when the terminal voltage falls outside the voltage limits defined on the 'Basic Options' page. The factor is cumulative, so using the previous example and a additional factor of 20,000/% with a vmin of 0.975, the fictitious cost becomes $300,000 (5% * 10,000 + 2.5% * 20,000) * 3.

Note The values for the two voltage penalties 'weight' and 'weight2' should be carefully chosen because the target optimization func-tion is a sum of three objective functions (losses, capacitor cost and voltage deviation cost). If the voltage weights are too high, the algorithm might not consider the other two objectives. Likewise, if they are very low, the algorithm might not consider voltage viola-tions at all.

Print report after optimisation

The automatic printing of the optimisation results can be disabled by unchecking this op-tion.

34.1.7 Results

The last three OCP tool-bar buttons give access to the optimization results.

Show Nodes with New Capacitors

When pressing the icon , after a successful optimisation is complete, a list appears of all terminals where capacitors are proposed for installation.

Show New Capacitors

Pressing the icon shows a list of proposed new capacitors.

Output Calculation Analysis

This icon ( ) generates a report with the results of the sensitivity analysis and the final optimization procedure.

34 - 12


Viewing results on the Voltage Profile Plot

Following a successful optimization, the 'new' capacitors can be visualized on the voltage profile plot of the feeder. To enable this, navigate to the voltage profile plot display after

the optimization and click the rebuild button. An example of such a plot showing the placed capacitors is shown in Figure 34.7.

Fig. 34.7: Voltage profile plot showing the new capacitors after an Optimal Capacitor Optimisation.

Removing Capacitors Placed by the Optimal Capacitor Placement Routine

The capacitors placed by the OCP command can be removed at any time after the analysis

has been completed by using the button. This button is like an 'Undo' for the 'Optimal Capacitor Placement'.

34.2 Tie Open Point Optimization

The function of the 'Tie Open Point Optimization' (TOPO) is to optimize a radial system of connected feeders by determining the best location for network open points. An open point can be moved by the TOPO tool by opening and closing switches on the networks to be optimized.

This chapter is separated into three sub-sections. Firstly, the steps to access the TOPO tool are described. Next, the background and function of the TOPO tool is presented and finally the procedure for running a Tie Open Point Optimization is described.

34 - 13


34.2.1 How to Access the Tie Open Point Optimization Tool

The Tie Open Point Optimization Command can accessed as shown in Figure 34.8.

.Fig. 34.8: How to find the Tie Open Point Optimisation Command

34.2.2 Tie Open Point Optimization Background

The function of the 'Tie Open Point Optimization' TOPO tool is best explained using an example. Consider the network illustrated in Figure 34.9.

Fig. 34.9: Example network for Tie Open Point Optimization

The network consists of three feeders, one from each of the three 'stations'. Each feeder begins at a 'station' and ends at one of the two illustrated open points.

The two open points in this network are not necessarily the optimum open points. For example, it might be more economic (less network losses) to shift these open points by closing the open switches and opening two switches in different positions on the feeders. The purpose of the TOPO tool is determine these optimum open points automatically. Ad-ditionally, the TOPO tool can automatically consider network voltage and thermal con-

‘Additional tools’ where the Tie Open Point Optimisation Command is found.

Button to open the Tie Open Point Optimisation Com-mand Dialog.

34 - 14


straints - for instance it might be economic to shift an open point in terms of reducing systems losses, however doing so might cause a cable to overload.

34.2.3 How to run a Tie Open Point Optimization

This section describes the procedure for using the Tie Open Point Optimization Tool (TOPO) tool. There are several steps you must complete to run a TOPO. These are:

• Creating Feeders for the radial networks that you wish to optimize;

• Defining a set of feeders for the TOPO tool to use for the optimization;

• Selecting the basic options for the optimization;

• Choosing the constraints to consider (optional); and

• Configuring the advanced options (optional);

These steps are explained in the following sections.

Creating Feeders

The TOPO tool requires that feeders are defined for the section of the network that you wish to optimize. Additionally, the TOPO tool only works on radial feeders - mesh systems cannot be optimized automatically. Furthermore, it is recommended that the target feed-ers for optimization do not have any overloaded components or voltage violations in the base case.

The basic procedure for defining a feeder is to right click on the cubicle at the head of the feeder and select the option Define -> Feeder. Alternatively, for fast creation of multiple feeders right click the bus the feeder/s are connected to and select the option Define -> Feeder. More information on feeders and feeder creation can be found in Chapter 15.5.

How to create a set of Feeders

The TOPO tool always requires a set of feeders to optimize. To create a set of feeders, follow these steps:

1 Choose the Feeders icon from the 'Edit Relevant Objects for Calculation' Filters.

2 In the list of Feeders that appears, choose the feeders to optimize by multi-selecting them using the <CTRL> key.

3 Right click one of the feeders in the selection and choose the option Define -> General Set. A dialog will appear showing the contents of the set you just created.

4 Close the dialog.

How to configure the Tie Open Point Optimization Command

After you have created a set of feeders for optimization, the next step is to open the TOPO tool and configure the basic options. Follow these steps:

1 Select the Additional Tools toolbar .

2 Open the dialog for the Tie Open Point Optimization tool using the icon.

34 - 15


3 Use the selection control for Feeding Points to select the set of feeders you previously defined. Normally, the set of feeders will be found within the active Study Case.

4 Optional: Enable the option 'Force elements on outage when not switchable’. This option allows the TOPO routine to place objects in the feeder out of service if it is not possible to switch them out using conventional switches. For example, if placing a line out of service could reconfigure the feeders in such as way as to optimize the losses but the line has no circuit breakers at either end to isolate it, then the tool could place the line out of service instead.

5 Optional: You can inspect and alter the settings of the load-flow command that is used for determining the losses and identifying the constraints of the system by clicking the blue selection arrow next to load-flow command.

6 Optional: Change the 'Saving of solution' option. The two options are as follows:

- Change Existing Network (Operation Scenario). This is the default option. The TOPO tool modifies the base network model.

- Record to Operation Scenario. If you choose this option a selection control appears and you can choose an existing operation scenario to save the results of the Optimization procedure to. Alternatively, you can leave the selection empty and PowerFactory automatically activates a new Operation Scenario called 'Tie Open Point Optimization Results'. Any changes made to the network as a result of the optimization procedure are stored within this operation scenario. You can revert to the original network by disabling this scenario.

7 Optional: Disable the 'Report' flag. This control, enabled by default, allows you to turn off the automatic printing of an ASCII report to the output window.

How to configure constraints for the Tie Open Point Optimization

It is optional whether you choose to consider network and voltage constraints for the Tie Open Point Optimization. If you wish to consider constraints follow these steps:

1 Open the Tie Open Point Optimization dialog and select the Constraints tab.

2 Optional: Choose to enable or disable the option 'Consider thermal constraints'. If enabled, the TOPO tool will automatically consider thermal constraints in the network. Therefore, if an optimal point were to cause an thermal overload on any system component, then this would not be considered as a valid open point for reconfiguration of the system. There are two more options for thermal constraints:

- Global constraint for all components. This is the default option. If enabled you must enter a maximum thermal loading percentage in the 'Max. thermal loading of components' field. Note this option overrides the individual component thermal limits.

- Individual constraint per component. Select this option to automatically consider each component’s unique thermal rating. Note, the thermal rating for each component is determined by the field 'Max Loading' within the Tie Open Point Optimization tab of each component.

3 Optional: Choose to enable or disable the option 'Consider Voltage Constraints'. If this option is enabled then each terminal in the system is checked against the Lower and Upper limit of allowed voltage. If a particular open point causes a voltage violation, then such an open point cannot be considered as 'optimal'. There are two options for configuring the upper and lower voltage limits:

34 - 16


- Global constraints for all terminals (absolute value). If you choose this option then you must enter an upper and lower voltage limit in the two corresponding fields within this dialog box.

- Individual constraint per terminal. If you choose this option, then each terminal has a unique voltage limit which is assigned on the Tie Open Point Optimization tab of each terminal.

4 Choose the 'ignore all constraints for...' option. You can use these options to optionally ignore constraints where the nominal voltage is above or below user-defined thresholds entered here. This can be useful for example to exclude all LV systems (say less than 1 kV) from the constraints identification process as these can often have voltages outside the normal range.

How to configure the Advanced Options

Most of the time the options in the Advanced tab should be left on default values. How-ever, if you wish to make changes to these then the meaning of the options is as follows:

• Maximum number of outer loops. This option controls the maximum number of outer loops which is the total number of times the optimization procedure will be repeated when trying to find an optimal solution.

• Maximum change in system losses. This option determines the threshold above which a change in open point is considered. For example, if changing an open point causes a reduction in losses (a more optimal point), but the change is less than this threshold, then the original open point is retained.

34.3 Cable Size Optimization

The cable size optimization can be selected using the general tools and pressing the icon for cable size optimization:

• Cable Size Optimization

34.3.1 Objective Function

The objective function for the optimization minimizes the annual cost of the network by choosing the optimal 'types' for the selected feeder. The cost of each line including invest-ment, operational cost and insurance fees is also considered by the algorithm. The follow-ing constraints are considered in the optimization process:

Maximum admissible line loadingAn admissible overloading percentage can be defined by the user to avoid over-rating of the lines. Typically any overloading can be avoided by selecting the appropriate type of conductor for cables and overhead lines. The penalty factor for these lines therefore is fixed and cannot be defined by the user.

Maximum voltage dropDepending on the system topology, on the loads and on the length of the feeder, it might not be possible to avoid voltage band violations of some nodes due to

34 - 17


voltage drop. This can be mitigated by the installation of a capacitor during a post-processing optimization.

The specific penalty cost of the optimization therefore is a parameter that can be defined by the user to weight the voltage loss against the line investments.

34.3.2 Optimization Procedure

The optimization process minimizes the annual cost of the network. As constraints for the optimization it uses the admissible voltage band (in terms of max. voltage drop along the feeder) and loading limits for the planned network. The optimization does not need a load curve or a load forecast, as the impact of the conductor type on the cost of losses is not considered within the function. Input data for the reinforcement optimization is a network model that is complete for load-flow calculation. In addition to the network model, the planner has to provide the following information:

• A library section with standard line types (cable or overhead line) that are available for the new type assignment.

• A value for the max. voltage drop that is allowed for the new network topology.

The result of the optimization is a report about the recommended new cable/overhead types for the lines in the network and the cost evaluated for the recommended upgrading.

34.3.3 Basic Options Page

The basic parameter page for the Cable Reinforcement function is shown in Figure 34.10. The options are explained as follows:

FeederSpecific Feeder element that supplies the network region where the cables have to be reinforced. This must be created by the user prior to running the Cable Size Optimisation.

Cable TypesReference to folder that contains the allowed new types for overhead lines and cables.

Load-FlowThis is a reference (pointer) to the load-flow command used by the optimisation algorithm.

Cable OverloadsDefines how to deal with cable overloads detected during the optimization.

Consider Cable OverloadsIf this option is enabled, then cables are allowed to be overloaded to the maximum value specified in the 'Maximum Loading' parameter.

Max. LoadingLimit for the cable loading if the 'Consider Cable Overloads' is enabled.

34 - 18


Fig. 34.10: Basic Options page for Cable Reinforcement Optimisation

Check ConsistencyThis option, if enabled forces the optimisation routine to complete a final 'consistency' check. It is explained in detail later in this section.

Voltage ProfileThis option forces the optimisation algorithm to consider voltage constraints.

Consider Voltage ProfileThis checkbox must be 'checked' to force the algorithm to consider voltage constraints.

Maximum Voltage Drop Limit value (in %)This parameter defines the maximum permissible voltage drop along the feeder. The voltage drop is calculated as the absolute voltage difference between the source terminal of the feeder and the final terminal of the feeder.

OutputVarious output options for the optimization results are possible.

Report OnlyAny new types for cables and overhead lines are listed in a pre-defined report displayed in the Output Window.

Automatic Type ReplacementIf this option is selected, the Report will be generated and the optimisation routine will update the network model with the proposed types. Note, this option modifies your original network model.

Report FormatThis is a reference (pointer) to the result report output. For more information about the result language format see Section 19.1.1.

34 - 19


Explanation of the Consistency Check Algorithm

The consistency check option discussed previously involves assessing the network for 'consistency' based upon either of two criteria:

1 Sum of feeding cables >= sum of leaving cables; or

2 Smallest feeding cable >= biggest leaving cable.

To explain what is meant by 'feeding cable' and 'leaving cable' consider the small example feeder shown in Figure 34.11. This small network is defined as a single 'feeder' that be-gins at the 'Source' terminal. Consider now 'Terminal A'. This terminal is supplied by 'Line A' and is also connected to two other lines, 'Line B' and 'Line C'. In this case, for 'Terminal A', 'Line A' is considered as a 'feeding cable' and lines B and C as 'leaving cables'. Consid-ering now 'Terminal B', Lines B and C are feeding cables whereas Lines D and E are 'leav-ing cables'. Put more formally, 'feeding cables' are defined as those cables that are the closest to the beginning of the feeder for each terminal. All other cables are defined as 'leaving cables'.

In consistency check option 1, the cross sectional area of the feeding cables is summated and compared with the sum of the cross sectional area of the leaving cables for each ter-minal. If the sum of the leaving cables is greater at any terminal then the network is con-sidered non-consistent.

For consistency check option 2, the smallest feeding cable (by cross sectional area) is compared with the largest leaving cable for each terminal. If the largest leaving cable is bigger than the smallest feeding cable, then the network is considered non-consistent.

Note: The consistency check can use 'nominal current' instead of cross sectional area. This option can be enabled on the advanced options tab of the Cable Reinforcement Optimisation command.

Fig. 34.11: Example feeder network

34 - 20


34.3.4 Advanced Options Page

The advanced parameter page for the Cable Reinforcement function is shown in Figure 34.12. The options are explained as follows:

Fig. 34.12: Advanced Options page

Voltage ProfileThe voltage profile is treated as a constraint of the optimization process. A plane with two slopes at the lower and upper limits adds penalty cost to the optimization result in case of violations. The options are as follows:

Penalty Factor 1Penalty cost for voltage drop lower or equal than admissible limit defined on the basic parameter page (typically this value is set to 0).

Penalty Factor 2Penalty cost for voltage drop higher than the admissible limit defined on the basic parameter page. The value entered here describes the weight of the voltage band limit in comparison to the investment cost for the cable/OHL reinforcement. Typically this value is set very high, so that an adequate cable will always be chosen despite a higher cable cost.

Consistency Verification/Voltage DropThis option is used to select how the consistency check evaluates the 'size' of the cables.

Cross SectionIn this case, the selection of types is based on the cable cross sectional area.

Nominal CurrentIn this case, the selection of types is based on the rated current of the cable/OHL.

34 - 21


34 - 22

DIgSILENT PowerFactory Protection

Chapter 35Protection

The PowerFactory protection modeling features have been implemented with the following philosophy in mind.

• The protection modeling should be as realistic as possible

• The user must be able to create new complex protection devices or alter existing ones

• Although the protection models may show high complexity, their use must be kept easy

• All protection models will act on switches.

These specifications led to the following principles.

• A fuse is modeled as a time-overcurrent relay acting on a switch

• A distinction is made between defining or altering new relay models, which is described in the Technical References, and the use of those models, which is described in this chapter.

35.1 Using Protection Devices

Editing or creating protection devices in a cubicle can be done in several ways:

• by right-clicking a switch-symbol in the single line graphic. This will bring a pop up menu with the options Edit Devices and New Devices

• by editing the object which is to be protected (line, transformer, load, etc.) and

pressing the button at the cubicle field. See Figure 35.1 for example. The option Edit Devices will bring a list of all protection devices in the cubicle. New devices may

be then created with the icon.

Hint: To select the cubicle by means of right-clicking the switch, make sure the element is previously un selected and perform the right-click directly on the switch. If successfully done, only half of the el-ement will be marked as selected.

35 - 1


Fig. 35.1: Editing line protection devices

In all cases, selecting the option to create a new protection device will bring a list with the following options:

• Relay Model (ElmRelay)

• Fuse (RelFuse)

• Current Transformer (StaCt)

• Voltage Transformer (StaVt)

Each of these options will open a dialogue to specify the device that is to be created. Newly created Devices are stored in the cubicle that was selected. Although a relay can be stored everywhere in the grid folder, as a rule it is best stored in the same folder as the voltage and/or current transformers which it uses.

35.1.1 The Relay Model

The relay model (ElmRelay) is a general 'frame-object' which consists of a relay frame with slots and one or more elements which occupy those slots. All protection relays, except for the fuse models, are modeled as relay models.

A newly created relay can‘t be used ‚as-is‘. Without a specified type the "Slot Definition" list is empty and the relay is not functional. After a relay type has been selected, the "Slot Definition'' list will be filled automatically with the correct slot elements. The current and voltage transformers, however, are not created automatically, although available CT's and VT's are selected automatically. See Fig. 35.2 for an example of the relay model dialog.

Editing the settings of the relay model is done by editing the settings of the listed slot elements. Double-clicking a slot element in the "Slot Definition'' list will open the dialogue of that element. See 35.2 (Basic Protection Devices) for further information about the different elements used in protection relays.

The "Application" and "Device Number" fields are for documentation purposes only. The "Location" field is automatically read from the cubicle the relay is stored in.

35 - 2


Fig. 35.2: Relay model dialog with selected type

Max./Min. Fault Currents

This tab can be used to enter the minimum and/or maximum fault currents occurring at the location of the relay. These values are used to scale the Time-Overcurrent plot according to the given fault currents. They can be entered either manually or calculated with the Short-Circuit-Command.

Note The currents entered on this page will not affect the relay model. They are for plotting purposes only.

35.1.2 The Fuse Model

The fuse model is implemented as a special instantaneous overcurrent relay which does not need a current transformer. A fuse is always located in a cubicle and will trip the phase which current exceeds the melt curve. Optionally, all three phases will be tripped if one of the phase currents exceeds the melt curve.

35 - 3


Fig. 35.3: The Fuse model dialogue

The calculation of the trip time is either based on the minimum melt curve or on the total clear curve. An example of these curves are shown in Figure 35.4.

Optimization Tap

At the optimization tab, the fuse can be excluded from the open-tie-optimization-algorithm (see 34.2: Tie Open Point Optimization). This option is to be considered only if the "Fuse Type" is set to something different than "Fuse".

35 - 4


Fig. 35.4: Fuse melt characteristics

35.2 Basic Protection Devices

As already has been explained in the introduction of this chapter, the whole hierarchy of objects that is used to build protection devices can be divided into

• objects which are needed to define new types of protection devices

• objects which are needed to define specific relay models.

The first group of objects are treated in detail in the Technical References manual. The second group of objects are treated in this section. The explanations for the blocks are sorted in order of appearance in most standard relay models.

35.2.1 The Current Transformer

A new current transformer (CT) can be created by right-clicking a cubicle in the single line diagram and selecting "New Protection Device - Current Transformer'' or by using the "Create CT" button in the relay model dialog. The dialogue as depicted in Figure 35.5 will then pop up.

35 - 5


Fig. 35.5: The Current Transformer dialogue

A thus created CT will be stored in the cubicle that was right-clicked or the cubicle the relay is stored in. The "Location'' fields "Busbar'' and "Branch'' will be set automatically in both cases.

A current transformer needs a current transformer type if it is required to have a tap ratio. Otherwise the only ratio available is 1A/1A, as depicted above.

The top "Location'' field is used either

• to select a cubicle when the CT is created from outside the cubicle,

• to select the preceding CT in the case of an auxiliary CT.

After selecting the type and the setting of the current transformer, its set ratio is shown in the dialogue (Ratio). In very special cases CTs may be connected in series, that is the output of one CT is used as the input of the second CT. In this application the second CT will show a Ratio (the actual ratio of the CT) and a Complete Ratio, (the ratio between the primary branch flow and the secondary CT current, which is the overall ratio of all CTs connected in series).

The primary connection type is only available in the case of an auxiliary CT. The number of phases can be set to 3, 2 or 1. For a 3- or 2-phase CT, the secondary connection type can be set to D or Y. For a 1-phase CT, the phase can be set to

• a, b or c phase current

• N = 3*I0

• I0 = I0

35 - 6


The primary and secondary tap settings are limited to the values defined in the current transformer type.

The Current Transformer Type

The current transformer type dialogue, as depicted in Figure 35.6, defines the single phases of a CT. The information about the connection of these phases (Y or D) is defined in the CT element that uses the CT type.

Fig. 35.6: The Current Transformer Type dialogue

The current transformer type defines the primary and secondary taps of the transformer. The "Additional Data page'' is used only when saturation is considered, to set the accuracy parameters:

• The accuracy class

• The accuracy limit factor

• either

- The apparent power (acc. to IEC)

- The burden impedance (ANSI-C)

- The voltage at the acc. limit (ANSI-C)

35.2.2 The Voltage Transformer

A new voltage transformer (VT) can be created by right-clicking a cubicle in the single line

35 - 7


diagram and selecting "New Protection Device - Voltage Transformer'' or by using the "Create VT" button in the relay model dialog. The dialogue as depicted in Figure 35.7 will then pop up.

Fig. 35.7: The Voltage Transformer dialogue

A thus created current transformer will be stored in the cubicle that was right-clicked or the cubicle the relay is stored in.

A voltage transformer needs a voltage transformer type, if it is required to have a tap ratio. The "Location'' field is used either

• to select a cubicle when the VT is created from outside the cubicle

• to select the preceding VT in the case of an auxiliary VT

After selecting the type and the setting of the current transformer, its set ratio is shown in the dialogue (Ratio).

The primary winding is defined by selecting a tap and a connection type. The available tap range is defined in the voltage transformer type.

The secondary winding is defined by the secondary winding type, the tap setting and the connection type. The available tap range is defined in the secondary winding type. A voltage transformer has at least one secondary winding. If no type is selected for the first secondary winding, it is assumed to be ideal and has the standard tap range 100V-130V available. More windings can be defined by pressing the button "Additional Secondary

35 - 8


Windings''. This will bring a list of all previously defined secondary windings. New

windings can be created by pressing the icon.

The connection type "O'' for the secondary windings is the "Open Delta'' connection, as depicted in Figure 35.8.

Fig. 35.8: The open delta (O) winding connection

The connection type "V'' for the primary and secondary windings is depicted in Figure 35.9. Selecting a "V'' connection for the primary winding automatically sets the secondary winding to a "V'' too.

Fig. 35.9: The "V'' winding connection

The VT Secondary Winding

A secondary winding element is needed when a voltage transformer with two or more secondary windings has to be modeled. The edit dialogue for the voltage transformer provides parameters to define the first secondary winding.

35 - 9


Fig. 35.10: The VT secondary winding dialogue

The secondary winding element requires a type and a reference to the voltage trans-former. The tap settings range is defined by the windings type.

The Voltage Transformer Type

The voltage transformer type, as depicted in Figure 35.11 defines the primary winding of the voltage transformer. The secondary windings are defined in the voltage transformer element.

Fig. 35.11: The voltage transformer type dialogue

35 - 10


The VT Secondary Winding Type

The secondary winding type, as depicted in Figure 35.12, defines the burden and tap range for one phase of a voltage transformer. The phase connection type (Y, D, etc.) is defined in the secondary winding element. The secondary tap settings defined in the secondary winding type determine the available tabs for the secondary winding element.

Fig. 35.12: The VT secondary winding type dialogue

The secondary tap settings defined in the secondary winding type determine the available tabs for the secondary winding element.

35.2.3 The Measurement Block

The measurement block uses the 'raw' signals produces by the current or voltage trans-formers to calculate 'measured signals'.

The measurement block allows for setting the nominal current and voltage. Both are limited by the measurement unit type. If a relay does not need a nominal voltage (i.e. in the case of an overcurrent relay) or if there is only one nominal value to choose from, the nominal voltage and/or current field will normally be disabled.

35 - 11


Fig. 35.13: Measurement block

35.2.4 The Frequency Measurement Block

The frequency measurement unit is used to calculate the electrical frequency for the given "Measured Voltage''. The Nominal Voltage is needed for per unit calculations. The Frequency Measurement Time defines the time used for calculating the frequency gradient.

Fig. 35.14: Frequency measurement block

35.2.5 The Directional and Polarizing Blocks

The directional relay cannot be used 'as-is', but is always a part of a relay model. For more information about relay models, see Section 35.1.1 (The Relay Model)

The directional relay calculates the angle between a 'polarization' voltage or current and an 'operating' current. The polarization current or voltage is rotated to the amount of the expected angle first. The relay trips if the remaining angle is smaller than 90° and if both the polarization and the operating voltage/currents are large enough. This principle is

35 - 12


shown in Figure 35.15.

Fig. 35.15: Directional relay principle diagram

The polarization quantity Apol is rotated over the angle MT, which is the "Max. Torque Angle'' set in the relay edit dialogue. The rotated polarization quantity A'pol defines a half plane which forms the first tripping condition. Further conditions are the projection of the operating quantity on A'pol, which must be larger than the operating current setting, and the polarization quantity, which must be larger than the polarization setting.

The polarizing block also allows for settings of earth fault and mutual earth fault compen-sation parameters, if those features are available in the relay model.

More details about the polarization methods and the tripping conditions can be found in the Technical References manual. An example for a polarizing block can be seen in Figure 35.16.

The choice for the type of operating and polarization quantity is made in the Directional Relay Type object. The relay object itself allows for the setting of the tripping direction, the polarization method when both methods (voltage and current) are available, and the polarization criteria. See Figure 35.17.

35 - 13


Fig. 35.16: Polarizing block

Fig. 35.17: Directional block

35 - 14


35.2.6 The Starting Block

The starting block is used exclusively in distance relays, as a means to detect fault condi-tions. It sends the starting signal to all timer blocks in the relays, if the fault conditions are met. The selectable fault conditions range from simple overcurrent detection to complex impedance polygons. For an example of a simple overcurrent starting block, see Figure 35.18. For detailed information please refer to the Technical Referencesmanual.

Fig. 35.18: Starting block

35.2.7 The Instantaneous Overcurrent Block

The instantaneous overcurrent block allows for the setting of the pickup current and the time dial. Both entries are limited by the type. See Figure 35.19.

35 - 15


Fig. 35.19: Instantaneous Overcurrent block

The instantaneous overcurrent block is a combination of a direct overcurrent relay and an optional time delay. The pickup time Ts is the minimum time needed for the relay to react. Additionally, a time dial Tset may be specified. The block will not trip unless the current exceeds the pickup current Tsetr for at least Ts+Tset. See Figure 35.20.

Fig. 35.20: Instantaneous overcurrent tripping area

The block will not reset until the current drops under the reset level, which is specified by the relay type in percent of the pickup current: Ireset=IpsetKr/100%. See Figure 35.21 for a typical timing diagram.

35 - 16


Fig. 35.21: Instantaneous overcurrent timing diagram

35.2.8 The Time Overcurrent Block

The time-overcurrent block allows for the selection of one of the I-t curves ('character-istic') which are available for the selected relay type. The I-t curve is further specified by the pickup current and the time dial. Both values must be in the range specified by the I-t curve definition. See Figure 35.22 for an example.

Fig. 35.22: Time overcurrent block

The time dial settings will scale the I-t curve in the Time vs. I/Ip plot, according to the curve definition. See Figure 35.23 for example.

35 - 17


Fig. 35.23: I-t curves for different time dials

The pickup current defines the nominal value Ip which is used to calculate the tripping time. The I-t curve definition states a minimum and a maximum per unit current. Lower currents will not trip the relay (infinite tripping time), higher currents will not decrease the tripping time any further. These limits are shown in Figure 35.24.

Fig. 35.24: I-t curve limits

The pickup current may be defined by the relay type to be a per unit value, or a relay current. The nominal current defined by the measurement unit (see 35.2.3 (The Measurement Block)) is used to calculate Ip in the case of a per unit value. The relay current value already equals Ip.

Altering the pickup current will thus not change the I-t curve, but will scale the measured current to different per unit values. The following example may illustrate this:

• Suppose the minimum current defined by the I-t curve is imin=1.1 I/Ip.

• Suppose the measurement unit defines Inom=5.0 rel.A.

35 - 18


• Suppose pickup current Ipset=1.5 p.u. relay will not trip for I<1.1*1.5*5.0 rel.A = 8.25 rel.A

• Suppose pickup current Ipset=10.0 rel.A relay will not trip for I<1.1*10.0 rel.A = 11.0 rel.A

35.2.9 The Distance Polygon Block

The distance polygon block is used to model the different zones of distance protection relays. The kind of polygon modelled by the block depends on the block type. Available polygons range from Mho circles, for modelling of older electro-mechanical distance relays, to polygones with load encroachment, like they are used by modern digital protection devices. Depending on the kind of polygon, the block allows for the setting of reactance and resistive reach, high resistance ground fault reach and different angles for different edges of the polygon. For an example with a rectangular polygon, see Figure 35.25. The Block can also be configured to be directional.

Note: In order to function properly, there has to be a directional block present in the relay and connected to the polygon block. This is in-dicated by the active button Directional Unit, next to the drop down menu. Otherwise the block will never trip, because it can‘t receive directional information.

The Impedance section at the bottom of the dialog shows the reach of the zone in absolute values, as well as relative to the element directly connected to the cubicle where the relay is defined. The R and X values of this element are also shown as a reference for the setup of the zone.

Since the distance polygon block does not have a time dial itself, it needs an extra timer block, that controls the tripping time of a zone. The timer block connected to the zone can be selected with the Timer button.

Note: If the Timer button of a zone is greyed out, this means there is no timer block directly connected to the zone. This can be the case, if the zone is designed for instant tripping.

35 - 19


Fig. 35.25: Distance polygon block

35.2.10 The Timer Block

The timer block is used to either control the tripping time of distance polygon blocks or to realize other time delays in a relay, that can‘t be realized inside a block. For an example, see Figure 35.26. If the timer block is used to control a distance polygon, the delay is started with a signal from the starting block.

35 - 20


Fig. 35.26: Timer block

35.2.11 The Frequency Block

The frequency block either trips on an absolute under-frequency (in Hz), or on a frequency gradient (in Hz/s). Which condition is used depends on the selected type. The type also defines the reset time, during which the frequency condition must be met again for the relay to reset.

The time delay set in the relay element defines the time during which the frequency condition must be violated for the relay to trip. See Figure 35.27.

Fig. 35.27: Frequency block

35.2.12 The Under-/Overvoltage Block

The under-/overvoltage relay type may define the block to trip on either

• Either one of the three phase line to line voltages

• One particular line to line voltage

35 - 21


• The ground voltage U0.

• The positive sequence voltage U1

• The negative sequence voltage U2

The relay element allows only for setting the pickup voltage and the time delay. See Figure 35.28.

Fig. 35.28: Under-/Overvoltage block

35.2.13 The Logic Block

The logic block is the front end part of a relay configuration. It combines all internal trigger signals by successive AND and OR operations and produces one single output. The block type specifies the logical operation, the logic block itself specifies the switches which will be opened when the relay trips. See Figure 35.29.

Fig. 35.29: Logic block

35 - 22


If the relay is located in a cubicle and no switch has been specified, the breaker in the cubicle will be opened by default.

The following section explains the special features of the time-overcurrent plots.

35.3 Time-Overcurrent Plot

The plot VisOcplot is showing different relay and fuse characteristics in one time-overcurrent plot. Additionally the damage curve and characteristic currents of electrical equipment in the network can easily be shown. This will help to set the relay tripping times and current settings and the selecting of fuses for a good and thorough protection of the equipment.

There are several ways to create a time-overcurrent plot (VisOcplot):

• The easiest way to create and show a VisOcplot is to select one switch, where overcurrent relays or fuses are installed. Right-click the switch to open the context sensitive menu. This will show the options Create Time-Overcurrent Plot and Add to Time-Overcurrent Plot. PowerFactory will then create a new diagram showing the time-overcurrent plot for all relays selected.

• Another way is to right-click an path element and select Path... Time-Overcurrent Plot from the context sensitive menu.

• Also a relay element ElmRelay can be chosen from the list of calculation-relevant objects or in the data manager. Right-click the relay on the right side of the data manager or in the list of relays. Then select Show Time-Overcurrent Plot to create a new plot or Show Add to Time-Overcurrent Plot to add the characteristic to an existing plot.

• Additionally other elements like one or more transformers, cables or motors can be selected and right- clicked. The context sensitive menu will show the options Show Time-Overcurrent Plot to create a new plot and Show Add to Time-Overcurrent Plot to add the characteristic to an existing plot.

Note To show the relay locations and thus to visualize the switches with relays definitions these can be highlighted by setting the color rep-resentation of the single-line diagram to "Relay Locations''. By right-clicking these elements the option Show Time-Overcur-rent Plot is available and can be chosen.

In all these cases, it is also possible to select the option Add to Time-Overcurrent Plot. This will pop up a list of previously defined over current plots from which one has to be selected.

The overcurrent plot shows

• the time-overcurrent characteristics of relays

• the damage curves of transformers or lines

• motor starting curves

• the currents calculated by a short-circuit or load-flow analysis and the resulting tripping times of the relays

See Figure 35.30 for an example.

35 - 23


Fig. 35.30: A time-overcurrent plot with short-circuit results

The time-overcurrent plot shows the results of the short-circuit or load-flow analysis as a vertical 'x-value' line across the graph. Because the currents differ for each particular relay, a current line is drawn for each relay. The intersection of the calculated current with the time-overcurrent characteristic is labelled with the tripping time. A 'grading margin' line, which shows the difference between the tripping times, may be added by right-clicking the plot and selecting "Show Grading Margins''.

It is also possible to create an user defined 'x-value' by right-clicking the graph and selecting the Set Constant x-value option. The vertical line will show the values at the intersections of all displayed characteristics. To move the line left, drag it with the mouse.

35.3.1 Changing Tripping Characteristics

The time overcurrent plots may also be used to change the relay characteristics graphi-cally. Because a relay characteristic is normally the minimum of two or more sub-charac-teristics, it has to be split first in order to change the sub-characteristics.

A characteristic is split by

• right-clicking the characteristic

• enable the split option

The relay characteristics can also be split by opening the edit dialogue of the plot and enabling the option Split Relay in the table Relay, where all relays are listed.

The sub-characteristics are now visible. Each of them can be left clicked and dragged along the time-overcurrent plot area. However, they cannot be dragged outside the allowed range which has been defined for the relay type. After the relay sub-character-istics have been changed, they can be combined again into one single characteristic by disabling the split option again.

The plot option dialogue, which is opened by right-clicking the plot area and selecting Options, has an option for showing the grading margins when the time overcurrent characteristics are dragged. The grading margin may be set to a fixed time. The grading

35 - 24


margins are shown as two lines, plus and minus the grading margin above and below the dragged tripping characteristic. See Figure 35.31 for an example: the original character-istic is labelled "1'', the new position as "2'', and the grading margins are labelled "a''.

Fig. 35.31: Moving a characteristic with grading margins

Conductor/Cable Damage Curve

The conductor and cable damage curves are used to evaluate a protection coordination variation and as guides for positioning the time-overcurrent characteristics.

A damage curve can be added by

• right-clicking a line object in the single line diagram or the data manager and selecting Show Add to Time-Overcurrent Plot

• right-clicking the plot area and selecting Add... Conductor/Cable Damage Curve

Hint: If the damage curve is added via the „Add to Time-Overcurrent Plot“Option, the parameters for the curve will be read from the Short-Circuit and Protection pages of the element type automati-cally.

35 - 25


Fig. 35.32: Conductor/Cable damage curve

The Rated Short-Circuit Current and time of the cable can be inserted. Also typical Cable Parameters for the conductor, insulation factor, K, are given in figures 35.33 and 35.34. These tables show the temperature range for the cables:

• T1 = maximum operating temperature in º C

• T2 = maximum short-circuit temperature in º C

and the K factor for a cross section in mm2, CM, MCM and inch2.

35 - 26


Fig. 35.33: Typical damage parameters for copper conductor cables

Fig. 35.34: Typical damage parameters for aluminium conductor cables

Transformer Damage Curve

The transformer damage curves are used to evaluate a protection coordination variation and as guides for positioning the time-overcurrent characteristics.

To add an ANSI/IEEE C57.109 damage curve to a time-overcurrent plot

• right-click the transformer object in the single line graphic or the database manager and select the option Show Add to Time-Overcurrent Plot

• right-click the plot area and select Add... Transformer Damage Curve

Hint: If the damage curve is added via the „Add to Time-Overcurrent Plot“ Option, the parameters for the curve will be read from the Short-Circuit and Protection pages of the element type automati-cally.

35 - 27


Fig. 35.35: Transformer damage curve

An example of a time-overcurrent plot with two relay characteristics and a transformer damage curve is shown in Figure 35.36.

Fig. 35.36: Transformer damage curve

Motor Start Curve

The motor start curves are used to evaluate a protection coordination variation and as guides for positioning the time-overcurrent characteristics.

To add a motor starting curve to the time-overcurrent plot

35 - 28


• right-click the motor object in the single line graphic or the database manager and select the option Show Add to Time-Overcurrent Plot

• right-click the plot area and select Add... Motor Starting Curve

Hint: If the damage curve is added via the „Add to Time-Overcurrent Plot“ Option, the parameters for the curve will be read from the Short-Circuit and Protection pages of the element type automati-cally.

Fig. 35.37: Motor start curve edit dialogue

The characteristic currents and durations given in the edit dialogue result in a step wise motor start current plot, as depicted in Figure 35.38.

35 - 29


Fig. 35.38: The motor start curve

Overcurrent Plot Settings

The time-overcurrent plot settings can be accessed by selecting the Options from the context-sensitive menu. The dialogue shows the following options:

Current UnitThe current unit may be set to either primary or secondary (relay) ampere.

Show RelaysThis option is used to display only certain types of relay characteristics.

Recloser OperationThe different recloser stages can be shown simultaneously or switched off in the diagram.

Display automaticallyThis option is used to select how the calculated load-flow or short-circuit currents will be displayed. Either the current lines, the grading margins, both or none may be selected.

Voltage Reference AxisMore than one current axis may be shown, based on a different voltage level. All voltage levels found in the path when a time overcurrent plot is constructed are shown by default. An user defined voltage level may be added. Optionally, only the user defined voltage level is shown.

Cut Curves atnormally the curves of different relay zones cut at the same tripping current.

Show Grading Margins while Drag&DropWhen dragging the curves up and down resp. right and left, the grading margins of the curve will be shown according to the margin entered.

35 - 30


Fig. 35.39: Overcurrent Plot Settings

The advanced options are:

Drag & Drop Step SizesThese are used to set the step change in the relay settings when a time-overcurrent plot is dragged with a continuous time dial or pickup current.

Time Range for Step SizesEnter the tripping time range for the y-axis.

'Color for Out of Service' UnitsThe characteristics for units that are out of service are drawn invisible by default. However, a visible color may be selected.

Brush Style for FusesThis defines the fill style for fuse curves

Nr. of points per curveThe number of points can be changed to either refine the plotted curves for more detail, or to speed up the drawing of the diagram.

35.4 The Time-Distance Diagram

The time-distance plot VisPlottz shows the tripping times of the relays depending on the short-circuit location. It is directly connected to a path definition, so it can only be created if a path is already defined. For more informations about path definitions, see 35.4.1: Path Definitions.

35 - 31


How to create a time-distance diagram:

• The easiest way to create and show a VisPlottz is to right-clicked an element, which is already added to a path definition. From the context sensitive menu the option Show Time-Distance Diagram can be selected. PowerFactory will then create a new object VisPlottz showing the time-distance plot for all distance relays in the path.

• Another way is to right-clicked an path element and select Path... Time-Distance Diagram from the context sensitive menu. Like above this will create a new object VisPlottz.

• Also path object SetPath can be chosen in the data manager under Database\ Projectname\ Paths. Select the "Paths'' folder and right-click the path object on the right side of the data manager. Then select Show Time-Distance Diagram from the context sensitive menu.

Note To show the path definition, and thus to visualize the elements contained, the path can be highlighted by setting the color repre-sentation of the single-line diagram to "Path Definitions''. By right-clicking these elements the option Show Time-Distance Dia-gram is available and can be chosen.

35.4.1 Path Definitions

A path in a single line diagram is defined by selecting a chain of two or more busbars or terminals and inter-connecting objects. The pop-up menu which opens when the selection is right-clicked will show a Path... option. This menu option has the following sub-options:

Newthis option will create a new path definition

Editthis option is enabled when an existing path is right-clicked. It opens a dialogue to alter the color and direction of the path

Add Tothis option will add the selected objects to a path definition. The end or start of the selected path must include the end or start of an existing path.

Remove PartlyThis will remove the selected objects from a path definition, as long as the remaining path is not broken in pieces

RemoveThis will remove the firstly found path definition of which at least one of the selected objects is a member

Editing, adding objects to or removing objects from path definition is only possible when the option coloring "Path Definitions'' was chosen in the Color Representation of Graphic

dialogue (SetColgr). This dialogue is opened by pressing the icon on the graphics toolbar.

A path may be used as a selection for a calculation by selecting one or more objects from

35 - 32


the path definition. This will select the whole path.

35.4.2 The Time-Distance Plot

Fig. 35.40: A time-distance plot

The time-distance plot in Figure 35.40 is separated in two different diagrams. The upper diagram shows all relay tripping times in the forward direction of the path. The lower diagram shows the reverse direction. There are three different options for displaying the diagrams. These are:

Forward/ReverseBoth diagrams are shown.

35 - 33


ForwardOnly forward direction diagram

ReverseOnly reverse direction diagram

The Path Axis

Fig. 35.41: A path axis

The path axis in Figure 35.41 shows the complete path with busbar and relay locations. Busbars/Terminals are marked with a tick and the name. The coloured boxes represent relays and the left or right alignment represents their direction.

35.4.3 Time-Distance Plot Settings

Methods for calculation of tripping times

There are several methods to calculate the tripping times shown in the plot. To change the method, select the Method option in the context sensitive menu or double-click the plot to access the time-distance plot dialogue and edit the Methods option on the Relays page.

The methods differ in exactness and speed. The set of possible units for the x-Axis depends on the method used. The methods are:

Short-Circuit Sweep MethodThe short-circuit sweep method is the most accurate method for calculating the short-circuit locations. A short-circuit sweep is calculated over the branches between the first and the last busbar in the path. At each short-circuit location the relay tripping times are established. The disadvantage of this method is it's low speed. Whenever the rebuild button of the graphics window is pressed the sweep is recalculated. The possible units for the short-circuit location are position in km or reactance in primary or relay ohm.

Kilometrical MethodThis method is the fastest but most inaccurate one. Tripping time and location are determined with the intersection of the impedances and the relay characteristic. The impedances used for calculation are the impedances of the device. If there is more than one intersection at the same impedance the smallest tripping time is used. The possible units for the short-circuit location are position in km or reactance, resistance and impedance, each in primary or relay ohm.

35 - 34


Fig. 35.42: The Time-Distance plot edit dialogue

The kilometrical method is applicable only for the following paths

• There are no parallel branches in the path.

• The path is fed from only one side or there is no junction on the path.

Short-Circuit Calculation Settings

If the method for the calculation of the time-distance plot is set to "Short-Circuit Sweep'', the short-circuit sweep command object ComShcsweep is used. There is either the option Shc-Calc... in the context menu of the plot or the Shc-Calc... button in the "Time Distance Plot'' edit dialogue to access the sweep command.

Some of the settings in the command are predefined by the time-distance plot. These settings are grayed out when the sweep command is accessed through the plot. The short-circuit command for the calculation is set in the sweep command. To change the short-circuit method, i.e. from "IEC60909'' to "Complete'', open the sweep command and edit the short-circuit dialogue.

Note The easiest way to recalculate the short-circuit sweep for the time-distance plot is by simply pressing the button .Mind that this is only needed when using the Short-Circuit Sweep method. The Kilometrical method does not need the short-circuit

35 - 35


sweep command.

The x-Unit

There is a set of possible x-units depending on the method used. See the methods description for details. The short-circuit sweep method needs a relay to measure the impedance, named the reference relay. If there is no reference relay selected, the distance is measured from the beginning of the path.

The options available for the x-unit are:

Lengthx-axis is shown depending on the line/cable length from the reference relay in"km''.

Impedance (pri.Ohm)x-axis is shown depending on the impedance from the reference relay.

Reactance (pri.Ohm)x-axis is shown depending on the reactance from the reference relay.

Impedance (sec.Ohm)Here the impedance from the reference relay is measured on the secondary side.

Reactance (sec.Ohm)Here the reactance from the reference relay is measured on the secondary side.

The Reference Relay

The x-Axis positions or impedances are calculated relative to the beginning of the path. If a reference relay was set the positions/impedances are relative to the reference relay. The sweep method needs always a reference relay. If no reference relay was set the first relay in the diagram's direction is taken for reference relay.

The busbar connected to the reference relay is marked with an arrow pointing in the diagrams direction.

The reference relay is set either using the graphic or by editing the "Time Distance Diagram'' dialogue. Changing the reference relay graphically is done by clicking with the right mouse button on the relay symbol and selecting "Set reference relay'' in the context menu. If there is more than one relay connected to the selected busbar PowerFactoryprompts for the relay to use. In the dialogue of the "Time Distance Relay" the "Reference Relay'' frame is located on the bottom. Change the "Relay'' reference to set or reset the reference relay.

Capture Relays

The Capture Relays button enables the user to chose additional relays in the path to be displayed in the time-distance diagram. In order to delete a relay from the diagram, the respective line in the relay list has to be deleted.

35 - 36


35.4.4 Other Options

Double-Click Positions

The following positions can be double-clicked for a default action:

AxisEdit scale

CurveEdit step of relay

Relay boxEdit relay(s)

Path axisEdit Line

Any otherOpen the "Time Distance'' edit dialogue

The Context Sensitive Menu

If the diagram is right-clicked at any position, the context sensitive menu will pop up similar to the menu described in Section 19.4.2 (Plots) for the virtual instruments.

There are some additional functions available in addition to the basic VI-methods for the time-distance plot.

GridShows the dialogue to modify the grid-lines.

Edit PathOpens the dialogue of the displayed path definition (SetPath).

MethodSet the used method for calculating the tripping times.

x-UnitSet the unit for the x-Axis, km impedances,...

DiagramsSelect diagrams shown forward, reverse or both.

Consider Breaker Opening Time

ReportThis option prints out a report for the position of the relays, their tripping time as well as all calculated impedances in the output window.

Shc-Calc... Show "Short-Circuit Sweep'' command dialogue.

35.5 Relay Plot

The relay or R-X plot VisDraw is showing the impedance characteristics of different distance protection relays in one or several R-X plots. Additionally the impedance of connected lines and transformers in the network nearby the protection equipment can

35 - 37


easily be shown. Thus the impedances of the different zones of the relay and the tripping time can easily be adjusted and checked for a good and thorough protection of the equipment.

There are several ways to create a relay plot (VisDraw):

• The easiest way to create and show a VisDraw is to select one cubicle, where a distance relay is installed. Right-click the switch to open the context-sensitive menu. This will show the options Create R-X Plot and Add to R-X Plot. PowerFactory will then create a new diagram showing the R-X plot for all relays in the selected cubicle.

• Another way is to right-clicked an element which is belonging to a defined protection path and select Path... R-X Plot from the context-sensitive menu.

• Also a distance relay element ElmRelay can be chosen from the list of calculation-relevant objects or in the data manager. Right-click the relay on the right side of the data manager or in the list of relays. Then select Show R-X Plot to create a new plot or Show Add to R-X Plot to get a selection of already created plots to add the characteristic to an existing plot.

Note To show the relay locations and thus to visualize the switches with relays definitions these can be highlighted by setting the color rep-resentation of the single-line diagram to "Relay Locations''. By right-clicking these elements the option Show R-X Plot is avail-able and can be chosen.

The R-X plots show

• the impedance characteristics of selected distance relays including the different zones.

• impedance curve of the lines and transformers near the relay location.

• the location of other distance relay nearby.

• the short-circuit impedance depending on the location and the fault impedances.

• the tripping time of the relay.

35 - 38


Fig. 35.43: A R-X plot with short-circuit results and two relays

In Figure 35.43 an example is shown for the R-X plot, where two relay characteristics and the transmission line impedances are displayed.

Furthermore shows the location of the short-circuit or load-flow calculation as a equivalent impedance point in the plot. For every relay displayed in the graph also a legend is shown containing the relevant information regarding the short-circuit calculation of each relay:

• name of the relay,

• measured impedances seen from the relay location,

• the fault type,

• the actual tripping time of the relay,

• which zone is tripped.

The information shown may be changed in the relay plot settings. For details please refer to Section 19.4.2 (Plots).

35.5.1 Modifying the Relay Settings

From the R-X plot the characteristics of the relays shown can easily be changed according to the impedances of the electrical equipment, which is to be protected.

By double-clicking the characteristic of a relay zone the settings dialogue of the zone will be opened and can be modified. Here the relay specific information of the impedance characteristic can be entered. Also the information of the line branch connected to the relay in "forward'' direction is shown in the dialogue. If the OK button is selected the characteristic of the relay will be updated.

35 - 39


It is also possible to edit the lines or transformer elements shown in the plot. Holding the mouse pointer over the element for a second will show the name of the element in a balloon help box. If one of the lines is double-clicked, the edit dialogue of the element pops up like in the single-line graphics. In this way the line impedances can easily be accessed.

Relay Plot Settings

The R-X plot settings can be accessed by selecting the Options from the context-sensitive menu or by pressing the Options button in the edit dialogue of the plot.

Basic Options:

The dialogue shows the following options:

UnitThe current unit may be set to either primary or secondary (relay) ampere.

Relays UnitsThis option is used to display only certain types of relay characteristics.

ZonesHere the zone can be selected which is to be shown. Also All zones of the relays can be displayed in one graph (default).

DisplayThis option is used to select how the calculated load-flow or short-circuit current/equivalent impedance will be displayed. Either as an short-circuit arrow, a cross or none may be selected.

Show Impedance

Color out of service unitsZones being out of service can be shown in a different color.

35 - 40


Fig. 35.44: R-X-Plot Settings

Additionally, the show/hide option for the starting, overreach zones, power swing units and the complete shape of the diagrams can be selected in the dialogue.

Branch Impedances:

There are special options to modify the appearance of the branch impedances:

Number of Relay LocationsOnly the branches are shown up to the x-th next relay location. If zero, no branches are shown at all.

Branches, max. DepthMaximum number of branches shown from each relay location. If zero, no branches are shown at all.

Ignore TransformersTransformer impedances are ignored when activated.

MethodMethod for determining the line impedances.

Show Branch OptionsHere the line style and width can be selected.

Legend:

In the legend belonging to each relay different information and calculation results are displayed. Here the user can choose, which results are to be shown.

35 - 41


35.6 Protection Analysis Results

After all protection devices have been configured and thoroughly graded, it is often desirable to create reports for future reference. Aside from exporting the time-overcurrent, R-X or time-distance plots as pictures (see 19.4.9: Tools for Virtual Instru-ments), there are several other methods to report the relay settings.

Reports

The icon "Output Calculation Analysis'' ( ) in the main menu, will open the "Output'' dialogue (ComSh). The results of the load-flow or short-circuit analysis, for a range of relays, can be generated in the output by selecting the options

• Results

• Relays

To generate a report for one or more relays, or for one or more previously defined paths, the data manager may be used to select one or more relays or paths and right-clicking the selection. The menu will show the option Output-Results if at least one relay was found amongst the selected objects or in one of the selected paths. If a busbar was selected, then all relays in connection with that busbar are selected too.

Results in Single Line Graph

The names of the relays or the tripping times may be made visible in the single line graphic by selecting the following options in the main menu.

1 Output - Results for Edge Elements - Relays 2 Output - Results for Edge Elements - Relay Tripping Times

The first option ("Relays''), which is always available, will show the names of the relays in all cubicles. The second option will show the tripping times of the relays after a load-flow or short-circuit calculation has been made. If a relays does not trip, then a tripping time of 9999.99 s is shown.Fig. 35.45:

35.7 Modelling Protection Devices

The main focus of the previous paragraphs was to describe the general handling of protection devices. As stated in the introduction of this chapter, there is a difference between using existing models (i.e. from the PowerFactory protection database) and defining new models or altering existing ones.

This chapter shall provide an overview over the modelling philosophy behind protection devices. Understanding this philosophy is vital to modelling new relays or changing existing ones. In order for the relay to function properly with the standard functions, like the short-circuit calculation, certain design rules have to be obeyed.

35.7.1 The Modelling Structure

Protection devices form a group of highly complex and non-uniform power system

35 - 42


devices. This places any program for modeling them for a difficult dilemma. On the one hand, the relay models should be as flexible and versatile as possible, to ensure that all types of protection relays can be modeled with all of their features. On the other hand, the relay models should be as simple as possible in order to reduce the amount of work and knowledge needed to define power system protection devices.

This dilemma is solved by PowerFactory by modelling protection devices in three different levels. These levels are:

• the relay frame

• the block types

• the block elements

Each of these levels fulfill a different role in the modelling process of a protection device. Figure 35.46 shows the relation of those three levels graphically.

Fig. 35.46: Modelling structure for protection devices

35 - 43


35.7.2 The Relay Frame

The relay frame is the base of a protection device. Therein defined are the different slots and signal pathways available to the model. It is similar to the frames of composite models and is create in the same way. See 27.7.3 (The Composite Frame) for more information.

The only difference to the creation of a composite frame is, that you only need to define in- and output signals and that the class name has to be defined. Figure 35.47 shows an exemplary relay frame for a two stage overcurrent relay. As you can see, there is a slot for each block, that can be found in the model.

The frame can be assigned to a newly created relay type in the Equipment Type Library .

To create a new relay type, click the icon in the library and select "Special Types -> Relay (TypRelay)". Once The frame is assigned to the type, perform a slot update for the relay type to automatically create all block types needed.

Hint: To enable the automatic creation of blocks the "Automatic, model will be created" option has to be enabeld in the respective slot def-inition of the frame. This should be done with all blocks, except the ones for the meassurement transformers.

Fig. 35.47: Examplary relay frame

35.7.3 The Block Type

As already mentioned, the blocks represent the different functionalities of a relay. The various block types (i.e. TypIoc) are stored within the relay type (TypRelay) and define

35 - 44


those functionalities. Depending on the kind of block, the user can define boundaries for time dials and current ranges or select the available characteristics. Figure 35.48 shows the type dialog of an instantaeneous overcurrent block as an example. Parameters that normally can not be influenced by the user, like the Pick-up Time, are defined in the type as well. For a detailed description of the different options and parameters for each block type, please refer to the Technical Reference section.

Fig. 35.48: Type dialog of an instantaneous overcurrent block

If all block types for a new model have been configured, a default relay can be created. This default relay can be used to save default settings for each block, which are loaded if a model of the newly defined type is created in the network.

To create a default relay, use the icon in the data manager or right-click on an empty space and select "New -> Others -> Others -> Net Elements (Elm*) -> Relay Model (ElmRelay)"

Note: The default relay has to be saved inside the relay type. It doesn‘t need meassurement transformers like CTs and VTs.

35.7.4 The Block Element

The block elements (i.e. RelIoc) represent the user frontend of the relay. They are created if a new type is selected for a relay model (ElmRelay). Which kind of block element is created depends on the block type (Typ*) that occupies the same slot in the relay type (TypRelay). The settings made in a block element are only valid for the block

35 - 45


element itself, whereas changes in the block type will be applied to all blocks depending on this particular type. Figure 35.49 shows the block element dialog belonging to the typ dialog in Figure 35.48.

Fig. 35.49: Element dialog of an instantaneous overcurrent relay

35 - 46


35 - 47


35 - 48

DIgSILENT PowerFactory Network Reduction

Chapter 36Network Reduction

This chapter explains how to use the PowerFactory Network Reduction tool. A typical application of Network Reduction is when a network that is part of or adjacent to a much larger network must be analyzed, but cannot be studied independently of the larger network. In such cases, one option is to model both networks in detail for calculation purposes. However, there might be situations when it is not desirable to do studies with the complete model. For example, when the calculation times would increase significantly or when the data of the neighboring network is confidential and cannot be published.

In these cases, it is common practice to provide a simplified representation of the neigh-boring network that contains only the interface nodes (connection points). These can then be connected by equivalent impedances and voltage sources, so that the short circuit and load-flow response within the kept (non reduced) system is the same as when the detailed model is used.

PowerFactory’s Network Reduction algorithm produces an equivalent representation of the reduced part of the network and calculates its parameters. This equivalent represen-tation is valid for both load flow and short-circuit calculations, including asymmetrical faults such as single-phase faults.

The chapter is separated into five parts. Firstly, the technical background of the Power-Factory Network Reduction algorithm is explained. Section 36.2 discusses the steps needed to run a Network Reduction and section 36.3 explains in detail each of the options of the PowerFactory Network Reduction tool. The penultimate part, section 36.4, pres-ents a simple example and the final section provides some 'tips and tricks' to consider when working with the Network Reduction tool.

36 - 1



Some additional technical background on the Network Reduction tool is provided in the following sections.

36.1.1 Network Reduction for Load Flow

Network reduction for load flow is an algorithm based on sensitivity matrices. The basic idea is that the sensitivities of the equivalent grid, measured at the connection points in the kept grid, must be equal to the sensitivities of the grid that has been reduced. This means that for a given (virtual) set of P and Q injections in the branches, from the kept grid to the grid to be reduced, the resulting u and (voltage magnitude and voltage phase angle variations) in the boundary nodes must be the same for the equivalent grid as those that would have been obtained for the original grid (within a user defined toler-ance).

36.1.2 Network Reduction for Short-Circuit

Network reduction for short-circuit is an algorithm based on nodal impedance/nodal admittance matrices. The basic idea is that the impedance matrix of the equivalent grid, measured at the connection points in the kept grid, must be equal to the impedance matrix of the grid to be reduced (for the rows and columns that correspond to the boundary nodes). This means that for a given (virtual) additional I injection (variation of current phasor) in the boundary branches, from the kept grid to the grid to be reduced, the resulting u (variations of voltage phasor) in the boundary nodes must be the same for the equivalent grid, as those that would have been obtained for the original grid (within a user defined tolerance).

This must be valid for positive sequence, negative sequence, and zero sequence cases, if these are to be considered in the calculation (unbalanced short-circuit equivalent).

36.2 How to Complete a Network Reduction

This section explains the process for running a Network Reduction. There are several steps that you must complete to successfully reduce a network:

• Create a boundary and define the 'interior' and 'exterior' regions.

• Create a backup of the project intended for reduction (optional).

• Activate the additional tools toolbar and configure the Network Reduction Tool options.

• Run the Network Reduction Tool.

You must define a boundary before you can proceed further with the Network Reduction. This process is described in detail in Section 15.3 (Boundaries). However, to summarize, the boundary divides the network into two regions, the area to be reduced which is referred to as the 'interior region' and the area to be kept which is referred to as the 'exte-rior region'.

The following section describes the process of backing up the project, running the Network Reduction tool using the default options and describes the expected output of a

36 - 2


successful network reduction. For more information about the options available within the Network Reduction tool, see Section 36.3: Network Reduction Command.

36.2.1 How to Backup the Project (optional)

By default, the Network Reduction tool keeps all the original network data and the modi-fications needed to reduce the network are stored within a new expansion stage that is part of a new variation. It will only destroy the original data if the associated option within the command is configured for this (see Section 36.3.2: Outputs).

However, if you want extra security to guarantee against data loss, in case for instance you accidently select the option to modify the original network, then you should make a backup copy of the project before completing the Network Reduction. There are three possible ways to do this:

• make a copy of the whole project and paste/store it with a name different to that of the original project; or

• export the project as a *.dz- or *.pfd file (for information about exporting data please refer to Section 10.1.4: Exporting and Importing of Projects); or

• activate the project and create aVersion of the project. For information about Versions please refer to Section 20.1 (Project Versions).

36.2.2 How to run the Network Reduction tool

This sub-section describes the procedure you must follow to run the Network Reduction using the default options. Proceed as follows:

1 Activate the base Study Case for the project you wish to reduce.

2 Define a boundary that splits the grid into the part to be reduced (interior region), and the part to be kept (exterior region). See Section 15.3 (Boundaries) for the procedure.

3 Open the boundary object and use the Check Split button in the ElmBoundary dialogue to check that the boundary correctly splits the network into two regions. See Section 15.3 (Boundaries) for more information about boundaries.

4 Select the Additional Tools icon ( ) from the main toolbar. This is illustrated in Figure 36.1.

5 Press the Network Reduction icon ( ) from the Additional Tools icon bar (Figure 36.1). This opens the dialogue for Network Reduction Command (ComRed).

6 Select the boundary you previously defined using the selection control ( ).

7 Optional: If you wish to modify the settings of the command, do so in this dialog. The settings and options are explained in Section 36.3 (Network Reduction Command). However, the default options are recommended, unless you have a specific reason for changing them.

8 Press the Execute button to start the reduction procedure.

36 - 3


Fig. 36.1: The Network Reduction Button in the Additional Tools Icon Bar

36.2.3 Expected Output of the Network Reduction

This sub-section describes the expected output of the network reduction tool after successfully executing it. The output varies depending on whether the reduced project was created in V13.2 or earlier and contains system stages, or if it was created in V14.0 or higher. Both output scenarios are explained in the following sections. Also, the addi-tional objects that the Network Reduction tool creates are explained.

Changes to the network model for projects created in V14.0 or higher

The default behavior of the Network Reduction command is to create a Variation containing a single Expansion Stage called 'Reduction Stage'. For more information see Chapter 17: Network Variations and Expansion Stages. The Variation will be named auto-matically according to the reduction options selected in the basic options tab of the Network Reduction command. For example, for the default options the Variation will be named 'Equ-LF[EW]-Shc[sym]@Boundary'. Figure 36.2 shows an example of a network data model after a successful Network Reduction.

Fig. 36.2: Project Data tree showing the network model after a successful Network Reduction using the default options.

Network Reduction

New Variation and Ex-pansion Stage created by the Network Reduc-tion tool.

New Study Case creat-ed by the Network Re-duction tool.

36 - 4


The Network Reduction tool also creates a new Study Case with a name that matches the new Variation name. To return to your original network, all you need to do is activate the original study case that you used to initiate the Network Reduction.

Note: The Variation and Study Case created by the Network Reduction tool are automatically activated when the tool is run. To return to your original model you need to reactivate the 'base' Study Case.

Changes to the network model for projects created in V13.2 or lower

For projects imported from V13.2, if they contain System Stage(s) (superseded by Varia-tions in V14.0), then the Network Reduction does not create a Variation in the project. Instead, a system stage is created within each active grid. Therefore, if there are 'n' active grids when the Network Reduction process is initiated, there will be 'n' System Stages created. The naming convention for the System Stage(s) is the same as the naming convention for the Variations described above. The new System Stage(s) will be automat-ically activated in the created study case.

If one or more single line graphic diagrams were in the System Stage(s) within the original grid, these graphics will also be kept in the new System Stage(s) within the combined (partly kept and partly reduced) grid. The first time that the new study case is activated (automatically, at the end of Network Reduction procedure), the graphics will be displayed. The elements contained in the part of the grid which was reduced (if any of them were previously shown), will appear grey in colour, as 'ghost' elements. Deactivating and re-activating the project will make them disappear permanently (they are graphic elements only, and have no corresponding elements in the database in the new System Stage(s)).

New objects added by the Network Reduction command

Depending on the network configuration and the options chosen within the Network Reduction command, during the Network Reduction process some new objects might be created. There are two possible new object types:

• AC Voltage Source (ElmVac) ; and

• Common Impedance (ElmZpu)

By default, there will be one voltage source created for every boundary node and one common impedance between every pair of boundary nodes (unless the calculated mutual impedance is greater than the user-defined threshold described in Section 36.3.3). These objects are stored in the database but are not automatically drawn on the single line graphic. If you need to see these objects on the single line diagram, you must add them manually using the PowerFactory tool 'Draw Existing Net Elements', which is explained in Section 11.4 (Drawing Diagrams with already existing Network Elements).

36.3 Network Reduction Command

In this section, the Network Reduction command options are explained.

36 - 5



This section describes the options on the Basic Options tab of the Network Reduction command as shown in Figure 36.3.

Fig. 36.3: Network Reduction Command (ComRed) Basic Options

Boundary

This selection control refers to the boundary that defines the part of the grid that shall be reduced by the reduction tool. Note, the project Boundaries folder might contain many boundaries, but you must select only one boundary from this folder. This selected boundary must separate the original grid into two parts, the part that shall be reduced (interior region) and the part that shall be kept (exterior region). For more information about boundaries, please refer to Section 15.3 (Boundaries).

Load Flow

Calculate load flow equivalent

If this option is enabled, the load flow equivalent model will be created by the reduction tool. This option is enabled by default.

Equivalent Model for Power Injection

The load flow equivalent is composed of mutual impedances between boundary nodes and power injections (and shunt impedances) at boundary nodes. The power injection can be represented by different models. For the load flow equivalent there are three options (models) available:

• Load Equivalent: a load demand

• Ward Equivalent: an AC voltage source which is configured as a Ward Equivalent

36 - 6


• Extended Ward Equivalent: an AC voltage source which is configured as an Extended Ward Equivalent

Short-Circuit

Calculate short-circuit equivalent

If this option is enabled, the short-circuit equivalent model will be created by the Network Reduction tool. Currently, only the complete short-circuit calculation method is supported.

Asymmetrical Representation

This option is used to specify whether an unbalanced short-circuit equivalent will be created. If this option is disabled, only a balanced short-circuit equivalent will be created, valid for the calculation of 3-phase short-circuits. If this option is enabled, an unbalanced short-circuit equivalent is created, valid for the calculation of single-phase and other unsymmetrical short-circuits. This means the network representation must include zero sequence and negative sequence parameters, otherwise the unbalanced calculation cannot be done.

36.3.2 Outputs

The section describes the options available on the Outputs tab of the Network Reduction command as shown in Figure 36.4. These options define how the Network Reduction command modifies the network model.

Fig. 36.4: Network Reduction Command - Outputs

Calculation of Parameters Only

The equivalent parameters are calculated and reported to the output window. If this option is selected then the Network Reduction command does not modify the network model.

Create a new Variation for Reduced Network (Default)

The equivalent parameters are calculated and a Variation will be automatically created to store the reduced network model. If the project already includes System Stage(s) (from PowerFactory version 13.2 or earlier versions) then System Stage(s) will be created instead of a Variation.

Reduce Network without Creating a New Variation

The Network Reduction command will directly modify the main network model if this options is selected. Therefore, this option will destroy data by deleting the 'interior' region

36 - 7


of the selected boundary, and replacing it with its reduced model, so this option should be used with care. To avoid losing the original grid data, backup the project as described in Section 36.2.1 (How to Backup the Project (optional)).

36 - 8



This section describes the Advanced Options for the Network Reduction command as shown in Figure 36.5.

Fig. 36.5: Network Reduction Command - Advanced Options

Mutual Impedance (Ignore above)

As part of the Network Reduction process equivalent branches (represented using Common Impedance elements) will be created between the boundary nodes, to maintain the power-flow relationship between them. If such branches have a calculated impedance larger than this parameter they will be ignored (not added to the network model).

By default, the number of these branches created will be N*(N-1)/2, where N is the number of boundary nodes. A boundary node is defined for each boundary cubicle. There-fore, the number of created branches can be very high. Normally many of these equiva-lent branches have a very large impedance value, so their associated power flows are negligible and the branch can be ignored.

The default value for this parameter is 1000 p.u (based on 100 MVA).

Calculate Equivalent Parameters at All Frequencies

This option enables the calculation of frequency-related parameters. By default, the short-circuit equivalent parameters are calculated at all frequencies relevant to short-circuit analysis (equivalent frequencies for calculating the d.c. component of the short-circuit current):

• f = fn

• f / fn = 0.4

• f / fn = 0.27

• f / fn = 0.15

• f / fn = 0.092

• f / fn = 0.055

fn is the nominal frequency of the grid (usually 50 Hz or 60 Hz).

If only transient and sub-transient short-circuit currents are important in the reduced network, the calculation of frequency-related parameters can be skipped by unchecking this option.

36 - 9


36.3.4 Verification

The verification tab of the Network Reduction tool is shown in Figure 36.6. The options are explained below.

Fig. 36.6: Network Reduction Command - Verification

Check Equivalent Results

If the option Check load flow results after reduction is enabled, the load flow results at the boundary nodes after the network reduction will be checked against the original network results. A warning message will be given if the results do not match (within the user defined 'Threshold for check').

The results of the comparison between the original network and the reduced network are printed to the output window.

Check Deviation of Operating Point

If the option Save original operating point to result file is enabled, the base operating point for the Network Reduction will be automatically saved to two result files. These two created files are:

• LdfResultforNR.ElmRes: voltage magnitudes and angles of all boundary nodes; and

• ShcResultforNR.ElmRes: short-circuit level at all boundary nodes, including Ik'' (Ikss), Ik' (Iks), ip (ip), ib (ib), Ib (Ib), Xb/Rb (XtoR_b), and X/R (XtoR).

36.4 Network Reduction Example

This section presents a Network Reduction example using a small transmission network feeding a distribution system from 'bus 5' and 'bus 6' as shown in Figure 36.7. The distri-bution system is represented by Load A and Load B and the corresponding two trans-formers. As a user you would like to study the distribution system in detail but are not concerned with the detailed power flow within the transmission system. Therefore, the Network Reduction tool can be used to create a equivalent model for the transmission system.

The interior region (the area that shall be reduced) is shown shaded in grey, whereas the non-shaded area is the exterior region that shall be kept. The procedure for completing the Network Reduction according to these parameters is as follows (you can repeat this example yourself using the 'nine bus system' within the demo user of the PowerFactory database - the network used in the example is slightly modified from this):

36 - 10


Fig. 36.7: Example System with Original Network

1 Select cubicles that will be used to define the boundary. These are highlighted in Figure 36.8. (Use the freeze mode to make selection of the cubicles easier.)

Fig. 36.8: Cubicles used for the boundary definition.

Interior Region

Bus 10 Bus 11

Bus

7

Bus 5

Bus 4

Bus 6

Bus

3

Bus

9

Bus

8

Bus

2

Bus 1

T4

T5

Load A

Line

1 Line

6Li

ne 5

Load B

T3

G ~ G3

Line 4

Load

C

Line 3

T2G~G2

External ..

Line

9

Line

2

DIg

SIL

EN

T

Bus

7Bu

s 7

Bus

7Bu

s 7

Bus

7Bu

s 7

Bus

7

Bus 5

Bus 4Bus 10 Bus 11

Bus 6

Bus

3

Bus

9

Bus

8

Bus

2

Bus 1

Load A

Line

1T4

T5

External ..

Line

6

Line

9

Line

2

Line

5

Load B

T3

G ~ G3

Line 4

Load

C

Line 3

T2

G~G2

DIg

SIL

EN

T

36 - 11


2 Right-click one of the selected cubicles and choose the option Define -> Boundary ... The boundary dialog appears.

3 Alter the boundary cubicle orientations so that the 'Interior' region is correctly defined. The cubicle orientation for the T4 and T5 cubicles should be set to 'Busbar'. This means that the boundary interior is defined by 'looking back' at the bus from these cubicles. The orientation for the Line 1 and Line 6 cubicles remains on Branch (looking into the branch).

4 Open the Network Reduction command dialog and select the boundary defined in steps 1-3 using the selection control.

5 Press Execute. The Network Reduction tool will reduce the system.

6 Optional: draw in the three new common impedance elements and three equivalent ward voltage source objects using the Draw Existing Net Elements tool. The result of the Network Reduction is shown in Figure 36.9.

A load flow calculation or a short-circuit calculation in the reduced network gives the same results for the distribution network as for the original (non-reduced) network.

Fig. 36.9: Example System with Reduced Network

Bus 10Bus 10 Bus 11

Bus 5Bus 5

Bus 4

Bus 6

Bus 1Bus 1Bus 1Bus 1Bus 1

XW

eqVac-2

XW

eqVac-1

XW

eqVac-0

Zeq

Zpu-

1-2

Zeq

Zpu-

0-2

ZeqZpu-0-1

T4T4

T5

Load A Load BLoad BLoad B

External ..External ..External ..External ..External ..External ..External ..External ..

Line

9

DIg

SIL

EN

T

36 - 12


36.5 Tips for using the Network Reduction Tool

This section presents some tips for using the Network Reduction tool and some solutions to common problems encountered by users.

36.5.1 Station Controller Busbar is Reduced

Sometimes a interior region might be defined such that it contains the reference bus of a station controller. The generators belonging to this station controller are in the exterior region. During the reduction process the 'reference bus' will be reduced (removed) from the model, yet the station controller and generators will remain part of the new system. In such a situation, attempting to run a load-flow after the reduction will fail with an error message similar to that shown in Figure 36.10.

Fig. 36.10: Error message showing a station controller error

There are two possible solutions to this problem:

• Modify the boundary definition slightly such that the station controller bus is excluded from the exterior region; or

• Set the station controller out of service and the generators to local PV mode.

36.5.2 Network Reduction doesn’t Reduce Isolated Areas

By default, the boundary definition search stops when encountering an open breaker. This means that isolated areas can sometimes be excluded from the 'interior' region and there-fore are not reduced by the Network Reduction tool. The solution to this problem is to disable the boundary flag 'Topological search: Stop at open breakers'. This option is enabled by default in all boundary definitions. It is recommended to disable it before attempting a Network Reduction.

A related problem occurs with the project setting (Edit -> Project -> Project Settings -> Advanced Calculation Parameters) 'Automatic Out of Service Detection'. It is recom-mended that this option is disabled before attempting a Network Reduction. However, it is disabled by default, so if you have not made changes to the default project settings you should not need to make any changes to this setting.

36.5.3 The Reference Machine is not Reduced

The Network Reduction tool will not reduce a reference machine defined within the inte-rior region. It also leaves all network components that are topologically one bus removed from the reference machine (and of non-zero impedance). For example, if the reference machine is a typical synchronous machine connected to the HV system through a step up

36 - 13


transformer, then the reduction tool will leave the synchronous machine, the LV bus, the step up transformer and the HV bus within the reduced network.

It is recommended that the reference machine is found within the exterior region before attempting a Network Reduction. The reference machine can be identified by checking the output window following a successful load-flow calculation as illustrated in Figure 36.11.

Fig. 36.11: Output window showing the load-flow command output and the indication of the reference machine

The reference machine is shown in the first line of the load-flow command output.

36 - 14

DIgSILENT PowerFactory State Estimation

Chapter 37State Estimation

The State Estimator (SE) function of PowerFactory provides consistent load flow re-sults for an entire power system, based on real time measurements, manually entered data and the network model. Before any further analysis, such as contingency analy-sis, security checks etc. can be carried out, the present state of a power system must be estimated from available measurements. The measurement types that are pro-cessed by the PowerFactory State Estimator are:

• Active Power Branch Flow

• Reactive Power Branch Flow

• Branch Current (Magnitude)

• Bus Bar Voltage (Magnitude)

• Breaker Status

• Transformer Tap Position

Unfortunately, these measurements are usually noisy and some data might even be totally wrong. On the other hand, there are usually more data available than absolute-ly necessary and it is possible to profit by redundant measurements for improving the accuracy of the estimated network state.

The states that can be estimated by the State Estimator on the base of the given mea-surements vary for different elements in the network:

• Loads

- Active Power, and/or

- Reactive Power, or

- Scaling Factor, as an alternative

• Synchronous Machines

- Active Power, and/or

- Reactive Power

• Asynchronous Machines

- Active Power

• Static var System

- Reactive Power

• 2- and 3-winding transformers

- Tap Positions (for all but one taps).

37 - 1


37.1 Objective Function

The objective of a state estimator is to assess the generator and load injections, and the tap positions in a way that the resulting load flow result matches as close as pos-sible with the measured branch flows and bus bar voltages. Mathematically, this can be expressed with a weighted square sum of all deviations between calculated (calVal) and measured (meaVal) branch flows and bus bar voltages:

The state vector contains all voltage magnitudes, voltage angles and also all vari-ables to be estimated, such as active and reactive power injections at all bus bars.

Because more accurate measurements should have a higher influence to the final re-sults than less accurate measurements, every measurement error is weighted with a weighting factor wi to the standard deviation of the corresponding measurement de-vice (+transmission channels, etc.).

In this setting, the goal of a state estimator is to minimize the above given function f un-der the side constraints that all load flow equations are fulfilled.

37.2 Components of the PowerFactory State Estimator

The State Estimator function in PowerFactory consists of several independent compo-nents, namely:

1 Preprocessing

2 Plausibility Check

3 Observability Analysis

4 State Estimation (Non-Linear Optimization)

Figure 37.1 illustrates the algorithmic interaction of the different components. The first Preprocessing phase adjusts all breaker and tap positions according to their measured sig-nals.

f x wi calVali x meaVali–2

i 1=

n

=

x

37 - 2


Fig. 37.1: Variation of the PowerFactory state estimator algorithm

The Plausibility Check is sought to detect and separate out, in a second phase, all mea-surements with some apparent error. PowerFactory provides various test criteria for that phase of the algorithm.

In a third phase, the network is checked for its Observability. Roughly speaking, a region of the network is called observable, if the measurements in the system provide enough (non-redundant) information to estimate the state of that part of the network.

Finally, the State Estimation itself evaluates the state of the entire power system by solv-ing the above mentioned non-linear optimization problem. PowerFactory provides var-ious ways for copying with non-observable areas of the network.

In order to improve the quality of the result, observability analysis and state estimation can be run in a loop. In this mode, at the end of each state estimation, the measurement devices undergo a so-called ”Bad Data Detection”: the error of every measurement device can be estimated by evaluating the difference between calculated and measured quantity. Extremely distorted measurements (i.e. the estimated error is much larger than the stan-dard deviation of the measurement device) are not considered in the subsequent itera-tions. The process is repeated until no bad measurements are detected any more.

In the following, the distinct components of the PowerFactory state estimator are ex-plained in detail.

Plausibility Check

State Estimation(non-linear Optimization)

Preprocessing

“Repair” Unobservability”

Bad Data Detection

No Bad Measurements Exists

Still Unobservable? Observable?

Eliminate Errornous Measurements

OK

Elim

inate

Bad

Mea

sure

men

ts

37 - 3


37.2.1 Plausibility Check

In order to avoid any heavy distortion of the estimated network-state due to completely wrong measurements, the following Plausibility Checks can be made before the actual State Estimation is started. Every measurement that fails in any of the listed Plausibility Checks will not be considered.

• Check for consistent active power flow directions at each side of the branch elements.

• Check for extremely large branch losses, which exceed their nominal values.

• Check for negative losses on passive branch elements.

• Check for large branch flows on open ended branch elements.

• Check whether the measured branch loadings exceed the nominal loading value of the branch elements.

• Node sum checks for both, active and reactive power.

Each test is based on a stochastic analysis which takes into account the measurement’s individual accuracy. The strictness of the above mentioned checking criteria can be con-tinuously adjusted in the advanced settings.

The result of the Plausibility Check is reported, for each measurement, on a detailed error status page (see Section 37.5).

37.2.2 Observability Analysis

A necessary requirement for an observable system is that the number of available mea-surements is equal or larger than the number of estimated variables. This verification can easily be made at the beginning of every state estimation.

But it can also happen that only parts of the network are observable and some other parts of the system are not observable even if the total number of measurements is sufficient. Hence, it is not only important that there are enough measurements, but also that they are well distributed in the network.

Therefore, additional verifications are made checking for every load or generator injection whether it is observable or not. The entire network is said to be observable if all load or generator injections can be estimated based on the given measurements. PowerFactory does not only solve the decision problem whether the given system is observable or not: If a network is not observable, it is still useful to determine the islands in the network that are observable.

The Observability Analysis in PowerFactory is not purely based on topological argu-ments; it heavily takes into account the electrical quantities of the network. Mathemati-cally speaking, the Observability Check is based on an intricate sensitivity analysis, involving fast matrix-rank-calculations, of the whole system.

The result of the Observability Analysis can be viewed using the data manager. Besides, PowerFactory offers a very flexible color representation both for observable and unob-servable areas, and for redundant and non-redundant measurements (see Section 37.5.4).

Observability of individual states

The Observability Analysis identifies not only, for each state (i.e., load or generator injec-

37 - 4


tions) whether it is observable or not. It also subdivides all unobservable states into so-called ”equivalence-classes”. Each equivalence-class has the property that it is observable as a group, even though its members (i.e., the single states) cannot be observed. Each group then can be handled individually for the subsequent state estimation.

Redundancy of measurements

Typically, an observable network is overdetermined in the sense that redundant measure-ments exist, which—for the observability of the system—do not provide any further infor-mation. During the Observability Analysis, PowerFactory determines redundant and non-redundant measurements. Moreover, it subdivides all redundant measurements ac-cording to their information content for the system’s observability status. In this sense, PowerFactory is even able to calculate a redundancy level which then indicates how much reserve the network measurements provide. This helps the system analyst to pre-cisely identify weakly measured areas in the network.

It should be remarked that the non-linear optimization part of the State Estimator may highly profit from these ”redundant” measurements; thus, redundant measurements will not be neglected in the state estimation.

37.2.3 State Estimation (Non-Linear Optimization)

The non-linear optimization is the core part of the State Estimator. As already mentioned in the introduction, the objective is to minimize the weighted square sum of all deviations between calculated and measured branch flows and bus bar voltages whilst fulfilling all load flow equations.

PowerFactory uses an extremely fast converging iterative approach to solve the prob-lem based on Lagrange-Newton methods. If the Observability Analysis in the previous step indicates that the entire power system is observable, convergence (in general) is guaranteed.

In order to come up with a solution for a non-observable system, various strategies can be followed: One option is to reset all non-observable states, such that some manually entered values or historic data is used for these states. An alternative option is to use so-called pseudo-measurements for non-observable states. A pseudo-measurement basically is a measurement with a very poor accuracy. These pseudo-measurements force the al-gorithm to converge. At the same time, the resulting estimated states will be of correct proportions within each equivalence-class.

In the remaining sections of this guide of use, the instructions related to Data Entry, Op-tions and Constraints, and Visualization of Results are presented.

37.3 State Estimator Data Input

The main procedures to introduce and manipulate the State Estimator data are indicated in this section. For applying the PowerFactory State Estimator, the following data are required additional to standard load flow data:

• Measurements

- Active Power Branch Flow

- Reactive Power Branch Flow

37 - 5


- Branch Current (Magnitude)

- Bus Bar Voltage (Magnitude)

- Breaker Status

- Transformer Tap Position

• Estimated States

- Loads: Active Power (P) and/or Reactive Power (Q), or the Scaling Factor, as an alternative.

- Synchronous Machines: Active Power (P) and/or Reactive Power (Q)

- Asynchronous Machines: Active Power (P)

- Static var Systems: Reactive Power (Q)

- Transformers: Tap Positions

For the measurements listed above, PowerFactory uses the abbreviated names P-mea-surement, Q-measurement, I-measurement, V-measurement, Breaker-measurement, and Tap position-measurement. Similarly, as a convention, the four different types of es-timated states are shortly called P-state, Q-state, Scaling factor-state, and Tap position-state.

37.3.1 Measurements

All measurements are defined by placing a so-called ”External Measurement Device” in-side a cubicle. For this purpose, select the device in the single-line graphic and choose from the context menu (right mouse button) ”New Devices” and then ”External Measure-ments...” (see Figure 37.2). Then, the new object dialogue pops up with a predefined list of external measurements. Please select the desired measurement device among this list (see Figure 37.3).

37 - 6


Fig. 37.2: External Measurements that are located in a cubicle

Fig. 37.3: Defining new external measurements

37 - 7


The following measurement devices are currently supported

• (External) P-Measurement (StaExtpmea)

• (External) Q-Measurement (StaExtqmea)

• (External) I-Measurement, current magnitude (StaExtimea)

• (External) V-Measurement, voltage magnitude (StaExtvmea)

• (External) Breaker Signalization Breaker Status (StaExtbrkmea)

• (External) Tap-Position Measurement Tap Position (StaExttapmea)

Any number of mutually distinct measurement devices can be defined in the cubicle.

Branch Flow Measurements

Any branch flow measurement (StaExpmea, StaExtqmea) is defined by the following val-ues (see figures 37.4 and 37.5):

• Measured value (e:Pmea or e:Qmea, respectively)

• Multiplicator (e:Multip)

• Orientation (e:i_gen)

• Accuracy class and rating (e:Snom and e:accuracy)

• Input status (to be found on the second page of the edit object, see Figure 37.5): E.g., tele-measured, manually entered, read/write protected, . . . (e:iStatus). It is important to note that the state estimator takes into account only measurements, for which the ”read”-Status is explicitly set and for which the ”Neglected by SE”-Status is unset.

Fig. 37.4: Dialogue for an external P-measurement

The accuracy class and the rating are used for weighting the measurement element. In

37 - 8


case of redundant measurements, a more accurate measurement will be higher weighted than a less accurate measurement.

Using the flag ”orientation”, it is possible to define the meaning of the active or reactive power sign. Load orientation means that a positively measured P or Q flows into the ele-ment, generator orientation defines a positive flow as flowing out of an element. With the ”multiplicator”, a measured quantity can be re-rated. E.g., if a measurement instrument indicates 150kW (instead of 0.15MW), the ”multiplicator” can be set to 0.001 and the measured value is set to 150 resulting in a correct value.

It is important to note, that External P- and Q-measurements have the additional feature to possibly serve as a so-called (externally created) pseudo-measurement. This feature is activated by checking the corresponding box (e:pseudo). Pseudo-measurements are special measurements which are ignored during the regular calculation. They are activat-ed in a selective manner only if the observability check found unobservable states in the network (see Section 37.4.1: Basic Setup Options for details).

Current Measurements

The External I-measurement (Staextimea) plays a special role and slightly differs from the External P- and Q-measurements (see Figure 37.6): Besides specifying the measured current magnitude (e:Imea), the user is asked to enter an assumed (or measured) value for the power factor cos (e:cosphi and e:pf_recapr).

Fig. 37.5: Second page ”Status” of the dialogue for an external P-measurement

Internally, the measured current magnitude is then additionally transformed into two fur-ther measurements, namely an active and a reactive current. This is due to the fact that current magnitude does not provide information on the direction of the flow, which — on the other hand — is essential to avoid ambiguous solutions in the optimization.

In this sense, an external I-measurement may play the role of up to three measurements:

37 - 9


1 as a current magnitude measurement.

2 as a measurement for active current.

3 as a measurement for reactive current.

The decision which of these measurements shall participate in the state estimator is left to the user by checking the boxes (e:iUseMagn,e:iUseAct, and/or e:iUseReact). In any case, the corresponding ratings for the used measurement types need to be spec-ified. This is done (accordingly to the flow measurements) by entering the pairs of fields ((e:SnomMagn,e:accuracyMagn), (e:SnomAct,e:accuracyAct), and (e:SnomRe-act,e:accuracyReact), respectively).

Voltage Measurements

Voltage measurements (StaExvmea) need to be placed in cubicles as well. The measure-ment point then is the adjacent terminal.

Fig. 37.6: Dialogue for an external I-measurement

A voltage measurement basically has the same properties as a flow measurement, except, for the rating, only a single value for the accuracy needs to be specified. The correspond-ing internal reference is the nominal voltage of the terminal which serves as measurement point.

37 - 10


Breaker and Tap Position Measurements

Both breaker and tap position measurements are assumed to measure the corresponding discrete breaker status and tap position signal accurately. Hence, no ratings needs to be specified.

Tap position measurements have a conversion table as extra feature. The conversion table allows any discrete translation mapping between external tap positions (Ext. Tap) and tap positions used by PowerFactory (PF Tap).

37.3.2 Activating the State Estimator Display Option

To access and enter data for State Estimator calculations in the appropriate elements of the grid, the pertinent ”Display Options” must be selected as follows:

a) Click the icon , or select from the main menu ”Options User Settings”. Change to the tab page ”Functions”. The window shown in Figure 37.7 will appear.

b) Enable the Display Function ”State Estimator” as shown below.

c) Exit the window clicking the OK button.

Fig. 37.7: User Settings for State Estimation

With this display function enabled, a new tab called ”State Estimator” appears in the State Estimator related elements of the grids in the activated project. The State Estimator data

37 - 11


manipulation of the different elements is indicated below.

37.3.3 Editing the Element Data

In addition to the measurement values, the user has to specify which quantities shall be considered as ”states to be estimated” by the SE. Possible states to be optimized whilst minimizing the sum of the error squares over all measurements are all active and/or re-active power injections at generators and loads and all tap positions.

Loads

For each load (ElmLod), the user can specify whether its active and/or reactive power shall be estimated by the state estimator. Alternatively, the state estimator is able to es-timate the scaling factor (for a given P and Q injection). The specification which parameter shall be estimated, is done by checking corresponding boxes on the ”State Estimator” page of the load (see Figure 37.8). When these options are disabled, the load is treated as in the conventional load flow calculation during the execution of the SE.

Fig. 37.8: Editing element data for loads

Synchronous Machines

Similarly, for synchronous machines (ElmSym), the active and reactive power can be se-lected as a control variable for being estimated by the state estimator. Again, the user will find corresponding check boxes on the ”State Estimator” page of the element.

If the corresponding check box(es) are disabled, the synchronous machine behaves as in the conventional load flow calculation.

Asynchronous Machines

For asynchronous machines (ElmAsm), the active power may serve as a state to be esti-mated. Once again, the corresponding box has to be checked on the ”State Estimator” page.

If the corresponding check box is disabled, the asynchronous machine behaves as in the conventional load flow calculation.

37 - 12


Static var Systems

For static var systems (ElmSvs), the reactive power may serve as a state to be estimated. Again, the corresponding box has to be checked on the ”State Estimator” page.

If the corresponding check box is disabled, the static var system behaves as in the con-ventional load flow calculation.

Transformers

In the 2-winding transformer elements (ElmTr2), the tap position can be specified as a state to be estimated by the State Estimator (see Figure 37.9). Tap positions will be esti-mated in a continuous way (without paying attention to the given tap limits).

For 3-winding transformers, any two of the three possible tap positions (HV-, MV-, and LV-side) can be selected for estimation (see Figure 37.10).

The corresponding check boxes are found on the ”State Estimator” page of the transform-ers. If the check box is disabled the State Estimator will treat the tap position of the trans-formers as in the conventional load flow calculation.

Fig. 37.9: Editing element data for 2-winding transformers

Fig. 37.10: Editing element data for 3-winding transformers

37 - 13


37.4 Running SE

The following steps should be performed to execute the State Estimator:

• Start from a case where the conventional power flow converges successfully.

• Make sure that in the toolbar selection, the icon is chosen.

• Execute the SE by clicking the icon .

• Select the desired options for the State Estimator run (see below).

• Select EXECUTE.

37.4.1 Basic Setup Options

Recall that the State Estimator in PowerFactory consists of three different parts (Plau-sibility Check, Observability Analysis, State Estimation (non-linear optimization)) and an additional precedent Preprocessing step (see Figure 37.1). This variation is reflected in the Basic Options dialogue (see Figure 37.11).

Fig. 37.11: Editing the basic options page of the ComSe

37 - 14


Preprocessing

The algorithm distinguishes between breaker- and tap position-measurements on the one hand, and P-,Q-,I-, and V-measurements on the other hand. Breaker- and tap position-measurements are handled in the preprocessing step, whereas the latter types are pro-cessed in the subsequent parts or the state estimator.

Adapt breaker measurementsIf this check box is marked, all measured breakers statuses will be set to the corresponding measured signal values.

Adapt tap position measurementsIf this check box is marked, all measured tap positions will be set to the corresponding measured values.

Plausibility Check

The algorithm offers various kinds of plausibility checks to validate measurements. Each measurement undergoes the checks selected by the user. If a measurement fails any of the required tests, it will be marked as erroneous and will be neglected in all subsequent steps. A complete error report can be obtained via the error status page of each measure-ments (see Section 37.5).

The following checks can be enabled by marking the corresponding check boxes.

Consistent active power flow direction at each branchChecks for each passive branch, whether all connected P-measurements comply with a consistent power flow direction. More precisely, if some flow out of a passive element is measured while, at the same time, no flow into the element is measured, then all P-measurements connected to this element fail this test. For this check, a P-measurement is said to measure a ”non-zero” flow if the measurement value is beyond a value of , where and rating are the accuracy and the rating, respectively, of the measurement.

Branch losses exceed nominal valuesChecks for each passive branch, whether the measured active power loss exceeds the nominal loss of the branch by a factor of 1 + . This check only applies to passive branches which have P-measurements Pmea1 , . . . ,Pmear in each of its r connection devices. The threshold , by which the nominal loss shall not be exceeded, is given by:

, where i and ratingi are the accuracy and the

rating, respectively, of measurement Pmeai.

Negative losses on passive branchesChecks for each passive branch, whether the measured active power loss is negative, i.e., if a passive branch is measured to generate active power. This check only applies to passive branches which have P-measurements Pmea1 , . .. , Pmear in each of its r connection devices.

rating

i ratingii 1=

r

=

37 - 15


The measured power loss of the branch is said to be negative if it is

below the threshold ( ).

Large branch flows on open ended branchesChecks for each connection of the element, whether the connection is an open end (i.e., switch is open, or it is connected to only open detailed switches). If the connection is open and there exists a (P-, Q-, or I-) measurement which measures a ”non-zero” flow, then the corresponding measurement fails the test. Again, a measurement is said to measure a ”non-zero” flow if the measurement value is beyond a value of ·rating.

Branch loadings exceed nominal valuesChecks for each connection of the element, if the measured complex power (which is computed by the corresponding P- and/or Q-measurements) exceeds the rated complex power value by a factor of 1 + s. Here, s is the accuracy of the P- and/or Q-measurement(s).

Node sum checks for active and reactive powerThis check applies to P- and/or Q-measurements. Checks, for each node of the network, if the node sum of the measured values in the adjacent branches is zero. If this is not the case, i.e., if the P- and/or Q-sum exceeds a certain threshold value, all adjacent P- and/or Q-measurements fail the test. Again, ”not being zero” means that the sum of the measured values of the adjacent P-measurements Pmea1 , ... ,

Pmear has magnitude below the threshold (similarly

for Q-measurements).

Observability Analysis

The Observability Analysis is an optional component of the State Estimator. If activated, it checks whether the specified network is observable, i.e., whether the remaining valid P-, Q-, V-, and I-measurements (which successfully passed the plausibility checks) suffice to estimate the selected P-, Q-, Scaling Factor-, and Tap position-states. In addition, the Observability Analysis detects redundant measurements. Redundancy, in general, yields more accurate results for the following state estimation.

Moreover, if the Observability Analysis detects non-observable states, upon user selection, it tries to fix this unobservability by introducing further pseudo-measurements.

Check for observability regionsIf the corresponding check box is marked by the user, the execution of the State Estimator will run the Observability Analysis (prior to the state Estimation optimization).

Treatment of unobservable areasIn case of unobservable states, the user has different options to cope with the situation:Stop if unobservable regions exist. The algorithm terminates with the detection of unobservable states. The Observability Analysis groups all non-observable states into different ”equivalence classes”. Each

i ratingii 1=

r

–

i ratingii 1=

r

37 - 16


equivalence class consists of states that carry the same observability information through the given measurements. In other words, the given measurements can only distinguish between different equivalence classes, but not between various states of a single equivalence class. The results can be viewed by the user (see Section 37.5: Results).Use P-, Q-values as specified by model. If this option is selected, the algorithm internally drops the ”to be estimated” flag of each non-observable state and uses the element specifications of the load flow settings instead. For example, if a P-state of a load is unobservable, the algorithm will use the P-value as entered on the load flow page. Hence, the network is made observable by reducing the number of control variables.Use predefined pseudo-measurements. Using this option, the algorithm ”repairs” the unobservability of the network by increasing the degrees of freedom. For that purpose, at the location of each non-observable state, the algorithm tries to activate a pseudo-measurement of the same kind. Hence, if a P- (Q-)state is non-observable in some element, the algorithm searches for a P-(Q-)pseudo-measurement in the cubicle of the element carrying the non-observable state. In case of a non-observable scaling-factor both, a P- and a Q-pseudo-measurement are required. The introduced pseudo-measurements remain active as long as needed to circumvent unobservable areas.Use internally created pseudo-measurements. This option is similar to the previous one, except the algorithm automatically creates and activates a sufficient number of internal pseudo-measurements to guarantee observability. More precisely, internal pseudo-measurements are created at the locations of all elements that have non-observable P-(Q-, scaling factor-)state. For each such element, the pseudo-measurement value for P (Q, P and Q) is taken from the element’s load flow specification. All internally created pseudo-measurements use a common setting for their rating and accuracy, which can be specified on the advanced setup options page for the observability check.Use predefined and internally created meas. This mode can be considered as a mixture of the latter two options. Here, in case of a non-observable state, the algorithm tries to activate a predefined pseudo-measurement of the same kind. If no corresponding pseudo-measurement has been defined, then the algorithm automatically creates an internal pseudo-measurement.

State Estimation (Non-Linear Optimization)

The non-linear optimization is the central component of the State Estimator. The under-lying numerical algorithm to minimize the measurements’ overall error is the iterative La-grange-Newton method.

Run state estimation algorithmCheck this box to enable the non-linear optimization. Note that after convergence of the method,—upon user settings on the advanced state estimation option page—PowerFactory performs a bad data check which eliminates the worst P-,Q-,V-, and I-measurements among all bad data. Observability Analysis and State Estimation are run in a loop

37 - 17


until no further bad measurements exist (recall the algorithm variation as shown in Figure 37.1).

37.4.2 Advanced Setup Options for the Plausibility Check

Each Plausibility Check allows for an individual strictness setting. Note that all checks rely on the same principle: namely, the given measurement values are checked against some threshold. Recall, for example, that the ”node sum check for P” tests whether the active

power sum at a node is below a threshold of . The user has the pos-sibility to influence the strictness of this threshold. Therefore, the settings provide to enter so-called ”exceeding factors” fac > 0 such that the new threshold is fac · instead of . E.g., in the case of the node sum check for P, the user may define the corresponding factor fac_ndSumP.

The higher the exceeding factor, the less strict the plausibility test will be. Similar exceed-ing factors can be specified for any of the given tests.

37.4.3 Advanced Setup Options for the Observability Check

Rastering of sensitivity matrix

Internally, the Observability Check is based on a thorough sensitivity analysis of the net-work. For that purpose, the algorithm computes a sensitivity matrix that takes into ac-count all measurements, on the one hand, and all estimated states on the other hand. This sensitivity matrix is discretized by rastering the continuous values.

The user can specify the precision of this process by defining the number of intervals into which the values of the sensitivity matrix shall be rastered (SensMatNoOfInt), the threshold below which a continuous value is considered to be a 0 (SensMatThresh) in the discrete case, and the mode of rastering (iopt_raster). It is highly recommended to use the predefined values here.

Settings for internally created pseudo-measurements

If, on the basic option page, the mode for the treatment of unobservable regions is set to ”use only internally created pseudo-measurements” or to ”use predefined and internally created pseudo-measurements”, the user may specify a default power rating (SnomP-seudo) and a default accuracy class (accuracyPseudo). These default values are used for all automatically created internal pseudo-measurements.

37.4.4 Advanced Setup Options for Bad Data Detection

Recall that the state estimator loops Observability Analysis and State Estimation as long as no further bad measurement is found (see Figure 37.1). The following settings allow the user to control the number of iterations performed by the loop.

i ratingii 1=

r

=

37 - 18


Maximum number of measurements to eliminate

The variable iBadMeasLimit specifies an upper limit on the number of bad measure-ments that will be eliminated in the course of the State Estimation.

Tolerance factors for bad measurement elimination

A measurement is declared to be bad, if the deviation of measured against calculated val-ue exceeds the measurement’s accuracy, i.e., if

Eqn 37.1:

where calVal and meaVal are the calculated value and the measured value, respective-ly. The user may modify this definition by adjusting tolerance factors for bad measure-ments. More precisely, a measurement is declared to be bad, if the left-hand side in equation (37.1) exceeds . Here facErr > 0 is a factor which can be specified by the user for each group of measurements individually. Use the factors facErrP, facErrQ, facErrV, facErrIMagn, facErrIAct, and facErrIReact for P-, Q-, V-measurements, and the three types of the I-measurements (magnitude mea-sure, active current measure, reactive current measure).

37.4.5 Advanced Setup Options for Iteration Control

Initialization

The non-linear optimization requires an initialization step to generate an initial starting configuration.

Initialization of non-linear optimization

The user may specify whether the initialization shall be performed by a load flow calcula-tion or by some flat start. If it is known in advance that the final solution of the optimiza-tion part is close to a valid load flow solution, initializing by a load flow calculation pays off in a faster convergence.

Load Flow

Specifies the settings of the load flow command which is taken for initialization in case

no flat start is used.

Stopping criteria for the non-linear optimization

The non-linear optimization is implemented using an iterative Newton-Lagrange method. Recall that the goal of the optimization is to minimize the objective function f (i.e., the square sum of the weighted measurements’ deviations) under the constraint that all load

calcVal meaVal–rating

--------------------------------------------- accuracy100

---------------------

facErr accuracy 100

37 - 19


flow equations are fulfilled. Mathematically speaking, the aim is to find

under the constraint that

where is the set of load flow equations that need to be fulfilled. By the Lagrange-New-ton method, we thus try to minimize the resulting Lagrange function

with the Lagrange multipliers .

The following parameters can be used to adapt the stopping criteria for this iterative pro-cess. The algorithm stops successfully if the following three issues are fulfilled:

1. The maximum number of iterations has not yet been reached.

2. All load flow constraint equations are fulfilled to a predefined degree of exactness, which means:(a) all nodal equations are fulfilled.(b) all model equations are fulfilled.

3. The Lagrange function itself converges. This can be achieved if(a) either the objective function itself converges to a stationary point, or(b) the gradient of the objective function converges to zero.

The following parameters serve to adjust these stopping criteria. The user unfamiliar with the underlying optimization algorithm is urged to use the default settings here.

Iteration Control of non-linear optimization

The user is asked to enter the maximum number of iterations.

Convergence of Load Flow Constraint Equations

The user should enter a maximal error for nodal equations (where the deviation is mea-sured in kVA), and, in addition, a maximally tolerable error for the model equations (in %).

Convergence of Objective Function

The user is asked choose among the following two convergence criteria for the Lagrangian

min f x

g x 0=

g

L x f x T

g x +=

g x 0=

L x

37 - 20


function: Either the function itself is required to converge to a stationary point, or the gra-dient of the Lagrangian is expected to converge.

In the first case, the user is asked to enter an absolute maximum change in value of the objective function. If the change in value between two consecutive iterations falls below this value, the Lagrangian is assumed to be converged.

In the latter case, the user is asked to enter an absolute maximum value for the gradient of the Lagrangian. If the gradient falls below this value, the Lagrangian is assumed to be converged.

It is strongly recommended—due to mathematical preciseness—to use the criterion on the gradient. The other option might only be of advantage if the underlying Jacobian ma-trix behaves numerically instable which then typically results in a ”toggling” of the con-vergence process in the last iterations.

Output

Two different levels of output during the iterative process can be selected.

37.5 Results

The presentation of the State Estimator results is integrated into the user interface. The solution of the non-linear optimization in the State Estimator is available via the complete set of variables of the conventional Load Flow calculations. It can be seen in the single line diagram of the grid or through the browser.

37.5.1 Output Window Report

The PowerFactory State Estimator reports the main steps of the algorithm in the output window (see Figure 37.12).

For the Plausibility Checks, this implies the information on how many models failed the corresponding checks. For the Observability Analysis, the report contains the information on how many states were determined to be observable, and—in addition—how many measurements were considered to be relevant for observing these states.

37 - 21


Fig. 37.12: Report in the output window

Non-linear optimization reports, in each iteration step, the following figures:

• The current error of the constraint nodal equations (in VA) (Error Nodes).

• The current error of the constraint model equations (Error ModelEqu).

• The current value of the gradient of the Lagrangian function (Gradient LagrFunc).

• The current value of the Lagrangian function (LagrFunc).

• The current value of the objective function f to be minimized (ObjFunc).

37.5.2 External Measurements

Deviations

Each branch flow measurement (StaExtpmea, StaExtqmea) and each voltage mea-surement (StaExtvmea) offers parameters to view its individual deviation between mea-sured value and computed value by the State Estimation. The corresponding variables are:

• e:Xmea: measured value as entered in StaExt*mea

• e:cMeaVal: measured value (including multiplier)

• e:Xcal: calculated value

• e:Xdif: deviation in % (based on given rating as reference value)

• e:Xdif_mea: deviation in % (based on the measured value as reference value)

• e:Xdif_abs: absolute deviation in the measurement’s unit

Here X is a placeholder for P, Q, or U in the case of a P-, Q-, or V-measurement.

Recall that a StaExtimea plays a special role, since a current measurement may serve as up to three measurements (for magnitude, for active current, and/or for reactive cur-rent). Hence, a current measurement has the above listed variables (with X being re-placed by I) for each of the three measurement types. In order to distinguish between the three types, for a StaExtimea, the variables carry the suffixes Magn (for magnitude

37 - 22


measurement), Act (for active current measurement), and React (for reactive current measurement).

Fig. 37.13: For description page for external measurements (StaExtvmea,

StaExtqmea, StaExtvmea).

Error Status

All measurements (StaExt*meas) which possibly participate in the Plausibility Checks, the Observability Analysis, or the State Estimation provide a detailed error description page (see figures 37.13 and 37.14) with the following information:

• General Errors:

- Is unneeded pseudo-measurement (e:errUnneededPseudo)

- Its input status disallows calculation, i.e., input status does not allow ”Read” or is already marked as ”Wrong Measurement” (e:errStatus)

- Measurement is out of service (e:errOutOfService)

• Plausibility Check Errors:

- Fails test: Consistent active power flow direction at each side of branch (e:errConsDir)

- Fails test: Large branch losses (e:errExcNomLoss)

- Fails test: Negative losses on passive branches (e:errNegLoss)

- Fails test: Large branch flows on open ended branches (e:errFlwIfOpn)

- Fails test: Branch loadings exceed nominal values (e:errExcNomLoading)

- Fails test: Node sum check for P (e:errNdSumP)

- Fails test: Node sum check for Q (e:errNdSumQ)

37 - 23


• Observability Analysis Errors:

- Measurement is considered to be redundant for observability of the network, i.e., observability is already guaranteed even without this measurement. Nevertheless redundant measurements are used in the non-linear optimization since, in general, they help to improve the result (e:errRedundant).

- For redundant measurements, also the redundancy level is indicated on this page (e:RedundanceLevel). The higher the redundancy level, the more measurements with a similar information content for the observability analysis exist.

• State Estimation Errors:

- Measurement is detected to be bad, has been removed and was not considered in last non-linear optimization loop (e:errBadData)

This detailed error description is encoded in the single parameter e:error that can be found on the top of the error status page. Again, we have the convention that, for a StaExtimea, the variables e:errRedundant, e:RedundanceLevel and e:errBad-Data carry the suffixes Magn (for magnitude measurement), Act (for active current mea-surement), and React (for reactive current measurement).

37.5.3 Estimated States

Which states participated as control variables?

Recall that —depending on the selected ”treatment of unobservable regions”— not all states that were selected for estimation (see Section 37.3.3: Editing the Element Data) will necessarily be estimated by the algorithm: In case of non-observability, it may happen that some control variables need to be reset.

To access the information which states were actually used as control variables, Power-Factory provides a flag for each possible state. These flags are called c:i{P,Q,Scale,Tap}Setp for P-, Q-, Scaling factor-, and Tap-states, respectively. They can be accessed through the Flexible Data Page as Load Flow calculation parameters for the following elements: ElmLod, ElmAsm, ElmSym, ElmSvs, ElmTr2, and ElmTr3.

Observability of individual states

The Observability Analysis identifies, for each state, whether it is observable or not. More-over, if the network is unobservable, it subdivides all unobservable states into ”equiva-lence-classes”. Each equivalence-class has the property that it is observable as a whole group, even though its members (i.e., the single states) cannot be observed. The equiv-alence classes are enumerated in ascending order 1, 2, 3, . ...

37 - 24


Fig. 37.14: Detailed error description page for external current measurements

(StaExtimea).

For this purpose, the Observability Analysis uses the flags c:i{P,Q,Scale,Tap}obsFlg for P-, Q-, Scaling factor-, and Tap-states, respectively. These parameters exist for all elements which carry possible states (ElmLod, ElmAsm, ElmSym, ElmSvs, ElmTr2, ElmTr3). The semantics is as follows:

• a value of -2 means that the correspond state is not estimated at all.

• a value of -1 means that the correspond state is unsupplied.

• a value of 0 means that the corresponding state is observable.

• a value of i > 0 means that the correspond state belongs to equivalence-class i.

37.5.4 Colour Representation

In addition, PowerFactory provides a special coloring mode ”Observability” for the sin-gle line diagram which takes into account the individual measurement error statuses and the states to be estimated (see Figure 37.15). The coloring can be accessed by clicking

the icon on the task bar.

The color representation is valid as soon as an Observability Analysis has been performed

37 - 25


successfully.

The color representation paints the location of measurements (of a specific type) and the location of states (of a specific type) simultaneously.

Fig. 37.15: Coloring of measurement error statuses and estimated states.

Estimated States

The user selects to color states of a specific type (P-, Q-, Scaling factor-, or Tap position-states). Distinct colors for observable, unobservable, non-estimated states, and states with unclear observability status can be chosen.

External Measurement Locations

The user selects to color measurements of a specific type (P-, Q-, V-, or I-measurements). Distinct colors for valid, redundant and invalid measurements can be chosen. A measure-ment is said to be valid if its error code (e:error) equals 0.

Besides, measurements with a specific error code can be highlightened separately using an extra color. To select such a specific error code press the Error Code button and choose from the detailed error description list any ”AND”-combination of possible errors.

37 - 26


37 - 27


37 - 28

DIgSILENT PowerFactory

Appendix

DIgSILENT PowerFactory Glossary

Appendix AGlossary

Appliance

A specific physical, installed, power system component: a specific generator, transformer, busbar, etc. Example: a piece of NKBA 0.6/1kV 4 x 35sm cable, 12.4 meters long.

Base Case

A Base Case is considered to be the basic power system design, from which one or more alternative designs may be created and analyzed. When working with system stages, the Base Case is considered to be the highest level in a tree of hierarchical system stage de-signs.

Block Definition

A block definition is a mathematical model which may be used in other block definitions or in a composite model. Examples are all default controllers (i.e. VCO's, PSS's, MDM's), and all additional user-defined DSL models. A block definition is called "primitive'' when it is directly written in DSL, or "complex'' when it is build from other block definitions, by drawing a block diagram.

Block Diagram

A block diagram is a graphical representation of a DSL model, i.e. a voltage controller, a motor driven machine model or a water turbine model. Block diagrams combine DSL prim-itive elements and block definitions created by drawing other block diagram.

The block models thus created may (again) be used in other block diagrams or to create a Composite Frame.

See also: DSL primitive, Composite Frame

Branch Elements

A one port element connected to a node, such as a load or a machine. See also nodes, edge elements.

A - 1


Busbars

Busbars are particular representations of nodes. Busbars are housed in a Station folder and several busbars may be part of a station.

Class

A class is a template for an element, type or other kind of objects like controller block diagrams, object filters, calculation settings, etc. Examples:

• The 'TypLne' class is the type model for all lines and cables

• The 'ElmLne' class is an element model for a specific line or cable

• The 'ComLdf' class is a load-flow command

• The 'EvtSwitch' class is an event for a switch to open or close during simulation

Composite Frame

A composite frame is a special block diagram which defines a new stand-alone model, mostly without in- or outputs. A composite frame is principally a circuit in which one or more slots are connected to each other.

A composite frame is used to create composite models by filling the slots with appropriate objects. The composite frame thus acts as template for a specific kind of composite mod-els.

See also: Block Diagram, Slot

Composite Model

A composite model is a specific combination of mathematical models.These models may be power system elements such as synchronous generators, or block definitions, such as voltage controllers, primary mover models or power system stabilizers.

Composite models may be used to create new objects, such as protection devices, to 'dress-up' power system elements such as synchronous machines with controllers, prime movers models, etc., or for the identification of model parameters on the basis of mea-surements.

Cubicle

A cubicle is the connection point between a edge or branch element and a node (repre-sented by a busbar or terminal). It may be visualized as a bay in a switch yard or a panel in a switchgear board. Elements such as CT's, protection equipment, breakers and so forth, are housed in the cubicle, as one would expect to find in reality.

DAQ

Abbreviation for "Data Acquisition''.

A - 2


Device

A certain kind of physical power system components: certain synchronous machines, two-winding transformers, busbars, or other kinds of equipment. Example: a NKBA 0.6/1kV 4 x 35sm cable.

DGS

Abbreviation for "DIgSILENT Interface for Geographical Informations Systems''.

DOLE

Abbreviation for "DIgSILENT Object Language for Data Exchange''. DOLE was used in pre-vious PowerFactory versions, but replaced by DGS meanwhile. Now, use DGS instead, please.

The DOLE import uses a header line with the parameter name. This header must have the following structure:

• The first header must be the class name of the listed objects.

• The following headers must state a correct parameter name.

DPL

Abbreviation for "DIgSILENT Programming Language''. For further information, please re-fer to Chapter E (The DIgSILENT Programming Language - DPL).

Drag&Drop

"Drag&Drop'' is a method for moving an object by left clicking it and subsequently moving the mouse while holding the mouse button down ("dragging''). Releasing the mouse but-ton when the new location is reached is called "dropping''. This will move the object to the new location.

DSL

Abbreviation for "DIgSILENT Simulation Language''. For further information, please refer to Chapter 27.9 (The DIgSILENT Simulation Language (DSL)).

DSL primitive

A DSL primitive is the same as a primitive block definition. A DSL primitive is written di-rectly in DSL without the use of a block diagram.

Examples are PID controllers, time lags, simple signal filters, integrators, limiters, etc. DSL primitives are normally used to build more complex block definitions.

See also: Block Definition, Block Diagram

Edge Elements

The elements between two nodes. May also be termed 'two port element.' Source, topo-

A - 3


logical studies; picture a 3 dimensional box, the corners of the box would be called the nodes, and the edges between corners are hence 'edges.' See also nodes, branch ele-ments.

Element

A mathematical model for specific appliances. Most element models only hold the appli-ance-specific data while the more general type-specific data comes from a type-reference. Example: a model of a piece of NKBA 0.6/1kV 4 x 35sm cable, 12.4 meters long, named "FC 1023.ElmLne".

Graphics Board Window

The graphics board window is a multi document window which contains one or more graphical pages. These pages may be single line graphics, virtual instrument pages, block diagrams etc.

The graphics board shows page tabs when more than one page is present. These tabs may be used to change the visible page or to change the page order by drag&drop on the page tab.

See also: Virtual Instrument, Block Diagram, Page Tab, Drag&Drop

Grid

A Grid is a collection of power system elements which are all stored in one so-called "Grid Folder'' in the database. Normally, a grid forms a logical part of a power system design, like a the MV distribution system in a province, or the HV transport system in a state.

Object

An object is a specific item stored in the database. Examples are specific type or element models which have been edited to model specific devices or appliances. Examples: the element "FC 1023.ElmLne", the type "NKBA_4x35.TypLne", the load-flow command "3Phase.ComLdf"

Node

The mathematical or generic description for what are commonly known as busbars in the electrical world. In PowerFactory nodes may be represented by "Busbars" or "Termi-nals" of various kinds. These are treated in the same manner in mathematical terms but treated slightly differently in the database. As far as possible the user should use terminals as Busbars can be somewhat inflexible. See also Busbars, Edge Elements, Branch Ele-ments.

Operation Scenario

An Operation Scenario defines a certain operation point of the system under analysis, such as different generation dispatch, low or high load, etc.Operation Scenarios are stored inside the Operation Scenarios folder.

A - 4


Page Tab

Page tabs are small indexes at the edge (mostly on the top or bottom) of a multi-page window. The tabs show the titles of the pages. Left-clicking the page tab opens the cor-responding page. Page tabs are used in object dialogues, which often have different pag-es for different calculation functions, and in the Graphics Board Window, when more than one graphical page is present.

Project

All power system definitions and calculations are stored and activated in a project. The project folder therefore is a basic folder in the user's database tree. All grids that make out the power system design, with all design variants, study cases, commands, results, etc. are stored together in a single project folder.

Result Object

A result object keeps one or more lists of parameters which are to be monitored during a calculation. Results objects are used for building calculation result reports and for defining a virtual instrument.

See also: Virtual Instrument

Slot

A slot is a place-holder for a block definition in a composite frame. A composite model is created from a composite frame by filling one or more slots with an appropriate object.

See also: Block Definition, Composite Frame.

Study Case

A study case is a folder which stores a list of references or shortcuts to grid or system stage folders. These folders are (de)activated when the calculation case folder is (de)ac-tivated.

Elements in the grid folders that are referenced by the study case form the 'calculation target' for all calculation functions. Elements in all other, non-active, grid folders are not considered for calculation.

Besides the list of active folders, the calculation case also stores all calculations com-mands, results, events, and other objects which are, or have been, used to analyze the active power system.

See also: Grid, System Stage

System Stage

A system stage is an alternative design or variation for a particular grid. A system stage is stored in a system stage folder, which keeps track of all differences from the design in the higher hierarchical level. The highest level is formed by the base grid folder. It is pos-sible to have system stages of system stages.

See also: Grid, Base Case

A - 5


Type

A mathematical model for devices: general models for two-winding transformers, two-winding transformers, busbars, etc. A type model only contains the non-specific data valid for whole groups of power system elements. Example: a NKBA 0.6/1kV 4 x 35sm cable type, named "NKBA_4x35.TypLne"

See also: System Stage, Grid

Variation

A Variation defines an expansion plan composed of one or more expansion stages, and which are chronologically activated. Variations, like all other network data, are stored in-side the Network Data folder.

Virtual Instrument

A virtual instrument is a graphical representation of calculation results. It may be a line or bar graph, a gauge, a vector diagram, etc. A virtual instrument gets its values from a result object.

See also: Result Object.

Virtual Instrument Panel

Virtual instrument panels are one of the possible types of pages in a graphics board win-dow. Virtual instrument panels are used to create and show virtual instruments. Each vir-tual instrument panel may contain one or more virtual instruments.

See also: Graphics Board Window, Virtual Instrument

A - 6


A - 7


A - 8

DIgSILENT PowerFactory Hotkeys Reference

Appendix BHotkeys Reference

B.1 Graphic Windows Hotkeys

Combination Where/When Description

Ctrl + - Single Line Graphic, Block Diagrams, Vi's

Zoom out

Ctrl + + Single Line Graphic, Block Diagrams, Vi's

Zoom in

Ctrl + Scrollen Single Line Graphic, Block Diagrams, Vi's

Zoom in/out

Ctrl + Double-click Busbar system Open detailed graphic of substation

Press Mouse Scroll Wheel + Moving

Single Line Graphic, Block Diagrams, Vi's

Panning, Moving the visible part of the graphic

Alt + Rubberband Only textboxes inside the rubber band are marked, no parent objects

Alt + Left-click Textbox Textbox und Parent-Object are marked

Alt + Left-click (multiple times)

Element All the connected elements will be marked

Ctrl + A All elements are marked

Ctrl + Alt + Shift + P Element Dialogue Save a screenshot of the complete monitor as bitmap under C:\Digsi\snapshots

Ctrl + Alt + Moving Marked Object Single Objects from a Busbar system can be moved

Ctrl + Alt + Moving Marked Busbar Single objects from a Busbar System can be increased or reduced (size)

Ctrl + Alt + Moving Block The stub length of blocks in block diagrams remains when shifting

Ctrl + Alt + Moving Marked Terminal Line-Routes will move to the terminal, instead of terminal to the line

Ctrl + Alt + Moving Marked Node Symbol of the connected branch element will not be centered

B - 1


Ctrl + C Marked Element

Ctrl + L Single Line Graphic, Block Diagrams

Will open the Define Layer dialogue to create a new layer

Ctrl +Left-click Element Multiselect elements, all clicked elements are marked

Ctrl + Left-click Inserting Loads/Generators

Rotate element 90°

Ctrl + Left-click Inserting Busbars/Terminals

Rotate element 180°

Ctrl + M Element Dialogue Mark Element in the graphic

Ctrl + Q Single Line Graphic, Block Diagrams

Open Graphic Layer dialogue

Ctrl + X Marked Element Cut

Esc Connecting Mode Interrupt the mode

Esc Inserting Symbol Interrupt and change to graphic cursor

Esc Animation Mode Interrupt mode

S + Left-click Element Mark only the symbol of the element

S +Moving Marked Element Move only the symbol of the element

Shift + Moving Marked Element Element can only be moved in the direction of axes

Shift + Moving Marked Textbox After rotation, textbox can be aligned in the direction of axes

Tab Inserting Symbol Change connection side of symbol

Left-click Inserting Symbol Place symbol, press mouse button and move cursor in the direction of rotation to rotate the symbol in this direction


B - 2


B.2 Data Manager Hotkeys


Alt + F4 Close data manager

Alt + Return Right; Link Open the edit dialogue of the element

Backspace Jump one directory up

Pag (arrow: up) Right Scroll a page up

Pag (arrow: down) Right Scroll a page down

Ctrl + (arrow: up) Edit dialogue open Call the edit dialogue of the next object from the list and closes the current dialogue

Ctrl + (arrow: down) Edit dialogue open Call the edit dialogue of the previous object from the list and closes the current dialogue

Ctrl + A Right Mark all

Ctrl + Alt + P Save screenshot of the data manager as bitmap under C:\Digsi\snapshots

Ctrl + Alt + Shift + P Save screenshot of the complete monitor as bitmap under C:\Digsi\snapshots

Ctrl + B Detail-Modus Change to next tab

Ctrl + C Marked object, marked symbol

Copy marked object

Ctrl + C Marked cell Copy the value of the marked cell

Ctrl + D Change between normal and detail mode

Ctrl + F Call the Filter dialogue

Ctrl + G Right Go to line

Ctrl + I Right Call the dialogue Select Element, in order to insert a new object. The object class depends on the current position

Ctrl + Left-click Select the object

Ctrl + M Move the object

Ctrl + O Change between the display of out of service and no relevant objects for calculation

Ctrl + Q Right; station, Busbar or element with a connection

Open the station graphic

Ctrl + Q Right, element with more than one connection

Call the dialogue Select Station, which lists all the connected stations

Ctrl + R Project Activate the project

Ctrl + R Study case Activate study case

B - 3


Ctrl + R Grid Add the grid to the study case

Ctrl + R Variant Insert the variant to the current study case, if the corresponding grid is not in the study case

Ctrl + Tab Detail-Modus Change to next tab

Ctrl + V Insert the content of the clipboard

Ctrl + W Change the focus between right and left side

Ctrl + X Marked object, marked symbol

Cut object

Ctrl + X Marked cell Cut cell content

End Right Jump to the last column of the current row

Del Right, symbol Delete marked object

Del Right, cell Delete the content of the cell

Esc Right; after change in the line Undo the change

F2 Right; cell Change to edit mode

F3 Close all open dialogues and return the selected object from the top dialogue

F4 Activate/Deactivate Drag&Drop-Mode

F5 Update

F8 Right, Graphic Open the graphic

Pos1 Right Jump to the first column of the current row

Return Right Call the edit dialogue of the marked object

Return links Display or close the content of the marked object

Return Right; after change in the line Confirm changes

Return Right; link Call the edit dialogue of the original object

Shift + Left-click Select all the objects between the last marked object and the clicked row


B - 4


B.3 Dialogue Hotkeys


Ctrl + A Input field Mark the content

Ctrl + Alt + P Save screenshot of the dialogue as bitmap under C:\Digsi\snapshots

Ctrl + Alt + Shift + P Save screenshot of the complete monitor as bitmap under C:\Digsi\snapshots

F1 Online help

B - 5


B.4 Output Window Hotkeys


Pag (arrow: up) Page up

Pag (arrow: down) Page down

Ctrl + A Mark the content of the output window

Ctrl + Pag (arrow: up) Like Ctrl + Pos1

Ctrl + Pag (arrow: down)

Like Ctrl + End

Ctrl + C Copy the market report to the clipboard

Ctrl + E Open a new empty editor

Ctrl + End Set the cursor in the last position of the last row

Ctrl + F Open the Search and Replace dialogue

Ctrl + F3 Cursor in a Word Jump to next same word; New searched string becomes the word on which the cursor is currently positioned

Ctrl + O Call the Open dialogue

Ctrl + P Call the Print dialogue

Ctrl + Arrow (up) Page up

Ctrl + Arrow (down) Page down

Ctrl + Pos1 Set the cursor in the first position of first row

Ctrl + Shift + End Set the cursor in the last position and marks the report in between

Ctrl + Shift + home Set the cursor in the first position and marks the report in between

Ctrl + Shift + F3 Cursor in a Word Jump to previous same word; New searched string becomes the word on which the cursor is currently positioned

End Set the cursor in the last position of the row

F3 Cursor in a Word Jump to next same word of the current searched string

Arrow (up) Set the cursor one line above

Arrow (right) Set the cursor one position after

Arrow (down) Set the cursor one line below

Arrow (left) Set the cursor one position before

home Set the cursor to the first position of the row

B - 6


Shift + Pag (arrow: up)

Set the cursor one page up and select the in between content

Shift + Pag (arrow: down)

Set the cursor one page down and select the in between content

Shift + F3 Cursor in a Word Jump to previous same word of the current searched string


B - 7


B.5 Editor Hotkeys


Ctrl + O Open file

Ctrl + S Save

Ctrl + P Print

Ctrl + Z Undo

Ctrl + C Copy

Ctrl + V Paste

Ctrl + X Cut

Ctrl + A Select all

Ctrl + R Comment selected lines

Ctrl + T Uncomment selected lines

Ctrl + F2 Set bookmark / Remove bookmark

Del Delete

F2 Go to next bookmark

Shift + F2 Go to previous bookmark

F3 Cursor in a word Jump to next same word of the current searched string

Shift + F3 Cursor in a Word Jump to previous same word of the current searched string

Ctrl + F3 Cursor in a Word Jump to next same word; New searched string becomes the word on which the cursor is currently positioned

Ctrl + F Open „Find“ dialogue

Ctrl + G Open „Go to“ dialogue

Ctrl + H Open „Find and Replace“ dialogue

Ctrl + Y Remove current line

Ctrl + Shift + T Replace blanks by tabs in selected text

Ctrl + Alt + T Show / Hide tabs abd blanks

Strg + Shift + Space Replace tabs by blanks in selected text

Alt + Return Open user settings dialog on "Editor" page

Backspace Delete character in front of cursor

Insert Switch between insert and replace mode

B - 8


Arrow (right) One char right

Shift + Arrow (right) Extend selection to next char right

Ctrl + Arrow (right) Set cursor to beginning of next word

Ctrl + Shift + Arrow (right)

Extend selection to beginning of next word

Arrow (left) One char left

Shift + Arrow (left) Extend selection to next char left

Ctrl + Arrow (left) Set cursor to beginning of previous word

Ctrl + Shift + Arrow (left)

Extend selection to beginning of previous word

Arrow (down) One line down

Shift + Arrow (down) Extend selection one line down

Ctrl + Arrow (down) Scroll down

Ctrl + Shift + Arrow (down)

Change selected text to lower case

Arrow (up) One line up

Shift + Arrow (up) Extend selection one line up

Ctrl + Arrow (up) Scroll up

Ctrl + Shift + Arrow (up)

Change selected text to upper case

home Set cursor to first pos. in line

Ctrl + home Set cursor to beginning of text

Shift + home Extend selection to beginning of line

Ctrl + Shift + home Extend selection to start of text

end Set cursor to last pos. in line

Ctrl + end Set cursor to end of text

Shift + end Extend selection to end of line

Ctrl + Shift + end Extend selection to end of text

Pag (arrow: down) Set cursor one page down

Shift + Pag (arrow: down)

Extend selection to one page down

Pag (arrow: up) Set cursor one page up


B - 9


Shift + Pag (arrow: up)

Extend selection to one page up

F1 Open manual and search for word in which cursor is placed

F9 Set break point / remove break point (but no effect)


B - 10


B - 11


B - 12

DIgSILENT PowerFactory The DIgSILENT Output Language

Appendix CThe DIgSILENT Output Language

When more than just the variable name, value and unit has to be displayed, if the use colors is preferred, or other special formats, the DIgSILENT Output Language can be used.

By selecting the Text Editor input mode, all entries on first page of the Form Editor disap-pear, except for the form name, and the editor on the second page is activated (see Figure C.1).

Fig. C.1: The Form text editor

Almost all textual output that is produced in PowerFactory, is defined by a report form. The use of report forms range from the simple and small result forms that specify the con-tents of the single line result boxes to large and complex forms that are used to print out complete system reports.

In all cases, the text in the editor field of a IntForm object specifies the report that is to be generated. For result boxes, that text is normally created automatically in the IntForm dialogue by selecting "Predefined Variables'', or any other set of variables, and some ex-tra's such as the number of decimals and if an unit or name should be shown. These op-tions will automatically create a report form. That automatic form is normally used as it is, but it may be altered manually. This is shown in Figure C.1, where report format is changed such that the variable name of the loading factor is deleted and replaced by the fixed text 'ld', because the variable name "loading'' is felt too long compared with the names of the other two variables ("P'' and "Q''). The shown format will produce result box-es like

P 12.34 MW Q 4.84 Mvar

C - 1


ld 103.56 %

Defining single line result boxes only asks for a basic understanding of the DIgSILENT output language. For more complex reports, many different variables from all kinds of ob-jects have to be printed as listings or tables. Such a report would require macro handling, container loops, selection of parameters, headers, footers, titles, colors, etc. The DIgSI-LENT output language offers all this, and more.

The basic syntax, which is primary used for defining result boxes is given in the following overview.

Format string, Variable names and text Lines

A standard line consists of three parts (see Figure C.2):

1 A format string, containing placeholders, macros and/or user defined text.

2 An 'end of line' character like '$N', '$E' or '$F'

3 Variable names, separated by commas, which are used to fill in the placeholders.

Fig. C.2: Basic parts of the report format

The format string is normally much longer.

Placeholders

A placeholder for strings like variable names or whole numbers is a single '#'-sign. For real numbers, the placeholder consists of

• a single '#' for the integer part

• a point or comma

• one or more '#'-signs for the fractional part

The number of '#'-signs after the decimal point/comma defines the number of decimals.

The '#'-sign itself can be included in user-defined text by typing '\#'.

Variables, Units and Names

The variable name can be used to display the name of the variable, its value or its unit. The possible formats are ('xxx' = name of variable):

xxx returns the value

%xxx returns the long variable name, as used in the edit dialogues

&xxx returns the short variable name, as used in the database browser

[xxx returns the unit

xxx the object dependent name of the variable (default name)

"%width.precision,xxx''uses special formatting.

C - 2


The special formatting %width.precision is explained by the following examples:

• "%.60,TITLE:sub1z'' outputs TITLE:sub1z 60 column width, left aligned.

• "@:"%1.0,s:nt'' inserts s:nt as an integer at the placeholder's position

• ""%1.3,s:nt'' writes s:nt with 3 digits precision at the placeholder's position

The centering code | may be used in front of the formatting code for centering at the placeholder, for example "|%.60,TITLE:sub1z''.

The insertion code @ is used to switch to insert mode, for example,

|#|$N,@:loc_name

will output

|aElmSym|.

The cformat string may be used to alternatively reserve place for a value or text. A cformat of ’%10.3' will reserve 10 characters for a number with 3 decimals. The first number can be omitted for text: ’%.6' will reserve 6 characters for the text field. The cformat syntax allows for centering text by adding the ’|'-sign to the `%'-sign:

’|%.10' will reserve 10 characters and will center the text.

Free, language dependent text can be defined by use of the format

{E|a text;G|ein Text}. This will produce 'a text' when the user has selected the English language (see the user settings dialogue), and 'ein Text' when the language has been cho-sen to be German.

Special commands for access of Elements

OBJECT(cls)Gets Element of class cls. Used to access a variable name or unit without actually accessing such an object. Used in header lines.

argumentcls (obligatory): The name of the class

example:[OBJECT(ElmTerm):m:Skss

writes the unit of the busbar variable Skss

EDGEGets an arbitrary object with at least one connection, i.e. a Load, a Line, etc. Used to access a variable name or unit without actually accessing such an object.

example:%EDGE:m:U1:bus1

writes description of the variable U1

CUBIC(idx)Returns the cubicle (StaCubic) at bus index idx of branch

argument:idx: index of branch, the currently set bus index is used when idx<0

example:CUBIC(0):e:loc_name

returns name of cubicle at busindex 0

C - 3


TITLEGets the title that is set in the output command (ComSh or ComDocu)

example:TITLE:e:annex

writes annex of title

VARIANTGets the active variant in which the current object is stored

example:VARIANT:e:loc_name

writes the name of the variant

NETGets the grid in which the current object is stored

example:NET:e:loc_name

writes the name of the grid

CMDReturns the last calculation command, i.e. a Short-Circuit (ComShc), Load-flow (ComLdf),...

example:CMD:pabs

writes the short-circuit position on the line after calculation of a short-circuit.

CASEReturns the currently active calculation case

example:CASE:e:loc_name

writes the name of the active calculation case

DEFReturns the default object. The default object depends on the currently processed output.

example:DEF:e:loc_name

writes the name of the default object

STALNEReturns the station if the current object is a busbar. Returns a line if the current object is a terminal between line routes. Otherwise, nothing is returned, and the entry will be ignored.

example:STALNE:e:locname

writes the name of the line or station.

RESReturns the currently active results object (ElmRes) used by simulation, harmonics or other calculation modules

example:RES:e:desc

C - 4


writes the first line of the description of the results object

Color

A line can be set to another color by adding a '_LCOL(c)' command directly after the '$N,' marker. This will color the whole line according to the color number c.

Table C.1: Color Codes

iA single item can be colored by using the '_COLOR(Variable name; color code)'.

Advanced Syntax Elements

The advanced syntax is mainly used for writing forms for larger and more complex re-ports. An example is a short-circuit result form, which lists all the short-circuit parameters for all busbars and for each busbar for all connected elements.

Line Types and Page Breaks

The character '$' ends a format line. A line without this ending will be interpreted as a normal '$N' line type. The following line type are available:

'$N' Normal line

'$H' Header on the top of each page

'$F' Footer on the bottom of each page

'$T' Title line, only appears on top of the first page

'$C' Comment line (not used for output)

'$R' Marker that make that the line will only be used when the specified results are valid

The line type '$H', '$F' and '$T' will be treated as normal ('$N') line types when used inside a loop command. Line type codes may be made language dependent by adding a 'E', for English lines or a 'G' for German lines, i.e. '$HG' specifies a German header line.

A report format must at least contain one normal ($N) line.

The following commands are used for page and line controls. They can only be used di-rectly behind the line type codes '$N', '$F' or '$H'.

a black i gray

b black j light gray

c red k bordeaux

d green l dark red

e blue m dark green

f brown n light green

g cyan o marine

h magenta p dark blue

C - 5


_PAGEBREAKForces a page break after the current line

_AVAILBREAKEnables page breaking after the current line (default)

_NOBREAKDisables page breaking directly after the current line

_LCOL(c) Changes the color of the current line, c is the color code.

_OBJ(ClsNam)The current line will only be used for objects from the class "ClsNam''.

_BUS(inum) The current line will only be used for objects which connect to exactly inum nodes

_FIRST The current line will only be used when the loop index is 0 (first passage)

_NFIRST The current line will only be used when the loop index is not 0 (all but the first passages)

_IF(boolean expression)The current line will only be written when the expression is true. Example: _IF(m:u:bus1>0.95)

_IFNOT(boolean expression)The current line will only be written when the expression is false. Example: \IF(m:u:bus1<0.95)

Example:

| #.## # #.## # #.## |$R,_NOBREAK, ..

Predefined Text Macros

The following macros will produce specific names or other texts.

_DATE(c) present date: c='e' give the English format, c='g' the German one.

_TIME present time

_VERSION version number of the DIgSILENT PowerFactory software.

_BUILD build number of the DIgSILENT PowerFactory software.

_VERBUILD combines _VERSION and _BUILD

_ORDER order title, if a title has been defined previously

_CLASS class name of the object

_LINE current line number in page

_ALLLINE current line number in report

_PAGE current page number

_LOCALBUS name of the local busbar

_CALC(c) name of last performed calculation. c=1 returns a long description.

_SHORT short object name

_FSHORT short name of parent object

C - 6


_CLS class name without the 'Elm', 'Sta', 'Typ', etc. part.

_ANNEX the annex number

_NGB neighborhood depth

_TEXT(E | text;G | Text)language dependent text (E=English, G=German)

Object Iterations, Loops, Filters and Includes

To create a report that creates a table with the voltages for all busbars, command are needed to filter the busbar objects and to create a loop that outputs a line of text for each busbar. A loop or filter command consists of the following parts:

• the keyword "$LOOP'' or "$CLOOP''

• the filter or loop name

• the format text

• the keyword "$END''

Example: $LOOP,_LROUTES() | # |,$N,loc_name $END

This example uses the filter "_LROUTES()'', which filters line route objects (ElmLner-oute). The format text has one line, which prints the object name.

C - 7


C - 8

DIgSILENT PowerFactory Element Symbol Definition

Appendix DElement Symbol Definition

The symbols used in the graphic windows of PowerFactory are defined by the so called 'Symbol' objects (IntSym). DIgSILENT provides a complete set of symbols to represent any of the defined network components; additionally the users have the possibility to de-fine their own symbols and use them in the graphical windows of their projects.

In the proceeding sections the variables used to define symbol objects are presented.

D.1 General Symbol Definition

The general definitions of the symbols are given in the 'General' page of the object's dia-logue.

Symbol DescriptionThe description of a symbol is shown in the list of symbols when "Show Layer..." is used and a symbol has to be selected on the page "Configuration"

Object TypeClass name of the element which shall be represented.

Type of RepresentationBranch or node object

IDThe icon ID of the icons from the graphic toolbar. If this value is set the symbol will be used when a new element is inserted. In case of '0' the symbol will not be used as default.

Width/HeightThe width and height is defines the range of the fang. The marking of an element in the graphic makes this range visible.

VisibleVisibility of the symbol

MirrorDefines if the symbol can be mirror (right mouse button entry)

D - 1


Allow MovingAllows moving in graphic

Show Connection AttributesShows the square (resulting state of composite switches) at the end of connection lines

Insertion ReferenceDefines the insertion point of an element (e.g. rectangular terminal = 4 -> top left).The following matrix describes the relation between the insertion points and the insertion numbers:4 3 25 0 16 7 8

Additional AttributesOnly used for elements whose representation shall be able to alter via specific changes of the element parameters (e.g. shunts, couplers)

Connection PointsDefines the position on the symbol where the connection lines start. The number of connection points is defined by the number of lines unequal (-9999,-9999). The points should be located on the grid, i.e. they should be a multiple of 4.375 (mm)

ContentsContaining objects of type "SetVitxt" defining the layout of the text boxes. The names must be unique. Labels beginning with "Label..." and result boxes beginning with "Res...". The name of symbol must also be part of the name of the SetVitxt.

D.2 Geometrical Description

The geometrical description of the symbol is given in the 'Geometry' page of the dialogue. The geometry can be specified by means of geometrical primitives in the 'Geometrical Components and Attributes' field.

Circle (C,iStyle,rWidth,iFill,iColor,iRsz,nPts,rMx,rMy,rPx,rPy)Defines a Circle by the center (rMx, rMy) and a point on the edge (rPx,rPy). Parameter nPts must be 2.

Arc (A,iStyle,rWidth,iFill,iColor,iRsz,nPts,rMx,rMy,rPx1,rPy1,rPx2,rPy2)Defines an arc by the center (rMx,rMy) and 2 points (rPx1,rPy1) (rPx2,rPy2) on the edge, drawn clockwise. nPts must be set to 3.

Polyline (L, iStyle,rWidth,iFill,iColor,iRsz,iRot,nPts,rPx,rPy)Defines an open polygonal line with nPts points. rPx andrPy are the coordinates of peg points. iRot can be defined as:

D - 2


n -> randomy -> only rotatable to the bottom and the right (used in symbols)

Polygon (G, iStyle,rWidth,iFill,iColor,iRsz,nPts {,rPx,rPy})Defines a closed polygonal line with nPts points. rPx and rPy are coordinates of peg points

Text (T, iColor,iRsz,iFont,iAlign,rHeight,iOri,iRot,sString,rPx,rPy)Defines a text with the following attributes:

iFont font number ( > 0)

iAlign insertion point (0 = left top, 2 = center)

rHeight height ( > 0 )

iOri orientation ( 0 = horizontal , 1 = vertical )

iRot rotate text with object ( 0 = no, 1 = yes, 2 = vert./horiz.,3 = only to the bottom and right, -- used in symbols only --)

sString text (max. 80 characters)

rPx,rPy coordinates of insertion point

iRsz resize_Mode (0=not possible, 1=shift only, 2=keep ratio,3=any (RS_NONE,RS_SHIFTONLY,RS_KEEPXY, RS_FREE)

All geometrical elements have the following attributes in common:

iStyle (Line style)1 = normal line2 = dotted3 = dashed4 = dotted and dashed

rWidth (Line widht in mm ( > 0))

iFill (Fill style) 0 = not filled1 = filled 100%2 = horiz. stripes3 = vertical stripes4 = horizontal and vertical stripes5 = diagonal from left bottom to right top6 = diagonal from right bottom to left top7 = diagonal grid of stripes8 = filled 25%9 = filled 50%10 = filled 75%

iColor (Colour)-1 = colour of object0 = white1 = black2 = bright red

D - 3


3 = bright blue4 = bright green5 = yellow6 = cyan7 = magenta8 = dark grey9 = grey10 = red11 = dark rot12 = dark green13 = green14 = dark blue15 = blue16 = white17 = bright grey

iRsz (Resize mode)0 = not resizable1 = shift only 2 = keep ratio3 = resizable in any direction

In version 13.0 additional parameters were added:

iSBNo. of area (1..32, can only be used if set in source code, e.g. vector groups

iLayNo. of graphic layer

iSN Connection number (0..4)

iIPObject is used for calculation of intersections (=1 only for node objects)

xOff, yOffOffset used when object is inserted (optional)

D.3 Including Graphic Files as Symbols

Graphic files in WMF and bitmap format can be selected as "Symbol File". The definitions of the geometrical primitives are not used if a "Symbol File" is defined.The picture will be adapted to the size of symbol in the single line diagram. After selection of a WMF file in the top entry field for the Symbol File (not rotated) a button "Create all other files" ap-pears which allows to create automatically WMF files in the same folder with a rotation of 90, 180 and 270 degrees. Additionally pictures for open devices with the same angles can be entered in the bottom lines.

D - 4


D - 5


D - 6

DIgSILENT PowerFactory User’s Manual Index

Appendix EIndex

Symbols(n-1) system ......................................... 31-49(n-k) system .......................................... 31-49

AAbout this Guide ....................................... 1-1abs

DPL .................................................... 21-7AC OPF .................................................... 33-1

Advanced Options ........................... 33-15Basic Options .................................... 33-1Initialization ..................................... 33-14Iteration Control .............................. 33-15Output ............................................. 33-17

ACCI (Reliability Analysis) ..................... 31-10ACIF (Reliability Analysis) ....................... 31-7ACIT (Reliability Analysis) ....................... 31-7acos

DPL .................................................... 21-7Active Failure ........................................ 31-48Adequacy .............................................. 31-48Administrator ............................................ 7-2AENS (Reliability Analysis) .................... 31-10AID (Reliability Analysis) ....................... 31-11Analyses

General Information ............................ 9-1Analysis

General Information ............................ 9-1API Interface ......................................... 22-51Appliance .................................................. A-1Area ......................................................... 15-1ASAI (Reliability Analysis) ....................... 31-8asin

DPL .................................................... 21-7ASUI (Reliability Analysis) ....................... 31-8atan

DPL .................................................... 21-7Availability ............................................. 31-49

BBase Case ................................................. A-1Base State ............................................. 31-49Basic Project Definition ........................... 10-1Block Definition ........................................ A-1Block Definition Dialogue (DSL) ............ 27-51Block Diagram ....................11-37, 27-36, A-1

BooleanExpresions ......................................... 21-9

Boundary ................................................. 15-4Branch Elements ...................................... A-1break

DPL .................................................... 21-9Busbars .................................................... A-2

CCable Size Optimisation

Basic Options .................................. 34-18Cable Size Optimization ........................ 34-17

Advanced Options ........................... 34-21Objective Function .......................... 34-17Optimization Procedure .................. 34-18

CAIDI (Reliability Analysis) ..................... 31-8CAIFI (Reliability Analysis) ...................... 31-7Calculation

Compare Results ............................. 19-12Result .................................................. 9-3Update Database ............................ 19-13

Calculation Time ..................................... 13-3CASE

DIg Output Language .........................C-4ceil

DPL .................................................... 21-7ChaMat .................................................... 5-33ChaPol ................................................... 25-19ChaVec .................................................... 5-33ChaVecfile ............................................. 18-10CIM Interface ........................................ 22-20Circuit ...................................................... 15-6Class ......................................................... A-2class .......................................................... 5-1Classes ...................................................... 5-1CMD

DIg Output Language .........................C-4ComCabsize ........................................... 34-17

Basic Options .................................. 34-18Objective Function .......................... 34-17Optimization Procedure .................. 34-18

ComCamoAvailable Capacitors .......................... 34-7

ComCapo ................................................. 34-1Basic Options .................................... 34-5Load Characteristics .......................... 34-8

ComCimexp ........................................... 22-22ComCimimp ........................................... 22-21ComContingency

Contingency analysis with multiple time phases ................................... 30-3

ComDbupd ............................................ 19-13ComDiff ................................................. 19-12ComDocu ................................................. 19-5

E - 1


ComDpl .................................................... 21-2ComEd ................................................... 12-22ComExport ............................................... 22-6ComExppsse .......................................... 22-13ComFlickermeter ..................................... 26-4ComFsweep ............................................. 25-5ComGenrel ............................................. 32-15ComGenrelinc ........................................ 32-12ComHldf ................................................... 25-2ComIdent ................................................ 29-1ComImport .............................................. 22-3ComInc .................................................... 27-4ComLdf .................................................. 23-19ComMerge ............................................... 20-9ComMod .........................................28-1, 28-6

Advanced Options ............................. 28-8How to Complete a Modal Analysis ... 28-5

ComModres ........................................... 28-18Common Mode Failure .......................... 31-20Common Model ..........................27-21, 27-32

Structure ......................................... 27-32ComNeplan ............................................ 22-16ComNew ................................................ 11-21ComNmink ............................................. 30-32ComOp .................................................. 12-23ComOpf ................................................... 33-1ComOutage ........................................... 30-18ComPause .............................................. 12-23Composit Frame .................................... 27-29Composite Block Definition ................... 27-36Composite Block Definitions (DSL) ....... 27-50Composite Frame ..................................... A-2

Additional Equations ....................... 27-43Block Definition ............................... 27-31Drawing ........................................... 27-37Multi-Signal Connection .................. 27-41Signal Connection ........................... 27-41Signals ............................................. 27-31

Composite Model ................27-21, 27-26, A-2Slot Update ...................................... 27-27Step Response ................................ 27-27

ComPr .................................................... 12-23ComPsse .................................................. 22-7ComRd ................................................... 12-23ComRed ................................................... 36-1ComRel3

Network reliability assessment ....... 31-30ComRes ......................................19-10, 19-63ComSe ................................................... 37-14ComSeteval ........................................... 28-20ComSh .................................. 19-4, 19-7, 25-7ComShc ................................................. 24-19ComSim ................................................. 27-20ComSimoutage ........................................ 30-7ComStationware .................................... 22-24ComStepres ........................................... 27-27

ComStop ................................................ 12-23ComTieopt ............................................. 34-13ComUcte ................................................ 22-18ComUcteexp .......................................... 22-19ComVsag ............................................... 31-41ComVstab .............................................. 23-40ComWr .................................................. 12-23Contact ...................................................... 2-1Contingency .......................................... 31-48Contingency Analysis .............................. 30-1

Comparing Results .......................... 30-35Contingency Cases .......................... 30-18Creating Contingencies using Contingency

Definitions ........................... 30-32Creating Contingencies using Fault Cases

and Fault Groups ................. 30-28Executing Contingency Analyses ...... 30-6Result Analysis ................................ 30-37Single Time Phase ............................. 30-7Technical Background ....................... 30-1

Contingency Case .................................. 30-18Contingency Constrained DC OPF ......... 33-31

Advanced Options ........................... 33-37Basic Options ................................... 33-32Initialization ..................................... 33-37Iteration Control .............................. 33-37Output ............................................. 33-37Reports ............................................ 33-38

Contingency Definition .......................... 30-32Contingency OPF ................................... 33-31continue

DPL .................................................... 21-9Convergence

Iteration Control .............................. 23-26LF Troubleshooting ......................... 23-33

cosDPL .................................................... 21-7

coshDPL .................................................... 21-7

Cost Functions ......................................... 33-2CSSL (DSL) ............................................ 27-46CUBIC

DIg Output Language ........................ C-3Cubicle ...................................................... A-2Curve Input

Context-sensitive Menu ................... 19-52Create Diagram ............................... 19-51

DDAQ .......................................................... A-2Data Management ................................... 20-1Data Manager .......................................... 12-1

Database Browser ............................. 12-1Database Tree ................................... 12-3

E - 2


Settings ............................................... 8-4Data Model ................................................ 5-1Database

Multi-User ............................................ 7-2Single-User .......................................... 7-2

DataManager ........................................... 12-1DC OPF .................................................. 33-20

Advanced Options ........................... 33-27Basic Options .................................. 33-21Initialization ..................................... 33-26Iteration Control .............................. 33-28

DEFDIg Output Language .........................C-4

Defining Element Symbols ....................... D-1Demo Account ........................................... 7-4Device ...................................................... A-3DGS Interface ......................................... 22-1Diagram Colouring ................................ 11-45DiaGrfopts ............................................. 11-34DiaPagetyp ............................................ 11-21DIg Output Language

Filters ..................................................C-7Includes ...............................................C-7Line Types ...........................................C-5Loops ...................................................C-7Page Breaks ........................................C-5Text Macros .........................................C-6

DIgSILENT Output Language ...................C-1Format .................................................C-2

DIgSILENT Programming Language ....... 21-1Distribution Function ............................. 31-49do() while{}

DPL .................................................... 21-9Documentation .......................................... 3-1DPL .......................................................... 21-1

Access to Objects ............................ 21-11Assignments ...................................... 21-7break ................................................. 21-9Constant Parameters ........................ 21-7continue ............................................ 21-9External Objects .............................. 21-14Functions & Subroutines ................. 21-17input ................................................ 21-10Local Objects ................................... 21-12Object Variables & Methods ........... 21-12output .............................................. 21-10Standard Functions ........................... 21-7Subroutines ..................................... 21-16Variable Definitions ........................... 21-6

DPL (DIgSILENT Programming Language) 21-1DPL Advanced Options ............................ 21-4DPL Command Execute .......................... 21-4DPL Command Libraries ........................ 21-15DPL Command Object ............................. 21-2DPL Command Set .................................. 21-3

DPL Internal Methods ........................... 21-17DPL Script Editor ..................................... 21-5DPL Script Language ............................... 21-6DPL Script Page ...................................... 21-5Drag and Drop ......................................... A-3DSL ........................................................ 27-54

Advanced Features ......................... 27-50Defining Models .............................. 27-50Definition Code ............................... 27-57Equation Code ................................. 27-61Events ............................................. 27-46Example .......................................... 27-64Expression ....................................... 27-61General Syntax ................................ 27-55inc .................................................... 27-58inc0 .................................................. 27-58incfix ................................................ 27-58Initial Conditions ............................. 27-58intervalinc ........................................ 27-59loopinc ............................................. 27-58Macro Handling ............................... 27-62Macros ............................................. 27-62Model Description ........................... 27-49newtoninc ........................................ 27-59Output ............................................. 27-46Structure ......................................... 27-46

DSL Block Definition .............................. 27-21DSL Model Components ........................ 27-49DSL Models ........................................... 27-43DSL primitive ............................................ A-3DSL Reference ...................................... 27-54DSL Structure ........................................ 27-56DSL Variables ........................................ 27-56Dynamic Model

Concept ........................................... 27-21

Ee

DPL .................................................... 21-8EDGE

DIg Output Language .........................C-3Edge Elements ......................................... A-3Edit

Detail Mode ..................................... 12-17Object Mode .................................... 12-17

EditorSettings ............................................... 8-6

EIC (Reliability Analysis) ....................... 31-11Eigenvalue Bar Plot ............................... 19-25Eigenvalue Calculation ............................ 28-1Eigenvalue Plot ..........................19-25, 28-11Element .................................................... A-4ElmArea ................................................... 5-14ElmBmu ................................................... 5-14

E - 3


ElmBoundary ........................................... 5-14ElmBranch ............................................... 5-11ElmCircuit ................................................ 5-15ElmComp ............................................... 27-26ElmCompare ............................................ 29-1ElmDsl ................................................... 27-32ElmFeeder ............................................... 5-15ElmFuse ................................................... 35-3ElmMeteostat .......................................... 32-6ElmNet ..................................................... 5-12ElmOperator ............................................ 5-15ElmOwner ................................................ 5-16ElmRelay .................................................. 35-2ElmRes ............................................13-9, 19-8ElmRoute ................................................. 5-16ElmSite .................................................... 5-12ElmStactrl .............................................. 23-12ElmSubstat .............................................. 5-11ElmTerm .................................................. 5-10ElmVac ................................................... 36-12ElmWindzone ........................................... 32-6ElmZone .................................................. 5-16ElmZpu .................................................. 36-12EMT Simulation ....................................... 27-1EMT Simulations ...................................... 27-1ENS (Reliability Analysis) ...................... 31-10Equipment Type Library .......................... 14-1Equivalent Network ................................. 36-1Event ..................................................... 27-15

Inter-Circuit ..................................... 27-19Load ................................................. 27-19Outage ............................................. 27-19Parameter ........................................ 27-18Short-Circuit .................................... 27-18Switching ......................................... 27-18Synchronous Machine ..................... 27-19

Events .................................................... 27-15EvtLod

Data Model ........................................ 13-7EvtOutage

Data Model ........................................ 13-7EvtParam

Data Model ........................................ 13-7EvtShc ................................................... 24-17

Data Model ........................................ 13-7EvtShcll

Data Model ........................................ 13-7EvtSym

Data Model ........................................ 13-7Expansion Stage ...................................... 17-1Export

Curve Data ...................................... 19-63to Spreadsheet Programs (e. g. MS EXCEL)

............................................. 12-25exps

DPL .................................................... 21-7

FFailure .................................................... 31-48Failure Effect Analysis ........................... 31-12fault

DSL .................................................. 27-63Fault Case .............................................. 30-30Fault Clearing (Reliability) ..................... 31-13Fault Group ........................................... 30-31Fault Isolation (Reliability) .................... 31-14FEA (Failure Effect Analysis) ................. 31-32Feeder ..................................................... 15-6Filter Analysis .......................................... 25-7Flexible Data Page ................................ 12-20Flicker Analysis

Assignment of Flicker Coefficients .. 25-26Continuous Operation ..................... 25-22Definition of Flicker Coefficients ..... 25-25Flicker Contribution of Wind Turbines 25-

25Result Variables ............................... 25-27Switching Operations ...................... 25-23

Flicker Analysis IEC 61400-21 ............... 25-22Flickermeter ............................................ 26-1

Advanced Options ............................. 26-6Calculation of Long-Term Flicker ...... 26-2Calculation of Short-Term Flicker ..... 26-2Data Source ....................................... 26-4Signal Settings .................................. 26-5

floorDPL .................................................... 21-7

for(){}DPL .................................................... 21-9

Forced Outage ....................................... 31-47Form Editor ............................................. 19-1Format Editor

Predefined Variables ......................... 19-1Text Editor ......................................... 19-1User Selection ................................... 19-1

fracDPL .................................................... 21-7

Frequency Dependent Parameters ....... 25-19Frequency Sweep .................................... 25-5

Advanced Options ............................. 25-7Basic Options ..................................... 25-6

GGeneral Selection (DPL) ........................ 21-13Glossary .................................................... A-1Graphic

Already Existing Network Elements 11-24Attributes ......................................... 11-32Balloon Help .................................... 11-48Colour .............................................. 11-45Edit Result Box ................................ 11-49

E - 4


Imported Data ................................ 11-25Insert ............................................... 11-31Interconnect ...................................... 11-6Layers .............................................. 11-41Legend Block ................................... 11-47Mark Element .................................... 11-5Options ............................................ 11-34Print ................................................. 11-31Rebuild ............................................ 11-31Reference Point ............................... 11-48Remove Page .................................. 11-32Rename Page .................................. 11-32Result Box ....................................... 11-47Result Boxes .................................... 11-34Title Block ........................................ 11-46Toolboxes ........................................ 11-23Zoom ............................................... 11-30

Graphic WindowNew ................................................. 11-21Page Tab ......................................... 11-22

Graphic WindowsSettings ............................................... 8-2

Graphics Board ...................................... 11-16Graphics Board Window ........................... A-4Grid ........................................................... A-4Grouping Objects .................................... 15-1

HHarmonic

Filter Analysis .................................... 25-7Harmonic Analysis ................................... 25-1Harmonic Calculation

Definition of Result Variables .......... 25-27Modelling

Assignment of Harmonic Injections 25-16

Definition of Harmonic Injections 25-9Frequency Dependent Parameters 25-

19Harmonic Distortion Results 25-17IEC 61000 Harmonic Sources 25-11Magnitudes and Phase Values 25-13Phase Correct Harmonic Sources 25-10Waveform Plot 25-21

Modelling Harmonic Sources ............ 25-9Waveform Plot ................................ 25-21

Harmonic Impedance .............................. 25-5Harmonic Load Flow ............................... 25-2

Advanced Options ............................. 25-4Basic Options .................................... 25-2IEC 61000-3-6 ................................... 25-4Result Variables ................................ 25-4

Harmonic Sources ................................... 25-9Harmonics Analysis ................................. 25-1

Definition of Result Variables .......... 25-27Filter Analysis .................................... 25-7Flicker Analysis IEC 61400-21 ........ 25-22Frequency Sweep .............................. 25-5Harmonic Load Flow ......................... 25-2Modelling Harmonic Sources ............ 25-9

Hazard Rate Function ........................... 31-49Help ........................................................... 3-1Hidden Failure ....................................... 31-48HMC ......................................................... 25-1HmcCur ................................................... 25-9Hotkeys .....................................................B-1Hotkeys References ..................................B-1

IIEAR (Reliability Analysis) ..................... 31-11IEC 61000-3-6 ......................................... 25-4IEC 61000-4-15 ....................................... 26-1

Advanced Options ............................. 26-6Data Source ...................................... 26-4Signal Settings .................................. 26-5

IEC 6100-4-15Calculation of Short-Term Flicker ..... 26-2

IEC 6100-4-15 Calculation of Long-Term Flick-er ............................................................. 26-2IEC 61400-21 ........................................ 25-22

Assignment of Flicker Coefficients .. 25-26Continuous Operation ..................... 25-22Definition of Flicker Coefficients ..... 25-25Flicker Contribution of Wind Turbines 25-

25Result Variables .............................. 25-27Switching Operations ...................... 25-23

if(){}DPL .................................................... 21-9

if(){}else{}DPL .................................................... 21-9

Importfrom Spreadsheet Programs (e. g. MS EX-

CEL) ..................................... 12-26inc

DSL .................................................. 27-58inc0

DSL .................................................. 27-58incfix

DSL .................................................. 27-58input

DPL .................................................. 21-10IntCase .................................................... 13-1

The Study Case Edit Dialogue .......... 13-4IntCbrating .............................................. 5-23Interconnect ............................................ 11-6Interfaces ................................................ 22-1

API ................................................... 22-51

E - 5


CIM .................................................. 22-20CIM Data Export .............................. 22-22CIM Data Export General Settings .. 22-22CIM Data Import ............................. 22-20CIM Data Import General Settings . 22-21DGS ................................................... 22-1DGS Export ........................................ 22-5DGS Export General Settings ............ 22-6DGS Import ....................................... 22-3DGS Import General Settings ............ 22-3DGS Structure ................................... 22-2MATLAB ........................................... 22-23NEPLAN ........................................... 22-15NEPLAN Import ............................... 22-15NEPLAN Import General Settings .... 22-16OPC .................................................. 22-23PSS/E ................................................. 22-6PSS/E Dyn.Data Import .................. 22-11PSS/E Dyn.Data Import General Settings

22-12PSS/E Dyn.Data Import Options ..... 22-12PSS/E Export ................................... 22-12PSS/E Export General Settings ........ 22-13PSS/E Export Options ...................... 22-14PSS/E Import ..................................... 22-6PSS/E Import General Settings ......... 22-7PSS/E Import Graphical Options ..... 22-10PSS/E Import Options ....................... 22-8StationWare ..................................... 22-24UCTE-DEF ........................................ 22-17UCTE-DEF Data Export ................... 22-19UCTE-DEF Data Export General Settings .

22-19UCTE-DEF Data Import ................... 22-17UCTE-DEF Data Import General Settings

22-18Interior Point Method .............................. 33-1Interruption ........................................... 31-48intervalinc

DSL .................................................. 27-59IntEvt ....................................................... 5-27IntEvtshc ............................................... 24-17IntFaultgrp .............................................. 5-29IntFltcases ............................................... 5-26IntFltgroups ............................................. 5-26IntForm ................................................... 19-1IntGrf ......................................................... 5-8IntGrfnet ................................................ 11-32

Options ............................................ 11-32IntLogon .................................................... 6-1IntMon ........................................13-11, 19-14IntMonsel .............................................. 12-20IntNewobj ................................................ 12-4IntOutage .......................................5-24, 5-29

Demad Transfer ................................ 5-25IntPrj ....................................................... 10-3

IntPrjfolder ................................................ 5-2IntQlim .................................................... 5-29IntRunarrange ......................................... 5-31IntScenario .............................................. 16-1IntScensched ......................................... 16-10IntScheme ............................................... 5-17IntSscheduler .......................................... 17-6IntSstage ................................................. 5-17IntSubset ............................................... 16-13IntSym ...................................................... D-1IntTemplate ........................................... 11-11IntVersion ................................................ 20-1Iterations

Iteration Control .............................. 23-26LF Troubleshooting ......................... 23-33

LLCOL

DIg Output Language ........................ C-5Limits (Active and Reactive Power) ...... 33-10Linear Programming .............................. 33-20LMPs ...................................................... 33-25ln

DPL .................................................... 21-7Load Flow Analysis .................................. 23-1

Active Power Control ....................... 23-21Adv.Simulation Options ................... 23-29Advanced Load Options .................. 23-12Advanced Options ........................... 23-24Basic Options ................................... 23-19Coincidence of Low Voltage Loads . 23-16Executing LF .................................... 23-19Feeder Load Scaling ........................ 23-13Iteration Control .............................. 23-26Load Scaling Factors ....................... 23-15Low-Voltage Analysis ...................... 23-28Output ............................................. 23-27Reactive Power Control ................... 23-20Result Analysis ................................ 23-30Sensitivities ..................................... 23-40Technical Background ....................... 23-4Temperature Dependency .............. 23-17Troubleshooting .............................. 23-33Voltage Dependency of Loads ........ 23-12

Load Shedding (Reliability) ................... 31-16Load Transfer (Reliability) ..................... 31-16Load-Flow

Optimizing ......................................... 33-1Locational Marginal Prices ..................... 33-25log

DPL .................................................... 21-7Log-on ....................................................... 6-1Logon

Advanced Settings ............................... 6-5

E - 6


Long-Term Flicker ................................... 26-2loopinc

DSL .................................................. 27-58Lost load ................................................ 31-47LPEIC (Reliability Analysis) ................... 31-10LPENS (Reliability Analysis) .................... 31-9LPES (Reliability Analysis) ....................... 31-9LPIF (Reliability Analysis) .............31-7, 31-11LPIT (Reliability Analysis) ............31-7, 31-11

MMacro

DSL .................................................. 27-62Maintenance .......................................... 31-47MATLAB Interface ................................. 22-23Matlab Interface

Concept ........................................... 27-67Matlab File ....................................... 27-70Model Implementation .................... 27-67

maxDPL .................................................... 21-7

minDPL .................................................... 21-7

Modal Analysis ........................................ 28-1Exporting a Modal Analysis Plot to External

Software .............................. 28-17Exporting Results to External Software 28-

20How to Complete a Modal Analysis .. 28-5Participation Factor ........................... 28-1Plots ................................................ 19-25Result Plots ..................................... 28-11Showing the Modal Analysis Data Browser

28-18Validity of Results ............................. 28-4Viewing Modal Analysis Results ........ 28-9Viewing Results in the Data Browser 28-18

Modal Analysis CommandAdvanced Options ............................. 28-8Basic Options .................................... 28-6

Mode Bar Plot ........................................ 28-14Mode Phasor Plot .................................. 28-16Model Analysis

Theory ............................................... 28-1Model Parameter Identification .............. 29-1Modeling and Simulation Tools ............. 27-46modulo

DPL .................................................... 21-7

NNEPLAN Interface ................................. 22-15NET

DIg Output Language .........................C-4

Network ModelVariations .......................................... 17-1

Network Reduction ................................. 36-1Example .......................................... 36-10Handling ............................................ 36-2Options .............................................. 36-5

Network Variations .................................. 17-1newtoninc

DSL .................................................. 27-59Node ......................................................... A-4NULL ........................................................ 21-7

OOBJECT

DIg Output Language .........................C-3Object ....................................................... A-4Objects

Edit .................................................. 11-18Filtering ........................................... 12-13Search ............................................. 12-12Sorting ............................................. 12-12

Objects relevant for Calculation ................ 9-3OPC Interface ........................................ 22-23Open Tie Optimization .......................... 34-13Operation Scenario ......................... 16-1, A-4Operation Scenarios

Scenario Scheduler ......................... 16-10Operational Data ..................................... 14-2Operator .................................................. 15-9OPF .......................................................... 33-1Opt, Capacitor Placement

Available Capacitors .......................... 34-7Opt. Capacitor Placement

Basic Options .................................... 34-5Objective Function ............................ 34-2Optimization Procedure .................... 34-4Voltage Violation Cost ....................... 34-2

Optimal Capacitor Placement .................. 34-1Load Characteristics .......................... 34-8

Optimal Power Flow ................................ 33-1Optimal Power-Flow ................................ 33-1Optimization Tools for Distribution Networks .34-1Outage .................................................. 31-47output

DPL .................................................. 21-10DSL .................................................. 27-63

Output of Device Data ............................ 19-4Documentation .................................. 19-6Filter/Annex ....................................... 19-6

Output of Results .................................... 19-7Output Window

Context Sensitive Menu .................... 4-17Copy .................................................. 4-19

E - 7


Legend ............................................... 4-18Settings ............................................... 8-5

Output window ........................................ 4-15Overload Alleviation (Reliability) ........... 31-15Owner ...................................................... 15-9

PPage Tab .................................................. A-5Parallel Computing ................................ 30-16Parameter Characteristics ....................... 18-1Parameter Identification ......................... 29-1

Application ......................................... 29-8Comparison Slot ................................ 29-4Measurement File .............................. 29-3Model Creation .................................. 29-4Performing ......................................... 29-6Target Function ................................. 29-2

Passive Failure ....................................... 31-48Path ....................................................... 15-10pi

DPL .................................................... 21-8pow

DPL .................................................... 21-7Power at Risk ........................................ 31-15Power Restoration (Reliability) ............. 31-15PowerFactory Overview ............................ 4-1Primitive Block Definitions (DSL) .......... 27-51Print Graphic ......................................... 11-31Probability Density Function ................. 31-49Program Administration ............................ 6-1Program Configuration .............................. 6-1Program Installation .................................. 6-1Project ...................................................... A-5

Basic Defintion .................................. 10-1Validity Period ................................... 10-5

Project Settings ....................................... 10-4Protection ................................................ 35-1PSS/E Interface ....................................... 22-6

RReducing Network ................................... 36-1Reduction ................................................ 36-1Redundant Unit ..................................... 31-49RelDir ..................................................... 35-12RelFmeas ............................................... 35-12RelFrq .................................................... 35-21RelFuse .................................................... 35-3Reliability Analysis

Advanced Options ........................... 31-35Basic Options ................................... 31-30Calculated Results ............................. 31-6FEA Options ..................................... 31-32Glossary ........................................... 31-47

Options ............................................ 31-36Outputs ............................................ 31-32State Enumeration .......................... 31-11Stochastic Models .............................. 31-4

Reliability Assessment ............................. 31-1Technical Background ....................... 31-3

Reliability ModelInterruption Cost ............................. 31-24

RelIoc .................................................... 35-15RelLogic ................................................. 35-22RelMeasure ............................................ 35-11RelToc ................................................... 35-17RelUlim .................................................. 35-21Remote Scripts (DPL) ............................ 21-15Repair .................................................... 31-48Reporting Results .................................... 19-1RES

DIg Output Language ........................ C-4Result Box

Edit .................................................. 11-49Result Comparison

Setup ............................................... 19-12Result Export ......................................... 19-10Result Object ...................................19-8, A-5Results ..................................................... 19-1

DIgSILENT Output Language ............ C-1RMS Simulation ....................................... 27-1round

DPL .................................................... 21-7

SSAIDI (Reliability Analysis) ..................... 31-8SAIFI (Reliability Analysis) ...................... 31-7Scheduled Outage ................................. 31-47Security ................................................. 31-49SEL .......................................................... 21-7Sensitivity Analysis ................................ 23-40SES (Reliability Analysis) ....................... 31-10SetColgr ......................................11-39, 11-45SetCondmg ............................................ 35-25SetCrvfilt ................................................ 19-62SetCubop ................................................. 11-3SetDisplt ................................................ 35-40SetFilt .................................................... 12-12SetGrfpage ............................................ 11-41SetLevelVis ............................................ 11-42SetMotorst ............................................. 35-28SetOcplt ................................................. 35-30SetPath ............................. 5-16, 35-31, 35-32SetPrj ....................................................... 10-4SetTime ................................................... 13-3Settings

Data Manager ...................................... 8-4Directories ........................................... 8-6

E - 8


Editor ................................................... 8-6Functions ............................................. 8-5General ................................................ 8-1Graphic Windows ................................ 8-2Output Window ................................... 8-5

SetTitm .................................................. 11-46SetTrfdmg ............................................. 35-27SetTrigger ....................................5-33, 13-12SetUser ...................................................... 8-1SetValue ................................................ 12-17SetVilytaxis ............................................ 19-67SetVilytpage .......................................... 19-67SetVilytplot ............................................ 19-67SetViPage .............................................. 19-25Shadow Prices ....................................... 33-25Shed load .............................................. 31-47Short-Circuit Analysis .............................. 24-1

Adv.Options ANSI ........................... 24-29Adv.Options Complete M. ............... 24-33Advanced Options IEC/VDE ............ 24-24Basic Options (All Methods) ............ 24-19Basic Options ANSI ......................... 24-27Basic Options Complete M. ............. 24-31Basic Options IEC 61363 ................ 24-35Basic Options IEC/VDE ................... 24-23Calculation Method ......................... 24-19Calculation Options ......................... 24-19Executing SC ................................... 24-14Explanation ANSI Method ................. 24-9Explanation Complete Method ........ 24-11Explanation IEC/VDE Method ........... 24-4Fault Type ....................................... 24-20IEC Correction Factors ...................... 24-6Line Faults ....................................... 24-16Multiple Faults ................................. 24-17Result Analysis ................................ 24-37Technical Background ....................... 24-2Verification ...................................... 24-22

Short-Term Flicker .................................. 26-2sin

DPL .................................................... 21-7Single Line Graphic ....................11-37, 11-38Single Time Phase Contingency Analysis 30-7sinh

DPL .................................................... 21-7Slot ........................................................... A-5Spare Unit ............................................. 31-48sqr

DPL .................................................... 21-7sqrt

DPL .................................................... 21-7Stability Analysis

Models ............................................. 27-21Stability and EMT Simulations ................ 27-1Stability Simulation ................................. 27-1StaCt ........................................................ 35-5

StaCubic .................................................. 5-10STALNE

DIg Output Language .........................C-4StaSwitch ................................................ 5-10State Enumeration ................................ 31-11State Estimation ...................................... 37-1

Basic Options .................................. 37-14Components of the SE ...................... 37-2Data Input ......................................... 37-5Executing SE ................................... 37-14Objective Function ............................ 37-2Result Analysis ................................ 37-21StaExtpmea ..................................... 37-22StaExtqmea ..................................... 37-22StaExtvmea ..................................... 37-22

StationWare Interface ........................... 22-24Statistic .................................................. 31-47StaVt ........................................................ 35-7StaVtsec .................................................. 35-9Stochastic .............................................. 31-47Stochastic Models

Busbar ............................................. 31-18Cable ............................................... 31-19Common Mode ................................ 31-20Line .................................................. 31-19Terminal .......................................... 31-18Transformer .................................... 31-19

StoCommon ........................................... 31-20StoGen .................................................... 32-4StoTypbar .............................................. 31-18StoTyplne .............................................. 31-19StoTyptrf ............................................... 31-19Study Case ...................................... 13-1, A-5

Study Time ........................................ 13-3Study Cases ............................................. 13-1Study Time .............................................. 13-3Subplot (VI) .......................................... 19-32Support ..................................................... 2-1Symbols .................................................... D-1Symbols of Elements

Editing and Changing ...................... 11-47System Stage ........................................... A-5

Converting into Variations .............. 17-11

Ttan

DPL .................................................... 21-7tanh

DPL .................................................... 21-7Tariff Systems for External Grids ............ 33-3The ............................................................ 6-1The Graphics Editor ................................ 11-1this .......................................................... 21-7Time Phases ............................................ 30-3

E - 9


Time-Domain Simulation3-phase EMT Simulation ................... 27-43-phase RMS Simulation ................... 27-3Advanced Options ............................. 27-9Balanced RMS Simulation ................. 27-3Basic Options ..................................... 27-6Calculation Methods .......................... 27-3Events .............................................. 27-15Load Flow ........................................ 27-12Long-Term Stability ......................... 27-11Noise Generation ............................. 27-12Reference System ........................... 27-10Result Objects ................................. 27-13Run .................................................. 27-20Setup ................................................. 27-4Simulation Results ........................... 27-14Step-Size Adaption ...................27-7, 27-8

Time-Domain Simulations ....................... 27-1TITLE

DIg Output Language ........................ C-4Toolbar Definitions .................................. 4-11Trace ..................................................... 30-28Transient Analysis ................................... 27-1Transients

electromagnetical .............................. 27-2electromechanical ............................. 27-2long-term ........................................... 27-2

TriCont ..................................................... 18-6TriDisc ..................................................... 18-5TriFreq ..................................................... 18-7TriVal ....................................................... 18-2trunc

DPL .................................................... 21-7TTF (Reliability Analysis) ......................... 31-5TTR (Reliability Analysis) ........................ 31-5twopi

DPL .................................................... 21-8TypCt ....................................................... 35-7Type ......................................................... A-6

Define element type .......................... 5-21TypHmcCur .............................................. 25-9TypPowercurve ........................................ 32-5TypVt ..................................................... 35-10TypVtsec ................................................ 35-11

UUCTE-DEF Interface .............................. 22-17User Accounts ........................................... 7-1User Groups .............................................. 7-1User Interface ........................................... 4-8User Settings ............................................. 8-1

VValidity Period ......................................... 10-5Variable Sets ......................................... 19-14VARIANT

DIg Output Language ........................ C-4Variation ..........................................17-1, A-6Vector Diagram

Changing the object ........................ 19-44Changing the Variables ................... 19-44Coordinates ..................................... 19-43Editing the Unit/Tick ....................... 19-43Label of Vectors .............................. 19-44Origin ............................................... 19-43X and Y Axes ................................... 19-43

VecVis .................................................... 19-41Version .................................................... 20-1VI

Constant Value ................................ 19-59Curve Filter ...................................... 19-62Curve Input ..................................... 19-51Defining Styles ................................ 19-67Edit Dialogues ................................. 19-56Embedded Graphic Windows .......... 19-54Export Curve Data ........................... 19-63Export Curve Graphic ...................... 19-63FFT Plot ........................................... 19-41Format Label ................................... 19-58Labelling Plots ................................. 19-56Plot Style ......................................... 19-68Pre-defined Style ............................. 19-69Status Bar ........................................ 19-56Straight Line .................................... 19-62Styles ............................................... 19-66Text Label ........................................ 19-57Tools for Virtual Instruments .......... 19-56User-defined Styles ......................... 19-66Value Label ...................................... 19-57Vector Diagram ............................... 19-41Voltage Profile Plot .......................... 19-44Waveform Plot ................................. 19-49X-Y-Plot ........................................... 19-40

VI PanelAutomatic Arrangement .................. 19-27Automatic Scale Buttons ................. 19-27Background ..................................... 19-30Context Sensitive Menu .................. 19-30Create Virtual Instruments .............. 19-31Default Styles .................................. 19-31Defining Styles ................................ 19-67Edit .................................................. 19-26Moving and Resizing ....................... 19-28Page Format .................................... 19-28Plots ................................................. 19-31Results ............................................. 19-30Title Block ........................................ 19-29Variables of Plots ............................. 19-28

E - 10


Virtual Instrument .................................... A-6Virtual Instrument Panel .......................... A-6Virtual Instrument Panels ..................... 19-25Virtual Instruments ................................. 19-1

Types ............................................... 19-23Types Feeders ................................. 19-25Types Harmonics ............................ 19-25Types Protection ............................. 19-24

Virtual Power Plant ................................. 15-1VisDefcrv ............................................... 19-51VisDraw ................................................. 35-37VisEigen ................................................. 28-11Viseigen ................................................. 19-25VisFft ..................................................... 19-41VisHrm ................................................... 19-49VisLabel ................................................. 19-58VisModbar ..................................19-25, 28-14VisModphasor ........................................ 28-16VisOcplot ............................................... 35-23VisPath .................................................. 19-44

Creating a voltage profile plot ........ 19-45Customising a Voltage Profile Plot .. 19-46Interpreting a Voltage Profile Plot .. 19-45Schematic Visualization ................... 19-48

VisPlot ................................................... 19-32Curves ............................................. 19-37Editing Subplots .............................. 19-32Setting the X-Axis ........................... 19-34Setting the Y-Axis ........................... 19-35

VisPlot (2 Y-Axes) ................................. 19-39VisPlot2 ................................................. 19-39VisPlottz ................................................. 35-31VisValue ................................................. 19-57VisXvalue ............................................... 19-59VisXYPlot ............................................... 19-40Voltage Profile Plot

Customising the Voltage Profile Plot 19-46How to create a Voltage Profile Plot 19-45Interpreting a Voltage Profile Plot .. 19-45

Voltage Sag Analysis ............................. 31-41Options ............................................ 31-41Results ............................................. 31-43

WWaveform Plot ...................................... 25-21while(){}

DPL .................................................... 21-9

ZZone ...................................................... 15-10

E - 11

Documents

PFManual 14 1 en Ed1 Vol II PDF