ISO NE Experiences with Internal and External Model Impacts on

the State Estimator Model • Impacts • Challenges

Sriram Ramesh, Tim Murphy, Dave Krueger, Yuan Li, Audrey Newcomb

National Harbor, MD

2014 July 31

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Table of Contents

• NETWORK MODEL Page 3 – INTERNAL MODEL Page 4 – EXTERNAL MODEL Page 5 – EXTERNAL MODEL contd. Page 6

• ISO-NE STATE ESTIMATOR Page 7

• STATE ESTIMATOR MANAGEMENT Page 8 – ACCURACY CLASS Page 9 – RTNET SOL. QUAD DISPLAYS Page 10 – SAVE ESTIMATES QUAD DISPLAYS Page 11 – INITIALIZATION BUTTONS Page 12 – LOAD TREE Page 13 – ON-CALL CHECK Page 14

• STATE ESTIMATOR PERFORMANCE METRICS Page 15

• FUTURE CHALLENGES Page 17

NETWORK MODEL

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INTERNAL

CONNECTICUT

MASSACHUSETTS

RHODE ISLAND

VERMONT

NEW HAMPSHIRE

MAINE

EXTERNAL

NEW YORK

NEW BRUNSWICK

HYDRO QUEBEC

INTERNAL MODEL

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• Detailed model of 345, 230, 138, 115 kV

transmission system.

− Down to 69 kV in some cases

• Lower kV buses modeled in detail for

generators

• Good measurement observability with

very few unobservable areas

• Transmission parameters very accurate

− Separate process for obtaining and

validating these parameters like R, X etc.

EXTERNAL MODEL

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• New Brunswick

− 138/230/345 kV explicitly

modeled

• Hydro Quebec

− Ties to New England

modeled

EXTERNAL MODEL contd.

• New York

− 345 kV modeled in detail

− Plans to complete the 230 kV model by 2015

− 115/138 kV – explicit model up to 2 buses away from ties

− Equalized model outside of 2 buses from the ties

− Equivalent NY model being updated : 2013-2015

− Changes to the NY model after the update will be

maintained by the model exchange process

− NY model will have accurate parameters when the process

is complete

− Less measurement observability

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ISO-NE STATE ESTIMATOR • Online Network Sequence consists of:

– RTNET – Once every 3 minutes or on manual request

– RTCA – Once every 6 minutes or on manual request

• Primary CA Application that allows controller movement (units, transformers, shunts on AVR)

– RTCAJR – After every RTCA run

• Secondary CA Application allows only unit controller movement

• Total Run time of about 54s

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STATE ESTIMATOR MANAGEMENT

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• Several tools used to manage inaccuracies that arise from Internal and

External models

− Accuracy Classes

− Visual Tools

o RTNET Solution Quad Displays

o Save Estimates Quad Displays

o Initialization Buttons

− Load Tree

• Control room has the ability to temporarily manage most internal

model problems with regard to SE

• On-Call SME intervention usually required for External model problems

that cause Excess Mismatches or Invalids

STATE ESTIMATOR MANAGEMENT ACCURACY CLASS

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• About 31 accuracy classes in our current system

• Separate sets of accuracy classes for Internal and External

model management

• Unique accuracy classes

− Internal and external

generators

− Tie line measurements

− Critical transformer and line measurements

− Phase Shifters

BASE VALUE BREAK POINT MANUAL STDEV

P.U.

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STATE ESTIMATOR MANAGEMENT RTNET SOLUTION QUAD DISPLAYS

• Internal Network Quadrants

– Displays stations in the internal model and stations associated with Tie-lines

• External Network Quadrants

– Displays stations in New York, New Brunswick and Hydro Quebec

• Displays the various RTNET solution metrics after every SE run

• Display divided into 4 quadrants

SOLUTION MISMATCH BUS FLOW MISMATCH

BUS MEASUREMENT MISMATCH SCADA/RTNET MW ANALOG DELTAS

STATE ESTIMATOR MANAGEMENT SAVE ESTIMATES QUAD DISPLAYS

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• Internal Save Mismatch Estimates

− Displays mismatch estimates at stations in the internal model and tie lines

• External Save Mismatch Estimates

− Displays mismatch estimates at stations in the external model

• Displays the various MW/MVAR bus mismatch estimates after every SE run

• Display divided into 4 quadrants

MW LOAD MISMATCH MW GENERATION MISMATCH

MVAR LOAD MISMATCH MVAR GENERATION MISMATCH

STATE ESTIMATOR MANAGEMENT INITIALIZATION BUTTONS

• Tools that the Control Room uses to manage Mismatches/Invalids

• Very useful to provide temporary control of the SE before the on-call SME

can intervene

• Some of the buttons are:

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– Warm Initialization

– Cold Initialization

– Initialize Topology

– External Mismatch

STATE ESTIMATOR MANAGEMENT LOAD TREE

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• Internal Model

− Load Tree in real-time updated

automatically by the SE

− Load Tree for study applications

updated based on historical data

− Minimal manual intervention

required for SE

• External Model

− Manually maintained for both Real

time and Study applications

STATE ESTIMATOR MANAGEMENT ON-CALL CHECK

Review RTNET, Save Estimates

Quad displays

Ensure critical parameters are

within tolerance

e.g. Net Area Bus Mismatch

Investigate stations repeatedly

causing mismatches

Examine stations with SCADA vs

RTNET MW/MVAR/kV differences

Monitor phase shifters

Review stale data

Check stations with anomalous

equations

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STATE ESTIMATOR PERFORMANCE METRICS

• 15,000 SE runs per month on an average

• 99.5% valid solution rate

• 300,000 SE runs since EMP26

– ISONE upgraded to EMP26 in Nov 2012

• Less than 10% stations (both Internal and External combined) have

anomalous equations

• Jan 3rd 2014

– Invalid SE solutions due to High Cost

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FUTURE CHALLENGES

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• Enhance External Model

− Explicitly model and improve our external model

− Increase observability in the external areas by adding more measurements

• PMU

− Integrate PMU measurements into our State Estimator

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