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PG&E 500 kV Series-Compensated Transmission Line Relay Replacement: Design Requirements and RTDS

Testing

PG&E

Davis ErwinRafael PinedaMonica Anderson

SEL, Inc.

Demetrios A.TziouvarasRick Turner

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• Existing solid-state relay systems reached

the end of their useful life

• Systems placed out-of-service because of

• Misoperations and

• Lack of replacement parts

• Risk of forcing 500kV lines out of service

• NERC could impose substantial monetary

fines

Present Reliability of 500kV Protection

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• Six lines required immediate relay system

replacement to:

• Improve reliability

• Maintain maximum availability

• Used existing protection design philosophy

on 5 of the 6 lines

• The 6th line required special considerations

not covered by this paper

Mitigation Plan

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Project Flow

Define

Project Scope

Targeted relay

replacement,

maintain

existing

scheme

philosophy

Engineering Design

Develop Settings

Based on steady-

state fault studies

Develop

RTDS Model

Gather detailed

system data;

determine

boundaries

RTDS Testing

Prove and

adjust settings

Field Work

Obtain

clearances;

install and

commission

test devices

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Relay Replacement Project

Permissive Overreaching Transfer Trip (POTT)

Set A- Dedicated Microwave

Set B or C- Switchable Carrier

Project Replacement

No high speed communication

Set D- Time Delayed Back-Up

Set A552-2

552-1

Set D

Set B

Set C

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• Improve system transient stability

• Maintain 500kV system availability

• Reduce damage to insulators and

conductors

• Permit high-speed reclosing

• Reduced Zone 1 reach in SC lines

• One level of high-speed pilot protection is

required at all times for coordination

Justification for High-Speed Protection

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Series-Compensated Line Protection ChallengesVoltage Inversion

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Series-Compensated Line Protection ChallengesCurrent Inversion

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Series-Compensated Line Protection ChallengesSubharmonic Oscillations

Zone 1 distance element overreach

0 2

X (

Oh

ms)

1-1-2

4

3

2

1

0

R (Ohms)

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• Introduce a Zone -1 time delay – not

recommended

• Further reduce Zone 1 reach and use

RTDS testing to validate setting

• Enable SC logic to block Zone 1 for faults

beyond a SC located in front of the relay

Options to Prevent Zone 1 Overreach

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• Used steady-state short circuit fault data

to develop initial relay settings

• Steady-state short circuit program cannot

model series compensation transients

• Relay settings for SC lines should be

verified using RTDS transient testing

Relay Setting Considerations and Criteria

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West-Generator Station Line Under Study

Line under study

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West-Generator Station LineSteady-State Settings

• Used multiple short circuit study base

cases to calculate relay settings

• Determined the required base cases

using all possible bypass combinations

on neighboring line series capacitors

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Bypassed Capacitors

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Steady-State Settings for West-Generator Station Line

• Determined minimum and maximum fault

currents and apparent impedances for

the line under study

• Considered additional cases because a

generator or transformer can be off-line

for extended periods

• Used an Excel macro to tabulate all of

the single outage contingencies

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Cases Created for West-Generator Station Line

Fault Data

Case South PathNorth –South

North –West

West –South

1

2 BP

3 BP

4 BP BP

5 BP

6 BP BP

7 BP BP

8 BP BP BP

9 BP

10 BP BP

11 BP BP

12 BP BP BP

13 BP BP

14 BP BP BP

15 BP BP BP

16 BP BP BP BP

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External Faults Past Capacitors

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Series Compensation LogicGenerator Station

• Observed lower apparent impedances at

the GS for faults beyond the SCs on the

• North-West and

• South-West lines

• Used the series compensation logic to

block Zone 1 for a fault beyond a capacitor

• Applied a capacitor setting equal to the

highest XC value at the West bus

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Series Compensation LogicWest Station

• Enabled series compensation logic

• Set XC to “OFF”

• Allows setting the Zone 1 element to

• Desired sensitivity

• Be secure during voltage inversions for

faults on neighboring SC lines

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Custom Secure Echo Back POTT Logic

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Custom Secure Echo Back POTT Logic

• Supervised logic by all poles being open

• Prohibits echo keying for subsequent out-

of-section faults that occur during single-

pole open conditions

• Feedback loop ensures that a 4-cycle

echo only occurs once per 10-cycle

period

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RTDS Modeling

• Accurately modeled network around the

line under test

• Created reduced network model

• Matched load flow and short circuit currents

• Modeled SC MOV and TPSC protection

• SC bypass breakers and their controls

• High-MOV energy and current bypass

• SC reinsertion controls

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RTDS Modeling

• Simulated single- and three-pole reclosing

controls for line under test

• Simulated relay operation and reclosing

controls for adjacent lines

• Modeled CCVT transient response

• Modeled frequency dependence of lines

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RTDS Testing

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• Continuous real time with a 50 – 70 µsec

time step

• Simulator is connected directly to relays

• COMTRADE files

• Analog voltages and currents

• Monitored pertinent digital elements to

capture as discrete points in time

RTDS Testing

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RTDS Testing Order

• Compare RTDS fault currents with short circuit steady-state base case

• Verify proper connections to the relays and RTDS

• Perform manual tests for extreme conditions

• Perform scripted tests for

• External faults

• Internal faults

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RTDS Manual Testing

• Verify relay operation for

• Switch on to fault

• Loss of potential and

• Faults during a single-pole trip open interval

• Apply ground faults with varying fault resistance

• At the zero-sequence center of the line

• Determine relay sensitivity for High-R faults

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• Tests relays with different level of dc transients

• Generates different levels of subharmonic

frequency transients

RTDS TestingVariation of Fault Inception Angle

VA

0º 90º

45º

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Automatic RTDS Scripting

• Automates fault simulation and data collection

• Generates thousands of test cases in a relatively short period of time

• Software analysis tools simplify the analysis of the large amount of data

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Faults for One RTDS Script Test

Power Flow Cases &

Contingencies

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Fault Locations 10

Fault Types 10

Fault Inception Angles 3

Total (4 • 10 • 10 • 3) = 1,200

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RTDS ASCII File Discrete Points

– Reclose block and initiate

– Zone 1 pickup (phase or ground)

– Zone 2 pickup (phase or ground)

– POTT forward ground overcurrent pickup

– POTT key permissive

– POTT receive permissive

– POTT reverse element pickup

– Series compensation block Zone 1

– Out-of-step blocking (if utilizing this element)

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RTDS Data Capture

• Captured the operating time of the monitored points in a text file

• Created a file for each fault location within each tested scenario

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• Created an Excel workbook to assist in the data analysis

• The workbook utilizes a VB macro

• Analyzed internal and external fault simulation data

• Graphs illustrate important data results

RTDS Data Manipulation

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• Formatted cells indicate relay tripping action (green) and nonaction (red)

RTDS Internal Fault Data Manipulation

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RTDS Internal Fault Data Manipulation

Relay Operating Time – Left Terminal

Fault Location 5 (30 faults per case, 10% from generator bus)

Left Generator Terminal Zone 1 Statistics

Case1I_G 2U_A 2U_C 2U_E

30

25

20

15

10

5

0

0.049

0.042

0.033

0.025

0.017

0.008

Seconds

30

25

20

15

10

5

0

Number of Zone 1

Operations

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• Formulas calculate the results of the Zone 1 elements for each line terminal as a percentage of all faults simulated at each location

• The histogram displays the effect of the right terminal adjacent line series capacitors on the Zone 1 reach of the left terminal

RTDS Internal Fault Data Manipulation

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RTDS Internal Fault Data Manipulation

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RTDS External Fault Data Manipulation

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RTDS External Fault Data Manipulation

• The summary worksheet has two tables

• One table displays the results of the relays

for faults behind the left terminal

• The other presents the results for faults

behind the right terminal

• For each fault location, a column is

created with four rows of data

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RTDS External Fault Data Manipulation

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Conclusions

• RTDS transient testing is the best method

to verify relay settings and custom logic

• Increases familiarity with applied relays

and 500kV SC system transients

• Helps to identify and improve relay designs

• Provides updated 500kV transient model

for future project work

• Ready pool of COMTRADE files for

accurate field End-to-End testing