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Simulation of Power System Faults for Protection Performance Analysis

-Case Studies of Tata Power By

S G Patki M V Kini P K Jain G T Jawale

Presented at:International Conference on Power System Protection,

CPRI, Bangalore

20-21st February, 2007

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Introduction

Need for Simulation Tool

Methodology Adopted for Power System Simulation

Salient features of Dynamic test kit

Setup of Dynamic test kit

Benefits of Analyzing faults using Simulation Tool

Two case studies – 1. Mal-operation of Protection

2. Non-operation of Protection

Overview

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TPC Inducted Numerical Protection Relays and Fault Disturbance Recorders (FDRs) since early 90s

Fault details can be obtained from the Software supplied by FDR Manufacturers. Some software include tools for

a) Distance to fault location

b) Impedance Locus

c) Harmonic analysis, etc

Advantage of stand-alone FDR – High Sampling Rate for event recording. Therefore, Reproduction of disturbance record captured by Standalone FDR found to be better than the events recorded byNumerical Protection Relay

Introduction

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Numerical Protection relays of different makes, types and version can exhibit different behavior during abnormal power system condition

Selection of Appropriate relays

Routine and Acceptance Testing by conventional methods may not reveal the deficiencies in the relays either due to inherentprotection algorithm or due to incorrect adopted configuration /setting

Need for Simulation Tool

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Analyzing and comparing performance of Numerical relays during dynamic power system condition.

Dynamic Simulation tool allows simulation of power system condition as well as replay of captured current and voltage signals from fault disturbance records

Computer aided system simulation tool for analysing mal-operation / non-operation of protective relays

Methodology Adopted for PS Simulation

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Can be used without PC (local mode) or with PC

Can be used for testing relays based on Voltage, Current and Frequency in local mode

However, With PC, few advanced functions such as Replaying of disturbance records, injection of Harmonic voltages / currents, Automatic Relay Testing etc.

Attaching a pre-fault waveform to the waveform recorded during fault

Selection of CTR / PTR is possible in software depending on 1 / 5 Amp for currents and PT ratio for Voltage Waveform

Truncation of waveform to find out the point on the waveform where the relay has operated

Salient features of Dynamic test kit

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Setup of Dynamic test kit

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Benefits of using Simulation Tool

The disturbance records captured by the numerical relays and fault disturbance recorders can be used to simulate the disturbance and play the same on various types of devices

Fault library can be maintained and used for evaluating / accepting new relay products

Reduction in Cycle Time for acceptance testing of new relays

Analysis of the protection performance will help in improving the power system protection and maintaining grid stability

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Case Study – I: Mal-operation of Distance Relay

220 kV220 kV

Salsette

220 kV TPCL N/W

G

Tata Trombay

220 kV

MSETCL Trombay

Kalwa

3 Lines

MSEB N/W Bkrs Tripped

220 kV Trombay – Salsette line # 1 / 2 tripped by Distance Protection for fault in reverse direction

Details of the Line: Line Length – 23.98 km; CTR – 2000/1; PTR – 240 kV / 120 VLine Impedance: Z+/- = 1.457 + j 9.428; Zo = +j30.806

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Waveform captured by Disturbance Recorder during the fault

Waveform Produced by simulation tool for replaying on the relays

Case Study – I: Mal-operation of Distance Relay

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Protection Provided on Line – Main I (Distance), Main II (Distance) and Directional O/C relays

During the disturbance Main – II relay, which is of switched Distance relay type operated and Main I relay, which is of non-switched distance relay type did not operate

The Fault Disturbance Record captured is replayed on another type of non-switched relays and the relays found to be stable

Case Study – I: Mal-operation of Distance Relay

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Case Study – II: Non-operation of Under frequency Relay

Under frequency relays at receiving & Generating stations for Load shedding and Islanding Scheme

Under frequency relay of Islanding scheme at 110 kV Salsette R/S failed to operate during one of the System Disturbances. However, the fault got isolated by the operation of distance protection

Under frequency relay settings: Stage I: 47.6 Hz, 0.15 Sec

Stage II: 47.0 Hz, 0.2 Sec

During the disturbance, frequency dropped from 50.3 to 46.7 Hz and TPC system islanded from rest of the Grid

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Frequency TrendSystem islanding on 21/09/05 at 0958 hrs.

46

46.5

47

47.5

48

48.5

49

49.5

50

50.5

51

51.5

52

52.5

-12

-10

-8.5 -7

-5.5 -4

-2.4

-0.9

0.72

2.36

3.97

5.55 7.1

8.64

10.2

11.7

13.2

14.6

16.1

17.6

19.1

20.6

22.1

23.5 25

26.5 28

29.5 31

32.5 34

35.5 37

time (s)

Freq

uenc

y (Hz)

-df/dt = 2.5 Hz/s

df/dt = 0.45 Hz/s

2.43s

frequency plot during system disturbance

(recorded by frequency trend monitor)

Case Study – II: Non-operation of Under frequency Relay

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Waveform captured by Disturbance Recorder during the fault

Waveform Produced by simulation tool for replaying on the relays

Case Study – II: Non-operation of Under frequency Relay

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Under frequency relays was of static type self powered relay (Powered by PT Supply) with built-in U/V block at voltage below 70 % of rated voltage

Relay operation was getting inhibited due to under voltage condition on 110 kV bus during system disturbance

The Waveform was replayed on Numerical Relay on which U/V blocking can be set manually. Initially Numerical relay also didnot operate with U/V setting at 70 %. However, by lowering the U/V block setting, the relay operated correctly

Case Study – II: Non-operation of Under frequency Relay

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Conclusions

Numerical Protection relays of different makes, types and version can exhibit different behavior during abnormal power system condition. Conventional testing of the relays may not reveal thedeficiencies in the relays either due to inherent protection algorithm or due to incorrect adopted configuration / setting

The disturbance records captured by the numerical relays and fault disturbance recorders can be used to simulate the disturbance and play the same on various types of devices

The typical fault records can be preserved as fault library and used for evaluating new relay products

Analysis of the protection performance will help in improving the power system protection and hence contribute to grid reliability and stability