Simulation of Power System Faults for Protection Performance Analysis -Case Studies of Tata Power

Transcription

1 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 st February,

2 Overview 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 2

3 Introduction 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 by Numerical Protection Relay 3

4 Need for Simulation Tool 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 inherent protection algorithm or due to incorrect adopted configuration / setting 4

5 Methodology Adopted for PS Simulation 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 5

6 Salient features of Dynamic test kit 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 6

7 Setup of Dynamic test kit 7

8 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 8

9 Case Study I: Mal-operation of Distance Relay 220 kv 220 kv 220 kv G Salsette 220 kv TPCL N/W Kalwa 3 Lines MSETCL Trombay Tata Trombay MSEB N/W 9 Bkrs Tripped 220 kv Trombay Salsette line # 1 / 2 tripped by Distance Protection for fault in reverse direction Details of the Line: Line Length km; CTR 2000/1; PTR 240 kv / 120 V Line Impedance: Z+/- = j 9.428; Zo = +j30.806

10 Case Study I: Mal-operation of Distance Relay Waveform captured by Disturbance Recorder during the fault Waveform Produced by simulation tool for replaying on the relays 10

11 Case Study I: Mal-operation of Distance Relay 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 nonswitched 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 11

12 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 12

13 Case Study II: Non-operation of Under frequency Relay Frequency Trend System islanding on 21/09/05 at 0958 hrs Frequency(Hz) df/dt = 2.5 Hz/s df/dt = 0.45 Hz/s s time (s) frequency plot during system disturbance (recorded by frequency trend monitor) 13

14 Case Study II: Non-operation of Under frequency Relay Waveform captured by Disturbance Recorder during the fault Waveform Produced by simulation tool for replaying on the relays 14

15 Case Study II: Non-operation of Under frequency Relay 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 did not operate with U/V setting at 70 %. However, by lowering the U/V block setting, the relay operated correctly 15

16 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 the deficiencies 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 16