Minutes of the Meetings of PSAG-13 held at Raichur (PG) and RTPS in connection with the multiple tripping that occurred there on 9th March and 11th April 2015

A team of Officials from SRPC, SRLDC, PGCIL (SR-I), KPCL, KPTCL visited Raichur (PG) and RTPS during 22-23 April, 2015 to analyze the cause of multiple trippings that occurred there on 09.03.2015 & 11.04.2015. The list of participants is given at Annexure-I. The single line diagrams of Raichur (PG) and RTPS are given at Annexure-II.

Tripping at 6:36 hrs on 09-03-2015

During this event, 400kV Raichur TPS-Raichur(PG) line-1&2, 400kV Raichur-Mahboobnagar, Unit#7 at RTPS tripped during the incident.

As informed by Powergrid representative, B-phase(of RYB) to earth fault had occurred at 6:36:18 hrs in 400kV Raichur TPS-Raichur line-1 and fault was near to RTPS end. Distance protection at Raichur (PG) sensed the fault in zone-2 and line auto reclosed from Raichur(PG) end on carrier aided protection. Breaker at RTPS end did not auto-reclose and all three poles of breaker got tripped.

A second fault i.e a Y-B phase fault occurred at 06:36:31 hrs in 400kV Raichur-RTPS line-1. Breaker of line-1 was in tripped condition at RTPS end and breaker was in closed position at Raichur(PG) after 1st fault. Distance protection at Raichur(PG) sensed fault in zone-2 and tripped in zone-2 time as RTPS end did not sense the fault due to breaker open condition at RTPS i.e. fault could not be cleared immediately with carrier aided protection. 400kV Raichur TPS-Raichur line-2 tripped at Raichur TPS end on zone-2 start/ SOTF indication on distance relay (Ir-0.69 kA, Iy-6.32kA, Ib-2.2kA, Va 203kV, Vb 132kV, Vb – 299kV). 400 kV Raichur-Mahboobnagar line tripped from Mahboobnagar end due to suspected mal-operation of distance protection (Main-2 distance relay).

RTPS

1

Raichur(PG)

Z-1 (SOTF)

Z-2 (Bn)

2

First fault: 6:36:18 hrs

1

Z-2 (SOTF)

Z-2 (Y-B)

2

Veltoor (Mehabubnagar)

G7 GT

distance protection (Bn)

REF of GT

Second fault: 6:36:31 hrs

B

Y-B A/R

Raichur(PG) RTPS

Unit-7 at RTPS tripped on operation of restricted earth fault protection (REF) protection. It was informed by KPCL representatives that REF protection for GT of Unit-7 maloperated during 1st fault in 400kV Raichur-RTPS line-1.

Observations and recommendations of committee 1. It was observed that Raichur PG-1 line did not auto reclose from RTPS end during occurrence

of 1st fault. It was informed by POWERGRID that relay gave a 3 phase trip as CB status of B-pole breaker was not available to distance relay due to problem in auxiliary contact of circuit breaker. The matter was taken up with OEM of relay which had confirmed the same after offline simulation of the event. Presently the status of breaker to relay has been made continuously high by shorting of faulty auxiliary contact. POWERGRID had informed that the auxiliary contact block for breaker of Raichur PG-1&2 lines at RTPS will be replaced on 29 April 2015.

2. 400kV Raichur PG-2 line tripped from RTPS end on Zone-2 start with SOTF during occurrence of 2nd fault in 400kV Raichur PG-1 line. It was observed by committee that the relay was reading 127% for the fault at nearly 190% of Line length as fault was near 2nd tower from gantry of Line-1 at RTPS. Present implemented zone settings at RTPS for Raichur PG -1&2 lines are Zone-1 : 2.48ohm, Zone-2 : 4.65 ohm with 500ms, Zone-3 : 20.95 ohm with 1.5sec, Zone-rev : 0.62 ohm with 1.6 Sec, CT ratio 2000/1A. Committee had recommended referring the event to OEM as relay at RTPS over-reached in zone-2 and sensed the fault near to RTPS end. POWERGRID had asked 1 month time to rectify the same.

3. Committee had suggested considering implementation of differential protection for 400kV Raichur PG-1&2 lines as they are short lines and important as Raichur PG station is connected to western grid. Any unwanted outage of these lines may affect the security of national grid. POWERGRID informed that the matter will be referred to Corporate O.S & Engineering of POWERGRID for their reviews and recommendations.

4. POWERGRID had informed that at Mehaboobnagar end, the Main-2 distance relay (ABB-REL 316) of RTPS-Mehaboobnagar line will be replaced within 2 to 3 days’ time. It was also informed that the PLCC panels of the line would be replaced at both ends.

5. Committee checked the REF scheme for GT of Unit-7. REF scheme is provided for HV side of GT. KPCL informed that 250MVA GT of Unit-7 was replaced by 315MVA during November-2013. The implemented current setting for REF is 0.1 Ampere as suggested by OEM. KPCL had informed that REF scheme will be checked during next shut down. D.R is not available to validate the pickup current of REF relay.

Tripping at 18:04 hrs on 11-04-2015

400kV Raichur(PG)-Gooty line-2, 400kV Raichur TPS-Raichur(PG) line-1&2, 400kV Raichur-Mahboobnagar, Unit#5 at RTPS, 765kV Raichur-Kurnool line tripped during the incident.

POWERGRID, KPCL and KPTCL representatives briefed the committee about the above tripping:

1. 400kV Raichur-BTPS line tripped at 17:52 hrs due to B-phase fault. Line did not auto reclose and tripped from both ends. It was informed by KPCL that Auto-reclose is implemented at RTPS end and not commissioned at BTPS. It was informed that line did not auto reclose due to auto reclose block command in distance relay which was due to fuse fail start/on condition.

2. 765kV Raichur-Kurnool tripped due Y-B fault in line at 18:04:05 hrs. Same was validated with DR of line.

3. As per FIR from POWERGRID, at 18:04:17 hrs, R-phase lightening arrestor of 400kV RaichurGooty line-2 failed at Gooty end. Line tripped at both ends due to operation of distance protection. From Gooty end D.R and PMU plots, it was observed that line tried to auto reclose and as it was permanent fault due to LA failure, there was a 3 phase trip.

4. 4. 400kV Raichur(PG)-Raichur TPS line-1&2 tripped on operation of overvoltage protection. The same has to be validated with D.R of respective lines. From PMU data of gooty end, it was observed that the voltage was well below the over voltage stage-1 settings. Hence this

Kurnool

Raichur (PG)

765 kV 400 kV

1

2 Gooty (PG)

Swing of conductors

LA failure (R)

O/V St.2 trip

U5

GT

GT Class B trip

Mehabubnagar BTPS

Z1 (B) Z1 (R)

RTPS

Z1 (Y-B)

1 17:52

2 18:04:05

3 18:04:17

4

5

6 18:07

needs further investigation. Both line-1&2 were holding from RTPS end. The reason for nontransmission of direct trip to other end needs further investigation.

5. 400 kV Raichur-Mahboobnagar line tripped from Mahboobnagar end due to suspected mal-operation of distance protection. Main-2 distance protection had sensed fault in R-phase, Zone-1.

6. Unit#5 at RTPS tripped at 18:05 hrs due to operation of Class-B master trip relay. It was informed that no class-B trip relay had initiated trip to the Master relay.

7. 220kV Sedam-Tandur and 220kV Regulapadu-Alipur lines had tripped at 18:12 hrs and 18:13 hrs due to transient fault in line. Auto reclose provision is not available for these lines.

Observations and recommendations of committee 1. The tripping of 765kV Raichur-Kurnool line was in order. Shutdown of line was taken on 17th

April 2015 to measure the sag in line where conductors were changing from horizontal to vertical configuration on towers before the gantry tower at Raichur (PG). The Y-phase to B phase clearances were found to be less when compared to the R phase to Y phase clearances. The sag was adjusted.

2. 400kV Raichur-Gooty line-2 tripped due to failure of R-phase L.A at Raichur(PG). It was informed that L.A broke down due to turbulent wind. The line protection tried auto reclose once and gave a 3 phase trip due to permanent fault. Powergrid was asked to submit the equipment failure report to CEA.

3. 400kV RTPS-Raichur PG-1&2 tripped on operation of overvoltage stage-2 protection at Raichur(PG). Committee observed the D.R of 400kV RTPS-Raichur PG line-1&2 and Gooty line-1. The setting of overvoltage stage-2 is 149% i.e. 345kV phase to earth with 100ms delay. It was observed that stage-2 overvoltage protection of RTPS-Raichur PG-1&2 got operated during auto reclose attempt by 400kV Raichur-Gooty line-2. Following was observed from D.R at Raichur(PG) end Line R to earth Y to earth B to earth RTPS-Raichur PG-1 126kV 252kV 394kV RTPS-Raichur PG-2 109kV 226kV 369kV Raichur-Gooty-1 138kV 332kV 111kV Committee had asked to monitor/check the transient behaviour of CVT and refer same to OEM of CVT. 400kV RTPS-Raichur PG-1&2, 400kV Raichur-Gooty-1&2 are having same make CVT’s. POWERGRID was asked to investigate reason for such high over voltage (phase to earth) on healthy phases during R-phase fault in 400kV Raichur-Gooty line-2. It was observed that Direct trip was not sent to remote end when over-voltage protection had operated at Raichur(PG) end. It was informed by POWEGRID and KPCL that Channel-1&2 of both 400kV RTPS-Raichur PG-1&2 were having receive(Rx) fail alarm at RTPS end. It was informed by KPCL that receive(Rx) fail alarm was persistent in PLCC Channel-1&2 of line-2 from couple of days before occurrence of fault. PLCC Channel-1&2 fail alarm for line-1

appeared before tripping of 400kV RTPS-Raichur PG-1&2 lines. POWERGRID had informed that frequency drift was being frequently observed in PLCC panels of RTPS-Raichur PG-1&2 lines, inspite of repeated tuning. Committee had recommended to replace the PLCC panels at both ends at the earliest. At Gooty end, Time synchronization of Gooty-1 feeder D.R was found to be out of sync with GPS. Same was asked to be rectified.

4. For non-auto-reclosing of RTPS-BTPS line, it was informed that line did not auto reclose due to auto reclose block command in distance relay at RTPS end which was due to fuse fail start/on condition. Committee had asked to take up with OEM and check the configuration for auto reclose in relay as block for auto reclose should not initiate with fuse fail On/ start. KPCL had informed that the same will be checked and feedback regarding remedial action will be given at the earliest. Committee had asked to implement auto reclose scheme at BTPS end at the earliest. KPCL informed that they are taking up with OEM for the same. Also Committee had asked that KPCL may ensure that auto-reclose is implemented when 400kV RTPS-BTPS line is LILO’d at Yeramarus TPS. Committee had proposed for differential protection for 400kV RTPS-Yeramarus-BTPS section. KPCL had informed that the LILO at Yeramarus TPS is temporary and hence distance protection will be implemented with auto-reclose.

5. For tripping of Unit-5 on operation of class-B protection it was observed that no class-B initiation relay had operated as seen from sequence of events. The protection DC was checked for earth fault. The DC source-1&2 were found to be in-order. Committee asked to simulate the sequence of event for relays which trigger Class-B master relay and also check up the pick-up voltage of Class-B Master trip relay. KPCL had informed that such tripping of master trip relay without initiation from Class B relays was observed for the 1st time.

6. 220kV Sedam-Tandur line tripped at sedam end only on operation of backup protection. It was informed that the back up relay had mal-operated. Committee had asked to check the relay and if required replace the same.

7. 220kV Alipur-Regulapadu line tripped at Alipur end only on operation of distance protection. It was informed that the line is radial from Alipur end. Committee had asked to submit the D.R for the event to validate the tripping.

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Annexure-I

Annexure-I

Annexure-II

SHAHPUR-1

SHAHPUR-2