Mailing list

1 GM , POSOCO, WRLDC, MIDC Area, Andheri (East), Mumbai-400 093.(MAH)

2 AGM (O&M), WRTS-II, PGCIL, HQ, 5th Floor, Vidyut Bhavan, Kareli Baug, Vadodara,-390 018 (GUJ)

3 AGM (O&M), WRTS-I, PGCIL, Sampriti Nagar, Nari Ring Road, Nagpur-440 026 (MAH)

4 DGM( E M), NTPC, Sipat Super Thermal Power Station, Sipat, Bilaspur- 495 450. (CHG)

5 DGM(O S), NTPC, WRHQ-I, Samrudhhi Venture Park, 2nd Floor, MIDC Area, Andheri (East), Mumbai-400 093 (MAH).

6 DGM(O S), NTPC, WRHQ-I, Samrudhhi Venture Park, 2nd Floor, MIDC Area, Andheri (East), Mumbai-400 093 (MAH).

7 Director (Grid Mgt.) Grid Management Direct., Central Electricity Authority, Sewa Bhawan, R K Puram, New Delhi-110 066.

8 Regional Executive Director (WR-I), NTPC Ltd, WRHQ-I, Samrudhhi Venture Park, 2nd Floor, MIDC Area, Andheri (East), Mumbai-400 093. (MAH)

9 Regional Executive Director (WR-II), NTPC Ltd., WRHQ-II, Magneto Conclave,3rd floor,Lobhandi, G E Road, NH-6, Raipur-492991 (CHG)

10

ANNEXURE-I

1 Shri S.S. Sen GM , NTPC, Mumbai

2 Shri S. Paul AGM (OS-WR-1), NTPC, Mumbai

3 Shri E.P.Rao AGM (Comml.), NTPC, Mumbai

4 Shri Harinath AGM (OS), NTPC, Mumbai

5 Shri Anil Nautiyal AGM (Comml.-WR-I), NTPC

6 Shri Parmanand Nagrj DGM (OS), NTPC, Mumbai

7 Shri Oswald Menezes DGM (OS),WR-1, NTPC

8 Shri Somes Bandyopadhyay AGM (OS-CC), EOC, NTPC

9 Shri Arun Kumar Sharma Dy. Mgr. (PEE), EOC, NTPC

10 Shri D. Roy Chowdhary AGM (Elect.),WR-II, NTPC

11 Shri P.K. Chakraborty AGM (EMD), NTPC, Sipat

12 Shri V.K. Khare GM ( O & M), POWERGRID

13 Shri Naveen Srivastava DGM, POWERGRID

14 Shri P. Pentayya G M, WRLDC, POSOCO

15 Shri V K Shrivastava AGM,WRLDC, POSOCO

16 Shri V.A. Murty DGM,WRLDC, POSOCO

17 Smt. Pushpa Seshadri CM,WRLDC, POSOCO

18 Shri S D Taksande Member Secretary I/C

19 Shri Satyanarayan S. Superintending Engineer (O&S)

20 Shri M M Dhakate Superintending Engineer (P)

21 Shri P D Lone Executive Engineer (Comml)

NTPC Ltd. (National Thermal Power Corporation Limited)

PGCIL (Power Grid Corporation of India Limited)

LIST OF PARTICIPANTS

Meeting regading Sipat STPS occurrence held on 21st September 2012 at NTPC office,Mumbai.

POSOCO ,WRLDC (Western Regional Load Dispatch Centre)

WRPC (Western Regional Power Committee)

1

Report of the Grid Disturbance at NTPC Sipat on 14.09.2012 at 1834 hrs

1.0 Introduction:

On 14.09.2012 at NTPC Sipat STPS, there was a occurence resulting in a total loss of

generation of the order of 2100-2300 MW at Sipat STPS. A meeting amongst WRPC,

WRLDC, NTPC, PGCIL was held on 21.09.2012 at NTPC office Mumbai to analyze the

occurrence and suggest remedial measures to prevent recurrence of the same.

List of participants is enclosed at Annexure-1.

2.0 Prefault Conditions:

The antecedent conditions (at 18:57:30 Hrs) to the incident are given under:- 1. NEW Grid Frequency: 49.921Hz. 2. WR Demand Catered: 29530 (Approximately.) 3. Net Inter Regional Export: 2994 MW Constituent-wise generation and demand details prior to the event (As per WRLDC SCADA data) at 18:57:30 Hrs:

WR Constituents

Demand(in MW)

Generation(in MW) Thermal & Gas Hydro Nuclear Wind Solar

Gujarat 8379 4962 399 - 947 0Maharashtra 12751 6307 1446 - N/A N/AMadhya Pradesh

4753 1367 1653 - - -

Chhattisgarh 2517 1756 120 - - - Goa 300 0 0 - - - DD 233 0 0 - - - DNH 597 0 0 - - - ISGS -- 11094 1238 1235 - - Total 29530 25486 4856 1235 947 0

*As per WRLDC SCADA data.

Power flow on major lines/ICT in the area (prior to the incident) at18:57:30 Hrs

Sl. No. Name of the line/ICT Power Flow(in MW)*1 765 kV Sipat-Bilaspur I 932 2 765 kV Sipat-Bilaspur II 890 3 765 kV Bilaspur-Seoni I 981 4 765 kV Bilaspur-Seoni II 982 6 765 kV Seoni –Wardha II 1205 7 400 kV Sipat-Ranchi II 204 8 400 kV Sipat-Raipur I 66 9 400 kV Sipat-Raipur II 66 10 400 kV ACBIL-Bilaspur I 92

2

11 400 kV ACBIL-Bilaspur II 92 12 400 kV Seoni –Khandwa I 346 13 400 kV Seoni-Khandwa II 350 14 400 kV Seoni-Satpura 298 15 400 kV Seoni- Bhilai -324

*As per WRLDC SCADA data. Generating Units’ status(prior to the incident) at 18:57:30 Hrs

Sl. No.

Name of the Generating Unit

Installed Capacity(MW)

Actual Generation (in MW) *

1 Sipat Unit 1 660 626 2 Sipat Unit 3 660 628 3 Sipat Unit 4 500 470 4 Sipat Unit 5 500 474 5 ACBIL Unit 1 135 92 6 ACBIL Unit 2 135 92

*As per WRLDC SCADA data.

2.1 Major line, ICTs and units under outages :

1 765 kV Seoni- Wardha-I2 765 kV Seoni-Bina 3 400 kV Sipat-Ranchi-I4 Sipat Unit 2 -660 MW

2.2 Initiating Cause & Sequence of Events :

The bus and line arrangement at NTPC Sipat is shown in Figure-1.1 & 1.2 (before the

incident) and Figure-2.1 & 2.2 (during the incident).

Sl No Event Time

1 DT Receive, CB open status of all poles. 18.57.38 Hrs

2 Circuitry fault alarm in bus bar. 18.57.52 Hrs

3 1852 SF6 Alarm, SF6 lock out, Fault incident. 18.58.05 Hrs

4 400KV Ranchi-2 Trip on reactor REF. 18.58.05 Hrs

5 400KV Raipur-1&2 trip on Z2 from remote end. 18.58.06 Hrs

6 765KV Bharari-2 trip on reactor EF. 18.58.06 Hrs

7 765/400KV ICT trip on backup EF. 18.58.07 Hrs

8 Tripping of all generating Units From 18.58 Hrs to 19.02 Hrs

9 765KV Bharari-1 Trip on Over Voltage. 19.02.28 Hrs.Red-Closed condition; Green-Open condition

3

Figure-1.1

-----------------------------------------------------------------------------------------------------------------

Figure-1.2

4

Figure-2.1

-----------------------------------------------------------------------------------------------------------------

Figure-2.2

5

-----------------------------------------------------------------------------------------------------------------

Description : Ranchi Line-1 reactor was kept charged as Bus reactor since 08.09.12 and the line was open from both ends. On 14th September 2012, at 18.58 hrs, Ranchi Line main breaker 1852 tripped on receipt of spurious direct trip (DT) from remote end for opening of main breaker at Sipat. As per event recorder all the three poles got opened. After 13 seconds Circuitry fault appeared in the bus bar protection. Breaker 1852- Y phase blasted after another 12 seconds as evident by appearance of SF6 low alarm and SF6 lock out in the event logger. Subsequent to blasting of 1852 Y phase breaker, following feeders got tripped in sequence:

1. 400 KV Ranchi-2 line tripped at Sipat end on reactor REF protection. 2. 400KV Raipur-1&2 tripped at remote end on Zone-2 protection. 3. 765KV Bharari-2 tripped on reactor E/F protection at Sipat end. 4. 765/400 KV ICT-1&2 tripped on backup Earth Fault protection.

After tripping of both ICT-1&2 and all 400KV lines, both 400 KV bus became dead. This in turn caused loss of 132 KV System and loss of station supply. Because of fault current in 400 kV 1852 Y Phase CB, system voltage got dipped resulting dip in 11KV bus in all running units. As a result HT drives in all running tripped on under voltage leading to disturbance and tripping of units as below.

1. 18.58.28 Hrs. Unit-5 tripped on loss of fuel. 2. 18.58.33 Hrs. Unit-3 tripped on excitation failure.

6

3. 18.59.48 Hrs. Unit-1 tripped on eco flow low. 4. 19.02.23 Hrs. Unit-4 tripped on low vacuum.

(Unit-2 was out prior to the occurrence)

After tripping of all units at 19.02.28 over voltage protection operated at Bharari (Bilaspur) end and 765KV Bharari-1(Bilaspur) line tripped on receipt of direct trip.

The members discussed the occurrence and tried to answer following queries :

2.2.1 Why DT is received when the line was open at both ends?

2.2.2 Why breaker failed to operate and blasted ?

2.2.3 Why LBB at Sipat did not operate?

2.2.4 Why bus bar protection did not operate?

2.2.5 Why Ranchi-II tripped on REF ?

2.2.6 Why Ranchi-II did not tripped on Zone-II ?

2.2.7 Why 765 kV Sipat- Bharari-1(Bilaspur) operated on REF when there was no reactor

commissioned?

2.2.8 Why 765/400 kV ICT-1&2 tripped on back up E/F ?

2.2.9 Why all units at Sipat tripped ?

2.2.10 Other issues

2.2.1 The issue of DT receipt at Sipat end of Ranchi line-II was discussed and it was found

that at Sipat there were three flags received while at Ranchi end of the line-II there was no

logging of DT sent. The time difference between the flags was 300 ms. Therefore

Committee came to conclusion that multiple DT receipt indication was clear case of

chattering and maloperation of the relay. PGCIL clarified that there was no work going on at

Ranchi at the time of occurrence.

Secondly, it was found that there was no interlock of isolator provided in the DT circuit and

the only way to bypass DT is to switch off the PLCC. PGCIL representative clarified that as

per guidelines, when reactor is connected as bus reactor, PLCC is required to be switched off.

Sipat representative clarified that there cannot be interlock of isolator provided in the circuit

for automatic blocking of DT. However, it can be done through manual intervention as

manual intervention is necessary while taking line reactor into service as bus reactor.

Committee recommended that in the event of using line reactor as bus reactor PLCC

should be switched off at both ends.

2.2.2 The issue of failure of breaker to operate and subsequently blasting was discussed and it

was found that PIR was heated and caught fire. As per design PIR is inserted just before

7

closing of breaker contact and supposed to be opened after closing of main contact of the

breaker. However, as per the event log PIR was not opened and fault current (reactor current

only as there was no fault) continued through PIR causing heating and result into fire.

Breaker pole failed to open and arcing of low current which lasted for more than 10 seconds

lead to blasting of main breaker. Report from Areva is awaited.

Committee also discussed the provision of Control Switch Relay(CSR) which is not been

installed at Sipat which is meant for reducing stress on breaker while closing of the breaker.

PGCIL representative intimated that experiments of CSR is still going on and nobody is

confident whether to use it or not. Committee however felt that had CSR been used, the

stresses on the breaker could have been minimised and saved the occurrence. Also, in

the event of non-availability of CSR, frequent switching of reactor as bus reactor should

be minimised to reduce stress on breaker.

2.2.3 The issue of non-operation of LBB was discussed and it was found that for operation of

LBB three conditions viz. command for trip, actual current more than set current value(200

mA in this case) and time delay of more than 200 ms is required however, in the incidence the

actual current being a reactor current only was not sufficient to trigger the LBB. Also,

phenomenon of nature of arc in the breaker pole cannot be visualised. As per event logger

Breaker took almost 27 seconds to blast since it received open command. Committee opined

that the non-operation of LBB is in order.

2.2.4 The issue of non-operation of bus bar protection was discussed and it was found that

low fault current during arcing which persisted for more than 10 sec, was sensed by the

current circuit supervision of bus bar differential protection and blocked the bus-bar

protection scheme as per design feature of scheme itself. NTPC Sipat representative intimated

that for blocking of CT supervision circuit two conditions viz. current more than 50 A and

time of 5 second is essential and both Zone-I and Zone-II bus protection were blocked.

Committee opined that the non-operation of bus-bar protection is in order.

2.2.5 The issue of Ranchi-II operation on REF was discussed and wherein NTPC

representative stated that there is 145 kV LA in between NGR and reactor star point which

had operated spuriously many times previously and hence failure of LA is suspected.

However, this can only be confirmed after megger, leakage current and tan delta test are

carried out on LA. NTPC further clarified that this LA is already planned for replacement.

PGCIL representative offered to carry out necessary test on the above LA.

2.2.6 The issue regarding non-tripping of Ranchi-II on Zone-II was discussed and it was

intimated by PGCIL that zone-II protection at Ranchi-II might have picked up but as the fast

8

operation of REF protection than zone-II the Ranchi-II line did not tripped at Ranchi. PGCIL

representative agreed for submitting the details for the same in due course.

2.2.7 The issue regarding operation of REF protection on 765 kV Sipat- Bharari -1(Bilaspur)

when there was no reactor installed on the said line was discussed and it was found that it is a

clear mal-operation. NTPC representative intimated that CT cables leakage or grounding or

multiple earthing might be the cause for operation of REF protection. Day before also

Reactor Oil Temperature high protection operated on this line. Committee opined that all

reactor related protections on this line to be kept off/bypassed till reactor is installed and all

above cited tests for cables are carried out. Sipat representative intimated that the reactor

related protection is already switched off after the incidence.

2.2.8 The issue regarding operation back up E/F of ICT-1&2 was discussed and it was

intimated that Sipat representative that there was no additional protection for ICTs and back

up E/F timings are DMT with 1.8 Seconds. Committee recommended that the

characteristics and timing of the back up E/F protection should be changed to IDMT on

both sides of ICTs.

2.2.9 The issue of tripping of all units at Sipat were discussed wherein it was clarified by

NTPC representative that 24/11 kV unit bus voltage dipped to 8 kV thereby tripping of all HT

drives on undervoltage and subsequent tripping of Units. Committee felt that 24/11 kV Unit

bus voltage might have been dipped due to tripping of 765 kV Sipat-Bilaspur II on L/R earth

fault protection or increase in fault current in 400 kV later on which was sensed by 765kV

Sipat bus which occurred almost simultaneously.

Due to dip in voltage at 11 kV unit bus all HT drives in all running tripped on under voltage leading to disturbance and tripping of units as below :

1. 18.58.28 Hrs. Unit-5 tripped on loss of fuel. 2. 18.58.33 Hrs. Unit-3 tripped on excitation failure. 3. 18.59.48 Hrs. Unit-1 tripped on eco flow low. 4. 19.02.23 Hrs. Unit-4 tripped on low vacuum.

It was also intimated that the unit auxiliaries tripped before tripping of ICTs. Committee

recommended that the timing delay of the 11 kV should be revised to 2-3 seconds after

necessary studies by NTPC.

2.2.10 Due to tripping of Units, high voltage appeared across the connected Substations

leading to tripping of various lines on Over-Voltage from Seoni and Bilaspur. ACBIL units

also tripped due to tripping of evacuation lines i.e. 400 kV ACBIL-Bilaspur I & II.

9

Committee also observed that tripping of 400KV Sipat-Raipur-1&2 on Z2 from remote end

& 765KV Sipat-Bharari-1on Over Voltage was in order.

2.3 Other issues & Recommendations (in addition to above)

• GM, WRLDC intimated the PMUs should be installed at prime locations such as

KSTPS, VSTPS and SSTPS to get all the data in case of any occurrence. WRLDC

also offered to temporarily provide the PMUs to NTPC till PMUs are installed in

UTRDMS scheme at these stations by POWERGRID.

• GM, WRLDC intimated that 3x80 MVAR line reactors at Sipat end of 765 Sipat-

Bilaspur-I&II are kept out after the original lines 765 kV Sipat-Seoni were made

LILO at 765 kV Bilaspur. It is observed from the studies that taking in of these

reactors would help in controlling the volatages at 765 kV Sipat, Bilaspur and Seoni

as well as 400 kV voltages at Sipat and Seoni buses. Before taking the reactors into

service, oil testing and all the protection testing of reactors shall be ensured by NTPC

and charging code should be taken from WRLDC.

• GM, WRLDC intimated that the issue of tripping of 400 kV Bhilai-Seoni on high

voltage on 14.09.2012 which caused heavy loading on 400 kV Bhilai-Koradi and the

effect of removal of LILO at Seoni by opening the breaker at Seoni of Bhilai-Satpura

is not recommended as it will increase the risks in operating a very long line (400 kV

Bhilai-Satpura-385 kms) and also increase the 400 kV voltage at Seoni.

• Committee agreeing with the views expressed by GM, WRLDC suggested following

additional recommendations :

1. Over voltage trip setting at Seoni end can be increased to 110%.

2. Manual control of backing down generation at JPL, Lanco etc.

3. Raise generation in Maharashtra in Koyna area

4. Proposal for one additional line from Sipat to Korba pooling station

5. Automatic control through new SPS

10

2.4 Exhibits

2.4.1 Photographs of failed equipments

11

12

13

2.4.2 Event logger screen

14

15

2.4.3 DR charts

Ranchi-2 React REF

Raipur-2 Z2 trip at Raipur

16

Raipur-1 Z2 trip at Raipur

Bharari-2 Reactor EF

17

765/400KV ICT Dir EF

Bharari-1 OV at Bharari

18

11KV 5UA BUS VOLTAGE TREND

-----------------------------------------------------------------------------------------------------------------

2.5 Maintenance history of 1852 Breaker

Ranchi-1 Bay No-18 commissioned on dtd-31/12/2008 with all recommended tests and

proper commissioning procedures.

ANNUAL MAINTENCE REPORT: Date-16/08/2009

• breaker pole contact resistance-R-104 µohm,Y-88.3 µohm,B-82µohm

• opening time-TC1-R-22.4ms,Y-21.4 ms,B-22.2 ms

• closing time-R-115.2 ms,Y-114.2 ms,B-113 ms

• CO Time-R-166 ms,Y-163 ms,B-161.3 ms

• SF6 pressure-7.7bar

• No SF6 leakage observed in leak detector

• Counter reading after test completion:313

ANNUAL MAINTENCE REPORT: Date-09/03/2011

• breaker pole contact resistance-R-104.1 µohm Y-88.2 µohm,B-87.7µohm

• opening time-TC1-R-22.4,Y-21.8,B-22.4 ms

• opening time-TC2-R-22.4,Y-21.8,B-22.6 ms

19

• closing time-R-116 ms,Y-115.0 ms,B-112.4 ms

• CO Time-R-165.8ms,Y-164.4 ms,B-164 ms

• SF6 pressure-7.6bar

• No SF6 leakage observed in leak detector

• Date-06/01/2012

• breaker pole contact resistance-R-101.6 µohm,Y-87.3 µohm,B-88.6 µohm

• opening time-TC1-R-22.4ms,Y-21.6,B-22.6 ms

• opening time-TC2-R-22.4ms,Y-21.8,B-22.4 ms

• closing time-R-114ms,Y-115.0ms,B-112.6 ms

• CO Time-R-164ms,Y-164.2,B-163.4 ms

• SF6 pressure-7.5bar

• No SF6 leakage observed in leak detector

• Counter reading after test completion:366

BREAKER DAILY/MONTHLY MONITORING ACTIVITY INCLUDES:

• Daily SF6 gas pressure monitoring and physical checking:

Monthly Thermo graphy: Date: 08.07.12

– Isolator A side clamp temp:28.3 deg cel

– Capacitor stack:30.6deg cel

– CT side clamp: 27.6 deg cel.

Monthly Thermo graphy:Date: 12.09.12

– Isolator A side clamp temp:32.9 deg cel

– Capacitor stack:31.7 deg cel

– CT side clamp: 31.9 deg cel.