SOUTHERN REGIONAL POWER COMMITTEE BENGALURU

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4 SOUTHERN REGIONAL POWER COMMITTEE BENGALURU Minutes of the 49 th Meeting of Protection Coordination Sub-Committee (PCSC 49) of SRPC held on Introduction The 49 th meeting of Protection Coordination Sub-Committee (PCSC-49) was held on 30 th November, 2015 in Mangalore, Karnataka. The list of participants is enclosed at Annexure-I. Sh. R.C. Bhat, Station Head, UPCL extended warm welcome to Sh. S.R. Bhat, Member Secretary (MS), SRPC, Sh. P. Raghuram, Executive Director (ED), SRLDC, and other Officials from State & Private Power Utilities, SRLDC & SRPC. He thanked MS, SRPC for giving them the opportunity to host PCSC meeting, and added that Team UPCL had put in all efforts to ensure a comfortable and enjoyable stay for all participating members. Then, a presentation was given by UPCL team highlighting the achievements and road-map of Adani Group with specific focus on Power Sector. Sh. S.R.Bhat, Member Secretary (MS), SRPC thanked Adani UPCL management for the excellent hospitality, and all the due care they have taken in making arrangements for the smooth conduct of the meeting. He then welcomed the Members and Participants to the meeting and briefed them on the following points: Briefed the members on the proceedings of the third Grid Study Committee meeting held on 18 th November, 2015, wherein the Draft Report on Task-1 activities (Review of implementation of Enquiry Committee recommendations given consequent to Grid Disturbance in July, 2012) prepared by the Consultant (M/s Tractebel Engg.) was discussed. As the performance of the Southern Region according to the report was not very satisfactory, it was high-time Constituents make concerted efforts to resolve/ complete long-pending issues from their respective sides. The draft report was also circulated all SR-Constituents for comments, however PGCIL (SR-II), KPTCL and KSEB only responded. Informed the members that the Task-2 data (relating to 15 Stations identified from SR for audit-check by the Consultant) furnished by the respective Constituents had been forwarded to the Consultant through NLDC for scrutiny and analysis, and the actual audit of the Stations would commence shortly. In this regard, a meeting was also held (via VC) with NLDC and the Consultant on 24 th December, 2015 to discuss the modalities of protection audit, wherein it was decided that the concerned Constituent-owner of the Station would provide extracted relay settings (in pdf. format), if not already given to the Consultant, and the Consultant would in turn provide their recommended relay settings (based on the data already made available to them for each of the 15 stations) to the concerned Constituent-owner of the Station well before the actual protection audit is Minutes of the 49 th PCSC Meeting held on Page 1

5 undertaken for that particular Station. It was reasoned that by doing so, not only do the concerned Constituent/ Station personnel get an opportunity to peruse the to-be-revised settings, and prepare themselves for the protection audit, but it would also facilitate in finalizing the settings during actual protection audit. To start with, NLC TPS-II of NLC (Audit schedule: 4 th, 5 th & 7 th December, 2015) and Alamathy S/S of TANTRANSCO (Audit schedule: 9 th, 10 th & 11 th December, 2015) would be audited in the first round and the schedule for the other Stations would be intimated soon. He requested Constituents active cooperation in completing Task-2 activities to the satisfaction of all parties involved. Informed the members that the issue of implementation of Power-Swing protection philosophy as recommended by the Rama Krishna Committee would be discussed in the forthcoming meeting of National Power Committee (NPC), and requested to present their views when the issue is taken up for discussion later in the meeting. Reminded members of nearing dead-lines of time-extensions given to SR-Constituents by Hon ble CERC for completion of their respective Protection Audit Remarks (PAR). KPCL, KPTCL, TSTRANSCO were requested to approach CERC for extension of time-lines with proper facts. In this regard, KPTCL representative informed that their R&U proposal was approved during Appraisal Committee meeting held on and sent to CERC for further processing of the scheme as per PSDF disbursement procedure. Early sanctioning of PSDF grants from Monitoring Committee was awaited and thereafter LOI would be issued to the successful bidder M/s Alstom. The execution time finalized for completion of works related to 93 substations is 15 months from the date of award, since sub stations are scattered throughout the state and many works require planned outages. 26 numbers of audited substations are planned to take up in the first phase. However, as CERC, after hearing the petition filed by KSEB, TamilNadu in its Order dated , has reiterated the deadline for completion of the R&U project by KPTCL as which was requested by KPTCL in the affidavit filed during September 2014 and has also confirmed that no request for further extension of time would be considered, a decision has been taken at KPTCL management level to file a petition before CERC with all facts requesting for extension of time for execution of the project. Brought to members attention the obligation of fulfilling their requirements under Regulation 5.2 (r) of IEGC, as per which all Users, STU/ SLDC, and CTU are required to furnish for analysis purpose the relevant information relating to tripping events in their system along with Disturbance Recorder (DR) and Event Logger (EL) to SRLDC/ SRPC within 24-hrs of occurrence of the same. Though this issue was regularly brought to Constituents attention vide various SRLDC & SRPC (fort-nightly) letters, still data w.r.t. all events was either not being furnished or being made available with unacceptable delay of few weeks. Constituents were urged to strictly comply with Regulation 5.2 (r) of IEGC, and furnish the data in time. Minutes of the 49 th PCSC Meeting held on Page 2

6 Stressed upon the need to furnish remedial measures taken by the Constituents for the forced outage of the transmission elements incident to their respective systems in time as the same was also being monitored by the Office of Member (GO&D), CEA. Finally requested members active participation in the ensuing discussions so as to raise the quality standards to a new bar commensurate with the amazing ambience of Mangalore city as orchestrated by Adani UPCL Team. 2. Confirmation of the Minutes of the 48 th PCSC meeting held on SE (Protection), SRPC stated that the Minutes of the 48 th meeting of the PCSC had been circulated vide SRPC letter No. SRPC/SE-III/ PCSC-48/ 2015/ dated As no comments had been received from any of the Constituents, the Minutes of the 48 th meeting of PCSC were confirmed. 3. Details of Grid Disturbances (GD s), Grid Incidents (GI s), Line Trippings due to Auto-Reclose non-operation and PLCC mal- operation. The trippings due to GD s, GI s, Auto-Reclosure failure/ non-operation, and PLCC mal-operation that had occurred during the period October-November, 2015 were discussed in the Meeting. The deliberations and recommendations of the PCSC-forum are enclosed at Annexure II. In the meeting ED,SRLDC informed that SRLDC would be approaching Hon ble CERC for all the Grid Occurrences (GD s and GI s) which occurred due to abnormal delayed clearance. 4. Status of pending PCSC recommendations The status of implementation of pending PCSC recommendations was discussed in the meeting. The Constituents had been requested to kindly submit the status of their compliance latest by The updated status of the same as on is enclosed at Annexure III. 5. Remedial measures/ Action taken for the tripping incidents of the transmission elements under forced outage The tripping incidents of the transmission elements under forced outage for which the remedial measures/ actions taken still awaited were discussed in the meeting. The Constituents had regularly been kept apprised of the tripping events incident to their respective systems vide various SRPC mails. However, no replies have been received from APGENCO, TSTRANSCO during the period to : The Constituents have been requested to kindly furnish the remedial measures/ action taken in time so as to forward the same to Central Electricity Authority. The updated list of the same as on is enclosed at Annexure-IV. Minutes of the 49 th PCSC Meeting held on Page 3

7 6. Certificate for Healthiness of Batteries As per the MoP/ CEA direction given in pursuant to recommendations of the Enquiry Committee (NEW grid disturbance on 30 th & 31 st July, 2012), RPC s are required to obtain from their respective Constituents the monthly certificate for healthiness of batteries, installed at 220 KV and above voltage level Substations (for power supply to Relays, RTUs and PLCC equipment) and furnish the same to CEA/ MoP. With reference to above, the Constituents have been requested to submit the certificate on healthiness of batteries on monthly basis (i.e. status for a month may be sent by the 7 th day of the following month) to SRPC. The sought status for the month of October, 2015 has not been received from the following SR- Constituents: APTRANSCO, TSGENCO (Hydro), PED, MAPS, SEL, CEPL, TPCIL 7. NPCIL Agenda Items (i) Frequent tripping of 230 kv KKNPP-Tuticorin S/c line: 230 kv switchyard of KKNPP is connected to TN STU network through 2 circuits of 230 kv (one S/C each to Tuticorin and Nagercoil). These circuits are meant to provide "Off Site Power" to KKNPP. It has been observed that 230 kv KKNPP-TTPS line has been tripping very frequently on Zone-2 protection. As frequent tripping of the line degrades the reliability of "Grid supply" and loss of the same at 230 kv may affect the stability of nuclear units, TANTRANSCO has been requested to present action taken to ensure requisite stability. In this regard, Action Taken Report furnished by TANTRANSCO vide their letter dated (copy enclosed at Annexure-V) was discussed and noted that requisite action has been initiated/ taken by TANTRNSCO to address the concerns raised by KKNPP. (ii) Outage of Units -1&2 at MAPS due to the loss of evacuation lines on 9 th November, 2015 On , MAPS Unit -1&2 were generating 215 MW and 172 MW respectively with three 230 kv lines in service (D/C to SP Koil Station and S/C to Acharapakkam Station). 230 kv MAPS- Arni line had tripped on previous day at 18:35 hrs. On next day ( ) starting from 08:22 hrs to 09:33 hrs, the cascade tripping of these 3 lines resulted in the outage of both the units. The issue was discussed in the meeting. The deliberations and recommendations of PCSC forum are given at Grid Disturbance I.5 in Annexure-II. 8. Power Swing Protection Philosophy The Power swing protection philosophy as recommended by the Ramakrishna Committee (Task Force on Power System Analysis under Contingencies) [copy given at Annexure-VI] was discussed in the meeting. It is observed that while PGCIL, NTPC, NPCIL, NLC, and State Utilities of Karnataka, Kerala are in line with Task force recommendations in so far as unblocking it Zone-1 and blocking it in other zones, the State Utilities of Andhra Pradesh (AP), Telangana (TS), and TamilNadu (TN) are found to be blocking it in all Zones. Minutes of the 49 th PCSC Meeting held on Page 4

8 In this regard, it was agreed in the meeting that the matter would be favorably looked into by the above Constituents (of AP, TS & TN) and they would revert with their views after discussing with their respective managements. 9. Network configuration changes As per the information furnished by SR-Constituents to the OCC forum in their 113 th meeting held on (Minutes circulated on ), the following network configuration changes (additions/ deletions/ modifications of transmission elements) took place in the southern grid during the month of October, COD 220 kv Appayyadorapalem (ADR Palem) in Vizianagaram district was commissioned on by APTRANSCO 220/132 kv Miyapur S/s of 1x160 MVA Transformer Capacity was augmented to 2x160 MVA Transformer Capacity on by TSTRANSCO. 220 KV D/C XLPE UG Cable from 220 kv Moulali SS to 220 KV GIS at Osmania University in Hyderabad of ckm was commissioned on by TSTRANSCO. 220 KV line on Narrow Based Multi Circuit Towers with 4 Circuits for LILO of both Circuits of Dindi - Chandrayangutta 220 KV D/C Line to the proposed 220 kv SS, Bonguloor of ckm 2 was Commissioned on by TSTRANSCO. LILO of 220kV Ramagundam- Mandamarry circuit-i to 220/6.6kV LI SS Murmur in Karimnagar district of 3.9 ckm was commissioned on by TSTRANSCO. 220 KV 2nd ckt stringing from 220 KV RSS 220 KV Mandamarry (34 KM) in Karimnagar of 34 ckm was commissioned by by TSTRANSCO. LILO of 220kV Ogulapur- Durshed to 220/6.6kV LI SS Bommakal in Karimnagar district of ckm was commissioned on by TSTRANSCO. 220/132 KV GIS Osmania University in Chilakalaguda, Hyderabad was commissioned on by TSTRANSCO. 220/6.6KV Murmur LI substation in Karimnagar district was commissioned on by TSTRANSCO. 220/6.6KV Bommakal LI substation in Karimnagar district was commissioned on by TSTRANSCO. 220/6.6KV Mallaram LI substation in Medak district was commissioned on by TSTRANSCO. 220/132 KVSS Bonguluru in Ranga Reddy Dist. (originally charged with 1x100MVA) was commissioned on by TSTRANSCO. PGCIL vide their letter dated informed that consequent to the successful completion of Trial Operation, Transmission system associated with Kaiga 3 & 4 (2x235 MW) Project (Mysore-Kozhikode 400 D/C line along with new 400/220 kv S/S with 2x315 MVA ICTs and 2x50 MVAR switchable line reactors at Kozhikode and associated bay equipment at Mysore Substation) had been put under COD w.e.f 00:00 hours of 16th October 2015 in terms of Clause 4 of CERC(Terms and Conditions of Tariff) Regulations Minutes of the 49 th PCSC Meeting held on Page 5

9 10. Instances of SPS Operations Based on the information furnished by SRLDC, it is informed that there were no instances of SPS operations in SR during the period Compliance of Hon ble CERC Orders 11.1 Petition No. 146/MP/2013 with I.A. 36/2013: Order dated Compliance of Regulations 5.2 (r) of the Grid Code: Issue regarding non-furnishing of FIR / Trip Analysis Report, EL, DR, etc. was also highlighted. It is pointed out that the above reports are to be submitted / uploaded on SRLDC web application within 24 hours as mandated under IEGC / CEA Regulations. Implementation of Phase-I and Phase-II of Protection Audit Recommendations: All the constituents are requested to submit the updated status of the compliance (those who have not completed recommendations mentioned in the Phase I and Phase II) to SRPC Secretariat at the earliest. Compliance of Regulations 5.2 (e) & 5.2 (l) of the Grid Code and Regulation 3(1)(e) of CEA Grid Standards: The constituents are requested to strictly comply with these provisions by ensuring standard protections systems having the reliability, selectivity, speed and sensitivity to isolate the faulty equipment and protect all components from any type of faults, within the specified fault clearance time and providing protection coordination Ensuring proper maintenance of transmission lines and adopting best O&M practices: The constituents are requested to conduct line patrolling regularly as per the SRPC transmission line patrolling guidelines (available under the menu item "All Uploads Operation Miscellaneous Transmission Line Patrolling Protocol / Guidelines for Southern Region" on SRPC website). ( Petition No. 167/Suo- Motu/2012: Order dated The Constituents are requested to follow approved protection philosophy ISTS licensees are requested to submit details of updated distance protection relay setting of all inter-regional lines to POSOCO & RPCs. All SLDCs are requested to install/activate sound recording system in their control rooms within three months from the date of issue of this order. The Constituents are requested to submit the progress of implementation to SRPC and SRLDC as specified in the Hon'ble CERC Order Petition No. 263/MP/2012: Order dated Constituents are requested to implement the quantum of relief by AUFR and df/dt relays by identifying additional feeders and keep them functional within one month of issuing this order. SLDCs are also requested to map these relays on their respective SCADA system within three months of issuance of this order. The Constituents are requested to submit the progress of implementation to SRPC and SRLDC as specified in the Hon'ble CERC Order APTRANSCO s Petition No.95/MP/2015: Date of hearing Minutes of the 49 th PCSC Meeting held on Page 6

10 It was noted in the Analysis and Decision part of the Order that: 8. Noting the submissions of the petitioner, SRPC and SRLDC and activities initiated by the petitioner for procurement of materials required for implementation of the remarks of protecting audit, we allow time to the petitioner till for completion of our directions in Order dated in Petition No. 146/MP/ SRPC is directed to monitor the status of completion of works relating to protection audit remarks in respect of 7 nos 400 kv sub-stations and 11 nos 220 kv sub-stations of APTRANSCO, protection audit remarks in Protection Coordination Sub-Committee (PCSC) meetings and coordinate the periodic protection audit to be carried out in Southern Region after deliberation in SRPC and submit bi-monthly report to the Commission TSTRANSCO s Petition No.83/MP/2015: Order dated It was noted in the Order that: 12. Noting the submission of the petitioner, SRLDC and SRPC and considering the actions already initiated by the petitioner for implementation of works relating to protection audit, we allow time till and for implementation of Phase-I and Phase -II works respectively. The petitioner is directed to submit affidavit confirming the completion of Phase I of protection audit remarks by and Phase-II of protection audit remarks by SRPC is directed to monitor the status of completion of remarks in these substations vis-à-vis protection audit remarks in Protection Coordination Sub Committee (PCSC) meetings. SRPC is further directed to coordinate the periodic protection audit to be carried out in Southern Region after deliberation in SRPC Order in Petition No. 86/MP/2014 and 374/MP/2014: Order dated The time-lines given to the various SR-Constituents for completion of Phase-I and Phase-II activities of Protection Audit Recommendations vide above Order are given below: (A) KSEBL: 18. Noting the submission of KSEBL, SRLDC and SRPC and considering the actions already initiated by KSEBL for implementation of remarks of protection audit, we allow time till and for implementation of Phase-II works and R&M works at Idduki HEP respectively. (B) TANTRANSCO: 21. After considering the submissions of TANTRANSCO, SRLDC and SRPC, it is noted that TANTRANSCO`s request for time till for implementation of Phase I activities of providing numerical relays for feeder protection and Auto transformer protection is already over. We allow time till for other Phase-I activities such as provision of line VT, 5 core CT, Time synchronizing with GPS, Disturbance recorder & event logger and Phase-II activities. According to SRLDC, total implementation period is 15 to 16 months for items which involve major procurement, design changes with major site modification/civil activities. Accordingly, we allow 16 months time i.e up to , Minutes of the 49 th PCSC Meeting held on Page 7

11 for Renovation and Modernization of Singarpet, Singaperumalkoil, Salem and Tondiarpet 230 kv sub-stations from the issue of the order. (C) NLC: 22. NLC has sought time upto and for completion of Phase-I work of Numerical Relay Retrofitting and for Phase-II works of providing second battery bank of PLCC respectively. It is noted that the completion dates for Phase-I and Phase-II of protection audit remarks as requested by NLC are already over. Therefore, no direction is required in this regard. However, we direct NLC to file a confirmation report regarding completion of protection audit works for Phase-I and Phase-II. (D) KPTCL: 23. Considering the submission of KPTCL and SRLDC, we allow time to KPTCL time till for completion of Phase-I and Phase-II of protection audit remarks. No further extension shall be granted in this regard. (E) KPCL: 24. Considering the submission of KPCL and SRLDC, we allow time to KPCL till and for completion of Phase-I for Phase-II of protection audit remarks respectively. No further extension shall be granted in this regard. 26. We direct SRPC to (a) submit status of protection audit remarks in respect of APGENCO, NTPC (SR), Talcher, Puducherry, PGCIL (SRTS I & II), MAPS and TANGEDCO, (b) monitor the status of completion of remarks of protection audit in respect of all constituents of Southern Region in Protection Coordination Sub-Committee (PCSC) meetings, and (c) to coordinate periodic protection audit to be carried out in Southern Region after deliberation in SRPC. All the constituents of Southern Region are directed to file their status with SRPC on regular basis to facilitate proper monitoring in PCSC meetings. SRPC is directed to submit bi-annually status report to the Commission confirming the completion of Phase-I, Phase-II and R&M works of protection audit remarks of the constituents of Southern Region. 12. Nomenclature for naming various files uploaded in Web based Tripping Monitoring System of SRLDC Portal The nomenclature to be followed by the Constituents in naming various files (FIR, DR, EL, TR) corresponding to a tripping incident was brought out in the SRPC letter No. SRPC/ SE-III/ PCSC- 45/ dated and in the minutes of PCSC-45 issued vide SRPC letter No. SRPC/SE-III/ PCSC-45/ 2015/ dated As illustrated therein, the format to be followed for the user entered part-name is given below: Transmission Element Transmission line File name to be given by the user SSN_DSN_line#_FT Minutes of the 49 th PCSC Meeting held on Page 8

12 Inter-connecting Transformer Generating Transformer Generating Unit SSN_ICT#_FT SSN_GT#_FT SSN_Unit#_FT Where, SSN = Source Station Name/ From end Station Name/ Sending end Station Name DSN = Destination Station Name/ To end Station Name/ Receiving end Station Name FT = File Type (FIR/ DR/ EL/ TR) All SR-Constituents are requested to kindly intimate the above file naming nomenclature to all the concerned and ensure that it is followed at all stations in their control area so that tripping analysis can be done systematically. 13. Date & Venue of the next Meeting It is informed that the 50 th PCSC meeting will be held on (Tuesday) at 10:30 hrs in the Conference Hall of SRPC, Bengaluru. 14. Vote of Thanks Member Secretary, SRPC thanked the members and other participants for their active contribution in the deliberations. Sh. Uday Trivedi, AVP, UPCL thanked all the Members for their cooperation. ***** Minutes of the 49 th PCSC Meeting held on Page 9

13 Annexure-I

14 Annexure-I

15 Annexure-I

16 Annexure-I

17 Annexure-II Grid Occurrences 1. Details of Grid Disturbances (GD s): 1 Complete outage of 220kV Chikodi substation of KPTCL (GD-1) (i) Date and Time of Event at 00:30 hrs (ii) Location 230kV Chikkodi Substation (iii) Reported Disturbance / Fault Tripped due of failure of 220kV Bus-2 PT at Chikkodi substation. Lines tripped on zone-2 from Talandage and Mudshingi on operation of Zone-2 protection. Bus bar protection is not available at 220kV Chikodi substation (iv) Load Loss (v) Category GD-1 SLD: As per FIR of KPTCL: Grid Occurrences discussed during 49 th PCSC Meeting on /29

18 KPTCL: Pre fault: Entire Chikkodi and Belgaum sub station loads were fed from Maharashtra system. At Chikkodi, both the buses were tied through bus coupler.220kv Gataprabha 1 &2 lines were kept open at Chikkodi as Gataprabha SS was on Karnataka system. At Chikkodi, normally Talandage and Mudshingi lines are generally kept on different buses, however due to some metering arrangement constraint (PT input) both lines were brought on to same bus, viz., Bus-B. At 00:30hrs, R phase PT of 220kV Bus A failed and the incoming lines tripped at Talandage and Mudashinge Zone-2. This resulted in bus shut down at Chikkodi. At Chikkodi, there was no bus-bar protection. Further as Bus Coupler s O/C operating time is more than that of Zone-2, the lines got opened from remote ends in Zone-2. During the incident, Load Loss: 143 MW for about 1 Hr 15 minutes. Energy unserved is MU Remedial Action: When enquired about provision of A/R on these inter-state lines, KPTCL representative informed that control panels had already been replaced, but due to problem with output cards of REL-511, the matter was taken up with M/s ABB (OEM), and the relays would be soon replaced by REL-760, and the work is likely to be completed by December, Regarding provision of bus-bar protection, it was informed that the same would be provided as part of their R& U proposal covering 96 SS in Karnataka, for which funding was sought from PSDF. It was also informed their proposal was approved during Appraisal Committee meeting held on and sent to CERC for further processing of the scheme as per PSDF disbursement procedure. Early sanctioning of PSDF grants from Monitoring Committee was awaited and thereafter LOA would be issued to the successful bidder M/s Alstom. SRLDC/SRPC: PMU plot shows the occurrence of two successive faults; while the first fault got cleared within 320ms, the second fault got cleared in 360ms. After the breaker got opened upon first fault, reasons for the second fault need to be investigated. Whether this could be correlated with the burning of R-ph Wave-Trap at Talandage end on 220 kv Chikkodi Talandage line as mentioned in the FIR may be seen by KPTCL. 2 Complete outage of IL&FS power station (GD-1) (i) Date and Time of Event at 19:43 hrs (ii) Location 400kV IL&FS Station Annexure-II (iii) Reported Disturbance / Fault Complete outage occurred at IL&FS due to tripping of evacuating lines i.e. 400kV IL&FS-Nagapatinam line-1&2. Both lines tripped due to mal-operation of Bus-1 and Bus-2 bus bar protection (iv) Generation Loss 400 MW (v) Category GD-1 SLD: 404, 405, 406 are in one dia with ILFS-1 line connected between 405 & 406; 407, 408, 409 are in one dia with ILFS-2 line connected between 408 & 409; Grid Occurrences discussed during 49 th PCSC Meeting on /29

19 Annexure-II Pre-Fault: Post-Fault: 400 kv Nagapattinam ILFS line-1: Nagapattinam (PGCIL-SR2) end: As per FIR/ TR, line tripped at 19:44 hrs due to BBP operation caused due to mal-operation of CB-406 & CB-407 s Gas Density Monitor on 3 rd Stage. (But from DR, only CB-406 got opened. Tie-CB 405 observed to be in OPEN condition prior to occurrence of this fault). As per DR/ EL, the lines tripped at 19:44: hrs due to BBP (96A) operation. IL&FS end: As per FIR/DR/EL/TR, the line tripped at 19:35: hrs due to DT receipt from Nagapattinam PS. From EL, it is observed that DT has been received several times starting from 19:35:02 hrs. to 19:44:46 hrs. The resolution in EL was limited to seconds only. 400 kv Nagapattinam ILFS line-2: Nagapattinam (PGCIL-SR2) end: As per FIR/ TR line tripped at 19:44 hrs due to BBP operation caused by mal-operation of CB-406 & CB-407 s Gas Density Monitor on 3 rd Stage.(But from DR, only CB-409 got opened. Tie-CB 408 observed to be in OPEN condition prior to occurrence of this fault) As per DR/ EL, the lines tripped at 19:44: hrs due to BBP (96A) operation. IL&FS end: As per FIR/DR/EL/TR, the line tripped at 19:44: hrs due to DT receipt from Nagapattinam PS. The resolution in EL was limited to seconds only. Grid Occurrences discussed during 49 th PCSC Meeting on /29

20 PGCIL-SR2: Gas Density Monitor (GDM) operation consist of three stages as given below: Normal stage SF6 Pressure:0.67Mpa Stage1: <=0.64Mpa, Stage2:<=0.62Mpa, Stage3:<=0.60Mpa. It s third stage operation causes BBP operation of the bus to which the concerned CB is connected. In the instant case, first CB-407 s GDM operation in third stage caused BBP operation for Bus Bar -1 (top bus in the diagram). Then after 9 sec, CB-406 s GDM operation in third stage also caused BBP operation for Bus Bar 2 (Bottom bus in the diagram). However as all Tie-CBs remained in service, the lines NLCTPS-Exp1 & NLC TPS 2 and, Trichy-1 & Trichy-2 got connected through Tie-CB 411 and Tie-CB 414 respectively. On Examination at site, the pressure in 406-CB and 407-CB is found normal and tripping occurred due to maloperation of gas density monitoring associated circuit. The moisture entry in the associated circuit of gas density 3 rd stage, caused mal-operation due to some contact problem with the miniature relays, and resulted in bus bar protection operation. It was also found that the space heaters which keep LCC panels dry got accidentally got switched off On this point, KKNPP representative informed that in their GIS, space heaters associated with GDM were not provided separately, but came as a built-in feature of GDM. Then, it was opined that could be due to design difference as PGCIL s GDM is of China-make, and that of KKNPP is of Russian-make. Remedial action: The Gas leakage detector healthiness checked. Precautions to avoid moisture entry in the panels have been taken to ensure no repetition of such occurrences takes place. SRLDC/SRPC: As the Tie-CB s 405 and 408 were found to be OPEN condition prior to occurrence of BBP operation from the DR s furnished, PGCIL (SR-II) needs to substantiate their statement by providing all the relevant EL s. At IL&FS end, the time-scale resolution in EL s should be configured for msec. Time-sync for DR and EL needs to be ensured at IL&FS. 3 Complete outage of 220kV Ambewadi Substation of KPTCL (GD-1) (i) Date and Time of Event at 14:34 hrs (ii) Location 220 kv Ambewadi Substation Annexure-II (iii) Reported Disturbance / Fault 220kV Nagjheri-Ambewadi line-1 tripped at 13:33 hrs due to B phase to earth fault. Ambewadi was radially fed from Nagjheri power station through 220kV Nagjheri-Ambewadi line-2. Tripping of this line caused 220kV Bus shut down at Ambewadi and remaining lines and transformers were hand tripped (iv) Load Loss Karnataka: 14 MW and Goa: 97 MW (v) Category GD-1 Grid Occurrences discussed during 49 th PCSC Meeting on /29

21 Annexure-II SLD: Hand trip AMBEWADI- 220kVAMBEWADI- 220kV Out of service (Maintenance) Line MVA XELDOM 55 MVA Z1 Line-2 Line-1 Z2 Line-2 Z2 20 MVA As per TR of KPTCL: NK No Generation Ambewadi (KPTCL) end: Prefault conditions: 220kV Ambewadi-Narendra 1 & 2 lines are under LC due to failure of insulator strings. Supa generation - Nil; Goa load on 14.00Hrs- 97MW; Karnataka load (11kV load of Ambewadi & 110kV loads) - 14MW At 13:33hrs, Ambewadi-Nagjheri line-1 tripped on distance protection due to line fault and declared faulty. Line Clear was availed by TLI staff. At 14:36 hrs, 220kV Ambewadi-Nagjheri line-2 tripped at Nagzari end on DPR in Zone-2(BN, 25km). This resulted in loss of supply to Ambewadi station as only source to Ambewadi was 220kV Nagjheri line kV Ambewadi-Ponda line-1& 2 were hand tripped. Load loss - Karnataka load : 14MW; Goa load:97mw and energy unserved was MU Restoration: 220kV Bus was restored by charging 220kV Nagjheri Ambewadi line- 2 at 14:50 hrs and 220kV Ambewadi-Ponda line-1 was charged at 15:13hrs. Grid Occurrences discussed during 49 th PCSC Meeting on /29

22 KPTCL also informed that Ambewadi Narendra D/C line which were taken on outage replace insulator strings would be put into service by mid-december, KPCL Presently A/R & Carrier protection is not present on Nagjheri Ambewadi lines due to absence of CVT s at Nagjheri. However, as the material was already received (in third week of November, 2015), carrier protection and A/R will be provided in 3-month period. To this, SRLDC insisted KPCL for providing the same in one month time, to which KPTCL also conveyed their preparedness. Recommendations: KPCL to provide A/R on all 220 kv lines emanating from Nagjheri PH. KPTCL to provide A/R on all 220 kv lines emanating from Ambewadi SS. 4 Complete outage of 220kV Ambewadi Substation of KPTCL (GD-1) (i) Date and Time of Event at 16:54 hrs (ii) Location 220 kv Ambewadi Substation Annexure-II (iii) Reported Disturbance / Fault 220kV Nagjheri-Ambewadi line-1 & 2 tripped at ambewadi end only on operation of DEFR. This resulted in loss of supply to Ambewadi station. Fault had occurred in 220kV Nagjheri-Hubli line-2 (iv) Load Loss 4 MW (v) Category GD-1 SLD: Hand trip AMBEWADI- 220kVAMBEWADI- 220kV Out of service (Maintenance) PONDAP ONDA 110 kv 20 MVA 100 MVA NK XELDOM 55 MVA DEFR DEFR Line-1 Line-2 Line-1 Line-2 NAGJHERI NAGJHERI SUPA HPS (2X50 MW) SUPA HPS (2X50 MW) No Generation 220kV Ambewadi SS end: Prefault Conditions: 220kV Ambewadi-Narendra 1 & 2 lines were under LC due to failure of insulator strings. Supa generation : Nil Goa load on 16.00Hrs- 103MW Karnataka load (11kV load of Ambewadi & 110kV loads) - 12MW NARENDRA F (B-N) Grid Occurrences discussed during 49 th PCSC Meeting on /29 Z2 DEFR HUBLI

23 As per TR of KPTCL: At hrs, 220kV Ambwadi Nagheri lines - 1 &2 tripped at Ambewadi end on DEFR. Due to this 220kV Bus got de-energized and the remaining lines and transformers were hand tripped. Restoration: 110kV bus restored at hrs by charging 110kV NK-2 line (220kV Sirsi source). 11kV Load of Ambewadi for about 4 MW was restored immediately. 220kV bus restored at Hrs and 220kV Ponda -1 line restored at Hrs. Load loss : 11kv load of 4 MW for 20 minutes ( Karnataka) Goa load of 103MW for 53 minutes. Energy Unserved in MU: MU. KPTCL: Details of trippings occurred at Nagjheri were collected and it was observed that 220kV Ambewadi- 1 & 2 lines were not tripped at Nagzari end during the instance. However 220kV NPH-Hubli-2 line was tripped during the instance with following relay indications: At Nagjheri : 220kV Hubli-2 line tripped on DPR, Zone-2,CN, 88.5km, 3.1kA; At Hubli: NPH-2 tripped on DEFR. Suspected transient fault in the line. This line was restored at 18.24Hrs on During this time, there was reversal of power flow on the Nagjheri - Ambewadi lines 1 & 2, i.e. from Ambewadi to Nagjheri on account of acting of tertiary winding of the transformers at Ambewadi in shunt to the fault (thus contributing to the fault point) even though there was no source at Ambewadi. Remedial Action: As NPH- Hubli, NPH-Ambewadi lines are passing through dense forest, these lines are prone to high resistance faults. Hence resistive reaches of distance relays of NPH connected lines at remote end sub stations i. e. at Hubli, Bidnal and Ambewadi have been revised to 75 ohms (primary). DEFR time-lever has also been increased to Upon enquiry by SRLDC regarding non-furnishing of DR for the tripping event, KPTCL informed that presently DEFR operation was not configured for triggering DR. So it was recommended that KPTCL configure DEFR output also for triggering DR at Ambewadi SS. 5 Complete outage of S.P.Koil station of TANTRANSCO and generation loss at Madras Atomic Power station(maps) (GD-1) (i) Date and Time of Event at 9:33hrs Annexure-II (ii) Location 230 kv MAPS Station and 230kV S.P.Koil Substation (iii) Reported Disturbance / Fault Fault had occurred in 230kV MAPS-S.P.Koil feeder-1. LBB protection got operated as breaker of this feeder was under lockout and resulted in tripping of 230kV bus at S.P.Koil. Unit- 1&2 at MAPS due to loss of evacuating feeders i.e. 230kV MAPS- S.P.Koil feeder-1&2 (iv) Generation Loss 250 MW (v) Load Loss 150 MW (vi) Category GD-1 Grid Occurrences discussed during 49 th PCSC Meeting on /29

24 Annexure-II SLD: Grid Occurrences discussed during 49 th PCSC Meeting on /29

25 Annexure-II Grid Occurrences discussed during 49 th PCSC Meeting on /29

26 Annexure-II MAPS is connected to four 230 kv lines, viz., SPKoil lines 1 & 2 (L1 & L2); Acharapakkam line (L4); and Arni line (L3). As per the Report dated furnished by MAPS: 230 kv Kalapakkam Arani line (L3) was tripped on first at 18:35 hrs, and then again at 19:06 hrs due to snapping of conductor between B-ph Wall Bushing & First Tower from MAPS. Strain insulator in the B-ph of first tower (towards switchyard) was also observed to have been damaged. 230 kv Kalapakkam Acharapakkam line (L-4) was tripped on at 08:21 hrs due to snapping of Y-ph & B-ph conductors from First Tower to Second Tower from MAPS. 230 kv Kalapakkam SP Koil line-2 (L-2) tripped on at 09:02 hrs due to B-ph fault; and the line could not be normalised due to breaker problem at SP Koil end. 230 kv Kalapakkam SP Koil line-1 (L-1) tripped on at 09:33 hrs due to line fault. As a result of losing of all four evacuating lines, both Units of MAPS tripped on Turbine Over Frequency protection. No FIR/ DR/ EL furnished relating to tripping of Kalpakkam SP Koil D/C lines and both Units of MAPS by NPCIL (MAPS). As per the Report dated furnished by TANTRANSCO: Grid Occurrences discussed during 49 th PCSC Meeting on /29

27 Annexure-II 230 kv Kalapakkam SP Koil line-2 (L-2): SP Koil (TANTRANSCO) end: As per FIR/ TR, the line tripped at 9:06 hrs on B-E fault due to DPR, Z2 operation. It was stated that A/R was in locked-out condition. From DR, the line got tripped on B-E fault at 08:39: hrs. (Digital inputs were not shown) EL furnished was not proper (It does not show SOE). Time sync of DR & EL needs to be checked. From synchro-phasor data, the fault seemed to have got cleared in 160 msec. This means that the fault got cleared due to DPR, Z1 operation from MAPS end. 230 kv Kalapakkam SP Koil line-1 (L-1): SP Koil (TANTRANSCO) end: As per FIR/ TR, On at 06:00 hrs., the CB at SP Koil end on SP Koil MAPS line-1 was under lock-out due to Compressor s low SF6 pressure. Subsequently at 09:32hrs., line fault occurred in the above feeder, but due to lockout condition the breaker had not tripped; as a result, LBB relay acted and tripped all the 230kV feeders & all the 4 Auto transformers. EL furnished does not show events after time 9:03:36:416 hrs. (After this, only following two events were shown: Monday 09 November :24: : Any Pole Dead OFF Monday 09 November :24: : All Pole Dead OFF) From DR, the line trip happened at 08:32: hrs on Y-E fault due to DPR, Z1 operation. But due to A/R s lock-out condition, 3-ph trip was given. However, only R-ph and B-ph currents only became zero. It is observed that Y-ph current became zero only after 560 msec. (It was also observed that similar operation, viz., R-ph and B-ph currents becoming zero, and the y-ph current becoming zero only after 560 msec. was also observed in the DR furnished for SP Koil end on SP Koil Kalavindapattuu 230 kv S/C line). Hence, whether this happened because of sluggish operation of LBB relay or PD relay needs to be found out). From Synchrophasor data, fault clearing time was observed to be 560ms. Hence, the operation of LBB protection needs to be validated. Time sync of DR & EL also needs to be checked. TANTRANSCO: On the tripping day, there was heavy rain and thunderstorms around SP Koil area due to which operators could not attend to the low air pressure of compressor in time which resulted in locked-out condition of A/R relay. This resulted in tripping of the SP Koil MAPS lines on line faults subsequently. MAPS: MAPS being a Nuclear Power Station, the evacuating lines from MAPS need proper line maintenance by TANTRANSCO. Further, when it was already known that MAPS was operating under depleted network conditions due to tripping of MAPS Arani line the previous day, more vigilance should have been exercised by SLDC so that MAPS remained in grid mode of operation. As such incidents happened in the past also, SRPC is requested to form a sub-committee to look into all protection & operational issues concerning MAPS, and suggest suitable corrective measures. SRLDC: The breaker of 230kV SP.Koil-MAPS feeder-1 was under lockout due to SF6 gas pressure low from 6:00 AM of and no actions were taken by TANTRANSCO to rectify the same till teh occurrence of the fault at 9:33 AM. Apart from the line maintenance related issues, the proposed sub-committee may look into the following issues concerning MAPS: Connectivity of MAPS from Bhavini for increasing the reliability of secure grid-operation of MAPS. Carrier Communication & PLCC related issues; Modalities to bring down generation at MAPS in case of tripping of few evacuating lines from MAPS may also deliberated by the proposed sub-committee. Grid Occurrences discussed during 49 th PCSC Meeting on /29

28 Annexure-II SRPC: A sub-committee consisting of Officals from SRPC, SRLDC, PGCIL (SR-II), TANTRANSCO & MAPS would conduct a Protection System Analysis Group (PSAG-14) meeting at MAPS, Kalapakkam and deliberate on all protection & operational issues concerning MAPS. Recommendations: TANTRANSCO to ensure correctness of operation of LBB relays at SP Koil. TANTRANSCO & MAPS to furnish their respective compliance report of the recommendations of to-beconducted PSAG-14 meeting at MAPS, Kalapakkam. 2. Details of Grid incidents (GI s): Sl. No. क र.स. 1 SLD: घटन क व रण / Details of Event Multiple tripping at Nagjheri Hydro power station of KPCL त र ख/ Date & समय /Time at 11:43 hrs क रण / Reason 220kV Nagjheri- Bidnal line tripped on operation of Directional earth fault protection due to suspected high resistance fault in line. Running Units -1&2 at Nagjheri power station tripped on operation of high set of back-up earth fault protection of Generator transformer protection. Remaining feeders at Nagjheri, i.e., Ambewadi-1, 2 and Hubli- 1 & 2 were not affected. Hubli-3 feeder was under shutdown श र ण / Category GI-1 Nagjheri Capacity: 885 (5x x 135) MW. Pre-fault conditions: o Nagjheri Kodasalli lines 1 & 2 were kept open. o Nagjheri Hubli line -3 was under LC. (Check this because Nagjheri Kubli is a D/C line only) o Units in service at Nagjheri: Unit-1 & Unit kv Nagjheri Bidnal line: Bidnal (KPTCL) end: As per FIR, line tripped at 11:44 hrs on B-E fault due to OCR operation. No DR/EL furnished. Nagjheri (KPCL) end: As per DR/EL/ TR, the line tripped at 11:43: hrs on B-E fault due to operation of DEF (67N) protection. In DR, no digital inputs (signals) were shown. In DR & EL the events/ signals or which protection operated to open the line were not shown. It was stated that other 220 kv lines had not tripped. Grid Occurrences discussed during 49 th PCSC Meeting on /29

29 Annexure-II Nagjheri Units -1 &4 tripping: As per TR, the Units tripped due to operation of (High Set of) GT OC & E/F protection. (Time not mentioned, Instantaneously?). DR & EL were not furnished for any of the Units. SRLDC: Delayed clearance of the fault on Nagjheri Bidnal line-1 was observed from PMU plot. The fault was observed to have sustained from 11:42: hrs to 11:42: hrs to 11:42: hrs sec & 160 msec. All trippings with delayed fault clearance (more than 1 sec) would be informed to CERC. When asked about operation of SPS, KPCL replied that SPS at NPH was provided for Units- 3 & 6 only which were not in service during the tripping event. KPCL: Remedial action: Settings of Instantaneous elements of Generator Transformer back up protection would be reviewed. The IDMT relay responsible for delayed fault clearance would soon be replaced. KPTCL also informed that resistive reaches of distance relays of NPH connected lines at remote end sub stations i. e. at Hubli, Bidnal and Ambewadi had been taken up for review and revised to 75 ohms (Primary). Tripping of 765kV 2 Kurnool-Tiruvalam line-2 Tiruvalam (PGCIL-SR2) end: Kurnool (PGCIL-SR1) end: at 11:18 hrs Buchholz-2 of B-ph line reactor at Kurnool maloperated and caused tripping of Line. Direct Trip was received at Thiruvelam end. As per FIR/ DR/ El/ TR, the line tripped at 11:18: hrs due to DT receipt from Kurnool end. As per FIR/ DR/ EL/ TR, the line tripped at 11:17: hrs due to mal-operation of Buchholtz-2 of B-ph Line Reactor. PGCIL (SR-I): It is a typical case of mal-operarion as the Buchholtz relay contacts were latched without any pressure variation. Remedial Action: In fact, in all the newly commissioned 765 kv lines, they have been experiencing problems with WTI and Buchholtz relays, and the issue has been taken up with OEM. All the Buchholz / PRD WTI / OTI Relays supplied under package are being replaced by OEM. Already WTI relay was replaced at Kurnool; Buchholtz would also be replaced shortly. When enquired by SRLDC regarding time-frame of completion of above work, he informed that the work would be completed in 3 months time. When asked about spare transformers WTI and Buchholtz relays, it was informed that they were also being replaced. GI-2 3 Tripping of 220kV Edamon-Tirunelveli line-1& at 21:30 hrs 220 kv Edamon Tirunelveli line-1: Edamon (KSEB) end: As per DR, the line tripped at21:47: hrs due to BBP operation. EL not furnished (Uploaded EL was same as FIR) Tirunelveli (PGCIL-SR2) end: 220kV Edamon-Tirunelveli lines -1&2 got tripped due to operation of Bus Bar protection which was due to human error GI-1 Grid Occurrences discussed during 49 th PCSC Meeting on /29

30 Annexure-II As per FIR, the line was holding from their end. 220 kv Edamon Tirunelveli line-2: Edamon (KSEB) end: As per DR, the line tripped at 21:35: hrs due to BBP operation. EL not furnished (Uploaded EL was same as FIR) Tirunelveli (PGCIL-SR2) end: As per FIR, the line was holding from their end. Time sync between DR s of both lines at Edamon end needs to be ensured. As per KSEB letter dated : SRLDC: Had the tripping been due to accidental pressing of TEST LBB button of LBB, DT should have been sent to the remote end. But as this did not happen, KSEB should investigate the same. Recommendations: KSEB to furnish reasons for DT not being sent to the remote end during the tripping event along with remedial measures taken to PCSC forum. 4 SLD: Tripping of 400kV Gooty-NPS line at 10:15 hrs Direct Trip was sent to NPS end of line-1 during opening of Main CB of Gooty-NPS line-2 at Gooty end. This resulted in tripping of line-1 at NPS and line was holding from Gooty. Over voltage protection got operated at NPS end and resulted in tripping of line GI-2 Grid Occurrences discussed during 49 th PCSC Meeting on /29

31 Annexure-II 400 kv Gooty NPS line-1: Gooty (PGCIL-SR1) end: As per FIR, the line tripped at 10:15 hrs due to DT receipt from NPS end. From EL, DT receipt was observed at 10:09: hrs from NPS end. [Prior to this, it was observed that both Tie-CB 2952 and NPS-II Main-CB 2852 were in OPEN position] DR (trigger time = 10:12: hrs) furnished was not readable. Also the cause of trip was not clear (as no relevant digital signals were shown) As per TR, while manually tripping Tie-CB (2952) and Main-CB (2852) of NPS-II, DT was sent to NPS end. Subsequently on receipt of DT from NPS end, the line tripped at Gooty end. It was stated that at the time of hand tripping of Main-CB of NPS-II, DT was sent to NPS-I end wrongly. Due to this, 400 kv Gooty-NPS line-1 tripped at NPS end. Subsequently, OVR, Stage-I protection operated at NPS end, and sent DT to Gooty end, due to which Gooty-NPS line-1 tripped at Gooty end. However, there was no evidence for OVR, Stage-I operation at NPS end. Time sync of DR, EL needs to be ensured. NPS (PGCIL-SR1) end: As per FIR/ TR, the line tripped at 10:15 hrs due to DT receipt from Gooty end. As per EL, DT receipt ALARM (NOT TRIP) only was observed at 10:15:33 hrs. Further, Time-Stamp was not configured to show events at msec level. The events corresponding to OVR, Stage-I operation were not recorded. As per DR, the line tripped at 10:15: hrs due to DT receipt from Gooty end. Time-sync of NPS and Gooty with GPS needs to be ensured. PGCIL (SR-I): Prior to tripping event, 400kV Gooty-NPS Line-2 was out of service. Line Reactor (LR) at Gooty end for line-2 was being used as bus reactor. Line-2 was to be taken into service. For opening LR, Main & Tie breakers of line-2 were opened at Gooty end. However due to wiring problem (during commissioning stage), DT was sent to line-1 at NPS end which resulted in tripping of line-1 CB s at NPS end. Line-1 was holding from Gooty end. The DT-sent was also a spurious operation due to latching of CB auxiliary contacts. Then, Over voltage, Stage-I protection got operated at NPS end and resulted in tripping of line-2. Remedial action: Problem with wiring connections got rectified. Latched CB auxiliary contacts were also replaced. Recommendations: PGCIL (SR-I) to configure time scale resolution in Event Logger to msec. at Nelllore PS (NPS) and furnish DR corresponding to OVR, Stag-I operation at NPS end during the tripping event. PGCIL (SR-I) to ensure time-sync of DR s and EL s with GPS at Gooty and NPS. 5 Tripping of Gazuwaka Pole at 12:28 hrs HVDC Pole-2 win-2 breaker tripped on operation of differential protection of Bus-2 of east side. Loss of East Bus-2 voltage led to tripping of Pole-2 SLD: Grid Occurrences discussed during 49 th PCSC Meeting on /29

32 Annexure-II Pre-Conditions: System Normal with Jeypore-Gazuwaka Line I & II along with Line Reactors are in service Total Power Flow: 600MW E S Pole - 1: 250 MW E S Pole - 2: 350 MW E S Pole-2 East side WA2.W1.Q1 CB, connected to East Bus-1 was under shutdown condition for identification of SF6 Leakage points vide CPCC Code-CP/10/389 from 09:35 onwards. Pole-2 East Bus voltage extended through WA2.W1.Q3 CB, connected to East Bus-2. Description of Fault: At 12:28:06 Hrs on 13/10/2015, Voltage dip in the East Side was observed and HVDC POLE-2, East Bus-2 connected Breakers i.e WA2.W1.Q3 & WIN2.Q1 breaker tripped due to operation of WIN2 Differential Current Phase L3 Trip of East Bus-2. Since East Bus Voltage was extended only through WA2.W1.Q3 Breaker i.e East Bus-2 as WA2.W1.Q1 CB (connected to East Bus-1) was under shutdown condition and tripping of WA2.W1.Q3 CB & WIN2.Q1 CB on above protection caused Loss to East Bus Voltage thereby tripping HVDC Pole-2 on LOW DC VOLTAGE TRIP. Analysis: DR Prints revealed current ZERO in Phase L3 (B-Phase) of WA2.W1.T3 CT connected to WA2.W1.Q3 Bay at the time of tripping, whereas the other two phases are showing healthy conditions i.e 182-Amps causing operation of WIN2 Differential Protection of East Bus-2 and loss of East Bus Voltage for HVDC Pole-2, thereby tripping the Pole on Low DC Voltage Trip On detailed investigation it was found that the Core-4 B-Phase cable coming from WA2.W1.T3 CT Junction Box to Pole-1 Control room RTI-A System for East Bus Differential Protection had failed/earthed. The failure of particular core was confirmed through Continuity Check and Insulation Resistance measurement. Remedial action: The trip was initiated by differential protection of RTI-A System. The protection in RTI-A system was disabled and the same protection was made ACTIVE in redundant RTI-B system. The faulty CT cable from WA2.W1.T3 CT Junction box to Pole-1 Control room of length 1.5 km was pleaced by spare, and PO for new cable ad already been placed. Normalization: At 14:06 Hrs, Pole-2 was Deblocked vide codes CPCC-414, NLDC- 433, SR-445, ER-351. Grid Occurrences discussed during 49 th PCSC Meeting on /29

33 Annexure-II UPCL: Since, the said cable is of 1.5 km length, line differential protection may be provided for protecting the same. Provision of CT supervision may also be explored. 6 7 Tripping at 220kV Nunna Substation of APTRANSCO. 400/220kV ICT-2 at Vijayawada substation also got tripped at 16:14 hrs 220kV bus bar protection operated at 220 kv Nunna APTRANSCO substation due to fault. All elements connected to 220kV bus-2 got tripped As per FIR/TR of Nunna (PGCIL-SR1), ICT-2 tripped at 16:14 hrs due to BBP operation of 220 kv Bus of APTRANSCO. As per DR of Nunna (PGCIL-SR1), ICT-2 tripped at 16:14: hrs (the causing digital signal was not shown) As per DR of Nunna (APTRANSCO), BBP of 220 kv Bus-2 operated at 15:12: hrs due to Y-ph bus fault. Time sync of Nunna (APTRANSCO) SS. Remedial Action: APTRANSCO informed that Aluminium wire had fallen on the 220KV BUS-2 and created the bus fault. Bus bar protection operated and cleared the fault by tripping the Bus -2 connected Feeders, ICTs/PTRs. Protection was in order. When enquired about time sync of Nunna-AP SS, APTRANSCO representative informed that GPS is not available at Nunna. However, they have planned to provide the same in a phased manner. Tripping of 765/400kV ICT-2 at Kurnool Substation at 17:10 hrs ICT tripped due to mal-operation of B-phase HV WTI trip As per FIR/ TR, ICT-2 tripped at 17:10:12 hrs due to mal-operation of HV B-ph WTI Trip. As per DR/ EL, ICT-2 tripped at 17:10:13 hrs due to mal-operation of HV B-ph WTI Trip. EL resolution was not configured to show events at msec level. Remedial action: This problem which was being experienced in all the newly commissioned 765 kv lines was taken up with OEM and all the Buchholz / PRD WTI / OTI Relays supplied under package would be replaced by OEM. At Kurnool, WTI relays were replaced by availing shut down on 17 th and 18 th Nov, GI-I GI-2 8 Tripping of 400kV Vemagiri-Sattenapalli line and 400kV Vemagiri-Kalpakka line at 10:56hrs B-phase to earth fault had occurred in line. From Vemagiri end D.R, three phase trip and Tie-CB LBB operated was observed. Sattenapalli end had auto-reclosed, however breaker at Satenapalli tripped 8 sec after A/R on receipt of DT from Vemagiri as observed from EL of Satenapalli station. GI-2 For 400k Vemagiri-Kalpakka line at Vemagiri end, Tie LBB operation and Grp-A/B trip was observed and direct trip was sent to Kalpakka end 400 kv Vemagiri Sattenapalli line: Vemagiri (APTRANSCO) end: As per DR/EL, line tripped at 10:55: hrs on B-E fault due to A/R operation. During A/R dead time, T-LBB operated at 10:55: hrs to result in 3-ph trip. Grid Occurrences discussed during 49 th PCSC Meeting on /29

34 Sattenapalli (APTRANSCO) end: As per EL, the line tripped at 10:56: hrs on B-E fault due to A/R operation, and successfully autoreclosed after one second. But it again tripped at tripped at 10:56: hrs due to DT receipt from Vemagiri. DR furnished was for second event (DT receipt) only. DR for the first event (for A/R operation) was not furnished. If this DT receipt was due to T-LBB operation at Vemagiri end, then this time delay of 10 sec is inadmissible. 400 kv Vemagiri Kalpakka line-1: Vemagiri (APTRANSCO) end: As per DR/EL, the line tripped at 10:55: hrs due to operation of Tie-CB LBB protection. Kalpakka (APTRANSCO) end: As per EL, the line tripped at 10:53: hrs due to DT receipt from Vemagiri As per DR, the line tripped at 10:57: hrs due to DT receipt from Vemagiri Time sync of DR & EL needs to be ensured. Annexure-II APTRANSCO: Vemagiri Sattenapalli line and Vemagiri Kalpakka line-1 are in the same dia. In the above dia at Vemagiri, Tie-CB has two auxiliary relays; o One is for tripping its corresponding Main-CB and sending DT to Kalpakka and o The other is for tripping corresponding Main-CB sending DT to Satenapalli and. On Tie LBB operation at Vemagiri end, Kalapkka line got tripped at Kalpakka end on DT receipt. On B-phase to earth fault, Satenapalli line auto-reclosed successfully. But after 8 seconds, Satenapalli line tripped on OVR, Stage-I operation at Vemagiri. Remedial Action: APTRANSCO representative informed that Tie-CB LBB auxiliary trip relay mal-operated. It was replaced with spare relay, and feeders taken into service. SRPC: The tripping of Vemagiri Sattenapalli line due to T-LBB / OVR, Stage I operation could not be conclusively established from the DR & EL furnished in this regard. Recommendations: APTRANSCO to furnish a report on the tripping of 400 kv Vemagiri Sattenapalli line along with relevant DR & EL showing clearly the successful operation of A/R followed by T-LBB/ OVR, Stage-I operation. 9 Tripping of 400/220 kv ICT-3 at Thrissur substation at 11:04 hrs Tie LBB protection of CB 405 resulted in tripping of breakers connected to 400kV Bus-1 along with main breaker of ICT-3. This in turn resulted in tripping of ICT-3 at Thrissur. GI-2 KSEB: Grid Occurrences discussed during 49 th PCSC Meeting on /29

35 Annexure-II Remedial action: Grading capacitor across CB-401 was replaced. The CBF relay was sent for repair works. Grid Occurrences discussed during 49 th PCSC Meeting on /29

36 Annexure-II 10 Tripping of 400kV Gooty - NPS line at 14:30 hrs Line tripped on operation of REF protection at Gooty end and Direct Trip was sent to NPS end. GI-2 Gooty (PGCIL-SR1) end: As per FIR/TR, the line tripped due to operation of Reactor s REF protection (64R). DT was also sent to NPS-1 end. As per EL, the line tripped at 14:28: hrs due to Grp A & B trip relay operation. As per DR, the line tripped at 14:29: hrs. NPS (PGCIL-SR1) end: As per FIR/DR/EL/TR, the line tripped at 14:30: hrs due to DT receipt from Gooty end. PGCIL (SR-I): There was a problem with NGR-CT polarity, due to which its REF protection operated accidentally. Subsequently, it was rectified. 11 Tripping of 400/220 kv ICT-2 at Kurnool Substation and 400kV Kurnool-Srisailam line at 14:31 hrs 400kV Kurnool-Srisailam line - distance protection zone-2 had operated at Srisailam end. However from DR, R-phase to earth fault and zone-2 start were observed. Breakers at Kurnool end tripped on direct trip receive from Srisailam end. GI-2 ICT-2 Main-CB tripped due to operation of bus bar protection, and Tie-CB tripped due to DT receipt from Srisailam SLD: The SLD of 400/220 kv Kurnool SS as provided by APTRANSCO is attached at the end for reference. At 400 kv Kurnool SS, ICT-2 and Srisailam line are in the same dia. 400 kv Kurnool Srisailam line: Kurnool (APTRANSCO) end: As per FIR/ TR, the line tripped at 14:31 hrs due to DT receipt from Srisailam end DR, EL were not furnished to verify above operation. Srisailam end: As per FIR, the line tripped at 14:31 hrs on R-E fault due to DPR, Z2 operation. As per DR/ EL, the line tripped at 14:29: hrs. But only Z2 Start (at 14:29: hrs) and DEF Start (at 14:29: hrs) were seen. Tripping of ICT-2 at Kurnool SS of APTRANSCO: As per FIR, ICT-2 Main-CB tripped at 14:31 hrs due to operation of BBP; Tie-CB tripped on receipt of DT signal from Srisailam end. DR, EL not furnished. APTRANSCO: ICT-1 Main-CB was availed Shutdown due to isolator problem. During maintenance, isolator of its earth switch got closed accidently which created a bus fault. Due to this, ICT-2 Main-CB got tripped. The Tie-CB tripped along with Main-CB of Srisailam line due to DT receipt from Srisailam end. In the past also, APTRANSCO lines s connected to Srisailam LB received DT in case of any kind of fault occurring at Srisailam LB or on lines emanating from Srisailam LB. Grid Occurrences discussed during 49 th PCSC Meeting on /29

37 Annexure-II TSGENCO: At Srisailam end, newly commissioned relays (numerical) appeared to have configuration problems due to which DT is being sent to remote ends wrongly. Remedial action: The matter had already been taken up with their OEM, and hope to resolve it at the earliest. Recommendations: TSGENCO in coordination with APTRANSCO to carry out end-to-end testing of PLCC channels by on 400 kv Srisailam Kurnool S/C line and 400 kv Srisailam Sattenapalli D/C line. TSGENCO and APTRANSCO to make A/R functional on 400 kv Srisailam Kurnool line. TSGENCO to resolve configuration problems with the newly commissioned relays at Srisailam LB so that unwarranted DT sending to remote ends is addressed. 12 Tripping of 400/220kV ICT-2 at Chittoor substation at 17:00hrs ICT-2 at Chittoor tripped due to suspected maloperation of Buchholtz relay. As per FIR, ICT-2 tripped at 16:59 hrs due to operation of Buchholtz relay. From DR, ICT-2 tripped at 16:59: hrs due to operation of Buchholtz relay. The causing event was not recorded in the EL furnished. Remedial action: APTRANSCO representative informed that the line tripped due to mal-operation of ABB-make Buchholtz relay. As a remedial measure, it was replaced with another relay of Areva make. GI-2 13 SLD: Tripping of running Units 1 & 3 at Rayalaseema TPS of APGENCO at 03:30 hrs While synchronizing Unit-5 with grid, Bus bar protection of 220kV Bus-1 operated which resulted in de-energization of 220kV Bus-1. This resulted in tripping of running Unit-1&Unit-3, 220kV lines Pulivedula-1, Yeralaguntla-1, Chinakampalli-1, Timmapura GI-1 ** Above is a part-sld showing Unit-IV and Unit-V. Complete SLD is enclosed at the end. Grid Occurrences discussed during 49 th PCSC Meeting on /29

38 Annexure-II Tripping of Units 1 & 3 of Rayalaseema TPS of APGENCO: As per FIR/ TR of APGENCO, Unit-5 of Rayalaseema TPP got tripped at 01:24 hrs on Flame Failure. In the process of taking Unit-5 back, TG set was kept 3000 RPM. During building-up of Generator Voltage, GT-5 LBB operated resulting in actuation of BBP of 220KV Bus-1. As a result, all out going feeders, GT-1, GT3, ST-1 &ST- 5 on Bus-1 got tripped at 03:30 hrs. From DR of Unit-5, it was observed that at 03:30: hrs that voltage was absent in R-phase. Also Dead- Machine condition and Class-A trip were observed 80 msec. subsequent to that. From PMU data, dip in R-phase voltage was observed for 320ms. APGENCO: While synchronizing Unit-5 manually, as the voltage build-up of generator reached around 10.5 kv, GCB got closed accidentally, and resulted in shorting/ burning of control cables. Due to this, closing pulse from the CB was not received by the main-relay, and dead-machine condition prevailed. This led to Class-A trip of Unit-5 generator protection. However, as the breaker failed to open, it resulted in BBP operation of 220 kv Bus-1. Remedial action: The GCB Closing circuit was thoroughly checked in the presence of M/S. BHEL engineer from EDN Bengaluru. 25CX (sync check relay) and k3-02 (GCB closing command) NO contacts have been incorporated in the negative path of the GCB closing circuit along with the existing positive side. In the closing circuit of GCB, the Auto synchronising path and DEAD BUS closing path were completely removed. Only manual closing path is kept after verifying thoroughly. New cables were laid for 220 Volts DC supply to GCB marshalling box for closing and tripping circuits. Close & open feedbacks of GCB poles are hooked up in protection relay disturbance record. The closing command output at GCB local panel was monitored by introducing an auxiliary relay. A NO contact of this relay was connected to disturbance record of RET-670 relay. In the DVR auto channel soft start time was increased to 45seconds from 12 seconds in order to build up the generator voltage in slow ramp to avoid inrush current. In manual channel Ifo (NO LOAD FIELD CURRENT), setting S885 was changed to position 0 from position A. It will help in building up of generator voltage in slow ramp so that inrush current due to generator transformer charging shall be avoided. After all the above checks the closing and protection tripping of GCB was checked and found OK As regards keeping synchronization facility in auto-mode, it was informed that in the past with sync-facility in auto-mode, a fire accident took place in the cable gallery in which several control cables got burnt. Also they generally experienced abrupt changes in voltages and currents with auto-mode. As such, they have kept it in manual mode. The matter was referred to their OEM, M/s BHEL who had suggested to keep it under observation in mode for some time. NLC: Auto synchronization should be enabled where 25Ax relay is available, for it not only monitors the preconditions for synchronising, but also activates on-line correction signals, if necessary, to satisfy the conditions for synchronising, and ensures proper closing at right time. This is in place at NLC stations. UPCL: For CB closing circuit, negative breaking system, in which the sync-pulse will be transmitted from (-)ve, may be employed to secure operation of primary switching. (In this regard, a paper presented by Sh. Sanjay Bhatt, UPCL is enclosed at Reference-I for kind perusal). Recommendations: In view of the availability of 25AX, APGENCO shall keep synchronizing facility in auto-mode after getting it s operation verified by its OEM, M/s BHEL. Grid Occurrences discussed during 49 th PCSC Meeting on /29

39 14 Tripping of 220kV Ambewadi-Ponda line at 11:51hrs Annexure-II Line tripped on operation of directional earth fault protection, and distance protection had not sensed the fault. As per FIR, the line tripped on operation of DEF (67N) protection, and distance protection had not sensed the fault. The Currents recorded were Ia-284.2A, Ib-309.5A, Ic-566.9A. The DR (with trigger time = 10:51: hrs) furnished may not be related to this tripping event, as while Ia, Ib became zero, Ic did not. Also no digital signals were shown. In the EL furnished, no events relating to present tripping were observed between 10:00 hrs to 12:00 hrs. KPTCL: The fault was well beyond the resistive reach of the distance relay. Remedial measures: The resistive reaches of distance relays of NPH connected lines at remote end sub stations i. e. at Hubli, Bidnal and Ambewadi were taken up for review and revised to 75 ohms (Primary). DEFR time lever was also modified to 225ms. GI-1 15 Trippings at Raichur TPS at 00:30 hrs RTPS Configuration: 400 kv 1090 (4x210 MW + 1x250 ) MW 220 kv 630 MW (3x210) MW SLD: Running Unit-4, 5 and Unit-8 and 400kV RTPS- Yeramaras TPS feeder got tripped due to deenergization of both 400kV Bus-1&2 at Raichur TPS GI-2 As per TR of RTPS of KPCL: Running Units - 4, 5 & 8 and 400kV RTPS-Yeramaras TPS feeder got tripped due to de-energization of both 400kV Buses - 1&2 at Raichur TPS. Remaining 400kV lines, Units at 220kV level (Unit1,2 &3) and 400/220kV ICT-1&2 were not affected during the incident. Unit-6 is under planned shutdown for annual overhaul from Unit-7 was tripped on auxiliary supply failure on Generation loss was 460 MW due to tripping of Units - 4, 5 & 8. Triggering incident: While building up voltage in Unit-7, (around 10kV) Unit-7 got tripped on operation of GT neutral over-current protection. Simultaneously Main and Tie CB s LBB of Unit-7 got operated. As a result, Main breakers connected to 400kV Buses - 1&2 got tripped (there was no other element in dia of Unit-7). 400kV Raichur line-1 got connected to ICT-2 through Tie-CB Mahboobnagar line got connected to Munirabad line through Tie-CB. Units - 4, 5 & 8 got tripped as the Main and Tie breaker are connected to Bus-1 & Bus-2 respectively (there was no second element in the respective dia s). As Unit-6 was already under planned shutdown, Yeramarus feeder got tripped on tripping of Main breaker connected to 400kV Bus-2. Grid Occurrences discussed during 49 th PCSC Meeting on /29

40 Annexure-II It was stated that as bus bar protection was electromechanical, DR & EL were not available for the incident. What about Stand-alone EL? Reasons for operation of GT neutral over-current protection, and subsequent LBB-operation of Main-CB and Tie-CB of Unit-7. SRLDC: From PMU plots, three faults were observed, which got cleared with a delay of 320 ms, 400 ms, and 120 ms. Reasons for 3 successive faults and their delayed clearance. SOE of RTPS was not recorded at SLDC SCADA and same needs to be checked. Reasons for why the fault went undetected by GT s primary protection (Differential or REF) need to be seen. KPCL: On at 00:30hrs, during voltage build up of Unit-7 around 10KV, Unit-7 tripped on operation of GT neutral over current protection (51NGT) due to surface conduction over the Main & Tie breakers. LBB relays of Main & Tie breakers got operated leading to Bus-1 & 2 bus bar relay operation. Observation: As informed by the shift staff that, heavy sound & arcing observed near Unit-7 Main & Tie breakers. On detailed inspection it is observed that, B-pole (RYB) of Unit-7 Tie breaker interrupter got ruptured. Due to this 51 NGT of Unit-7 operated and initiated class-a & LBB. Since, the surface current was persisting more than 200 milli seconds leading to tripping breakers connected to bus-2. Due to surface conduction over the Unit-7 main breaker, (Bus-1) LBB relay of main breaker also operated simultaneously, leading to tripping breakers connected to bus-1. Reason : The reason for surface current is due to deposition of ash, heavy mist & humidity. The Unit-7 bay is very near to the cooling towers. When enquired about hot-line washing, it was informed that an accident happened while carrying out hotline washing of RTPS connected lines some time ago, subsequent to which it was temporarily put on hold. To this, SRLDC stated that hot-line washing is essential to avoid fog-trippings and other unwarranted trippings due to deposition of dust on insulators. UPCL: Under the circumstances as above, a dedicated breaker-flashover protection comes in handy. Breaker failure schemes are specifically employed to provide backup protection in the event that a circuit breaker fails to operate properly during fault clearing. (In this regard, a write-up on Breaker flask-over protection, and a paper presented by Sh. Sanjay Bhat, UPCL on Adaptive Logic for Breaker Flashover protection are enclosed at Reference-II and Reference-III for kind perusal). Recommendations: KPCL to carry out hot-line washing of RTPS-connected lines regularly to avoid trippings due to fog and dust. KPCL may see the feasibility of providing breaker flashover protection at RTPS, and implement the same if possible. 3. Failure/ Non-operation of Auto-reclose during transient fault Sl. No. Element Date & Time Reason 1 Tripping of 220kV Sabarigiri-Theni line at 16:56 hrs Theni (TANTRANSCO) end: As per FIR/ TR, the line tripped at 16:56 hrs on R-E fault due to carrier-aided trip. Line tripped on a R-phase to earth fault. At Sabarigiri, relay gave a 3 phase trip after 220ms. From Theni end D.R, auto reclose block was observed. Grid Occurrences discussed during 49 th PCSC Meeting on /29

41 From DR, the line tripped in R-ph at 16:49: hrs on R-E fault due to carrier-aided trip. However, within 100 msec, A/R block was observed; EL not furnished (Furnished EL was the last part of DR) Sabarigiri (KSEB) end: As per FIR/ TR, the line tripped at 16:56 hrs on R-E fault due to DPR, Z1 operation (Distance 52.8 km). From DR/ EL, R-E fault got detected at 17:02: hrs; however, as the A/R status was not ready, it gave a 3-ph trip and sent carrier to the other end at (17:02: hrs ms). It was also observed that EF trip was blocked. The delay in fault clearance for DPR, Z1 operation needs to be explained. KSEB: The fault was of high resistance type due to arcing to tree branches in the forest. It was suspected that the fault could have been first picked up by DERF (this explains A/R not ready status), and it slowly developed into a Zone-1 fault, due to which line tripped sending carrier to the remote end. Recommendations: KSEB to furnish a report on the tripping incident along with the remedial measures taken to PCSC forum. Tripping of 220kV at 23:22 As per FIR, line tripped on a Y-phase to 2 Gummidipoondi-Sullurupeta line hrs earth fault. Line did not auto-reclose. Gummidipoondi (TANTRANSCO) end: As per FIR/DR/EL/TR, line tripped at 11:20: hrs on Y-E fault due to DPR, Z1 operation (Distance = km). As A/R provision was not present, the line tripped in 3-ph. Remedial Action: Temporary fault; Feeder charged from Sullurpeta end at 23:38 hrs and tied at Gummudipoondi end 23:40 hrs. Sullurupeta (APTRANSCO) end: As per FIR, the line tripped at 23:17 hrs on Y-E fault due to DPR, Z1 operation. As per DR/EL, the line tripped at 11:17: hrs on Y-E fault due to DPR, Z1 operation. As A/R provision was not present, the line tripped in 3-ph. Status of Provision of A/R: TANTRANSCO and APTRANSCO informed that A/R would be made functional on Gummidipoondi Sullurupeta line by the last week of December, As regards providing A/R on 400 kv Chittoor Tiruvalam D/C line, material procurement it was informed that material procurement is under progress, and A/R would be made functional in one to two months time. 3 Tripping of 220kV Ambewadi- Ponda line at 14:01 hrs Annexure-II line tripped on a B-phase to earth fault. There is no provision for auto-reclose for line Ambewadi (KPTCL) end: As per FIR, the line tripped on B-E fault (fault current = 6.87 ka, fault distance = km) due to DEFR and DPR, Z1 operation. From DR/EL (trigger time = 13:58: hrs), the fault current seemed to have sustained for 750 msec, after which only Any Trip acted. KPTCL: As per the information available from the field people, it was definitely a Zone-1 fault. However, the reasons for delayed fault clearance would be analysed and furnished to PCSC forum. The A/R for this line was covered under KPTCL s U&R proposal for their 93 SS, and would be provided under those works. Grid Occurrences discussed during 49 th PCSC Meeting on /29

42 4 Tripping of 400kV Krishnapatnam-Chittoor line at 07:49 hrs R-phase to earth fault had occurred in line. Chittoor end tried for auto-reclose. However, due to persistent fault, breaker at Chittoor end tripped. Krishnapatnam end relay did not try for auto-reclose and gave a 3 phase trip as observed from D.R Krishnapatnam TPS (APGENCO) end: As per FIR/ DR/ EL, the line tripped at 07:49: hrs on R-E fault due to DPR, Z1 operation (fault distance = 58.1 km). The line did not try for A/R, and simply gave a 3-ph trip. Why? (In DR, addition signals - TEF1_STFW, ZCOM_CS were observed) Chittoor (APTRANSCO) end: Annexure-II As per FIR/ DR/ EL, the line tripped at 07:49: hrs on R-E fault due to DPR, Z1 operation. The line tried for A/R, but gave 3-ph trip due to persistent fault. APGENCO: A/R was kept out of service at the time occurrence of tripping as there were only two evacuating lines [SDSTPS Chittoor & SDSTPS Nellore (AP)] then. Now with the commissioning of second circuit of both the lines in November, 2015, APGENCO agreed to put A/R into service. To this, SRLDC requested to keep A/R functional on all lines emanating from Krishnapatnam TPS by 10 th December, Recommendations: APGENCO to make A/R functional on all lines emanating from Krishnapatnam TPS by 10 th December, Tripping of 400kV Kaniyambeta at 12:08 Line tripped on a Y-phase to earth fault. 5 Kadakola line hrs There is no provision for auto-reclose Kaniyampeta (KSEB) end: As per FIR/ DR, the line tripped at 12:08: hrs on Y-E fault due to DPR, Z1 operation (FD = km; FC = 1643 A) No EL furnished. In DR, various Voltages & Currents should be shown separately (instead of superimposing); Time scale was also very restrictive (configured to show only 300 msec). Remedial Action: As per the information from field, after line patrolling, no fault or permanent tree touching found in the Kerala area. A semi permanent fault is suspected to be in the maintenance area of Kadakola. (The fault location is around 35km). Kadakola (KPTCL) end: As per FIR/ DR. the line tripped at 12:02: hrs on Y-E fault due to DPR, Z1 operation (FD = 69.5 km; FC = 8 p.u.). No EL furnished. 3-ph trip happened due to absence of A/R Remedial action: Transient fault; stood OK after test charging. SRLDC: KPTCL should provide 1-ph A/R from Kadakola end, as in case of transient faults supply can be restored within one second. Recommendations: KPTCL to provide A/R on Kadakola Kaniyampeta line at Kadakola end. Grid Occurrences discussed during 49 th PCSC Meeting on /29

43 4. Lines tripping due to tripping at one end/plcc mal-operation Annexure-II Sl. No. क र.स. 1 घटन क व रण / Details of Event Tripping of 400 kv Mysore-Kozhikode line-2 त र ख/ Date & समय /Time Kozhikode (PGCIL-SR2) end: As per FIR, the line was kept holding at 16:19 hrs क रण / Reason Line tripped at Mysore end only on Direct trip receipt. Mysore (PGCIL-SR2) end: As per FIR/ DR/ EL/ TR, the line tripped at 16:19: hrs due to DT receipt from Kozhikode end. Remedial Action: Tripped at Mysore end only on receipt of DT from Kozhikode end. Suspected DC earth fault at Kozhikode. The DC earth fault was rectified. SRPC/ SRLDC: PGCIL (SR-II) may carry out PLCC end-to-end testing for this line to ensure carrier communication is intact. 2 Tripping of 400 kv JSW-BTPS line at 12:14 hrs Line tripped at BTPS end only and was holding from JSW. R- phase CVT fuse fail had caused tripping at BTPS end JSWEL end: As per FIR/ TR, the line was kept holding. BTPS (KPCL) end: As per FIR/ DR/ TR, the line tripped at 12:12: hrs due to External Trip caused due to R-ph fuse failure of CVT Remedial Action: KPCL: Trip occurred due to CVT "R" Phase fuse failure. CVT Fuse replaced. Tested and found OK. SRLDC: In case of VT/ CVT fuse failure, the relay should block tripping. However, during such block if a fault occurs (this can be detected from neutral current), the block should be released. Grid Occurrences discussed during 49 th PCSC Meeting on /29

44 Annexure-II SLD of Rayalaseema TPS (Courtesy: APGENCO) Grid Occurrences discussed during 49 th PCSC Meeting on /29

45

46 Annexure-III Implementation of PCSC Recommendations (30th to 49th) Meeting No / Index 42/II/3 Details of Event Outage at Regulapadu station of APTRANSC O Date Reason PCSC Recommendations Utility Responsible for implementat ion at 00:49 hrs Y-Ph Metering PT failed at 220KV Ragulapadu Substation. Fault got cleared by tripping of lines from remote ends. Andhra Pradesh APTRANSCO to furnish the remedial measures taken in consequent to the tripping incident along with the status of bus bar protection and bus coupler at Regulapadu S/s. A/R feature to be enabled on Regulapadu Alipuira 220 kv inter-state line. APTRANSC O Status of Recommendations as on Mail recieved on : APTRANSCOhas planned to commission ABB make ETL-41 type PLCC terminal along with NSD-50 type protection coupler at Ragulapadu end towards Alipura. vide our Ltr Dt , it is requested KPTCL to arrange ABB make ETL-41 cabinet with NSD- 50 type protection coupler for establishing PLC communication between Alipura- Ragulapadu. Remarks 45/II/14 Tripping of 400/220 kv ICT-1&2 at Gooty substation at 06:37 hrs As per FIR, ICT-1&2 tripped on operation of directional overcurrent and earth fault protection. It was reported that there was fault in 220kV APTRANSCO system 1. APTRANSCO to check resistive reach of the distance relays on 220 kv Gooty SS Gooty RS line 2. APTRANSCO to check time coordination of distance relay on Gooty SS Gooty RS line at Gooty SS with Gooty ICT s (1 & 2) back-up protection. APTRANSC O Yet to be informed 49/II/8 Tripping of kV at 10:56 hrs Vemagiri- Sattenapalli line and 400kV Vemagiri- Kalpakka line B-phase to earth fault had occurred in line. From Vemagiri end D.R, three phase trip and Tie-CB LBB operated was observed. Sattenapalli end had auto-reclosed, however breaker at Satenapalli tripped 8 sec after A/R on receipt of DT from Vemagiri as observed from EL of Satenapalli station. For 400k Vemagiri-Kalpakka line at Vemagiri end, Tie LBB operation and Grp-A/B trip was observed and direct trip was sent to Kalpakka end APTRANSCO to furnish a report on the tripping of 400 kv Vemagiri Sattenapalli line along with relevant DR & EL showing clearly the successful operation of A/R followed by T- LBB/ OVR, Stage-I operation. APTRANSC O Yet to be informed Page 1 of 24

47 Annexure-III 49/II/13 Tripping of running Units at 03:30 hrs 1 & 3 at Rayalaseema TPS of APGENCO While synchronizing Unit-5 with grid, BBP of 220kV Bus-1 operated which resulted in deenergization of 220kV Bus-1. This resulted in tripping of running Unit- 1&Unit-3, 220kV lines Pulivedula- 1, Yeralaguntla-1, Chinakampalli- 1, Timmapura In view of the availability of 25AX, APGENCO shall keep synchronizing facility in auto-mode after getting it s operation verified by its OEM, M/s BHEL. APGENCO Yet to be informed 49/III/4 Tripping of 400kV Krishnapatna m-chittoor line at 07:49 hrs R-phase to earth fault had occurred in line. Chittoor end tried for autoreclose. However, due to persistent fault, breaker at Chittoor end tripped. Krishnapatnam end relay did not try for auto-reclose and gave a 3 phase trip as observed from D.R APGENCO to make A/R functional on all lines emanating from Krishnapatnam TPS by 10th December, APGENCO Yet to be informed 44/III/2 Tripping of 400kV Ghanapur- Mamidapalli line at 2:03 hrs Line tripped at Mamidapalli end only and was holding at Ghanapur. Overvoltage protection had operated at Mamidapalli TSTRANSCO to make DR functional at Mamidipalli Telangana TSTRANSC O TSTRANSCO informed vide their mail dated that the existing relays would be replaced with numerical relays in DPR works. Page 2 of 24

48 Annexure-III 47/I/1 (GD) Disturbance in Srisailam left bank power station at 15:25 hrs 400kV Srisailam-Mamidapalli line- 2, 400kV Srisailam- Satenapalli line-2 and 400 kv Srisailam- Kurnool line tripped during multiple tripping at Srisailam power station. 400kV Srisailam- Mamidapalli-1 and 400kv Srisailam-Satenapalli-1 was kept out of service due over-voltage conditions. There was no generation at Srisailam left bank power station. Triggering incident was failure of CT in 400kV Srisailam- Satenapalli line-2 at Srisailam end. 1. TSGENCO to disable sensitive earth fault protection provided as supplementary to static bus-bar protection at Srisailam LB (GIS). 2. TSGENCO to set the current setting for phase-to-ground faults for numerical bus-bar protection at a suitable value so that the prominent high-resistance earth faults occurring within the bus-zone are covered at Srisailam LB (GIS). TSGENCO Yet to be informed 47/II/6 Tripping of 400kV Khammam- KTPS line at 6:08 hrs Y-phase to earth fault had occurred in line. From Khammam end DR it was observed that the relay after dead time tried for auto-reclose. The fault was persisting and relay gave a single phase trip instead of a 3 phase trip after 1.25sec. R& B pole voltage dip after 2 sec possibly due to operation of pole discrepancy. Auto-reclose close command observed after 2.5 seconds and all poles got closed. 1. TSGENCO to check the reclaim time of A/R and set it at 25 sec at KTPS. 2. TSGENCO to carry out PLCC end-to-end testing in coordination with PGCIL (SR-I) for KTPS Khammam line-2; retrofitting of Protection Coupler may be carried out based on the test results. TSGENCO Yet to be informed 48/II/5 Tripping of kV at 2:58 hrs Nagarjunsaga r- Mahboobnaga r line Line tripped on operation of OV protection at Mahboobnagar and DT received at N sagar station. DT receive was observed in DR and EL of N sagar station. D.R/EL of Mahboobnagar was not furnished to validate the overvoltage tripping TSTRANSCO to furnish a detailed report on the tripping event along with remedial measures taken to PCSC forum. TSTRANSC O Yet to be informed 48/III/4 Tripping of kV at 2:24 hrs Gajwel- Shankarapally line line tripped at Gajwel end on R- Phase to ground fault. Reason for non-auto reclose could be established as DR and EL of both ends were not furnished TSTRANSCO to furnish a detailed report on the tripping event along with remedial measures taken to PCSC forum. TSTRANSC O Yet to be informed Page 3 of 24

49 Annexure-III 30/I/A RTPS Mar-14 Tripping incidents and the Spl meeting held at RTPS on 13th and 14th March 2014 Spl meeting held at RTPS on 13 th and 14 th March 2014 Karnataka The PCSC forum recommended for replacement of existing electromechanical relays with Numerical relays. KPCL Mail recieved on and : 1) Replacement of Old electromagnetic relays with Numerical relays has been completed for RTPS-BTPS line & commissioned on Raichur-PG1 & Raichur-PG2 lines have already retrofitted with numerical relays. 2. Job order placed on on M/s Alstom T&D India Ltd. Chennai for retrofitting of relays for all 220kV lines at RTPS. 3. Retrofit of existing bus bar(cag-34) with numerical version Budgetary offers obtained and is under process. 34/III/1 400kV Raichur- BTPS line Transient fault in R-phase. Line did not auto reclose A/R at BTPS end to be made operational within one month KPCL 1. A/R for 220kV lines enabled already. 2. Shut down of lines availed to commission the auto reclosing schme for 400 kv line at BTPS. Mail recieved on : Timer relays have been received at site. A letter has been addressed to M/s Alstom to complete the work on priority basis. Mail recieved on : Commissioning of Autorecloser planned on 14, 15 & 16th of Dec subject to availability of LC. 38/GD/3. 5 GD-1 at Kadra and Kodasalli hydro power station at 19:31hrs A fault had occurred in 220 kv Kadra and Kodasalli. As A result, deenergization of 220kV bus occurred at Kadra and Kodasalli. 1. The PCSC forum requested KPCL to speed up the installation of Numerical Distance Protection relay in Kadra Kaiga and Kodasalli Kaiga. 2. The PCSC forum requested KPCL to submit the implementation status of PSAG-10 recommendations within a week s time. KPCL Mail recieved on : NIT floated on through e-portal. Bid evaluation completed. LOA's issued to M/s Schneider Electric Infrastructure Ltd. on Mail recieved on : LOA's issued to M/s Schneider Electric Infrastructure Ltd. on Engineering work is in progress. Page 4 of 24

50 Annexure-III 34/I/6 400/220 kv ICT-1 & 2 at MUNIRABA D As reported directional over current relay of ICT s operated due to snapping of line jumper in 220kV Lingapur line. 1. Bus bar protection shall be provided by asset owner ( i.e KPTCL). 2. Settings for main distance protection & Overcurrent protection shall be examined and reviewed. KPTCL Mail recieved on (KPTCL): 1. KPTCL has taken action to provide bus bar protection to 220kV buses. 2. Over current relay Settings of ICTs to be reviewed by PGCIL. 3. Time synchronization of the Substation shall be ensured. 4. Correct DR shall be submitted to the SRLDC for trip analysis. Mail received on (KPTCL): Initial Tendering stage 38/GD/3. 1 GD-1 at Mahalingapur a Substation of KPTCL Fault had occurred in 220kV Mahalingapura-Narendra line-2. Due to the failure of relay operation at Mahalingapura, breakers at remote end tripped which resulted in bus dead condition. 1. PCSC forum recommended KPTCL to replace the old static distance protection relays with numerical relays. 2. PCSC forum also requested KPTCL to provide a broken conductor alarm indication in Control Room. 3. Standing instruction needed to be given to the all substation personnel for not changing the relay settings without approval of RT/MRT wing. KPTCL Mail received on (KPTCL) & : 1.Existing Back up relays will be replaced by numerical type distance relays.procurement is in tendering stage. Remaining observations were attended. 38/GD/3. GD-1 at 2 Guttur Substation of KPTCL at 11:42 hrs Circuit breaker of 400kV Guttur- Hiriyur line-1 failed at Guttur end while availing shutdown for replacement of CVT. The failure of breaker caused bus fault at Guttur. KPTCL was requested to expedite the early implementation of pending recommendations of: 1. Protection Audit (Phase-I & Phase-II) 2. PSAG-4, PSAG-5, and PSAG-8 KPTCL Mail received on & : Latest satus of implementatin of Phase-1 &2 recommendations, PSAG 4,5 and 8 is being obtained from field. The Status will be updated witin a weeks time. 39/I/5 Tripping of 400/220kV ICT-2 at Hoody substation of KPTCL Suspected mal-operation of 220kV side Rphase over current relay 1. PCSC forum recommended KPTCL to replace the relay with a different make. 2. KPTCL was also requested to train the O&M personnel adequately before performing any maintenance works to avoid such unwanted trippings. KPTCL Mail received on & : C&R panels of 500MVA ICT 1&2 will be replaced under scheduled R&M works. O&M personnel are instructed to take sufficient care in order to avoid unwarrented trippings. Page 5 of 24

51 Annexure-III 40/I/1 GD-1 at 220kV Ambewadi Station of KPTCL at 21:22 hrs Triggering incident was B-phase to earth fault in 220kV Ambewadi- Nagzari line-1. B-pole of breaker did not open at Ambewadi end. LBB protection not available at Ambewadi end. All elements tripped on Zone-2 from remote ends. 1. Till the completion of R&M works for bus bar and LBB protection, KPTCL shall explore the possibility of having split bus operation at Ambewadi and submit the details of the same to PCSC forum. 2. KPTCL shall provide the details of the tripping of Supa hydro station connected downstream from 110 kv bus. KPTCL Mail recieved on : Action is being taken by KPTCL for operating Ambewadi in split bus mode. Problem in bus coupler breaker is attended.isolator overhaulling work is completed.pts are already provided to 220kV Bus-II. After commissioning of Bus-II PTs, Ambewadi can be operated in split bus mode. works will be completed within a months time. 40/IV/1 220kV Sedam Tandur line at 22:20 hrs Line tripped on Yphase to earth fault from both the ends KPTCL was requested to explore the possibility of providing A/R feature to this line and submit the remedial measures to the PCSC forum. KPTCL Mail recieved on : Carrier protection is being restored for 220kV Sedam-Tandoor line at Sedam end. After restoring the carrier protection, AR will be enabled. 41/I/1 GD-1 at kV Kadra at 12:56 hrs power Station of KPCL Triggering incident was B-phase to earth fault had occurred in 220kV Kadra-Kodasalli line. Line tripped from Kodasalli end only. 220kV Kaiga-Kadra tripped in Zone-3 from Kaiga end. Tripping of evacuating lines caused bus shut down at Kadra hydro station. 1. KPCL to make functional the Main2 (EPAC) relay with the help of KPTCL at the earliest. 2. KPCL to investigate the reason for DC fuse fail during transient fault in 220kV Kadra- Kodasalli line including the testing/ checking of DC supply cables, breaker control cables, and trip coils. 3. KPCL to ensure supply for Main-1& Main- 2 protections, Trip Coils (TC1, TC2) from separate battery banks. KPCL Mail received on : 1. Main-2 relays already installed and commissioned. 2. DC fuses are intact. Till date no such incidence occurred. 3. Possibility of DC-1 & DC-2 arrangement and splitting of DC will be reviewed. Mail received on , and : 1. Completed. 2. Completed. 3. Possibility of DC-1 & DC-2 arrangement and splitting of DC will be reviewed. 41/I/4 Complete outage at at 8.00 hrs 220kV Sedam Substation of KPTCL (GD- 1) R-Phase to ground fault occurred 1. KPTCL to provide Bus bar and LBB on 220kV Sedam-Shahpur line. protections for 220 kv bus at Sedam S/s. Fault not cleared from Sedam end 2. KPTCL to implement A/R feature on 220 due to stuck-breaker condition. kv Sedam-Tandur inter-state line. While the Sedam- Sahapur line tripped from Shahapur end in Zone- 1, the other 220 kv lines from KPTCL Mail received on : 1. Procurement of Bus bar and LBB protection is in the final tendering stage. 2. Action is being taken to restore the carrier protection for 220kV Sedam-Tandoor line. AR will be enabled after restoration of PLCC. Page 6 of 24

52 Annexure-III Sedam tripped at remote ends in Zone-2. This caused complete outage of 220kV Sedam substation. 42/I/1 (GD) Complete outage of at 14:24 hrs 220kV Sedam substation of KPTCL Fault occurred in 220kV Sedam- Shahpur line 1. KPTCL to provide Bus Bar protection and LBB protection at Sedam S/s and furnish the status of their implementation to PCSC forum. 2. KPTCL to implement A/R feature on 220 kv Sedam-Tandur inter-state line. KPTCL Mail received on : 1. Procurement of Bus bar and LBB protection is in the final tendering stage. 2. Action is being taken to restore the carrier protection for 220kV Sedam-Tandoor line. AR will be enabled after restoration of PLCC. 42/I/2 (GD) Complete outage of 220kV Ambewadi substation of KPTCL at 7:51 hrs Fault in 220kV Ambewadi- Nagjheri line-2 1. KPTCL shall provide A/R feature on Ambewadi Ponda 220 kv D/C inter-state line. 2. Till the completion of R&M works for bus bar and LBB protection, KPTCL shall explore the possibility of having split bus operation at Ambewadi and submit the details of the same to PCSC forum. KPTCL Mail received on : 1. Procurement of Bus bar and LBB protection is in the final tendering stage. 2. Action is being taken to restore the carrier protection for 220kV Sedam-Tandoor line. AR will be enabled after restoration of PLCC. 42/II/2 Tripping of 220kV Chikodi- Talandage and Mudshingi line at 06:40 hrs Lines tripped during test charging 220kV Chikodi-Belgaum line-2 from Chikodi end. 1. KPTCL to provide A/R feature on the 220 kv Chikkodi Talandage, and 220 kv Chikkodi Mudashinge inter-state lines. 2. KPTCL to carry out E/F relay coordination for Chikkodi - Talandage and Chikkodi Mudashinge lines in coordination with Maharashtra. KPTCL Mail received on : Action is taken for enabling AR for Mudashinge and Talandage lines. Work is scheduled during first week of August Page 7 of 24

53 Annexure-III 43/II/14 Tripping of 400/220kV ICT-1 at BTPS at 1:09 hrs ICT tripped due to operation of Over current and Earth fault relay KPCL to check the possibility of providing line differential protection between RTPS and Yermarus stations. KPCL Mail received on , and : Revised relay settings are awaited from KPTCL. Revised relay settings furnished by KPTCL will be incorporated in coordination with KPTCL shortly. 44/II/3 Tripping of kV at Kaiga- 20:28 hrs Kodasalli and 220kV Kodasalli- Nagjheri line kV Kodasalli-Nagjheri line-1 tripped from Kodasalli end on operation of distance protection, zone kV Kodasalli-Nagjheri line- 1&2 is kept opened from Nagjheri end, hence fault could not be cleared with carrier aided protection. Backup earth fault relay at Kaiga end got operated during the event and resulted in tripping of 220kV Kaiga- Kodasalli line from Kaiga end. 1. KPCL to check the possibility of implementing Permissive Over Reach (POR) with Echo feature at Kodasally end. 2. If the above is not possible, KPCL shall check the possibility of keeping the 220kV Kodasalli-Nagjheri lines OPEN at Kodasalli end and idle-charged at Nagjheri end, and implement the same. KPCL Mail received on : The matter had been discussed with KPTCL. KPTCL recommended to keep Zone-2 time lever to zero. If this is acceptable, then the same shall be incorporated immediately. Mail received on , and : The matter has been discussed with KPTCL. KPTCL recommended to keep Zone-2 time lever to zero. If this is acceptable to SRLDC, then the same shall be incorporated immediately.reply from SRLDC is awaited. 45/III/12 Tripping of 400kV Raichur- BTPS line at 01:02 hrs line tripped on R-phase to earth fault. Line did not auto-reclose KPCL to make A/R operational on 400 kv RTPS BTPS S/C line at both ends. KPCL Mail recieved on : Completed at RTPS end. 46/II/21 Trippings at 220kV Raichur TPS at 01:35 hrs 1. KPCL to check the operation of antipumping relay on 220 kv side and keep it in healthy condition. 2. KPCL to provide manual reset to the 220 kv side master trip relay. 3. KPCL to use both the 220 kv buses as main buses under normal operation, and should go for single bus operation only during emergencies. KPCL Mail recieved on : 1) Completed 3) Two bus operation for 220kV buses : In place of existing CT switching relays, High speed manual heavy duty change over switch of sufficient current capacity will be retrofitted to all feeders at 220kV station and same will be operated manually during changeover of feeder by one bus to the other and this arrangement may facilitate to put both buses in service. Time required for this retrofit is around 90days. However, this work will be taken up only after retrofitting of electromagnetic relays with numerical relays for Main-2 protection of all 220kV lines, for which work is in progress. Page 8 of 24

54 Annexure-III 47/II/13 Tripping of Unit-1&2 along with 400/220kV ICT-2 at Raichur TPS at 4:51 hrs 220kV RTPS-Lingasugur line-2 KPTCL to activate non-directional Over tripped at TPS end on operation of Current protection with a time delay of 600- distance protection zone msec for Fuse 400/220kV ICT-2 got tripped on failure condition at Lingasugur. operation of earth fault protection. 220kV RTPS-Lingasugur line- 1&3 tripped on distance protection zone-2 and zone-3 respectively. Due to tripping of ICT-2, the running units got overloaded and it was mentioned that under frequency occurred as units are on load control. The Units got tripped on under frequency. KPTCL Yet to be informed 47/III/8 Tripping of 220kV Ambewadi- Ponda line at 13:20 hrs Line tripped on a transient fault in B-phase. There is no provision for auto reclose. Till A/R is put into service on Ambewadi- Ponda line-1, KPTCL to reduce Zone-2 time setting to zero sec. at Ambewadi end. KPTCL Yet to be informed 47/III/10 Tripping of 220kV Ambewadi- Ponda line at 10:51 hrs and at 11:15 hrs at 13:20 hrs Line tripped on a B-phase to earth fault. Line tripped as there is no provision for auto-reclose 47/III/12 Tripping of 220kV Ambewadi- Ponda line-1 Line tripped on a transient fault. There is no provision for Auto reclose. 48/I/2 (GD) Complete outage of 220kV Peenya Substation in Karnataka at 4:23:17 hrs All connected 220kV lines and KPTCL to revise distance relay settings at transformers were taken on 220kV Nelamangala end for 220 kv Nelamangala North bus as South bus was under Hebbal - Peenya line 1 for the effective line shut down for conversion of strung length of 17 km. These new settings can be bus to rigid bus and isolator appropriately reviewed as and when the tiearrangement at Hebbal is done away with. replacement under R&M works. Failure of HV side Y phase CT of 150MVA Transformer-3 occurred at Peenya Substation which resulted in operation of Differential and HV REF protection. The failure of CT also resulted in a 220kV bus fault in North Bus. KPTCL Yet to be informed Page 9 of 24

55 Annexure-III 48/I/3 (GD) Outage of 220kV Ambewadi station in Karnataka at 10:41 hrs 220kV Ambewadi-Nagjheri line-2 tripped on B-phase to earth fault. This resulted in loss of supply to 220kV Ambewadi bus. 220kV Ambewadi-Ponda line-1&2 were hand tripped after deenergization of bus at Ambewadi. KPTCL to fast-track providing A/R on all 220 kv lines emanating from Ambewadi SS to prevent Station shut-down on temporary faults. KPTCL Yet to be informed 48/I/4 (GD) Complete outage of 220 at 16:32 hrs kv HSR substation of Karnataka All connected 220kV lines at 220kV HSR substation i.e. Somanahalli, EPIP, Hoody and Nagnathapura tripped during the incident. Triggering incident was fault in 220kV HSR-EPIP line KPTCL to review distance relay settings at Naganathpura SS in view of LILO arrangement at HSR Lay-out. KPTCL Yet to be informed 49/I/1.3 (GD) Complete outage of 220kV Ambewadi Substation of KPTCL at 14:34 hrs 220kV Nagjheri-Ambewadi line-1 tripped at 13:33 hrs due to B phase to earth fault. Ambewadi was radially fed from Nagjheri power station through 220kV Nagjheri- Ambewadi line-2. Tripping of this line caused 220kV Bus shut down at Ambewadi and remaining lines and transformers were hand tripped 1. KPCL to provide A/R on all 220 kv lines emanating from Nagjheri PH. 2. KPTCL to provide A/R on all 220 kv lines emanating from Ambewadi SS. KPTCL Yet to be informed 49/II/15 Trippings at Raichur TPS at 00:30 hrs Running Unit-4, 5 and Unit-8 and 400kV RTPS-Yeramaras TPS feeder got tripped due to deenergization of both 400kV Bus- 1&2 at Raichur TPS 1. KPCL to carry out hot-line washing of RTPSconnected lines regularly to avoid trippings due to fog and dust. 2. KPCL may see the feasibility of providing breaker flashover protection at RTPS, and implement the same if possible. KPCL Yet to be informed 49/III/5 Tripping of at Line tripped on a Y-phase to earth KPTCL to provide A/R on Kadakola 400kV Kaniyambeta- Kadakola line 12:08 hrs fault. There is no provision for auto-kaniyampetreclose line at Kadakola end. KPCL Yet to be informed Page 10 of 24

56 Annexure-III 43/II/5 Tripping of 400kV Alamathy- SVChatram line-1&2 and 400/230kV ICT at S.V.Chatram at 15:29 hrs Line-2 tripped on R-phase to earth fault. Line autoreclosed at SVChatram end and failed to reclose at Alamathy end. Bphase to earth fault in line-1. Line tried for A/r but due to permanent fault line did not reclose. ICT tripped on operation of over flux protection. Tamil Nadu TANTRANSCO was requested to swap the relays between two stations, so that Main-1 and Main-2 will be of different make at each station. TANTRANS CO TANTRANSCO vide their mail dated informed that different relays in Main-I & Main-II would be ensured at the earliest. Mail recieved on : Different relays in Main-I & Main-II will be ensured. 45/II/12 Multiple tripping at 400/230kV Alamathy substation at 09:08hrs As per FIR, failure of R-phase CT of 230kV Alamathy-Manali feeder occurred at Alamathy end. Hence 230KV BBP Zone 1 & 2 Operated at Alamathy substation. All the 230KV feeders, 230KV BC, ICT-3, 4 & 5 LV breakers got tripped. TANTRANSCO to furnish a detailed tripping report including reasons for delayed clearance of fault at Almathy. TANTRANS CO Mail received on : The faults were cleared with out time delay at Alamathy SS. Detailed Tripping report sent vide Lr.No.CE/P&C/SE/D/ EPC4/AEE3/F.SRPC/ D.21/15, dated The reasons for the delayed clearance of the third fault not furnished. 48/I/1 (GD) Disturbance in 220kV Tamilnadu system at 14:04 hrs Complete outage of 230kV Palladam, 230 kv Othakalmandapam S/s, 230 kv Coimbatore S/s, 230 kv Thudialur and 230 kv Sadayapalayam S/s TANTRANSCO to take suitable measures like installing more stub-towers along 230 kv OK Mandapam Myvady line to avoid excessive sag due to over-loading. TANTRANS CO Yet to be informed 48/II/6 Tripping of 400/220kV Alamathy ICT-3,4& at 04:24hrs Triggering incident was failure of Y & B phase CT failure in 230kV Korattur feeder 1. TANTRANSCO to furnish a detailed report on the tripping event covering the sequence of events, and the remedial measures taken to PCSC forum. TANTRANS CO Yet to be informed 2. TANTRANSCO to configure Bus-Bar protection at Alamathy for instantaneous operation. Page 11 of 24

57 Annexure-III 49/I/1.5 (GD) Complete outage of S.P.Koil station of TANTRANS CO and generation loss at Madras Atomic Power station(map S) at Fault had occurred in 230kV 09:33 hrs MAPS-S.P.Koil feeder-1. LBB protection got operated as breaker of this feeder was under lockout and resulted in tripping of 230kV bus at S.P.Koil. Unit-1&2 at MAPS due to loss of evacuating feeders i.e. 230kV MAPS-S.P.Koil feeder-1&2 1. TANTRANSCO to ensure correctness of operation of LBB relays at SP Koil. 2. TANTRANSCO & MAPS to furnish their respective compliance report of the recommendations of to-be-conducted PSAG-14 meeting at MAPS, Kalapakkam. TANTRANS CO Yet to be informed 44/I/1 (GD) Complete outage of at 12:30 Hrs Idukki Hydro Power Station (GD-1) 220 kv breaker of unit-3 at Idukki Power house flashed and bus differential protection acted. All Generators (6Nos.) along with all 220 kv feeders tripped during the incident. Kerala 1. KSEB to reduce sensitivity of REF protection appropriately at Idukki PH. 2. KSEB to replace/ repair the faulty breaker. 3. KSEB to check the PLCC equipment at New Pallam and inform the remedial measures taken to PCSC forum. KSEB Mail recieved on : 1. Purchase procedures is still in progress. 2. Replaced. 3. PLCC equipment Tested and found OK. (Recomm endation No.1) 49/II/3 Tripping of 220kV Edamon- Tirunelveli line-1& at 21:30 hrs 220kV Edamon-Tirunelveli lines - KSEB to furnish reasons for DT not being KSEB Yet to be informed 1&2 got tripped due to operation of sent to the remote end during the tripping event Bus Bar protection which was due to human error along with remedial measures taken to PCSC forum. 49/III/1 Tripping of 220kV Sabarigiri- Theni line at 16:56 hrs Line tripped on a R-phase to earth KSEB to furnish a report on the tripping fault. At Sabarigiri, relay gave a 3 incident along with the remedial measures phase trip after 220ms. From Theni taken to PCSC forum. end D.R, auto reclose block was observed. KSEB Yet to be informed Page 12 of 24

58 Annexure-III 34/I/7 HVDC BHADRAV ATHI POLE As reported pole-2 tripped due on 5th harmonic alarm. PGCIL 1. Complete analysis of the faults and rectification/remedial action taken to avert similar occurrence in the HVDC Back to Back station shall be submitted. PGCIL Reply received during 46th PCSC meeting: Being pursued with POWERGRID, WR-1 2. The PCSC forum recommended PGCIL, SRTS-I take up the issue with WRTS to submit the report as per IEGC guidelines. 3. SRLDC is also requested to send a letter to WRLDC to submit the reports to SR also. 4. Based on the SRTS/SRLDC correspondences, SRPC would take it up with WR and PGCIL if the issue is not getting resolved. 41/III/2 Tripping of 400kV Udumalpet- Palakad line- 1& 400 Udumalpet- Arasur line at 9:50hrs PLCC of Udumalpet-Arasur-2 maloperated PGCIL to furnish remedial measures taken. PGCIL to properly tune PLCC panels. PGCIL Mail received on : The issue was referred to BPL and OEM suggested to upgrade the panels with design modifications. LOA has been placed on BPL for the same. Work is expected to be completed by Nov'15 end. 42/II/7 Tripping of 400kV Jeypore- Gazuwaka line- 1&2 and tripping of HVDC back to back pole- 1&2 at Gazuwaka at 13:34 hrs HVDC pole-1 got tripped due to failure of 4 no. power supply card. HVDC pole-2 tripped on DC low voltage trip. 400kV Jeypore-Gazuwaka line- 1&2 tripped due to operation of Over voltage protection at Gazuwaka end. PGCIL (SR-II) to submit the report of M/s ABB s on preventing supply card failures. PGCIL Yet to be informed 42/II/22 Tripping of HVDC pole- 1&2 at Gazuwaka and 400kV Jeypore Gajuwaka line at 17:12 hrs HVDC Pole-1 at Gazuwaka tripped due to tripping of filter banks and Pole-2 tripped due to operation of differential protection. 400kV Jeypore-Gazuwaka line-1 tripped on over-voltage from Gazuwaka end. PGCIL (SR-I) to furnish the reasons for Converter Transformer differential protection operation for Pole-2 along with the remedial measures taken. PGCIL Reply received during 46th PCSC meeting: Operation is in-order as per OEM manual (ABB HVDC) Page 13 of 24

59 Annexure-III 42/II/23 Tripping of HVDC Bhadravathi Pole at 13:55 hrs Pole tripped due to failure of auxiliary supply PGCIL (SR-I) to submit the compliance report on PSAG-11 recommendations to PCSC forum. PGCIL Reply received during 46th PCSC meeting: Tertiary Transformer charged and auxiliary power for HVDC is being availed from tertiary widings of ICT. Page 14 of 24

60 Annexure-III 43/II/2 Multiple tripping at 15:40 hrs at 400/230kV Hosur substation of Powergrid 230kV Bus-2 at Hosur (PG) got tripped as spurious initiation got extended to LBB relay of 230kV Hosur-Hosur(PG) line at Hosur(PG) end due to shorting of contacts in lockout relay. 400/230kV ICT-2, ICT-3, 230kV Hosur-Vinnamangalam, 230kV Hosur(PG)-Hosur which were connected to Bus-2 got tripped along with bus coupler breaker PGCIL (SR-II) to check the possibility of providing re-trip feature in LBB relay. PGCIL Mail received on : The scheme was tested thoroughly found normal. 44/I/3 (GD) 765 kv Raichur- Sholapur line 1 & 2 tripped at 19:19 hrs Tripped on Overload. 1. PGCIL to provide the status of healthiness of SPS contact logic in SRLDC s SCADA. 2. PGCIL to furnish the details of the implemented SPS-7 scheme including logic diagram to PCSC forum. PGCIL Yet to be informed 44/II/4 Tripping of 400kV Ramagundam- Hyderabad line-3, 400kV Hyderabad- Malkaram line-1 and 400kV Bus-1 at Hyderabad at 15:11 hrs 400kV Ramagundam-Hyderabad line-3 at ramagundam end only due to DT receive. 400kV Hyderabad-Malkaram line- 1 tripped at Hyderbad end only and was holding from Malkaram end. 400kV Bus-1 at Hyderabad due to operation of bus bar protection. PGCIL (SR-I) to check healthiness of PLCC panels at Hyderabad SS, and repair/ replace them, if necessary. PGCIL Yet to be informed 44/II/6 Multiple tripping at Vemagiri substation of APTRANSC O at 10:04 hrs 400kV Vemagiri-Vijayawada line- 1&3, 400kV Vemagiri-Goutami line-2, 400kV Vemagiri- Konaseema line-2 and 400/220kV ICT-2 at Vemagiri tripped during the incident. Triggering incident was failure of B-phase L.A in 400kV Vijayawada-Vemagiri line-1 at Vemagiri end. 1. PGCIL (SR-I) to enable Auto reclosure feature at Vijayawada end. 2. PGCIL (SR-I) to check distance relay settings for Vijayawada Vemagiri line 3, and furnish a compliance report to PCSC forum. PGCIL Yet to be informed Page 15 of 24

61 Annexure-III 44/II/7 Tripping of 765kV Kurnool- Tiruvalam line-1 and 765kV Kurnool- NPS at 18:10 hrs REF protection of Line reactor of Nellore-1&2 and Tiruvalam line-1 maloperated due to DC earth fault 1. PGCIL (SR-I) to submit the action taken report on the measures suggested by their OEM. 2. PGCIL (SR-I) to check for the availability of Chatter Disable feature in P141 and configure it appropriately to block operation of REF protection on DC fluctuations. PGCIL Yet to be informed 44/II/8 Tripping of 400kV Gooty-NPS line at 13:16 hrs R-phase to earth fault had occurred in line. Lines auto-reclosed at gooty end and later tripped due to DT receive from NPS end. PGCIL (SR-I) to coordinate STUB protection settings with the distance protection time settings at NPS. PGCIL Yet to be informed 45/II/15 Tripping of 765kV Raichur- Solapur line- 1& at 4:13 hrs Lines tripped on transient fault. To avoid tripping of transmission lines on Auto reclose was un-successful. SR transient faults, PGCIL is recommended to &NEW grid separated due to carry out periodic patrolling of lines, and tripping of 765kV lines ensure their proper maintenance by carrying out jungle/ bushing clearance and trimming of tree branches within the RoW of transmission lines as per the SRPC transmission line patrolling guidelines (available under the menu item "All Uploads Operation Miscellaneous Transmission Line Patrolling Protocol / Guidelines for Southern Region" on SRPC website). PGCIL Yet to be informed 45/II/21 Tripping of 400/220kV ICT-1 at Gooty Substation at 12:30 hrs ICT tripped due to mal-operation of differential relay 1. PGCIL to follow IS and CEA regulations while carrying out maintenance work. 2. PGCIL to furnish a report on what caused the ICT-1 tripping including remedial measures. PGCIL Yet to be informed Page 16 of 24

62 Annexure-III 45/II/29 Tripping of HVDC at hrs Talcher-Kolar Pole-2. DC line fault To avoid tripping due to transient faults, PGCIL (SR-I) is recommended to carry out periodic patrolling of lines, and ensure proper maintenance of transmission lines by carrying out jungle/ bushing clearance and trimming of tree branches within the RoW of transmission lines as per the SRPC transmission line patrolling guidelines (available under the menu item "All Uploads Operation Miscellaneous Transmission Line Patrolling Protocol / Guidelines for Southern Region" on SRPC website). PGCIL Mail received on : Major Shut Down of HVDC Bi-pole line for replacement of insulators in Polluted Streched is planned from 07th 11th January-16 scheduled. 46/II/1 Tripping of 400/220kV ICT-2 at Nagarjunsaga r Station at 18:12 hrs& 19:18 hrs ICT-2 tripped due to mal-operation of 86B relay due to suspected DC earth fault. PGCIL (SR-I) to furnish a detailed report on ICT-2& Bus II outage at hrs on along with the remedial measures taken. PGCIL Yet to be informed 46/II/4 46/II/13 Tripping of 400/220kV ICT-2 at Gooty substation Tripping of 400kV Gooty- NPS line at 13:06 hrs at 09:59 hrs At 220kV Gooty Switching Station, 220KV Gooty Receiving Station feeder line side Y-Phase jumper connected between line isolator to boom resulting in a 220kV Bus fault. This resulted in tripping of ICT-2 and 220kV feeders connected to 220KV BUS- II Breaker at NPS end tripped on Direct Trip receipt from NPS end. After 4 seconds, over voltage protection operated at NPS end as observed from EL, and direct trip was sent to Gooty. PGCIL (SR-I) to furnish a detailed report as to what caused LBB operation at 400 kv Gooty SS along with the remedial measures taken. 1. PGCIL (SR-I) to furnish a report detailing the sequence of events including the remedial measures taken to PCSC forum. 2. PGCIL (SR-I) to verify and ensure timesynchronizationof DR& EL with GPS at both Gooty and NPS. 3. PGCIL (SR-I) to check and resolve,in coordination with APTRANSCO, the professed Phase-Discrepancy that is found to be occurring between 400 kv Gooty (PG) SS and the surrounding 220 kv network of APTRANSCO in the event of a fault. PGCIL Yet to be informed PGCIL Yet to be informed Page 17 of 24

63 Annexure-III 46/II/22 Separation of SR-grid and NEW-grid at hrs. 1. PGCIL (SR-I) to obtain from PGCIL (WR-l) the reasons for DT receipt from Sholapur end and furnish thesame along with the remedial measures taken to PCSC forum. PGCIL Yet to be informed 2. PGClL (SR-I) to verify the logic implemented of SPS-1 and SPS-7 for the 76S kv Raichur - Sholapur link byavailing the line shutdown at the earliest opportune time. 3. PGCIL (SR-I) to furnishthe details of the implemented SPS-1 and SPS-7 schemes including their logicdiagrams to PCSC forum. 47/II/11 Tripping of HVDC Bhadrawati Pole at 10:53 hrs Main pump-2 of valve cooling got tripped during dip in 33kV auxiliary bus voltage. Valve cooling flow got reduced due to tripping of pump and resulting in tripping of pole-1 PGCIL (SR-I) to furnish compliance report on PSAG-11 recommendations without further delay to PCSC forum. PGCIL Yet to be informed 47/II/ kv RAICHUR - SHOLAPUR 1 and at 19:25 hrs Sholapur -1 and 2 Feeder got tripped at Raichur end on operation of over current protection in Main-1 distance relay and holding from Solapur end on at 19:24:42 Hrs 1. PGCIL (SR-I) to check the A/R scheme implemented through BCU s at all its GIS/ SAS substations for correct operation. 2. PGCIL (SR-I) to ensure timesynchronization of DR & EL of 765 kv Kurnool SS with GPS. PGCIL Yet to be informed 765 KV RAICHUR at KURNOOL 2 19:25 hrs Kurnool -II Feeder got tripped on B-3. PGCIL (SR-I) to sort out the LEGEND N fault and holding from Kurnool ISSUE related to tripping of the lines in the end (successfully auto-reclosed at Event Logger of Raichur. Kurnool end) subsequently tripped at other end on operation of OV stg- 1 protection at Raichur end on at 19:24 Hrs 4. PGCIL (SR-I) to check & ensure the functionality & healthiness of synchronization facility at Raichur end at the earliest opportune time. 49/II/4 Tripping of at 400kV Gooty- 10:15 hrs NPS line-1 DT was sent to NPS end of line-1 during opening of Main CB of Gooty-NPS line-2 at Gooty end. This resulted in tripping of line-1 at NPS and line was holding from Gooty. OV protection got operated at NPS end and resulted in tripping of line 1. PGCIL (SR-I) to configure time scale resolution in Event Logger to msec. at Nelllore PS (NPS) and furnish DR corresponding to OVR, Stag-I operation at NPS end during the tripping event. 2. PGCIL (SR-I) to ensure time-sync of DR s and EL s with GPS at Gooty & NPS. PGCIL Yet to be informed Page 18 of 24

64 Annexure-III 41/II/12 Tripping of 400KV Coastal- NTPL line at 22:54 hrs Line tripped B-phase to earth fault and later tripped on R-Y phase fault. From Coastal end D.R, Y & B poles of breaker opened first and R-pole appears to be opened on Pole discrepancy. Others CEPL to check A/R scheme at their end. CEPL Yet to be informed 41/IV/2 400kV Tuticorin PS- NTPL line at 03:17 hrs Y-phase to earth fault had occurred in line. Line auto reclosed at Tuticorin PS end and failed to reclose at NTPL end. NTPL to check A/R scheme at their end. NTPL Yet to be informed 44/III/4 Tripping of 400kV Coastal (CEPL)- Tuticorin pooling station at 12:35 hrs Line tripped at Coastal energen end only and was holding from TTRNPS CEPL to furnish a detailed report on this trip event to PCSC forum. CEPL Yet to be informed 46/II/3 Tripping of kV at 03:27 hrs Ramagundam- Dichipalli line Line tripped on operation of 1. NTPC, Ramagundam to investigate the overvoltage protection at reasons for OV alongside checking the drop off- Ramagundam end and direct trip to- pick-up ratio of the OV relay. was received at Dichipalli. Overvoltage operation could not be adopted for OV, Stage-I protection (Grading is 2. The tripping is not as per the grading established with D.R & E.L C2: 110% and 6 sec time delay) at submitted by Ramagundam station. Ramagundam. NTPC, Ramagundam to check up the same. NTPC Yet to be informed 47/III/2 Tripping of 400kV Vemagiri GVK (JPD) line at 17:02 hrs R-phase to earth fault had occurred in line. Line auto reclosed at Vemagiri end and failed to reclose at GVK end. GVK to put A/R into service at GVK Jegurupadu end on 400 kv GVK (Jegurupadu) Vemagiri line-2. GVK Yet to be informed 48/II/16 Tripping of 400 kv Hassan - Udupi line at 13:33 Line tripped due to B-E fault in Z2. UPCL to furnish reasons for delayed operation Main 1 relay tripped in Z2. 3 phase of distance relay in Zone-1 at their end, and the trip operated at Hassan. AR remedial measures taken, if any. successful at other end and line was charging from other end. Then OV stage 1 picked up in Main2 relay and operated in OV after the time delay UPCL Mail recieved on (UPCL): The fault was of resistive nature, was sensed from Hassan end in Zone- 2 reach. The DR from UPCL indicates resistive high current prior to operation of Zone-1 in C Phase. This is seen as development of Zero sequence voltage and current prior to Zone -1 operation. The operation of single phase Z1 from UPCL end was correct followed by successful AR operation. Page 19 of 24

65 Annexure-III 36/II/8 400kV Raichur- Munirabad line Miscellaneous B-phase to earth fault had occurred KPTCL: in line. PD (pole discrepancy) time delay would be Line auto reclosed at Munirabad changed. end and failed to reclose at Raichur end. PGCIL / KPTCL Yet to be informed 38/II/5 400kV Ramagundam- Hyderabad line Line tripped on Bphase to earth fault. Line did not auto reclose at Hyderabad end due to PLCCmal-operation. Planned to replace the PLCC system within a week's time at both the ends during the shutdown. NTPC/ PGCIL Yet to be informed. 39/I/2 Tripping of 400Kv Ghanapur- Mamidipally line at 10:52 hrs, at 11:32 hrs, at 16:16 hrs Due to PLCC Mal-operation at HYD S/S end, DT received at MMPLY end and line got tripped. PGCIL is requested check up with the manufacturer to resolve the issue and submit remedial measures to PCSC forum. PGCIL/ TSTRANSC O Mail received on from TSTRANSCO: On PGCIL requested to arrange services of OEM(Manufacturer)for identifying the problem. TSTRANSCO arranged the same on and the manufacturer testing and concluded that the problem in not in the newly erected digital protection coupler at both ends and the issue is related to relay panel at Ghanapur. [OEM minutes enclosed] Page 20 of 24

66 Annexure-III 40/II/3 Tripping of 400 kv TALAGUPP A HASSAN line at 13:38 hrs On account of R-phase to earth fault, line tripped at Hassan end due to operation of distance Zone-2 and non-receipt of carrier. From D.R of Talaguppa end it is observed that fault had occurred in Yphase. 1. PGCIL and KPTCL to ascertain the reason for the phase discrepancy in the relay operation and take suitable remedial measures. 2. KPTCL to check the PLCC operation at Talaguppa end and submit the report to the PCSC forum. PGCIL/ KPTCL Mail received on (KPTCL) & : End to end testing of PLCC has been done and problem in the PLCC is atttended. Phase discripancy in the relay operation is to be checked jointly. Mail recieved on : Problem is in identification of phases at Talguppa end. To be rectified by M/s KPTCL. 41/I/2 Complete outage at 220kV Bahoor Substation of Pondicherry (GD-1) at 11:20 hrs Bus fault occurred in 110kV bus at 230/110kV Bahoor substation due to failure of Y-phase main bus strain insulator. 220kV lines connected to Bahoor (viz., Bahoor- NLC TPS II and Bahoor Pondy) tripped from remote end on operation of B/U protection. 1. PED to investigate the cause of nonoperation of ICT s protection system (differential protection, back-up protection) and review the relay settings suitably. 2. PGCIL to check the settings of distance relay and back-up relays for correctness of operation. PED/PGCIL Mail received on and : All the relay settings were checked and found ok with PED. 42/II/1 Tripping of 400kV Coastal- Tuticorin PS line at 16:37 hrs Line tripped at Coastal end only due to suspected PLCC maloperation and was holding from Tuticorin PS end. Running Unit at Coastal energen also got tripped during the event. PLCC end-to-end testing shall be carried out by CEPL and Tuticorin PS (PGCIL-SR II) by CEPL/ PGCIL(SR- II) Mail received on and : On PLCC testing carried out by M/s ABB Engineer. ABB suspects that the problem is with frequency interference related issue, and suggested to change to new frequecies. with CEPL Page 21 of 24

67 Annexure-III 42/II/18 Multiple tripping at Raichur thermal power station of KPCL at 06:36 hrs 400kV Raichur TPS-Raichur(PG) line- 1&2, 400kV Raichur- Mahboobnagar, Unit#7 and ICT-2 at RTPS tripped during the incident. B phase to earth fault had occurred in 400kV Raichur TPS-Raichur line-1 1. KPCL to review REF setting (DMT or IDMTL) for unit-7 by first week of April, 2015 and inform the same to PCSC forum. 2. TSTRANSCO to furnish Mehaboobnagar s DR and EL and the reasons for distance relay operation at their end within a week s time. 3. PGCIL (SR-I) to rectify the issues relating to A/R operation, relay reach (Z2), reverse reach (Z4) and SOTF auxiliary contacts within a week s time, and submit the actions taken to PCSC forum. KPCL/TSTR ANSCO/PGC IL (SR-I) Mail received on from TSTRANSCO: It is found that the main-2 ABB make REL316 type distance relay was defective and same was replaced with MICOM P444 by M/s.PGCIL on After replacement of main-ii, DR can be extracted from this relay. For EL in to service, some field winding is pending which is being taken up in this month. 43/II/12 Multiple tripping at 400kV Raichur(PG) and RTPS of KPCL at 18:04 hrs 400kV Raichur(PG)-Gooty line-2, 400kV Raichur TPS-Raichur(PG) line-1&2, 400kV Raichur- Mahboobnagar, Unit#5 at RTPS tripped during the incident KPCL, KPTCL and PGCIL (SR-I) to furnish the action taken report on the recommendations given by PSAG members held at Raichur on and KPCL/KPTC Yet to be informed L/ PGCIL(SR- I) 44/I/3 (GD) Tripping of Unit 1 at NCTPS Tripping of Unit 1 at MEPL at 19:13 hrs at 19:13 hrs ID Fan trip Coal Mill tripped 1. All Tripped units, viz., Krishnapatinam, MEPL, Raichur, NCTPS to submit a detailed report on this event including the remedial measures taken to PCSC forum. 2. KPCL to check the excitation system of Unit 8 of RTPS, and submit the remedial measures taken to PCSC forum. KPCL/ MEPL/ APGENCO/ TNEB TANGEDCO vide their mail dated informed that as per the discussion and recommendation of 44th meeting of PCSC held on , a time delay of 2 Sec had been introduced for the above tripping for all the ID fans at NCTPS-II. MEPL vide their mail dated informed that they have implemented 2 seconds delay for under voltage tripping of all Drag Chain Feeder Conveyors. And this has been done for both the Units. with KPCL, APGEN CO Tripping of Unit 1 at Krishnapatna m at 19:17 hrs Generator Protection operated Tripping of Unit-8 at RTPS at 19:19 hrs Tripped on Overvoltage. Page 22 of 24

68 Annexure-III 45/I/2 (GD) Complete outage of MEPL power station at 20:38 hrs Y phase CT failure at MEPL led to tripping of 400kV NPS-MEPL, 400kV SEPL-MEPL line and Unit- 2 at MEPL. Uni-1 was not in service at the time of tripping 1. MEPL to ensure healthiness of all CT s by carrying out Tan Delta and DGA tests wherever necessary. 2. MEPL to take suitable action to correct the operation of tie-cb Bay Control Unit that caused LBB/ BBP operation. MEPL/ PGCIL(SR- I)/ SEL MEPL vide their mail dated : informed the following 1. Tan Delta Testing of winding and DGA of Insulating Oil for all CTs was carried out and normal. 2. Could not find any problem during internal checks hence we are in touch with ABB for rectification work. Will be done by the end of 15th Oct'15 3. PGCIL (SR-1) to carry out end-to-end PLCC testing in coordination with MEPL and ensure that carrier-aided protection on MEPL NPS line is in healthy condition. 3. End to end testing of Carrier signals was carried out and found them healthy. 4. SEL to properly time-coordinate their Over Current phase and Earth fault relays in consultation with MEPL. 47/I/2 (GD) Complete outage of Krishnapatna m TPS at 18:20 hrs As per FIR submitted, CT damage observed in Chitoor-Main bay (404). Main breakers connected to bus-1 (401, 404, 407, 410) got tripped on operation of bus bar protection. Unit-1 tripped on operation of MFT. Unit-2 was not in service 1. APGENCO to furnish to PCSC forum (i) A3- size SLD of SDSTPS, and (ii) the sequence of events with time stamp showing the protection that opened Tie-CB (405) at SDSTPS. 2. APGENCO to review STUB/TEED protection in all dias at SDSTPS and ensure that they are configured for instantaneous operation. APGENCO/ PGCIL (SR- I) Yet to be informed 3. APGENCO to properly configure the STATE of the tripping events so that they get recorded appropriately like TRIP/ OPERATED in their corresponding EL. 4. APGENCO to ensure time sync of all DR s and EL s at SDSTPS. 5. PGCIL (SR-I) to provide line differential protection for 400 kv NPS Nellore-PG lines 1 & 2. 47/II/7 Tripping of kV Kadra- at Karwar line- 11:44 hrs 1&2 and 220kV Kaiga-Kadra line 220kV KAdra-Karwar lines-1&2 tripped on earth fault in B-phase in zone-2. Kaiga-Kadra line tripped at Kaiga end only on operation of directional eath fault protection. 1. KPTCL/ KPCL to see the possibility of implementing Weak Infeed logic with Echo feature enabled by Under Voltage (27) element on Kadra-Karwar lines 1 &2, and implement the same if feasible. KPTCL/ KPCL/ NPCIL Yet to be informed Page 23 of 24

69 Annexure-III 2. NPCIL to time-coordinate Kaiga s DEFR settings with (i) Zone-2 settings at Kaiga, and (ii) primary protections of the lines emanating from Kadra and Kodasalli. 3. KPCL to ensure time-sync of EL s, and healthiness of the Fault Locators at Kadra. 47/II/9 Tripping of 400kV Coastal- NTPL line and running units at NTPL at 15:43 hrs R-phase to earth fault had occurred in 400kV Coastal NTPL line. Line autoreclosed at NTPL end and failed to reclose at Coatal end. Auto reclose block was persisting due to PLCC channel fail. Also running Units- 1&2 at NTPL tripped on operation of GT differential protection. 1. NTPL to ensure (i) proper DATE settings, and (ii) time-sync with GPS for DR and EL at NTPL. 2. CEPL to furnish remedial measures taken regarding PLCC channel failure. NTPL/ CEPL Yet to be informed 48/III/11 Tripping of kv at 04:40 hrs Kurnool on Srisailam line Tripped at both ends on Y-Phase to ground zone-1fault. Attempt for auto-reclose could not be established. TSGENCO/ APTRANSCO to carry-out PLCC end-to-end testing in co-ordination with APTRANSCO/ TSGENCO to sort out reception of signals on 400 kv Kurnool Srisailam line. TSGENCO/ APTRANSC O Yet to be informed 49/II/11 Tripping of /220 kv at 14:31 hrs ICT-2 at Kurnool Substation and 400kV Kurnool- Srisailam line 400kV Kurnool-Srisailam line - distance protection zone-2 had operated at Srisailam end. However from DR, R-phase to earth fault and zone-2 start were observed. Breakers at Kurnool end tripped on direct trip receive from Srisailam end. 1.TSGENCO in coordination with APTRANSCO to carry out end-to-end testing of PLCC channels by on 400 kv Srisailam Kurnool S/C line and 400 kv Srisailam Sattenapalli D/C line. 2. TSGENCO and APTRANSCO to make A/R functional on 400 kv Srisailam Kurnool line. TSGENCO/ APTRANSC O Yet to be informed ICT-2 Main-CB tripped due to operation of bus bar protection, and Tie-CB tripped due to DT receipt from Srisailam 3. TSGENCO to resolve configuration problems with the newly commissioned relays at Srisailam LB so that unwarranted DT sending to remote ends is addressed. Page 24 of 24

70 Annexure-IV Remedial Measures/ Actions taken for the Critical Tripping Incidents (as on ) Sl.No. Element Name Outage date/time Revival date/time Reason for Outage Sender/ Receiver Remedial Measures/ Actions taken Kv KRISHNAPATNAM - NELLORE /11:27: /12:00:00 BUS -1 TRIPPED : REASON AWAITED APGENCO/ APTRANSCO APGENCO: BUS-1 was tripped at Power Grid Sub- Station(PGCIL), Nellore during the operation of the Isolators, which is not pertaining to APGENCO. APTRANSCO: Line tripped at Krishnapatnam end only.line is in service from Nellore-AP. PGCIL (SR-I): kv AMBEWADI - PONDA /15:53: /16:38:00 DUE TO BUS DEAD AT AMBAWADI STATION KPTCL/ GOA To-be-discussed kv AMBEWADI - PONDA /15:53: /18:43:00 DUE TO BUS DEAD AT AMBAWADI STATION KPTCL/ GOA To-be-discussed Page 1 of 8

71 Annexure-IV Kv NCTPS - SVCTM-I /14:31: /15:44:00 TRIPPED ON R- PH FAULT TANGEDCO/ TANTRANSCO TANTRANSCO: Temporary fault. AR lockout at both ends. Feeder normalised at 15:43 hrs. on TANGEDCO: Kv VTPS - MALKARAM /11:40: /16:01:00 TRIPPED ON B- PH FAULT APGENCO/ TSTRANSCO To-be-discussed Kv VTPS - MALKARAM /12:55:00 B-N FAULT APGENCO/ TSTRANSCO To-be-discussed 7 400/220 kv ICT-1 AT BTPS /21:02: /22:42:00 TRIPPED KPCL To-be-discussed Kv GAJWEL - SHANKARPALLY /11:33: /11:59:00 R-N FAULT TSTRANSCO To-be-discussed Kv GAJWEL - SHANKARPALLY /12:22: /14:40:00 R - N FAULT TSTRANSCO To-be-discussed /220 kv ICT-2 AT KAIGA /08:26: /09:49:00 TRIPPED ON DIFFERENTIA L PROTECTION KAPS To-be-discussed /110 kv ICT-3 AT SALEM /03:49: /05:04:00 DUE TO OVER FLUX RELAY ACTED TANTRANSCO TANTRANSCO: Due to raise in 400 KV grid voltage, Over fluxing relay operated. The Frequency variation from Hz to Hz was recorded during the tripping of all ICTs. Page 2 of 8

72 Annexure-IV /230 kv ICT-1 AT SALEM /03:53: /04:49:00 DUE TO OVER FLUX RELAY ACTED TANTRANSCO TANTRANSCO: Due to raise in 400 KV grid voltage, Over fluxing relay operated. The Frequency variation from Hz to Hz was recorded during the tripping of all ICTs /230 kv ICT-2 AT SALEM /03:51: /04:57:00 DUE TO OVER FLUX RELAY ACTED PGCIL (SR-II)/ TANTRANSCO TANTRANSCO: Due to raise in 400 KV grid voltage, Over fluxing relay operated. The Frequency variation from Hz to Hz was recorded during the tripping of all ICTs. PGCIL (SR-II): /110 kv ICT-4 AT SALEM /02:29: /07:17:00 TRIPPED DUE TO OVER FLUX TANTRANSCO TANTRANSCO: Due to raise in 400 KV grid voltage, Over fluxing relay operated. The Frequency variation from Hz to Hz was recorded during the tripping of all ICTs /230 kv ICT-4 AT SALEM /04:42: /17:58:00 TRIPPED DUE TO OVER FLUX PGCIL (SR-II)/ TANTRANSCO TANTRANSCO: Due to raise in 400 KV grid voltage, Over fluxing relay operated. Carried out the maintenance work and the overfluxing relay was tested and healthiness was ensured. PGCIL (SR-II): Page 3 of 8

73 Annexure-IV kv KAIGA - GUTTUR /18:21:00 TRIPPED ON R- PH FAULT KAPS/ KPTCL PGCIL-SR2: Portion of the line in which fault occured owned and maintained by M/s KPTCL. May be clarified from M/s KPTCL KPTCL: KAPS: kv KAIGA - GUTTUR /22:04:00 DISTANCE PROTECTION KAPS/ KPTCL To-be-discussed Kv NCTPS - SVCTM-I /17:24: /18:28:00 Y -N FAULT TANGEDCO/ TANTRANSCO TANTRANSCO: Temporary fault. Feeder normalised at 18:28 hrs. on TANGEDCO: kv CHITTOR - THIRUVALEM /11:20: /16:18:00 BUSBAR PROTECTION CTR END APTRANSCO/ TNEB TANTRANSCO: There was no tripping of 230kV Thiruvalam Chitoor feeder on at Thiruvalam end. APTRANSCO: Kv KRISHNAPATNAM - CHITTOOR /07:18:00 CB PROBLEM APGENCO/ APTRANSCO To-be-discussed kv KAIGA - GUTTUR /13:15: /19:39:00 DISTANCE PROTECTION KAPS/ KPTCL To-be-discussed Page 4 of 8

74 Annexure-IV Kv HASSAN - UPCL /12:53: /13:14:00 B-PH ZONE-1 DISTANCE PROTECTION OPERATED PGCIL-SR2/ KPTCL/ UPCL To-be-discussed kv KAIGA - GUTTUR /15:07: /16:11:00 R-G FAULT KAPS / KPTCL To-be-discussed /220 kv ICT-2 AT BANGALORE /18:47: /19:26:00 BUS BAR PROTECTION ACTED PGCIL (SR-II) To-be-discussed /230 kv ICT-3 AT UDUMALPET /11:25: /11:34:00 TRIPPED ON MAL OPERATION PGCIL (SR-II) To-be-discussed /230 kv ICT-3 AT UDUMALPET /17:25: /18:38:00 RELAY MALOPERATI ON PGCIL (SR-II) To-be-discussed Kv ALM - SVCTM-II /15:40: /16:37:00 C -G FAULT TANTRANSCO TANTRANSCO: 400kV S.V.Chatram - Alamathy -1 feeder 'C' phase jumper got cut at Loc.No.178 from Alamathy end and created temporary fault with 400kV S.V.Chatram - Alamathy - 2 feeder 'A' phase jumper. Both feeders runs on the same tower. PUTT Trip and AR successful at S.V.Chatram end. AR lockout at Alamathy end kv KANIAMPET - KADAKOLA /09:55:00 TRIPPED ON DISTANCE PROTN KSEB / KPTCL To-be-discussed Page 5 of 8

75 Annexure-IV Kv ALM - SVCTM-I /15:40:00 SWITCH ON TRANSIENT FAULT TANTRANSCO TANTRANSCO: AR lockout at both ends. C-Phase jumper cut at LOC.NO.178 from Alamathy SS end was attended. Feeder normalised on at 12:45hrs /220 kv ICT-1 AT BANGALORE /18:47: /19:15:00 BUS BAR PROTECTION ACTED PGCIL (SR-II) To-be-discussed kv KAIGA - GUTTUR /14:09: /16:20:00 B-N FAULT KAPS / KPTCL To-be-discussed kv KAIGA - GUTTUR /01:04:00 TRIPPED ON R- N FAULT KAPS / KPTCL To-be-discussed kv KAIGA - GUTTUR /01:04:00 TRIPPED ON R- N FAULT KAPS / KPTCL To-be-discussed kv DICHIPALLY - RAMAGUNDAM /02:46: /04:13:00 B-N FAULT TSTRANSCO / NTPC To-be-discussed kv DICHIPALLY - RAMAGUNDAM /12:40:00 TRIPPED ON B- Y FAULT TSTRANSCO / NTPC To-be-discussed kv TALAGUPPA - NEELAMANGALA /16:20:00 TRIPPED ON LINE FAULT KPTCL To-be-discussed Kv NCTPS - SVCTM-I /03:54: /04:58:00 TRIPPED ON B- PH FAULT TANGEDCO / TANTRANSCO TANTRANSCO/TANGEDCO: Temporary fault. AR lockout at both ends. No visible fault and feeder normalised on at 04:58 hrs. TANGEDCO: Page 6 of 8

76 Annexure-IV Kv HASSAN - UPCL /10:40: /10:56:00 TRIPPED ON R- N FAULT PGCIL (SR-II) / UPCL To-be-discussed kv NEYVELI TS 2 - NEYVELI TS2 EXP /20:35: /23:03:00 DT RECEIVED NLC To-be-discussed kv NEYVELI TS2- NEYVELI TS- I /23:12: /00:46:00 MALOPERATI ON NLC To-be-discussed /220 kv ICT-3 AT TRICHUR /13:50: /21:38:00 REF OPERATED KSEB To-be-discussed Kv NPS - TPCIL /03:48: /04:56:00 RELAY MALOPERATI ON AT TPCIL END To-be-discussed Kv VIJAYAWADA - NELLORE - AP /10:51: /11:46:00 TRIPPED DUE TOBACKIP IMPEDANCE RELAY ACTED To-be-discussed kv KALPAKKA - VEMAGIRI /15:20: /16:20:00 BUS BAR PROTECTION KLPAKA To-be-discussed kv SIMHADRI - KALPAKKA /15:20: /16:30:00 BUS BAR PROTECTION KLPAKA To-be-discussed /220 kv ICT-2 AT CHITTOOR /07:12: /16:23:00 BUCHOLZ RELAY OPERATION To-be-discussed Page 7 of 8

77 Annexure-IV kv TRIVENDRUM - TIRUNELVELI /04:56:00 B-N FAULT To-be-discussed KV ALAMATHI - THIRUVALLAM /22:42:00 Y-PH LA THVLM END To-be-discussed kv ALAMATHI - VALLUR /22:42:00 Y-PH LA THVLM END To-be-discussed Page 8 of 8

78 Annexure-V 'I From ErJ.Rexline Terese M.E Chief Engineer, Protection and Commu nication 5B Block, IfIoor, 144 Anna salai, TNEB comple, Chennai -2 Lr.No.CE/ P&C/ SEt 01 Chi EPC4j AEE3 Sir, TANTRANSCO To The Member Secretary, I SRPC, Bangalore. F. _SRPC /0. 3 (, 15 dated 2.& Sub: Elecy - Operation Circle / Tirunelveli - Tripping of 230KV TIPS Koodankulam feeder - Action taken report - furnished -Reg 230KV TIPS-Koodankulam feeder tripping for the period from October 2013 to November 2015 is listed in the Agenda for 49 h PCSC meeting. I n thi s regard the following det ails are furn ished Nos. tripping were due to flashed over disc insulators - (Breakdowns). 2. During rainy season, most of the trippings occurred (28 Nos.) which were due to heavy rain, thunder and lightning for the period from October to December Nos. tripping were due to earth wire cut. 4. I I Nos tripping were passing fault (Bird fault). Earlier the 230kV TIPS- SR Pudur line made LILO at Koodankulam. The frequent tr ipping of feeder may be due to the deposition of fly ash on the insulator s coming out from TIPS and NTPL for a radial distance of 5 Km. Replacement of the old insulator s and corroded earth wi re in and around TIPS area have already been sanctioned and work is in progre ss. 70% of disc insulators have already been replaced by Composite Polymer insulators. So deposition of fly ash problem will be elimi nated in due course. In order to avoid frequent tr ippings and breakdowns, it is programmed to replace the corrod ed earth wire after the monsoon is over. Chief Engineer/P&C

79 Report of the Task Force on Power System Analysis Under Contingencies Annexure-VI Appendix-9.1 (Page 5/7 of Appendix) Various types of directional elements may be employed to control operation of ground over current (zero sequence over current) protection response. The most common approach is to employ Phase angle difference between Zero sequence voltage and current, since the relaying signals can easily be derived by summing phase current signals and by summing phase voltage signals from a suitable voltage transformer. However, this method is not suitable for some applications where transmission lines terminated at different substations, run partially in parallel. In such cases following type of directional control is recommended to be used for the directional earth fault relay. Relative phase of negative sequence voltage and current To ensure proper coordination, operating time must be set according to following criteria: The DEF protection should not operate when the circuit local backup protection of remote end clears a fault in an adjacent circuit i.e DEF should be coordinated with the remote end LBB. 12. POWER SWING BLOCKING FUNCTION While the power-swing protection philosophy is simple, it is often difficult to implement it in a large power system because of the complexity of the system and the different operating conditions that must be studied. There are a number of options one can select in implementing power-swing protection in their system. Designing the power system protection to avoid or preclude cascade tripping is a requirement of modern day power system. Below we list two possible options: Block all Zones except Zone-I This application applies a blocking signal to the higher impedance zones of distance relay and allows Zone 1 to trip if the swing enters its operating characteristic. Breaker application is also a consideration when tripping during a power swing. A subset of this application is to block the Zone 2 and higher impedance zones for a preset time (Unblock time delay) and allow a trip if the detection relays do not reset. In this application, if the swing enters Zone 1, a trip is issued, assuming that the swing impedance entering the Zone-1 characteristic is indicative of loss of synchronism. However, a major disadvantage associated with this philosophy is that indiscriminate line tripping can take place, even for recoverable power swings and risk of damage to breaker. Page 1 of 2 Page 113

80 Report of the Task Force on Power System Analysis Under Contingencies Annexure-VI Appendix-9.1 (Page 6/7 of Appendix) Block All Zones and Trip with Out of Step (OOS) Function This application applies a blocking signal to all distance relay zones and order tripping if the power swing is unstable using the OOS function (function built in modern distance relays or as a standalone relay). This application is the recommended approach since a controlled separation of the power system can be achieved at preselected network locations. Tripping after the swing is well past the 180 degree position is the recommended option from CB operation point of view. Normally all relay are having Power swing Un-block timer which unblocks on very slow power swing condition (when impedance locus stays within a zone for a long duration). Typically the Power swing un-blocking time setting is 2sec. However, on detection of a line fault, the relay has to be de-blocked Placement of OOS trip Systems Out of step tripping protection (Standalone relay or built-in function of Main relay) shall be provided on all the selected lines. The locations where it is desired to split the system on out of step condition shall be decided based on system studies. The selection of network locations for placement of OOS systems can best be obtained through transient stability studies covering many possible operating conditions. Till such studies are carried out and Out-of-Step protection is enabled on all identified lines, it is recommended to continue with the existing practice of Non- Blocking of Zone-I on Power Swing as mentioned under Option-12.1 above. However, it should be remembered that with this practice the line might trip for a recoverable swing and it is not good to breakers. Committee strongly recommends that required studies must be carried out at the earliest possible time (within a timeframe of one year) to exercise the option-12.2 & 12.3 above. 13. LINE OVERVOLTAGE PROTECTION FOR 400kV LINES: Low set stage (Stage-I) may be set in the range of 110% - 112% (typically 110%) with a time delay of 5 seconds. High set stage (Stage-II) may be set in the range 140% - 150% with a time delay of 100milliseconds. FOR 765kV LINES: Low set stage (Stage-I) may be set in the range of 106% - 109% (typically 108%) with a time delay of 5 seconds. High set stage (Stage-II) may be set in the range 140% - 150% with a time delay of 100milliseconds. However, for over voltage Stage-I protection, a time grading of 1 to 3 seconds may be provided between overvoltage relays of double circuit lines. Grading on overvoltage tripping for various lines emanating from a station may be considered and same can be achieved using voltage as well as time grading. Longest timed delay should be checked with expected operating time of Over-fluxing relay of the transformer to ensure disconnection of line before tripping of transformer. It is desirable to have Drop-off to pick-up ratio of overvoltage relay better than 97% (Considering limitation of various manufacturers relay on this aspect). Page 114 Page 2 of 2

81 Reference- I PRACTICAL INTERLOCK LOGICS TO PREVENT UNDESIRED CIRCUIT BREAKER CLOSING, ISOLATOR OPENING & CHARGING OF BAY IN SUB STATION USING IEDS Sanjay U Bhatt, Protection, Automation and Metering Department Adani Power Ltd, Ahmedabad Sanjay.bhatt@adani.com ABSTRACT Un desired charging of a bay / equipment when is ready to charge or immediately after getting isolated, due to accidental closing of circuit breaker or breaker flash over may result in severe undefined damage / loss to equipment / system stability / human loss, as well financial burden due to huge repairing cost and outage period till normalcy. This paper describes practical interlock logics using IEDs for (1) controlling DC negative source to circuit breaker closing circuit and (2) Auto opening of Isolators after opening of circuit breaker. KEYWORDS Circuit Breaker closing circuit logic, DC negative source breaking for CB closing, Isolator Auto opening logic, safety interlock for CB and isolator. Accidental shorting of DC+ve to close CB 1. INTRODUCTION The essential element of a protection & control circuit design is to have inclusion of all engineering aspects for control, protection, monitoring & measurement having considerations for technical & operational limitations and capabilities of equipments, system and switchgear, operation possibilities & flexibilities with safety interlocking. Fig. 1 is a typical such circuit conventionally used for a Circuit Breaker closing purpose. Fig 1- Typical Closing circuit of a circuit Page 1 of 11

82 Reference- I The safety interlocking involves design of circuit in a controlled manner, by which ultimately actuates the operating mechanism of relevant circuit breaker / isolators / contactors / solenoids etc. for bridging primary connections to charge or operate the equipment. CASE-I An automatic and comprehensive logic which can detect successful opening of breaker and initiate command to open the outgoing circuit isolator with flexibility of closing operation will be very useful to be secure against such wrong energisation of equipments In case of a circuit breaker for closing circuit interlock, the auxiliary supply (DC +ve or Phase) is extended from source to actuating point connection of closing coil of a circuit breaker through various permissive contacts ensuring healthy operating conditions, CB readiness, and absence of any abnormalities. The cables are routed through all relevant location of interlock contacts. DC ve or Neutral is directly connected to other end of closing coil. A typical circuit is shown at Fig. 1. The opening of isolator on load is also such kind of operation due to similar reasons indicated above. CASE-II In addition to the undue closing of circuit breaker, the undesired energizing of equipment (Transformer, Generator, Line etc.) may also happen in case of breaker flash over (internal or external), particularly in case of Generator or two charged line from different sources, when going to synchronize or after isolated from grid. This is due to external insulation failure or arcing within breaker chamber, causing out of phase connection of two vector (peak to peak twice magnitude) causing severe oscillation and damage to equipment. The detection of breaker flash over reliably and isolation is still a serious concern especially in case of one and half breaker arrangement. Fig.2 shows a typical bay arrangement for a Generator with possible peak to peak voltage vector from Grid and Generator causing flash over.. Fig 2- Typical One and Half CB arrangement possible breaker flash over due to peak to peak voltage across CB open contacts Breaker Page 2 of 11

83 Reference- I 2 A CASE STUDY FOR GENERATOR BREAKER RECLOSING AFTER TRIPPING. Recently at one of the large power plant the Generator Transformer Bushing of a phase failed which led to tripping of unit on operation of overall differential protection with tripping of both Main & Tie breaker. Due to heavy flash over and burning of insulation & oil, there was heavy fire and hot oil spread in nearby MK box & cable trench. This led to damage of all cables as shown in the pictures. Minutes the Main breaker got closed due to shorting of cable carrying DC+ve and return for closing. However the tripping command was persisting on operation of lockout relay hence tripping of breaker was taking place immediately on closing this sequence repeated multiple times and then stopped on blowing of main DC fuse. Due to very short time closing, opening of B phase HV bushing of GT and residual rolling of turbine, nothing further damaged occurred. Fig-3, indicates the control cables route for CB closing from switchyard kiosk to Generator Relay Panel and Synchronizer panel located at Main C/R. The cable trench route is passing near GT area where fire took place. The detailed closing control circuit is shown at Fig-4. It is therefore must to review the conventional closing circuit scheme for breaker & Isolator and cabling practices. Fig 3- Showing location of Bay Kiosk, CB, GT and Main C/R with route of control cable. Page 3 of 11

84 Reference- I Figure-4- A Generator Breaker Closing circuit, event of closing control cable shorted resulting in undesired closing of circuit breaker Interlocks CB cubicle at Switchyard Generator Relay Panel interlock for closing circuit Control cables in cable trench from Switchyard to Main C/R Due to fire cable damaged and shorted core to complete the closing circuit path for DC Positive return to Circuit Breaker Closing circuit. Synchronizing interlock for closing circuit and closing command from Main Control Room Page 4 of 11

85 Reference- I 3. ISSUES WITH CONVENTIONAL CIRCUIT BREAKER CLOSING & ISOLATOR OPEN CIRCUIT. Please refer case study mentioned earlier, where the breaker closing circuit philosophy used is conventional as described previously. The scheme is simple and being used everywhere. Pl. refer Fig.1, and case study occurrence, it is seen that extension of DC +ve supply to closing coil terminal is the only deciding factor for closing operation of breaker and also opening sequence of isolator. Any undue extension of DC+ve to operating coil may lead to undesired operation of equipment. The undue extension of DC+ve to closing circuit/isolator opening circuit may happen due to (1) shorting of control cable carrying DC+ve and return path after permissive and command towards CB/Isolator, and (2) Simultaneous grounding of DC+ve system and terminal connected to CB closing / Isolator Open circuit. The sample case for CB are mentioned in following sections which will also apply to Isolator open circuit with due modifications. Existing Closing Circuit Digital / Analogue Interlock I/O Close Guard I/P. Fig. 5a- Closing circuit DC Negative breaking with CMR operated from Logical operation of IED / circuit. CMR placed at Breaker MK box. Digital / Analogue Interlock I/O 4. SOLUTION TO BREAKER CLOSING DUE TO UNDESIRED SHORTING OF DC+VE. The mishap due to above indicated DC+ve shorting can be avoided by breaking DC-ve immediately after closing CB and the same can be made through just before closing CB, command through SCADA/IED. The simple solution is to switch OFF the closing supply immediately after closing CB and make ON when required to close. The same can be made by breaking DC +ve as well with the method described here. However this may involve addition of circuits and contacts for +ve at DC source also, with simultaneous operation of contacts on both sides, adding more complexity and online monitoring of closing circuit also is not possible. So for our purpose DC-ve breaking scheme is sufficient. Fig. 5b- Closing circuit DC Negative breaking with Output of IED / Logical circuit scheme placed at Control panel Page 5 of 11

86 Reference- I Fig. 5a and 5b above indicate the methods of breaking DC-ve using logical operation performed from numerical IEDs or such circuit from conventional relay, contactor, timers etc. A simple way of breaking DC-ve is to route it from Master trip relay contacts where DC+ve for closing permissive is also routed. However in case of manual opening or isolation Master Trip relay may not operate or can be reset after tripping for further interlocks and operations in a Generating Station. So it is also not covering complete risk. In method 5a the CMR (Contact Multiplier Relay) placed in CB MK box is used to isolate the DC ve. The CMR is operated by a separate DC/AC source from IED/ Logical device. As shown the CMR energizing supply is also wired from two separate contacts from IED at C&R panel. This will ensure complete secured operation of CMR even in case of the cable damage for CMR. In method 5b the DC-ve is routed through contacts of IEDs/Device placed at Kiosk in Switchyard interfaced with SCADA. Method 5a is the most appropriate one for all cases due to secured operation of CMR placed very near to CB closing circuit in MK box. The CMR method should be used where there is no S/Y Kiosk near to CB and C&R panels are located at Main C/R directly connected with CB for control. All above method should ensure secure operation with flexibility to operator and monitoring feedback. It should also supervise the shorting of cable or undue extension of DC+ve in closing circuit by guarding method. 5. LOGIC FOR BREAKING DC-VE USING IEDs & SCADA. A practical logic using IEDs and SCADA interface implemented at the power station where the undesired closing of Generator Breaker happened as referred in case study is shown here at Fig. 6a and 6b. Explanation of the logic: Please refer Fig 6a, where a concept circuit is shown for placing of IED /CMR contact in the Negative terminal of closing coil (CC). The Guard input from DC+ve circuit is connected before CB auxiliary switch contact which is closed when breaker is OPEN or immediately after closing contact circuit. The guard input turns in high state when Close command is extended or any undue positive is extended in close circuit. Please refer Fig 6b, the main logic part which can be built in IED (Relay/Bay Control Unit BCU / RTU having required logical blocks with IEC61850 accepting GOOSE signal and hard wired Binary I/O signal from scheme wiring and interfacing with local SCADA. This is generally available now with all IEDs installed in a switchyard. The logic uses RS Flip Flop block having reset priority for latching output OPEN / CLOSE. The Flip Flop get reset and breaking DC-ve when Circuit Breaker is closed successfully. Lock out / Master trip relay operated. Circuit Breaker Pole Discrepancy Relay (PDR) operated. Circuit Breaker closeing permissive interlock NOT OK. Negative Bypass command from Switchyard SCADA is given for Manual Bypass purpose. All above condition will cause Flip Flop to reset and opening of contact to break DC-ve. Page 6 of 11

87 Reference- I Fig-6a- Concept Circuit for Breaker Closing circuit Various external interlocks / commands Guard BI of BCU / IED Breaker MK / Control Box 52b Breaker Aux. contact CC IED/ CMR Contact DC ve DC +ve Fig 6b - Logic for DC-ve breaking for Circuit Breaker Closing circuit CB CLOSE (Except Line Bay) CB-PDR Operated RESET Lock out relay Operated OUT Manual Reset (Pulse) from OWS CB closing permissive OK +ve Guard input High 200 ms SET RS Flip-flop IED Contacts to operate CMR or to DC ve circuit of CB as per scheme adopted. CLOSE circuit through command (Pulse) from OWS Interlock status feedback to SCADA / OWS NOTE: The logic can be built in IED (Relay/Bay Control Unit BCU / RTU having required logical blocks with IEC61850 accepting GOOSE signal and hard wired Binary I/O signal from scheme wiring and interfacing with local SCADA. This is generally available now with all IEDs installed in a switchyard. Necessary wiring / GOOSE configuration should be worked out for I/O as per logic. The Close circuit through command from OWS (Operator Work Station of SCADA) to extend DC-ve for manual close should be initiated before closing of breaker so that ve circuit to closing coil will be extended. In case of any unwanted DC +ve extension in closing circuit will be monitored by Guard circuit and will not allow the flip flop to set to extend DC ve to closing coil. Which is monitored in SCADA also. The Guard timing is considered as 200 ms allowing closing of breaker normally. The above circuit can also be used for isolator control circuit with modification in input logic and other interlocks. Page 7 of 11

88 Reference- I The Flip Flop will be set to drive BO to extend DC-ve under following condition. Though manual command from OWS (SCADA) when it is really required to close breaker, if the DC Guard input is NOT High more than 200 msec. Immediately after closing of CB the Flip Flop will get reset breaking DC-ve till a manual intervention is made which should be done just before closing the breaker. In case of line after closing of breaker to allow Auto Reclosure operation DC-ve is not being broken, however except in case of three phase tripping. Further it is also important to have wire cores for DC +ve source of closing circuit going to external wiring and return from CB MK should be in different cable and not in same cable. Above logic has been implemented and proven well working taking care for all possible abnormalities. The same can also be used to take care for undue opening of Isolator with some modification of logic such as the phase and neutral (OR DC +ve and ve) will be extended simultaneous when any open command generated from valid open sequence and other interlocks. Snap of logic and control built in SCADA database is mentioned as under for a Generator Circuit Breaker. Page 8 of 11

89 Reference- I 6. LOGIC FOR AUTOMATIC OPENING OF ISOLATOR AFTER TRIPPING OF CIRCUIT BREAKER. AUTO OPEN Logic SCADA interface It is well known that an Isolator is OFF Load and Circuit Breaker is ON Load circuit breaking equipments. Opening of an Isolator on load will lead to a severe damage to equipment and human also. Due to this reason to avoid accidental opening of isolator a routine practice is being adopted for an isolator, to switch OFF isolator Driving Motor supply after closing electrically or manually. However in case of ABCB earlier, due to risk of getting closing of circuit Breaker on low air pressure automatic opening of isolators on immediate opening of CB was used using hard wired CB status based logic. Now days all isolators are remotely operated from SCADA and also with concept of unmanned S/S the Isolators are kept ready to operate with all auxiliary sources in service. With this arrangement it is must for isolator to have DC-ve and also automatic opening of isolator breaking logic schemes. Please refer Section 2 Case-II and case study of occurrence, the reclosing of Circuit Breaker due to any reason or flash over subsequent to opening of breaker or before synchronizing will defiantly damage the equipment connected. In the referred case, the immediate opening of circuit (Line) isolator on opening of CB would have saved the impact on Transformer and Generator, if so designed in the scheme. The manual opening of isolator immediately after tripping of CB is also not expected due to human action. The logic implemented at Sub station referred earlier is mentioned at Fig 7 & 8 using Bay Control Unit, GOOSE signal for status / Analogue signal over IEC The output of Auto OPEN Logic is configured with same output of the existing logic for OOPEN sequence of isolator taking status and feedback as per logic. Existing CLOSE sequence Explanation of the logic: Existing OPEN sequence BCU Output for Isolator OPEN & CLOSE Please refer Fig. 8, the Auto Open sequence will be initiated after proposed time delay of 5 sec, when (i) Under current relay picks up AND (ii) Main Breaker is not CLOSED AND (iii) TIE Breaker is not CLOSED AND (iv) Isolator closed status is high. For secure operation the interlock of load current and breaker status has been incorporated. The Auto open sequence will be automatically latched for next operation when (1) Under current relay resets OR (ii) Main Breaker CLOSED OR (iii) Tie Breaker CLOSED, after a proposed time delay of 5 sec. The next closing sequence will be initiated by Manual command from SCADA OWS for SET command to the RS Flip-Flop, and when it is set will allow manual CLOSE sequence to operate making the operation more secure and enhancing the CLOSE logic also. Again after opening of breaker and sensing of under-current will allow Auto opening of isolator as per logic. The implemented logic screen snap is also indicated at Fig-9. Page 9 of 11

90 Reference- I Fig 8 - Logic for Auto open of Isolator after opening of Circuit Breaker I<1 Under Current Main Breaker CLOSE TIE Breaker CLOSE & Timer OPEN Command to Isolator Isolator CLOSE status Manual SET (Pulse) from OWS O R 5 S T RESET SET OUT To Isolator CLOSE logic interlock to ensure SET condition of Auto Open sequence Existing LOGIC for Isolator CLOSE command & CLOSEE Command to Isolator NOTE: Manual SET command from OWS SCADA should be SET before Closing of Isolator. The Logic is built in BCU and connected with existing OPEN command of isolator. Manual Set command latch O/P from flip flop is interlocked with Existing Logic for Isolator Closing Required modification & configuration of relevant relay for under current setting and Logic should be worked out. Timing for Auto Open Isolator may be set at 5 second after opening of CB. Fig 9 Implemented Logic for Auto open of Isolator after opening of Circuit Breaker Page 10 of 11

91 Reference- I 7. CONCLUSION The described engineering practice should be implemented as a standard scheme for operation of Circuit Breaker and Isolators looking to secure operation of primary switching. Because numbers of incidences are being occurred on account of damaged cables or DCgrounding or mal-operation even during fault finding or testing of control wiring. The use of latest technology or equipment without reliable operating mechanism is waiting for a disaster always. Availability of Numerical technological IEDs and GOOSE signals over IEC61850 protocol with SCADA has made the task very easy and secure. (1) Circuit Breaker Closing circuit should be equipped with DC-ve breaking as near as possible to Closing Coil with Contact Multiplying relay / IED (Relay) contact with secured logic, control and monitoring facility in SCADA. (2) Isolator OPEN circuit should also be equipped with similar above scheme logic indicated at (1). (3) Circuit (Line) Isolator should be automatically opened immediately after tripping /Opening of CB/s. The logic should be secured enough to ensure complete OFF Loading of circuit and also with no confliction with CLOSE sequence operation. (4) The control cables carrying DC-ve from CB / Isolator and to IED/Relay at C&R panel should be in different cable, preferably separate route to avoid any possibility of malfunction of the above discussed circuit itself. (5) All the input / output and logical status should be configured in event of IED and SCADA for future analysis on event of occurrence. (6) The new specification for C&R panel and scheme should be included with above said requirements. REFERENCES: (1) Various schemes drawing for different substations. (2) AREVA make application manuals on BCU MICOM C264 /EN/AP/ C30, PACIS Operation Interface for Automation and other IEDs (3) ABB make application manuals on 670 series IEDs. AUTHOR: Sanjay U. Bhatt, working as DGM (Protection) at. Adani Power Ltd, Ahmedabad, (Protection Automation & Metering Department), from January B.E. (Electrical) from L.E. College Morvi,. Gujarat (India). Worked: In G.S.F.C.-Jamnagar, as Ele. Maintenance Engr. In Govt. Polytechnic, as a lecturer on clearing GPSC. In GSECL as Junior Engineer at Sikka Power station as Electrical Testing & Maintenance engineer and at SLDC during commissioning of SCADA and related system. As Deputy Engineer at GSECL corporate office as Testing engineer. Page 11 of 11

92 Application Notes Reference-II P34x/EN AP/G44 MiCOM P342, P343, P344 Page 129 of 176 For generator applications the undercurrent elements should be measuring current from CTs on the terminal side of the generator. This is because for an internal fault on the generator after the CB has tripped the generator will still be supplying some fault current which will be seen by undercurrent elements measuring current from CTs on the neutral side of the generator. This could thus give false indication of a breaker fail condition. The voltage dependent overcurrent protection and underimpedance protection used for back-up protection of system faults are usually connected to the neutral side CTs so that the generator is in the zone of protection. These protection functions use the IA, IB, IC current inputs in the P343/4. Therefore, if the IA, IB, IC inputs are connected to neutral side CTs then the IA-2, IB-2, IC-2 inputs should be selected for the undercurrent elements using the setting I< Current Input - IA-1, IB-1, IC-1/IA-2, IB-2, IC-2. DDB #162 : Any Trip (RL3) DDB #380 : Ext. Trip 3ph DDB #631 : IA< Start OR S R Q SETTING [4502] : CB Fail 1 Status G37-0 : Disabled SETTING [4503] : CB Fail 1 Timer tbf1 AND DDB #493 : Bfail1 Trip 3ph DDB #632 : IB< Start G37-1 : Enabled 0s AND SETTING [4505] : DDB #633 : IC< Start CB Fail 2 Timer DDB #635 : IN< Start SETTING [4504] : CB Fail 2 Status G37-0 : Disabled AND tbf2 DDB #494 : Bfail2 Trip 3ph DDB #447 : ISEF>1 Trip OR G37-1 : Enabled 0s AND OR DDB #294 : CB Fail Alarm DDB #162 : Any Trip (RL3) S Q x 2 Stages DDB #634 : ISEF< Start R DDB #453, 457 : V< Trip x 2 Stages AND S OR DDB #461, 465 : V> Trip Q x 2 Stages R DDB #451, 457 : VN> Trip x 4 Stages DDB # : F< Trip x 2 Stages DDB #497, 498 : PSlipz Trip DDB #416 : 100% ST EF Trip x 2 Stages DDB #475, 476 : Power Trip x 2 Stages DDB #495, 496 : SPower Trip x 2 Stages OR S R Q DDB #422, 423 : Field Fail Trip SETTING [4506] : Volt Prot Reset AND SETTING [4507] : Ext Prot Reset AND DDB #429 : V/Hz Trip x10 Stages G68-0 : I< Only OR G68-0 : I< Only OR DDB # : RTD Trip G68-1 : CB Open & I< G68-1 : CB Open & I< x 2 Stages DDB #473, 474 : F > Trip G68-2 : Prot Reset & I< AND G68-2 : Prot Reset & I< AND DDB #757 : All Poles Dead DDB #380 : Ext. Trip 3ph P2181ENa Figure 52: CB fail logic 2.29 Breaker flashover protection Prior to generator synchronization, or just following generator tripping, where the protected generator could be slipping with respect to a power system, it is possible to establish at least twice rated phase-neutral voltage across the generator circuit breaker. An even higher voltage might briefly be established just after generator tripping for prime mover failure, where the pre-failure level of excitation might be maintained until AVR action takes place. Whilst generator circuit breakers must be designed to handle such situations, the probability of breaker interrupter breakdown or breakdown of open terminal switch gear insulators is increased and such failures have occurred. Page 1 of 2

93 P34x/EN AP/G44 Page 130 of 176 Reference-II Application Notes MiCOM P342, P343, P344 This mode of breaker failure is most likely to occur on one phase initially and can be detected by a neutral current measuring element. If the generator is directly connected to the power system, the second stage of stator earth fault protection ( ΙN>2... ) could be applied as an instantaneous element by setting the time delay ΙN>2 TimeDelay to 0s, to quickly detect the flashover. To prevent loss of co-ordination this stage must be blocked when the circuit breaker is closed. This can be programmed by correct configuration of the programmable scheme logic and can be integrated into the circuit breaker fail logic, as shown in Figure 53. Where the machine is connected to the system via a step-up transformer a similar scheme can be arranged. The P34x relay standby earth fault protection element can be connected to measure the transformer HV earth fault current to provide the breaker flashover protection, via suitable scheme logic. The machine earth fault protection can be provided by the P34x sensitive earth fault protection element, as shown in Figure 54. Scheme logic in PSL DDB 39 L8 52-B IN>2 Trip DDB 205 & DDB 168 Extern Trip 3ph IN ISEF MiCOM P343 DDB 310 Bfail1 Trip 3ph R5 CD fail trip DW 100 P2182ENa Figure 53: Breaker flashover protection for directly connected machine Scheme logic in PSL DDB 39 L8 52-B IN>2 Trip DDB 205 & DDB 168 Extern Trip 3ph This CT shall be provided additionally. IN ISEF MiCOM P343 DDB 310 Bfail1 Trip 3ph Figure 54: Breaker flashover protection for indirectly connected machine R5 CD fail trip DW 100 This CT is connected to P141realy (GRP-C). This CT signal shall P2183ENa be extended to P344relay by connectingboth relay terminals in series. Page 2 of 2

94 Adaptive Logic for Breaker Flashover Protection of Generator. Sanjay Bhatt Protection Automation and Metering Group Adani Power Training and Research Institute Adani Power Limited, Ahmedabad Reference- III 1. ABSTRACT: Flashover can occur on any breaker in the network where an overvoltage condition is present, but the probability is higher for breakers being used to synchronize two isolated power systems; e.g. on generator breakers, line breaker connecting two separate sources or grids. For Generator/line breaker, the Period is considered as critical in view of withstanding rise in voltage vector appearing across poles of Circuit Breaker and the arc quenching process before generator/line synchronization, or just following generator/line tripping respectively. The circuit breaker for above said applications for must be designed capable of maintaining the sufficient insulation level to withstand the same. The detection of flashover reliably and operating protection to isolate the affected breaker and generator in possible minimum time calls for a logic based on immediate sensing of arc current supported by breaker status to reliably declare a flash. This paper describes the logic adapting the numerical relaying logic blocks with current status different from conventionally used and also described in IEEE guideline for Generator Protection C KEYWORDS: Breaker Flashover, Generator Protection for GT Breaker flashover, unintended arc across Generator breaker 3. INTRODUCTION: (I) It is because the vectors of the protected generator and grid vector across circuit breaker poles are slipping with respect to a power system. This will lead to a condition to establish at least twice rated phase-neutral voltage across the generator circuit breaker. Due to the system and machine operation condition it is quite often possible that even higher voltage may be established. This will lead to establishment of arc between two poles of circuit breaker, which may be internal or external, leading to failure of breaker damaging self and also nearby equipments and persons. Further the establishment of arc will also lead to the asynchronous energisation of Generator with grid and create oscillation damaging Generator Transformer / Generator. Detecting the flashover The abnormal rise in voltage just after generator tripping is most likely due to following reasons, Prime mover failure: which is associated by the excitation level not matching instantly with the lowering of active power, where the prefailure level of excitation might be maintained until AVR action takes place. AVR malfunction: this is associated with failure of AVR to discharge energy through discharging resistor at the time of tripping boosted by residual flux. Page 1 of 7

95 Reference- III The peak to peak voltage appearing across circuit breaker is indicated at Fig.1 below. The flash over thus occurred in most of the cases are of single phase in nature as because of probability of maximum peak to peak voltage at a time is for one phase and very rare may be of two phases depending up on deterioration of insulation and repeated peak across each phase. (II) Detection of Flash over The detection of arc as a fault is very tricky due to lower magnitude and also resembling the breaker status with selectivity among various normal and abnormal grid behavior and remote fault. The arc current will always reflect as a Zero sequence or Negative sequence current which can be detected typically as under. Fig 2a- Typical CT connection to detect breaker arc current as residual current for Generator directly connected to Grid Fig 1- Typical One and Half CB arrangement possible breaker flash over due to peak to peak voltage across CB open contacts Breaker During the synchronization process, the outof-phase angle between breaker contacts changes from 0 to 360 degrees continuously. Voltage between breaker contacts reaches its maximum instantaneous value when the angle difference between the voltages is 180 degrees, with a magnitude equal to double the nominal phase-to-ground peak voltage; posing severe stress to the insulation. May also result in out of step and swing. Fig 2b- Typical CT connection to detect breaker arc current as residual current for Generator connected to Grid through Transformer. Adaptive Logic for Breaker Flash over protection of Generator. Page 2 of 7 2

96 Reference- III Typically the detection of Neutral over current from Generator or Generator transformer as referred in fig (2a & 2b) with Breaker OPEN status is interpreted as breaker flash over condition, and after certain small time delay tripping is declared out. Alternatively detection of Negative sequence current at Generator Neutral and phase side with Breaker status is also used for detection of breaker flash over condition. Breaker OPEN Status IN> Breaker OPEN Status I2p> I2n> (III) Action: Tripping of associated bus is essential here, because, merely tripping of Generator or excitation will also initiate tripping of Generator breaker and still the breaker is shunted by flash arc current, with the breaker is already in OPEN status, will subsequently cause initiation of LBB and after certain time delay of LBB timer will trip Bus breakers, which is delayed tripping as per LBB setting and initializing scheme. (IV) & & Time Time Fig 3- conventional logic to detect breaker flash over Reliability & Selectivity. TRIP Excitation & BUS TRIP Excitation & BUS (a) Limitation of above logic remains always within the reliability of the breaker status, because defective status of breaker obtained through breaker auxiliary switch many times falsify due to switch and related gearing alignment and contact issues. During the defective status of breaker associated with remote fault or short duration unbalance due to auto reclosing will cause to operate the logic undesirably causing tripping of Generator and bus also. However use of GT neutral current with interlocking of GTCB may lead to maloperation when the Breaker contact is defective, which enables the function during normal operation of unit. Further the setting of IN for Flash over detection is kept low enough for effective detection of flash current therefore any earth fault or unbalance in the grid / line may lead to operation of the function. Use of Generator Neutral CT will avoid the possibilities of above mal-operation during grid disturbances. However pure single phase flash may not be reflected at Generator Neutral side because of the zero sequence isolation at generator side for faults on GT side. (b) In case of Generator connected with one and a half breaker bus arrangement detection of breaker flash over if actual, will not identify the breaker (Main or Tie) which has undergone flash over. Pl. refer fig 1, where it has been indicated that the Generator / Line can be connected either from Main or Tie breaker and therefore the flash over condition may be for either of two breaker. Thus the automatic and reliable detection of the breaker which has undergone the mishap must be identified and output action should be relevant to the identification. It is now obvious that action to isolate the Generator from Grid should be separate for each condition with unique identification. Merely detecting breaker flash over condition from the breaker status (composite may be of Main and Tie) and neutral current from Generator Transformer or Generator, with action for Tripping of Bus bar and Class A tripping for Generator is not sufficient as well not truly as per requirement defeating the aim for Breaker flash over protection intended so. Above limitation for reliability and selectivity will place a threat to undesired tripping, delayed tripping or stability aspects too. Adaptive Logic for Breaker Flash over protection of Generator. Page 3 of 7 3

97 Reference- III (V) Solution: Addressing above limitations with feasible solution is possible with following considerations. As earlier discussed Broadly two criteria are required to detect breaker flash over (i) Breaker OPEN status (ii) sensing of Neutral current at GT or Negative sequence current at Generator terminal and (iii) third one essential for One and Half breaker Bus arrangement is, identifying the affected breaker. The output actions are then decided and forwarded with suitable circuit schemes. (a) Detection of Breaker Status. Indirect assessment of breaker pole status can only be done by detecting flow of current through all three phases simultaneously registering a status in logic block and removing also the register status as low, i.e. using flipflop block triggered by current threshold. Also as per IEEE GUIDE FOR AC GENERATOR PROTECTION: Std C , Open generator breaker flashover protection: Generator breaker flashover may also be detected by breaker pole disagreement relaying. This relay monitors the three-phase currents flowing through the breaker and senses whether any phase is below a certain low threshold level (indicating an open breaker pole) at the same time that any other phase is above a substantially higher threshold level (indicating a closed or flashed-over pole). Logic using FlipFlop : Above logic criteria are indicated at Fig 4. The flow of current through circuit breaker at HV side of Generator Transformer is considered as Phase current (Iph) and IN as GT neutral current. The OPEN status is detected when all three phases detect current below 2% (or practically as low possible setting available in relay which can be detected reliably. The OPEN status implies isolated condition of Generator from grid and SET the FlipFlop. The output of FlipFlop makes input of AND gate high arming for Breaker flashover protection active. On detection of neutral current in GT or Negative sequence current at Generator will operate breaker flash over protection trip output. The normal operation of Generator can be considered as (i) Before & During synchronizing (ii) After Synchronizing and (iii) Grid fault when Generator is normal in service (iv) After isolating from grid. (i) Before & during synchronizing there is no current flow and hence FlipFlop O/P is High. There will not be Iph and IN hence keeping the logic O/P as low. (ii) Immediate after synchronizing there will be Iph >5% (or to be set as possible initial loading normally) resetting the FlipFlop after 200 ms. (iii) Machine running normally will also prevail condition (ii) above. (iv) After tripping of machine there will be Iph<2% as set above will immediately put function in service. IPh <2% 3 Phase IPh > 5% 3 Phase IN> 10 to 20% T = 200 ms & SR Flip Flop S R T = 100 ms O TRIP ALL / BUS TRIP Iph= Phase current, IN = GT Neutral current For 1-1/2 Breaker bus, separate logic for Main and Tie breaker path current. Fig 4- Breaker open status Detection logic based on current threshold using SR FlipFlop 4 Adaptive Logic for Breaker Flash over protection of Generator. Page 4 of 7

98 Reference- III Logic using AND OR blocks : Some of the basic versions of IEDs do not have the Flip Flop logical blocks, for which following logic using basic AND OR and Timer blocks can be used as indicated at Fig-5 here under. IPh-A <2% IPh-B <2% IPh-c <2% IPh-A >5% IPh-B >5% IPh-C >5% IN> 10 to 20% O R O R DO Tim er 200 ms & PU Time r = 100 ms Iph= Phase current, IN = GT Neutral current For 1-1/2 Breaker bus, separate logic for Main and Tie breaker path current Fig 5- Breaker open status Detection logic based on current threshold using AND-OR blocks. Annunci ation & SOE in SCADA / DCS TRIP ALL (Class A & BUS TRIP The lower current threshold for any one phase is monitored for OPEN status, this implies for resetting only when all three phases have current more than 2% i.e. all poles closed. The drop out timer is intended for keeping function armed for 200 ms. after synchronizing during which practically picking up of load by Generator more than 5%. All four conditions mentioned in earlier paragraph for Generator are addressed here also detecting reliably the breaker flash over condition. The IN setting for 10 to 20% is intended for detecting lower arc current as low as 10% keeping in consideration normal maximum unbalance current. The delay in output is chosen as 100 ms for stability and reliability purpose considering normal breaker closing time and inherent difference in closing of individual pole and also initial unbalance current owing to measurement and magnetizing effect for lower magnitude. OUTPUT Action:- The output action of the protection must isolate the Generator from grid and also removal of excitation to Generator. The conventionally action for a LBB protection is similar to the required one for Breaker Flashover condition. The difference here is the detection at a lower magnitude of current without any trip initiation and also operating time is much less than typical LBB time of 200 to 250 ms. I>20% LBB Initiation Breaker Flash over O/P & Timer 250 ms O R Fig 6: Output action for LBB and Breaker flash over protection TRIP ALL (Class A & BUS TRIP Adaptive Logic for Breaker Flash over protection of Generator. Page 5 of 7 5

99 Reference- III (V) Solution (b) Selectivity of Breaker Flash over for One and Half Breaker system arrangement of Bus. Main-Line TIE Main-Gen Line Feeder Y D G Iph-TIE Iph-MAIN G Fig 7: Current detection for selectivity for One and Half Breaker arrangement for breaker flash over protection. The One and half breaker arrangement is mainly having advantage of redundant connectivity for feeders. As shown in fig-7, the Phase current used for Breaker flash over can be referred from Main or Tie breaker CTs. The breaker flash over may occur for Main or Tie breaker during synchronizing or after isolation from Grid. So both the paths must be IN separately detected for flash arc current i.e. Main and Tie breaker. The action required after detection of flashover are different as detailed below. (1) MAIN Breaker flash over Tripping of Generator in Class-A to trip excitation immediately and stop prime mover for any rise in voltage due to residual magnetism. Open all bus breaker to isolate the affected breaker from grid. (2) TIE Breaker flash over. Tripping of Generator in Class-A to trip excitation immediately and stop prime mover for any rise in voltage due to residual magnetism. Trip Main breaker of Line side. Send Direct Trip Transfer signal to isolate source from remote end. The logic described for Current detection as Iph-A-B-C in earlier paragraphs equally used separately for Main and Tie breaker. The CT input for Main and Tie paths are indicated in fig-7. Two separate logics should be built as conveniently in bay IEDs like, BCU or back up relay with separate set of actions as described above. Please note that the neutral current here and elsewhere in document is indicated from GT neutral, whereas can also be used as Negative sequence current of Generator Phase connection also. The setting values shown here are from experienced values for a 660 MW Generator, however can be considered on typical machine behavior and normal operation. Adaptive Logic for Breaker Flash over protection of Generator. Page 6 of 7 6

100 Reference- III (VI) CONCLUSION; (VIII) Acknowledgement: The breaker flash over phenomena is a very typical one to detect reliably and opt for action like isolation of bus and feeder at minimum possible time. Typical logic are offered by various manufacturer as indicated earlier, however use of reliable detection and output action is a part of scheme designing and adaption of philosophy. Reliable detection and comprehensive logic is now very easy to be built in IEDs having numerous logical blocks, I/O configuration and even use of GOOSE signals for interlocking. Breaker flash over protection must be used as a critical protection function particularly the locations like sea shore based or saline atmosphere surrounded installations, where chances of external flash over is higher. The lower flash arc current may also cause severe oscillation and asynchronous energisation may lead to damage to TG set or transformer. Careful design should be carried out to handle flash over detection and isolation for one and Half breaker arrangement. Author takes opportunity to express gratitude and special thanks to HOD of P&M Group of Adani Power Ltd., his guideline & knowledge, Adani Power Training & Research Institute, APL management for granting permission and inspiration to think and present this paper. (IX) Author: Sanjay U. Bhatt, working as DGM (Protection) at Adani Power Ltd, Ahmedabad, (Protection Automation & Metering Department), from January B.E. (Electrical) from L.E. College Morvi, Gujarat (India). Worked: o In G.S.F.C.-Jamnagar, as Ele. Maintenance Engr. o In Govt. Polytechnic, as a lecturer on clearing GPSC. o In GSECL, Gujarat as Junior Engineer at Sikka Power station as Electrical Testing & Maintenance engineer and at SLDC during commissioning of SCADA and related system. o As Deputy Engineer at GSECL corporate office as Testing engineer. (VII) REFERENCES a. IEEE Guide for AC Generator Protection: Std C , b. Guide for Ac Generator Protection, ANSI/IEEEC c. Application manual AREVA Micom P34x relay. Adaptive Logic for Breaker Flash over protection of Generator. Page 7 of 7 7

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