SOUTHERN REGIONAL POWER COMMITTEE

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2 SOUTHERN REGIONAL POWER COMMITTEE BENGALURU Minutes of the Meeting of Protection System Analysis Group - 14 (PSAG-14) held on 16 th December, 2015 at MAPS, Kalpakkam a) The Protection System Analysis Group (PSAG-14) meeting was held on 16 th December, 2015 at Madras Atomic Power Station (MAPS), Kalpakkam. Shri R. Satyanarayana, Chief Superintendent, MAPS welcomed the members and participants. The List of Participants is enclosed at Annexure - I. b) MAPS on 230 kv side is equipped with 2x265 MVA, 230/16.5 kv GTs, 2x25 MVA, 230/7 kv SUT s four grid connected feeders, [viz., 230 kv MAPS SP Koil line-1 (L-1); 230 kv MAPS SP Koil line- 2 (L-2); 230 kv MAPS Arani line (L-3); and 230 kv MAPS Acharapakkam line (L-4)], two radially connected feeders to IGCAR through 2x25 MVA, 230/33 kv transformers, and one radially connected UG cable to BHAVINI. The station is equipped with two buses named Main Bus and Transfer Bus. There is a bus sectionalizer on the Main Bus. Functionally, Station is operating on Single Bus. The Station SLD is enclosed at Annexure-II. c) S.P. Koil SS on 230 kv side is equipped with a Main bus and Auxiliary bus with Bus-coupler. There are six feeders emanating from this substation, viz., MAPS - 1 & 2, Kalavindapattu, Veerapuram, Oragadam, and Tiruvalam. Functionally, Station is operating on Single Bus. The Substation SLD is enclosed at Annexure-III. d) MAPS personnel delivered a presentation regarding the Grid Disturbance that occurred on The following issues were deliberated in the meeting: A. Action taken by MAPS and TANTRANSCO w.r.t the recommendations given by the System Studies Sub-Group of SRPC in its meeting held on (Minutes issued vide SRPC letter no: SRPC/SE/ SG/2014/ dated ) The compliance status of the said recommendations as informed to the PSAG-team is enclosed at Annexure-IV. B. Analysis of the Grid Disturbance that occurred at S.P. Koil & MAPS on It is brought out with concern that MAPS have not uploaded the copies of DR / EL / Numerical relay indications / SoE in the required manner in to the web portal of SRLDC for detailed analysis. MAPS confirmed that the same will be strictly ensured in future kv Kalapakkam Arani line (L3): The line tripped at 18:28 hrs on first on B-E fault (fault current ka) due to DPR, Z1 operation at a distance of m from MAPS. The line was kept holding from Arani end. As the line was in charged condition from Arani end, MAPS personnel had tried to charge the line by closing the

3 corresponding line-cb at 18:55 hrs. However, the line tripped again on B-E fault (fault current ka) due to DPR, Z1 operation at 82.5 m from MAPS end. Cause of the event: On field visit, it was observed the B-ph (RYB) Tension insulator at 1 st tower towards switchyard end got broken, and on impact over head conductor clamp at tower end got cut and conductor had fallen on ground causing ground fault. It was found that the stem of ball-andsocket assembly got fully corroded and pin got broken even for the moderate wind speed. Action taken: Line-3 was declared faulty and message given to TNEB for attending the fault. TNEB team arrived on and replaced the tension insulator string with a new one and reconnected the conductor using jumper. Line-3 was taken back in to service at 21:45 hrs on Issue: Line tripped at MAPS end only, and was holding from Arani end. Explanation: The snapping of conductor created a Ph-Ground fault for MAPS, and Open-conductor fault for SP Koil. Due to this, even though protection at MAPS end acted in time to result in 3-ph trip at MAPS and consequent sending of carrier to SP Koil end, protection at SP Koil end neither sensed the fault nor received the carrier. Similarly, as the above fault resulted in 3-ph trip MAPS, brokenconductor condition could not be sensed by the protection at SP Koil end, even though the same has been kept enabled for Alarm. Accordingly, it is found that the operation of the protection system is in order kv MAPS Acharapakkam line (L4): Line tripped at 08:21 hrs on on Y-B fault due to DPR, Z1 operation at a distance of 352 mts from MAPS end. Cause of the event: For line-4, the portion between MAPS 1 st tower to 2 nd tower after crossing main road for Y and B phases got cut and fallen on ground on the road, obstructing movement of vehicle on main road. For Y-phase, tension string insulator at 1 st tower got cut, and on impact the conductor clamp at 1 st tower end got cut and conductor had fallen on ground. For B-phase, tension string insulator at 2nd tower got cut, and on impact the conductor clamp at 2 nd tower end got cut and conductor fallen on ground. It was found that the stem of ball-and-socket assembly got fully corroded and pin got broken even for the moderate wind speed. Action taken: Line-4 was declared faulty and message given to TNEB for attending the fault. On 1 st tower, the tension insulator string was replaced for Y phase, and the conductor was reconnected using jumper. On 2 nd tower, the tension insulator string was replaced with spare and conductor was reconnected using a jumper. Line 3 was taken back in to service at 23:45 hrs on Accordingly, it is found that the protection system operated correctly kv MAPs SP Koil line (L2): As per MAPS, the line tripped at MAPS end at 8:50 hrs on on B-E fault due to DPR, Z1 operation at a distance of km from MAPS.

4 As per TANTRANSCO, the line tripped at 9:06 hrs on on B-E fault due to DPR, Z2, Carrier- Aided-Trip operation. Issue: Even though the line tripped at 9:06 hrs, it could not be normalized till 10:45 hrs due to apparent breaker problem at SP Koil end. TANTRANSCO representative informed that there was a false SF6 gas pressure low alarm for line-1 CB, which the operator mistook for line-2. As there was a heavy downpour accompanied by strong winds outside, the shift personnel took time in mobilizing their resources to inspect the switchyard and attend to the problem. Finally, the line was restored by 10:45 hrs. It is noted that though the tripping of line is with correct operation of respective protection system, the attempt for immediate trial charging could not be done due to misunderstanding of the Substation operator during heavy rain. The situation could have been averted, had A/R been enabled at both ends in line with CEA s Technical Standards and insistence of SRPC forum in various PCSC meetings kv MAPS SP Koil line (L1): As per MAPS, the line tripped at 9:32 hrs on on Y-E fault due to DPR, Z1 operation at a distance of 9.15 km from MAPS. As per TANTRANSCO, on since 06:00 hrs the line-cb at SP Koil end on SP Koil MAPS line-1 was under lock-out due to Compressor s low air-pressure. Subsequently at 09:32hrs., line fault occurred in the above feeder; however the breaker had not tripped due to lock-out condition; as a result, LBB relay acted and tripped all the 230kV feeders & all the four Auto-transformers. From the DR furnished by TANTRANSCO, it was seen that LBB protection had taken 560 msec for its operation. Issues: The breaker of 230kV SP.Koil-MAPS feeder-1 at SP Koil end was under lock-out due to airpressure lock-out of the compressor since 6:00 am on , but no actions were taken at SP Koil end to rectify the same till the occurrence of the line fault at 9:32 hrs. LBB protection acted with a delay of 560 msec. TANTRANSCO representative informed that due to shorting of supply cable to Compressor motor, air pressure lock-out occurred for Compressor. The fault current had persisted for 560 msec due to sluggish operation of LBB relay, and the matter was taken up with their OEM and would soon revert on the action taken. In this regard, TANTRANSCO is recommended to provide (i) separate alarm window for Air Pressure & SF6 Pressure indication in the Sub-station (SP Koil) Control room, and (ii) Standby Compressor arrangement in all critical sub-stations like SP Koil. 5. Tripping of both Units at MAPS: With the tripping of Acharapakkam line (L-4) at 8:20 hrs on , Reactors power was reduced in both units by 5%. Currents on lines 1, 2, 3, and 4 were monitored and maintained at (400/360/0/0) AMPS respectively. Subsequently, when the SP Koil line-2 (L-2) also tripped at 9:02 hrs on , the current on the only remaining line (L-1) shot up to over 500 A due to which both Units small dump valves

5 opened; as a result, generation got reduced to 130 / 112 MW (e) and line current on L-1 was brought down to 480 Amps. Finally, when the only evacuating line, viz., SP Koil line-1 (L-1) also tripped at 9:32 hrs, both units got tripped on high frequency and total class IV failure. Both Reactors also got tripped on high boiler delta-t. From the above, it is observed that had one Unit been withdrawn on tripping of three evacuating lines, the station could have survived on house load with one Unit in service during the loss of evacuation of the station (i.e., during tripping of the fourth line). Therefore, for the survival of the nuclear station, it is always advised to ensure generation level of MAPS without compromising (n-1) condition of evacuation system. C. General Operational & Protection Issues pertaining to MAPS in the context of the Grid Disturbance that occurred on Replacement of Disc type string insulators on all the 230 kv lines emanating from MAPS. It is seen that Arani & Acharapakkam lines tripped due to the failure of disc type string insulators of the 230kV towers at MAPS end due to wear of ball and socket assembly on corrosion. Also there are more no. of jumpers existing on lines 3 & 4 at first & second towers from MAPS end. To this, TANTRANSCO informed that for the total 688 towers, 159 cut joints had already been replaced. The work relating to replacement of disc type string insulators by polymer type at all tension towers is already under progress, and will be completed by April, The action plan for the same at all suspension towers will also be furnished shortly. In this regard, TANTRANSCO is recommended to furnish their comprehensive plan for replacing disc insulators by polymer type at all tension and suspension towers on all the 230 kv lines emanating from MAPS before the 50th Protection Co-ordination Sub-Committee (PCSC) meeting scheduled to be held on 27 th January, Improving the flow/ exchange of information between MAPS and TANTRANSCO substations for the faults occurring on the connecting lines. Between the trippings of MAPS SP Koil line-2 (L2) at 9:06 hrs and SP Koil line-1 (L1) at 9:32 hrs on , it is seen that due to delay in exchanging proper information on the fault data, opportunity has been lost in taking the necessary remedial action to bring back MAPS - SP Koil line-2 into service. As the shift personnel at SP Koil end were under the impression that the line CB was under lock-out due to SF6 pressure low, proactive action was not initiated even though MAPS personnel had tried to contact them over phone. It is seen that even though MAPS was already operating under depleted network conditions at the time of tripping of SP Koil line-2 [due to tripping of MAPS Arani line (at 18:28 hrs on ) and MAPS Acharapakkam line (at 08:21 hrs on )], concerned shift personnel have not shown the alertness required in handling the distressed system. It was emphasized that to avoid similar incidents in future, better vigilance and alertness need to be exercised by the shift personnel.

6 In this regard, it is agreed by MAPS and TANTRANACO that whenever any fault takes place on the transmission lines between MAPS and TANTRANSCO substations, the relevant fault data, viz., location, zone, magnitude and phase of the fault current will be mutually exchanged, within minutes. Parallelly, the concerned shift personnel will also put efforts to get first hand information on the condition of the equipment involved by physically inspecting the yard. Thus both the ends shall ensure trial charging of the line within 15 (Fifteen) minutes of tripping of the element, if the tripping was on single phase fault. 3. Providing dual AC supply to Compressor Motor and redundant Compressor Unit. It is seen that the lock-out of the SP Koil end line-cb on the MAPS SP Koil line 1 (L1) happened due to air lock-out of the Compressor unit, which in turn occurred because of the failure of the Compressor Motor due to shorting of its supply cable. Had the redundancy been provided to the supply to the compressor motor and/ or the Compressor unit, the breaker s lock-out could have been prevented. In this regard, TANTRANSCO is recommended to provide (i) dual AC supply to Compressor unit of the CB s, and (ii) a redundant/ standby Compressor unit that would automatically takeover in case the main unit stops functioning at SP Koil end for the CB s on the MAPS-bound lines 1 & 2. As SP Koil is essentially on single-bus operation, the issue of providing bus-sectionalizer CB was also discussed. To this, it was informed that as SP Koil was a very old station, there was no space available to make way for bus-sectionalizer. TANTRANSCO is advised to consider the possibility of providing bus-sectionalizer breaker arrangement during renovation. It was also noticed that DG-set had been kept in manual mode during tripping event at SP Koil. As this is not desirable for handling emergency situations, TANTRANSCO is recommended to keep DG set always in auto-mode at its SP Koil SS. 4. Carrier communication/ PLCC related issues on 230kV MAPS-Arani line (L-3). It is noted that MAPS have not provided any relevant files like Event Logger and Disturbance Recorder to verify the issues relating to carrier communication on 230 kv MAPS Arani line. However, to ensure healthiness of carrier communication on L-3, the following is recommended to be carried out by MAPS and Arani SS personnel in coordination: Healthiness of PLCC system components (hardware and software) at both ends shall be checked and faulty components shall be repaired/ replaced. End-to-end communication for DT/ permissive & other signals may be ensured by testing at both the ends. 5. Status of providing Line CVT s in the Y phase of all feeders excepting SP Koil-2. This is one of the recommendations given by the audit team that carried out protection audit of MAPS switchyard in the year TANTANSCO informed that the procurement of line CVTs had been completed, and line CVT s would be commissioned soon. To this, TANTRANSCO was requested to furnish the schedule of commissioning of line CVT s before the 50 th PCSC meeting scheduled to be held on 27 th January, 2016.

7 6. Provision of Auto-reclosure (A/R) on all 230kV lines emanating from MAPS. TANTRANSCO informed that though A/R is available at their end on all evacuating lines of MAPS, the same was not put into service in view of MAPS decision to not to provide A/R at their ends. MAPS informed that due to the possibility of damage to/ reduction in life of turbine and generator rotor, NPCIL management have decided not to keep A/R in service on all 230 kv lines emanating from their Nuclear stations. It is noted with concern that in spite of the CEA s mandated requirement of providing auto-reclose on all 220 kv/ 230 kv lines, and the earlier recommendation of sub-group which held its meeting on to that effect, A/R has not been put into service on any of the four evacuating lines of MAPS by TANTRANSCO as well as MAPS at their respective ends. In this regard, SRLDC mentioned that either single phase A/R scheme or three phase A/R scheme as felt appropriate by MAPS can be implemented at MAPS end. However, if MAPS feels that attempt for A/R is to be prevented strictly from MAPS end, then a Lead-Follow three phase A/R scheme could be followed by MAPS to comply with CEA s standards and maintain grid discipline. It was explained that the proposed lead-follow A/R scheme would effectively take care of chances of generating end closing on to a permanent fault. In this master-follower A/R supervision scheme, the grid-station end would reclose first, and send a permissive-signal to the generating end on successful auto-reclosure. By ensuring that the generating end would reclose only after the receipt of the permissive signal from the remote end after a predetermined time (say 1.5 sec, this shall be less than the pole discrepancy relay operation time), the chances of it closing on to a permanent fault can be eliminated. In the event of non-receipt of carrier signal, the generating end can go for 3-ph trip. In this regard, the Topic 6.1 on Common Considerations for Auto-reclosing of the IEEE Guide for Automatic Reclosing of Line Circuit Breakers for AC Distribution and Transmission Lines may be referred to. It was reiterated that as providing auto-reclose on all 220 kv/ 230 kv lines is mandatory under Regulation 43 (2) (c) of CEA s Technical Standards for Construction of Electrical Plants & Electric lines, action plan for providing A/R on all 230 kv evacuating lines of MAPS has to be provided by MAPS. It is therefore recommended that MAPS shall take up the issue of providing lead/follow A/R scheme on its 230 kv evacuating lines with their Management and present their action plan for implementing the same before the 50 th meeting of PCSC scheduled to be held on 27 th January, Ensuring Grid Connectivity of MAPS. MAPS informed that the following mechanism exists at MAPS to bring down generation in case of tripping of evacuating lines of MAPS: When two of the four evacuating lines go out, 5% reduction in generation output is effected. It was, however, informed that due to the limitation imposed by nuclear reactor s controls, such reduction can at most be sustained for a period of 30 minutes before which requisite action should be taken to bring back lines into service, lest the reactors may get poisoned out. Under these conditions, when one more line goes out, and the flow on the only remaining line crosses 500 Amps, generation output is further reduced to 130/112 MW in each Unit by venting

8 out the excessive steam (by opening small dump valves), and the current will be brought down to 480 Amps. It was, however, informed that such operation can be entertained for at most 15 minutes before which requisite action should be taken to bring back lines into service, lest the reactors may get poisoned out. At MAPS, the power from 2x220 MW Units is being evacuated through the following four evacuating lines (Kunda type conductors with 213 MVA rating), viz., (i) 230 kv MAPS SP Koil line-1 (L-1); (ii) 230 kv MAPS SP Koil line-2 (L-2); (iii) 230 kv MAPS Arani line (L-3); and (iv) 230 kv MAPS Acharapakkam line (L-4). In addition to above, there is one radially connected Under Ground (UG) Cable to BHAVINI to supply start-up and commissioning power to BHAVINI. The cable has been provided with line differential protection as primary protection and over current and earth fault protections as back-up protection. From the above, the non-availability of (n-1) when two of the four evacuating lines get tripped is quite apparent. To provide (n-1), the combined generation of two Units has to be brought down to MW. However, as brought out above, the generation can only be brought down to 130/ 110 MW in each Unit (thus 260/220 MW in total) by resorting to extreme contingency measure of venting out excessive steam, which operation can be sustained for at most 15 minutes without any of the Reactor s getting poisoned out. Moreover, once such a thing happens, it takes one-to-three days to bring Units back on to bars. It was therefore originally proposed to utilize the existing UG Cable between MAPS and BHAVINI to its fullest capacity by connecting it to the grid at BHAVINI. However, considering its rating (133 MVA or 106 MW), it can be seen that (n-1) will not be fulfilled even after connecting this Cable to grid when MAPS operates with two evacuating lines. Considering the above limitations, and the need to ensure better connectivity of MAPS to grid, it is proposed to lay a Single-Circuit Over-Head Transmission Line with Twin-Moose type Conductor along the RoW of the present UG Cable. As the distance between MAPS and BHAVINI is only 800 mts., the proposed S/C over-head transmission line would be the ideal solution in the long-term to evacuate power from MAPS with (n-1) even after losing the two out of the four existing evacuating lines. MAPS and BHAVINI are therefore recommended to examine this proposal, and, after obtaining the consent of their respective managements, are requested to approach SP&PA Division of Central Electricity Authority to get the scheme ratified in the Standing Committee on Power System Planning for Southern Region (SCPSPSR) for implementation. Till such time, MAPS is recommended to maintain the generation level such that the line loading of available evacuation system will always satisfy the requirement of n-1 criteria. In the process, if the situation requires withdrawing one of the two Units, the same may be followed by MAPS to avoid tripping of both Units on loss of evacuation.

9 The necessary system studies to make out a strong case for the above proposal have been carried out, and are presented at Annexure-V. The assumptions made and the scenarios considered for the above studies are detailed below: Assumptions made/ Data considered: (i) The following UG Cable characteristics as informed by BHAVINI have been considered: Sl. Description Value No. 1 Rating Voltage: 230 kv (Max. 245 kv) Current: 850 A in air 646 A in duct 335 A when directly buried in ground [Cable is directly buried in ground] 2 Length of the Cable 3 runs of 800 mt. cable 3 Conductor Max. DC Resistance per km (i) At 20 C Ω/ km (ii) At 90 C Ω/ km 4 Positive & Negative sequence reactance per km j Zero sequence data per km j Protection equipment rating at both ends of the Cable VT 100 VA; CT 30 VA (ii) Share of various States in BHAVINI s first Unit of 500 MW capacity has been considered as follows: Andhra Pradesh + Telangana Karnataka TamilNadu Kerala Puducherry Unallocated Power 132 MW 72 MW 167 MW 43 MW 11 MW 75 MW (iii)expected commissioning schedule of the first Unit of BHAVINI (of 500 MW capacity) has been taken as September, (iv)the Ex-bus generation considered for MAPS and BHAVINI are 2x200 MW and 1x450 MW respectively. (v) For the studies with & without generation at BHAVINI, present operational base-case only has been considered, as the effect of transmission elements that would get added to the grid by September, 2016 would be minimal on the existing 230 kv network in & around MAPS.

10 Various Scenarios considered: Sl. CASE No. Scenario considered Line flow violations No. 1 Base Case (BC) MAPS with L1, L2, L3 & L4 in service NIL 2 CASE-1 BC + Outage of [L1] NIL 3 CASE-2 BC + Outage of [L1 + L3] 235 MW on L2 4 CASE-3 BC + Outage of [L1 + L3 + L4] 400 MW on L2 5 CASE-4 (BC1) BC kv MAPS BHAVINI Cable NIL 6 CASE-5 BC1 + Outage of [L1] NIL 7 CASE-6 BC1 + Outage of [L1 + L3] NIL 8 CASE-7 BC1 + Outage of [L1 + L3 + L4] 320 MW on L2 9 CASE-8 [= New Base Base Case (BC) MW generation at NIL Case (NBC)] BHAVINI 10 CASE-9 NBC + Outage of [L3] NIL 11 CASE-10 NBC + Outage of [L3 + L2] 215 MW on L1 12 CASE-11 NBC + Outage of [L3 + L2 + L1] 400 MW on L4 13 CASE-12 (NBC1) NBC kv MAPS BHAVINI Cable NIL 14 CASE-13 NBC1 + Outage of [L3] NIL 15 CASE-14 NBC1 + Outage of [L3 + L2] MMW on L1 16 CASE-15 NBC1 + Outage of [L3 + L2 + L4] MW on L1 17 CASE-16 (BC2) Base Case (BC) kv MAPS BHAVINI NIL Twin Moose S/C line 18 CASE-17 BC2 + Outage of [L1] NIL 19 CASE-18 BC2 + Outage of [L1 + L2] NIL 20 CASE-19 BC2 + Outage of [L1 + L2 + L3] NIL 21 CASE-20 BC2 + Outage of [L1 + L2 + L3 + L4] NIL 22 CASE-21 (NBC2) Base Case (BC) MW generation at NIL BHAVINI kv MAPS BHAVINI Twin Moose S/C line 23 CASE-22 NBC2 + Outage of [L1] NIL 24 CASE-23 NBC2 + Outage of [L1 + L2] NIL 25 CASE-24 NBC2 + Outage of [L1 + L2 + L3] NIL 26 CASE-25 NBC2 + Outage of [L1 + L2 + L3 + L4] NIL

11 Short Circuit Studies for various scenarios have also been carried out and tabulated below: Since both MAPS and BHAVINI stations have been designed for a Short Circuit Level of 10,000 MVA, it can be concluded from the above that laying of Twin-Moose type S/C Over-Head transmission line between MAPS and BHAVINI poses no problem. 8. Furnishing of tripping details in compliance of Regulation 5.2 (r) of IEGC, and providing monthly status of healthiness of batteries MAPS s attention has been brought to their obligation of fulfilling 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 (including MAPS) 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. MAPS is recommended to upload various tripping files (FIR/ DR/ EL/ TR) whenever any tripping involving their station takes place in SRLDC s web-portal within 24-hrs of the occurrence of the tripping event in compliance of Regulation 5.2 (r) of IEGC. 9. Patrolling Protocol/Guidelines for Over Head Transmission Lines: SRPC brought to the notice of TNEB regarding the Patrolling Protocol/Guidelines for Over Head Transmission Lines to be followed by them. It was noted that in compliance of Hon ble CERC Order dated in respect of Petition No. 146/MP/2013 wit IA 36/2013, Patrolling Protocol/Guidelines for Over Head Transmission Lines had been formulated by SRPC Secretariat in due consultation with all the stake holders and the same had been communicated to Hon ble CERC and all the Transmission Utilities (Central/State) vide SRPC letter dated with a request to strictly follow the guidelines. It was noted that as per Guidelines, each transmission utility should furnish the Annual Schedule of Patrolling to SRPC/SRLDC along with Annual Outage data by October each year and compliance report of the patrolling/maintenance carried out during previous month with respect to schedule would be furnished to SRLDC/SRPC in the OCC Meeting. TANTRANSCO agreed to follow the same and requested SRPC to kindly furnish a copy of the Patrolling Protocol/Guidelines for Over Head Transmission Lines to help in their needful action. In this regard, a copy of the sought Guidelines is enclosed at Annexure-VI.

12 10. Line Clearance issues: The following suggestions/recommendations given by the System Studies Sub-Group of SRPC which held its meeting on regarding line clearance were reiterated: Information regarding the lines kept open in MAPS vicinity to be informed to MAPS. Restoration of the same also may be informed pertinently. If any line clearance (LC) is there in downstream/upstream MAPS area for maintenance, then further opening of the lines which may cause non availability of evacuation lines from MAPS have to be restricted for avoiding undesired island formation of MAPS generation with TANTRANSCO loads/house Load operation of MAPS Units / Poisoning of Units etc. 11.Providing information relating to line outages and Declared Capacity (DC) revision in case of generating Unit outages SRLDC mentioned with concern that revision of DC by MAPS is not being done by MAPS as and when there is tripping / synchronization / change in level of generation. This lead to operational difficulties as well as huge financial implication on the constituents when the corrections were incorporated post facto. MAPS assured for necessary action in this regard and strict compliance in future. The issue of not providing proper information to SRPC/ SRLDC regarding line outages and in case of line outages by TANTRANSCO was also discussed. TANTRANSCO assured that they would take effective steps to ensure that such lapses won t take place. *****

13 Page 1 of 2 Annexure-I

14 Page 2 of 2 Annexure-I

15 Page 1 of 2 Annexure-II

16 Page 2 of 2 Annexure-II

17 Page 1 of 2 Annexure-III

18 Page 2 of 2 Annexure-III

19 Action taken by MAPS and TANTRANSCO w.r.t the recommendations given by the System Studies Sub-Group of SRPC in its meeting held on Sl. No. Observation/ Recommendation Action taken Annexure-IV 1 It was learned in the sub-group meeting at Chennai on that PHT pump-7 of the Unit-I tripped on under frequency or other supply conditions. Though pumps of the both the units were subjected to same frequency and other supply conditions, only the specific pump of Unit-1. On account of this, MAPS is requested to review the protection settings of the affected pump of Unit- 1 and furnish a detailed report to the SRPC indicating the protection settings (for voltage, current, frequency, etc.) of the pump, and exact reason for tripping of the pump of Unit-I and corrective actions taken to prevent reoccurrence. 2 MAPS is also requested to draw an action plan for facing the similar situation (i.e. that was experienced on ) due to countless & unforeseeable combinations of arrangement of network elements in the vicinity of MAPS. This plan of action shall include retaining auxiliary supply and ensuring successful and sustained house load operation till grid returns to normalcy. 3 TANTRANSCO was requested to carry out line patrolling for locating any trouble spots, if any. 4 If any Line Clearance (LC) is there in that area for maintenance, then further opening of the lines have to be restricted for avoiding undesired island formation of MAPS generation with TANTRANSCO loads. 5 Alternate anchoring through Oragadam Bus coupler and SP Koil Bus coupler could be provided (Study results are attached in the Annexure). At least 2-3 links to be ensured with N-1 in future to avoid islanding of critical areas/generation complexes. 6 Line loadings should be controlled by taking up adequate load shedding, especially during a critical shutdown, rather than resorting to network rearrangement. N-1 to be ensured in real time operation. Page 1 of 2 Action taken by MAPS in this regard is awaited. Complied by MAPS. It was informed that Transient Handling Procedure (THP) is in place to successfully handle the house load operation. Complied by TANTRANSCO. From the events leading to Grid Disturbance on , it is seen that due diligence has not been exercised by TANTRANSCO in preventing the same. The issue was discussed in detail in PSAG-14 meeting. Complied by TANTRANSCO. Complied by TANTRANSCO. It was informed that with the commissioning of additional 400 kv and 230 kv lines, TANTRANSCO is relying on load shedding rather than resorting to

20 network rearrangement Annexure-IV to ensure line loadings stay within permissible limits during critical shutdown. 7 Many of the 230 KV and below lines in Chennai area are heavily loaded without N-1. Systematic augmentation for the same needs to be planned and executed on priority. 8 AIR facility to be provided on all lines from MAPS as well as critical S/Ss of TANTRANSCO to guard against transient faults. Action taken by TANTRANSCO in this regard is awaited. MAPS: Not complied. TANTRNSCO: Though A/R was provided at their Substations for all connecting 230 kv lines to MAPS, the same was kept disabled. The issue was discussed in detail in PSAG-14 meeting. 9 Information about lines kept open in MAPS vicinity is to he informed to MAPS. Information about status is to be given to MAPS while restoration also. 10 Outage of both circuits of 400 KV Kalivandapattu-Vallur would cease to be a concern when 400 KV Kalivandapaltu-Pugalur/Thiruvalam are in place. Complied by TANTRANSCO. TANTRANSCO informed that this had been taken care of by the commissioning of 400 kv KV Pattu Pugalur D/C line. Page 2 of 2

21 BHAVANI ARNI MAPS SIRSERI H 50.0H SPBUDUR SPET SPKOIL ACHARAP BASECASE Annexure-V Page 1 of 26

22 1 CASE-1: BASECASE + 230kV SP KOIL- MAPS -1 OUTAGE SIRSERI2 Annexure-V BHAVANI SPET ARNI SPBUDUR MAPS SPKOIL ACHARAP Page 2 of R 39.0R

23 1 CASE 2 : CASE kV MAPS - ARNI S/C OUTAGE SIRSERI2 Annexure-V BHAVANI SPET ARNI SPBUDUR MAPS SPKOIL ACHARAP Page 3 of R 28.8R

24 1 CASE 3: CASE kV MAPS - ACHARAPKAM S/C OUTAGE SIRSERI2 Annexure-V BHAVANI SPET ARNI SPBUDUR MAPS SPKOIL ACHARAP Page 4 of R 25.6R

25 1 CASE 4 : BASECASE + 230kV MAPS - BHAVINI CABLE IN-SERVICE SIRSERI2 Annexure-V BHAVANI SPET ARNI SPBUDUR MAPS SPKOIL ACHARAP Page 5 of H 50.0H

26 1 CASE 5 : CASE kV MAPS - SP KOIL -1 OUTAGE SIRSERI2 Annexure-V BHAVANI SPET ARNI SPBUDUR MAPS SPKOIL ACHARAP Page 6 of R 43.2R

27 1 CASE 6: CASE kV MAPS - ARNI S/C OUTAGE SIRSERI2 Annexure-V BHAVANI SPET ARNI SPBUDUR MAPS SPKOIL ACHARAP Page 7 of R 34.3R

28 1 CASE 7 : CASE kV MAPS - ACHARAPAKAM S/C OUTAGE SIRSERI2 Annexure-V BHAVANI SPET ARNI SPBUDUR MAPS SPKOIL ACHARAP Page 8 of R 29.1R

29 1 CASE 8 : BASECASE + BHAVINI 450 MW GENERATION SIRSERI2 Annexure-V BHAVANI SPET ARNI SPBUDUR MAPS R SPKOIL ACHARAP Page 9 of R 37.0R

30 1 CASE 9 : CASE kV MAPS - ARNI S/C OUTAGE SIRSERI2 Annexure-V BHAVANI SPET ARNI SPBUDUR MAPS R SPKOIL ACHARAP Page 10 of R 31.1R

31 1 CASE 10 : CASE kV MAPS - SP KOIL-2 OUTAGE SIRSERI2 Annexure-V BHAVANI SPET ARNI SPBUDUR MAPS R SPKOIL ACHARAP Page 11 of R 17.1R

32 1 CASE 11 : CASE kV MAPS - SP KOIL - 1 OUTAGE SIRSERI2 Annexure-V BHAVANI SPET ARNI SPBUDUR MAPS H SPKOIL ACHARAP Page 12 of R 17.4R

33 1 CASE - 12: CASE kV MAPS - BHAVINI S/C CABLE IN-SERVICE SIRSERI2 Annexure-V BHAVANI SPET ARNI SPBUDUR MAPS R SPKOIL ACHARAP Page 13 of R 35.0R

34 1 CASE 13: CASE kV MAPS - ARNI S/C LINE OUTAGE SIRSERI2 Annexure-V BHAVANI SPET ARNI SPBUDUR MAPS R SPKOIL ACHARAP Page 14 of R 28.3R

35 1 CASE 14: CASE kV MAPS - SP KOIL-2 OUTAGE SIRSERI2 Annexure-V BHAVANI SPET ARNI SPBUDUR MAPS R SPKOIL ACHARAP Page 15 of R 13.2R

36 1 CASE 15: CASE kV MAPS - ACHARAPAKAM SC OUTAGE SIRSERI Annexure-V BHAVANI SPET ARNI SPBUDUR MAPS H SPKOIL ACHARAP Page 16 of R 7.9R

37 1 Annexure-V CASE 16: BASECASE + 230kV MAPS - BHAVINI TWIN MOOSE SC LINE SIRSERI BHAVANI SPET ARNI SPBUDUR MAPS SPKOIL ACHARAP H 50.0H Page 17 of 26

38 1 Annexure-V CASE 17: CASE kV MAPS - SP KOIL -1 OUTAGE SIRSERI BHAVANI SPET ARNI SPBUDUR MAPS SPKOIL ACHARAP H 50.0H Page 18 of 26

39 1 Annexure-V CASE 18: CASE kV MAPS - SP KOIL -2 OUTAGE SIRSERI BHAVANI SPET ARNI SPBUDUR MAPS SPKOIL ACHARAP H 50.0H Page 19 of 26

40 1 Annexure-V CASE 19: CASE kV MAPS - ARNI SC OUTAGE SIRSERI BHAVANI SPET ARNI SPBUDUR MAPS SPKOIL ACHARAP H 50.0H Page 20 of 26

41 1 Annexure-V CASE 20: CASE kV MAPS - ACHARAPAKAM S OUTAGE SIRSERI BHAVANI SPET ARNI SPBUDUR MAPS SPKOIL ACHARAP H 50.0H Page 21 of 26

42 1 Annexure-V CASE 21: CASE kV MAPS - BHAVINI TWIN MOOSE S/C LINE SIRSERI BHAVANI SPET ARNI SPBUDUR MAPS H SPKOIL ACHARAP R 3.4R Page 22 of 26

43 1 Annexure-V CASE 22: CASE kV MAPS - ARNI SC OUTAGE SIRSERI BHAVANI SPET ARNI SPBUDUR MAPS H SPKOIL ACHARAP R 7.2R Page 23 of 26

44 1 Annexure-V CASE 23: CASE kV MAPS - SP KOIL -2 OUTAGE SIRSERI BHAVANI SPET ARNI SPBUDUR MAPS H SPKOIL ACHARAP R -1.4R Page 24 of 26

45 1 Annexure-V CASE 24: CASE kV MAPS - SP KOIL - 1 OUTAGE SIRSERI BHAVANI SPET ARNI SPBUDUR MAPS H SPKOIL ACHARAP R -20.1R Page 25 of 26

46 1 Annexure-V CASE 25 : CASE kV MAPS - ACHARAPAKAM SC OUTAGE SIRSERI BHAVANI SPET ARNI SPBUDUR MAPS H SPKOIL ACHARAP R -16.0R Page 26 of 26

47 Page 1 of 12 Annexure-VI

48 Page 2 of 12 Annexure-VI

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51 Page 5 of 12 Annexure-VI

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58 Page 12 of 12 Annexure-VI