SOUTHERN REGIONAL POWER COMMITTEE BENGALURU

Transcription

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2 SOUTHERN REGIONAL POWER COMMITTEE BENGALURU Minutes of the Special Meeting held on 21 st June, 2017 at TPCIL plant in Nellore w.r.t. perturbations at their plant in Nellore in the recent past A. Introduction A Special Meeting was held on 21 st June, 2017 at TPCIL plant in Nellore to deliberate on all outstanding protection issues noticed w.r.t. perturbations experienced at their plant in Nellore in the recent past. The list of participants is enclosed at Annexure-I. The issue was discussed in the 64 th meeting of PCSC held on , when the following were noted: It was noted that there were no actual tripping of any of TPCIL evacuating lines in any of the stated events. However, experience of perturbations in line/ GT relays had been a recurrent phenomenon at TPCIL end. From the corresponding PMU plots presented by SRLDC (Annexure-IV), it was noted that in almost all of the perturbation events, there was flow of negative and zero sequence currents, which pointed to occurrence of actual faults. Further, it was also noted that there was not a single instance of delayed clearance of faults, which meant that the protection systems in place had operated correctly. Accordingly, the issue came down to one of identifying the plausible locations of the fault so that suitable remediable measures for such frequent occurring of faults could be suggested. Thus, to zero in on the plausible fault locations, it was felt necessary to analyze SRLDC SCADA Sequence of Events (SoE) by juxtaposing it with that of SLDC of Andhra Pradesh. The idea was since protection systems were found to have operated correctly in the stated instances, it is appropriate to go into the reasons for such high frequency of trippings by identifying the probable fault locations. Further, since TPCIL is connected to Nellore Pooling Station (NPS) of PGCIL (SR-I), to ascertain whether protection systems put in place are being properly maintained, it was also decided to conduct protection audit of 765/ 400 kv NPS. Subsequently, as decided in PCSC-64 meeting, SCADA data correlation with perturbation events, and protection audit of 765/ 400 kv NPS were conducted. Further, the settings adopted by TPCIL for their protection relays had also been verified for correctness. The observations made and recommendations/ measures suggested to various Utilities w.r.t. the issues involved are detailed in the following Sections. B. Protection Audit of 765/ 400 kv Nellore PS of PGCIL (SR-I) Protection audit of 765/ 400 kv Nellore PS of PGCIL (SR-I) was conducted by a team comprising Officials from SRPC, SRLDC, APTRANSCO and TPCIL during June, 2017 to ascertain whether protection systems put in place are being properly maintained. The remarks of the audit team for compliance by PGCIL (SR-I) are given at Annexure-II. Minutes of the Special Meeting on TPCIL Perturbations held on 21 st June, 2017 Page 1

3 After observing the state of various protection systems in place and verifying the settings adopted for various protection relays at Nellore PS, the audit team concluded that there was nothing suspicious that could have contributed to perturbations experienced at TPCIL plant. C. Identification of probable fault locations The list of perturbation events provided by TPCIL is given below: Sl. No. Date & Time of Perturbation Nature of Perturbation (Voltage dip / Current Variation / Voltage Variation With Voltage Details)(Fault Phase ref- RYB) @2.01&7.38hrs Fault on B, IN> @18.03hrs Fault on R, Zone @ 4.55hrs, 6.01hrs, 6.15hrs, 6.25 & 6.54hrs @ 4.53hrs, 5.15hrs, 5.44hrs & 6.36hrs hrs, 3.55hrs, 3.55hrs, 5.02&6.05 IN>1 Fault on B,V< 1 Fault on B, Zone3&V< @ 2.41 & 2.56hrs Fault on Y, Zone @ 2.51hrs IN> @ 2.50, 3.59 & 4.38hrs Fault on Y, IN> @ 13.40, 14.05, 14.38, 14.58, & 16.16hrs Fault on Y, Zone-3, IN>1, V<1 Since in most of the above events, TPCIL end relays had sensed the apparent faults in Zone-3, it was set out to arrive at the possible paths for Zone-3 as given below: For this, since TPCIL is connected to NPS, and Zone-3 reach at TPCIL has been set as to protect the longest line connected to NPS, which is 400 kv NPS Gooty line of length 289 km, other possible paths falling in Zone-3 reach for TPCIL end relays have been arrived at by considering various transmission line (s) emanating from NPS subject to total line length of 289 km. 400 kv NPS TPCIL D/C line = 32.7 km 400 kv NPS Gooty D/C line = 289 km 400 kv NPS SGPL D/C lines = 33.5 km 400 kv NPS MEPL line = km 400 kv NPS SEL line = km 400 kv NPS Nellore-PG D/C line = 6.7 km 765 kv NPS-Kurnool D/C line = km Minutes of the Special Meeting on TPCIL Perturbations held on 21 st June, 2017 Page 2

4 400 kv Nellore-PG Sriperumbudur D/C line = 189 km Sriperumbudur SV Chatram D/C line = 17.9 km SV Chatram NCTPS D/C line = 95 km NCTPS-II NTECL-Vallur = 3.5 km NCTPS-II Alamathy D/C line = 84 km Nellore-PG Tiruvalam D/C line = km SDSTPS Nellore-AP D/C line = km SDSTPS - Chittoor D/C line = 189 km Minutes of the Special Meeting on TPCIL Perturbations held on 21 st June, 2017 Page 3

5 To further zero in on the probable fault locations, SCADA sequence of events (SoE) were obtained from SRLDC & SLDC, APTRANSCO and juxtaposed with the TPCIL provided perturbation events. From this, it can be concluded that Zone-3 perturbations as experienced by TPCIL end relays could be attributed mainly to (i) the faults on the 400 kv transmission lines emanating from generating stations (Vallur TPS, NCTPS) in the Chennai metro area, and (ii) the faults on 400 kv Nellore-AP (Manubolu) Krishnapatnam (SDSTPS) D/C line (esp. within 10 km radius from SDSTPS). In this connection, it may be noted that some of these events had already been discussed & addressed appropriately in regular monthly meetings of PCSC. The correlated data along with related PCSC deliberations is enclosed at Annexure-III. In this connection, it was noted that some of the SCADA events recorded by SLDC, APTRANSCO had not been captured in SRLDC s SCADA system. It was therefore recommended that SRLDC and SLDC, APTRANSCO may appropriately address the underlying communication issues involved. It was also noted that Auto-reclosure (A/R) feature kept in service from Krishnapatnam (SDSTPS) end on 400 kv Krishnapatnam Nellore-AP D/C line at Krishnapatnam end was unhealthy and found to be operating erratically. It was therefore recommended that APGENCO (SDSTPS) take steps to rectify A/R logic at SDSTPS end, and make it functional at the earliest. C.1 Measures taken with respect to reducing frequency of faults on transmission lines in Chennai metro area: The issue had been elaborately dealt with by PCSC forum in their 64 th meeting held on The measures taken and stated to be under progress by the concerned utilities [TANTRANSCO & PGCIL (SR-II)] as brought out in the minutes of PCSC-64 meeting are reproduced below: *********************************************************************************** Deliberations w.r.t. GD-I.1 & GD-I.2 & GD-I.3: Insulators Replacement: It was noted that the above GDs were mainly due to Insulators flashovers/ decapping on the 400 kv evacuating lines of NCTPS, Stage-II. Since the Chennai (NCTPS) area falls in the most vulnerable terrain (coastal & pollution & generating) category, the applicable patrolling protocol and maintenance procedures along with necessary remedial measures required to be taken had been suggested way back in April, 2014 when similar trippings had been encountered. Then it was decided that all conventional insulators in the stretches prone to pollution & saline effects would be replaced with polymer type insulators. When asked about the status of replacement of insulators on their lines, TANTRANSCO informed that the Insulator replacement works on the fault-prone stretches on all six evacuating lines of NCTPS-II had already been completed. And the present status in this regard was as follows: Insulators replacement on 400 kv NCTPS2 Vallur lines 1 & 2 had been completed. Insulators replacement on 400 kv NCTPS2 SV Chatram lines 1 & 2 was presently going on, and would be completed soon. Insulators replacement on 400 kv NCTPS2 Alamathy lines 1 & 2 would be completed in 3-month time. When asked about the status of replacement of insulators on the portions of the lines belonging to them, PGCIL (SR-II) informed the following: Insulators replacement on 400 kv Vallur - Alamathy lines 1 & 2 had been completed. Minutes of the Special Meeting on TPCIL Perturbations held on 21 st June, 2017 Page 4

6 Insulators replacement on major portion of the 400 kv Vallur Kalavindapattu lines 1 & 2 had been completed. The left out portions would be completed in 2-3 months. In this regard, the need to undertake various maintenance activities like hot-line washing of insulators and condition-based monitoring of equipment including attending to hot-spots was emphasized. Auto-Reclosure Issues: When enquired about the remedial action taken w.r.t. restoring A/R on the evacuating lines of NCTPS-II, TANTRANSCO informed the following: FO link on 400 kv NCTPS2 Alamathy lines 1 & 2 was restored on FO link on 400 kv NCTPS2 SV Chatram lines 1 & 2 was restored on FO link on 400 kv NCTPS2 Vallur lines 1 & 2 was restored on When asked about the undue delay (about 20 days) taken in restoring the above links, TANTRANSCO informed that due to the critical nature of the areas through which above lines were passing, they had to grapple with various operational & logistical issues, and assured that efforts would be made to reduce FO link restoring time to the minimum possible in future. In this regard, TANTRANSCO was asked to ensure that A/R is functional on all 400 kv lines in Chennai area and steps shall be taken to restore promptly any disruptions on account of FO link failures. Recommendations: TANTRANSCO and PGCIL (SR-II) to take steps to complete insulator replacement works on the 400 kv lines owned by them in Chennai area within 3 months. Deliberations w.r.t. GD-I.4: When enquired about the status of insulators replacement on the 230 kv lines in NCTPS area, TANTRANSCO informed that the works are under progress. To this, it was emphasized that the same level of seriousness given for 400 kv lines should also be given for 230 kv lines in replacing conventional insulators with that of polymer type. When enquired about the status of A/R implementation on 230 kv lines emanating from NCTPS-I, originally A/R had not been provided due to NCTPS-I being a generating station. However, in line with extant regulations and guidelines, they have decided to implement A/R on those transmission lines where one end is connected to a generating station. As already intimated to SRPC, steps would be taken to provide the same in 6 months. Recommendations: TANTRANSCO to take steps to complete insulator replacement works on the 230 kv lines owned by them in NCTPS area within 6 months. TANTRANSCO to take steps to implement A/R on all 230 kv lines emanating from NCTPS-I at the earliest. ********************************************************************************************* Minutes of the Special Meeting on TPCIL Perturbations held on 21 st June, 2017 Page 5

7 C.2 Measures taken with respect to reducing frequency of faults on 400 kv Krishnapatnam (SDSTPS) Nellore-AP (Manubolu) D/C line: It was noted that the primary cause of the faults was basically insulator flashovers/ failures/ tracking. It was further noted that 400 kv Krishnapatnam Nellore-AP D/C line is of length km, and covers about 140 tower locations. It was further noted that this D/C line [owned/ maintained by APTRANSCO], have conventional disc type insulators; whereas all other lines in Nellore complex [owned/ maintained by PGCIL (SR-I)], have composite polymer type insulators which explains the frequent occurrence of faults on the former. It was also noted that when the occurrence of the faults due to insulator failures on 400 kv Krishnapatnam Nellore (AP) D/C line was on the rise a couple of years ago, APTRNSCO had then replaced insulators on first 20 tower locations starting from SDSTPS, after which the faults frequency came down. Now again when these were on the rise in the past few months, APTRANSCO had started replacing conventional insulators with SCR polymer type insulators covering tower locations When enquired about the present status, APTRANSCO informed that they had completed insulator replacement works for tower locations 21 40, and that for is under progress, and is expected to be completed by mid-july, To this, it was pointed out that since the lines are of only km length, and are subjected to severe pollution & saline effects on continuous basis, replacement of conventional insulators on all 140 tower locations is an effective solution to avoid similar faults in future. Accordingly, APTRANSCO was recommended to replace conventional disc-type insulators with SCR/ CLR polymer type insulators on all 140 tower locations in 400 kv Krishnapatnam Nellore (AP) D/C line. APTRANSCO was also suggested make provision for composite polymer type insulators whenever they undertake to plan evacuation system for a generator coming up in coastal & highly polluted areas. In this context, it was also informed that as per the SRPC issued Transmission Line Patrolling Protocol/ Guidelines, in coastal and heavy to-medium polluted areas, the line maintenance activities including hot-line/ cold-line washing of insulators are to be carried out at least once in every four months, and TPCIL, PGCIL (SR-I), APGENCO, APTRANSCO were asked to strictly adhere to these guidelines. D. Status-Check of various protection settings adopted at TPCIL It was noted that by and large, the settings adopted in various protection relays at 400 kv TPCIL Switchyard are in order except for the following: 1. Presently, Zone-2 time delay for distance relays has been kept at 300 msec. However, since Nellore Pooling Station is connected to Nellore-PG SS by very short lines (of length 6.7 km), to allow proper time-coordination, it is recommended to keep Zone-2 time delay of 500 msec. 2. In setting resistive reach values for various zones, load resistance, R(L), has been calculated considering 1.2 times the full load current. It is recommended to revise resistive reach values for various zones by considering a load resistance that has been obtained with 1.5 times the full load current. Minutes of the Special Meeting on TPCIL Perturbations held on 21 st June, 2017 Page 6

8 3. Since the Zone-4 (reverse) primarily provides back-up to busbar protection, the present Zone-4 (reverse) time delay of 1.1 sec may be suitably revised to a lower value (say, 0.5 sec). 4. It is noted that back-up directional over-current protection (67) has been kept enabled on 400 kv feeders, and its setting is based on the CT ratio of 3000/ 1 A, which is in much excess of full load current. Even though this may not pose any problem as of now, as and when TPCIL decides to use CT s of lower ratio (say, 2000/ 1 A), the back-up directional over-current protection (67) shall be kept disabled. 5. It is noted that Over Voltage Protection settings have been presently kept as Stage-I: 110 %, 3 sec; Stage-II: 160 %, 0.5 sec. These shall be changed to SRPC provided settings intimated vide letter no: SRPC/SE-III/OVR/2017/ dated These are given below for kind reference: 400 kv TPCIL NPS line-1: OVR, Stage-I: A (111% of Vnom, 10 sec); OVR, Stage-II: 140% of Vnom, 100 msec. 400 kv TPCIL NPS line-2: OVR, Stage-I: D (110% of Vnom, 8 sec); OVR, Stage-II: 140% of Vnom, 100 msec. 6. It is further noted that Directional Earth Fault Protection (DEF, 67N) and Distance Protection (DP, 21) have been simultaneously kept enabled on 400 kv feeders. Since, this may create time-coordination issues, it is recommended, in line with SRPC philosophy, to keep DEF protection in blocked condition as long as Distance Protection is active, and shall be configured to become active only when distance protection does not pickup. ***** Minutes of the Special Meeting on TPCIL Perturbations held on 21 st June, 2017 Page 7

9 Annexure - I

10 Annexure- II Remarks of Protection Audit Team vis-à-vis 765 / 400 kv Nellore Pooling Station of PGCIL (SRTS-I) Sl. No. Observations on which action may be taken 1 Substation is well maintained in all aspects. 2 The following have been found to be satisfactory: (i) Operation of various electrical & mechanical interlocks (ii) Remote operation of Isolators from work-station (iii) No oil leakage from any of the CT's & ICT's & Reactors. 3 As most of the numerical relays have completed 4-years of in-service operation, comprehensive testing of the same may be carried out. 4 In addition to blocking of distance protection under VT fuse-fail conditions, it shall be ensured that upon detection of a fault (sensed by negative sequence component), blocking of distance protection gives rise to operation of its inherent Over- Current protection with a suitable definite time delay of (say) 500 msec. 5 It is observed that Zone-1 time delay for Gooty lines 1 & 2 is kept as 100 msec, which may be clarified/ reviewed. 6 Z2, Z3 and Z4 Resistive reaches for Ph-G faults for Main-I & Main 2 have been found to be kept differently on 400 kv NCC lines 1 & 2, 400 kv Gooty lines & 765 kv Kurnool lines, which may be reviewed. 7 PLCC db level (signal strength) measurements are being done on yearly basis.

11 Perturbation Events Correlation with SCADA Data Annexure-III Sl. No. Date & Time Nature of Perturbation (Voltage dip / Current Variation / Voltage Variation With Voltage Details)(Fault Phase ref- RYB) at 2.01 hrs Fault on B, IN>1 SLDC, APTRANSCO: No Trippings recorded by SRLDC at 7.38 hrs Fault on B, IN>1 SLDC, APTRANSCO: No Trippings recorded by SRLDC at hrs Fault on R, Zone-3 No Trippings recorded by SLDC, APTRANSCO No Trippings recorded by SRLDC at 4.55 hrs IN>1 (PCSC-62 held on ) No Trippings recorded by SLDC, APTRANSCO PCSC Deliberations: Page 1 of 10

12 Annexure-III at 6.01 hrs, IN>1 (PCSC-62 held on ) No Trippings recorded by SLDC, APTRANSCO PCSC Deliberations: Page 2 of 10

13 Annexure-III at 6.15hrs IN>1 (PCSC-62 held on ) No Trippings recorded by SLDC, APTRANSCO PCSC Deliberations: at 6.25 hrs IN>1 (PCSC-62 held on ) No Trippings recorded by SLDC, APTRANSCO PCSC Deliberations: Page 3 of 10

14 at 6.54 hrs IN>1 (PCSC-62 held on ) Annexure-III No Trippings recorded by SLDC, APTRANSCO PCSC Deliberations: at 4.53 hrs Fault on B,V< 1 SLDC, APTRANSCO: No Trippings recorded by SRLDC at 5.15 hrs Fault on B,V< 1 (PCSC-63 held on ) SLDC, APTRANSCO: PCSC Deliberations: Page 4 of 10

15 at 5.44 hrs Fault on B,V< 1 Annexure-III No Trippings recorded by SLDC, APTRANSCO No Trippings recorded by SRLDC at 6.36 hrs Fault on B,V< 1 No Trippings recorded by SRLDC SLDC, APTRANSCO: at 1.57 hrs Fault on B, Zone3 & V<1 (PCSC-63 held on ) at 2.04 hrs Fault on B, Zone3 & V<1 No Trippings recorded by SLDC, APTRANSCO No Trippings recorded by SRLDC at 3.55 hrs Fault on B, Zone3 & V<1 (PCSC-63 held on ) SLDC, APTRANSCO: Page 5 of 10

16 PCSC Deliberations: Annexure-III at 5.02 hrs Fault on B, Zone3 & V<1 No Trippings recorded by SRLDC SLDC, APTRANSCO: at 6.05 hrs Fault on B, Zone3 & V<1 No Trippings recorded by SRLDC SLDC, APTRANSCO: at 2.41 hrs Fault on Y, Zone-3 (PCSC-64 held on ) SLDC, APTRANSCO: Page 6 of 10

17 PCSC Deliberations: Annexure-III at 2.56 hrs Fault on Y, Zone-3 No Trippings recorded by SRLDC SLDC, APTRANSCO: at 2.51 hrs IN>1 (PCSC-64 held on ) SLDC, APTRANSCO: PCSC Deliberations: at 2.50 hrs Fault on Y, IN>1 SRLDC: Page 7 of 10

18 SLDC, APTRANSCO: Annexure-III at 3.59 hrs Fault on Y, IN>1 (PCSC-64 held on ) SLDC, APTRANSCO: PCSC Deliberations: at 4.38 hrs Fault on Y, IN>1 SLDC, APTRANSCO: PCSC Deliberations: Page 8 of 10

19 at hrs Fault on Y, Zone-3, IN>1, V<1 Annexure-III No trippings recorded by SLDC, APTRANSCO SRLDC: at hrs Fault on Y, Zone-3, IN>1, V<1 (PCSC-65 held on ) No trippings recorded by SLDC, APTRANSCO PCSC Deliberations: Kurnool-PG (PGIL-SR1) end: As per FIR/EL/TR, line tripped (in Y-ph) at 14:05: hrs on Y-E fault due to DPR, Z1 (A/R, 3.28 km, 16.6 ka) operation, and successfully auto-reclosed after about 1.1 sec. After about further 6 sec (i.e., at 14:05:50.470), line tripped in 3-ph due to receipt of DT from the remote end. It was stated in FIR that 765 kv Kurnool NPS line-1 was under LVRD. (Always keep second ckt of D/C line out of service for voltage regulation --- to SRLDC). As per DR, line tripped (in 3-ph) at 14;05: hrs due to DT receipt from remote end. DR corresponding to successful A/R operation not furnished. NPS (PGIL-SR1) end: FIR & DR furnished were that of Kurnool station. As per DR/EL, line tripped (in 3-ph) at 14:05: hrs on Y-E fault due to A/R (Z2, CAT) operation. It was noted from EL that A/R LOCKOUT had operated around the same time due to which line had not tried for A/R. From EL, it was further observed that DT was sent to the remote end at 02:05: hrs. However, the cause of DT send was not recorded in EL. DR pertaining to DT send was not furnished. If DT send was because of OVR-I protection operation, then also tripping was not in order, as it does not match with the settings provided at hrs Fault on Y, Zone-3, IN>1, V<1 No trippings recorded by SLDC, APTRANSCO PCSC Deliberations: FNN not followed by APTRANSCO and APGENCO SDSTPS (APGENCO) end: As per FIR/DR/EL, line tripped (in 3-ph) at 14:41: hrs on R-E fault due to DPR, Z1 (62.8 km) operation. It was observed from EL that the line was given 3-ph trip straight way without initiating A/R. Reasons for 3-ph trip and A/R failure? Chittoor (APTRANSCO) end: As per FIR/DR/EL/TR, line tripped (in R-ph) at 14:41: hrs on R-E fault due to DPR, Z1 (114.7 km) operation, and auto-reclosed successfully after about 1sec. However, it was observed that only Main-CB got auto-reclosed successfully; whereas Tie-CB got tripped in 3-ph while attempting A/R. Page 9 of 10

20 at hrs Fault on Y, Zone-3, IN>1, V<1 Annexure-III SLDC, APTRANSCO: SRLDC: at hrs Fault on Y, Zone-3, IN>1, V<1 No trippings recorded by SLDC, APTRANSCO SRLDC: ***** Page 10 of 10

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