1. Description of purpose/cause of hold/curtailment: Flowgate 6023 flow gate consists of the following elements.

Transcription

1 MISO Investigation Report on the NERC TLR Level 5 Event North Platte Stockville 115kV for the loss of the Gentleman Red Willow 345kV Flowgate 6023 August 22 nd / 23 rd, 2002 Report issued: September 3 rd, 2002 This report is submitted in accordance with the NERC Transmission Loading Relief (TLR) Investigation Procedure for the TLR event that occurred on Flowgate 6023 on August 22 nd and 23 rd, Flowgate 6023 is a Nebraska Public Power District (NPPD) Flowgate. The duration of TLR Level 5 was approximately five hours, and resulted in the partial curtailment of firm transmission service as well as Network and Native Load (NNL) Service relief. The NERC TLR Log is included as Appendix A. 1. Description of purpose/cause of hold/curtailment: Flowgate 6023 flow gate consists of the following elements. Monitored Facility: North Platte - Stockville 115kV Line Contingent Facility: Gentleman Red Willow 345kV Line On Thursday August 22 nd, 2002 the Gentleman-Red Willow 345kV line loading increased quickly and exceeded the OSL. Loading on the flow gate did not exceed the 455mw OSL for 30-minutes or longer at any point in time throughout this event. NERC TLR 5a was initiated after a 3b failed to provide sufficient flow gate relief. The high or heavy loading on this flow gate is a nightly occurrence. Export flows in the MAPP region increase significantly during the off-peak hours. The Western Nebraska Western Kansas interface operating guide calls for NERC TLR non-firm curtailments to be implemented in order to maintain the loading within the limit parameters. If all nonfirm schedules have been curtailed, and still a loading problem continues on the flow gate, the opening of the 115kV breaker 1110 at Red Willow is initiated as long as the real-time security analysis application provides adequate support for this action. Opening breaker 1110 isolates the 115kV system from the voltage stability concern as identified in the operating guide. However, on the eve of August 22 nd and the early morning of August 23 rd, there were storms throughout much of Nebraska and Kansas. The storms prevented opening breaker 1110 at Red Willow. 2. Facility/Flowgate limitations and flow at the time the TLR was initiated: The Western Nebraska Western Kansas (WNE_WKS) Interface is currently defined as both a post-contingent voltage constrained interface and a post-contingent thermally constrained interface. The worst contingency for the WNE_WKS Interface is loss of the Gentleman-Red Willow and Gentleman -Sweetwater Circuit #2 345 kv double-circuit. Loss of the 345 kv double circuit results in post-contingent voltages at or near the 0.90 p.u. emergency limit, as well as post-contingent line loadings at or near the overload limit of 110%. With Page 1 of 9

2 the Gentleman - Red Willow 345 kv line open, bulk transmission system power flows are imposed across the parallel 115 kv lines to get back to the low impedance path on the 345 kv line from Red Willow to Mingo. Although the 345 kv double circuit outage is the worst contingency, sensitivity analysis has demonstrated that monitoring and limiting the flows on the GGS-Red Willow 345 kv line alone is adequate to address operating security limits associated with the WNE_WKS Interface. It has been determined through studies that the voltage based flow limit for the Gentleman-Red Willow 345kV line is 455MW. This is the level of loading on that facility that has been determined to cause voltage stability problems for the underlying 115kV system, which includes the North Platte-Stockville 115kV line. At 2205 the flows on the Gentleman-Red Willow 345kV line were at 458MW. A TLR 1 was issued with expectations of non-firm curtailments, and then NPPD opening breaker 1110 at Red Willow to alleviate the problem. As flows started to increase, NPPD informed MISO St Paul they would be unable to open the breaker due to storms in the Red Willow area and requested relief to maintain 455MW. A TLR 3b was initiated for across 2230 CDT with all non-firm scheduled curtailed (51MW of relief was implemented). A TLR 3a was issued at 2227 for across 2300 CDT continuing all nonfirm scheduled curtailed. At 2237 CDT the flow increased to 484MW, and the IDC was projecting the flow gate loading to continue to increase. A NERC TLR 5a was initialized with relief requested for across 2300, and remained in effect until 0432 CDT, with one exception. At 0133 CDT, the flow on the Gentleman-Red Willow decreased to 356MW. A level 3a was issued across 0200 CDT with all non-firm schedules remaining curtailed. (42MW of relief continued), and all firm curtailments released. At 0205 CDT the flow increased to 480MW when SPS lost the 540MW Tolk unit. A TLR 5b with 60MW of relief was issued for across 0230 CDT, and reissued as TLR 5a across 0300 CDT continuing current relief level and remained in effect until 0432 CDT when firm schedules were allowed to reload and a TLR 1 was issued. Storms in Nebraska had cleared by this time, and breaker 1110 was opened at The event concluded with a TLR 0 at 0603 CDT. 3. TLR Levels, timing (CDT) and relief amounts TLR LEVEL TIME (CDT) Flowgate Relief Entered into IDC (MW) Number of transactions curtailed, priority, and magnitude of transactions b (1NS) 275 MW schedules curtailed. 4 (2NH) 245 MW schedules curtailed. 1 Page 2 of 9

3 (5NM) 50 MW schedule curtailed. 3 (6NN) 245 MW schedules curtailed. 3a Did not take effect due to change to 5a. 5a (1NS) 250 MW schedules curtailed. 5 (2NH) 270 MW schedules curtailed. 1 (5NM) 50 MW schedule curtailed. 3 (6NN) 270 MW schedules curtailed. 24 (7F) 254 MW schedules curtailed, a (1NS) 70 MW schedules curtailed. 2 (6NN) 270 MW schedules curtailed. 26 (7F) 315 MW schedules curtailed, a (1NS) 70 MW schedules curtailed. 2 (6NN) 270 MW schedules curtailed. 25 (7F) 260 MW schedules curtailed, a (1NS) 70 MW schedules curtailed. 2 (6NN) 270 MW schedules curtailed. 5b (1NS) 70 MW schedules curtailed. 2 (6NN) 270 MW schedules curtailed. 25 (7F) 164 MW schedules curtailed, a (1NS) 70 MW schedules curtailed. 2 (6NN) 270 MW schedules curtailed. 24 (7F) 145 MW schedules curtailed, a (1NS) 95 MW schedules curtailed. 2 (6NN) 270 MW schedules curtailed. 23 (7F) 82 MW schedules curtailed, 18.2 MW NNL prescribed End Event Page 3 of 9

4 4. Transmission and generation outage or changes from prediction that may have contributed: Loading on this flow gate typically increases during off-peak hours. It is normal to implement NERC TLR non-firm curtailments, and then open breaker 1110 thereafter in order to maintain the loading on the flow gate within the safe operating parameters. However as far as other impacts, we did experience the flow dramatically increase when SPS lost the Tolk unit 540MW at Procedures implemented prior to hold/curtailment: There were no procedures implemented prior to hold/curtailment. No operating procedures or reconfiguration actions were available for mitigating the loading problem. 6. Compare Complete Transaction Curtailment List with the Whole Transaction List as generated by the IDC, before and after curtailments: All non-firm transactions that impacted Flow gate 6023 by 5% or greater were curtailed and reloaded as required by NERC policy. Firm transactions impacting flow gate 6023 by 5% or greater were partially curtailed and reloaded per NERC policy. 7. Known Transactions not in the IDC and actions taken: There were no known transactions not in the IDC at the time this TLR was in effect that were impacting this flow gate. 8. RCIS or other system messages: Information was provided to NERC Reliability Coordinators via the NERC IDC. The IDC automatically sent TLR Level information via the RCIS. Curtailment information was sent out via the MISO MCN. 9. State estimator snapshots and security analysis including contingency analysis or stability analysis along with any other recorded data indicating the need for TLR: Relief requirements were calculated by using real-time loadings on monitored and contingent elements. Real-time security analysis was monitored at the NPPD control center, as well as at the MISO St. Paul Security Center. NPPD confirmed that the MISO results were consistent with their state estimator/contingency analysis results. Page 4 of 9

5 10. ATC Limitations before, during, and after the event: There were no ATC / AFC limitations on this flow gate. The ATC s was zero throughout the entire night, which is normal for when the interface is operating at the limit. No new reservations on the MAPP or MISO tariff that impact this flow gate by 5% (or greater) were approved. 11. Description of actions taken to avoid future hold/curtailments: As soon as the storms moved out of the area, breaker 1110 at Red Willow was opened to permit the transactions to be reloaded. 12. Re-dispatch actions taken: There was no system emergency declared. The re-dispatch actions associated with the NERC TLR level 5 for mitigating the NNL was the only re-dispatch ordered or implemented. 13. If Firm transaction curtailments took place, description of Transactional Contribution Factor calculation and results as well as how necessary relief was obtained through network service and native load contributions: Per the IDC file, there were five MISO control areas with NNL responsibilities. (NPPD, LES, MEC, WAPA and WPEK). GSF s were attained from the IDC. 1) NPPD decremented Gentleman and increased the McCook generation. In addition, NPPD decremented Gentleman generation as control area irrigation load was intentionally decreased. NPPD complied with the NNL responsibility. 2) MEC took off-line and purchased energy from WPEK generation. MEC and WPEK complied with the NNL responsibility. 3) WAPA increased flow west on the Miles City DC tie. This increased the south to north and east to west flow which reduced the Gentleman Red Willow 345kv line flow. WAPA complied with the NNL responsibility. 4) LES had firm schedules curtailed that were serving native load, and replaced the energy with the Rokeby generators in Lincoln. In addition, LES backed down its share of Laramie River Station during the later stages of the TLR which increased the south to north and east to west flow which reduced the Gentleman Red Willow 345kv line flow. The double counting in the IDC for LES has been resolved. Per the IDC, LES had an NNL reduction responsibility based upon their share of ownership of the Gentleman, Cooper and Sheldon generators. However, the LES ownership megawatts are tagged and were curtailed. The firm LES tags are NPPD_LES _LES, NPPD_LES _LES, and NPPD_LES _LES. Changes have been made in the IDC to identify the LES ownership of each generator Page 5 of 9

6 correctly, and therefore will remove LES from having any NNL responsibility in the future per firm curtailments on this flow gate that were caused by these particular generators. I.e. the double counting has been eliminated. Control area actions to mitigate the NNL requirements: for 2300 to 0000 CDT NPPD ** 41.5 Mccook (46) Dec load (34) Dec load (26) GGS (46) GGS1 (34) GGS2 (26) LES 7.7 * * * * MEC 3.4 WPEK (14) MEC (14) WAPA 5 WAPA E WAPA W WPEK 5.8 WPEK (26) MEC (26) Control area actions to mitigate the NNL requirements: for 0000 to 0100 CDT NPPD 49.8 Mccook(46) Dec load (68) Dec load (52) GGS (46) GGS1 (68) GGS2 (52) LES 9.3 * * * * MEC 4.1 WPEK (14) MEC (14) WAPA 6 WAPA E WAPA W WPEK 7 WPEK (26) MEC (26) Page 6 of 9

7 Control area actions to mitigate the NNL requirements: for 0100 to 0200 CDT NPPD 42.8 Mccook (46) Dec load (68) Dec load (52) GGS (46) GGS1 (68) GGS2 (52) LES 7.8 * * * * MEC 3.4 WPEK (14) MEC (14) WAPA 5.1 WAPA E WAPA W WPEK 5.9 WPEK (26) MEC (26) ***A TLR level 3A was implemented for across All firm was restored across At 02:08, flows significantly increased again, requiring a TLR level 5B to be initiated at 02:17. Control area actions to mitigate the NNL requirements: for 0217 to 0300 CDT NPPD 24.9 Mccook (46) GGS (46) LES 4.6 * * * * MEC 1.8 MEC (10) WPEK (10) 30 3 WAPA 2.9 WPEK 3.4 WAPA E WPEK (20) WAPA W MEC (20) 30 6 Page 7 of 9

8 Control area actions to mitigate the NNL requirements: for 0300 to 0400 CDT NPPD 21.8 Mccook (46) GGS (46) LES 4 * * * * MEC 1.6 MEC (10) WPEK (10) 30 3 WAPA 2.6 WPEK 3 WAPA E WPEK (20) WAPA W MEC (20) 30 6 Control area actions to mitigate the NNL requirements: for 0400 to 0432 CDT NPPD 12 Mccook (46) GGS (46) LES 2.2 * * * * MEC.9 MEC (10) WPEK (10) 30 3 WAPA 1.4 WPEK 1.6 WAPA E WPEK (10) WAPA W MEC (10) Other options considered before/during to avoid hold/curtailment: Curtailing non-firm and opening the 115kV breaker at Red Willow is a nightly action. The severe weather removed the option of opening the breaker, forcing a NERC TLR level 5 to be declared. 15. Lessons learned: Even though the NERC TLR timing requirements with respect to the TLR procedure, and TLR level 5 procedures are communicated to the control area operators at the regional spring and fall training seminars, we have discovered that we need to train more frequently. Some control areas knew exactly what was required with the NNL reduction requirements. Others required extra time of the Reliability Coordinator in order to discuss what needed to be done. We will work on improving this training process in order to be able to reach more system operators. Page 8 of 9

9 Appendix A NERC TLR Log for Flowgate 6023 (North Platte-Stockville 115kV flo Gentleman-Red Willow 345kV) Page 9 of 9