Flowgate 3707, an OTDF Flowgate, consists of the following elements.

Transcription

1 MISO Investigation Report on the Level 5 TLR Event Lore-Turkey River 161kV for the outage of Wempletown-Paddock 345kV Flowgate 3707 February 8, 2002 Report issued: February 25, 2002 This report is submitted in accordance with the NERC Transmission Loading Relief (TLR) Investigation Procedure for the TLR event that occurred on Flowgate 3707 on February 8, Flowgate 3707, Lore-Turkey River 161kV for the outage of Wempletown-Paddock 345kV, is an Alliant Energy flowgate. Alliant Energy owns both the monitored element and the contingent element facilities. American Transmission Company (ATCo) is the contractor transmission operator for these facilities. The duration of TLR Level 5a 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 3707, an OTDF Flowgate, consists of the following elements. Monitored Facility: Lore-Turkey River 161kV Line Contingent Facility: Wempletown-Paddock 345kV Line On Friday February 8, 2002 the loss of the 515 MW Columbia Unit #1 resulted in increased loading on the Flowgate. Analysis projected that an overload of the Lore- Turkey River 161kV line would occur during the contingency of an outage of the Wempletown-Paddock 345kV Line. NERC TLR had been issued at a Level 3 throughout the morning and early afternoon due to loading and outages throughout the area. A TLR level 5a was initiated after the loss of the Columbia Unit #1 in order to return the anticipated post-contingency flow on the Lore-Turkey River 161kV line to within its short-term thermal limit. Other generation in the area that was out of service at the time included the Nelson-Dewey Unit 1 scheduled outage, the Genoa Unit 3 (DPC) scheduled outage, and the forced outage of a unit at Pleasant Prairie. Also contributing to the loading problem was a planned maintenance outage in the Commonwealth Edison area (Zion-Arcadian 345kV) that increased flows on the Wempletown-Paddock 345kV line. 2. Facility/Flowgate limitations and flow at the time the TLR was initiated The short-term thermal limit of Flowgate 3707 (Lore-Turkey River for Wempletown- Paddock) was 223MVA. Analysis conducted by the MISO showed that the LODF (percentage of flow on the contingent facility Wempletown-Paddock 345kV line transferring onto the Lore-Turkey River 161kV line) for Flowgate 3707 was 12.5% on this day (12.7% was indicated in the NERC IDC). The Flowgate was in TLR level 3a from 0727 CST until 1302 CST. The Columbia Unit #1 tripped offline at approximately Page 1 of 10

2 1200 CST and a TLR 3b was issued at 1302 CST and then re-issued as a TLR 3a at 1330 CST. As loading continued to remain high and all non-firm transactions were curtailed, a TLR 5a was issued at 1430 CST and remained in effect until 1930 CST when firm schedules were allowed to reload and a TLR 3a was issued. The event concluded with a TLR 0 at 2003 CST. The chart below compares the calculated post-contingent loading on Flowgate 3707 to the short-term thermal limit of the Flowgate throughout the course of the event. FG 3707 Loading 300 Max. Line Rating Post-Contingent Loading MW TLR 3A > Columbia 1 trips > TLR 3B > TLR 5A > TLR 3A > TLR 0 > : : : : : : : : : : : : : : : : : : : : : : : : : : : : : :00 8-Feb-2002 (CST) From the above graph, it can be seen that the post-contingent loading on the Lore Turkey River 161 kv line exceeded the maximum line rating before TLR 5 curtailments reduced the flows. However, if the worst single contingency occurred, the outage of Wempletown-Paddock 345kV, MISO and ATC analysis foresaw no collapsing or cascading scenario. The actual flow on Lore-Turkey River 161kV reached its maximum of 133 MW during the event at 1303:20. Page 2 of 10

3 3. TLR Levels, timing (CST) and relief amounts TLR LEVEL TIME (CST) Flowgate Relief Entered into IDC (MW) Number of transactions curtailed, priority, and magnitude of transactions 3a a a a a a a b (6NN) 25 MW Schedule curtailed. No other non-firm schedules available. 3a (6NN) 25 MW Schedule curtailed. No other non-firm schedules available. 5a (6NN) 25 MW Schedule curtailed, 20 (7- F) Schedules curtailed for a total of 281 MW, 1.4 MW NNL relief prescribed. 5a (6NN) 25 MW Schedule curtailed, 20 (7- F) Schedules curtailed for a total of 202 MW, 1 MW NNL relief prescribed. 5a (6NN) 25 MW Schedule curtailed, 20 (7- F) Schedules curtailed for a total of 214 MW, 1 MW NNL relief prescribed. 5a (7-F) Schedules curtailed for a total of 181 MW, 1.5 MW NNL relief prescribed. 5a (7-F) Schedules curtailed for a total of 297 MW, 2.4 MW NNL relief prescribed. 3a End Event 4. Transmission and generation outage or changes from prediction that may have contributed Flows were dramatically increased due to the loss of the Columbia Unit #1. In addition, Nelson Dewey Unit 1 and Genoa Unit 3 were scheduled off-line and a unit at Pleasant Prairie tripped offline. The planned outage of a parallel 345 kv line (Zion-Arcadian external to the MISO) also contributed to the necessity to move to a TLR 5a and firm curtailments. Page 3 of 10

4 5. Procedures implemented prior to hold/curtailment There were no procedures implemented prior to hold/curtailment. No operating procedures or reconfiguration were available to mitigate loading. 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 Flowgate 3707 by 5% or greater were curtailed and reloaded as required by NERC policy. Firm transactions impacting flowgate 3707 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, however MISO encountered a few problems with the IDC during this TLR event. There is a known problem associated with the IDC that occurs when multiple Flowgates that are impacted by flows in similar directions are simultaneously in TLR. The IDC restricts the ability to reload any tags, firm or non-firm, when those tags impact another Flowgate in TLR by 5% or greater. Therefore, in order to partially reload Firm (7-F) transactions through TLR 5a, it was necessary to first release the TLR 3a on Flowgate Otherwise, the Firm (7-F) transactions that impacted Flowgate 3012 by 5% or greater were to be held to current curtailment levels while other Firm (7-F) transactions were allowed to reload. Additionally, the Network and Native Loading (NNL) requirements are miscalculated when this situation arises. After re-issuing TLR 5a on Flowgate 3707 with new curtailment amounts, the TLR 3a on Flowgate 3012 was able to be re-instated. Since MISO was the owner of both Flowgates this was not a serious issue at the time, however in the future this problem could be seriously compounded if there are multiple TLR events issued by several security coordinators that restrict flows in similar directions. In addition, another problem occurred with the IDC when the TLR 5a was being reduced to a TLR 3a. MISO was unable to confirm the reduction to TLR 3a. The IDC help desk was contacted and the problem was resolved, in the mean time the notice to reload the firm schedules was sent out via the MISO Messaging System. Control Areas in which curtailed firm transactions were sinking were called to verify receipt of the message allowing them to reinstate firm transactions. ALTW was also called to verify receipt of the message permitting them to discontinue their re-dispatch requirement for NNL. Page 4 of 10

5 8. SCIS or other system messages Information was provided to NERC Security Coordinators via the NERC IDC. The IDC automatically sent TLR Level information via the SCIS. Curtailment information was sent out via the MISO Messaging System to the MISO Control Areas. Also, a message was sent out over the SCIS indicating that the IDC was not working properly (the MISO Security Coordinator was having difficulty going from TLR5a to TLR 3a), and that this problem was reported to IDC Helpdesk. At 15:00 CST Time Error Correction I began. 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. Post-contingency flow was calculated using the LODF (Line Outage Distribution Factor). ATC confirmed MISO results were consistent with their state estimator/contingency analysis results. 10. ATC Limitations before, during, and after the event Available Flowgate Capability (AFC) Lore-Turkey River 161kV for the outage of Wempletown-Paddock 345kV 1 Date Hours (EST) Firm (MW) 2 Non-Firm (MW) 2/7/ Ranged from 69 to 101 2/7/ /7/ /7/ Ranged from 33 to 39 2/7/ /7/ /8/ Not Available 3 Ranged from 21 to 104 2/8/ Not Available 3 0 1: MISO calculates AFC rather than Available Transmission Capability (ATC) and offers transmission service via OASIS on the basis of AFC. 2: Last AFC value remaining on 2/7/02 for firm service on 2/8/02. 3: Firm service is not available for same day service. Therefore, firm service was not available for 2/8/02 on 2/8/02. Non-firm AFC was zero during the event. Page 5 of 10

6 11. Description of actions taken to avoid future hold/curtailments Alliant Energy, the owner of the limiting element, has revised the rating on the Lore Turkey River 161 kv line by increasing the rating on the Lore current transformer. The Lore - Turkey River 161kV short-term thermal limit changed from 223 MVA to 268 MVA. The next line section in series with Lore Turkey River 161 kv, Turkey River Cassville 161 kv line (235 MVA rating), will now be the most limiting facility in the area. This new rating may assist in avoiding future firm curtailments. Firm curtailments may also be avoided by implementing System Re-dispatch once the planned MISO System Re-dispatch is available May 1, Re-dispatch actions taken Re-dispatch was performed to meet NNL obligations. Alliant redispatched its west and east Control Areas (ALTW and ALTE). This redispatch was effected by ALTW limiting the dynamic tie flow from ALTW to ALTE during the course of the TLR 5. This flow is scheduled as tag from ALTW to ALTE. The chart below shows the IDC MW capacity of tag as a result of firm curtailments, the additional MW reduction of tag needed to satisfy NNL requirements, the total flow allowed on tag 23785, and the actual integrated flow of tag that occurred for each hour of the TLR 5 event. Hour Ending (CST) IDC MW Capacity Additional NNL Curtailment MW (11.3% TDF) Maximum Total Flow Allowed (MW) Integrated Flow (MW) 16: (1.4 relief)* : (1.0 relief) : (1.0 relief) : (1.5 relief) : (2.4 relief) *For HE 16:00 (CST) a miscalculation called for an additional 4 MW reduction of the dynamic tie flow in order to cover NNL requirements. At 11.3% TDF, the reduction should have been 13MW in order to achieve 1.4 MW of NNL relief. The maximum total flow allowed should have been 41 MW. However, the integrated flow of the dynamic schedule for HE 16:00 (CST) was 16 MW. 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. Page 6 of 10

7 According to the IDC there was a small generation to load distribution factor (GLDF) that was attributed to ALTW. Their Network and Native Load (NNL) responsibilities ranged from 1 MW to 2.4 MW during the TLR 5a event. The relief associated with this NNL responsibility was obtained through the adjustment of the dynamic schedule between ALTE and ALTW. The amounts of relief that were achieved on the Flowgate due to the NNL and transactional impact are shown in ITEM 3 above. 14. Other options considered before/during to avoid hold/curtailment. There were two other options considered before issuing NERC TLR level 5a and implementing firm curtailments. The first was the possibility of issuing a TLR 3a on the contingent element to relieve flow on the Wempletown-Paddock 345kV line. This action would not have resulted in enough relief to reduce Lore-Turkey River below its shortterm thermal limit with the loss of Wempletown-Paddock and would have resulted in curtailing transactions with a OTDF of less than 5% on the Lore-Turkey River 161/Wempletown-Paddock 345 kv flowgate. The next option was to have ATCo implement a local re-dispatch to alleviate the congestion. There were not obligations to perform local redispatch prior to implementing TLR 5. Page 7 of 10

8 Appendix A NERC TLR Log for Flowgate 3707 (Lore-Turkey River 161kV for the loss of Wempletown-Paddock 345kV) Page 8 of 10

9 Appendix B NERC TLR Log for Flowgate 3012 (Paddock XFMR for the loss of Paddock-Rockdale 345kV) Page 9 of 10

10 Appendix C Weather temperatures during event. Page 10 of 10