SPP REPORT ON TLR EVENT ON APRIL 23, 2006 On April 23, 2006, SPP initiated a TLR on the SphWmcSumEmc flowgate, #5204 that proceeded to the point of firm curtailments. In response to NERC reporting requirements, SPP prepared a report on this event addressing fourteen bullet points associated with an initial investigation. The following is the report submitted by SPP for the April 23, 2006 flowgate event addressing each of those points. 1. Description of purpose/cause of curtailment The purpose of this TLR initiated by SPP on April 23, 2006 was to relieve the South Philips Junction-West McPherson 138 kV line (Monitored Element) of excessive loading that would have resulted from an unexpected loss of the Summit-East McPherson 230 kV line (Contingency Element). This facility is modeled as a flowgate labeled “SphWmcSumEmc” (flowgate # 5204) in the Interchange Distribution Calculator (IDC) for which an Outage Transfer Distribution Factor is calculated based on the loss of the Contingency Element. 2. Facility/flowgate limitations and flows at the time the TLR was initiated. The Monitored Element has a static emergency rating of 148 MVA but this rating is adjusted dynamically based upon ambient temperature and loading on the line. When the TLR Level 5 was issued the flow was 89 MW on the monitored element, as indicated in the NERC TLR Procedure Log provided in Appendix A. Loading on the contingent element was 269 MW at the time the TLR Level 5 was issued. The postcontingent flow was 241 MW at the time the TLR Level 5 was issued. A graph in Appendix B shows the post-contingency flowgate loading as well as the dynamic rating of the flowgate throughout the event. 3. TLR levels, timing and relief requested amounts Appendix A contains the NERC TLR Procedure Log for the April 23, 2006 TLR event on the SphWmcSumEmc flowgate. This log contains timing of TLR actions, TLR levels, requested relief and the number, priority and amount of curtailments. All times are in CST. 4. Transmission and Generation outages or changes from prediction that may have contributed. There were no transmission outages in the vicinity of the flowgate that significantly contributed to this TLR event. 5. Procedures implemented prior to curtailment. The flowgate started loading up mid-morning on April 23, 2006. A Level 1 TLR was issued at 11:10 CDT with post-contingency loading at approximately 220 MW. Loading continued to increase and a Level 3A TLR was issued at 11:29 CDT curtailing the one non-firm tag impacting the flowgate at that time. Loading continued to increase on the flowgate with a Level 5A TLR issued at 13:36 CDT.
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SPP Report on TLR Events on April 23, 2006
6. Complete Transaction Curtailment lists & comparison to IDC Transaction Lists both before and after curtailment. Appendix C contains the Congestion Management Reports generated by the IDC during this TLR event. The Congestion Management Reports contain the transaction curtailment lists. All tags indicated by the IDC were curtailed appropriately during the event. 7. Known transactions not in the IDC & actions taken. There were no known transactions occurring that were not already in the IDC. 8. Relevant excerpts from RC Operations Log Relevant excerpts from SPP Reliability Coordinator’s Log regarding this TLR event are contained in Appendix D. 9. Flowgate limitations as identified by security analysis for the day prior to the TLR event. Anticipated flowgate loadings from SPP’s Next Day Analysis conducted on April 22, 2006 are contained in Appendix E. Loading on the SphWmcSumWmc flowgate is shown to be relatively low, approximately 44% on the 23rd. This is an error. Subsequent review of this and other studies from that period revealed there was a process error in the macro used to populate the table. Anticipated flowgate loading was actually approximately 97%. This process error has since been corrected. 10. State Estimator snapshots and security analysis including any contingency analysis or stability analysis along with any other recorded data indicating need for Transmission Loading Relief Appendix F contains screen prints of flowgate loading obtained from flowgate monitoring software that SPP uses to monitor current and anticipated flows on the SPP flowgates. These particular prints were made during the initial issue and for each subsequent reissue of the Level 5A TLR and indicate that the flowgate loading was near or at its emergency limit. This is also shown in the graph of flowgate loading in Appendix B. 11. ATC limitations before, during and after the TLR event. The SphWmcSumEmc flowgate had been in a Level 3A TLR prior to the Level 5A on April 23rd. The flowgate has also experienced Level 3 TLRs on April 17 and 22. 12. Description of actions taken to avoid future curtailments Apart from upgrading the capacity of the flowgate, the only other option is to further restrict sales of capacity on this flowgate. SPP has already implemented an impact threshold of 3% for sales of transmission service on all flowgates. 13. IDC Congestion Management Reports. Copies of the Congestion Management Reports from the IDC for this event are contained in Appendix C. 14. Re-dispatch actions taken.
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SPP Report on TLR Events on April 23, 2006
The only re-dispatch action was taken after the initial issue of the Level 5A TLR. For each reissue of the TLR during the event, the Congestion Management Report indicated that generators serving native load or providing network service in the Westar and WPEK Balancing Areas contributed to the post-contingency loading on the flowgate. The curtailment prescriptions and NNL responsibility for each issuance of the TLR issuance are shown in the Congestion Management Reports found in Appendix C. A summary table that indicates the time of issue, a breakdown of the relief and how much NNL relief was actually provided by each Balancing Area can be found in Appendix G. Times are in CDT. Westar and WPEK provided the native load and network service relief assigned to them by redispatch.
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