MISO Investigation Report on the NERC TLR Level 5 Event Alliant Energy Flowgate 14266: Wisdom-Triboji 161kV flo Sherco #3 June 11, 2007 Report submitted to NERC on: July 12, 2007. This report is submitted in accordance with the NERC Transmission Loading Relief (TLR) Investigation Procedure for the TLR events that occurred on Flowgate 14266 June 11, 2007. The MISO systems detected high post-contingent flows on Wisdom-Triboji 161kV line for loss of (flo) the Sherco #3 unit. This event resulted in curtailment of firm transmission service and a reduction obligation (or requirement) due to Network/Native Load (NNL) impacts. 1. Description of purpose/cause of hold/curtailment: The definition of flowgate 14266 is listed below. Monitored Facility: Wisdom-Triboji 161kV Contingent Facility: Sherco #3 2. Facility/Flow gate limitations and flow at the time the TLR was initiated: Flowgate 14266 measures and captures the flow on the Wisdom-Triboji 161kV line for the loss of the Sherco #3 unit. The Wisdom-Triboji 161kV line is limited by 223 MVA thermal emergency rating. On June 11, 2007, heavy south to north power transfer through Iowa caused an increased flow in Wisdom-Triboji 161kV line for the loss of Sherco #3 unit. At 11:00 EST, the calculated post contingency flow on Wisdom-Triboji 161kV line for the loss of Sherco #3 unit reached 229 MVA. The MISO RC initiated internal MISO market redispatch as well as committed MISO market generation to reduce the post contingency flow in the flowgate. At 15:15 EST, the calculated post contingency flow on Wisdom-Triboji 161kV line for the loss of Sherco #3 unit reached 249 MVA. At this point, NERC IDC showed there was not sufficient non-firm scheduled on FG14266 and TLR 5B was issued at 15:20 EST for FG 14266 to be effective across 15:30 EST. At this time the MISO RC contacted MEC to assist them in finding a generation pairing to fulfill their NNL obligation as prescribed by the NERC IDC. MEC decided to curtail a transaction with WAPA that would result in the proper amount of relief for their NNL obligation. As the NERC IDC showed the insufficiency of non-firm schedule curtailment to relieve flow, TLR 5 was issued for a total of three continuous issuances. The TLR was reduced to level 3A x 18:00 EST and was terminated at 20:00 EST when flows decreased to acceptable levels. Page 1 of 5
3. TLR Level 5 issuance information, timing (EST), firm tag and NNL reduction information obtained for flowgate #14266 June 11, 2007: TLR LEVEL TIME (EST) 5B 15:30 5A 16:00 Firm Transaction / Curtailment Information 3 tags of (7-F) = 3 MW schedules curtailed to provide.2 MW relief MISO Market responsibility = 43.3 MW 4 tags of (7-F) = 19 MW schedules curtailed to provide 1.4 MW relief MISO Market responsibility = 46.4 MW 5A 17:00 MISO Market responsibility =.7 MW None 3A 18:00 All firm schedule and NNL were reloaded 0 20:00 NNL Reduction Requirement MEC 6.6 MEC 8.8 NNL Mitigation: MEC NNL obligation was met by curtailing a schedule with WAPA which increased Oahe and decreased the output of the Wisdom CT. MISO Market responsibility was met by internally committing and dispatching market generation via the AREVA UDS dispatch tool. 4. Transmission and generation outage or changes from prediction that may have contributed: Significant Transmission Outages: Raun-Lakefield 345kV line Planned outage Elk-Brewster 161 kv - Planned outage Pomeroy-NW Fort Dodge 161 kv - Planned outage Significant Generator Outages in the Region: King = 585 MW Boswell 4 = 580 MW Leland Olds 1 = 222 MW Square Butte 2 = 455 MW Coal Creek 1 = 550 MW Mankato 2 = 182 MW Faribault 1 = 160 MW Total Generation off = 2734 MW System Condition Summary: Heavy south-to-north power transfer across northwest Iowa occurred due to the outages as above and high load to the north. The heavy south-to-north power flows increased the post contingent loading in Wisdom-Triboji 161kV line. Page 2 of 5
It should be noted that MISO next day analysis did not show this violation originally, however the subsequent rerun following the Boswell 4 forced outage did show this constraint loaded to 106%. The Coal Creek emergency outage started at 14:05 EST, this was not included in either study. 5. Procedures implemented prior to hold/curtailment: MISO Market redispatch was implemented prior to the TLR event. 6. Compare Complete Transaction Curtailment List with the Whole Transaction List as generated by the IDC, before and after curtailments: Firm transactions impacting the flow gate by 5% or greater were curtailed. 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 sends TLR Level information to the RCIS. Curtailment information was communicated to the MISO control areas via the MISO MCN and ICCS messaging systems. 9. State estimator snapshots and security analysis including contingency analysis or stability analysis along with any other recorded data indicating the need for TLR: Real-time security analysis was monitored by the System Operator at the ATC control center and by the Reliability Coordinator at the MISO West Reliability Center. TLR relief requirements were calculated by using the real-time security analysis tool, and by monitoring the real-time loading on the monitored element. 10. ATC Limitations before, during, and after the event: There were no ATC limitations for this event. 11. Description of actions taken to avoid future hold/curtailments: The MISO RC followed the direction given in the special operating guide for the Raun- Lakefield 345kV planned outage which identified this constraint. 12. Re-dispatch actions taken: This was a thermal overload. Re-dispatch procedures were used in addition to mitigate NNL responsibility as prescribed by the NERC TLR procedure. 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: MEC NNL obligation was met by curtailing a transaction from their Wisdom CT to Oahe in WAPA. Page 3 of 5
Non-Market Balancing Authority actions to mitigate the NNL requirements: 1530-1600 EST CA IDC NNL INC (MW) DEC (MW) GSF % Actual NNL Response MEC 6.6 WAPA - Oahe Wisdom 22.3 6.7 MW Non-Market Balancing Authority actions to mitigate the NNL requirements: 1600-1700 EST CA IDC NNL INC (MW) DEC (MW) GSF % Actual NNL Response MEC 8.8 WAPA - Oahe Wisdom 22.3 8.9 MW 14. Other options considered before/during to avoid hold/curtailment: The MISO Reliability Coordinator brought on line all available quick start units in the MISO market and re-dispatched market generation for this constraint. The following units were called on line to relieve loading: Lime Creek CT 1 Lime Creek CT 2 Pleasant Valley CT 1 Pleasant Valley CT 2 Pleasant Valley CT 3 Anson CT 2 Lakefield CT 2 Lakefield CT 3 Lakefield CT 4 Lakefield CT 5 Lakefield CT 6 Cambridge CT Inver Hills CT 1 Inver Hills CT 2 Inver Hills CT 3 Inver Hills CT 4 Inver Hills CT 5 Inver Hills CT 6 Page 4 of 5
15. The following chart identifies the flowgate loading for the TLR level 5 event: Wisdom-Triboji 161kV flo Sherco #3 on June 11, 2007. 300 250 200 MW 150 100 50 0 8:32:23 10:20:06 11:19:46 12:31:05 13:17:07 14:02:23 14:50:20 15:40:15 16:34:04 17:33:20 Time (EST) RTCA Flow Emergency Limit 16. Lessons Learned In summary, the combination of planned outages, the forced outages of Boswell 4 and Coal Creek 1 caused significant stress to the Wisdom-Triboji 161kV line. The MISO RC did have an agreed upon plan with MEC and CBPC to take the Wisdom CT off line in the event of the Sherco #3 trip. This along with the curtailments and re-dispatch would relieve the loading on the Wisdom-Triboji 161kV line in the event of the contingency. This is shown on the graph with the post contingent flows dropping as the Wisdom CT started down between 15:00 EST and 16:00 EST, coming off line at 1800 EST. Page 5 of 5