MISO Investigation Report on the NERC TLR Level 5 Event Alliant Energy Flowgate 14266: Wisdom-Triboji 161kV flo Sherco #3 June 12, 2007

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1 MISO Investigation Report on the NERC TLR Level 5 Event Alliant Energy Flowgate 14266: Wisdom-Triboji 161kV flo Sherco #3 June 12, 2007 Report submitted to NERC on: July 26, This report is submitted in accordance with the NERC Transmission Loading Relief (TLR) Investigation Procedure for the TLR events that occurred on Flowgate June 12, 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 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 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 12, 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 10:15 EST, the calculated post contingency flow on Wisdom-Triboji 161kV line for the loss of Sherco #3 unit reached 231 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 11:13 EST, the calculated post contingency flow on Wisdom-Triboji 161kV line for the loss of Sherco #3 unit reached 241 MVA. At this point, NERC IDC showed there was not sufficient non-firm scheduled on FG14266 and TLR 5B was issued at 11:15 EST for FG to be effective across 11:30 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 use the Riverside and Louisa units as a raise and decrease the Wisdom CT. At 11:58 EST, the Dysart-Washburn 161kV line returned to service from an extended forced outage. This reduced the loading on the Arnold-Hazleton 345kV and the Emery- Lime Creek 115kV lines which enabled the MISO RC to once again utilize the postcontingent reconfiguration of opening the Wisdom-Triboji 161kV line. A Study was performed by the MISO Regional Operations Engineer (ROE) to confirm this option. At 12:32 EST, the MISO RC reissued the TLR as a level 3A effective across 13:00 EST. Page 1 of 5

2 As the NERC IDC showed the insufficiency of non-firm schedule curtailment to relieve flow, TLR 5 was issued for a total of one issuance. The TLR was terminated at 20:00 EST when flows decreased to acceptable levels. 3. TLR Level 5 issuance information, timing (EST), firm tag and NNL reduction information obtained for flowgate #14266 June 12, 2007: TLR TIME LEVEL (EST) Firm Transaction / Curtailment Information 4 tags of (7-F) = 6 MW schedules 5B 11:30 curtailed to provide.4 MW relief MISO market responsibility = 54.9 MW 3A 13:00 MISO market responsibility = 4.7 MW None 0 20:00 NNL Reduction Requirement MEC 4.7 NNL Mitigation: MEC NNL obligation was met by increasing Riverside and Louisa while decreasing 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

3 It should be noted that MISO next day analysis did not show this violation on this day. Load in the West Market footprint was 250MW above the previous day and the output of the NE Iowa wind farms was 150MW higher. These are possible reasons the constraint was not identified in the day ahead studies as they both would add to the loading of this constraint. 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 increasing the output of Riverside and Louisa while decreasing the output of Wisdom. Page 3 of 5

4 Non-Market Balancing Authority actions to mitigate the NNL requirements: EST CA IDC NNL INC (MW) DEC (MW) GSF % MEC 4.7 Riverside & Louisa Actual NNL Response Wisdom 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 Lakefield CT 1 Anson CT 2 Blue Lake CT 1 Blue Lake CT 2 Blue Lake CT 3 Blue Lake CT 4 Cambridge CT 1 Cambridge CT 2 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

5 15. The following chart identifies the flowgate loading for the TLR level 5 event: Wisdom-Triboji 161kV flo Sherco #3 on June 12, MW :28:37 10:56:28 11:22:25 11:51:02 12:18:36 12:49:54 13:28:08 13:54:58 Time (EST) RTCA Flows 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 was able to terminate this TLR 5 event once the forced outage of the Dysart-Washburn 161kV line was returned to service at 11:58 EST. This dropped flows on the transmission system in the area enough to allow the agreed upon post-contingent reconfiguration plan of opening the Wisdom-Triboji 161kV line to be utilized. Page 5 of 5