Outage Coordination Overview

1. Outage Coordination Overview D.W. Rickerson ERCOT Outage Supervisor 12/1/2008

2. Outage Coordination Process Outage Coordination Contingency Definitions Network Model Supplied every 2 weeks Includes latest system changes Outage Base case N-1 Secure Market Solution Approved outages Base case Generic dispatch (N-1 secure) No outages Outage Evaluation Process SPS/RAP updates Conting definitions Basecase Conditioning Process completed by Operations Planning Load Forecast for recent day Recent Generation Plan Approved and Proposed outages Conditioned Reliability Coordination Basecase w/ contingency file SRs Economic Coordination Outage Notes Approved Outages decisions Outage Scheduler Outages MISPosting Market Participant Modeling Group Market Participant Outage Group Forced ERCOT Modeling ERCOT Outage Cord. Day-Ahead and Real Time Analysis ERCOT Oper Planning ERCOT Operations

3. Reliability Coordination • Objective – find a market solution that reliably allows a combination of requested outages to be approved (cost not part of the evaluation). • Protocols • 8.3.1 ERCOT shall approve Planned Outages and accept Maintenance Outages of Transmission Facilities schedules unless, in ERCOT’s determination, the requested Transmission Facility Planned Outages or Maintenance Outages of Transmission Facilities would cause ERCOT to violate applicable reliability standards. • 8.3.6 If ERCOT believes it cannot meet the applicable reliability standards and has exercised reasonable options, ERCOT shall have the authority to withdraw approval for a Planned Outage or Maintenance Outage schedule. • 8.3.7 In considering TSP requests, ERCOT shall give priority to approved Planned Outage and Maintenance Outage schedules previously posted to the ERCOT MIS.

4. Reliability Coordination 8.3.10 Evaluation of Transmission Facility Planned Outage or Maintenance Outage Requests ERCOT shall evaluate requests for approval of Transmission Facility Planned Outages and Maintenance Outages to determine if any one or a combination of proposed Outages may cause ERCOT to violate applicable reliability standards. ERCOT’s evaluations shall take into consideration factors including, but not limited to, the following: • Forecast of peak Demand conditions; • Outage plans submitted by Resource Entities and TSPs pursuant to Section 8.1, Planned Outages and Maintenance Outages of Transmission and Resource Facilities; • Forced Outages of Transmission Facilities; • Potential for the proposed Outages to cause irresolvable transmission overloads or voltage supply concerns based on the indications from contingency analysis software; • Previously approved Planned Outages and Maintenance Outages; • Impacts on the transfer capability of DC Ties; and (7) Good Utility Practice with respect to Transmission Facility maintenance.

5. Economic Coordination • Objective – find a market solution that reliably allows a combination of approve outages (cost not part of the evaluation). • In the course of finding a market solution, if a Coordinator has to substantially deviate from a generation pattern he has pulled in from real-time he may consider investigating it as a economically sensitive outage. • Investigates the root cause • Problem associated with another transmission outage (combination) • Problem associated with a resource outage • Problem associated with wind • Problem associated with season or time of day • Remedies include • Contacting the “last in” submitter to request a reschedule • Moving transmission outage to coincide with an existing resource outage • Requesting a change in the time-of-day the outage occurs • If no resolution is found, Outage Coordination Supervisor has the ability to escalate the “costly” outage to ERCOT Director and PUCT. • Approximately 30 to 40 of these types of outages each year.

6. Outage Notes Outage Notes for Saturday April 12, 2008 The following outages were studied with an estimated ERCOT load of 34,000 Mw ONCOR has aone day outage on the Graham (GRSES) to Long Creek Switching Station (LNCRK) 345kV Line (6024_A) Saturday 04/12/08 from 06:00 until 20:00 to pull wire. Estimated emergency restoration time is for 9 hours. Note 1:  The below contingency is with Oklaunion on line. Contingency: FISHER ROAD SW- OKL & BOWMAN 345KV Overloaded Element a: ABSO _PUTN_1A @ ABSO Overloaded Element b: ABSO _PUTN_1E @ POTOSI_T Overloaded Element c: PCN_PUT @ PCNBYU Overloaded Element d: 6070_A @ PUTN Overloaded Element e: 6856_B @ BMRTN TOAP: STNET studies indicate lowering the Wind generation relieved the overloaded elements. (S4 & S5)This outage may affect the West to North and the North to West import. The Operations Engineering Group has been consulted and will determine operational limits to support this outage. CPL/AEP has daily outages on the Nelson Sharpe (N_SHARPE) to Ajo (AJO) and the AJO to Rio Hondo (RIOHONDO) 345 kV circuits (AJO_SHARPE_1A, AJO_RHOND_1A) starting Monday 04/07/08 until Tuesday 04/08/08 from 05:00 until 13:00 (daily) and from Tuesday 04/08/08 until Monday 04/21/08 from 23:00 until 13:00 (daily) to cut in new AJO substation. Recommended Generation: Silas Ray Estimated emergency restoration time is 6 hours. Contingency: NORTH EDINBURG - RIO HONDO 345KV Overloaded Element a: SMCAL_STWRT_1A @ S_MCALLN Overloaded Element b: SMCAL _ STWRT_1B @ L_MILPAS TOAP 1: STNET studies indicate increasing SILAS RAY generation and lowering FRONTERA, NEDIN and DUKE generation relieved the overloaded elements. TOAP 2: See CPL/AEP Mitigation Plan at the end of this document for post- contingency load shed information. Note: The North Weslaco (NWESLACO) to North Alamo (N_ALAMO) 138kV circuit is tied together via Weslaco Switch (WESLACO). To simulate this in your case, close the following devices at WESLACO: 6678, 2384, 2385, 2386 and 6677. This outage may affect the Valley Import Limit. The Operations Engineering Group has been consulted and will determine operational limits to support this outage.

7. Generation Pattern Tool • Using Pi data • Pulls a historic generation pattern (including outages) for a given historic point in time. • Useful in obtaining a real Market Solution for a given load at a given time.

8. Conditioning Generation Profiles Conditioning is required in order to simulate a worse case (yet still reasonable) scenario for outage approval. • As cases are scaled some generation needs to stay at a set amount • Wind is blocked to 3500-MW • System won’t support higher export • Nuclear is blocked to PMAX • Some coal is blocked to PMAX • Generation in historically troublesome spots is often blocked so that outages in those areas will show up in the analysis.

9. Load Forecast • Two different Load forecasts used: • Short-term process uses the mid-term forecast • Same forecast used by Day-Ahead study • Studies continually update for forecast • Long-term process uses the long-term forecast (planning forecast) that is based on a typical year and scaled to expected demand. • Long-term coordinator will adjust according to his own experience • Typically study cases that are 3%-5% higher than the forecast.

10. Outage Count • Approximately 35,000 Outages a year

11. Network Model • Approx. 1500 Service Requests (SRs) annually • Majority come from 16 different Market Participant modeling groups. • Approx. 12 ERCOT FTE’s to maintain model (Zonal) • 54,963 elements in Model • 3759 Substations • 5515 Lines • 5043 Loads • 37755 Breakers/Switches • 1343 Transformers • 934 Shunts •   614 Units

12. Outage Coordination Contingency Definitions • No-Wind Contingency • Generator plus line Contingencies • Double element Contingencies • Different than double circuits • Double Unit Contingencies

13. MIS Posting