1. Current Operational Challenges Computing the West – North Limits Potential IROLs Local Voltage & Thermal issue (OOME) High Voltage Outages

2. Computing the W-N Limits Power Flow Analysis –Build base case Determine next day’s peak hour using load forecast Use peak hour load and generation plan Include scheduled outages for peak hour –Must clear any base case violations where Normal Rating ≥ 100%. –Save as STNET case: x_basecase_mmddyy_initials

3. Computing the W-N Limits West – North thermal SOL –Increase West – North transfer Increasing generation at West and Far West zones Scaling load up in the North Central zone and scaling load down in the West and Far West zones if more transfer is need –The sum of the flow on Graham-Parker and Graham-Benbrook 345 kV DBL Ckt is W-N thermal SOL

4. West-North CSC WN

5. 6 lines –345 kV Graham SES – Long Creek Switch –345 kV Graham SES – Bowman Switch –345 kV Graham SES – Tonkawa Switch –345 kV Graham SES – Sweetwater Generation Plant –345 kV Bowman Switch – Jacksboro Switch –345 kV San Angelo Red Creek – Comanche Switch Number of units on-line at each plant site Status of Power System Stabilizers West and Far West plants Outages Transient Limit Several conditions that are controlled by ERCOT operators W-N Transient Stability Limit

6. W-N Stability Limit

7. Objectives for SOLs and IROLs Know the definitions and the differences between an SOL and an IROL Understand the steps in determining an IROL.

8. What is an SOL? System Operating Limit (SOL) – The value (such as MW, MVAR, Amperes, Frequency, or Volts) that satisfies the most limiting of the prescribed operating criteria for a specified system configuration to ensure operation within acceptable reliability criteria. SOLs are based upon certain operating criteria. These include but are not limited to: –Facility Ratings (Applicable pre- and post- Contingency equipment on facility ratings) –Transient Stability Limits (Applicable pre- and post- Contingency Stability Limits) –Voltage Stability Limits (Applicable pre- and post- Contingency Voltage Stability) –System Voltage Limits (Applicable pre- and post- Contingency Voltage Limits)

9. What is an IROL? Interconnected Reliability Operating Limit (IROL) – System Operating Limit that, if violated, could lead to instability, uncontrolled separation, or Cascading Outages that adversely impact the reliability of the Bulk Electric System. IROLs are a subset of SOLs. If a limit is violated for more than 30 minutes then we are in violation of NERC Operating Criteria.

10. How do you Identify an IROL? Use the following criteria to disqualify exceeded limits. –Magnitude and Time over Limit: SOLs which are not exceeded by 100% of the calculated value, using the emergency rating, for over 30 continuous minutes are considered controllable and not IROL violations. –Double Circuit Contingencies: Post Contingency Overloads as a result of the outages of multiple elements that are considered as feasible due to proximity of each other (i.e. shared structure or right-of-way) and not due to the absence of circuit breakers between elements. –System Impact: SOLs exceeded that would not expose a widespread portion of ERCOT even under worst-case scenarios. Some contingencies may cause overloads to equipment that if lost would not credibly result in cascading outages, instability, or uncontrolled separation.

11. How do you Identify an IROL? If an IROL is identified, must report to NERC within 72 hrs of the event: –Determine which form(s) needs to be filled out. Interconnected Reliability Limit violation non-compliance report NERC Operating Security Limit and Preliminary Disturbance Report DOE Form EIA- 417 Emergency Incident and Disturbance Report –Email report to NERC within the appropriate time frame. (If report cannot be sent within the time frame, call NERC and/or DOE and report a brief summary. Then fill out report and send in As Soon As Possible).

12. Active Constraints vs. Congestion Management Challenges with current Market Operator Interface (MOI) Congestion Management tools –Monitor Actual Zonal Flows vs. calculated CSC Limits –MOI Utilizes Calculated Flows Operator must enter new projected constraint limit in MOI prior to the execution of the Real Time Balancing Market (RTB) –Entered into the MOI 30 – 40 minutes before the interval is completed –Monitor Real Time Contingency Analysis (RTCA) –Must not violate NERC Operating Criteria

13. MOI Constraint Management

14. Wind QSE Low & High Frequency Excursions

15. High Voltage

17. W N S Zonal Transfers

18. Outages affecting Wind 345 kV Graham SES – Sweetwater Generation Plant 345 kV Graham SES – Long Creek Switch 345 kV Long Creek Switch– Abilene Mulberry Creek 138 kV Putnam – Leon Switch 138 kV Adamsville – Evant 60% due to maintenance to improve reliability during light load season 40% due to W-N transfer

19. Questions?