1. © Property of ERCOT 2001 ERCOT Limit Calculation Process John Adams Operations Engineer

2. © Property of ERCOT 2001 Philosophy  Prevent ERCOT from entering a state in which a single contingency leads to cascading outages or instability

3. © Property of ERCOT 2001 Process  Review Outage Coordinator notes.  Model most severe expected conditions next day using a power flow case describing resource plan & outage schedule conditions.  Perform contingency analysis and analyze most severe consequences of forced outages on planned operations.  For each contingency leading to post contingency loading over 110% rating: Review to determine if cascading

4. © Property of ERCOT 2001 Process  If post contingency overloading appears to be both real, and cascading: prepare an operational limit  Prepare daily limits sheet and provide to operations desk

5. © Property of ERCOT 2001 Review CSC Limits  Operation Engineer reviews limits on CSC’s for next day. Sandow-temple – performs a power flow and contingency analysis describing this particular interface; Increasing the loading until post contingency loading of 110% of the thermally adjusted rating is reached.

6. © Property of ERCOT 2001 Review CSC Limits  Operations Engineer reviews limits on CSC’s for next day. STP-WAP – review with a power flow study ~once/week. Apply temperature de-rating daily.

7. © Property of ERCOT 2001 Review CSC Limits  West-north – review with power flow once/week. Review stability limits from file studies daily in light of units online. If necessary apply a reduced limit  North-west – review with power flow once/week.

8. © Property of ERCOT 2001 Outage Coordinator Studies  On many occasions, the outage coordinator studies have alerted operations to a security limit which has been studied by the TDSP or the outage coordinators. These limits are provided to operations via the outage notes. Generally, outage coordinators ask operations engineering to review all such limits.

9. © Property of ERCOT 2001 Distribution of Limits Sheets  Limits sheets are faxed to transmission operators monitoring the CSC interfaces.

10. © Property of ERCOT 2001 Enforcement  Operator enters CSC limits on “real time transmission constraints limits.”  These limits are automatically posted on the “actual system demand” page of the ERCOT web site.  Transmission & security operator monitors these limits, and adjusts the OC1 constraints to hold actual flows below the physical limit.

11. © Property of ERCOT 2001 Enforcement  On operational congestion limits, the operator normally asks the operations engineer to calculate shift factors for units in the area, and create an OC2 constraint to control this limit.  To create these shift factors, the operations engineer normally performs a MUST study.