Managing of Limits during Loss of Analysis Tools/ EMS April 23, 2014

2 Overview During Normal Operations ERCOT ISO utilizes Real Time tools to determine limits. ERCOT has procedures to account for the times when Real Time tools may be unavailable. ERCOT has procedures to account for the loss of its EMS.

3 Interface stability limits Due to the nature of stability limits being different than facility ratings, they are monitored and operated to independently of the facility rating. Typically these stability limits are also considered Generic Transmission Limits (GTLs) Procedures have typically specified the IROL’s in the hotline call, but closely monitoring other stability limits during analysis tool outages may enhance reliability.

4 Considerations for Analysis Tool Outages If ERCOT’s Real Time analysis tools (SE/RTNET, RTCA, TSAT, VSAT) are unavailable, ERCOT can still monitor the interface flows vs the last determined limit as long as SCADA/ICCP and the EMS is still available. The last determined stability limit is still a valid limit if the topology of the system that makes up that interface or impacts the limit does not change. Transmission Operators should be aware of unavailability of ERCOT’s Real Time analysis tools and monitor their system and GTLs in its area during this time and notify ERCOT of changes in the status of facilities that make up the interface or impacts the limit. Goal is to enhance awareness during an abnormal condition and be prepared for the possibility of continued degradation of system tools.

5 Current Procedure: Analysis Tool Outages [SE/RTCA] Transmission Security Desk Procedure: Section 3.3. Analysis Tool Outages Typical Hotline Script: “This call requires everyone to remain on the line until it is complete. [TO] I will be asking you for the repeat back. This is ERCOT operator [first and last name], at [xx:xx], ERCOT is issuing an Advisory due to ERCOT’s State Estimator has not solved in the last 30 minutes. Please monitor your own service area and notify ERCOT if you exceed the emergency ratings of your transmission elements. Report West - North and North – Houston stability limits if power flows reach 70% of their respective limits. Notify ERCOT of any forced line operations. [TO] please repeat that back to me.”

6 Proposed Procedure: Analysis Tool Outages [SE/RTCA] Typical Hotline Script: “This call requires everyone to remain on the line until it is complete. [TO] I will be asking you for the repeat back. This is ERCOT operator [first and last name], at [xx:xx], ERCOT is issuing an Advisory due to ERCOT’s [State Estimator/RTCA] has not solved in the last 30 minutes. Please monitor your own service area and notify ERCOT if you exceed the normal ratings of your transmission elements. Report if power flows on any GTLs reach 85% of their respective limits and notify ERCOT of any forced line operations. [TO] please repeat that back to me.”

7 Current Procedure: Analysis Tool Outages [VSAT] Transmission Security Desk Procedure: Section 3.3. Analysis Tool Outages Typical Hotline Script: “This call requires everyone to remain on the line until it is complete. [TO] I will be asking you for the repeat back. This is ERCOT Operator [first and last name]. ERCOT is issuing an Advisory due to ERCOTs Voltage Security Assessment Tool has not solved in the last 30 minutes. We will be monitoring the West - North and North – Houston flows to the last posted limits. Please notify us if there is a topology change that could affect these interfaces. Notify ERCOT if you have reactive reserve issues within your system. [TO] please repeat this back to me.”

8 Proposed Procedure: Analysis Tool Outages [VSAT] Typical Hotline Script: “This call requires everyone to remain on the line until it is complete. [TO] I will be asking you for the repeat back. This is ERCOT Operator [first and last name]. ERCOT is issuing an Advisory due to ERCOTs Voltage Security Assessment Tool has not solved in the last 30 minutes. We will be monitoring the GTL flows to the last posted limits. Please notify us if there is a topology change that could affect these interfaces. Notify ERCOT if you have reactive reserve issues within your system. [TO] please repeat this back to me.”

9 Current Procedure: Analysis Tool Outages [TSAT] Transmission Security Desk Procedure: Section 3.3. Analysis Tool Outages Typical Hotline Script: Notify ONCOR: “This is ERCOT Operator [first and last name]. ERCOTs Transient Security Assessment Tool has not solved in the last 30 minutes. We will be monitoring the West - North flow with the last posted limits. Please notify us if there is a topology change that could affect the W-N interface. Please repeat that back to me.”

10 Proposed Procedure: Analysis Tool Outages [TSAT] Typical Hotline Script: Notify ONCOR:*All TOs. “This is ERCOT Operator [first and last name]. ERCOTs Transient Security Assessment Tool has not solved in the last 30 minutes. We will be monitoring the West - North flow with the last posted limits. Please notify us if there is a topology change that could affect the W-N interface. Please repeat that back to me.”

11 Considerations for loss of EMS If ERCOT loses substantial ICCP data or its EMS it will not have the capability to aggregate flows through the EMS to monitor and assess stability limit interface flows vs limits. The last determined stability limit is still a valid limit if the topology of the system that makes up that interface or impacts the limit does not change. Transmission Operators should be aware of unavailability of ERCOT’s EMS and monitor their system and GTLs in its area during this time and notify ERCOT of changes in the status of facilities that make up the interface or impacts the limit. TOs should also monitor aggregated flows vs the limits and notify ERCOT if the flow approaches the limit if they have the capability/SCADA to aggregate the flows of an entire interface independent of ERCOT. If a TO does not have the capability/SCADA to aggregate flows independent of ERCOT for an entire interface, the TOs associated with an interface should notify ERCOT of variations of flows on facilities that make up the interface greater than 10%. Goal is to enhance awareness during an emergency condition, be prepared for the possibility of continued degradation of system tools, and for coordination with ERCOT and or other TOs/REs to address potential limit exceedances. ERCOT will declare an emergency notice.

12 Current Procedure: Loss of PCC Functionality DC Tie Desk Procedure: Section 4.4. Loss of Primary Control Center Functionality Typical Hotline Script: “This call requires everyone to remain on the line until it is complete. [TO] I will be asking you for the repeat back. This is ERCOT Operator [first and last name]; at [xx:xx], ERCOT is issuing an Emergency Notice due to the loss of primary control center functionality and is transferring operations to the alternate control center. Please monitor your own service area and notify ERCOT if you reach the emergency rating of your transmission elements. Report when the West - North limit reaches 70% or the North – Houston limit reaches 80% of the posted limit. Continue to monitor voltages in your area and notify ERCOT of any forced line outages. Direct all urgent phone calls thru the [Bastrop][Taylor] OPX. [Select TO], Please repeat this back for me.”

13 Proposed Procedure: Analysis Tool Outages [TSAT] Typical Hotline Script: “This call requires everyone to remain on the line until it is complete. [TO] I will be asking you for the repeat back. This is ERCOT Operator [first and last name]; at [xx:xx], ERCOT is issuing an Emergency Notice due to the loss of primary control center functionality and is transferring operations to the alternate control center. Please monitor your own service area and notify ERCOT if you reach the normal rating of your transmission elements. Report if power flows on any GTLs reach 85% of their respective limits. For the W-N limit, report if any facility for that interface has a greater than 10% increase in flow. Continue to monitor voltages in your area and notify ERCOT of any forced line outages. Direct all urgent phone calls thru the [Bastrop][Taylor] OPX. [Select TO], Please repeat this back for me.”

14 Next Steps ERCOT System Operator Desk Procedure modifications in next couple of weeks. ERCOT recommends those entities that have a GTL in their area to have the limit telemetered to them through ICCP. ERCOT recommends (not required) that TOs that share an interface consider providing telemetry independent of ERCOT to be able to aggregate real time flows for an interface. ERCOT recommends TOs train personnel to support response to Real time instructions as identified in ERCOT procedure modifications.

15 Questions