December 7, 2012

ERCOT Planning Horizon SOL Methodology Update

Jeff Billo

RPG

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Background

• Per FAC-010-2.1 the Planning Authority (ERCOT) is to establish a documented SOL methodology for its area

– ERCOT has issued a change to the methodology and communicated that change per Requirement 4

• Why are we making these changes?

– Better align planning horizon SOL/ IROL methodology with TPL-003 and PRC-023

– Learn from Southwest Event

• What changes are we making?

– General rewrite

– Add SOL/ IROL identification for steady-state cascade conditions

– Better define IROL identification

– Effective January 1, 2013

December 7, 2012 RPG

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How does PRC-023 fit in?

• Defines transmission circuit relay loadability requirements for Transmission Owners

• Provides 13 different methods for TOs to set their phase protective relay settings– Based on this we have used the conservative assumption that

transmission circuits loaded above 150% of their normal rating or 115% of their emergency (2-hour) rating will trip

– Assumption used for screening purposes only

• Limitation– Applies only to facilities 200 kV or higher or 100-200 kV facilities

that the Planning Coordinator identifies as ‘critical to the reliability of the BES’

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PRC-023 Side Note

• Assume all 345 kV facilities set per PRC-023

• Run separate analysis to identify 138 kV circuits that will lead to Cascade event if relays are set between 100% loading and PRC-023 loadability requirements– Report 138 kV circuits as ‘critical to reliability’ if meet this

criterion

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How is ERCOT applying this?

• In ERCOT’s TPL standard analysis, no facilities should be loaded above 100% for Category A or B contingencies

• If the analysis shows that for a Category C (multi-element) contingency facilities will be loaded above 150% of the normal rating or 115% of the emergency rating then we will assume that the facility will trip– If this causes a Cascade condition then ERCOT Planning will

investigate and take one or more of the following actions if the Cascade condition is confirmed (per Category C Planning process):

• Plan an upgrade

• Plan a Mitigation Plan (including RAPs and/or load shed)

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How is ERCOT applying this?

• An SOL will be created when …

1. Manual system adjustment (switching, load shed, etc.) is required in order to prevent cascading or voltage collapse;

2. A stability limit is identified;

3. Voltage stability margin is less than 5% for NERC Category B contingencies or 2.5% for Category C contingencies; or

4. Post disturbance frequency is not within 59.4 Hz to 60.4 Hz

• The SOL will be classified as an IROL if the load loss (either via manual load shed or as a consequence of the event) is greater than four times 1% of the load in the case

• The IROL Tv will be defined as the lower of the relay trip setting time delay or 30 minutes

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Comments or Questions?

Send formal comments to:

jbillo@ercot.com

RPG

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Appendix

RPG

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Quick Example on Facility Ratings (courtesy of WECC)

December 7, 2012

Load Shed (15 min)

Emergency (2 hour)

Normal (continuous)

0 MVA

Limit Exceedance = Go beyond limit

Limit Violation = Exceed limit for a time duration longer than required mitigation time

RPG

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Quick Example on Facility Ratings

December 7, 2012

Load Shed (15 min)

Emergency (2 hour)

Normal (continuous)

0 MVA

Operate in this range all you want. Nothing is being exceeded, nothing is being violated.

RPG

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Quick Example on Facility Ratings

December 7, 2012

Load Shed (15 min)

Emergency (2 hour)

Normal (continuous)

0 MVA

Operate in this range for no more than 2 hours:

1.You are exceeding the normal rating.2.You are violating the limit if you operate in this range for longer than 2 hours.

RPG

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Quick Example on Facility Ratings

December 7, 2012

Load Shed (15 min)

Emergency (2 hour)

Normal (continuous)

0 MVA

Operate in this range for no more than 15 minutes:

1.You are exceeding the emergency rating.2.You are violating the limit if you operate in this range for longer than 15 minutes.

RPG

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Quick Example on Facility Ratings

December 7, 2012

Load Shed (15 min)

Emergency (2 hour)

Normal (continuous)

0 MVA

You can’t operate over this limit. If you do you may damage equipment, cause safety problems and/or trip the facility

1.You are exceeding the load shed rating.2.To exceed the highest time-limit rating established is to violate the limit.

RPG

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Quick Example on Facility Ratings

December 7, 2012

Normal (continuous) = Emergency (2 hour) = Load Shed (15 min)

0 MVA

If all ratings are the same, you can never operate over the normal limit. If you do you may damage equipment, cause safety problems and/or trip the facility

1.You are exceeding the load shed rating.2.To exceed the highest time-limit rating established is to violate the limit.

RPG