Document name

WECC Pre/Post-Contingency Plan Guideline

Category

( ) Regional Reliability Standard ( ) Regional Criteria ( ) Policy (X) Guideline ( ) Report or other ( ) Charter

Document date

February 21, 2014

Adopted/approved by

OIWG/Operating Committee

Date adopted/approved

2/21/2014/05/20/2014

Custodian (entity responsible for maintenance and upkeep)

Operational Issues Work Group

Stored/filed

Physical location: Web URL:

Previous name/number

(if any)

Status

( ) in effect ( ) usable, minor formatting/editing required ( ) modification needed ( ) superseded by _____________________ (X) other _____________________________ ( ) obsolete/archived

W E S T E R N E L E C T R I C I T Y C O O R D I N A T I N G C O U N C I L • W W W . W E C C . B I Z 155 NORTH 400 WEST • SUITE 200 • SALT LAKE CITY • UTAH • 84103-1114 • PH 801.582.0353 • FX 801.582.3918

WECC Pre/Post-Contingency Plan Guideline

Introduction The Arizona-Southern California Outages on September 8, 2011 report identified concerns where entities were operating in an insecure N-1 state on September 8, 2011, and were relying on post-contingency mitigation plans that did not provide sufficient time to mitigate the contingencies. An N-1 insecure operating state is characterized as a state where the BES is exposed to instability, uncontrolled separation, or cascading outages following a single contingency. Purpose This Guideline helps identify for entities when they need to take pre-contingency actions to prevent post-contingency problems and when its acceptable for an entity to rely on post-contingency actions to mitigate the impacts of a contingency after the a contingency occurs. Additionally it recommends best practices for use by transmission entities in the Western Interconnection to ensure that pre- and post-contingency mitigation plans prevent unacceptable post-contingency system performance and reflect the time necessary to take mitigating actions, including control actions, to return the system to a secure N-1 state. Pre/Post Contingency Pre-contingency mitigation measures are necessary when operators are faced with potential post-contingency conditions that result in facilities exceeding their highest available emergency rating. To ensure that the transmission system is operated so that instability, uncontrolled separation, or cascading outages will not occur as a result of the most severe single contingency and credible multiple contingencies, entities should comply with applicable versions of TOP-004, Transmission Operations, and other applicable reliability standards. As per the Peak Reliability SOL Methodology (based on NERC Standard, FAC-011, R2.1), acceptable pre-contingency system performance is characterized as the following: •

The Bulk Electric System (BES) shall demonstrate transient, dynamic and voltage stability.

•

All Facilities shall be within their continuous Facility Ratings and thermal limits

•

All Facilities shall be within their pre-contingency voltage limits Page 2 of 5

•

All Facilities shall be within stability limits.

As per the Peak Reliability SOL Methodology (based on NERC Standard, FAC-011, R2.2), acceptable post-contingency performance is characterized as the following: •

The BES shall demonstrate transient, dynamic and voltage stability

•

All Facilities shall be within their applicable short-term Facility Ratings and thermal limits

•

All Facilities shall be within their post-contingency voltage limits

•

All Facilities shall be within stability limits

•

Cascading or uncontrolled separation shall not occur

The Peak Reliability SOL Methodology for the Operations Horizon states if any of the acceptable pre- or post-contingency system performance criteria stipulated in this Methodology are not being met, an SOL is being exceeded. Conditions that expose the system to unacceptable BES performance cannot be allowed to continue indefinitely. As such, when the system is experiencing unacceptable pre- or post-contingency performance, the system must be adjusted as soon as practicable, to prepare for the next contingency. When system studies conducted throughout the Operations Horizon (including Realtime Assessments) indicate that any of the acceptable post-contingency system performance criteria are not being met, the Transmission Operator (TOP) shall take precontingency actions to achieve acceptable performance. These actions may include 1, but are not limited to, the following: •

Commit and redispatch generation

•

Make adjustments to the uses of the transmission system (e.g., schedule curtailments/adjustments)

•

Make changes to system topology

Mitigation Plan Viability A Pre- or Post-Contingency Mitigation Plan is viable when: •

The TOP understands exactly what the limiting conditions/elements are.

•

The TOP knows specifically what the mitigation plan is, knows that the plan will actually resolve the reliability issue, and has communicated the specifics of the plan to impacted TOP’s and to the RC System Operator.

•

The mitigation plan does not adversely impact neighboring TOP and Balancing Authority Areas.

1

Notwithstanding anything in this guideline, TOPs maintain the authority to take action up to and including shedding firm load to ensure the reliability of the BES

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•

If the mitigation plan involves actions by neighboring TOPs and Balancing Authorities they have indicated their support of the mitigation plan through some form of bilateral coordination.

• •

The RC System Operator (RCSO) has evaluated the mitigation plan and determined that the plan resolves the reliability issue in a timely manner.

•

The TOP provides the RCSO adequate information on the time needed to complete mitigating actions that indicates that the plan can be implemented in sufficient time.

Even with operations planning processes and real-time tools and assessments, it is possible that a TOP may find themselves unexpectedly in an N-1 insecure state. TOPs should review existing operating processes and procedures to ensure that postcontingency mitigation plans reflect the time necessary to take mitigating actions, including control actions, to return the system to a secure N-1 state as soon as possible but no longer than 30 minutes following a single contingency. As part of this review, TOPs should consider the effect of relays that automatically isolate facilities without providing operators sufficient time to take mitigating measures. Automatic Mitigating Actions Automatic actions such as Remedial Action Schemes (RAS) or Special Protection Systems (SPS) are appropriate for mitigating post-contingency exceedances of Facility Ratings, bus voltage limits, or stability limits. The RAS or SPS must be available and armed for it to be considered a viable automatic mitigation plan. RTCA indication of any post-Contingency conditions demonstrating unacceptable N-1 system performance Western Interconnection entities should refer to the Peak Reliability Monitoring of RealTime SOL and IROL Exceedances Procedure, Section C that describes the appropriate actions for operating conditions where Real-Time Contingency Analysis (RTCA) indicates post-contingency exceedance of the highest available Facility Rating, voltage limit, or stability limit. The procedure describes when TOPs are required to take precontingency action to prevent unacceptable post-contingency system performance. Other Considerations This guideline describes general expectations for mitigating pre- and post-contingency exceedances in the Western Interconnection. There may be situations where due to planned or forced outages, for example, the system is unable to demonstrate acceptable post-contingency system performance without shedding load precontingency. In these situations, the TOP is expected to ensure that instability, cascading, or uncontrolled separation shall not occur. This is demonstrated through prior studies and using reasonable judgment in assessing the risks associated with post-contingency exceedances. Pre- or post-contingency mitigation should take place Page 4 of 5

through appropriate means depending on the risks and the options available to the TOP. TOPs judgment and other considerations such as safety, equipment damage, or regulatory or statutory requirements must always be considered.

It should be recognized that this is a Guideline and can be superseded by a Directive from the Reliability Coordinator. Approved By: Approving Committee, Entity or Person

Date

Operating Committee

May 20, 2014

Operating Issues Work Group

February 21, 2014

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