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Path Operator Task Force Recommendation. OC Meeting July 15 , 2014. POTF Strategy and Focus. POTF focus primarily on real-time operations, but covers the Operations Planning horizon (day-ahead through seasonal)

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Path operator task force recommendation

Path Operator Task ForceRecommendation

OC Meeting

July 15, 2014

Potf strategy and focus
POTF Strategy and Focus

  • POTF focus primarily on real-time operations, but covers the Operations Planning horizon (day-ahead through seasonal)

  • The POTF employed a three phased strategy for meeting the assigned JGC objectives:

    • Investigate the current Path operations paradigm and identify alternate approaches

    • Analyze the identified issues from the perspective of alternative approaches

    • Identify solutions and recommendations


Planning horizon (> 1 year out)

  • TPL standards – systemplanning

  • Three phase rating process

    • Determines the maximum reliable Path transfers

    • Protects allocations of existing Path owners

Background continued
Background (continued)

Operations horizon (real-time through seasonal)

  • Seasonal studies

    • Sub-regional study group studies determine if the Path Rating is achievable for the upcoming season

    • Path SOL is designated as the lesser of the Path Rating or the Path limitation identified in the seasonal study

    • Path Operator updates Path Operating Procedures

  • Post-Seasonal Operations Planning and Real-time studies

    • Path Operator subsequently updates the Path SOL as necessary for anticipated outage conditions

    • Pre-defined “outage SOLs” are often used

      Historical Path Operator role

      Perform studies to establish Path Operational Transfer Capability (OTC)

      Develop Path operating procedures

      Mitigate Path OTC exceedancesin real-time operations

Path operator
Path Operator

Historical Path Operator role:

  • Perform studies to establish Path Operational Transfer Capability (OTC)

  • Develop Path operating procedures

  • Mitigate Path OTC (now SOL) exceedancesin real-time operations

Nerc recommendation
NERC Recommendation

From the 9/13/12 Letter From Gerry Cauley(NERC CEO) to Mark Maher (WECC CEO at the time):

Role of Path Operators (ORG3)

“NERC is pleased to see that WECC is holding additional discussions to clarify the role of Path Operators, including the potential to implement contractual relationships and make use of RTCA and other tools to improve the accuracy of system operating limits. As these discussions continue NERC suggests that you also review the concept of Path Ratings and whether, as the Western Interconnection has become more highly interconnected, the Path Rating and Path Operator concept, along with the use of nomograms, still has merit for real-time operations. Other Interconnections do determine Flowgate limits for purposes of interchange scheduling, but rely more fully on RTCA for real-time operating reliability.”

Nerc industry direction
NERC/Industry Direction

  • Revised TOP/IRO standards emphasize:

    • Operational Planning Analyses (OPA) for assessing pre- and post-Contingency performance for next-day

    • Development of Operating Plans for issues identified in OPA

    • Real-time Assessments of actual pre- and post-Contingency state to determine if SOLs are being exceeded

    • Implement Operating Plans to prevent/mitigate SOL exceedance

    • Robust outage coordination process to ensure reliability under outage conditions

  • SOLs and SOL exceedance clarified in white paper – aligned with RC’s SOL Methodology and POTF recommendation

Potf recommendation
POTF Recommendation

There is a better way of doing what we do…

  • Improve reliability

  • Reduce unnecessary compliance liability

  • Increase utilization of transmission and generation assets

What s driving this recommendation
What’s Driving This Recommendation?

  • NERC recommendation and direction

  • Availability of quality data, models, and real-time tools

  • Current Path operations paradigm

    • Reliability risks

    • Unnecessary compliance risks

    • Financial risks

Path operations paradigm
Path Operations Paradigm

Identified Issues:

  • The Path SOL concept undermines the distinction between reliability limitations and commercial limitations

Path operations paradigm1
Path Operations Paradigm

Identified Issues (continued):

  • Path SOLs often do not take into consideration real-time tools and information

  • The Path SOL paradigm potentially disguises other critical limitations

  • The Path SOL paradigm results in “chasing the SOL”

  • The Path SOL paradigm results in unnecessary TOP and RC compliance risk

Path operations paradigm2
Path Operations Paradigm

Identified issues (continued):

  • The Path SOL paradigm pre-supposes the need for unique monitoring of all WECC Paths

  • The Path SOL concept is extraneous and redundant in light of the revised SOL Methodology

  • TOP designated as the Path Operator may have limited ability to manage Path SOL exceedances

  • The Path Operations paradigm prevents full utilization of transmission and generation investments

Proposed solution a new paradigm
Proposed Solution – a New Paradigm

  • Core concept – distinguishing “SOL” from “TTC”

  • NERC definition of Total Transfer Capability

    • The amount of electric power that can be moved or transferred reliably from one area to another area of the interconnected transmission systems by way of all transmission lines (or paths) between those areas under specified system conditions.

  • TTC is a better fit for WECC Paths

Distinguish sol from ttc
Distinguish SOL from TTC

Path SOL

  • Path TTC:

  • Not an SOL

  • Respects SOLs

  • Respects 3-phase Rating process, commercial issues, contracts, and allocations

  • SOLs:

  • Facility Ratings

  • Voltage limits

  • Stability limits

  • These are observed pre- and post-Contingency


  • TTCs represent a blending of both reliability and commercial limitations on the system

  • Paths can be scheduled up to the TTC, but not over

  • TTCs can be adjusted at any time, including in real-time

  • TTCs are not monitored as a real-time operating parameter


  • SOLs are pure reliability parameters – Facility Ratings, voltage limits, and stability limits observed pre- and post-Contingency

  • Paths do not have uniquely monitored SOLs unless they happen to be associated with a stability limit

  • SOL exceedance determined via Real-time Assessments of pre- and post-Contingency conditions – consistent with RC’s SOL Methodology and NERC SOL Whitepaper

  • SOL exceedance prevented or mitigated via implementation of Operating Plans

Rc s sol methodology
RC’s SOL Methodology

  • “The ultimate task of TOPs and the RC is to continually assess and evaluate projected system conditions as Real-time approaches with the objective of ensuring acceptable system performance in Real-time.”

  • “In the Peak RC Area, the BES is expected to be operated such that acceptable system performance is being achieved in both the pre- and post-Contingency state, regardless of the tools TOPs have available.”

  • “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.”

  • “TOPs may use Real-time tools or rely on prior studies, provided that those studies demonstrate acceptable BES performance for the current or expected system conditions.”

Potf recommendation1
POTF Recommendation

  • Improve reliability and utilization of generation and transmission assets by moving away from the Path SOL concept in the operations horizon, and moving towards full utilization of Real-time Assessments to ensure the transmission system is being operated within Facility Ratings, voltage limits, and stability limits in the pre- and post-Contingency state.

  • Rely on TOPs’ Operations Planning studies, Real-time Assessments, and operating plans to ensure system reliability.

  • Retire TOP-007-WECC-1 due to its redundancy with the RC SOL Methodology and existing reliability standards.

  • Dissolve the Path Operator concept and align the Western Interconnection with the NERC functional model and respective entity responsibilities and authorities.


  • Flow on these four lines generally goes in the same direction – either S>N or N>S.

  • These lines could be considered an interface or a “Path”

  • Some Paths are internal to a TOP Area as shown here, or…

TOP Area “A”


  • …Paths can connect two TOP Areas as shown here, or…

TOP Area “A”

TOP Area “B”


  • …Paths can connect more than two TOP Areas as shown here.

TOP Area “A”

TOP Area “C”

TOP Area “B”


  • Each line has a family of Facility Ratings

  • Each bus has pre- and post-Contingency voltage limits

  • These are always SOLs

  • Therefore, there is no unique SOL to “establish” or “determine”…

  • The expectation is to operate within Facility Ratings and voltage limits (SOLs) pre- and post-Contingency.

TOP Area “A”

TOP Area “B”


  • Prior transfer simulations show that at 1000 MW of N>S transfer, the loss a Facility somewhere results in another Facility hitting its emergency Facility Rating.

  • These transfer studies determine that 1000 MW is the amount of power that can be reliably transferred from TOP Area “A” to TOP Area “B”. By NERC definition, this is Total Transfer Capability.

TOP Area “A”

1000 MW

TOP Area “B”


  • Thermal/Voltage Limitations

  • Each Facility and each bus has its SOL

  • The 1000 MW maximum transfer level respects SOLs, but it is not the SOL itself.

  • Treating the 1000 MW as an SOL equates to using a “proxy” SOL.

  • The 1000 MW transfer limit is an appropriate SOL only when it is a stability limit

TOP Area “A”

1000 MW transfer capability – this is not an SOL

TOP Area “B”


  • Stability Limitations

  • Transfer studies show that at 1000 MW, the nose of the P-V curve is reached and voltage collapse occurs upon the identified contingency.

  • The 1000 MW (less some margin) is the SOL (or IROL).

  • Transfer studies may have encountered thermal or voltage limitations at lower levels of transfer, but the system was further stressed to reasonably expected maximum levels to determine whether stability limits exist.

TOP Area “A”

1000 MW voltage stability limit - this is an SOL (or IROL)

TOP Area “B”

Recommendation specifics
Recommendation Specifics

The POTF recommends moving to the proposed paradigm as described in the white paper. Under the proposed paradigm:

  • SOLs and TTCs are separate and distinguished, but they work together to ensure that reliability is achieved in real-time operations.

  • The Path Operator Role in Operations is eliminated, but the roles and responsibilities of the Path Operator are distributed among the TOPs and the RC.

  • Establish a SAR to retire TOP-007-WECC-1.

Recommendation specifics continued
Recommendation Specifics (continued)

  • Paths that are not associated with transient or voltage stability limits will not have uniquely monitored SOLs; however, they will continue to have TTCs.

  • Consistent with the RC’s SOL Methodology, SOLs are the Facility Ratings, voltage limits, and stability limits which are monitored pre- and post-Contingency.

  • TTC is the measure of maximum power transfer across a WECC Path that respects these SOLs pre- and post-Contingency. TTCs will still need to be determined through transfer analysis and prior studies.

Recommendation specifics continued1
Recommendation Specifics (continued)

  • Nomogramscan be used to determine TTCs and can provide guidance to operators as part of operating plans, but the nomogram itself may not be an SOL.

  • The WECC Path Rating Catalog will continue, and the WECC Path Rating Process remains unchanged; however, the resulting Path Rating will serve as a maximum TTC value – not as an SOL.

Potf recommendation2
POTF Recommendation

  • The POTF believes that implementing these eight recommendations will improve reliability, eliminates compliance redundancy, and better utilize transmission and generation infrastructure.

  • These recommendations are aligned with the suggestions given by NERC and are consistent with the RC’s SOL Methodology and the NERC SOL Whitepaper.

Next steps
Next Steps

  • OC/MIC/PCC endorsement vote on POTF Whitepaper (email ballot, in August)

  • Submit SAR to retire TOP-007-WECC-1

  • Implementation Planning

Sar for retiring top 007 wecc 1
SAR for Retiring TOP-007-WECC-1

  • POTF created a “crosswalk” for each requirement

  • Provides a justification for retiring the standard

  • Describes how the requirements are already addressed elsewhere