Category / () Regional Reliability Standard
() Regional Criteria
() Policy
() Guideline
(x) Report or other
() Charter
Document date / September 5, 2014
Adopted/approved by / Path Operator Task Force / OC
Date adopted/approved / September 5, 2014 / October 8, 2014
Custodian (entity responsible for maintenance and upkeep) / Path Operator Task Force
Stored/filed / Physical location:
Web URL:
Previous name/number / (if any)
Status / () in effect
() usable, minor formatting/editing required
() modification needed
() superseded by ______
() other ______
() obsolete/archived)
WESTERN ELECTRICITY COORDINATING COUNCIL •
155 NORTH 400 WEST • SUITE 200 • SALT LAKE CITY • UTAH • 84103-1114 • PH 801.582.0353
September 5, 20141
White Paper
A New Paradigm for Path Operations
Phase III Final Deliverable
by
Path Operator Task Force
September 5, 2014
Table of Contents
Executive Summary
Background
Problem Description
Reliability Risk
Compliance Risk
Financial Risk
Solution
Introduction
POTF Strategy
The Current Path Operations Paradigm (POTF Phase I)
Identified Issues
Alternate Approaches Considered (POTF Phase II)
Proposed Solution – an Alternative Paradigm: (POTFPHASE III)
Path Operator Comparison
New Paradigm Solutions
Conclusions and Recommendations
Executive Summary
Background
WECC Paths have historically been used to support both the commercial and reliability needs of the Western Interconnection.A WECC Path is subjected to a Path Rating process designed to determine the maximum amount of power that can be transferred reliably on the Path and to protect the transmission service allocations of the existing path’s owners.
Within the Operations Horizon, the Paths are studied, Path System Operating Limits (SOL) are reassessed and used as the Path Total Transfer Capability (TTC), transmission service is sold, and the system is prepared for reliable operations. Though NERC Reliability Standards assign responsibility for establishing SOLs to the Transmission Operators (TOP), in the Western Interconnection, the Path Operator has historically been the entitywith the expectation for establishing and monitoring Path SOLs.
The study processes that develop Path Ratings in the planning horizon and subsequently reassess Path SOLs in the operations horizon are intended to ensure that the transmission system is prepared for reliable operations. The Path Operator Task Force (POTF) was formed to identify issues and make recommendationsregarding path operations and the use of Path SOLs in real-time operations.
Problem Description
The POTF has determined that the Path Operator concept and the current approach to real-time Path operations create reliability risks, compliance risks, and financial risksprimarily forTOPs and Reliability Coordinators (RC) in the Western Interconnection.The risks manifest themselves in the form of a less-than-optimal use of generation and transmission assets; alack of situational awareness, tools and authority; and inappropriate operator actions.
Reliability Risk
Reliability studies are performed weeks, months, and years in advance to identify SOLs on WECC Paths.If the reliability studies performed in the operations horizon do not identify a limitation at a lower value than the Path Rating, the SOL defaults to the Path Rating.These advance studies do an excellent job in helping TOPs to identify potential reliability risks and to establish operating plans that address those risks, but these studies can fall short when used to determine a Path SOL for use in real-time operations.
Many assumptions about system load, generation, and facility status that are made in those studies vary significantly from real-time system conditions, resulting in an SOL that is often inaccurate and inappropriate for real-time use.After-the-fact analysis of events has shown that a Path SOL that is too low can result in unnecessary operator action or automatic action that may actually cause reliability problems such as low frequency due to excessive generation drop or curtailments.A Path SOL that is too high can mask actual reliability issues, resulting in inadequate situational awareness and a false sense of security for system operators.
With realtime tools and assessments, TOPs and the RC can identify whether the system is exceeding Facility Ratings, voltage limits, or stability limits [1]– the actual reliability objective that Path SOLs are intended to accomplish.Additionally, Path Operators currentlymay not have sufficient resource capabilities or authority to properly mitigate SOL exceedances on WECC Paths.These issues can easily lead to less-than-reliable operation of the Western Interconnection.
NERC has made it abundantly clear that it wants to see enhancements in WECC’s approach to ensuring real-time reliability in the Western Interconnection, as seen in Gerry Cauley’s, NERC’s CEO, letter to WECC following the September 8th, 2011 Pacific Southwest event:
“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.”
Compliance Risk
When a TOP establishes an SOL, per NERC Standards, the transmission system must be operated within the SOL and any exceedance of the SOL must be mitigated.Under the current Path operations paradigm, Path SOL exceedances must be mitigated even if Real-time Assessments indicate no reliability issue actually exists.This has resulted in unnecessary compliance reporting and enforcement actions, such as fines and compliance mitigation plans.
Financial Risk
When SOLs are exceeded, the system needs to be adjusted through curtailment of tags, redispatch of generation, phase shifting, adjustment of the transmission system, or load shedding.Path SOLs that are unnecessarily conservative often result in an underutilization of the transmission and generation infrastructure investment.
Solution
The POTF recommends the following:
- Improve reliability and utilization of generation and transmission assets by moving away fromthe Path SOL concept in the operating horizon, and moving toward 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.
Introduction
In response to the September 8th event, the Pacific Southwest Entities met on several occasions to discuss the concerns and challenges of the role of a Path Operator. Those entities are Arizona Public Service (APS) Company, California Independent System Operator(CAISO), Comisión Federal de Electricidad(CFE), Los Angeles Department of Water & Power(LADWP), San Diego Gas & Electric (SDG&E), Southern California Edison(SCE), Western Area Power Administration (WAPA), Western Electricity Coordinating Council (WECC), and the WECC RC (now Peak Reliability). The WECC Joint Guidance Committee (JGC) formed the Path Operator Task Force (POTF) in January 2013 to address these concerns. Bert Peters (APS) was appointed chair, primarily because of his close involvement in previous discussions held among the Pacific Southwest entities in response to the September 8, 2011 Event Recommendations. The original direction from the JGC for the POTF was to evaluate how Path Operations are coordinated today and to seek to understand any contractual impacts related to the Path Operator definition.
The POTF held its initial kick-off meeting on April 3, 2013 and has since identified several issues with path operations in general, including several specific issues some Path Operators are currently experiencing.There has been solid participation in the POTF effort, including participation from APS, CAISO, CFE, LADWP, SDG&E, SCE, WAPA, Salt River Projects (SRP), Bonneville Power Administration (BPA), BC Hydro, Tri-State, Colorado Springs Utilities, and Peak Reliability.The issues identified were compiled and presented to the JGC at itsMay31,2013 meeting.The JGC voiced itssupport for continuing the POTF efforts and provided additional direction for the POTF to address the following:
- Coordinate with the RC System Operators to understand and review operating guidelines for paths;
- Coordinate with the WECC Path Concepts Task Force;
- Continue to investigate current path operations including but not limited to paths currently coordinated via contracts, agreements, etc.;
- Identify and analyze all relevant standards, guidelines, etc., (both current and/or being formally developed by a delegated regulatory body) that affect path operations; and
- Identify a series of recommendations for improving path operations and present these recommendations to the JGC.
POTF Strategy
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.
For more details, reference the document titled “POTF Strategy Document.”[2]
The Current Path Operations Paradigm (POTF Phase I)
In the Western Interconnection, Path Ratings are developed in the planning horizon based on reliability analyses to determine thermal, transient stability and post transient limits in accordance with the Path Rating Process.Once the path’srating is established, Path Operators perform subsequent seasonal analyses under the auspices of subregional study groups to determine whether the Path Rating is achievable for the upcoming season based on updated system assumptions and anticipated operating conditions.Once these studies are completed, the Path SOL is designated as the lesser of the Path Rating or the Path Limitation identified in the seasonal study. The Path Operator then updates the Path SOL as necessary for real-time operations based on anticipated outage conditions.These updates are often based on pre-defined “outage SOLs.”
While no formal definition of a Path Operator exists, the roles and responsibilities of Path Operators are generally understood. Prior to the existence of mandatory Reliability Standards, a number of WECC Criteria and procedures established limited obligations for Path Operators regarding their associated Paths, including performing studies for establishing Operational Transfer Capability (OTC) on those Paths and addressing OTC exceedances on those Paths in real-time operations.As reflected in these procedures, Path Operators were charged with working with other transmission entities and the RC to address Path loadings, but unless an operating agreement exists, Path Operators do not have the authority over the operation of all Path facilities.
The POTF identified several issues with the Path operations concept as part of Phase I.Summaries are included in this section.
Identified Issues
- The Path SOL concept undermines the distinction between reliability limitations and commercial limitations.
Under the current Path SOL paradigm, Transfer Capability, scheduling limits, allocations, commercial considerations, and historical reliability assessments performed in years past are all rolled up into a parameter that is monitored in real-time operations as an SOL (i.e., the Path SOL).In the Western Interconnection, Path SOLs are the WECC Path Ratings unless studies indicate the need for a lower Path SOL value.
While WECC Path Ratings have a basis in reliability studies performed in the planning horizon, the Path Rating process and the granted Path Rating exist primarily to safeguard the protection of investments and to ensure that the reliability impacts of a new transmission project are understood and mitigated before the transmission project becomes operational.Because of the different ways the Path SOLs have been calculated for real-time operations,it is often unclear whether a Path SOL used in real-time operations is intended to address an actual reliability issue, whether the SOL is “flow limited” due to modeling/simulation constraints, or whether the Path SOL is intended to accommodate scheduling allocations among the owners or other commercial issues.
- Path SOLs may not take into consideration real-time tools and information.
Currently, thermal and steady state voltage-limited Path SOLs are established and adhered to in real-time operationsregardless of information provided by real-time tools and assessments. It is not uncommon to see a thermal- or voltage-based Path SOL being exceeded, but real-time tools show no indication of thermal or voltage problems pre- or post-Contingency;however, the opposite can also be true.
Establishing a thermal- or voltage-based Path SOL ahead of time and treating it as a real-time operating limit almost guarantees that for most conditions, the Path SOL will be too high or too low in real-time. Path SOLs that are too low may result in unnecessary and costly mitigation actions (e.g., redispatch, schedule curtailments, load shedding).Path SOLs that are too high may result in reliability issues that are missed or disguised. There have been several instances where drastic mitigations have been implemented in response to Path SOL exceedances when real-time tools indicate no reliability issues. In these cases, the unnecessary Path SOL mitigations included significant amounts of generation reductions that caused system frequency to drop.
- The Path SOL paradigm potentially disguises other critical limitations.
Path SOLs are generally determined priorto real-time by conducting studies that stress the Path to the point where either the Path Rating is reached or the first limiting reliability criteria is reached. Under this approach, Path flows higher than this point will not be studied.For example, a particular thermally limited Path SOL of 1000 MW could have a major stability issue at 1100 MW.Under the current paradigm, this stability limit may go undetected.
- The Path SOL paradigm results in “chasing the SOL.”
Under the current Path SOL paradigm,TOPscontinually have to recalculateor otherwise revisethe Path SOL in response to changing system conditions and events.Real-time tools could be used to determine whether acceptable pre- and post-Contingencysystem performance is being demonstrated rather than relying on pre-determined SOLs.
- The Path SOL paradigm results in increased TOP compliance risk.
The reliability standard TOP-007-WECC-1 requires a 30-minute mitigation time for Path SOL exceedances for the list of WECC Paths designated in the standard.Since this reliability standard mandates the existence of a Path SOL, there islittle flexibility for TOPs to ensure acceptable pre- and post-Contingency system performance by any other means.If Transfer Capability on a WECC Path was distinct from the SOL, then establishment of the TTCs and SOLs would be handled under appropriate standards.
- The Path SOL paradigm pre-supposes the need for unique monitoring of all WECC Paths.
The Path SOL paradigm necessitates monitoring of WECC Path SOLs, including Paths not explicitly identified in TOP-007-WECC-1.The Western Interconnection should not pre-suppose that all WECC Paths need to be monitored uniquely to ensure reliability by virtue of being a “Path.”Some WECC Paths should beuniquely monitorednot because they are designated as a Path, but rather because they represent a stability risk to the system.
- The Path SOL concept is extraneous and redundant in light of the revised Peak Reliability SOL Methodology.
The Peak Reliability SOL Methodology[3] (RC SOL Methodology) contains specific requirements that the entire Bulk Electric System (BES) demonstrate acceptable pre- and post-Contingency system performance with regard to Facility Ratings, voltage limits, voltage stability limits, and transient stability limits. Operating within these limits ensures operational reliability across the board.WECC Path Facilities are included under the larger BES umbrella.There is no reliability benefit in treating WECC Paths with any degree of uniqueness when the RCSOL Methodology already requires that the entire BES demonstrate acceptable pre- and post-Contingency performance.Having specific requirements for a subset of facilities (i.e., WECC Path Facilities) is extraneous and redundant in light of the requirements set forth in the RCSOL Methodology.