WECC-0113 FAC-010-2.1 Request to Retire Regional Difference

White Paper

Retirement of WECC Regional Difference

FAC-010-2.1 System Operating Limits Methodology for the Planning Horizon

155 North 400 West, Suite 200

Salt Lake City, Utah 84103-1114

Developed as WECC-01131

WECC-0113 FAC-010-2.1 Request to Retire Regional Difference

Executive Summary

The WECC-0113 Drafting Team (DT) makes the following recommendation regarding the retirement of the FAC-010-2.1, System Operating Limits Methodology for the Planning Horizon (FAC), Regional Difference (RD).

Recommendation

Under Project 2015-03, Periodic Review of System Operating Limit Standards, NERC has initiated a FAC standards project to retire FAC-010.[1] Because the FAC RD is entirely dependent on the underlying NERC Standard, if the NERC-initiated retirement of the underlying NERC Standard is approved prior to completion of this project, the entirety of the associated RD should be retired coincident with the retirement of that underlying standard, subject to the following caveat.

Because the loss of Sections 1.3, 1.1.5, and 1.1.6 could impact the WECC Path Rating process, the DT is recommending the substance of these sections migrate into the WECC Path Rating process, or into a peripheral supporting document.

Analysis

After analysis of the FAC RD[2], the WECC Reliability Subcommittee (RS) acting in its role as a subcommittee of the WECC Planning Coordination Committee (PCC) concluded that the FAC RD should be retired in its entirety as its content is outdated and/or redundant to existing NERC Standards.

The DT concurs with the RS analysis except in regards to Sections 1.3, 1.1.5, and 1.1.6. The drafting team is concerned that retirement of the FAC RD will change the implementation of the WECC Path Rating process thereby creating one rating system for existing paths and another for new paths.[3] As new paths are rated using new criteria it could affect the rating of existing paths as well; albeit, a primary goal of the rating process is to protect existing path ratings.[4] Further, the drafting team is concerned that retirement of Sections E.1.3, 1.1.5 and 1.1.6 will delete requirements to examine specific criteria beneficial to the rating process. As such, the recommendation is to retire the entire RD except for Sections 1.3, 1.1.5, and 1.1.6; then, move the substance of those three sections either into the WECC Path Rating process or other supporting documentation.

Both of the FAC for the planning horizon and FAC-011-2, System Operating Limits Methodology for the Operations Horizon, contain identical RDs even though they are two very difference standards applicable in two different time horizons. The purpose of this recommendation is to provide background and justification for retirement of the FAC RD subject to the proposed preceding condition.

Introduction

On April 10, 2003, WECC merged its transmission planning standards with that of the North American Electricity Reliability Corporation (NERC[5]) creating a single document titled NERC/WECC Planning Standards (PS). Noting that in some circumstances WECC’s criteria were more stringent than that of NERC, WECC adopted the approach that “the more restrictive reliability criteria and guides must be observed.”[6]

In April 2005, WECC moved its transmission planning criteria into the WECC Reliability Criteria, Part I, as approved in April 2005.

In November 2006, the NERC Board of Trustees approved FAC-010-1, System Operating Limit Methodology for the Planning Horizon that included a WECC Regional Difference (RD) reflecting WECC’s more stringent planning criteria in effect at the time.

In June 2008, the Federal Energy Regulatory Commission (FERC) approved the version two of the FAC (later subject to 2.1 errata) with an Effective Date of July 1, 2008. [7]

In the 7 years since the approval of the FAC, WECC’s planning criteria have continued to evolve based on current and best practices;[8] however, the FAC still reflects the planning criteria of 2003, rendering that RD over a decade old and without updates. In addition to the outdated nature of the FAC RD, FERC has approved a number of NERC Standards that now stand in conflict with the RD, creating: 1) duplicate Requirements, 2) conflicting Requirements, 3) ambiguities of Requirements, and/or 4) the impossibility of implementation of Requirements.

The language of the impacted NERC Standard and the associated regional difference is included in Attachment A.

An implementation plan for complete retirement of the RD is included in Attachment B.

FAC-010-2.1 Analysis for Retirement

The WECC RD associated with the FAC only affects Requirement R2 (Sections 2.5 and 2.6) of the underlying FAC. Requirement R2 requires that each Planning Authority’s System Operating Limit (SOL) Methodology include a requirement that SOLs provide performance at a specified threshold.

Requirement R2.5 requires performance with all Facilities in service and following any of the multiple “Contingencies identified in Reliability Standards TPL-003”-0b, System Performance Following Loss of Two or More Bulk Electric System Elements (Category C) (TPL), currently listed by NERC as an inactive reliability standard[9].

Requirement R2.6 requires that when determining acceptable response to any of the TPL Contingencies, the following conditions are allowed: 1) planned or controlled interruption of electric supply to customers, 2) the planned removal from service of certain generators, and/or 3) the curtailment of contracted Firm electric power Transfers.

Sub Section 1.1

In FAC RD Section E. Regional Differences, Subsection 1.1, the FAC RD includes seven criteria in conjunction with requirement R2.5 and R2.6.

FAC RD 1.1.1 states:

“1.1.1 Simultaneous permanent phase to ground Faults on different phases of each of two adjacent transmission circuits on a multiple circuit tower, with Normal Clearing. If multiple circuit towers are used for only station entrance and exist purposes, and if that do not exceed five towers at each station, then this condition is an acceptable risk and therefore can be excluded.”

Analysis

The language included in 1.1.1 requiring a mandate to address multiple circuit towers is redundant to requirements in other NERC standards. Further, there is no technical justification for the requirement.

The underlying Requirement R2.6 incorporates by reference TPL-003[10] slated for replacement by TPL-001-4, Transmission System Planning Performance Requirements[11]. That Requirement requires that the Transmission Planner and Planning Coordinator maintain planning models that contain certain specifications, many of which are included in Table 1 of that document. Among the modeling criteria specified in Table 1 is Category P7, Multiple Contingency, addressing “the loss of: 1) Any two adjacent (vertically or horizontally) circuits on common structure, 2) Loss of a bipolar DC line.” Because the RD is addressed in other NERC standards, it should be deleted from FAC as it adds no additional reliability margin but does create the potential for double jeopardy.

In addition to this redundancy, the common stability programs in use today are based upon positive sequence modeling and do not have the ability to simulate a simultaneous ground fault on different phases of two different circuits. Further, no reliability benefit is obtained by simulating a single phase-to-ground fault on two different phases of two transmission circuits nor was the RS able to find where any technical study on the matter was ever performed. As such, the legacy language is arbitrary and should be retired. [12]

Recommendation

Whereas the language of 1.1.1 is redundant to other NERC standards, creates the potential for double jeopardy, and is not based on any technical study, the entirety of the language should be retired.

FAC RD 1.1.2 states:

“1.1.2A permanent phase to ground Fault on any generator, transmission circuit, transformer, or bus section with Delayed Fault Clearing except for bus sectionalizing breakers or bus-tie breakers addressed in E1.1.7”

Analysis

This requirement is addressed in NERC Standard TPL-001-4, Table 1, Category P4 and P5 contingencies.

Recommendation

Whereas the language of 1.1.2 is redundant to other NERC standards and creates the potential for double jeopardy, the entirety of the language should be retired.

FAC RD 1.1.3 states:

“1.1.3Simultaneous permanent loss of both poles of a direct current bipolar Facility without an alternating current Fault.”

Analysis

This requirement is address in the NERC Standard TPL-001-4, Table 1, Category P7 contingency.

Recommendation

Whereas the language of 1.1.3 is redundant to other NERC standards and creates the potential for double jeopardy, the entirety of the language should be retired.

FAC RD 1.1.4 states:

“1.1.4The failure of a circuit breaker associated with a Special Protection System to operate when required following: the loss of any element without a Fault; or a permanent phase to ground Fault, with Normal Clearing, on any transmission circuit, transformer or bus section.”

Analysis

This requirement is addressed in NERC Reliability Standard PRC-012-0[13], Special Protection System Review Procedure, at Requirement R1.3.:

“R1.3. Requirements to demonstrate that the RAS shall be designed so that a single RAS component failure, when the RAS was intended to operate, does not prevent the interconnected transmission system from meeting the performance requirements defined in Reliability Standards TPL-001-0, TPL-002-0, and TPL-003-0.”

The PRC-012-0 Requirement requires that failure of a single component does not prevent the interconnected system from meeting required performance in the TPL-related standards. This reliability concern is also addressed in NERC Standard TPL-001-4, Table 1, Category P4 and P5 contingencies, which specifies system performance requirements for stuck breaker and protection system failure.

Recommendation

Whereas the language of 1.1.4 is redundant to other NERC Standards and creates the potential for double jeopardy, the entirety of the language should be retired.

FAC RD 1.1.5 states:

“1.1.5A non-three phase Fault with Normal Clearing on common mode Contingency of two adjacent circuits on separate towers unless the event frequency is determined to be less than one in thirty years.”

Analysis

Requirement E1.1.5 extends the requirement of NERC Reliability Standard TPL-001-4, Table 1, Category P7 contingency to “two adjacent circuits” on separate structures. Within the NERC TPL-004-0a and on adoption of TPL-001-4 this contingency is considered an extreme event as indicated below in TPL-001-4 Requirements 3.5 and 4.5 incorporating Table 1 – Steady State & Stability Performance Extreme Events as follows:

  • Steady state item 2.b

2. Local area events affecting the Transmission System such as:

a. Loss of a tower line with three or more circuits.

b. Loss of all Transmission lines on a common Right-of-Way.

c. Loss of a switching station or substation (loss of one voltage level plus transformers).

d. Loss of all generating units at a generating station.

e. Loss of a large Load or major Load center.

  • Stability item 1
  1. With an initial condition of a single generator, Transmission circuit, single pole of a DC line, shunt device, or transformer forced out of service, apply a 3Ø fault on another single generator, Transmission circuit, single pole of a different DC line, shunt device, or transformer prior to System adjustments.

In 2003, when the FAC RD was written there was no action required in the NERC Standards for multiple contingencies in the same rights-of-way. Within TPL-001-4, Transmission Planners are now required to conduct simulations of multiple circuit outages in the same rights-of-way as an extreme event and if the analysis concludes there is Cascading caused by the occurrence of extreme events, an evaluation of possible actions designed to reduce the likelihood or mitigate the consequences and adverse impacts of the event(s) shall be conducted. While the extreme event assessment is to evaluate possible actions, it does not require a corrective action plan. Thus for a contingency of two adjacent circuits on separate towers , TPL-001-4 does not require a corrective action plan, whereas FAC-010-2.1 Requirement E.1.1.5 does require the same performance as a P-7 contingency if the event frequency is greater than one in 30 years.

In addition, Requirement E1.1.5 uses the term “adjacent circuits” but the term is not defined in the NERC Glossary of Terms Used in Reliability Standards (NERC Glossary). This lack of definition in the NERC Glossary creates ambiguity in the implementation of the RD.[14] Although WECC has made efforts to clarify the ambiguity through approval of a WECC Regional Criterion TPL-001-WECC-CRT-2, System Performance Criterion (CRT) [15] and the associated definition of Adjacent Transmission Circuits[16] because the CRT only augments the standard, the CRT is not the definitive authority on how the standard must be implemented. As such the ambiguity would be eliminated if the language was deleted.[17]

Finally, at the time the FAC RD was developed, it was believed that the rate of common mode outages of adjacent circuits on separate structures was similar to that of any two circuits of a multiple circuit tower line (covered by Category P7). As such, it made sense to apply the same performance criteria to both classes of contingencies. However, actual performance data for 230kV and above transmission lines in the Western Interconnection indicate that the average outage rate per 100 miles of line is actually less than one-half the rate for circuits on common structures as shown in the table below.

The actual outage rate for circuits on common rights-of-way but on separate structures is also less than that for any two circuits not on a common right-of-way. The reason for these statistical differences is the configuration of the substation. Adjacent circuits are typically connected into separate bays of a substation, which reduces the common mode outages of breaker or protection system failures. Therefore, Requirement E1.1.5 can be deleted without adversely impacting the reliability of the Bulk Electric System.

Table A
Outage Comparison of Circuits on Common ROW and/or Structures when 2 or more circuits went out of service.
Western Interconnection Average Data
2008-2012 / Circuits on Common Structure / Circuits on Common Right-of-Way Separate Structures / Circuits not on Common ROW or Structure
Transmission Miles / 8,822 / 14,782 / 51,649
Number of Events / 24 / 22 / 103
No. of Outages/ 100 miles of line / 0.271 / 0.147 / 0.207

The above table is based upon six years of historical data collected by WECC. WECC began collecting right-of-way outage data in 2008.[18]

WECC Path Ratings for a number of major paths within the Western Interconnection have been established applying the performance requirements of Requirement E1.1.5. If the performance requirements of TPL-001-4 with the contingency being considered an extreme event is applied, as opposed to the contingency being treated as a P7 contingency as per Requirement E1.1.5, it will result in potential for changes in path ratings for these paths.

Currently the WECC Path Rating process requires extreme events (Category D) to be assessed but does not require mitigation in establishing path ratings. If the language is retired, it could result in new path ratings under one set of criteria juxtaposed to existing path ratings created under a different and pre-existing set of criteria.

This performance requirement change leads to a process issue affecting path ratings and the associated allocations. For example, should the existing paths be re-rated applying the new performance requirements before other paths can apply the new performance requirements to establish their ratings in the WECC Path Rating Process? The drafting team does not posit an answer; it merely highlights the issue.

Recommendation

Whereas the loss of Section 1.1.5 could impact the WECC Path Rating process, the DT is recommending the substance of this section migrate into the WECC Path Rating process, or into a peripheral supporting document.

FAC RD 1.1.6 states:

“1.1.6A common mode outage of two generating units connected to the same switchyard, not otherwise addressed by FAC-010.”

Analysis

Requirement E1.1.6 requires that a common mode outage of two generating units connected to the same switchyard demonstrate transient, dynamic, and voltage stability and does not allow for cascading. Within the NERC TPL-004-0a and on adoption of TPL-001-4 this contingency is considered an extreme event as indicated below in TPL-001-4 Requirements 3.5 and 4.5 incorporating Table 1 – Steady State & Stability Performance Extreme Events as follows:

  • Steady-state Item 1
  1. Loss of a single generator, Transmission Circuit, single pole of a DC Line, shunt device, or transformer forced out of service followed by another single generator, Transmission Circuit, single pole of a different DC Line, shunt device, or transformer forced out of service prior to System adjustments.
  • Steady-state Item 2.d

2. Local area events affecting the Transmission System such as:

a. Loss of a tower line with three or more circuits.

b. Loss of all Transmission lines on a common Right-of-Way.

c. Loss of a switching station or substation (loss of one voltage level plus transformers).

d. Loss of all generating units at a generating station.

e. Loss of a large Load or major Load center.

  • Stability Item 1
  1. With an initial condition of a single generator, Transmission circuit, single pole of a DC line, shunt device, or transformer forced out of service, apply a 3Ø fault on another single generator, Transmission circuit, single pole of a different DC line, shunt device, or transformer prior to System adjustments.

In 2003 when the FAC RD was written, there was no action required in the NERC Standards for loss of two generating units at a generating station resulting from contingencies beyond those specified in Table 1. Within TPL-001-4, Transmission Planners are now required to conduct simulations of simultaneous loss of multiple generators as an extreme event; and, if the analysis concludes there is Cascading caused by the occurrence of extreme events, an evaluation of possible actions designed to reduce the likelihood or mitigate the consequences and adverse impacts of the event(s) shall be conducted. While the extreme event assessment is to evaluate possible actions, it does not require a corrective action plan for cascading. Thus, if a common mode contingency of two generating-units results in cascading, TPL-001-4 does not require a corrective action plan, whereas FAC-010-2.1 Requirement E.1.1.6 does require a corrective action plan (establishment of an SOL in this context).

WECC Path Ratings for a number of major paths within the Western Interconnection have been established applying the performance requirements of Requirement E1.1.6. If the performance requirements of TPL-001-4 with the contingency being considered an extreme event is applied, as opposed to requiring mitigation for cascading as per Requirement E1.1.6, it will result in potential changes in path ratings for these paths.

Currently the WECC Path Rating process requires extreme events (Category D) to be assessed but does not require mitigation in establishing path ratings. If the language is retired, it could result in new path ratings under one set of criteria juxtaposed to existing path ratings created under a different and pre-existing set of criteria. Among others, this raises the question as to whether the existing paths should be re-rated using a different set of criteria. The drafting team does not posit an answer; it merely highlights the issue.