The Federal Energy Regulatory Commission on Jan. 23 approved a reliability standard for transmission system planning performance requirements submitted by the North American Electric Reliability Corporation.
FERC said that the new reliability standard TPL-001-5 improves upon an existing reliability standard by addressing the study of single points of failure of protection systems and planned maintenance outages and stability analysis for spare equipment strategies.
Significantly, FERC declined to adopt a proposal included in a 2019 Commission notice of proposed rulemaking that would have directed NERC to require corrective action plans for protection system single points of failure in combination with a three-phase fault if planning studies indicate potential cascading.
This had been a key point of concern raised by the American Public Power Association, the Large Public Power Council and other trade groups.
NERC submitted reliability standard in December 2018
NERC submitted reliability standard TPL-001-5 to FERC in December 2018 for Commission approval. NERC said that the reliability standard addresses directives laid out by FERC in Order No. 786. In that order, the Commission approved the currently effective version of the transmission system planning standard, reliability standard TPL-001-4, and issued several directives to NERC.
NOPR issued in June 2019
On June 20, 2019, the Commission issued a NOPR that proposed to approve reliability standard TPL-001-5, saying the reliability standard largely addressed the directives in Order No. 786 (RM19-10).
The NOPR also proposed to direct NERC, pursuant to section 215(d)(5) of the Federal Power Act, to modify the reliability standard to require corrective action plans for protection system single points of failure in combination with a three-phase fault if planning studies indicate potential cascading.
The NOPR stated that NERC had not adequately justified categorizing protection system single points of failure in combination with a three-phase fault as an extreme event that only requires study, but not a corrective action plan, when there is the potential for cascading.
The NOPR also expressed concern with NERC’s assessment that such events do not necessitate corrective action plans because of their rarity. The NOPR proposed to direct NERC to submit the modified reliability standard for approval within twelve (12) months from the effective date of a final rule.
FERC approves reliability standard
In approving reliability standard TPL-001-5, FERC concluded that the revised standard is an improvement over reliability standard TPL-001-4 “and will improve bulk-power System reliability by requiring enhanced transmission system planning regarding the study of protection system single points of failure in combination with a single-line-to -ground fault, as discussed in Order No. 754.” The Commission also approved the associated violation risk factors, violation severity levels, and implementation plan.
In Order No. 754, the Commission determined that there may be a system protection issue that merits further exploration by technical experts and that there is an issue concerning the study of the non‐operation of non‐redundant primary protection systems; e.g., the study of a single point of failure on protection systems. To address this concern, the Commission directed Commission staff to meet with NERC and its appropriate subject matter experts to explore the reliability concern, including where it can best be addressed, and identify any additional actions necessary to address the matter.
In its order issued on Jan. 23, FERC also determined that reliability standard TPL-001-5 satisfies the Order No. 786 directives regarding planned maintenance outages and stability analysis for spare equipment strategies.
For example, reliability standard TPL-001-5 provides for a more complete consideration of factors for selecting which known outages will be included in near-term transmission planning horizon studies, FERC noted.
FERC declines to adopt proposed directive
At the same time, FERC said it would not direct NERC to develop and submit modifications to the reliability standards to require corrective action plans to address protection system single points of failure in combination with a three-phase fault if planning studies indicate potential cascading.
“We are persuaded by NERC and other commenters of the improbability of single points of failure in combination with three-phase faults resulting in cascading outages,” FERC said.
Trade groups submitted comments in response to NOPR
In response to the NOPR, the Edison Electric Institute, the American Public Power Association, the Large Public Power Council, and the National Rural Electric Cooperative Association filed comments.
The trade groups said they did not support the Commission’s proposal to direct NERC to modify TPL-001-5 to require corrective action plans for protection system single points of failure in combination with a three-phase fault if the planning studies indicate potential cascading.
“The proposed reliability standard provides targeted protections based on the level of risk posed without imposing unnecessary CAPs [corrective action plans] in circumstances in which such changes will yield few reliability benefits,” EEI, the American Public Power Association, the LPPC and NRECA said in their Aug. 26, 2019 comments.
In its final rule, FERC said that its determination is also supported by a 2015 NERC report’s assessment that the probability of an adverse system impact from a three-phase fault accompanied by a protection system failure is low enough that it does not warrant being a planning event (i.e., requiring a corrective action plan).
Although the Commission previously noted that there is an average of approximately one three-phase fault event every three months since 2011, only ten indicated instances of a protection system single point of failure, “which we agree is a rare occurrence,” FERC said.
“Given the NERC standard drafting team’s assessment of the improbability of single points of failure in combination with three-phase faults resulting in cascading outages, we determine that it is reasonable to address such occurrences as extreme events only requiring analysis and evaluation of possible mitigating actions designed to reduce adverse impacts.”
The final rule will take effect 60 days after publication in the Federal Register.
