By Rich Heidorn Jr.
FERC last week gave final approval to a NERC reliability standard on protective relays and a preliminary endorsement to rules that would ensure small generators are able to stay connected to the grid during abnormal frequency and voltage events.
NERC standard PRC-026-1 is intended to ensure the use of protective relay systems that can differentiate between faults and stable power swings. The standard applies to all planning coordinators and to generation and transmission owners that use certain load-responsive protective relays (RM15-8).
FERC ordered NERC to develop the standard in 2010, citing findings that the cascading 2003 Northeast blackout was accelerated by relays that tripped facilities because they could not differentiate between dynamic, but stable, power swings and actual faults.
The order told NERC to consider requiring the retirement of such relays. But NERC declined to include a prohibition, saying such a rule “may have unintended negative outcomes for bulk power system reliability.”
“It is generally preferable to emphasize dependability over security when it is not possible to ensure both for all possible system conditions,” NERC said.
FERC agreed with NERC’s argument, saying that two existing reliability standards require covered entities to develop corrective action plans to address relays not covered by the new standard.
Small Generators
The commission also issued a Notice of Proposed Rulemaking that would revise the pro forma small generator interconnection agreement (SGIA) to require generators smaller than 20 MW to “ride through” abnormal frequency and voltage events and not disconnect (RM16-8).
FERC said its action was warranted by the increase in grid-connected solar PV generation and generator interconnection requests driven by state renewable portfolio standards.
“The commission already requires generators interconnecting under the large generator interconnection agreement to have this capability, and it would be unduly discriminatory not to also impose these requirements on small generating facilities,” the commission said.
The commission cited NERC reports warning that the increasing penetration of distributed energy resources could harm reliability without corrective action. Without the new rule, FERC said, “small generating facilities, in the aggregate or in significant combination, could exacerbate an initial disturbance by tripping offline instead of riding through a disturbance.”
It said small generators now have more ability to ride through disturbances because of smart inverters and a new standard from the Institute of Electrical and Electronics Engineers (IEEE) that allows wider trip settings.
The commission said it was not seeking to adopt specific frequency and voltage ride through parameters. “Instead, we propose to allow for the development of appropriate system-specific standards, which we expect will be based on work by recognized standards setting bodies, such as IEEE.”
FERC also said the NOPR is not intended to interfere with state interconnection procedures and would apply only to interconnections made subject to a jurisdictional open access transmission tariff (OATT).
The new rule would apply to any new small generating facility that executes an SGIA after the effective date of the rule. Comments on the rule change will be due 60 days after publication of the NOPR in the Federal Register.
