The Federal Energy Regulatory Commission has proposed to strengthen a reliability standard to ensure transmission planners come up with an action plan to address certain events on the electric grid that could lead to cascading outages.
The North American Electricity Reliability Corp. last year proposed a reliability standard (TPL-001-5) to require transmission planners to do more comprehensive studies on how to protect the electric system in places where there is a single, non-redundant point of protection that could fail.
The studies would look at commonplace scenarios as well as extreme scenarios that could lead to uncontrolled and widespread cascading outages. The standard would require planning entities to develop a plan of action to fix problems revealed by the studies.
FERC PROPOSAL
FERC on Thursday proposed (RM19-10) to adopt the standard, but also said it should be strengthened.
The commission noted that non-redundant protection systems can also misoperate when faced with a three-phase fault. "Because three-phase faults are more serious than single-phase-to-ground faults, the consequences can be more severe, including cascading," FERC said.
But NERC's proposed reliability standard does not require a plan to address these types of events, saying the likelihood of these events occurring and resulting in the most severe impacts would be small.
FERC disagreed with NERC's rationale. "We are not persuaded that such events do not necessitate corrective action plans because of their alleged rarity, particularly because their potential impacts may result in cascading," FERC said.
NOT SO RARE
Plus, it is unclear that such events are actually that rare, FERC said. It is not uncommon for a single-line-to-ground fault to evolve into a multi-phase fault, the commission explained. And NERC's data shows that these events -- involving protection system single point of failure in combination with a three-phase fault -- occur every eight months, the commission said.
So FERC on Thursday proposed to direct NERC to change the standard to require corrective action plans for protection system single points of failure in combination with three-phase faults if planning studies indicate potential cascading.
"While we are aware of the potential for increased cost under this proposal, we understand that there are likely cost-effective actions that could be taken to mitigate a protection system single point of failure in combination with a three-phase fault," FERC said.
Meanwhile, FERC proposed to adopt a separate part of the standard that addressed FERC's concern that transmission planners should study significant planned outages even if they are less than six months in duration. The standard also changes requirements for an entity to assess the impact of the possible unavailability of long-lead time equipment, consistent with the entity's spare equipment strategy.
