The Federal Energy Regulatory Commission last week approved a revised definition of the bulk electric system (BES) that refines the exclusions for radial facilities and local networks.

The commission’s order (RD14-2) approved changes drafted by the North American Electric Reliability Corp. in response to FERC and industry concerns over how NERC was identifying facilities that are subject to its mandatory reliability rules.

In Orders 773 (December 2012) and 773-A (April 2013), FERC approved a new definition of BES facilities, eliminating regional discretion and establishing a “bright-line” threshold including most facilities operating at or above 100 kV. (See Seeking “Bright Line,” FERC Leaves BES Appeal Rules Unclear.)

Although the new definition supersedes the Order 773 definition in total, it will “result in minimal changes to the elements included in the bulk electric system,” FERC said.

NERC said the revised rules respond to the technical and policy concerns raised in the prior orders by adding “clarity and granularity that will allow for greater transparency and consistency in the identification of elements and facilities that make up the bulk electric system.”

The changes, effective July 1, 2014, mostly affect inclusion I4 (dispersed power producing resources) and exclusions E1 (radial systems), E3 (local networks) and E4 (reactive power devices).

In addition, there are minor clarifications to inclusions I1 (transformers), I2 (generating resources) and I5 (static or dynamic reactive power devices). No changes were made to the core definition, inclusion I3 (black start resources) or exclusion E2 (behind the meter generation). (See Bulk Electric Systems (BES) Inclusions and Exclusions.)

Exelon Corp., the American Public Power Association, the Transmission Access Policy Study Group (TAPS) and Public Utility District No. 1 of Snohomish County submitted filings supporting NERC’s revisions. APPA and Snohomish praised the new definition for its focus on core facilities that present the greatest risks of reliability failure.

FERC rejected requests from several other intervenors, including the American Wind Energy Association (AWEA) and the Electricity Consumers Resource Council (ELCON), for changes in NERC’s proposal.

AWEA and First Wind Holdings LLC had asked the commission to modify inclusion I4 to exclude individual power producing resources. The commission said the purpose of inclusion I4 is to include all forms of variable generation. “As we noted in Order No. 773, there are geographical areas that depend on these types of generation resources for the reliable operation of the interconnected transmission network,” the commission said. “… Nothing in the AWEA and First Wind pleadings have convinced us that our determinations in Order No. 773 need to be revisited.”

FERC cited a 2009 NERC report on variable generation that concluded that “[d]istributed variable generators, individually or in aggregate (e.g. small scale photovoltaic), can impact the bulk power system and need to be treated, where appropriate, in a similar manner to transmission connected variable generation.”

The commission said wind farms larger than 75 MVA can affect reliability if all of its wind turbines trip offline simultaneously after small fluctuations in voltage or frequency. “Because variable generation can impact the interconnected transmission network, we anticipate that wind plant owners whose facilities meet the inclusion I4 criteria who seek to exclude individual wind turbines from the bulk electric system through the exception process will be infrequent,” the commission wrote.

In other reliability actions last week FERC also:

• Approved five standards requiring generators owners and, in some cases, transmission owners to provide verified data for certain power system planning and operational studies. The rules are intended to improve the accuracy of the studies and the coordination of protection system settings.
• Proposed revisions to an existing standard on Transmission Relay Loadability and a new standard on Generator Relay Loadability designed to prevent generators from tripping offline unnecessarily during a system disturbance.
• Denied rehearing of Order No. 791, which approved version 5 of the Critical Infrastructure Protection standards.