FERC told to go bigger on power line ratings rule as industry urges caution

The Federal Energy Regulatory Commission received a wave of feedback March 22 on a proposed rule to improve the nation's electric transmission capacity by squeezing better performance out of existing power lines.

A coalition of companies that produce grid-enhancing technologies urged FERC to go further than an initial proposal by directing regional grid operators in some cases to use dynamic line ratings, or DLRs, which can produce hundreds of millions of dollars in savings in wind-rich areas.

But investor-owned utilities and federal power administrations in the U.S. West warned that even a less complex type of line rating required by the proposal, called ambient adjusted ratings, or AARs, may not be economic for large swaths of the country.

At issue is a November 2020 proposed rule (RM20-16) that would effectively require all U.S. transmission providers to implement AARs on power lines that now use less accurate seasonal and static line ratings. In issuing the proposal, FERC noted that "the current use of seasonal and static assumptions results in transmission line ratings that do not accurately represent the transfer capability of the transmission system."

Unlike seasonal or static line ratings, which may overstate or understate a line's transfer capacity, AARs adjust a line's rated capacity based on near-term forecast air temperatures. Notably, FERC's proposal stopped short of requiring grid operators and transmission providers to implement DLRs, which are updated more frequently and are based on knowable information such as wind speed.

Support for DLRs, AARs

When FERC issued the proposal, then-Commissioner Richard Glick, now chair of the agency, urged commenters to weigh in on whether FERC should actually require DLRs in cases where they make sense. In its proposed rule, the commission noted that DLRs rely on a range of inputs beyond just ambient temperature, including wind speed, cloud cover, solar irradiance intensity, precipitation, and line conditions such as tension or sag.

In arguing that FERC should require DLRs where appropriate, the Working for Advanced Transmission Technologies, or WATT, Coalition noted that wind speed is by far the most significant factor affecting line capacity. DLRs account for the cooling effect of wind speeds on a line, but AARs do not, the group said. Its membership includes companies such as LineVision Inc., which is already working with Xcel Energy Inc. to deploy DLR technology across the utility's service area in Colorado, Minnesota and Wisconsin.

"Where factors influencing the amount of capacity that is available and in demand by transmission customers are readily knowable, that information should be incorporated into line ratings," the WATT Coalition said.

As an example of the potential benefits of doing so, the group cited a study developed on its behalf by consulting firm The Brattle Group that found that a combination of grid-enhancing technologies including DLRs could produce $5 billion in annual energy cost savings if deployed at a nationwide scale. The study also found that DLR implementation could cut carbon emissions in wind-rich states such as Kansas and Oklahoma by unlocking stalled renewable energy projects.

Turning to AARs, the Transmission Access Policy Group, or TAPS, a coalition of transmission-dependent utilities in 35 states, said AARs' "broad application" will reduce opportunities for discrimination in areas without independent system operators or regional transmission organizations.

"The opportunity for [transmission providers] to selectively implement AARs in a manner that favors their own generation and load is of particular concern in non-RTO regions where there is no independent monitoring," TAPS said.

TAPS also urged FERC to issue a final rule that requires grid operators to use a "look-up" table similar to that already used by the PJM Interconnection, where the RTO adjusts a line's rating based on a range of temperatures submitted by its owner and on temperature data received from local weather stations.

Utility industry concerns

Calling for a more measured tack, the Edison Electric Institute, or EEI, recommended a "staggered approach" for AAR implementation that allows transmission providers to identify and prioritize lines that would benefit most from that technology. Following an initial rollout, the EEI said another study should be done on the benefits of AARs to help determine whether more facilities would benefit from their use.

For reliability purposes, the EEI also said AARs should only be used for real-time operations. That recommendation stands in contrast to FERC's proposal to require AARs for transmission service requests that end within 10 days of the request and for determinations about resource curtailment, interruption or redispatch anticipated to occur within those 10 days.

The North American Electric Reliability Corp. reiterated that FERC should be mindful of how line rating changes might interact with its now-effective reliability standards.

The Southwest Power Pool, where wind generation outpaced coal-fired power in 2020, asked FERC to clarify that AARs will only be required for transmission service requests with a duration of less than a year. If the proposal were to apply to requests longer than a year, the SPP warned that "the use of AARs may be especially problematic to incorporate into long-term planning processes that are typically attempting to project likely system conditions one to ten years or longer into the future."

Federal power administrations weigh in

Farther west, the Western Area Power Administration, or WAPA, and the Bonneville Power Administration separately chimed in with concerns about how the proposed rule could impact transmission systems that traverse vast expanses.

"The installation of monitoring equipment on a single line may cost over $1 million depending on the terrain, length of line, and specific line characteristics," the Bonneville Power Administration said. "Bonneville operates 15,000 circuit miles."

Similarly, WAPA said it "does not believe there are significant benefits to the majority of WAPA's customers associated with the use of AAR on non-congested paths." Rather than requiring AARs for all transmission lines, WAPA said FERC should explore using emergency line ratings to clear congestion on short-duration transmission paths.

EDF Renewables urged FERC to harmonize its line rating proposal with a separate rulemaking (RM20-10) on transmission incentives. Glick, who partially dissented from the incentive rulemaking as a commissioner, has said he wants the final rule to include better incentives for transmission lines pursuant to state and federal public policies.

"The commission has the opportunity to create an integrated transmission policy that combines both regulatory requirements and economic incentives," EDF said.