By Michael Brooks

WASHINGTON — FERC staff last week held a technical conference to receive input from RTO officials and stakeholders on dynamic and ambient-adjusted line ratings, including whether and how the commission should require transmission owners to implement them (AD19-15).

Much of the two-day conference held at FERC headquarters focused on the current limited use of the practices on the grid, the different kinds of devices and how RTOs accommodate them. But staff — and Commissioner Richard Glick, who attended parts of the conference each day — received plenty of advice, with some urging a requirement for TOs to use ambient-adjusted ratings (AARs), and others stressing caution against a one-size-fits-all approach. Others urged the commission to force TOs to disclose how they calculate their ratings.

All seemed to agree, however, about the potential benefits of dynamic line rating (DLR) technology.

“If this country is going to meet its numerous clean energy targets established by numerous states and corporations, we’re going to need a more vibrant transmission system,” Glick said in opening the conference Sept. 10. “And part of that is we’re going to need more transmission capacity. But it also means using our existing system more efficiently. … Certainly, this commission needs to consider whether there are alternative mechanisms for establishing line ratings … that can squeeze more out of the transmission system without impairing reliability.”

A transmission line’s rating determines how much electricity can flow through it. TOs provide their line ratings to their RTOs/ISOs. Most are static — rarely changing throughout the line’s lifetime — and very conservative, often based on worst-case scenarios: high temperatures, cloudless days and minimal wind.

Some TOs use seasonal ratings, allowing for more power flow in the winter months — though a TO’s definition of “winter” can vary, with some increasing the rating beginning in October and maintaining it all the way into April. As one panelist noted, April temperatures are quite different from those in January.

AARs, which change every so often (the frequency can vary from as high as every 15 minutes to daily) based on temperature forecasts, are widely used in PJM and ERCOT, and see limited use in MISO and SPP. Rarer still are dynamic line rating (DLR) devices, some of which can take into account not only temperature, but humidity, wind speed, sunlight and precipitation; others simply measure the sag of a line and adjust its rating accordingly.

Many TO representatives who spoke at the conference were positive about the technology, pointing to specific experiences their companies have had in using certain devices. But they cautioned against a hard rule from FERC for widespread implementation.

“At a high level, the concept of AARs sounds appealing and relatively simple: adjust line ratings based upon current or near-term environmental conditions (ambient temperature and sometimes wind velocity) to increase the efficiency of energy flow on the bulk electric system,” Dennis Kramer, senior director of transmission policy for Ameren, said on behalf of MISO’s TOs. “The broad implementation of AARs, however, is not simple and could be very complex with impacts on multiple existing processes and procedures, as well as requiring creation of entirely new policies, requirements, obligations and capabilities.”

“Individual transmission owners should be given an opportunity to determine whether implementing AAR on a particular transmission line would be beneficial to the transmission system in either alleviating congestion or enhancing the reliability of the transmission system,” said Rikin Shah, principal engineer for PacifiCorp. “Requiring the transmission owners to implement AARs on every single transmission line may result in unnecessary capital investment without the return that was expected and put additional burden on consumer rates.”

Carlos Casablanca, director of advanced transmission studies and technology for American Electric Power — which he said has been using AARs for more than 10 years in several RTOs — encouraged FERC to require TOs to use the technology on most of their lines, as they “can increase the value of a robust transmission system to the benefit of our customers and bring flexibility to the transmission operations environment.”

But even he said that not all lines would benefit from their use. “We have some assets that are over 100 years old in some regions. … We don’t think it may be safe or prudent to apply [AARs] to those facilities.”

Joe Bowring, PJM’s Independent Market Monitor, said not requiring TOs to use AARs “is akin to saying, ‘You have your ratings wrong most of the time.’ … PJM real-time prices are calculated every five minutes. The system operates in real time. There’s no reason for line ratings to be the same [every] season, at all hours of the day.”

Transparency Concerns

But regardless of the TO and their position on AARs or DLRs, line rating practices vary dramatically. As multiple speakers pointed out, for example, there is no uniform methodology for calculating static line ratings — and no requirement for TOs to explain how they calculate them.

Advocates for FERC stepping in seized upon those differences in making their case.

“The same facilities should have the same ratings under the same operating conditions regardless of the transmission owner,” Bowring said. “Transmission owner discretion should be minimized or eliminated in line ratings.”

Speaking about MISO, Michael Chaisson of Potomac Economics, the RTO’s Monitor, echoed Bowring’s sentiments. He presented a histogram showing how many TOs used certain ratings in the winter for their 115-kV lines. “You can see it’s all over the map … but this isn’t even the worst of it,” he said. “This histogram actually proceeds several more pages off to the right with outliers. … You can’t effectively monitor without knowing the basis for the ratings.”

Michelle Pivach Bourg of Entergy Services pushed back, pointing to NERC Reliability Standard FAC-008-3’s requirement that TOs make their methodologies for calculating ratings available to their RTOs and reliability coordinators upon request.

But RTOs don’t review the line ratings that TOs submit for accuracy, the Monitors said. Both Bowring and Chaisson said their respective RTOs monitor for abnormal ratings and only then request information from the TOs.

Bowring said to Bourg, “I never said that the information was not available to the RTOs. I said they don’t actually do the review. There’s a difference.”

“I think the key phrase is ‘upon request,’” Chaisson said. “What we’re seeing in practice at MISO is that they don’t have a comprehensive folder with all these methodologies stored, and they don’t have a comprehensive database with the limiting elements. … All they have are the ratings the TOs gave them and the ability to ask about particular ones, which they do from time to time.”

Bowring also recommended that the commission require TOs to “at least engage in” pilot programs for DLR technology, not necessarily to permanently install the devices, “but to get the data.”

“There’s been a lot of talk about ‘smart grids,’” he said. “This seems to me one of the basic elements of what a smart grid would be. You can’t be smart without information.”

Adam Rousselle Sr., president of Alternative Transmission Inc., agreed. “What we’re seeing is the advent of great new information, and we’re asking questions about how to integrate it with a system designed not to have it. … I think we have to have the data, and after we have it, we’ll have better opportunities to steer.”

Rousselle advocated for “a broad, systemwide and immediate evaluation of every bulk electric transmission circuit’s facility rating. … If you put a blood-pressure cuff on every circuit … there would be no doubt at what the rating was.”

Mike Kormos, senior vice president of transmission and compliance for Exelon, balked at these suggestions. “I’d be happy for that rate base,” he joked. “I think it’s a real waste of money.

“Please recognize that the vast amount of line ratings on the system have no impact. Those lines are not overloaded; those lines do not go into congestion,” said Kormos, a former PJM executive. “For those lines that are in routine congestion or extreme congestion, even for a short period of time, I can assure you that the first question asked is, ‘Are the ratings right?’ … When I was at PJM, I asked, and now that I’m with Exelon, I will provide.”