By Amanda Durish Cook
MISO staff are considering how to respond to transmission owners’ adoption of dynamic line ratings, acknowledging that changes in systems and operations would likely be necessary with widespread use.
Acting on a recommendation from the RTO’s Independent Market Monitor, staff broached the topic with a presentation during a Dec. 13 conference call of the Market Subcommittee.
Operations engineering manager Jay Dondeti said MISO already allows TOs to submit dynamic line ratings, though most don’t. Dynamic line rating technology provides real-time data on environmental conditions near transmission lines, including ambient temperature, solar radiation and wind speed, allowing lines more capacity in cooler conditions.
Currently, TOs can provide line ratings to MISO through one of four ways: a seasonal ratings table with ratings for up to four seasons; a ratings lookup table based on temperatures; supplying specific ratings through the Inter-Control Center Communications Protocol; and submitting hourly and current day ratings through direct data files.
MISO staff and systems would not be able to process dynamic line ratings if every TO in its network decided to use them, and it’s unclear how much dynamic data the RTO can handle.
Widespread use is a long way off. Dondeti said about 93% of MISO TOs currently use seasonal ratings, with the “vast majority” of them providing ratings for two seasons, not four. He said less than 1% of line segments in the Midwest use some form of temperature-based ratings. In MISO South, however — where Entergy has adopted some temperature-based ratings using the filing approach — the percentage goes up to 5%.
Some stakeholders are echoing the Monitor’s calls to adopt dynamic line ratings. (See “Dynamic Line Ratings,” MISO Market Subcommittee Briefs: Oct. 11, 2018.)
“We see the transmission system as underutilized in the day-ahead and real-time markets because of static line ratings,” WEC Energy Group’s Chris Plante said.
Kevin Murray, representing the Coalition of MISO Transmission Customers, said dynamic line ratings might have helped the RTO mitigate some of its recent maximum generation events by transporting additional capacity stranded by static line ratings.
Entergy’s Mark McCulla said his company provides temperature-adjusted line ratings using historical and forecasted weather conditions near a facility to help increase the carrying capability of static line ratings. The company does not factor wind speeds into its more detailed ratings, instead using a 2-feet/second estimate. Entergy provides dynamic ratings to MISO on an hourly, daily and two-day-ahead basis.
“There can be a large swing in ambient temperatures in the Entergy region regardless of season. As a result, Entergy does not use seasonal ratings but instead uses the more granular temperature-adjusted ratings,” McCulla said.
Of Entergy’s more than 2,300 69-kV and above transmission facilities, 978 are in Entergy’s temperature-adjusted ratings database and 140 have short-term emergency ratings.
Entergy said it has experienced a 11% average increase over base facilities ratings when using temperature-adjusted ratings and a further 13% rating increase when coupled with short-term emergency ratings.
Plante asked if Entergy has experienced reliability risks since using the ratings. Entergy representatives said they have yet to experience an overload.
IMM staffer Michael Wander said the Monitor supports using temperature-adjusted ratings, saying MISO’s static line ratings are often conservative.
Wander agreed to appear at future MSC meetings to discuss the economic benefits of dynamic line ratings. He said the Monitor is not advocating a “one-size-fits-all” approach to ratings, but an RTO review process.
Dondeti said MISO will likely have to assess how it would handle the volume of ratings adjustments if dynamic line ratings become routine among TOs. He said it would need to figure out how often line ratings would be changed and how many staffers would need to process them.
RTO officials said they would report on the benefits and potential cost of processing dynamic line ratings in the first half of 2019. MSC Chair Megan Wisersky told stakeholders to expect discussion on the topic at upcoming subcommittee meetings.