PJM Shares Progress on ‘Smart Grid’ Line-Rating Technology

FERC looks at best use of technologies that show how transmission lines’ capacity expands or contracts with changing conditions


As the Federal Energy Regulatory Commission (FERC) considers how to integrate dynamic line-rating technologies into the federal regulatory framework, PJM Interconnection staff shared research and insight to demonstrate how such technologies promote efficiency and save money.

Dynamic line-rating technologies have the potential to increase efficiency and reliability in the electrical grid by allowing operators to better understand how the capacity of transmission lines increases or decreases with changing conditions. FERC’s stated goal during a technical conference on Sept. 10–11 in Washington, D.C., was to explore which “transmission line rating and related practices might constitute best practices, and what, if any, Commission action in these areas might be appropriate.”

FERC is considering whether to require ambient-air ratings on transmission lines and/or whether to mandate grid operators to implement new software and communications capabilities to enable the sharing of more sophisticated dynamic line-rating data in real time.

Although ambient-air ratings for transmission have been utilized in PJM for years, the use of dynamic line ratings is a newer technology and was largely the focus of the conference.

Current Line-Rating Practices Predate Today’s Technology

Transmission owners have historically used line ratings to illustrate the current-carrying capacity of overhead wires.

These static line ratings dictate how much current a line would be permitted to carry under conservative worst-case scenarios. Those conservative scenarios can be extreme. One transmission owner’s ratings referenced by FERC were set under conditions of 104 degrees Fahrenheit on a clear day under noontime sun intensity – conditions which would likely limit a line’s carrying capacity. But if the wind is blowing, for example, it helps keep a line cool and prevents it from overheating. This cooling effect can raise the current-carrying capacity of a line.

One solution to more accurately model system conditions is to calculate ambient-air ratings, which account for projected or current real-time temperatures, resulting in a more frequent adjustment of ratings throughout the day.

Ambient-air-adjusted ratings are currently employed by PJM and ERCOT. When planning for demand for its Day-Ahead Energy Market, a PJM computer program estimates transmission line ratings based on temperature data received from local weather stations.

Dynamic line ratings would account for the actual condition of the line in real time, potentially offering even greater efficiency and reliability. Both ambient-air ratings and dynamic line ratings can reduce congestion by allowing dispatchers to see when lines have greater capacity due to current conditions.

In advance of this month’s technical conference, FERC staff issued a paper analyzing the potential of line-rating technologies.

Technology Changing Line-Rating Practices

Line-rating technologies vary in how they assess environmental conditions. In some instances, electronic sensors installed on lines, or nearby on the ground, measure temperature, wind speed, rain, line tension and more to calculate and communicate ever-changing line capabilities. In other methodologies, data about existing weather conditions is used remotely in calculations to arrive at a dynamic line rating for a particular line segment.

As noted by FERC, PJM already uses some limited temperature-modeling methodologies to promote market efficiency.

In many instances, dynamic line rates indicate capacity above a line’s static rating, PJM’s Shaun Murphy, senior business solution engineer – Market Services, stated in his written testimony for the FERC technical conference. Put another way, this technology holds the potential for a smarter grid that more accurately indicates a line’s ability to perform during real-time operating scenarios.

A representative from the PJM independent market monitor, Marketing Analytics, also testified at the technical conference. Dr. Joseph Bowring, president of Marketing Analytics, stressed the need for the information that dynamic line ratings could provide to the marketplace and argued against FERC providing any incentives for the deployment of this technology.

Great Potential, Standards Needed

Since 2016, PJM has played an important role in dynamic line rating research, participating in studies of the technology with the Oak Ridge National Laboratory and other industry partners. One finding among that body of research estimated savings of up to $4.2 million in annual transmission costs in one heavily congested area of the PJM footprint, Murphy said.

“PJM has demonstrated its support for field testing and piloting this technology and sees promise that the technology can help make real-time markets and operations more efficient and more optimally utilize existing transmission assets,” Murphy said.

Further exploration in two key areas is necessary before dynamic line-rating technologies can be fully used by grid operators, Murphy said.

  1. FERC is examining its incentive policies for building new transmission assets that include advanced technologies, but there is no clear focus on how to incentivize better use of existing assets with these technologies.
  • Through the North American Electric Reliability Corporation, the electric utility industry, as a whole, need a cohesive philosophy on developing static- and ambient-temperature-adjusted transmission line ratings that includes implementation guidelines and operating standards for dynamic line-rating technologies.

Some parties urged FERC to mandate the use of dynamic line ratings – or to at least impose standards for a uniform methodology for calculating existing static line ratings.

“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,” Bowring said.

FERC is recommending further study of highly congested transmission lines, which is similar to the work PJM has done.

“PJM looks forward to continued engagement with FERC and the industry on further development and use of ambient-temperature-adjusted facility ratings and dynamic line-rating technologies,” Murphy said.