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Technology that uses data analytics to give real-time transmission capacity measurements could help bring more renewable generation online

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This item is part of the Data Analytics and Intelligence - November/December 2022 SPECIAL ISSUE, click here for more

Reaching President Biden’s goal of 100% carbon-pollution-free electricity by 2035 will require renewable generation to be deployed at an unprecedented rate, according to a study by the Department of Energy’s National Renewable Energy Laboratory.

It likely also will require transmission capacity to be increased at an unprecedented rate, as much of the renewable generation will be located in remote areas, meaning power from it will have to be transported to population centers.

Since planning, getting approval for, and building electric transmission infrastructure typically takes a long time, methods of increasing transmission capacity that minimize the amount of new infrastructure that will have to be constructed are going to be welcomed wherever they can be used.

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One such method is dynamic line rating (DLR), which uses analytics to crunch real-time data measurements of the state of a transmission line and the environment around it to determine how much power the line can safely handle at any given moment. Environmental measurements it uses include temperature; wind speed and direction; and solar radiation. It also takes into account such line conditions as tension or sag.

How DLR can boost renewable generation

The amount of power allowed to be sent over a transmission line typically is based on a static rating for the line that is calculated using standardized worst-case conditions. As a result, most transmission lines operate at less than their maximum capacity nearly all the time. Basing the amount of power allowed to be sent over a transmission line on the line’s DLR enables the line to be operated closer to its maximum capacity.

For example, a 2010 study by The Valley Group found that a 20-mile transmission line with a static line rating (SLR) of 787 amps based on conditions in the middle of a summer day (no wind and a temperature of 40 degrees Celsius) could handle 874 amps if the temperature dropped 10 degrees; 929 amps in the middle of the night; and 1,060 amps if the wind increased by a little more than 2 miles per hour from the northeast.

DLRs could increase the amount of renewable generation the grid can handle in two ways. One is by boosting the transmission capacity of the nation’s existing transmission infrastructure. The other is by reducing the amount of transmission infrastructure that needs to be constructed to connect renewable generation in rural areas to the grid, as this 2019 Business & Technology Advisory from the National Rural Electric Cooperative Association points out.

DLR deployments

One of the largest DLR deployments to date was in 2014 by Elia. The Belgium transmission system did the deployment to compensate for the loss of 3,000 MW of nuclear generating capacity due to technical issues. Elia deployed DLR on 35 lines and 167 devices to increase the amount of power it could import from other countries by 1,000 MW, or 30%, and to increase its system’s capacity to handle north-south power flows prior to its winter peak loads.

In the U.S., PPL Electric Utilities is testing DLR on three historically congested transmission lines in northeastern Pennsylvania. Grid operator PJM Interconnection said it has been using forecast and real-time thermal facility rating updates from the DLR systems for reliability and markets processes governing the lines since October 6.

National Grid said in October that it is installing DLR technology on power lines in western New York to increase their capacity and reduce curtailment of planned renewable generation projects. The company also is rolling out DLR in its home country, where it has launched a two-year trial of the technology on a 275kV circuit in the north of England.

Other GETs

DLR is one of several grid-enhancing technologies (GETs) being looked at as ways of boosting the grid’s ability to handle renewable generation. Two others are:

  • Topology optimization software, which automatically finds paths to route power around congested grid elements, much as the Waze app routes users around traffic jams.
  • Power flow controllers, which the DOE defines as “hardware and software used to push or pull power, helping to help balance overloaded lines and underutilized corridors within the transmission network” and likens to “traffic control for the transmission system.”

A 2021 study prepared by The Brattle Group for the WATT (Working for Advanced Transmission Technologies) Coalition found that using DLR in conjunction with the two other GETs mentioned above would more than double the amount of wind and solar generation based in Kansas and Oklahoma that could be integrated into the Southwest Power Pool grid by 2025. The study also found that the $90 million cost of implementing the GRTs would be paid back in less than a year and thereafter would cut power generation costs by about $175 million annually.

Regulatory take on DLR

DLR has caught the interest of the Federal Energy Regulatory Commission, but the agency so far has stopped short of mandating its use.

In its Order No. 881, issued late last year, FERC directed transmission operators to replace SLRs with ambient-adjusted ratings (AARs). These occupy a middle ground between SLRs and DLRs, as they involve measuring the conditions of transmission lines and their environment as frequently as every 15 minutes, but not continually in real time like DLRs do.

 A study by three Massachusetts Institute of Technology researchers that was released in July compared the three line rating methods on a simulated version of the Electric Reliability Council of Texas’ grid and found that replacing SLRs with DLRs could produce twice the benefits of replacing SLRs with AARs in terms of system costs, renewable curtailment and emissions.

In Order No. 881, FERC did require regional transmission organizations and independent system operators to establish and maintain systems and procedures for facilitating the use of DLRs by transmission owners.

In February, FERC issued a notice of inquiry to examine DLR use. Generally, the utility industry filed comments saying it wasn’t necessary and shouldn’t be mandated, while smart grid and renewable energy trade groups were supported it.

For example, the Edison Electric Institute, which represents investor-owned utilities, said, “FERC should not mandate the use of DLRs due to the need for flexibility, operational differences between transmission systems, and the need to gain experience with AAR implementation.”

Meanwhile, in their comments, the WATT Coalition and three clean power groups said FERC should implement DLRs because doing so would reduce congestion costs; enable more renewable generation to be connected to the grid; and reduce renewable generation curtailment.

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