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Technology that can boost transmission capacity gaining foothold in US

image credit: © LineVision
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  • Aug 5, 2021
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A relatively new way to increase the amount of power that transmission lines can handle is increasingly being tried out in the U.S., in at least one case with good results.

 

At least three pilot programs of dynamic line rating have been announced this year — one by PPL Electric Utilities; one by the New York Power Association; and one by the company supplying DLR technology to the Sacramento Municipal Utility District.

 

PPL said in April that it had installed sensors that enabled it to use DLR on two transmission lines last winter in partnership with PJM Interconnection. The NYPA announced in June that it had installed weather sensors that would enable DLR in 10 locations on its Moses-Willis-Plattsburgh transmission lines. Also in June, LineVision said its monitoring system will be installed on power lines in the greater Sacramento region for SMUD. (A component of LineVision's system is shown above.)

 

If it lives up to its promise and becomes widely used, DLR could reduce the amount of transmission infrastructure that needs to be constructed to boost the grid’s reliability, resilience, and ability to deal with more renewable generation, all of which are needed to decarbonize the grid and increase its ability to stand up to the effects of climate change.

 

What DLR does

 

The amount of power that a transmission line can handle is limited by, among other things, how much the power causes the line to heat up. That, however, isn’t constant, because a transmission line likely will heat up more on a calm day than it will a windy one due to the cooling effect that wind can have on the line. 

 

Static line ratings don’t take that into account. As the Department of Energy so memorably put it in a June 2019 report to Congress about DLRs: “… static line ratings (SLRs) are usually calculated using conservative assumptions about the transmission-line operating environment, producing an inflexible constraint that does not take advantage of changing or favorable environmental conditions (e.g., wind cooling) that allow for greater transmission usage.”

 

DLR, the report said, helps transmission system operators determine how much power a transmission line can carry given the current conditions around it, thus allowing its operator to relax SLR-based constraints when the weather makes doing so feasible and safe.

 

Enabling DLR requires being able to accurately gauge in real-time the conditions of transmission lines and the environment around them. There are multiple ways of doing that, each of which, the DOE said in its report, “has advantages and disadvantages when it comes to accuracy, reliability, capital cost, ease of installation and integration, and maturity.”

 

As a result, the DOE concluded: “Despite DLR’s potential for realizing cost savings and its ability to increase grid reliability and resilience, several challenges remain that prevent its widespread adoption. Implementation of DLR must ensure that new hazards are not created and be tempered with consideration for other system limitations and the potential for unintended consequences.”

 

While the DOE’s cautions are correct, they make systems for implementing DLR sound more unproven than they are.

 

DLR users

 

Elia, the Elia Group subsidiary that operates the Belgian transmission grid, says on its website that it has been working with Ampacimon since 2008 to develop and test technology capable of measuring transmission line capacity based on historical data, weather measurements and forecasts.

 

Ampacimon, which describes itself as “the global leader in deployed dynamic line rating systems,” said in a slide deck that from April 2014 to December 2018, its observation system showed that DLR could enhance the capacity of Elia’s transmission system 98% of the time. On average, Ampacimon said, its system showed DLRs for Elia's transmission lines were 127-130% of the lines' nominal ratings; 90% of the time it showed they were 110%-116% of the lines' nominal ratings; and 95% of the time, it showed they were105-115% of the lines nominal ratings.

 

That would seem to indicate that DLR can be used to forestall the need for building new transmission infrastructure and PPL said its pilot showed that to be the case.

 

The company said the pilot in which it installed sensors on two transmission lines was meant to determine if the devices could help it better manage congestion and to provide PJM with real-time information to optimize the lines’ performance and help it make infrastructure investment decisions.

 

PPL called the pilot a success, saying that the data from the sensors enabled PJM to determine that PPL didn’t need to rebuild the lines or add new ones to manage congestion.

 

NYPA said its pilot will demonstrate the capabilities of the DLR technology developed by WindSim Power in a collaboration involving Idaho National Labs.

 

The results should be interesting because the weather in the northern New York state areas where the lines having sensors installed on them are located can change dramatically based on wind and light conditions.

 

“We will monitor real-time conditions, refine our forecasting and share our results,” said Chunchuan Xu, a senior engineer at NYPA.

 

WindSim’s DLR technology could enhance the transmission capability of selected transmission lines up to 60%, according to Alan Ettlinger, NYPA’s senior director of research, technology development, and innovation.

 

SMUD will use the LiDAR-powered monitoring system developed by LineVision in its pilot. The system uses sensors that collect real-time data on critical parameters of overhead power lines, such as line temperature, sag, horizontal motion, and anomalous motion and can be installed without having to de-energize lines or use live-line working techniques.

 

“This has the potential to help unlock additional capacity on SMUD’s existing transmission lines, allowing more renewable generation assets to be added to the grid,” said Frankie McDermott, SMUD’s chief operating officer.

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John Simonelli's picture
John Simonelli on Aug 15, 2021

I have said it before in several other mediums, DLR does a great job of increasing the thermal capability of transmission lines based on current ambient conditions. However, it does not address the current carrying limitations associated with other equipment most notably in the substations that may preclude the line from operating at higher ampacity. There's also concern in systems with voltage and/or transient stability limitations. DLR will not increase these limits and in fact loading lines heavier using DLR might aggravate the voltage and transient response of the system. So while DLR is a great tool to address straightforward thermal limitations, one needs an in-depth analysis of the system to ensure it can be operated at the higher capabilities and not "bump" into other system limitations.

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