Dynamic Line Rating

Improving Energy Distribution Solutions

Grid transmission lines are given static ratings based on maximum ampacity and temperature limits. The weather conditions used by regulators in these methods are typically constant values year-round or with seasonal patterns and are set using conservative assumptions for the conditions. By not accounting for additional cooling during periods of high wind or low ambient temperature, there is likely unused head room on many overhead transmission lines.

What is a Dynamic Line Rating?

Dynamic Line Rating (DLR) is a changing transmission line rating based on local conditions rather than a static rating assumption and provides additional ampacity capacity to a transmission line. The U.S. Department of Energy has identified DLR as a transmission and distribution infrastructure solution to defer upgrades, support line outages and increase yields of distributed power. DLR is one of many solutions known as Grid Enhancing Technologies. Idaho National Laboratory is leading research and analysis on industry hardware and software DLR solutions. The conservative nature of transmission line standards and the regional transmission operators can be hard to adjust, so research showing the benefits of DLR is important to prove the benefits of the method.

How Does DLR work?

The ampacity of transmission lines is defined as the maximum amount of current the conductor can safely carry. Transmission line operators must apply ampacity limits due to the thermal properties of the conductor. Dynamic Line Rating (DLR) is a technology and technique that uses the environmental conditions or a set of the conditions to calculate the ampacity of the conductor. The way DLR is calculated has depended on some amount of physical technology to implement the solution.

Technical Articles and Papers

Electric Power Systems Research, 170, 326-337 (2019)

This study looks at forecasted dynamic line ratings in southern Idaho by using data from the high resolution rapid-refresh (HRRR) model for forecasted weather conditions.

IEEE Transactions on Power Delivery, 35(2), 745-753 (2019)

Dynamic line rating is a technology that allows for the rating of electrical conductors to be calculated based on local weather conditions rather than using “worst-case” assumptions of weather conditions.

IEEE Transactions on Power Delivery, 33(4), 1853-1863 (2018)

Most of the existing overhead transmission lines (TLs) are assigned a static rating by considering the conservative environmental conditions (e.g., high ambient temperature and low wind speed).

IEEE Transactions on Power Delivery, 34(6), 2100-2109 (2019)

Power flow, on both AC and DC overhead transmission lines, is limited to keep the conductor temperature below a maximum (TC

Study of Concurrent Cooling Effects for a Proposed Wind Farm (2021)

A report for the DOE Wind Energy Technology Office on the cost reducing outcomes of maximum wind farm power output coupled with additional convective cooling on the gen tie-line.

Grid Enhancing Technology Fact Sheets

Dynamic Line Rating Overview

The U.S. electrical grid includes about 7,000 operational power plants that send electricity over 642,000 miles of high-voltage transmission lines and 6.3 million miles of distribution lines.

Transmission Line Modeling Tool Suite

The more electric current an electric line carries, the hotter it gets. After a certain point, a line operator cannot add additional current without overheating and damaging the line.

A Novel Wind Atlas Modeling Method

Almost every country has created wind resource maps to find potential windy places suitable for building new wind plants.

General Line Ampacity State Solver (GLASS)

Wind power researchers at Idaho National Laboratory believe moving more electricity through existing transmission lines is both possible and practical.

Safe Integration of New Grid Technologies

Utility operators have a massive amount of information to monitor in a control room.

Conferences and Presentations

Computerized Wind Farm Generation … Footprint Routing and Subsequent DLR

Transmission lines are the backbone of the U.S. electrical grid. Due to increased penetration of renewable resources, there is an increasing need to connect the often remote resources to existing transmission line infrastructure. To view presentation, click here.

Using Dynamic Line Ratings for Wind Farm Gen-Tie Line Considerations

IEEE/CIGRE standards provide a base for overhead transmission line ratings.

Measuring many types of sensors could provide more capacity as a time varying capability.
Wide Area Weather-based DLR can provide a calculation of the moment-to-moment steady-state rating.

Forecasting Dynamic Line Rating with Spatial Variation Considerations

Dynamic Line Rating is a technology that allows the ampacity of an electrical conductor to be calculated using real-time or forecasted weather conditions. To view presentation, click here.

Sensitivity Effects of High Temperature Overhead Conductors to Line Rating Variables

For traditional overhead transmission lines, the maximum allowable conductor operating temperature on ASCR, AAC or AAAC lines for determining the static line ratings can be quite low, typically well under 100 Celsius. At these low temperatures, the primary driver for determining static line ratings are assumptions made about the wind speed and direction and the ambient temperature.

Contact Information

Jake Gentle

(208) 526-1753

Additional Links

Dynamic Line Rating might not be something that gets discussed around the dinner tables of America, but it could play a significant role in keeping the lights on and affordable.

Close to 70 people from the U.S. Department of Energy and the electrical utility industry came to Idaho Falls for a Dynamic Line Rating (DLR) workshop hosted Nov. 7-9 by Idaho National Laboratory. The workshop also provided a backdrop for the launch of a new industry group focused on upgrading the nation’s transmission network.

At issue was how to integrate new ideas and techniques into a grid that is changing for a number of reasons.

Wind power and other renewables, combined with changing consumption patterns and smart grid management, have opened up new possibilities to grid operators. In the past, transmission and distribution networks have been operated in a conservative fashion, resulting in a typical usage rate lower than the maximum transmission capacity. The more electric current a line carries, the hotter it gets and the more it sags. After a certain point, a line operator cannot add additional current without overheating and damaging the line. Planning has involved worst-case scenarios and static line ratings.

Taking wind and weather conditions into account, along with solid modeling and control approaches, DLR has shown potential to unlock latent network transmission capacity – a welcome development, as it typically takes five to 10 years to bring new transmission from the planning stage to construction and operation, costing millions of dollars of investment per mile.

To use dynamic line ratings, engineers need accurate real-time information about wind conditions and factors such as the line’s temperature and amount of current it’s carrying. That information then needs to be conveyed to utility operators in a way that enables them to quickly and safely adjust generation to meet load demands while operating within transmission safety limits.

Along with all the discussions of ampacity (the maximum amount of current a line can safely handle) and load at the INL workshop, financial considerations were never far from the presentations and panel discussions. For a utility to invest in new hardware and software, it has to make financial sense, said Mark Lancaster of Southwire, a large wire and cable manufacturer based in Carrollton, Georgia. “Utilities exist to make money for shareholders,” he said.

Cost, practicality and maintainability are the major factors in any line enhancement or upgrade, said Dave Angell of Idaho Power Co. Planning has to be long range. “Two years from now is already in the past,” he said. And rate pressure from customers and public utility regulators is always top of mind.

In addition to enhancing transmission line capacity, DLR has the potential to boost grid reliability and resiliency, said Charlton Clark, program manager for grid integration in DOE’s Wind Energy Technologies Office. While the concept has been around a long time, new developments in the speed of computation and communication have made DLR more feasible. Whether it’s incorporated into existing infrastructure or integrated into new transmission lines, “It’s a very inexpensive insurance policy,” he said.

Idaho Power has been working on DLR solutions with INL for nine years, and the utility now has roughly 450 miles of transmission line in two test beds set up to provide real-time weather information. This has been integrated with INL-developed software called General Line Ampacity State Solver (GLASS), a finalist for a 2017 R&D 100 Award.

The Java-based GLASS software dates back to around 2010, when INL researchers studying wind power plants noticed that transmission lines being cooled by the wind seemed able to handle more load. Using a commercial computational fluid dynamics (CFD) program, the team blended data from commercially available weather monitors and electric utility load data with CFD-enhanced weather analysis algorithms.

The commercial program developed by WindSim, a Norwegian company, was originally designed to optimize placement of wind turbines. While WindSim’s collaboration with INL has allowed the company to broaden its solutions, the current challenge is “de-risking the path to market and deployment,” said Catherine Meissner, the company’s software development manager and a panelist at the DLR workshop.

The biggest challenge could be creating vision in the industry, Southwire’s Lancaster said. “(Without) that, there is no market for DLR equipment. You really need a product line and help educating utilities. The value is not in how much or even what you know, but in how you use it.”

The INL-hosted workshop also provided the occasion to launch Working for Advanced Transmission Technology (WATT), a coalition of representatives from technology companies that have developed tools and processes to make the grid more reliable, flexible and cost-effective.

“The question is whether we can put the right incentives in place so that utilities who deploy them will share in the rewards,” said Todd Ryan, director of regulatory affairs at Smart Wires and chairman of the coalition. WATT’s goal is to promote the deployment of advanced power flow control, dynamic line ratings, topology optimization and other technologies with the potential to deliver more energy to customers over existing grids.

“We’ve been encouraged by the support from regulators, grid operators and transmission owners,” said Hudson Gilmer, vice president of Genscape and the coalition’s chair-elect. “We see an important role for WATT to engage these groups and inform them about the compelling benefits of advanced transmission technologies.”

Posted Dec. 6, 2017

By Paul Menser for INL Public Affairs and Strategic Initiatives

Tagged Feature Story

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