Power line test bed energizes technologies for increasing grid capacity

As population growth and extreme temperatures strain the United States power grid, utilities and equipment manufacturers are looking for ways to increase the amount of electricity the grid can carry. The Powerline Conductor Accelerated Testing Facility, or PCAT, located at the Department of Energy’s Oak Ridge National Laboratory, is one of the only facilities in the country where companies can try out new transmission line technologies for long time periods in extremes of wind, weather, temperature and electrical load conditions.

 “We’re looking at the impact of new materials, advanced coatings, coating methods and integrated features, to understand how they compare to existing technology,” said ORNL’s Brian Rowden, PCAT manager. The research generally has some combination of three goals: increase the amount of current the line can handle, increase the operating lifetime, and reduce the operating temperature through materials and design choices.

PCAT is a test bed consisting of isolated power transmission lines mounted in spans across three towers and monitored by a suite of sensors. Testing is funded by users or through federally funded collaborations. The outdoor lab is used to monitor the performance of new conductor materials, sensors and controls, as well as coatings.

Recently, PCAT was used for extended testing of a robot-applied coating called E3X, invented and patented by Prysmian, a multinational cable manufacturing company. On a baking hot summer day – the kind that can reduce the current that power lines carry or cause them to sag dangerously close to trees -- technicians hauled the robot skyward in a bucket truck. Resembling an oblong, open box of metal tubes twined with colorful wires, the robot dispensed the coating as it traversed the power line.

The product reduces the amount of heat retained in the cable. This allows the existing power line to carry more current, essentially increasing its capacity without replacing the line, said Joe Coffey, director of overhead transmission for Prysmian. To measure the potential improvement, an uncoated power line was compared to a coated version as both endured the same loadings and weather conditions for almost six months.

The Prysmian coating had already been used on thousands of miles of new power lines after being applied in a factory, Coffey said. But the company, whose customers include utilities and renewable energy developers, wanted to learn whether the product would perform as effectively when applied by the robot as an upgrade to existing power lines.

“ORNL has a lab that simulates real world operation where we can get direct measurements of conductor operating conditions, unlike any other facility where you are doing smaller-scale studies,” Coffey said. “ORNL can load the lines to simulate emergency conditions that are rarely seen in actual utility operations, so we’re planning and testing for the worst case.”

Prysmian began utilizing PCAT for joint studies with ORNL in 2015. “Oak Ridge has been a partner in validating the first tests and providing important proof to help the industry get comfortable with advanced conductors,” Coffey said.

PCAT enabled Prysmian to test its coating performance after extensive mechanical cycling and high constant current loads while tracking the line temperature, ambient temperature and wind velocity. Power cycling tests showed the E3X coated line remained as much as 57 degrees Celsius cooler, allowing the same conductor to carry more current while also operating more efficiently.  

Cycling tests can mimic the effect of aging on the capacity of the line and the amount it sags, which can cause safety risks. These tests can help more accurately demonstrate how a technology will perform across a wide range of operating conditions.

“Being able to cycle current to achieve specific temperature extremes helps us see how the conductor resistance may change with the expansion and contraction of conductors, connectors and other components over time when they are hanging under tension from a tower at high elevation,” Rowden said. All these factors affect how much electricity the lines can transport.

This is especially important in regions where transmission capacity is already stretched to the limit as cities expand, homes switch from gas to electric heat and drivers switch to electric vehicles. Recent federal infrastructure and renewable energy incentives have driven demand for transmission lines to carry renewable energy from rural areas to distant cities, in a grid that was mostly created piecemeal by regional utilities serving local customers. Expanding transmission capacity in a century-old power system will be key to meeting U.S. carbon reduction goals for slowing climate change.

According to DOE, independent estimates indicate transmission systems will need to expand capacity 60% by 2030 and may need to triple capacity by 2050 to meet clean energy demands.

“In some cases, we need to push more power to the same location,” Rowden said. “In other areas, it’s about introducing new technology, like incorporating new solar and wind energy generation on existing networks. That really means we either need more conductors running through different areas, larger-sized conductors, or the ability to carry more current on the conductors we have today.”

PCAT testing not only enables technologies like the Prysmian coating but also the deployment of new conductor technologies such as various aluminum core shapes, novel aluminum alloys and carbon fiber to replace aluminum or steel cores. These innovations can also help reduce the amount of electricity lost during transmission. Such losses occur because all conductors present some resistance to energy flow. Pushing against this resistance converts some of the electric energy to heat, which is released. These losses can be limited by choosing the right materials and loads.

Using advanced conductors can increase physical transmission capacity from 1.5 times to 3 times what conventional conductors can carry, according to a recent DOE report. When combined with other solutions such as advanced power flow control, these technologies could unlock up to 50% more carrying capacity on the same lines.

The DOE Office of Electricity has provided funding support for advanced conductor testing at PCAT as part of ongoing efforts in advanced conductor research.

UT-Battelle manages ORNL for the Department of Energy’s Office of Science, the single largest supporter of basic research in the physical sciences in the United States. The Office of Science is working to address some of the most pressing challenges of our time. For more information, please visit energy.gov/science.