Researchers with the U.S. Army Engineer Research and Development Center’s Cold Regions Research and Engineering Laboratory in Hanover, New Hampshire, are working with a power company to learn more about icing on high-voltage electric power transmission lines.
During winter ice storms, power lines become covered with ice, which can result in higher tension in the wires and greater stress in the support structures from the increased weight. In remote areas it can be difficult for line crews to get to and repair damaged lines. These transmission lines carry power from generators to the substations that provide power to distribution lines in cities and towns.
"This research helps provide engineers and utilities with information they need to design power transmission lines for the level of risk they are willing to assume," said Kathy Jones, a CRREL research physical scientist. "For example, they might design a crucial line that proves power to a population center for a 400-year mean recurrence interval, and design another line in a system with more redundancy for a 100-year mean recurrence interval."
Jones, along with CRREL's Chris Williams, an electronics engineer, and John Gagnon, a civil engineering technician with expertise in the use of web cameras for research, are working together to provide American Electric Power data on icing conditions at high elevations in their service area near Roanoke, Virginia.
"We are looking at icing from super-cooled clouds, like occurs frequently on Mount Washington," said Jones, who has worked on Mount Washington measuring the properties of supercooled clouds. "For this project, we are monitoring three sites where AEP has had problems with high ice loads in the past."
Initially a five-year program, the data collection has been extended an additional two years. The researchers continue to remotely monitor icing, using web cameras to capture images of the ice-covered conductors and weather instruments to measure the conditions during icing. Images are captured every hour, from 8 a.m. to 5 p.m., during the cold weather months, at the three summit locations (at elevations between 3,400 and 4,200 feet) near the West Virginia border. Information is automatically transmitted to CRREL in New Hampshire where the data are saved and analyzed.
At each of the three sites are a CRREL-developed data acquisition system, web camera, and solar panels, mounted on one of the lattice towers of the transmission line.
"The off-the-shelf electronic components that comprise the data acquisition system are housed in a 14- by 12-inch fiberglass box," said Williams. "This system monitors the lines by taking and transmitting meteorological data – temperature, relative humidity, and wind speed and direction. The web cameras provide a visual of the ice accumulation on the conductors. The data acquisition systems and web cameras run autonomously powered by solar panels that keep the batteries charged."
"The web cameras are designed to be used in temperatures that range down to minus 40 degrees Fahrenheit," said Gagnon. "The web cameras we are using at the three sites are in enclosures to protect them from the weather, with a window heater to clear ice from the window in front of the camera lens."
According to Jones, the monitoring locations were chosen by AEP based on their experience with severe icing events at those locations.
Unbeknownst to Jones, AEP had been having a sort of turf-war with the local ravens. AEP had even called in raven experts to better understand how to deal with them. Late in the summer of 2012, ravens had attacked the solar panel and the wiring to the batteries, so the site had no power when the storm hit, and unfortunately was unable to collect data during the ice storm.
Setting up and maintaining the monitoring system calls for specially trained line crews.
"Chris works closely with the AEP line crews," said Jones. "Working high above ground on a lattice tower is difficult, so Chris designed the system to make installation, trouble shooting, and repairs as easy as possible for them."
This research provides real-world data for comparison to simulations of in-cloud icing from historical weather data or from simulations using the Weather Research and Forecasting Model, a weather prediction system designed for both atmospheric research and operational forecasting needs.
Learn more about the Weather Research and Forecasting Model at http://www.wrf-model.org/index.php.