Modernizing the Nation’s Electric Power System with Dynamic Line Rating Technology
“Smartening up” our power grid by replacing the old parts with new, innovative equipment and, most importantly, installing much-needed computer controls and software will guard against power outages and provide higher reliability, greater national security, lower costs, and reduced foreign dependency.
The U.S. power grid, the interconnected system of electricity production and use, is made up of an aging infrastructure with reliability and cost effectiveness issues that have serious implications for the economy and national security. Bringing the power grid up to 21st century “smart grid” standards requires use of sensors, two-way communications, and computer software to better monitor, control, and protect the electric power system—all part of a technology approach known as Dynamic Line Rating (DLR).
The National Energy Technology Laboratory (NETL) is working to create a more economic and secure power grid. Part of that effort involves management of 32 separate Smart Grid Demonstration projects worth more than $770 million. The goal of the work is to help transition the Nation to a modern power system with greater efficiency, reduced cost, reduced emissions, and improved reliability.
There are seven principal characteristics for the “smart grid” or “modern grid” that researchers consider essential in modernization efforts. The new “smart grid” must:
Be self-healing from power disturbance events
Enable active participation by consumers in demand response
Operate resiliently against physical and cyber attack
Provide power quality for 21st century needs
Accommodate all generation and storage options
Enable new products, services, and markets
Optimize assets and operating efficiently
The condition of the grid has serious implications for the U.S. economy and national security.
To maximize those characteristics, researchers are working on a range of issues to incorporate renewable energy, energy storage, various types of distributed generation, and consumer devices capable of responding to price signals.
Much of the transition to a modern grid is occurring within the distribution and consumer systems, but several important modernization deployments are occurring within the transmission system. Because the efficient incorporation of smart sensors, two-way communications, and controls can enable more automation and better management by operators of the transmission system, some of NETL’s work on the grid upgrade is centered on DLR technology.
Improving Electric Transmission with DLR
DLR technology can help power companies improve power transmission. The technology takes into consideration a range of factors that affect transmission lines and enable operators to improve their ability to make important service decisions. For example, electric transmission lines are constrained by capacity—the upper limit of power that the line’s conductors can carry without violating safety codes, damaging the conductors, and threatening grid reliability. Capacity decreases when conductor temperatures increase from line current, warmer temperatures, increased solar radiation, or decreased wind speed. In addition, as the conductor temperatures increase, they elongate and sag, decreasing the clearance between the conductors and the ground, threatening trees, buildings, or other electric power components.
When capacity decreases, transmission congestion is more likely to occur and power customers may experience price increases for the cost of power delivery in the form of “congestion charges.” In 2010, transmission bottlenecks cost New York State consumers about $1 billion.
Currently, transmission operators are able to measure real-time load, but they have limited ability to measure the real-time capacity of their system. As utilities face increased congestion, higher power costs, and concerns with reliability, DLR technology presents a way for operators to address those issues by adjusting transmission capacity in real time.
DLR technology deploys weather sensors to detect and record wind speed, ambient temperature, and solar radiation along with sensors for conductor temperature and line tension or sag. New communication technologies can transfer that data to specially developed DLR software, which is then used to determine the real-time capacity of the transmission lines. Consequently, transmission operators can make better informed operational decisions that increase reliability and reduce the threat of higher costs.
Texas Smart Grid Demonstration Project Shows DLR Commercial Viability
NETL, on behalf of the Energy Department’s Office of Electricity Delivery and Energy Reliability, manages a portfolio of 16 Smart Grid regional demonstration projects and 16 utility-scale energy storage projects. One of the utility-scale energy storage projects that highlights DLR potential was with Oncor Electric Delivery Company of Texas. That project successfully demonstrated that a fully integrated DLR system can work on a commercial scale and increase grid capacity and reliability while reducing the cost of electricity.
A dynamic line rating system gives operators an accurate, in-the-moment measurement of how much power
a line may safely carry. (Image courtesy of Oncor Electric Delivery Company)
The Oncor DLR system monitored the real-time capacities of eight transmission lines in daily operation for both a transmission owner and the independent system operator, the Electric Reliability Council of Texas (ERCOT). With an overall project budget for the project of more than $7.3 million including a DOE contribution of $3.5 million, the NETL–Oncor demonstration project mitigated congestion, led to strategies for better capital spending, and showed that installing DLR systems is often more economical than other transmission congestion solutions.
Oncor deployed Nexans’ CAT-1 System to measure conductor tension and sensors to measure net radiation temperature. Two additional DLR technologies were installed for validation and verification testing as part of the project: EDM International Inc.’s Video Sagometer system, which measures conductor sag, and Promethean Devices’ Real-Time Transmission Line Monitoring System, which measures conductor clearance.
But Oncor took additional innovative approaches to integrate DLR technologies. For example, the DLR data was fed directly into ERCOT’s dispatch tool for automatic use in real-time situations. In addition, Oncor built data validation tools into the DLR system to make sure that the ratings transmitted to ERCOT were accurate. If the ratings were invalid, the system could then default to the lines’ ambient temperature-adjusted ratings. As a result, ERCOT operators did not need to first determine the accuracy of the dynamic ratings or even whether to apply them in operations.
When the results were analyzed, Oncor determined that, for most transmission lines, the dynamic rating typically delivered increased real-time capacity— 6–14 percent greater than ambient-adjusted rating for 345 kV lines and 8–12 percent greater than ambient-adjusted rating for 138 kV lines. This additional capacity was available 84–91 percent of the time. The DLR system also was effective in regulating capacity on lines to ensure that other grid elements did not exceed physical operating limits.
The project paved the way for future DLR deployment and was recognized as one of two finalists in the Smart Grid category for the POWERGRID International Projects of the Year award. Based on success of the demonstration project, Oncor is investing in additional DLR systems to address capacity needs elsewhere in its service territory. Additional lines for DLR deployment are under assessment, based on planning needs and congestion exposure during the rest of 2013 and beyond.
NETL will continue efforts to improve the Nation’s power grid through a series of technology demonstration projects, like the DLR effort, that are aimed at improving reliability for a stronger economy and enhanced national security.