Lee Harrison, EPRIsolutions
A new "Transmission Line Life Extension" service offered by EPRIsolutions is designed to help utilities cope with increasing pressures to minimize operating costs, reduce capital spending, and maximize the use of existing facilities.
"By combining test data, performance indices, and the latest inspection technologies, we are able provide utilities a clear indication of the remaining service life of their most critical power lines," says Mark Ostendorp, the EPRIsolutions program manager. "This information often allows utilities to defer capital expenditures for line expansion or refurbishments, thereby saving millions of dollars. In several cases we have also been able to identify hidden capacity in existing transmission lines, and that has allowed our clients to increase revenues substantially."
As Ostendorp explains, when the EPRIsolutions' staff undertakes a trans-mission line life extension review, they evaluate the asset's performance history, work with the utility to identify critical components, and develop an appropriate condition assessment strategy. Following this phase, the EPRIsolutions team performs a comprehensive field inspection on selected groups of key components. This process allows utilities to define the "as-is" condition of the line.
Next, a limited but representative set of component samples is retrieved from the line for detailed laboratory evaluation using a variety of electrical, mechanical, and structural testing and methods. The resulting data is compared to similar data from power lines of equivalent age and similar characteristics to form a benchmark for developing a new inspection, maintenance, and refurbishment strategy for the line. At the same time, the performance history, outage records, inspection and test data are compared to an extensive set of system and component service-life expectancy charts that EPRIsolutions has developed for this service based on more than 30 years of testing, analysis, and research.
The results of this effort provide utilities with a comprehensive assessment of the asset, the expected service life remaining, and the associated risk for each critical component. In addition, the results highlight any "hidden" or "reserve" capacity that may lead to a higher utilization of the existing asset.
 Corrosion of steel strands in 65 yrs old ACSR conductor |
Although the transmission line life extension program is a recent addition to the portfolio of services offered by EPRIsolutions, the program has already proven effective.
In one recent application, a northeastern utility was considering refurbishing a 25-mile-long, single-circuit, 115-kV wood H-frame transmission line that was nearly 65 years old. While the performance of the line was generally acceptable, trends indicated reduced reliability, and the utility was not certain how long the line could be operated economically. Indeed, the utility was facing replacement of the phase conductors, static wires, insulation, attachment hardware, and re-conditioning of the support structures and crossarms. The total cost of work was estimated to be in excess of $7 million.
EPRIsolutions' program clearly identified insulation as the critical component, and it predicted a remaining service life of 15 years at a marginally higher but acceptable risk. By deferring capital expenses for 10 years, the utility expects to save $ 4,200,000.
In another application EPRIsolutions was asked to evaluate a 69-kV, 800-mile-long system that was nearly 55-year-old. The utility's primary concerns were the performance and remaining service life of the conductors and static wires, insulation, and hardware, and it wanted to use the results of the program to develop a strategy for refurbishing the line. The EPRIsolutions team identified the conductors as the critical components, and suggested work could be delayed for a period of five years, saving the utility in excess of $2,700,000 in finance charges. However, the team also showed that system ampacity ratings could be increased by 5%, which would markedly increase utility revenues.
EPRIsolutions is the premier engineering and consulting company created by EPRI to apply its expertise—and the latest technology—to help utilities meet the challenges of the competitive power marketplace.
Lee Harrison is a senior technical editor at EPRIsolutions.
For more information on the transmission line life extension program, please contact Mark Ostendorp, PhD, PE, Manager, EPRIsolutions, Inc., 100 Research Drive, Haslet, TX, 76052, (817) 439-5900/Tel; (817) 439-1001/Fax; mostendo@eprisolutions.com.
