Condition assessment of extruded underground residential distribution cables after four decades of service

Many power cables with extruded insulation installed in the 1970s are approaching the end of their manufacturer´s design life. Cable replacement strategies based solely on cable age, insulation type, and average failure rates seem inadequate given shrinking capital and maintenance budgets, on the one hand, and a greater demand for improved reliability, on the other hand. This is particularly challenging in the management of an aging population of extruded cables in underground residential distribution (URD) systems. A condition-based cable management program has been developed to replace cables only where needed and to closely monitor cables remaining in service. The program relies on off-line partial discharge (PD) technology to assess the condition of extruded URD cables that have been in service for as long as 40 years. Cables are selected for PD measurement based on historical performance and vintage. The test results are used to assist in making asset management decisions such as replacement, repair, and rejuvenation. This paper describes the URD cable condition assessment program and presents the results from a pilot program conducted on an URD primary distribution system serving a number of densely populated neighborhoods in a suburban area of Metropolitan New York. It also discusses the challenges encountered and measures developed to overcome them during the pilot program.