Extending the Service Life of 15KV Polyethylene URD Cable Using Silicone Liquid

In the late 1960's and early 1970's many electric utilities installed URD HMWPE and XLPE cable throughout their service territories. Within ten years, many utilities began to experience decreased service reliability and a major cause of the increased interruptions was failure of the URD cable. As early as the late 1970's, Orange and Rockland Utilities became interested in rehabilitating URD cable since there appeared to be an extensive economic advantage over direct replacement of the failing URD cable. Early in the 1980's, Orange and Rockland Utilities, in cooperation with the Empire State Electric Energy Research Corp., Inc. (ESEERCO), demonstrated the restoration of URD cables which contained electrochemical trees in the cable insulation of sufficient severity to cause extensive service failures. The ESEERCO project essentially removed the moisture in the cable by pushing nitrogen gas through the cable interstices until it was dried, and then impregnated the same cable with liquid acetophenone in order to restore the dielectric strength of the cable. While this method worked well, and to date no failures of the treated cable have occurred, the liquid had limitations since it changed its liquid state at lower temperatures. In addition, perpetual maintenance of the treated cable was required. Thus, a substrate liquid was pursued. Orange and Rockland Utilities sought an improved liquid to rehabilitate failing HMWPE and XLPE cables and Dow Corning Corp. developed a specific silicone fluid.     

Application of high resolution radar to provide non-destructivetest techniques for locating URD cable faults and splices

A nondestructive, high resolution radar system that precisely locates URD power cable faults and splices has been developed. High resistance faults are identified without thumping via a low energy, battery-powered snapshot unit. Only enough DC voltage to initiate and maintain one flashover at the fault is applied; the duration is limited to four milliseconds. Pinpointing the fault or splice is accomplished by detecting the radar signal above ground. When the antenna is directly over the fault or splice, the location is confirmed. The ability to receive the signal from the cable makes the pinpointing step independent of cable propagation velocity     

Extending the service life of 15 kV polyethylene URD cable usingsilicone liquid

The authors describe methods and materials used to extend the useful life of extruded polyethylene insulated cables rated at 15 kV that have developed electrochemical trees in the insulation of sufficient severity to cause service failures. Earlier rehabilitation methods treated extruded dielectric cables with both gases and insulating liquids. This new method fills the cable and impregnates the insulation with a silicone liquid. This liquid, which is reactive, significantly improves the voltage breakdown strength of the cables, which had been reduced by electrochemical trees, and extends the useful service life of the cable. A review of the criteria used to develop the silicone liquid for this application and the methodology used to inject it into the cable are presented. An assessment of the costs for this life extension indicates a significantly lower cost than conventional cable replacement with little disturbance to the service and property of the customer