Investigation of the performance of field aged HMWPE and XLPE cables

A field-aged, cable AC breakdown program was performed to assist in the management of Pacific Gas and Electric Company´s underground assets. The performance of cross-linked polyethylene, XLPE, and high-molecular weight polyethylene insulation, HMWPE was determined and fitted inverse power curves for both insulation types predict AC breakdown strengths in excess of operating stress at thirty years life. Testing entire runs of field-aged cables showed that an AC breakdown test on a single section is most likely to produce the average and not the lowest value. The testing demonstrates that a better diagnostic is needed to help prioritize cable replacement. Attempts to convert the field-aged XLPE and HMWPE cable AC breakdown data to single cumulative distribution functions were only successful for very limited cases. The field history could not be incorporated into the transformation. A replacement program based on one manufacturer´s distribution function whose cables were the oldest submitted for test and failed the earliest would be very conservative.