Further experience with the measurement of dielectric anomalies in field aged XLPE cables

In a paper by Y.P. Aksenov et al. (see 1994 Symposium on Electrical Insulation, p.89-94), methods were described for evaluating the insulation of service aged XLPE cable. These consist of measuring the magnitude and location of anomalies in cable surge impedance which result from the application of various conditioning voltages, as well as the magnitude and location of PD sites. The new work described here concerns the selection of conditioning voltage levels which do not accelerate the failure of aged cable, and in addition the new instrumentation and high voltage test equipment which has been developed. Using the revised conditioning voltage levels, and the new test equipment, measurements have been made on installed cable of at least 20 years of age. Subsequently, 60 Hz breakdown tests, followed by dissections have been carried out on some of the cable, and the available results are included in the paper.