New Techniques for Determining Condition of XLPE Cable Insulation from Polarization and Depolarization Current Measurements

This paper describes how a commercially available test set has been used to make preliminary determinations of condition of XLPE cable insulation at remote sites in NE Queensland. Polarization and depolarization currents are measured with an injection voltage of 5 kV with observed depolarisation period of 60 seconds. It is shown that misleading results may be obtained by this technique due to rapid drying out of cable insulation after removal of the cable 50 Hz normal supply and laboratory experiments to systematically examine this effect are reported. Procedures needed to obtain consistent field test results are recommended as are diagnostic criteria to provided an indication of cable insulation condition.. It is concluded that whilst the technique can provide evidence of poor insulation quality, it is not possible to distinguish between water trees in insulation and poor joint insulation; additional research work to solve this problem is suggested.