Research on the discharge characteristics of XLPE insulated DC cables

This paper focuses on the discharge of cross-linked polyethylene (XLPE) insulated DC cables, which has become a concern of power utilities when carrying out a voltage withstand test or an outage maintenance. Based on the electrical tree initiation test of XLPE block samples under grounded DC voltages, the main cause and key factors for damages of DC insulation resulted by grounding discharge were investigated, and the allowable voltage level to start the accelerated discharge operation was estimated. By the laboratory tests of two XLPE cable samples discharged under different conditions, the basic discharge rules were observed, the equivalent circuit was set up, and the equipment parameters were determined. In addition, a method to estimate the discharge time for cable lines with different lengths was proposed. Finally, the on-site measured data of decay voltage and leakage current were presented for a 200 kV DC XLPE cable line which had been discharged steppedly through a resistance grounding device after the DC voltage withstand test, and the experimental results were found to be in good agreement with the theoretical data.