Trap features of retired high-voltage XLPE cable insulation material by thermally stimulated depolarization current

The properties of the crosslink polyethylene (XLPE) after laboratory accelerated aging and the materials from retired cables may have some difference for different ageing condition. Then, it is necessary to understand the insulation property of the high-voltage XLPE cable after operation. In this paper, a total of three high-voltage XLPE cables operated for different years were collected. Then, the cable insulation material was divided into inner, middle, and the outer layers. Trap features of the three layers were studied by using the thermally simulated depolarization current (TSDC). According to the results of TSDC experiment, the trap features such as trap depth, trap charge, and temperature of current peak were calculated. Experiment results showed that two current peaks existed at 190 K to 375 K; one peak showed β relaxation (low temperature) and the other showed α relaxation (high temperature) for the XLPE insulation material. Trap parameters of α relaxation showed that the middle layer samples had relatively low value of trap depth and trap charge, whereas the outer layer samples had the largest values of these parameters. The trap charge of the outer layer decreased with the service time of XLPE cables. However, the trap parameters of the inner and middle layers of the three cables were almost the same.