Effect of temperature on space charge detrapping and periodic grounded DC tree in cross-linked polyethylene

In a high voltage direct current (HVDC) cross-linked polyethylene (XLPE) cable system, the temperature of the insulation varies with the load condition, which significantly influences the electrical performance of the XLPE. In this study, space charge detrapping and periodic grounded DC tree in XLPE are investigated and analyzed at various electric fields in a broad temperature range of 20-80 °C. Results reveal that with the increase in temperature, the apparent trap-controlled mobility of space charge becomes larger while its decay rate becomes smaller in the initial phases of depolarization. These findings indicate that charge detrapping becomes easier at higher temperature. The electrical tree initiation ratios, lengths, and widths all increase as temperature increases, except for the negative tree width under 16 kV at 80 °C. An increment in length and width of positive trees is observed at 80 °C. Electrical trees become thicker at higher temperature, and branches into the direction perpendicular to the applied electric field are observed at temperatures above 60 °C. Furthermore, the negative trees are easier to initiate and are thicker in shape than positive trees, and sometimes have an advantage over positive trees in length and width in the temperature range of 20-60 °C.