Effects of heavy load temperature rise on the dynamic charge transport characteristics of XLPE/SiR heterogeneous insulation

Abstract

The space charge accumulation in the heterogeneous insulation composed of cross-linked polyethylene (XLPE) cable and silicone rubber (SiR) accessory poses a serious threat to the safe operation of the high voltage direct current (HVDC) cable. When the cable is in heavy load, the charge transport behaviour in XLPE/SiR becomes more complicated due to the high temperature. In order to investigate the charge transport characteristics of XLPE/SiR under heavy load condition, the simultaneous measurement of space charge and relaxation current is performed on XLPE/SiR at both 70°C and 30°C with different polarities. The results show that the polarity of the interface charges in XLPE/SiR is always consistent with that of the SiR side electrode, and the influence of high temperature (70°C) caused by heavy load on the interface charge accumulation of XLPE/SiR is reversed at different polarities. The interface trap depth of XLPE/SiR is consistently greater than the bulk trap depths in both XLPE and SiR. When at high temperature of 70°C, the depth and density of interface traps increase, and the bulk traps in XLPE and SiR also exhibit increased depth. The component of polarisation relaxation current associated with space charge activity increases and exhibits longer decay time at 70°C, indicating more active and complex charge trapping-detrapping activities under heavy load condition. In this paper, an advanced simultaneous measurement is used to correlate the internal charge distribution with the external current for analysis, and the charge transport characteristics of XLPE/SiR under heavy load condition is revealed. The results can provide reference for the operation and maintenance of HVDC cable, and can also provide a basis for the space charge regulation of heterogeneous insulation at HVDC cable accessories.