Effect of temperature on space charge characteristics in epoxy resin

Epoxy resin has been widely used as the dry-type insulation in high voltage direct current bushing. The temperature of the central conductor can go up to 90-105°C when working at the rated power flow. Thus, the inner insulation made of epoxy resin sustains these high temperatures. In order to study the effect of temperature on the dielectric performance, the space charge characteristics of epoxy resin at different temperatures (21, 40, 60, 80 and 100°C) have been studied with an improved pulsed electro-acoustic set-up. Moreover, the temperature dependence of the volume resistivity has also been measured. Only homocharge close to the electrodes can be found in all tests. The higher the temperature, the more serious the electric field distortion is in the bulk of a sample. The threshold for space charge accumulation decreases remarkably with increasing temperature. Both the apparent trap-controlled charge mobility and the dc conductivity show similar positive temperature dependence, which increases with the elevation of temperature, resulting in different charge decay characteristics at different temperatures. The apparent trap depths corresponding to different temperatures have also been obtained.