Space charge behavior of epoxy resin at high temperature

Epoxy resin has been widely used in dry-type insulation application, such as dry-type bushings. This study focuses on the temperature effect on the space charge characteristics and dielectric properties of epoxy resin. The space charge distribution measurement has been performed at different electric fields and temperatures by the PEA method, ranging from 2kV/mm to 60kV/mm at 291K, 313K and 343K respectively. The dielectric parameters including relative permittivity, dielectric loss factor, have also been measured in the frequency range 10^-1Hz~10⁶Hz at temperatures from 173K to 473K. The a-relaxation in the high temperature region and the weaker ß-relaxation in the low temperature region can be detected. Both temperature dependence of the a-relaxation rate and the dc conductivity show the Vogel-Fulcher-Tammann law. The space charge measurement results show that the temperature plays an important role on the charge transport and storage in epoxy resin materials. The threshold for space charge accumulation decreases significantly with increasing temperature, while the amount of injected homocharge goes up. These results would be benefit for the structure optimization of bushings which is a critical component of the dry-type converter transformer used in the ultra-high voltage direct current power transmission system.