Temperature gradient dependence on electrical tree in epoxy resin with harmonic superimposed DC voltage
Boxue Du, Meng Tian, J. G. Su, Tao Han
Abstract
Transient superimposed voltage, which is accompanied by a temperature gradient caused by Joule heat, can threaten the insulation safety of high-voltage direct current (HVDC) cable terminations. In this study, an electrical treeing experiment was conducted on epoxy resin with temperature gradient under harmonic superimposed DC voltage. The temperatures in the high voltage side and ground side were controlled by heaters within that maintained the range of 30 to 120 °C, while the DC voltage was ±12 kV. An isothermal surface potential decay (ISPD) experiment was used to obtain the trap level distribution. The effects of the temperature gradient and voltage polarity on the tree growth were depicted by the tree morphology, tree length and accumulated damage. The results show that the temperature gradient affects the tree structure and accelerates its growth. The tree growth rate has a nonlinear trend under an increased temperature in the high voltage side, and shows a steady increase under an increased temperature in the ground side. The positive voltage has a more obvious acceleration effect on the tree growth than the negative voltage does. A charge transport model is proposed to describe the tree behavior under a temperature gradient. The nature of the charge carrier accounts for the trap distribution and polarity effect. The local temperature rise and superimposed voltage pose a threat to the insulation safety, and more attention should be given to the operation of the electrical apparatus.