Electrical Tree in HTV Silicone Rubber With Temperature Gradient Under Repetitive Pulse Voltage.

High temperature vulcanized silicone rubber (HTV SIR) is important insulation for high voltage direct current (HVDC) cable accessories. The pulse voltage in the HVDC system may initiate an electrical tree in SIR insulation. During the operation, there is a temperature gradient in SIR caused by the different temperatures of conductor and external environment. So it is necessary to research the electrical tree initiated by pulse voltage under the temperature gradient. In this paper, electrical trees in SIR with different temperature gradients were recorded. The inception voltage, tree length, and accumulated damage (AD) distribution were analyzed. The experiment results indicate that tree inception voltage decreases with the increase of temperature of the ground electrode when the needle temperature is 90 degrees C, it also decreases with the increase of needle temperature when the ground temperature is 90 degrees C. All the trees are in bush structure when the ground temperature is 90 degrees C, the structure changes from branch to bush with the increase of ground temperature when the needle temperature is 90 degrees C. When the needle temperature is 90 degrees C, AD distribution changes obviously with the increase of ground temperature. The conductivity of SIR under different temperatures and electric fields was tested. The effect of changing conductivity on tree inception was discussed. Surface potential decay (SPD) at different temperatures was tested. The trap characteristics and charge kinetic properties influenced by temperature may be the main reasons for the change of tree structures in the growth process.