Growth Characteristics of Electrical Tree in Silicone Rubber

Electrical tree in PE or XLPE cable,one of the electrical degradation phenomena,is considered an important reason for aging of the cable insulation.The cable accessories made of silicone rubber suffer from high intensity of electric field,therefore,it is necessary to investigate the tree growing chracteristics and mechanism in silicone rubber.In this study,silicone rubber for the stress cone was tested to investigate its electrical aging process.By applying DC and a series of AC voltages to the needle-plate electrodes,the growth characteristics and structures of electrical tree in the rubber were observed by a digital camera.Partial discharge appeared with the growth of electrical tree.The investigation shows that: the tree channel composed of silicone compounds in the rubber is non-conductive,which is quite different from the conductive or semi-conductive carbonized channel in PE and XLPE cables;the electrical tree’s growth rate and structure exhibit remarkable dependence upon the frequency,amplitude,and type of voltage applied,and the growth rate accelarates with increasing voltage frequency and amplitude.