Influence of Frequency on Tree Initiation Voltage and Electrical Tree Shape in Silicone Rubber

To investigate the influence of frequency on the electrical tree characteristics and the damage mechanism of such insulation,the characteristics of electrical tree in silicone rubber under AC voltage of different frequency ranging from 50 Hz to 130 kHz were studied.The tree initiation voltage was measured at room-temperature and the processes of electrical tree were observed via a digital micro-observing system.From the experiments,it is found that the electrical tree in silicone rubber is greatly affected by the frequency of applied voltage.With the increase of frequency,tree initiation voltage of silicone rubber decreases.And the frequency can be separated into four stages,while tree initiation voltage appears different magnitude of decrease.There are 3 kinds of electrical tree during the experiments: branch tree,trunk tree and pine tree.The branch tree and pine tree are the primary shapes in the range of low frequency,while the bush tree is the primary shape in the range of HF.The dielectric spectroscopy of silicone rubber was also measured.At last,the influence of frequency on electrical tree in silicone rubber was analyzed.The repeated electro-mechanical stresses applied to the needle tip under high frequency may lead to the decrease of tree initiation voltage of silicone rubber.And with the increase of frequency,the serious erosion in silicone rubber by electrical tree may be caused by the great increase of dielectric losses.