Formation mechanism of space charge in silicone rubber insulation under low DC stress

The study of production, transfer and accumulation of space charge in silicon rubber (SIR) under direct current (DC) is significant for the research of new high voltage (HV) DC cable accessories and the accessories´ stable operation. In this paper, based on SIR materials used for cable accessories and the actual low working stress, the accumulation of space charges in SIR was measured under low DC stresses (6-15kV/mm), different temperatures (room temperature and the 40? temperature difference) and different applied voltage patterns (independent voltage and stepped voltage). The results show that the major polarization type in SIR is the dipole´s steering polarization when the voltage is applied. Moreover the higher the applied stress the stronger the dipole´s polarization. As a result, the amount of charges near the electrode is reduced. Besides, the form of injection channel under the step voltage indicates the presence of large numbers of deep traps in SIR, the deep traps are easy to trap charges and to form conductive channels. The channels are helpful for migration and dissipation of local injected charges. In addition, Temperature gradient facilitates to enhance charge injection from high temperature electrode, weaken dipole moment and lead to more injected charges in SIR bulk.