Degradation induced by charge relaxation in silicone gels under the ultra-fast pulsed electric field

Abstract

The insulating properties of silicone gel used for silicon carbide-insulated gate bipolar transistors encapsulation may deteriorate seriously under ultra-fast pulsed electric fields. The essence of insulation degradation lies in the deterioration of materials caused by dynamic phenomena at microscopic scale, such as charge trapping and detrapping. Different from the steady-state operating condition, insulating materials exhibit a sharp decrease in their insulating properties when subjected to a rapidly changing electric field. To investigate the insulation failure of silicone gel materials under an ultra-fast pulsed electric field, Marcus hopping mechanism for charge response is proposed. By calculating the relaxation time with different defects, we characterise the degradation of the materials. According to the force analysis of space charge, the authors establish a relationship between insulation failures and charge relaxation time. Combined with the experimental results on electrical treeing in silicone gel, the feasibility of the theory is verified. The experimental phenomenon can be well explained, that is, the initial voltage of the electrical trees decreased sharply with shortening the edge time of the pulsed electric field, especially on the nanosecond time scale.