Comparison of two charge packet models under dc electric fields

Charge packet under high electric dc fields has been observed in polyethylene and its formation has been closely associated with ageing and breakdown of the insulating material. To understand the mechanisms several models have been proposed. In this paper, two models originated from completely different approaches have been reviewed. The first model proposed is based on bipolar charge injection together with electric field dependent mobility. It has been found that the negative differential mobility with the electric field is essential for the formation of charge packet. On the other hand, the second model considers the change in conductivity after charge injection. By assigning different conductivities to two different zones it is possible to form a charge packet that bears some similarity with the observed features. Simulations based on these two models have been carried out and both dynamics of charge packet and resultant current in the two models are compared and discussed.