Numerical modeling of space charge in polyethylene under AC fields

A bipolar charge transport model has been developed to simulate the dynamics of space charge under dc fields. The modeling shows space charge build-up and decay comparable to experiments. In this paper, this bipolar charge transport model is taken further to simulate the space charge in polyethylene under ac fields. The results show that there is small quantity of phase-dependent bipolar charge accumulation mostly in the vicinity of the electrodes instead of moving into the bulk under ac fields. This causes a slight distortion of the local field in the bulk. However at lower frequencies (less than 1Hz) there is increased charge accumulation and penetration. The conduction current is quite small and hence the displacement component dominates the total current. Bipolar charge recombination is going to reach a saturation level after a certain ac stressing time. Increasing the ac voltage will normally increase the amount of total charge and the charge recombination rate.