Simulation of space charge distribution in polyethylene under a temperature gradient

Abstract

It has been reported that a temperature gradient can have a major influence upon the space charge distribution in polyethylene (PE) and oil-impregnated paper however details of the mechanism by which these modifications are produced have not yet been clarified. The experimental results for PE under a temperature gradient show clear evidence of heterocharge next to the electrodes. This feature has been simulated previously using a bipolar injection model that includes blocked extraction. A direct comparison with PEA experiments however is difficult because the finite spatial resolution of the measurement causes the bulk space charge to overlap with that of the electrodes leaving the experimental values as a mixture of the two quantities that are generated separately in the simulation. Here we allow for the finite spatial resolution of the experimental technique by broadening the simulated charge density values using a Gaussian function. This allows us to compare the simulation and the measurements more effectively. The space charge distribution in PE is simulated by including a temperature dependent charge injection and charge transportation. Under these conditions it is found that the simulation results give a detailed match to the experimental results. They also show that both the temperature dependent charge injection and temperature dependent charge transportation are of importance in determining the space charge distribution in PE under a temperature gradient.