High field AC conduction mechanism in nonpolar polymers

Non-polar polymers, such as polyethylene and polypropylene, are widely used as electrical insulation for high voltage cables and capacitors. Earlier, it was reported that the conductivity, which is the dominant mechanism under high temperature-high electric field conditions, does not depend on the frequency of the applied ac voltage, in the range from 50 Hz to 400 Hz. In this paper, the frequency dependence of electroluminescence (EL) pulses under ac voltage is examined. It is shown that in XLPE the EL pulses occur at the same phase angle of the ac voltage, irrespective of the frequency in the range of 60 to 900 Hz. EL emission and conductivity occur due to carrier injection from the electrode and space charge formation. Also, the peaks of the EL pulses and the dissipation current occur just before the peaks of the positive and negative half-cycles of the applied voltage. From these results, the high field conduction mechanism and the effect of space charge in XLPE subjected to ac voltage is discussed