High-field conduction and electrical breakdown of polyethylene at high temperatures

The mechanism of the breakdown occurring when a dc ramp voltage is applied to low-density polyethylene (LDPE) and silane cross-linked PE at high temperatures is discussed, using experimental results on the Young's modulus Y , high-field conduction and pre-breakdown currents. The electric strength F B of PE was found to be a function of Y , irrespective of cross-linking. It was also found that, over a wide temperature range, a sharp pre-breakdown current increase could not be detected till a time before breakdown of 100 ns, the resolution limit of the measuring system. The results showed that, under the present experimental conditions, thermal breakdown is not applicable to PE over a wide temperature range and that breakdown is initiated by an electronic process which has a very short time lag to breakdown of the order of some tens of ns or less.