In-situ photoelastic monitoring of electrical treeing in polyethylene

The authors investigate the influence of both passive internal strains in drawn PE (polyethylene) samples with semiconductive electrodes and active internal stresses around embedded steel electrodes on the electrical tree growth. Results of insitu photoelastic measurements showing the fringe pattern evolution accompanying tree propagation are also presented. It has been found that the internal stress model developed by J. V. Champion et al (1992) for embedded electrodes in an epoxy resin block can be successfully applied to polyethylene samples. Photoelastic measurement is an efficient and simple tool for experimental determination of such stresses. The electrical performance of polyethylene samples show complex variations in the presence of increasing internal strain. Orientation effects (passive internal stresses) and residual stresses (active internal stresses) might make different contributions, possibly in opposite directions. Nevertheless, it is believed that polyethylene specimens oriented perpendicularly to the make electric field have better resistance to electrical treeing than unoriented samples