Electric breakdown and space charges in ethylene-vinyl-acetate (EVA) incorporated polyethylene

Some dielectric properties of polyethylene incorporated with ethylene-vinyl acetate (EVA) have been measured as functions of EVA content. The results show that the space charge concentration produced either by corona injection or by mechanical friction decreases significantly, but both the electrical tree initiation voltage and the breakdown voltage increases with increasing EVA content. Photoconductivity and thermally stimulated current measurements indicate that the incorporation of EVA in polyethylene tends to reduce the concentration of deep traps but to increase the concentration of shallow traps, thus increasing the average carrier concentration and mobility. The suppression of deep traps or the replacement of deep traps with shallow traps implies that the energy released from trapping and recombination is reduced, thus reducing the concentration of trapped space charges and the probability of forming low-density regions based on K.C. Kao´s model (1984). This would then lead to an increase in both the electrical tree initiation voltage and the breakdown voltage