Phase-field Modeling of the Propagation of Electrical Trees in PP/POE Blends

Polypropylene (PP)/polyolefin elastomer (POE) blends are considered to be HVDC insulating materials that are replaceable with cross-linked polyethylene (XLPE). To analyze and compare subtle changes in electrical trees among different PP/POE blends, this study simulated growth of the electrical trees under a needle-plate electrode configuration and investigated the effect of mechanical stress on the resulting electrical tree characteristics using the phase-field method. The growth of electrical trees in PP is observed to be promoted by the addition of POE. The width, length and damage area of the electrical tree increase with increasing POE content and decrease with increasing intrinsic breakdown strength of the POE. Electric field distortion and the lower intrinsic breakdown strength of POE are the two main factors affecting the growth of electrical trees. In addition, mechanical stress can cause diverse effects on electrical tree growth, which depends on the direction relationship between the mechanical stress and the needle electrode. The mechanical stress perpendicular to the axis of the needle electrode greatly increases the width and damage area of the electrical tree, while the mechanical stress that is parallel to the axis of the needle electrode shortens the blend breakdown times.