Electric field distribution distorted by voids inside power cables

The present paper reports findings of electric field distribution iri power cables with voids entrained in the insulation. The shapes of voids studied are cylindrical and spherical types. Samples studied are oil-impregnated paper-insulated cables arid polymer-insulated cables of single-core. The model selected for study is a single void adhered to the conductor surface. Both field distributions inside and outside the void have been studied. Analytical and numerical methods were used for comparison. It was found that the electric field is distorted outside a cable void and enhanced as well as slightly non-uniform inside the void. The non-uniformity of Held distribution in a cable void has never been reported in the literature; however, under certain circumstances. it is important in case of estimating the insulation strength of a cable. It was also found that in comparison with a numerical method, it is sufficiently accurate to use an approximate analytical formula for cable field calculations. which is accurate for a uniform field, if the formula is point-wisely or piece-wisely employed. It is still found that iii estimating the inception discharge voltage of multiple-void cases, die field distortion effect can be neglected if the voids are circular distributed around the cable conductor. Moreover, for polymeric distribution cables of small conductors. a single-void model is a reasonable reduction for the multiple-void case in reality.