Characteristics of surface charge on oil impregnated pressboard under non-uniform DC stress

It is very important of the surface charge distributions on the oil impregnated pressboard under nonuniform DC electric field, for the design and application issue of a converter transformer, which is not reported in the literature. In order to have a better understanding of the characteristics of the surface charges on oil impregnated pressboard produced by the non-uniform DC electric field, we studied surface charge distribution on oil impregnated pressboard produced by the needle plate electrode based on an electrostatic capacitive probe measuring system. It is found that under the highly non-uniform electric field, the surface charge polarity on oil impregnated pressboard mainly depend on the polarity of applied voltage and the accumulation and dissipation characteristics of the surface charges under the positive stress are different from that under the negative stress.