Surface charge accumulation on 500kV cone-type GIS spacer under residual DC voltage

In recent years, GIS compact design has gradually been recognized and adopted by the industry. In the trend of the compact design, the insulation performance of the cone-type spacer is getting more and more attention by GIS manufacturers and grid operators and maintenance departments. In particular, under the action of DC residual pressure, the insulation properties of cone-type spacer become the focus of attention of all parties. Based on the field equipment operating conditions, the experimental study of DC residual voltage for the true cone-type spacer insulation performance is significant. In order to obtain the proposed pre-stressed time of DC voltage and distributions of surface charge, for the insulation test of 500 kV cone-type spacer under lightning impulse with DC voltage superimposed. A full scale surface charge measurement platform is build up for 500 kV GIS spacer. Then, long-term DC voltage experiments were carried out to obtain the distributions of surface charge on spacer in stationary state under different voltages. Moreover, the saturation time of surface charge accumulation under different DC electric stress is calculated and discussed. The study results show that (1) the distribution of surface charge on spacer is not uniform. It can be observed that on most areas of 500 kV spacer concave surface is dominated by the electric conduction through the volume with positive charges. (2) The time constant of surface charge accumulation decreases with the residual DC voltage amplitude, it can be estimated that the saturation time of surface charge accumulation on 500 kV cone-type spacer is about 23 h for the residual DC voltage reach to 1.0 p.u. The study results are thought to be helpful to the insulation test of 500 kV conetype spacer under impulse voltage with a superimposed residual DC voltage.