Analysis of Surface Charge Accumulation on DC-GIS Insulating Spacer Based on Surface Trapping Model

In DC gas-insulated switchgear (DC-GIS), surface charge accumulation on an insulating spacer is regarded as a cause of electric field distortion and flashover voltage reduction. In this study, we measure surface charge distribution on a downsized DC-GIS epoxy spacer by electrostatic probes and develop a simulation model of surface charge accumulation based on charge transport in the presence of deep traps on the spacer surface. A bipolar charge transport model is adapted to calculate the evolution of space charge distribution. Trap density and trap depth on the spacer surface are evaluated based on the isothermal surface potential decay (ISPD) model from the experimental results of surface charge decay. Both the experimental and simulated results show that the homo-charges are concentrated near the electrodes at 40 degrees C, while they extend over the spacer surface at 70 degrees C. The temperature dependence of surface charge accumulation can be described by the temperature dependence of charge injection and de-trapping. This result indicates that deep traps on the spacer surface dominate the surface charge accumulation.