Surface charge measurement on epoxy spacer in HVDC GIS/GIL in SF6

The design of reliable high voltage equipment remains a challenge nowadays. The surface charge accumulation at gas/solid interface is a major problem of HVDC GIS/GIL. The electric field can be distorted and the dielectric strength of the system can be thus reduced dramatically due to surface charges. This paper presents the measurement of surface charge (surface potential) on spacer in DC GIS/GIL under pressurized SF6 condition. The surface potential distribution on the spacer is obtained by an electrostatic probe connected to a displacement system. FEM simulations are also performed in order to have a better understanding about surface charge accumulation process. The conduction in gas is modelled considering charge generation and transport under electric field phenomenon. The dependence of surface and volume conductivities of epoxy resin on electric field is also taken into account. Firstly, the importance of preparation process for DC GIS/GIL spacer for the measurement of surface charge is introduced. The influence of DC voltage, electrode roughness to surface charge accumulation and the time constant of the system is then investigated. Finally, a comparison between simulation and experimental results is presented.

C. T. VU, L. ZAVATTONI, P. VINSON and A. GIRODET