Electrical Field Distribution along SF6/N2 Filled DC-GIS/GIL Epoxy Spacer

The flashover faults due to the accumulation of surface charge have restricted the further development of spacers in HVDC GIS/GIL transmission systems. Many researchers have proposed a variety of mathematical models to simulate the surface charge accumulation process; however, few of them have taken into consideration the gas collision ionization and charge trapping-detrapping processes. This paper combines plasma hydrodynamics and charge transport equations to build a modified model. For the basin-type spacer, the model shows that the surface charge has the same polarity as the applied voltage on the lower surface but the opposite polarity on the upper surface of the spacer. A decreased charge density and even a polarity reversal is seen near the conductor. For the disc-type spacer, the surface charge has the same polarity as the applied voltage near the shell but opposite polarity near the conductor under negative voltage. But, under positive voltage, negative charge exists almost on the whole surface. The most serious distortion of the electric field occurs at the triple junction of the epoxy spacer. Under load condition, joule heating of the conductor increases the temperature which has a great influence on the electric field distribution. As the conductor temperature increases, the field strength near the conductor is reduced owing to the temperature-dependent volume conductivity of the epoxy spacer. The application of shielding electrodes grades the electric field at the triple junction, and is referred to as the DC GIS/GIL design.