Abstract
The paper studied charge accumulation on a supporting insulator and the behaviour of metallic particles which should be especially taken into consideration for DC-GIS. In the studies, we tried to observe the phenomena which happen in a large-scale apparatus, using a 125kV and a 500kV DC-GIS bus model. Distributions of charge accumulation on a cone-type spacer were measured by static probes, changing the magnitude, polarity and duration of dc voltages. Based on the test results, the mechanisms of charge accumulation were proposed. The cone-type spacer designed for DC-GIS showed excellent insulating properties even at the polarity reversal test. We also conducted the calculation studies for the worst case of charge accumulation that a metallic particle standing on the inside of the sheath works as an emission source of the charges. The analysis showed that the electric stresses along the spacer were below the flashover level even at the worst case. In the latter of the paper, the behaviour of the metallic particles placed on a dielectric coated sheath were studied. The studies revealed that the dielectric coating could make the particles inactive up to high electric stress.
