Surface Charge Measurement of Insulating Spacer Simulating Temperature Gradient Environment in DC-GIS

In DC gas-insulated switchgear (DC-GIS), temperature of high-voltage busbar rises due to Joule heat, and a temperature gradient is generated in an insulating spacer. The effect of temperature gradient on charge accumulation of the spacer needs to be clarified. In this study, surface charge distribution on a disk-type downsized epoxy spacer is measured under temperature gradient and compared with the measured results under uniform temperatures. The experiments are carried out in 0.1 MPa-abs SF
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under three temperature conditions: (a) 40°C and (b) 70°C without temperature gradient, and (c) with temperature gradient, 70°C at the center and 40°C at the edge of the spacer. Surface charge density distribution on the spacer is obtained by an inverse calculation from measured surface potential using an electrostatic probe. As a result, positive charge density near the high-voltage electrode is larger when the electrode is at 70°C than when it is at 40°C, while the positive charge density away from the central electrode is larger under (C) than (a) and (b). This result indicates that charge injection from the high-temperature electrode is more significant than that from the low-temperature electrode, and charge accumulation from high-temperature electrode propagates dominantly.