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Interfacial E-field self-regulating insulator considered for DC GIL application

The non-uniform electric field (E-field) distribution is typically considered a key factor in triggering surface flashover inside gas insulated lines (GILs). To improve the E-field distribution along GIL insulators, this study proposes the concept of an interfacial E-field self-regulating (IER) insulator. The capability of the IER insulator with a resistivity-nonlinear (ρ-nonlinear) skin layer to regulate the E-field distribution is validated via theoretical analysis. In this paper, cone-type insulators are coated with epoxy (EP)/SiC composites to fabricate EP/SiC coated IER insulators. Next, an electrical simulation model is built to calculate the E-field distributions and energy losses of the insulators. As the coating thickness or SiC content increases, the E-field regulation function of the EP/SiC coated insulator becomes increasingly significant with increasing leakage current and energy loss. Under DC voltage, nearly 24 hours is required for the E-field distribution along the conventional insulator to reach the steady state. When the SiC content in the coating layer is increased, the transient time of the EP/SiC coated insulators decreases because of the reduced volume resistivity. Furthermore, coating thickness measurements and DC flashover tests are conducted. The coating thickness of the EP/SiC coated insulator is found to increase with increases in the SiC content because of the higher viscosity of the liquid-state coating. The DC flashover voltage of the EP/SiC coated insulator is found to be higher than that of the conventional insulator, with the flashover voltage increasing with the SiC content in the coating layer.