Impulse Insulation Characteristics of a Composite Insulation System Having a Wedge Gap in SF6 Gas

Impulse insulation characteristics were investigated in a composite insulation system having a wedge gap in SF6 gas. The partial discharge inception voltages of wedge gaps with various types of film were measured and compared with the calculated breakdown voltages estimated from the paschen's curve of SF6 gas. It was discussed how the charge accumulated on the film surface due to a partial discharge had an effect on the creepage breakdown voltage. Partial discharge inception voltages in wedge gaps were higher with higher SFs gas pressures and with lower film permitivities. Creepage breakdown voltages scarcely depended on gas pressures or on creepage distances. The dependency of breakdown voltages on gas pressures and the effect of polarity on the breakdown voltage differed with the types of film. This may be partly because the charge on the film due to partial discharge had an effect on the discharge propagation, and that charging of the film differd with the types of film.