Effect of the thickness and the relative permittivity of epoxy resin coating on the hemispherical tip electrode to the first flashover voltage in pressurized dry air

Summary

SF6 gas has high dielectric strength and current interrupting ability, so it has been widely used in electric power apparatus such as Gas Insulated Switchgear (GIS), gas circuit breaker and so on. However, since the global warming potential of SF6 gas is 22,800 times higher than that of CO2, dry air is going to be used as insulation medium for GIS. However, since the dielectric strength of dry air is 1/3 of that of SF6, very high gas pressure is necessary to fulfil the insulation requirement by dry air. Therefore, pure dry air insulation technique is not a realistic way of high voltage insulation in GIS. Instead, the composite insulation system which combines relatively high gas pressure dry air and solid insulating material becomes an important technology. In this investigation, we setup a composite insulation system, and clarified the initiation points of discharge using the ICCD camera. We also investigated the effects of the thickness of epoxy resin coating on the hemispherical tip electrode, diameter of the hemispherical tip electrode, and the kinds of epoxy resin to the first flashover voltage (the first FOV) in dry air at 0.24 MPa. The results obtained are as follows; the discharge occurred between the tip of epoxy resin coated electrode and the counter plane electrode, the first FOV increased with the increase of the thickness of the dielectric coating and with the increase of the electrode radius. The electric field calculation showed that the electric field strength at the surface of dielectric coating decreased with the increase of thickness of coating in both cases, which explains the experimental results. The first FOV increased a bit with the decrease of relative permittivity of epoxy resin from 4.5 to 3.6. The results also can be explained by the change of the electric field strength by the permittivity of dielectric material.

Additional informations

Authors

Misaki Daiki, Kamimura Shusaku, Okada Yoshihiro, Osawa Naoki, Yoshioka Yoshio, Hanaoka Ryoichi, Yanase Hironori, Hatakenaka Hayato, Okamoto Kenji