Flashover characteristics of impulse voltages on solid dielectric surfaces under high humidity

For the design of electrical insulating devices, it is very important to observe discharge phenomena on the needle-to-plate electrode gap under high humidity. In this study, impulse flashover phenomena in a needle-to-circular-electrode gap on solid dielectric surfaces under a high humidity condition have been discussed. As a result, it was found that impulse flashover voltages are greatly influenced by both horizontal and vertical gap lengths. When the horizontal gap length is shorter than the vertical one, the flashover characteristics approach those in air. On the other hand, if the horizontal gap length is longer than the vertical one, characteristics more closely approach those on the dielectric surface. The flashover characteristics also depend upon the polarity of the needle electrode. The characteristics for positive polarity seems to be similar to those in air, and those for negative polarity approach the creepage characteristics on the dielectric surface.