Surface Resistivity of Insulating Films to Prevent Penetration by Lightning Impulse Discharges

We investigated penetration probability in order to clarify threshold of surface resistivity that can prevent breakdown of insulating film by discharge. Insulating films were polyethylene terephthalate films that were coated by a conductive carbon-nanotube-added ink to modify surface resistivity, and we applied discharge to the insulating film. As a result, it was found that penetration probability due to discharge was 0% when surface resistivity of insulating film was 8.10×103 Ω/sq. or lower. Furthermore, it is considered that potential propagates due to time constant calculated by surface resistivity and capacitance between insulating film and ground. When surface resistivity is 8.10×103 Ω/sq. or lower, time constant is 4.0 ns or less, which is shorter than propagation time of creeping discharge. Because electric field at tip of discharge is relaxed, it is difficult to penetrate insulating film.