DC breakdown in liquid-nitrogen/PET-film composite under point-plane electrode system

Breakdown phenomena in a liquid-nitrogen/polyethylene-terephthalate-film composite subjected to DC ramp voltage (0.5 kV/s) were studied. When the film was set on a plane-cathode (covered-cathode system), breakdown voltage of the composite increased with increasing the film thickness. This suggested that a complete breakdown of the composite was induced by a film breakdown due to positive charges deposition and subsequent electron emission from the film breakdown spot. When the film was set on a plane-anode (covered-anode system), the film breakdown occurred at relatively low applied voltage and it could not induce the complete breakdown directly. Initial images of the complete breakdown were observed by the use of a long image guide scope. Results of the photographic observation supported the assumption that the electron emission had an important role for the complete breakdown on both polarities