Interaction of partial discharge streamer in cryogenic fluids with polymeric films

Erosion by partial discharge and layer effect on breakdown characteristics of polymeric films immersed in cryogenic fluid were examined. The results obtained are following. (1) V-t characteristics of polymeric films immersed in LHe are inferior to those in LN₂. (2) Observation of the eroded films by a scanning electron microscope made it clear that partial discharge in LHe produced a mesh-like pattern on the surface while in an uneven surface was formed. The layer effect depends on the waveform and the magnitude of the applied voltage. Under impulse voltage and under ac low voltage, the sample with the larger number of layers shows the higher resistance to breakdown. Under ac high voltage, however, the superiority is reversed. This phenomenon is understood by the occurrence of partial discharge in LN₂ between films in the multi-layered sample.