Impulse Breakdown of Polymer Dielectrics in the NS Range in Divergent Fields

The short time impulse breakdown of polymer dielectrics, polyethylene (PE), polyethylene terephthalate (PET), polycarbonate (PC), polystyrene (PS), and polymethyl methacrylate (PMMA) in a pointplane electrode system has been studied using a ns rise time pulser. A polarity effect was found in all polymers: a highet voltage is required to induce breakdown for a negative point than for a positive point. This effect usually increases with increasing gap distance except for PMMA, in which the ratio of the negative to the positive breakdown voltage is small even for longer gap distances. There is much difference in the results of the 50% breakdown voltage Vb for pulses of 100 ns duration for each polymer. Vb for PS is the very highest among polymers tested in both negative and positve points. Vb for PET and Vb for PMMA are the lowest in the positive point and in the negative point, respectively, in the thicker gap region. The formative time lag is, in most cases, less than about 10 ns.