抄録
The electrical breakdown phenomena in Polymethylmethacrylate (PMMA) for positive polarity with point-to-plane electrode configuration has been investigated using a photo-optical currentmeasuring technique and a 760 ns rectangular high-voltage pulse generator in conjunction with an image convertor camera. The high-speed framing photography revealed the propagation velocity of breakdown channel to be between 30 and 120km/s for positive 50kV point voltage. The waveforms of the prebreakdown current in PMMA is essentially the same as those in liquid dielectrics. The breakdown time lag was precisely measured from the current. A linear relation between formative time lag and gap spacing is observed for gap length greater than a critical value, indicating another constant propagation velocity in this region. The velocity is deduced from the relation to be 2.2km/s for a positive point at 50kV. This value is fairly close to that of longitudinal waves in the solid.
