High-Speed Electro-Optical Measurement of Pre-Breakdown Current in Dielectric Liquids

The electrical prebreakdown currents in dielectric liquids have been investigated using photo-optical measuring techniques and ns pulses applied to a pointto-plane gap. The measured relation between breakdown time lag and gap spacing has been used to deduce the streamer propagation velocities in the fluids studied. Discharges from positive points generally were more intense and faster than those from negative points. The streamer transit times were found to be proportional to gap spacing, indicating a constant velocity. This velocity was unaffected by point radius and gap spacing for a fixed magnitude of the applied voltage, Temperature effects were determined for the case of positive points. CC14 with a positive point exhibited different current waveform shapes and very fast streamer velocities.