Effect of viscosity on pre-breakdown conduction pulses at a point cathode in silicone oils

The occurrence of prebreakdown pulses at a point cathode under DC has been observed to be strongly influenced by insulating-liquid viscosity. Using a high bandwidth detection system it is revealed that each burst is composed of a well-structured set of pulses which increase in amplitude, initially in a linear fashion, with time before becoming irregular. The order of occurrence of these pulses and the time lapse obeys a proper law, and the total time domain of this linear regime is viscosity-dependent. Increasing the viscosity results in an increase in the duration of the burst and in the time interval between the pulses within the burst. Using the onset of each pulse or burst to trigger the capture of a shadowgraph produces an associated low-density region. The size of the shadow region increases with the burst duration. A preliminary model for the initial growth of the low-density region associated with these pulses is presented