Tree channel formation in solid dielectrics. Low variance observations and mechanism of formation

Under impulse conditions, the energy to form a tree channel must come from the electric field, as formation of a substantially conducting channel "shorts out" part of the field. We report measurements of channel formation voltage with extremely small variance under multiple shot and single shot impulse conditions for a needle plane geometry. As would be expected, the single shot PD inception voltage is less than the multiple shot voltage as a result of space charge effects. In addition, we report computations of the change in electrostatic energy resulting from channel formation, including the effect of field-dependent polymer conductivity and relate these computations to the energy required for channel formation.