On variations in the propagation of positive discharges between transformer oil and silicone fluids

The propagation of the positive discharge in transformer oil is compared with that in silicone oils of two different viscosities. Once initiated, in transformer oil, the discharge propagates readily, being little influenced by variations in the applied voltage or by the position of the tip within the gap. In the case of the silicone fluids the tip velocity is a strong function of its position within the gap and of the applied voltage. The discharges have characteristic forms; a bush-like structure in transformer oils and a tree-like structure in silicone fluids. The results presented support a model of discharge propagation based on a field ionisation process at the tip leading to heating and dissociation with the discharge filament.