Influence of co-field motion on the conduction current and breakdown voltage in mineral oil under highly nonuniform direct fields

The effect of enforced co-field motion on conduction and breakdown in transformer oil was studied using a point-to-plane electrode geometry. Tests were carried out on degassed oil and O₂-saturated oil for negative and positive point polarities and gaps ranging from 200 to 900 μm. For stationary oil the presence of oxygen raised the breakdown voltage and decreased the conduction current for both polarities of the point electrode. For degassed and O ₂-saturated oil the axial flow increased the breakdown voltage and produced a significant reduction in the conduction current; the faster the flow, the greater the reduction in current. With oxygen in solution, current fluctuations were much greater than for degassed oil, and an unexpected result was the consistent finding that an increase in pressure produced an increase in the conduction current