Influence of co-field motion on the conduction current in oil under nonuniform dc fields

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