Effect of forced co-field flow on the breakdown voltage and conduction current in transformer oil under highly nonuniform fields

This paper presents results of the effect which co-field oil flow has on the direct breakdown voltage and conduction current in transformer oil using a point-to-plane electrode geometry for both polarities of the point. Tests were carried out on degassed oil, oil saturated with O₂ and with N₂ and oil with 1-methylnaphthalene and dimethylaniline as additives. The oil flow velocity varied from 0 to 170 cm/s. For degassed oil, N₂-saturated oil and oil with DMA as additive, the results show that for both point polarities the breakdown voltage increases with increasing oil velocity, attains a distinct maximum value at a certain velocity and then decreases for higher velocities. For O₂-saturated oil and oil with MN as additive the breakdown voltage increases with increasing flow velocity and attains a quasi-saturation value for velocities in the range 100-120 cm/s. With N ₂ and DMA, breakdown voltages were in general lower than those for degassed oil, where as with O₂ and MN they were substantially higher. In general, oil flow tended to produce a decrease in conduction current with increasing oil velocity in all cases examined. Both O₂ and MN produced a 50% reduction in current compared with degassed oil. A possible explanation of the reported results is proposed