Effect of liquid flow velocity on the breakdown voltage of mineral oil under highly nonuniform fields

The effect of forced flow velocity on the breakdown voltage/gap length characteristics of transformer oil was studied using a needle point and a mesh plane electrode system. The velocity of the axial (co-field) oil flow varied from 0 to 280 cm/s. Tests were carried out on degassed oil, O₂-saturated oil, and SF₆-saturated oil for negative and positive point polarities. For degassed oil there was a large increase in the breakdown voltage with increasing oil velocity for both polarities of the point and over the whole range of gaps examined. For O₂- and SF₆-saturated oils a similar increase in breakdown voltage was observed only with the point negative. With the point positive, velocities above 90 cm/s had no effect