Measurement of transformer oil dielectric strength

This paper deals with the breakdown studies of transformer oil under ac voltage. The oil was filtered, degassed, and then allowed to get saturate with dry air. The breakdown studies were carried out on processed oil at room temperature using brass made spheres of 12.5 mm diameter and Rogowski electrodes of 30.0 mm overall diameter. The vast breakdown voltage data generated by conducting large number of experiments have been found to be normally distributed. Furthermore, it has been observed that for a given value of breakdown probability, the voltage is always higher in case of spheres than Rogowski electrodes for a given oil gap. The breakdown characteristics are also drawn in terms of oil gap for two different electrode systems which may be used as a ready reference for the purpose of designing.