The Relationship Between Ultrasonic and Electrical Measurements of Under-Oil Corona Sources

In order to predict the usefulness of ultrasonic techniques for detecting and locating transformer coronas or partial discharges, it is necessary to determine the relationship between electrical and ultrasonic values of different coronas within an unobstructed oil environment. Experiments are reported in which typical corona sources, ranging in value from ~5-~105 pC, were energized within an oil-filled transparent tank and the ultrasonic emissions recorded via a transducer on the tank outer wall. Several distinct modes, changing with magnitude, of the oil discharges were observed, and the relationship between charge measurements Q and ultrasonic values P were found to vary from P ∝ Q1/2to P ∝ Q.