Investigation on emitted energy during breakdown in transformer oil under AC voltage

The risk of breakdown in mineral insulating oil constitutes a critical part in the insulation of high voltage apparatus such as transformer. This paper presents an experimental investigation on transformer oil dynamic breakdown characteristics when subjected to AC voltage. Breakdown tests were carried out on mineral oil samples using a sphere-sphere electrode test cell for various gap lengths 1 mm, 2.5 mm and 5 mm and at different voltage speed ramps: 0.5kV/s, 2kV/s and 3.5kV/s. The emitted energy of the mineral oil samples was determined from the instantaneous product of voltage and current. Such emitted energy can be used to explore the properties of the arc and its development within the oil. The results of this investigation show that the gap length and the voltage speed ramp have a significant influence on the emitted energy of the oil during breakdow