Partial discharge inceptions and patterns in arc experienced transformer oils

Transformer oil is an important part in a high voltage transformer. Under excessive condition, electric arc may occur in the transformer oil. The electric arc may reduce the performance of the transformer oil. This paper explains the experimental results on the effects of electric arc on the partial discharge (PD) inception and patterns in mineral transformer oil. In the experiment, electric arc was generated under highly divergent electric field by applying AC voltage to a needle-plane electrode system. The energy level of the produced electric arc introduced to the oil was adjusted by adjusting the distance between electrode and varying the duration of arc application. The experimental results showed that arc treatment significantly reduced the PD inception voltage. The negative PD inception was slightly higher than positive PD inception. Under constant applied voltage, stronger electric arc increased significantly the PD activity as indicated by the higher PD magnitude and PD number. In most cases the PD pulses were concentrated around the peak of applied voltage at both positive and negative half cycles. This indicated the role of instantaneous applied voltage on the PD occurrence in the transformer oil.