Partial discharges in transformer oil

Since a long time the existence of Partial discharges (PD) in transformer oil was doubted because breakdown and inception levels are very close. This confirms the presently accepted fact that [1] PD occur in oil. In the breakdown process the formation of a “bubble” or “cavity” is accepted generally as a part of the initiatory process. When the bubble reaches a “critical size” a discharge occurs [2]. When such a discharge occurs it can be shown that the bubble can grow in size leading to second discharge which grows to a breakdown. If it bursts into smaller sizes the discharge stops [3,4]. The probability of this is very low.