Comparison of the Behavior of the Free Bubble and the One Located on the Electrode at AC Action

This article reports an experimental study on partial discharges (PDs) in bubbles, either floating or developed on an electrode in a transformer oil. In a test cell, the PD occurrence was a very rare event. The voltage of the appearance of the PD in both cases was approximately the same. Moreover, the waiting time for the PD in the bubble at the electrode was noticeably longer than that for the free bubble. The moisture content of the oil, as well as the addition of surfactants, had no effect on the occurrence of PD. Analysis of the data showed that only two mechanisms stimulated PD: pulsed X-ray radiation or the presence of water microdroplets. The reason for all these features is the formation of an initiating electrons.