Vibration of Bubble Generated by Partial Discharge in Silicone Gel

We have studied the electrical treeing generated in silicone gel used as an encapsulant for power electronics modules. The treeing which consist of bubbles and strings was named Pearl-chain-type treeing. Under AC voltage application, the bubble vibrated with repeating expansion and shrinkage. We have obtained new insight that the expansion of the bubble at polarity inversion was very important for the development of the tree.