Acoustic Emission Distributions and Types of Electrical Trees in Polyester Resin

Acoustic emission (AE) characteristics have been investigated during electrical tree growth from a needle tip in a plastic insulating material. Alternating voltages (50 Hz) of 16, 20, and 24 kV rms were applied. Various patterns of tree growth, branch-like, bush-like, and filamentary trees, and formation of voids were observed. The amplitude of AE from the branch-like and filamentary trees was relatively small, and the amplitude distribution exhibited a sharp peak at small amplitude. On the other hand, the amplitude of AE from the bush-like tree and at void formation was large, and the amplitude distribution covered a wide range. The number and the amplitude of AE events were studied in relation to the phase of alternating voltage. The largest number of events was observed at the peak of the applied voltage for the branch-like and filamentary trees, and before the voltage peak for the bush-like trees. Most AE signals were detected when the absolute value of the voltage increased for the branch-like, bush-like, and filamentary trees but were detected in all voltage phases when voids formed. During tree activity, the AE amplitude was tended to be largest at the voltage peaks, but during void formation, was largest just after the change of voltage polarity.