Discharge magnitude distribution and discharge luminescence in an electrical treeing (Polarity effects for prediction of tree initiation)

The authors investigate how to improve the prediction of tree initiation by the polarity effects indicated in the discharge magnitude distributions. This work measures particularly the negative discharge pulses in addition to positive. During sample heating, a steel needle electrode (diameter:1 mm) was inserted into polymethylmethacrylate. The experimental samples consisted of an artificial fine void (length:1.5 mm) with air at 1 atm. The test voltage was AC 50 Hz, 14 kV. The discharge magnitude, the discharge luminescence and the tree configurations were measured and observed until 30 minutes after the tree initiation. The experimental procedure was carried out at room temperature in silicone oil and 30 samples were tested