Mechanism of tree propagation from a simulated tree channel

In this paper, we investigate partial discharge (PD) in a simulated tree channel and tree growth from its tip. Influences of the channel diameter, voltage amplitude and temperature are examined. Voltage dependences of total number of PD pulses required for initiation of tree growth and the shape-parameters deduced from Weibull distributions were obtained. The shape-parameter m changes from m/spl les/1 (early/random failure) to m>1 (fatigue failure) with increasing applied voltage. The mechanism of tree growth was discussed based on the shape-parameter. The cause of early/random failure is considered to be statistical-randomness of PD generation for smaller diameter channel but structural weak point for larger diameter channel. Voltage region where m>1 tends to shift to lower voltage side with temperature and that where m/spl les/1 disappears above 40/spl deg/C. The relationship between the total number of PD pulses and the reciprocal temperature (Arrhenius plot) allows to estimate activation energy of tree growth to be about 20 kJ/mol.