抄録
Recently, it is becoming important to establish the way to diagnose the deterioration of insulating materials and to predict the insulation breakdown. The object of this research is the diagnosis of the tree initiation by partial discharge magnitude distribution. Polymethylmethacrylate with an artificial needle-shaped void was used for experiments. The discharge magnitude distribution in relation to phase angle of the applied voltage was measured by a partial discharge measuring system. In this system, one cycle of the 50Hz AC applied voltage is divided into twenty equal phase areas. The phase areas were labelled as ∅1-∅20, ∅1 being at the negative peak of applied voltage in order from the negative peak of applied voltage. It was confirmed that the discharge magnitude distribution of positive and negative showed the different characteristic respectively. Two parameters were proposed to predict the tree initiation, one was gravity center of the discharge magnitude distribution and the other is the maximum discharge magnitude in each phase angle area. Using two parameters for the positive and the negative distributions. The occurrence probability of pre-tree-initiation phenomena was improved up to 90‰.
