Diagnosis of tree initiation by analysis of discharge magnitude and discharge luminescence at each phase angle area

In this study, we present a new method which the diagnosis of tree initiation by measuring discharge magnitude and discharge luminous image at each phase angle area. We measured discharge magnitude and discharge luminous image by the original measurement system to analyze discharge pulses and discharge luminescence at several phase angle areas of applied voltage. As the measuring section, one cycle of applied voltage was divided into twenty areas, which were named from φ₁ to φ₂₀ in order from the negative peak point of applied voltage. Then, we defined effective instantaneous value considered from each equivalent circuit before and after tree initiation, which we took into consideration that the influence of the residual electric charge which stored the tip of void and tree channel. As a result, the product of effective instantaneous value and dv/dt was in proportion to discharge magnitude and luminous quantity. However, each coefficient of correlation differed before and after tree initiation. So, we were able to know the tree initiation by the change of each coefficient of correlation. Therefore, this method facilitated to diagnose the tree initiation only by measuring discharge magnitude at each phase angle area. It was considered to be more useful information for diagnosis of degradation by electrical treeing