Assessment of Charge Behavior in Electrical Tree Tube Based on Characteristics of Partial Discharge Waveform

Electrical trees are the final stage of an insulation degradation with partial discharge (PD). In a practical situation, a detection circuit that consists of a coupling capacitor and a detection impedance is applied to the PD measurement. The high-frequency signal associated with a PD pulse flows through a coupling capacitor and a detection impedance. Since a detection impedance is conventionally an RLC circuit having a large impedance with a certain frequency band, the observed PD signal is stretched by a transfer function of the detection circuit. For this reason, PD phenomena are not generally discussed by using PD waveform itself. It mostly investigated the occurrence time (phase) and the charge amount as the parameters; however, the original PD waveform shows the behavior of charges in the discharge space. The information on degradation characteristics can be obtained by analyzing the change of the PD waveform. In this study we constructed a device which can be acquired all the original PD waveforms. The charge behavior in the electrical trees was evaluated based on the characteristics change of the PD waveform.