INSULATION DETERIORATION DIAGNOSIS METHOD FOR HIGH VOLTAGE OVERHEAD DISTRIBUTION CABLE

PURPOSE:To realize highly accurate diagnosis of deterioration of insulating state by removing noise from signal through interphase differentiation, for example, thereby measuring a partial discharge signal accurately. CONSTITUTION:Signal measuring electrodes 6, 7, 8, 9 are disposed at four joints of a pi-type branch joint 5 on the outside of the housing. Consequently, they are provided at twelve points for each assembling. Partial discharge takes place upon occurrence of dielectric deterioration in a joint. Occurrence of partial discharge is detected through capacitive coupling of a partially discharging part and the electrodes 6, 7, 8, 9 and a potential variation is detected in the form of a patial discharge signal. In other words, signals obtained from the electrodes 6, 7, 8, 9 are connected with a signal switch 11 in order to take a difference between two electrodes being selected. Output from the signal switch 11 is fed to a difference amplifier 12 for removing same type of noise component. Output from the difference amplifier 12 is fed to a signal analyzer 13, e.g. a spectral analyzer or an oscillator, and a partial discharge signal is detected.