Dissipation current waveforms monitoring in LDPE sheet under water tree deterioration test

The dissipation current waveform monitoring method is considered one of possible way as a diagnostic method for un-bridged water tree on the high-voltage class (22-77 kV) power cable. In previous CEIDP, it has reported that the amplitude and the phase of the fundamental and the 3rd harmonic components have varied with the progress of the un-bridged water tree deterioration and the phase of the 3rd harmonic component became close to 0 degree with the un-bridged water tree growth. In this study, in order to clarify the influence that the un-bridged water tree´s number or length give the detected dissipation current waveform, the dissipation current waveform monitoring has been carried out. Here, the magnitude of the scratched areas has been controlled in divided four divisions of LDPE sheet. 2.0 kV, 1.0 kHz ac high voltage has been applied to the 0.6 mm thick LDPE sheet for 300 hours. As the results of experiments, it was indicated that the magnitude of un-bridged water tree deterioration the number of un-bridged water tree influenced into the 3^rd harmonic component of dissipation current rather than the maximum length of un-bridged water tree.