Dissipation current waveform and its spectrum of water tree deteriorated Low Density Polyethylene sheet

Deterioration with water tree phenomenon is the one of typical problem on the electrical insulation of the high-voltage class power cable. A water tree which bridges a cable insulation between inner and outer screen makes the insulation resistivity low, then it is possible to apply the conventional way, such as leakage current measurement and so on. However, for an un-bridged one, which induces the sudden breakdown, the variation of resistivity at the insulating part is quite small. Then the dissipation current waveform observation method is considered one of possible way as diagnostic method for this un-bridged water tree on the high-voltage class power cable. The harmonics´ phase, which consists from the harmonics of dissipation current and that of displacement current, is focused on and is related with the progress of severity of deterioration with water tree. The signals from the deteriorated Low Density Polyethylene sheets with water tree were investigated by using the dissipation current waveform observation method and its behaviors were estimated. In this paper, the results of these investigations are introduced and are discussed.