New approach to diagnostic method of water trees

A novel method for the detection of high-field AC conduction loss current containing harmonics in polymeric insulating materials is presented. The method is based on the use of the unbalanced operation of a current-comparator-type capacitance bridge and the deconvolution technique of signal processing. This technique was experimentally applied to the diagnosis of water trees in CV power cables by detecting the waveform of the high-field AC conduction current of the cables with and without water tree degradation. The distortion of the current waveform measured for the water-tree-degraded cable appeared to be larger than that observed for nondegraded cables. This result might be related to the nonlinear electric field dependence of the AC conduction loss current around water trees