The loss current method and the residual charge method had been developed as diagnosis method for water tree deterioration of XLPE cable bodies. Fundamental investigation of these method is mainly for vented trees generated from inner or outer semiconducting layers. However, bow-tie trees generated from voids or contaminants in the insulation layer have become main degradation cause because of application of the triple extrusion method for forming the cable core in order to reduce the generation of vented trees. Therefore, evaluation of applicability of the loss current method and the residual charge method for the bow-tie trees is important for the insulation diagnosis of the present XLPE cable body with these methods.
From these viewpoints, firstly we established the development method of the artificial bow-tie trees in a XLPE sheet specimen. Then, we demonstrated that the bow-tie tree could be detected with residual charge method and loss current method. And space charges accumulated around the bow-tie tree were measured with PEA method to evaluate possibility of the residual charge method to diagnose the bow-tie tree degradation.
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