Diagnostic Method for Power Cable Insulation

Diagnostic methods for two major cables, OF and XLPE cables, are presented. As a new diagnostic method for the OF cable insulation, an analysis of the insulation oil sampled from the splices or the end sealing box is proposed. As for diagnostic methods for the XLPE cable insulation, several methods are described to detect water tree deterioration, which is the only major problem with XLPE cables. These methods are classified into off-line and live-line tests. Especially, newly proposed diagnostic methods are discussed, which can be applied to live-line XLPE cables. These are a measuring method of dc current component in ac charging current of cables containing water trees, a method to measure insulation resistance, and a method of detecting electrical tree deterioration in XLPE calbe insulat ion on site.