Relationship of electric insulation void content with electric cable normalized capacitance

For aging nuclear power stations and other facilities, a need exists for monitoring aging degradation effects in electric cable insulation. Our current research efforts are pursuing a non-destructive in situ approach for determining remaining life of cable insulation through detection of real time age-dependent void characteristics and comparison to known end of life void parameters. In many cases, a critical cable may be inaccessible because of location within conduits, in concrete, or underground making void detection impractical. This paper reports on initial efforts to correlate our void detection approach to a technique proposed by Chang-Liao et al.(ANS NPIC&HMIT, Nov. 2000), which appears to be promising for inaccessible cable. This paper postulates that the detected change in capacitance reported by Chang-Liao et al. is related to the void growth that occurs with aging and discusses a possible correlation between ionized void content (caused by the applied dc potential) and the value of capacitance.