A NEW TEST METHOD FOR CABLE INSULATION DEGRADATION ASSESSMENT: CAPACITIVE SENSING

摘要

Integrity of nuclear power plant (NPP) cable insulation has been identified as a crucial factor in extending the life of NPPs. The present acceptance criterion for cable insulation in NPPs is derived from elongation-at-break (EAB) measurements (destructive, mechanical tests), requiring EAB > 50 % for acceptance. Measurements of indenter modulus (IM), which can be performed on cables in situ and are nondestructive, have been previously related to the EAB acceptance criterion through extensive correlation studies. Here, measurements of EAB and IM are correlated with values of permittivity and loss tangent, measured by an interdigital capacitive clamp sensor, on two types of thermally- and radiation-aged cables. One type is insulated with flame-retardant ethylene-propylene rubber (FR-EPR) and the other with silicone rubber (SIR). The measured IM and dielectric loss tangent show a high degree of correlation for FR-EPR whereas EAB correlates most strongly with IM in the case of SIR. In future, values of breakdown voltage (VBD) will be measured on aged insulation samples in order to develop a new acceptance criterion for cable insulation based directly on VBD rather than EAB. Other types of common insulation material will also be studied.