Effect of insulator environment on thermal ageing estimations for ethylene propylene rubber insulated nuclear power plant cables

Thermal ageing estimations merely focus on the degradation of cable insulator materials without considering their arrangement within the cable structure, by surrounding jacket or colorant pigments. This study reconsidered thermal ageing estimations based on the insulator elongation at break (EAB) degradation progress for flame retardant ethylene propylene rubber (FR-EPR) insulators within the whole cable structure. FR-EPR insulators were aged using two methods. In the first method, the insulators were heated, including jacket material at 125 degrees C, 150 degrees C, and 160 degrees C for 2208, 336, and 264h, respectively. In the second method, the insulators were heated without jacket at 125 degrees C for 3480h, and at 160 degrees C for 264h. It was expected that the EAB degradation progress would be more severe when the FR-EPR insulators were aged without jacket. However, the results contradicted previous expectations, and the special heat-resistant polyvinyl chloride jacket accelerated the EAB degradation. In addition, the black FR-EPR insulators showed values that deviated from the predictions for the activation energy (E-a) and equivalent times compared to the white and red insulators due to the use of carbon black as a pigment. The reduced equivalent times for thermally aged FR-EPR insulators with jacket in this study were evident compared with the current degradation database for FR-EPR insulators degraded without jacket.