Monitoring Techniques for NPP Electrical Cables Condition

The international practice for ageing assessment is monitoring the mechanical, physical or chemical parameters of the insulation materials. Due to the influence of the external factors, the equipment, the measurements results are different from one laboratory to another, a comparison between them being difficult. Therefore, it is necessary for each Nuclear Power Plant (NPP) to preserve the data referring to the condition indicator value of the cable material ageing. For monitoring techniques development, the considered cable samples have already an accelerated thermal aging. The readiness cable types were: HXH 180 E90, 3x25 mm+16 mm and PVC 3x25 mm. The cables have accelerated thermal aged into enclosure facilitating the thermal aged evenly at full length of the samples. The samples' length was 4 m. The thermal ageing of the electric insulating materials for the four cable samples has carried out by an overrated electric current injection into conducting wires. The service limit values for the accelerated thermal aged cables found out by development of the condition monitoring techniques for the electric cables were: PVC cable type: IM = 110 N⋅mm; TGA 5% isn't sensitive versus ageing; HXH cable type: IM = 121.1 N⋅mm; TGA 5% = 271 °C. For checking the ageing condition of the NPP cables and if these have reached the lifetime service limit, the TGA 5% and IM parameters' values have to be measured, and then compared with the values determined at the accelerated thermal ageing. (author).