Experience in using different diagnostics methods for field testing of medium-voltage cables with extruded insulation in Nuclear Power Plants

Medium-voltage cables represent an important component of the Nuclear Power Plant (NPP) nuclear island as well as of its balance of plant. Therefore, it is reasonable to monitor their aging process and expected reliability. There are, however, many electrical, thermal, mechanical and radiation stresses, which, through time, can influence the occurrence of insulation degradation. Assessment and evaluation of the condition of cable insulation is supposed to be carried out periodically, during the scheduled outages and maintenance activities. Accordingly, it is necessary to carefully select the proper efficient diagnostic methods and different scrutinises, particularly studied and purposeful for determining the aging grade and overall adequacy of the cable insulation. To avoid unplanned failures with loss of critical equipment, the insulation must be properly tested. Therefore electrical and non-electrical diagnostic methods are used to ensure proper assessment of cable insulation deterioration. This paper reports on experience with application of different diagnostic methods boosting tendency to improve monitoring of the condition of the cable insulation in the NPP Krško, The diagnostic testing and measurements on cables recommended to be done in nuclear power plant respecting a good practice of asset maintenance management is discussed.