Heating-Assisted Current Integration Method as a Tool for Evaluating the Leakage Current in Cable Insulation

Cables installed in a boiling water nuclear power plant (NPP) were removed from three places. The electrical insulation performance of their flame-retardant (FR) ethylene-propylene-diene rubber insulation is examined by the current integration method. Namely, the electric charge stored in a measuring capacitor set in series with the sample cable is measured when a high dc voltage is applied. The ratio of the charge stored in the capacitor in the whole period of voltage application to the initial one is found to be a direct indicator of the leakage resistivity of cable insulation. The resistivity is measured much lower when a part of the cable sample is heated to 80 °C than when the whole length is kept at room temperature. This means that the heating-assisted current integration method can be a tool for locating deteriorated positions in the cable insulation. It has also become clear that the cables removed from the three places possess high enough insulation resistivity.