Dielectric loss and extended voltage response measurements for low-voltage power cables used in nuclear power plant: potential methods for aging detection due to thermal stress

This paper discusses the effect of thermal stress on the electrical properties, conduction and polarization, of low-voltage CSPE/XLPE-based power cables used in a nuclear power plant. The cables were subjected to an accelerated thermal stress at 120 degrees C for an equivalent service period of 20, 40, 60 and 80 years. The capacitance, tan delta, resistivity at different frequencies and extended voltage response were the methods used for the investigation. A significant variation in the values of tan delta at low frequency, i.e., at 100 Hz, was observed. For the extended voltage response measurement, the decay voltage slope increased, showing the increase in the conduction particles inside the insulation material. While the decrease in return voltage slope showed that the slow polarization processes occurring at very low frequencies were decreased with aging. A strong correlation between the tan delta and decay voltage slope was also observed, which increased as the insulation aging increased. The results showed that the methods could be used for the in situ measurement of conduction and polarization phenomenon in the low-voltage cables, and hence helping in the assessment of the condition of cable insulation.