Electrical and Mechanical Condition Assessment of Low Voltage Unshielded Nuclear Power Cables Under Simultaneous Thermal and Mechanical Stresses: Application of Non-Destructive Test Techniques

Low voltage cables play a crucial role in the safe and reliable operation of nuclear power plants. This paper discusses the effect of simultaneous combined thermal and mechanical stresses on the overall insulation of unshielded low voltage power cables used in nuclear power plants. Cable samples based on XLPE/CSPE insulation were exposed to thermal-mechanical combined accelerated aging tests for an extended period lasted to 907 hours. Time and frequency domain dielectric spectroscopy were applied to reveal the degradation level of the core insulation and jacket due to combined stresses. The former technique was conducted through the measurement of the decay and return voltage slopes, while the latter technique was based on the measurement of the complex permittivity. Moreover, the mechanical properties of the cable insulation were investigated by applying the measurement of the Shore D hardness. The results showed that the combined aging affects both the electrical and mechanical properties of the overall insulation. The complex permittivity at 100 Hz, the decay voltage slope, and the hardness had an upward trend with aging, while the return voltage slope showed an inverse trend. In addition, the results of the electrical and mechanical measurements showed strong correlation with aging time and further correlation was observed between the dielectric and mechanical properties. The correlation between aging time and test results suggests that the presented test methods are promising tools for in situ condition monitoring of low voltage unshielded cables in nuclear power plants.