Life Estimation of XLPE Cable Under Electrical and Thermal Stress

Estimating the lifetime of XLPE insulated cables is utmost important as it determines the reliability of the cable under service. The cable insulation under normal service condition experiences various stress such as cyclic thermal stresses associated with load cycles, electric stress produced due to applied voltage, humidity etc. In this work, lifetime of a single core 33 kV XLPE insulated cable being employed in wind farms is estimated, considering the impact of different stress conditions. The effect of electrical stress i.e. produced due to applied voltage, thermal stress associated with load cycle and combination of both the stresses are studied. The electric field and thermal stress distibution analysis in cable insulation is carried out using FLUX, an electromagnetic field and thermal distribution analysis software. The stress values obtained from FLUX are used in insulation life models to estimate the approximate life of XLPE cable insulation. Further, the lifetime analysis is performed at higher stress levels compared to rated conditions in order to understand the feasibility to carried out experiments under laboratory conditions. This study shows that electrical and thermal stress has strong impact on insulation lifetime. Also it is observed that the estimated life depends on applied voltage profile and insulation thickness. In addition, the lifetime estimation models also plays an important role.