Life model and reliability of a complete HVDC cable system. Parametric analysis focused on role of terminals.

The goal of this Master Thesis is to estimate the life model and reliability of a complete HVDC 500 kV XLPE cable system, including EPR terminals. Cables and terminals are subjected to Electrical Type Test conditions, as outlined in CIGRÉ Technical Brochure 852, during which a series of load cycles (LC) with a DC voltage U_T=1.85U_0 (rated voltage) are applied. The simulation of the above mentioned test was conducted by implementing a MATLAB code, consisting of the following steps: 1) Transient thermal gradient calculations: 2) Electric field calculations: Performed over the insulation thickness, recognizing that DC field profiles are highly sensitive to the electrical conductivity σ of the insulation. Since σ depends on the coefficients α and β, a parametric sensitivity analysis was conducted to illustrate the extent of changes in field profiles and life expectancy estimates for both the cable and terminal when σ varies due to changes in α and β. 3) Life calculations: Life estimations were calculated at many noteworthy points within the insulation thickness. A parametric analysis was also conducted here by examining the influence of changes in the cable and terminal life models as the IPM electric life model and the Arrhenius thermal life model change. An adjustment in the approach used to calculate the life of the cable and terminal has been implemented: Old approach: The design life (at U=U_0) of the cable and terminal insulation was set to 40 years with a DC design field at U=U_0. New approach: The Type Test duration (at U_TT=1.85U_0) has been set to 30 days with a DC Type Test field at U_TT=1.85U_0. Finally, the reliability of the complete cable system was assessed, taking into account the combined presence of cables, joints, and terminals, with fixed values of n_D and B to evaluate how changes in the number of joints and different types of materials affect the overall reliability. This thesis work was carried out in support of "NEWGEN" project.