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

The goal of this Mater Thesis is to evaluate the life model and reliability of a complete HVDC 320kV XLPE cable system including accessories under Type Test (TT), as outlined in CIGRE Technical Brochure (TB) 852. To do so, two different simulations are considered: 1) Parametric analyses on a single component to study the role of two important parameters for the insulation’s life and reliability: the voltage endurance coefficient (VEC) n and the Arrhenius thermal life model parameter B. Single components analysed for this thesis are the HVDC 320kV XLPE cable and the HVDC joint assumed with EPR insulation. 2) Reliability estimation of the complete HVDC 320kV XLPE cable system by variating the VEC value and the number of joints. Parametric analysis was conducted by implementing a MATLAB code composed by the following steps: 1) Transient temperature profile calculation over the insulation thickness for 24-hour and 48-hour load Cycles, as defined in CIGRE TB 852. 2) Transient electric field calculation over the insulation thickness, considering the effect of the conductivity σ. 3) Life calculation for 5 fixed points within the insulation thickness of the HVDC cable and joint using a combination of the IPM electric life model and the Arrhenius thermal life model. More in detail, the parametric analysis was performed with two different approaches: 1) The old approach where the design life of the cable and joint is set equal to 40 y with a DC design field at U = Uo. 2) The new approach, which is an upgrade of the old approach where TT duration has been set to 30 days with a DC Type Test field at UTT = 1.85Uo. As a final point, the reliability of the complete HVDC cable system, under TT was estimated by considering the presence of a unipolar HVDC cable, 2 terminals and a variable number of joints. This thesis work was carried out in support of the Horizon Europe Program entitled “NEWGEN”. For more information, visit the website: https://www.newgen-project.eu/.