Life-based Geometric Design of HVDC cables. Part 1: Parametric Analysis

This study, in two parts, investigates the cable design of HVDC cables depending on life modelling of the insulating material. This paper is the first part, in which a parametric analysis is carried out, illustrating the way in which different parameters affect the lifebased feasible designs of an HVDC cable with known nominal voltage and ampacity. An ad hoc Matlab code has been developed for this study. Results show great sensitivity of the lifetime to insulation geometry, as a slight variation in inner and outer insulation radii leads to a significant variation of cable life due mainly to the related electric field variation. The effect of temperature can be hardly observed in the life map due to the predominant effect of electric field. Increasing the maximum conductor temperature may not necessarily extend the feasible design area, which is also limited by the maximum temperature drop across insulation thickness. The higher the applied voltage, the greater the cable dimensions. This study also emphasizes the need to keep a low enough value of soil thermal resistivity, which considerably reduces the cable dimensions. Temperature coefficient of conductivity shows a nonlinear (mainly drastic) effect on the life. On the contrary, Field coefficient of conductivity shows a slight positive effect on the life. Part 2 of this study will investigate the effect of electrical and thermal transients on the lifebased geometric design of HVDC cables.