The effect of temperature and stress coefficients of electrical conductivity on the life of HVDC extruded cable insulation subjected to type test conditions

This paper investigates the effect of temperature and stress coefficients of electrical conductivity of the insulation material on the life and reliability of HVDC extruded cables subjected to type test load cycles according to CIGRe Technical Brochure 496. The investigation is done by refining a procedure for the estimation of cable insulation life and reliability in the presence of load cycles, developed and implemented in a previous stage of this research, but applied so far to prequalification test load cycles only. Electric field is calculated using both the rigorous approach based on Maxwell's equations for transient electric field computation (exact method) and the closed-form steady-state Eoll's formula often employed in the preliminary design of DC cable insulation (approximated method). This enables also to assess the accuracy of the overall approximation involved by Eoll's formula in the case of type test conditions.