A New Approach to the Inverse Power Model in Qualification Load Cycle Planning and Life Estimation for HVDC Extruded Cables

Cigrè Technical Brochure 852:2021 has confirmed the voltages and durations of qualification load cycles for HVDC extruded cables as in former Technical Brochures 219:2003 and 496:2012. These values rely on the Inverse Power Law Model with life exponent set to n = 10, considered in Cigrè 852 a conservative basis for estimating cable life. The value n = 10 has been left unchanged over more than 20 years to date despite new compounds with n up to 26 have emerged thanks to the technological improvement of polymeric DC cable insulation. Relying on this Technical Brochure 852, so far the author has used the same approach to estimate the life of HVDC extruded cables under qualification test load cycle conditions. This paper proposes a new approach to the Inverse Power Model in the selection of voltage levels and durations of qualification load cycles. Such new approach exploits the evidence that qualification tests are passed with broad margin by “good” cable systems, and highlights the improved voltage endurance of new cable insulation compounds with greater n. The satisfactory performance of this approach on both these respects is proven by an illustrative application to life estimation of HVDC cables subject to type test load cycles.