A deeper insight into the application of the enlargement law to HVDC cable lines

In this paper the innovative theoretical approach to the enlargement law for HVDC cables previously developed by the authors is investigated in more detail, by evaluating the role played by the main quantities that appear in the enlargement law. Firstly, the paper studies the effect of the Weibull shape parameter and of conductor temperature on the reduction of breakdown voltage with cable length in the enlargement from test to power HVDC cables by considering quantities related to typical extruded compounds for DC applications, thereby demonstrating a major role played not only by Weibull shape parameter, but also by volume electrical resistivity of the insulation, hence by the different compounds. Secondly, the behaviour of the cumbersome function H_DC appearing in the enlargement formula for HVDC cables is analyzed via the Monte Carlo method and approximate expressions for H_DC are proposed that are useful for insulation coordination and design.