The enlargement law as a tool for comparing the breakdown performances of power cables: the role played by conductor radius and insulation thickness

As shown in previous papers by the authors, the “enlargement law” can be used for selecting the best among two compounds for power cable insulation, by evaluating the so-called crossing quantities, namely the values of length, dielectric strength and breakdown voltage of the cable line at which a crossover in the breakdown performances of the two compounds occurs. This paper investigates the effect of conductor radius and insulation thickness on crossing quantities. For this purpose, a theoretical analysis of the mathematical relationships between crossing quantities and cable conductor radius plus insulation thickness is carried out. Such analysis is supported by applicative examples relevant to a comparison between two typical XLPE– based compounds for cable insulation, subjected in laboratory to lightning-impulse breakdown tests in the form of mini-cables.