The Effect of Conductor Radius and Insulation Thickness in the Application of the Enlargement Law for Comparing Power Cable Breakdown Performances

Previous investigations by the Authors of this paper showed that the so-called crossing quantities - i.e. cable length, strength and voltage at which a crossover in the breakdown performances of two compounds for power cable insulation occurs - are a strong function of cable size and voltage rating. Here, it is proved that also conductor radius and insulation wall thickness do play an important role, as witnessed by the functional expressions of crossing quantities. The investigation carried out in this paper takes advantage of a rigorous analysis of the mathematical formulae that express the influence of conductor radius and insulation thickness on crossing quantities. Moreover, a comparison is reported between two EPR-based, as well as between two XLPE-based, compounds for HV applications, for which the results of lighting impulse breakdown tests realized on mini-cables are available. In this framework, useful guidelines for the choice of the best compound for power cable insulation are derived, in the light of the dependence of cable breakdown performances on the dimensional parameters of the cable, i.e. cable line length, conductor cross section and insulation thickness.