A new approach to the statistical enlargement law for comparing the breakdown performances of power cables - part 2: application

A new theoretical approach to the application of the enlargement law for assessing the breakdown performances of shielded power cables was illustrated in the companion paper (Part 1) of this series. In the present paper, practical case-studies of the proposed theory are presented. The so-called crossing quantities of two cable lines, i.e. crossing length, crossing dielectric strength and crossing breakdown voltage, are analyzed on the basis of the results of dielectric strength tests performed on cable models insulated with different commercial compounds. In particular, the application is relevant to mini-cable samples realized with two ethylene-propylene rubber (EPR) compounds, and with two cross-linked polyethylene (XLPE) compounds, all subjected to standard lightning impulse dielectric strength tests. The estimation of the crossing quantities, performed for various power cable voltage ratings, shows that the crossing length - if any - is a strong function of the cable size and voltage rating. Thus the choice of the best compound should be based on a comparison between the value of crossing length and the typical lengths of full-size cables. Furthermore, since the crossing quantities are strongly affected by the values of the Weibull parameters estimated from the dielectric strength tests, a sensitivity analysis of such quantities to the uncertainty in the estimation of the Weibull parameters is also carried out.

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