Enhancement of the thermal analysis of harmonics impacts on low voltage underground power cables capacity

Abstract

This article investigates the harmonic impacts on the underground low voltage cables by using new algorithm. The heating of cables by harmonics may lead to form dry zones around the cables causing insulation failure. De-rating factors due to the influence of the load harmonics for different soil types as back-fill materials are presented. The de-rating factors are calculated for different typical non-sinusoidal current loads with different harmonic order ingredients. The influences of the harmonics in the cable current and also the effect of the dry zone formation in the soil surrounding the cable on the cable capacity and its temperature rise are investigated. New thermal model of three-cores with a neutral low voltage cable that is usually used in low voltage distribution circuits is considered. The proposed technique is based on the heat balance at any node of the cable thermal equivalent circuit. The influences of the neutral conductor area of low voltage cable, on the cable conductor's temperature and cable current are investigated. One of the advantages of the proposed method is that different percentages of harmonics can be considered for each phase separately and the mutual heating between the three phases and neutral cable conductors is considered. De-rating factors due to the harmonic influence on the cable buried in different soil types with and without dry zone formation in the soil surrounding the cable are presented.