Calculation of overhead and underground cable parameters at harmonic frequencies

Abstract

This paper presents a new method for the comprehensive calculation of power cable parameters at the fundamental and harmonic frequencies and for the assessment of the power cable’s frequency responses. In spite of its growing technical importance, there seem to be very little information in the open literature about resonances in power cables, particularly, when it comes to the so-called supra-harmonic frequencies, which lie in the range 2–150 kHz. At harmonic frequencies, various phenomena, such as skin effect, ground and metallic return loops, a strong capacitive effect, long-line effects, geometric imbalances and cable cross-bonding have all a marked influence on the responses of both overhead and underground cables. The cable resistances and inductances vary in a nonlinear fashion with frequency, and the latter will cancel out with the cables’ capacitive effects at some specific frequency values giving rise to alternate resonant points along the frequency spectrum. All the relevant construction details of the cable together with its electrical and operational parameters need to be processed by suitable models and methods coded into software for the fast and accurate calculations of the frequency responses of the power cables. A computer program has been developed as part of this research, using the formula and methods outlined in the paper. The usefulness and accuracy of the new methodology are demonstrated by resorting to numerical examples.