Cable impedance calculations with parallel circuits and multi-neutral returns in distribution networks

This paper addresses impedance calculations in distribution networks. Two sets of paralleled, three-phase conductors with concentric neutrals and also a separate neutral are considered. An approximate method to calculate the impedance for this configuration is to calculate the impedance for one three-phase set of conductors, and then to divide this result by two. This paper compares this common practice with a more exact calculation that considers the mutual coupling between two sets of three-phase conductors. Errors in the current practice are shown to be significant. Comparisons are made for both phase and sequence impedances. Also, a common configuration of parallel conductors of different types is studied. It is shown that the approximate method may have up to 30% errors in the positive sequence impedance and power flows.