The Magnetic Field in the Vicinity of Parallel and Twisted Three-Wire Cable Carrying Balanced Three-Phased Current

An analysis of the low-frequency magnetic field in the vicinity of three-wire cable carrying three-phase current is presented. Parallel wire systems and twisted wire systems are considered. Radial and tangential components for the parallel wire system are obtained as a function of the position of the observation point in a polar coordinate system. The magnitude of both components approach equality at large distances and at these distances become invariant with angle around the cable. At positions close to the cable the tangential component is maximum opposite to each wire but the radial component has a mimum at different angular positions at different distances. The twisted cable analysis extends earlier work with two-wire single-phase systems. The results show that the behavior at large distance is very similar for the two- and three-wire systems, the only difference being that the latter has a constant multiplier of 0.75. Detailed curves of fields for the parallel wire case are presented. A combined curve for tangential field for parallel wire cable at small distances and the asymptotic field for twisted wire cable at large distances is also presented.