Electrical properties and magnetic fields of a coaxial bus bar

Instead of shielding disturbing busbars consisting of conductors with rectangular cross-section by wrapping them with high permeable material, the authors propose the use of busbars which are formed by coaxial tubes of circular cross-section. Due to their rotational symmetry, they do not generate a resulting magnetic field in their surroundings. In addition this specific form is endowed with some more advantageous qualities, e.g. low inductivity of the impedance matrix, little power loss, high mechanical stability in the case of short-circuit currents, and little influence of eddy current and proximity effect. They investigate the properties of an N-tube conductor system by solving a volume integral equation, where all interesting parameters can be calculated analytically. As numerical results for a three-phase busbar carrying arbitrary alternating currents, they display 3D-plots and diagrams showing how current density, power loss and voltage drops depend on frequency and geometrical relations. Furthermore, by comparing these results with those of a common bus bar which contains conductors of rectangular crosssection, the advantage of the coaxial busbar is demonstrated.