Transmission of the electric power is accompanied with generation of low –frequency electromagnetic fields. Electromagnetic compatibility studies require that the fields from sources of electric power be well known. Unfortunately, many of these sources are not defined to the desired degree of accuracy. This applies e.g. to the case of the twisted-wire pair used in telephone communication; already practiced is twisting of insulated high-voltage three phase power cables and single-phase distribution cables as well. The paper presents a theoretical study of the calculation of magnetic fields in vicinity of conductors having helical structure. For the helical conductor with finite length the method is based on the Biot-Savart law. Since the lay-out of the cables is much more similar to a broken line than to strait line, in the paper the magnetic flux densities produced by helical conductor of complex geometry are also derived. The analytical formulas for calculating the 3D magnetic field can be used by a software tool to model the magnetic fields generated by e.g. twisted wires, helical coils, etc.

The study presents a calculation method of the voltage induced by power-line sagged conductor in an inductively coupled overhead circuit of arbitrary configuration isolated from ground. The method bases on the solution utilizing the magnetic vector potential for modeling 3D magnetic fields produced by sagging conductors of catenary electric power lines. It is assumed that the equation of the catenary exactly describes the line sag and the influence of currents induced in the earth on the distribution of power line magnetic field is neglected. The method derived is illustrated by exemplary calculations and the results obtained are partially compared with results computed by optional approach.