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 relevance of this research work is due to the fact that farms and other farms are located at a considerable distance from sources of centralized power supply. Therefore, it is necessary to introduce autonomous generators as the main units that ensure the uninterrupted functioning of energy systems. The purpose of this research work is to analyze the features of the functioning of an autonomous constant voltage generator, as well as to determine the basic physical laws that are of fundamental importance in its operation. The basis of the methodological approach in this scientific study is a combination of methods of system analysis with an analytical study of the general principles of operation of such devices, which are of fundamental importance from the point of view of ensuring the proper level of operational reliability. The main results obtained in this research work should be considered the definition of equations for calculating the instantaneous values of the three-phase excitation current, as well as the peak value of the three-phase excitation current of an autonomous constant voltage generator. The results obtained in the course of this scientific research and the conclusions formulated on their basis are of fundamental importance for developers of modern technological systems, including autonomous constant voltage generators, as well as for employees of technological services of modern industrial enterprises, whose professional responsibility includes the practical operation of such devices to solve a complex of technical tasks facing these enterprises.

The classic relationships concerning the harmonic content in the air gap field of three-phase machines are presented in form of series of rotating waves. The same approach is applied to modeling of permanent magnet motors with fractional phase windings. All main reasons of non-sinusoidal shape of flux density distribution, namely, magnets’ shape and their placement, slotting, magnetic saturation and eccentricity are also related to their counterparts in modal-frequency spectrum. The Fourier 2D spectrum of time-stepping finite element solution is confronted with results of measurements, with special attention paid to accuracy of both methods.