General Specification of Six-Phase Windings of Alternating Current Machines
In this chapter, some specific theoretical problems of six-phase electrical machines were analyzed. It was evaluated theoretically which harmonics or rotating magnetomotive force and of what type may emerge in the six-phase symmetric electric current systems. It was proven that the harmonics that are multiples of three as well as all remaining even harmonics of rotating magnetomotive force cannot appear in such systems, contrary to the three-phase current systems.
Further, in order to supply power to six-phase motors, it is recommended to use a step-down voltage transformer that changes the number of phases; in such transformer, at the terminals of the secondary six-phase winding, a guaranteed symmetric six-phase voltage system is obtained, where alternation of voltages is the closest to the sinusoidal law. It was graphically shown, that in the symmetric six-phase system, contrary to the three-phase system, the phase and line voltages are of an equal magnitude. Six possible variants of connecting both positive and negative voltage phase sequences to the terminals of the motor were presented in the tables.
In this chapter, the general aspects of the six-phase windings were also analyzed, their main equations were presented, and symmetric spatial arrangement of the starting and ending points of these windings was determined graphically.
In the last subsection of this chapter, the evaluation of electromagnetic properties of six-phase windings based on two methods is presented. The first method of investigation is partial, and it is based on the calculation of the winding factors for the fundamental and higher-order harmonics. The second method of research is more comprehensive but also more difficult. It is based on harmonic analysis of instantaneous spatial distributions of rotating magnetomotive force generated by six-phase windings. On the basis of the results of this analysis, the electromagnetic efficiency factors of such windings are calculated.