Magnetomotive Force and Winding Coefficients of Alternating Current Windings

The physical nature of the magnetomotive force (MMF) of an alternating current winding, discretely located in slots and being a source of a magnetic field that has both potential and vortex components, the latter being limited in the space of the slot, is considered. It is shown that in this capacity the role of the MDS is played by a set of magnetic sheets of slot currents, which, in terms of location and duration of sections with linear and nonlinear changes, can differ significantly from the generally accepted (classical) MDS winding. An analytical description of the stepped classical MMF curve of a winding with an integer and a fraction is proposed in the form of a set of expansions into a trigonometric series of MMF curves of coils, presented in the form of two-pole rectangles, having different heights and bases with a shortened winding pitch. It is shown that the frequency response of a fractional winding can be used to find the spectrum of its distribution coefficients for a known arrangement of coils in the slots. It was found using the example of a fairly simple fractional winding with a fractional denominator equal to 2 that, firstly, determining the spectrum of distribution coefficients using a well-known formula for windings with an integer by replacing this number with some equivalent one can lead to significant errors; secondly, variation in the winding pitch significantly changes the amplitudes of the higher harmonics of the MMF, including the appearance of harmonics with an order that is a multiple of three.