Background. Multi-pole electric motors use fractional tooth armature winding with discrete distribution over the slots. It leads to appearance of minor low and high spatial harmonics of the magnetic field with significant amplitudes, which cause high differential scattering, pulsation of the electromagnetic torque, dips in the mechanical characteristic, increase of additional losses, levels of electromagnetic noise and vibrations. Thus, it is important to improve the harmonic composition of the magnetic field of such windings, and reduce the amplitudes of minor harmonics.
Materials and methods. During the study a three-phase 6-zone fractional tooth winding is replaced by a three-phase combined 12-zone winding. It consists of two three-phase fractional tooth windings, one has star connection, the other one has triangle connection. The efficiency of the windings is estimated based on changes in the harmonic amplitudes, differential scattering coefficients and non-sinusoidality of field distribution. Modeling of the magnetic field using the finite element method has been carried out.
Results. The structure of a three-phase symmetrical combined fractional tooth winding has been developed. The examples of windings have been given. The parameters of magnetomotive force diagrams have been calculated, and magnetomotive forces and inductions have been distributed. The authors have determined harmonic amplitudes, differential scattering coefficients and non-sinusoidality of field distributions. When combining the star and delta circuits in three-phase fractional tooth windings, the amplitude of the fundamental harmonic of the magnetomotive force of the combined winding increases by 3,38 %, the induction of the armature magnetic field by 4,69 %, the induction of the resulting magnetic field under load by 1,3 %, compared to the uncombined winding. The differential scattering coefficient of the combined winding decreases by 25,8 % in contrast to the coefficient of the uncombined winding. The harmonic distortion coefficients are lower. The magnetomotive force of the armature is by 8,0 % lower, the induction of the armature magnetic field is by 8,49 %, the induction of the resulting magnetic field under load is by 3,29 %. The winding coefficient of the combined fractional tooth winding is 3,5 % higher compared to the uncombined winding.
Conclusions. Combination of the star and delta circuits in a fractional tooth winding, fulfillment of the conditions for its implementation and the proposed winding structure allows us to reduce the amplitudes of minor harmonics of the magnetic field, improve its harmonic composition, bring the field shape closer to sinusoidal, reduce the coefficients of differential scattering, harmonic distortions of the magnetomotive force and magnetic field induction in three-phase multi-pole electric motors. It allows us to reduce additional losses in the motor, noise and vibration. The winding coefficient of the combined fractional tooth winding increased by 3,5 % improves the efficiency of electric motors with such a winding.