New 3-phase winding of low m.m.f.-harmonic content

A new method of connection for 3-phase windings is described. It is shown that a conventional 60° phase-spread winding can be subdivided into two components, one of which is connected in delta and the other in star, the two winding components being connected in parallel to a 3-phase supply. Theoretically, the new principle is only applicable where the number of slots per phase is infinite, but it is demonstrated that entirely satisfactory results can be achieved with reasonably small numbers of armature slots. Simplicity of construction is considered to be very important, and, in each of the windings discussed, all the coils are identical and carry currents of equal magnitude. Theoretical examination shows that the new method gives a higher fundamental spread factor than for a conventional 3-phase winding, and a superior m.m.f. waveform, as well as providing a means of reducing the effective number of turns in series per phase. The theoretical studies were verified by tests on a 3-phase squirrel-cage induction motor.