Induction Motor Equivalent Circuit
239
Primary winding Magnetic flux
(a)
Secondary winding Air-gap
(b)
Air-gap
Primary (stator) winding Secondary (rotor) winding
(c) Figure 7.1 Sketch showing similarity between transformer and induction motor
. Only one-third of the slots are taken up because the remaining twothirds will be occupied by the windings of the other two phases: these have been omitted for the sake of clarity. . The magnetic circuit has two air-gaps, and because of the slots that accommodate the coils, the Xux threads its way down the teeth, so that it not only fully links the aligned winding, but also partially links the other two phase-windings. . When the rotor turns, the rotor winding also turns and it therefore links less of the Xux produced by the stator. If the rotor in Figure 7.1(c) turns through 908, there will be no mutual Xux linkage, i.e. the degree to which the two windings are magnetically coupled depends on the rotor position. If the two windings highlighted in Figure 7.1(c) were used as primary and secondary, this set-up would work perfectly well as a single-phase transformer.