Typically the rotor full speed will between 2 and 6% that of the synchronous speed. The rotor can never rotate at synchronous speed, otherwise there would be no induced current. The stator magnetic field rotates at the motors synchronous speed ( n s). Before jumping into the equivalent circuit, a few concepts are useful. One way to analyse and understand the operation of an induction motor is by the use of an equivalent circuit. The rotor current produces it's own magnetic field, which then interacts with the stator field to produce torque and rotation. Within the induction motor, an electrical current in the rotor is induced by a varying magnetic field in the stator winding. These two winding factors are discussed in a little more detail below.Induction motors are frequently used in both industrial and domestic applications. The breadth factors are ratios of flux linked by a given winding to the flux that would be linked by that winding were it full- pitched and concentrated. These are usually called pitch and breadth factors, reflecting the fact that often windings are not full pitched, which means that individual turns do not span a full π electrical radians and that the windings occupy a range or breadth of slots within a phase belt.
Two winding factors are commonly specified for ordinary, regular windings. The winding factors are often expressed for each space harmonic, although sometimes when a winding factor is referred to without reference to a harmonic number, what is meant is the space factor for the space fundamental. Since each winding has a winding factor that influences its linking flux, and since the mutual inductance must be reciprocal, the same winding factor must influence the MMF produced by the winding.
That is, if the windings are designated one and two, the mutual inductance is flux induced in winding one by current in winding two, and it is also flux induced in winding two by current in winding one.
The argument goes as follows: mutual inductance between any pair of windings is reciprocal. It is relatively easy to show, using reciprocity arguments, that the winding factors are also the ratio of effective MMF produced by an actual winding to the MMF that would have been produced by the same winding were it to be full- pitched and concentrated.
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