Rotating Magnetic Field and Induced Voltages

 Rotating Magnetic Field and Induced Voltages

Consider a simple stator having 6 salient poles, each of which carries a coil having 5 sums Fig. 

Coils that are diametrically opposite are connected in series by means of three jumpers that respectively connect terminals a-a, b-b, and ce. 

This creates three identical sets of windings AN, BN, CN, which are mechanically spaced at 120 degrees to each other. 

The two coils in each winding produce magneto motive forces that act in the same direction. 

The three sets of windings are connected in wye, thus forming a common neutral N. 

Owing to the perfectly symmetrical arrangement, the line to neutral impedances are identical. 

In other words, an regards terminals A, B, C. the windings constitute a balanced 3-phase system. 

For a two-pole machine, rotating in the air gap, the magnetic field (ie., flux density) being sinusoidally distributed with the peak along the centre of the magnetic poles. 

The result is illustrated in Fig. The rotating field will induce voltages in the phase coils as, bb', and cc'.

Expressions for the induced voltages can be obtained by using Faraday laws of induction.

Downside Figure Elementary stator having terminals A, B, C connected to a 3-phase source (not shown). 

Currents Blowing from line to neutral are considered to be positive.

Air gap flux density distribution.