# Mutual inductance

1. Jun 2, 2011

### Cooler

im trying to understand the mutual inductance in induction motor operation...How the mutual inductance occur in induction motor? what it does with the rotating magnetic field?

2. Jun 3, 2011

### Zryn

The windings in the stator are excited by 3 phase currents which create a magnetic field (since any conductor with current flowing through it is an electromagnet) which then induces current into the rotor (just like the two windings in a transformer) which also creates a magnetic field in the rotor, and then the two fields try to align themselves like two normal bar magnets would, N to S and S to N.

The trick is that the phase currents in each of the stator windings are changing magnitude as they cycle through each sinusoidal period of 2pi, resulting in the bar magnets (they appear in each instance of time as bar magnets) in the stator changing magnetic field strength and polarity depending on the sinusoidal current that is flowing through it.

As the current through winding A reaches its maximum (the other two phases each being 120 degrees apart from it) the rotor will attempt to align with this winding.

Next, winding B current reaches its maximum and the rotor will shift and attempt to align with it, and then winding C current reaches its maximum and the rotor will shift again to align with it, and so on and so forth, and the rotor will always be playing a game of catchup as it try's to align itself to ever changing magnetic fields rotating around the windings.