The production of Rotating magnetic field in 3 phase supply is very interesting.
When a 3-phase winding is energized from a 3-phase supply, a rotating magnetic field is produced. This field is such that its poles do no remain in a fixed position on the stator but go on shifting their positions around the stator. For this reason, it is called a rotating field.
It can be shown that the magnitude of this rotating field is constant and is equal to 1.5 fm where fm is the maximum flux due to any phase.
The three-phase currents flow simultaneously through the windings and are displaced from each other by 120° electrical. Each alternating phase current produces its own flux which is sinusoidal.
So all three fluxes are sinusoidal and are separated from each other by 120°.
If the phase sequence of the windings is R-Y-B, then mathematical equations for the instantaneous values of the three fluxes ΦR , ΦY ,ΦB can be written as,
Case 1 : ωt = 0
Case 2 : ωt = 60
Case 3 : ωt = 120
Case 4 : ωt = 180