Single phase motors work on the same principle as 3 phase motors except they are only run off one phase. One important thing to note for 3 phase motors is that because they run off of three phases that are offset from each other, they are self-starting. The interaction between the stator and rotor magnetic fields causes the rotor to rotate. The current in the rotor sets up its own magnetic field. This rotating magnetic field induces a current in the bars of the rotor. The magnetic field rotates due to the 120° phase offset in each phase of the power supply. The current in the stator of a three phase motor (the stationary coils in the motor) sets up a rotating magnetic field. In order to understand how an AC induction single phase motor operates, it is helpful to understand the basics of a three phase induction motor.
