Basic Electricity: induction motor
The three-phase induction motor:
The induction motor is the most commonly used type of motor because it is rugged, relatively cheap, and efficient. It consists of two units: the stator and the rotor. When the stator winding is energized, the rotating magnetic field in the stator induces a corresponding magnetic field in the rotor. The magnetic field in the rotor always lags the rotating field in the stator by about 5%. The difference between the full load RPM and the synchronous RPM (1800 RPM in a four-pole motor) is called the slip. The direction of rotation is determined by phase sequence of the three-phase voltage source. The motor can be reversed by interchanging any two leads.