The fundamentals of electric machines

Motors and generators are key elements in electrical drives. Three‐phase alternating current (AC) machines represent the most important family of electric machines for industrial drives and other heavy‐duty applications. Induction machines can be divided into two categories: squirrel‐cage machines and wound rotor machines with slip rings. In AC machines, a travelling wave of magnetic flux is the basis for electromechanical energy conversion. The travelling magnetic field follows the air gap between the stator and rotor of the machine. The most common industrial machine type is the squirrel‐cage induction motor. In the rotor of such a machine, there is a short‐circuited squirrel‐cage arrangement of winding conductors. A damper winding resembles the squirrel cage of an induction motor. Most electric machines in use today have three‐phase or two‐phase windings. Direct current (DC) machines with commutators have armature windings on the rotor and several other windings in the stator.