ABSTRACT
An induction motor (IM) can be understood as a polyphase transformer with shortened and freely rotating secondary winding. It generates torque based on the electromagnetic induction. The amount of induction is proportional to the speed slip between the stator field and the rotor. An IM can therefore work without an electrical connection to the rotor. Thus, brushes and commutator are not necessary. Therefore, IMs require minimum maintenance and are robust against mechanical shock and vibration. Furthermore, IMs are made of inexpensive ordinary materials like iron, copper, and aluminium. In addition, IMs can be driven by the grid lines. Therefore, they are widely used in industry and domestic appliances; blowers, pumps, cranes, conveyer belts, elevators, refrigerators, traction drives, etc. In fact, 90% of industrial motors are IMs. In this chapter, basic IM operation principle is illustrated using an equivalent circuit model, and the torque speed curve is derived. Various torque profiles are studied with regards to the rotor slot shape. The Heyland diagram and variable voltage variable frequency (VVVF) control are briefly reviewed.
