As the name suggests, a three-phase induction motor is one which works on three-phase AC supply, and converts three-phase AC electricity into mechanical energy. Three-phase induction motors are the most extensively used electric motors in industries. These motors run at almost a constant speed from no-load to full-load, i.e., they have good speed regulation. Although the speed of three-phase induction motors depends on the supply frequency and number of poles in the machine and therefore, it is quite difficult to change their speed.

Just like any other electric motor, a typical three-phase induction motor also consists of two main parts namely stator and rotor. The stator is a stationary part and carries a three-phase winding, called stator winding. The rotor is a rotating part of the motor and carries a short-circuited winding, called rotor winding.

The stator winding of a three-phase induction motor is fed from a three-phase balanced AC supply, while the rotor winding derives its working voltage and power from the stator winding via electromagnetic induction. This is why, it is named so.

A three-phase induction motor may be considered to be a three-phase transformer with a rotating secondary winding. Therefore, it could be described as a transformer-type AC machine. The only difference is that the induction motor converts electricity into mechanical energy.

Types of Three-Phase Induction Motors

According to the rotor construction, three-phase induction motors are classified into the following two basic types −

• Squirrel-Cage Induction Motor

• Slip-Ring Induction Motor

Advantages of Three-Phase Induction Motors

Here is a list of some of the major advantages of three-phase induction motors −

• The design and construction of three-phase induction motors are quite simple.

• They have robust construction.

• Three-phase induction motors require less maintenance.

• Three-phase induction motors have self-starting property.

• These motors have reasonably good power factor.

• Three-phase induction motors are more economical.

• They have high efficiency.

Disadvantages of Three-Phase Induction Motors

The major disadvantages of three-phase induction motors are listed below −

• Three-phase induction motors are essentially constant speed motors, and require complex mechanism to change the speed.

• Three-phase induction motors always work on lagging power factor.

• These motors draw very high starting current.

Applications of Three-Phase Induction Motors

The major applications of three-phase induction motors are given below −

• The squirrel-cage type three-phase induction motors are suitable for driving blowers, fans, machine tools, centrifugal pumps, etc.

• Three-phase induction motors are also used for driving different industrial load like compressors, crushers, conveyors, reciprocating pumps, etc.

• The slip-ring induction motors are best suited for driving loads that require high starting toque like crushers, plungers, cranes, elevators, hoists, conveyors, etc.