- Three Phase Induction Motor Definition: A three-phase induction motor is an asynchronous motor that operates at a speed different from the synchronous speed, using three-phase power.
- Stator: The stator is the stationary part of the motor that receives the three-phase supply to generate a rotating magnetic field.
- Rotor: The rotor, connected to the mechanical load, rotates within the stator’s magnetic field.
- Types of Rotors: There are two types of rotors in three-phase induction motors: squirrel cage rotor and slip ring rotor.
- Types of Three Phase Induction Motor: Three-phase induction motors are classified as squirrel cage induction motors and slip ring induction motors based on the rotor type.
An induction motor is defined as an asynchronous motor because it runs at a speed different from the synchronous speed. Like other electrical motors, it has two main parts: the rotor and the stator.
Stator
As the name indicates stator is a stationary part of induction motor. A three phase supply is given to the stator of the induction motor.
Rotor
The rotor is a rotating part of induction motor. The rotor is connected to the mechanical load through the shaft. The rotors of the three phase induction motor are further classified as:
- Squirrel Cage Rotor
- Slip Ring Rotor or Wound Rotor or Phase Wound Rotor
Depending upon the type of rotor used the three-phase induction motor is classified as:
- Squirrel Cage Induction Motor
- Slip Ring Induction Motor or Wound Rotor Induction Motor or Phase Wound Induction Motor
The construction of stator for both the kind of three phase induction motor remains the same and is discussed in brief below.
Stator of Three Phase Induction Motor
The stator of the three phase induction motor consists of three main parts:
- Stator frame
- Stator core
- Stator winding or field winding
Stator Frame
The stator frame is the outer part of the three-phase induction motor. It supports the stator core and field winding, providing protection and mechanical strength to the inner parts. Made of die-cast or fabricated steel, the frame must be strong and rigid to maintain the small air gap between the rotor and stator, preventing unbalanced magnetic pull.
Stator Core
The stator core’s main function is to carry alternating flux. It is laminated to reduce eddy current losses, with each lamination being 0.4 to 0.5 mm thick. These laminations are stamped together to form the stator core, which is housed in the stator frame. Made of silicon steel, the laminations help reduce hysteresis loss.
Stator Winding or Field Winding
The slots on the periphery of stator core of the three phase induction motor carries three phase windings. This three phase winding is supplied by three phase ac supply. The three phases of the winding are connected either in star or delta depending upon which type of starting method is used.
The squirrel cage motor is mostly started by star-delta stater and hence the stator of squirrel cage motor are delta connected. The slip ring three phase induction motor are started by inserting resistances so, the stator winding can be connected either in star or delta. The winding wound on the stator of three phase induction motor is also called field winding and when this winding is excited by three phase ac supply it produces a rotating magnetic field.
