Construction of Three-Phase Induction Motor

The construction of an induction motor is very simple and robust. It has mainly two parts;

1. Stator

2. Rotor

As the name suggests, the stator is a stationary part of the motor. The stator of the induction motor consists of three main parts;

1. Stator Frame

2. Stator Core

3. Stator Winding

4. 
   

Stator Frame

The stator frame is the outer part of the motor. The function of the stator frame is to provide support to the stator core and stator winding.

It provides mechanical strength to the inner parts of the motor. The frame has fins on the outer surface for heat dissipation and cooling of the motor.

The frame is casted for small machines and it is fabricated for a large machine. According to the applications, the frame is made up of die-cast or fabricated steel, aluminum/ aluminum alloys, or stainless steel.

Stator Core

The function of the stator core is to carry the alternating magnetic flux which produces hysteresis and eddy current loss. To minimize these losses, the core is laminated by high-grade steel stampings thickness of 0.3 to 0.6 mm.

These stampings are insulated from each other by varnish. All stampings stamp together in the shape of the stator core and fixed it with the stator frame.

An inner layer of the stator core has a number of slots.

Stator Winding

The stator winding is placed inside the stator slots available inside the stator core. Three-phase winding is placed as a stator winding. And three-phase supply is given to the stator winding.

The number of poles of a motor depends on the internal connection of the stator winding and it will decide the speed of the motor. If the number of poles is greater, the speed will less and if the number of poles is lesser than the speed will high. The poles are always in pairs. Therefore, the total number of poles always an even number. The relation between synchronous speed and number poles is as shown in the below equation,

NS = 120f / P

Where;

1. f = Supply Frequency

2. P = Total Number of Poles

3. Ns = Synchronous Speed

As the end of winding connected to the terminal box. Hence, there are six terminals (two of each phase) in the terminal box.

According to the application and type of starting methods of motors, the stator winding is connected in star or delta and it is done by the connection of terminals in the terminal box

Rotor

As the name suggests, the rotor is a rotating part of the motor. According to the type of rotor, the induction motor is classified as;

Squirrel Cage Induction Motor

Phase Wound (Wound Rotor) Induction motor / Slip-ring Induction Motor

The construction of the stator is same in both types of induction motors. We will discuss the types of rotors used in 3-phase induction motors in the following section of types of three phase induction motors.

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