Electric Motors
Electric Motors

3 phase induction motor construction (main parts of induction motor)

3 phase induction motor construction

At this topic, I will explain in details about 3 phase induction motor construction … before we talked about parts of the electric motor generally … but at this topic, we will go deep for 3 phase induction motor construction only.

Nikola Tesla who invents 3 phase induction motor in 1886 and it is considered to be the most widespread in the industrial world today.

Nikola Tesla

3 phase induction motor is the most prevalent in the industrial world today.

We know that in America alone, more than 50 million of these species are collected by 150 million horsepower, which is believed to increase by about one million motors every year.

3 phase induction motor

This widespread of the induction motor is due to its advantages such as durability, the simplicity of installation,  low price compared to other electric motors and lack of maintenance.

Induction motor also has capabilities ranging from a part of the horse to more than 10,000 horsepower.

It does not need any means of excitation in addition to its high efficiency.

The advantages of operating it are good and satisfactory in a business that does not require a change in speed.

The disadvantages of 3 phase induction motors are that it is not easy to control its speed and the starting current of this engine is six to eight times full load current as well as the low power factor at light loads.

But we find that the advantages of this motor outweigh its defects in most industrial applications and have recently found electronic controls and drives that led to overcoming these defects.

3 phase induction motor construction:

The 3 phase induction motor is composed of two main components, such as any other motor:



3 phase induction motor construction

These are the main parts you can check full details about all parts of motors here >> parts of a motor.

The Stator:

The stator is composed of magnetic strips of magnetic iron.

ranging from 0.3 mm to 0.6 mm in size according to the size of the induction motor.

Isolated from each other with an electric insulator.

Where together they form a cylindrical object with a number of sewers inside it to install the winding.

3 phase induction motor stator

The aim of manufacturing stator with this method is to reduce the iron heat generated by the eddy current that formed by the iron exposure to the variable magnetic field within the motor.

Large motors usually have ventilation holes between the slides in the stator.

After completing the manufacture of the stator in this way we divide it into the required number of electrodes and divide the sewage in all pole into the three phases and then the windings are installed each phase in the sewer under each pole to separate each phase and the last 120 degrees electric.

3 phase induction motor stator wiring

  At the end of the winding process, three phases have been installed in the fixed member of each winding. These terminals will be fed by the stator after connecting them either as a star or delta.

Delta Connection for 3 phase induction motors

Delta Connection for 3 phase induction motors


Star Connection for 3 phase induction motors

Star Connection for 3 phase induction motors

The Rotor

There are two different types of the structure and similar in electrical properties.

 The 3 phase induction motor is usually called according to the type of its rotor to distinguish between the two types.

Wound rotor type

Squirrel cage rotor type

Wound rotor type:

The rotor is composed of concentric strips of magnetic iron isolated from each other.

Mounted on the motor shaft and engraved with a number of sewers to install the winding.

The rotor is divided into a number of poles equal to the poles of the stator.

wound rotor type of 3 phase induction motor

The sewer is divided into each pole into three sections. Each section is fitted with the winding of one of the three sides so that between each phase and the last 120 degrees of electricity.

Usually, these three windings arrive in the shape of a star where three limbs are shortened together within the rotor while the other three are connected to three sliding rings mounted on the same shaft through sliding rings and carbon brushes for sliding rings during rotation.

The rotor coil is connected to the outside of the motor to control the start of the motor’s rotation; or to regulate its speed by connecting external resistors to these three sides.

slip ring 3 phase induction motor

Therefore, this type of induction motor has the potential to change the characteristics of its operation on a large scale by connecting the windings rotor through an external circuit.

Squirrel cage rotor type

The squirrel cage rotor is very similar to the rotor in the wound rotor type in terms of mechanical structure. Instead of placing windings in the sewer, copper or aluminum rods are placed. The ends of these bars are shortened at two sides through two rings of the same material.

squirrel cage induction motor

This type is not divided into a certain number of poles; but can automatically adapt to the number of poles and phases of the stator in which it will be installed.

3 phase squirrel cage induction motor

Since it does not have slip rings, it cannot be connected to an external circuit.

And therefore the properties of the squirrel cage induction motor cannot be changed or controlled at its speed.

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Electrical Engineer