3 phase induction motor is a type of AC motor that is widely used in industrial applications. It is a simple, robust, and reliable motor that is capable of providing high torque at low speeds. In this article, we will discuss the construction, working principle, types, and applications of 3 phase induction motors, which will be helpful for students who are studying electrical engineering or related fields.
Construction of 3 Phase Induction Motor
A 3 phase induction motor consists of two main parts: the stator and the rotor. The stator is the stationary part of the motor and is made up of a core, winding, and frame. The core is made up of laminations of silicon steel that are stacked together to reduce eddy currents. The winding is made up of three-phase windings that are connected to a three-phase power supply. The frame is made up of cast iron or aluminium and provides mechanical support to the motor.
The rotor is the rotating part of the motor and is made up of a core, winding, and shaft. The core is made up of laminations of silicon steel that are stacked together to reduce eddy currents. The winding is made up of conductors that are placed in the slots of the rotor core. The shaft is made up of steel and provides mechanical support to the rotor.
Working Principle of 3 Phase Induction Motor
The working principle of a 3 phase induction motor is based on the production of a rotating magnetic field in the stator of the motor. When a three-phase power supply is connected to the stator winding, a rotating magnetic field is produced. This rotating magnetic field rotates at a synchronous speed, which is determined by the frequency of the power supply and the number of poles in the stator winding.
The rotating magnetic field induces a current in the rotor winding, which in turn produces a magnetic field. The interaction between the rotating magnetic field and the magnetic field produced by the rotor winding causes the rotor to rotate. This is known as the principle of electromagnetic induction.
The direction of rotation of the rotor can be determined by Lenz’s law, which states that the direction of the induced current in the rotor winding will be such that it opposes the change in the magnetic field that produced it. As a result, the rotor will rotate in the direction of the rotating magnetic field produced by the stator winding.
Types of 3 Phase Induction Motor
There are several types of 3 phase induction motors, each with its own characteristics and applications.
Squirrel Cage Induction Motor
The squirrel cage induction motor is the most commonly used type of 3 phase induction motor. It has a simple and robust design, with no moving parts in the rotor. The rotor consists of conductive bars or “squirrel cages” that are connected by end rings. When the stator windings produce a rotating magnetic field, it induces a current in the squirrel cage rotor, which in turn produces a magnetic field that interacts with the stator field to produce torque. The squirrel cage motor is low maintenance and has high efficiency, but its speed cannot be easily controlled.
Wound Rotor Induction Motor
The wound rotor induction motor, also known as a slip-ring motor, has a more complex design than the squirrel cage motor. The rotor winding is connected to slip rings, which allows for external control of the motor’s speed and torque characteristics. The slip rings are connected to an external resistance, which can be adjusted to control the motor’s starting torque and speed. The wound rotor induction motor is used in applications that require variable speed control, such as cranes, elevators, and rolling mills.
Double Squirrel Cage Induction Motor
The double squirrel cage induction motor has two sets of squirrel cage rotors that provide higher starting torque and reduced slip. The inner rotor has a higher resistance and lower reactance, while the outer rotor has a lower resistance and higher reactance. Double squirrel cage induction motors are used in applications that require high starting torque and low starting current.
Synchronous Induction Motor
The synchronous induction motor operates at synchronous speed and is used in applications that require constant speed. The rotor rotates at the same speed as the stator magnetic field, which is determined by the frequency of the power supply and the number of poles in the stator winding. Synchronous induction motors are used in applications such as pumps, compressors, and fans. The synchronous motor is not self-starting and requires an external means to bring it up to synchronous speed.
Applications of 3 Phase Induction Motor
Three-phase induction motors are widely used in various industries and applications due to their robustness, reliability, and high efficiency 1. Here are some common applications of 3 phase induction motors:
Industrial Applications: Three-phase induction motors are used in various industrial applications such as pumps, compressors, conveyors, and fans. They are also used in the manufacturing of steel, cement, and other heavy industries 2.
Commercial Applications: Three-phase induction motors are used in commercial applications such as elevators, escalators, and HVAC systems 3.
Agricultural Applications: Three-phase induction motors are used in agricultural applications such as irrigation pumps, grain dryers, and feed mills 4.
Transportation Applications: Three-phase induction motors are used in transportation applications such as electric trains, trams, and trolleybuses 5.
3 phase induction motors are widely used in various industries and applications due to their robustness, reliability, and high efficiency.
