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Induction Motor, Working Principle, Types Of Induction Motor

Induction motors are the most commonly used motors in most of the applications. Learn more about the types of induction motors in comprehensive guide.

Pratibha Bohra8 Dec, 2023

Induction Motor: An induction motor, also known as an asynchronous motor, is a popular type of AC electric motor. It works in a simple way: the rotating magnetic field from the motor's stationary part (called the stator) generates electric currents in the moving part (called the rotor) using a process called electromagnetic induction.

This creates the necessary torque to make the motor spin. The rotor can be either a squirrel cage rotor or a wound-type rotor. Induction motors are widely used due to their straightforward design and efficient operation.

What is an Induction Motor

An induction motor is a type of electric motor used for various industrial and commercial applications. It's a widely used motor due to its robust construction, reliability, and relatively low cost. Induction motors work on the principle of electromagnetic induction to convert electrical energy into mechanical energy, which drives the rotation of the motor's shaft.

Induction Motor Working Principle

The working principle of an induction motor is based on the concept of electromagnetic induction. It involves the interaction of magnetic fields to produce the rotation of the motor's shaft.

Rotating Magnetic Field: The motor has two main components - the stationary part called the stator and the rotating part called the rotor. When AC (alternating current) electricity flows through the stator windings, it creates a rotating magnetic field around the stator.
Induced Current in Rotor: As the rotating magnetic field cuts across the rotor, it induces a flow of electric current in the rotor's conductors (wires). This is similar to how a moving magnet can induce current in a coil of wire.
Interaction of Magnetic Fields: The induced current in the rotor creates its own magnetic field. This induced magnetic field interacts with the rotating magnetic field of the stator.
Torque and Rotation: The interaction between the stator's rotating magnetic field and the rotor's induced magnetic field results in a force, known as torque. This torque causes the rotor to start rotating and follow the rotation of the stator's magnetic field.
Continuous Rotation: As long as the stator is supplied with AC power, the rotating magnetic field will persist, continually inducing currents in the rotor and keeping the motor rotating.

Types of Induction Motor

Induction motors can be categorized into two main types:

Single-phase induction motors
Three-phase induction motors

Single-Phase Induction Motor

The single-phase induction motor has various subtypes, which are:

Split Phase Induction Motor: This type uses a special winding arrangement to create a rotating magnetic field and start the motor.
Capacitor Start Induction Motor: It employs a capacitor to create a phase difference, enabling the motor to start smoothly.
Capacitor Start and Capacitor Run Induction Motor: This motor utilizes two capacitors to enhance its starting and running performance.
Shaded Pole Induction Motor: This simple motor design uses shading coils to create a rotating magnetic field, making it economical but less powerful.

Three-Phase Induction Motor

The three-phase induction motor consists of two primary types:

Squirrel Cage Induction Motor: It is the most common type, with a rugged and straightforward design, suitable for various applications.
Slip Ring Induction Motor: This type has external resistors and rings, allowing control of the starting torque and speed.

Now, let's clarify the concept of a "self-starting" motor. A self-starting motor is one that can begin running automatically without requiring any external force. For instance, when you turn on a fan, it starts rotating on its own, making it a self-starting machine.

Difference Between Synchronous and Induction Motor

Check the difference between synchronous and induction motor:

Difference Between Synchronous and Induction Motor
Feature	Synchronous Motor	Induction Motor
Operation Principle	Operates at synchronous speed with a fixed relationship between rotor and stator magnetic fields.	Operates at a speed slightly lower than synchronous speed due to slip between rotor and stator fields.
Starting	Requires external means to bring it up to synchronous speed before it can generate power.	Self-starting; starts automatically once power is supplied to the stator.
Speed Control	Speed is constant and depends on the frequency of the power supply and the number of poles.	Speed control is limited, typically achieved through changes in load or using variable frequency drives (VFDs).
Efficiency	Generally more efficient at higher loads and constant speeds.	Efficiency is good over a wide range of loads and speeds, making it suitable for variable loads.
Applications	Power generation, precision machinery, synchronous clocks, and where constant speed is crucial.	Industrial applications, household appliances, pumps, fans, conveyors, and variable load situations.
Rotor Construction	Rotor contains either a wound rotor with slip rings or a permanent magnet rotor.	Rotor is usually a squirrel cage type, made of conductive bars embedded in the rotor core.
Maintenance	Requires more maintenance due to brushes and slip rings in some types.	Requires less maintenance since there are no brushes and slip rings in the standard design.
Power Factor	Can be adjusted to have a leading or lagging power factor by adjusting field excitation.	Typically has a lagging power factor, which can be improved using power factor correction techniques.
Complexity	More complex construction and control mechanisms.	Simpler construction and easier to control, leading to widespread use in various applications.

Why is Three Phase Induction Motor Self Starting?

In a three-phase system, there are three individual power lines with a 120° phase difference between each. This phase difference creates a rotating magnetic field, which in turn causes the rotor to move. Let's think of the three phases as A, B, and C. When phase A is energized, it attracts the rotor towards its winding. As the next moment comes, phase B gets energized, pulling the rotor towards its winding, and then it's the turn of phase C. This continuous energization of different phases keeps pulling the rotor, making it rotate continuously. In summary, the three-phase system creates a rotating magnetic field by energizing each phase in sequence, causing the rotor to move and rotate smoothly. This principle is at the heart of how three-phase induction motors work.

Why Single Phase Induction Motor is not Self Starting?

The concept of a single-phase induction motor is fascinating because, despite having only one phase, it can make the rotor rotate. However, initially, single-phase induction motors face a challenge of not being self-starting. This happens because the AC supply creates a pulsating magnetic field in the stator winding, and at the starting point, the two oppositely rotating magnetic fields cancel each other out, resulting in no torque to make the motor run. To overcome this problem, we use a clever solution. We add an auxiliary winding along with the main winding and connect a capacitor in series with the auxiliary winding. The capacitor creates a phase difference when current flows through both windings. This phase difference generates a starting torque in the rotor, allowing the motor to start rotating smoothly. In practical scenarios, you might have noticed that a fan won't start rotating when the capacitor is disconnected, but if you give it a gentle push, it starts moving. The capacitor is the key to solving this issue in single-phase induction motors. The advantages of induction motors are many, with high efficiency being one of the significant benefits, which can go as high as 97%. However, the motor's speed varies with the applied load, which is a notable disadvantage. For three-phase induction motors, changing the direction of rotation is as simple as changing the phase sequence of the three-phase supply. For single-phase motors, the direction can be reversed by switching the capacitor terminals in the winding. In summary, single-phase induction motors are intriguing because of their ability to rotate the rotor with just one phase. The addition of capacitors overcomes the starting challenge, allowing the motor to work effectively. Induction motors, whether single-phase or three-phase, find a wide range of applications due to their high efficiency and versatility.

Induction Motor FAQs

What is an induction motor?

An induction motor is a type of electric motor used in various industrial and commercial applications. It works on the principle of electromagnetic induction, where a rotating magnetic field in the stator induces currents in the rotor, causing it to rotate.

How does an induction motor work?

An induction motor's working principle involves creating a rotating magnetic field in the stator using AC electricity. This rotating field induces currents in the rotor, producing a torque that drives the rotor's rotation.

What are the types of induction motors?

Induction motors can be classified into two main types: single-phase induction motors and three-phase induction motors. Each type has further subtypes with different characteristics and applications.

What is the difference between a single-phase and a three-phase induction motor?

The primary difference lies in the number of power phases. Single-phase motors have only one phase, while three-phase motors have three individual phases, resulting in more efficient and powerful performance for three-phase motors.

Is an induction motor self-starting?

Three-phase induction motors are self-starting, meaning they start rotating automatically once power is supplied. On the other hand, single-phase induction motors require additional means, such as capacitors, to start smoothly.

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What is an Induction Motor

Induction Motor Working Principle

The working principle of an induction motor is based on the concept of electromagnetic induction. It involves the interaction of magnetic fields to produce the rotation of the motor's shaft.

Rotating Magnetic Field: The motor has two main components - the stationary part called the stator and the rotating part called the rotor. When AC (alternating current) electricity flows through the stator windings, it creates a rotating magnetic field around the stator.
Induced Current in Rotor: As the rotating magnetic field cuts across the rotor, it induces a flow of electric current in the rotor's conductors (wires). This is similar to how a moving magnet can induce current in a coil of wire.
Interaction of Magnetic Fields: The induced current in the rotor creates its own magnetic field. This induced magnetic field interacts with the rotating magnetic field of the stator.
Torque and Rotation: The interaction between the stator's rotating magnetic field and the rotor's induced magnetic field results in a force, known as torque. This torque causes the rotor to start rotating and follow the rotation of the stator's magnetic field.
Continuous Rotation: As long as the stator is supplied with AC power, the rotating magnetic field will persist, continually inducing currents in the rotor and keeping the motor rotating.

Types of Induction Motor

Induction motors can be categorized into two main types:

Single-phase induction motors
Three-phase induction motors

Single-Phase Induction Motor

The single-phase induction motor has various subtypes, which are:

Split Phase Induction Motor: This type uses a special winding arrangement to create a rotating magnetic field and start the motor.
Capacitor Start Induction Motor: It employs a capacitor to create a phase difference, enabling the motor to start smoothly.
Capacitor Start and Capacitor Run Induction Motor: This motor utilizes two capacitors to enhance its starting and running performance.
Shaded Pole Induction Motor: This simple motor design uses shading coils to create a rotating magnetic field, making it economical but less powerful.

Three-Phase Induction Motor

The three-phase induction motor consists of two primary types:

Squirrel Cage Induction Motor: It is the most common type, with a rugged and straightforward design, suitable for various applications.
Slip Ring Induction Motor: This type has external resistors and rings, allowing control of the starting torque and speed.

Difference Between Synchronous and Induction Motor

Check the difference between synchronous and induction motor:

Difference Between Synchronous and Induction Motor
Feature	Synchronous Motor	Induction Motor
Operation Principle	Operates at synchronous speed with a fixed relationship between rotor and stator magnetic fields.	Operates at a speed slightly lower than synchronous speed due to slip between rotor and stator fields.
Starting	Requires external means to bring it up to synchronous speed before it can generate power.	Self-starting; starts automatically once power is supplied to the stator.
Speed Control	Speed is constant and depends on the frequency of the power supply and the number of poles.	Speed control is limited, typically achieved through changes in load or using variable frequency drives (VFDs).
Efficiency	Generally more efficient at higher loads and constant speeds.	Efficiency is good over a wide range of loads and speeds, making it suitable for variable loads.
Applications	Power generation, precision machinery, synchronous clocks, and where constant speed is crucial.	Industrial applications, household appliances, pumps, fans, conveyors, and variable load situations.
Rotor Construction	Rotor contains either a wound rotor with slip rings or a permanent magnet rotor.	Rotor is usually a squirrel cage type, made of conductive bars embedded in the rotor core.
Maintenance	Requires more maintenance due to brushes and slip rings in some types.	Requires less maintenance since there are no brushes and slip rings in the standard design.
Power Factor	Can be adjusted to have a leading or lagging power factor by adjusting field excitation.	Typically has a lagging power factor, which can be improved using power factor correction techniques.
Complexity	More complex construction and control mechanisms.	Simpler construction and easier to control, leading to widespread use in various applications.