Induction Motors: Working Principle and Types (Guide)

There is something complicated about induction motors, as if they are something that powers a huge machine. Everyday life processes rely on induction motors. The components can be found in many different products, such as air conditioners, refrigerators, automobiles, and air compressors. How do they work, and what are they? We need to explain a little. Because of this, I wrote this in-depth article for you guys. So without further ado, let's get started! You can also check out the Cross Sectional Area of Wire.

What is Induction Motors?

Electric motors that use electromagnetic induction, also known as asynchronous motors, are called induction motors. Using electromagnetic induction, this motor produces torque by inducing current through the stator winding's magnetic field. Compared to other types of electric motors, induction motors are simpler, more robust, and more durable due to the lack of brushes and commutators. In an AC motor, when connected to an AC power source, the stator produces a rotating magnetic field. Inside the stator is the rotor, which rotates. The rotor's magnetic field interacts with the stator's magnetic field when the rotating magnetic field induces a current in it. This causes the rotor to spin.

It is widely known that induction motors are reliable, efficient, and require little maintenance. Industrial settings often use them to power machinery, pumps, and fans. Refrigerators, washers, and air conditioners are among the home appliances that use induction motors, as well as industrial applications. Basically, there are two types of induction motors: single-phase and three-phase. When it comes to power requirements and industrial applications, three-phase motors are usually better than single-phase motors. Several devices and systems rely on induction motors for reliable performance due to their versatility, durability, and cost-effectiveness.

Working Principle

A rotating magnetic field induces currents in the rotor, which cause the rotor to rotate, according to the principle of electromagnetic induction. An induction motor's working principle is explained in detail below:

Stator and Rotor Construction: Stator and rotor are the two main components of an induction motor. It consists of a core made of laminated steel sheets. The stator is the stationary component of the motor. Copper or aluminum windings are insulated in slots evenly spaced in the stator core. Industrial applications typically use three-phase AC power supplies with these windings.

Three-Phase AC Supply: In the presence of three-phase AC voltage, rotating magnetic fields are generated in the stator windings. Based on the frequency and number of poles in the stator winding, a rotating magnetic field rotates at a synchronous speed.

Induction of Current in Rotor: Squirrel cage rotors are wound around a cylindrical core and have separate windings, or slip ring rotors are wound around conductive bars. Electromagnetic induction occurs when the rotating magnetic field from the stator cuts across the rotor conductors and induces current (eddy currents).

Production of Torque: A rotor current creates a magnetic field according to Faraday's law of electromagnetic induction. A torque is produced on the rotor when the rotating magnetic field of the stator interacts with the magnetic field of the rotor. By attempting to align the rotor with the stator's rotating magnetic field, the torque tries to align the rotor with the stator's rotating magnetic field.

Rotor Rotation: Rotation begins when torque is produced. It is necessary for the rotor to induce currents in the stator that the rotor's speed is slightly lower than the stator's synchronous speed because of slip.

Operation without Electrical Connections: It is not necessary to connect wires to the rotor of an induction motor, unlike a DC motor or synchronous motor (with the exception of wound rotor motors that use slip rings). Electromagnetic induction transfers power from the stator to the rotor.

Types of Induction Motor

Squirrel Cage Induction Motor:

It is most common to use squirrel cage induction motors since they are simple, rugged, and require little maintenance. These motors are composed of laminations that contain slots for copper or aluminum bars, resembling squirrel cages. A short-circuited end ring finishes off the ends of these bars. Due to electromagnetic induction, a rotating magnetic field is created when power is applied to the stator windings. By interacting with the rotating magnetic field of the stator, these currents produce a magnetic field that causes the rotor to rotate. For applications that require constant speeds, squirrel cage motors are highly efficient, robust, and reliable.

Wound Rotor Induction Motor:

Rotor windings in wound rotor induction motors are visible outside slip rings, unlike those in stator induction motors. The slip rings on the rotor can be used to connect external resistors and devices. As a result, the motor's speed and torque characteristics can be controlled externally by controlling the rotor resistance. When compared to squirrel cage motors, wound rotor motors have higher starting torque and can be used in applications that require smooth acceleration and variable speed.

Single-Phase Induction Motor:

Residential and light industrial applications with limited three-phase power can use single-phase induction motors, which are designed to run on single-phase AC power. Fan motors, washing machines, pumps, and compressors are examples of household appliances which use them. A rotating magnetic field and starting torque are typically provided by auxiliary windings or capacitors in single-phase motors.

Three-Phase Induction Motor:

The most popular type of induction motor in industrial applications is the three-phase induction motor, which is highly efficient, reliable, and can provide a constant power output. Their stator produces a rotating magnetic field which induces current in the squirrel cage rotor when they are powered by a three-phase AC supply. There are several types of three-phase motors, including squirrel cages, wound rotors, and double squirrel cages, each catering to a particular torque, speed, or power requirement.

Double Squirrel Cage Induction Motor:

An inner set of rotor bars and an outer set of rotor bars separate a double squirrel cage induction motor by a high-resistance member. In comparison to standard squirrel cage motors, this design provides higher starting torque and efficiency. In applications such as cranes, hoists, and conveyors that require high starting torque and frequent starts and stops, double squirrel cage motors are used.

Polyphase Induction Motors:

Several phases of an AC supply are required for polyphase induction motors. Industrial applications such as drives for large industrial machines and high-performance machinery require precise control of speed and torque with these motors.

Faqs

Question 1: What does an induction motor operate at?

Answer: Unlike synchronous motors, induction motors rotate at speeds that are close to but less than synchronous speeds. In the same direction as the rotor field, slip is negative when the rotor speed exceeds the synchronous speed.

Question 2: Why do we choose induction motors?

Answer: It is simple, durable, and cost-effective to use an induction motor. It has the ability to operate at variable speeds and loads directly from the line, and it can be started directly from the line. There are, however, some disadvantages associated with induction motors, such as their low efficiency, power factor, and torque. Furthermore, synchronous motors generate more heat, noise, and slip than asynchronous ones.

Wrapping Up

Induction motors are fundamental to the design, operation, and maintenance of electrical systems, so engineers and technicians must understand their working principle. Electromagnetic induction drives torque and rotation in the rotor by inducing currents in the stator by rotating the magnetic field. Among the different types of motors are squirrel cage, wound rotor, single-phase, three-phase, dual-phase, and polyphase, each featuring unique characteristics appropriate for a particular application. Electrical energy can be converted into mechanical power using induction motors regardless of whether they are used in industrial equipment, household appliances, or specialized equipment. Check out more on Blikai Electronic.