Applications of Three-Phase Induction Motor

An electromechanical energy converter known as a three-phase induction motor, which converts the three-phase electrical input power into mechanical power at the output.

A stator and a rotor make up a 3-phase induction motor. The stator is wound with three phases, whereas the rotor has a short-circuited winding known as the rotor winding. The stator winding is powered by the three-phase supply.

Working Principle of a 3-Phase Induction Motor

A part of a 3-phase induction motor may be used to demonstrate how it functions as follows:

When a balanced 3-phase supply is used to power the 3-phase stator winding, a rotating magnetic field (RMF) is produced in the motor. The synchronous speed at which this RMF revolves around the stator is determined by,

Synchronous speed Ns = 120f / P

• The rotor conductors, which are still stationary, are severed by the RMF after it passes through the air gap. Due to the relative motion of the stationary rotor conductors and the RMF, EMFs are produced in the rotor conductors. Currents begin to flow in the rotor conductors as the rotor circuit is shorted out.
• Since the magnetic field generated by the stator winding is where the current-carrying rotor conductors are located. The rotor conductors therefore encounter mechanical force. The torque created by the combined mechanical forces acting on each conductor of the rotor causes it to move in the same direction as the revolving magnetic field. Consequently, a three-phase induction motor converts the three phases of electric power input into mechanical power at the output.
• In addition, the rotor should travel in the stator field's direction in accordance with Lenz's law, which states that rotor currents should generally run counter to the force that created them. The rotor currents in this scenario are due to the relative speed between the RMF and the rotor conductors. To reduce this relative speed, the rotor starts to revolve in the same direction as the RMF.

Applications of 3-Phase Induction Motors

Three-phase induction motors with warped rotors or slip rings have a variety of uses.

1. Slip ring induction motors are appropriate for applications demanding low beginning current and loads requiring high starting torque.
2. When used with heavy loads, slip ring induction motors experience extremely large rotor energy losses during acceleration.
3. The application of slide ring induction motors extends to loads that must be gradually increased.
4. They are used when a load has to have its speed regulated.
5. A few examples of typical machinery that employ winding rotor or slip ring induction motors are crushers, plunger pumps, cranes & hoists, elevators, compressors, and conveyors.

Applications of 3-Phase Squirrel Cage Induction Motors

Induction motors with squirrel cages come in a variety of standard designs to meet the various starting and operating needs of various industrial applications. The most crucial design element for squirrel cage motors is the effective resistance of the rotor cage circuit.

The following list includes the uses for several kinds of squirrel cage induction motors:

Class A Motors

Normal beginning torque, high starting current, and minimal operating slip are all characteristics of class-A squirrel cage induction motors (from 0.005 to 0.015). This motor's single-cage rotor offers a low resistance. The efficiency of class-A motors is great at full load. As a result, these motors are appropriate for loads such as:

1. Blowers, Driers
2. Fans, Coolers
3. Machine tools, and
4. Centrifugal pumps etc.

Class B Motors

The beginning torque, starting current, and operating slip of Class-B motors are all normal. Utilizing a double-cage or deep bar rotor will preserve the beginning torque while decreasing the starting current by increasing the leakage reactance. The majority of people utilize these motors for full-voltage starting. As a result, they are also employed for loads like centrifugal pumps, fans, and blowers, among other things.

Class C Motors

High beginning torques and low starting current are characteristics of class-C motors. These motors use deep-bar rotors or twin cages with strong resistance. Class-C motors are used for basically constant-speed loads with moderately high torque and low beginning current requirements. Therefore, these motors are employed to move loads like reciprocating pumps, conveyors, compressors, and crushers.

Class D Motors

The class-D motors have the highest starting torque of any squirrel cage induction motors. These motors employ high resistance materials like brass for the rotor conductor bars instead of copper or aluminum. Low starting current and high operating slip (between 0.08 and 0.15), which result in low running efficiency, are characteristics of class-D squirrel cage motors. Therefore, these motors are utilized to power intermittent loads like punch presses, bulldozers, die-stamping machines, and shears that require heavy impact and quick acceleration. The motor is to be connected to a flywheel, which supplies the kinetic energy upon impact.