AC or alternating current is what the power companies transmit through the electric wires to us. It is mainly used in electricity distribution systems for numerous reasons. But the most important reason is, it can be transformed from one voltage to another very easily. As it travels in both directions, transformers may raise and lower the voltage.
This current is utilized in AC motors for conversion into mechanical energy at its shaft. The conversion of electrical energy to mechanical energy is through a coupling medium of magnetic flux. This flux is set up in the air gap of the AC motor, where the supplied electrical energy is converted into mechanical energy. For this reason, an AC motor is known as an electromagnetic device.
Types of AC Motors
As there are various types of AC motors available out there, it is highly essential to know about the different classifications to be matched perfectly with the demand. An AC motor can be classified based on various points.
AC Motor Classification Based on the Principle of Operation
a. Synchronous Motor
In this type of AC motor, the rotation of the shaft is synchronized with the frequency of the supply current. Its rotation period is exactly equal to an integral number of AC cycles. This motor contains a multiphase AC electromagnetic on the stator to create a magnetic field that can rotate in time with the vibrations of the line current.
As a result, the rotor gives the second synchronized rotating magnetic field. This motor isn’t used to drive a load. But to improve the power factor of a local grid to which it is connected, it can act as a synchronous condenser. It is also used in high-precision positioning devices like modern robots.
b. Induction Motor
In this type of AC motor, the electromagnetic induction from the magnetic field of the stator winding obtains the electric current in the rotor needed to produce torque. This is why this motor can be made without electrical connections to the rotor. An alternative name to an induction motor is the ‘asynchronous motor.’ In this motor, the armature winding serves as both the armature winding and field winding.
A flux is produced in the air gap when the stator windings are connected to an AC supply. This flux rotates at a fixed speed which induces voltages in the stator and the rotor winding. A torque is produced when the rotor circuit is closed because the current reacts with the rotating flux.
This induction motor is the most common type of AC motor. It is used for various kinds of pumps, compressors and acts as prime movers for many pieces of machinery. Based on the rotor construction, these motors are classified into two types, namely squirrel-cage and wound-type.
AC Motor Classification Based on the Type of Current
a. Single Phase
If the AC motor has one stator, it is a single-phase motor. It doesn’t have a rotating magnetic field. Instead of a rotation, the winding of the stator creates a field that pulsates. Then the stator field creates currents in the rotor when it is at rest.
The current creates an opposite polarity which applies a turning force to the upper and lower parts of the rotor. The rotor remains stationary because the force remains equal in each direction.
A Single-phase motor is mostly used for small power conversion as it is nearly tiny in size. Almost all domestic appliances, such as refrigerators, fans, washing machines, hairdryers, portable power tools, mixers, grinders, etc., use a single-phase AC motor.
b. Poly Phase
If an AC motor has two or three-phase motors, it is a polyphase motor. This motor operates with a rotating magnetic field, which is created by a two or three-phase current. The current flows through two or more groups of coils. The polyphase AC motor is mainly used for high-power applications.
It can give a bulk power conversion from electrical to mechanical. For example, power drives for compressors, hydraulic pumps, air conditioning compressors, irrigation pumps, etc.
AC Motor Classification Based on the Speed of Operation
a. Constant Speed
This type of AC motor is either constant in speed or does not vary much in a materialistic sense. A few examples of constant speed motors are the synchronous motor, the induction motor with a small slip, the direct-current shunt motor.
It is specially designed to adapt to the driving loom spindles, d-c generators, circular saws, printing presses, etc. In general, it is for equipment that doesn’t require more than 150 percent of full-load torque in the starting.
b. Variable Speed
When a motor has a variable frequency drive or similar technology installed to control motor speed and torque, it is a variable speed motor. This type of motor offers a means for products and production facilities to significantly reduce the amount of energy consumed by the motors in their devices. It can be used to establish a line of pool pumps or upgrade the blower on a consumer refrigeration unit.
c. Adjustable Speed
The adjustable speed drive motors are used for any application in which there is mechanical equipment. This type of motor provides exact control to ramp and maintain the speed up and down. This can save up energy from 25% to 70%. The drive of this motor can vary the operating speed by changing the electrical frequency input to the motor.
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