AC or alternating current is what the power companies transmit through the electric wires to us. It is mostly 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, so that they can 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. To create a magnetic field that can rotate in time with the vibrations of the line current, this motor contains a multiphase AC electromagnetic on the stator. 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 ‘asynchronous motor’. In this motor, the armature winding serves as both the armature winding and field winding. A flux is produced in the gap of the air 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. When the rotor circuit is closed, a torque is produced because the current reacts with the rotating flux. This induction motor is the most common type of AC motor. It is used for various types 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 small in size. Almost all the 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 poly-phase 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 mostly used for applications that require high power as 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 those types of equipment that don’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 greatly reduce the amount of energy being consumed by the motors in their devices. It can be used for establishing a line of pool pumps or upgrading 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 extremely precise control to ramp and maintain the speed up and down. This can save up energy from 25% to 70%. The drive of this motor is able to vary the operating speed by changing the electrical frequency input to the motor.
Also read: What is ac motor and how does it work