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AC ELECTRIC MOTORS

Working principle
AC motor is a device which converts alternating current right into a mechanical device by using an electromagnetic induction phenomenon. The AC motor contains two basic parts an outside stationary stator having coils supplied with an alternating current to produce a rotating magnetic field and an inside rotor mounted on the output shaft producing another rotating magnetic field.

The rotor can be an electric conductor which is suspended inside a magnetic field. Since the rotor is continually rotating there is a change in magnetic field. Based on the Faraday’s legislation, this change in magnetic field induces an electric current in the rotor.

Types of AC Electrical Motor
The AC motors can be basically categorized into two categories, synchronous, and asynchronous motors
Synchronous Motor
These motors operate at a synchronous quickness and convert AC electrical power in to the mechanical power.
When the power supply is put on the synchronous motor, a revolving field is established. This field tries to drag the rotor towards it but due to the inertia of the rotor, it cannot do it. So, you will see no starting torque. As a result, the synchronous motor isn’t a self-starting motor.

Principles of operation

This motor has two electrical inputs. One is the stator winding which comes by a 3-stage supply and the various other one may be the rotor winding which is supplied by a DC supply. Thus, two magnetic areas are stated in a synchronous motor.

The 3-phase winding produces 3-phase magnetic flux and rotor winding produce continuous flux. The 3-stage finding generates a magnetic field which rotates at a velocity called synchronous speed.

When rotor and stator begin rotating, at some time the rotor and stator have the same polarity causing a repulsive force upon the rotor and for another second, they cause an attractive drive. But rotor continues to be in standstill condition due to its high inertial instant. Therefore, the synchronous engine is not self-starting.

Advantages

The motor speed is continuous hzpt motor irrespective of the load.
Electromagnetic power of the synchronous engine varies linearly with the voltage.
Compared to an induction motor, this operates at higher efficiencies at reduce speeds
Disadvantages

It isn’t self-starting. It needs some arrangement for starting and synchronizing.
Since its starting torque is zero, it can’t be started while having a load
It can’t be used for applications which require frequent beginning so when self-starting is required.
Application

Dampers
Conveyor systems
Variable transformers
Cryogenic pumps
Induction Motor
The induction motor is also named as Asynchronous not since it always runs at a speed less than the synchronous speed. The induction engine could be classified into generally two sub-classes. The single-phase induction engine and the 3-phase induction motor.

In an induction motor, the single armature winding acts both as an armature winding in addition to a field winding. The flux is certainly produced in the air gap whenever the stator winding comes to the Air Gap. This flux will rotate at a set speed. Therefore, it will induce a voltage in the stator and the rotor winding.
The existing flow through the rotor winding reacts with the rotating flux and produces the torque.

Basic Working Principle

When an AC supply is fed to the stator winding within an induction engine, an alternating flux will be produced. This flux rotates at an asynchronous rate and this flux is known as the rotating magnetic field. Because of the relative speed between your stator RMF and rotor conductor, an induced EMF is created in the rotor conductor. A rotor current is certainly then produced due to this induced EMF.

This induced current lags behind the stator flux.

The direction of the induced current is in such a way that it tends to oppose the foundation of its production. The foundation of the production may be the relative velocity between rotor stator flux and rotor. The rotor will try to rotate in the same direction as a stator to be able to reduce the relative velocity.

The speed of rotating magnetic field is distributed by

DC motor

Single phase induction Motor
AC electric motor which utilizes one phase power supply is named single phase induction motor.it is commonly used in the domestic and commercial application.it contains stator and Rotor component. A single-phase power is directed at the stator winding. A squirrel cage rotor laminated with the iron primary is connected to a mechanical load with the aid of the shaft.
Principle of operation

When the single-phase supply is given to the stator winding an alternating flux will produce in the stator winding.

A squirrel cage engine is attached to the mechanical load with the aid of the shaft. Because of the rotating flux in the stator, an alternating electromagnetic field can be induced in the rotor. But this alternating flux didn’t provide required rotation to the rotor. This is why the single phase motors aren’t self-starting.

To be able to achieve self-beginning convert this single phase motor right into a two-phase electric motor for temporarily. This could be achieved by introducing a starting winding

Advantages

Lightweight
Efficient transmission
Fewer substations required
Disadvantages

Cannot handle the overload
No uniform Torque
High insulation cost
Application

Refrigerator
Pumps
Compressor
Portable drills
Three Phase Induction Motor
Whenever a three-phase supply is linked to the stator winding, this kind of motor is called three-phase induction motor. As being a single phase motor, it has also both stator and rotor winding. The stator wounded by a 3-stage winding supplied by a 3-stage supply generates an alternating flux which rotates at a synchronous acceleration.
Working principle

When AC supply is given to the 3-phase winding of the stator, it creates an alternating flux which revolves with synchronous swiftness. This rotating magnetic field induced an EMF in the rotor which produced an induced current which flows in a path which reverse that of the rotating magnetic field, create a torque in the rotor. The velocity of the rotor will not be same as that of the stator. If acceleration fits no torque will produce

Advantages

Simple and rugged construction
High efficiency and great power factor
Minimum maintenance
Self-starting motor.
Disadvantages

Speed decreases with increase in load
Speed control is difficult
Having poor starting torque and high hurry current.
Application

Large capacity exhaust fans
Driving lathe machines
Crushers