AC ELECTRIC MOTORS

Working principle
AC motor can be a device which converts alternating current right into a mechanical device through the use of an electromagnetic induction phenomenon. The AC motor contains two basic parts another stationary stator having coils supplied with an alternating current to produce a rotating magnetic field and an inside rotor attached to the output shaft generating a second rotating magnetic field.

The rotor is an electric conductor which is suspended inside a magnetic field. Because the rotor is constantly rotating there exists a change in magnetic field. According to the Faraday’s legislation, this change in magnetic field induces a power current inside a rotor.

Types of AC Electrical Motor
The AC motors could be basically classified into two categories, synchronous, and asynchronous motors
Synchronous Motor
These motors operate at a synchronous velocity and convert AC electrical energy into the mechanical power.
When the power supply is put on the synchronous electric motor, a revolving field is set up. This field tries to drag the rotor towards it but due to the inertia of the rotor, it cannot perform it. So, you will see no starting torque. Because of this, the synchronous motor isn’t a self-starting motor.

Principles of operation

This motor has two electrical inputs. One is the stator winding which is supplied by a 3-phase supply and the other one is the rotor winding which comes by a DC supply. Thus, two magnetic fields are produced in a synchronous motor.

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

When rotor and stator start rotating, at some time the rotor and stator have the same polarity leading to a repulsive force upon the rotor and for another second, they cause an attractive push. But rotor continues to be in standstill condition because of its high inertial minute. Therefore, the synchronous engine is not self-starting.

Advantages

The motor speed is constant irrespective of the strain.
Electromagnetic power of the synchronous electric motor varies linearly with the voltage.
Compared to an induction motor, this operates in higher efficiencies at lower speeds
Disadvantages

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

Dampers
Conveyor systems
Variable transformers
Cryogenic pumps
Induction Motor
The induction motor is also named as Asynchronous not because it always runs at a speed lower than the synchronous speed. The induction engine could be classified into generally two sub-classes. The single-phase induction motor 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 definitely produced in the atmosphere gap whenever the stator winding comes to the Atmosphere Gap. This flux will rotate at a set speed. Therefore, it’ll 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 electric motor, an alternating flux will be produced. This flux rotates at an asynchronous velocity 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 then produced for this reason induced EMF.

This induced current lags behind the stator flux.

The direction of the induced current is in such a way that it will oppose the source of its production. The foundation of the production may be the relative velocity between rotor stator flux and rotor. The rotor will attempt to rotate in the same path 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 electric motor which utilizes single phase power supply is called single phase induction motor.it is commonly found in the household and commercial application.it consists of stator and Rotor part. A single-phase power is directed at the stator winding. A squirrel cage rotor laminated with the iron core is connected to a mechanical load by making use of the shaft.
Principle of operation

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

A squirrel cage motor is attached to the mechanical load with the help 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 necessary rotation to the rotor. This is why the solitary phase motors aren’t self-starting.

To be able to achieve self-starting convert this solitary phase motor right into a two-phase electric motor for temporarily. This could be attained 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
hzpt motor Compressor
Portable drills
Three Phase Induction Motor
Whenever a three-phase supply is connected to the stator winding, this kind of motor is called three-phase induction motor. Just like a single phase electric motor, it has additionally both stator and rotor winding. The stator wounded by a 3-phase winding given by a 3-stage supply creates an alternating flux which rotates at a synchronous speed.
Working principle

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

Advantages

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

Speed decreases with upsurge in load
Speed control is difficult
Having poor beginning torque and high rush current.
Application

Large capacity exhaust fans
Driving lathe machines
Crushers