AC ELECTRIC MOTORS

Working principle
AC motor is a device which converts alternating electric current right into a mechanical device by using an electromagnetic induction phenomenon. The AC motor consists of two basic parts another stationary stator having coils given an alternating current to make a rotating magnetic field and an internal rotor attached to the output shaft generating another rotating magnetic field.

The rotor is an electric conductor which is suspended hzpt motor inside a magnetic field. Since the rotor is continually rotating there exists a change in magnetic field. Based on the Faraday’s regulation, this alter in magnetic field induces an electric current inside a rotor.

Types of AC Electric Motor
The AC motors can be basically classified into two categories, synchronous, and asynchronous motors
Synchronous Motor
These motors operate at a synchronous rate and convert AC electrical power in to the mechanical power.
When the energy supply is put on the synchronous engine, a revolving field is set up. This field attempts to drag the rotor towards it but due to the inertia of the rotor, it cannot perform it. So, there will be no starting torque. Consequently, the synchronous motor is not 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 additional one is the rotor winding which is supplied 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 creates a magnetic field which rotates at a quickness called synchronous speed.

When rotor and stator begin rotating, at some point the rotor and stator have the same polarity leading to a repulsive force on the rotor and for the next second, they cause an attractive force. But rotor remains in standstill condition due to its high inertial second. Therefore, the synchronous engine is not self-starting.

Advantages

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

It is not self-starting. It needs some arrangement for beginning and synchronizing.
Since its beginning torque is zero, it cannot be started whilst having a load
It can’t be used for applications which require frequent starting 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 can be classified into mainly two sub-categories. The single-phase induction engine and the 3-phase induction motor.

In an induction electric motor, the single armature winding acts both as an armature winding as well as a field winding. The flux can be produced in the surroundings gap whenever the stator winding comes to the Surroundings 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 electric motor, an alternating flux will be produced. This flux rotates at an asynchronous speed and this flux is called the rotating magnetic field. Because of the relative speed between your stator RMF and rotor conductor, an induced EMF is usually created in the rotor conductor. A rotor current is certainly then produced for this reason induced EMF.

This induced current lags behind the stator flux.

The direction of the induced current is so that it tends to oppose the source of its production. The source of the production is the relative velocity between rotor stator flux and rotor. The rotor will attempt to rotate in the same direction as a stator in order 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 single phase power supply is called single phase induction engine.it is commonly used in the domestic and commercial application.it consists of stator and Rotor component. A single-phase power is given to the stator winding. A squirrel cage rotor laminated with the iron core is linked to a mechanical load by using 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 mounted on the mechanical load by using the shaft. Because of the rotating flux in the stator, an alternating electromagnetic field is usually induced in the rotor. But this alternating flux did not provide needed rotation to the rotor. This is why the one phase motors are not self-starting.

In order to achieve self-starting convert this single phase motor into a two-phase electric motor for temporarily. This can 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
When 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 electric motor, it has additionally both stator and rotor winding. The stator wounded by a 3-stage winding given by a 3-phase supply generates 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 rate. This rotating magnetic field induced an EMF in the rotor which in turn created an induced current which flows in a path which reverse that of the rotating magnetic field, create a torque in the rotor. The speed of the rotor will not be identical to 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 upsurge in load
Speed control is difficult
Having poor beginning torque and high rush current.
Application

Large capacity exhaust fans
Driving lathe machines
Crushers