AC ELECTRIC MOTORS

Working principle
AC motor is a device which converts alternating current into a mechanical device by using an electromagnetic induction phenomenon. The AC motor contains two basic parts an outside stationary stator having coils given an alternating current to make a rotating magnetic field and an internal rotor mounted on the output shaft making a second rotating magnetic field.

The rotor can be an electric conductor which is suspended in the magnetic field. Because the rotor is constantly rotating there exists a modify in magnetic field. Based on the Faraday’s law, this modify in magnetic field induces a power current in the rotor.

Types of AC Electrical 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 into the mechanical power.
When the power supply is applied to 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. Consequently, the synchronous motor is not a self-starting motor.

Principles of operation

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

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

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

Advantages

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

It is not self-starting. It requires some arrangement for beginning and synchronizing.
Since its beginning 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 can be named as Asynchronous not because it always runs at a speed lower than the synchronous speed. The induction electric motor could be classified into primarily two sub-types. The single-phase induction electric motor and the 3-phase induction motor.

In an induction electric motor, the single armature winding acts both as an armature winding in addition to a field winding. The flux can be produced in the atmosphere gap whenever the stator winding comes to the Surroundings Gap. This flux will rotate at a fixed 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 in an induction engine, an alternating flux will be produced. This flux rotates at an asynchronous rate and this flux is called the rotating magnetic field. Because of the relative speed between your stator RMF and rotor conductor, an induced EMF can be developed in the rotor conductor. A rotor current is usually then produced due to this induced EMF.

This induced current lags behind the stator flux.

The direction of the induced current is so that it will oppose the foundation of its production. The source 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 decrease 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 named single phase induction electric motor.it is commonly used in the household and industrial application.it contains stator and Rotor part. A single-phase power is given to the stator winding. A squirrel cage rotor laminated with the iron primary is linked to a mechanical load with the aid 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 electric motor is attached to the mechanical load by making use of the shaft. Due to the rotating flux in the stator, an alternating electromagnetic field is induced in the rotor. But this alternating flux did not provide required rotation to the rotor. This is why the one phase motors are not self-starting.

In order to achieve self-starting convert this one phase motor right into a two-phase motor for temporarily. This can 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
Compressor
Portable drills
Three Phase Induction Motor
Whenever a three-phase supply is connected to the stator winding, this type 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-stage supply creates an alternating flux which rotates at a synchronous swiftness.
Working principle

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

Advantages

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

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

Large capacity exhaust fans
Driving lathe machines
Crushers