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AC ELECTRIC MOTORS

Working principle
AC motor is certainly a device which converts alternating current into a mechanical device through the use of an electromagnetic induction phenomenon. The AC motor consists of two basic parts an outside stationary stator having coils supplied with an alternating current to make a rotating magnetic field and an internal rotor mounted on the output shaft creating a second rotating magnetic field.

The rotor is an electric conductor which is suspended inside a magnetic field. Since the rotor is continually rotating there exists a change in magnetic field. Based on the Faraday’s regulation, this change 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 quickness and convert AC electrical power into the mechanical power.
When the energy supply is applied to the synchronous electric motor, 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, you will have no starting torque. Because of this, 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 other one is the rotor winding which is supplied by a DC supply. Thus, two magnetic fields are stated in a synchronous motor.

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

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

Advantages

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

It isn’t self-starting. It requires some arrangement for starting and synchronizing.
Since its beginning torque is zero, it can’t be started whilst having a load
It cannot be used for applications which hzpt motor require frequent beginning 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 less than the synchronous speed. The induction motor can be classified into generally two sub-categories. The single-phase induction motor and the 3-stage 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 air gap whenever the stator winding is supplied to the Atmosphere Gap. This flux will rotate at a fixed speed. Therefore, it’ll induce a voltage in the stator and the rotor winding.
The current 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 called the rotating magnetic field. Because of the relative speed between your stator RMF and rotor conductor, an induced EMF is developed in the rotor conductor. A rotor current is definitely 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 will oppose the source of its production. The foundation of the production is the relative velocity between rotor stator flux and rotor. The rotor will try to rotate in the same direction as a stator in order to decrease the relative velocity.

The speed of rotating magnetic field is given by

DC motor

Single phase induction Motor
AC electric electric motor which utilizes single phase power supply is named single phase induction motor.it is commonly used in the household and commercial application.it contains stator and Rotor part. A single-phase power supply is given to 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 electric motor is mounted on the mechanical load with the help of the shaft. Because of 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. That is why the solitary phase motors are not self-starting.

To be able to achieve self-starting convert this single phase motor into a two-phase engine 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 type of motor is called three-phase induction motor. Just like a single phase electric motor, it has also both stator and rotor winding. The stator wounded by a 3-stage winding given by a 3-phase supply creates an alternating flux which rotates at a synchronous velocity.
Working principle

When AC supply is directed at the 3-phase winding of the stator, it produces an alternating flux which revolves with synchronous acceleration. This rotating magnetic field induced an EMF in the rotor which in turn produced an induced current which flows in a direction which reverse that of the rotating magnetic field, produce a torque in the rotor. The quickness of the rotor will not be identical to 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 increase in load
Speed control is difficult
Having poor starting torque and high hurry current.
Application

Large capacity exhaust fans
Driving lathe machines
Crushers