AC ELECTRIC MOTORS

Working principle
AC motor can be a device which converts alternating current into a mechanical device by using an electromagnetic induction phenomenon. The AC motor includes two basic parts another stationary stator having coils supplied with an alternating current to produce a rotating magnetic field and an internal rotor mounted on the output shaft creating another rotating magnetic field.

The rotor is an electric conductor which is suspended in the magnetic field. Because the rotor is continually rotating there exists a modify in magnetic field. According to the Faraday’s regulation, this alter 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 acceleration and convert AC electrical energy in to the mechanical power.
When the energy supply is put on the synchronous 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 do it. So, there will be no starting torque. Consequently, the synchronous motor isn’t a self-starting motor.

Principles of operation

This motor has two electrical inputs. One may be the stator hzpt motor winding which comes by a 3-phase supply and the additional one is the rotor winding which comes 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 constant flux. The 3-stage finding generates a magnetic field which rotates at a quickness called synchronous speed.

When rotor and stator begin rotating, at some time the rotor and stator have the same polarity leading to a repulsive force on the rotor and for the next second, they trigger an attractive drive. But rotor remains in standstill condition because of its high inertial moment. Therefore, the synchronous electric motor is not self-starting.

Advantages

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

It isn’t self-starting. It needs some arrangement for beginning and synchronizing.
Since its beginning torque is zero, it cannot be started while having a load
It cannot 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 because it always runs at a speed lower than the synchronous speed. The induction electric motor could be classified into mainly two sub-categories. The single-phase induction electric motor and the 3-stage induction motor.

In an induction motor, the single armature winding acts both as an armature winding as well as a field winding. The flux is usually produced in the surroundings gap whenever the stator winding comes to the Surroundings 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 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 can be created in the rotor conductor. A rotor current can be 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 tends to 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 try to rotate in the same path as a stator to be able 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 one phase power supply is named single phase induction engine.it is commonly used in the domestic and commercial application.it consists of stator and Rotor part. A single-phase power supply is given to the stator winding. A squirrel cage rotor laminated with the iron primary 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 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 needed rotation to the rotor. That 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 is often 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 connected to the stator winding, this type of motor is named three-phase induction motor. As being a single phase engine, it has also both stator and rotor winding. The stator wounded by a 3-phase winding supplied by a 3-phase supply produces an alternating flux which rotates at a synchronous quickness.
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 created an induced current which flows in a direction which opposite that of the rotating magnetic field, produce a torque in the rotor. The quickness of the rotor will not be same as that of the stator. If acceleration matches 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 starting torque and high rush current.
Application

Large capacity exhaust fans
Driving lathe machines
Crushers