AC ELECTRIC MOTORS

Working principle
AC motor is a device which converts alternating electric current into a mechanical device by using an electromagnetic induction phenomenon. The AC motor includes two basic parts another stationary stator having coils given an alternating current to produce a rotating magnetic field and an inside rotor attached to the output shaft making a second rotating magnetic field.

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

Types of AC Electric Motor
The AC motors could be basically categorized into two categories, synchronous, and asynchronous motors
Synchronous Motor
These motors operate at a synchronous rate and convert AC electrical energy in to the mechanical power.
When the power supply is put on the synchronous engine, 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, there will be no starting torque. As a result, 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-phase supply and the additional one may be the rotor winding which comes 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 produce constant flux. The 3-stage finding creates a magnetic field which rotates at a quickness 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 the next second, they trigger an attractive drive. But rotor remains in standstill condition because of 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 decrease speeds
Disadvantages

It is not self-starting. It needs some arrangement for starting and synchronizing.
Since its starting torque is zero, it cannot be started while 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 can be named as Asynchronous not since it always runs at a speed lower than the synchronous speed. The induction electric motor could be classified into primarily two sub-classes. The single-phase induction electric motor and the 3-phase induction motor.

In an induction engine, the single armature winding acts both as an armature winding as well as a field winding. The flux is certainly produced in the air flow gap whenever the stator winding comes to the Air Gap. This flux will rotate at a fixed speed. Therefore, it will 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 in an induction motor, an alternating flux will be produced. This flux rotates at an asynchronous swiftness and this flux is known as the rotating magnetic field. Due to the relative speed hzpt motor between the stator RMF and rotor conductor, an induced EMF can be created in the rotor conductor. A rotor current is then produced because of 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 foundation 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 path as a stator in order to reduce the relative velocity.

The speed of rotating magnetic field is given by

DC motor

Single phase induction Motor
AC electric motor which utilizes one phase power supply is called single phase induction engine.it is commonly found in the domestic and industrial application.it contains stator and Rotor component. A single-phase power is directed at 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 given to the stator winding an alternating flux will produce in the stator winding.

A squirrel cage engine is attached to the mechanical load by using the shaft. Due to 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 single phase motors are not self-starting.

In order to achieve self-beginning convert this solitary phase motor right into a two-phase motor for temporarily. This is often 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 kind of motor is named three-phase induction motor. As being a single phase motor, it has additionally both stator and rotor winding. The stator wounded by a 3-phase winding supplied by a 3-stage supply generates 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 speed. This rotating magnetic field induced an EMF in the rotor which created an induced current which flows in a path which opposite that of the rotating magnetic field, create a torque in the rotor. The rate of the rotor will never be same as that of the stator. If speed 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 beginning torque and high rush current.
Application

Large capacity exhaust fans
Driving lathe machines
Crushers