AC ELECTRIC MOTORS
AC motor is definitely a device which converts alternating electric current right into a mechanical device by using an electromagnetic induction phenomenon. The AC motor includes two basic parts an outside stationary stator having coils given an alternating current to produce 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 in the magnetic field. Because the rotor is continually rotating there is a change 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 classified into two categories, synchronous, and asynchronous motors
These motors operate at a synchronous speed and convert AC electrical power into the mechanical power.
When the power supply is applied to the synchronous engine, a revolving field is set up. This field attempts to drag the rotor towards it but because of the inertia of the rotor, it cannot do 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 is supplied by a 3-stage supply and the other 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 continuous flux. The 3-stage finding generates a magnetic field which rotates at a swiftness called synchronous speed.
When rotor and stator start rotating, at some time the rotor and stator have the same polarity causing 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 minute. Therefore, the synchronous engine is not self-starting.
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, it operates at higher efficiencies at decrease speeds
It isn’t self-starting. It requires some arrangement for starting and synchronizing.
Since its starting torque is zero, it can’t be started whilst having a load
It can’t be used for applications which require frequent beginning and when self-starting is required.
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 primarily two sub-classes. The single-phase induction motor and the 3-phase induction motor.
In an induction motor, the single armature winding acts both as an armature winding in addition to a field winding. The flux is usually produced in the air gap whenever the stator winding is supplied to the Air flow 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 in an induction electric motor, an alternating flux will be produced. This flux rotates at an asynchronous swiftness and this flux is called the rotating magnetic field. Due to the relative speed between your stator RMF and rotor conductor, an induced EMF is definitely developed in the rotor conductor. A rotor current can be 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 will oppose the source 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 direction as a stator in order to reduce the relative velocity.
The speed of rotating magnetic field is given by
Single phase induction Motor
AC electric motor which utilizes single phase power supply is named single phase induction engine.it is commonly found in the domestic and commercial 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 core is connected 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 attached to the mechanical load with the help of the shaft. Due to the rotating flux in the stator, an alternating electromagnetic field is definitely induced in the rotor. But this alternating flux did not provide necessary rotation to the rotor. That is why the solitary phase motors aren’t self-starting.
In order to achieve self-starting convert this single phase motor right into a two-phase electric motor for temporarily. This could be attained by introducing a starting winding
Fewer substations required
Cannot handle the overload
No uniform Torque
High insulation cost
Three Phase Induction Motor
Whenever a hzpt motor three-phase supply is linked to the stator winding, this type of motor is named three-phase induction motor. Just like a single phase engine, it has also 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 speed.
When AC supply is given to the 3-phase winding of the stator, it produces an alternating flux which revolves with synchronous quickness. This rotating magnetic field induced an EMF in the rotor which created an induced current which flows in a direction which reverse that of the rotating magnetic field, create 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
Simple and rugged construction
High efficiency and good power factor
Speed decreases with upsurge in load
Speed control is difficult
Having poor starting torque and high rush current.
Large capacity exhaust fans
Driving lathe machines