AC ELECTRIC MOTORS
AC motor is definitely a device which converts alternating current right into a mechanical device by using an electrohzpt motor magnetic induction phenomenon. The AC motor contains two basic parts another stationary stator having coils given an alternating current to make a rotating magnetic field and an inside rotor attached to the output shaft creating another rotating magnetic field.
The rotor can be an electric conductor which is suspended inside a magnetic field. Since the rotor is continually rotating there exists a modify in magnetic field. Based on the Faraday’s law, this change in magnetic field induces a power current in the rotor.
Types of AC Electric Motor
The AC motors can be basically classified into two categories, synchronous, and asynchronous motors
These motors operate at a synchronous acceleration and convert AC electrical power into the mechanical power.
When the power supply is put on the synchronous engine, a revolving field is set up. This field tries to drag the rotor towards it but due to the inertia of the rotor, it cannot perform it. So, you will see 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 comes by a 3-stage supply and the additional one may be the rotor winding which comes 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-stage finding generates a magnetic field which rotates at a velocity 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 on the rotor and for the next second, they cause an attractive push. 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 load.
Electromagnetic power of the synchronous electric motor varies linearly with the voltage.
In comparison to an induction motor, it operates in higher efficiencies at lower speeds
It is not self-starting. It needs some arrangement for starting and synchronizing.
Since its starting torque is zero, it can’t be started while having a load
It cannot be used for applications which require frequent starting and when self-starting is required.
The induction motor is also named as Asynchronous not since it always runs at a speed lower than the synchronous speed. The induction engine could be classified into mainly 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 surroundings gap whenever the stator winding comes 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 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 electric motor, an alternating flux will be produced. This flux rotates at an asynchronous swiftness and this flux is called the rotating magnetic field. Because of the relative speed between the stator RMF and rotor conductor, an induced EMF is definitely developed in the rotor conductor. A rotor current is certainly 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 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
Single phase induction Motor
AC electric electric motor which utilizes single phase power supply is called single phase induction electric motor.it is commonly used in the household and commercial application.it includes stator and Rotor part. A single-phase power is directed at 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 given to the stator winding an alternating flux will produce in the stator winding.
A squirrel cage electric motor 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 usually induced in the rotor. But this alternating flux didn’t provide necessary rotation to the rotor. That is why the single phase motors are not self-starting.
To be able to achieve self-beginning convert this single phase motor into a two-phase electric motor for temporarily. This can be achieved by introducing a starting winding
Fewer substations required
Cannot handle the overload
No uniform Torque
High insulation cost
Three Phase Induction Motor
Whenever a three-phase supply is connected to the stator winding, this kind of motor is called three-phase induction motor. Just like a single phase motor, it has also both stator and rotor winding. The stator wounded by a 3-stage winding given by a 3-stage supply generates an alternating flux which rotates at a synchronous swiftness.
When AC supply is directed at the 3-phase winding of the stator, it produces an alternating flux which revolves with synchronous speed. This rotating magnetic field induced an EMF in the rotor which in turn created an induced current which flows in a direction which opposing that of the rotating magnetic field, create a torque in the rotor. The velocity of the rotor will never be same as that of the stator. If rate fits no torque will produce
Simple and rugged construction
High efficiency and good power factor
Speed decreases with increase in load
Speed control is difficult
Having poor starting torque and high hurry current.
Large capacity exhaust fans
Driving lathe machines