AC ELECTRIC MOTORS
AC motor is usually a device which converts alternating electric current right into a mechanical device through the use of an electromagnetic induction phenomenon. The AC motor includes two basic parts an outside stationary stator having coils supplied with an alternating current to make a rotating magnetic field and an internal rotor attached to the output shaft generating a second 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. According to the Faraday’s legislation, this modify in magnetic field induces a power current inside a rotor.
Types of AC Electrical Motor
The AC motors can be basically categorized into two categories, synchronous, and asynchronous motors
These motors operate at a synchronous quickness and convert AC electrical hzpt motor energy into the mechanical power.
When the energy supply is put on the synchronous engine, a revolving field is established. This field attempts to drag the rotor towards it but because of the inertia of the rotor, it cannot perform it. So, there will be no starting torque. As a result, the synchronous motor isn’t 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 may be the rotor winding which is supplied 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 begin rotating, at some point 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 pressure. But rotor continues to be in standstill condition because of its high inertial moment. Therefore, the synchronous motor is not self-starting.
The motor speed is constant irrespective of the strain.
Electromagnetic power of the synchronous engine varies linearly with the voltage.
In comparison to an induction motor, it operates in higher efficiencies at cheaper speeds
It is not self-starting. It needs some arrangement for starting and synchronizing.
Since its beginning torque is zero, it can’t be started whilst having a load
It can’t be used for applications which require frequent beginning so 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 electric motor can be classified into generally two sub-types. 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 in addition to a field winding. The flux is usually produced in the surroundings gap whenever the stator winding comes 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 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 motor, an alternating flux will be produced. This flux rotates at an asynchronous quickness 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 certainly developed in the rotor conductor. A rotor current is definitely then produced for this reason 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 foundation of its production. The foundation 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 to be able to reduce the relative velocity.
The speed of rotating magnetic field is distributed by
Single phase induction Motor
AC electric engine which utilizes one phase power supply is called single phase induction engine.it is commonly used in the household and commercial application.it contains stator and Rotor part. A single-phase power supply is directed at the stator winding. A squirrel cage rotor laminated with the iron primary is linked to a mechanical load with the help 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 with the aid of the shaft. Because of the rotating flux in the stator, an alternating electromagnetic field is usually induced in the rotor. But this alternating flux didn’t provide required rotation to the rotor. That is why the single phase motors are not self-starting.
To be able to achieve self-beginning convert this one phase motor into a two-phase electric motor for temporarily. This could be achieved by introducing a starting winding
Fewer substations required
Cannot handle the overload
No uniform Torque
High insulation cost
Three Phase Induction Motor
When a three-phase supply is connected to the stator winding, this kind of motor is called three-phase induction motor. As being a single phase engine, it has also both stator and rotor winding. The stator wounded by a 3-stage winding supplied by a 3-phase 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 generates an alternating flux which revolves with synchronous quickness. This rotating magnetic field induced an EMF in the rotor which in turn created an induced current which flows in a path which opposite that of the rotating magnetic field, create a torque in the rotor. The acceleration of the rotor will not be identical to that of the stator. If speed fits no torque will produce
Simple and rugged construction
High efficiency and great power factor
Speed decreases with increase in load
Speed control is difficult
Having poor beginning torque and high rush current.
Large capacity exhaust fans
Driving lathe machines