AC ELECTRIC MOTORS
Working principle
AC motor can be a device which converts alternating electric current into a mechanical device through the use of an electromagnetic induction phenomenon. The AC motor consists of two basic parts another stationary stator having coils given an alternating current to make a rotating magnetic field and an internal rotor attached to the output shaft creating another rotating magnetic field.
The rotor is an electric conductor which is suspended inside a magnetic field. Because the rotor is continually rotating there is a modify in magnetic field. According to the Faraday’s regulation, this alter in magnetic field induces a power 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 swiftness and convert AC electrical power in to the mechanical power.
When the energy supply is put on the synchronous electric motor, a revolving field is established. This field attempts to drag the rotor towards it but due to 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 comes by a 3-stage supply and the additional 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 hzpt motor produce continuous flux. The 3-stage finding produces 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 causing a repulsive force upon the rotor and for the next second, they trigger an attractive force. But rotor continues to be in standstill condition because of its high inertial second. Therefore, the synchronous electric motor is not self-starting.
Advantages
The motor speed is continuous irrespective of the load.
Electromagnetic power of the synchronous motor varies linearly with the voltage.
Compared to an induction motor, it operates at higher efficiencies at reduced speeds
Disadvantages
It isn’t self-starting. It requires some arrangement for starting and synchronizing.
Since its starting torque is zero, it cannot be started whilst having a load
It can’t be used for applications which require frequent starting and 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 less than the synchronous speed. The induction electric motor can be classified into mainly two sub-categories. The single-phase induction 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 can be produced in the surroundings gap whenever the stator winding is supplied 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 in an induction electric motor, an alternating flux will be produced. This flux rotates at an asynchronous rate 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 created in the rotor conductor. A rotor current is usually 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 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 decrease the relative velocity.
The speed of rotating magnetic field is distributed by
DC motor
Single phase induction Motor
AC electric motor which utilizes one phase power supply is called single phase induction electric motor.it is commonly found in the domestic and industrial application.it consists of stator and Rotor component. 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 with the aid 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 engine is mounted on the mechanical load by making use 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 didn’t provide necessary rotation to the rotor. This is why the one phase motors are not 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 called three-phase induction motor. Just like a single phase electric motor, it has also both stator and rotor winding. The stator wounded by a 3-stage winding given by a 3-stage supply produces an alternating flux which rotates at a synchronous velocity.
Working principle
When AC supply is given to the 3-phase winding of the stator, it produces an alternating flux which revolves with synchronous swiftness. 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, produce a torque in the rotor. The acceleration of the rotor will not be same as that of the stator. If acceleration fits no torque will produce
Advantages
Simple and rugged construction
High efficiency and good power factor
Minimum maintenance
Self-starting motor.
Disadvantages
Speed decreases with increase in load
Speed control is difficult
Having poor starting torque and high hurry current.
Application
Large capacity exhaust fans
Driving lathe machines
Crushers