Induction Motor and its Working Principle

One of the most common electrical motor used in most applications which is known as induction motor . This motor is also called as asynch...

One of the most common electrical motor used in most applications which is known as induction motor. This motor is also called as asynchronous motor because it runs at a speed less than its synchronous speed. Here we need to define what is synchronous speed. Synchronous speed is the speed of rotation of the magnetic field in a rotary machine and it depends upon the frequency and number poles of the machine. An induction motor always runs at a speed less than synchronous speed because the rotating magnetic field which is produced in the stator will generate flux in the rotor which will make the rotor to rotate, but due to the lagging of flux current in the rotor with flux current in the stator, the rotor will never reach to its rotating magnetic field speed i.e. the synchronous speed. There are basically two types of induction motor that depend upon the input supply - single phase induction motor and three phase induction motor. Single phase induction motor is not a self starting motor which we will discuss later and three phase induction motoris a self-starting motor.

Working Principle of Induction Motor

We need to give double excitation to make a machine to rotate. For example if we consider a DC motor, we will give one supply to the stator and another to the rotor through brush arrangement. But in induction motor we give only one supply, so it is really interesting to know that how it works. It is very simple, from the name itself we can understand that induction process is involved. Actually when we are giving the supply to the stator winding, flux will generate in the coil due to flow of current in the coil. Now the rotor winding is arranged in such a way that it becomes short circuited in the rotor itself. The flux from the stator will cut the coil in the rotor and since the rotor coils are short circuited, according to Faraday's law of electromagnetic induction, current will start flowing in the coil of the rotor. When the current will flow, another flux will get generated in the rotor. Now there will be two flux, one is stator flux and another is rotor flux and the rotor flux will be lagging w.r.t to the stator flux. Due to this, the rotor will feel a torque which will make the rotor to rotate in the direction of rotating magnetic flux. So the speed of the rotor will be depending upon the ac supply and the speed can be controlled by varying the input supply. This is the working principle of an induction motor of either type – single and three phase.

Types of Induction Motor

Single Phase Induction Motor
1.Split phase induction motor
2.Capacitor start induction motor
3.Capacitor start capacitor run induction motor
4.Shaded pole induction motor

Three Phase Induction Motor
1.Squirrel cage induction motor
2.Slip ring induction motor

We had mentioned above that single phase induction motor is not a self starting and three phase induction motor is self starting. So what is self starting? When the machine starts running automatically without any external force to the machine, then it is called as self starting. For example we see that when we put on the switch the fan starts to rotate automatically, so it is self starting. Point to be noted that fan used in home appliances is single phase induction motor which is inherently not self starting. How? Question arises How it works? We will discuss it now. 

Why is Three Phase Induction Motor Self Starting?
In three phase system, there are three single phase line with 120° phase difference. So the rotating magnetic field is having the same phase difference which will make the rotor to move. If we consider three phases a, b and c, when phase a is magnetized, the rotor will move towards the phase a winding a, in the next moment phase b will get magnetized and it will attract the rotor and then phase c. So the rotor will continue to rotate.

Why Single Phase Induction Motor is not Self Starting?
It will be having only one phase still it makes the rotor to rotate, so it is quite interesting. Before that we need to know why single phase induction motor is not a self starting motor and how the problem is overcome. We know that the ac supply is a sinusoidal wave and it produces pulsating magnetic field in uniformly distributed stator winding. Since pulsating magnetic field can be assumed as two oppositely rotating magnetic fields, there will be no resultant torque produced at the starting and due to this the motor does not run. After giving the supply, if the rotor is made to rotate in either direction by external force, then the motor will start to run. This problem has been solved by making the stator winding into two winding, one is main winding and another is auxiliary winding and a capacitor is fixed in series with the auxiliary winding. This will make a phase difference when current will flow through the both coils. When there will be phase difference, the rotor will generate a starting torque and it will start to rotate. Practically we can see that the fan does not rotate when the capacitor is disconnected from the motor but if we rotate with hand it will start to rotate. So this is the reason of using capacitor in the single phase induction motor. There are several advantages of induction motor which makes this motor to have wider application. It is having good efficiency up to 97%. But the speed of the motor varies with the load given to the motor which is an disadvantage of this motor. The direction of rotation of induction motor can easily be changed by changing the sequence of three phase supply, i.e. if RYB is in forward direction, the RBY will make the motor to rotate in reverse direction. This is in the case of three phase motor but in single phase motor, the direction can be reversed by reversing the capacitor terminals in the winding.

COMMENTS

Name

BASIC ELECTRICAL,12,BATTERIES,4,CIRCUIT THEORIES,9,CONTROL SYSTEMS,3,DC MOTOR,1,DIGITAL ELECTRONICS,1,DISTRIBUTED GENERATION,2,DISTRIBUTION,6,ELECTRICAL DRIVES,1,ELECTRICAL LAWS,8,ELECTRONICS DEVICES,2,General,7,GENERATION,3,GENERATOR,1,HIGH VOLTAGE,4,ILLUMINATION,1,INDUCTION MOTOR,7,MATERIALS,1,MEASUREMENT,1,MOTOR,1,POWER ELECTRONICS,2,PROJECTS ON INDUCTION MOTOR,1,PROTECTION,1,SMART GRID,3,SWITCHGEAR,4,SYNCHRONOUS MOTOR,1,TRANSFORMER,6,TRANSMISSION,4,
ltr
item
Electrical for Us: Induction Motor and its Working Principle
Induction Motor and its Working Principle
https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgaLr1HMiWTV2tVlssmlkf4OtkDJxhuDJAfRlyl85vKXUiX02KQ19P6k63BLhE4bwhYr_3JnwkQeNRpB0XPUinuuI9VWbyCEQF6h-qBsD8rg8b32rD9lu8HzsI4nIiMhmNNW_5FcHhBvFdY/s1600/motor1.jpg
https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgaLr1HMiWTV2tVlssmlkf4OtkDJxhuDJAfRlyl85vKXUiX02KQ19P6k63BLhE4bwhYr_3JnwkQeNRpB0XPUinuuI9VWbyCEQF6h-qBsD8rg8b32rD9lu8HzsI4nIiMhmNNW_5FcHhBvFdY/s72-c/motor1.jpg
Electrical for Us
http://www.sanjaysah.com.np/2016/11/induction-motor-working-principle-types.html
http://www.sanjaysah.com.np/
http://www.sanjaysah.com.np/
http://www.sanjaysah.com.np/2016/11/induction-motor-working-principle-types.html
true
3851448774078769448
UTF-8
Loaded All Posts Not found any posts VIEW ALL Readmore Reply Cancel reply Delete By Home PAGES POSTS View All RECOMMENDED FOR YOU LABEL ARCHIVE SEARCH ALL POSTS Not found any post match with your request Back Home Sunday Monday Tuesday Wednesday Thursday Friday Saturday Sun Mon Tue Wed Thu Fri Sat January February March April May June July August September October November December Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec just now 1 minute ago $$1$$ minutes ago 1 hour ago $$1$$ hours ago Yesterday $$1$$ days ago $$1$$ weeks ago more than 5 weeks ago Followers Follow THIS CONTENT IS PREMIUM Please share to unlock Copy All Code Select All Code All codes were copied to your clipboard Can not copy the codes / texts, please press [CTRL]+[C] (or CMD+C with Mac) to copy