The Electric motor have a most important role in modern technology. To start and running the motor with safely, different types of starter are used like as DOL starter, Star Delta starter,etc. When motor is connected to these starter the motor is running its rated speed. If we need to run the motor low speed (less than rated speed). so, control the electrical motor with variable speed and Torque. VFDs are used in industries to controlling the motor speed according to requirements of the load and our needs by controlling the frequency.
What is Variable frequency drive (VFD)?
A variable frequency drive (VFD) is used to drive an AC motor with variable speed. It is a type of motor controller. The main function of VFD to varying the frequency of the supply voltage to control the motor speed (rpm).
A VFD is also known as the Adjustable frequency drive AFD, Micro drive etc. Mostly people it's called drives.
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A VFD is give a smooth startup to start an electrical motor with safely.
Speed of electrical motor is directly related to the frequency of voltage which is provided to the motor, that means if the frequency of the supplied voltage to motor is 50Hz (standard frequency of the countries like as 50Hz in India).
The electric AC motor work at it's rated speed. If the frequency of supply voltage is decrease from 50Hz ( Fs < 50Hz) then the motor speed will be also decrease than it's rated speed and if the frequency of supply voltage is increases above 50Hz then the motor speed will be increases than its rated speed. But the frequency of supplied voltage is greater than 50Hz from rated frequency is harmful which coused to any type of damages to motor winding.
The speed of the motor depend on the number of poles inside the motor and its supply frequency.
Ns =120f/p
Where Ns =speed of the motor
F= frequency
P = Number of poles
From above formula it is clear that the speed of the depends upon the frequency of the supply voltage and Number of poles inside the motor.
The number of poles of the motor are fixed after construction. Due to The number of poles not possible to be changed after construction. But changes in the frequency of the supply voltage is possible.
How does work VFD
VFD is electronic device which makes from different types of electronics components like as the diode, transistors, capacitors and many more solid state electronics components.
A VFD first convert AC to DC with the help of diode and these DC clean with capacitor again these filtered DC convert into AC with adjusting the frequency of the supply voltage by the transistors acting as a switches.
Advantages of variable frequency drive (VFD)
1) Speed control - A VFD is use to control speed of the motor according to requirement of the process.
2) Torque control - A VFD is use to control the torque or power of the motor drive system according to the requirement of the process.
3) Energy Saving - A VFD is used for save the energy by reducing the energy consumption. And a VFD also reduce the energy cost by energy saving.
4) Power Factor - Improving the efficiency of drive systems by increasing the power factor. Generally a induction motor have low power factor up 0.85 in order to increasing the power factor VFD to be used.
5 )Machine life - To reduce the machenical stress of the machine and increase its Lifespan. And it required less maintenance.
Disadvantages of variable frequency drive (VFD).
1)Higher Initial cost
Appliances of Variable frequency drive.
VFDs are mostly used in industries to controlling the motor.