Difference between soft starter and VFD

Soft starter and variable frequency drive called VFD.  A soft starter is a regulator actually for motor statting and it just changing the output voltage. VFD is for AC motor speed control it is not only changing the output voltage but it will also change the frequency. VFD has all the features of soft starter but the price is much more expensive than the soft starter and its structure is much more complex. There are some basic differences between these two soft starters vs VFD.

What is a soft starter?

As we know that, a soft starter is a device that starts motors with reduced power supplied at the start-up reducing the power reduces potentially damaging electrical and mechanical shocks on the system.

What is VFD?

Before we learn about VFD first let us understand what is the full form of VFD? 
VFD stands for variable frequency drive, It is a type of motor controller that drives an electric motor by varying the frequency and voltage supplied to the electric motor. A basic VFD system generally consists of an AC motor, it is a controller and an operator interface.

Difference between a soft starter and Variable frequency drive :

  • Soft starters are used to start and stop a motor smoothly, Variable frequency drives are used to start and stop and control a motor throughout its operation.
  • Soft starter most of the time bypassed as soon as the motor reaches its full speed, but in variable frequency, drives to control a motor throughout its operation.
  • A soft starter is not harmonics while in VFD is harmonics are injected to the mains, hence additional filters should be used.
  • Soft starter saves less energy throughout is life while VFD can save more energy throughout is life.
  • VFD is more expensive as compared to the soft starter.
  • VFD has more space needed as compared to the soft starter.

Where we have to use soft starters:
  • In an application where speed control is not essential.
  • In low and medium torque applications.
  • Reduce wear and tear during start and stop.
  • In an application where the initial cost is low.

Where we have to use a variable frequency drive:
  • Variable frequency drives are used in applications where complete control over the speed is essential.
  • In high torque applications.
  • Where the initial cost and size are no problem.

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