Call us: +91-9920192438

Variable Frequency Drive (VFD): Types And Features

Posted at 11:37h in Uncategorized by

The functioning of an electric motor can be compared to the functioning of your car. It is important to start the car at nominal speed and increase the same while moving ahead. If you do not control the speed of your car, there are high chances of meeting with an accident.

Similarly, it is important to control the speed of an electric motor or your machine will start experiencing issues. You can manage this speed by controlling the voltage or frequency of the device. Variable Frequency Drive comes into picture when you need to control the frequency of your motor.

What Is A Variable Frequency Drive?

Variable Frequency Drive (VFD) is a device that helps you in converting the fixed voltage and frequency of the input power provided to the motor, into variable voltage and frequency. This conversion regulates the functioning of your electric motor.

Majority of applications need variable speed during peak load and a constant speed when the load and current is normal. The key use of a VFD is to maintain the speed of a motor at a constant level even if there are disturbances in load and input.

Also Read : What is VFD?

Types Of Drives

There are two major types of drives used in appliances – mechanical and electrical.

Types of Mechanical Drives

  1. Traction Drive

In this VFD, the diameter of the contact path belonging to two mating metal rollers is adjustable, resulting in variable output speed.

  1. Variable Pitch Drive

This VFD is a belt and pulley drive where the pitch diameter of the pulley (one or both) is adjustable according to specific requirements. This mechanism exerts a multi ratio, ultimately leading to variable output speed.

  1. Hydraulic Hydrostatic Drive

This drive consists of a positive displacement hydraulic pump and motor. Here, a change in the volumetric fluid output of the pump is carried out using valves or varying the displacement.

  1. Hydraulic Hydro Viscous Drive

In this variable frequency drive, multiple discs on the input shaft are pressed against several discs on the output shaft. Between these discs is a thin film of oil. Here, the torque transfer is varied by making changes in the pressure in squeezing the discs together.

  1. Fluid Coupling

Also called Hydraulic Hydrodynamic Drive, this is the most commonly used VFD in the industries. Here, two impellors are joined (coupled) together using a hydraulic fluid.

The amount of coupling from primary to output is adjustable for obtaining variable speed by varying the volume of the fluid used.

Types Of Electric Drives

1. Eddy-current Coupling

This VFD is present between the fixed speed motor and the application driven by the motor. It contains a fixed speed motor and a variable speed motor. Both of these components are separated by a small air gap.

2. DC Drives

DC drives involves the DC converter turning the AC supply of power into a DC voltage of variable magnitude. This voltage is supplied to the armature winding of the concerned DC motor. These drives make use of thyristor technology and are used in an array of applications.

3. AC Drives

There are three major types of VFDs here, all of which convert AC input into DC, followed by changing DC into a variable AC output with the help of an inverter. The three different AC VFDs are Current Source, Voltage Source and Direct Conversion drives.

Important Features of VFDs

Now that you are well-versed with the different types of VFDs and applications of the same, let us look at a few key features of the same.

  1. Line Voltage

It is important to state the operating voltage of a variable frequency drive. This reading generally comes to 240VAC or 480VAC. A voltage variation of 10% can be allowed in the reading.

It is advisable to consider power deviations while recording a voltage reading for any major application.

  1. Continuous Run Current Rating

This is the value depicting the maximum root-mean-square (rms) current your VFD can safely handle under all operating conditions with a constant ambient temperature (usually 40 degrees Celsius).

This rating is important because it should be equal to or more than the motor ball load sine wave currents for proper functioning of an electric motor.

  1. Overload Current Rating

In simple terms, this is the maximum amount of current your VFD can produce for a given period of time. It is expressed as an inverse time/current rating.

Based on the manufacturer, common overload current ratings are 110% to 150% overcurrent for 1 minute. You can increase these ratings by over-sizing your variable frequency drive.

It is extremely important to maintain your VFDs and undertake periodic checks. If you find any issue in their functioning, it is advisable to avail Variable Frequency Drive repair services from a reliable service provider. A healthy VFD would always ensure a healthy appliance.