When Should You Choose a VFD (Variable Frequency Drive)?

In many cases, a VFD (Variable Frequency Drive) is required for electric motors to ensure optimal performance of an application.
5 April, 2021 by
When Should You Choose a VFD (Variable Frequency Drive)?
T&T Power Group.

Let’s talk about the certain situations where you should definitely choose a VFD, as well as situations where a VFD is not required.

You SHOULD be using a Variable Frequency Drive if:

• The application you’re running requires precise control:

If smooth, seamless control is a necessity for your application, or if you require multiple motors to perform in sync, a VFD can accomplish this. VFD's like the VACON 100 Flow, even have dedicated functionality for controlling pumps, fans and compressors.

• Your application contains a variable load:

This tends to be a regular occurrence with HVAC and pumping applications. VFDs are capable of running motors at a reduced speed, which can in turn save a ton of energy.

• Your application involves regular starting and stopping, as is the case with some conveyor applications:

VFDs can perform as soft-starters, and can gradually increase their motors to the desired speed. When it comes to line power, motors will generally begin at full speed which can lead to mechanical stress and other issues.

• Your motor is running at full speed with throttled output:

Throttling the output of your motor is actually incredibly wasteful - so it’s highly advised to use a drive in this scenario, as it will aid in significant cost and energy savings.

You should NOT be using a Variable Frequency Drive if:

• You own an older motor:

Contrary to most newer motors that are created to withstand the voltage pulses of VFDs, older motors that were manufactured prior to the early 2000s are incapable of handling VFD output - and will overheat while running at lower speeds or experience failed insulation. It’s probably best to swap your old motor for a new one anyway, as modern motors have higher efficiencies.

• Your motor has a constant load with zero restrictions on the output:

If your motor happens to be running at full speed with no throttling or damping, using a VFD will not save you any energy - it will in fact do more harm than good as you will lose some efficiency.

• Your application requires very low or very high speeds:

Overheating can result from extremely low speeds, with mechanical damage a possibility with extremely high speeds. In this case, a gearbox or another type of converter would be ideal vs. using a VFD.

• Your motor and drive cannot be positioned closely together:

When a motor and VFD are too far apart from each other, this places the motor at an increased risk for electrical damage - with standard recommendations from manufacturers ranging from 100 to 250 feet maximum. Keep in mind however that line reactors are an inexpensive add-on that will diminish the potential for problems over longer distances.

• Your motor experiences problems with power quality:

VFDs can actually worsen any existing issues with voltage sag or harmonics, as well as with assorted transients. This can be negated, however, with the correct harmonic filtration components, and VFDs will certainly improve power quality regardless.

Our motor control experts are always here to help.

Ready to choose a VFD to improve your application’s efficiency? Our team can help.

Contact T&T Power Group today to get started.

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