Considerations for Applying VFDs on Existing Motors

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According to Global Market Insights, the US drive market is set to surpass $19 billion by 2024, with over 3% growth from 2018-2024. Growth in Variable Frequency Drives (VFDs) comes from many companies looking for ways to increase energy efficiency as regulatory bodies, such as the U.S. Department of Energy, require new energy efficiency standards to drive the change.

As the transition towards using VFDs continues, many companies are faced with the challenge to apply a VFD to an existing motor. Here are a few factors to consider, according to an article from Processing Magazine, Inc.

  1. Temperature: most standard variable torque motors depend on a shaft-driven fan. However, with the installation of a VFD, the motor shaft speed will reduce, likely eliminating the necessity of the shaft driven fan. All VFDs produce some additional level of heat in motors, but many models harmonically clean heat output waves. Checking with your VFD supplier to determine any heat considerations is crucial.
  2. Motor Voltage: VFD output voltages should match almost any existing motor voltage unless the output increases beyond a 13,800-volt output, seen in only about 1% or less of very high-voltage motor applications.
  3. Bearings – antifriction bearings are well suited for variable speed operation whereas sleeve bearings might need special lubrication when operating at lower speeds.
  4. Resonance – high-speed induction motors (designed to run at 3,600 rpm) have a shaft critical resonance in the rame of 2,200 to 2,800 RPM which won’t impact if running at constant speed. With VFD, however, any speed is within allowable range, taking care to examine options to “skip” and avoid certain frequencies when programming the VFD will avoid any issues.

These are some helpful considerations when applying a VFD motor to an existing application. It is important to work with a knowledgeable motor vendor, and Elite Controls, Inc. has the expertise with not only VFDs, but with the entire control system. We work with multiple VFD manufacturers and can help you with the application questions you have.