Using RIB® Relays with Variable Frequency Drives (VFDs)

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On my last technical support day, I received a few questions about whether our RIB® current sensors work well with variable frequency drive (VFD) motor controllers. The short answer is yes, but there are a couple key points worth noting.

Determining Sensor Placement

When using a RIB® current sensor to monitor the status of a VFD, the sensor should be placed on the line side of (before) the VFD, with the ideal frequency of the monitored wire at or around 60Hz. If it is placed on the load side of (after) the VFD, expect erratic or no operation of the current sensor. This is due to the frequency being altered at the output of the VFD controller.

Using a Model with an Adjustable Threshold

There’s a good chance that the VFD consumes some power without the motor turning. That little bit of power is what I call leakage or standby current, and it may be enough to make the current sensor contacts close. This could result in a “false-positive” in terms of feedback. By using an adjustable model, the threshold may be fine-tuned to ignore the leakage/standby current, giving you the desired feedback from the current sensor.

I hope that this blog helps address any concerns regarding our RIB® current sensors in a VFD application. As always, feel free to call or email us if there are any other questions or concerns. We’ll be happy to help!

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Sam Klennert

Meet Samuel Klennert – you can call him Sam. He was born and raised amongst the farmland of Indiana, which includes corn, soybeans, and sometimes wheat. Sam graduated from Purdue University with a Bachelors degree in Electrical and Computer Engineering Technology in 2015.

Outside of work, Sam enjoys spending time with his wife and dog – whether it’s inside or outside their home. Sam can also be seen serving at his local church and glorifying God with other believers, which is by far his favorite way to spend time.

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