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Thursday, August 22, 2019
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Choosing a Line Reactor for a VFD
How to choose a line reactor for a VFD?


I am working on VFDs, and I am unable to decide what rating of line reactor to use with different VFDs.

Can someone please guide me in choosing the right line reactor for my VFDs?

Further, I was told that I have to install another choke in the output of the VFD, as well as the distance between the motor and the VFD is large. Is there any difference in choosing the chokes for input and output of a VFD? How does it differ? I tried to find sources online but i could not get much help.

Please help me in choosing the right chokes for my VFDs.


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When I'm specifying such things, as well as the line-side protection for the drives, I consult the user manual for the drive. The ones I've worked with have that all spelled out.

The VFD mfg should offer line/load reactors that they've tested for performance.

Line and Load reactors can add life and some protection for VFD's and Motors. Motor windings are typically insulated to 1600V and on 460V systems, load reactors help reduce the motors exposure to transients over 1600V. Motors continually exposed to 1600V+ spikes will eventually show pitting in the laminations, though I think it can take awhile to happen.

At 230V or less, I don't think Load Reactors do much, though that's likely to invite disagreement.

Here's some light reading material:

Transcoil supplies a lot of the VFD mfg's with line/load inductors (aka chokes, reactors, filters).

If dealing with long lines from the VFD to the motor, it is a very good idea to review the application with the VFD Manufacturer's Application Engineering group. By long, I typically hear 350 feet or more, however, I've heard of runs of 200' impacted by poor power. They may recommend specific cable or suggest a larger wire gauge.

Load reactors do add extra "load" to the vfd, so there is some power loss at the motor.