Re: Question on VFD line rectors

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "washcomp" <jeff@w...> wrote:

> I'm planning on adding a VFD to my Bridgeport (varying the speed
> from my CNC controller). They recommend the use of a line reactor
> on both the input and the output sides.
>
> Locally, I have 208V 3 phase A.C. 60Hz.
> I have a 1.5 HP motor on my Bridgeport
>
> I came across this and was wondering if it would be the proper one
> my application:
>
> http://cgi.ebay.com/ws/eBayISAPI.dll?
> ViewItem&category=42881&item=2570523396
>
> Thanks and regards,
> Jeff

The line reactor is used to add impedance to the VFD's input, thereby
limiting the peak current through the rectifiers when they charge the
bus capacitors. Rarely is this reactor needed except in industrial
facilities fed by a local pad-mounted transformer.

A reactor on the motor side of the VFD - called a load reactor in that
position - is used to help integrate the current pulses to a sine
wave, especially if the motor is oversized compared to the VFD rating.
This is not a good situation, but not because of the danger to the VFD
- they'll usually do a good job of protecting themselves from overload
- but because of the large eddy currents this induces in the motor's
ball bearings. The currents will erode the balls inside leading to
their very premature demise.

If you don't win the auction, I have some small 3 phase reactors that
would be suitable for your application, but keep in mind that unless
this machine is running several hours a day it's probably not really
necessary to put them in.

-Jeff