VFD and GFCI

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STucker said:
If I'm understanding this correctly, they want to use a VFD to act as a transformer, and then a second VFD to do phase conversion and drive the pump? I'm fresh out of school so there's a vast collection of things I have yet to see, but this seems overly complicated...and expensive. Just to pick some brains:

-Wouldn't it be much more cost effective to use a transformer for 120-230V?(Assuming there's a rated enclosure involved)
-If there's already 480V available, couldn't a single 480V drive set to output only 230V accomplish the same task?
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There are VFD's out there with 120 V single phase input and 240 three phase output. About 1 Hp max is all you will find, but the application typically only uses 1/3 -1/2 hp motors so not a problem.

It would be less complicated and less expensive to just use a 480 volt drive to begin with, 480 volts is normally the supply voltage to this application.
 
ptonsparky said:
The system they had here worked just fine with a GFCI in front of it. We ran it thru the whole range of pressures. While the VFD nameplate did say 16+amp input, we never went above 4.4 on my TRMS amp clamp.

I made the suggestion that they include the 480v step down in their equipment. It is not a fly by night operation and they are based in California for whatever that means.
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Tom,
So they sent one that was to be hooked up to a 120V GFCI and it worked fine? Was there anything else special about the circuit or the VFD? This issue comes up a lot, I'd like to be able to make recommendations to people. So far, the solutions I have SEEN work were to use a shielded isolation transformer between the GFCI and the VFD input (which is bulky and expensive), or to add an additional EMI filter ahead of the VFD, or use a VFD with one built-in (less bulky, more expensive). I have HEARD of trying a ferrite bead CM noise choke on the input AND output conductors, but I have no personal experience or feedback of that working. I'm thinking of building a test bench unit for that when I have time though. That would be a simple and cheap fix if it works.

Also, I've heard that on the 120V input VFDs, the QUALITY of the "voltage doubler" circuit that takes the 120V up to 330VDC so the VFD can make 230VAC is a key factor in whether or not it trips the GFCI. I know some "bargain" mfrs use a half wave rectifier for this because although it's nasty, the VFD has DC bus caps anyway that make that irrelevant to the drive, but it exacerbates the leakage current issue when it comes to GFCIs. The only drives I have available to test with all have full wave voltage doublers, and although I cant make them trip the GFCI setup I made here at my office, I'm not convinced that my bench top system is a good representation of real world installations. I need to take it home and try it on my table saw. In the rain...
 
From the operating manual, it is a Lenze. ESV751- -1S- -. Voltage doubler model.
Leakage current may be >3.5ma or is greater than 3.5ma, depending on which page of the manual you read.

Motor label: 446 watt 3 phase 230 volt, 2.9 amps
They are running the test unit I saw from a 16 gauge 120 volt pigtail. A far cry from the #10 the drive manual calls for.
 
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