Which VFD to avoid GFCI tripping?

[bikemaniac]

Hi,
I want to build an industrial sewing machine drive using a small VFD and a small AC motor. The AC motor will be a 4 pole 1400 rpm 0.25 kW induction motor and the VFD should be a 1ph 240V AC in and 3ph 240V AC out. There will also be a mechanical gearbox between the motor and the sewing machine to get the nominal speed in the correct range. The wire length from the VFD to the motor will be less than 1 foot. The wire length from the VFD to the 240V socket will be approx 10 feet.

I want to use my sewing machine at home where GFCIs are mandatory and I am worried that I will get tripping problems. Can anyone guide me in a direction in what VFD to buy ... or are ALL brands struggling with the GFCI problems? Or do I need to buy some extra equipment to make it work? Do I need to look for a particular VFD feature in the data sheets which eliminate the GFCI problem?

Thanks in advance

Lucas

 

[Skogsgurra]

All PWM inverters have a problem with capacitive leakage current. There is one drive that doesn't have that problem. Or any problem - it can be installed without filters or screened cables and it doesn't interfere with home electronics. See

http://www.nfodrives.se/en/index.htm

The text says that it can be used with 30 mA RCDs. That is true, but the text doesn't say that it also can be operated with 10 mA RCDs, which also is possible. In fact, the residual current in a typical installation is below 2 mA.


Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[jraef]

GFCI implies that you are in North America, where that term is specifically defined as being Class A, which means the trip point is 4-6 mA. I seriously doubt you will find a commercial off the shelf VFD cabable of running off of a GFCI without some serious additional filtering. The reason is, VFDs are designed for permanent installations, meaning hard wired, where Class A GF protection is not required.

So what kind of sewing machine are you designing that will be plugged in and used in wet environments where a GFCI is going to be necessary?

"Will work for (the memory of) salami"

 

[Skogsgurra]

As I said: "In fact, the residual current in a typical installation is below 2 mA"

That, I have measured, on a 400 V, 2,2 kW motor. The current was 0,7 mA RMS and that is without any filters and screened Cables. It is a fact and that is why DeLaval, the farm equipment producers, have selected this VFD for their milking and other machinery.



Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[ScottyUK]

Different jurisdiction where GFCIs are called RCDs, but my home workshop has a handful of VFDs happily working including a little Eurotherm (now Parker) 605, a 15kW A-B 1336 and an old 2.2kW A-B 1331. These are all on my domestic supply which has a 30mA RCD and I don't get nuisance tripping. My broadband connection doesn't like the 1336 though.

 

[Mobius44]

Lucas-
As JRaef notes GFCI for ground fault protection are normally only found in wet environments (bathrooms, kitchens, outside, etc.), and not all over the home. Perhaps you're thinking of AFCI for arc fault protection? They have much broader use, but shouldn't interfere with a VFD.

Gunnar-
The NFO drives are interesting, but I have yet to find anyone offering them in North America. I'd love to try one out if they were available.

-Sean

 

[bikemaniac]

The Danish term for GFCI is HPFI, I just tried to google it, and ground fault circuit interrupter came up. In my home it cuts out at 30 mA (Schneider electric ID K 40A) and not 4 to 6 mA. That should give more room for electrical noise. We have these interrupter installed everywhere - not only in wet environments.

The Swedish inverter is highly interesting - however approx 10x more expensive than conventional ones - I got some prices from the Danish distributor.

I am happy to read that scottyUK does not have problems with his 30mA installation ... so maybe I should just go for a normal one.

Lucas

 

[Skogsgurra]

Ten times more expensive!? You must be joking - or is there a mistake with Euros and Swedish Crowns? If you got the cost in Swedish Crowns and think it is in Euros, then that could explain things.



Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[ozmosis]

Be careful.
Using a drive on a domestic supply shouldn't just be viewed with the ( common) problem of tripping the breaker due to the leakage current. It should be viewed for protection. A fault on a device with a non-linear load ( eg a VFD) could a be a non-sinusoidal earth fault and not picked up by certain types of RCD(GFCI or HPFI). This means, the 'problem' would be that there could be a fault with a drive and the RCD does not trip.
The correct type of RCD should be used with a standard VFD. Unless of course, you use an nfo...

 

[bikemaniac]

I just looked at the price list again.

2 picks from the list:

A 0,37 kW NFO costs the equivalent of approx 1600 Euros incl 25% Danish VAT (for end consumers).
A 15 kW NFO costs the equivalent of approx 5500 Euros incl 25% Danish VAT (for end consumers).

The abovementioned prices are without any rebates.

I am very sure that I can manage to find a 0,37 kW conventional VFD for 160 Euros incl 25% Danish VAT.

Lucas

 

[racookpe1978]

Well, 0,37 Kw compared to 15,0 Kw is 40x the capacity, and explains a lot of the large price difference. .....

 

[Mobius44]

It seems to me Lucas compares the 1600 Euro 0.37kW NFO VFD to a 160 Euro 0.37kW conventional VFD, not the cost differences of the 0.37kW and 15kW NFO VFD's.

Thus the pricing Lucas obtained for NFO appears to be about 10x higher than conventional VFD's. This could help explain why NFO drives aren't more prevalent and available, given their other advantages. I still hope they enter the North American market so I can try them out someday.

-Sean

 

[jraef]

Looks like they are available in the US through Delaval as an accessory for use in their vacuum pumps for dairies, likely because of stray current issues with using VFDs in dairies.

http://www.delaval.com/en/-/Product...Transport/Vacuum-pump/DeLaval-NFO-Drive-22kW/

I looked into them a few years back (at Gunnar's suggestion), the problem they have for our marketplace is that they stop at 400V class and range up to 440V +10%, but that's not adequate for the real world of US 480V nominal systems, which frequently climb to 500+. So here in the US, they would only be able to be used in 230V applications, and that market is saturated with VERY cheap drives from Asia.

"Will work for (the memory of) salami"