OT: Earth leakage current (VFD)

Hi There!

A customer of us wants to add a earth leakage protection (max 400mA) device in de power supply of my control cabinet. This cabinet houses several frequency converters.

What I know so far: earth leakage of Danfoss VLT2800 drivers is >3.5mA. SEW tells me the same but they make a note that the earth leakage current is also depending on motor cable length and other factors. They tell me a typical earth leakage current will be approx 25mA.

There are RFI filters available in "low leakage" style. But they limit the cable length to a maximum off 10mtr. Then I need to install motor filters as well to allow for longer motor cables.

Some manuals of frequency inverters also make note the the Inrush current of the RFI capacitor in the drive is a lot higher. (And might trip the earth leakage protection).

What is youre experience with this?

In my opinion it is not possible to connect a large (10 or more VFD in one panel) industrial control cabinet behind a 400mA earth leakage current protection. But my customer is demanding that my cabinet can be connected behind this device...

At the moment I'm not able to find solutions for this, do you know any solutions?

I believe in the United States we refer to a "earth leakage protection device" as GFCI (Ground Fault Circuit Interupt).

Maybe searching here and the web for "GFCI" will turn up some useful information.

Wish I knew more, but it is a start.

I think that a reasonable case could be made for the drives being their own GFCI even tho the detection level might be different. When you turn on the drive ground fault protection, leakage to ground is monitored and will fault the drive at set limits. This system only works properly if you have a balanced, grounded neutral power supply (not floating delta or corner-grounded delta).

I doubt that the additional ground leakage detector will work properly or even provide any additional protection due to the internal CE RFI/EMI filters inside the drives.

Werner

What is volt and current rating of DC power supply?
What does DC power supply feed power to?

If power supply is just for control power and is less than 1Kw I am not sure a ground detector is needed especially if on isolated power supply (transformer with separated primary and secondary windings).

You may also need to ground the DC depending on local rules.

If DC power supply is feeding the VFDs by tying DC output direct to VFD DC bus then that may be another thing and you may need a ground detector.

I am not certain of what you are doing so need more info.


Dan Bentler

Take a look at ABB's F204AC-25/0.03 for Earth Leakage Detector. This is a 3-phase unit, which can work without a neutral. It is indeed quite like a GFI, but not quite exactly the same.

I can hardly imagine that any kind of ground fault detector ahead of a VFD represents any real safety. The drive has enough stored energy in its DC bus to kill for several seconds after the input is released.

This whole concept seems like a mistake, to me.

To respond on some of youre comments:

I don't want to use this GFCI but the customer. My control panel will be supplied with 3x400VAC+N+PE at 50Hz. The customer want's to connect a GFCI to the PE lead connected to my control panel. (So it's not my plan to install several GCFI's in my panel, but the customer will install one GFCI at the power cabinet which will supply my control cabinet...Hope youre still with me...)

In my opinion the earth leakage current of all the VFD's summed together is already enough to trip the GFCI. In Europe a GFCI for home based solutions must be unstalled by law. For industrial purposes I'm not sure the customer must install a GFCI.

Does anybody know off regulations which state the GFCI must be used for industrial machinery?

I use VSDs and RCDs all the time for swimming pools. The RCDs are set at 30ma. I use separate RCDs for each circuit. The VSDs I buy are locally manufactured and are modified with low leakage EMI filters. They are also rated at IP66 so we mount them on a frame alongside the motor and only have to use a very short length of the very expensive shielded cable.
One of the problems with the filters is that they filter to ground. Removal of the ground filter connection will usually solve the problem but then the drive will probably not comply with you local EMI/RFI etc requirements.

Werner
You said My control panel will be supplied with 3x400VAC+N+PE at 50Hz. The customer want's to connect a GFCI to the PE lead connected to my control panel.


OK
so you are bringing in 3 phase from a wye (I hope??) transformer secondary feeding distribution panel with neutral and a grounding conductor (The PE).

Is this setup one of those high impedance ground setups?

Customer wants to detect current in the PE (grounding conductor) and use that to trip the breaker feeding the control panel using a shunt trip breaker I presume. Assuming single phase loads are tied to the neutral and separately derived ie control power are bonded to the PE (grounding) and IF it were "standard" relay type motor control I would predict no problem.

HOWEVER in the case with VFDs with filters and IF long motor leads are bonded to the PE I wonder about current in the PE (grounding) being high enough to cause erroneous tripping.

What I am really starting to wish for is having gone to school and studying EE and having better understanding of these induced in cable voltages and currents and "bleeding them to ground" and the total implications of the big picture.

Dan Bentler

Werner said:

To respond on some of youre comments:

I don't want to use this GFCI but the customer. My control panel will be supplied with 3x400VAC+N+PE at 50Hz. The customer want's to connect a GFCI to the PE lead connected to my control panel. (So it's not my plan to install several GCFI's in my panel, but the customer will install one GFCI at the power cabinet which will supply my control cabinet...Hope youre still with me...)

In my opinion the earth leakage current of all the VFD's summed together is already enough to trip the GFCI. In Europe a GFCI for home based solutions must be unstalled by law. For industrial purposes I'm not sure the customer must install a GFCI.

Does anybody know off regulations which state the GFCI must be used for industrial machinery?

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