VFD intermittently trips breaker on bypass relay

[eci22]

Hi all,

I have a huayang YL-620L VFD with a 2.2Kw water cooled spindle, i am having issues with intermittent breaker trips and need to work out which component is to blame.

After powering the VFD via a contactor (ABB AF09) a few seconds later (~2-3) there is a 'click' sound, I believe this is the bypass relay kicking in. Sometimes this works fine and sometimes it trips my 20A breaker, not the RCD but the MCB. As far as I know this is not an inrush current issue, the point of the bypass relay kicking in there should be no noticeable current draw on a properly working unit. Is that correct ? The VFD is connected to the motor but at no point is the motor spinning when the breaker trips.

Here's the sequence of events from the other day, I wanted to check I could turn it on and off a few times without problems as i thought i had resolved the issue-
Turned on the VFD-> booted up fine. waited ~15 seconds turned it off.
Turned on the VFD->booted up fine. waited ~30 seconds (until the VFD fans stopped spinning), turned it off.
wanted to try one last time-
Turned on the VFD when the bypass relay kicks in i heard a pop sound and my contactor let out a puff of smoke. The A1 A2 coil is gone (it reads 15 mega ohms), this is the first time i've seen this and this time the breaker did not trip. This was quite a significant failure.


So it sounds like the VFD is not 'filling' up on the initial power on and the bypass relay is then creating a surge in current ?
At this point it could be a bad VFD unit, but is there a chance the spindle could be at fault or the EMI filter ?

When i first got everything hooked up, I successfully sent serial commands from linux cnc to the VFD to start and stop the motor, the motor was on for a few seconds only a few different times, but it didn't have water running through it, as there was no load on the spindle i thought this would be ok just to check it works. Could i have damaged the spindle and the actual VFD is not the issue ? Can the motor cause this issue even if it is not spinning ?

I'm in the process of moving to a 32 amp breaker but plan to put a 20 amp breaker in the cabinet to protect the house fusebox.

Any ideas or help would be very much appreciated.

Thanks

[Muzzer]

The MCB should never emit smoke or suffer a burnt out coil, no matter what load you present it. That suggests you either had a duff MCB or it was connected up incorrectly. Assuming this is a Type B (or Type C) breaker, you shouldn't need anything like a 20A or 32A rating just for a 2-3kW VFD.

If the inrush limiter / soft start relay is causing the problem upon closing, it suggests an intermittent fault in the VFD.

You mention an EMI filter. I wasn't aware these Huayang VFDs had any filtering. If you have fitted one yourself, that's A Good Thing but it shouldn't in any way cause the behaviour you are seeing.

[eci22]

The MCB didnt smoke, it was the contactor- A1-A2 coil.
The tricky thing is sometimes the VFD will start fine, to the point it will communicate with linuxCNC start the spindle over serial etc and sometimes the breaker trips but it always trips at the same point, not at power up but a few seconds in, when the click of the internal relay happens (I assume it's a relay making this sound). I', thinking if the wiring was faulty it would present this issue everytime, but that isn't the case. I added the EMI filter, it's not part of the VFD.

[routercnc]

I've installed quite a few of these Huanyang VFDs on different machines in my workshop and all have worked for years except one a long time ago which went bang a few seconds after the first switch on. Luckily the seller replaced it. So like all things faulty units are possible.

In most inverter manuals they show a circuit breaker between the mains supply and the inverter but I've always connected them directly to the mains using the supplied plug. Industrially this would not be allowed as the inverter remains powered and should power down (after a delay) with the estop. Anyway the reason for me saying this is that when they switch on there is a short delay, maybe 1 or 2 seconds, before they actually come on and then there is a click from the relay inside the inverter. So I read your first post above and wanted to check if you meant the delayed click came from the VFD or the contactor. Pretty sure you meant from the inverter, and this normal. I've always assumed it is limiting current to the big capacitors inside.

So unless Muzzer has a different view on this I would try plugging the inverter in directly to eliminate the contactor (which has blown now anyway) and remove the EMI filter assuming it is just an external unit you wired in line (just for now). My inverters are not on special slow blow type C or D circuit breakers at the consumer unit so can't imagine they need anything special and they don't trip anything.

You mention running the water cooled spindle with no water, but no load for a bit of a test run at the beginning. I see absolutely no issue with that so I very much doubt that has done anything to the wiring etc. Extended running over 12000 rpm and under some load would get some heat into it, especially the bearings which is probably the bit the water is protecting the most but I don't think you went anywhere near that condition.

If all else fails these inverters are pretty cheap so maybe 'just' buy another one if you are not getting anywhere? Or is it new enough to ask the seller for a refund?

[m_c]

I don't quite understand why the contactor coil would burn out, as that should be totally independent of anything that the VFD is doing.

It does sound like an issue with the VFD though.
I've never really paid much attention, but I'm guessing the internal relay only powers up once the capacitors have charged, to ensure the control circuitry powers up cleanly.
Something like a shorted Mosfe/IGBT/<whatever power switching semiconductor is being use> would cause a trip at that point.

I'd try what routercnc suggest, and power it directly, but also disconnect any other wiring to eliminate any external issues.