VFD (?) tripping RCD

[Jonathan]

[Edit - sorry this has ended up being a very long post. Wanted to mention everything so that everyone doesn't reply saying to do something I've already done!]
"
Refrained from posting this yesterday afternoon when the problem started as I expected to have found what's wrong by now. Sadly that's not the case.

In short RCD has started tripping when I run the router.

It's happened 4 times this weekend, all on the same aluminium part. Today and yesterday the machine ran for roughly half an hour then the main 40A breaker for the workshop went (switching off everything including the lights which is a bit annoying). Yesterday when that happened I switched everything back on, zeroed it ... lasted about 30 seconds and tripped again. Then I tried to start again, but found the parallel port on that computer is now broken :cry: Switched to backup computer, all seemed fine after running for a couple of minutes then bang... electric went again. By that time it was past midnight and I'd spent about 5 hours trying to cut a simple Z-axis plate, so I left it. Tried again today, same again ... worked for about half an hour then tripped ... then worked for 10 mins without tripping which was enough to finish that part. At least the cutter survived every time. Spindle was left at 185Hz throughout ... not getting hot either.

The RCD trips at a seemingly mundane time - not when the VFD is turned on, or when the current changes quickly or anything like that.

Things I've tried, all of which made no difference:



After the first fault I measured the voltage between machine frame/spindle at various points and earth. Less than a volt AC and DC in all cases. Machine frame and spindle are both earthed.

Measured the voltage above with the spindle running, same result. If I disconnect the earth wire I get 180VAC between frame and earth...so I didn't do that for long!

Measured voltage as above between everything I could reach with the meter with the spindle running and touching the aluminium it was cutting.

Switched of all non essential appliances - i.e. left air compressor, heater and de-humidifier off. So just stepper drivers, spindle, computer+monitor and lights. It has only tripped with the router on, never without so it must be the router or something related.

Connected the earth wires a bit more securely.

Cleared about 5kg of aluminium swarf, made by the router, off the floor. Though it might be conducting or something...yes I was desperate!

Searching on google.

I've not changed anything since last weekend and the weekend before when the machine was fine. Even using the same cutter and same aluminium!

Measured current to earth ... negligible reading.

Measured insulation resistance from the 3 phase wires to earth (spindle body). It's high, megaohms.



I've heard and read before that you shouldn't use an RCD with a VFD, but mine's been working fine for almost a year now with one so I didn't worry about it. How could it suddenly be causing a problem. I don't really want to just bypass it without knowing why it's tripping and without good reason.

Maybe the VFD is on it's last legs? Hope not...bit worried about starting again as whatever the fault is appears to have already killed one computer which is quite impressive seeing as it's optically isolated!

Really want to get this sorted soon as I've got parts that need cutting asap.

Left my oscilloscope at uni, so if it's not sorted by next weekend I'll bring it back to aid diagnosis - might pick up something the multimeter wont.

I'll go and make some bits on the lathe now, which I power from the same VFD (got a big switch to swap them over). Hope it works.

[Web Goblin]

I've had a fair amount of bacardi and coke but will try to help. First thing is never to disconnect and earth conductor with the main supply still live. This is a very easy way to kill yourself and wont really tell you much. Do you have a 40 amp mcb and seperate rcd or is it a combined rcd and mcb? It doesnt take alot to trip a 30mA rcd, apart from 30mA a dodgy computer power supply or filter unit could do it. Does the protection trip with only the router,vfd and the computer/ cnc running? Can you run the vfd and router on its own without the cnc controller? If it still trips this way and doesnt trip when you use your lathe then it could be the spindle motor. You will need an insulation tester to check the windings. A multimeter wont find any high resistance faults.
Ran out of bacardi now:cry:

[m_c]

I know it's not the most ideal way to test, but ammeter in the earth wires to see if there's any measureable leakage?

Should at least be able to isolate if it's the VFD, or motor causing problems.

[Jonathan]

First thing is never to disconnect and earth conductor with the main supply still live. This is a very easy way to kill yourself and wont really tell you much.

I know ... I was getting a bit desperate thinking if doing that still got no reading then it implies something's wrong with my earth or my meter. I kept one hand in pocket whilst doing that for obvious reasons. Isolated the supply, connected the meter etc ... switched it on, saw the voltage and switched it off straight away. You're right of course I probably shouldn't have done it.


Do you have a 40 amp mcb and seperate rcd or is it a combined rcd and mcb?

To be precise, It's one of these, which is what trips every time:
http://www.europacomponents.com/product_desc.php?prd_id=646&prd_image=WEB0012.gif&prd_name=2%20Pole%206KA&pso_id=

6A one of these for lighting, and 32A for the ring main.
http://www.europacomponents.com/product_desc.php?prd_id=639&prd_image=WEB0009.gif&prd_name=1%20Pole%20MCB%206KA%20B%20Curvepso_id=

Armored cable up the garden (maybe 20 meters) from house to workshop.


a dodgy computer power supply

Using a different computer after the first one just broke, and it's not likely that they're both dodgy.


Does the protection trip with only the router,vfd and the computer/ cnc running?

Yes - but it's only happened whilst cutting.


Can you run the vfd and router on its own without the cnc controller?

Started just that as soon as I read your post ... nothing interesting has happened yet.


You will need an insulation tester to check the windings. A multimeter wont find any high resistance faults.

Ahh, I suppose a multimeter doesn't test at anywhere near a high enough voltage.

Seeing as it only happens after the machine *has been* on for a while that implies something is accumulating, then setting it off. So what could that be, charge, heat...? Maybe the spindle insulation is breaking down once it's been on for a while and causing it to trip. I really hope not as those things are not cheap.

[Jonathan]

I know it's not the most ideal way to test, but ammeter in the earth wires to see if there's any measureable leakage?

Should at least be able to isolate if it's the VFD, or motor causing problems.

I did that, second to last bullet point. But thanks anyway...

If the problem persists I could try putting a shunt resistor in the earth wire and leaving the oscilloscope (DSO) monitoring it. Set the trigger to whatever voltage corresponds to say 10mA, or just under 30mA (something like that) and see what I get when it trips.

[m_c]

Ah, you did mention that (I've been helping a mate move house today, so am currently a bit tired!).

I'd be more inclined to try it with an ammeter, as that way things are still tied to earth, and give a better idea if it's something slowly building to tripping point, or something causing a more sudden spike. Of course an oscilloscope would be better, but you may as well try with what tools you've got to hand first.

[Jonathan]

I'd be more inclined to try it with an ammeter, as that way things are still tied to earth, and give a better idea if it's something slowly building to tripping point, or something causing a more sudden spike. Of course an oscilloscope would be better, but you may as well try with what tools you've got to hand first.

I have so far only tried it with the ammeter. Oscilloscope (http://uk.farnell.com/gw-instek/gds-1022/oscilloscope-dso-25mhz-colour/dp/1563796) goes down to 2mV/div ... so I could in theory use an about 0.5ohm resistor and it'd still show 30mA.

Spindle is still running ... that's been over half an hour. Only difference I suppose is it's now running unloaded, so not going to heat up much unless I restrict the cooling. Not going to try that as I'm a fan of non destructive analysis!

[mocha]

Assuming you haven't overlooked anything or missed something in the tests you have already done... It sounds similar to a problem I had with radios some years ago. ...

Bring some power from the house or from next door! but bypassing the RCD unit, with a standalone RCD if necessary, (but if you are happy to have a hand in your pocket while disconnecting earths you probably wont want to! lol)

Try plugging each of the suspect items; the VFD? into the extension lead with everything else plugged into the main RCD, as soon as it stops dying or the problem disappears you have the suspect device cornered for further investigation

or... find a way of removing DC from the AC line back to the RCD, or split board supply??

The RCCD you point to; 40amp? is it 30 or 100 mA?

[NB70]

Jonathan,

there's been discussion about this recently on the EMC2 mailing list - something to do with filters in the VFD providing a path to earth - which then trips the RCD. So it might not be a fault per se, just the way the VFD is designed to work. I know Andy Pugh and others experienced this issue (and hopefully solved it). He frequents the EMC2 forum - it might be worth asking a question over there:

Link: EMC2 forums (http://www.linuxcnc.org/component/option,com_kunena/Itemid,20/lang,english/)

Nathan
Sorry Jonathan just re-read your post properly - since your set up was working fine for a year this is unlikely to be the cause

[Swarfing]

I thought i should give you an experience i suffer from which may help?

50% of the time i switch my lathe on i trip the main breaker. This is because of the in rush of current to the 2kw inverter controlling the lathe (tested this by switching inverter on before applying breaker and all ok).

When the lathe is running it will trip out the main breaker, took ages to work out why. The reason for this is because the oven is on in the house, when the temp on the oven gets to a certain point the temperature control causes an earth problem (expansion). A known issue with a lot of ovens if you google it

To fix my issue when i get time is to run new armored cable i bought to the workshop. I shall connect it to a type 'D' RCBO to the none RCD side of the consumer unit in the house and use type'D' mcb's in the consumer unit of the workshop.

If the misses is really lucky i might get a new temp control for the cooker ;-)

In short look for other items that are on for a while as the problem may not happen until warmed up? i appreciate what your going through as it too was a long time for me to find my issue. For the time being i can work round it so no rush.

[Jonathan]

Left the spindle on for about an hour last night. It was fine. Just been using the lathe for quite a while and no problems there. So the former implies it's not the spindle and the latter implies it's not. That or it's nothing to do with the VFD.


The reason for this is because the oven is on in the house, when the temp on the oven gets to a certain point the temperature control causes an earth problem (expansion). A known issue with a lot of ovens if you google it

We do have dinner late ... but not past 11pm when it tripped! So I doubt it's the oven.


Bring some power from the house or from next door!

Next door, too many awkward questions like 'What's a CNC Router'!
I'm going to try it once more as normal, then if that fails I'll use an extension lead.


The RCCD you point to; 40amp? is it 30 or 100 mA?

30mA ... more is surely not safe?

[russell]

After the first fault I measured the voltage between machine frame/spindle at various points and earth. Less than a volt AC and DC in all cases. Machine frame and spindle are both earthed.

I would hope so! The IEE recommend (0.1 + cable resistance) ohms earth continuity ,say 0.125 ohms. To get a volt of difference you will need 8 Amps of earth current! If you can, borrow an earth continuity tester and make sure the resistance between parts is less than 0.1 ohm.


Measured the voltage above with the spindle running, same result. If I disconnect the earth wire I get 180VAC between frame and earth...so I didn't do that for long!
Although a potentially unsafe practice this shows no problem. Assuming you are using a digital multimeter as opposed to an old AVO, the input impedance of the meter will be about 10 MΩ. So you are measuring a current of only 18 μA.

something to do with filters in the VFD providing a path to earth - which then trips the RCD
All VFDs produce high levels of RF. In order to comply with the EMC directive they are fitted with RF filters on the mains input. These have relatively high capacitance to earth which results in a high reactive current to earth and can trip RCDs.
Try measuring the leakage current of the VFD on its own. If that is the problem connect it via a separate, lower sensitivity RCD but make sure your earth bonding is good!

Russell.

[mocha]

All VFDs produce high levels of RF. In order to comply with the EMC directive they are fitted with RF filters on the mains input.

Russell, are the Chinese spindle / VFD combinations likely to do this too?? I suppose I'm asking if this filter is an "EU" thing or world wide??

[russell]

Russell, are the Chinese spindle / VFD combinations likely to do this too?? I suppose I'm asking if this filter is an "EU" thing or world wide??
For anything to be "placed on the market" i.e., sold anywhere in the EU it must comply with all relevant EU directives. It is not a worldwide thing. However for such things to be sold in the USA it must comply with FCC regulations which are basically the same. As that is the largest market for Chinese goods they are likely to comply.

Russell.

[Toddy]

It might help to try and replace the mains rcd, i had the same problem with the house main fuse popping all the time(through the night also) it turns out that after a couple of times the main rcd was too sensative,all fuses are ment to be changed after a couple off trips.(told by an electrition)

[Jonathan]

Update... worked for a long long time running the lathe and coolant pump in parallel (machining stainless). Long enough for the cast iron headstock to warm up a bit.
Failed after about 3 minutes on the router, but this time only the VFD, circuit breaker didn't trip. I just got the 'ELuS' error... I've only had an error before on the VFD when I've been getting a bit carried away on the lathe and overloaded it (so not often).

I'm going to buy another VFD now as I could do with having two anyway as then I can run the lathe and router at the same time. I think I'll get a 3kW one as the lathe plus pump is borderline on the 2.2kW. It will help diagnose the problem, though I hope to have sorted it by then.


If you can, borrow an earth continuity tester and make sure the resistance between parts is less than 0.1 ohm.

Considering they wouldn't even let me borrow a soldering iron for a couple of hours from Uni, I think there's not much hope of that. Unless there's somewhere else...



Although a potentially unsafe practice this shows no problem. ... measuring a current of only 18 [FONT=Times New Roman, serif]μA.

Yes DVM, so that's true. I did consider putting a high-ish value resistor from the frame to earth with that test and measuring the voltage across it to see if it will sustain a higher current. Is it worth it?


Try measuring the leakage current of the VFD on its own. If that is the problem connect it via a separate, lower sensitivity RCD but make sure your earth bonding is good!

I will try that again next weekend. This weekend I only managed to cut one part on the router, and some bits on the lathe :mad:

[luke11cnc]

Just a thought Jonathan But

Have you checked your water pump and pipes ?? on the router

would it help if I came with my VFD at the weekend to try ??

James

[Jonathan]

Have you checked your water pump and pipes ?? on the router

I have checked the integrity of the pipes, but I've not tried running it without the pump as I do not want to risk the spindle.


would it help if I came with my VFD at the weekend to try ??

It would help, thank you very much for the offer. However I don't want to risk your VFD as clearly the VFD getting turned off by the breaker is bad for the IGBTs inside it and could well damage or ultimately break them. It's not worth it particularly as your machine is so close to being finished now. Would have finished the parts by now if it wasn't for this.

[Web Goblin]

Jonathan,
make sure your RCD is rated at 30mA and NOT 100mA. Around 50mA can kill with the correct fault path through your body, which I think is from your left hand through your body to right foot then to ground.

Ian

[luke11cnc]

have you checked for rodent damage ??

as you are away from your work shop in the week rodents will get in and chew cables (just a thought)

has your water pipe got a blockage if a filter is fitted it my be blocked, is the water flowing around your motor ??

James

James

[Jonathan]

have you checked for rodent damage ??

as you are away from your work shop in the week rodents will get in and chew cables (just a thought)

has your water pipe got a blockage if a filter is fitted it my be blocked, is the water flowing around your motor ??

Erm, how do I check for rodent damage, my Mum suggested that too! The cable up to the workshop is armoured, and the cables inside are concealed behind the insulation so I think it's unlikely?

The water is flowing.

Update:

Apparently changing PD200 from 0 to 65535 (2^16-1) and PD209 to 50 can help. It didn't, breaker still tripped.

Tried extension lead from house socket to workshop as the house wiring is old so it's just got wire fuses and predictably that fuse didn't blow. The VFD still stopped after 15 mins, the motor and displayed an error. I think last time I remembered the error wrong as having seen the error code definitions it makes even less sense than the correct code!

If I look in PD177-180 for the previous faults it's EOCn, ELUNn, EOUd and EOCn in that order. The last error I saw, via house ring main, was EOCn so I've had that one at least twice now. The definition for that error is:

Over current at constant speed. They suggest in the manual:

1) Check whether the motor has got short circuit and whether the insulation of the output wires is good.
2) Check whether the motor is blocked and whether there is a sudden change of mechanical load.
3) Check whether the inverter's capacity is too small and increase its capacity.
4) Check whether there is a sudden change in the power supply voltage.

2 and 3 don't apply, 3 for obvious reasons and 2 since it's stalling whilst the cut is constant and I'm nowhere near the power limit - only about 1.1A.

So that implies it's either an insulation fault with the spindle, or the supply. Unlikely to be the supply since I've tried it from two points. So that leaves the spindle, oh no! For what it's worth I measured each phase resistance and the insulation resistance from each phase to the spindle body at the VFD end (to include the wire) directly after it faulted. Phase resistances are balanced and the rest out of range for the meter.

Suspicion that it's the spindle is backed up by the VFD working just fine on the lathe.

New VFD is on the way, ordered Monday. Think I'll dismantle my VFD now to see if there's anything obvious, like vented caps...


Jonathan,
make sure your RCD is rated at 30mA and NOT 100mA. Around 50mA can kill with the correct fault path through your body, which I think is from your left hand through your body to right foot then to ground.

Or hand to hand (as current path is via the heart) I believe ... it is 30mA and I was aware of that. Much less than 30mA can kill if it's for long enough.

[Jonathan]

Took the case off the VFD, couldn't see anything wrong so I wiggled the wires a bit and now it works! :smile:
Ran fine for over an hour cutting Luke11cnc's parts...

[russell]

Took the case off the VFD, couldn't see anything wrong so I wiggled the wires a bit and now it works! :smile:
Ran fine for over an hour cutting Luke11cnc's parts...
Great. When you get a chance it will be worth rechecking all the internal connections. Loose connector? Dry joint?

Russell.