Welder Power Supplies

jclarke4

Hi,

In an installation there are 6no. Eurarc 420 welders supplied from dedicated 40Amp single phase RCBO's housed within a dedicated distribution baord. The welders can be operated as either single or three phase via a selector switch. The current arrangement is single phase with ABB 32A plug/socket connections. The rated max load in single phase is 93Amps. The users of the welders only use up to 3.25mm electrodes which the manufacturer tells me that using these types of electrodes would only use max of 35Amps.

The RCBO's are 30mA C type and keep tripping out once welding commences. It will be a big job not to mind expensive to change out to hard wired connections via isolators and MCB's so I was proposing to change the RCBO's to D or even K type as the issue may just be in-rush current but I suspect that there may be a problem with earth leakage.

Anybody any thoughts???

John.

2011

The RCBO's are 30mA C type and keep tripping out once welding commences

Ok fair enough, but do you know why it is tripping?? What I mean is it could be tripping because:

1. The RCD part of the RCBO is operating due to an difference in current between the live and the neutral of more than 30mA

OR

2. The MCB part of the RCBO is operating due to the large inrush of current.

I would suggest that you find out what it is first. You could do this by installing a seperate RCD and MCB rather than an RCBO just on a temporary basis to see where the problem lies.

It will be a big job not to mind expensive to change out to hard wired connections via isolators and MCB's

Not really. I guess you mean isolators rather than sockets? Therefore RCD protection is not required as it is fixed equipment. This was an option I was thinking of. If at all possible I would always like to keep an RCD in circuit (but perhaps this is not an option).

I was proposing to change the RCBO's to D or even K type as the issue may just be in-rush current but I suspect that there may be a problem with earth leakage.

There would be no earth leakage issue if you did this because you would no longer have any protection installed that would operate due to earth leakage current. The MCB will not operate even if a couple of amps are flowing to earth, the RCBO will at 0.03 amps!! Do a bit of investigating before you go making any decisions is my advice.

BTW there is an RCD on the market that self resets when the fault is removed. This may be a simple solution for you.
How ofetn do the RCBOs operate?? Frequently or only the odd time???

clinchy

isnt it d type mcbs for transformers and welders ?

jclarke4

Thanks 2011.

I am going to try to see what exactly is tripping out the welders by installing seperate MCB and RCD on one of the welders tomorrow. From this I can determine the problem.

If it is a problem with earth leakage and I have to replace the RCBO's with welders, this will be a big enough job and costly as I will then have to change the plug/sockets to hard wired isolators to conform with the regs.

I haven't come across the RCD's you are talking about. Have you any other details?

FYI, I have uploaded the spec of the welder...

davelerave

At a guess i would think the c-type is the problem(prob should be D).
You shouldn't need to remove rcd protection for these afaik(they are mobile so plug/socket arrangement is prob best)
Some welders are single phase or 2-phase if memory serves(could this be the case here?)
As 2011 pointed out.Sometimes the combined protection is a nuisance when troubleshooting.

2011

I haven't come across the RCD's you are talking about. Have you any other details?

Yes, here is an example of an 80 Amp 30mA single phase Hager RCD

If it is a problem with earth leakage and I have to replace the RCBO's with welders, this will be a big enough job and costly as I will then have to change the plug/sockets to hard wired isolators to conform with the regs.

It wont be that costly.
Not too much work as all of the wiring is in place.
Anyway, first see where the problem is with just one welder.

I just looked at your datasheet. I am not sure what "maximum absorbed power 13kW" means to be honest. But I do know that to supply 13kW takes about 53 amps at from a 230 volt single phase supply!

Tell me, have you got a 3 phase supply??? If so use it and I think your problems may be solved. Even if this does not solve your problem it would be better practice and will result in less dimming of the lights!!

davelerave

I think they're wired either standard single-phase or 2P+earth (same lead) if memory serves.
The 2phase +earth would be preferable anyhow if that's the case but you will surely need 'D' type.
Haven't done that much with welders but i think that's the arrangement.

2011

davelerave wrote: »

I think they're wired either standard single-phase or 2P+earth (same lead) if memory serves.

That is the way I am reading it too.

2phase +earth

Yes, this would be best.

Haven't done that much with welders but i think that's the arrangement.

neither have I but
that's right as far as I know.

jclarke4

Thanks for all the threads lads.

I spoke to the welder manufacturer again and he tells me that there should be no problem operating on 230Volts and using 3.25mm electrodes when welding would only generate approx 35Amps max and that there should be no problem with earth leakage. Apparently it is only when using larger electrodes that the current gets up to 53 amps.

I am setting up a D and K MCB with seperate RCD's today to see which one trips. From talking to the user of the welders it seems that there were approx 4 welders starting up ok but when the operator switched them off and back on again, the breakers would trip out. To me this seems like a current surge problem.

Will let ya all know the outcome. I do accept that 3 phase was the way to go but as the manufacturer said, they should work ok on single phase with RCD protection.

2011

But have you got a 3 supply at your disposal?

6 of those welders is a large amount of power!!

Will let ya all know the outcome. I do accept that 3 phase was the way to go but as the manufacturer said, they should work ok on single phase with RCD protection.

He may well be right but the fact is your welders will all perform better and cause less problems for other equipment if they are fed from a 3 phase supply.

I think the ESB would also have issues if 6 welders like that were to be fed from a single phase. You would also be in danger of blowing the main fuse!!

You really need to look at this. When you use a 400 volts rather than 230 volts the current is reduced. Also with 6 welders the load can be distributed across 3 phases. The welders can cause the supply voltage to dip.

jclarke4

2011, there is a 3 Phase supply to the building. However, there are 6 welders with 2no. welders per phase i.e. 2 on L1, 2 on L2 and 2 on L3. This would equate to approx 70Amps per phase from the main supply with the welders configured in single phase. The remainder of loads in the building are quite small. These welders have been operating on single phase for the last 3/4 years without any problems.

Running on dedicated 3 phase supplies to each welder, the manufacturer said that they would draw approx 25Amps per phase using 3.25mm electrodes.

davelerave

Did you check if welders are actually 3-phase.i think they're prob 2-wire+earth 230v/380v.If that's the case the higher-voltage will work better.

2011

jclarke4:

there are 6 welders with 2no. welders per phase i.e. 2 on L1, 2 on L2 and 2 on L3.

OK so you have balanced the phases, that is good.

jclarke4:

These welders have been operating on single phase for the last 3/4 years without any problems.

I dont doubt you, but if the welders were supplied from a 3 phase supply then the current drawn would be reduced by about 43% for the same output. What will this mean to you?
1. A noticable increase in performance from your welders
2. Less chance of nuisance tripping
3. Also less volt drop which may cause lights to flicker, or damage to electronics.

But if it is not practical fair enough, I have not seen the job in question, so I will take your word for it.

jclarke4:

Running on dedicated 3 phase supplies to each welder, the manufacturer said that they would draw approx 25Amps per phase using 3.25mm electrodes.

That sounds about right. If you devide the current that one welder takes from a single phase 230 volt supply by 1.732 (the square root of 3) you will get the current that would be drawn if you were using a 3 pahse supply.

I am setting up a D and K MCB with seperate RCD's today to see which one trips.

I take it that the RCBOs are C type at present? Go with the same type of of MCB so that you are comparing like with like.

From talking to the user of the welders it seems that there were approx 4 welders starting up ok but when the operator switched them off and back on again, the breakers would trip out

When switched back on did the RCBOs stay on? Often transformers do this. When a transformer is plugged in at first it is like a short circuit causing a large current to flow. This current can cause the MCB part to operate. Once a back emf is set up this current drops significantly. One possible simple solution is to buy sockets that have the RCBO at the socket making it easy to reset if this is the case.




Dave:

Did you check if welders are actually 3-phase.i think they're prob 2-wire+earth 230v/380v.If that's the case the higher-voltage will work better.

A welder that is described as "3 phase" only uses 2 of the 3 phases. Yes I agree with you that it will work better than with the 230 volt single phase supply.

controle

The rated max load in single phase is 93Amps

I take it that the 93 amps is on the output side of the welder and the welder is not drawing 93 amps from the mains at 230 volts, right?

davelerave

ya.the 2-phase 380v seems to be commonly referred to as 3-phase.i'm not that familiar.