UK 3 phase inverter welder from Split Phase / Bi Phase supply 480v

[robertl]

Hello all,
I have discussed my power install before as i am sure a lot of you will remember as it is quite different to a normal setup.
I have a split phase / Bi Phase system, 2 phases coming into the workshop from a center tapped transformer. 240v phase to neutral and 480 phase to phase.
I have been looking at machinery and have bought some of the equipment already which is running on VFD's so not an issue power wise.
I now need to get a large Mig welder to complete the set, most of them as soon as you go over 250A they have to be 3 phase.
My question is relating to the inverter type welders on the market, i am not sure if what i am going to ask is even remotely possible but with my minimal knowledge on these welders and what i can find on the internet it seems like it may be possible.

My question is as follows, can i take the 2 legs i have with 480v between them, say put them in L1 and L2 of the welder and then put a series of links in between L1, L2 and L3 to in effect make the machine think i am powering it from 3 phase. i.e it will see power across all phases. the only thing with this is the phases wouldn't be balanced 120 degrees apart but i am not sure the machine would be this "clever" and would more be looking for a voltage across each leg.

In my simple understanding of the way these inverters work they take in a "3 phase" supply and convert it to DC and output it through a second inverter in the machine.

Any help on this would be greatly appreciated.
It is a big outlay to buy a 3 phase welder of this size and not much point doing it if this wont work.

My other possible options are a Rotary converter, or a Drives Direct digital one.

Thanks in advance
Robert

 

[Lucien Nunes]

Re 480V split-phase vs. 3-phase; on the 3-phase supply, the highest RMS voltage between any two points is 400V and the internals of the welder inverter are designed for this voltage. Applying 480V could result in serious damage, not least exploding electrolytic smoothing capacitors. It might actually work briefly, but go up in smoke soon afterwards.

As for the single vs. 3-phase (assuming the voltage is OK), again in general terms unless the unit is specifically rated for use on single-phase supplies (and some might be) then it probably won't be a good idea. Single-phase AC voltage rises to a peak, drops to zero, then a negative peak etc. With three phases all reaching their peaks at different times, there's never a moment at which the available voltage from the mains is zero. 3-phase-only equipment can therefore use smaller smoothing capacitors handling less ripple current to smooth the peaks out to give DC. If a single-phase supply is connected instead, the smoothing capacitors would have to work much harder to fill in the gaps where the other two phases' peaks should be, so they and the rectifier bridge (which will be subject to much higher currents too) could overheat and fail, and the DC voltage ripple is likely to be much higher affecting output quality.

Manufacturers might have units available that will accept your split-phase supply, you would have to check, I am talking in the general case of connecting it to normal 3-phase equipment.

 

[robertl]

Re 480V split-phase vs. 3-phase; on the 3-phase supply, the highest RMS voltage between any two points is 400V and the internals of the welder inverter are designed for this voltage. Applying 480V could result in serious damage, not least exploding electrolytic smoothing capacitors. It might actually work briefly, but go up in smoke soon afterwards.

As for the single vs. 3-phase (assuming the voltage is OK), again in general terms unless the unit is specifically rated for use on single-phase supplies (and some might be) then it probably won't be a good idea. Single-phase AC voltage rises to a peak, drops to zero, then a negative peak etc. With three phases all reaching their peaks at different times, there's never a moment at which the available voltage from the mains is zero. 3-phase-only equipment can therefore use smaller smoothing capacitors handling less ripple current to smooth the peaks out to give DC. If a single-phase supply is connected instead, the smoothing capacitors would have to work much harder to fill in the gaps where the other two phases' peaks should be, so they and the rectifier bridge (which will be subject to much higher currents too) could overheat and fail, and the DC voltage ripple is likely to be much higher affecting output quality.

Manufacturers might have units available that will accept your split-phase supply, you would have to check, I am talking in the general case of connecting it to normal 3-phase equipment.

Thankyou for the detailed reply.
To let you know the welders i have been looking at are rated 400 to 560v (something maybe to do with them being a USA design)
So with that 480v is well within the limits of them.
With that in mind would what i wrote have any hope of working?
Thanks

 

[Lucien Nunes]

I would ask the manufacturers. Only they will know whether their rectifier bridge and smoothing components are suitable for single-phase (and in this context, your supply is 480V single-phase).

 

[robertl]

I would ask the manufacturers. Only they will know whether their rectifier bridge and smoothing components are suitable for single-phase (and in this context, your supply is 480V single-phase).

How is it not 2 phases though? As they are not the same phase?

 

[Lucien Nunes]

Two wires are different phases if they reach their peak voltage at different times.

Split phase has two line conductors but they both peak at the same time, with opposite polarity relative to neutral. L1 & L2 both peak, then both drop to zero. Then another peak (with the opposite polarity) and back to zero.

With an actual 2-phase supply (used historically but superseded by 3-phase) first L1 peaks, then L2 a quarter of a cycle later, then L1... there's never any point where they are both zero.

 

[pc1966]

How is it not 2 phases though? As they are not the same phase?

Normally what you have would be described as centre-tapped or split-phase, as they are generated from a single phase supply.

While 0 and 180 deg phasing is one definition of 2-phase it is not that special as you can only generate 0/180 deg.

A 2-phase system has 90 deg phase shift (so drawn as a phasor diagram they are at 90 deg) and with suitable transformer(s) you could generate any angle (and thus any polyphase system).

But 2 phase is hardly ever seen as 3-phase has several advantages over it, the main one is with a balanced load you don't need any neutral so it has a significant cost advantage over other systems if you looks at power delivered for a given amount of conductor and a given voltage-to-ground limit.

 

[robertl]

I would ask the manufacturers. Only they will know whether their rectifier bridge and smoothing components are suitable for single-phase (and in this context, your supply is 480V single-phase).

Would this work? certainly looks capable of taking the voltage but is asking for a 3 phase supply? just depends i guess if its looking for 3 voltages, or 3 balanced phases?

Item Not Found

www.rapidwelding.com

 

[pc1966]

Would this work? certainly looks capable of taking the voltage but is asking for a 3 phase supply? just depends i guess if its looking for 3 voltages, or 3 balanced phases?

Anything that says "3-phase" will expect 3 balanced phases at 120 deg, the world standard arrangement.

You will have to contact the makers of (probably various) welders to ask about operations on split-phase (USA style, but higher voltage here) and if they do any of the ratingf you want that are single-phase capable.

However, if you are expecting to have a lot of machinery and that might be sevaral items that need 3-phase you might have to look at the cost to get 3-phase supplied, or the cost of a converter to generate 3 phase from your 240-0240 split phase supply.

 

[JD6400]

We do quite a few grain stores and come across spit phase supplies every so often , I was told by one of the dealer's who we install for that most spilt phase motors and gear comes from Italy !?
Have no idea why this is the case , but may be worth a look at Italian spec welders ?
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Don't forget your fuse board and associated gear should be rated to the higher voltage across phase's.
Been a couple of year since the the last one but from memory Schneider is about the only make that complies.