Delta 3 Phase Center Grounded

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Craigpor said:
Yes the machine is European. The transformers came with it. There are (3) dry type transformers that go from 240 to 380. This is for the main 100 amp feed to the press. There are ink dryers that I am told are 240 volt , 3 phase center grounded, 60 amp.
Thanks
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ActionDave said:
I agree for the most part. Thing is there are people that work on these presses for a living. That's the guy you want to talk to.


No. No buck/boost. I have not worked on a lot of presses so I do not fell comfortable giving a lot of advice about them but my experience has been isolation transformers are SOP for changing voltage from 208 to 240 or even going from 240 to 240 then on to the machine.
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If the front end supply of the machine is a 240 to 380 transformer, most likely all it needs is 240 volts with three lines that have a 120 degree phase angle between them (grounded or ungrounded) and it will work fine.

Sounds like the last place it was connected to had a 240 delta supply with a mid point ground on one phase. Doesn't necessarily mean it can only be connected to that type of source, especially if there is no "neutral" required from the supply circuit.

Chances are the 240 to 380 transformer was added on whenever this thing was initially installed in the US. If installed in a place that has a 380/220, 400/230, 415/240 system, it would probably direct connect to it.

If OP does not have the transformer as the "front end" of the supply to the machine, we probably need more details to be of much help.
 
To get a true 240 volt phase to phase and center grounded, you need a 240 volt wye (Y) secondary. A very very rare beast. I do see a Zig Zag transformer available from Acme. That is their only off the shelf solution.

240 volt Delta can not get you a center ground.

I agree with JR's hypotheses of what is really inside the machine.
 
Frank DuVal said:
To get a true 240 volt phase to phase and center grounded, you need a 240 volt wye (Y) secondary. A very very rare beast. I do see a Zig Zag transformer available from Acme. That is their only off the shelf solution.

240 volt Delta can not get you a center ground.

I agree with JR's hypotheses of what is really inside the machine.
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I agree. I also can see a 240 volt delta with a high leg as being what one thinks fits that description. It is grounded at the mid point of one phase, but that point is not a true neutral to the entire system.
 
kwired said:
I agree. I also can see a 240 volt delta with a high leg as being what one thinks fits that description. It is grounded at the mid point of one phase, but that point is not a true neutral to the entire system.
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Hooking up two transformers in series like this in close proximity is really asking for trouble with circulating currents. I would double check your taps and review the specs of the existing transformer, making sure it's also step up rated.
 
ActionDave said:
Correct, '14 code I think. From what I can tell the only difference between an old transformer wired up backwards and a new step up rated one is words on paper saying so.
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There is a fair chance that a transformer rated for use in either direction will be wound in a way that reduces the asymmetry between input transient currents on energizing, perhaps at the expense of a small reduction in efficiency in the "preferred" direction.
Or at least that the asymmetric energizing current is documented somewhere in the specifications so that you can take steps to accommodate it.
 
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