Sorta of a brainer teaser

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ronaldrc

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Remember this? Well just sitting here thinking about this stuff. Got to thinking, what would the voltage be to the neutral if I used a three phase transformer 120/208 secondary in this fashion? I do not have a three phase
electrical system here at my residence nor do I have a three phase 120/208 volt transformer.

Please remember we are just hooking two ungrounded lines not all three.

We do know the higher voltage will match the source voltage but what do you all think lower voltage to the
neutral would be?

A-120 volts or
B-104 volts

I do not know the answer to this although I think it will be half the source in this case 104 volts.



Create-120,%20240-with-a-neutralb.jpg


Thanks :)
 
mikeames said:
This has already been posted it will be as the diagram shows.
Click to expand...

No Mike that was my post or diagram originally.

Here I am asking about using a three phase 120/208 secondary instead of a single phase 120/240 volt and just hooking two legs. :)

Would the voltage be half the source or 120 volts?
 
Are you hooking up 2 phases of a three phase wye system or is this a single phase transformer with a 208 volt secondary as your pic describes?
 
Two phases from a WYE system will have 120 volts between each phase and the neutral and 208 volts between the two phases.
 
Yes you are right I am hooking two phases of a 208 transformer on a
208 three phase system.

What would the voltage be to X0 from those two legs 208 legs?
 
Rob

You don't think the missing third leg will have effect on the voltage.

Don't forget some have looked at this diagram as a voltage divider. :)
 
ronaldrc said:
Rob

You don't think the missing third leg will have effect on the voltage.

Don't forget some have looked at this diagram as a voltage divider. :)
Click to expand...


Let me see if we're on the same page:

208Y/120 volt system.
208 volts phase to phase
120 volts phase to neutral
 
infinity said:
Let me see if we're on the same page:

208Y/120 volt system.
208 volts phase to phase
120 volts phase to neutral
Click to expand...


Yes but only using two legs say line #1 and line #2
hooked as single phase.

I have been temporary retired from a broken leg from a bike accident.

I can not at this time get to a place to run this test. :)
 
ronaldrc said:
No Mike that was my post or diagram originally.

Here I am asking about using a three phase 120/208 secondary instead of a single phase 120/240 volt and just hooking two legs. :)

Would the voltage be half the source or 120 volts?
Click to expand...


Sorry I jumped in. I should have put more though into it. :)
 
For a 208Y/120 volt system:

Phase to phase is 208 volts, that's for A-B, A-C and B-C.

Phase to neutral is 120 volts, That's A-N, B-N and C-N.

It's really that simple, not sure what else you're asking?
 
ronaldrc said:
Yes but only using two legs say line #1 and line #2 hooked as single phase.
Click to expand...

The coil you are feeding is seeing 208-volts. With only 2 wires, it looks like single-phase (and actually is with nothing else to use as a reference).

The center of that coil (grounded and called neutral) will be 1/2 of the voltage across the coil (assuming it is in the middle).
 
hardworkingstiff said:
The coil you are feeding is seeing 208-volts. With only 2 wires, it looks like single-phase (and actually is with nothing else to use as a reference).

The center of that coil (grounded and called neutral) will be 1/2 of the voltage across the coil (assuming it is in the middle).
Click to expand...


Where would you have a center tap on a 208 volt coil?
 
If you do not bring in the neutral conductor from the wye system you only have single-phase 208V, period.

If you feed this single 208V to your series connected transformers you will end up with 104V across each winding. Your resultant output will be 104/208.

However if you bond your new neutral point to ground you will create a short circuit (there is a 16V difference between the input and output side L-G). This is why 208-240V buck-boost transformers should only be used with L-L loads.
 
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