- Location
- New Jersey
- Occupation
- Journeyman Electrician
Lou,
I was under the impression that this was a 208Y/120 volt system not a single phase 240 volt system. If so that diagram would not apply.
Sorta of a brainer teaser
- Thread starter ronaldrc
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Lou,
I was under the impression that this was a 208Y/120 volt system not a single phase 240 volt system. If so that diagram would not apply.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
Lou
I also think it would be 104 or half, maybe someone check it out for us?
Ron,
What is the system voltage that you're asking about? We're getting all different conflicting information making it impossible to properly answer the question.
hardworkingstiff
Senior Member
- Location
- Wilmington, NC
Jim,
How would the current flow on that short circuit (keep it simple {if you can} please).
hardworkingstiff
Senior Member
- Location
- Wilmington, NC
My understanding is he was wondering what voltages would be if he applied 208-volts instead of 240-volts in drawing #5.
Jim's point is very interesting.
hardworkingstiff
Senior Member
- Location
- Wilmington, NC
Is this a dumb question?:-?
If you are bringing in 2 phases from the 120/208 3? system, without the neutral, grounding the center point of the transformer winding will make a connection through the earth to the neutral. This will produce unstable voltages and is an NEC violation. The legs would be 120 volts if there were a solid metallic connection to the 120/208 neutral point, but 104 volts if there were an infinite resistance through the earth.
hardworkingstiff
Senior Member
- Location
- Wilmington, NC
Would the short circuit be driven by 120-volts or by 16-volts?
hardworkingstiff
Senior Member
- Location
- Wilmington, NC
Here is the circuit instead of a single phase 120/240 volt transformer.
My 'guess' is if you didn't ground XO, you would have 104-volts. If you did ground it, you would have 120-volts with the ground path being a CCC.
hardworkingstiff
Senior Member
- Location
- Wilmington, NC
Does that cc mean you won five bucs and are going to cc's or what?
CCC= current carrying conductor?
winnie
Senior Member
- Location
- Springfield, MA, USA
- Occupation
- Electric motor research
As I understand the OP, the 'brain teaser' is about using the secondary of a transformer only, with nothing connected to the primary.
There are two examples given, in post #1 and post #5, each using the secondary of a single phase transformer to derive a missing voltage in a single phase system, either getting the opposite leg from a single 120V L-N, or deriving the neutral from a 240V L-L.
The 'teaser' is what happens if you try to do the same thing using the secondary of a three phase transformer.
I don't think that we can answer without knowing the characteristics of the three phase transformer being used, and would expect different answers depending upon how the primary was connected and if the three phases are mounted on separate cores or on a single three leg core.
The big difference is that in the single phase case, all of the coils, both primary and secondary, and both halves of the secondary, are mounted on the same core. Thus the same magnetic flux threads each coil, and the same 'volts per turn' is developed in both halves of the secondary.
In the three phase case, you can have different volts per turn on the different coils.
I think that to go further we would need to define the particulars, eg 120V or 240V in, and what sort of transformer is being used.
-Jon
There are two examples given, in post #1 and post #5, each using the secondary of a single phase transformer to derive a missing voltage in a single phase system, either getting the opposite leg from a single 120V L-N, or deriving the neutral from a 240V L-L.
The 'teaser' is what happens if you try to do the same thing using the secondary of a three phase transformer.
I don't think that we can answer without knowing the characteristics of the three phase transformer being used, and would expect different answers depending upon how the primary was connected and if the three phases are mounted on separate cores or on a single three leg core.
The big difference is that in the single phase case, all of the coils, both primary and secondary, and both halves of the secondary, are mounted on the same core. Thus the same magnetic flux threads each coil, and the same 'volts per turn' is developed in both halves of the secondary.
In the three phase case, you can have different volts per turn on the different coils.
I think that to go further we would need to define the particulars, eg 120V or 240V in, and what sort of transformer is being used.
-Jon
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Jon,
I took the revised teaser as feeding 208V to the original single phase transformer not to a new three phase unit.
winnie
Senior Member
- Location
- Springfield, MA, USA
- Occupation
- Electric motor research
I agree with Lou in regard to his answer in post #31 about the drawing in post #29. Further if the X0 terminal were connected to the supply neutral, then I believe that the third phase would be developed.
I believe that even though the transformer is nominally rated for a 208V secondary, that in this application (with the X0 terminal _not_ connected, single phase supply) that it could be used at 240V line-line.
I think that a harder question is 'what happens with a 120V supply', such as in the diagram in post #1.
-Jon
I believe that even though the transformer is nominally rated for a 208V secondary, that in this application (with the X0 terminal _not_ connected, single phase supply) that it could be used at 240V line-line.
I think that a harder question is 'what happens with a 120V supply', such as in the diagram in post #1.
-Jon
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Jim and Jon
I was really thinking along the lines of a single core 480/208 delta wye dry type transformer.
I still believe the voltage would be 104 volts with single core, three phase or single.
it would act like a voltage divider I think.
My oops.
But if the delta primary windings are left open,a single phase 2-conductor 208V input would be across two 120V windings in series. From this point on my analysis remains the same.
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