I had a question brought to me by one of our operations guys regarding the voltage on the floating ground of a Wye-Delta transformer bank. I am unsure on how to go about calculating this voltage. If somebody could point me in the right direction I would greatly appreciate it. If you need to know it is a 14400V primary L-G and a 120/240V secondary bank. Thanks in advance!
Wye-Delta Floating Ground Voltage
- Thread starter ztg123
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kwired
Electron manager
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- NE Nebraska
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- EC
Are you asking about voltage on a floating wye point of the primary winding?
"Floating ground"? If it is grounded it has a ground reference, "floating" usually means there is no ground reference.
Your 120/240 secondary is likely grounded at midpoint?
LarryFine
Master Electrician Electric Contractor Richmond VA
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- Henrico County, VA
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Welcome to the forum.
The only way to get 120/240v from a 240v delta transformer bank is with one center-tapped secondary to derive a neutral; you'd have 208v to neutral from the high leg.
Forgetting the neutral (which is normally grounded) for the moment, the voltages to ground on a floating system are meaningless. What you should have is a 240v delta (no 120v).
The only way to get 120/240v from a 240v delta transformer bank is with one center-tapped secondary to derive a neutral; you'd have 208v to neutral from the high leg.
Forgetting the neutral (which is normally grounded) for the moment, the voltages to ground on a floating system are meaningless. What you should have is a 240v delta (no 120v).
oldsparky52
Senior Member
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- Wilmington, NC USA
As far as I know, the only "floating ground" would be on an ungrounded delta which would be just 240V phase to phase and no neutral (nor ground reference) would exist.
electrofelon
Senior Member
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- Cherry Valley NY, Seattle, WA
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- Electrician
Conjecture here, but I think OP is referring to the rating /writing on the individual transformers. Usually I see utility transformers marked "straight 120/240" which of course connected into the common wye configuration gives 208/120.
The line to ground voltage on an ungrounded 240 Delta would probably show up as 138 when measured with a high impedance meter due to capacitive coupling, but it could be "unbalanced". To figure it out, draw a wye inside the Delta triangle and compute it will just be L-L voltage divided by sqrt(3). Reiterating what others have said, this voltage is pretty much meaningless.
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