I have a 120/208 to 277/480 volt 150kva transformer installed about 6 months ago. Doing some pm on it today and the output voltage is only 460 volts with no load. Didn’t install the transformer so not sure what the original readings were. Trans is tapped at its highest setting. I’m thinking there is a factory issue with the windings somehow? Anybody with any insight on this?
Transformer output
- Thread starter fireryan
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GeorgeB
ElectroHydraulics engineer (retired)
- Location
- Greenville SC
- Occupation
- Retired
If the taps are, as usual, on the input (208 windings), LOWERING the tap will raise the output voltage. Attach a photo of the nameplate. It is unusual to have a wye:wye transformer, but certainly not unheard of.
MD Automation
Senior Member
- Location
- Maryland
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- Engineer
What is the voltage line to line on the primary when you read 460 on the secondary?
Also, maybe a dumb question, but are you sure this is an actual 208 -> 480 step up transformer? And not a (more common) step down transformer that is being backfed? I ask only because you say you did not install it. If it is a backed xfrmr, then any winding compensation works against you and the taps won't work like normal either.
And yes, like GeorgeB indicated, you seem to indicate it's a Wye-Wye, which would be unusual.
Also, maybe a dumb question, but are you sure this is an actual 208 -> 480 step up transformer? And not a (more common) step down transformer that is being backfed? I ask only because you say you did not install it. If it is a backed xfrmr, then any winding compensation works against you and the taps won't work like normal either.
And yes, like GeorgeB indicated, you seem to indicate it's a Wye-Wye, which would be unusual.
Yes George I am thinking of this backwards. The tap is set at 220 not 208. So lowering the tap to 208 should increase the secondary voltage not decrease it.
Primary is 212 L-L. It is indeed a step up trans. Primary is 208. Secondary is 277/480. I typed that wrong
- Location
- Illinois
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- retired electrician
Actually designed and manufactured as a step up transformer, or just being used as one?
That is how it is being used. Physically the coils are designed cooling wise with the primary coil on the inside and secondary on the outside for cooling reasons. If you reverse this it won’t cool properly so you have to derate a transformer that is used “backwards” (step down design used to step up).
curt swartz
Electrical Contractor - San Jose, CA
- Location
- San Jose, CA
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- Electrical Contractor
So this transformer is Wye/Wye? Not Delta/Wye? You said the primary is 120/208. Is there a neutral connected to the primary (208) side?
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
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- Electrical Contractor
For wye-wye, the primary neutral is used and connected. Otherwise, the wye secondary voltages could vary.
No primary is just 208. Had a typo
- Location
- New Jersey
- Occupation
- Journeyman Electrician
If you're applying 212 volts then obviously something is wrong with your output of only 460 volts. Some photo's would help.
They can vary anyway. A YY works like 3 single phase transformers. No phase shift so each phase is independent of the others.
It’s a tap difference.
Sounds like it’s on the most extreme tap.
480/208 = 2.307
460 / 212 = 2.170
Comes out to -5%. It’s on the highest tap setting. If this is a dry transformer the taps might be missing. Put a jumper on the middle tap position.
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