Unusual Secondary Voltage off of a Transformer

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jonny1982

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I have a 112.5 KVA 277/480 primary, 120/240 secondary. I have 277/480 going in (double checked, all legs are the same around 277) but for the secondary, I have 120 on black, 212 on red, and 120 on blue (hot to ground). All line to line read around 240 though. Has anybody ever ran into this? I don't know why I have 212 on red. Taps are all set the same to 480 volts. Also, I know some transfomers hum pretty loud, but it seems to be humming a little louder than normal. Any feedback would be appreciated.

Thanks.
 

Jljohnson

Senior Member
Location
Colorado
212 Volts is not to far out of the ordinary for the B phase of a 120/240 volt delta wound secondary, mathematically it should be 208 volts ( 120 x 1.732). As far as the loud humming goes, have you tried loosening the rubber mounting straps slightly? a lot of manufacturer's tighten them down pretty snug for shipping purposes. If that doesn't quiet it down any, try putting rubber/cork isolation pads under the mounts on the feet of the transformer.
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
I agree 3?, 4W Delta because you couldn't have 120/240 with a WYE secondary. What does the nameplate say?
 

Cow

Senior Member
Location
Eastern Oregon
Occupation
Electrician
I have a 112.5 KVA 277/480 primary, 120/240 secondary. I have 277/480 going in (double checked, all legs are the same around 277) but for the secondary, I have 120 on black, 212 on red, and 120 on blue (hot to ground). All line to line read around 240 though. Has anybody ever ran into this?

If you want 120V to neutral on all three phases you would need a 480V x 208Y/120V transformer. Which would give you 208V line to line.
 
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