Transformer

[Karl H]

Does anyone know off-hand what the +/- percentage of the secondary
voltage is, when you tap up or tap down the primary on a transformer?

480 primary/ 208 secondary

 

[brian john]

Standard on small dry type is 2.5%.

 

[jim dungar]

Transformers up to about 30kVA often have 5% taps. Above this the taps are usually 2-1/2% each. The quantities of taps are often +2 and -2 taps although +2 and -4 are not uncommon.

 

[Karl H]

Thank you both! I had just got a call about a voltage drop problem
on a MRI fed from a common panel and I was thinking about re tapping
the transformer. But, I could not remember if it was 2% or 20%
increase/decrease,before I go out to do field testing, and even consider this
an option. I'm suggesting a data log first. It's been a long day and here I go
again.

 

[Karl H]

False alarm.

Facilities managers are servicing a compressor and have a rental
compressor on site as stand-by. Guess what panel they chose to power it
from? Compressor starts and the MRI gets 185 volts to do it's job.
MRI's are corn fed,they need a full dinner to operate.

Thanks for the help guys!!