Reverse feed a transformer, Am I gonna have issues?

[Mario Dealba]

I work for a plating company, I am an industrial engineer, I am not an electrician but I do understand the basics. The city provides us with 300 KVA and LV 208Y/120 three phase voltage. In our anodizing lines we will need 300+ Amps of 480V three phase for the DC rectifiers.
I have been looking for step up transformers to take what the city gives us to what we need, so 208 primary and 480 sec. I am on a budget here and it has been a total hustle to find a "true" step up transformer of that size (300KVA 208 pri and 480 sec) for a prize that fits my budget, now it has been very easy to find step down transformers that fit those requirements for a much lesser price. my question is, Am I gonna have a problem with just buying a step down transformer, reversing it and hooking it up to what I got? and if not, what kind of connections Ys or Deltas on which side should I be looking for??
Thank you for your input!
Mario

 

[augie47]

Here is what one manufacturer (Acme) says about rerverse hook-up:

ACME dry-type distribution transformers can be reverse
connected without a loss of kVA rating, but there are
certain limitations. Transformers rated 1 kVA and larger
single phase, 3 kVA and larger three phase can be reverse
connected without any adverse effects or loss in kVA
capacity. The reason for this limitation in kVA size is, the
turns ratio is the same as the voltage ratio. Example: A
transformer with a 480 volt input, 240 volt output? can
have the output connected to a 240 volt source and thereby
become the primary or input to the transformer, then the
original 480 volt primary winding will become the output
or 480 volt secondary. On transformers rated below 1 kVA
single phase, there is a turns ratio compensation on the
low voltage winding. This means the low voltage winding
has a greater voltage than the nameplate voltage indicates
at no load. For example, a small single phase transformer
having a nameplate voltage of 480 volts primary and 240
volts secondary, would actually have a no load voltage
of approximately 250 volts, and a full load voltage of 240
volts. If the 240 volt winding were connected to a 240 volt
source, then the output voltage would consequently be
approximately 460 volts at no load and approximately
442 volts at full load. As the kVA becomes smaller, the
compensation is greater? resulting in lower output voltages.
When one attempts to use these transformers in reverse, the
transformer will not be harmed; however, the output voltage
will be lower than is indicated by the nameplate.​

As far as connections are concerned, I feel any infor along those lines should be provided by the professional who completes the install. In that your forte' is not eletrical, the limited advice we give in that reagrd may prove to be harmful.

For that reason I am closing the thread.​