Maximum Transformer Input Voltage?

Question

My multi-tap 3ph transformer (12KVA) has an primary input rating of 90V~440V, my line voltage is actually 483V. Can I hook my 483V line to this 440V tap?

Answer 1

Yes you can hook it up to your 483 volts supply.

Don't exceed the max KVA rating of the transformer.  Remember this is 3 phase so don't forget the sqroot of 3 in the KVA equation.

KVA = E*I*sqroot(3)  

so your limiting factor is your current output from the transformer.  Its like a black box.  Max power input = Max Power output.  so Your Current equation would be:

I = KVA rating of transformer / (E * sqroot(3))

@ your supply voltage this will = your primary side Maximum current draw through the transformer.  Then run this formula for your secondary voltage and work it backwards to figure your max secondary current.

follow that formula and you can't go wrong.

Answer 2

Instead of guessing with voltages at that level, I suggest contacting either the manufacturer, or a licensed (USA, CDN: professional or UK: chartered) electrical engineer.

Edit:

There are legal liability issues involved here.  Given a make and model number for your transformer, anyone suggesting a method to use it outside its rated parameters could be legally responsible for any advice given or acted upon.  I doubt a qualified engineer would risk jeopardizing public safety or their license without fully investigating the issue - but, I can suggest you research the dielectric breakdown voltage of the insulation on  / between the windings.

Answer 3

You can be pretty confident that a power transformer will be designed to tolerate an operating voltage least 10% above the nominal voltage rating. At 483V you would be operating at that limit. Your utility probably doesn't guarantee that the voltage won't be 5% or even 10% high at the service entrance. Since 480V is a standard supply voltage, I am surprised that your transformer is marked 440. Is it an older transformer? Could it be a 400V, 50Hz transformer that has a 10% high tap? If it is a 50Hz transformer, it should be able to tolerate 20% higher voltage on 60Hz (20% higher frequency). I assume that your supply is 60Hz because I don’t think that 480V is used anywhere that 50Hz is used. The 90V tap is strange. Is that supposed to be 190V? I think that 190 is the lowest 3-phase voltage that is used anywhere. The transformer will probably be fine, but for a reliable installation, you should know the manufacturer’s voltage tolerance specifications for the transformer and the utility supply voltage variation policy.

Answer 4

You can apply the 483V to the Xfmr, however, the rating of 12KVA should not be over loaded. 12KVA / 483V = 24.8Amps. The rating is based on continuous duty due to affects of heating of the coil.  

Answer 5

yes it will be ok, 440 and 480 are the same... like 110 and 120 or 220 and 240, your output voltage will be higher and check it against what ever device you will be powering