# Determining Transformer KVA?



## AmazingTrans (Jan 13, 2010)

Good Morning,

I have a question about calculating a 380V to 460V step-up transformer *kVA*. How do I determine a kVA of a transformer if i have the load size for certain equipments? For eg: (Values are from distribution panels Circuit Breakers)

Main Drive - 460Volts, 400Amps, Three phase
Control Transformer - 460Volts, 50Amps, Single phase
Aux - 120Volts +/-15%, 15Amps, single phase

From my point of view, the calculation will be:-
kVA = V x I x √3 ÷ 1000 (Three Phase)
kVA = V x I ÷ 1000
Therefore:-

Main Drive takes 318.68kVA (460*400*1.732 / 1000)
Control Xfrm takes 23 kVA (460 * 50 / 1000)
Aux takes 1.8kVA (120 * 15 / 1000)

Total : - 343.48kVA
Is this how I calculate a total kVA in reality ?

Hope someone can help me. Thank You.


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## kbsparky (Sep 20, 2007)

Looks good to me. While "efficiency" is not mentioned here, stepping up to the next size unit should cover you.


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## AmazingTrans (Jan 13, 2010)

kbsparky,

Thank you for your confirmation. When you say efficiency, do you mean +/- Voltage %?

Thanks again.


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