3 Phase delta/wye transformer sizing

[ktm400sx]

Iam trying to size a transformer for an existing load.
From my motor load (full load for 3 phase motors from NEC) I get 1694 amps.
I also have 300 amps worth of lighting and heating.

Do I simply size the transformer by multiplying the amps by the voltage by 1.73 to get kva?

Thanks for any help

 

[hector pe]

Iam trying to size a transformer for an existing load.
From my motor load (full load for 3 phase motors from NEC) I get 1694 amps.
I also have 300 amps worth of lighting and heating.

Do I simply size the transformer by multiplying the amps by the voltage by 1.73 to get kva?

Thanks for any help

Reply:

You need to add kva for the motor , which is 1694 x voltage x 1.732 for 3 phase.
Then you take 300 amps, assuming is 1-phase multiply by voltage to obtain the other part of kvas. The total kvas will be the minimum size transformer needed. Bear in mind you need to provide for growth, as a 30% minimum I recommend.

Regards,

hector pe

 

[cleveland]

Well your calculation would give the minimum kva for a steady state load. You might want to consider inrush current for your largest motors and some spare for future growth. Since this is existing load there must be a transformer somewhere...... could you see how large that is? Transformers come in pretty set sizes too in the size you are looking at..............