I want to use a step down Xfmr to power a tool with a 60KVA rating (160A @ 220V). What should my Xfmr be?

Question

The Machine is a Doosan Machining Center CNC. The required voltage is 60KVA (160@220V). How do I rate my step down transformer with a primary supply voltage of 480 Volts?

Answer 1

For a 3-phase load, the KVA for 160A at 220V is 160 X 220 X 1.732 = 61KVA. The transformer would be rated for nominal 480V primary and 240V secondary. The KVA for 160A at 240V is 67KVA. I would use a transformer that is rated at least 67KVA. A lot of the machining center load probably consists of electronic adjustable speed motor drives. The drive input current likely has significant harmonic content. You should probably use a "drive isolation" transformer or a "K-rated" transformer in order to be sure that the transformer can tolerate the harmonic current. If you don't use a transformer that is rated for harmonics, oversizing to 75 or 100KVA might be a good idea. The machining center manufactorer or supplier might have advice also.

Answer 2

You can use 3-single phase transformers rated 480/240 volts 25KVA

each but, to be connected in bank for a total of 75KVA. Standard distribution transformers are rated only 25 KVa, but, specially assembled units may be available at 20 kva each unit.