WTB 600V<->240V 7-10 KVA 3-ph transformer or autotransformer

I have a Canadian Aciera F5 mill with two 550-V motors, one 3-hp for the spindle and one 1-hp for the feed. I have an RPC with 245-V well-balanced output (two legs 120-V to ground and a wild leg). I need a 240 <-> 600 transformer or autotransformer with adjustable taps. I have a brand new 208 <-> 600 10 kVA autotransformer that came with the mill, but its output is 717 V on 245-V input. Yikes. It has no adjustment taps.

Anyone have a transformer or autotransformer that fits the bill kicking around? They seem to be not so rare in Canada, but I am in California USA.

with your high input voltage, I wonder if a very common 220/480 transformer (with taps) would work ?

IIRC the high end has some up near 500 volts, and if the low end had a lower than 240 volt winding,
it just might work.

Good idea. It looks like a 208Y <-> 480 might work, as it would give me 565V on 245-V input. If the high side is delta with no neutral, how do I keep the corners from running to wild voltages?

Feeding 245V to a 208V winding is not such a good idea, surely the transformer will be running saturated. Taps on the HV side will do nothing for adjusting the overvoltage input on the 208 side.

If it were me, I would buck the 245V down to 200V and use the transformer supplied with the mill. Then everything would run within it's rating.

A 245 to 550 unit will be a special wound unit, not likely available in the used market.

SAF Ω

SAF

I guess I need some education on transformer saturation. Being a mechanical guy, I would have thought it was current, not voltage that generated the magnetic field and could cause saturation. In my simple mind, if the power throughput stays the same but the voltage goes up, the current should go down.

Regards,

RKlopp

RKlopp,

If voltage didn't matter, there would be no need for the plethora of transformer models available. Most units are designed to handle +/-10% variation from the nameplate.

Magnetic saturation of the iron core is a pretty complex subject, and normally left to transformer engineers. Running at undervotage is usually not detrimental but overvoltage is. Effects are overheating, a clipped voltage output, poor regulation and harmonics on the output. Resulting in poor life and improper output.

Over Fluxing in Transformer | Electrical4u

Practical Considerations - Transformers : Transformers - Electronics Textbook

I can think of 2 ways to buck your existing 245 to 200 and use your existing autotransformer but would lack tap adjustments.

Another alternative would be to use 2) 600/120x240 1Φ transformers wired in a open delta bank to go from 240V to 600V 3Φ. In the size range your considering, some units come with taps on the high side for adjusting the output 600,570,540V. Bank sizes available are 8.6,12.9,17.3 KVA

If that interests you send a PM with a mail address and I can send you some documentation on it.

SAF Ω