Which buck boost transformer (S)

Have a machine with a 220-230V requirement line voltage is 240, have seen it as high as 245. Machine has a rating of 20 KVA. Machine book Spec calls for 10% max or less and 15% low (max) voltage.

I'm looking at pg 3573 of the MSC current catalog, having trouble figuring what type and how many I need.

Per their equation my machine is 20 kva so that works out to a 2 KVA transformer, but they have the option of 12/24 and 16/32 secondaries. What should I use, and do I need multiple units for three phase?

This all running off of a 20 HP phase perfect.

Dave

Here's info right from Acme - http://www.electricalpowertransformer.com/acme-transformer-selection.html

You don't need a transformer.

If you add 10% of 230v to the specified voltage, you get a max input voltage of 253v. Your 245 isn't going to hurt anything. Even if you went with 10% of the low end of 220v, that's still +22v, which would be 252. You're well within the range of the tolerance for the machine, and a transformer is going to be a waste of $$$.

If you insist on a transformer, you'd need a 20kva.

That percentage is the percentage of difference in the line voltage that the machine will accept without hurting it, not a percentage to determine the size of the buck boost transformer. Your machine draws 20kva, so you'd NEED a transformer that can supply 20kva. Now what might be a problem is as you load a transformer, the voltage output drops. You might want to get a slightly bigger (maybe 25KVA) transformer than you need to avoid excessive voltage drop. I'd say you don't need a transformer at all, especially if the voltage is normally 240v. If you insist on getting one, you don't want to cause yourself problems. Some people are kinda anal about this kind of stuff, but the machine SHOULD be able to handle 245v if they specify a max of 10% deviation from line voltage. If it can't the engineer did a PISS POOR job of designing the electrical stuff.

Buck/boost transformers do NOT supply the entire load current to the machine.

The are autotransformers and as such only have to be rated for the increment/decrement
of voltage times the current draw. Manufacturers of the transformers explain this
in the selection criteria.

It does sound as though he would be inside the specs without using buck boost
transformers.

Jim