Buck Transformer

I found this 208v-120/240V buck transformer and was wondering if it will suit my needs. I have about 244 volts on my RPC incoming. I would like to get that down below 220. The calculation I did was:

If I wanted to go from 250-220 at 100AMPS I get 5190VA That is roughly 5KVA right?

My line fluctuates from 242-250 depending on the temp, and I would much rather be a bit lower then 220 rather than higher. Will this suit my needs. Can I tap my 2 phases to the 120-240 side and then tap the other side as output, and have somewhere in the right ball park with enough KVA to suit? Hope I am making sense. Thanks.
_Greg

Hi Greg,

A "buck" transformer and a "step-down" transformer are two very different animals, and of very different sizes for the same load ratings.

A buck transformer has a line-voltage primary and a low-voltage secondary. The secondary is connected in series between the supply and the load. The voltage at the load will be greater than or less than the supply, depending on how the secondary is connected.

The secondary voltage (usually 24 volts) determines the difference between the supply and the load. The power rating of the transformer is the load current times this secondary voltage. For a 100-amp load, this would be 24 * 100 = 2400 VA or about 2.5 KVA.

A step-down transformer has a line-voltage primary and a full-voltage secondary, i.e. it supplies all of the power to the load. This configuration requires a much larger transformer than the buck (or boost) transformer. For a 240-volt 100-amp load, the transformer would be rated 240 * 100 = 24,000 VA or 24 KVA, which is 10 times the rating of the buck transformer for the same load.

- Leigh