No you can not use two transformers to feed the panel. Check with your supplier for a larger one. A 167.5 KVA is a standard transformer. There are much bigger ones available.
He probably has no choice now, but designing it from scratch the loads should have been distributed somewhat evenly on the three-phase system. Here are two options:
1) If the loads are all 120, or capable of operating on 208, use a 208/120
3-phase panel and a 208/120 Y secondary on the transformer.
2) If you need 240 volts, split the loads onto three individual 240/120 panels on separate 240 volt transformers, one on each phase. Or use option
1, and a small 240 volt transformer where needed.
There are probably other ways also. It depends on the nature and size of the loads.
My preference would be for #2 based on experience seeing A/C motors burn out when trying to run on 208 volts ... until they finally got a 208 volt motor (special order) in it (why it couldn't use a 3 phase motor I am not sure, but it may have been a wiring issue). Other 240 appliances, if present, might not work as well, such as electric stoves, kilns, etc, not functioning at the level intended (e.g. slower to heat up to temperature).
The catch is #2 is more expensive at the transformers. But the panels can be a lot cheaper because costs start to go up fast after the 200 or 225 amp level (if you have 600 amps of load, this could be the way to go). I've not worked out the pricing, but maybe I should do that and see (since I've downloaded both the Cutler-Hammer and Square-D catalogs).
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