15kva DELTA to WYE tranformer loading

[wwilson]

I am in process of designing a machine that requires a 15kVA transformer to accommodate international voltages.
INPUT: DELTA 380/400/415/480 L1-L2-L3, Earth
OUTPUT: 208 L1-L2-L3-N (N bonded to Earth)
The balanced loads will be a 6kw heater (30% duty cycle) and a 1hp blower. The remaining loads are all single phase. I plan to balance the loads as best as possible across the 3 phases.
I can hook up a majority (but not all) of the loads L-L (208 across 2 phases) or L-N (120 single phase) since they are universal voltage switching power supplies. Does anyone see a problem with placing the loads L-L rather than L-N? Especially a problem with the transformer – circulating currents, neutral issues, etc.?
Thanks, wwilson

 

[peebee]

If your power supplies have standard 120-volt receptacles, I would STRONGLY recommend you wire them at 120 volts, or change the plug or plug & cord out for use at 208 volts. That's the only problem I'd foresee with going L-L.

Beyond that, L-L will probably help with load balancing, but will require 2-pole breakers rather than single-pole breakers be used for each load. L-L may permit you to use slightly smaller wire than with L-N.

I don't see where L-L vs. L-N would have any impact on either circulating currents or neutral issues given the loads you've described, as there's nothing there that sounds like a high-harmonic load.

 

[jbartos]

Suggestion to the original posting: L-L single phase loads will need twin-breakers for the circuit protection, which is somewhat more cumbersome than L-N single phase circuit loads protected by single pole circuit breakers. Also, some L-L loads are not permitted, e.g. fluorescent fixtures in some jurisdictions. The benefit of L-L circuits and loads is in smaller wire gage and potentially smaller physical sizes of the loads.