10kVA 3-phase Y-Y 400/220V transformer; how much 1-phase loads can I connect per phase?

Question

for a 10kVA 3-phase transformer, how much power in kVA can be connected for each phase, can the transformer take 10 kVA 1-phase load per phase (L-N)? or it should be 3.33kVA per phase?

Answer 1

The 10 kVA rating is the total for all 3 phases.

A Y-Y connection may handle a substantial imbalance in the secondary loads, depending on the transformer you select.  You should try and balance the load at 3.33 kVA per phase, but an inbalance of up to about 20% is tolerable.  (Note: this is not the case with a Delta connected secondary).

A Y-secondary is usually used for lighting and 'wall' power.  Those loads are constantly being changed (lights on and off, appliances/computers plugged into wall outlets constantly changing, etc.)

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