Questions:

What is the maximum full-load primary current that you could safely design for a three phase 500 kVA transformer bank to provide if it has a high-voltage winding of 25GndY/14.4 kV?

What does the notation 25GNDY/14.4kV really mean?

Is it 25kV three phase and 14.4kV single phase?

Relevant equation i found during research:

Full load current = VA / 1.73*Primary Voltage

Attempt at solution:

Full load current = 500kVA / (1.73*25kV) = 11.56A *Assuming 25kV for primary voltage
Full load current = 500kVA / (1.73*14.4kV) = 20.07A *Assuming 14.4kV for primary voltage

 

The notation looks weird but it's probably a Y transformer rated at 25kV phase to phase and 14.4kV phase to neutral. 14.4 = 25/sqrt(3). It looks like it was written the other way around where 25kV was phase to ground but that wouldn't make sense.

http://www.allaboutcircuits.com/tex...t/chpt-10/three-phase-y-delta-configurations/

I think you would want to assume a balanced load, so if the transformer is rated for 500kVA then each phase will carry 1/3 of the power.