Transformer Configuration

[paulow]

Within a AC to DC / DC to AC inverer there is a delta - star 3 phase transformer which steps up 110Vac to approx 450Vac when working in the direction of DC to AC.
The inverter powers mainly induction motors, lighting circuits and other machinery.
The DC end is supported by a 250Vdc battery.
Why has a delta - star configuration been chosen and what are the advantages?

 

[Claude Abraham]

The delta-wye is great for stepping voltages up. A delta has phase current of only 57.7% of the line current, but phase voltage is equal to line voltage. The 57.7% is just 1/sqrt3.

A wye has phase voltage of 57.7% of line voltage, with phase current equal to line current. Thus a wye requires less insulation at higher voltages, and a delta requires less copper at higher currents.

The low voltage side of any transformer carries the higher current. Thus delta is great for low V high I, and vice versa for wye. However, there is no reason why it couldn't work the other way around. The transformer would be slightly larger or the regulation would be slightly reduced, but it would work just fine.

For stepping up, delta primary w/ a wye secondary is optimum regarding regulation vs. size/weight. Again, other configurations like Y-D, D-D, etc. can also work.