Ungrounded, corner grounded delta systems

[jim dungar]

Is there something wrong with my logic ?

Yes, it only works where a single load is served by the three phase delta-wye transformer. What happens to the currents in the delta windings when you serve (3) balanced L-L loads instead, don't they need to be sized for 100% current?

 

[dnem]

That means that the delta connection, which puts higher voltage across a coil, will need more turns of wire.

Voltage, yes

That's the "down" side to a delta [but you can't really call it a down side in voltages under 1 or 2 thousand]. . The delta coils "see" the same voltage as phase to phase conductors, while wye coils "see" lower voltage than phase to phase conductors. . That voltage difference doesn't mean a whole lot in lower voltage transformers. . The wye coils "see" the same amperage as phase to phase conductors, while delta coils "see" lower amperage than phase to phase conductors. . That amperage difference makes a significant difference.

That means that the delta connection, which puts higher voltage across a coil, will need more turns of wire. For the same output power level, the delta connection has lower current flowing in each coil. So the 'Delta' connection will have more turns of thinner wire to get the same current density in the copper.

Yes, that's the same thing that I'm talking about.

The net result is that for the same output KVA rating, you have the same amount of copper as with the 'wye' connection.

Because KVA is voltage times amperage. . But you don't build based on voltage times amperage. . You choose your coil wire size based on amperage and coil insulation [and spacing] based on voltage. . Until you get into higher voltages, it doesn't impact the insulation or spacing that much. . But in all transformers, coil amperage significantly impacts wire size, cost, weight, physical dimensions.

 

[dnem]

Yes, it only works where a single load is served by the three phase delta-wye transformer. What happens to the currents in the delta windings when you serve (3) balanced L-L loads instead, don't they need to be sized for 100% current?

You may have point there. . I need to think about that one.

Also the point was made earlier that it wouldn't matter for 3phase loads, which I agreed with.
3 balanced single phase loads would mimic a single 3phase load, wouldn't it ?