Distribution transformer primary connections

[Retiring Soon]

What are the ramifications of connecting distribution (overhead, single phase)transformers, phase to phase on a Grd Wye feeder? Hypothetically, there would be multiple single phase connections. A to B, B to C, C to A, on different poles with varying sizes. I was always taught to connect all transformers, phase to neutral on Gnd Wye feeder, not phase to phase.
Without getting too technical, what can go wrong? Also, secondaries will be a standard 120/240 for the most part. In this case, the voltage is would be 12,470 GndY/7200. So, the transformer primary coils will need to be rated for 12,470. Thanks for any input.​

 

[davidbeach]

You'll use a more expensive transformer, and there are various faults that will result in only one of the fuses blowing so that the high-side winding remains at line voltage to ground.

I’ll see your silver lining and raise you two black clouds. - Protection Operations

 

[Retiring Soon]

Thanks for the quick reply David.

So, fairly straight forward. Obviously, the energized coil is a serious operational issue.

Now, if a close delta bank was installed, there would be the same energized coil issue, but could there be other issues with ferroresonance, harmonics, or transients?

Thanks.

 

[jghrist]

A 7200/12470Y transformer is rated for 7200 V connection. If you connect it between phases of a 12.47 kV line, the voltage will be too high. The transformer will oversaturate and the secondary voltage will be high by a factor of sqrt(3). You need a transformer rated 12470 to connect it between phases.