Thought experiment:

Three single phase pole mount transformers 4160/240 CT

High voltage is 4160 Wye, Low votage 120/240 CT delta.

High voltage and low voltage share common neutral/earth.

Car accident isolates neutral from rest of power distribution network. The three 4160 lines are still intact, the earth connection via building bonds still intact.

Q1) If transformers are equally loaded, no shift on high voltage side. Correct?

Q2) Assuming stable transformer loading, no shift on low voltage side too?

Q3) What happens when most of 3 phase loads dissapear, leaving a significant single phase load?

Thanks

LarryC

The line to neutral loads will balance, just like in a regular120/240. If one side is more heavily loaded, the magic smoke will be coming out of the other side. Motors on both sides are in danger.

Would the HV "neutral" shift with the unbalance and difference between this "neutral" and the rest of the power company "neutrals" in the area, result in current thru all available paths like the plumbing and the earth itself?

If you are talking about losing the neutral on the line side of the pole pigs, it would really depend on where you lived. Some places have a better "ground" than others. If this was metal water piping, all the way back to the pumping station, you might not even notice the neutral was gone. If you are in Florida with plastic piping and sand around the electrodes, you are still going to balance the loads and the neutral will track that ratio. This is where you could be saved by diversity. The more customers you have on the load side of the break, the better chance you have that the loads will balance. It is still going to be pretty unstable.