I was looking at a webpage that showed typical power transformer connections for different types of services. In addition to the usual 120V/240V single phase and 120V/208V three phase configurations, they showed a few odd ones One was 3 240V transformers in a delta configuration with the center tap of one of them grounded. The leg not connected to the grounded transformer was referred to as the 'wild' leg and apparently carries a voltage of 208V to ground. What sort of devices would one have that would cause one to request such a service from the electric company?3 phase motors with a requirement for 240V delta seem like they'd be kind of oddball, esp with 208V equipment being common. A motor connected in a Y would be even odder, it would get 138V (if my math is correct) and its neutral would be 70 volts above ground.
Also in the examples shown sometimes one of the3 transformers (not the one with the ground) was omitted.
Even weirder was a "Scott" arrangement, two transformers fed from 3 phases so to produce two phases at 90 degrees. What would want to be fed with _that_?
I've also wondered about a small industrial building. It has 3 individual heavy wires from the pole to the building, the pole has 3 "cans". I found this odd, there should be 4 wires. Looking closer the secondaries are in a delta configuration and none are grounded as far as I could see. The same building has a second feed which appears to be a standard Y setup, 3 hots and a neutral. So the first must be some special equipment.
Also what are the advantages of Y and delta configurations for power wiring? Y provides a natural neutral for one. For secondary wiring (the 11,000 volts or whatever that run down your street) it appears most of it is Y connected but older is delta. Why? From what I can see the very high voltage power lines are always delta. Why? Also, if a power line is described as carrying 345kV, is that phase to phase or345kV phase to ground?