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 the
3 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 or
345kV phase to ground?