The difference between doing with a delta and a wye system is that in a wye system, the voltage on one wire will be low enough not to require a real insulator. This means that you save an insulator per pole.
Single-phase branches from a wye system also allow the use of a xfmr with only a single hi-pot bushing, which also helps to save costs.
Single-phase spur lines in countries like England rarely extend more than a very short distance to serve a couple of xfmrs. But in places such as the U.S., Canada, Australia, etc. where the population density is much lower and distances much greater, I understand that the savings add up considerably.
You might find this document interesting:
www.ieconsult.fr/etc155.pdf P.S. The site seems rather slow to respond at the moment. I guess with the heatwave sweeping across France (over 100 in places yesterday!) that the electrons can't be bothered to travel at their usual speed.
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[This message has been edited by pauluk (edited 08-06-2003).]
