13-10-2012, 08:40 AM
(11-10-2012, 06:31 PM)Skywave Wrote: Thanks Lawrence - but the drawings there confuse me even more!
On p.6, there are 3 configuration drawings shown. One drawing shows 3-phase and no neutral feed to the load, the other two drawings show 3-phase and a neutral feed to the load. Can't have both!
The Wiki. drawing shows no N feed to the load: hence my previous remark.
With 3-phase, it's entirely possible to have no neutral.
Without the neutral, you have a Delta system. This is used for distribution - obviously it saves copper.
When you do have a neutral, this is a Star system. To convert between Star and Delta, you use special transformers: http://en.wikipedia.org/wiki/Delta-wye_transformer
These are typically what you find in sub-stations. Incoming 11kV is stepped sown to 415V 3-phase star with 230V between neutral and each phase, which is very convenient for distributing to a mix of houses and small businesses (that require just a single phase supply), and slightly larger premises that might need 3-phase.
This looks like quite a good article: http://www.epemag.net/electricity-generation6.html
Cheers,
Mark
