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Posted by Tomi Engdahl (195.197.151.211) on December 11, 2003 at 03:41:32:
In Reply to: Re: three phase generator to single phase posted by Dean Huster on December 10, 2003 at 23:42:40:
: Actually, Miguel, that's not 100% accurate. Most homes expect to see 120/240 volt bi-phase power
This assumptation applies to USA and other Norhern American countries. But this is not the situation in all countries around the world.
In USA homes get two-phase 120v. In a typical home in the states you have 3 cables coming into your panel from the service. Basically, there's a center-tapped step-down (few kV distribution voltage to 120V+120V AC) transformer on the electrical line pole, with the tap earthed (at least in theory) and each socket connected across one side of the transformer. Larger devices (electric stoves, central air conditioning units, electric dryers, etc.) are wired across the entire transformer, receiving 240v. How much current is fed to the house varies on the needs of the house.
In USA 3-phase power is not typically available in homes in the US. 3-phase power is it is common in commercial and industrial installations.
Within the European Community the mains voltage is currently 230V +10/-6% (50Hz) between the LIVE and the NEUTRAL terminals. The history for 50 Hz frequency is form Germany. At the beginning of 1900 in Germany, AEG had a virtual monopoly on electrical power systems. AEG decided to use 50 Hz and this standard spread to the rest of the continent.
The power to most houses in Europe (mainland Europe) are provided either as single phase power (230V AC, phase wire + neutral wire) or three phase power (230V AC from phase to neutral, 400V between phases, three phase wires + neutral wiring). Which one method is used depends somewhat on the country, site of load and sometimes from electrical company used. Usually larger sites and houses are powered with three phase power. Three phase power is sometimes supplied to high power appliances (large electrical motor, powerful heaters, ovens etc.) directly through permanent wiring or three phase power socket (nowadays most often CEE 17/ IEC 309 socket). Generally the neutral of the mains input power is bonded to the house main grounding point (connected to house plumbing and metal paets) at the main electrical panel or separate house grounding bar.
: and using only one phase of the generator will supply either the 120v or the 240v, but not both,
This is usually he case with generators.
: and you certainly can't use two of the phases to substitute, either, since they're 120° out of phase vs. 180° out of phase.
Would it be so out of question ?
US practice of power distribution is often to distribute at high voltage (several kilovolts) and provide small transformers to individual properties or small groups of properties.
Things are nowadays somewhat changing. Now, it is common in urban residential areas to have large transformers serve many residences. It would not be uncommon to see a one or two large transformers serve a city block in a residential area.
If we are talking about a three phase service (practically never seen in a home situation), the transformer is set up in a "y" configuration with 208 volts between any two secondaries and 110 between any one secondary and the centre tapped neutral. In some areas, you get 2 legs of a 120/208 wye instead of the usual 120/240 split phase service. A large three phase bank will serve perhaps a block of a small city with 120/208 three phase. Any single phase services get two legs of this. This is done because of the mix of small three phase commercial and single phase residential customers. You'll also see this in a fair number of apartmemnt complexes. The building has three phases coming in, and four wires will run up to the roof (the three phases plus neutral, plus a safety ground) to run heavy equipment such as air conditioning. Each apartment along the way will get three wires (two hot ones and a neutral. And a ground) tapped off of two hot wires. The problem here is that the hot-to-hot voltage is 208 rather than 240, and while most appliances can deal with either, some will complain.
: The easiest solution would be to feed the one phase to a transformer with a center-tapped secondary (240 volts, center-tapped).
This is one possibility if you have suitable transformer easily available.
: Still, you're going to have a generator with an unbalance.
This is true. Unbalanced load on generator might not work as well as if it were loaded in well balanced manner.
: You could use three transformers, one for each phase, each phase/transformer combination operating 1/3 of the house.
Sounds complicated and potentially risky.
For more information read Electrical Wiring Page at http://www.epanorama.net/links/wire_mains.html
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