3-phase to 1-phase

Most recent answer: 03/04/2011

Q:
can we convert 3-phase system of AC circuits into single phase system?
- Anumehana (age 17)
Warangal, Andhrapradesh,India
A:

Sure, it's done all the time. I'm not sure what the system is in India, but here I think it works this way. (Thanks to an alert reader for catching an error in my first version.) All three phases are carried by wires from the power plant. Only two of the phases are connected to the primary of any particular transformer used to make the power for some houses. In some systems just one phase is used, with the other connection going to neutral. (See The secondary of that transformer then usually is wired with a center tap at neutral and two opposite phases at the two ends. You can either get a high voltage between the ends or half of it between neutral and one end.

Mike W.


(published on 03/04/2011)

Follow-Up #1: how three-phase wiring connects to houses

Q:
The answer provided is not accurate to my knowledge. Three phases are transmitted from the generator at high voltage to minimize loss (not sure about the exact number though). The high voltage is stepped down a number of times down to 240V. Then, only one the phases is transmitted to a neighborhood. The single-phase 240V reaches a local transformer (which you can see on the pole near you). This transformer is a center taped transformer which generates two 120V which are 180 degrees out of phase. Both phases go into the house and both are used separately for 120V applications. In the few cases (stove, oven, ..) where 240V is required, both phases are used together. Since one is the invert of the other (180 degrees out of phase), it is easy to create a 240V out of them.
- Anonymous
A:

Thanks for this important correction. I've removed my earlier incorrect surmise.

You're right that the key piece of evidence is that high-voltage home outlets are around 115V*2=230 V, not 115V*Sqrt(3)=200V.

Here's a nice link with diagrams:

Mike W.


(published on 10/29/2013)