what are 3 phase circuits?

Answer 1

When power is transmitted as sine waves, it is possible to have single phase where one sine wave is going up and down. If power were generated this way, there would be a lot of vibration in the generator as the emf load went up and down, so generators are built with three sets of coils that produce 3 overlapping sine waves so the power is more even. Power companies deliver power this way to people who use a lot of power. It is important to keep the load balanced between the three lines and companies will be punished if they put unbalanced loads on the lines. For an image of the waves see the link below.

Answer 2

It is an AC circuit running three AC sources at the same frequency, but offset by 120 degrees from one another. The current in power lines is three phase; the three phases are split at the curb, with one phase going to each of three houses. Washer and dryer, which have large current requirements, run their own line out to the curb and get all three phases. So, in the United States and Canada, for example, the frequency is 60 Hz and the voltage 110 volts. You would find in the line three different sinusoids:

110 sqrt2 cos 2pi*60t
110 sqrt2 cos(2pi*60t - 120)
110 sqrt2 cos(2pi*60t - 240)

Answer 3

3- phase refers to industrial power systems where you have 3 active branches, each120 degrees out of phase with each other. Most motors used in these applications are star configuration, and heating elements are delta.

Answer 4

http://www.3phasepower.org/3phasewiring.htm
http://www.faqs.org/faqs/electrical-wiring/part2/section-10.html