What is the purpose of using three-phase than using a single phase electric system?
Answer:
- you can use only two windings on a transformer instead of all three (if it's a delta)
- Requires less copper (or aluminum) to carry the same amount of current. If the phases are balanced, the current in the return line will be small (if not zero) for a Y, so the return wire can be small and carries the return for all three legs. Delta has no return line.
- 3 phase motors are cheaper to buy, require less maintenance and are more efficient to run.
- less time between peaks means smoother AC to DC conversion (less ripple).
- you can tap a single phase from a 3 phase, but you can't change a single phase into a 3 phase.
I like 3-phase because you can run single-phase just by using any two of the 3 leads. So with 3-phase you have more flexibility. You can't run something that's 3-phase from a single-phase source.
Also, less current per line for a given voltage/wattage.
One more thing. If you draw single phase and 3-phase next to each other you'll see that there's less of a droop in between waves. Someone else can explain it better.
We use three phase because turbines generate electricity more efficiently that way, and motors use electricity more efficiently that way.
Also, in a ballanced three phase system (say, a power plant connected to a city), you need a line for each phase but you don't need a neutral or return line. As long as the system is balanced, no current would flow in a return line even if there was one - the three phases add to zero.
No links, sorry.
3 phase motors have the potential of generating more torque due to phase overlap there is less time interval in terms of angular rotation between effective flux regions and thus production of torque is more constant
3 Phase is a rotating voltage therefore is ideal for driving rotating machines (motors) which make up the biggest demand in an industrial facility. Single phase requires some other means of creating the rotational field for starting (capacitors etc).
Currents are also kept lower for the same power.
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