Confusion regarding three phase system

I'm confused regarding 3 phase systems.

In some texts I have seen three independent and separate sources. In some YouTube videos I have also seen the same, especially in software simulation, but in some other scenarios I have seen one source and three wires.

I am very confused. What actually happens in a 3 phase system?

Is there one source, out of which there are three wires, each having separate phase, or are there three separate and independent sources each having its own one wire?

• Either. If each source has only one wire (rather than two) there must be a common neutral, in what is called a Y connected system, as opposed to a Delta connection. (This neutral is simply the result of connecting the second wire from each source together).
– user16324
Commented Oct 28, 2021 at 13:53

3 Answers

Typically, one three-phase machine will have three wires, whether it's a generator, transformer or motor. Within that machine however, each phase will be handled by a separate winding.

In simulators, we tend to build three phase sources from three single phase sources, there's no reason not to.

It doesn't really matter as long as they have the same voltage, same frequency, and the correct phase relationship — but in practice they would usually be taken from three windings of a single generator, as that's the simplest way to get there.

In a three phase system, there are three phase (hot, live) wires, and there may be a common neutral. The three phases are at exactly the same frequency, but shifted so that they are all one third of a wave period apart. Or 120 degrees apart, if you are thinking about it as a sine wave.

In practice, this is very difficult to achieve with three separate generators. They would keep drifting out of phase with each other.

It's much simpler to use an alternator with three phase windings. Or if it's an inverter powered by solar panels or a wind turbine, then the three phases are all generated electronically within the same unit.