What are “phases” in terms of electrical systems?

Question

I work with equipment that operates on three phase electrical circuits. I can’t get my head around the concept of “phases.”

In: 17

Answer 1

Generation occurs when a wire has relative motion with a magnetic field in such a way the the coils of wire cut the lines of magnetic flux. In other words, wave a coil past a magnet, or a magnet past a coil, and it will induce a voltage in that wire.

Hold that thought. For matters of ELI5, if you wave the magnet down past the coil, it will generate a voltage with a specific polarity. Wave it in the opposite direction, and the polarity will reverse.

Take a magnet and put it on a rotating wheel. Place a coil on opposite sides of the wheel…for imagery, imagine the magnet as the hand of a clock with a coil at 9:00 o’clock and its other half at 3:00 o’clock.

As the hand (magnet) rotates in a clockwise manner, its flux lines will cut the coil at 3:00. Let’s say that generates a positive pulse. As it continues to rotate, it will cut the lines on the opposite side of the coil at 6:00, but since it’s going in the opposite direction (relative to the flux lines), it will generate a negative pulse.

So the magnet is rotating inside the coil. As it approaches 3:00 o’clock, the voltage rises to a peak as it passes 3:00, then decays back to zero as it approaches 6:00 (since it is no longer cutting lines of flux).

As it approaches 9:00 o’clock, the voltage rises in the opposite direction (negative) and decays to zero after it passes and approaches 12:00.

You’ve just built a sinusoidal wave. The voltage builds from zero to a maximum positive peak, then decays back to zero and immediately starts building to a negative peak, before declining again. A single phase generator.

Nice, but inefficient. Let’s add magnets. Put one at 11:00 and 5:00, and one at 1:00 and 7:00.

Time out. Since the clock numbers don’t work, but for imagery, imagine the magnets are equally 120 degrees apart from each other. This is close enough for ELI5.

So now you’ve got coils at three positions. As the magnet passes each one, the voltage in each coil will rise and decay, but each will be 120 degrees behind the next one. Now you’re generating 3 phases, 120 degrees apart, that peak at the same magnitudes, but at different times.

Bear in mind that this can be picked apart technically, but for ELI5, it will give you the basic idea.