The mysterious three phase power ...

Foundations of Amateur Radio

There are times when you realise that you've always nodded your head when a particular topic came up and after doing that for long enough, you think you know what's going on.

Turns out that, no, you didn't, but that the topic itself was interesting enough to learn from. In my case, Three Phase Power. I came upon this topic over the past month while I struggled with power interruptions, blinking lights, weirdness throughout my house. Turns out that it's been happening for a lot longer than I've lived here.

After spending some time with the local power company, which I was told was filled with people who didn't care, turns out that they do, but they're busy people. After some back and forth, some logging, some finger pointing and head-scratching, the solution to my woes was to move me from the White Phase to the Blue Phase.

I nodded and smiled and everything was well with the world.

I know that there are three phases, Red, White and Blue. If you have overhead power in your street you'll likely notice four wires strung from pole to pole. One for each phase and one for neutral.

Apparently there's a standard for which is neutral and the order, but there are too many exceptions for me to spell that all out here, so I'll move on.

So, what's with these three phases?

If you spin a magnet between two coils you have a generator. As the magnet spins, the magnetic field increases through each coil, then peaks, then reduces, and as the next magnetic pole comes along, the magnetic field reverses, increases, peaks, reduces, etc.

If that sounds familiar, it's because I've just described a sine-wave. Every revolution of the magnet is a cycle and if you cycle, say 50 times, you get 50 cycles per second, or 50 Hz. For some countries it's not 50 Hz, but 60. Same thing, just faster.

That single set of opposing coils and magnet is a single phase. If you add another set of coils, 120 degrees further along, you get the same phenomenon, completely independently from the first set of coils.

That's the second phase. Rinse and repeat for the third phase.

To get that power to the rest of the suburb, you need to run a single wire for each phase and a common neutral wire, giving you the four wires that you see on a power pole.

Theoretically you could run with more phases, but you need to run more copper into the street, so power companies stopped at three.

You can think of these as three completely independent circuits, but they all share the same neutral, so there are some subtle interactions, like if the neutral becomes disconnected, bad news happens, especially in a place like Western Australia where ground conductivity is very poor.

In a normal home you'll get fed by one of those phases, in my case I changed over from the white phase to the blue phase. This means that each phase has a different set of users in the street. Roughly a third are using each phase.

Looking at the actual voltage and current that comes through at high enough resolution and you'll begin to recognise it as an RF spectrum with harmonics, variations, interference and other artefacts that make power show up as a varying feast, rather than the rock-solid expectation of 240V, 50 Hz you see on the sticker.

Three Phase Power, now you can nod along like I did and know how it actually works.

I'm Onno VK6FLAB.