Foundations of Amateur Radio #166:
August 11, 2018
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The mysterious three phase power ...
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
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
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.
To listen to the podcast, visit the website:
and scroll to the bottom for the latest
episode. You can also use your podcast tool
of choice and search for my callsign,
VK6FLAB, or you can read the book, look for
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visit my author page:
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If you'd like to join the weekly net for new
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