
A Field Guide to Power Transmission Lines - szczys
https://hackaday.com/2019/06/11/a-field-guide-to-transmission-lines/
======
femto
> Thicker wires will heat up less for a given amount of current, increasing
> the carrying capacity of the circuit. One solution to increasing the
> effective thickness of a conductor is to “bundle” several conductors a few
> inches apart from one another, allowing for a larger increase in current for
> less cost than a conductor that is simply double the size.

In power engineering at university we were taught that the separation of the
wires within a conductor, to increase the effective diameter, is primarily
about reducing the self-inductance rather than dissipating heat. From memory,
it's along the lines that the separation effectively increases the diameter of
the conductor, which in turn reduces the intensity of the magnetic field,
reduces the self-inductance and allows more power transfer for a given voltage
and current.

The article got it right in saying spacing the wires gives an increase in
current for a given cross-section of conductor, but the main reason is reduced
inductance rather than the reduction in resistance due to it running cooler.
There will be some reduction in resistive losses due to cooler conductors, but
the main gain is the reduction in reactive power, which otherwise causes
current flow with no power transfer.

~~~
brandmeyer
(I'd edit my post, but its long since too late for that... mea culpa)

There's a couple of things being mixed up here. Stranded wire versus bar is a
mechanical issue. But what you were talking about is the separators you
sometimes see to run several separate cables alongside each other in the same
phase. In this case, there are a couple of things being overcome. For
starters, the skin depth of Al and Cu is only about 10mm at 50-60 Hz. However,
the form of the limit is not the reactive power loss, its the resistive power
loss of the conductor. Eventually, making it thicker just stops decreasing its
resistance at that frequency.

The article hinted at this in the discussion on cable construction, when the
author was describing wraps of aluminum conductor around a steel core. Now,
imagine an A/B comparison, where the A side is a very large diameter cylinder
of Al strands around a large steel core. The B side is three smaller such
cylinders separated by air, with the same total circumference of Al. The B
side is much lighter overall for the same current-carrying capacity. You might
like to hollow out the A side, except that you need to endure the compressive
stress of the outer sheath of Al conductors bearing down on the structural
core somehow. Enter the periodically spaced triangular separators that
actually are present on the B side.

------
stickfigure
I saw this linked from the comments, and agree with the commenter that if you
liked that, you'll love this:

"Why three prongs?"

[http://amasci.com/amateur/whygnd.html](http://amasci.com/amateur/whygnd.html)

~~~
Stratoscope
Thank you!

I read this wonderful article a few years ago and have been looking for it
ever since.

I recommend it highly to every engineer who builds software, hardware, or
whatever. A great story of what can go wrong ( _very_ wrong) and how even the
best attempts to fix it may not work and may in some cases make things worse.

It's superbly written and very educational. The "Age of Electrical Outlets
Having a Little Face and Different Sized Eyes," indeed. :-)

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CaliforniaKarl
Here in California, the State government has maps of all of the transmission
infrastructure, from the generating stations to the utility substations, and
the transmission lines in between.

[https://www.energy.ca.gov/maps/](https://www.energy.ca.gov/maps/)

~~~
agwa
See also [https://openinframap.org/](https://openinframap.org/) which pulls
from OpenStreetMap. (I'm one of the contributors to the mapping of the Bay
Area's electrical infrastructure.)

~~~
rhacker
Unrelated but DAAAAMN OpenStreetMap is blowing away Google Maps in terms of
performance here.

~~~
txcwpalpha
What you're seeing on that site isn't actually OpenStreetMap. It's data points
from OpenStreetMap that are overlayed on top of Mapbox [1], with the vector
tiles served up by Tegola.

1: [https://docs.mapbox.com/mapbox-gl-js/api/](https://docs.mapbox.com/mapbox-
gl-js/api/)

2: [https://tegola.io/](https://tegola.io/)

------
tanderson92
From the end of the piece:

>Moving into the future, it’s hard to say how much more modern the power grid
can get since the underlying principles are so simple: three phases per
circuit and structures large enough to keep them from sagging into something
that could cause a fault. There is a lot of talk of the smart grid, but the
solution to most of the issues with the power system is often simply to build
more circuits as the demand for electricity rises. It’s a difficult problem to
engineer ourselves out of, especially with the increasing age of the power
grid itself, and at some point is simply becomes a numbers game of how many
watts can be moved from place to place.

Technological progress could change the landscape quite a bit:
[https://en.wikipedia.org/wiki/Space-
based_solar_power](https://en.wikipedia.org/wiki/Space-based_solar_power)

~~~
mikepurvis
I wonder if this will be a tough sell to the generation that grew up playing
Sim City 2000, which had this kind of system going haywire as a disaster
scenario.

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kev009
There is a book from the mid 1960s (I think the last revision, a few older
ones) that is still basically current (hehe) by Westinghouse called
"Electrical Transmission and Distribution Reference Book"

If you liked this you will like it: [https://www.amazon.com/Electrical-
Transmission-Distribution-...](https://www.amazon.com/Electrical-Transmission-
Distribution-Reference-Book/dp/B000AOMQV2)

~~~
nkurz
Thanks for the recommendation. For a more modern take, the chapter on "The
Power Grid" in Brian Hayes' "Infrastructure" is tremendous as well:
[http://industrial-landscape.com](http://industrial-landscape.com)

------
barbecue_sauce
Related: [https://hackaday.com/2016/02/22/a-field-guide-to-the-
north-a...](https://hackaday.com/2016/02/22/a-field-guide-to-the-north-
american-utility-pole/)

~~~
pdx_flyer
And in the underground world things get a little more complicated with
submersible transformers, vaults, etc. but the general concepts are the same.

------
barryparr
What’s the meaning of “phase” as used in this article, as in a “three phases
per circuit”?

~~~
jbay808
AC power has a voltage that (in North America) oscillates high and low at a
rate of 60 cycles per second.

Three phase AC power sends power along three wires. The timing of the
oscillations on each wire is shifted by one-third of a cycle relative to the
other wires, so they all reach peak voltage at slightly different times. We
call this a "phase shift" between the voltages, or that the voltages are "out
of phase".

If these wires were connected to a 3-phase AC motor, the motor would spin
because the current is drawn in succession along one coil and then the next,
leading the rotor to follow. The motor coils are also called "phases".

Each wire is sometimes called a "phase" as shorthand.

~~~
vorpalhex
That is a best explanation of three phase I have ever read, and I have read a
lot of different explanations.

~~~
el_benhameen
Yeah, it had never quite clicked for me, but now it makes so much sense that I
kind of feel silly. Great explanation.

~~~
jbay808
Thank you both, I am really happy to hear that =)

------
scrumper
Well this was an educational read, thanks for sharing. I particularly enjoyed
finding out about surface transmission characteristics of alternating current
and ACSR bundles. More on HVDC would be good.

It was uncomfortable too: I feel about power lines the way some people feel
about snakes or heights. I find being near or under them extremely
disconcerting. I even have an infrequently recurring nightmare where I find
myself having to crawl near one of the thick cables. They make my skin crawl.

~~~
floatrock
> More on HVDC would be good.

Agreed. There's two things about HVDC worth mentioning:

It is High-Voltage because high voltage is efficient for transmission. On a
first-order approximation, resistive losses are proportional to _current,_ not
power. Since P=VA, the resistive losses decrease for a given power as more of
the power shifts from the A to the V.

Second, a neat property of DC transmission is it allows phase-decoupling
between grids. For you to get a clean 120V, 60Hz power line at your outlet,
all the transmission and distribution infrastructure needs to be tightly
balanced. When that 60Hz starts to deviate by like 0.01%, alarm bells start
going off at the utility. Now imagine keeping that AC stuff sync'd on a state-
wide transmission line. If you make the line DC instead, you can transmit
power willy-nilly across the length of the line and just make sure it syncs up
at the ends when you change it back to AC.

We haven't traditionally used DC because it has higher transmission losses
than AC until you get up to the ultra-high voltages (that's famously why
Edison's AC system won out to Tesla's DC in NYC back in the day). My
understanding is it's just been really hard to get up to the ultra-high
voltages needed to make it work. 12V DC transmission barely works at even
house-scale because of the resistive losses, but when you get up to 1MV like
they're building in China, it starts to get attractive, especially when
linking different sub-grids half a continent apart.

~~~
hansthehorse
I believe Edison was the DC backer while Tesla was behind AC.

~~~
floatrock
You're right, I had it backwards. Thanks!

------
twic
In France i saw some pylons which reminded me of sleeping owls:

[https://www.flickr.com/photos/128452384@N02/43626380385/](https://www.flickr.com/photos/128452384@N02/43626380385/)

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iscrewyou
The transmission towers might be easy to design for flat lands and plateaus
but not so much for hilly areas. I am a always fascinated by transmission
towers in the mountains, wether I’m driving on the highway and see them far
away or I’m hiking and run into one. I’m amazed by how they get such big
structures up and running in those areas.

Edit: I just think the author kind of rubbed them off is all.

------
jefurii
In 2015 the Center for Land Use Interpretation did a bus tour of high-voltage
infrastructure in Southern California. The write-up has some interesting
photos:

[http://www.clui.org/newsletter/winter-2015/high-voltage-
bus-...](http://www.clui.org/newsletter/winter-2015/high-voltage-bus-tour)

------
choeger
Reading this I wonder how the circuit is actually closed? Are there always
pairs of conductors on each line?

~~~
hoofhearted
When the power is generated, it is usually done so by a 3 phase generator that
is separated by 120 degrees of rotation. All 3 phases inside the generator are
bonded together on one end. The other end are the 3 current carrying
conductors leaving the generator. The bonding of the phases on each side of
the conductors is what creates the closed circuit.

[https://en.wikipedia.org/wiki/Three-
phase_electric_power](https://en.wikipedia.org/wiki/Three-
phase_electric_power)

------
DigitalTerminal
“the voltages can be as high as 500 kV” actually the highest voltage lines are
slightly north of 1MV

------
hoseja
I always assumed those triangle lines carried all three phases, one in each
wire.

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LiamPa
If only Mr Tesla got the investment and we wouldn’t have to see these things.

[https://teslaresearch.jimdo.com/wardenclyffe-
lab-1901-1906/c...](https://teslaresearch.jimdo.com/wardenclyffe-
lab-1901-1906/connection-to-earth/)

------
amelius
Title should say "Power Transmission Lines", because transmission lines are a
broader concept.

[https://en.wikipedia.org/wiki/Transmission_line](https://en.wikipedia.org/wiki/Transmission_line)

~~~
dsfyu404ed
>transmission lines are a broader concept.

Indeed...

[https://www.f150online.com/galleries/images/7538-10939-17442...](https://www.f150online.com/galleries/images/7538-10939-174420.gif)

