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.
The data center I work in has 415 VAC power coming in to each rack, with three phases and a neutral. Equipment gets a phase and a neutral, for 240 VAC (though not in a configuration you’d normally expect).
It’s important to remember that everything is contained in equipment made by companies that I trust (Rittal and Eaton and APC). Also, everything is grounded (the doors to the racks, the racks to the cable ladder, and the cable ladder to a special ground), which is in addition to the equipment ground. Finally, I know (and work with) the people who build and maintain the infrastructure.
As for the thick cable, if you’re up to it, here’s a video showing a process for joining the cables together: https://youtu.be/EvWx-VKVvmo
The thing to note, is the layers of copper ground that are wrapped around each conductor line, as well as the bundle itself.
Thanks. Had to do some reading to understand that, made more sense once I learned the phase-neutral voltage was the supply voltage / sqrt(3) not just divided by 3. Then I started reading about wye configurations and now it's time to stop.
There's a marvelous video somewhere on YouTube showing someone splicing a _live_ conductor while dangling from a helicopter. Can't find it now. Yours still gave me the willies though! Horrid big deadly snakey things. Ugh.
Power transmission in China has passed the 1 megavolt level. 12 gigawatts. China's best energy sources are in the northwest, and the biggest loads are in the southeast. Hence the demand for very long transmission lines.
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.
Volt for volt, doesn't AC have higher transmission losses than DC because of the skin effect? I was under the impression AC was what we chose for the grid because transformers make it cheap and easy to step up and step down voltage.
"Early DC power stations had a dynamo for every light bulb. Source unknown." No way. Edison's first Pearl St station, which is very well documented, did not work that way. Edison's Menlo Park NJ demo did not work that way. Some really early arc lamp plant, maybe.
There's a problem with paralleling DC generators. Edison hit that and solved it. Scaling problems, the early years.
I've worked in big piles of 3-phase power cables (though not quite as fat as in those other videos!). It's not bad. It's not any different than working with radiation, or at height, or around table saws, or crossing the street. You learn how it works, and how it can go wrong and hurt you. You practice good work habits, and learn to trust your equipment and training and coworkers. You recognize that it would take 2 or 3 things all going wrong at once for it to really fail, so you report any 1 issue right away.
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.