Page 5 of 5

Re: How does our electrical grid work?

Unread postPosted: Wed 11 Jan 2017, 11:37:50
by efarmer
Way back in the beginning Mr. Edison who was very much in the battery business in a big way proposed that the electrical distribution would consist of DC generators and buildings full of batteries getting sprinkled all over creation and homes would be providedf with DC power. Light bulbs run on AC or DC as they simply turn some of the heat they generate into light, motors of the period were DC motors. Nikola Tesla after a stint at Edison's labs broke free and attached to George Westinghouse (inventor of air brakes to enable trains to stop quicker and therefore to operate at higher speeds), Tesla had an insight that AC could run motors via methods of motor coils responding to rotating magnetic fields, and once he had proven this in Westinghouse's labs, the ability to run motors on AC setup a great exploit, wherein alternators (alternators make AC, generators make DC) could be coupled to step up transformers and create very high voltages to overcome vast distances of wiring with much less loss of the power in the wiring from heat produced by the wire resistance loss and then be stepped down to household power levels by another transformer at the point of power consumption. The wires subject to long spans on towers had to be a combination of a good conductor like copper and a strong metal like steel to handle wind loads and ice loads. This system won and is the system we have in use. When current flows in a conductor it makes two fields around the conductor, an E field that is electrostatic and an H field that is magnetic. The H field is exploited to coil up wires to concentrate the magnetic field and put it to work in things like transformers and motors. The E field is large around high voltage wiring such as transmission lines and should one just get close to the wires without touching them while being at ground or some other differentially great potential, the E field can actually burn you by electrostatically delivering power, even if arcing or flashing to ionize air and use it as a conductor to conduct power does not take place. To make the system work on a distributed grid, all the power in AC form has to be synchronzed so that the system does not see contributing sources of power on the grid as spurious loads instead of collaborative contributors. In the contempory era, High Voltage DC transmission lines, Solar power arrays, and other DC sources can be on the electrical grid via the use of inverters, which chop DC power and create AC power, and then once again precisely synchronize it to the electrical grid power so it can be delivered in harmony with all other connected sources of power. The electrons do not squirt through a wire like water as KJ mentioned, rather they pass atom to atom like "hot gossip" with each conductor atom becoming excited and passing this on to the adjacent atoms and remaining an intact atom. The speeds involved are very high, essentially a majority of the speed of light but never at or above it.

Now for some fun, I was helping a relative replace an outlet, he is a very adept craftsman but not electrically inclined, I asked him to turn off the breaker associated with the branch circuit we were going to work on, and he hollered up from the basement that he had it off. I inserted a primitive neon bulb tester and the outlet was still on. He emerged from the basement and seeing my test light glowing asked me how much power it took to run, when I told him it was miniscule, (40 microamperes) he asked if the test light was just "bleeding off what was left in the wires". My joy with P.O. is that we have some illuminated people in petroleum geology and many other disciplines who will tutor the uninitated and then engage them in discourse and exploration. This partially offsets the loss of ignorant bliss when one realizes the scope and complexity of the challenges faced by our species by the methods we have used to successfully build out to where we are right now. For me it is a journey of once using the price at the pump to attempt to necromance the petroleum industry and state therof, which of course left me pursuing knowledge and real data. So here we are, dithering between "we are all screwed, hoard and hunker down" and how does all this stuff we are contemplating the possible loss of really work?
Thanks P.O. !

Re: How does our electrical grid work?

Unread postPosted: Wed 11 Jan 2017, 15:51:24
by KaiserJeep
You are welcome, and sparky and I need to re-focus on the big picture and less on minutia. But one final digression (I just love this stuff):

On top of the hill above my house, through the old Santa Teresa mercury mine, runs a high tension power line, one of the 3-phase (i.e. three hot wires plus one neutral) "medium voltage" (below 69 kV) lines used for transmission around residential areas. Within the last decade our power company PG&E has quadrupled the capacity of this line. They replaced the large single copperweld cables with four separate aluminum/composite core cables and a series of conductive spacers that kept the conductors separated by a few inches.

The towers themselves remain the original galvanised steel lattice structures. The original single copperweld cables were replaced with "quad bundle" carbon-core aluminum cables, which look like this on the tower:
...and the construction of each cable is like this:
...where a carbon fiber composite core, clad in woven composite sheathing, is surrounded by two layers of spiral-wrap aluminum conductors, wrapped in opposite directions. The aluminum has a clear "anodized" finish that is further weatherproofed and passivated by chemical "greases" injected between them as the cable is crimped round in roller dies.

The net/net is that the quad bundle of four new technology carbon fiber/aluminum cables carries four times the current and power of the old copperweld single cable, while weighing only slightly more, even when you add in the weight of the spacer/dampeners.

While I never worked in Power Engineering (which was part of my common core EE curriculum)(my trade was computer hardware design) and I studied the topic decades before the new technology cables existed, I learned the above facts from one of the PG&E crew foremen, who happened to share my love for PNG (Papua New Guinea) coffee, one afternoon at the local coffee shop.

Incidentally, the mechanical tension on the composite power cables is even higher than on the copperweld original, to control wind movements. The carbon fiber core carries all the weight of the soft aluminum conductors, and has almost no stretch in it compared to the original and much more elastic steel.

Re: How does our electrical grid work?

Unread postPosted: Wed 11 Jan 2017, 20:08:24
by efarmer
Very interesting KJ, I attempted a thumbnail on how the original grid emerged and works, and this is proof that the technology of the grid continues to get bumped forward with better materials science and technology. I have spent 42 years on analog and digital design projects and embedded systems,
and so "the grid" is a marvel to ponder while I instrument or code something that fits on a bench top.

Re: How does our electrical grid work?

Unread postPosted: Wed 11 Jan 2017, 21:09:19
by KaiserJeep
I'll mention that the original reason that the PG&E crews were on the hill is that they were being paid to add fiber optic cable bundles to the neutral/ground conductor on top of the tower, to add web bandwidth to this part of Silly Valley. PG&E took advantage of this presence to add capacity to the high tension feeder - one of three redundant power feeds to the extreme South Valley area.

My web bandwidth noticeably improved after the project was complete, and our few power outages declined in frequency and duration - typically less than 10 seconds. It still amazes me that the fiber optic cable on top of the power line is hanging off a ground conductor that in turn shields the three hot wires from lightning. Yet the fiber optic signals are unaffected when a lightning bolt strikes a tower or cable two inches away from these signals.

Re: How does our electrical grid work?

Unread postPosted: Wed 11 Jan 2017, 23:30:21
by sparky
Aluminium / Carbon fiber + digital highway , just love it !

Probably cheaper too , a very elegant solution.

Re: How does our electrical grid work?

Unread postPosted: Fri 13 Jan 2017, 13:13:40
by hvacman
The reason for going with the carbon fiber structural core and the conductive aluminum "jacket" is that high-voltage AC creates inductive currents that limit current density at the core of a conductor, called the "skin effect". Basically, the core of a thick high-voltage AC conductor is not usable as a current-carrier - most of the current is carried on the skin. So a composite cable with a structural core and a conductive skin is the optimal high voltage AC cable.

The skin effect is one reason that HVDC transmission is gaining popularity for long-distance power transmission- no skin effect. The whole cable cross-section can be an effective conductor.