Tuesday, January 26, 2016

Tesla-Edison Redux -- Wind Power In North Dakota -- January 26, 2016


Later, 4:42 p.m. Central Time: at great peril of opening a can of worms I will post this from a reader who has a long background in electricity transmission:
"High voltage transmission" -- 500 KV AC --  isn't unusual for cross country ( high voltage/low current).
Heat, waste energy, is best understood as I^2 x R (I is current, R is resistance) [actually in AC "R" is reactance and impedance but don't let that confuse you].
When this high voltage arrives at the edge of a city "sub-station" the voltage is easily and efficiently typically "transformed"100 KV for "distribution" throughout the city. Shortly before entering households, the voltage is dropped again by going through a transformer to "an even safer" 240 volts.
This 240 volts of AC powers your furnace/air conditioner/clothes dryer.
By connecting the "outlets" between "one leg" of the 240 volts and "ground" an "even safer" 120 volts is available for your other appliances.
All these utilities/devices run on "60 cycle"AC.
A few devices like your computer run on DC so the 120 volts is "transformed" to 12 volts and then routed thru a "rectifier" to produce DC power.
60 cycle AC means that the current changes direction 60 times/second. This constant changing of direction is why AC power has "more resistance" (reactance/impedance) to current flow than DC.
For that reason huge blocks of power are moved more efficiently, for example from the power plant at Center, ND, when the power is "converted" from the AC from the generator to DC via a "converter."
This DC power is applied to the Square Butte high voltage DC line to Duluth, MN. It would not be economically practical to "invert" this DC back to AC at several locations along the way, because with current technology it "ain't easy." But converting it only once is "okay."
This is where the research comes in: NDSU is trying to find a more efficient way to convert AC to DC at the source and then invert it back to AC at the consumer end.
It's a great idea, but lots of luck: solid state electronics vastly improved this AC/DC/AC transition process about 30 (?) years ago. The world could well use another technological breakthrough (but not for worthless wind turbines which have no redeeming value in this era of excess, inexpensive cheap energy, and need back-up power anyway). 
I think I understand it better. Thank you. The above was edited slightly; if there are errors in the note above it is due to my editing / misunderstanding of the original note.

Original Post
This gets us back to the Tesla - Edison story. I'm afraid to even go here because
  • it's way beyond my comfort zone; I do not understand electricity
  • the Tesla-Edison "story" seems to shift with whomever is reporting
  • no matter what I say, folks will write me to correct me
... but ignorance hasn't stopped me before. From the linked article:
War of Currents! Edison’s least favorite of Tesla’s “impractical” ideas was the concept of using alternating current (AC) technology to bring electricity to the people. Edison insisted that his own direct current (DC) system was superior, in that it maintained a lower voltage from power station to consumer, and was, therefore, safer.
But AC technology, which allows the flow of energy to periodically change direction, is more practical for transmitting massive quantities of energy, as is required by a large city, or hub of industry, say.
At the time, DC technology only allowed for a power grid with a one-mile radius from the power source. The conflict between the two methods and their masters came to be known as the War of Currents, forever immortalized by the band AC/DC.

The Bet. Tesla insisted that he could increase the efficiency of Edison’s prototypical dynamos, and eventually wore down Edison enough to let him try. Edison, Tesla later claimed, even promised him $50,000 if he succeeded. Tesla worked around the clock for several months and made a great deal of progress. See link for rest of story if interested.

The rift. Tesla eventually raised enough money to found the Tesla Electric Light Company, where he developed several successful patents including AC generators, wires, transformers, lights, and a 100 horsepower AC motor. Tesla ended up selling most of his patents to George Westinghouse, who had himself been feuding with Edison for years. Their partnership, one can imagine, made the eventual popularizing of AC that much more bitter for Edison.

“Post-war” history. In the end, AC won out. Mostly. Westinghouse fulfilled Tesla’s dream of building a power plant at Niagara Falls to power New York City, and built upon its principles the same system of local power grids we use today. Edison’s original point about the practicality of DC is well-taken, however: The average person can’t have alternating currents flooding massive amounts of energy into their household appliances, so most plug-in devices must internally convert AC back to DC (that’s what’s going on inside the brick of your laptop cord).
That conversion wastes a lot of energy (think of all the heat coming from the brick of your laptop cord). Major studies are beginning to examine ways in which AC and DC power can work together with modern energy-harnessing technology, to run our overall grid more efficiently.
So, with all that as background, The Dickinson Press is reporting that North Dakota State University is conducting research to see if wind power could be made more reliable and efficient.

And now I'm confused. Didn't the linked article above say that AC was the best way to transmit electricity over long distances.
But AC technology, which allows the flow of energy to periodically change direction, is more practical for transmitting massive quantities of energy, as is required by a large city, or hub of industry, say.
But now, at The Dickinson Press article:
“One of the key aspects of this study is to research the possibility of using DC (direct current) grids,” said Nilanjan Ray Chaudhuri, assistant professor with the North Dakota State University electrical and computer engineering department who will run the research project. “With that, we’ll be able to increase wind energy penetration.”
The United States is lagging when it comes to direct current power transmission technology, missing on the benefits DC provides — benefits that could one day transform how the nation gets its power, according to Ray Chaudhuri.
And more:
Most U.S. wind energy potential is in the Midwest, where less power is in demand, said Ray Chaudhuri, adding that requires longer transmission lines to get the power to more highly populated areas. In the case of long distance, he said DC transmission technology is more economical. Switching transmission will require more infrastructure to be built but, in the end, it will be more reliable and efficient than alternating current.
A DC system also can help overcome the problem of fluctuating power that plagues wind today, allowing the power to be moved longer distances when the wind is blowing one place but not another, Ray Chaudhuri said.
 Maybe it's all consistent, but I'm not seeing it.

Wiki suggests AC is more efficient transmitting electricity long distances.
Quora says DC is a better fit for long distance transmission.

Unlike global warming, it appears the science behind AC vs DC for long-distance transmission of electricity is not settled.

TeslA (AC) and EDdison (DC).

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