I'm in awe of double Es. My understanding of AC ends at right about this neighborhood:
Posted on 11/20/2011 9:56:06 PM PST by neverdem
Thomas Edison and his direct current, or DC, technology lost the so-called War of the Currents to alternating current, or AC, in the 1890s after it became clear that AC was far more efficient at transmitting electricity over long distances.
Today, AC is still the standard for the electricity that comes out of our wall sockets. But DC is staging a roaring comeback in pockets of the electrical grid.
Alstom, ABB, Siemens and other conglomerates are erecting high-voltage DC grids to carry gigawatts of electricity from wind farms in remote places like western China and the North Sea to faraway cities. Companies like SAP and Facebook that operate huge data centers are using more DC to reduce waste heat. Panasonic is even talking about building eco-friendly homes that use direct current.
In a DC grid, electrons flow from a battery or power station to a home or appliance, and then continue to flow in a complete circuit back to the original source. In AC, electrons flow back and forth between generators and appliances in a precisely synchronized manner — imagine a set of interlocking canals where water continually surges back and forth but the water level at any given point stays constant.
Direct current was the electrical transmission technology when Edison started rolling out electric wires in the 19th century. Alternating current, which operated at higher voltages, was later championed by the Edison rivals Nikola Tesla and George Westinghouse.
The AC forces won when Tesla and Westinghouse figured out how to fine-tune AC transmission so that it required far fewer power plants and copper cable.
DC didn’t die, however.
AT&T adopted direct current for the phone system because of its inherent stability, which is part of the reason that landline phones often survive storms better than the electric grid...
(Excerpt) Read more at nytimes.com ...
That is a very strange statement.
DC's "inherent stability?" Why didn't the author simply say that they decided to run the central office phone equipment on DC because they could use batteries that way, thus obtaining the "inherent stability?"
And how did they charge the batteries? Why, with commercial power from the grid, of course. And which type of commercial power was best suited for charging battery banks? What do you know--AC, when transformed and rectified.
And even the “best for solar” is a canard. They have to step up the output of solar panels with what? AC technology (inverters). The choice of the type of output from the inverters can be either AC or DC; the fact that the panel output was originally DC is irrelevant.
It was really a plot to make it difficult for students to gain admittance to grad school, preying on their susceptance to fads, while impeding their progress, taxing their capacitance to learn, and overcoming their resistance to doing so.
Thanks neverdem. Photovoltaic arrays 100 miles on a side (four of those) can supply our needs (during the day), but produce DC. Weird coincidence.
I guess there's no way to get around AC.
≤}B^(
"imagine" that?
Only a EE geek would find that funny...
Another virtue of DC.
≤}B^)
≤}B^)
The bigger problem is that some liberal arts liberal is going to Google “acres of hamsters” and somehow use this forum as justification for promoting the idea as a replacement for Solyndra. ;-) They will get it backwards, and then try to use non-performance as justification for doing it.
I'm in awe of double Es. My understanding of AC ends at right about this neighborhood:
Looks line a Wheatstone bridge used in phone circuits to power ringers and allow both ac and dc in the same circuit. The diodes keep the ac from returning back through the dc circuit?
BTTT
Telco CO gear does run on 48DC but not for th
e reasons in this story
Standard power cable insulations are rated for 600V per the national electric code.
You can get lower voltage levels for thin cables used in instrumentation system or communication or low-voltage systems.
But your standard household wiring is rated for 600V AC or DC.
E/IR isn’t just a good idea. It’s the Law!
That’s essentially my point.
The author is confused.
Can you phase invert a hamster?
In Edison's day, there was not a realistic way to step-up and step-down the DC voltage as economically as transformers.
In Modern times, however, we do use some DC transmission lines where large amounts of power are transmitted long distances with few (if any) intermediate taps.
Typically these are on the scale of 500VDC. We have transmission lines like this in the US and have done so purely as an economic transmission system and not related to solar or wind power.
HV Direct Current Transmission System
http://www.energy.siemens.com/hq/en/power-transmission/hvdc/
The DC line cost more at the terminals where power is stepped up or stepped down using power electronics. But the Transmission line cost less money and has less line losses. If you go a long enough distance with only power taps at the beginning or end, DC will cost less over a long distance (hundreds of miles).
The towers are easy to identify as they don't have three phases.
For example, the Pacific DC Intertie is a 500kV DC line bringing power from the Northwest hydro-generation to Los Angeles.
This line was first energized back in 1970 and was later increased from 400 to 500 kV. It is now rated for 3,100 MW of transmission.
Pacific HVDC Intertie
http://www.abb.com/industries/ap/db0003db004333/95f257d2f5497e66c125774b0028f167.aspx
I’ve heard it called a bridge rectifier. I think it converts AC to DC like in your car’s alternator. Hopefully someone will confirm/deny. ;)
Disclaimer: Opinions posted on Free Republic are those of the individual posters and do not necessarily represent the opinion of Free Republic or its management. All materials posted herein are protected by copyright law and the exemption for fair use of copyrighted works.