Free Republic
Browse · Search
News/Activism
Topics · Post Article

Skip to comments.

From Edison’s Trunk, Direct Current Gets Another Look
NY Times ^ | November 17, 2011 | MICHAEL KANELLOS

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 ...


TOPICS: Business/Economy; Culture/Society; News/Current Events; Technical
KEYWORDS: cronycapitalism; directcurrent; electricity; hvdc; physics
Navigation: use the links below to view more comments.
first previous 1-2021-4041-6061-8081-91 next last
To: Sequoyah101

Are they taught the “electron theory” or the “conventional theory?”

Most people don’t know the difference between the two.


61 posted on 11/21/2011 7:02:22 AM PST by DH (Once the tainted finger of government touches anything the rot begins)
[ Post Reply | Private Reply | To 7 | View Replies]

To: Ramcat; SnuffaBolshevik

Wheatstone bridge is used with resistance to measure voltage.

What was pictured is a simple rectifier.

http://www.magnet.fsu.edu/education/tutorials/java/wheatstonebridge/index.html


62 posted on 11/21/2011 7:07:15 AM PST by thackney (life is fragile, handle with prayer)
[ Post Reply | Private Reply | To 51 | View Replies]

To: Antonello

Negatory. Telco runs on hook at -48VDC on ring nominally but upwards of -52VDC is allowable due to voltaic loss across distance. You see the real reason for DC in phone systems is because the nature of analog communications works better with DC than AC. When you go off hook a switch detects the short from the phone completing the circuit and the voltage drops to about -9 to -15VDC off hook.

The ohms resistance across the loop has to be within certain thresholds for the switch to detect the short. I can’t recall the specs on a modern 5ESS switch but that’s why the further out you go the lower the gauge. So if you’re 15 miles from the main office you can expect 19ga copper.

The twisting on the pair is to reduce Induction between the pairs and AC systems. If you run voltage over a copper wire it’ll induce across any line running parallel.

Also with DC telecom you need to balance the pair and have the same capacitive length on each side to reduce noise.

Telephone work is easy though. But doing it well is the hard part.


63 posted on 11/21/2011 7:08:00 AM PST by Bogey78O (Don't call them jihadis. Call them irhabis. Tick them off, don't entertain their delusion.)
[ Post Reply | Private Reply | To 12 | View Replies]

To: SnuffaBolshevik

No, AC has not ended there.

The original AC current is changed from 60HZ AC to 120PPS DC power through the rectifier, through the load, and back from the load as 120pps DC, through the rectifier again and back to 60HA AC, then back to the generator.

There is an unmovable law of electronics: 100% of the current generated from an electrical source always returns to that power source.


64 posted on 11/21/2011 7:13:56 AM PST by DH (Once the tainted finger of government touches anything the rot begins)
[ Post Reply | Private Reply | To 50 | View Replies]

To: Antonello

I was also a radar (fire control systems) tech for F-100s in the Air force.

I had a chance to watch a base photographer’s entire flash bulb satchel instantaneously light up when I transmitted when he walked in front of the jet. It was priceless.

The radar would also light steel wool on fire too.


65 posted on 11/21/2011 7:21:28 AM PST by DH (Once the tainted finger of government touches anything the rot begins)
[ Post Reply | Private Reply | To 21 | View Replies]

To: packrat35

Edison was.....an interesting man.


66 posted on 11/21/2011 7:35:07 AM PST by FourPeas ("Maladjusted and wigging out is no way to go through life, son." -hg)
[ Post Reply | Private Reply | To 13 | View Replies]

To: D-fendr

My guess is: both.


67 posted on 11/21/2011 7:43:56 AM PST by Mr. Lucky
[ Post Reply | Private Reply | To 35 | View Replies]

To: Mr. Lucky

Can you imagine a company today killing a bunch of animals publicly with the competitor’s product to sway public opinion against the competitor?

http://www.wired.com/science/discoveries/news/2008/01/dayintech_0104


68 posted on 11/21/2011 8:03:08 AM PST by thackney (life is fragile, handle with prayer)
[ Post Reply | Private Reply | To 67 | View Replies]

To: thackney

Thanks for your post. Very informative and well done, and, obviously, I didn’t know that.


69 posted on 11/21/2011 8:14:10 AM PST by D-fendr (Deus non alligatur sacramentis sed nos alligamur.)
[ Post Reply | Private Reply | To 59 | View Replies]

To: thackney
The 20th Century was so barbaric.

In the 21st Century, we protect wild animals and murder unborn children to display our political enlightenment.

70 posted on 11/21/2011 8:16:53 AM PST by Mr. Lucky
[ Post Reply | Private Reply | To 68 | View Replies]

To: D-fendr
I was on a construction site for a Natural Gas pipeline compressor station years ago next that line on the map.

I was disappointed when none of the electrical guys could spot what was “different” about the tower supporting the electrical transmission line.

Eventually I told them to count the phases. They still had a hard time believing me it was DC.

71 posted on 11/21/2011 8:17:41 AM PST by thackney (life is fragile, handle with prayer)
[ Post Reply | Private Reply | To 69 | View Replies]

To: thackney

Thanks for clearing that up. You’re correct of course.


72 posted on 11/21/2011 8:22:48 AM PST by Ramcat (Thank You American Veterans)
[ Post Reply | Private Reply | To 62 | View Replies]

To: Erasmus
And now all that leftover space is getting repopulated by routers and server farms. ≤}B^)

I'm a grown Bell Brat LOL. My dad was a 45 year man with most of it spent in what they called 4-A the old mechanical switching long distance office. When they switched over in the 1980's to ESS he went back outside and worked on data circuits till retirement. I spent many an evening in the 4-A office when I was growing up.

73 posted on 11/21/2011 8:57:27 AM PST by cva66snipe (Two Choices left for U.S. One Nation Under GOD or One Nation Under Judgment? Which one say ye?)
[ Post Reply | Private Reply | To 48 | View Replies]

To: Fresh Wind
They use both AC and DC on the same phone lines for different functions. They use DC to register an off-hook condition and to power the carbon transmitters (microphones) and AC to operate the ringers. Later phones use the same DC to power the touch-tone electronic circuitry. It’s about simplicity, not stability.

AC is not on a phone line. Pulsating DC is what operates the ringers. On the older western electric phones a capacitor sat across the ringer {bell} in the phone. That was how people got busted back in the day for having an extension phone they were not paying for. The Test Board could read the induction of the capacitor. Cut that capacitor and they had no clue LOL. That doesn't matter now though. A Capacitor will pass PDC that is why they used PDC as PDC doesn't produce A/C HUM. The voltage was 96 PDC. You do not want A/C directly on phone cable.

74 posted on 11/21/2011 9:12:06 AM PST by cva66snipe (Two Choices left for U.S. One Nation Under GOD or One Nation Under Judgment? Which one say ye?)
[ Post Reply | Private Reply | To 39 | View Replies]

To: El Gato; Ernest_at_the_Beach; Robert A. Cook, PE; lepton; LadyDoc; jb6; tiamat; PGalt; Dianna; ...
Today's teens will die younger of heart disease Really?

Sorry, Strivers: Talent Matters

As probiotics use grows for gut health, VSL#3 has designations for specific GI issues

Particle Smasher Hints at Physics Breakthrough

FReepmail me if you want on or off my health and science ping list.

75 posted on 11/21/2011 9:27:25 AM PST by neverdem (Xin loi minh oi)
[ Post Reply | Private Reply | To 1 | View Replies]

To: Antonello
My dad was XO/CO on the Arlington during the time when the astronauts returned from the moon. His ship was a critical "ground station" for some of the activities. The RF on the old "flight deck" was more than enough to light up fluorescent tubes.
76 posted on 11/21/2011 9:57:03 AM PST by Myrddin
[ Post Reply | Private Reply | To 21 | View Replies]

To: Walmartian
E=IZ isn't just a good idea. It's the Law!

There, fixed it for ya'!

Hey, what can I say, I'm a fan of Tesla. :)

Cheers
77 posted on 11/21/2011 9:59:28 AM PST by DoctorBulldog (I'm a Cainiac! Get over it. -- If the dress aint got no stain, you MUST acquit Cain! 999!!!)
[ Post Reply | Private Reply | To 56 | View Replies]

To: 6SJ7
Can you phase invert a hamster?

Get away from my pets, you sick bastard.

78 posted on 11/21/2011 10:33:51 AM PST by ReignOfError
[ Post Reply | Private Reply | To 58 | View Replies]

To: NVDave; Erasmus

Easy for you to say! I resemble that remark being a poor old Civil and Petroleum and Mechanical Engineer, not necessarily in that order. There was no doubt I did not want to be an Electrical Engineer. What good is it if you can’t hit it with a big hammer?


79 posted on 11/21/2011 1:29:11 PM PST by Sequoyah101 (Half the people are below average.)
[ Post Reply | Private Reply | To 10 | View Replies]

To: SnuffaBolshevik
That looks suspiciously like a swastika, mein Herr.
80 posted on 11/21/2011 3:32:15 PM PST by Erasmus (I love "The Raven," but then what do I know? I'm just a poetaster.)
[ Post Reply | Private Reply | To 50 | View Replies]


Navigation: use the links below to view more comments.
first previous 1-2021-4041-6061-8081-91 next last

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.

Free Republic
Browse · Search
News/Activism
Topics · Post Article

FreeRepublic, LLC, PO BOX 9771, FRESNO, CA 93794
FreeRepublic.com is powered by software copyright 2000-2008 John Robinson