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 ...
Are they taught the “electron theory” or the “conventional theory?”
Most people don’t know the difference between the two.
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
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.
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.
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.
Edison was.....an interesting man.
My guess is: both.
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
Thanks for your post. Very informative and well done, and, obviously, I didn’t know that.
In the 21st Century, we protect wild animals and murder unborn children to display our political enlightenment.
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.
Thanks for clearing that up. You’re correct of course.
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.
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.
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Get away from my pets, you sick bastard.
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?
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