The Last DC Power Grid Shut Down in NYC 533
cell-block-9 writes "Today the last section of the old Edison DC power grid will be shut down in Manhattan. 'The last snip of Con Ed's direct current system will take place at 10 East 40th Street, near the Mid-Manhattan Library. That building, like the thousands of other direct current users that have been transitioned over the last several years, now has a converter installed on the premises that can take alternating electricity from the Con Ed power grid and adapt it on premises.' I guess Tesla finally won the argument."
Re:Tesla won but... (Score:5, Informative)
Re:Advantages? (Score:2, Informative)
Re:Advantages? (Score:5, Informative)
There was an article on
Is there 600VDC in Boston? (Score:4, Informative)
Later elevators still used 600VDC but used a dynamotor; that whine you used to hear when you pressed an elevator button elsewhere was the dynamotor starting, to convert to 600VDC from the 120VAC line current. Eventually, elevator manufacturers stopped using it, but when you hear that whine in a medium-old elevator, you know what is is.
The article was wrong about subways (Score:5, Informative)
AC's advantage of high voltage transmission doesn't apply to subways as 1200V seems to be the limit for third rail. 2400VDC was tried in 1915 on the Michigan Railways (an electric interurban in central Michigan) with abysmal results - the voltage was changed to 1200V within a year of the initial installation.
Re:Tesla won but... (Score:2, Informative)
If I ever make it to Belgrade, I'm planning to check out the Nikola Tesla Museum [tesla-museum.org].
Re:ComEd not Con Ed (Score:3, Informative)
Idiot.
Re:Advantages? (Score:4, Informative)
Re:ComEd not Con Ed (Score:2, Informative)
I know an excellent surgeon who can remove that foot from your mouth.
Re:DC, actually, nowadays makes a lot of sense. (Score:3, Informative)
So what you need to achieve is high voltage. But in the past, that wasn't possible with DC, because there was no _efficient_ way to transform the voltage/current aspect of the power line for DC, only for AC.
DC still in use (Score:3, Informative)
Re:Advantages? (Score:5, Informative)
Re:DC vs AC (Score:2, Informative)
About the only time it isn't is in totally self contained systems such as ships, cars, and planes.
Re:DC vs AC (Score:5, Informative)
Do you have transmission lines that are three blocks in diameter? Then it's more efficient to convert at the source. What? You don't? Then I guess converting at the point of use is more efficient. Transporting the 5V and 12V levels that most consumer electronics use internally would be insane over more than a few feet because of voltage drop [wikipedia.org].
See Electric power transmission: History [wikipedia.org] for more information.
Re:Tesla won but... (Score:3, Informative)
Tesla died broke because he spent all his money trying to create a "wireless power distribution" that made no sense. If he had spent more time reading physics and less time building 100+ foot Tesla coils. Were some of his inventions stolen? Undoubtedly. But I think he has only himself to blame for losing all his money.
Except that now MIT has developed wireless power transmission [arstechnica.com]. Guess they need to learn physics as well, oh and stop faking having powered a light bulb wirelessly [mit.edu].
FalconRe:Tesla won but... (Score:3, Informative)
Misinformation (Score:5, Informative)
Over the short-haul, this is good since losses are primarily resistive and losses are related to the amount of current flowing in the conductors. Power in my neighborhood is delivered at 12,000V and down-converted to 120/240 by transformers located every few houses. Delivering power at 120V would require 100 times the current and massively larger conductors. Once it gets to my house, with the exception of some motors and some lights, everything from TV to stereo to computer ends up having to take that power and reconvert it to DC.
But AC has far higher losses through capacitance and inductance which become severe over long distances. This is why some current and other planned long-haul transmission routes use DC. A good example of this is the 800-kilovolt DC line that connects into the Sylmar Terminal Station near Los Angeles.
Apparently, the use of Extra High Voltage DC is being proposed for a number of new long-haul transmission systems and it is the high losses incurred by AC over long distances that is driving the use of DC.
Re:DC vs AC (Score:5, Informative)
It would be more efficient to transmit DC, if we are talking about the same voltages. AC is impeded by inductance as well as resistance, so in addition to the inefficiencies of converting, you also are better off transmitting DC if it is the same voltage.
The trick is, transmitting at higher voltages is more efficient than transmitting the same power at lower voltage. This is because to send the same power at low voltage, you must send more current, and more current means more energy wasted as heat from the resistance of the line. So voltages from the generator are stepped way up before being transmitted.
And the reason AC won out is that it is much, much cheaper and easier to step up AC voltage (you just need a transformer, which is nothing but a couple coils of wire around an iron core) than to step up DC voltages (which requires a boost converter, which at its heart is a giant transistor [big enough to survive the voltages and currents of a power plant in this case] and a huge inductor [big fat coil of wire] along with timing and firing circuits to control the action of the transistor).
Boost converters are expensive, but over a long enough run of transmission line the advantages of DC over AC do make up the difference (as I recall, the break-even point is about a 400 mile long line). So you do find some long distance transmission lines that are DC. I know there is one out here in Sylmar, California that runs up to Washington state somewhere.
Re:Advantages? (Score:5, Informative)
Personal identification number number?
Direct current current?
See wiki [wikipedia.org].
Re:Yep, Tesla won alright (Score:5, Informative)
http://en.wikipedia.org/wiki/General_Electric [wikipedia.org]
GE's divisions include GE Commercial Finance, GE Industrial, GE Infrastructure (including GE-Aviation and Smiths Aerospace), GE Consumer Finance, GE Healthcare, and NBC Universal, an entertainment company.
Re:ComEd not Con Ed (Score:4, Informative)
DC transmissions still exists as HVDC (Score:4, Informative)
There are some advantages (source: http://en.wikipedia.org/wiki/HVDC#Advantages_of_HVDC_over_AC_transmission [wikipedia.org]):
Here's a list of notable places that use it:
http://en.wikipedia.org/wiki/List_of_HVDC_projects [wikipedia.org]
Re:DC vs AC (Score:5, Informative)
DC has two main problems
1: it is a pain to voltage convert. Voltage conversion is pretty vital to our modern use of electricity, you don't want 11KV in your home but you don't want to be transmitting 240/415 three phase or worse 120/240 split phase any significant distance. You also want much lower voltages for loads of equipment.
For equipment power supplies it isn't so bad, they generally don't have particularlly high efficiancies anyway, they tend to run at fairly low power and they tend to be in a nice indoor environment but building a DC equivilent of a pole pig with similar efficiancy and reliability would get pretty expensive.
2: DC is a pain to switch, switches and breakers would have to be either much bigger or much more complex for a given DC voltage than for the same AC voltage (the zero crossings of AC tend to break arcs).
Re:uh (Score:3, Informative)
Too bad these aren't the real definitions. Look it up. Your definition of "democracy" is actually the definition of "direct democracy", while your definitino of "republic" is actually the definition of "indirect democracy" or "representative democracy". A republic can be a direct democracy, a representative democracy, or neither.
The Backstory (Score:4, Informative)
Re:DC vs AC - not true today (Score:2, Informative)
Re:DC vs AC (Score:2, Informative)
Re:I know everything technically is DC.. (Score:4, Informative)
Re:DC vs AC - not true today (Score:3, Informative)
Although the UK and France both operate at a nominal 50Hz, it is normal for actual grid frequency to vary slightly throughout the day. The way this was explained to me was fairly intuitive: when you load the grid, you load the generators and in turn they load the turbines, which slow down ever so slightly. Because turbines have very large inertia, their response time to step loads is rather long. In order to pump power into the grid, a generator has to have a phase lead to overcome its self inductance. A shift in the phase means a shift in the power being pumped.
France is 1 hour ahead of the UK and have different norms regarding hours of work, cooking etc, all of which mean they have a different load profile. Combining the UK and French grids would only be possible if the link were much greater than 2GW thus able to cope with the difference in power swing. The link was never intended to serve that purpose. Perhaps, like Concord[e] and the Chunnel, it was more a punctuation of the ongoing Entente Cordiale than a technical necessity.
Re:DC vs AC (Score:3, Informative)
So they're not DC transformers, they're DC-DC converters
(Why yes, as a matter of fact I do know a lot about AC to AC, AC to DC, DC to AC, and DC to DC power conversion - at least, up to the 10's of kilowatts level...)
Re:Progress. (Score:3, Informative)
It's been pushed to its absolute limits in terms of age and longevity. The subways have served us well, but it's only been in the last few years that we've stopped neglecting them, and replacing outdated/dangerous systems with more efficient modern counterparts. (There was also the issue that the only people who knew how to service some of the archaic equipment that the MTA was running had been dead for at least 20 years)
The pumps used to clear stormwater from the subways today are the same exact ones used to pump out the Panama canal when it was under construction. (Literally --- NYC purchased them as surplus after construction of the canal was complete)
The electrical grid has issues. Remember the Queens blackouts 2 years ago? Con Ed would replace the feeder cables the failed, turn the power back on, and a dozen more cables would fail down the line. I don't even think that they ever determined why the blackout was as bad as it was apart from "aging infrastructure"
Earlier this year, the bowels of hell opened up when an 80 year old high-pressure steam pipe exploded [wikipedia.org] under 42nd street.
I'm a big proponent of "If it ain't broke, don't fix it," but it's pretty clear that NYC's infrastructure is in dire need of attention.
Re:DC vs AC (Score:2, Informative)
Don't forget that most AC-DC converters (like 110V->9V) are in fact DC-DC converters. The AC power is rectified immediately and then a switched DC converter is used, which can achieve efficiencies of more than 98%, using very small transformers, coils and capacitors.
I don't see AC transformers for a long time now. Only SMPS.
Re:DC vs AC (Score:3, Informative)
The only way you are going to convert one DC voltage to a higher DC voltage is:
CNN article more detailed than NYTimes (Score:2, Informative)