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Power United States Science

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."
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The Last DC Power Grid Shut Down in NYC

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  • Re:Tesla won but... (Score:5, Informative)

    by Anonymous Coward on Friday November 16, 2007 @07:35PM (#21385277)
  • Re:Advantages? (Score:2, Informative)

    by ChrisMounce ( 1096567 ) on Friday November 16, 2007 @07:42PM (#21385331)
    The advantages of AC are mostly in transportation from the power station to the consumer. Internally, electronics use mostly DC, I think (correct me if I'm wrong here). Batteries store and release DC current, a computer's power supply converts to DC, etc.
  • Re:Advantages? (Score:5, Informative)

    by oo7tushar ( 311912 ) <> on Friday November 16, 2007 @07:42PM (#21385345) Homepage
    For short distances and for use within IC it's quite useful. The conversion from AC to DC at lower voltages for use within computers produces quite a bit of heat (hence the fan in your PSU, yes I realize that even DC from a higher voltage to DC at a lower voltage produces quite a bit of heat) and so you find that some data centers are moving to converting from AC to DC outside of the cases and transporting DC directly to the servers.

    There was an article on /. about this a while back and perhaps somebody who'd like to be modded up a bit can post the link.
  • by leighklotz ( 192300 ) on Friday November 16, 2007 @07:47PM (#21385381) Homepage
    When I lived in Cambridge, I sometimes visited friends in Boston who had 600VDC elevators using power from the city.
    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.

  • by IvyKing ( 732111 ) on Friday November 16, 2007 @07:48PM (#21385389)
    The reason the subways use DC was that at the time the subways were developed, DC motors were smaller, lighter, cheaper and more efficient than variable speed AC motors. AC series motors were developed for railway service (e.g. the New Haven electrification between NYC and New Haven), but those required lower frequency (typically 25 Hz in the US, one exception was the Visalia Electric at 15 Hz and 16 2/3Hz in Europe). Commercial frequency electrification didn't become practical until the 1950's with the development of ignitron and silicon rectifiers.

    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)

    by urcreepyneighbor ( 1171755 ) on Friday November 16, 2007 @07:51PM (#21385427)
    While the majority of people don't know who Tesla [] was or what he contributed [] to the modern world, it's safe to say that most of the people here on /. are - at least - aware of him.

    If I ever make it to Belgrade, I'm planning to check out the Nikola Tesla Museum []. :)
  • Re:ComEd not Con Ed (Score:3, Informative)

    by Volante3192 ( 953645 ) on Friday November 16, 2007 @07:53PM (#21385441)
    No, it's Con Ed for Consolidated Edison.

  • Re:Advantages? (Score:4, Informative)

    by TigerNut ( 718742 ) on Friday November 16, 2007 @07:56PM (#21385463) Homepage Journal
    As related here [] high-voltage DC transmission is more efficient than high voltage AC transmission for a number of reasons, and it has other benefits as well in allowing potentially unsynchronized AC systems to transfer power. The main problem is efficient voltage conversion, which requires more infrastructure than an AC system with equivalent power transfer capability.
  • Re:ComEd not Con Ed (Score:2, Informative)

    by PorkNutz ( 730601 ) on Friday November 16, 2007 @08:03PM (#21385513) Homepage
    Com Ed is Illinois, Con Ed is New York.

    I know an excellent surgeon who can remove that foot from your mouth.

  • by blind biker ( 1066130 ) on Friday November 16, 2007 @08:18PM (#21385647) Journal
    The loss is due to low voltage/high current --> high joule loss.

    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)

    by TobinFricke ( 1190177 ) on Friday November 16, 2007 @08:24PM (#21385701)
    DC is actually used extensively in modern power grids, the main advantage being that there is no need to synchronize the phase from different generating stations or subgrids. For example, the Pacific Intertie [] transmits three gigawatts of direct current between Los Angeles and eastern Washington state. (Power is sent from LA to Washington in the winter, covering the demand of electric heating in the pacific northwest; and from Washington to LA in the summer to power our air conditioners.)
  • Re:Advantages? (Score:5, Informative)

    by gangien ( 151940 ) on Friday November 16, 2007 @08:30PM (#21385757) Homepage
    for those who don't get it []
  • Re:DC vs AC (Score:2, Informative)

    by peragrin ( 659227 ) on Friday November 16, 2007 @08:37PM (#21385817)
    um the fact that we use AC for long distances means that it is in fact better to convert locally to DC, and transmit AC.

    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)

    by dgatwood ( 11270 ) on Friday November 16, 2007 @08:44PM (#21385861) Homepage Journal

    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 [].

    See Electric power transmission: History [] for more information.

  • Re:Tesla won but... (Score:3, Informative)

    by falconwolf ( 725481 ) <<falconsoaring_2000> <at> <>> on Friday November 16, 2007 @08:54PM (#21385921)

    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 []. Guess they need to learn physics as well, oh and stop faking having powered a light bulb wirelessly [].

  • Re:Tesla won but... (Score:3, Informative)

    by Nazlfrag ( 1035012 ) on Friday November 16, 2007 @08:57PM (#21385951) Journal
    You do realise that he repeatedly succeeded in wirelessly distributing power. We've been wirelessly distributing power for over a century thanks to his discoveries, from powering a crystal radio from the airwaves to RFID chips. Rather, I'd suggest he was too busy writing the physics books to make much money from them.
  • Misinformation (Score:5, Informative)

    by linuxwrangler ( 582055 ) on Friday November 16, 2007 @09:00PM (#21385981)
    It keeps being repeated, even in this article which says "it can be transmitted long distances far more economically than direct current", that AC is more efficient. This is not really true. The advantage (and pretty much the only advantage) that AC has over DC is that it is relatively simple to change voltages.

    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)

    by MorePower ( 581188 ) on Friday November 16, 2007 @09:06PM (#21386033)

    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)

    by momerath2003 ( 606823 ) * on Friday November 16, 2007 @09:07PM (#21386039) Journal
    Automated teller machine machine?
    Personal identification number number?
    Direct current current?

    See wiki [].
  • by TooMuchToDo ( 882796 ) on Friday November 16, 2007 @09:08PM (#21386049)
    Let's be honest though. The conglomerate known as General Electric is nothing like the company it was when Edison was around: []

    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)

    by Fnkmaster ( 89084 ) on Friday November 16, 2007 @09:19PM (#21386111)
    In Chicago it's ComEd, for Commonwealth Edison. In New York, it's Con Ed for Consolidated Edison. I think Massachusetts used to have a ComEd, though not sure if that was the same company as in Chicago, it stood for Commonwealth Edison (but these days it's called NSTAR in Mass).
  • by MoFoQ ( 584566 ) on Friday November 16, 2007 @09:22PM (#21386135)
    Especially in the form of High-voltage transmissions. (

    There are some advantages (source: []):

    • Undersea cables, where high capacitance causes additional AC losses. (e.g. 250 km Baltic Cable between Sweden and Germany[9]).
    • Endpoint-to-endpoint long-haul bulk power transmission without intermediate 'taps', for example, in remote areas.
    • Increasing the capacity of an existing power grid in situations where additional wires are difficult or expensive to install.
    • Allowing power transmission between unsynchronised AC distribution systems.
    • Reducing the profile of wiring and pylons for a given power transmission capacity.
    • Connecting remote generating plant to the distribution grid, for example Nelson River Bipole.
    • Stabilizing a predominantly AC power-grid, without increasing maximum prospective short circuit current.
    • Reducing line cost since HVDC transmission requires fewer conductors (i.e. 2 conductors; one is positive another is negative)
    Shoot, it's used in the US and UK (in the "Chunnel").

    Here's a list of notable places that use it: []
  • Re:DC vs AC (Score:5, Informative)

    by petermgreen ( 876956 ) < minus city> on Friday November 16, 2007 @10:05PM (#21386461) Homepage
    DC doesn't require high voltages, a DC line at a given voltage is slightly more efficiant than an AC line of the same voltage.

    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)

    by belmolis ( 702863 ) <billposer@a l u m . m> on Friday November 16, 2007 @10:18PM (#21386575) Homepage

    Democracy: people vote and the power and law are made directly (volatile) Republic: people vote and representatives implement the power and law (slow change over time, more stable)

    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)

    by goodie3shoes ( 573521 ) on Friday November 16, 2007 @10:23PM (#21386605)
    This story explains what the original FA obscures; that some old buildings had elevators and pumps designed to run on DC. Sue me if the link doesn't work. []
  • by Anonymous Coward on Friday November 16, 2007 @10:35PM (#21386685)
    Yeah, but it is a pain to make HVDC or step it down to lower levels for distribution. After all there is no such thing as a DC transformer (which of course wouldn't make sense). People build contraptions like motor-generators and big SCR controlled devices to convert HVDC to AC for distribution. They are not particularly efficient or cheap. Add in the fact that DC has the big grounding issue while 3 phase AC will work just fine with a single ground (and transformers can isolate grounds between sections). And note that most industrial electric motors are 3 phase AC motors. I don't think we are going to see a big future with HVDC distribution systems.
  • Re:DC vs AC (Score:2, Informative)

    by MorePower ( 581188 ) on Friday November 16, 2007 @10:38PM (#21386709)
    Well, like I sort-of said at in my other reply to you (but I'll repeat here in case anyone needs more clarification), there is no such thing as a "DC transformer". A transformer relies on changing (AC) current to do its transforming, it won't work at all with DC. The equivalent devices for DC are Buck (for stepping down) or Boost (for stepping up) converters, and they are much more complicated devices that need a transistor (or similar switch) to rapidly switch current on and off to an inductor to do their converting.
  • by The Cisco Kid ( 31490 ) on Friday November 16, 2007 @10:41PM (#21386727)
    Uhm, no, everything is *not* technically DC. Yes, anything that uses electronic controls or is electronics will have either an internal transformer/rectifier or an external wall-wart, but lots of things use AC directly. Motors in power tools, dishwashers, refrigerators, vacuum cleaners, and most power electric appliances (not to mention modern elevators) are AC motors. Incandescent *and* flourescent lighting is a direct AC user (but LED's use DC, of course). Fans (not the PC kind), blowers, electric lawnmowers, even electric heat, all use AC directly.
  • by residents_parking ( 1026556 ) on Saturday November 17, 2007 @06:13AM (#21388499)
    Yes, DC wins when using cables with high capacitance and also between power grids of different frequency. About 5 mins walk from my house is the anchor point for the UK France cross-channel HVDC link. The converter station is at Sellinge, about 10 miles away, and can ship up to 2GW in either direction. However, due to higher capacity on the French side (they have more nuclear), I understand the UK are net consumers of energy.

    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)

    by NoMaster ( 142776 ) on Saturday November 17, 2007 @07:17AM (#21388753) Homepage Journal

    BTW, there are DC transformers known as flyback converters. Look it up on wikipedia.
    Yes. They work by converting the DC to AC by switching, passing it through a transformer, then rectifying it back to DC. Look it up on Wikipedia.

    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)

    by moosesocks ( 264553 ) on Saturday November 17, 2007 @08:19AM (#21388987) Homepage
    This should give you a pretty good idea of the state of NYC's infrastructure.

    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 [] 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)

    by alvieboy ( 61292 ) on Saturday November 17, 2007 @12:39PM (#21390439) Homepage

    Transformers are highly efficient (>80%), but only work with AC. Power electronics work with DC, but are less efficient than transformers

    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)

    by Wonko the Sane ( 25252 ) * on Saturday November 17, 2007 @03:55PM (#21391781) Journal
    A switching power supply can efficiently reduce voltage, but raising voltage is another matter entirely.

    The only way you are going to convert one DC voltage to a higher DC voltage is:
    1. with a motor-generator
    2. charging and discharging a reactive component (which really means DC-AC-DC)
  • by mcpublic ( 694983 ) on Saturday November 17, 2007 @09:50PM (#21394219) Homepage
    The CNN article [] has a much more informative article than the New York Times article cited in the Slashdot article.

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