The Last DC Power Grid Shut Down in NYC

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."

Tesla won but...

[Bryansix (761547)]

most people don't even know who Tesla was or that he pushed for the system that we now use to distribute electricity.

Re:Tesla won but...

[by Anonymous Coward]

http://en.wikipedia.org/wiki/War_of_Currents [wikipedia.org]

Re:Tesla won but...

[Scaba (183684)]

Good to see Wikipedia hold up under the mad scramble of 10,000 Slashdotters racing to be the first to update that entry to reflect today's event.

Re:Tesla won but...

[Kagura (843695)]

Haven't these bureaucratic fools actually seen what alternating current does to animals?!

Go Safe, Go Direct!

Re:Tesla won but...

[oo7tushar (311912)]

Just like most of us here on Slashdot don't know (without the assistance of a search engine) who won the 1982 Super Bowl. Different things matter to different people and most people have things to worry about rather than wondering who the proponents of power transport via AC were.

Most of us here on /. certainly know who Mr. Tesla is and what he pushed for and we should take pleasure in being in such distinct company...except for the trolls and turds.

Re:Tesla won but...

[Paul_Hindt (1129979)]

Even trolls need electricity.

Re:Tesla won but...

[Bastard of Subhumani (827601)]

You can have a 10,000 volt current and it won't kill you if there is no amperage.

That could only occur if you had infinite ohmitude.

Re:DC vs AC

[dgatwood (11270)]

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:DC vs AC

[MorePower (581188)]

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:DC vs AC - not true today

[rubycodez (864176)]

actually no, that means 80+ years ago that was true but now a high voltage dc transmission system is in fact more efficient, uses less condutors, eliminates need for sychnonization between different systems. HVDC also preferred for undersea long distance transmission because of less capacitive losses.

Re:DC vs AC - not true today

[petermgreen (876956)]

DC is still far more of a pain to convert than AC at least if you want high efficiancy and high reliability. While HVDC is certainly more efficiant for very long or undersea transmission lines it would be extremely difficult to build a power distribution grid based on it.

Re:Circular gets the square

[xSauronx (608805)]

Im going to remember to make that very point next time the misses balks at anal...

Re:Circular gets the square

[kennygraham (894697)]

Just hope she doesn't use the same reasoning when she reaches for the strap-on.

Re:DC vs AC

[petermgreen (876956)]

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:Tesla won but...

[MikeFM (12491)]

Or that he died broke and alone because people like Edison stole his ideas and robbed him blind. Tesla was a genius and could have done so much more for the world if only things weren't controlled by rich people with no vision further than how much money they can make, right away, off an idea. Tesla's failure is a perfect example of capitalism at work.

uh

[circletimessquare (444983)]

do you have a superior system than capitalism in mind?

people are fond of pointing out democracy's many failures too

but the real overriding realization with democracy and capitalism is that however much you think they suck, and they do suck in many ways, they are still better than any other system we can think of and have tried

so please, criticize capitalism. but unless you can enunciate a superior alternative, your criticism means absolutely nothing

Re:uh

[ResidntGeek (772730)]

No. Capitalism is the best system available, but that doesn't make it fair. It is up to the people within the system to try to make it fair. That includes pointing out the problems with it. His criticism isn't meaningless, it's important.

Re:uh

[Pharmboy (216950)]

Winston Churchill - The inherent vice of capitalism is the unequal sharing of blessings; the inherent virtue of socialism is the equal sharing of miseries.

Re:uh

[sweatyboatman (457800)]

do you have a superior system than capitalism in mind?

I'm sure Tesla wrote it down somewhere.

dude, calm down

[circletimessquare (444983)]

all you did is enunciate standard real world checks and balances on the ideas

no one expects pure capitalism or pure democracy to ever be able to exist

i'm taking umbrage with radical fundamental departures from the core concepts: communism instead of capitalism, for example, or theocracy versus democracy

not capitalism, tweaked, or democracy, tweaked

the core ideas are always tweaked in one way or another to fit in the real world

Re:Tesla won but...

[Tablizer (95088)]

Or that he died broke and alone because people like Edison stole his ideas ... Tesla's failure is a perfect example of capitalism at work.

Much of the good ideas that really propel technology are that way. Capitalism rewards manipulative wheeler-dealers far more than creativity. It rewards those who can best exploit creative ideas, not make them.
     

Re:Tesla won but...

[vought (160908)]

It's kinda funny that the Tesla Roadster runs off of DC batteries :)

Not when you consider that there are no such things as A/C storage batteries... :-)

Re:ComEd not Con Ed

[Fnkmaster (89084)]

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).

That's as maybe

[JamesRose (1062530)]

But Edison electrocuted an elephant, which quite frankly is just an awesome smear campaign.

A powerful, electrifying news story

[Phat_Tony (661117)]

Frankly, I'm shocked that there was still a DC power system in use in the US.

Re:A powerful, electrifying news story

[by Anonymous Coward]

Frankly, I'm shocked that there was still a DC power system in use in the US.

You're obviously not aware of current events.

Signed,

AC

(How apropos: my catchpa is betatron [wikipedia.org]

Re:MOD PARENT "FUNNY"!

[RedWizzard (192002)]

Some people disagree with the Slashdot system that "funny" mods don't contribute to karma. So some people choose a different positive mod to use when something's funny.

I tend to agree. If I find something worthy of using a mod point for any reason, then I think it should be reflected in that user's karma. Why discriminate against humor?

Because most of the "funny" posts aren't very funny at all (i.e. the quality of "funny" moderations is lower than the quality of other moderations)?

Because Slashdot is intended to generate informative and insightful discussion rather than humor?

Deliberately using the wrong category when moderating reduces the readers ability to filter the posts in the way that they want. Moderators are supposed to categorize posts. They are not supposed to care about the karma of the authors.

DC to AC converter inside?

[themushroom (197365)]

Okay, so if the building was running DC, what did the electronics and appliances inside plug into?

Is there 600VDC in Boston?

[leighklotz (192300)]

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.

Re:Is there 600VDC in Boston?

[Animats (122034)]

Later elevators still used 600VDC but used a dynamotor

What you're hearing is not a dynamotor, but something called a Ward Leonard drive. It's a fixed-speed motor driving a generator, but its purpose is speed control. The field current of the generator, which is small, is adjusted to control the larger output of the generator. The variable output of the generator then drives the elevator motor. The Ward Leonard drive is thus a big power amplifier. Until power semiconductors got big enough, which wasn't really until the 1980s, this was the most effective way to smoothly speed-control large motors.

A dynamotor has a common field for the input and output sides, but a Ward Leonard drive does not.

Incidentally, the Wikipedia article in Ward Leonard drives is bogus. Here's a better reference. [google.com]

The article was wrong about subways

[IvyKing (732111)]

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.

DC, actually, nowadays makes a lot of sense.

[blind biker (1066130)]

First of all, let me tell you that Tesla is one of my role models. He is one of the reasons I studied electrical engineering - with a passion. And AC, if you want, is the "winner" for all intents and purposes. The future really validated Tesla's AC system. There have been other folks that helped the adoption of the AC system, like Proteus, another role model for me.

Said all that however, high-voltage DC, a transport technology that starts to make sense nowadays, thanks to high-power solid-state switching elements, has many advantages over AC in terms of losses and cable utilization. You can transport more energy via DC than AC, across the same thickness cable. And you have practically no losses due to parasitic capacitances and inductances. The corona effect is much easier to control, too.

So, if I was forced at gunpoint to make a prediction for the electricity transportation in 150 years from now, I'd say hihg-voltage DC.

Progress.

[LoRdTAW (99712)]

Kinda sad to me but it was in the way of progress. Lots and lots of buildings still use the old DC elevators here in New York City. Just yesterday I loaded in to Bayard's in downtown Manhattan into a 4x4 foot elevator that I swear Otis himself must have installed. I love how you have to hold the lever to go up and down and manually align the elevator to the floor. The elevator lights are powered by the DC current as well. At Pratt Institute they used to have those old DC elevators that were powered by an ancient motor generator set that was dated back to the 30's. Hell up until 1999 the MTA still had an old DC substation that had Rotary converters for the subway. ConEd also kept the 25 cycle plants running to feed those substations until the early 90's.

If you want a feel of old DC equipment from the days when if you wanted power you had to make your own, head down to Pratt Institute (located in Brooklyn on Willoughby ave. and Hall st.). They still have 3 steam driven reciprocating piston dynamos built by Ames Iron Works. They work but are only for show. And to top it off they also have a steam turbine dynamo all of which is hooked to a large open marble panel board with knife switches, carbon arc circuit breakers and blade fuses. The panel is still live on the AC side. The Motor generator I mentioned is still there. You can go down to the Pratt engine room and get a tour from Conrad Milster, the Chief engineer who keeps the place running. The large 1930's brick steam boiler still heats the campus and the surrounding neighborhood. The site is an IEEE land mark and walking down there is like going back in time, a real treat.

Misinformation

[linuxwrangler (582055)]

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.

DC transmissions still exists as HVDC

[MoFoQ (584566)]

Especially in the form of High-voltage transmissions. (http://en.wikipedia.org/wiki/HVDC)

There are some advantages (source: http://en.wikipedia.org/wiki/HVDC#Advantages_of_HVDC_over_AC_transmission [wikipedia.org]):

• 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:
http://en.wikipedia.org/wiki/List_of_HVDC_projects [wikipedia.org]

The Backstory

[goodie3shoes (573521)]

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. http://query.nytimes.com/gst/fullpage.html?res=940CE7DF173DF93BA25750C0A9679C8B63&sec=&spon=&pagewanted=print [nytimes.com]

I hope...

[Lord Byron II (671689)]

I hope that the current HD-DVD vs Blu-Ray debate is resolved a bit quicker

Mercury Arc Rectifiers

[bitrex (859228)]

I think the most beautiful piece of old AC to DC conversion technology was the mercury arc rectifier...apparently these devices were still used on some branches of the NYC subway until late in the 20th century. A video of one in operation can be seen at http://www.youtube.com/watch?v=Rt-a8fxgtno [youtube.com]

A center-tapped transformer was connected to two anodes to form a full-wave rectifier(some had more anodes and were used for 3 phase power), and a pool of liquid mercury was used as the cathode material which would form an arc only if the anode was positive. A keep-alive electrode kept the interior full of vaporized mercury to facilitate the discharge. I'd sure like to have my own. Unfortunately an average sized mercury arc rectifier contains around 2 pounds of liquid mercury, so if it ever broke, my neighborhood would have to be decontaminated, my home razed to the ground, and the rubble buried in a concrete encasement.

Re:Advantages?

[irn_bru (209849)]

Depends if you are an elephant or not.

Re:Advantages?

[gangien (151940)]

for those who don't get it http://www.roadsideamerica.com/pet/topsy.html [roadsideamerica.com]

Re:Advantages?

[oo7tushar (311912)]

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.

Re:Advantages?

[Four_One_Nine (997288)]

Do ATM machines (where we enter our PIN numbers) run on DC current?

Re:Advantages?

[momerath2003 (606823)]

Automated teller machine machine?
Personal identification number number?
Direct current current?

See wiki [wikipedia.org].

Re:Advantages?

[Jerry Coffin (824726)]

A few, but not very many. The main one is that many power uses require DC in the end, so AC has to be rectified and filtered before it's used -- and in doing so, some power is lost. When/where you're using a lot of power in a relatively restricted area, that can make a meaningful difference. Automobiles, for one obvious example, mostly use 12V DC systems (nominally 12V -- really around 14V). Aircraft, for another example, mostly run on 48V DC (IIRC). Some data centers have also gone to having a single big power supply, and then piping DC around to the individual computers. I haven't measured it personally, but they claim this can cut power usage by around 30% in some cases.

Another difference is that getting shocked by DC tends to be slightly less dangerous than the same shock from AC. A 110V DC shock to bare (unbroken) skin is is quite mild feeling, where most people in the US have found (sometime or other) than 110V AC is fairly uncomfortable, though usually not particularly dangerous (i.e. for every person who dies of electrocution, an unknown but certainly large number of others are shocked with no real consequence beyond surprise and discomfort).

Re:Advantages?

[TigerNut (718742)]

As related here [wikipedia.org] 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:Advantages?

[vacantskies9 (1190171)]

Actually DC current is more efficient than AC in transmitting power due to there being no reactive component of the power. The main problem with DC is that it cannot be transformed to higher voltages which save a lot of energy losses. There is actually a very long DC transmission line to California that uses DC power. They convert to AC at the end of the line. AC is also a much safer means for transmitting power. It is nearly impossible to extinquish a fault on a DC line because the voltage never reaches a zero point. Protection devices on AC lines rely upon the zero point to extinquish faults.

Re:Advantages?

[jallen02 (124384)]

You never, ever, have to say "correct me if I am wrong" on Slashdot. Someone will gleefully correct you if you are wrong.

Re:Advantages?

[stg (43177)]

...and even if you are right...

Re:Yep, Tesla won alright

[TooMuchToDo (882796)]

Let's be honest though. The conglomerate known as General Electric is nothing like the company it was when Edison was around:

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:I know everything technically is DC..

[The Cisco Kid (31490)]

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.