# Edison - how could direct current ever be practical? **URL:** \ **Category:** Factual Questions\ **Created:** [August 14, 2005, 8:42pm UTC](https://boards.straightdope.com/t/edison-how-could-direct-current-ever-be-practical/317002 "2005-08-14T20:42:04Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![wolf\_meister](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/wolf_meister/32/15202_2.png) [@wolf\_meister](https://boards.straightdope.com/u/wolf_meister)\ **Post date:** [August 14, 2005, 8:42pm UTC](https://boards.straightdope.com/t/edison-how-could-direct-current-ever-be-practical/317002/1 "2005-08-14T20:42:04Z")
As we know, **Thomas Edison** was a major proponent for using direct current and he argued it was the _only_ choice for household electrical power. As we also know **George Westinghouse** (working from the ideas of **Nikola Tesla** ), argued for alternating current. The big advantage of AC over DC is that AC “travels” better. AC can be stepped up to higher voltages sent along power lines and then stepped down. This allows for the use of thinner power lines _and_ allows AC to travel much farther (further?) than DC (no, _not_ the city). I think direct current can only travel a few miles before it loses sufficeient power to be usable. So, how did Edison plan on generating and “delivering” direct current for homes? It seems he would have had to build a power station for each city and town. How extensive were Edison’s direct current electric companies before it was realized that AC was the way to go? ---
**Author:** ![astro](https://avatars.discourse-cdn.com/v4/letter/a/9dc877/32.png) [@astro](https://boards.straightdope.com/u/astro)\ **Post date:** [August 14, 2005, 9:01pm UTC](https://boards.straightdope.com/t/edison-how-could-direct-current-ever-be-practical/317002/2 "2005-08-14T21:01:36Z")
> [@wolf\_meister](#): > > As we know, \*\* > > So, how did Edison plan on generating and “delivering” direct current for homes? It seems he would have had to build a power station for each city and town? That was the plan. [AC vs. DC: The Struggle for Power](http://www.ieee-virtual-museum.org/collection/event.php?id=3456872&lid=1) > [@](#): > > Edison was less than thrilled with the emergence of Westinghouse’s technology, which threatened his own dominance in a field he virtually created. He also had genuine concerns about the safety of AC. The two men engaged in a public relations battle to determine which system would become the dominant technology. In an attempt to discredit AC power Edison stooped to some low tricks. He paid schoolboys a quarter for each dog or cat they delivered to him and then he electrocuted the animals in deliberately gruesome public experiments. In another desperate attempt to sway public opinion against AC, Edison recommended that the state of New York use electrocution by means of AC power as its method of capital punishment. He even suggested calling the electric chair the “Westinghouse Chair” and recommended that the verb “Westinghoused” be used to describe electrocution. ---
**Author:** ![engineer\_comp\_geek](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/engineer_comp_geek/32/504_2.png) [@engineer\_comp\_geek](https://boards.straightdope.com/u/engineer_comp_geek)\ **Post date:** [August 14, 2005, 9:45pm UTC](https://boards.straightdope.com/t/edison-how-could-direct-current-ever-be-practical/317002/3 "2005-08-14T21:45:29Z")
There were a lot of rather interesting systems developed in the early days of electricity. You can set up motor-generator sets which will effectively create DC “transfomers”, but obviously these are a lot more expensive and complex than AC transformers. There was even one distribution setup where a bunch of motor/generator sets were run in series in one really big loop. The advantage of this of course was that there was only one wire going around the loop. The disadvantage was also pretty obvious. If anything in the loop breaks the entire system goes down. At really high voltages, DC has smaller losses due to capacitance and corona discharge, which can offset the expense of more complex transformers being required at either end (not to mention that at some point you have to convert the power to AC to make it play nice with the rest of the power system). The cost of the transformers doesn’t make it practical for neighborhood type power distribution, but if you need to get a whole lot of power from over here to someplace way over there, DC can be used, and in fact is used in several places around the world. ---
**Author:** ![ftg](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ftg/32/2801_2.png) [@ftg](https://boards.straightdope.com/u/ftg)\ **Post date:** [August 15, 2005, 1:29am UTC](https://boards.straightdope.com/t/edison-how-could-direct-current-ever-be-practical/317002/4 "2005-08-15T01:29:37Z")
An example of a non-trivial DC power line is the [Pacific NW-SW Intertie](http://www.usbr.gov/dataweb/html/pninter.html) system. The original line “only” goes from the Columbia river in N. Oregon to near L.A. 845 miles as the juice flies. ---
**Author:** ![friedo](https://avatars.discourse-cdn.com/v4/letter/f/8edcca/32.png) [@friedo](https://boards.straightdope.com/u/friedo)\ **Post date:** [August 15, 2005, 1:37am UTC](https://boards.straightdope.com/t/edison-how-could-direct-current-ever-be-practical/317002/5 "2005-08-15T01:37:37Z")
> [@ftg](#): > > An example of a non-trivial DC power line is the [Pacific NW-SW Intertie](http://www.usbr.gov/dataweb/html/pninter.html) system. The original line “only” goes from the Columbia river in N. Oregon to near L.A. 845 miles as the juice flies. Surely there’s a good reason for that. Why would they choose to use DC for long-distance transmission? ---
**Author:** ![David\_Simmons](https://avatars.discourse-cdn.com/v4/letter/d/9de053/32.png) [@David\_Simmons](https://boards.straightdope.com/u/David_Simmons)\ **Post date:** [August 15, 2005, 2:20am UTC](https://boards.straightdope.com/t/edison-how-could-direct-current-ever-be-practical/317002/6 "2005-08-15T02:20:00Z")
> [@friedo](#): > > Surely there’s a good reason for that. Why would they choose to use DC for long-distance transmission? There are some advantages now that we have the technology to do it at 1.5 million volts. You aren’t using current through the resistance of the line to continually charge and recharge the line capacity. No radiation loss. And that’s just off the top of my head. However, I’m not sure the advantages are enough to make it worth while. The Pacific Intertie DC line is now something like 30 or 40 years old and it’s still all by itself as a long distance DC transmission line in the US. The line runs down the eastern side of the Sierra Nevada range about 15 miles west of here. It crosses a campground on the Owens River up north of here and I think I’ve mentioned that when I am under it I never erver point my finger at it when telling people what it is. Why take even a super remote chance on raising the voltage gradient in your vicinity? ---
**Author:** ![engineer\_comp\_geek](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/engineer_comp_geek/32/504_2.png) [@engineer\_comp\_geek](https://boards.straightdope.com/u/engineer_comp_geek)\ **Post date:** [August 15, 2005, 4:16am UTC](https://boards.straightdope.com/t/edison-how-could-direct-current-ever-be-practical/317002/7 "2005-08-15T04:16:03Z")
I dug out one of my old EE textbooks which has a couple of pages about DC power transmission. The book was printed in 1982 so some of it is a bit out of date, but here are a few excerpts you might find interesting: > [@](#): > > The year 1954 is generally recognized as the starting date for modern high-voltage dc transmission when a dc line began service at 100 kV from Vastervik on the mainland of Sweden to Visby on the island of Gotland, a distance of 100 km (62.5 mi) accross the Baltic Sea. > [@](#): > > In the United States a dc line operating at 800 kV transfers power generated in the Pacific Northwest to the southern part of California. As the cost of conversion equipment decreases with respect to the cost of line construction the economical minimum length of dc lines also decreases and at this time is about 600 km (375 mi). > [@](#): > > Operation of a dc line began in 1977 to transmit power from a mine-mouth generating plant burning lignite at Center, North Dakota to near Duluth, Minnesota, a distance of 740 km (460 mi). Preliminary studies showed that the dc line including terminal facilities would cost about 30% less than the comperable ac line and auxiliary equipment. The line operates at +/- 250 kV (500 kV line-to-line) and transmits 500 MW. From “Elements of Power System Analysis” fourth edition, by William D. Stevenson, Jr. (1982) The advantages of DC (aside from cost) according to that book are: 1. Voltage regulation is less of a problem since at zero frequency inductance is no longer a factior, whereas it is the chief contributer to voltage drop in an ac line 2. The transmission line can be operated monopolar in an emergency if one of the lines gets grounded 3. (no the book does not say Hi Opal) 4. DC works better underground over long distances, like in the English Channel 5. The distances between conductors is smaller, which in addition to the cost savings for towers also means a smaller right of way of land is needed 6. Since AC has to be insulated for the highest peak to peak voltage, the insulation required for DC is much less for the same average voltage The book also mentions that ac circuit breakers can extinguish the arc that develops between the conctacts because there is a zero crossing twice on each cycle. No dc equivalent of this exists (or didn’t when the book was written). ---
**Author:** ![David\_Simmons](https://avatars.discourse-cdn.com/v4/letter/d/9de053/32.png) [@David\_Simmons](https://boards.straightdope.com/u/David_Simmons)\ **Post date:** [August 15, 2005, 5:48am UTC](https://boards.straightdope.com/t/edison-how-could-direct-current-ever-be-practical/317002/8 "2005-08-15T05:48:40Z")
> [@engineer\_comp\_geek](#): > > The advantages of DC (aside from cost) according to that book are: > > 1. Voltage regulation is less of a problem since at zero frequency inductance is no longer a factior, whereas it is the chief contributer to voltage drop in an ac line > 2. The transmission line can be operated monopolar in an emergency if one of the lines gets grounded > 3. (no the book does not say Hi Opal) > 4. DC works better underground over long distances, like in the English Channel > 5. The distances between conductors is smaller, which in addition to the cost savings for towers also means a smaller right of way of land is needed > 6. Since AC has to be insulated for the highest peak to peak voltage, the insulation required for DC is much less for the same average voltage > > The book also mentions that ac circuit breakers can extinguish the arc that develops between the conctacts because there is a zero crossing twice on each cycle. No dc equivalent of this exists (or didn’t when the book was written). Interesting. I knew about the Russian line but the North Dakota one is news. Another advantage is that less conductor is needed. For example a 1 million volt DC line carrying 1000 amp. is a 1000 megawatt line and consists of two wires. The same capacity 3-phase AC line at 550 kV would have 1050 amp but would use 3 lines of the same size as the DC line. ---
**Author:** ![Crafter\_Man](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/crafter_man/32/458_2.png) [@Crafter\_Man](https://boards.straightdope.com/u/Crafter_Man)\ **Post date:** [August 15, 2005, 4:13pm UTC](https://boards.straightdope.com/t/edison-how-could-direct-current-ever-be-practical/317002/9 "2005-08-15T16:13:43Z")
All else being equal, it is inherently more efficient to transfer power via DC (vs. AC) when you only consider the conductors. There are many reasons for this, as other posters have stated. I believe the most significant factor is that there are no reactive losses at DC. Here’s another reason: Let’s say your power source is operating at 60 Hz and a foreign customer located 1000 miles away wants to buy your power at 50 Hz. To convert the 60 Hz to 50 Hz, you first have to convert the 60 Hz to DC, and then convert the DC to 50 Hz. For reasons stated above, it would be more efficient to convert the 60 Hz to DC at the power source, transfer the power over long distance at DC, and then covert the DC to 50 Hz at the customer’s location. ---
**Author:** ![Kevbo](https://avatars.discourse-cdn.com/v4/letter/k/e47774/32.png) [@Kevbo](https://boards.straightdope.com/u/Kevbo)\ **Post date:** [August 15, 2005, 5:59pm UTC](https://boards.straightdope.com/t/edison-how-could-direct-current-ever-be-practical/317002/10 "2005-08-15T17:59:32Z")
And it’s not only an issue of frequency, but also phasing. All the AC on particular grid must be in phase, or bad things happen when generators are connected. A DC intertie allows two non-synchronized grids to share power. ---
**Author:** ![19ForMe](https://avatars.discourse-cdn.com/v4/letter/1/439d5e/32.png) [@19ForMe](https://boards.straightdope.com/u/19ForMe)\ **Post date:** [August 15, 2005, 6:56pm UTC](https://boards.straightdope.com/t/edison-how-could-direct-current-ever-be-practical/317002/11 "2005-08-15T18:56:19Z")
I know very little about this topic but I’m sitting by a large wall map of the US power grid. I count five long distance DC power lines. 1. As mentioned - Oregon (the Dalles) to LA 2. Central Utah (Intermountain) to LA 3. Central South Dakota (Young) to Daluth, MN 4. Central South Dakota (Coal Creek) to Minneapolis, MN 5. Off the map northern Quebec to Reading, Mass This thread is helpfully answering questions I’ve had about the confusing map. Thanks a lot. ---
**Author:** ![octothorpe](https://avatars.discourse-cdn.com/v4/letter/o/b77776/32.png) [@octothorpe](https://boards.straightdope.com/u/octothorpe)\ **Post date:** [August 15, 2005, 10:09pm UTC](https://boards.straightdope.com/t/edison-how-could-direct-current-ever-be-practical/317002/12 "2005-08-15T22:09:58Z")
As an aside, the 430 mile DC line from central North Dakota to the Twin Cities was the subject of huge controversy with rural Minnesotans sparking a rebellion in which, at its peak in 1978, nearly 50% of the state’s highway patrolmen were tasked with protecting the line. The original course of the line appeared to have been decided upon by simply drawing a line without regard to inconvenience to landowners and farmers. Supposedly, in the original plan, a structure was to be placed in someone’s front yard. After energization of the line, ‘bolt weevils’ caused many structures to collapse by removing key braces from the towers. Because of this, there is now a federal law regarding purposeful damage to transmission lines. For a more complete telling, pick up _ **Powerline** The First Battle of America’s Energy War_ by **Senator Paul Wellstone** and **Barry M. Casper** _(University of Minnesota Press)_ # ---
**Author:** ![wolf\_meister](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/wolf_meister/32/15202_2.png) [@wolf\_meister](https://boards.straightdope.com/u/wolf_meister)\ **Post date:** [August 16, 2005, 2:19am UTC](https://boards.straightdope.com/t/edison-how-could-direct-current-ever-be-practical/317002/13 "2005-08-16T02:19:52Z")
It seems **astro** answered my question in the second posting but wow - this thread has become more interesting than I ever thought it would be. Well then, I guess I have some more questions. What about generating AC or DC. Which is easier or cheaper to do? From what I’ve read so far, it seems DC now has the advantage over AC. Will DC eventually be the preferred method of electrical distribution? ---
**Author:** ![David\_Simmons](https://avatars.discourse-cdn.com/v4/letter/d/9de053/32.png) [@David\_Simmons](https://boards.straightdope.com/u/David_Simmons)\ **Post date:** [August 16, 2005, 3:28am UTC](https://boards.straightdope.com/t/edison-how-could-direct-current-ever-be-practical/317002/14 "2005-08-16T03:28:10Z")
> [@wolf\_meister](#): > > It seems **astro** answered my question in the second posting but > wow - this thread has become more interesting than I ever thought it would be. > > Well then, I guess I have some more questions. > > What about generating AC or DC. Which is easier or cheaper to do? > From what I’ve read so far, it seems DC now has the advantage over AC. Will DC eventually be the preferred method of electrical distribution? The normal output of a rotating machine of this sort is an approximately sinusoidal AC signal. It takes extra effort to turn it into DC. Batteries on the other hand easily generate DC and it takes extra effort to produce AC… ---
**Author:** ![engineer\_comp\_geek](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/engineer_comp_geek/32/504_2.png) [@engineer\_comp\_geek](https://boards.straightdope.com/u/engineer_comp_geek)\ **Post date:** [August 16, 2005, 4:45am UTC](https://boards.straightdope.com/t/edison-how-could-direct-current-ever-be-practical/317002/15 "2005-08-16T04:45:05Z")
> [@wolf\_meister](#): > > Will DC eventually be the preferred method of electrical distribution? I personally doubt it, especially now that the infrastructure is in place for AC. The minimum distance for DC to be economical is still pretty long, though I think it will get shorter and shorter over time. I think DC is also going to start being used more often to get electricity to places that really need lots of it (like california and the northeast) but I think the extra costs of DC are always going to outweigh its benefits at shorter distances and lower voltages. ---
**Author:** ![wolf\_meister](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/wolf_meister/32/15202_2.png) [@wolf\_meister](https://boards.straightdope.com/u/wolf_meister)\ **Post date:** [August 16, 2005, 2:26pm UTC](https://boards.straightdope.com/t/edison-how-could-direct-current-ever-be-practical/317002/16 "2005-08-16T14:26:18Z")
**engineer\_comp\_geek** It is funny that you said “_The minimum distance for DC to be economical is still pretty long._” In Edison’s day (due to different technologies) the statement would have been the _maximum_ distance for DC to be economical would be _very short_. ---
**Author:** ![Madd\_Maxx](https://avatars.discourse-cdn.com/v4/letter/m/5f9b8f/32.png) [@Madd\_Maxx](https://boards.straightdope.com/u/Madd_Maxx)\ **Post date:** [August 16, 2005, 4:24pm UTC](https://boards.straightdope.com/t/edison-how-could-direct-current-ever-be-practical/317002/17 "2005-08-16T16:24:15Z")
Actually, almost everyone has DC going into their homes. Telephones use DC. That is why when the power goes out, your phone still works. ---
**Author:** ![friedo](https://avatars.discourse-cdn.com/v4/letter/f/8edcca/32.png) [@friedo](https://boards.straightdope.com/u/friedo)\ **Post date:** [August 16, 2005, 4:36pm UTC](https://boards.straightdope.com/t/edison-how-could-direct-current-ever-be-practical/317002/18 "2005-08-16T16:36:28Z")
> [@Madd Maxx](#): > > Actually, almost everyone has DC going into their homes. Telephones use DC. That is why when the power goes out, your phone still works. One has nothing to do with the other. Telephones have their power supplied by the central office which has battery backups in case of a blackout. The fact that the power distribution for telephones is separate from the main power grid is why it stays up when there is a blackout. ---
**Author:** ![Madd\_Maxx](https://avatars.discourse-cdn.com/v4/letter/m/5f9b8f/32.png) [@Madd\_Maxx](https://boards.straightdope.com/u/Madd_Maxx)\ **Post date:** [August 16, 2005, 4:52pm UTC](https://boards.straightdope.com/t/edison-how-could-direct-current-ever-be-practical/317002/19 "2005-08-16T16:52:38Z")
Right, the Telco’s use DC power in the Central Office. The equipment is powered by either DC or AC depending on manufacturer, office location, equipment type etc. The battery backups are often recharged by diesel generators in the case of many large CO’s. ---
**Author:** ![Madd\_Maxx](https://avatars.discourse-cdn.com/v4/letter/m/5f9b8f/32.png) [@Madd\_Maxx](https://boards.straightdope.com/u/Madd_Maxx)\ **Post date:** [August 16, 2005, 4:59pm UTC](https://boards.straightdope.com/t/edison-how-could-direct-current-ever-be-practical/317002/20 "2005-08-16T16:59:52Z")
Damn, hit reply too soon. This [link](http://www.tkk.fi/Misc/Electronics/circuits/telephone_ringer.html) can explain it better than I could without getting something wrong. [Next page](https://boards.straightdope.com/t/edison-how-could-direct-current-ever-be-practical/317002.md?page=2)