Talk:War of the currents
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AC vs. DC
Someone (User:cataclysm) recently took it upon himself to change the section where the basic advantage of AC over DC is discussed. Yes, AC is slightly more efficient than DC due to the effect mentioned, and high frequencies better than low - but this is NOT the principal reason why AC is used instead of DC. The overwhelming advantage of AC is that it can be transformed to a high voltage and high voltage/low current distribution will only suffer relatively minor power losses due to line resistance. Besides, this explantion can be understood easily by the layman (remember, our dear readers?) whereas the electron behaviour that transfers the charge is a far more esoteric effect (and wrongly given, in this context). Graham 06:29, 4 Apr 2005 (UTC)
- I thought that the discussion of Ohm's law didn't do much for AC vs. DC, as it applies equally to both. Maybe this could be moved. These days, DC-DC inverters can easily change the voltage of a DC supply (and are small enough to fit in laptop displays) - I guess this is a bit out of context as DC-DC inverters weren't available at the time. I kinda hoped my explanation was accessible, but obviously not (I guess that's what you get for hanging around with engineers). I would say that the transmission loss in DC vs. AC is a more significant problem than voltage conversion as far as infrastructure goes... could you imagine a power station every block, with a fuel supply etc.? On a personal note I think "took it upon himself" and "wrongly given, in this context" is a bit harsh. Yours, Cataclysm 06:44, Apr 4, 2005 (UTC)
- Apologies for the personal remarks, on reflection they probably are a bit harsh. I wasn't contesting that what you wrote was factually correct, just whether it was appropriate in this context. The high voltage/low current does apply equally to AC and DC of course, but it was the simple ability to transform AC to a high voltage using a transformer that allowed power distribution over any worthwhile distance at the end of the 19th century, and so was instrumental in its rapid adoption worldwide. This was an era long before DC-DC converters were conceived of, as you rightly point out. Also, a DC-DC converter does not easily approach the efficiency of a simple transformer, which can easily be 98%+, so even if we were starting now with inventing a power distribution system, AC would still be chosen, but not for the reason you put forward. For the record I thought your explantion was accessible enough - just irrelevant in the context of the "war of currents", at which time I doubt this physical difference was even known. Perhaps your contribution would find a better home at alternating current? Graham 12:14, 4 Apr 2005 (UTC)
In central business districts, DC was used very successfully for many years. A 120 or 120/240 volt network was installed below street level with a network vault outside major buildings. Heavy fused leads carried the current into the building to the building panel, and circuits from there went to all the floors to operate lights, the elevator, fans, pumps, toasters, vacuum cleaners, radios, and all manner of office equipment. A 10 story building might be thus served by 120/240 volt DC risers. A massive central battery maintained the current if the generators all failed simultaneously. Rotary converters were used to convert DC to AC or AC to DC or AC of 60 Hz to AC of lower frequency for railroads. Customers loved the continuity of the power, which remained on through power storms and failures of a transmission cable, since the transmission was redundant and the distribution had battery backup. Eventually, by the 1930's engineers at GE and Westinghouse developed Network Protector switches and relays which allowed the replacement of the DC network by a low voltage senondary AC network, at 120 volts per phase or 208 volts between phases. The protector closed automatically when the transformer was energized on the high side and the phase relationship was correct for power to lflow to the secondary low voltage grid. Continuity of power to the customer was achieved by the fact that four or more 12kv AC lines could be used to power several transformers each at various spots around the grid, which could be many blocks by many blocks. Such a grid might go for decades without even a momentary interruption, unlike normal AC service where a line can be interrupted by lightning or tree contact, or an underground line by cable failure. The grid would continue to be supplied by the remaining lines, and the network protector would open automatically to isolate the faulted primary. Secondary faults would literally burn clear, with 50,000 amps or so of available fault current. When the changeover from DC grid to AC grid was made, the customer did not notice any change for the most part. Universal motors worked on AC as well as DC, and mercury rectifiers were supplied to power big DC motors. With AC available, building transformer vaults were added as well as spot networks on various floors of high rises. This part of the history should be added to the article, I think, with suitable references. Most of the Wikipedia articles give the impression that DC distribution was abandoned by the end of the 19th century, which was certainly not the case for central business districts of many large cities around the world. Edison 21:36, 30 August 2006 (UTC)
- Yes, rotary converters, in different forms, were used for AC/DC conversion. Also, generators (AC or DC) in series, electrically isolated, to get higher voltages. And a little later, and at lower power such is in cars, vibrators were used for DC to AC conversion. They were especially needed for vacuum tube car radios. Much fun and variety in designs, until things settled down to what we see today. Gah4 (talk) 00:50, 28 November 2023 (UTC)
DC alive if not well
As of late June, 2007, the article claims: "In January 2005, Consolidated Edison announced that it would cut off DC service to its remaining 1600 customers (all in Manhattan) by the end of the year." While literally true, that is not particularly interesting. As with many prior "final cutoffs," the one named was abandoned. At www.coned.com/sales/business/bus_elec.asp, a reader will find that Con Ed went for the gold instead, proposing surcharges ranging from $588 to $91,000 per year plus $0.0231 per kWh, approved in part. This was an increase from previous suracharges starting at $385 per month (Jay Romano, A push to unplug DC power, NY Times, March 18, 2001).
Energy treatise of transmission line theory
Is there any energy domain treatise of transmission line theory? I remember there were few out there.
Edison would have had AC banned I believe. But it is ironic that he had to fight against the gas companies, during the early years, to get electricity up and running.
It is also ironic that all "useable" equipment is DC, wonder if "gas" was indeed better than sitting and computing power factors and impedence losses!
Any chances of adding 2 capacitors in series and tapping the load across each "half" to step down the voltage?
Seems to work like the fridge for me ;o)
well well why is it that all grids lock back on DC? there must be a reason for this.
Etymology
Who named it "War of Currents"? Being capitalized I presume it has been labelled as a proper name by someone, which means it should have a reference and be explained. If a wikipedian made it up then renaming should be discussed. Cburnett 05:26, 24 September 2006 (UTC)
- It is, at least, the name of a book. The movie is called The Current War. Gah4 (talk) 00:54, 28 November 2023 (UTC)
Question about current, voltage and power loss
"Since metal conducting wires have a certain resistance, some power will be wasted as heat in the wires. This power loss is given by P = I2R"
P = I2R shows that if we say double the current, the power loss more than doubles. Which equation shows the effect of increasing the voltage? Doing some rearranging I came up with P = V2/R, is this correct? If so it would show mathematically that doubling the voltage does not lead to as much power loss as doubling the curent. However this only follows if R > 1 and I have no idea what typical values for R would be. Have I got this completely wrong?Shorvath 05:56, 31 March 2007 (UTC)
- It depends on where you're measuring R - none of us electrical types have managed to explain this correctly. When we say the power loss is proportional to I*I*R we mean the R of the conductors. POwer lost as heat in the conductors represents a loss. It might be better to say the power supplied to the line is the sum of the power delivered by the line plus power lost. There's two R's then, one in the conductors, one in the load. --Wtshymanski 14:30, 31 March 2007 (UTC)
- the continuous current carried is essentially reactive, with a value typically in the 3000-4000 A range. The power loss is then due to the resistance of the line when this current goes through : R*I*I, the other formula that you use does not apply because the line does not carry a resistive current !. Dingy 02:33, 1 April 2007 (UTC)
Interesting, but take this perspective: let V be the rms AC voltage /or flat DC voltage, R be the resistance and X be the impedence. Hence the actual power used Active power = V.I.cos(phase) = V^2 .R /(R^2+X^2) R/(R^2+x^2) being I cos(phase) now if the voltage source was DC power consumed = V^2/R < V^2.R/(R^2+X^2) as (R^2+X^2)/R > R So is it correct to say that DC would actually consume less power i.e if there was no impedence to worry about, (other than the transient) a DC transmission line would actually use less power? As far as current goes and conductor rating goes, for any high voltage you need a thicker wire till it melts, however assume one was to send rms value(220V) DC instead of AC one would need the same type of cables and yet experience less power loss? —Preceding unsigned comment added by Alokdube (talk • contribs) 07:07, 3 October 2007 (UTC)
- Just to comment on the new perspective, actually the transmission by HVDC has less losses than HVAC due to the skin effect and the corona discharges of ac voltage. HVDC-HVDC inverters were invented recently, so changing the whole grid wouldn't be such a good idea. Besides the power lost in the inverter section would also be big... But HVDC transmission (not distribution!!) is actually already in use (https://pscad.com/resource/File/Library/BasisPrinciplesofHVDC.pdf). —Preceding unsigned comment added by Tarkul (talk • contribs) 21:53, 12 June 2010 (UTC)
- The thyratron goes back to the 1920's, and was used over the years for DC to AC converter. The mercury arc rectifier was used for high current AC to DC conversion, also for many years. Gah4 (talk) 01:08, 28 November 2023 (UTC)
Skin effect is a function of frequency only. 60 Hz leads to 8.5 mm as characteristical depth of current flow in a conductor of copper. Only hollow tubes make sense for high-current applications at 60 Hz instead of massive cylindrical rods (wires), if more than (+/-) 17 mm diameter would be necessary for a fitting conducting cross section area. (Copper, eventually silverplated) litz wire make sense only for frequencies above 100 kHz where skin depth decreases to 0.2 mm and less, and it works only if all its parallel tiny filaments are isolated from each other, usually by enamel. --Helium4 (talk) 10:13, 10 June 2011 (UTC)
- Not just frequency. The resistivity and permeability of the material also enter into the calculation, as anyone shopping for cookware to use with an induction cooker gets to find out. --Wtshymanski (talk) 13:15, 10 June 2011 (UTC)
I would still relook the VI cos phase approach. Remember we are interested in transmitting power from A to B, so the actual power is the active component. While the reactive component is available in the line and can be dissipated out over time, the actual measure is "how much active was transmitted". — Preceding unsigned comment added by 115.99.182.242 (talk) 12:19, 12 October 2015 (UTC)