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Registered Member #56
Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445
This has been answered in severalplaces before, you have less corona losses from a dc wire of the same voltage then of an AC one. It should also be noted that you loose some energy from capactitve losses when using AC lines.
Registered Member #78
Joined: Thu Feb 09 2006, 11:27AM
Location: Sydney, Australia
Posts: 133
HV AC is affected by the skin effect, and electromagnetic induction. ie. current likes to travel primarily on the surface of the wire, while radiating out more EMR.
Registered Member #75
Joined: Thu Feb 09 2006, 09:30AM
Location: Montana, USA
Posts: 711
I think EVR also has a valid stand here. Resistive losses go with the square of the current, so with the same RMS current, an AC line will suffer greater resistive losses.
Registered Member #187
Joined: Thu Feb 16 2006, 02:54PM
Location: Central Ohio
Posts: 140
Not sure about this, but I think that because AC current is a cyclic zero crossing voltage, when the voltage is near zero the resistive losses are greatest.
Registered Member #56
Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445
Power companies have found a way around the skin losses, they use hollow conductors--so no gain there.
I also highly doubt that for a given current 1a at 60hz will cause any more resistance heating (ignoring the skin losses) then 1a dc, look up ohms law and what RMS has to due with it... If you drop 1v rms across the line it is the same thing as dropping 1vdc...
You have to think like a power company... You need to run a really long wire, that needs to carry a lot of power. You could use a piece of copper 10' thick and run it at 100v to minimise corona losses, but that would cost too much. So you realise that if you run at say 100kv you only need a piece of wire that is 3" in diameter (but with a .1" wall) --but you are going to loose some energy to corona losses. So you have your engineer runs the calcs and find out that it is cheaper to take the losses due to corona, and use less copper. So then you are wondering if you can squeeze any more efficiency out of your wire, and realise that dc lines have less corona than ac ones (from wikipedia--dc lines have 1/2 the corona losses compared to a ac system of the same length/power), and don't capacitively couple to the ground/other wires. So you run some cost analysis and find that buying the inverters will be cheaper than losses due to corona--but only for really long lines that have a lot of corona losses.
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DC / AC transmission lines
