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by deelowe 3803 days ago
Higher voltages and frequencies is how you get less loses as resistance is coupled to current. The lower the current, the less the resistance affects transmission. However you can only increase ac voltage and/or frequency so much before you have another issue, the impedence of the air itself starts to create loses Also, because AC doesn't fully penetrate the wire, you have to run much larger wire sizes to achieve the same affect. At a certain point, you simply can not push more power using AC without resulting to things like superconductors.

DC OTOH, does not have the skin effect issue and so because more desirable in certain cases. In fact, high voltage DC is how they electricity directly to LA all the way from Oregon/Washington state: https://en.wikipedia.org/wiki/Pacific_DC_Intertie
2 comments
amalag 3803 days ago
I read further on wikipedia and it mentions that these lines can also be underground. DC cables do not suffer from capacitance issues that AC cables do: "Long underground DC cables have no such issue and can run for thousands of miles." https://en.wikipedia.org/wiki/Electric_power_transmission#Un...
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deelowe 3802 days ago
yeah. HVDC is pretty interesting. Lots of great applications.
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digerata 3803 days ago
The forth paragraph in that link really sums up the difference for my poor brain:

"One advantage of direct current over AC is that DC current penetrates the entire conductor as opposed to AC current which only penetrates to the so-called skin depth. For the same conductor size the effective resistance is greater with AC than DC, so that more power is lost as heat. In general the power losses for HVDC are less than an AC line if the line length is over 500 -600 miles and with advances in conversion technology this distance has been reduced considerably."

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deelowe 3803 days ago
Right. Additionally, frequency plays a role and AC can ionize the air at higher voltages, which increase impedance super-linearly. Basically, high voltage DC is probably going to become a very attractive option as high voltage transistors become commonplace. The reason AC was so attractive previously was b/c it's very easy to convert voltage to current and vice versa with just some coils of wire. With silicon based solutions, that's becoming a much less efficient (and even cost more costly) option.
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