Losses in AC and DC power tranfer

[wmac]

Hello,

I have forgotten most of the electricity physics we studied and I have problem describing/understanding a concept.

Does AC current produce less loss than a DC current? I found this statement in a website: "AC electricity loses less power over power lines than DC" (http://www.blueraja.com/blog/176/wh...c-instead-of-direct-current-dc-in-power-lines).

1- Is above statement correct? Could you describe it with electricity formulas?

2- In network engineering we prefer a line encoding (method of converting 0 and 1s into electrical signals) that produces a signal with a surface under the curve being almost zero (integral of the signal level being zero). Why is that? Does it result in less losses on the line?

Thanks

 

[Puma]

Looks like 1 is incorrect, AC has more of a loss due to capacitive effects in the surroundings - but it is much more complex than that:

http://www.extremetech.com/extreme/...ve-is-it-finally-time-to-switch-from-ac-to-dc

 

[Svein]

2- In network engineering we prefer a line encoding (method of converting 0 and 1s into electrical signals) that produces a signal with a surface under the curve being almost zero (integral of the signal level being zero). Why is that? Does it result in less losses on the line?

No. The reason we do that, is to ensure that there is no DC component in the signal. This is important if we want the signal to pass through a transformer on the way.

 

[anorlunda]

The amount of losses is mostly poroprtional to I^2. For the same power a higher voltage nees less current and thus less resistive losses. That is true AC or DC.

But the lack of capacitance problems with DC, allows the use of higher voltages. But it comes at the substantial cost of AC-DC conversion at each end and each tap point. At high voltages, corona losses also become significant.

DC is also useful to connect AC nets that are not synchronized with each other.