[bsder]

This is, in fact, precisely backward.

DC is great for transmitting power. You crank the voltage, use all of the copper wire (no pesky skin effect), and sync to the grid at the DC-AC conversion point.

The limiting factor to DC was conversion losses. The Pacific DC Intertie needed to use gigantic, toxic mercury vapor tube diodes for the conversion for a very long time.

Now that we use high voltage semiconductors, that's no longer a problem. We easily convert between DC voltages as well as AC with quite remarkable efficiency.

[jacquesm]

At your typical power distribution frequencies (50 Hz, 60 Hz) the skin effect is negligible.

[bsder]

You are simply wrong.

Skin effect at 60Hz is about 8mm. Power transmission (especially the long distance ones) conductors are normally quite a lot larger than that. Even the wires coming into your house are probably pretty close to that so there will be some effect even if it's not huge.

[jacquesm]

8 mm (in copper, which is rarely used for powerlines, if at all, it is super expensive and heavy) is huge for a single conductor, and your typical overhead powerline is concentric shells of tens of conductors. Negligible: has no practical effect on the construction. It's in the 4th significant decimal or so for a typical powerline segment, dwarfed by plain resistive losses.

You want those multiple conductor arrangements anyway to reduce the corona discharge.

If you go up to multiple KHz then it will become a problem.

[borodi]

Reactive power losses due to the cable's inductance are probably the largest factor in the efficiency boost of using DC. Also you can use a somewhat higher voltage since you don't have to account for the AC peak, it does mean however that breaking a DC arc is harder since the is no 0 crossing.

[jacquesm]

Depends greatly on the material used and the cable construction. Typical: 60 strand aluminum (better skin effect properties than copper by the way) around a steel carrier. And yes, those are the largest factors in the boost to DC, but that's mostly because the resistance losses are there regardless so there isn't much else that you could improve on.

If you transmit a lot of power over very long distances then the higher the voltage the lower the current and DC gets rid of the skin losses so there's the case for HVDC transmission lines (which are extremely impressive feats of engineering, as are the substations).

Finally found a good picture of a cross section of a HV AC transmission cable:

https://en.wikipedia.org/wiki/Aluminium-conductor_steel-rein...

Based on that ruler that makes the AL wires about 3 mm each, and the skin depth at 50 Hz would be about 11.5 mm or so, so well within the range where the skin losses are extremely small (they are still there though, and when you're transferring Gigawatts every little bit helps).