[sbaiddn]

AC has two problems:

1. Long lines become a "transmission line" in the sense that you get reflections. These have to Z matched and you also have to get the phase angle right.

2 Capacitance loss to ground. The lines are a massive capacitor to ground. The longer the line the more power shorts to ground

2a Because of 2. You dont use AC lines underwater. The increased dielectric means that you loose too much power from anything but the shortest runs.

You could change the frequency to a do the long runs at a lower f, and itd have its benefits, but its outweighed by the drawbacks (namely transformer saturation)

[andromeduck]

3. Skin effect becomes more of a factor. HVDC can use the whole cross section of the wire to carry power whereas AC only uses the surface. At longer distances, the material savings of thinner/lighter wires offset the higher equipmet costsat eitherend.

[sbaiddn]

That's not really a problem because the current caring portion of the cable is an aluminum sheeth (good conductor, but expensive and not as strong) over a steel core (poor conductor but strong)