HV-DC transmission

[Barbqranch]

I am curious about HV-DC transmission. I look at the local (HV-AC) towers, and they have 3 current carrying conductors (naturally, 3 phase power). When they use DC, do they have a different arrangement of wires? Just 2? And if it is, say, 500 KVDC, is there a wire at +250 KVDC and one at -250 KVDC (relative to earth), or one at +500 and another at 0? Or one at +500, and another at -500? Or do they use the earth for the return? :?

Thanks, and I wish you all a happy and successful New Year!

 

[electrofelon]

From the wikipedia article, the pacific DC intertie is bipolar, +/- 500 KV so 1000kv pole to pole. The pictures show two pairs of conductors (in addition to the shield wires), but the text says:

A 846-mile (1,362 km) overhead transmission line consisting of two ACSR conductors each 1.6" diameter in cross sectional area (1,171 mm2 ).

So I think that text is wrong or poorly written.