TomGeorge:
Hi,We have an under sea power link between Victoria and Tasmania and it is a DC Bus, to prevent cable losses if AC is used.
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Tom..
We have a similar set up here between the Dalles dam on the Columbia river and Los Angeles. This runs at 250,000 volts DC. They designed it to run at 500,000 volts DC, but had to use the ground for the return line. Raised hell with all the pipes in the ground and all the electric fences between Oregon and California, so limit is 250kv.
In the 1970's, a group from the Oregon Amateur Radio club had a tour of the Dalles converter station. At that time, we got to go walk through the actual array of mercury vapor controlled rectifiers. Huge devices. Now all solid state.
Then it was controlled on both ends by a DEC minicomputer. I don't know what they use today. Power could be reversed and sent back from LA to Oregon.
The operation was begun at the 3-phase dynamos in the Dalles dam. Six of the dynamos were phased to produce an AC of 18 phases, then through transformers as applied to the rectifiers to produce the DC.
On the LA end, the DC was converted to AC using the controlled rectifiers to switch the DC input to transformers.
The computer control could switch directions of the power in just a few seconds, and also was able to shut the whole operation down in just a few seconds during an earthquake in LA.
The link from Australia to Tasmania is under sea, so a single set of wires with ground return would not cause a problem. Perhaps they have good enough insulation to allow a complete wired circuit. Must be many wires of huge surface area.
Paul