On 05/01/2018 12:22, The Other Mike wrote:
On Thu, 4 Jan 2018 16:12:00 +0000, newshound
wrote:

On 04/01/2018 15:36, Andy Burns wrote:
The Natural Philosopher wrote:

cost of repairing overhead 11KV fault. £2000.
Cost of undergrounding it - £30,000 per kilometer.

£250m for 8 miles in Stratford

https://www.arup.com/projects/london-2012-powerlines-undergrounding

Not 11 kV though: 132 and 400 kV.

A bit more detail here

http://www.icevirtuallibrary.com/doi....2011.164.6.11

Tunnels were 4.15 and 2.8 metres diameter.

I guess trenched undersea cables are much more lossy. It would be
interesting to know at what point it becomes worth going to DC.

65 miles is the worlds longest undersea AC cable (Blackpool - Isle of Man) but
is only 90kV. The distance / voltage for that project was as far as is both
technically feasible and financially viable.

Direct burial of supergrid circuits at 400kV AC under the sea doesn't happen in
the UK, the crossings that do exist are all in tunnels, with overheads for all
the others. For DC the cost of the AC/DC conversion stations nearly always swamp
the cable costs.

As an aside the Western HVDC interconnector (2.2GW) down the Irish sea from
Hunterston to Deeside working at 600kV (a new record for undersea HVDC) started
operation a month ago.

Thanks, very interesting. (Probably off to the IOM in a couple of weeks).