On Tue, 20 Aug 2013 12:15:01 +0100, tony sayer wrote:

In article , The Other Mike
scribeth thus
On Mon, 19 Aug 2013 22:06:50 +0100, Nightjar
wrote:

On 19/08/2013 21:36, Tim Streater wrote:
...
And the cost, 10 times that of pylons. Anyone know the highest voltage
they put underground?


The National Grid provides design data for 400kV underground cables, so
presumably they have some of those.

Quite a few of them, some under major cities.

For instance in London, mainly 400kV cables

http://www.nationalgrid.com/NR/rdonl...5FF88A1BB361/4
8551/TQNW.pdf


In the UK the highest voltage is 450kV for the BritNed link (submarine +
underground) There are 500kV underground cables in USA & Canada.

There is / was an overhead only line operating at over 1000kV in Kazakhstan and
there are lots of 765kV lines in North and South America, South Africa, India &
China.



A point is could they have done that when the 400 kV grid was being
built back in the what was it, 50's or 60's?..

The distances in the UK don't justify any higher voltages and at the time of
original deployment each voltage level was approaching what was achievable in
practice.

275kV is early 50's, 400kV is more 60's and 70's Some switchgear at 400kV
originally had lots of problems requiring regular inspection and preventative
maintenance. Now it more or less just works for a decade before any
inspection. Pity it's all imported from Europe than home produced though.

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