On 04/08/14 02:26, John Rumm wrote:
On 28/07/2014 16:06, Tim Watts wrote:
On 28/07/14 14:48, wrote:
Nightjar wrote:
It's losses in the dielectric, so it applies to underground cables
too.
Like the man says, although the problem is significantly greater under
water. 30km is about the limit for AC transmission under water, (...)

Sorry, I still don't understand this. We're talking cables not
capacitors.
How does a 16mm2 PVC insulated cable have a higher resistance if it's
immersed in water than if it's in a vacuum?


It doesn't. It has a lower Line-Earth reactance (capacitative) - at
least that is what's being claimed.

However, the cables are all armoured so it does not really matter if
they are in a dry tunnel or under the sea.

I would have thought that enclosing a cable in water would change the
relative permeability of the arrangement, and hence the inductance per
metre of the cable?

(too long since I played with transmission line theory!)


I guess it might - I was considering the capacitative effects only.

But assuming the armour is steel wire - how much I wonder?