On 28/07/14 19:16, The Natural Philosopher wrote:
On 28/07/14 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.

Mmm. Not sure that is so, but cant put a finger on why I feel its
different..

A normal armoured cable would have a pretty effective faraday screen
around the live cores.

Not sure about mega HV cables but I'd be surprised if they were not
fully screened too.


The big difference is a cable vs overhead lines.


Yes.