On 28/07/2014 11:52, The Natural Philosopher wrote:
On 28/07/14 08:19, John Williamson wrote:
On 28/07/2014 01:56, The Natural Philosopher wrote:
On 27/07/14 22:24, newshound wrote:
On 27/07/2014 21:40, wrote:
Nightjar wrote:
AC for simple long-distance transmission...
Except for underwater cables, where it can cause unacceptable
transmission losses.

How does immersing a 11kV AC cable in water increase transmission
losses? This isn't a joke question, I can't see how the medium
surrounding a cable changes the action of the cable itself, other
than cooling effects.

jgh

It's losses in the dielectric, so it applies to underground cables too.
Dielectric losses in air are low.

No it really isn't dielectric losses.


It's capacitive loading.

Exactly.

But the power isn't lost *in* the dielectric, its lost in driving the
current down the wires *to* the dielectric.

You are quite right, of course. But the term "dielectric loss" is the
one which CEGB trainers used to use when lecturing mixed classes of
mathematicians, physicists, and all types of engineer to explain why
pylons were the prefered method of transmission, with underground cables
the least desirable from the viewpoint of efficiency.

It's a convenient if not very precise shorthand.