On 28/07/14 17:11, John Williamson wrote:
On 28/07/2014 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?
The *resistance* doesn't change. When transmitting AC, however, the
*impedance* does change, both due to the capacitance to earth,
so far so good
and, if
the frequency is high enough, "skin effect", which is where the current
flow is restricted to the areas near the surface of the strands also
starts to come into play.
Yep a couple of hundred megahertz is what we transmit power at these days!
--
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