RE: Why no corona? AC / DC transmission lines

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-qwest-dot-net>" <jimlux-at-earthlink-dot-net>

At 08:12 AM 9/10/2002 -0600, you wrote:
>Original poster: "Mccauley, Daniel H by way of Terry Fritz 
><twftesla-at-qwest-dot-net>" <daniel.h.mccauley-at-lmco-dot-com>
>
>
>Sure, there are transmission lines that run up to 768kV or better.
>I've even heard of megavolt lines (anyone know where these are?)
>
> >>>>>>They have quite a few now 1 Megavolt DC transmission lines which are
>basically bipole
>transmission lines (+/- 500,000VDC).  Seems Edison could be happy right now.
>DC high voltage lines are run
>because of their lower reactive losses and are under a lot of study right
>now.

Another BIG advantage of a DC link is that system stabilization is much 
easier.  You don't have to match phases on the sending and receiving ends 
(which is quite a trick when you've got 100s of km of wire out 
there).  Also, controlling power flow is much simpler. One end is a current 
sink, the other a voltage source (or vice versa...Thevenin equivalents and 
all that).

>I think i heard before that over 30% of power is lost in AC high voltage
>power lines just due to losses.  Of course in DC transmission lines you do
>get a large amount of losses in the step-up / step-down converter systems.

In an AC system you get losses in all the reactive components necessary to 
get the power flow stabilized. Considering the economic analysis that goes 
into building EHV equipment (AC or DC), I suspect that all those losses are 
carefully calculated out and taken into account.

> >>>>>>>>Not really, DC tranmission lines exist and they have just as much
>corona as 60Hz lines.
>
>Dan

Well.. it's not quite that simpleCorona is related more to peak voltage, 
not average or RMS, and a 500 kVRMS AC line has peaks of 700 kV.  The DC 
line stays at 500 kV, so less corona for the same power transmitted for a 
monopolar line.  Interestingly, for a bipolar line, there's more corona 
loss, because the ions from one side reach the other side, particularly if 
the wind is blowing across the line.


Typical corona loss on a 500 kV AC line is 0.3 to 1.7 kW/conductor/km, 0.7 
to 17 kW for 700 kV (EPRI, 1979), fair weather.  So, 200 km long line at 
500 kV with 3 conductors would be around 600-1000 kW loss from corona (on a 
line carrying 1500 MW...).  Resistive losses would be much greater 
(considering it takes a fair amount of heat to get the line up to 100C).