[BC] Happy birthday and thanks for the electricity Nikola

[PeterH]

On Jul 10, 2009, at 7:23 PM, Dana Puopolo wrote:

> DC is still used on many high tension lines because the energy  
> potential for a
> volt of power is much higher with DC-those areas outside the sine  
> wave.

No, not on "many" transmission lines, but only "some" transmission  
lines.

The West has two dc transmission lines, only: the Celilo to Sylmar  
line which my employer in an earlier lifetime constructed (the so- 
called DC Intertie) and the Mountain to Lugo line which a consortium  
of utilities, including my former employer, built. Both are 1,000,000  
volts as +/- 500,000 volts (bipolar). Both are point-to-point.

Dc makes sense in these applications because the transmission  
distance is rather long, perhaps 1,000 miles, but there are NO  
intervening stations, only stations at the endpoints.

All of the remainder of power in the West is ac, usually at 230 kV or  
higher, with the highest power density being handled by 500 kV. There  
is 500 kV all over the West. Some 345 kV in AZ, some 287.5 kV from  
Hoover to L.A., and loads and loads of 230 kV everywhere else, and  
eventually connected to the so-called AC Intertie at many points.

There is one installation of note which is only dc, and that is the  
three lines from Three Gorges which is 500 kV dc to points far  
distant from the dam site.

DC makes sense for undersea cables.

It's really an AC world, with DC having very limited applications:  
point-to-point over very long distances; and cases where frequency  
conversion is required, such as interconnecting a 50 Hz system with a  
25 or 60 Hz system.

The exceptionally high cost of the conversion equipment is what  
prevents DC from having more than just end-point conversion stations.  
Perhaps that may change in the future.