[GreenKeys] Creed 7B with DC Only Mor

[Richard Knoppow]

On 2/23/2015 4:43 PM, Thomas Tillson via GreenKeys wrote:
> I notice that the link is broken, so I have attached a copy of the 
> article:
> TT
>
      An interesting article, thank you.  A slightly nit-picking 
comment:  the author states that DC lost out to AC  because it is not 
suitable for transmission over long distances.  That needs a 
qualification.  Its not too suitable at _usable voltages_ . One of the 
big advantages of AC is that its easy to change voltage with a 
transformer with little loss of energy.  So, high voltages can be used 
for distribution at a distance and then lowered for practical use.   Not 
so with DC which in the old systems had to be transmitted at the working 
voltage.  However, for very long distance transmission high voltage DC 
does have an advantage, namely less loss from the inductance of the 
lines.  The roughly thousand mile Pacific Intertie transmission system 
runs at nearly one million volts DC between the hydroelectric generating 
station at the Dales in Washington state and Los Angeles.   Converstion 
to DC and back to AC is made electronically,  I don't know what sort of 
devices are used  now but when I toured the Sylmar termination in the 
San Fernando Valley it was  by means of extremely large thyratrons. 
Solid state devices may be used now.  The system has the capability of 
supplying _all_ the power demand of the city although it usually 
supplies about half.  The problem with Edison's system is that it ran at 
most a few hundred volts where the I^2*R losses are very great.  In an 
AC system the distribution lines can be run at several thousand volts 
the current and resistive losses being in inverse proportion to the 
voltage.
      DC was also used in traction systems but so was AC.  The New York 
Central and the late, lamented New Haven ran 600 VDC on a third rail 
where the Pennsylvania ran 11,000 volts, 25 Hz AC on overhead 
catenaries.  The voltage reduction taking place on board the locomotive.


-- 
Richard Knoppow
1oldlens1 at ix.netcom.com
WB6KBL

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