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Re: East Coast outage?
From: Jay Hennigan <jay () west net>
Date: Sat, 16 Aug 2003 10:07:30 -0700 (PDT)


On Sat, 16 Aug 2003, Chris Adams wrote:

Basic physics.  To run DC at the power levels required, the "wire" would
have to be over 100 feet in diameter IIRC.  Look up the Edison vs. Tesla
power arguments for all kinds of information on AC vs. DC.

Edison and Tesla's arguments took place long before switching power supplies
and the development of insulating materials capable of withstanding hundreds
of kilovolts.

The size of the conductor is a function of IR losses.  Losses are a function
of the resistance of the conductor and the current passing through it.  By
raising the voltage, the current drops proportionally for the amount of
power delivered, and hence the conductor size also drops.  The problem in
the Edison/Tesla days was a practical way to convert high voltage DC to low
voltage (120 volts or so) power for distribution to homes and businesses.
200KV light bulbs and switches are kind of impractical for home use.  :-)

The advantage of AC is that a simple transformer can be used to step down
the voltage from transmission to distribution levels.  Before high voltage
semiconductors and switching supplies, high voltage DC transmission was
useless as there was no practical means to convert it to the lower voltage
levels useful in homes.  Rotary motor-generator sets would have been the
only choice.  Huge, not very efficient, lots of (big) moving parts.  Not
trivial to maintain.

AC still makes sense for distribution, but HV DC transmission lines are
becoming the norm.  Think about some very large SCRs and associated parts
to convert to AC for distribution.

-- 
Jay Hennigan - CCIE #7880 - Network Administration - jay () west net
WestNet:  Connecting you to the planet.  805 884-6323      WB6RDV
NetLojix Communications, Inc.  -  http://www.netlojix.com/


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