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RE: East Coast outage?
From: "McBurnett, Jim" <jmcburnett () msmgmt com>
Date: Sun, 17 Aug 2003 09:09:09 -0400




--Huh ? Where in the physics of ohms law is Hz a factor ? Having lived off
--the grid, where systems are often at max 48v, yes the wires have to be
--several 0's of gage to carry the lagre amperages. Much the same in A/B DC legs in
--a colo. Up the volts and the amps go down to produce the same power (watts
--or work).

HMM, it's been a LONG time but I remember high amp, low voltage
The formula makes it a swap out. Raise the voltage drop the current, or lower the
voltage and raise the current if the resistance stays constant.


--I am a little rusty on this one, but I seem to remember that AC travels
--only on the outside skin of the wire but DC uses all the wire.

This is called the skin effect, and from my RF days we did not consider it
to be an issue until you get to close the KHz range. In high voltage
transmission lines it may get a little higher than 60 Hz, but I don't think by much.
I have many UPS that track HZ and I have seen it coming in from 59.8 to 60.2.
The skin effect was a really big deal in the L band systems where I used to work.
1.2 GHz to 1.6 GHz. And in the S Band we had to use pressurized dehumidified 
transmission Waveguide due to freq and power levels (2 Megawatts).

We did AC/DC conversion and worked with 400 Hz power for those systems, and we were
not concerned with skin effect at all. But we were concerned with RF induction into
the power systems supply lines that could dirty up the power input and 
create problems for the ac/dc conversion for the discrete electronics.

anyway-it's been awhile...

J


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