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Re: 220v/50hz power rig
From: Vadim Antonov <avg () exigengroup com>
Date: Thu, 6 Sep 2001 13:35:24 -0700 (PDT)




On Thu, 6 Sep 2001, Lincoln Dale wrote:

HZ moving around causes far more problems -- makes peoples clocks go slow 
and fast.  for that reason, HZ is very tightly regulated - if it goes over 
for a period, they'll make it go under to even it out.

Sorry for the nit-picking... Grid AC frequency is tightly controlled for
entirely different reason - imagine what happens when you have two
generators on the same grid, out of phase from each other.  (In really
large grids, like ex-USSR's United Energy System wave propagation delays
make the whole synchronization dance quite interesting, particularly
considering that turbines start rotating faster if load drops, etc).

There other, as imprtant, reasons to keep frequency stable: for example,
phase difference determines the direction of energy flow in an inter-tie
transmission line! (see, for example, analysis of coupled oscillators in
Feynman's lectures on physics).  And there's a whole can of worms in
keeping right the angle between voltage and current :)

Actually, a lot of what grid control automatics people do could be a very
well worth to learn for the network people.  Grid control requires very
fast redistribution of the load to keep parts of grid in sync; miss the
time window, and you have to live in panic mode, effectively shutting down
and patritioning grid to protect equipment against cascading effects.

That forced automation designers to go into a lot of very heavy trickery,
like pre-computing failure modes, and then quickly selecting the right
scenario. Of course, no in-line signalling foolishness there :) 

--vadim


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