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Re: 220v/50hz power rig
From: Lincoln Dale <ltd () interlink com au>
Date: Thu, 06 Sep 2001 18:04:11 -0700
At 01:35 PM 6/09/2001 -0700, Vadim Antonov wrote:
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,
i tend to think of electricity grids in the form of "organised chaos". its
really just one big phase-locked-loop setup where the producers are always
second-guessing what the consumers want.
in the four power-stations i've worked on the construction of (doing
automated power-station controllers), we used automatic-phase-loop
balancing that removed the "manual" part out of closing a circuit-breaker
of a generator coming online - it'd do it for you, and it'd only do it when
it was "in-phase".
the hard part them comes dealing with a "black start" - ie. where there has
been a total power failure and there is no phase to sync on to.
i've also had the somewhat dubious honor of getting the automated
power-station stuff wrong too. the somewhat dubious honour i can claim is
that i caused a blackout of an entire nation. (the Kingdom of Tonga).
its very difficult to physically close a circuit-breaker when its
out-of-phase. if you do manage to do it (eg. you have a hydraulic or
compressed-air based breaker that DOES have enough force to manage to close
it out-of-phase), then obviously "bad things"(tm) happen to that generator.
legend has it (and i don't know if this is true or not) that there is a
generator (or, at least the Alternator) in the Swan River in East Perth
(Western Australia) that 'jumped'
considering that turbines start rotating faster if load drops, etc).
that is true of all engines. its always a supply/demand driven system,
with the engine typically always operating at a fixed RPM. if supply
exceeds demand, the engine spins faster (and HZ goes up). if demand
exceeds supply, the engine slow down slightly (and HZ goes down).
the role of the governor is to try to keep a stable frequency while
governing the amont of fuel being added to the engine.
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 :)
the kVARs, yes. :-)
i've was also at one installation where the kVAR balancing was awry between
generators in the same power-station. the [electronic] governors were
basically 'battling' with each other but never getting in sync with each
other. the net-effect there was that we had the HZ so far out (and
oscillating) that it was evident by street lightbulbs
pulsating. (thankfully, that didn't occur on a power-grid, but at an
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.
power grids typically always have trip-alarms based on all sorts of things
-- KVars out of sync, Frequency out of range.
things tend to 'work' providing there is a large enough pool of producers
and consumers. its large load-spikes and load-dips that cause things to break.
i still find it incredible that power is as reliable as it is. (i don't
live in Califormia, so i can make that statement. :) ).
in either case, i think this discussion has probably exceeded its usefulness.
Re: 220v/50hz power rig Lincoln Dale (Sep 06)
Re: 220v/50hz power rig David Lesher (Sep 06)
Re: 220v/50hz power rig Sean Donelan (Sep 05)
Re: 220v/50hz power rig Steven M. Bellovin (Sep 06)
Re: 220v/50hz power rig Sean Donelan (Sep 06)