[55677] in North American Network Operators' Group
Re: Cascading Failures Could Crash the Global Internet
daemon@ATHENA.MIT.EDU (N. Richard Solis)
Thu Feb 6 19:14:02 2003
Date: Thu, 6 Feb 2003 19:13:15 -0500
From: "N. Richard Solis" <nrsolis@aol.net>
To: "Vadim Antonov" <avg@kotovnik.com>
Cc: nanog@merit.edu
In-Reply-To: <Pine.LNX.4.21.0302061514160.18737-100000@gato.kotovnik.com>
Errors-To: owner-nanog-outgoing@merit.edu
<br>
Vadim Antonov wrote:
<p> </p>
<blockquote type="cite"
style="border-left: thin solid blue; padding-left: 10px; margin-left: 0pt;"> <tt> <br>
<br>
On Thu, 6 Feb 2003, N. Richard Solis wrote: <br>
<br>
> The main cause of AC disruption is a power plant getting out of
phase <br>
> with the rest of the power plants on the grid. <br>
<br>
This is typically a result of sudden load change (loss of transmission <br>
line, short, etc) changing the electromagnetic drag in generators, and, <br>
therefore, the speed of rotation of turbines. <br>
<br>
> When that happens, the plant "trips" of goes off-line to protect
the <br>
> entire grid. <br>
<br>
Some difference in phase is tolerable, the resulting cross-currents <br>
generate heat in the trasmission lines and transformers. <br>
<br>
It is not sufficient to disconnect a generator from the grid. Since
water <br>
gates or steam supply can not be closed off fast, the unloaded turbine <br>
would accelerate to the point of very violent self-destruction. So the <br>
generators are connected to the resistive load to dump the energy
there. <br>
Those resistors are huge, and go red-hot in seconds. If a gate or
valve <br>
gets stuck, they melt down, with the resulting explosion of the
turbine. <br>
<br>
> You lose some generating capacity but you dont fry everything on
the <br>
> network either. <br>
</tt><tt><br>
Well... not that simple. A plant going off-line causes sudden load <br>
redistribution in the network, potentially causing overload and phase <br>
shifting in other plants, etc. A cascading failure, in other words. <br>
</tt></blockquote>
Yeah yeah yeah. I know that everything isn't simple. I actually
worked at a power plant so none of this is new to me. Can cascading
failures occur? Yes. Witness the Great Blackout in NYC. My point was
that there are places where the electrical network is designed to "blow
the bolts" to TRY and protect everything. Does it work? Most of the
time, yes. All of the time? NO.<br>
<br>
It is a complicated problem but you'd be suprised at how fast things
can happen when you HAVE to keep the system running. There is a
tremendous amount of skill concentrated in that field and they do a
good job of keeping everything running well. How many turbine
overspeed events do you get notified about? Those guys can do a rapid
shutdown of a plant VERY quickly. Turning it back on though is a whole
different matter. We needed to have one station operating so that we
could actually get the big one going. Then we'd take the small one
offline and bring it back up quickly to handle specific load peaks.<br>
<br>
The loss of a single transmission line isn't going to cause a whole
station to trip. If you're losing a bunch though, you've probably got
lots of other problems to worry about.<br>
<br>
<blockquote type="cite"
style="border-left: thin solid blue; padding-left: 10px; margin-left: 0pt;"><tt><br>
--vadim <br>
<br>
<br>
</tt> </blockquote>
