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Re: Cascading Failures Could Crash the Global Internet
From: Vadim Antonov <avg () kotovnik com>
Date: Thu, 6 Feb 2003 15:25:43 -0800 (PST)



On Thu, 6 Feb 2003, N. Richard Solis wrote:

The main cause of AC disruption is a power plant getting out of phase
with the rest of the power plants on the grid.

This is typically a result of sudden load change (loss of transmission
line, short, etc) changing the electromagnetic drag in generators, and,
therefore, the speed of rotation of turbines.

When that happens, the plant "trips" of goes off-line to protect the
entire grid. 

Some difference in phase is tolerable, the resulting cross-currents
generate heat in the trasmission lines and transformers.

It is not sufficient to disconnect a generator from the grid. Since water
gates or steam supply can not be closed off fast, the unloaded turbine
would accelerate to the point of very violent self-destruction.  So the
generators are connected to the resistive load to dump the energy there.
Those resistors are huge, and go red-hot in seconds.  If a gate or valve
gets stuck, they melt down, with the resulting explosion of the turbine.

You lose some generating capacity but you dont fry everything on the
network either.

Well... not that simple.  A plant going off-line causes sudden load
redistribution in the network, potentially causing overload and phase
shifting in other plants, etc.  A cascading failure, in other words.

--vadim


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