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Re: Cascading Failures Could Crash the Global Internet
- From: Vadim Antonov
- Date: Thu Feb 06 18:45:16 2003
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.