[AusNOG] Lessons Learned From SA Blackout

[Ben Buxton]

On Fri., 30 Sep. 2016, 18:44 Mark Newton, <newton at atdot.dotat.org> wrote:

>
> It shouldn’t have happened like that: The network was working before the
> transmission lines fell over, and it’s working now while they’re still on
> the ground, unrepaired. The question is why it couldn’t work during the
> state transition, and I expect that’s what most of the upcoming
> investigation and resulting post-mortem will be concentrating on.
>

When a whole bunch of power suddenly stops being fed into the network by
say a toppling tower, the rest of the network has to supply it. Some
inter-network feeds trip because they aren't provisioned to provide the
sudden relative demand. Remaining generators that could normally scale to
handle the load were running at lower power but suddenly found themselves
with a much bigger relative demand (ie within a second).

Just like a car engine, they immediately start to slow down from the
increased load. The slowdown caused a frequency shift which turns into a
phase shift which is Really Bad News. Protection circuits trip.

No matter how fast operators react, it always takes some time to turn up
the thermal source. That time will be greater than the protection trip
time. Thus, state goes on the blink.

The reason power is restored now despite the towers still being down is
that they would have made sure the available generators were cranked to
supply the full demand before turning the switch back on.

(The above is my armchair EE hypothesis but based on casual studying of
power systems in general. Plus much of the theory is fundamentally the same
as IP networking)


Bb
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