[AusNOG] Lessons Learned From SA Blackout

[Nick Stallman]

That implies that you want to continue powering the load. If load 
shedding could occur quicker and more automatically you'd just ditch 
excess load available power < required power at any given point.

I believe I also heard that the still powered sections surged when their 
load was very suddenly removed (current flowing through an inductor 
wants to stay flowing) and that would have also tripped additional 
protection circuitry.
This one would actually be very dangerous to anything connected to that 
side of the grid if the surge wasn't quenched very quickly and that was 
probably done just by pulling the plug.

So both sides of a downed transmission tower can trip even if they still 
have power, but for different reasons.


On 30/09/16 19:22, Ben Buxton wrote:
>
>
> On Fri., 30 Sep. 2016, 18:44 Mark Newton, <newton at atdot.dotat.org 
> <mailto: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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-- 
Nick Stallman
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The Real Estate Web Developers
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