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<p>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.</p>
<p>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.<br>
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.</p>
<p>So both sides of a downed transmission tower can trip even if
they still have power, but for different reasons.<br>
</p>
<br>
<div class="moz-cite-prefix">On 30/09/16 19:22, Ben Buxton wrote:<br>
</div>
<blockquote
cite="mid:CAA05ne=8w739ie5omWTHJEMD9oiY7FUP-Nt_g9=AQ3z05qb1gw@mail.gmail.com"
type="cite"><br>
<br>
<div class="gmail_quote">
<div dir="ltr">On Fri., 30 Sep. 2016, 18:44 Mark Newton, <<a
moz-do-not-send="true" href="mailto:newton@atdot.dotat.org">newton@atdot.dotat.org</a>>
wrote:<br>
</div>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex"><br>
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.<br>
</blockquote>
</div>
<div><br>
</div>
<div>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).</div>
<div><br>
</div>
<div>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.</div>
<div><br>
</div>
<div>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.</div>
<div><br>
</div>
<div>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.</div>
<div><br>
</div>
<div>(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)</div>
<div><br>
</div>
<div><br>
</div>
<div>Bb</div>
<div><br>
</div>
<div><br>
</div>
<div><br>
</div>
<div class="gmail_quote">
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
</blockquote>
</div>
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</blockquote>
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