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Old 10.04.2013, 11:14
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Re: Global Warming - what's behind it?

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I'm not familiar with the details of the UK grid.

But look at the graph below. This one is from the US as you can easily see because of the 60Hz. It shows the grid frequency responding to a major plant (probably circa 0.5 GW) being disconnected unexpectedly, presumably due to a fault. the initial reaction of the grid is that the other rotating masses in the other power plants across the whole of the region, which is about one third of the US, slow down by about 0.1 Hz, and that provides sufficient energy to keep the grid ticking. After that the frequency picks up again as first level governors kick in on the plants that have them, forcing them to increase their power. Manual connection of standy plants is going to take minutes, and is thus far beyond the timescale of this graph. The frequency will not fully recover until these can be connected (or users can be disconnected).

So to run some simple maths over what we are seeing here, assuming this was a 0.5GW plant that went down, and assuming demand didn't change at the same time, we are seeing the rotating masses in the grid outputting circa 0.5GW within 6 seconds of the initial event. The governors don't kick in until after that, so that triangular area (from the initial event down to C) represents energy drawn from rotating masses and that is 0.5GW * 6s = 3GWs of energy that can be recovered just by slowing down rotating masses by 0.1 of a Hertz during 6 seconds. Of course if you're prepared to allow the rotating masses to slow down even more than that you can recover even more stored energy. Of course there are limits as you don't want the frequency to deviate too far. But those are criteria imposed by design choices, not by rigid impossibility. And in future the acceptable band of tolerance may have to be raised as more and more unpredictable generation comes online.

Now what about solar panels you may ask, they don't have rotating masses, so if we have too many of them, will they dimish the resilience of the grid? Well, that depends on design, as you don't need rotating masses to do this. DC link capacitors in the DC-AC converters can provide the same ride-through if properly designed.
Thanks, now I understand what you are saying. Yes, I can believe that there is enough kinetic energy in the generators to keep the frequency constant for around 6 seconds as shown in the US graph plus enough to slow the frequency drop for 6 (or more) seconds.

I just got a bit confused when you wrote " active increases in generation have a response time in the order of magnitude of 15 minutes" & with the implication that somehow there is enough kinetic energy in the generators to balance this delay.
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