London power outage(s)

[Andy Burns]

[newshound]

All credit to them for providing an accessible display.

[Andy Burns]

turns out it was a substation fire

[Scott]

How do the generators cope with a sudden reduction in demand? What happens in the period between the fall in demand and the shutting down of the power station / windfarm? What's to prevent a surge in voltage for all those not affected by the power cut?

[Fredxx]

There is a huge inertia in the system, comprising of generators and motors that keep the frequency within limits.

Voltage is a secondary artefact for load changes. Where necessary transformer tap changes are made.

I recall when there was a significant outage a year or two ago that mains frequency did go out of limits.

[newshound]

Which generators do you mean? You mean ones connected to the National Grid? The point about the national grid is that it all runs at the same frequency and phase. Every attached generator is at the same frequency too (the phase may lag or lead slightly). So if a local area disconnects, because a substation trips, the grid frequency rises. All the generators sense frequency. I guess solar panels and windmills disconnect, if it goes too high, and windmill brakes come on. For thermal generators, the steam input is throttled down, so their electrical output reduces.

There is a lot going on to maintain grid stability at local and at large scales.

As long as there is enough thermal plant on the bars (this has plenty of stored energy in the rotating parts), the frequency stays within defined margins. If a big fault occurs then other protection measures kick in, like disconnecting areas near the fault if the frequency drops too far. Steam turbines all have overspeed trips to prevent mechanical failure, so "high frequency" faults cut the power supply.

[newshound]

Those of us of a certain age will remember lights getting dimmer in the winter tea-time peak, and then TV screens turning into letterboxes.

Indeed. A big windfarm tripped, I think there was a second near-simultaneous fault. The grid normally carries "running spare", thermal plant operating at below its maximum output, in that case the lost load exceeded the spare capacity. There are also "current limits" on transmission lines for the case where all the supply is at one end of the country and all the load at the other.

[Andy Burns]

none of the grid frequency monitors seemed to notice 38,000 people being cut off today, e.g.

[newshound]

Interesting that the distribution is bimodal. I suppose that is because there is a "dead band"?

[Andy Burns]

Yes, I don't think it had the frequency distribution graph last time I looked.

I suppose as soon as you gain or lose a few cycles, you've got to lose or gain a few the opposite way to tip the cycle count back to 360,000/day for all those synchronous clocks.

[SH]

errr....

I make that 50 Hz x 60 seconds x 60 minutes x 24 hours = 4,320,000 cycles per day

[Andy Burns]

that'll be because my 'four' key is buggered

[The Natural Philosopher]

Unfortunately none of that inertia, which is not huge, but barely adequate, is conferred by roof top solar panels, windmill inverters or DC links to other countries.

Hence the need for batteries.,

High levels of 'renewable' energy make the grid inherently unstable, frequency wise.

Worse, if the frequency does drop out of limits, all the renewable energy and interconnectors will disconnect, crashing (part of) the grid completely. This has already happened once.

yes...see above.

[williamwright]

Is that the number of bicycles stolen in Cambridge?

Bill

[Andrew]

Lots of domestic solar panels also shut down for safety once the grid power vanished. Double whammy.

[newshound]

Time for a new keyboard! I don't have that embarrassment with the sticky "d" key.

[Andy Burns]

Not so easy on a laptop, it's the 4 Z \ Fn and Vol+ keys, so I suspect one row/column of the scan matrix, it did briefly work again, so probably needs degunging ...

[newshound]

Fair point. Although my "work" laptop is usually hooked up to a proper screen, and then I use a bluetooth keyboard and mouse from Perixx, which frees up desk space.

[Tim+]

Probably not as hard as you think. Lots of helpful videos on YouTube and keyboards are surprisingly reasonable on eBay.

Tim

[Andy Burns]

It's a fairly rare* laptop, I have had it apart once to replace NVMe, but it really doesn't like to be taken apart ...

[*] Huawei Matebook X (not the X pro) I can only see one and it's in Italy.