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  #1201  
Old 08-09-2019, 09:25 PM
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Default Re: First World Problems

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Originally Posted by SR71 View Post
“We would have expected the system to cope with this size of loss of generation,” an Enappsys spokesman said. “This implies that there may have been [other] issues at the time of the trips.”
It's like Chernobyl all over again.
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  #1202  
Old 08-09-2019, 10:27 PM
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Default Re: First World Problems

You should get that stutter checked out SR71

Got some frequency jitters of your own going on there
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  #1203  
Old 08-10-2019, 11:23 AM
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Default Re: First World Problems

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Well that was thoroughly unnerving. A power failure!












There, that should be enough to slow down this thread until we get to a new page.
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  #1204  
Old 08-10-2019, 11:28 AM
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Default Re: First World Problems

OK no wait








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  #1205  
Old 08-10-2019, 11:31 AM
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Default Re: First World Problems

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Originally Posted by SR71 View Post
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“We would have expected the system to cope with this size of loss of generation,” an Enappsys spokesman said. “This implies that there may have been [other] issues at the time of the trips.”
I recall that we the Newnited States recently did some cyber fooling with Russia's utilities and were none too subtle about it, intentionally, in retaliation foe similar hijinx on their part. May be some do unto otherism going on.
UK power cut: National Grid promises to learn lessons from blackout - BBC News

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Industry experts said that a gas-fired power station at Little Barford, Bedfordshire, failed at 16.58, followed two minutes later by the Hornsea offshore wind farm disconnecting from the grid.
Quote:
Mr Burt said the shutdown had "nothing to do with changes in wind speed or the variability of wind" and they were confident there was no "malicious intent" or cyber-attack.
Exactly what they would say. Gotta preserve the last shreds of consumer confidence.
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  #1206  
Old 08-15-2019, 09:14 AM
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Default Re: First World Problems

So ... not a one off thing:

National Grid 'had three blackout near-misses in three months' | Business | The Guardian

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“It would be easy for National Grid to write this incident off as a fluke event, but they have actually been aware of this potential issue for many years.”
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  #1207  
Old 08-15-2019, 08:20 PM
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Default Re: First World Problems

It seems odd to me that they refer to frequency as intensity. To my thinking the 50 Hz frequency is just how many times per second the current switches direction. I would think that voltage and reactance of the load (with the resultant change in time of current relative to voltage) would have more to do with intensity than frequency.

All of that aside, I suppose it is somewhat of a problem to get all of the sources synced up and all push/pulling in the same direction at the same time, and a sudden dropout of this or that source could make it more confounding. I know there are products available to resolve those issues. It hasn't been often said the transition to renewable would be easy. It has been said to be doable, though.
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  #1208  
Old 08-15-2019, 09:33 PM
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Default Re: First World Problems

It's the load that matters: the phase angle between the voltage and current doesn't change quickly over the whole country - so the phase angle is effectively constant and the load is directly proportional to the current drawn.

When the load increases too much, or some of the generating plants drop out, then the remaining generators are unable to supply the amps demanded, and they begin to slow down slightly - all the generators all over the country are locked in phase, so when the most overloaded ones slow down, the others have to slow down too (this is automatic because if one generator is ahead on phase compared to the others, then it automatically experiences a greater share of the load, so it is quickly slowed down to match the others - it's like a whole bunch of people trying to turn the same giant wheel - it's impossible for some of them to turn it faster than others, and if they try, they will do more work than everyone else but the wheel still won't turn much faster). The slowing down of the generators reduces the frequency of the mains supply.

There are automatic control systems that monitor the frequency - which should be 50Hz in the UK. When the frequency drops towards some critical value - I think it's 49.5Hz now (it used to be 49Hz years ago), then the automatic systems start disconnecting the supply to some areas, so reducing the load and allowing the system to recover back to 50Hz.

What politicians are demanding now, is that "critical infrastructure" should have privilege if and when this happens again. I could understand it if they mean railways*, hospitals and the like, but some politicians are claiming that the whole of London should be privileged, and it should be us plebs out in the sticks that get our power cut first, so that elite Londoners are not inconvenienced. :glare:

*Railways descend into chaos when the power is off - and even after it comes back on, all the trains are in the wrong place, so it takes ages for them to get back on timetable.
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  #1209  
Old 08-15-2019, 09:47 PM
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Default Re: First World Problems

TL/DR, the slower the frequency, the more their generators are choking on the load, unable to keep up. 2% under-frequency is a lot.

They said that awkwardly and didn't explain, probably copying a source. It means intensity, only in that grid frequency is determined by the speed of the generators supplying it, and drawing power slows these generators down. The grid itself synchronizes every generator together, to a point -- pushing back minutely against any generator that's too fast or too slow.

Ideally, any slowdown is minimal, and creeps in slow enough to detect and correct by throwing on more coal or whatever. If line frequency dips too low, it means they're not keeping up with demand - and that really bad things may be happening. Things like one turbine lagging so badly that it's drawing lots of grid power just to keep in sync. Eventually it'll bow the Great Big Breakers and disconnect itself from the grid...

Which puts ten megawatts more strain on anything that's left until another station goes offline, and another, and another, in a cascade blackout.

[edit] :shakeceptumus: You beat me to it, and with better words too
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  #1210  
Old 08-15-2019, 10:16 PM
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Default Re: First World Problems

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Originally Posted by ceptimus View Post
What politicians are demanding now, is that "critical infrastructure" should have privilege if and when this happens again. I could understand it if they mean railways*, hospitals and the like, but some politicians are claiming that the whole of London should be privileged, and it should be us plebs out in the sticks that get our power cut first, so that elite Londoners are not inconvenienced. :glare:
I'm not sure I follow. Are you implying somehow that you plebs have - if I've got this right - the same rights as us elite Londoners?

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*Railways descend into chaos when the power is off - and even after it comes back on, all the trains are in the wrong place, so it takes ages for them to get back on timetable.
Not just the trains in the wrong place (which also causes unbelievable chaos with adverse weather conditions, the wrong kind of leaves on the line, etc) - there were lots of cases of trains not being able to "reboot" when the power was restored, and needing engineers to go to them in person. Who designed trains that way?
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  #1211  
Old 08-15-2019, 11:06 PM
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Default Re: First World Problems

It still seems odd that they refer to frequency as intensity. For a sinusoidal supply, duty cycle isn't a factor.



As far as reactance, it certainly is a function of what types of reactive loads are connected, and it's up to the utility to maintain a decent power factor. I recall a a day here when power was so skewed that although the power was on and things continued to operate, there wasn't enough real power to heat a soldering iron hot enough to melt the solder. It was very hot that day so there were lots of air conditioners running, creating an overall inductive load.

I decided to look at it on scope and the mains power was severely distorted, as in the picture near the top of this ad for reactance compensation equipment.

Note that one of the selling points for their harmonic filtering equipment is "Reduces unplanned outages and increases power availability".
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  #1212  
Old 08-15-2019, 11:23 PM
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Default Re: First World Problems

To tidy that up a bit, frequency is a factor in reactive power Q. For example, for the capacitive case, Q=2 pi f * v^2 * C. From the ad,

"It is the Active Power that contributes to the energy consumed, or transmitted. Reactive Power does not contribute to the energy. It is an inherent part of the ‘‘total power’’ which is often referred as “Useless Power”."

Perversely, reactive power can not be consumed, but must be generated at a very real cost, so it's an expensive thing to have.
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Old 08-15-2019, 11:31 PM
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Default Re: First World Problems

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Not just the trains in the wrong place (which also causes unbelievable chaos with adverse weather conditions, the wrong kind of leaves on the line, etc) - there were lots of cases of trains not being able to "reboot" when the power was restored, and needing engineers to go to them in person. Who designed trains that way?
That would be the manufacturers who contract with customers to have their engineers go out and reboot them as needed.
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Old 08-16-2019, 01:32 AM
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Default Re: First World Problems

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It still seems odd that they refer to frequency as intensity.
Again, I don't think they understood what they were saying, and either repeated it out of context or rephrased it in a way that sounds the same to someone non-technical but isn't.
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Old 08-16-2019, 02:27 AM
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Default Re: First World Problems

I agree. It's sort of in the why the mainstream media sucks category. Can't they find anyone who knows a little about the subject to write the story?

It's a lot like climate change reporting. It's frequently clear the reporters don't know much about climate change yet they endeavor to report on it.

Somewhere out there is a budding young electronicist who is thinking they've just learned that electrical frequency is equivalent to electrical intensity.

I think that rates as a first world problem.
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  #1216  
Old 08-16-2019, 04:06 AM
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Default Re: First World Problems

Almost every time I see a news report concerning something I really know about, I spot numerous errors and/or misunderstandings by the news reporter. This leads me to believe that all the other news items concerning things I'm not so expert about, are also likely riddled with errors.

But perhaps it's only the science and technology reporters that are stupid. For all I know, the sports and political reporters might actually understand what they're reporting.
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  #1217  
Old 08-16-2019, 09:44 AM
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Default Re: First World Problems

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This leads me to believe that all the other news items concerning things I'm not so expert about, are also likely riddled with errors.
It also leads me to believe - or should that be confirms my assumption - that 90% of readers don't know enough about anything to spot errors and blindly believe everything.

Except sport, where you may be right that reporters actually understand it, and conversely most fans violently disagree with half of what they say.
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