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Large scale UK power cuts

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sunnyjoe
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Re: Large scale UK power cuts

#243981

Postby sunnyjoe » August 13th, 2019, 12:26 pm

tjh290633 wrote:With a wind turbine there may be two options, either feather the blades if they are variable pitch (unlikely) or to turn them into a position where the wind is not driving them, such as side on to the wind instead of facing into it.

TJH


Feathering the blades (pitch control) is used for nearly all modern large wind turbines. Each blde pitches independently and only one out of three is required to bring the turbine to an idle condition (triple redundancy)

Turning the whole nacelle to face out of the wind (yaw control) is used on some small (<5kW) wind turbines but not on large wind turbines.

In the past some large wind turbines have used air brakes either in the form of flaps or more commonly rotating blade tips

So far, there is no evidence that there was a problem with the wind turbines and there is industry speculation that there was an electrical problem related to the connection to shore.

mc2fool
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Re: Large scale UK power cuts

#243982

Postby mc2fool » August 13th, 2019, 12:35 pm

gryffron wrote:Right. So if you have a nuclear power station trying to run at 50.0Hz, and the rest of the country at 49.5Hz, then it all gets out of phase and you get rather spectacular fireworks. I guess I can see that.

Nuclear power station are steam powered rotating generators and, in this sense, are no different from coal, gas, water, etc, powered rotating generators, in that they all have governors to both try and match supply with demand and keep their AC in sync with the grid. If that stretches beyond their capability and they can't do that then they'll drop out.

Some generators are not rotating but oscillating. Especially the electronic inverters used by solar/wind.

Indeed, but those, along with the convertors (all solid state now) for the undersea High Voltage DC links between GB and Ireland, France and the Netherlands, will still have means to keep in sync with the grid.

gryffron
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Re: Large scale UK power cuts

#244008

Postby gryffron » August 13th, 2019, 3:03 pm

mc2fool wrote:Nuclear power station are steam powered rotating generators and, in this sense, are no different from coal, gas, water, etc /
convertors (all solid state now) ...still have means to keep in sync with the grid.

So back to the original question then. If all the individual parts can cope with lower frequency, Why does it matter? Why is it not better to have the whole system creaking along at 48Hz rather than shutting huge parts of the system down?

This is a genuine question. I'm not trying to get at you or criticise your answers. I genuinely don't understand why it can't just run slower when overloaded.

Gryff

dspp
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Re: Large scale UK power cuts

#244020

Postby dspp » August 13th, 2019, 3:54 pm

gryffron wrote:
mc2fool wrote:Nuclear power station are steam powered rotating generators and, in this sense, are no different from coal, gas, water, etc /
convertors (all solid state now) ...still have means to keep in sync with the grid.

So back to the original question then. If all the individual parts can cope with lower frequency, Why does it matter? Why is it not better to have the whole system creaking along at 48Hz rather than shutting huge parts of the system down?

This is a genuine question. I'm not trying to get at you or criticise your answers. I genuinely don't understand why it can't just run slower when overloaded.

Gryff


All of the machinery cannot cope. The analogy of a mechanical engine backfiring and doing serious damage is correct. That's why we (i.e. us engineers who do this) don't go down that pathway.

regards, dspp

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Re: Large scale UK power cuts

#244031

Postby Urbandreamer » August 13th, 2019, 5:04 pm

gryffron wrote:
mc2fool wrote:Nuclear power station are steam powered rotating generators and, in this sense, are no different from coal, gas, water, etc /
convertors (all solid state now) ...still have means to keep in sync with the grid.

So back to the original question then. If all the individual parts can cope with lower frequency, Why does it matter? Why is it not better to have the whole system creaking along at 48Hz rather than shutting huge parts of the system down?

This is a genuine question. I'm not trying to get at you or criticise your answers. I genuinely don't understand why it can't just run slower when overloaded.

Gryff


Well "the system" is constructed to have just ONE frequency. If you connect together two lumps (known as islands to power engineers) that are not sychronised then you get huge currrent flows surging from one to the other which will rapidly melt and destroy your connection. It IS possible to install equipment to allow sections to run at different frequencies, but the capital costs are similar to a small power station. Is it ever done, well yes it is.
https://en.wikipedia.org/wiki/Electrical_interconnector
Of note is the small map of Japan. Unusually parts of Japan are 60Hz and parts 50Hz. This means that they have to build interconnectors between different regions.

Now if you mean why can't the entire grid simply drop to 30Hz then the answer is that some of the generators and some of equipment would fail. By fail I mean need replacing after the event. Simple AC motors would run slow, which means fans cooling them would run slow, hence they could burn out.

TheMotorcycleBoy
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Re: Large scale UK power cuts

#244050

Postby TheMotorcycleBoy » August 13th, 2019, 5:46 pm

Some stuff about the recent power cuts:

https://www.drax.com/energy-policy/need ... frequency/
https://www.theguardian.com/business/20 ... t-blackout

my take on the frequency thing, is that all the generators in the grid have to Phase Lock to a given frequency. In order to sync to the frequency losses which will equate to massive thermal+mechanical load being incurred. That is, if you drive nose-to-tail on the motorway you may frequently have to gas and brake.... So when Lt Barford (which is bizarrely only about 40 miles away from me, but we had no power cut), frequency fell below 49.5hz it had to be disconnected, since the health and safety people are (rightly) concerned about the consequences at the other generators either trying to lock or compensate for LB's lower frequency. Or something.

Matt

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Re: Large scale UK power cuts

#244053

Postby jfgw » August 13th, 2019, 5:57 pm

Urbandreamer wrote:Simple AC motors would run slow, which means fans cooling them would run slow, hence they could burn out.


Three-phase induction motors are often run as variable speed drives via inverters. The required voltage is proportional to speed, and the speed is primarily determined by the frequency. An inverter varies the voltage as well as the frequency.

If the mains frequency dropped significantly without a drop in voltage, induction motors connected to that supply could burn out. Consider a 400V 50Hz induction motor being supplied with 45Hz. This would be ok if the voltage was reduced to 360V, however, if the voltage was kept at 400V, the motor would draw a considerably higher current than it is rated for. Even under no load, this could easily be enough to burn out the motor (although, hopefully, a circuit breaker would trip first).

Julian F. G. W.

sunnyjoe
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Re: Large scale UK power cuts

#244058

Postby sunnyjoe » August 13th, 2019, 6:15 pm



Good links thanks. The Drax link leads to this link about inertia, which we discussed earlier in this thread
https://www.drax.com/technology/shock-a ... id-stable/

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Re: Large scale UK power cuts

#244060

Postby vagrantbrain » August 13th, 2019, 6:31 pm

88V8 wrote:I suspect the power cuts were partly the EU's fault.

But before I get onto that, In the good old days rail signals were mechanical, no electric needed, and diesels and steam don't need electric either. So this problem is self-inflicted.

But back to the EU.
As has been said, the CEGB ran with plenty of reserve. Hot reserve that could be brought online quickly, and spinning reserve that could be switched in immediately. That costs, and post-privatisation it was allowed to decline.

In 2014, the Govt recognising the inherent dodginess of 'green' energy, initiated a scheme to incentivise greater resilience in the system, and this was approved by the EU Commission although why we have to ask them for approval of our domestic arrangements is another matter.
https://europa.eu/rapid/press-release_IP-14-865_en.htm

Then in 2018 the European Court ruled that the scheme amounted to illegal state aid, and must be terminated.
https://notalotofpeopleknowthat.wordpre ... -auctions/
So our govt instead of telling them where to go, cravenly did as instructed.

Post 31 October, I expect a suitable arrangement to be reinstated.

Funny that the pro-Remain BBC hasn't been publicising this aspect :}

V8

PS In the interests of balance, I must observe that the scheme was intended to provide winter capacity, so I cannot be sure that it would have helped during August. But never mind. Mustn't waste an opportunity to bash the interfering EU.


I'm not a fan of consipiracy theories but this other page made quite interesting reading: https://notalotofpeopleknowthat.wordpre ... us-energy/

In short, the company that led the legal challenge was newly formed and seems to exist only to make money from exploiting instability in the grid - instability introduced by the suspension of the capacity market after their court action. The secondary aim seems to be to force the situation that when the wind doesn't blow and the sun doesn't shine the UK simply uses less electricity. Quite a noble aim but it doesn't sit well with me that militant ecowarriors are using the legal system to push their political agenda, while simultaneously getting rich from the problems they caused.

JohnB
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Re: Large scale UK power cuts

#244062

Postby JohnB » August 13th, 2019, 6:39 pm

The Americans used to run with 3ish independent networks, with a big interconnect near Roswell, obviously to power the alien technology if they ever got it working!

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Re: Large scale UK power cuts

#244071

Postby dspp » August 13th, 2019, 7:22 pm

vagrantbrain wrote:
88V8 wrote:I suspect the power cuts were partly the EU's fault.

But before I get onto that, In the good old days rail signals were mechanical, no electric needed, and diesels and steam don't need electric either. So this problem is self-inflicted.

But back to the EU.
As has been said, the CEGB ran with plenty of reserve. Hot reserve that could be brought online quickly, and spinning reserve that could be switched in immediately. That costs, and post-privatisation it was allowed to decline.

In 2014, the Govt recognising the inherent dodginess of 'green' energy, initiated a scheme to incentivise greater resilience in the system, and this was approved by the EU Commission although why we have to ask them for approval of our domestic arrangements is another matter.
https://europa.eu/rapid/press-release_IP-14-865_en.htm

Then in 2018 the European Court ruled that the scheme amounted to illegal state aid, and must be terminated.
https://notalotofpeopleknowthat.wordpre ... -auctions/
So our govt instead of telling them where to go, cravenly did as instructed.

Post 31 October, I expect a suitable arrangement to be reinstated.

Funny that the pro-Remain BBC hasn't been publicising this aspect :}

V8

PS In the interests of balance, I must observe that the scheme was intended to provide winter capacity, so I cannot be sure that it would have helped during August. But never mind. Mustn't waste an opportunity to bash the interfering EU.


I'm not a fan of consipiracy theories but this other page made quite interesting reading: https://notalotofpeopleknowthat.wordpre ... us-energy/

In short, the company that led the legal challenge was newly formed and seems to exist only to make money from exploiting instability in the grid - instability introduced by the suspension of the capacity market after their court action. The secondary aim seems to be to force the situation that when the wind doesn't blow and the sun doesn't shine the UK simply uses less electricity. Quite a noble aim but it doesn't sit well with me that militant ecowarriors are using the legal system to push their political agenda, while simultaneously getting rich from the problems they caused.


See viewtopic.php?p=181404#p180706

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Re: Large scale UK power cuts

#244077

Postby mc2fool » August 13th, 2019, 8:03 pm

gryffron wrote:
mc2fool wrote:Nuclear power station are steam powered rotating generators and, in this sense, are no different from coal, gas, water, etc /
convertors (all solid state now) ...still have means to keep in sync with the grid.

So back to the original question then. If all the individual parts can cope with lower frequency, Why does it matter? Why is it not better to have the whole system creaking along at 48Hz rather than shutting huge parts of the system down?

This is a genuine question. I'm not trying to get at you or criticise your answers. I genuinely don't understand why it can't just run slower when overloaded.

You're focussing on the wrong thing here. The problem is overloaded, the frequency is just a symptom of that. Like most things, the electricity system can cope with a small amount of overload, within tolerance limits, but beyond that things start to break.

Think of trying to pull a heavy load with a car. You know that a heavier load will slow you down but when you get overloaded your concern isn't speed but busting an axle or similar with the effort.

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Re: Large scale UK power cuts

#244080

Postby Alaric » August 13th, 2019, 8:19 pm

vagrantbrain wrote: The secondary aim seems to be to force the situation that when the wind doesn't blow and the sun doesn't shine the UK simply uses less electricity.


Which means voluntary or compulsory power cuts.

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Re: Large scale UK power cuts

#244086

Postby dspp » August 13th, 2019, 8:35 pm

Alaric wrote:
vagrantbrain wrote: The secondary aim seems to be to force the situation that when the wind doesn't blow and the sun doesn't shine the UK simply uses less electricity.


Which means voluntary or compulsory power cuts.


No.

It means either paying upfront to add extra generating capacity, or paying upfront to add extra storage capacity, or paying upfront to add extra (and willing) loadshed takers (ak negawatt subscribers). The latter have always existed, but were seldom given much attention. Which of the three, or which combination of the three, is a economic optimisation problem, and of course a political (and legal) bunfight because the $$$ in play attract the usual suspects.

- dspp

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Re: Large scale UK power cuts

#244091

Postby scotia » August 13th, 2019, 9:13 pm

A technical fact that doesn't seem to have been discussed is the way in which frequency is used to balance the generation and load. In governor-controlled generators (e.g steam and hydro), if the frequency drops, then the generator slows, and the governor attempts to correct this. If it is determined to do it all by itself, it would fully open the inlet valve, and if every generator does this, then the frequency would go too high, all the valves would shut and we would oscillate back and forward. Instead all of the governors are set with a droop - which is the percentage frequency change that will open the valve from fully shut to fully open. So if the droop is 2%, then this full load action would take place on a 1Hz change in frequency. Or being more realistic, if a 0.1Hz fall in frequency takes place, then the generator would produce 10% more power. In the good old days when the vast majority of generating plant was controllable in this way, then fast fluctuations in demand were handled automatically with this mechanism, and the loading engineers at Grid Control could arrange on a slower time scale for more or less generation to be requested if the frequency was steadily drifting in a particular direction - or indeed they could also take such action if a significant change in load was expected - at the end of a particularly popular TV show.
But times have changed! The bulk of generation now fits less easily into such an automatically flexible generation scenario. And with numerous different owners of generation and load, and the transmission system operated by a further party - with all to be satisfied via some form of contract bidding, its a mystery to me how the system works at all.

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Re: Large scale UK power cuts

#244094

Postby Alaric » August 13th, 2019, 9:21 pm

dspp wrote:It means either paying upfront to add extra generating capacity, or paying upfront to add extra storage capacity, or paying upfront to add extra (and willing) loadshed takers (ak negawatt subscribers).


What is the difference apart from the fancy name between a "loadshed taker" and a voluntary power cut? Isn't it suggested that's what smart meters are partly about, to convert domestic consumers into "loadshed takers"?

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Re: Large scale UK power cuts

#244124

Postby servodude » August 14th, 2019, 2:48 am

Alaric wrote:
dspp wrote:It means either paying upfront to add extra generating capacity, or paying upfront to add extra storage capacity, or paying upfront to add extra (and willing) loadshed takers (ak negawatt subscribers).


What is the difference apart from the fancy name between a "loadshed taker" and a voluntary power cut? Isn't it suggested that's what smart meters are partly about, to convert domestic consumers into "loadshed takers"?


I think the point was that "loadshedding" (or Automated Demand Response) was not the only option
- It's needed only if you cannot generate sufficient power or have it avaialable in storage

well that's from the engineering side of it, more likely it's going to be driven in the future by the ability or willingness to pay the spot price (or conversley holding your power until you want to sell)

- sd

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Re: Large scale UK power cuts

#244178

Postby sunnyjoe » August 14th, 2019, 10:36 am

scotia wrote:A technical fact that doesn't seem to have been discussed is the way in which frequency is used to balance the generation and load. In governor-controlled generators (e.g steam and hydro), if the frequency drops, then the generator slows, and the governor attempts to correct this. If it is determined to do it all by itself, it would fully open the inlet valve, and if every generator does this, then the frequency would go too high, all the valves would shut and we would oscillate back and forward. Instead all of the governors are set with a droop - which is the percentage frequency change that will open the valve from fully shut to fully open. So if the droop is 2%, then this full load action would take place on a 1Hz change in frequency. Or being more realistic, if a 0.1Hz fall in frequency takes place, then the generator would produce 10% more power. In the good old days when the vast majority of generating plant was controllable in this way, then fast fluctuations in demand were handled automatically with this mechanism, and the loading engineers at Grid Control could arrange on a slower time scale for more or less generation to be requested if the frequency was steadily drifting in a particular direction - or indeed they could also take such action if a significant change in load was expected - at the end of a particularly popular TV show.
But times have changed! The bulk of generation now fits less easily into such an automatically flexible generation scenario. And with numerous different owners of generation and load, and the transmission system operated by a further party - with all to be satisfied via some form of contract bidding, its a mystery to me how the system works at all.


All generators connected to the transmission system or who have a contract with National Grid are obliged to have the capability to provide governor control as you describe above. National Grid decides which generators it will require and pay to provide governor service and this selection changes dynamically through the day. Governors are normally operated with a 4% droop.

Load and frequency fluctuations are getting faster, so the systems you described for managing fast fluctuations would probably have responded in 10 to 30 seconds. National Grid is now contracting with some battery operators to deliver services in less than 1 second

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Re: Large scale UK power cuts

#244180

Postby sunnyjoe » August 14th, 2019, 10:44 am

vagrantbrain wrote:
I'm not a fan of consipiracy theories but this other page made quite interesting reading: https://notalotofpeopleknowthat.wordpre ... us-energy/

In short, the company that led the legal challenge was newly formed and seems to exist only to make money from exploiting instability in the grid - instability introduced by the suspension of the capacity market after their court action. The secondary aim seems to be to force the situation that when the wind doesn't blow and the sun doesn't shine the UK simply uses less electricity. Quite a noble aim but it doesn't sit well with me that militant ecowarriors are using the legal system to push their political agenda, while simultaneously getting rich from the problems they caused.


I am no fan of conspiracy theories either and this one fits the bill perfectly. One man's "exploiting stability" is another man's "providing valuable stabilising services".

Not a fan of Tempus, nor a fan of climate change deniers / inactivists.

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Re: Large scale UK power cuts

#244189

Postby scotia » August 14th, 2019, 11:19 am

sunnyjoe wrote:All generators connected to the transmission system or who have a contract with National Grid are obliged to have the capability to provide governor control as you describe above. National Grid decides which generators it will require and pay to provide governor service and this selection changes dynamically through the day. Governors are normally operated with a 4% droop.
Load and frequency fluctuations are getting faster, so the systems you described for managing fast fluctuations would probably have responded in 10 to 30 seconds. National Grid is now contracting with some battery operators to deliver services in less than 1 second

Many thanks for your response. Its Interesting - I'm long out of touch. In my day conventional fossil-fueled steam plant could respond almost immediately - if the stream valve was on governor control (and was not fully open). Then as the steam pressure fell, before the boiler firing picked up, there was a dip which theoretically hydro could fill. The generators I worked on were set with a droop of around 3% - but I thought in my example that 2% would provide more easily digested numbers. Is 4% now standard?
How does solar provide governor control? And what about nuclear - I thought it ran at constant output. How does governor control work on the modern two-stage gas powered plant? Again, its a long, long time since I worked with gas turbine generators - effectively a Rolls Royce Avon turbojet who's output drove a big fan. Its only a little bit of an exaggeration to say that you got power or no power!
Its also interesting to see that local governor control of the system is still fundamental. I would have thought that by now, with widespread communications links, automatic generation changing could have been executed from Grid Control.


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