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Author Topic: Eastern UK Power cuts  (Read 4866 times)
oliver90owner
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« Reply #30 on: August 20, 2019, 11:56:57 AM »

I believe the grid has been operating for some time with only a 5% safety net of available standby generation.

Clearly a couple of ‘drop-outs’ in mid-winter, when the 5% is 2GW, might have been absorbed, but the question of surplus available generation at very short notice has been looked at carefully over the last couple of years.  The general consensus on the consumer side seems to be ‘not enough’.  They are cutting the safety net margins too tight, but spinning reserve costs money.

While some on this forum have been forecasting black-outs, they have avoided them - up until recently.  I, for one, will be making sure my home generator is in working order from now on. 

I wonder how long it would take the whole grid to restart if there was to be a very serious black-out and a ‘cold’ restart was necessary?  Any estimates?
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Philip R
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« Reply #31 on: August 20, 2019, 07:17:46 PM »

Following the 1987 hurricane, the southeast was islanded from the rest of the grid. It was isle of grain Ps that started the system runup in the SE with more units synchronising. It was re synched to the rest of the uk the following day.

A nationwide shutdown would require the grid to be reenergised with all loads disconnected. Then as generation availibility increases, the loads can be reconnected.
The former coal and oil plants had auxilluary gas aero derivative gas turbines for black starting. Many newer CCGTs do not,relying on grid power for restarting,as with the AGR reactors too.
I do not know if RWE is retaining the Avon gts at former Didcot A Ps?
(watched the 3 flower pots being felled on Sunday morning and the flashover too from Hagbourne hill,)

Philip R
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splyn
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« Reply #32 on: August 21, 2019, 01:04:34 AM »

National Grid's interim report:

https://www.nationalgrideso.com/document/151081/download

The detailed timeline of events starts on page 10.

The sequence at Little Barford is interesting:

Quote
Near instantaneous to the deloading at Hornsea, Little Barford Gas Power Station tripped with the immediate loss of the Steam Turbine (STC1) unit (244MW). RWE have confirmed that after approximately 1 minute the first gas turbine tripped due to excessive steam pressure in the steam bypass system. This trip occurred automatically and shut the gas turbine down. The second gas turbine was manually tripped by the by RWE operational staff in response to high steam pressures around 30 seconds later.

I wonder why STC1 tripped but neither of the gas turbines did? From the report:

Quote
The causes provided by RWE for the initiation of the trip of Little Barford steam turbine (ST1C) was the discrepancy between the three speed signals.

So why only trip out STC1 and not all three? Do all the generators have independant protection controls such that the disturbances from the lightning strike and/or the protection opening both ends of the Eaton Socon - Wymondley circuit reached the STC1 protection unit's threshold but not those of the GTs?

Perhaps there is an opportunity for more sophisticated protection controls - when STC1 tripped it was inevitable that both gas turbines had to be shut down whereas had one of the gas turbines tripped instead, then the other gas turbine and the steam turbine presumably would have carried on operating (albeit with lower STC1 output) as the steam pressure wouldn't have risen, which might have just been enough to avert the major outage. Another possibility is that STC1 could have been brought back online rapidly (automatically within a few hundred milliseconds perhaps) when the control system realised that it was a false alarm given that both gas turbine were still generating normally for at least another minute and presumably the grid connection wasn't overvoltage.

I guess the probability of such an event is so low that it didn't justify the investment when built, except that with the narrow reserve margins now being used, the increasingly variable generation and loss of rotational inertia in the grid that efforts to minimize avoidable consequencial loss of generation could change things. It may be quite a bit cheaper than building and maintaining more reserve generation.

Similarly with Hornsea which lost 737MW but managed to maintain 62MW. Presumably it wouldn't have taken the control systems long to realise the descrepancy and thus had the opportunity to reconnect asap (especially if the turbines are direct drive types with rapid responding invertors syncing to the grid).  The report does say that control parameters/thresholds etc. are being rethought but I'm guessing that automatic restoration still won't be possible due to a failsafe ethos whereby restoration is down to human operator to evaluate the cause of the trip and only reconnect when certain that it is safe to do so. Except that with this incident it was a fail-dangerous result given the large scale blackout with potential for loss of life due to accidents and loss of essential services including Ipswich hospital.
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azps
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« Reply #33 on: August 21, 2019, 06:59:08 AM »

Except that with this incident it was a fail-dangerous result given the large scale blackout with potential for loss of life due to accidents and loss of essential services including Ipswich hospital.

Those failures weren't down to Little Barford, Hornsea or National Grid, though. Just as with the train disruptions, those were failures due to other systems not performing as they should when the demand-curtailment signal went out. Maybe some people had gone for cheaper, interruptible contracts when they really shouldn't have. Maybe some big consumers had failed to test and maintain their backup systems.

This isn't too surprising after decades of cheese-paring. But more investigations are needed (and are ongoing) to work out why those downstream failures happened.
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dan_b
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« Reply #34 on: August 21, 2019, 07:49:45 AM »

Makes you realise how incredibly complex modern infrastructure is doesn’t it, and actually how little resilience any country has anywhere to anything on a large scale. 
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oliver90owner
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« Reply #35 on: August 21, 2019, 08:39:02 AM »

Except that with this incident it was a fail-dangerous result given the large scale blackout with potential for loss of life due to accidents and loss of essential services including Ipswich hospital.

Those failures weren't down to Little Barford, Hornsea or National Grid, though. Just as with the train disruptions, those were failures due to other systems not performing as they should when the demand-curtailment signal went out. Maybe some people had gone for cheaper, interruptible contracts when they really shouldn't have. Maybe some big consumers had failed to test and maintain their backup systems.

This isn't too surprising after decades of cheese-paring. But more investigations are needed (and are ongoing) to work out why those downstream failures happened.

Agree entirely.  Carp journalism (hype, instead of truth?) and still continuing weeks after the event.

In the olden days, if you ran out of petrol for your car, you replenished the tank and started off again.  Diesels were a bit more tricky - they needed bleeding, so there was more reliance on the owner filling up before the event occurred.  For the last thirty years diesel engines have had self-bleed injection pumps (common rail engines are different again)

Trains that momentarily ‘run out of power’ that require attention from non-present engineers is a ridiculous situation.  The train operators should crawl back in their shells, apologise and do the right thing - sort out their trains.  Instead it is blamed on the very short term power outage.

Same with the hospital.  Power can fail - that is why they have back-up generators - but those generators must be serviceable at all times - there is usually a second unit available for times when one unit is being maintained - but clearly this one was not (apparently the starting battery was discharged!).  Smacks of cost-cutting or emergency kit not being properly monitored!

I believe our local hospital, back in the old days (40 years, or more, ago), was connected to the Mirrlees Blackstone works for times when the grid power failed.  They had plenty of reserve power!

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Nickel2
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« Reply #36 on: August 21, 2019, 09:49:19 AM »

Interesting read! Further to the above, the bbc reports the following:
https://www.bbc.co.uk/news/business-49402296
If the power companies are fined, where does the money come from to pay the fines? (answers on a postcard, etc)
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Philip R
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« Reply #37 on: August 21, 2019, 10:00:57 AM »

At Ipswich hospital, all the 11 diesels started.
The fault was a flat battery associated with the switchboard control supplies.
The bbc article infers that the battery is a small sealed lead acid type like that in a domestic burglar alarm.

As for the failed train sets. Very poor procurement specification and testing imo. Had the pantograph dropped of the wire due to loss of compressed air and the air receivers were not full? Anyone here know? All down to cost again. But I hope NG do not pay compo to the train companies for this one.

Had RWEs little barford dream turbine been islanded by fault clearance on the grid, the shaft line could move axially away from the thrust bearing by a few more thou. This could have caused the speed discrepancy and tripped the steam turbine.
Usually though, there is a 2 out of three 3 system, do unlikely to fail unless one speed channel was u/s.

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dan_b
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« Reply #38 on: August 21, 2019, 10:07:16 AM »

So really a cascading failure of individually minor issues but all of which created a much bigger issue
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Philip R
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« Reply #39 on: August 21, 2019, 10:10:10 AM »

Regarding fines, I think ofgem should look hard at themselves. Their regulation has allowed these margins to be reduced.

Regarding system resiliance. Increased HVDC reliance  does not help as it reduces inertia on the Uk grid and the ability of other Uk generators to produce transient and subtransient currents when required to .

Overseas utilites cannot provide extra load through Hvdc at an instant. When all the battery backup arrives, then it will help, but some needs to be at grid level too.

Philip R.
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marshman
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« Reply #40 on: August 21, 2019, 12:02:18 PM »

Bear with me here as I am not a "grid" expert like some of you guys but I have a question.

As more renewables (wind, solar) etc. are added to the generation mix and more and more battery banks are added for short term "frequency response" we loose the "mechanical" inertia from the "old style" generators. As I understand it this means we did have a physical mass spinning which could not instantaneously change speed thus giving some frequency stability and very short term extra capacity to the grid.  Are there any schemes actual, proposed or being researched to add what I will call "spinning mass reserve" to the grid. I am thinking essentially some mahoosive flywheels driven by a motor/alternator permanently synchronised to the grid. Once up to speed the energy consumption should be minimal, but in the event of a grid failure would provide the kind of mechanical inertia that the "old style" stations gave and help mitigate against the recent incident happening again.

Roger
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« Reply #41 on: August 21, 2019, 12:23:38 PM »

Flywheels for energy storage and frequency response is an area of research yes - has kind of been overtaken in the market by the sexiness and energy density of batteries, but there are some installations around

https://www.solarpowerportal.co.uk/news/uk_to_host_europes_largest_battery_flywheel_system

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« Reply #42 on: August 21, 2019, 01:15:57 PM »

Flywheels for energy storage and frequency response is an area of research yes - has kind of been overtaken in the market by the sexiness and energy density of batteries, but there are some installations around

https://www.solarpowerportal.co.uk/news/uk_to_host_europes_largest_battery_flywheel_system



Not sure that is the same thing as I was trying to describe. That is just another form of energy storage. I assume to get the energy out it drives a generator which feeds into the battery inverter/grid connection so the rotational speed of the "flywheel" is not necessarily linked to the grid frequency - or is it? . I am assuming it does not use the rotational inertia to maintain the frequency. A large conventional station has spinning generators producing say 250MW directly at the grid frequency - with the associated rotating mass having considerable physical inertia which helps stabilise the grid frequency. Anything connected to the grid via some form of inverter -be it a small domestic PV installation through to large windfarms use the grid as frequency reference and just follow the grid frequency (with limits on upper and lower bounds and one assumes rate of change as well) - they do not try to maintain the current (excuse the pun) frequency - or do I have that wrong.

Roger
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« Reply #43 on: August 21, 2019, 02:00:07 PM »

I am no expert either but did read that the Tesla batt in S. Australia can deliver full capacity in 120 millisecs and has done when the coal fired stations dropped out. I understand this is FAR quicker than response from spinning reserve and is a huge $saving.  This is so successful that other grid tie batts are being built. 
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marshman
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« Reply #44 on: August 21, 2019, 02:23:02 PM »

I am no expert either but did read that the Tesla batt in S. Australia can deliver full capacity in 120 millisecs and has done when the coal fired stations dropped out. I understand this is FAR quicker than response from spinning reserve and is a huge $saving.  This is so successful that other grid tie batts are being built. 

I wasn't really meaning spinning reserve as such - especially as that usually implies FF generation which we need to do away with - I am thinking about frequency control/stability - which large rotating masses inherently provide but "free running" electronic inverters don't (or do they?). I guess Dinorwig provides some but at the time  of the last incident I would assume it was already running flat out).  I understand that large battery banks such as the Tesla installations are far quicker in their response and can/are better in many ways than spinning reserve BUT I would add a caution that if they respond too quickly there is a danger of overshooting resulting in too much generation on the grid. Trouble is I understand some of the principles and am familiar with control systems, damping factors etc. but with something as large as the grid my mind gets a bit overwhelmed by the interactions of all the connected forms of generation, their response times and what happens when big loads/generators come in or drop out.  120ms is 6 cycles at 50Hz - how quickly do things start to go wrong and relays start tripping out (not sure what the correct terminology is).

Sorry to drift a bit of topic but I do find it an interesting subject and something I feel I ought to be able to "wrap my head around" - I gave up trying to understand the econics bit (CFD's etc  Smiley )

Roger
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