Iberien Peninsular Blackout

There's also the V/f transformer saturation limitations. 

Which 'classical' frequency - power relationship were you thinking (i.e. wondering about hidden assumptions that bring frequency into the I.ac * V.ac = P.ac ?)

the classical relationship that a power shortfall leads to a drop in frequency, which can be corrected by injecting more power into the system. it's how both steam turbine governors and modern frequency-responsive battery systems work: there are smarter engineers than me out there, who can successfully integrate the old and the new

Thanks; That, for me, is the flywheel temporary energy storage of the rotating inertia.

It also shows how we can easily leap past an 'obvious' issue in discussions that can become 'untrue' when there's a technology update. We only get rotation rate drops because we were using rotation based temporary energy storage. If we aren't using rotation based energy storage we don't (automatically) get a drop in frequency.

We can also fall into the frequency-phase trap where it's unclear where we have set the reference, both locally and globally, such as : "Are we still maintaining electric synchronous clocks to the level that we used to, given most have been phased out". Locally (to a generator), we talk of both frequency changes, and phase changes, in the same discussion not realising the confusion.

We can know the destination frequency/phase before we generate, now that most lines have optic fibre incorporated (Synaptec..).

Thanks again for clarifying.

Roger B said:

There seems to be a general agreement that to just keep adding inverted coupled equipment to a conventional grid is not going to work and will result in various stability problems.

There are certainly technical solutions available, but are they viable?

Well if you look at the GB system, NESO are procuring stability services, to provide rotating inertia and short-circuit current contribution, services which previously would have only been available from conventional generation while it was running to generate active power. These services are now being provided, typically, from synchronous condensers (i.e, conventional generators connected to rotating mass, such as flywheels) which operate without generating active power, so the stability service is now split from, and independent of, the provision of active power so you can have the stability service without running coal/gas generation, so avoiding the need to curtail renewables in order to run conventional generation for stability purposes. 

There's already a number of assets providing these stability services and they have been in operation for some years now. 

In parallel, there's also been a number of new frequency response type services developed to take advantage of the very fast response times of battery assets, to help manage grid frequency. I think the first one was the Enhanced Frequency Response (EFR) service some years ago, where response times were sub-1 second. There's a new suite of Dynamic services which are being introduced geared around batteries and fast responding technologies.

Going back a few years, NESO was expecting it would be able to operate the grid with 100% green energy for periods of time around 2025 onwards, presumably through a combination of these new stability and frequency services but possibly benefitting from some conventional generation (nuclear). I'm not sure about the current status of this target, but they've been putting in place the building blocks to get there.

Roger B said:

Another Ball and Chain Historical Infrastructure problem is the British Railway loading gauge. Britain was the first and started out with the smallest. Now this places significant restrictions on what can be carried on British tracks. Could the loading gauge be enlarged? Technically yes, practically no.

Another example, closer to home, is Britain's electricity system, which itself developed in a non-standardised way with a mixture of DC systems, AC systems using a range of different frequencies, distributed at numerous different voltages. Britain was slow to standardise the electricity system, but it got there in the end, first with the standardisation of frequency at 50Hz AC as part of the development of the National Grid, which required the replacement of significant amounts of non-50Hz equipment, particularly the large 40Hz system in the North East. Then various, more localised measures, to standardise distribution to AC and to 230V over following decades.

If there's enough benefit, then eventually it happens. Or, people innovate to live with the constraints.

thanks, that's a useful expansion

being pedantic, synchronous condensers are there to control reactive power

that doesn't detract from your point about NESO procuring some big flywheels, as proposed in previous posts. I don't have the figures to hand but, at least in terms of GW connected, I think that NESO are procuring much more battery capacity than flywheels

it feels like NESO are on top of this:

a) make sure that there are enough big flywheels connected to smooth things out a bit and to preserve the classical frequency - power relationship

b) procure enough responsive generation to keep the frequency within 2% of target, to cater for credible loss of in-/out-feed

c) look to the distributors to shed load if the frequency falls below that 2% threshold, to save the wider system

that point about condensers and flywheels brings us neatly back to the original post. while the final report is yet to emerge, it looks like the issue on the Iberian Peninsula was cascade tripping on over-voltage rather than any kind of imbalance between production and consumption

Dave Miller said:

being pedantic, synchronous condensers are there to control reactive power

that doesn't detract from your point about NESO procuring some big flywheels, as proposed in previous posts.

Those flywheels are synchronous condensers. The synchronous condensers had traditionally been used primarily to provide reactive power control, but because they're a spinning mass they also provide inertia and being connected to a conventional, synchronous generator they also provide short-circuit fault current contribution - with these stability services being in demand now, with the shift toward inverter-based renewable generation.

I refer you to ENTSO-E:

https://www.entsoe.eu//technopedia/techsheets/synchronous-condenser/

Example project, installing a synchronous condenser for inertia and stability purposes:

new.abb.com/.../abb-synchronous-condensers-go-live-in-liverpool-to-stabilize-the-uks-power-grid

Some further thoughts:

I picked the railway loading gauge as an example as there are potential benefits that are probably not thought about in Britain.  

The first is to greatly increase passenger carrying capacity with double deck trains. There is a practical limit to the length of a train when connections are required due to the time taken to walk from the end of the train to the platform exit and then from the entrance of the next platform to the required carriage. This is somewhere around 12 – 14 carriages. Double deck carriages allow a 20-30% increase in passenger numbers, some space is lost to the stairs. The Southern railway did trial this in the 1940s but there was just not enough space:

https://en.wikipedia.org/wiki/SR_Class_4DD

The other major benefit is that the increased separation between tracks (6 foot way) allows adjacent tracks to keep running (at reduced speeds) while maintenance is carried out. This greatly reduces disruption to traffic.

Is it feasible to implement this in Britain today? Probably not. It was looked at by the government but rejected on cost grounds:

https://hansard.parliament.uk/commons/2012-06-28/debates/12062867000026/Double-DeckerTrains

The standardisation of local distribution to 240V 50Hz mostly took place while the system was growing and the end use of electricity was limited compared to today. The challenge now for local distribution is to increase the capacity to cope with EVs and heat pumps.

While upgrading takes place would it be better to convert the domestic feed to 3 phase as is normal in mainland Europe?

Installation of Megawatt charging stations for commercial vehicles is another supply and distribution challenge. The end technology is already here, but not the infrastructure:

https://www.hubersuhner.com/en/markets/industry/ev-charging-infrastructure

The problems in the Iberian Peninsular do seem to have been due to the loss of control of reactive power resulting in an overvoltage cascade failure. This was initially blamed on the network operator for not having enough suitable conventional generation available. As was noted in the latest report a thermal plant was being started but it was too late. There may well have been financial considerations behind these actions.

It may be possible with better software and electronics to maintain stability with a high proportion of inverter connected generation and loads but Andy M’s comment in the ID Cards thread comes to mind:

“My day job is in systems assurance for safety critical systems, and I can almost guarantee that in any new project which involves software at some point an engineer will say the dreaded words "the software won't let that happen". Well, years and years of experience have taught us that software will let "that" (whatever unwanted behaviour it is) happen. Even if we throw huge amounts of time and effort and money at it - for example as we do with safety critical software - there's still a finite probability that it will fail. And that's fine, provided we plan for that.”

I may be classed as a Luddite but a flywheel coupled to an alternator has fairly well-defined failure modes and a large overload capability. Electronics has a very limited overload capability and many failure modes that are very hard to detect.

It may be possible to model the influence of the transmission system on the network stability however, if you read the latest report, the network topography in also a dynamic system. Another level of complexity.

It was noted that the UK has some 5 GW of batteries installed although the storage capacity was not given. This may help with network stability, but considering that the UK has some 30 GW of installed wind power they won’t be able to do much in a ‘Dunkelflaute’.