Major UK power cut, 09/08/2019.

[Initiation]

I've been hearing a lot of complaints online that some hospitals were cut off. I understood things to be that hospitals weren't protected from blackouts such as these are were expected to have their own backup facilities. Is this correct? If it is, why has nobody actually pointed this out?

The Ofgem report specifically refers to Ipswich hospital. Grid power was not lost, however the hospital's own protection did trip and cut its own supply. In this case the DNO also said they were not part of the load shedding scheme.

The report refers to no other hospitals.

If they do have backup supply they are likely to be critical functions only. If the generators, or their fuel supply, are not maintained appropriately you can imagine a scenario where they wouldn't run.

[adam2]

Hospitals are NOT protected against power cuts.
They should have emergency generators to supply all important loads, and UPS systems in addition for the most critical loads.

When the power is cut off by either a sudden breakdown or by a pre-planned rota, then EVERY CUSTOMER in the area affected will be without power.

The only exceptions are a very limited number of vital consumers who are considered to be of vital national importance AND that have a dedicated high voltage grid connection.
For customers connected at low voltage (230/400 volts) or at 11Kv, 33Kv, or 66Kv, there can be no exceptions. When the supply is off, it is off for everyone connected to the relevant parts of the network.

Examples of vital loads include some defence establishments, natural gas pumping stations, electric railways, and the electrical supply industry itself, in order to assist in a prompt recovery, and to maintain safety at nuclear reactors.
Some large food storage or processing facilities that are judged to be of national importance AND that have a dedicated high voltage grid connection are also exempt.
There can be no exceptions for local food shops, wholesalers, depots, bakeries, and similar facilities.

[adam2]

I've been hearing a lot of complaints online that some hospitals were cut off. I understood things to be that hospitals weren't protected from blackouts such as these are were expected to have their own backup facilities. Is this correct? If it is, why has nobody actually pointed this out?

The Ofgem report specifically refers to Ipswich hospital. Grid power was not lost, however the hospital's own protection did trip and cut its own supply. In this case the DNO also said they were not part of the load shedding scheme.

The report refers to no other hospitals.

If they do have backup supply they are likely to be critical functions only. If the generators, or their fuel supply, are not maintained appropriately you can imagine a scenario where they wouldn't run.

Yes.
Ipswich hospital was NOT part of the load shedding, but this was NOT due to any form of exemption.
About 5% of the UK load was disconnected, and Ipswich hospital happened to be in the 95% that remained on.

[BritDownUnder]

Presumably wind farms use inverters to generate the HV AC for the grid - they are not synchronous generators. The load vs frequency drop does not apply to renewables - only to mechanically regulated turbine driven generators. Wind farms are either synchronised to their local distribution, or a central reference via radio, or they are not able to connect.

You raise a good point here and along with your later post about gas reliance.

From my understanding the frequency of a 50Hz grid must stay within 48 to 52Hz or bad things happen like motors overheat and below 48Hz some gas turbines I have worked with cannot cool themselves adequately and will trip automatically.

Hence maintaining reliable grid frequency is very important and any deviations must be controlled quickly or the whole grid will collapse. Why grid operators seem to like synchronous generation (from gas , coal or nuclear and NOT from wind, mostly or solar) is that they can act as a 'flywheel' and stop these sudden frequency variations.

On the other hand the inverters used for solar and a lot of wind, particularly older wind installations, tend to follow what the grid frequency does. While these inverters can put power into the grid at any frequency I am not certain that they have any 'flywheel' effect and can by themselves raise or lower frequency. You might think of this as stepping on the gas in a car to make the grid frequency speed up.

The grid tied inverters on a home solar installation certainly will just follow the grid frequency. Whether the latest inverter technology on a larger scale can help to maintain grid frequency with the narrow 48-52 or even 49-51Hz is something I don't know. Maybe Adam can comment on this.

[fuzzy]

As you say, lower than 50Hz and transformers and motors will run hotter. I can't think of a problem of going above 50 Hz if every generator was locked in phase, except your record player running fast. Maybe there is something else.

[BritDownUnder]

As you say, lower than 50Hz and transformers and motors will run hotter. I can't think of a problem of going above 50 Hz if every generator was locked in phase, except your record player running fast. Maybe there is something else.

I could be wrong but in some cases running over 50Hz can also have problems including overheating. I am pretty sure that if you plugged in a 60Hz device into a 50Hz system, even if the voltages were matched which in most cases they are not, would result in a flash and loud bang.

Modern equipment is designed to run at the limits of heat tolerance and peak efficiencies and if they are exceeded their lifetimes can be shortened considerably which costs $$$$ (sorry I no longer have the pound sign on my Australian computer) and the people with the money don't want that.

I am not suggesting that if you went slightly over 52Hz or below 48Hz briefly you would go to hell in a handbasket but I think the consequences would be a bit worse than a clock going too fast. However there are standards and in Australia certainly electrical standards are strictly adhered to or you get fined.

[Potemkin Villager]

Why grid operators seem to like synchronous generation (from gas , coal or nuclear and NOT from wind, mostly or solar) is that they can act as a 'flywheel' and stop these sudden frequency variations.

On the other hand the inverters used for solar and a lot of wind, particularly older wind installations, tend to follow what the grid frequency does. While these inverters can put power into the grid at any frequency I am not certain that they have any 'flywheel' effect and can by themselves raise or lower frequency. You might think of this as stepping on the gas in a car to make the grid frequency speed up.

My understanding is that grid tie inverters have to follow the grid requency so that, for example, the active power flow out of them is controlled to match the rotor mechanical power output and prevent shut down on rotor overspeed detection. Boy you do not want to see a wind turbine rotor overspeed!

Having less and less large synchronous plant on line at any time would seem to lead to less stability and faster rate of change of frequency. I suspect because the system is so even more complicated now with all sorts of smaller plant the dynamics are pretty impossible to model with any accuracy.

Noy that anybody is going to admit to that.

[adam2]

All grid tie inverters for wind turbines or for PV arrays are unavoidably linked to the grid frequency.
They can not ALTER this frequency, except indirectly by minutely tending to increase the grid frequency by adding power.

Allowing the grid frequency to vary excessively can have various undesirable effects, I feel however that the present limits could be relaxed a bit.
Perhaps by making the legal limits from 49 cycles to 51 cycles, with the day to day normal operational range being from 49.5 up to 50.5.
Some overseas grids vary by more than that as do many generators.

Appliances should work correctly and indefinitely over the range given, due again to the wider variations expected in some places to which the same appliances are exported.

[cubes]

Thanks for the answers to my questions. Pretty much as I had thought.

[adam2]

Fines totalling about £10.5 million have been imposed on the companies involved in the blackout.
https://www.bbc.co.uk/news/business-50971717