And very interesting thoughts come up, especially when you add newer developments like non-rotational-mass-based power sources (solar power, batteries, stuff like that) into the mix. Because at the moment with the high number of traditional steam-powered generators, the rotating mass of the turbines and their inertia serve as a kind of buffer against sudden swings in electricity demand with an ultra-quick response time of "basically no time". As a second buffer stage we have the steam supplies in the plants, which can be quickly accessed just by opening a valve, thus the response time is non-zero, but still quite short.
Now replace all those generators with some other power sources without those inherent balancing capabilities (that probably weren't explicitly built into them, but that just happen to be there because of their construction) and you'll get a network that is much more vulnerable to sudden changes on the demand side. Now, explicit mechanisms of storing energy in a way that can be accessed in literally zero time need to be introduced into the network, just to keep it stable and to provide other regulation mechanisms (of which a lot of them also have to be re-thought) with enough time to do their job.
I wouldn't wonder if there were already plans for building large rotating masses with motors on them that are kept at network frequency, with the motors switching over to serve as generators when the frequency drops.
Synchronous machines with no net shaft power are sometimes used to supply reactive power, but these also contribute a coupled rotating mass. (edit: Apparently English people call these "synchronous condenser")
The question of "how can we build a large and stable grid without thousands of tons of rotating mass?" is an area of very active research I've been told.
Aren't the large Tesla battery farms in Australia being used for that purpose? [1] Basically they use batteries and control systems to correct instead of a rotating mass. I'm not sure about the ability to push several hundreds of MW into the system but at least it gets something done.
The rotor in a synchronous machine is coupled magnetically to the grid (basically a spring-mass system where the spring is a rotary field); there is virtually no reaction time in this mechanism.
(It should be noted that other motors, including asynchronous machines, contribute as well)
AIUI the HPR has reaction times on the order of a few seconds.
> I wouldn't wonder if there were already plans for building large rotating masses with motors on them that are kept at network frequency, with the motors switching over to serve as generators when the frequency drops.
Definitely. Dinorwig[0] has the turbine hall built inside a mountain, using a lake in a disused slate quarry. Stop to maximum power in 12s or something similarly ridiculous. They do tours, which I highly recommend if you are in the UK. You go by bus (inside the mountain) to get to the interesting things.
It was also built to be able to do a black start (startup after a total grid outage).
Nope. They have to be able to cope with extreme changes in load, and I think have higher precision of frequency adjustment to pull the rest of the grid into sync.
Some coal plants had gas turbines[0] fitted solely to allow a black start, others a ton of diesel generators. Some plants need power from the grid to kick off - nuclear for instance. Only some percentage of the grid needs cold start capability, and the rest of the grid is bootstrapped from that.
[0] (edit) Think aero engine. Rolls Royce Avons were used at Didcot A, and the industrial Avon is still available after 60 years. That's the same basic engine found in the Hawker Hunter and EE Lightning.
I recently got to take a look around a small (~ 4MW) hydro station. Despite this being a tiny contributor to the overall grid, it is apparently a grid/regulatory requirement for them to be able to perform a black start.
For that reason, all the equipment in the generator building ran on 48V DC, supported by a large bank of batteries.
Additional anecdata: The sensors and controls in distribution substations are also DC although 48VDC is considered the low end in those places where it goes up to over 200V, according to the engineer from a municipal electric company met in an $OFFICE meeting Monday. The guy said they specify flooded lead acids and plan on them lasting 15 years before pre-planned change-outs.
In addition to the other answers, large generators usually use externally-energised coils to provide their magnetic field, so they can't generate unless there is already a supply of electricity. Then there's all the peripheral machinery of a power plant such as coal crushers and feeders, pumps, valves and so on.
Somewhere there will be a manual for the unfortunate operators who will have to restart the whole grid in the correct order, relying on the telephone company's backup generators to communicate.
Larger stations could take a long time (like a day) to start up, as there are trade-offs between start up time and operating efficiency. During that time, you still have to be able to run all the plant equipment - pumps, fans, coal grinders, conveyors, all the monitoring and control equipment. I expect there will be many stations that don't have anywhere near sufficient diesel generator capacity to allow start up without any supply from the grid.
Probably my favorite anecdote about the grid synchronization behavior is that the generator governor settings (e.g. how to react to changes in frequency) were developed early in the 100 year+ history of the grid, and now we don’t fully understand why the settings were chosen to be what they are, and all the engineers who developed them are long dead.
Now that a bunch of wind and solar is being added to the grid with completely different control schemes, there’s a lot of concern about whether the system will continue to stay reliably synced.
I thought that the frequencies were originally decided by whatever machine the generator was driving. Want your big saw to split logs at 100RPM? Make your water wheel drive a generator at 100Hz. IIRC every big motor was different and ran at its own frequency.
Only when people started interconnecting these generators in a grid did the need to settle on a single frequency arrise.
