When green energy ideology clashes with the laws of Engineering and physics…
Manfred Haferburg, power plant engineer, explains the problems of the German power grid in connection with the green energy transition at online site Achgut. The result is a very informative article. It is not primarily about blackouts due to a lack of power.
The author begins by explaining three important terms: The n-1 criterion, reactive power and instantaneous reserve.
“Let’s translate all the technical gobbledygook. The experts at the power transmission grid operators have been ‘preoccupied”‘ with the topic for a long time, but politicians have not understood it because ‘it is a very complex issue’. And then comes the kicker: the German transmission grid can no longer cope with the ‘n-1 error’ in every case. This means that if, in a tense situation, one of the large transmission lines suddenly fails due to a lightning strike, long-wave conductor vibrations in high winds and snow, sabotage or a transformer/high-voltage switch fault, ‘the electricity grid could become unbalanced’ – in other words, it could collapse in a domino effect. This could result in a partial grid failure or, in the worst case, a blackout. This time it’s not me saying this, but the team leader for system behavior in the strategic grid planning department at TransnetBW. I wrote this on this site years ago and was berated for it.”
“Here, too, an attempt at layman’s language: the large rotating generators of the power plants are ‘grid-forming’ machines; due to their large mass, they keep the frequency of 50 Hz constant in the range of seconds. For our colleagues at the Feferal Ministry of Economics and Federal Grid Agency, inertia is a physical property that ensures that power fluctuations are cushioned in a range in which the time for human intervention is too short. Wind turbines have only small masses and solar panels have no rotating parts at all, they are ‘grid-following’ with their inverters; this means that they are connected to the grid of the ‘grid-forming machines’ and do not have a stabilizing effect. Incidentally, gas-fired power plants tend to be ‘grid-following machines’. The large power plant generators have also been responsible for maintaining the voltage in the grid through reactive power control.”
At the end of the article, Haferburg comes to the conclusion that we will continue to see coal-fired power plants in operation for a very long time.
Read the full article on Achgut.
(Note: Today’s modern translation tools do a pretty good job at translating the text into English)
Not only are the huge rotating masses of primary generators essential from an inertial standpoint, but the automatic control systems are designed to prevent catastrophic self destruction of these huge rotating masses combined with huge rotating magnetic fields/forces.
There are phenomenon of a most serious nature regards [runaway] resonant vibrations such that you must ramp up or down the shaft speed rapidly to avoid these very bad resonant zones. Here in N America which uses the correct frequency of 60 Hz, when the generator rotating speed falls to only a few Hz below 60 this vibration/resonant problem will rapidly amplify to the point of shaking the beast to bits. So if a sudden load occurs and slows down the generator below a few Hz from nominal, the generator is tripped off and brakes applied.
Which is why cascading generator trips occur and a huge blackout can take place. If one line or generating facility goes down, the load shifts to others, which slow down too much and they trip too, etc.
It’s not just the rotating physical mass, but the magnetic forces acting on each of the many, many poles of a huge generator are each enough to tear your car in half in a heartbeat. And yes, it acts so fast if the load causes a slight drop in shaft speed, that no human controller could respond fast enough, so there are automatic safety systems in place to prevent catastrophic resonant feedback and destruction.
Sounds like you’re quite familiar with power generation engineering. Thanks for the comment.
Exactly so… we CANNOT go to strictly wind / solar… they do not add sufficient and stable grid inertia. If we had a grid-down situation, wind / solar would not be able to get the grid back up. If we had no physically massive turbine generators to get grid inertia back up, we’d never get the grid back up unless we could parallel a metric boatload of diesel generators.
I ran a 133 MW reactor and secondary systems on a fast-attack submarine (which relied upon turbine generators and motor generators as its inertial mass to keep frequency stable), and a 100 MW natgas / fuel oil peaker turbine generator plant, and a set of fourteen 1.5 MW diesel generators.
That peaker plant was always a pain to bring up… we had the resonant zone we had to avoid (~38 Hz – ~42 Hz), but we couldn’t bring it up too fast before the turbine blades were sufficiently warmed up or we’d risk cracking them because the turbine was about 50 years old… it was a balancing act. Low and slow until the blades warmed, then bring it up at 1 Hz / min, then skip through the resonant zone at a rate of 10 Hz / min, then back to 1 Hz / min once you’re above the resonant zone to 58 Hz, then approach 60 Hz at 1/2 Hz / min.
Yeah, it didn’t make much sense to have a peaker plant that took an hour to get the turbine up to speed, but they worked with what they had. Usually we’d get a call from the grid operator an hour and a half before we were needed, based upon projected load, so we’d be ready as load maxed out.
Once you’ve got it up to 60 Hz, you enable auto control, then the control room operator varies speed very slightly to sync with the grid, the switchyard disconnects are closed, then the control room operator varies excitation field strength to vary how much power is generated (usually he gets a call from the grid operator which tells him how much he should produce).
We could actually take the plant up to 120 MW, but due to its age, that wasn’t encouraged.
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