But Ganster sudden load drops happen all the time and the systems respond usually befor the operators do.
Now a widespread and severe sudden load drop might do it but it would take organized zombies to do that.
Nobody ever said the zombies were organized
Well, thank you very much. It’s just an area I know a bit about*, and have a bit of experience in, so I wanted to try to make a comprehensive article that was still readable.
*Power plants, not zombies. I need to learn more about zombies. Who doesn’t need to, after all?
On my staff are two engineers who spent a few years in power plants.
Their comments
Pony - familiar with the term. Usually heard it referenced with a startup assist motor but don’t disagree with the term used as una described…
turning gear - generator rotors spin at very high speeds so even a very slight sag in the rotor is serious. Turning gears very slowly and constantly turn rotors. Since rotors must be stationary occasionally they must be turned for a prescribed length of time following the still period. One of my guys said that after an outage requiring a still rotor they would probably turn the rotor for a few days until it would sag back to equilibrium.
zombies - work in coal power plants and drink lots of coffee
Not much to add here but WOW.
Great report, Una! I loved the union-non-union line.
But a question: Would non-union zombies be scabs?
:smack:
Una, thank you for this report.
The tireless efforts of you power engineers to keep us supplied with electricity during this unfortunate zombie plague are greatly appreciated.
Over here, we call it the “barring gear”. Maybe it’s a regional thing.
I’m thinking that if you left the open cycle gas turbines running at low-load (typically in diffusion rather than pre-mix mode) the EPA zombies would come and shut you down for producing excessive NO[sub]x[/sub].
Una, that’s a brilliantly entertaining Staff Report. Thank you!
I remember being told (as a kid) about the geothermal turbine at our local Paper Mill (Kawerau, New Zealand).
The pony did not disengage as the turbine spun up, and the motor disintegrated as the turbine reached operating speed.
The image of shattered motor casing and splayed out rotors have stayed with me for life.
Si
Great article. I have no engineering background, but it occurred to me that while it might look like hydro dams might be the longest lasting source of power, one if zombies attack in spring and the operators are zombified or on the run, who’ll open the spillways to relieve pressure on the dam (or, to maintain water)?
In quick zombification scenarios, the turbines and water flow would stay right where they were when zombies arose - this could let most of the reservoir drain or, if little or no water was flowing at the time, let water build up, possibly leading to a big problem. I don’t think most dams are designed to have water going over the top of them.
This was very interesting. However I think equally important is what happens after the power plants shut down? Do nuclear plants meltdown (irradiating and mutating the zombies), do coal plants start emitting toxic chemicals (mutating the zombies), Do long shut down hydro plants dams fail with cracks and flood the valleys before them?
Thank you for reading. You are correct in saying that most dams are not designed to have water going over them. In fact, according to the hydro guy I talked to today, water going over the top is considered to be a “worst case scenario”. I asked him if dam failure wasn’t in fact the worst case scenario, and he modified it by saying “second worst-case”.
He did say that many dams do have “emergency” spillways that are always open at or near the top, but that some dams do not have this. It depends a lot on the type. So there is a possibility that a dam or three could have a serious failure without human intervention, provided that there are no functioning automated or passive controls to prevent such a thing.
I can’t speak for nuclear plants. Gas plants are unlikely to have a serious problem, barring possible leaks if the pipes break or corrode through. Coal plants would be similarly benign. Unless, of course, the gas or coal plant had a large amount of ammonia on-site for NOx control of some sort (SCR or SNCR system), in which case down the road there is the potential for a large ammonia leak. How bad this is depends on the type of ammonia and quantity. Aside from this - the coal pile will very slowly degrade and become soil, and most items in the plant will rust/collapse into a large heap of metal.
Hydro plants will fail, eventually, but the process could take decades or longer, depending. By that time maybe the zombies will have evolved enough to learn to take care of the plants, and even restore electricity. Who knows - perhaps in some far distant age they may even be able to figure out how to keep their VCRs from flashing “12:00” at them all day.
I should think they’d achieve this laudable goal just as soon as they managed to wipe out the power grid. 
Hey Una,
That was my question! Thanks for answering it so well - great job! I enjoyed it immensely.
I’ve seen something in an auto parts store called “Sta-Bil”, which is supposed to “stabilize” gasoline so that it’ll last a lot longer before it “goes bad.”
Does this stuff actually make a difference, or is the company that makes it relying on the fact that most gasoline will last a long time without treatment anyway?
You’re welcome, and please take a look around the SDMB while you’re here. You can get the answers to all life’s questions…
Yeeesss…zombies are a clever lot…
Sadly, I have no experience with that. Maybe someone else has tried it.
Authors often do a lot of research before writing their novels and a couple really good stories come to mind…
The Stand by Steven King. No zombies but society does brake down and the power does go out. Lots of detail on what some survivors have to do to get a plant back on line (including shutting off all the clothes driers in the laudrymat to keep load down).
Lucifer’s Hammer by Larry Niven and Jerry Pournelle. Again no zombies but mass de-population via other means. Includes an almost epic battle to keep the juice running at a nuke plant.
Possibly nothing but pure fiction but entertaining none the less.
Anyone know much truth there is in these plot lines?
Bolding Mine
I haven’t read The Stand but during a recovery it makes more sense to disconnect sections of the power grid instead of trying to find and turn off appliances connected to the grid.
*The electricity system would fail almost certainly do to a failure in the transmission system from a drop in demand well before any of the power plants stopped operating.
The demand would plummet, while the power plants continue to produce electricity sending tons of power through the wires with no where for it to go. This would essentially cause the grid to fail and then the power plants would automatically trip off at that point.*
Not quite right. If demand drops the electricity doesnt get produced with no place to go-- the generators fell the lessened load and reflect back less mechanical load on the turbine, whose steam regulator turns down the amount of steam going to the turbine in order to maintain the same generator RPM. This adjustment happens automatically and continuously, in much less than a second, as the generator must stay in phase with the reset of the power grid-- it can’t be allowed to get even a fraction of a revolution ahead or behind the grid voltage.
The lessened demand for steam eventually shows up as a higher steam pressure in the steam collector manifolds, which is noticed by another automatic system which adjusts the fuel input accordingly. If the steam demand went down very quickly and significantly, there may be too much thermal inertia for this control loop to handle the rising steam pressure, in which case the extra steam must be blown off thru a overpressure valve or dumped through a condensor.
That’s for a coal or gas plant. They tend to be able to adjust relatively quickly to
For a nuclear plant things are not so simple. There’s about a bazillion different nuclear decay reactions going on at any instant. If the electricity demand drops, it’s as above reflected back as decreased demand for steam, which results in higher pressures in the reactor cooling loop, which affects the neutron absorption properties of the coolant. The control systems will try to lower the reaction rate by dropping in more control rods. But the rods cannot control all the decay reactions that are already under way. About 30% of the reactor’s heat production is from these secondary decays, which cannot be controlled at all. So even if the electric load goes to zero, there’s still about 30% of the reactor heat output that has to be dumped somewhere until the decays, well decay, whcih will be several hours. There’s also the curious problem of Xenon poisoning-- Xenon is a decay product that has a very large ability to squelch neutrons. In a stable reactor, the xenon poisoning is kept under control. But if the reactor power goes way down, the xenon poisoning has a chance to peak, making the reactor hard to control. The control algorithms try to keep all these bad things from cascading, but without a little human intelligence in the loop the reactor could easily trip off line.
And no, whatever abilities Stephen King has in a literary way, he generally botches anything technical, witness in THe Shining, the curious, unphysical behavior of the furnace and the snowmobiles (not attributable to spooks).