How on earth does the power supply to an entire Country fail?
In: Engineering
There is a problem with turning the power back on again that makes it difficult to do it:
Many appliances in a normal home are consuming a lot more electricity for a while when you start them up. Fridge? Needs more electricity. Freezer? Needs more electricity. Some tv start up, realise that they are not supposed to do anything and hibernate again. And so on.
Not to mention that a fridge that has been turned off for a day will have a pretty rough time cooling down the food in it again. It will consume a lot more electricity in the upcoming day than it usually does during a day, just because it has to catch up.
Now, imagine that a whole bloody country does this at the same time. It’ll demand so much from the producers that you literally can’t turn it all on at the same time. You have to turn on a section at a time. And pay attention to the load you get, and then carefully pick a section to turn on after an hour or two. And still pay close attention to the load.
And at the same time you run into other problems. When you turn on power, it’s a really large circuit breaker that has to be moved. I’m gonna bet you that if you open 20 really large circuit breakers that haven’t moved in a decade, then one or two of them will probably fail. Or at least be bit cranky.
And some of the large breakers are fully manual. How…how do you manage to get personell out to that breaker, when gas stations can’t sell gas to the company vans and cellphone towers are knocked out for lack of electricity?
There is a lot of practical problems that…are not necessarily solved in advance. Not all the line workers have satellite phones. Not all the depots got their own fuel depots with a hand-cranked pump for emergency refuelling. And…
Well. Yeah. Once it’s blacked out, you face a lot of practical problems with the restarting procedure, if you wait for too long before you get started.
As for the question on how things fail… that is a good question. But it literally only takes that a very, very, very large power line gets disconnected before there is a fault on it. Or that a large producer has a failure. I haven’t read up on what the problem actually is, but it’s usually one of those two. There is a problem with production or there is a problem with transmission.
EDIT: I browsed a news article or two about it.
The problem appears to be that the consumption is so large that the producers can’t meet demand. Producers can’t maintain the goal frequency on the production. Voltage goes down. Voltage goes up and down violently when the producers try to meet demand and can’t.
Eventually, lots of equipment will start to disconnect, because when the voltage does that, it’s…an obvious problem. In a perfect world, it means that the production units will have a less rough time keeping up. In a real world, it can mean that the producers loose *too much* consumption, and force them to do an emergency shut down because of that instead. And once a large producer shuts down, it’ll give too much load to all the others. And the vicious circle continues.
It’s all a matter of failed load balancing. Production can’t meet demands. And whoever it is that has balancing as their job failed at it. Or reacted a hint too slow. And now they have to start up slowly. From scratch. One consumer area at a time. one production unit at a time. Probably for days.
One possible scenario is that one or couple of generators could get disconnected from the system and the remaining generators are unable to sustain the load, they start slowing down, just like trying to get up the very steep hill with a bike. Because many devices and the generators themselves were not designed to to work at lower frequencies than nominal, at certain point the generators protections kick in and start disconnecting the generators from the grid. This lowers the frequency even further and other generators start disconnecting as well. So on the system comes to a complete halt. Nowadays I’ve not heard of such cases, because most of the time there is a sufficient reserve in the system to back up any generator that might unexpectedly fail. And if that is not enough, protections will start disconnecting users to reduce the load before they disconnect the generators.
Another reason for a blackout is related to the lines and orher type of current carrying components. The electrical system most of the time is connected in loops, so that if one line fails, the city or strategic point could get the energy from another line. The issue is that sometimes, due to economic, maintenance or other reasons, the loads and generators might distribute in such a way, that some of lines might get near to their capacities. And bam, a short circuit happens on one of the lines, because a tree fell on it and it gets disconnected. Then the other lines take on the load, but they don’t have sufficient capacity to carry so much power and their protections kick in, and disconnect them due to overload. Then the cascading begins and the system might get seperated into multiple smaller systems with uneven load-generation balances and they start collapsing on their own, just like in the previous case.
But today, not many blackouts happen, maybe in the third world countries, because people have gathered huge amounts of knowledge in this field and current protections are very well configured, there are plenty of redundancies, generation reserves and online contingency analisies being made to avoid such situations. In most cases multiple things need to fail at once or somekind of catastrophy to happen to take out the whole system.
In a smaller country, all of the power is connected on a single grid. (The USA has 5 grids, IIRC.) A problem in any one area is a problem for the entire grid, unless it is separated from the rest of the grid with circuit breakers to isolate it.
In most modern power systems, many of the circuit breakers are automated. When they sense too much current draw from an area, they activate and isolate it. If the circuit breakers are not automated, the entire grid will often fail before human operators can respond.
If there’s a problem with not having enough power generation to meet demand, then the grid can’t recover. As soon as enough parts of the grid are connected and drawing too much current, the voltage drops below acceptable levels everywhere. The circuit breakers then activate and things go down again.
No one wants power that is oscillating up and down (it can damage things) so most or all of the grid will remain down until supply and demand can be balanced. Then the grid is brought up, piece by piece. If the control systems aren’t good enough to recognize how to balance supply and demand, this can take some time, and it can get screwed up, bringing the whole shebang down again.
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