We had some power outages here due to high electricity demand (temperature is 40+ centigrade for the last three days).
That got me thinking: How do they turn the power on and off? All those electric devices that are connected on the grid will start drawing a helluva lot of a current at the same time when the power is turned on again. How do they avoid surge damage?
Also what kinds of switches are they using? It can’t be a contact switches because the arc would be immense.
Yes they are. They operate in oil which extiguishes the arc.
Here you go: Circuit breaker - Wikipedia
When you loose power during heavy demand periods it isn’t anyone intentionally shutting the power down its a weaker component failing do to demand beyonds its capacity. Sometimes they might shut something down before it explodes but it is far easier to find the problem after it melts itself to slag.
While there may be some amount power failures due to components failing because they are over loaded. There are also directed shutdowns of areas to lower the load of the overall system. They do this to avoid damaging things. I know during the California electric crisis there were planned rolling black outs. They would shut off power to small geographic location for a few hours then shut off an another section and turn others back on. There was one where I work we had a few hours notice,
California is kind of a weird case.
The “grid” isn’t a huge infinite bus, the way some people seem to think it is. You can’t just shove electricity into it in, say, Maine, and have it pop out on the other side, in say, California. The “grid” is really just the fact that all (or at least most) of the nation’s power systems are all interconnected, and within certain limitations, they can shuttle electricity back and forth.
Consider if there were three power systems, which we’ll call A, B, and C. A doesn’t quite have enough electricity (like California). B has just enough, and C has a surplus. Only, C isn’t directly connected to A. But, A is connected to B, and B is connected to C. In the winter months, there’s no problem, but in the hot summer, A has a problem because he doesn’t have enough generators to supply everything he needs. So, he needs to buy power from C. But, he can’t buy power directly from C. A has to buy power from B, and B has to buy power from C to make up for what it sells to A. The net result is the surplus provided by C ends up getting used by A, but it’s not quite as simple as C shoving power onto the grid and A taking it off.
In California’s infamous rolling blackouts, the problem often isn’t that A, B, and C all together don’t have enough power. They do. The problem is that all the bean counters couldn’t agree on what went where and when, so when A needed power, C had excess, and B couldn’t give any to A because all of the necessary agreements weren’t in place. The end result is A doesn’t have enough power and starts shutting people off before the entire system in A shuts down from overload.
That’s kinda glossing over the details, but that’s the basic idea of what went on.
The northeast can have rolling blackouts, but the northeast also occasionally experiences a thing called a “cascade failure”. Basically, A, B, and C are all humming along nicely, then A blows a generator or a line somewhere and all of a sudden doesn’t have enough power. B tries to supply the excess to A, but this overloads B, and B is now overloaded too and tries to draw more from C. C was already operating at full capacity, so when B draws more power, and C gets overloaded too. The net result is A, B, and C all go into the dumper, even though the fault was only on A’s system.
Power companies can switch things on and off with really big switches, and they also have really big circuit breakers which, although constructed a bit differently, do function similarly to the breakers in your house. When too much current flows, the breaker trips, and the power is switched off. Power lines will also often have automatic circuit reclosers on them. The purpose of a recloser is to automatically switch the line back on just in case the fault is a short lasting one (like a tree blows against a power line in the wind). You can think of a recloser as a guy standing next to your breaker box in your house. When the breaker trips, he automatically flips it back on. If it keeps tripping, he gives up after a couple of tries and leaves it off.
Here’s some videos you might find interesting:
