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Comment by yobbo | Hacker News Reader

My thoughts are that power plants don't stop completely in blackouts, they disconnect, power down, and idle. The reason they need to disconnect (in chain reactions) is that the load is too high for them to maintain frequency/keep in phase.

Starting back up is complex because loads need to be added to the network in some order they can be powered.

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Not all power plants can self-feed the power they need to keep generators working. Often this is a diesel generator on the plant because the only other source of power is 20MW generators that simply can't be tuned down enough to handle the few kilowatts it takes to keep the generators turning.

Almost all plants will trip from the grid if it gets bad and remain idling for some time. But if that happens, the grid is still dark and the black start generators are the best equipped to bootstrap the grid. You can't start with the big generators too, so you can initially only bring in small plants until the grid capacity is big enough to not trip out when the big generators come online in a wrong way.

There is a good chance that by the time the grid is stable, atleast some power plants will have had to shutdown entirely and spin back up from a black start with only external power.

The generators have safety systems in place when the grid tied frequency deviates too much from 50 or 60HZ - they then "trip" and disconnect themselves from the grid to prevent damage.

Powering them down to a complete stop is a rather long process taking hours.

One silly technician left a spanner in one turbine after maintenance, and it took about 2 years for a replacement part to be installed.

Black start is just that: powering up the whole grid from blackout. It requires stuff you might not think of like the gas turbine stations need a big spark to light the flame so a diesel generator isn't enough if the station breaker is open, you need a hv DC transformer.

Nukes will shut down in blackout conditions because of the two independent power feed safety requirement. You *really* do not want your nuke plant to run out of power (that *will* Fukushima) so when the number of available sources drops too low they shut down so as to reduce the damage should they actually go dark.

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