Practical Engineering did a video on the complexity of bringing a power grid back online, called "black start" (not cold start).
https://practical.engineering/blog/2022/12/5/what-is-a-black...
https://practical.engineering/blog/2022/12/5/what-is-a-black...
How could one possibly balance the load with the plants coming online? If the generation and load is too mismatched, the generators can literally automatically trip off the grid, so generation and load must be carefully balanced as things get brought back up.
One would almost need to shed nearly all the loads from the black grid (Which may have happened anyway as the grid collapsed, but any loads not already shed by the collapse could prove interesting), and re-add some some gradually as plants come online, which still seems crazy difficult.
And inrush current demands from many loads as they are get reconnected must be pretty insane.
Something about bringing up a designated plant and feeding the output over 'cranking' lines that other plants along the route can synchronize their output against. Then gradually adding load and source until the system is meta-stable again.
Edit: additional data
Not only synchronize, but also use for internal needs like all the pumps and particularly the 'excitation current' that establishes the magnetic field for the generator. It allows control over the output voltage. There are also other drawbacks to the more obvious solution of fixed magnets which can be oversimplified as 'ware'.
https://en.wikipedia.org/wiki/Permanent_magnet_synchronous_g...
The trickiness seems worst close to the very beginning when even relatively small misestimation of a chunk of load being restored would have a proportionally bigger impact. Many loads are not completely predictable, so presumably they would need to favor bringing some of the more stable loads online early so that normal variation from the loads that can only be predicted well in aggregate won't vary enough to trip everything back offline.