A team of snipers could disable a portion of the grid by shooting out the largest transformers.
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You think those huge transformers would be replaced in a few hours?
In my link it said that it took 18 months to replace the transformers that were shot by snipers although the power blackout was averted by switching load to another grid. Contrast with the Quebec blackout where the generators went down, fuses blew, etc. The transformers were fine and electricity was back for most custoers within a few hours. The point is that the generators are safe from surges and they are not safe from snipers.