How quickly can emergency generators power-up? Maybe not quick enough.
There's nothing to say, from what I've read, that the power cables were indeed the main supply to the airport, so the question may not be relevant.
Time to cut over to emergency power/alternative main supply is a function of the airport Category, with Cat III, for sure, requiring "no-break cut in", ie generators permanently running (if they are the alternative supply) and automatic switch-over on sensing a loss of main supply
I can't remember the requirements for other Categories, but I'm sure someone can.
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