I used to work at a plant that had three services all pulling just under a gigawatt (1,000,000,000w). The POCO had an automatic cut-out if it went over, which I remember happening at least once. This was caused by large shorts on our end.
-production staff would go to 'general coffee', and the emergency generator would hopefully start
-everyone would shut up on the radio, except the electricians
-the electrical super or plant engineer would assign tasks to 3-14 electricians, depending on the time of day (24/7 production, $20,000/min downtime)
-we would then start isolating sections of the plant
-the power would return automatically
Start panicking, but remain calm and follow instructions.
-we had to bring everything back online in an order that both avoided inrush trips, as well as the most cost effective order for production
-the short would usually show up at this time, and trip us out again.
Remember which breaker you were turning on when the lights went out the second time.
Power failures from outside would have a similar procedure.
The plant has been expanding since construction in the '60s-'70s, and the staff keeps tuning the procedure. My contribution was putting an emergency light in the electrical shop.