Connecting to a backup power generator

I am trying to gather information from the output of a 165 kVA backup power generator that starts automatically when there is a power failure. This is to see, for example, when the generator started and stopped and how much power was produced.

What is the best way to set this up ? If I just connect the counter to the lines, it will only be active when there is a power failure, but it would make more sense if it is visible at all times. Is there a way to do this ?

Any help would be greatly appreciated.