Thanks for the reply and the link.

A machine with infinite inertia would resist any frequency change and instantly go to maximum or minimum power upon any grid frequency deviation.

A 25s inertia constant is impressive. The hydro units I work on are anywhere from 1s for newer units to 7s for older ones intended to run isolated networks. And then the ease of frequency regulation on the unit is dictated by the inertia of the water in the water conveyance system “water starting time”

So 25s inertia constant would appear to be a response to frequency change much faster and greater than the typical 5% droop implemented by the governors controlling mechanical power applied to the shaft.

Wild stuff!