The shafts are so enormous and heavy that they must be driven by an auxiliary motor when not in use in order to prevent them from permanently sagging.

I assume this sag is something that would only become relevant over a fairly long period of time? Otherwise how were the devices constructed originally, I doubt they were spinning instantly.

They can presumably be fully braced when not in use, but not in the application?

The "European" grid also expands to northern Africa[0]. The Wikipedia map is a little weird, because I remember doing consulting for an energy company at the time the two Danish grids were combined. I suppose it has to do with transmission capacity, but technically Denmark can route power from west to east (the other way is typically less useful as the majority of the power generation is in the west). Western Denmark also has cable running to at least Sweden and so does Germany, so why it's not viewed as one network seem strange.

0) https://en.wikipedia.org/wiki/Synchronous_grid_of_Continenta...