25hz is part of the "around 30hz" I mentioned. It was a compromise for the Niagra falls turbines between 16.7hz which was good for large motors at the time and

25hz is part of the "around 30hz" I mentioned. It was a compromise for the Niagra falls turbines between 16.7hz which was good for large motors at the time and flickering lights for which Westinghouse wanted at least 33.3hz.