It depends on the number of poles of your generator.
2-pole generator, 3000 rpm
4-pole generator, 1500 rpm
6-pole generator, 1000 rpm
p >8-pole generator, 750 rpm
10-pole generator, 600 rpm
12-pole generator, 500 rpm
Generator 20 poles, 300 rpm
30 pole generator, 200 rpm
40 pole generator, 150 rpm
60 pole generator, 100 rpm /min
100 200-pole generator, 60 rpm
200-pole generator, 30 rpm