thank you all.
Yes power has to be derated in ratio 50/60. Also Voltage has to be derated in same relation or otherwise excitation has to be raised in ratio 60/50 to keep original voltage.
But this would most probably go over limit of the winding rating. Flux will also increase and most probably...
Will receive offer for review data of a Generator constructed to operate at 60Hz, 3.600RPM, to be used at 3.000RPM in 50Hz Grid.
What do I have to consider may vary, besides cooling?
Waveform (Harmonics) may change, how much?
Shall it be rewound to counter this, changing auxiliary winding...