Q: Has anyone got experience in using a 50 Hz Alternator of about 20 MW, in a 60 Hz system country? What are the changes required in the alternator? Is it economical to carry out this change or one has to go in for a new alternator for 60 Hz only. There are lots of commercial requests for such usages of 50 Hz machine in 60 Hz locations and vice versa.
A: You can use a 50 Hz alternator in 60 Hz power system without changing the internals. The concern though, is the operational speed of the alternator as it increases by 20% and definitely affects the natural frequency of the component - subsequently the resonant and running speed vibration amplitudes. The operating voltage will likewise go up with the same ratio that could have adverse effect on the winding harmonics - leading to overheating. There are risks involved in operating a 50 Hz alternator in a 60 Hz power system and the best way to do is perform risk analysis and cost/benefit study.
Another concern is the driver of the alternator if it is designed for 50 Hz system. You have to contend with the same problem on the natural frequency - which is now coupled with issue on the torque and inertial force that the driver will be subjected to due to the increase in operating speed.
There is a good market for used equipment like 50Hz on 60Hz. When evaluating your alternatives, consider selling your 50 Hz system and buying one that's designed for 60 Hz. It may not cost you that much to do that.