AC Generator Underfrequency Protection
212,
You are correct re the S-70 model line having AC Gen underfrequency protection. If I recall, that will keep the main AC Gens online down to something like 67% Nr ( assuming one is airborne and the WOW switch is functional )*. On the ground, the underfreq will drop the Main AC Gens at 94-96% Nr ).
The discussion needs to recognize that many aircraft have an APU and a third AC Generator these days, in addition to some sort of DC battery. Typically this third generator is not driven off the main gearbox.
* On reconsideration, I believe that what triggers the drop off is the under/over voltage protection circuit within the GCU ( Generator Control Unit ). Sorry.
Thanks,
John Dixson
Last edited by JohnDixson; 25th August 2011 at 11:40.
Reason: Further consideration