The Camara book gives a pretty good summary of the general concepts involved, but a good machines textbook might be a good backup. If I remember correctly, machines (motors, transformers and generators) make up a significant portion of the Power afternoon session. If you had no studies of...
I used the study guide by John A. Camara, and highly recommend it. Check out Amazon.com for it - about $110. It provided a broad overview, and served as a valuable reference during the exam.
When purchasing a 1500kW genset recently, I noticed that the generator capacity exceeded the prime mover's capacity. In short, the generator may be switchable, but as has been previously mentioned, it is worthwhile to ensure that the prime mover can handle both speeds, as well.
The supplier may be taking this opportunity to update the order with current comodity pricing for steel, iron, and copper. Raw materials are becoming a large portion of transformer costs.
Just remember - It is mostly about temperature. High temps hurt, whether by overcurrent (overload) or higher ambient.
A higher S.F. motor can be used to give you a little margin for either case.
In power plants, we typically specify motors to be 1.15 S.F., and that the motor must drive...