The paper deals mainly with the MVA rating or the power factor rating, and with the synchronous-reactance value of large, non-salientpole synchronous generators. Essential factors for selecting these values are discussed and a method of making that selection is proposed. An analysis is made of the manner in which the two values affect the operation of the generator. From a power chart based on the classical circle diagram, diagrams of “working area” limitations are derived and represented in co-ordinates of reactive power versus active power, power factor versus active power and excitation current versus active power. These diagrams are suitable both for comparing properties of different generators when ordering new units, and for supervision of operation of generators. Problems of capacitive loads and of synchronous stability of generators are discussed. From a comparison of external characteristics of an isolated generator, with different load characteristics, conceptions of voltage stability and of “absolute power limit” in respect of that voltage stability are derived. The influence is discussed of stator-winding resistance and of saturation on representative diagrams and curves. The paper is illustrated by an example of an actual 50-MW, 58-MVA turbo-generator.