The doubly fed machine

SYNCHRONOUS machines, operating with a-c excitation on both stator and rotor are used in many applications, for example, as induction frequency converters, as power and instrument Selsyn drives, and as variable speed power drives. Reference 1 has mentioned particularly the variable speed fan drive, and presented equations for the small oscillations of one such doubly fed machine. Reference 2 has also previously given the equations of hunting of the doubly fed machine (part XIV, section IV) in connection with the general study of oscillations of rotating machines. However, since the present authors have been using in their own work equations which seem to them to be more convenient and simpler in form for calculations, and since it now seems desirable to present not only general equations but also some of the more fundamental and significant performance characteristics of these machines, it is thought that this paper may now be appropriate. The form of the equations developed possesses the additional novelty of facilitating the setting up of equivalent circuits for hunting on the a-c network analyzer, and allowing the quick determination of the damping and synchronizing torques directly by wattmeter readings.