Considerations concerning a modified Kramer system

A variable-speed drive can be obtained by means of a modified Kramer system consisting of a polyphase induction motor, the rotor circuit of which is connected through a 3-phase bridge rectifier to the armature of a d.c. motor directly coupled to the induction motor. Control is obtained by varying the separate excitation of the d.c. motor. The operation of such a system is considered in respect of the commutating reactance, the speeds at which locking torques due to current harmonics could occur and, very briefly, the possible magnitudes of the current harmonics and the losses.