Abstract: A synchronous machine with alternating-current exciter, wherein the stator of the exciter machine, the rotor of which runs in the opposite direction of rotation to that of the stator field, is fed from a three-phase power controller. The voltages induced in the rotor of the alternating-current machine are rectified by diodes in a three-phase star circuit. In order to minimize the effect of the voltage peaks originating from the hole-storage effect during the commutation of the diodes, which peaks are abnormally high as a result of the mutual interaction of the harmonics, there is produced a parallel path for high-frequency currents in the form of a protection circuit having low-pass characteristic so that the mutual interaction between stator and rotor harmonics if greatly reduced. Because of the risk of self-excitation, the elements of the protection circuit are matched to the machine and cause as few additional losses as possible.

Abstract: A protective circuit for reducing subsynchronous natural resonant frequency signals in a multiphase power supply system includes a damping resistor connected in series with each phase winding of the system. A resonant circuit tuned to the rated line frequency of the system is connected in parallel with each resistor so that signals having frequencies other than the rated line frequency will be damped by the resistors. An inductor can also be placed in parallel with each resistor to maximize the damping effect of each resistor at predetermined subsynchronous frequencies.

Abstract: A synchronous motor incorporates a rotor structure having solid poles. In order to improve the starting characteristic of the motor and protect the pole claws against burning, conductive bars are arranged at each side of the pole below the pole shoe and are electrically connected with the pole to form a quadrature-winding which provides a conductive path for currents induced at the pole surfaces by the time-variable quadrature-field and causes such currents to close around the quadrature-field thereby eliminating current from pole-to-pole by way of the claws. The quadrature-winding also forms a circuit parallel to the solid pole surfaces which thereby improves the asynchronous torque characteristics at low slip rates and reduces the oscillating torque.