Abstract: A method and apparatus for measuring the resistance of a winding of a converter-fed single- or three-phase machine during operation by means of a d-c measuring current. The firing instant of at least one up-commutating valve of a maching converter is delayed by a predetermined variable setting angle for generating d-c measuring currents in the phase currents, whereby the current conduction time of the up-commutating valve is shortened and the current conduction time of a valve commutating down with the valve which is commutating up with delay, is lengthened. The generated d-c measuring current is filtered out of the measured machine current and the generated interlinked d-c measuring voltage is filtered out of a measured terminal voltage of the single- or three-phase machine, and the winding resistance is determined from the linked d-c measuring voltage and the d-c measuring current by forming a quotient.

Abstract: To utilize the full power capacity of alternators 1, the alternator phases are connected through a transformer 9 to the rectifier 4 which provides rectified output to a battery 8. The transformer 9 has tapped windings, the taps being placed in circuit with the alternator-rectifier network in dependence on a speed control signal, for example derived from the frequency of the alternator, to effect tap changing and matching of the internal impedance of the alternator 1 to the battery 8/load L combination. In accordance with one feature (FIGS. 2, 3), the taps are on the primary, and a-c switches such as triacs 15 are selectively energized as the speed of the generator changes; in accordance with another embodiment (FIGS. 4, 5), the taps are on the secondary of the transformer, and unilaterally conductive switches, such as thyristors or SCRs 48, can be used, in parallel with the rectifier diodes 47 of the rectifying array, and selectively fired as a function of speed.