GB186087A - Improvements in apparatus for regulating the phase compensation of asynchronous electric machines by means of commutator machines connected in cascade with the rotor circuits thereof - Google Patents

Abstract

186,087. Marks, E. C. R., (Siemens- Schuckertwerke Ges.). April 8, 1921. Alternating-current induction machines.--An asynchronous machine is phase-compensated by means of a commutator machine cascaded with its rotor and having a stator compensating winding, the excitation of the commutator machine being supplied to slip-rings at the frequency of the supply to the asynchronous machine or at approximately this frequency. The compensation is regulated in the continuous current circuit of a synchronous exciter or in the transformers in the alternating-current circuits, or by shifting the stator or brushes of the commutator machine. As shown in Fig. 1, -the synchronous exciter h of the commutator machine d is directly mounted on the shaft of the asynchronous machine b under compensation, and the commutator machine d is driven from the main supply a by a motor i, one phase only being shown. The commutator machine takes its excitation through slip-rings g, and its stator e and commutator f are in series with the rings c of the asynchronous-machine. The commutator machine may be directly mounted on the shaft of the main machine and excited from the mains a through a transformer. Fig. 3 shows such an arrangement with the further feature that the stator compensating- windings e of the commutator machine are adjustable by means of a shunting resistance r. This arrangement, with the inclusion of a switch l, enables the commutating machine to be used as an induction motor on the mains a, when the switch l is open, for starting the main motor b or to relieve the main motor b of part of the load by acting partly as an induction motor and partly as a phase-shifter when the switch is closed. The method is applicable to machines, such as singlephase induction machines, having pronounced higher harmonics in their secondary circuits. Such harmonics as may pass through the stator of the commutating machine produce no armature field owing to the effect of the compensating- coils.