GB273330A - Improved means for exciting cascaded commutator machines with the supply circuit frequency - Google Patents

Abstract

273,330. Siemens - Schuckertwerke Ges. June 28, 1926, [Convention date]. Alternating-current commutator and induction machines.-The excitation at supply frequency of a commutator machine cascaded with an induction machine for phase compensation or speed control is affected by a set comprising an asynchronous motor driving an asynchronous generator which provides the excitation for the cascaded commutator machine and is itself provided with a mechanically coupled cascaded commutator a machine excited from the main supply circuit. The regulation of the main machine is carried out by variation in the excitation of the commutator machine cascaded with the asynchronous generator. In the form shown in Fig. 1, the main asynchronous machine 1 is cascaded with the commutator machine 21 provided with a compensating winding 3 and excited through its rotor at circuit frequency from the asynchronous generator 4 of the exciting set. This set is driven by an induction motor 6 and comprises also a commutator machine 5 cascaded with the asvnchronous generator, compensated at 8 and rotor-excited at circuit frequency through a regulating transformer 7. Thus, the excitation transmitted to the machine 2 is also at circuit frequency, its valve and phase being controlled by means of the transformer 7. It is shown in the Specification that this transformer need be designed to carry only about 3 per cent of the output of the machine 2. By means of a current transformer 9 in the circuit of the main machine 1 and a further transformer 18 in the secondary side of the transformer 7, the system is compounded to allow speed control of the machine, the excitation of the machine 2, for such control, being varied from a given maximum to zero and reversed when hyper-synchronous speeds are reached. The machines 4, 5 may be directly driven by the main machine 1 instead of by a separate motor 6. Where the main machine is used only as a wattless current machine and a large speed range is not required, the driving motor 6 and asynchronous generator 4 may be combined, as shown in Fig. 2 at 10, choking coils 11 being connected in the circuit of the line-fed stator coils of the combined machine. The excitation of the machine 2 is derived from separate stator coils 12, and by varying the exciting current in the secondary side of the machine 10 bv means of the commutator machine 5 the wattless current taken by the machine 10 from the .supply. mains and the choking effect of the coils 11 are varied. Hence the exciting voltage in the windings 12 may be controlled. The exciter sets above described mav be used in combination with direct excitation of the machine 2 from the supply mains, the direct excitation, for instance, being used for phase compensation and the special exciting set for speed control.