GB285478A - Improvements in or relating to the coupling of two alternating current mains of different frequencies - Google Patents

Abstract

285,478. Siemens -- Schuckertwerke Akt.-Ges., (Assignees of Siemens-Schuckertwerke Ges.). Feb. 18, 1927, [Convention date]. Rotary transformers; alternating-current induction machines. - A motor-generator for coupling two alternating current mains of different frequencies comprises on one side a synchronous machine cascaded with a commutator machine, and in order to regulate the total power transmission in accordance with some prescribed law, the commutator machine has separate rotor and stator excitations which can be regulated independently. As shown in Fig. 1, the motorgenerator comprises a synchronous machine 2 connected to three-phase mains 1 and coupled to a synchronous machine 3 connected to singlephase mains 4. The rotor of the synchronous machine is cascaded with a commutator machine 5 which has a counter-compound winding 8 and a winding 13 connected through a resistance 14 between the slip rings 6 of the machine 2 and a frequency transformer 9. If constant power transmission independent of the frequency ratio is desired, the cascade machine 5 is stator excited only, but if a buffer action is required in the event of a change in the frequency ratio of the two mains, the necessary regulation is effected by the series transformer 16 in the rotor circuit of the commutator machine 5 and the extent of this buffer action can be regulated by an adjustment of the transformer 17. If it is desired to maintain a certain power ratio between the generators feeding the mains 1, 4, the arrangement shown in Fig. 3 may be adopted. In this case, the rotor of the cascade machine 5 is fed through a group constituted by a synchronous machine 22 driving an alternating current generator 18 and a separately excited rotary converter 21. The machine 18 has a field winding connected to a continuous-current source of constant voltage, and a winding connected in series with the rotary converter 21, the two windings being displaced by 90‹. By dispensing with the rotor excitation of the machine 5, the motor generator may give constant power transmission or it may act as a buffer machine. To avoid loss of power in the resistance 14, Fig. 1, when large powers are transmitted, the arrangement shown in Fig. 4 may be employed. In this modification an exciter 23, preferably having strong armature reaction is interposed between the cascade machine 5 and the frequency transformer 9. The exciter 23 is driven by a synchronous motor 28 which also drives a machine 29 similar to the machine 18, Fig. 3.