GB339273A - Improvements in or relating to alternating-current dynamoelectric machines - Google Patents

Abstract

339,273. British Thomson-Houston Co., Ltd., and Maggs, A. H. May 29, 1929. Alternating-current commutator machines.-In a reversible alternating-current commutator dynamo-electric machine for operation at two speeds with pole-numbers in the ratio 2 : 1, the stator has for each direction of rotation a pair of windings adapted to be connected in series for the higher pole number and in parallel for the lower pole number, and in addition, one or more windings arranged to produce the necessary change in the magnetic axis when connected in series with one or the other pair of main windings on the lower pole number, whereby the two speeds are obtained in either direction of rotation without change of brush connections or lifting any of the brushes. In Fig. 1, A, B are two windings adapted to be connected to the supply L1, L2 in series by means of switches 1, 2 to give a high pole number. For low pole number operation, the windings A, B, are connected in parallel with each other and in series with two sections E, F of an additional winding by closing switches 1, 3, 4. For low speed reverse operation windings D, C are connected in series to the supply by closing switches 5, 6 and for high speed reverse operation the windings D, C are connected in parallel with each other and in series with two sections G, E of the additional winding by closing switches 5, 7, 8. As shown in Fig. 3, the windings A, B are divided into two parts in order that the windings A, B, C, D may be disposed in the slots in a manner to equalize their reactances If such equalization is not desirable, the windings A, B may occupy one portion of the slots and the windings C, D another portion, but the effect of such an arrangement will be to impart operating characteristics to the machine which are not the same for both directions of rotation. The coils indicated by heavy lines have more turns than the others in order to maintain a symmetrical wave form of flux for each direction of rotation. With the switching connections described, the armature axis as determined by the brush setting, common to both numbers of poles, is arranged midway between the slots 16 and 1 and the slots 8 and 9. This arrangement yields at high speed a maximum running torque considerably in excess of the maximum running torque at low speed. If approximately equal maximum torques are required at both speeds, the common armature axis is arranged midway between the slots 4, 5 and the slots 12, 13. The windings A, B connected in series result in low speed forward operation as before, but for high speed forward operation windings C, D are connected in parallel and in series with winding sections G, E. For low speed reverse operation, windings C, D are arranged in series, and for high speed reverse operation, windings A, B in parallel are connected in series with winding sections E, F. The necessary number of terminals may be reduced to five by the connection shown in Fig. 5. With this system of connection the switch 4 is used for both directions of rotation and the switch 8, Fig. 1, is dispensed with. Fig. 4 shows the disposition and connections of the brushes for a four and two-pole machine. The two full lines represent the mean axes of the brushes in four-pole running, and the dotted line the mean axis for two-pole running. In the case of higher pole numbers, equalizing connections may be employed to avoid the necessity of providing a greater number of brushes.