GB556397A - Improvements in and relating to dynamo-electric machines - Google Patents

Abstract

556,397. Dynamo-electric machines. BRITISH THOMSON-HOUSTON CO., Ltd. March 20, 1942, No. 3710. Convention date, March 20, 1941. [Class 35] A crossfield machine is fed with alternating current of peaked wave-form to remove residual magnetism and hysteresis. The power-driven rotor 17, Fig. 1, is connected to a commutator provided with two sets of brushes, the primary set 15, 16 being short-circuited and secondary set 19, 20 being connected to a load circuit. The primary armature reaction flux 23 generates, in the secondary circuit, currents which produce a secondary flux 24. The stator 10 serves as a return path for these fluxes and has four salient poles carrying three windings 25, 26, 27 producing two pole fluxes as follows: winding 25, a controlling flux along the secondary commutating axis ; winding 26, a flux neutralizing the standing secondary flux 24 ; winding 27, a flux assisting the primary flux 23, to avoid its disappearance if the primary short circuit is removed. In addition, to remove effects due to hysteresis and residual magnetism, a fourth winding 33 giving a four pole flux is fed with alternating current of peaked wave form from a generator mounted on the same shaft 29, Fig. 3. This generator comprises a narrow permanent magnet rotor 36 rotting in a permeable disc 32 carrying, in opposite pairs of slots 35, a winding 34 of restricted arcuate span. The wave-form of the generated current is shown in Fig. 4. The disc 32 also acts as a baffle directing cooling air, drawn through the windings of the main machine, into the central part of fan 28 which expels the air through surrounding circumferential slots in the casing. Specification 539,835 is referred to.