Patent GB-252277-A (GB)
Abstract: 252,277. Hill, E. P., and Metropolitan- Vickers Electrical Co., Ltd. Feb. 25, 1925. Commutating windings.-In a dynamo-electric machine, such as a rotary converter or continuouscurrent generator, provided with commutating interpoles, a winding embracing the main field magnetic circuit is directly or indirectly coupled with a winding embracing the interpoles so that a change in the. main flux which causes increasing current in the main exciting circuit causes over-excitation of the interpoles during that change. As shown in Fig. 1, the armature 10 is connected 'to the line 12 through an overload circuit-breaker 16 and to the other line 11 through the normal interpole winding 14. An auxiliary interpole winding 18 is connected in series with the shunt field winding 34. When the load current increases, armature reaction is increased, and increased current flows through the windings 34, 18 whereby the commutating-pole field is over-excited. Decrease of load current causes the armature reaction to diminish whereby the interpoles are underexcited. In a modification, the winding 18 may be supplied from a separate source or it may be in series with the field winding 34 and normally short-circuited. The short-circuit is opened when the load current increases by means of a relay, the operating coil of which is in series with the field winding 34. The contacts of the relay may be in series with the winding 18 and arranged normally to be open, but in this case the auxiliary interpole winding must be excited from a separate source or from the brushes of the machine. As applied to a compoundwound machine, Fig. 3, one side of the commutator is connected to the line 11 through a resistance 24 normally short-circuited by a highspeed circuit-breaker 20, the series field winding 42, the ordinary interpole winding 14 and a reactor 22 which energizes the circuit-breaker 20. The auxiliary interpole winding 18 is excited from a separate continuous-current generator 46, the field winding of which is connected across the series winding 42. When a short-circuit occurs between the lines 11, 12. the main current rush flows through the field winding of the exciter 46 and consequently the interpole is over-excited: when the circuitbreaker so opens, the resistance 24 is inserted in the main circuit, the excitation of the auxiliary generator is reduced, and the interpole is under-excited. In a further modification, Fig. 4, the auxiliary interpole winding 18 is connected to an additional winding 40 on the main magnetic circuit: the auxiliary interpole winding 18 may be dispensed with and the winding 40 directly connected to the ends of the ordinary interpole winding 14. The Provisional Specification describes also a machine in which auxiliary windings on the interpoles are normally short-circuited by a high-speed circuitbreaker which opens upon overload. More particularly in the case of a rotary converter, an auxiliary contact may be provided on the circuitbreaker for short-circuiting the main interpole winding and thereby reducing the excitation of the interpoles after the circuit-breaker has opened. The auxiliary windings may be connected in series with the load circuit with or without a current-limiting resistance, or they may be connected in parallel with an impedance connected in series with the load circuit.