Patent GB-196830-A (GB)
Title: Improvements in and relating to electric motors for use on alternative electric supply systems
IPC: H02K23/36
Filed: 1922-05-22
Abstract: 196,830. Western Electric Co., Ltd., (Western Electric Co., Inc.). May 22, 1922. Machines with two or more armatures; rotary machines; brush-holders; indicators, applications of.-A motor adapted to run on either of two systems of supply, e.g. alternating and continuous current is provided with means for automatically connecting one of its driving systems with its appropriate supply in the event of failure of the other supply which normally is connected to the other driving system of the machine, the transfer being instantaneous and without alternation in the speed or output of the machine. The two driving systems may consist of two independent armatures on a common shaft having two fields, as shown in Figs 2 and 3, or a single armature naving two commutators and sets of slip-rings or one commutator and set of rings, as shown in Fig. 4, and visual or other means may be provided for indicating when the machine is transferred from the normal to the emergency supply. The normal drive in the case of Figs. 2 and 3 is by means of a squirrel-cage armature 17 and field winding 15 fed from an alternating supply 57<1>, 53<1> through a switch 52 and a magnet 40. The emergency supply is shown as a battery 54 which feeds, through a switch 57, a shunt-wound motor 9, the field 16 of which is fed through a relay 32, and contacts 45, 46 controlled by the alternating-current relay 40. The armature brushes 29 are carried by the pivoted armatures 30 of the relay and are normally held away from the commutator by springs attached to the brush arms. For normal running, the switch 52 is closed, whereupon the squirrel-cage armature, 17 and field 15 drive the machine, the contacts 45, 46 being open so that no continuous current passes to the field 16. Failure of the alternating supply allows a spring to close the contacts 45, 46 and energize the field 16 from the emergency supply 54, the field current causing the relay 32 to pull the brushes 29 on to the commutator and so transfer instantly the drive to the armature 18. Fig. 4 shows a single armature machine 70 adapted to run as a synchronous or a continuous-current motor on a main alternating supply 94 or an emergency battery 105 respectively, the fields 110 being connected to the battery in both cases. The slip-ring brushes 85, 86 are carried by the pivoted armatures 89, 90 of a magnet 91 and are normally held on the rings to give synchronous running as soon as the switch 95 is closed. The motor current passes around a series coil 99 of a relay 100 having also a shunt coil 101 and normally holding open a contact 104 in the circuit of magnets 91, 82 on the battery 105. Pivoted armatures 80, 81 of the magnet 82 carry the continuous-current brushes 76, 77 which are normally held off by springs 8'4. Failure of the alternating supply allows the rotating armature 70 momentarily to generate a reverse current in the series coil 99, neutralizing the flux of the coil 101 and allowing closure of the contact 104. This energizes the magnets 91, 82 and lifts and lowers the brushes 85, 86 and 76, 77 respectively to transfer the drive to the battery until the alternating supply is re-established. A machine is also described in which the normal and reserve drives are given by two shunt-wound continuous-current armatures mounted on a common shaft and fed from high- and low-voltage supplies respectively. The high-voltage drive is through a relay having two coils in series with the motor armature and field and normally co-operating to close the armature circuit of the high-voltage armature and open that of the low-voltage machine by holding its brushes off the commutator. The high-voltage motor, if its supply fails, momentarily generates and causes opposing currents in the relay coils, thereby cutting itself out of circuit and lowering the brushes of the low-voltage motor. The relaying is such that the low-voltage field is established before the armature is energized, whereby the reserve drive is taken up without appreciable fall of speed. Fig. 7 shows the use of a lamp 22 or the like for indicating when transfer of the drive occurs in a machine having an alternating-current main drive comprising a squirrel-cage motor 1 supplied at 6, 7 and a continuous-current shunt motor emcrgency drive 5, 25 fed from a battery 18. Failure of the alternating supply closes the contact 17 and through the contacts 12, 12<1>, 13, 13<1> and relay 15 lowers the brushes 9 on to the commutator of the armature 25 which then carries the drive on the battery. Simultaneously, the signalling circuit is closed through the ground 19, battery, contacts 13, 13', conductor 26, contact 17. conductor 27, contacts 21, 21<1>, indicator 22 and ground 30. The invention is particularly applicable to motors actuating switching apparatus of the pawl type in automatic or semi-automatic telephone systems.