Patent GB-213037-A (GB)
Title: Improvements relating to synchronous electric motors
IPC: H02P1/50
Filed: 1923-01-11
Abstract: 213,037. Carr, L. H. A., and Metro politan-Vickers Electrical Co., Ltd. Jan. 11,1923. Exciting; dynamos, regulating; motors, controlling.-In an alternating current sychronous machine which runs during a part of its starting period as an induction machine and is subsequently synchronized by the application of continuous-current excitation, means are employed for ensuring that the continuous-current is only applied at an instant when the phase angle between the electromotive-force induced in the secondary circuit and the impressed excitation volts is such that no current surge can be produced between the machine and the supply source or other machines with which the machine is parallel. A switch 8 for this purpose is shown in Fig. 1 which in its lower position 11 connects the polyphase secondary 1, 2, 3 of the machine to the mains through a starting resistance 4 and in its upper position 12 connects the continuous-current exciter 13 to the part 2, 3 of the secondary for synchronous running. The switch is controlled by a polarized core and a solenoid 9 which during the starting period is short-circuited by a switch 10. To start the machine, the switch 10 and contact 11 are closed and the resistance 4 is cut out; the switch 10 is then opened and at the correct instant, when the secondary current is of proper magnitude and sign, the coil 9 closes the contact 12 for synchronous running. The solenoid 9 may be arranged for continuous energization, e.g. by the exciting current, when in the running condition, or a holding coil 30, indicated in dotted lines, may be used in place of the conductor 12a, in which case the switch 10 is preferably automaticallv closed when the switch 8 assumes the running position. Alternatively, the switch 8 may be arranged to remain in either of its positions and be reset by hand, and additional contacts may be provided either to short-circuit the solenoid 9 on completion of the starting or to open its circuit if the excitation current is confined to the coils 2, 3. The switch may also have a suitable time lag. The solenoid may be energized, alternatively, by a relay connected in shunt or in series with the switch 10, or, in another arrangement, the solenoid core may act as a magnetic lock on a hand device which prevents the switch 8 from closing the contact 12 until the phase relationship is such as to prevent range. Fig. 5 shows the application to a secondary winding, as described in Specification 196,391, comprising two parts 1, 2, 3 and 25, 26, 27 which are connected in series with continuous-current excitation from a supply 13 for synchronous running. A double-pole two-way switch 8 is employed, controlled by a solenoid 9. In the starting position shown, the switch 10 across the solenoid is open-circuited and the machine is run up as an induction motor on the windings 1, 2, 3 and rheostat 4. For synchronous operation, the switch 10 is closed and, at the the proper moment, the switch 8 connects both sections of the machine windings in series with the exciter 13. The invention is applicable to machines which approach synchronism either from above or below synchronous speed, whether they be motors or self-synchronizing generators.