| 摘要 |
629,359. Switching-systems; control by variable-frequency currents. WHITBY, E. Oct. 23, -1947, Nos. 10910/47 and 25530/48. [Class 38 (iv)] [Also in Group XXXVII] A frequency-responsive switching system, particularly for controlling the connection and disconnection of a consumer's non-essential load circuits by slight frequency variations of a remote generating station normally supplying these circuits, comprises a constant speed motor and a synchronous motor which runs at a speed proportional to the frequency of the generating station, the motors driving, respectively, and in opposite directions, the crown wheels of a differential gear, the planet carrier of which rotates a shaft carrying cams controlling contacts in the load circuits if the speeds of the crown wheels are unequal. The system may be combined with a maximum demand or overload cut-out arrangement for disconnecting some of the consumer's load circuits when his totaldemand exceeds a predetermined value. The two motors may normally run at the same speed so that the planet carrier is normally stationary, load switching being effected by temporarily increasing or reducing the station frequency to cause rotation of the carrier. Alternatively, the synchronous motor 13, Fig. 2, may drive the crown wheel 6 of the differential gear 3 at a speed normally slightly in excess of that of the crown wheel 2 driven by the constant speed motor 1, so that the carrier of the planet wheel 14 normally rotates and, through gearing 17, 18 and a slipping clutch 19 rotates the cam-shaft 16 to a position such that the cam switches 22-23 permit energization of all load circuits. A stop 21 prevents the cam-shaft from turning past this position, whilst the clutch 19 allows continued rotation of the planet carrier. To shed load the station frequency is temporarily reduced to such a value that the speed of the crown wheel 6 is less than that of crown wheel 2 so that the cam shaft 16 rotates in the reverse direction and progressively disconnects the load circuits, the operation being arrested when sufficient load has been shed by increasing the station frequency to such a value that the two crown wheels run at equal speeds. The constant speed motor may be an electrically-wound spring clock motor or a shaded pole or synchronous motor provided with an escapement device. The maximum demand cut-out arrangement may comprise a relay 59, Fig. 3 (not shown) having normally closed contacts in the supply circuit to motor 13, the relay winding carrying the total consumer load current so as to cause opening of the contacts on attainment of a predetermined load current. Motor 13 is thereby de-energized, so that motor 1 rotates the planet carrier in a direction causing the cam switches to shed load until the total load current is insufficient to maintain the relay contacts open. The least important loads should then be disconnected by isolating switches to prevent hunting of the system.
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