| 摘要 |
796,509. Automatic speed control systems. BRITISH THOMSON-HOUSTON CO., Ltd. Sept. 18, 1956 [Sept. 19, 1955], No. 26748/55. Class 38 (4). In a speed controlled Ward Leonard system wherein the voltage of the generator 1 is compared with an adjustable reference voltage 6 in a mixer 8 and used to control the excitation 4 of the generator, a relay 11 is shunted across resistor 5, which is the source of the fed-back voltage, so as to be responsive to a predetermined low value, and has its contacts 17 connected in a protective circuit including a reference supply interrupting relay 15 and the contacts 18 of a relay 19 responsive to the speed of the motor as indicated by a tachometer generator 20. Contacts 17 are normally opened and the contacts 18 of relay 19 are arranged to close at or above 50 per cent full speed. An alternative relay arrangement in which relay 15 is normally operated to connect the reference voltage, and normally closed no volt relay contacts are in parallel with normally open speed relay contacts in the protective relay path, is described with reference to Fig. 2 (not shown). |
