Automatic paralleling system

861,656. Synchronizing A.C. machines. WESTINGHOUSE ELECTRIC CORPORATION. Dec. 2, 1958 [Dec. 10, 1957], No. 38790/58. Class 38 (4). An automatic paralleling system for an A.C. generator comprises a transformer 10 having its primary winding energized from the generator 1 and a supply line 4, any phase, voltage or frequency difference being applied through a rectifier 11 and a Zener diode 15 to a transistor 16. Under asynchronous conditions the rectifier 11 output breaks down the diode 15, the transistor 16 conducts, connecting a conductor 42 to earth through a rectifier 22. The transformer 10 primary voltage is also applied to a pair of identical circuits, one of which comprises a potential divider 23, 24, a rectifier 26, a filter capacitor 27 and another potential divider 28 with its tapping connected to an over-voltage circuit comprising a Zener diode 33 connected to the base of a transistor 34. The tapping is also connected to an undervoltage circuit comprising a Zener diode 29, a rectifier 30 and a resistor 32. When the generator voltage is high, the diode 33 and hence the transistor 34 conduct, connecting the rectifier 36 to earth, and when the voltage is low the bias voltage on rectifier 30 is removed. The rectifiers 22, 30, 301, 36, 361 constitute a coincidence circuit and when they are all non-conducting the voltage on conductor 42 rises and applies a signal to a device 43 which effects closure of the circuitbreaker 6, 7. The device 43 is preferably a bistable circuit or an amplifier.