GB930129A - Improvements in or relating to field excitation arrangements for electric alternators - Google Patents

Abstract

930,129. Alternators ; automatic voltage control. GENERAL ELECTRIC CO. Ltd. March 9, 1962 [March 13, 1961], No. 9058/61. Classes 35 and 38 (4). The D.C. current flowing in the field of a selfexcited alternator is supplied from at least one semi-conductor controlled rectifier and is maintained, when the rectifier is non-conducting, by a rectifier connected with the right polarity in parallel with the field winding. The controlled rectifiers 5, 6 are fired simultaneously during each output cycle by applying a current pulse from resetting magnetic amplifier 7 to the gate of rectifier 5. The timing of the firing pulse, and thus the value of field current, depends on the voltage applied to winding 9 of the magnetic amplifier from transistor 18 and network 20, 21, 22, this voltage being proportional to the alternator output voltage. When the rectifiers are extinguished, during negative half cycles, no field current is supplied but inductive decay occurs in the parallel circuit of the field winding 2 and rectifiers 4 so that a continuous current appears in the winding. When the output voltage is low, e.g. on starting up, field current is supplied through rectifiers 23, 24 and controlled rectifiers 5, 6 are short circuited by means of normally closed contacts 25. Additionally the anodes and gates of each unit are connected through resistor/diode networks 32, 33 and 30, 31 respectively by means of contacts 29. When the output voltage reaches a preset value the contacts open in succession, contacts 25 first to prevent sparking.