GB738524A - Improvements in excitation systems for alternators - Google Patents

Abstract

738,524. Exciting alternators; automatic voltage control systems. LAURENCE, SCOTT & ELECTROMOTORS, Ltd., SCHWARZ, B., and SCHWARZ, K. K. April 22, 1954 [May 8, 1953], No. 12923/53. Classes 35 and 38 (4). A single or polyphase A.C. generator has one field winding connected for shunt or separate excitation by a substantially constant voltage source and another field winding for current compounding. In the single-phase form shown the shunt field winding 1B of alternator IA is fed through rectifier 2 and adjusting rheostat 3 with a smoothing condenser 4 while the current compounding field winding 1C is fed from adjustable-tap current transformer CS and rectifier 6 with smoothing condenser 7. For starting, a relay 8 connects the rectifier 6 directly across the alternator terminals at contacts 8B, or alternatively the winding 1C may be connected in parallel with field 1B. The current transformer is short-circuited during starting by contacts 8D while resistance 9 connected by contacts 8C prevents " flutter " of the relay when shutting down. If desired, the shunt winding may be fed from a tapping on the generator winding, the whole winding being used for build-up. The current transformer may be omitted and the series field fed by the whole load current with an adjustable shunting rheostat. Second order variations due to temperature, power-factor, speed variation, &c. may be corrected by an additional conventional automatic voltage control device, e.g. of saturable reactor, or vibratory type, connected in the shunt field circuit or in an additional parallel connected shunt field circuit. In a further modification, the winding 1B may be excited from a mains-fed rectifier or selfexcited D.C. exciter controlled by an automatic regulator to cover second order variations as above. The compounding winding may be of three-phase layout so as to provide a damping circuit.