GB740569A - Improvements in and relating to alternators with d.c. excitation - Google Patents

Abstract

740,569. Alternators. NAAMLOOZE VENNOOTSCHAP HEEMAF. May 7, 1953 [May 10, 1952], No. 12816/53. Class 35. In a compound excited alternator, the field winding 6 is fed from the output current and voltage through transformers and a rectifier 5, the current transformer secondary winding 7 and its shunting choke 4 being so dimensioned that the reactive voltage drop between the terminals of the winding 7 is always large compared with the resistive drop in the rectifier and field winding, thus providing uniformity of excitation irrespective of thermal resistance variations and generator speed. The excitation circuit may be used for a polyphase machine and, as shown in Fig. 3, the choking coil 4 may be combined with the secondary winding 7 in a single winding 47. In this form a three-phase core 8 provided with air-gaps 9 in each limb is wound with the transformer and choke windings for each phase, 3 being the current transformer primary and 47 the voltage or secondary winding. The no-load excitation may be adjusted by altering gaps 9. It is stated that the magnetic circuit of an asynchronous motor may be used as transformer. If desired, the coil 47 may be split and wound on different cores in zig-zag fashion to obtain power-factor compensation. A form is also described in which voltage compounding is achieved in a singlephase machine by means of a coil on a threelimbed transformer as in Fig. 3 fed from an auxiliary winding on the generator.