GB650801A - Improvements in and relating to excitation system for alternating current dynamo-electric machines - Google Patents

Abstract

650,801. Automatic voltage control systems. BRITISH THOMSON-HOUSTON CO., Ltd. Aug. 27, 1947, No. 23722. Convention date, Aug. 27, 1946. [Class 38 (iv)] The voltage of an alternator which is selfexcited by a rectifier supplied from current transformers and a potential transformer, is further regulated by D.C. saturating windings on the current transformers, the saturating current being controlled by a carbon pile regulator according to the generated voltage. The field 2 of the alternator 3 is supplied by a rectifier 5 which is fed by the star-connected current transformer 9 and by the potential transformer 6 which has a high reactance. The secondary windings of these two transformers are so connected that when the power factor of the alternator output is unity, their voltages are displaced by 90 degrees, therefore at lagging power factors there is a component of voltage additive to the voltage of the potential transformer to increase the field excitation, and conversely for leading power factors, the current transformers 9 also have saturating windings 12 supplied with D.C. by a battery 14 in series with a carbon pile regulator 13 actuated in response to generator voltage so as to reduce the A.C. fed to the rectifier as the output voltage tends to rise. In a modification, Fig. 3 (not shown), the potential transformer and current transformers feed separate rectifiers which are connected'in parallel to supply the field, power factor compensation being accomplished by means of three coupling transformers each having one winding in series with one phase of the potential transformer secondary and the other in series with the secondary of current transformer.