GB698901A - Improvements in and relating to circuits deriving unidirectional current from an a.c. source - Google Patents

Abstract

698,901. Transformers; transformer arrangements. BRITISH THOMSON-HOUSTON CO., Ltd. Feb. 14, 1951 [Feb. 14, 1950], No. 3579/51. Classes 38 (ii) and 38 (iv). [Also in Group XXXVII] A circuit arrangement for deriving variable D.C. from an A.C. source, e.g. for supplying electric locomotive traction motors, comprises two rectifiers 28, 29, each connected in series with a load across terminals 36, 37 between one end of a respective one of two secondary windings 22, 23 of a mains transformer 16 and the mid-point 40 of a secondary winding of an auxiliary transformer 32 whose primary winding is connected via a reversing switch 35 to a tapped third secondary winding 33 of the main transformer, and the ends of the auxiliary transformer secondary winding. are connected to respective other ends of the windings 22, 23 whereby, depending upon the positions of the switch 35 and a tapping selector 34, the voltage supplied by the latter windings to the rectifiers may be boosted or bucked to a variable extent by the winding 33. Application of supply to the rectifiers is controlled by contactors 24, 25, whilst additional contactors 46, 47 connected to low-voltage tappings on the auxiliary transformer secondary winding provide, during vehicle braking, excitation across. terminals 36, 37 for the motor field windings, the armatures then being connected across braking resistors. In modifications, the auxiliary transformer may be an auto-transformer or doublewound ; the rectifiers may additionally be gridcontrolled ; the rectifiers and tapping selector 34 may be of any type; the lead may comprise one or more motors of any equipment; additional main transformer secondary windings may supply vehicle auxiliaries and services; the primary winding 17 of the main transformer may have supply voltage regulation tappings.