GB473367A - Improvements in and relating to the control of direct current electric traction motors - Google Patents

Abstract

473,367. Control of D.C. motors. ENGLISH ELECTRIC CO., Ltd., BINNEY, E. A., and MARDIS, P. L. April 17, 1936, No. 11102. [Class 38 (iii)] Non-regenerative braking.-Electric traction equipment with provision for rheostatic braking comprises a D.C. motor of the augmented series field type, means such as contactors 9 for connecting the motor to a supply external to the vehicle for running, means such as tapping switches 6 or variable diverting resistances for varying the strength of the series field 2 during running, means such as a contactor 11 for connecting the armature 1 in a closed circuit for rheostatic braking, and means for applying to the motor, during such braking, a controllable excitation independent of the armature current. In the arrangement shown in Fig. 1, the independent excitation is obtained from a weak auxiliary field winding 3 with a series regulating resistance 7, which can be connected across the supply by closing a contactor 10. This winding can be used both for starting and for rheostatic braking, the motor being accelerated by cutting out the resistance 4 step-by-step by contactors 5, and subsequently cutting out the auxiliary field winding 3, and weakening the series field 2 by closing the contactor 6. For rheostatic braking, the contactors 9 are opened, and contactors 10 and 11 are closed, thereby disconnecting the armature from the supply and connecting it in series with the whole or part of the starting resistance 4. The field excitation may be strengthened as the motor slows down by cutting out the resistance 7 in one or more steps. An automatic strengthening of the field may be obtained by including a portion of the series field winding in the braking circuit or by including a portion of the resistance 4 in both the braking and auxiliary field circuits, Fig. 2 (not shown). In another arrangement, Fig. 3, the auxiliary field is dispensed with, and the series field is divided into two portions 2a, 2b, of which 2b may be included in the braking circuit, while the other and preferably larger portion 2a is excited from an auxiliary source of power 17 through a regulating resistance 19 for braking purposes. In another arrangement, Fig. 4 (not shown), the auxiliary source of power is connected across the whole of the series field for providing the excitation on braking, and a common resistance is included in both the armature and field circuits for automatically increasing the excitation as the armature current falls.