GB656062A - A braking system for electric motors - Google Patents

Abstract

656,062. Control of D.C. motors. LA TELEMECANIOUE ELECTRIQUE. Oct. 17, 1947, No. 27888. Convention date, March 28. [Class 38(iii)] A system in which electric motors run under the influence of the inertia of the driven mechanism or vehicle has means adapted to provide for changeover: from regenerative to rheostatic braking without discontinuity or variation of braking-effort, the changeover occuring at a speed dependent upon the excitation of the motors and being automatically effected without the intervention of the operator, and the system is conditioned for rheostatic braking, without intermediate braking, if the supply voltage is reduced to zero. As shown, traction motors are started with armatures 3, 4, connected in series by closing switches 14, 12, and reverser 5 or 6, resistors 7, 8 being gradually reduced. Transition to the parallel connection is effected by closing switch 11, opening switch 12, and setting resistors 7. 8 at their maximum values. Switches 16, 17 are then closed and switch 11 opened. To reach maximum speed resistors 7, 8 are again reduced. The vehicle runs under its own inertia when the control elements are restored to their rest position. For braking, switches 19, 21, 14, 16, and 17 are closed, field windings 1, 2 being energized from the line through resistors 7, 8. A voltage of the same sense as that during motoring is developed across aramture 4, relay 22 comparing this voltage with that of the line. When the armature and line voltages are equal relay 22 operates contacts 5 or 6, according to the direction of the motoring drive, and closes switch 14. Reduction of resistors 7, 8 increases the field excitation and causes the armature voltage to exceed the line voltage, the motors being regeneratively braked and the field windings energized in accordance with the difference of the line and regenerative currents. When this difference approaches zero the switch 14 is opened and rheostatic braking is introduced. The continued elimination of resistors 7, 8, increases the braking-effort, the switch 14 alternately engaging and disengaging until the vehicle is-stopped. If the line voltage fails rheostatic braking is immediatelyintroduced. Resistors 18, 20 provide the desired differential compounding. In the arrangement of Fig. 2 (not shown) the motors have divided field windings, the portions being connected cumulatively for starting and in opposition for braking. One portion of each field winding may be connected across a part of resistor 7 or 8, Fig. 3 (not shown). The series field windings may be divided into three parts, one of them being used to give differential compounding during regenerative braking, Fig. 4 (not shown).