GB430416A - Improvements in electric motor control systems - Google Patents

Abstract

430,416. Master control of D.C. motors. ENGLISH ELECTRIC CO., Ltd., 28, Kingsway, London, MARDIS, P. L., Burghley, Sedbergh Park, Ilkley, CALBECK, C. J., Woodcot Avenue, Ferniehurst Park, Baildon, both in Yorkshire, and MARTIN, J., 31, Southern Parade, Frenchwood, Preston, Lancashire. Dec. 12, 1933, No. 34890. [Class 38 (iii)] Regenerative and non-regenerative braking.- A motor is under the control of a combined armature resistance and field regulating controller adapted on its return movement from a field controlling position to actuate means first to connect starting resistance across the armature and after that to interrupt the supply to the armature, thereby giving a transition from power or regenerative braking to rheostatic braking without interruption of the armature circuit. Operation of the controller 3, Fig. 2 (Prov.), to position P2 connects the motor 6 to the supply and energizes a contactor R1 to cut out the first step of armature resistance 4, further movement through positions P3, P4 cutting out further steps of resistance. Movement to position P5 energizes the last resistance contactor R4 to cut out the whole of the armature resistance, de-energize the line contactor L1, and energize a self-maintaining change-over contactor S1. Further movement weakens the shunt field 7 in steps. Upon reverse movement the shunt field is strengthened to give regenerative braking, and, when position P4 is reached, the coil of a selfmaintaining rheostatic braking contactor P is energized and the rheostatic braking loop including the armature resistance 4 is completed. In closing the contactor P de-energizes the contactor R4 to disconnect the supply. Further backward movement cuts out armature resistance in steps and, due to the change-over switch S1, the order is the same as that on forward movement. Rheostatic braking cannot be effected until the controller has been moved to the position P5 and back to the position P4 in order to open both the contactors L1 and R4, to move the change over switch S1, and energize the contactor P, and after rheostatic braking, power can only be applied again by first moving the controller to the " off " position. The change-over switch may be mechanically operated, and a relay responsive to armature voltage may be provided to connect the same or a separate rheostatic braking resistance across the motor armature. In the arrangement shown in Fig. 2 (Comp.), the change over switch S1 may be operated by a coil s connected across the motor armature so that rheostatic braking is maintained down to a predetermined low speed. The rheostatic braking contactor P is energized in the position P1 of the controller and is provided with a time lag so that, by passing the position P1 quickly, the controller may be moved to the " off " position for coasting without rheostatic braking. Likewise by moving forward through the position P1 quickly, power may be applied without establishing rheostatic braking connections. The latter may be established at any time by pausing at the position P1. In the power starting position only the shunt field contactor F3 is closed so that the motor starts only with partial shunt field strength. On an additional starting notch P2, full shunt field is applied. In further arrangements described with reference to Figs. 3 and 5 (Comp.), not shown, no provision is made for cutting out resistance from the rheostatic braking circuit, but a relay influenced by the motor current and having one or two coils is provided in order that the change from regenerative to rheostatic braking takes place at a minimum regenerative current valve. In the arrangement shown in Fig 4 (Comp ), in which no provision is made for varying the rheostatic braking resistance, a brake switch BS, which may be operated by the mechanical brake pedal is provided so that rheostatic braking may be introduced at any time after starting the motor. Specification 418,765 is referred to.