GB674665A - Improvements in and relating to regenerative braking control systems for electric motors - Google Patents

Abstract

674,665. Control of D.C. motors. BRITISH THOMSON-HOUSTON CO., Ltd. March 15, 1950. [March 29, 1949] No. 6510/50. Class 38 (iii). A variable voltage generator 2 has a separately-excited field winding 2a and is adapted to supply a motor 1 which drives a load having substantial inertia. In an emergency the field winding is disconnected from its supply and is connected across a non-linear resistor 6 the resistance of which increases as the voltage applied to it decreases. The field winding is thereby discharged at such a rate that the generator voltage decreases in correspondence with the regenerative voltage of the motor, the braking torque being maintained substantially at the maximum obtainable with safe armature current-values. Closure of switch 13 energizes relays 12 and 18 in sequence, contacts 8b, 8c, being respectively opened and closed. A relay 11 is then energized, and, when a push-button 9 is depressed, relay 10 closes the supply-circuit for the field winding 2a, relay 3 completing the motor armature circuit. Acceleration is effected by increasing the voltage of the supply 4, 5. When emergency stop switch 18 is actuated, contactor 8 drops to connect field winding 2a across resistor 6. Relavs 12 and 11 are deenergized, the latter being of the time-delay type, so that, after a pre-determined interval greater than that required to brake the motor, the contactor 3 drops to open the armature circuit. In a modification, Fig. 3 (not shown), when the contactor 8 is de-energized in response to the operation of the emergency switch, the generator field winding is connected in series with the non-linear resistor to a low-voltage source for reverse energization. A small reverse current during stand-by minimises residual voltage of the generator. According to Fig. 4 (not shown), during braking operation, the positive terminal of the generator field winding may be connected through the non-linear resistor to the negative terminal of the generator, the negative field and positive armature terminals being connected. The non-linear resistor may take the form of a dry contact rectifier, of the selanium or copper oxide type, which is connected in series with a fixed resistor, Fig. 5 (not shown). The rectifier is permanently connected across the generator field winding and is poled to be non-conducting when the winding is connected to its separate excitation source. Specification 292,110, [Class 38 (ii)], is referred to.