GB555198A - Improvements in and relating to electric motor control systems - Google Patents

Abstract

555,198. Control of D.C. motors. BRITISH THOMSON-HOUSTON CO.. Ltd., (General Electric Co.). Nov. 4, 1941, No. 14216. [Class 38 (iii)] In a traction system a resistance 42 variable by a pilot motor, under the control of a vibrating accelerating relay, is cut out once during acceleration, but is cut out twice during braking from high speed. When a master accelerating controller is moved from " off " switches 101, 92a, 105, and 104 are closed and contact 47 is moved to its " B " position at a speed governed by the accelerating relay. A pilot controller associated with the pilot motor causes field diverters to be removed as contact 47 starts to move. Movement of the master controller towards the " run " position increases the spring bias on the accelerating relay and so causes a greater rate of acceleration. Switch 114 is closed as soon as the master controller is placed in the new position. When contact 47 reaches its B position, switch 116 closes and switch 114 also closes if it has not already closed, switch 170 opens and 171 closes. The diverters are placed across the fields 25, 26 and 27, 28. The pilot motor is reversed and moves contact 47 back to its "A" position at slow speed and during this movement each diverter is reduced in value. This gives full speed running. Coasting is obtained by returning the accelerating controller to " off." The "shut off " is given in a cushioned manner by opening in sequence switches 105, 114, 116, 101, and 104. Thereafter switch 92a opens and switches 84, 85 close, thereby forming a braking loop. The pilot motor adjusts the contact 47 so as to maintain a small constant current in this loop under the control of the accelerating relay whose coil is now shunted across part of the resistance 44. Braking is obtained by movement of a braking controller to a service position whereupon the setting of the accelerating relay is changed by inserting a resistance in series with its coil and by increasing the spring bias in accordance with the movements of the controller. The pilot motor maintains the desired braking current by moving contact to portion "M" whereupon switch 171 opens and 170 closes to substitute the resistance 42 for the resistances 43, 40, 41 and the contact 47 is moved back to its original "A" position. In the " full service " position of the controller an air brake is brought into operation. The motion of the pilot motor ensures that upon any change from accelerating to coasting or to braking, or resumption of accelerating after coasting or braking, the position of the contact 47 is approximately correct for initiation of the new condition. Specifications 513,114 and 514,263 are referred to.