GB617366A - Improvements in and relating to electric motor control systems - Google Patents

Abstract

617,366. Control of D.C. motors. BRITISH THOMSON-HOUSTON CO., Ltd. Sept. 27, 1946, No. 28875. Convention date, March 22, 1944. [Class 38 (iii)] An electric motor control system comprises a direct-current motor having an armature and a field exciting winding, a line switch for connecting the motor to a supply source, a reversing switch, operable only when the line switch is open, for reversing the motor armature connections without reversing the field connections, means independent of the supply for exciting the field winding while the line switch is open, and a relay arranged so as to prevent the line switch being closed while the motor is coasting in one direction with the reversing switch set for rotation in the other direction, until the speed falls to a predetermined value. A series traction motor 14 is adapted to be supplied from an engine-driven generator 11, which may be of the variable-speed type provided with a mechanically-coupled exciter 12, through a contact of line switch LS and contacts of a reversing switch RS, which co-operates with a reverser interlock device 22. The line and reversing contactors are governed by a master controller MC and a reversing controller RC which is so interlocked with the main controller, through means which may be of the type described in Specification 212,675, [Class 38 (iii)], as to be immovable except when the main controller is in the " off " position. A switch 35 is closed for starting, to energize a polarizing winding 32 of a relay PR, which is not, however, closed, and to close a relay AP to connect the motor series winding 15 to a battery 30. If the reversing controller is moved to a " forward " position, a winding 19 of the switch RS is energized and, upon closure of the main controller, a winding 39 of the switch LS is energized. A contact 13 is closed for forward motor operation and the motor series field winding is disconnected from the battery. Movement of the master controller to the " off " position causes the switch LS to drop out and a winding 31 of the relay PR is connected across the motor armature and the field winding 15 is re-connected to the battery. The traction motor therefore acts as a generator and applies a voltage to the winding 31, the polarity of which is such that the relay PR does not pick up provided that the reversing switch remains in its original position. If the reversing controller is moved to reverse the motor armature during coasting operation, the polarity of the winding 31 is reversed by movement of the switch RS and the relay PR picks up to open its contact 40. Thus, if the master controller is moved to an operative position, the winding 39 of the line switch will not be energized to reverse the motor whilst it is still in motion.