GB206615A - Improvements in and relating to electric motor control systems - Google Patents

Abstract

206,615. British Thomson-Houston Co., Ltd., Farmer, H. F., and Dreghorn, H. Aug. 24, 1922. Systems for alternating-current motors only.- In controlling alternating-current commutator motors for running printing presses and like machinery at ' creeping ' speed, the motor is started with resistance cut cut of the secondary circuit in order to give sufficient torque for starting, and afterwards resistance is automatically re-inserted by a device responsive to falling current in the secondary circuit. The system employs push-button control, providing both for ' creeping ' operation as described above and also for unrestricted starting with the falling current device out of action. To provide for different loads, as in printing papers with different numbers of pages, additional resistance sections and controlling devices may be employed. In the system shown, a three-phase commutator motor has a primary winding P connected to a line switch 1 and a secondary winding S having resistance R connected to a short-circuiting switch 2. When an inching button M is depressed, electromagnets are energized to close both primary and secondary switches, the motor thus starting with maximum torque. A relay 14 subject to a primary circuit coil Q and a secondary circuit coil T is arranged to re-open the switch 2 when the initial secondary current has died down, the motor then proceeding at slow speed. as long as the button M is kept depressed. For running at normal speed, the button M is left in the position shown, and a button W is depressed, the effect being to close the switches 1, 2 and to put the relay 14 out of action.