GB617563A - Improvements relating to electric motors and their control - Google Patents

Abstract

617,563. Control of several D.C. motors. KEMSLEY NEWSPAPERS, Ltd., REYROLLE & CO., Ltd., A., PAGE, S., and ROBERTSON, A. T. Oct. 7, 1946, No. 29873. [Class 38 (iii)] Normal speed operation of, for example, a printing press, is afforded by a main electric motor F energized from a supply-source A through a variable voltage rectifier A<1>, whilst for low-speed operation substantially independont of the torque, for inching and crawling, an auxiliary motor G is supplied from a lowvoltage source B. As shown, the sources A and B, and a further auxiliary source C which energizes the field winding of the low-speed motor and the control circuit contactors, consist of separate secondary windings of a mains transformer, the sources B and C being connected to a grid-controlled rectifier B<1> and a metal rectifier . C<1> respectively. Initially, switches B<2> and C<2> are closed to energize the motor G which is accelerated over the lower speed range by grid control of the rectifier B<1>. At the maximum crawling speed, switches A<2> and B<3> are closed, and, when the motor F takes up the load, the auxiliary motor is disconnected. The main motor is accelerated to the minimum normal operating speed by grid control of the rectifier A<1>, further increase of speed being effected by means of the rectifier B<1> which reduces the main motor field excitation. The system may comprise a plurality of main and auxiliary motors.