GB618515A - Improvements in or relating to electric motor controllers - Google Patents

Abstract

618,515. Automatic control systems for electric motors. IGRANIC ELECTRIC CO. April 9, 1946, No. 10893. Convention date, April 9, 1945. [Class 38 (iv)] [Also in Group XXXVII] Speed.-The balance between the three phase voltages applied to the stator of an induction motor is controlled automatically in accordance with departures from a desired motor speed to keep that speed constant. In Fig. 2 the back-to-back discharge devices 12 and 13, connected in series with one phase of the three-phase primary winding 10a of the motor 10 driving a printing press, are controlled by the phase of alternating potentials applied to grids 12c and 13c by transformer secondary windings 15b and 15c. The primary winding is connected between the mid-point of inductance 14 and the junction of variably saturable choke 17 with series resistance 15; which are connected, in parallel with inductance 14, across the A.C. supply. The phase of the grid potentials is varied by varying the inductance of choke 17 by the control coil 17b supplied with D.C. by source 43 through discharge device 41. Any difference between the voltage of tachometer generator 33 driven by motor 10 and the voltage across a tapped portion of potentiometer resistance 44, connected across supply 36, acts through the grid-controlled discharge devices 35 and 38, on the grid of device 41 to vary the impedance of choke 17, and hence the impedance of devices 12 and 13-in a sense tending to keep the speed of motor 10 constant. In a modification the devices 12 and 13 control ignitrons which are connected in one of the supply lines to the motor. Sufficient operating current may be maintained through the ignitions, at low motor current, by connecting in parallel with the motor winding a variable choke coil saturable by a control winding connected, in series with a rectifier, across the ignition terminals. The ignitions, or the discharge devices 12 and 13 in Fig. 2, may be shunted by impedances. One tachometer generator may control several mechanically coupled motors. One impedance device may jointly - control several motors in parallel.