GB900197A - Improvements in electric motor control apparatus - Google Patents

Abstract

900,197. Control of A.C. motors. BROOKE, W., and HOWE, H. March 30, 1960, No. 11271/60. Class 38 (3). A control arrangement for a polyphase slipring induction motor M comprises saturable reactors Cc, Cd, Ce, as described in Specification 864.714 [Group XXXIX], at least in the rotor circuits. The impedance of the reactors is kept constant during variations of load by internal feedback, and is determined by D.C. control windings energized from a transformer E and rectifiers F, through a controller K1. Further, similar reactors C, Ca, Cb in the stator supply are excited from the same source. Movement of the controller arm 45 first cutsout resistance 53, thus gradually increasing the excitation of the stator reactors, and so decreasing their impedance; for low tension motors the resistance 53 may be omitted and full excitation applied immediately. Further movement, across resistance 55, similarly decreases the impedance of the rotor reactors, causing the motor to accelerate to a speed determined by the position of the arm. Full speed as an induction motor is reached at position 1; further movement to position 2 injects D.C. into the rotor at its star point from an additional secondary winding ES1 on transformer E and rectifiers FB, to accelerate the motor to synchronism and then to give power factor correction. This injected current is controlled by further saturable reactors GR whose excitation is adjusted by a rheostat Kr. In alternative arrangements two reactors replace the three in either the stator or rotor of a three-phase motor, and an arrangement for a two-phase rotor is also described (Fig. 3, not shown). Specification 900,196 also is referred to.