GB504619A - Means for controlling the excitation of d.c. electric motors - Google Patents

Abstract

504,619. Control of D.C. motors. ENGLISH ELECTRIC CO., Ltd., and CARNEGIE, H. S. Oct. 25, 1937, No. 29131. [Class 38 (iii)] [Also in Group XXXV] Field control.-A motor 1 is excited from two exciters 3, 4, the exciter 4 being independently driven and having a field winding 4a supplied through a regulator 5 from a source independent of motor load or speed, and the exciter 3 being driven by the motor and exciting it as a continuous function of both its speed and its armature current, the compounding or decompounding being greater at high speeds than at low speeds. The motor 1 which may drive a reversible rolling mill is fed from a Ward-Leonard generator 2 and has its field 1a supplied from the exciters 3, 4, which may be connected in series and also in series with a separate source T1, T2. The field 3a of the exciter 3 may be connected across an inductive shunt 11 which may be adjustable, and the exciter may compound the motor during motoring and decompound it during regenerative braking, acting in the correct sense irrespective of the direction of rotation. In a modification, Fig. 2, the field 3a is directly in series with the motor armature, and the exciter 4 has an additional field 4b fed from the exciter 3 through a resistance 7 shunted by a rectifier 8. The field 4b gives a decompounding effect during motoring and a compounding effect during braking, and its inductance causes its effect through the exciter 4 to lag behind the change in armature current. In this way the field 4b tends to compensate for the inductance of the field 1a. An inductance 6 may be provided to increase the compensation. The rectifier 8 is effective to give different degrees of compounding for motoring and braking. A similar result may be obtained by connecting an additional motor field in series with a rectifier across the exciter 3. A polarized relay may be substituted for the rectifier. In a further modification, a third field on the exciter 4 opposing the winding 4b and fed from the exciter 3 is effective to cancel the field 4b, but at a predetermined current varying with speed a regulator increases its effect to increase or introduce the compounding action. The third field may alternatively be connected across 'a Wheatstone bridge connected to the exciter 3, resistance in the bridge circuit being adjusted by a regulator to bring the third field into action at a predetermined current. The regulator coil may be connected in the motor armature circuit or across the exciter 3. A vibratory regulator may be employed and the exciter 3 may supply part of the field 1a or an independent winding. A series winding may be provided on the excite r 4.