GB616917A - Improvements in and relating to control systems for electric motors - Google Patents

Abstract

616,917. Exciting dynamo-electric machines. HOLLYER, E. B., and METROPOLITANVICKERS ELECTRICAL CO., Ltd. Sept. 20, 1946, No. 28270. [Class 35] [Also in Group XXXVII] An electric motor control system of the type in which variation of line voltage in one direction or the other, or in both directions, from a nominal value is limited without affecting the control of the motor when the line voltage is within said limit or limits, is afforded with means for producing a voltage representative of the line voltage connected in circuit with rectifying means, said circuit including a source of reference voltage and control means governing the motor current whereby, in response to the line voltage varying beyond the value corresponding with said reference voltage, said first means will cause current to flow in said control means whereby to reduce the motor current, said rectifying means preventing flow of current in said circuit except when the voltage representative of the line voltage differs in the one sense from said reference voltage, thereby to inhibit operation of the control means to modify the normal operation of the motor except when the line voltage varies beyond the nominal value by a desired amount. As shown, motors M1 and M2 are supplied from a metadyne transformer MT, the secondary current of which is controlled by a variator winding 1 energized by an exciter 2. A field winding 4 of the machine 2 is adapted to be energized from a constant-speed exciter 5 which is provided with a field winding 6, connected across supply-lines L1 and L2, and an opposing field winding 7 which is connected with a constant source, for example a battery 8. The windings 6 and 7 are adjusted so that when the voltage across lines L1 and L2 has a rated value the output of the exciter 5 is zero. During regenerative operation, increase of line voltage will cause the exciter winding 6 to predominate and the exciter 5 will produce a voltage which is not effective, due to the rectifier arrangement shown to energize the winding 4 until it becomes greater than the opposing battery-voltage, whereupon the resultant excitation of the exciter 2 is such as to reduce the regenerated current of the motors M1 and M2 and the line voltage is thereby substantially limited to a desired maximum. During motoring operation, when the line voltage falls below its rated value, the exciter winding 7 becomes predominant and the exciter 5 produces voltage in the opposite sense to that obtaining during regeneration. Owing to the bridge connection of rectifiers 9 to 12, this voltage again opposes that of the battery 8 and the winding 4 is not excited until the v Itage of the exciter 5 is the greater. Energization of the winding 4 again effects reduction of the secondary current of the machine MT and the motor armature current is reduced to prevent further decrease of the line voltage. Single. rectifier arrangements may be used if it is desired to limit the change of line voltage in one direction only.