GB609227A - Improvements in or relating to control systems for direct current motors supplied from a constant current source - Google Patents

Abstract

609,227. Automatic speed control of motors; exciting dynamo-electric machines. WESTING- HOUSE ELECTRIC INTERNATIONAL CO. Dec. 21, 1945, No. 34677. Convention date, Nov. 16, 1944. [Classes 35 and 38 (iv)] [Also in Group XXXVII] A control system comprises a direct-current motor having an armature winding and field winding means, means for producing a directcurrent of constant magnitude for energizing said armature winding, means for producing an electrical potential of constant magnitude, means for producing an electrical potential varying in magnitude according to the motorspeed, means for energizing the field winding means in accordance with the difference of said potentials, and means for completely deenergizing said motor at a predetermined low motor-speed. The armatures of a plurality of direct-current motors are supplied from a constant current generator 1G, the control system of one of the motors 1M being shown in detail, the other motors being similarly controlled. The field winding 1MF of the motor 1M is energized from an exciter C which has a series winding CSF, a field winding CPF energized from a constant voltage generator 2G, and a differential field winding CVF excited by a tachometer generator PG. A variable resistor TR is adjusted so that the resistance-line of self-energization of the generator C is coincident with the initial straight line portion of its noload saturation curve. When the motor 1M is running, any deviation of its speed from that corresponding to the setting of a resistor AR1 will vary the excitation of the exciter C to correct the deviation. During the 'early part of the acceleration period, the generator C is operated on a level portion of its characteristic so as to provide substantially constant motor field excitation and torque. Similar conditions obtain during regenerative deceleration, the excitation of the generator C being controlled by the winding CVF. At a predetermined low motor speed, a switch S opens and a resistor 1R is placed in the motor circuit. A circuitbreaker CB is de-energized and closes contacts CB2 to short-circuit the motor armature across the resistor 1R. Contacts CB1 open to deenergize the motor field winding 1MF. The exciter field winding CVF may be connected across the armature of the motor 1M, to respond to its back-electromotive force. The motor may be provided with two field windings connected in a bridge circuit, two opposite corners of which are connected to a constant source and the other corners connected to a, potential varying with the speed of the motor and opposing the constant potential. Interlocking relays ensure that the differential energization does not become effective until a predetermined motor-speed is reached. The variable potential may be the back-electromotive force of the motor, or that of a tachometer generator.