GB609952A - Improvements in direct-current electric traction equipments - Google Patents

Abstract

609,952. Automatic control systems for electric motors. PRITT, S. E., and METROPOLITAN-VICKERS ELECTRICAL CO., Ltd. March 26, 1946, No. 9332. [Class 38 (iv)] [Also in Group XXXVII] Direct-current traction motors are connected across the generator of a motor-generator set, the motor and generator armatures of which are connected in series across a supply-source, and are controlled by variation of the generator excitation, the excitation of the motor of the said set being so controlled as to maintain the latter at a substantially constant speed. Motors M1, M2 and a generator G are mechanically coupled and are connected in series across a mains supply. Traction motors 1, 2, 3 and 4, which may be connected in series or parallelpairs, are placed across the generator armature. A generator field winding SG is supplied from a cross-field exciter E1 which is so energized through control windings W1 and W2 as to produce an output which is differentially responsive to current-components dependent respectively on the setting of a main control resistor 5 and upon the traction motor armature current, so maintaining a substantially constant armature current at each setting of the main controller. A control winding W3 of the exciter provides a component dependent upon the traction motor armature voltage which acts in opposition to the main reference component so that the traction motor armature current is so dependent upon the armature voltage that a desired drooping current-voltage characteristic is obtained. A control winding W4 provides a component dependent upon the rate-of-change of generator armature current to afford stabilising-action against surges therein. Field windings SM1 and SM2 of the motors M1 and M2 are energized from a cross-field exciter E2 having a constantly-excited control winding W5, and a control winding W6 which is excited according to the difference between an auxiliary mains-voltage and that due to a tachometer generator TG which is coupled to the motorgenerator set. A stabilising control winding W7 is provided. The excitation component due to the winding W6 is cumulative with that due to the winding W5, so that the motorgenerator set is operated at substantially constant speed. The control system may comprise a drum controller for varying the resistor 5, together with a series-parallel switch, a reversing switch, and interlocks to ensure correct switching-sequence. The system may be adapted to provide regenerative braking, in one arrangement the traction motor field windings being separately excited for this purpose. The motor-generator set may be provided with a fly-wheel.