GB604473A - Improvements in electric motor control systems - Google Patents

Abstract

604,473. Automatic current-control systems. ENGLISH ELECTRIC CO., Ltd., and WILSON, G. R. Oct. 29, 1945, No. 28251. [Class 38 (iv)] [Also in Group XXXVII] In a control system for electric motors driving coil-winding machines which are required to operate over wide ranges of coildiameters, the coil-winding motor armature current is maintained constant and the voltage is varied in proportion to strip-speed over a first part of the winding-range, and, over a second part of said range, the motor field strength is maintained constant and the armature voltage is varied in direct proportion to the product of the strip-speed and a factor which decreases linearly with increase of armature current according to a law so selected that the power is maintained nearly proportional to strip-speed. The armature 1a of a coiler-motor is connected in series with the armature 2a of a bucking generator across the armature 3a of a main generator which provides an outputvoltage proportional to strip-speed. The coilermotor has a constant excitation winding 1b and an opposing field-winding 1c which is energized, through a rectifier 4, from an amplifying exciter 5 having a constant-excitation winding 56 and an opposing field winding 5c. The winding 5c is excited proportionally to the coiler-motor armature current, so that, when the latter rises, the output of the exciter 5 tends to fall to increase the resultant excitation of the coiler-motor. A rheostat 7 sets the value of armature current thus maintained. The field winding 5c may be converted across a resistor in series with the coiler-motor armature, or, as shown, may be energized from an amplifying exciter 6 having a field winding 6a connected in series with the armature 1a. A field winding 2b of the bucking generator 2 may also be energized from the exciter 6. As the coil-diameter increases, the armature current is maintained substantially constant until the excitation of the winding 1c is reduced to zero thus providing maximum coilermotor field-strength, the rectifier 4 preventing reversal of current. Further increase of armature current increases the field excitation of the bucking generator to progressively decrease the voltage applied to the coiler-motor armature. An adjustable rheostat 8 provides means for adjustment of the rate of change of coilermotor armature voltage in relation to the armature current. This rheostat may be coupled to the rheostat 7. The bucking generator may be driven at constant speed or in proportion to the strip-speed. With the former arrangement, the bucking generator field excitation may be adjusted proportionally to strip-speed by a potentiometer 9. In a modification, the coilermotor is provided with two similar field windings connected to resistors to form a balanced bridge. A separate direct-current supply is connected across two opposite corners of the bridge, and the output of the exciter 5 is applied to the other corners. According to the Provisional Specification the constantcurrent control of the coiler-motor may be employed for the latter part of the coiling range, and a system of inverse variation of voltage with current, employed for the earlier part of. the range. The bucking generator may be omitted and a field winding corresponding to the winding 2b connected on the main generator. A main generator with a drooping characteristic may be employed, a, bucking generator of reduced size can then be used. Specification 506,742, [Group XXXVII], is referred to.