GB679392A - Improvements in the control of dynamo electric machines - Google Patents

Abstract

679,392. Control of D.C. motors. ENGLISH ELECTRIC CO., Ltd. Feb. 23, 1951. [Feb. 24, 1950] No. 4778/50. Class 38 (iii). [Also in Group XXXV] A rolling mill drive has a reel motor and a main mill motor (not shown) which are both supplied from a Ward-Leonard generator (not shown), the current in the reel motor armature 33 being compared with a reference current in field winding 34. For this purpose an exciter field winding 32 is connected across resistor 31 in the armature circuit of the reel motor, and the opposing winding 34 is connected across a potentiometer 35 supplied from a constant source 36. The output of exciter armature 37 is applied to field winding 40 so producing a voltage across armature 41 which is added to a constant voltage from terminals 42 for energization of the field winding 44 of the reel motor. A feed-back unit 45 supplies a stabilizing field winding 46. When the mill is operating at a steady speed a tendency for the reel motor armature current to deviate from a set value is substantially corrected by means of the field windings 32, 34. When it is desired to accelerate the mill, a push button 50 is actuated and causes a pilot motor 51 to move the field rheostat 52 of the Ward-Leonard generator to a new position, so increasing the speed of the main mill motor and allowing the reel motor to accelerate. If the reel motor armature current is kept constant, however, the tension of the strip would be reduced, and, in order to prevent this, an inertia compensating winding 53 is provided which allows increased reel motor current. Since the increase in voltage output of the Ward-Leonard generator lags behind the change in its field excitation, the application of voltage to the winding 53 is simultaneously delayed in order to avoid violet changes in the tension of the strip. Hence the winding 53 is connected across the armature 32 of an inertia motor having a separate field 23, so that upon actuation of push button 50, a voltage is applied through resistor 24 to armature 22. The voltage across armature 22 builds up slowly, so gradually increasing the excitation of the winding 53.