Patent GB-644868-A (GB)
Title: Improvements in control systems for dynamo-electric machines
Inventor: WILSON GRAHAM RUDGE
IPC: B65H23/182
Filed: 1947-06-24
Abstract: 644,868. Automatic control systems ; exciting dynamo-electric machines. ENGLISH ELECTRIC CO., Ltd. June 24, 1947, No. 16652. [Classes 35 and 38 (iv)] [Also in Group XXXVII] The armature current of a direct current dynamo-electric machine, which is coupled to a reel for winding strip material, is maintained constant to keep tension constant, by means of a first control means which varies the excitation in steps in accordance with the coil diameter, and a second control means arranged to vary the excitation during each step, so as to provide continuous variation. Fig. 2 shows the control system applied to a machine coupled to the coiling reel of a steel strip rolling mill. Two direct current motors 21 and 22 are coupled to the reel (not shown) and are supplied in series with armature current from generator 23. An amplifying exciter 26 is supplied via electronic amplifier 27 with a signal proportional to the armature current of the motors by means of resistance 30. The output from exciter 26 is applied to field windings 21b, 22b, associated with motors 21 and 22. Relay 29 operates to switch in the input to amplifier 27 when the armature current exceeds a certain value, and the excitation of motors 21 and 22 is then increased by the action of exciter 26. If this compensation is insufficient and the load is such that the armature current rises still further, relay 37 in the output circuit of exciter 26 operates, thereby energizing motor 36 which reduces the value of resistance 24 in circuit with field windings 21a and 22a thereby increasing the motor field still further until the armature current falls below the releasing level of relay 37 when motor 36 is de-energized. The action repeats itself if the armature current again rises sufficiently for relay 37 to operate. As the diameter of the strip coil on the reel steadily increases, a steadily increasing load on the motor results, giving rise to the above sequence of operations, with the result that variations in strip tension are avoided. A potentiometer 28 is provided in the input circuit to amplifier 27 to enable the datum level of armature current and therefore of strip tension to be adjusted. Potentiometer 38 is ganged to potentiometer 28, and current flows through auxiliary field winding 23a of generator 23 when relay 29 operates, to compensate for the I.R. drop in the armatures of motors 21 and 22. A differentiating circuit 34, 33, 35; is connected across the motor armature supply which varies as the strip speed of the mill, the output of the differentiating circuit being applied through amplifier 32 to amplifier 27, so that the motor field is also modified according to the rate of change of armature voltage in a direction tending to minimize changes in strip tension. Potentiometer 33 is ganged to potentiometer 24 so that the effect of the differentiating circuit varies substantially inversely with coil diameter. Field coils 21b and 22b may be connected in a bridge circuit across which is connected the output from exciter 26, and also that from supply lines 25 via resistance 24. The invention may be applied to a de-coiling operation, motors 21 and 22 then acting as generators to supply a braking torque, with corresponding reversal in the operation of the voltage amplifier and effect of resistance 24. A rectifier may be associated with relay 29 (see Fig. 1, not shown), to prevent false operation under reversed current conditions. A modification provides for motor 36 to be connected in series with a rectifier, directly across the output of exciter 26, in place of relay 37. A variable biassing voltage may be connected in the field winding of the exciter unit to provide the armature current and tension control means. Specification 579,570 is referred to in the Provisional Specification.