GB447402A - Improvements in or relating to electric motor control systems - Google Patents

Abstract

447,402. Control of several D.C. motors. BRITISH THOMSON-HOUSTON CO., Ltd., Crown House, Aldwych, London. Oct. 11, 1934, No. 29145. Convention date, Oct. 11, 1933. [Class 38 (iii)] A control system for rolling-mill apparatus having a pair of rolls 12 for reducing the thickness of a strip of material 10, and. having winding and unwinding reels 11, 13, for the strip, comprises a motor 14 for driving the rolls, a generator 16 for supplying voltage to said motor, a pair of dynamo-electric machines 27, 28, one connected to each of the reels, means including said generator 16 or an independent generator for supplying voltage to said machines, and an auxiliary generator 43 connected between the unwinding reel machine and its source so that the voltage of the auxiliary generator assists that of the unwinding reel machine in opposing that of the supply. The machines 27, 28 which operate, one as a motor and the other as a generator returning current to the system, and interchange their functions when the direction of movement of the strip is reversed, are field controlled by regulators 30, 31, respectively, which maintain constant current in the armature circuits of the machines. The strip is accelerated by first increasing the field of the generator 16 and then decreasing the field of the motor 14. The field 48 of the generator 43 is supplied from an exciter 50 coupled to the motor 14, and is thus proportional to the voltage of the generator 16, corrections for the draft of the mill and the field control of the motor 14 being effected by a resistance 52 in the field circuit of the generator 43 adjusted in accordance with the draft, and a resistance 51 in the field circuit of the exciter 50, adjusted simultaneously with the field adjustment of the motor 14. With 50 per cent draft the voltage of the generator 43 is such that the voltage of the machine 27 or 28 acting as a generator is one half that of the machine 28 or 27 operating as a motor. The generator 43 has an auxiliary field 53 whereby, when the mill is at rest the machine 27 or 28 which has been operating as a generator, is supplied with current and maintains a back tension. The direction of movement of the strip is determined by reversing contactors 22, 23, controlled by a switch 54 which also controls relays 40, 42, 55, 67, acting on the regulators 30, 31, and contactors 44-47 which determine the connections between the machines 27, 28 and the generators 16, 43, the control effected by these relays and contactors being such as to give connections appropriate to the particular direction of movement selected for the strip. In a modification, the machines 27, 28 are supplied from a separate generator, the field of which is controlled simultaneously with the control of the roll motor. The main field of the generator 43 in this arrangement is supplied by the voltage difference between two small generators driven by the strip on opposite sides of the rolls. These small generators, in a further modification, are driven by the respective reels and have their fields controlled bv resistances adjusted automatically in accordance with the variation of the diameter of the material on the reels.