Patent GB-617158-A (GB)
Title: Means for controlling the electric heating of a moving continuous metallic article
IPC: C25D5/50
Filed: 1945-05-30
Abstract: 617,158. Electric control systems. CARNEGIE-ILLINOIS STEEL CORPORATION. May 30, 1945, No. 13587. Convention date, Oct. 12, 1944. [Class 40 (i)] In a device for controlling the supply of heating current to a moving continuous metal article, a reference voltage having an R.M.S. characteristic and which is. a function of the article speed, together with the rectified heating voltage, are applied to separate uniting windings, in opposition, of an amplifying exciter which supplies the controlling windings of saturable reactors in the heating circuit and carries the voltage supplied to the article in a compensating sense as the speed changes. In Fig. 1, the strip S is heated by current flowing between conducting rollers 2, 3 connected through transformers 9, 10, saturable reactors 18, 19 and circuit breaker 17 to an A.C. supply. The tachometer generator 34 is driven from bridle roller 35 and its generated voltage is proportional to the strip speed. The rheostat 36 is adjusted in conjunction with rheostat 37, which is operated to control the speed of the strip, and limits the proportion of the voltage of tachometer 34 applied to field winding 33 in accordance with an R.M.S. law. The rheostat 38 accommodates for different strip sizes. In the amplifying regulating exciter 30, which may be an "Amplidyne," the output voltage is principally derived from and controlled by field windings 32, 33. The winding 33 is connected to raise the output voltage of exciter 30 and a restraining voltage proportional to the heating voltage is applied to winding 32 of exciter 30 from the conducting rollers 2, 3 through the transformer 40 and full-wave rectifier 41. Current strength is adjusted by rheostat 43 to keep the restraining field below that of 33 to maintain the desired heating current relative to the strip speed. The output from 30 energizing the exciting winding 29 of generator 24 which supplies the secondary saturating windings of saturable reactors 18, 19, the parallel primaries of which are connected in series with the supply to the primaries of transformers 9, 10. In commencing the operation, the line speed is increased, together with the speed of tachometer 34 and its output voltage. The voltage increase applied to 33 is limited by rheostat 36 to approximately an R.M.S. characteristic and raises the output voltage of exciter 30 and of generator 24 to raise the current through reactors 18, 19 and hence through rollers 2, 3. If the resultant heating current is excessive, the field 32 decreases the output voltage of 30. The tendency of the system to oscillate (i.e. hunt) under sudden changes of operating conditions is mitigated by the transformer 45, which by a first derivative control correctively reflects surges in the output voltage of 30 back to the field system through winding 44. To compensate for the residual voltage of generator 24 when the line is at rest, either the winding 47 is excited from a D.C. source in opposition to winding 33 or the primary circuit may be broken. In Fig. 2 (not shown), the reference voltage applied to winding 33 is shaped to an R.M.S. characteristic by an adjustable resistor and a second resistor determines the slope of the curve. Specifications 557,029, [Group XXXVI], 596,856 and 596,857, [both in Group XXXV], are referred to.