GB628104A - Improvements in and relating to electric arc furnace control systems - Google Patents

Abstract

628,104. Automatic control systems for electric arc furnaces. BRITISH THOMSONHOUSTON CO., Ltd. Aug. 31, 1944, No. 16609. Convention date, Aug. 31, 1943. [Class 38 (iv)] [Also in Group XXXVII] In an automatic electrode feeding arrangement for a single-phase arc furnace in which each of two electrodes is moved by an electric motor supplied from an electric generator, a first control field winding on the generator, excited in accordance with the electrode, current, acts in opposition to a second reference control field winding to maintain the electrode current constant and a switch permits de-energization of the first control field winding for manual control. Electrodes 11, 10 of a single-phase arc furnace, supplied from an A.C. source through a trasformer 20, are respectively raised or lowered through gearing 16, 17 by D.C. motors 14, 15 having separately-excited fields (not shown) and armatures supplied from separate amplidyne generators 23 driven by electric motors (not shown). For automatic operation, knobs 53 and 65 of control devices 49 and 50 are pulled upwards to close contacts 60 and 84 and energize a relay 85 from a D.C. source 37, 38 so that the following generator field windings are effective: (a) Windings 27, 27a energized is series from D.C. source 37, 38, tending to cause the electrodes to lower at a steady rate; (b) windings 28, 28a energized in series through a rectifier 45 from a current transformer 46, in opposition to windings 27, 27a, to maintain,-automatically, the arc current at a predetermined value; (c) windings 29, 29a, energized in series, in opposite senses, from the opposed rectified outputs of potential transformers 80, 82 to maintain, automatically, equal voltages between each electrode and the charge 12; (d) windings 26, 26a, which become energized in opposition to windings 27, 27a, to limit motor torque to a predetermined maximum by conduction of rectifiers 32, 34 when the volt-drops across resistances 30, 33 exceed a constant reference voltage obtained from an A.C. source through a rectifier 35; (e) series compensating windings 24, 24a; (f) anti-hunt windings 25, 25a. For manual control of motor 14 or 15, depression of the appropriate knob 53 or 65 opens contacts 60 or 84, to deenergize relay 85 so that windings (a), (b) and (c) above are de-energized and automatic control ceases, and closes contacts 58 or 70, to energize a relay 69 so that the appropriate winding 27 or 27a may be energized in one sense or the other to raise or lower an electrode by rotation of the depressed knob in one direction or the other to close contacts 56 or 57 (for motor 14) or contacts 66 or 67 (for motor 15). Notched discs 61 and projections 62 prevent rotation of knobs 53 and 65 from their central position until they have been depressed. Limit switches 63, 68 prevent the electrodes being raised too high during manual control. When starting, before an arc is struck, generator fields 28, 28a, 29, 29a are inoperative and a resistance 42 is included in series with windings 27, 27a to reduce the lowering speed. This resistance is short-circuited by a relay 87 energized from rectifier 45 when the arc is struck. Specification 539,835 is referred to.