Patent GB-180821-A (GB)
Title: Improvements in control systems for electric furnaces
IPC: H05B3/00
Filed: 1921-03-31
Abstract: 180,821. Sharples, O. G. March 31, 1921. Regulation, automatic systems and apparatus for.-The current supplied to an arc furnace is regulated by varying the position of the electrodes by means of reversible motors the relays of which are provided with independent means for moving the contacts into non-contacting positions periodically to prevent hunting. Each relay is provided with a second movable contact by means of which the regulating motor is operated continuously in the event of an overload, and a second fixed contact is provided by means of which a resistance is short-circuited to increase further the speed of the regulating motor. When a heavy overload causes a diminution of potentia. between the fixed and movable electrodes of the furnace, the motor is energized continuously to raise the movable electrode. Means are provided to cut out the automatic control and insert a manual control for each electrode. A movable electrode 1 is operated by a reversible motor 2 the direction of rotation of which is controlled by a relay K, the operating coils 13 and 14 of which are in turn controlled by a relay K<1>. The relay K<1> is provided with a coil 20, energized by a current transformer 23, and is provided with two armatures 18 and 19 mounted upon pivoted arms X and X' respectively. The positions of the arms X, X<1> are also controlled by springs 24 and 25 and dashpots 26 and 27. The arm X is provided with cam surfaces 30 adapted to be engaged by rollers 28 mounted upon a member 29 which is oscillated by a motor 31. When the current supplied to the electrode 1 is below normal, the arm X engages contact B to energize the coil 13 of relay K and contacts S, S' engage the lower contacts N, N<1> to connect the motor 2 to the mains R, Y. B', the arm 9 being in its lowest position in which contacts 10, 7 and 8 engage contacts 11, 5 and 6 respectively, and the electrode 1 is lowered. During this operation the arm X is separated periodically from the contact B by the oscillation of the member 29. When the current supplied to the electrode 1 is above the normal, the lever X is raised to engage the contact A to energize the coil 14 of the relay K and the contacts S, S' engage the upper contacts N, N<1> to connect the motor 2 to the mains R, Y, B' to raise the electrode 1. When an overload occurs, the arm X', controlled by a stronger spring than the arm X, is operated to engage a contact D to energize the coil 14 and the motor 2 is operated continuously to raise the electrode 1. A still further overload causes the arm X<1> to engage a contact E to energize a solenoid 36 to short circuit a resistance 46 in the rotor circuit. thereby increasing the speed of the motor 2. It a heavy overload occurs, a potential coil 32, connected across the electrodes 1 and 50, allows a member 38 to bridge the terminals 39, 40 and 41, and the coil 14 is energized to raise the electrode 1. A shunt resistance 56 controls the value of the contact at which the relay K<1> operates. To obtain hand regulation by the controller 51, the switch 41 is opened to de-energize the solenoid 12 and the arm 9 moves to the position shown.