US2292122A - Furnace regulator system - Google Patents

Description

g- 4 J. P. HOUCK HAL 2,292,122

FURNACE REGULATOR SYSTEM Filed Jan. 9, 1941 WITNESSES:

INVENTOR-S a James P/Vaucr and Patented Aug. 4, 1942 FURNACE REGULATOR SYSTEM James P. I-Iouck and Ralph A. Geiselman, Wilkinsburg, Pa., assignors to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a ccrporation of Pennsylvania Application January 9, 1941, Serial No. 373,857

2 Claims.

This invention relates to regulator systems, and particularly to regulator systems for governing the operation of the movable electrodes in electric furnaces.

Systems for regulating the operation of a motor for raising or lowering the electrodes of electric furnaces are well known and have been utilized for a number of years with good results. However, with these known systems, it has been found that during the melting down period, the are formed between the electrode and the cold scrap melts the scrap at the bottom of the pocket formed with the result that the molten metal spreads and causes a cave-in of the unmolten metal around the electrode. When the unmolten metal contacts the electrode, a short circuit condition is established between the electrode and the charge. This short circuit condition will vary in length of time depending upon the distance the electrode is submerged and the speed of the electrode motor in raising the electrode. It is, therefore, desirable to accelerate or obtain a speedy raising of the electrode under predetermined conditions. However, since in some cases the short circuit condition rapidly clears itself, it is also desirable that the acceleration or the increase in the speed of raising the electrode be delayed for a short period of time to permit the short circuit condition to clear itself.

An object of this invention is to provide a furnace regulator system that shall govern the operation of the movable electrodes and effect an acceleration or increase in speed of raising the electrodes under predetermined conditions.

Another object of this invention is to provide a furnace regulator system for controlling the normal raising and lowering of the movable electrodes and accelerate the raising of the electrodes under predetermined conditions after a predetermined time has elapsed from the initiation of the .predetermined conditions.

Other objects of this invention will become apparent from the following description when taken I is illustrated, the furnace comprising a receptacle l2 containing a bath of material l4 and three movable electrodes [6, I8 and 2B. The

electrodes 16, I8 and are directly connected to a three-phase supply circuit comprising conductors 22,24 and 26, respectively.

Each of the movable electrodes is provided with a motor for raising and lowering it and a regulator for governing the operation of the motor in accordance with the current flowing through the electrode and in accordance with the potential across the electrode arc. Since each of the regulators is of like construction and operates in the same manner, it is believed to be unnecessary to illustrate and describe more than one of them. Accordingly, only the regulator so associated with the electrode 23 is illustrated and will be described.

In the drawing, a motor 28 comprising an armature 3!], a commutating field winding 32 and a shunt field winding 34 is illustrated for raising and lowering the electrode 20. The armature is mechanically connected to the electrode 20 in any suitable manner as by means of the shaft 35, a winding drum 3B and a flexible conductor which passes over the pulley 42. The shunt field winding 34 is connected directly across supply conductors 44 and 46, a resistor 48 being disposed to be connected in series circuit relation with the winding 34.

A regulator 50 which normally controls the operation of the motor 28 comprises two main control electromagnets 52 and 54 which are, respectively, operated in accordance with the current flowing through the electrode 20 and in accordance with potential across the are produced by the electrode and two electromagnetic switches 56 and 58 which, respectively, serve to connect the motor across the supply conductors 44 and 46 in order to operate it in a clockwise and a counterclockwise direction.

The main control electromagnets 52 and 54 comprise an energizing winding 60 and 62, respectively, and a core armature 64 and 66, respectively. The energizing winding 60 of electromagnet 52 is connected to the three-phase conductor 26 by means of a current transformer 6i and its core member 64 is pivotally connected to a contact arm 65, the core member being provided with a dashpot 6'! for governing its speed of operation. The energizing winding 62 of electromagnet 54 is connected from one side by conductor 69 to the three-phase conductor 26 and electrode 20 and from the other side through conductor ll, the energizing winding 68 of an electromagnetic switch 16 and conductor 72 to the receptacle l2 containing the bath M. The core member 66 of electromagnet 54 is also pivotally connected to the contact arm and is provided with a dashpot 14 for governing the speed of its operation.

As illustrated, the contact arm 65 is pivotally mounted at a point intermediate the points of connection to the core members 64 and 66 and carries two main contact members I6 and I6 disposed for engagement with contact members 80 and 82, respectively, according to the position of contact arm 65. Springs 84 are connected to the arm 65 for maintaining it in a neutral position with the contact members I6 and I8 disengaged from the contact members 80 and 02 when the electromagnets 52 and 54 are deenergized. The contact members I6 and I8 are connected to the supply conductors 44 and 46 through a resistor 85.

The electromagnetic switch 56 comprises a Winding 86 which is connected across the supply conductors 44 and 46 upon engagement of contact members I6 and 80 and a core armature 88 which operates two contact members 90 and 92. The contact members 90 and 92 function upon operation of the electromagnetic switch 56 to connect the armature 36 of the motor 28 across supply conductors 44 and 46 for rotating the motor 28 in a clockwise direction to lower the electrode 25 in the furnace.

The electromagnetic switch 58 comprises a winding 34 which is connected across the supply conductors 44 and 46 upon engagement of the contact members I8 and 82 and a core armature 96 which operates two contact members 88 and I00. The contact members 98 and I60 function upon operation of the switch 58 to connect the armature 30 across supply conductors 44 and 46 for rotating the motor 28 in a counterclockwise direction to raise the electrode 25 in the furnace.

According to well known practice, a braking resistor I02 is also provided in circuit with the armature 30 and the contact members 92 and I60 complete a dynamic braking circuit for the motor 26 when the windings of the electromagnetic switches 56 and 58 are deenergized, thereby effecting a quick stopping of the motor 28. Although, not shown, suitable anti-hunting equipment may be provided in any well known manner to prevent overtravel of the moving parts of the regulator and to give a sensitive control of the operation of the motor 28.

The electromagnetic switch I6 is provided for controlling the energization of the shunt field winding 34 of motor 28. As illustrated, the energization of the winding 68 of switch I depends only upon the potential across the arc produced by the electrode 20. The operation of the switch I0 controls the operation of electromagnetic switch I04, the contact member I96 of switch I0 being disposed when the winding 68 is deenergized to close a circuit which extends from supply conductor 44 through conductor I08, winding IIO of switch I04, conductor II2, contact member I06 of switch I0 and conductor II4 to the supply conductor 46. A dashpot H6 is connected to the core armature of the electromagnetic switch I0 to provide a predetermined time interval or delay in the operation of the switch I0 when the Winding 68 is deenergized to prevent immediate return of the contact member I66 to its circuit closing position, the purpose of which will be explained more fully hereinafter.

The electromagnetic switch I64 also is provided with a core armature which carries a contact member IIB which is disposed when the winding I I0 is deenergized to close a circuit which extends from one end of the resistor 48 through conductor I20, contact member I I8 and conductor I22 to the other end of the resistor 48 to short circuit it from the circuit of the shunt field winding 34 of motor 28.

In operation, assuming that the system is functioning to position the electrode 20 with respect to the bath I4 for normal operation of the furnace, a normal current flows through the electrode 20 and a normal potential exists across the are from the electrode 20 to the bath I4. Although this potential is insuificient to so energize the winding 62 of electromagnet 54 to upset the balance between the pull of electromagnets 52 and 54, sufiicient potential exists to so energize the winding 68 of electromagnetic switch I0 to actuate its contact member I06 in an upward direction to open the circuit of the energizing winding IIO of electromagnetic switch I04. Under these conditions, the contact member II8 of the electromagnetic switch I64 short circuits the resistor 43 from the circuit with the shunt field winding 34 of the motor 26.

If for any reason the current flow through the electrode 26 is lowered below the normal value and the potential across the are formed by the electrode is above the normal value, the energization of the winding 60 of electromagnet 52 is decreased and the energization of the winding 62 of electromagnet 54 is increased to eli'ect engagement between contact members I6 and 80.

Upon engagement of the contact members I6 and 60, the winding 86 of switch 56 is energized by a circuit which extends from the supply conductor 44 through a portion of the resistor 85, contact arm 65, contact members I6 and and the winding 86 of the switch 56 back to the supply conductor 46. When the winding 86 is thus energized, the contact members 94 and 62 are actuated in an upward direction with the contact member 96 being in the circuit closing position and the contact member 92 in a circuit opening position to complete a circuit through the armature 30 and effect rotation of the motor 28 in a clockwise direction. The clockwise rotation of the motor 20 lowers the electrode 20 in the furnace to increase the current flow through it and lower the potential across the are formed by it. Throughout this operation the resistor 48 is short circuited from the circuit with the shunt field winding 34 of the motor 28. When the electrode 20 is lowered a sufiicient distance whereby the pull on the electromagnets 52 and 54 is balanced due to an adjustment in the current flow in electrode 20 and the potential across the arc, the balanced pull on the contact arm 65 effects a separation of the contact members I6 and 80 whereby the switch 56 is deenergized and the contact members 90 and 92 are returned to their circuit opening and circuit closing positions, respectively, and a dynamic braking circuit through the braking resistor I02 is established for the motor 28 to effect a quick stopping of the motor.

Assuming that the electrode 20 is in position with respect to the charge of the furnace to effect a melting of the charge, if due to the melting a portion of the cold charge should cave-in and come in direct contact with the electrode 20, a direct short circuit of the winding 62 of electromagnet 54 is established to immediately effect a separation of the contact members I6 and 80 and prevent further lowering of the electrode 20 in the bath. Under such short circuit conditions the winding 60 of electromagnet 52 is so energized as to actuate the contact arm 65 to the position where contact member I8 engages contact member 82 to close a circuit which extends from supply conductor 64 through a part of the resistor 85, contact arm 65, contact members I8 and 82 and the winding 54 of switch 58 to the supply conductor 45. When the winding 94 of switch 58 is thus energized, contact members 98 and I of switch 53 are actuated in an upward direction to their circuit closing and circuit opening positions, respectively, whereby a circuit is completed through the armature 30 to efiect rotation of the motor 28 in a counterclockwise direction to raise the electrode 20 from the bath.

At the same time that winding 62 of electromagnet 54 is deenergized, the winding E8 of the electromagnetic switch I0 is also deenergized. However, the contact member I06 of the switch I0 is not immediately returned to its circuit closing position, since the dashpot IIG associated with its core member prevents the return of the contact member I06 to its circuit closing position for a predetermined interval of time. This predetermined interval of time is usually so adjusted that for momentary short circuits the contact member I06 is retained in its circuit opening position.

However, since the speed of raising the electrode 20 under normal operating conditions is usually set at some constant speed, if the charge has so caved in about the electrode 20 as to effeet a short circuit of long duration, in order to accelerate or increase the speed of raising the electrode 20, after a predetermined time delay, the dashpot IIB functions to permit the contact member I06 to close the circuit extending from supply conductor 44 through conductor I08, winding III] of switch I04, conductor IIZ, contact member I06 of switch I0 and the conductor I I4 to the supply conductor 46. When the winding IIO of switch I04 is thus energized, the contact member H8 is actuated to its circuit opening position to remove the short circuit from around the resistor 48, thereby inserting the resistor 48 in series circuit with the shunt field winding 34 to thereby decrease its energization and permit the motor 28 to gain speed due to the weakened field. The change in the energization of the shunt field winding 34 of the motor 28 effectively accelerates or increases the speed of the raising of the electrode 20 from the bath I4 of the charge of material. Removal of the short circuit condition between the electrode 20 and the bath I4, of course, permits the pull of electromagnets 52 and 54 to again become balanced and the winding 68 of switch I0 to again become energized to deenergize the winding I I0 of switch I04 and again establish the short circuit about the resistor 48 to place the system in condition for normal raising and lowering operation of the electrode 20.

Modifications in the system and arrangement and location of parts may be made within the spirit and scope of this invention, and such modifications are intended to be covered by the appended claims.

We claim as our invention:

1. In an arc furnace-regulator system, a movable electrode, a motor provided with a shunt field winding disposed for raising and lowering the electrode, a resistor disposed to be connected in series circuit relation with the shunt field winding of the motor, a regulator comprising a current electromagnet energized in accordance with the current flowing through the electrode and a potential electromagnet energized in accordance With the potential across the electrode are for operating the motor to maintain the are produced by the electrode substantially constant, means in series circuit relation with the potential electromagnet and dependent only on the potential operable under predetermined conditions to connect the resistor in series circuit with the shunt field winding to acelerate the operation of the motor and effect an increase in the speed of raising the electrode, and means comprising a time delay device for preventing said means in series circuit with the potential electromagnet from connecting the resistor in series with the shunt field winding for a predetermined period of time to prevent premature acceleration of the operation of the motor.

2. In an arc furnace-regulator system, a movable electrode, a motor provided with a shunt field winding disposed for raising and lowering the electrode, a resistor disposed to be connected in series circuit relation with the shunt field winding of the motor, a regulator comprising a current electromagnet energized in accordance with the current flowing through the electrode and a potential electromagnet energized in accordance with the potential across the electrode are for operating the motor to maintain the are produced by the electrode substantially constant, an electromagnetic means disposed for normally short circuiting the resistor from the shunt field winding, means in series circuit relation with the potential electromagnet and dependent only on the potential operable under predetermined conditions to energize the electromagnetic means and actuate it to connect the resistor in circuit with the shunt field winding to accelerate the operation of the motor and effect an increase in the speed of raising the electrode, and means comprising a time delay device for preventing the energization and actuation of the electromagnetic means for a predetermined period of time to prevent premature acceleration of the operation of the motor.

JAMES P. HOUCK. RALPH A. GEISELMAN.

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