US2523110A - Arc furnace regulating system - Google Patents

Description

p 19, 1950 R. A. GEISELMAIN ET AL 2,523,110

ARC FURNACE REGULATING SYSTEM Filed June 11, 1949 INVENTORS RalphAGeiselmcn 8 Eorle H.Browning, Jr.

Patented Sept. 19, 1950 ARC FURNACE REGULATIN G SYSTEM Ralph A. Geiselman and Earle H. Browning, Jr.,

Pittsburgh, Pa.,

assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application June 11, 1949, Serial No. 98,576

13 Claims.

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

This application is a continuation-in-part of our copending application Serial No. 71,812, filed January 21, 1949, and entitled Arc Furnace Regulating Systems, now abandoned.

An object of this invention is to provide in a furnace regulating system utilized for controlling the positioning of electrodes, for preventing drifting of the electrodes downwardly when the system is in an otherwise balanced condition.

Another object of this invention is to provide in an arc furnace regulating system which utilizes a pair of opposed control windings responsive to are current and are voltage for controlling the operation of the system, means to prevent drifting of the electrode when the opposed windings are in a balanced condition in response to the arc current and arc voltage.

A more specific object of this invention is to provide, in an arc furnace regulating system which utilizes a pair of opposed control windings responsive to are current and arc voltage for controlling the operation of the system, for applying a given bias to one of the control windings to change the net effective energization of the windings to tend to elfect an operation of the system to raise the electrode, thereby preventing the electrode from drifting downwardly.

Other objects of this invention will become apparent from the following description when taken in conjunction with the accompanying drawing in which:

Figure 1 is a diagrammatic view of circuits and apparatus illustrating an embodiment of this invention, and

Fig. 2 is a diagrammatic view of a part of the circuits and apparatus illustrating another embodiment of this invention.

Referring to Figure 1 of the drawing an arc furnace ii) is illustrated having a metal receptacle or shell [2 containing a bath of material It and having three movable electrodes l6, l8 and 29 positioned adjacent thereto. The electrodes I6, l8 and 28 are directly connected to conductors 22, 24 and 26, respectively, which are connected through a power transformer 28 and circuit breaker SE! to a suitable source of power represented by conductors 32, 34 and 35. Means such as a flexible cable 38 and a pulley Ml are providedbeing associated with each of the electrodes for raising and lowering the electrode. Three rectangular areas 42, 44 and 45 are indicated as representing the apparatus associated with one of the three phases for operating the phase electrodes 20, I8 and 16, respectively. Since the operatin mechanism for each of the three phases is identical, only one of the operating mechanisms is illustrated in detail and shown enclosed in the rectangular area 42.

As illustrated, the flexible cable 38 may be wound upon a winding drum 48 operated by a reversible electrode motor 50. The electrode motor 50 comprises a field winding 52 disposed to be energized from any suitable direct-current source such as the battery 54, and an armature winding 56 connected by conductors 5i and 6G to be supplied with energy from a generator 62 that is driven by an alternating-current motor 64 and excited by an exciter generator 66. The main generator 62 comprises an armature winding 68, one terminal of which is connected to the conductor 58 and the other terminal of which is connected through a self-energizing field winding 10 to the conductor for supplying the motor 50 and a field winding 12 disposed to be supplied with energy from the armature wind ing 14 of the exciter generator 66. The exciter generator 66 in this instance is provided with a field winding '16 connected across the main generator 52 to be energized in accordance with the output thereof and two control field windings l8 and which are disposed to be so energized as to oppose each other and to cooperate in controlling the excitation of the exciter generator 66.

,The control field winding 18 is connected through a series connected rectifier 82 across the output terminals of a full-wave rectifier 84, the input terminals of which are connected to a current transformer 85 which is inductively associated with phase conductor 26 whereby the field winding 18 is supplied with a unidirectional current that is a measure of the alternating current flowing through the phase conductor 26 and the arc of that phase in the furnace in. The purpose of the series connected rectifier 82 will be explained more fully hereinafter.

The control field winding 80 is connected across the output terminals of a full-wave rectifier 88, one of the input terminals of which is connected by conductor to the casing or shell I2 of the furnace, the other input terminal being connected through an adjustable resistor 92 to the electrode 20. The resistor 92 is provided for adjusting the voltage supplied to the rectifier 83 with respect to the voltage across the furnace arc. The control field winding 86 is thus enerings of the transformer 94 are disposed to be connected by a contactor 96 across two of the conductors supplying the alternating-current motor 64.

In order to control the energization of the contactor 98 which is provided with an energizing winding 98, th cable 38 associated with the electrode is provided with a projecting member IUD clamped or otheiwise secured thereto and which carries a roller 52 at the end thereof disposed for engagement under predetermined positioning of the electrode 28 with an actuating arm 104 of a pivotally mounted switch member I06. As illustrated, a spring member 108 is provided for biasing the switch I06 to a position where the contact member IIU thereof engages fixed contact members i l2 and l l4 for closing an energizing circuit for the energizing winding 98 of the contactor 96 when the roller 02 is moved out of engagement with the arm N54. The projecting member i9?) is so positioned on the cable 38 that when the electrode 20 is out of arc making position with respect to the charge I in the furnace l2, the roller )2 engages the arm I04 of the switch 565 to interrupt the energizing circuit for the contaetor 9 3. Thus when the switch IDS is actuated to a circuit closing position and the contactor 9G is energized a predetermined voltage is applied to the rectifier 82 and a predetermined bias is therefore added to the output of the rectifier 84 for increasing the energization of the control field winding I8 a, predetermined amount for controlling the operation of the exciter generator 65, as will be described hereinafter.

When the circuit breaker is in a circuit making position and the operation of the furnace and regulating system is first started, the three electrodes l6, l8 and 20 are in a raised position out of contact with the body of the material 14 which is to be melted in the furnace receptacle l2 and the switch members 106 associated with each of the electrodes is in a circuit opening position. Under these conditions, no current will be flowing through the electrodes [6, l8 and 20 and no current will be flowing through the control field winding '18, the energization of which is a measure 0f the current through the phase circuit conductor 28. The voltage between the electrode 29 and the shell [2 will, however, be a maximum whereby the control field winding 80 will be fully energized. For the purpose of describing the operation, the effect of the actuation of the switch 186 as the electrode is lowered will be ignored until later in the description of the operation.

The control field winding 80 thus excites the exciter generator 66 to develop a voltage which is applied to the main generator field winding 12 having a polarity to cause the generator 62 to build up in a direction to operate the motor to move the electrode 20 downwardly. As the main generator 62 is thus energized, the fiow of current through the field winding 16 of the exciter generator 6G increases to increase the rate of voltage build up of the exciter generator 55, thus causing this voltage to build up more rapidly than it otherwise would. Thus under the influence of the field windings 16 and 80, the motor 50 is operated to rapidly lower the electrode 20 to a position where it contacts the material 14.

When the three electrodes [6, I8 and 20 are being lowered and the first one engages the charge [4, the voltage of the arc impressed across the rectifier 8B and consequently across the control field winding 80, collapses or drops to a very low value. Thus, in effect, the control field winding is shorted out of service and if the voltage on the control field winding 80 collapses, it causes a corresponding reduction in the output voltage of the exciter generator 68 and of the main generator 62 which is applied to the electrode motor 50. When one of the other electrodes [6 or 18 is lowered sufliciently to also engage th charge of material 14, current starts to flow through the charge between the electrodes and a resistance drop in voltage between the electrodes and the casing [2 appears, thus causing an increase in the voltage between the electrodes and th casing l2 and on the control field winding 80. The effect of the control field winding 80 on the excite]: generator 66 is in a direction to tend to operate the motor 50 in a direction to lower the electrode 20 as explained hereinbefore. However, since current is now flowing through the conductor 26, a voltage is applied from the current transformer 86 through the rectifiers 84 and 82 to the control field winding 18 in a direction to oppose the flux developed by the field winding 80. The direction in which the motor 50 will now operate is, therefore, dependent upon which of the two control field windings 18 and 80 predominate.

When the flux produced by the field winding 18 is greater than that produced by the control field winding 80, th flux will cause the exciter generator 66 to develop a voltage having a polarity such as to energize the main generator field winding 12 in a direction to impress a voltage on the motor armature 56 having a polarity to cause the motor 50 to operate in a direction to raise the electrode 20. In a similar manner, if the flux developed by the control field winding 80 is greater than that developed by the control field winding 18, the polarity of voltage developed by the exciter generator 66 will be reversed, thus impressing a voltage on the armature 56 of the motor 50 such as to cause the electrode 20 to be lowered. When the electrode is raised, the arc is lengthened, the arc current decreases and the arc voltage increases, and when the electrode is lowered, the arc current increases and the arc voltage decreases. The resulting effect is to move the electrode 20 to such a position that the flux developed by the two control field windings 18 and 80 so neutralize each other that such field windings will have zero net effective energization, in which position the electrode motor 40 will be at rest. As will be appreciated, there are different arcing positions of the electrodes l6, l8 and 20 depending upon the condition of the charge and the amount of the charge at which such Zero net effective energization will be obtained for maintaining the electrode in a given arcing position with respect to a balance between the arc current and the arc voltage. This will be appreciated for as the charge is melted, the relative positions of the electrodes with respect to the charge will have to be adjusted in order to maintain given arcing conditions.

In the description of the operation given hereinbefore, the effect of the added bias impressed on the energizing circuit for the control .field winding 18 from the rectifier 82 has been ignored in order to simplify the description of the operation. As will be appreciated, as the electrodes are moved downwardly to engage the charge and eifect an arc therebetween, the switch I06 is actuated to a circuit closing position where the winding 98 of the contactor 96 is energized to actuate the contactor 86 to a circuit closing position where the transformer 94 is energized to impress a predetermined voltage across the series connected rectifier 8 2. This voltage is small with respect to any voltage across the output terminals of the rectifier 84 and can be readily adjusted to give a desired or required bias on the control field winding 18.

As explained .herein'before, the normal energization of the control field windings I8 and 80 resulting from a measure of the arc current and arc voltage, respectively, is such that for a given arcing position the net effective energization of the control field windings I8 and 80 is to provide a zero effective energization on the exciter generator 66 to prevent an operation of the motor 50. However, in practice it is found that the weight of the electrodes and the shafts and other equipment associated therewith is such that where the net efiective energization of the control field windings 18 and 80 is zero, the weight of the electrodes causes the electrodes to drift downwardly whereby the arc current and arc voltage changes and causes an operation of the regulating system to again position the electrode.

This is undesirable as it effects a more or less,

continuous operation of the regulating system to overcome the drifting effect of the electrodes.

By impressing a predetermined bias from a separate source, as described hereinbefore, across the series connected rectifier 82, the predetermined bias tends to so increase the energization of the control field winding "I8 that the net effective energization of the control field windings l8 and 80 under otherwise normal positioning of the electrode to maintain a zero net e'iiective energization of the control field windings '78 and 80, changes in a direction to tend to so increase the energization of the exciter generator in a direction to cause the motor '50 to ten'd'to operate to raise the electrode 20. The bias applied to the control field winding 18 under such circumstances will be of only sufficient value to overcome the tendency of the electrode to drift, whereby the-change inthe-net effective energization of the control field windings l8 and 80 to tend to raise the electrode will only be sufiicient to maintain the electrode in a given arcing position and prevent drifting-of the electrode downwardly.

In the embodiment illustrated in Fig.2, the additional bias from the transformer 94 is applied to the control field winding 80 instead of the control field winding 18' of the exciter generator 66 as in theembodiment of Figure 1. Thus in Fig. 2 the control field winding 18 is connected directly across the'output terminals of the rectifier 84 to be energized directly in accordance with a measure of the'alternating current flowing through the phaseconductor 26 and the arc of that phase in thefurnace l-O.

As illustrated in Fig. 2 the output terminals'o'f the full wave rectifier 82 supplied from'the transformer 94 when'the contactor 96 is in a circuit closing position are connected'through a resistor I14 of high ohmic value with respect to 'thatof the control field winding 88 to the leads connecting the output terminals of the full wave rectifier 88 to the control field winding 80. The polarity of the voltage across the output terminals of the rectifier 82 is of opposite sense to the polarity of the voltage across the output terminals of rectifier 88 so that when the voltage across rectifier 82 is impressed across the control field winding it effects a net reduction in the voltage normally impressed thereacross from the rectifier-88.

This reduction in the energiza-tion of the control field winding 80 so changes the net eiiective energization of the control field windings 18 and 80 as to tend to increase the energization of the exciter generator 66 in a direction to cause the motor 50 to tend to operateto raise the electrode 20. The bias applied to the control field winding 80 under such circumstances Will be of only suflicient value to overcome the tendency of the electrode to drift, whereby the change in the net effective energization of the control field windings 18 and 80 to tend to raise the electrode will only be suificient to maintain the electrode in a given arcing position and prevent drifting of the electrode downwardly.

Thus whether the bias applied by reason of the voltage across the rectifier 82 is impressed on the control field winding 18 as in the embodiment of Figure l or is impressed on the, control field winding 80 as in the embodiment of Fig. 2 the result is that the change in the net effective energization of the combined control field windings l8 and 8.0 is to tend to increase the .energization of the exciter generator 66 to prevent drifting of the electrode downwardly.

As illustrated, the additional bias applied to the control field winding 18 as in Figure 1, or to the control field winding 80 as in Fig. 2, is applied thereto for all arcing positions of the electrode 20., the switch i 06 being effective to interrupt the energizing circuit of the contactor 96 only when the electrodes are in a non-arcing and raised position. Thus, even before an arc is struck, if the electrode tends to drift downwardly, the switch 06 is actuated to a .circuit closing position to efiect the actuation of the contactor 96 to a circuit closed position to energize the transformer 94 and impress a voltage of predetermined polarity on either control field winding 18 or 80 as described hereinbefore to tend to energize the exciter generator 66 to prevent drifting of the electrode downwardly.

This invention provides a means for overcoming a detrimental operational eifect commonly found in connection with regulating systems for regulating the positioning of the electrodes withoutv complicating the regulating equipment employed. This is apparentfor the bias is applied to the exciter generator without entailing any additional excitation windings therefor and is accomplished by the simple addition of a switch and a contactor for controlling the bias applied to a series connected rectifier in the energizing circuit for the control field winding 18 as in Figure l, or to the rectifier 82 connected in circuit with the control field. winding 80 as in the embodiment of Fig. 2.

The regulating system of this invention provides a simple automatic-control of the position of the electrodes in an arc furnace with means for'insuring the correct positioning of the electrodes to maintain a balance between the current and voltageof the arc; The system can be readily reproduced with standard-components.

We claim as our invention:

1. In a furnace-regulator system, the combination comprising, a movable electrode, a motor for operating the electrode, means for controlling the operation of the motor to control the arc, said means including a pair of control windings disposed to be oppositely energized in accordance with measures of the arc current and are voltage, and energizing means connected in circuit with one of the pair of control windings during drifting movement of the movable electrode while approaching or while in an arcing position to increase the net effective energization of the control windings in a direction to tend to effect the operation of the motor to raise the electrode and thereby prevent drifting of the electrode downwardly. I

2. In a furnace-regulator system, the combination comprising, a movable electrode, a motor for operating the electrode, means for controlling the operation of the motor to control the are, said means including a pair of oppositel disposed control voltages, one of said pair of control voltages being a measure of the voltage across the arc, the other one of said pair of control voltages being a measure of the current flowing through the arc, and energizing means disposed to be connected in circuit with the other one of said pair of control voltages during drifting movement of the movable electrode while approaching or while in an arcing position for increasing said other one of said pair of control voltages a predetermined amount to prevent drifting of the electrode in a downward direction.

3. In a control system for an electric arc furnace, the combination comprising, a movable electrode, a motor for operating the electrode, a source for supplying energy to the electrode motor in either of two polarities for rotating the electrode motor in either of two directions, said source including a pair of control field windings disposed to be oppositely energized, one of the control field windings being energized in accordance with a measure of the voltage across the arc, the other of the control field windings being energized in accordance with a measure of the current flowing through the arc, and means disposed to be connected in circuit with said other control field winding during a predetermined positioning of the movable electrode for increasing the energization of said other control field winding a predetermined amount to so control the supply of energy to the motor as to prevent drifting of the electrode downwardly.

4. In a control system for an electric arc furnace, the combination comprising, a movable electrode, a motor for operating the electrode, a generator for supplying effective operational energization for said motor, a pair of differentially connected field windings for the generator arranged to normall have zero net effective energization under predetermined balanced conditions of arc current and are voltage for different arcing positions of the electrode, and means disposed to be connected in circuit with one of the pair of differentially connected field windings during a predetermined positioning of the movable electrode to so increase the net effective energization of the pair of differentially connected field windings in one direction as to energize the motor to tend to raise the electrode thereby preventing drifting of the electrode downwardly from any of said different arcing positions of the electrode.

' 5. In a furnace regulator system, the comblnation comprising, a movable electrode, a motor for operating the electrode, means for controlling the operation of the motor to control the arc, said means includin a pair of control windings disposed to normally be oppositely energized in accordance with measures of the arc current and are voltage to have a zero net effective energization under predetermined balanced conditions of the arc current and arc voltage for different arcing positions of the electrode, a separate source of energy, a contactor disposed to be en ergized to connect the separate source of energy in circuit with one of the pair of control windings to effect a change in the net effective energization thereof in a direction to tend to effect the operation of the motor to raise the electrode and thereby prevent drifting of the electrode downwardly, and means controlled by the positioning of the electrode for effecting the energization of the contactor for the different arcing positions of the electrode.

6. In a furnace-regulator system, the combination comprising, a movable electrode, a motor for operating the electrode, means for controlling the operation of the motor to control the are, said means includin a pair of oppositely disposed control voltages, one of said pair of control voltages being a measure of the voltage across the arc, the other one of said pair of control voltages being a measure of the current flowing through the arc, a separate source of energy, a contactor disposed to be energized to connect the separate source of energy in circuit with the other one of said pair of control voltages for increasing said other one of said pair of control voltages a predetermined amount to tend to effect the operation of the motor to raise the electrode and thereby prevent drifting of the electrode downwardly, and means controlled by a predetermined positioning of the electrode for effecting the energization of the contactor.

7. In a control system for an electric arc furnace, the combination comprising, a movable electrode, a motor for operating the electrode, a source for supplying energy to the electrode motor in either of two polarities for rotating the electrode motor in either of two directions, said source including a pair of control field windings disposed to be oppositely energized, one of the control field windings being energized in accordance with a measure of the voltage across the arc, the other of the control field windings being energized in accordance with a measure of the current flowing through the arc, a separate source of energy, a contactor disposed to be energized to connect the separate source of energy in circuit with the other of the control field windings for increasing the energization thereof a predetermined amount to tend to rotate the motor in a direction to raise the electrode and thereby prevent drifting of the electrode downwardly, and means controlled by a predetermined positioning of the electrode for effecting the energization of the contactor.

8. In a control system for an electric arc furnace, the combination comprising, a movable electrode, a motor for operating the electrode, a generator for supplying effective operational energization for said motor, a pair of differentially connected field windings for the generator arranged to normally have zero net effective energization under predetermined balanced conditions of arc current and are voltage for different arcing positions of the electrode, a separate source of energy, a contactor disposed to be energized to connect the separate source of energy in circuit with one of the pair of differentially connected field windings to so increase the net effective energization of the pair of differentially connected field windings in a direction to tend to energize the motor to raise the electrode and thereby prevent drifting of the electrode downwardly from any of said different arcing positions of the electrode, and means controlled by the positioning of the electrode for effecting the energization of the contactor for the different arcing positions of the electrode.

9. In a furnace-regulator system, the combination comprising, a movable electrode, a motor for operating the electrode, means for controlling the operation of the motor to control the are, said means including a pair of control windings disposed to normally be oppositely energized in accordance with measures of the are current and arc voltage to have a zero net effective energization under predetermined balanced conditions of the arc current and are voltage for different arcing positions of the electrode, a separate source of energy, a contactor disposed to be energized to connect the separate source of energy in circuit with one of the pair of control windings to effect a change in the net effective energization thereof in a direction to tend to effect the operation of the motor to raise the electrode and thereby prevent drifting of the electrode downwardly, and a switch disposed to be actuated into circuit closing position during predetermined positioning of the electrode for effecting the energization of the contactor for the different arcing positions of the electrode.

10. In a furnace-regulator system, the combination comprising, a movable electrode, a motor for operating the electrode, means for controlling the operation of the motor to control the arc, said means including a pair of oppositely disposed control voltages, one of said pair of control voltages being a measure of the voltage across the arc, the other one of said pair of control voltages being a measure of the current flowing through the arc, a separate source of energy, a contactor disposed to be energized to connect the separate source of energy in circuit with the other one of said pair of control voltages for increasing said other one of said. pair of control voltages a predetermined amount to tend to effect the operation of the motor to raise the electrode and thereby prevent drifting of the electrode downwardly, and a switch disposed to be actuated into circuit closing position during predetermined positioning of the electrode for effecting the energization of the contactor.

11. In a control system for an electric arc furnace. the combination comprising, a movable electrode, a motor for operating the electrode, a source for supplying energy to the electrode motor in either of two polarities for rotating the electrode motor in either of two directions, said source including a pair of control field windings disposed to be oppositely energized, one of the control field windings being energized in accordance with a measure of the voltage across the arc, the other of the control field windings being energized in accordance with a measure of the current flowing through the are, a separate source of energy, a contactor disposed to be energized to connect the separate source of energy in circuit with the other of the control field windings for increasing the energization thereof a predetermined amount to tend to rotate the motor in a direction to raise the electrode and thereby prevent drifting of the electrode downwardly, and a switch disposed to be actuated into circuit closing position during predetermined positioning of the electrode for effecting energization of the contactor.

12. In a control system for an electric arc furnace, the combination comprising, a movable electrode, a motor for operating the electrode, a generator for supplying effective operational energization for said motor, a pair of differentially connected field windings for the generator arranged to norma1ly have zero net effective energization under predetermined balanced conditions of arc current and arc voltage for different arcing positions of the electrode, a separate source of energy, a contactor disposed to be energized to connect the separate source of energy in circuit with one of the pair of differentially connected field windings to so increase the net effective energization of the pair of differentially connected field windings in a direction to tend to energize the motor to raise the electrode and thereby prevent drifting of the electrode downwardly from any of said different arcing positions of the electrode, and a switch disposed to be actuated into a circuit closing position during predetermined positioning of the electrode for effecting the energization of the contactor for the different arcing positions of the electrode.

13. In a furnace-regulator system, the combination comprising, a movable electrode, a motor for operating the electrode, means for controlling the operation of the motor to control the arc, said means including a pair of oppositely disposed control voltages, one of said pair of control voltages being a measure of the voltage across the arc, the other one of said pair of control voltages being a measure of the current flowing through the arc, and energizing means connected in circuit with a predetermined one of the pair of control voltages during drifting movement of the movable electrode while approaching or while in an arcing position for increasing the effective voltage of said pair of opposed control voltages in a direction to tend to effect the operation of the motor to raise the electrode and thereby prevent drifting of the electrode downwardly. RALPH A. GEISELMAN. EARLE H. BROWNING, JR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,449,579 Boddie Mar. 27, 1923 2,351,420 Garr et a1 June 13, 1944 2,442,003 Harris May 25, 1948 2,450,159 Pickslay Sept, 28, 1948

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