US2432909A - Electrode feed control system - Google Patents

Description

Dec. 16, 1947. c. c. LEVY 2,432,90

ELECTRODE FEED CONTROL SYSTEM Filed Nov. 29, 1944 Currenz l l I I I Power Factor ffilowazfs INVENTOR Fig: ,2; Cyril C. Levy, Deceased By Helen ALeuy, Brecufrzx.

ATTO Y Patented Dec. 16, 1947 UNITED STATES PATENT-OFF ggsasoe ELEGTRODE FEED CONTROL SYSTEM Cyril C.

b Hel n Pittsburgh, Pa.,

Levy, deceased, late of Pittsbur h, Pa.,

assignor to Westinghouse Electric corporation; East Pittsburgh, Pa, a corporation of Pennsylvania Application November 29, 1944, Serial No. 565,721

9 Claims. (01. 314-75) l'ouit an hat the a r nt i u uall t o ,vision is made to compensate the regulating sysfor changes in the power factor of the arc to limit the power factor at which the furnace is operated. i

1:8 and 23 positioned adjacent thereto. The

electrodes l6, l8 and 29 are directly connected to conductors 1-2, 24 and 25, respectively, which are connected to a suitable source of power throueh a power transformer not sho wn). Means such as a fle ble ab 3 a a pulley 3.9 r p 'gleel being associated with each of the elect 119 ia in an l e ng th el t od .r ctaneul rea :32 :34 and it are indii and 2 whi a through conductors 85) cated each representing the apparatus associated with one of the three phases for operating the phase electrodes l6, l8 and 23, respectively Since the operating 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 36.

As illustrated the flexible cable 28 may be wound upon a winding drum 33 operated by a reversible electrode motor 46. The electrode motor 43 comprises a field winding 42 disposed to be energized from any suitable direct current source, such as the batter 44 and an armature winding 43 ermeate by conductorsfls and 58 to be supplied with energy fiorn'a main generator 52 that is driven by an -alternating current motor 5 4 and excited by an kciter generator 55; Themaingenerator "52 comprises an armature winding ifii connectd to the conductors 48 and Stand afield -wim'iing 6'53 disposedto be supplied w ith enery from the armaturewind'ing' @Zof the ezioiter geherator 56'. As illustrated, one terminal of the ethane winding 6'2 is connected through a surgeo field winding 64 atoneme t-or and conductor 65 to a terminal" of the field g fiilfthe other'terminal of the armature winding 62 being connected by conductor 68' to the Ether terminal of the field wrndmgfec ortne main generator 52. The exciter generatoiftdis also provided with two control fieldwindings it Y disposed to be so energized as to oppose each othe and o wes n trolling the ei zcitation of the exciter generator to. Ihecontrol field winding "l d is connected across the output terminals of a rectifiefl l, the input terminals of which are connected to a current transformer which is inductiyely associated with phase conductor'Zi whereby the field wind; ing lgl is supplied with a unidirectional current that is a measure of the alternating current f win hrough the phase ndu r 2% nd t arc of that phase in the furnace Asillus trated, one terminal of the control field winding It s c nn c ed b a con u torlii to n u p t terminal of the rectifier 14, the other terminal of the field win in 19 b n normally c nn ie and 3 2, bridging Co tact member 851 of a current relay as and conductor 88 to the other output terminal of the rectifier 74. The conductor 5?, bridging contact member 81} and conductor 88 are provided for normally shunting a resistor 90, the purpose of which will belegzplainedmore fully hereinafter.

The control field winding 72 is connected by conductors :92 and .194 to the output terminals of a full -wauere ctifier 95, one of the input terminals of which is connected by conductor [9. 0 to the casingorsh ell I2 of the rumace It], the other input terminal being connected throughjanadin tebl resi to 19 t th elec rode 5? T resistor I02 is provided for adjusting the voltage supplied to the rectifier 66 with respect to the voltage across the furnace arc. The control field winding I2 is thus energized at a voltage that is a measure of the drop in voltage across the furnace arc.

The resistor 90 referred to hereinbefore as being normally shunted from circuit with the field winding 10 is disposed under predetermined conditions to be connected in the circuit with the field winding I6 to impress a voltage thereon depending upon the power factor of the arc to increase the energization of the field winding 16 over the energization that is a pure measure of the current flowing through the electrode 26.

As illustrated, the resistor 60 is connected across the output terminals of a full-wave rectifier I04, the input terminals of which are connected across a resistor I06, the voltage drop across which is rectified and impressed across the resistor 90. The resistor I06 is disposed to be so connected in circuit with resistors I08 and H6 that the vector difference of the voltages across parallel connected resistors I06 and H is impressed on the resistor I66.

In order to provide that the vector difference of the voltages across resistors I08 and I I0 is an indication of the power factor of the arc, the resistor H0 is disposed to be connected through a phase shifting circuit II2 to the secondary winding II4 of a transformer II6, the primary winding II8 of which is connected across phase conductors 24 and 26. The secondary windin I I4 of the transformer I I6 is connected across the series connected capacitor I20 and adjustable resistor I22, the resistor IIO being connected across the midpoint terminal of the secondary winding H4 and the junction of the series connected capacitor I20 and resistor I22. By adjusting the number of sections of the resistor I22 connected in the phase shifting network system I I2, an adjustment is made in the voltage impressed across resistor I I0.

The voltage impressed across resistor I08 is in opposition to that impressed across resistor H0 and is dependent upon the phase angle of the current flowing through the electrode 20. Thus resistor I08 is connected across the secondary winding I24 of a saturating transformer I26, the primary winding I28 of which is connected across the current transformer I30 which is inductively associated with the phase conductor 26. As illustrated, the energizing winding I32 of the current relay 86 is connected between the transformers I26 and I30 whereby the relay 86 is energized and responds to the current flowing through the conductor 26.

Thus the voltage across resistor H6 is constant depending upon the adjustment of the resistor I22 and the voltage across resistor I66 varies in magnitude and phase angle with variations of the phase angle between the current and voltage in the supply circuit. It is apparent that the vector difference applied to resistor I06 when rectified gives a direct current potential proportional to the phase angle difference between the arc voltage and current. When resistor 90 is connected in circuit with the control field winding I0, this direct current potential is in series with the normal polarity of the field winding 18 so that as the electromotive force due to an increase in lagging phase angle increases the net voltage applied to the control field winding will increase.

In practice the relay 86 is designed so that when a predetermined current flows through conductor 26 the relay is energized to actuate the bridging contact member 84 to a circuit opening position to connect the resistor 90 in circuit with the control field winding 10.

Referring to Fig, 2 of the drawing there is illustrated the relation between the current and power factor and kilowatts input to the furnace. As illustrated by curve I33 as the current flowing through the are or electrode increases, the power factor decreases and as illustrated by curve I34, as the current increases the kilowatt input first increases and then drops off. The peak of efficient use of power is at about power factor as represented by the vertical line I36 and it is preferred to limit the power factor of the arc to approximately this value. By design, the relay 86 is constructed so that its bridging contact member 84 is actuated to a circuit opening position at approximately the value of current flowing through the are when the peak of the curve of the kilowatt input is reached or immediately thereafter. Thus the relay 86 is responsive to a predetermined flow of current through the are for modifying and in this case increasing the energization of the control field winding 10 in response to changes in the power factor of the arc.

When the operation of the furnace is started, the phase shifting circuit H2 is adjusted to provide a predetermined constant voltage across resistor H0 in accordance with the power factor which it is desired to limit. When the operation is first started the three electrodes I6, I8 and 20 are in a raised position out of contact with the body of the material I4 which is to be heated in the furnace receptacle I2. Under these conditions no current will be flowing through the electrodes I6, I8 and 20 and no current will be flowing through the control field winding 10, the energfzation of which is a measure of the current through the phase circuit conductor 26. The voltage between the electrode 20 and the shell I2 will, however, be a maximum whereby the control field winding 12 will be fully energized.

The control field winding 12 thus excites the exciter generator 56 to develop a voltage which is applied to the main generator field winding 60 having a polarity to cause the generator 52 to build up in a direction to operate the motor 40 to move the electrode 20 downwardly. As the exciter voltage in the armature 62 builds up, the flow of current through the self-energizing winding 64 increases to increase the rate of voltage build up of the eXCiter generator 56 thus causing this voltage to build up more rapidly than it otherwise would. Thus under the influence of the field windings 64 and I2 the motor 40 is operated to rapidly lower the electrode 20 to a position where it contacts the material I4.

When the three electrodes I6, I8 and 20 are being lowered and the first one engages the bath Hi, the voltage of the are impressed across the rectifier 96 and consequently across the control field winding I2 collapses or drops to a very low value. Thus in effect, the control field winding i2 is shorted out of service and if the voltage on the control field winding I2 collapses it causes a corresponding reduction in the output voltage of the exciter generator56 and of the main generator 52, which is applied to the electrode motor 66. When one of the other electrodes I6 or I8 is lowered sufiiciently to also engage the bath of material I4 a current starts to flow through the bath between the electrodes and a resistance drop in voltage between the electrodes and the voltage between the electrodes and the casing l2 and on the control field winding 12. The effect of the control field winding l2 on the exciter generator 56 is in a, direction to tend to operate the motor 48 in a direction to lower the electrode 20 as explained hereinbefore. However, since current is now fiowing through the conductor- 26, a voltage is applied from the current transformer 76 through rectifier 74 to the control field winding To in a direction to oppose the flux developed by the field winding 12. The direction in which the motor 48 will now operator's therefore, dependent upon which of the two control field windings l9 and 12 predominate.

When the flux produced by the field winding 10 is greater than that produced by the control field winding 12, the fiuX will cause the eXciter generator 56 to develop a voltage having a polarity such as to energize the main generator field cause the motor 40 to operate in a direction to raise the electrode 20. In a similar manner if the flux developed by the control field winding 12' is greater than that developed by the control field winding 10, the polarity of voltage developed by the exciter generator 56 will be reversed thus impressing a voltage on the armature 46 of the motor 40 such as to cause the electrode 29 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 eirect is. to move the electrode 20 to such a position that the flux developed by the two control field windings l and l2 neutralize each other in which position the electrode motor 4!} will be at rest.

During the normal operation of the system of this invention the electrode 28 is maintained in a substantially constant position relative to the bath of material I 4 so that the energization of the field windings Hi and 72 are substantially equal and in position to neutralize each other. I

This result may. be obtained resistors in the input circuits M and 96. If, however, the HI should cave in on the electrode causing a short circuit, with the result that a large current flows through the electrode 29, and as soon as the current reaches the predetermined value as represented by the vertical line I35 of Fig. 2, the winding 132 of relay 85 is so energized by adjusting the for the rectifiers bath of material as to actuate its bridging contact member 84 to an open circuit position, whereby the resistor 99 is connected in circuit with the control field winding '10.

.As the fiow of current through the electrode 20 and conductor 26 increases the vector difference of the voltages on resistors I58 and H0 increases whereby an increasing voltage is im pressed across resistor 99. Since this voltage is of the same polarity as that of the control field winding 18 it is apparent that immediately upon the operation of the relay 86 the ener'gization of the field winding 16 is so increased that the voltage output of the exciter generator 56 is increased to so energize the field winding so of the main 26 is decreased to maintain it at a value approximating the value represented by the vertical line I36 of Fig. 2. As

2e thereby H soon as-the' electrode 20 is actuated to a position where the current is decreased to the predeter mined value of power factor at which it is, desired to limit the-operation, the relay 86 is de the operation of the regulator is again maintained by balance of energization of the field windings l0 and 72 in response to the current fiow through and the voltage across the furnace are. In practice, the relay is so designed that once it is energized to the open circuit position, it remains in this position until the current is reduced to a value lower than the predetermined pick-up value, whereby continuous vibrating operation of the relay 86 is limited.

By utilizing the system of this invention, it is apparent that an automatic control of the positioning of the electrodes in an arc furnace is obtained so as to maintain a balance between the current and voltage of the arc. Further by this system it is possible to automatically limit the power factor of the arc and thereby operate the furnace so that the kilowatt input to the furnace is maintained at approx mately its peak value to give maximum efii-ciency in the operation of the arc furnace.

Although this invention has been described with reference to a, particular embodiment thereof, it is, of course, not to be limited thereto except insofar as is necessitated by the scope of the appended claims.

What is claimed is:

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 are, 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 relay means disposed for operation in response to only a predetermined flow of current through the arc to efiect' a modification of only said other one of said pair of control voltages in response to changes in the power factor of the arc. 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 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 means responsive only to a predetermined flow of current through the arc for modifying only the other one of said pair of control voltages in response to changes in the power factor of the arc. 3. In a, furnace-regulator system, the combination with a movable electrode, a motor for operating the electrode, and a main generator for supplying energy to the motor, of means for governing the operation of the motor to regulate the arc, said means comprising an exciter generator connected for exciting the main generator, 3, pair of oppositely energized control field windings for the exciter generator, means for energizing one of said pair of control field windings with at current that is a measure of the voltage across the arc, means for energizing the other one or said pair of control field windings with a current that is a measure of the current flowing through the arc, and relay means disposed for operation in response to only a predetermined flow of current through the arc to effect a modification of the energization of only said other one of said pair of control field windings in response to changes in the power factor of the arc.

4. In a furnace-regulator system, the combination with a movable electrode, a motor for operating the electrode, and a main generator for supplying energy to the motor, of means for governing the operation of the motor to regulate the are, said means comprising an exciter generator connected for exciting the main generator, a pair of oppositely energized control field winding for the exciter generator, means for energizing one of said pair of control field windings with a current that is a measure of the voltage across the arc, means for energizing the other one of said pair of control field windings with a current that is a measure of the current flowing through the arc, and means operative in response to only a predetermined value of current flowing through the arc for modifying only the energization of the other one of said pair of control field windings in response to changes in the power factor of the arc.

5. 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, another source of control voltage responsive to the power factor of the are disposed to be connected in circuit with the other one of said pair of control voltages, relay contact members for closing a circuit in shunt relation to said another source, and means responsive to a predetermined current flow through the are for operating the relay contact members to remove the shunt and connect said another source of control voltage in circuit for modifying the other one of said pair of control voltages in response to changes in the power factor of the are.

6. In a furnace-regulator system, the combination with a movable electrode, a motor for operating the electrode, and a main generator for supplying energy to the motor, of means for governing the operation of the motor to regulate the are, said means comprising an exciter generator connected for exciting the main generator, a pair of oppositely energized control field windings for the exciter generator, means for energizing one of said pair of control field windings with a current that is a measure of the voltage across the arc, means for energizing the other one of said pair of control field windings with a current that is a measure of the current flowing through the are, a source of control voltage responsive to the power factor of the are disposed to be connected in circuit with the other one of said pair of control field windings, relay contact members for closing a circuit in shunt relation to the source of control Voltage, and means responsive to a predetermined current fiow through the arc for operating the relay contact members to remove the shunt and connect the source of control voltage in circuit with the other one of said pair of control field windings to modify the energization thereof in response to changes in the power factor of the are.

I. 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 resistor in series circuit with the other one ofsaid pair of control voltages, relay contact members for closing a circuit in shunt relation to the resistor, means for impressing acontrol voltage responsive to the power factor of thearc across the resistor, and means responsive to a predetermined current flow through the arc for operating the relay contact members to remove the shunt and connect the resistor in circuit with the other one of said pair of control voltages to effect a change therein in response to the power factor of the arc.

8. In a furnace-regulator system, the combination with a movable electrode,-a motor for operating the electrode, and a main generator for supplying energy to the motor, of means for governing the operation of the motor to regulate the arc, said means comprising an exciter generator connected for exciting the main generator, a pair of oppositely energized control field windings for the exciter generator, means for energizing one of said pair of control field windings with a' current that is a measure of the voltage across the arc, means for energizing the other one of said pair of control field windings with a current that is a measure of the current flowing through the arc, a resistor in series circuit with the other one of said pair of control field windings, relay contact members for closing a circuit in shunt relation to the resistor, means for impressing a control voltage responsive to the power factorof the arc across the resistor, and means responsive to a predetermined current flow through the arc for operating the relay contact members to connect the resistor in circuit with the other one of said air of control field windings to effect a change in the energization thereof in response to the power factor of the arc.

9. In an electric arc furnace control having a charge portion in which the material to be melted is placed and a power circuit including a relatively movable electrode and a phase conductor therefor, in combination, a control means disposed to be normally energized in response to the fiow of current in the phase conductor, means responsive to only a predetermined flow of current in the phase conductor for modifying the energization of said control means in response to changes in the power factor of the power circuit from a predetermined value, and means responsive to said control means when the energization thereof is so modified for moving the electrode so as to change the power factor of the power circuit in a direction toward the predetermined value.

, HELEN A. LEVY, Emecutrix of the Estate of Cyril C. Levy, Deceased.

REFERENCES CITED UNITED STATES PATENTS Name Date Chapman July 9, 1935 Number

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