US2008537A - Electric furnace regulator system - Google Patents

Description

July 16, 1935. F, ACKLEY 2,008,537

ELECTRIC FURNACE REGULATOR SYSTEM Filed Oct. 26, 1952 Inventor": Frederick Ackle Hi 3 Attorne y.

Patented July 16, 1935 UNITED. STATES PATENT OFFICE ELECTRIC FURNACE REGULATOR SYSTEM Frederick E. Ackley, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application October 26, 1932, Serial No. 639,625

' 6 Claims. (01. 13-13) My invention relates to electric furnace regushown as a three-phase one it will be understood lator systems, more particularly to electric arc that my invention is also applicable to a single furnace regulator systems, and has for its obphase furnace. The electrodes are each adjustject the provision of simple and reliable means able in a vertical direction to vary the length of for adjusting the-electrodes so as to maintain a the arc in any suitable manner. This adjusting 5 predetermined current in the electrode circuit. means is shown diagrammatically for the elec- More particularly it is an object of my inventrode 15 only and comprises a suitable reversible tion to provide control means for the electrode electric motor '16 shown as a direct motor proadjusting means whereby the electrode is advided with a shunt field winding H, which motor justed quickly in response to changes in the elecis connected to rotate a fixed gearwheel l8 hav- 10 trode current and furthermore without over ing its bore threaded to receive a screw rod l3 adjustment or hunting action. The rate of adattached to the electrode l5. justment is made dependent upon, the amount of My invention relates in particular to a current the adjustment to be made in such manner that responsive control system for the electrode mothe electrode is adjusted rapidly for relatively tor Hi. It will be understood, of course, that 15 large changes in position, the rate of adjustment while only one control system for this one elecdecreasing as the electrode approaches its final trode is shown a similar control system will be position. provided as desired for each of the electrodes i3 In carrying out my invention, I provide a pair and M.

'20 of spaced contacts together with a cooperating The current responsive control system for the contact member provided with projections which electrode motor 16 comprises a contact device 20 is rotated at a predetermined speed between the provided with two pairs of spaced contacts 2|, 22 contacts. I also provide means for moving one and 21a, 220., shown as spring contact arms which or the other of the two contacts into engagement are mounted in insulated relation to each other on with the projections in response to the current in a suitable supporting member 24. This member 24 5 the electrode circuit and in dependence upon the is mounted on a pivot shaft 25 and is connected to direction of the necessary adjustment whereby an electric torque motor 26 for movement on its means are operated to controlv the electrode adpivot. The torque motor 26 is connected to be justing means. The length of time that the conenergizedfrom a current transformer 21 in the tact is in engagement with any one projection is circuit of the electrode l5. The torque motor is 30 dependent upon the amount of the correction. biased in one direction by means of the spring 28, For a small adjustment the contact is moved the torque applied by the motor being in opposimerely enough tojust make contact with these tion to the spring. An adjustable rheostat 29 is projections, the contact being quickly broken, connected across the current transformer 21 for whereas for a larger adjustment the contact is adjusting the current response of the torque mo- 35 moved farther so that it rides over the projection tor. Also a suitable fluiddamping device 30 is and maintains contact therewith for a longerinconnected to the torque motor. terval. I have also provided a second pair of A rotating contact member shown as a starcontacts between which is a rotating contact disc, wheel 3| is mounted between the pair of contact these contacts being adjusted to engage the disc arms 2 I, 22,it being secured to a shaft 32 driven by 40 upon a current change of a predetermined greater a suitable synchronous driving motor 33 which magnitude and thereby cause the motor to opis connected through a transformer 34 to the crate at a higher speed for a quick rough adjustsource of supply 35 for the furnace. The shaft 32 ment. is parallel with the pivot shaft 25 although this For a more complete understanding of my in relation has been modified somewhat in the 45 vention reference should be had to the accomdrawing for purposes of clarity. During the oppanying drawing, the single figure of which eration of the furnace the starwheel 3| is rotated shows in diagrammatic form an arc furnace regbetween the pa of c acts 22 at a subulator system embodying my invention. stantially constant speed. The distance between Referring to the drawing, I have shown my the.contacts is somewhat greater than the diam- 50 invention in one form as applied to an arc 'fureter of the starwheel so that when the contacts nace 10 comprising a suitable crucible II for a are in a central position, corresponding to the metallic charge 12 and suitable electrodes l3, I4 desired current in the circuit, the starwheel is free and I5 extending into the crucible into arced reto rotate without touching either contact. 7

lation with the charge. While the furnace is thus In the operation of the system, a decrease in current in-the circuit of the electrode belowv a predetermined value to be maintained, for which the torque motor 26 is adjusted by means of the resistance 29, results in a decrease in the torque of the motor 26 whereby the contacts are turned about the pivot 25 in a clockwise direction,

as viewed in the drawing, by means of the spring 28. This brings the contact 2| into engagement with the starwheel whereby a circuit is closed from one side of a suitable direct current supply source 36 through the conductor 31, the switches 38, 39'and 4|] which are normally closed, the conductor 4|, a collector ring 42 and thence through the shaft 32 or by means of a suitable conductor to the starwheel 3 I. From the starwheel the circuit continues through the contact 2|, the conductor 43, an operating coil 44, and conductor 45 back to the opposite side of the supply source 36. The operating coil 44 picks up a switch 46 in the circuit of the electrode motor |6 thus closing a circuit to start the motor in the direction to lower the electrode. The closing of the switch 46 at the same time opens a normally closed switch 41 which is mechanically interlocked with the switch 46. The circuit of the motor l6 may be traced from one side of the supply source 36 through the conductor, the resistance 69, the resistance 50, the switch 46, conductor 5 I, the series field 52 of the motor, the armature of the motor, conductor 53, a normally closed switch 54, the resistance 55, and conductor 45 back to the opposite side of the supply source. It will be understood that the normally closed switches 41 and 54 are suitably held in their closed positions, shown in the drawing, as by the friction in the switch parts or by means of suitable springs (not shown) It will be observed that if the change in the electrode current to be corrected for is relatively small, then the torque motor will give the contact 2| a relatively small movement so as to bring the contact into position to perhaps be barely touched by each projection of the starwheel as it moves past. In such case the motor operates only a relatively small part of the time, that is, while the contact is actually engaged by the'starwheel to close the circuit, the motor being stopped quickly by dynamic braking when the control circuit is broken by disengagement of the contact. The dynamic braking circuit for the motor |6 may be traced from one side of the armature through the conductor 5|, switch 41, a re-- sistance 55, switch 54, and the conductor 53 back to the other side of the armature. The particular dynamic braking switch 41 or 54 which is open when the, motor is in operation is immediately closed, when the control circuit is opened, by its respective operating coil 56 or 51. These coils are connected in parallel across the motor armature, and hence are energized by the counter-electromotive force ofthe motor to close the switch 41 or 54 which is open when the control circuit is opened.

In c'ase'a relatively great change in electrode current is to be corrected for, then the torque motor moves contact 2| a corresponding great distance so" that it will be engaged earlier by each projection of the starwheel, thatis, before the point of the projection reaches it. It will be observed that each projection of the starwheel is shapedlike a saw tooth, it being wider at the base. After engagement, the contact rides up and over the end of the projection to the other side by reason of the resiliency of its spring arm support thus maintaining the control circuit closed for a longer period of time with consequent increased period of operation of the electrode motor. As the current increases due to the corrective action, the torque motor moves the contact 2| away from the starwheel and consequently the periods of operation of the motor decrease with consequent slowing down in the rate at which the electrode is lowered. Finally when the predetermined current has been reestablished in the electrode circuit, the contact 2| will have been moved to a position where it is no longer engaged by the starwheel and the electrode motor consequently -into engagement with the starwheel whereby a circuit is closed for the operating coil 58, this circuit leading from the starwheel through the contact 22, conductor 59, the coil and conductor 45 to the other side of the supply source 36. This closes the switch 66 in the armature circuit of the electrode motor |6' whereby the armature is connected to the supply source 36 for opposite rotation, the braking switch 54 being at the same time opened since it is interlocked with the switch ,66. The circuit of the motor now leads through the-conductor 48, resistance 49, switch 66, conductor 53, the armature of the motor, the series field 52, conductor 5|, switch 41 and conductor 45 back to the supply source 36. This produces rotation of the electrode motor to raise the electrode, the motor being operated for short intervals of gradually decreasing duration, and stopped by dynamic braking, until the electrode current has been re-established'as will be understood from the previous description.

It will be observed that when the electrode is being raised theresistance 49 is included in the armature circuit of the motor |6 but not the resistance 50 whereas both resistances are included in the circuit when the electrode is lowered. This provides for the increased torque required to raise the electrode and also tends to cause the motor to operate at a lower speed when lowering the electrode.

Mounted on the shaft 32 between the pair of contacts 2|a, 22a is a conducting disc 6|. This disc is connected to the same circuit as the starwheel 3|. Upon a relatively great or maximum change in electrode current one or the other of these contacts is moved into engagement with the disc 6| whereby a circuit is closed for an op.-

erating coil 62 which opens a switch 63 and thereby opens a shunt circuit connecting the resistance 64 across the armature of the electrode motor. This auxiliary control means operates to continuously maintain the switch 63 open and thus prorent in one electrode such as might be caused, for

example, by the throwing of a shovelful of lime undemeath'one of the electrodes. The high resistance of the lime results in a decrease in the current in the electrode in contact therewith and therefore a decrease in the current in the other two electrodes. It is a characteristic of an are however that, assuming a given length of arc, the voltage across the arc varies inversely with the current through it. Therefore a decrease in the current through the other two arcs results in an increase in their voltage, and since a fixed voltage only is available from the source of supply 35, this increase in voltage across two of the arcs results in a lower available voltage across the lime, that is, between that electrode and the bath. If no protection were provided for this contingency the automatic regulators would operate to lower the electrodes.

To provide against this contingency I provide suitable means responsive to this decreased voltage from one electrode to the bath for preventing the automatic regulators from lowering the electrodes. Specifically I provide the three undervoltage relay switches 38, 39 and 40 which are normally held closed by operating coils 65, 66 and. 6'! connected respectively across the arcs to the electrodes l3, l4 and 15. As shown, one common connection for the three coils is made through a conductor 68 connected to the charge I2 which forms a neutral point of the three-phase circuit. Therefore, in case the voltage between any one electrode and the bath decreases to value below a predetermined minimum, the corresponding undervoltage relay drops out and opens its switch, thus preventing closure of any one of the control circuits for the three electrode motors. It will be understood that the conductor 4| leads, through the conductors 69 and 10, to the control circuits of the other two electrodes.

This means for preventing lowering of the electrodes is described and claimed in a copending application of Numan R. Stansel, S. No. 651,340, filed January 12, 1933, and assigned to the same assignee as this invention.

The torque motor 26 may be of any suitable type and may consist, for example, of two coils one of which is mounted for rotation and is connected to the support 24, these two coils being inductively related. A dephased current for one coil is provided by a resistance 'H and a condenser 12 in its circuit. Preferably adjustable stops 13 and 14 are provided for limiting the movement of the contact device in each direction and prevent damage to the device in the event of current surges. While I have shown a particular embodiment of my invention, it will be understood, of course, that I do not wish to be limited thereto since many modifications may be made, and I, therefore, contemplate by the appended claims to cover any such modifications as fall within the true spirit and scope of my invention.

-What I claim as new and desire to secure by Letters Patent of the United States, is:

1. An electric furnace regulator system, comprising in combination with an electrode, adjusting means for said electrode, means continu- 'ously driven for effecting intermittent operation of said electrode adjusting means to raise or to lower said electrode, means for varying the duration of the time of operation of said electrode adjusting means, means responsive to the current in said electrode for operating said duration adjusting means, and auxiliary means responsive to a predetermined maximum change in said current for controlling said electrode adjusting means.

2. An electric furnace regulator system comprising in combination with an electrode a motor for raising and lowering said electrode, switching means for intermittently closing the circuit of said motor for variable periods of time, means for continuously operating said switching means, means responsive to variations in the current in said electrode for operating said switching means to initiate closure of said motor circuit for operation to raise or to lower said electrode for periods of time dependent upon the magnitude of said current variations and auxiliary means responsive to current variations of a predetermined maximum magnitude for controlling said motor.

3. An electric furnace regulator system comprising the combination with an electrode, a motor for raising and lowering said electrode, circuits for said motor including a pair of movably mounted spaced spring contacts, a starwheel mounted for rotation between said contacts, means for rotating said starwheel, means responsive to the current in said electrode for moving one or the other of said contacts into engagement with said starwheel to close the circuit of said motor for operation to raise or to lower said electrode, a second pair of spaced contacts mounted for movement with said first pair, a disc mounted for rotation with said starwheel between said second pair of contacts, said second pair of contacts being arranged to engage said first contacts upon the occurrence of greater current variations, and means controlled by said second pair of contacts for continuously controlling said motor to give a more rapid movement of said electrode.

4. An electric furnace regulator system comprising in combination with an electrode, a motor for raising and lowering said electrode, selective switching means for intermittently closing the circuit of said motor for variable periods of time and for operation to raise or to lower said electrode, means for continuously operating said switching means, means responsive to a decrease in the current in said electrode below a predetermined value for operating said switching means to close the circuit of said motor for operation to lower said electrode, means responsive to an increase in the current in said electrode above a predetermined value for operating said switching means to close the circuit of said motor for operation to raise said electrode, said switching means being operated to maintain the circuit of said motor closed for periods of time dependent upon the magnitude of said current variations, and auxiliary means responsive to a decrease in current below said predetermined minimum value or an increase in current above said predetermined maximum value for establishing a continuous contact to control said motor for movement of said electrode at an increased rate.

5. An electric furnace regulator system comprising in combination with an electrode, a motor for raising and lowering said electrode, selective switching means for intermittently closing the circuit of said motor for variable periods of time and for operation to raise or to lower said electrode including an intermittent contact member, a second contact member cooperating with said intermittent contact member, said intermittent contact member being mounted for movement to make intermittent contact with said second contact member, means for driving said intermittent contact member, means responsive to a decrease in the current in said electrode below a predetermined value for operating said second contact member to close the circuit of said motor for operation to lower said electrode, means responsive to an increase in the current of said electrode above a predetermined value for operating said second contact member to close the circuit of said motor for operation to raise said electrode, means for establishing a dynamic braking circuit for said motor when its circuit is opened under the control of said intermittent contact member, and an auxiliary means responsive to a decrease in current below said predetermined minimum value or an in- I crease in current above said predetermined maxsaid motor. including a pair of spaced contacts mounted for movement in one or the other of two directions, a contact member mounted for rotation between said spaced contacts, means for rotating'said contact member, said contact member being provided with means arranged to intermittently engage one or the other of said spaced contacts when said contact member is rotated, means responsive to the current in said electrode for moving said contacts in one direction or the other to bring one or the other of said contacts into engagement with said intermittent contact member, an auxiliary pair of spaced contacts mounted for movement with said first pair of spaced contacts, an auxiliary rotatable contact member mounted for rotation with said first rotatable contact member and arranged to be engaged by said auxiliary pair of contacts to maintain a continuous contact to control said motor for increased rate of movement of said electrode, and means for dynamically braking said motor when its circuit is opened under the control of FREDERICK E. ACKLEY.

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