US3594486A

US3594486A - Process and equipment for operating electric arc furnaces

Info

Publication number: US3594486A
Application number: US861059A
Authority: US
Inventors: Manfred Jellinghaus
Original assignee: Heppenstall Co
Current assignee: Heppenstall Co
Priority date: 1969-09-25
Filing date: 1969-09-25
Publication date: 1971-07-20
Anticipated expiration: 1988-07-20

Abstract

A process and apparatus are provided for operating three-phase electric arc furnaces by maintaining equal impedance in all of the three electrode circuits. This may be accomplished by adjusting the relative sag of the circuit wires.

Description

United States Patent l I UN Inventor Mlnlred Jellinghans Rheinhluaen, Germany Appl. No. 861,059

Filed Sept. 25, 1969 Patented July 20, l97l Assignee Heppenshll Company Pittsburgh, Pa.

PROCESS AND EQUIPMENT FOR OPERATING ELECTRIC ARC FURNACES 5 Claims, 2 Drawing Figs.

US. Cl 13/13 Int. CL "05h 7/10 Field Search l3/9, l2,

[56] References Cited UNITED STATES PATENTS 3,078,325 2/1963 Dillon et a]. [3/9 3,156.754 ll/l964 Duchting it 4. 13/9 Primary Examiner-Bernard A Gilheany Assistant Examiner-R. N. Envall, Jr. Attorney-Rue", Blenko & Ziesenheim ABSTRACT: A process and apparatus are provided for operating three-phase electric arc furnaces by maintaining equal impedance in all of the three electrode circuits. This may be accomplished by adjusting the relative sag of the circuit wires.

PATENTED JUL20 1971 SHEET 2 OF 2 Fig.2.

mvsmon Manfred Jellinghuus PROCESS AND EQUIPMENT FOR OPERATING ELECTRIC ARC FURNACES This invention relates to methods and apparatus for operating electric arc furnaces and particularly to a process and equipment for operating electric arc furnaces on three-phase current for the production of steel.

In the case of known electric arc furnaces which can be tilted for the production of steel, the electric circuits for three electrodes which are arranged in a triangle are at one side of the furnace. Due to this arrangement, the circuits have different impedances which cause an irregular burning of the electrodes and the masonry of the furnace. Moreover, in operation, the circuits are changed in position due to the auto matic adjustment of the electrodes as a function of their burning. This also results in a change in the impedances.

In order to reduce this irregular wear which is caused by the variable impedances and which is called the sharp phase, the suggestion has already been made that the arc outputs of the individual electrodes be adjusted diITerently. In the case of another suggestion for reducing the irregular wear, three single-phase transformers which are placed next to each other are used. However, satisfactory results have not been obtained with either of these known devices.

Satisfactory results with respect to the uniform burning of the electrodes and the masonry of the furnaces have been obtained only with nontippable electric arc furnaces which are not used for ferrous alloys and which have single-phase transformers placed in a triangle around the furnaces. However, such an arrangement is not suitable for electric arc furnaces which are to be used to produce steel, since the single phase transformers prevent or even make impossible the tipping of the furnaces due to their triangular arrangement around the furnace.

Consequently, it is a purpose of the present invention to create a process and a device for the operation of threephase fed electric arc furnaces with which a uniform burning of the electrodes and a uniform wearing of the masonry of the electric arc furnaces can be obtained. The electric arc furnaces are to be usable especially for the production of steel.

This problem is solved according to the present invention by keeping the circuit impedances of the electrodes equal to each other. Hereby a uniform wear, both of the electrodes as well as the masonry of the electric arc furnace is assured. Since, for example, the transformer for the balancing of the three circuit impedance: does not need to be arranged around the furnace, the electric arc furnace can be tipped without hindrance by the transformer or circuits and thus can be used for the production of steel.

One advantageous embodiment of the present invention provides that the adjustment of the circuit impedances takes place by shifting the circuit cables. This is a very simple possibility of changing the impedances. According to another embodiment of the invention it is preferable that all the circuits are not changed but that the shifting of the circuits takes place only at the slack of the circuits.

The process according to the invention is suitable for electric are furnaces with a random arrangement of electrodes. However, the electrodes are preferably arranged in a triangle for one furnace and moreover two of the electrodes are preferably placed at the same distance from the transformer. Then it is advantageous to undertake the shifting either at the circuits of the center electrode or at both circuits of the two outer electrodes. Undertaking the shift at the two outer circuits has proved particularly advantageous.

A device according to the invention for executing the process is characterized by the fact that each electrode is connected with a measuring apparatus for the circuit: impedance which is connected to a comparison instrument for measuring values of the circuits impedancesand by the fact that at least one adjusting organ for shifting t8e circuit is actuated by the output signals of the comparison instrument. Preferably, an

adjusting organ is provided at both of the outer circuits. However it is also possible to connect adjusting organs to all circuits so that the compensation of the circuitss impedanccs can be undertaken at all circuits.

As a preferred device, the invention suggests that the adjusting organs be home by position support arms and have lifting and lowering devices to which the circuits are connected. lnsofar as tubes which direct the circuits over the electrode support arms have a flexible piece, the contact point of the lifting and lowering devices according to the invention should be at the end of the electrode support arm seen from the electrode out. By means of the lifting and lowering devices which are arranged with the electrode carrier arms, changes in the circuit impedances, which are also influenced to a large extent by the position of the electrode support arms with respect to each other, can be equalized by lifting and lowering the sag of the circuits.

In the foregoing general description certain objects, purposes and advantages of this invention have been set out.

Other objects, purposes and advantages will be apparent from a consideration of the following description and the accompanying drawings in which:

FIG. 1 is a side elevational view, partly in section, of an apparatus according to the invention; and

FIG. 2 is a schematic view of an apparatus such as that of FIG. I with a second embodiment of control.

Referring to the drawings l have illustrated an electric arc furnace 10 having three electrodes ll, 12 and I3, which are arranged in an equilateral triangle. Two of these electrodes II and I3 are placed equally distant from a transformer 14 which is housed within a walled area 15 having an opening I6 through which the connecting leads [7, I8 and 19 pass to the electrodes. Each of the electrodes 11, I2 and I3 is mounted on an adjustable

electrode support arm

20, 21 and 22 respectively. The electrodes II, 12 and I3 are connected to the transformer leads 17, I8 and I9 by

circuits

23, 24 and 25 respectively. Each of the

circuits

23, 24 and 25 passes over the

support arms

20, 2t and 22 respectively within

pipes

26, 27 and 28 supported on said arms. Each of the

outside pipes

26 and 28 have a

flexible portion

29 and 30. A lift and

lower mechanism

31 and 32 is mounted on each of the

outside support arms

20 and 22 and carries the

outside pipes

26 and 28. Each of the

circuits

23, 24 and 25 in the area between the end of

pipes

26, 27 and 28 and the transformer lead ins I7, I8 and 19 is suspended in the form of a U whose position is changed by lifting or lowering

pipes

26 and 28 by means of lift and lower mechanisms 3I and 32.

The apparatus works in the following manner. The sag in each of the two

outside circuits

23 and 25 is adjusted by lifting or lowering the

pipes

26 and 28 by means of lift and

lower mechanism

31 and 32. The lift and lower mechanism is controlled as a function of inductance. The control as shown in FIG. I consists in measuring the position of the individual supports arms relative to one another by means of

depth indicators

33, 34 and 35 and

slide rheostats

36, 37 and 38 attached thereto and comparing the two outer electrodes II and I3 with the center electrode 12. If a deviation from the normal position is found, the current path of the electrode in question is either raised or lowered by raising or lowering the

pipe

26 or 28 as the case may be to produce impedances in all circuits which are equal. If an irregular burning should occur at the electrodes 11, I2 or 13 during operation of the furnace, then the electrodes are adjusted as usual and the circuit impedances consequently assume different values which are corrected by the signal from the comparison measuring devices which signal the lift and

lower mechanism

31 and 32 through polarized

relays

39 and 40 which change the sag in the circuits in such a way that the impedances become equal in all circuits.

The apparatus shown in FIG. 2 is similar to that of FIG. I in having electrodes Ila, 12a and 13a and a transformer 14a spaced therefrom and connected to the electrodes through circuits 23a, 24a and 250. In this case, however, the position of the electrodes is determined by the relative phase position of the electrode. Here the phase position of the two outer phases is compared with that of the center or inside phase, When the cos it; of an outer phase deviates from that oftlie inside phase, this is detected by the phase measuring instru ments 4], 41a, 42, 42a; 43, 43a which signals the comparison instrument 50 made up of comparator 4 1, 45, 4b which signals the

motor controllers

48 and 49 so that the adjusting

device

310 and 320 are caused to change the sag in the corresponding circuit to restore phase coincidence.

In the foregoing specification certain preferred practices and embodiments of this invention have been set forth, how ever, it will be clear to men skilled in the art that the invention may be otherwise practiced lclaim:

l. A process for operating threephase electric arc furnaces having three electrodes, comprising the steps of connecting the three electrodes to a power source through three indepen dent lines each with a cable having a normal sag therein, moni' toring the impedance in each line and adjusting the relative sag in said cables as their impedance changes to maintain equal impedance in all of the electrode circuits 2v A process as claimed in claim I wherein equal impedance is achieved by arranging three electrodes, one for each phase, in a triangle with two of said electrodes equidistant from a common power source, monitoring the impedance of all three lines and automatically changing the relative sag ol' the cables connecting said two electrodes and the power source with respect to cables connecting the third electrode and said power source.

3 An apparatus for operating three-phase electric arc fur naces having three electrodes and a transformer spaced therefrom comprising cable connections between said trans- Former and each of said electrodes having a sag therein and forming with said electrodes three separate electrode circuits, means for measuring the impedance in each said electrode circuit and impedance a'djusting means acting on the cable sag in each circuit to alter said cable sag and thereby maintain equal impedance therein.

4. An apparatus for operating three'phase electric arc fur naccs having three electrodes and a transformer spaced therefrom comprising connections between said transformer and each of said electrodes forming with said electrodes, three separate electrode circuits, means for measuring the impedance in each said electrode circuit, said electrodes being carried on electrode arms overhanging the furnace and the electrode circuit including an elongated pipe carried on lift means responsive to impedance change mounted on the support arms and carrying a current wire connected to the trans former, said circuit wire having a sag therein adjusted by raising and lowering said elongated pipes relative to one another 5. An apparatus for operating thrcwphase electric arc furnae-es having three electrodes and a transformer spaced therefrom comprising connections between said transformer and each of said electrodes l'orming with said electrodes, three separate electrode circuits, means for measuring the impedance in each said electrode circuit and impedance-adjust mg means acting on each circuit to alter said circuits to maintain equal impedance therein, said impedance measuring means including means for measuring the effective length of each electrode and means for controlling the impedance adjusting means relative to the effective electrode length.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,59 1A86 Dated July 20, 1971 Inventor) Manfred Jellinghaus It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 7 4, "t8e" should read the Column 2, line 3, "circuits's" should read circuit a line 6, "position" should read electrode Column 3, line 8, before "31a" insert motors Signed and sealed this 10th day of October 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents A po'wso USCOMM-DC scan-Pee 9 Hrs, GOVERNMENT PRINTING OFFICE I'll OSSG'J.I,

Claims

1. A process for operating three-phase electric arc furnaces having three electrodes, comprising the steps of connecting the three electrodes to a power source through three independent lines each with a cable having a normal sag therein, monitoring the impedance in each line and adjusting the relative sag in said cables as their impedance changes to maintain equal impedance in all of the electrode circuits.

2. A process as claimed in claim 1 wherein equal impedance is achieved by arranging three electrodes, one for each phase, in a triangle with two of said electrodes equidistant from a common power source, monitoring the impedance of all three lines and automatically changing the relative sag of the cables connecting said two electrodes and the power source with respect to cables connecting the third electrode and said power source.

3. An apparatus for operating three-phase electric arc furnaces having three electrodes and a transformer spaced therefrom comprising cable connections between said transformer and each of said electrodes having a sag therein and forming with said electrodes three separate electrode circuits, means for measuring the impedance in each said electrode circuit and impedance-adjusting means acting on the cable sag in each circuit to alter said cable sag and thereby maintain equal impedance therein.

4. An apparatus for operating three-phase electric arc furnaces having three electrodes and a transformer spaced therefrom comprising connections between said transformer and each of said electrodes forming with said electrodes, three separate electrode circuits, means for measuring the impedance in each said electrode circuit, said electrodes being carried on electrode arms overhanging the furnace and the electrode circuit including an elongated pipe carried on lift means responsive to impedance change mounted on the support arms and carrying a current wire connected to the transformer, said circuit wire having a sag therein adjusted by raising and lowering said elongated pipes relative to one another.

5. An apparatus for operating three-phase electric arc furnaces haVing three electrodes and a transformer spaced therefrom comprising connections between said transformer and each of said electrodes forming with said electrodes, three separate electrode circuits, means for measuring the impedance in each said electrode circuit and impedance-adjusting means acting on each circuit to alter said circuits to maintain equal impedance therein, said impedance measuring means including means for measuring the effective length of each electrode and means for controlling the impedance adjusting means relative to the effective electrode length.