US1913161A - Electric arc furnace - Google Patents

Description

a w M m mi Wm 8 W W /J y B J. JONAS ELECTRIC ARC FURNACE Filed Jan. 51. 1951 June 6, 1933.

Patented June 6, 1933 PATENT orrics JULIUS JONAS, 01' will,

m: & 613,01 mm,

LAND

a lication Med January 31,1001, l i-1.1 Io.

-For operatin .a plurality of electric arc furnaces it has itherto been necessary to use separate transformers for feedin the individual furnaces, as it was regar ed as im possible to operate reliably in parallel several furnaces from a common transformer. For through the short-circuiting of the transformer consequent on electrodes of one furnace coming into contact with one another, the other furnaces will also be without/voltage and, on the electrodes being separated till the current is interrupted, the transformer, on account of the reduction in the ampere turns,has such a considerable stray field that the current of the other furnaces is choked to a very considerable extent.

The present invention relates to a method of and means for 0 rating a plurality of flame arc furnaces ed in parallel from a common transformer over rectifiers, by which this disadvantage is overcome.

According to -the invention this is efiected by each flame arc furnace bein fed from a separate secondary windin an by the secondar windings dispose on a common trans ormercore being extensively subdivided and the winding parts being intimately intermixed, and furthermore b the two end terminals of each of the secon ary windings being connected to the corresponding rectifier anodes over choking coils which are so interlinked that the successive half waves of current of opposite phase of the interlinked chokes magnetize their common iron core m the opposite sense, the flame arc furnaces associated with the secondary windings-being connected up in a known manner between the centre point of the secondarywindings and the rectifier cathode.

In the accompanyin drawing Fi 1 illustrates, in schematic fas ion,'one'em iment of the invention wherein a plurality of electric arc furnaces are supplied from separate rectifier elements fed from the common current supply transformer; and Fig. 2 illustrates, also in schematic fashion, another embodiment of the invention wherein the separate rectifier elements of Fig. 1 are com: bined in a single rectifier. 4

Referring now to the drawing by char- ABBIGIQB 1'0 AITIINGESELLSCHAFT BROWN 4 ,IL 10m STOCK QOHPANY Q1 SWITZER- inns-mic m rum uon 51am, m1 111 Germany Iebruary 1, 1m.

actors of reference and considering first the mvention according to Fig. 1, a and a, are flame arc furnaces workin in parallel, which are fed over the rectifiers 1, b, from the comformer limb opposite the rimary winding. 7

Each of the secondary win ings d d feeds a rectifier b b the end terminals of the secondary windin s being connected over the interlinked cho ing co1ls e e, to the associated rectifier anodes.- The centre points of the secondary windings are connected to the electrodes of the flame arc furnaces, the other electrodes being connected to the cathodes f f; of the rectifiers. A steadying choke g is preferably interposed in the primar circuit of the feeding transformer.

T s interlinked. choking coils are so de signed that, in the case of contact, being established between the electrodes one fur nace, that is to say in the case of a short circuit, they can take up the full voltage of the secondary, winding, without the magnetming current assuming a value which would endanger the operation of the-other furnace. The intermixmg of the arts of the secondary windings is preferab y carried so far that on the circuit of one furnace being interrupted, there will be no ap reciable choking of the current of the secon furnace.

Instead of using a separate rectifier for each of the flame arc furnaces working in parallel, a common rectifier having a suitable number of anodes may of course be used. For example, as shown in Fig. 2 of the drawing, the two rectifiers b 6, may be replaced by the single rectifier b having a single cathode f to which the lower electrodes of the furnaces a a, are multiply connected. The elements, connections and operation of Flg. 2 being otherwise as shown and described with respect to Fig. 1 of the drawing;Mi

Having now particularly descri and ascertained the nature of my ,said invention and in what manner the same is be performed, I declare that what I C18.1lIl 1SZ- 1. In an electric furnace system, the com bination of an alternating current supply line, a transformer havin aplurality of independent mid-tapped windings each divided into a plurality of sections and the respective sections of said windings being interlarded, a plurality of flame-arc electric furnaces each aving a pair of co-operating electrodes, rectifying means,'means comprising one of said windings and said rectifying means for supplying direct current from sa1d line to one 0 said furnaces, and means comprising another of said windin and said recti ing means for suppl ing irect current rom said line to anot er of said furnaces.

2. Inan electric furnace system, the combination of an alternating current line, a plurality of electric flame-arc furnaces each aving a pair of cooperating electrodes, electric current rectifying means, and a transformer comprising a piuralit of independent mid-tapped windings eac divided into a plurality of sections on each side of the mid-tap thereof and the end terminals thereof being connected with the said rectifying means to supply current thereto from" said line for conversion into direct current and the supply thereof to the said pairs of electrodes to establish and maintain an arc therebetween, one electrode of each of the said pairs being connected with the said rectifyin means and the other electrode thereof be ng connected with a different one of said mld-taps, and the respective sections of said windings being interlarded to thereby limit the rise of the inductance of any one thereof upon the occurrence of an interruption of the are between the electrodes of the furnace connected with another of said windings.

3. In an electric furnace system, the combination of an alternating current line, a plurality of electric flame-arc furnaces each aving a pair of coo ratin electrodes, an

electric current recti r, an a transformer comprising a pluralit of independent mid-tapped windlngs eac divided :t-into a pluralit of sections and the end terminals thereof ing connected with said rectifier to supply alternating current thereto from said line for conversion into direct current and the supply thereof to the said pairs of electrodes to establish and maintain an arc therebetween, one electrode of each of said pairs being connected with the said rectifier and the other electrode thereof bein connected with a different one of said mi -taps, and the respective sections of said windings being interlarded to thereby limit the rise ofzgthe inductance of any one thereof upon the occurrence-,of'an interru tion of the are between the electrodes of t e furnace connected with another of said windings.

4. In an electric furnace system, the combination of an alternating current line, a

plurality of flame-arc furnaces each having 'a pair of coo rating electrodes, an electric current recti or for each of saidfurnaoes, and a transformer comprisin a plurality of inde endent mid-tapped windings equal in num r to and separately connected with the said rectifiers to supply the latter with alternating current from said line for conversion into direct current and the supply thereof to the said electrodes of the associated ones of said furnaces to establish and maintain a flame-arc between such electrodes, each of said windings being divided into a plurality of sections on each side of the midtap thereof and the sections of the respective windings being interlarded to limit the rise of inductance of any one thereof upon the occurrence of an interru tion of the are between theelectrodes of a urnace connected with another of said windings.

5. In an electric furnace system, the combination of an alternating current line, a plurality of electric flame-arc furnaces each having a pair of cooperating electrodes, a rectifier for each of said furnaces having a cathode and a pair of anodes, a transformer comprising a primary winding connected with said line and a plurality of independent midtapped secondary windings corresponding in number to said rectifiers and having the end terminals thereof connected with the anodes thereof to supply alternating current from said line thereto for convension thereby into direct current and the supply thereof to the electrodes of the corresponding ones of said rectifiers to cause the simultaneous flow of an arc between the said electrodes thereof, the said secondary windings being divided into a plurality of sections on each side of.

the said mid-tap thereof and the respective sections of said windings being interlarded to prevent such decrease of flow of current therethrough as would effect interruption of the are between the electrodes of the furnace connected therewith upon the interruption of the arc between the electrodes of a furnace connected with another, and a reactance included in each of the said connections between the said secondary windin and the said anodes operative to limit t e flow of current therethrou h u n the occurrence of direct contact ":'of' t e e ectrodos of the furnace connected therewith.

6. The combination with a plurality of flame-arc furnaces each having a plurality of cooperating electrodes, and an alternating current line, of an electric current rectifier for each of said furnaces, a transformer having a lurality of'windings corresponding in num r to and separately connected with the said rectifiers o rative to supply the latter with alternating current from said line for conversion into direct current and the supply thereof to the said electrodes of the associated one of said furnaces to establish and maintain a flame-arc between such III electrodes, each of said windings being divided into a plurality of sections and the sections of the respective windings being interlarded to limit the rise of the inductance of any one thereof upon occurrence of an interruption of the are between the electrodes of a furnace connected with another of said windings, and reactor means included in the connections between said rectifiers and the said windings to stabilize the said arcs.

7 The combination with a pair of flameare electric furnaces each having a pair of cooperating electrodes, and an alternating current line, of an electric current rectifier for each of said furnaces, each rectifier comprising a cathode and a pair of anodes, a transformer having a primary winding connected with said line and a pair of secondary windings each havin a mid-tap and being divided into a plurality of sections on each side of the mid-tap thereof, the sections of the respective windings being interlarded and the terminals thereof opposite to the said mid-tap being separately connected with the anodes of one of said rectifiers to supply the latter with alternating current from said line for conversion into direct current and the supply thereof to the said electrodes of the associated one of said pair of furnaces to establish and maintain a flame-arc between such electrodes, the eiectrodes of the said furnaces vbeing connected res ectively with the cathode and the mid-tap o the associated said rectitier and secondary winding, and a pair of reactance coils arranged about a common magnetizable core included in said connections between each of the said secondary windings and the said anodes of the associated rectifier to thereby limit themagnetization of the core of said transformer upon the occurrence of direct contact of the said cooperating electrodes, the connection of the said coils of a pair with respect to each other being such as to effect magnetization of the said common core in the opposite sense.

In testimony whereof I have hereunto subscribed my name this 20th day of January A. D. 1931.

JULIUS JONAS.

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