US1122555A - Electric-arc-furnace plant. - Google Patents

Description

THGYE E. EDWIN, BLEGTRIG'ARG FURNACE PLANT, APPLIOATI'ON FILED JUNE 26, 191

will" that the current in each arc contributes to is true.

ETNAR TROYE AND EMIL EDWIN, OF CHRISTIANIA, NORWAY, ASSIGNORS TO NORSK HYDRO-ELEKTRISK KVAELSTOFAKTIESELSKAB, OF CHRISTIANIA, NOR'W'AY.

ELECTRIC-ARG-FURNACE PLANT.

To all whom it may concern Be it known that we, EINAR TROYE an EMIL EDWIN, subjects of the King of Norway, both residing at Christiania, Norway, have invented certain new and useful Improvements in-Electric-Arc-Furnace Plants; and we do hereby declare the following to be a full, clear, and exact description of the invention, such as will enable others skilled in the art to which it appertains to make and use the same, reference being had to the accompanying drawings, and to letters or figures of reference marked thereon, which form a part of this specification.

This invention relates to electric furnace plants of the kind, where the power is utilized for several arcs in a multiphase system, for example several arcs or furnaces of the Birkeland type.

By the transmission of power to plants with are furnacesit is very important, that the furnaces have the connection affording the greatest stability'because it is in this way that the best security of service and earning capacity is attained, while at the same time the necessary transforming of tension may be carried out with the best possible economy and with the simplest possible apparatuses. Both these objects are attained by the present invention, which is the result of extensive experiments and theoreti-' cal researches, and which will be best understood by means of .the following considerations: It-is known that, in any electric system all changes will be counter-acted by forces, which are created bythe change itself. When it is considered therefore, that the stability of an electric arc is due to the forces which counter-act the sudden changes which are produced in the arc current by means of exterior influences it will be evident that with regard to the first harmonic of the current it is important to placethe whole of the electric system obtained by the connection in such relation of dependence that all links of the system are utilized for the stabilizing of every separate link viz.

the stabilizing of all' the other. arcs in the system. The current curve of the arc approa'ch'es always to a certain degree' the sinusoid, and all the higher harmonics in the tension curve will therefore be idle. As these will accordingly l'essen'the total power factor, it is important to limitthelh as far as Specification of Letters Patent.

Application filed June 26, 1914. serial No. 347,510.

Patented Dec. 29, 1914.

' possible and then to localize them so that their eifecton the circuit or mains will be the smallest possible. For this reason and at the same time because they contribute 1 probably to a very great extent to the interlor. stability of the arc the higher tension-' harmonics should be localized to the arc to which they belong and be prevented from being transmitted to the electric circuit.

.1 The above considerations which have not yet to the knowledge of the applicants been taken up in literature make the foundations for the connections forming the present invention.

The objects of this invention with respect to the connection of the arcs are: To put the several links in depending connection with regard to the first harmonic of the current and make them independent of each other with regard to the higher harmonics of ten- SlOIl. N ow it appears that with regard to the connection of the arcs, the symmetrical multiphase system with star connection with or without a neutral capable of being switched oft satisfies best the requirements with regard to the current, as

the several links therefore being in direct dependence of each other. The second requirement withregard to the tension must this'connection, and. this can not only be obtained by means of a choking transformer (hedgehog transformer), but also by means of choking coils generally, whereby the connection described in the following is obtained: By the use of a choking transformer therefore be satisfied within the scope of one has also the advantage, that if the 0on ditions require a higher main tension, the necessary transforming down of this ten- S1OI1 may be performed by the choking trans- 1 is a diagram showing a Birkeland furnace in each phase connection of a three phase transformer and connected to a neutral wire.

Fig. 2 is another diagram, in which the furnaces are in induction circuits. a modification of Fig. 2, where a pluralityof furnaces are supplied with induced cur- 'rent from the sameprimary winding or coil.

Fig. 3 is a diagram illustrating the use of choking coils.

In a three-phase system the connection 4 may be carried out, so that the furnaces,

.viz. thearcs are connected in mesh. However according to the above considerations the connections as shown on Figs. 1, 2 and 3 on the accompanying drawing in connectionor not with a neutral would be the.

most advantageous system not only with regard to the stability but also with regard to regulating, security of service, and n this case also with regard to the transforming. It is evident from the above,'that in the following examples the word furnacemay also be adapted to one or more arcs ina furnace, so that the system may be used as well for the connection for instance of three furnaces, each having one or more arcs, as forthe connection of three arcs within the same furnace.

, It should be noted, that the diagrams have been made as simple as possible, but that also connection in parallel may be used. Also in Diagram 2 the furnaces or the arcs may be connected as shown on Fig. 2 where for each transformer one may have two or more furnaces-or arcs.

The three phase system aifords certain advantages technically, while .the multiphase system affords the advantage thata change in one of the several links of the system causesa comparatively smaller retr,o

this connection the neutral is formed by a 4:. Means tions.

action on the totalsystem, so that the stabilizing will be better. For simplicitys sake the accompanying diagrams are carried out. as three-phase systems.

On Fig. 1 a is a three phase choking transformer and b are the furnaces or the arcs of the Birkeland type, which are connected in star, having also a neutral point in the. choking transformer. The primary coil of the choking transformer may be connected in mesh or instar accoiding to the condi- In this condition the independence of the higher harmonics of tension are attained thereby that the high reactance 'of the choking transformer prevents the oscillations of tension created in each link from penetrating to the other furnaces connected ,to the system, while it is evident that dependence in the first harmonic of thecurrent may also be attained. The same object is attained in Fig. 2, where the three-phase choking transformer is divided into three single phase choking transformers 0. By

Fig. 2" is special transformer 0, which may be con structed with or without increased induction..

In Fig. 3 the connecting conditions for the arcs have been. attained without choking.

transformers by means of choking coils, the requirements for the current being obtained as before, while the requirements for the tension are attained by inclosing theoscillations of tension between parts of the reactance necessary for stabilizing and limiting them to" the arc itself; The furnaces or the arcs are indicated by b as before, while a indicatesparts of the stabilizing reactance. This'fsystemof connection may also be useful in other furnace connections as it lessens the danger of a puncture in the furnace. Choking-coil here indicates any kind of reactance.

By the connection shown it is not'possible in all conditions to start the furnaces without a connection between the star point of the furnace and the neutral of the system.

prising a plurality of arcs in combination with an electriccircuit including said arcs; means to-transform'the tension supplied to said arcs, a reactance 'in said circuit, a neutral pointin' mains of said circuit, and 'an electrical connection between said neutral point and the star points of the furnace system.

2; Means for stabilizing a plurality of arcs comprising a multiphase circuit including said arcs, means to supply multiphase current tosaid circuit, reactance in said circuittune'd to pass only. the first harmonic of the current, and a neutral electric return connection'common to all the arcs.

- 3. Means for stabilizing a plurality of arcs comprising a multiphase circuit including said arcs, means to supply multiphase current to said circuit, said circuit having reactance tuned to pass on the first current harmonic of each are, a grounded neutral metallic return connection and means in said connection between the arcs and the supply means for said arcs to interrupt the neutral metallic return, whereby the arcs become interdependent with respect to the firstihar monic only. I

for stabilizing a pluralityjiof mo arcs comprising a multiphase circuit, a multiphase'transformer in said circuit, an arc in each phase connection to said transformer, and a neutral connection between the neutral point of the transformer and the star points of the arc.

5. Means for stabilizing a plurality of arcs comprising a multiphase circuit, an are for each phase connection of said circuit,

and each phase connection having reactance turned to pass only the first harmonic of the current, a transformer connected'to said circuit and a grounded metallic neutral connection common to all the phase connections and connected to the neutral point of the transformer. i

7. Means for stabilizing a plurality of arcs comprising a multiphase circuit, an are for each phase connection of said circuit, and each phase connectionhaving reactance tuned to pass only the first harmonic of the current, a transformer connected to said circuit and ametallic neutral connection common to all the phase connections and connected to the neutral point of the trans former, and a switch in said metallic connection whereby the neutral point of the furnacesmay be made independent of the neutral point for the phase connections.

.8. Means for stabilizing a plurality of arcs comprising a multiphase star circuit, each phase connection supplying an are, re: actance means in each connection in which the arcs are interposed in series said means tuned to pass only the first harmonic of the current, a grounded neutral metallic connection common to said phase connections and the neutral point for said phase connections, and a switch in said metallic connections between said arcs andsaid neutral point. r,

In testimony that We claim the foregoing as our invention, We have signed our names in presence of two subscribing Witnesses.

EINAR TROYE. EMIL EDWIN. Witnesses:

H. GUTToRMsnN, RUTH Lmns'rnom.

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