US1278635A - Electric furnace and method of supplying current thereto. - Google Patents

Description

J. H. GRAY. ELECTRIC FURNACE AND METHOD OF SUPPLY ING CURRENT THERETO.

APPLICATION FILED JULY 20. I918.

Patented Sept. 10,1918.

2 SHEETSSHEET 1- INVENTOR JAMES H.6R/1Y flag nromver v J.H.GRAY. ELECTRIC FURNACE AND METHOD OF SUPPLYING CURRENT THERETO.

APPLICATION FILED JULY20.19I8.

Patented Sept. 10,1918 0 2 SHEETS-SHEET 2 1Z9? 2.

IIV VE N TOR Jaw/5's H. 6mm

, Arm/Mr during the refining-period. Durin UNITED STATES PATENT OFFICE.

d'AMES H. GRAY, OF NEW YORK, N. Y.

' ELECTRIC FURNACE AND METHODOF SUPPLYING- CURRENT THERETO.

Specification of Letters Iatent.

Patented Sept. 10, 191 s.

, Application filed July 20, 1918. Serial No. 245,843.

To all whom it may concern:

Be it known that I, JAMES H. GRAY, a citizen of the United States, residing in the city, county, and State of New. York, have invented. certain newand useful Improvements in Electric Furnaces and Methods of Supplying Current. Thereto, of which the following is a specifieation.

and'finishing period. During the finishing.

period the metal is inthe form otja'molten bath covered with molten slag and at this time it is desirable to use-short arcs to prevent an excessive amoun. of heat which would in a short time destroy the side walls and roof of. the furnace.

WVhen .using a three phase current, a desirable E. M. F. during the refining period is 100 volts. During the melting down period, it is desirable to introduceas much electric power, as measured by kilowatts as possible. With an E. M. F. such as 100 volts and a current of high strength such as 10,000 amperes this is d' cult, due to limitation of electrodes, conductors and reactance. Obviousl however, it is possible to increase the KW input without increasing the number of amperes b increasing the voltage.

A higher E. F., for instance 150 volts, canv be used effectively with the attendant long arc,

ing the meltin period, because the arcs used are buried or idden beneath the scrap. In consequence of these conditions, I provide the necessarg connections by which a relatively high M. F. can be obtained during the meltin down period and then a quick and easy 0 ange made to a lower E. M. F. the re-. fining eriod, when the lower E. F. is used with the correspondingly high current strength it is necessary to eliminate reactance to the greatest possible extent, in order to secure a good power factor, for instance .9, but when using the hi her voltage and long are, the fluctuations 0 current are 7 without injuring the furnace dur-..

' exceedingly great, causing-destructive surges on the power line and consequently frequent interruption of the 'continuity of the are,

thereby decreasing speed in the operation of melting the charge.

My invention provides 'for the utilization of a relatively high E. M. F. and long-arc during the meltingldown period and a lower Ff andshorter arc during the refining or finishing perio'd,and the introduction of reactance in theprimary circuitduring the former period to prevent excessive. surges on the line andthe consequent interruption of the arc.

In the accompanying drawings, Figure 1 illustrates diagrammatically an electric furnace and connections for varying the E. M:

F. to thereby give respectively a: long are during the melting. down 0 eration and a shortervarc during the finis ing operation,

bymeans of adjustin' taps on the primary windings of the trans ormer. In this figure, 'I- have shown what I- term a delta-delta combination indicating that the connections of both the primary and secondary windings on .the transformerare connected in delta;

' Fig. 2 illustrates an alternativearrangeme'nt of circuit connections wherein I vary the E. M. F. in the secondary circuitby changing the circuit of the primary connections from delta to star thereby changing the E. M. F. in a ratioofI173 to 100. In

this figure the secondary windings of the transformer and the electrodes are connected in star.

Referring to Fig. 1, when it is desired to melt down the charge the threeblades of the switch. A are closed asflshown'thereby connecting the. rimary windin' s P, P and P in delta wit the feed wires ,0 and D, leadingin the caseillustrated from a three phase generator..

Connected betweenthe switch A and the 'feed wires B, C and-D by wires 6, c and d .'are .reactance coils R, R and B. With the switch A closed the current from the feed wires flows throu h the reactances R, R and R; thereby exciting the primary windings P, P and I which are 'fed by t e wires 0', d and 6, leading to the adjustable taps T, Tand T on the. transformer, the current returning by way of wires 5, c and d to the feed wires B, C and D, thus connecting the primary windin in delta combination with the feed wires C and D.

operation, the switch A will first be opened and the switch, A will be closed, thereby again connecting the primary coils P, P and P in delta with the feed wires B, C and D in a similar manner to that already de-' scribed excepting that there are no reactances included in the primary circuit and that the current enters the transformer through different taps 0 d and 6 returning as before to the feed wires B, C and D by way of wires 6 o and d By means of adjusting the taps T, T and T on the primary coils of the transformer, I am obviouslyable to vary the E. M-. F. induced in the secondary windings in the transformer.

The E. M. F. may be varied either by adjusting the taps on the transformer as above described or by changing the high tension primary connections from delta to star as indicated in Fig. 2 or other phase combinations such as changing the primary connections from star to delta Or from delta-delta to star-delta 0r star-star to delta-star .or delta-star to star-star or star-delta to deltastar. changing by means of taps as shown in Fig. 1 a' combination of delta-delta, star-star, delta-star or star-delta maybe used as fixed connections in any of the above combinations. I introduce reactance preferably into the primary circuits as illustrated while the higher'of the two E. M. F.s is being used.

For controlling the primary circu t combinations, I emp oy the separate switches A and A of known type which are interlocked as indicated at L so that both switches, must be opened before either can be closed to prevent short circuiting.

In the alternative circuit arrangement illustrated in Fig. 2 the primary and secondary windings are connected in delta-star, combination when the switch A is closed and star-star combination when the switch A is closed, it being understood that in this illustration the electrodes E, E and E are connected in star with the secondary windings S, S and S of the-transformer. In melting down the charge the switch .A will be closed thereby cutting in the reactances R, R and R and connecting the primary windings P, P and 1:" in delta with the feed wires B, C and D, and inducing, for example, an E. M. F. of 173 volts on the sec- It should be understood that when ondary windings S, S and S of the transformer. a

When it-is desired to refine or finish the charge in the furnace, the. switch- A is opened and the switch A closed thereby connecting the. primary windings P, P and P of the transformer in star connection with the feed wires B, C and D from the three phase generator.

This current combination will cause a lower E; M. F., for example,.100 volts as compared'with the melting E. M. F.-of 173 volts. The lower E. M. F. will produce a shorter are within the furnace, which will not radiate suflicient heat. to destroy the side walls and roof of the furnace as would be the case-if the higher E. M. F. of 173 volts with a high current strength such as 10,000 amperes were used-.' 7 When the switch A is closed the current from feed wires B, C and D enters the primary windings P, P and P by way of wires 0 d and b the opposite ends of the primary coils being connected by wires 8, s and s to the blades of the switch A which coact with contacts a, n and n connected to the neutral point N- of the star connection.

While the arrangements illustrated are for three phase, threej wire circuits serving three electrodes, it-is to be understood that my invention is applicable to any of the various systems of introducing current into electric furnaces such. as single, two phase or three phase, employing either two, three or four wires and with electricfurnaces having any number of electrodes and with furnaces either provided with or without bottom connections.

In both figures of the drawing I have shown the reactance arranged on the high tension side of the transformer. It may however be arranged at the low tension side or it may be within the transformer with suitable switches or stops for cutting it in during the melting down operation and. out

a during the refining operation. 'And instead of providing for a reactance which is entirely in the circuit or entirely out out of it there may be used an arran ement for cutting in a large reactance uring the melting down operation and a smaller reactance during the refining operation. In fact, although I have described with great particularity in detail certain specific embodiments of m invention, yet, it is not to be understood therefrom that the invention is restricted to the, particular, embodiments disclosed. 'Various modifications may be made by those skilled in the art without departing from the invention as stated in the following claims What I claim is:

1. The method of melting and refining metal in anelectric furnace which consists in supplying a current of comparatively high E. M. F. to the electrodes during the melting down period to produce a comparatively long are and cutting a reactance into the primary circuit to thereby insure continuity of the arc and prevent surges on the power line.

2. The method of melting and refining metal in an electric furnace which consists in changing the E. M. F. from a higher to alower voltage when performing respectively the melting down and refining operations, reactances being introduced into the circuit at the time the charge is being melted down and the higher E. M. F. used.

3. The methods of varying .the KWH input into electric furnaces for melting down and refining the charge which consists in introducing a current of high E. through a reactance in the circuit to prevent surges on the power line and subsequently cutting out saidreactance and introducing a comparatively low E. M. F. during the finishing or refining period.

4. In combination with an electric furnace, circuit arrangements whereby a react-.

electric arc furnace, a transformer and means for varying the voltage impressed on the secondary windings of said transformer and means for cutting reactances into the primary circuit to prevent surges on the power line, and a' consequent interruption 40 in the continuity of the arc.

6. In combination with the electrodes, of

an electric furnace a transformer and'means whereby the E. M. F. and the reactance in the primary circuit may be varied to insure the continuity and vary the intensity of the arc within the furnace.

7. In combination with the electrodes of an electric furnace, a transformer, reactance coils and means whereby the reactance coils may be cut in circuit with windings of the transformer during the melting down of the charge to permit the use of a comparatively high -E. M. F. and long arc with a current of great strength without producing excessive current fluctuations or surges on the line, and means whereby a comparatively lower E. M. F. may be impressed on the windings of the transformer to give a shorter arc during a'finishing or refining period.

8. In combination withthe electrodes of an electric furnace, a transformer, reactance coils and means whereby circuit combinations may be effected to include said reactance coils in circuit with the primary windings of said transformer to impress a comparatively high E. M. F. on the secondary winding of the transformer during the melting down operation and means whereby said reactance coils may be cut out of circuit and other circuits made to impress a comparatively lower E. M. Ffon the windings of the transformer during the finishing or refining period.

In witness whereof, I have hereunto 75,

signed my name.

JAMES H. GRAY.

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