US1242464A - Electric metallurgical furnace and method of operating the same. - Google Patents

Description

W. E. MOORE.

ELECTRIC METALLURGHCAL FURNACE AND METHOD OF OPERATING THE SAME. APPLICATION FILED NOV. 2i. 1916.

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W E. MOORE.

ELECTRIC METALLURGICAL FURNACE AND METHOD OF OPERATING THE SAME.

APPLICATION FILED NOV. 21. 1916- 1 ,$%Q,4z64=. Patented Oct 9, 1917.

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WILLIAM E. MOORE, OF PITTSBURGH, PENNYLVANIA.

ELECTRIC METALLURGICAL FURNACE AND METHOD OF OPERATING THE SAME.

Specification of Letters Patent.

Patented Oct. 9, 1917.

Application filed November 27, 1916. Serial No. 133,648.

To all whom it may concern.

Beit known that I, IVILLIAM E. Moons, a citizen of the United States, residing at Pittsburgh, in the county of Allegheny and State of Pennsylvania, have invented certain new and useful Improvements in Electric Metallurgical Furnaces and Methods of Operating the Same, of which the following is a specification.

The object of this invention is to effect certain improvements "in the manufacture of steel, its alloys and other metals in electric furnaces. In the manufacture of steel, for example, in arc type electric furnaces, it is a common practice to charge the furnace with a supply of raw material or cold scrap, either with or without the addition of molten metal, melt this aw material down by means of an electric are or arcs playing from a carbon electrode or electrodes, and subsequently submitting the molten metal to a refining process ,during which heat is supplied by an are or arcs playing from the same electrodes to the molten bath. In the operation of such furnaces, for refining the metal, it is the practice to add basic materials such as lime, to the natural slag formed on the molten bath, the same as in open hearth practice. which becomes molten with the metal and forms a layer over the surface thereof. and during the refining operation current from the electrodes passes through this slag to and through the bath.

In such operation, it has heretofore been the practice to melt down the charge with substantially the same length of are and voltage as is employed in the refining operation. and in refining to reduce the power input by reducing the current to keep the temperature within the limits which the refractory linings of the sides and roof of the furnace will stand without too much deterioration. In operating furnaces in this way. enormous currents are required in the melting operation which in turn necessitates the employment of very large electrodes and correspondingly large conductors to convey the heavy currents to these electrodes. Also as the length of arc in refining may not be as great as in melting, owing to the deteriorating effect of greater arc length on the refractories of the furnace, as hereinafter more fully pointed out, if the same length of are be used in both melting and refining, the length of arc in melting, I find, is unnecessary limited.

I find that it is advantageous to operate a furnace of this type during the melting operation by employing a relatively long are and high voltage, and in refining to reduce the length of this are (to zero if desired) and to reduce the voltage without materially altering the current.

It is feasible to operate with a much longer are in melting than in refining without greater damage to the refractory sides and roof of the furnace for the following reasons: In melting there is a rapid absorption of reflected heat by the unmolten charge and no floating layer of slag present to reflect the heat against the refractories, and this layer of slag has a glassy surface and a very high heat reflecting power especially when neutralized by lime additions. The unmolten charge absorbs the heat and therefore does not radiate it as does the molten bath, and the heat which reaches the furnace linings from the arcs both by convection and radiation is radiated to the unmolten metal, the temperature of which cannot much exceed the fusion temperature of said metal until all of it becomes fluid. Therefore, so long as there is unmolten metal in the furnace, the linings are maintained at a safe temperature even though long arcs are used.

This method of operation has a number of distinct advantages: First, for the same power input to the furnace, it raises the power factor by decreasing the current and increasing the working voltage. thus reducing the inductance of the electric circuits, and effects a saving in the cost of electrodes and conductors, since the size of electrodes and cross section of conductors to lead the current thereto may be reduced in area in proportion to the current to be transmitted. In carrying out my invention. I preferably adopt a size of electrode which will be just sufficient without overheating to transmit the necessary amount of current to produce the required power input to the furnace with low voltage arcs of approximately 40 to (30 volts each. for refining, and produce the heat for melting by increasing the voltage say to 120 or 240 volts or more. In this way the minimum size of electrodes is used, which results in minimum oxidation losses, as a minimum area of electrode hot surface is exposed to oxidation. Also minimum size (cross section) switches and conductors to lead the power to the furnace are required. The power factor of the circuit is also increased by reason of the fact that the inductive drop through the furnace circuit is a smaller percentage of the total applied voltage than in the usual practice. IVhen there is cold scrap in the furnace, owing to the magnetic quality of this material, counter electromotive forces are set up which lower the power factor and these counter electromotive forces are of smaller percentage in the case of a long are than a short one.

I have found that it is desirable in melting down a charge of cold scrap to employ the longest practical arc and high arc voltage, also on account of the fact that the arc gyrates over a longer radius around the electrodes and thus fuses more of the metal which might otherwise fall in the cavity formed by .the arc and cause short circuits which would interfere with the regularity of the power supply and the operation of the furnaces. The desirablity for this long are required in melting does not apply after the charge has been once rendered fluid.

I find too, that with an are playing from a carbon or graphite electrode to a metal bath, or to a slag containing lime, silica, etc., that there is a rectifying effect on the alternating current tending to permit a heavier flow of current in one direction for one-half wave length than in the other. and that such rectified current may be utilized to an advantage in heating the bottom of the furnace and agitating the metal bath. Such rectified current if caused to flow down through the molten metal and furnace bottom heats the latter and prevents the formation of superficially frozen charges known as skulls thereon. This current also has an agitating or stirring effect on the molten bath which prevents the formation of hot spots and aids the mixture of any alloys or additions, and at the same time facilitates the elimination of objectionable elements such as sulfur, phosphorus, oxids, etc, by circulating the molten metal in contact with the purifying slag. While in ordinary cases this rectified current may be of suflicient volume to properly heat the furnace bottom and agitate the molten charge, in some cases it is advantageous to cause a portion or all of the alternating current to return through the furnace bottom. It is important to be able to vary the amount of current which passes through the furnace bottom to meet different operating conditions, for if too much current is caused to flow throu h the furnace bottom, the said bottom will ecome 'apidly worn away,.and if too little current be sent through it, the furnace bottom will build up and reduce the capacity of the furnace.

In the foregoing, as well as in the detail description to follow, I have assumed that the particular manufacture carried out by my invention is the melting and subsequent refining of steel or other metals. As will be later pointed out more fully, however, my invention is not limited to such specific manufacture. In order that my invention may be more fully understood, it will now be described in greater detail with reference to the accompanying drawings, and the novel features will be pointed out in the accompanying claims.

In the accompanying drawings Figure 1, illustrates apparatus embodying a form of my invention wherein the power is supplied from a two phase circuit and the furnace provided with four arcing electrodes;

Figs. 1 and 1 diagrams illustrating in av simplified way connections effected by switches shown in Fi 1;

Fig. 2, a diagram illustrating a form of my invention as applied to a three phase three arcing electrode furnace;

Fig. 3, a diagram illustrating my invention as applied to a six electrode furnace receiving current from a three phase circuit, and in which each transformer primary is provided with four subsections;

Fig. 4, a diagram showing the series multiple switching arrangement of Fig. l applied to a Scotts connection. I

The furnace proper or crucible here shown comprises, among other parts, a removable arched top 1, preferably of so-called acid brick, and the furnace is also lined with acid brick down to a point several inches above the normal slag level and preferably of basic brick below this point. The bottom lining of the furnace is formed preferably of two layers 3 and 4, the former being composed of magnesite, dolomite. chromite, ganister, or other suitable refractory material, and the latter of a mixture of refractory material and better electrically conduct ing material, such, for example. as carbon, 1 graphite, or other suitable conducting material progressively increasing in conductivitv toward the bottom and rammed or scintered in. The sides and bottom of the furnace-are inclosed in a metal casing or shell 5. In the drawings the metal 6 is shown in the molten state coveredby a layer 7 of slag. The upper layer of the furnace bottom is quicklv rendered conducting by the heat of the arcs and by reason of its absorption of metallic oxids. In order, however, to make the lower layer or layers of the furnace bottom conuse with the specific crucible described.

Referring now particularly to Fig. 1 of the drawings, 8 9 and 8 9* indicate four electrodes extending down through the furnace roof in the usual manner and'supported for vertical movement in the usual or any desired way. In the diagram referred to, I have shown but one of these electrodes provided with raising and lowering means, consisting of a cable 10, passing over pulleys 11 and 12, and attached to a drum 13 which may be operated in any desired way, it being understood that the other electrodes are provided with similar mechanism. lhe raising and lowering means shown, however, merely illustrates some suitable means for accomplishing this result.

Electrodes 89 and 8"9 are connected respectively to the terminals of two secondaries 14 and 15 of two transformersA. and B. Each of these secondaries is split into two sections 1 l14 and l515 respectively. Tapped onto the windings of these secondaries intermediate their subsections (neutral points) are two conductors 16 and 17 which connect through switches 16* and 16 to a common conductor 16, which in turn is electrically connected to the metal casing 5 of the furnace. By means of switches 16 and 16 either one or both of the transformer secondaries may be connected to the neutral wire of easing 5.

A pair of reversing switches 2st and 25 are also provided, whereby the furnace bottom may be connected to a neutral point in the secondary windings for operating the arcs of the respective pairs of electrodes in series, or the current in one section of each transformer secondary may be reversed as shown in Fig. 1*, so as to make the furnace bottom a part of a common return carrying the current from all four arcs which would then be in parallel. In the latter case a very strong current is thrown down through the furnace bottom. These connections provide a very flexible arrangement for varying the amount of curent sent through the furnace bottom.

For the purpose of varying the arc voltage between melting and refining, I provide each transformer, in this case, with two primary windings 1819 and 2021, and so connect these to two switches 92 and 23 that when switch 23 is closed and switch 22 and-switch 23 opened, they will be connected in series as illustrated in Fig. 1", thus varying the arc voltage in the ratio of 2 :1.

Where it is desired to obtain a greater ratio between the voltage in melting and refining, the secondary of each transformer would be divided into a greater number of sections. For example, if desired to obtain a ratio of 1, each transformer secondary would be provided with four coil sections instead of two. With the latter arrangement, a furnace could be operated with 3,000 k. w. for melting and 750 k. w. for refining.

In melting, switch 22 is opened and switch 23 closed, which connects the primaries in multiple. and the electrodes adjusted so as to produce-a long are of high voltage. The transverse dotted line near the lower end of each electrode indicates it in the raised po sition.

If it is desired to employ both pairs of electrodes, switches 24 and 25 are thrown so as to connect the secondaries in series as shown in Fig. 1. Switches 16 and 16 may or may not be closed during the melting operation; if both are opened no current will pass through the furnace bottom, the entire current passing in series between the elec trodes of the two respective phases. If both switches 16 and 16 are closed, then both transformer secondaries will be connected to the common return 16*. and when the furnace bottom becomes sufficiently heated to become conducting, a rectified current will pass from the respective pairs of electrodes through the metal; furnace bottom and common return.

In refining, switch 22 is closed, and switch 23 opened. thus connecting the primaries in series as in Fig. 1", thereby reducing the voltage of the arcs without materially varying the current. At this time the electrodes are lowered to produce the short are. If it be desired to send the entire current from all four electrodes in multiple, through the furnace bottom, switches 24 and '25 are thrown to their opposite poles (to the right in Fig. l). and switches 16 and 16 are both closed. This operation of the switches results in the connections shown in Fig. 1 that is, in the connection of the transformer secondaries whereby the furnace bottom becomes a common return for all four electrodes. This gives a lower arc voltage with the maximum current through the furnace bottom. If it be desired to reduce the amount of current passing through the furnace bottom, one of the switches 16 or 16 may be open, thus disconnecting either one of the transformer primaries from the common return, in which event current will pass through the furnace bottom and common return from one pair of electrodes only. A further variation may be obtained by closroe ing both switches 16 and l6 and throwing switches 24 and 25 in opposite directions, in which case all of the alternating current from one pair of electrodes and a portion of the current (rectified) from the other electrodes would pass through the furnace bottom.

Still further variation of the amount of current sent through the furnace bottom and common return may be effected by unbalancing the voltage of the arcs of either of the pair of electrodes. It is clear that with the switches 16 and 16 closed, and switches 2st and 25 thrown so as to connect the neutral wire 16 to the transformer secondaries, as shown in Fig. 1, that the current through each electrode of either secondary coil will be balanced so long as the voltage is balanoed. If the arc of either electrode of the two pairs be lengthened so as to interpose greater resistance, then the current through that are would be reduced and a portion of the current which formerly flowed through the other are of that pair would return through the furnace bottom. Therefore, the amount of electrical power flowing through the furnace bottom may be adjusted by varying the relative length of either or both of the two pairs of arcs.

Fig. 2 shows a form of apparatus embodying my invention as applied to a three phase supply circuit and a three electrode furnace, in which 26, 26 'and 26 indicate the supply wires from the power circuit, and 10 10 and 10 the three arcing electrodes of the furnace, it being understood that these electrodes may be provided with means for raising and lowering them as described with relation to the preceding figures of the drawings, or any other suitable means for accomplishing this. In this case (Fig. 2) the transformer primaries 27 27 and 27 are each divided into two sections connected respectively with switches 28, 28*, and 28, whereby the sections of the respective primaries may be connected either in series or in multiple.

There is also provided a switch 26, whereby the transformer primaries may be connected in either delta or Y formation.

Likewise, the transformer secondaries 29, 20 and 29" are each divided into two sections, and these sections connected respectively to switches 30, 30 and 30, whereby the sections of the respective secondaries may be connected in series or in multiple. A switch 28 is provided in the secondary system whereby the transformer secondaries may be connected in either delta or Y formation, and whereby when connected in the latter formation, the neutral of the secondaries will be connected to the metal casing 3 of the furnace through conductor 16.

A switch 27 and connections are provided whereby when the secondaries are connected in delta. the neutral of these secondaries may be connected to the metal casing 5 of the furnace through conductor 16.

A switch 29 is provided whereby one of the transformer secondaries may be reversed so as to unbalance the system and cause an increased flow of current to pass through the furnace bottom.

lVith this arrangement, it will be seen that quite a number of operating variations may be obtained.

lVith the switches set as shown in Fig. 2, the transformer primaries 27, 27" and 27 are connected in star or Y formation, and the sections of the individual primaries are in series. The transformer secondaries 29*, 29 and 29 are connected in delta formation with the conducting casing 5 connected to the neutral points of the respective secondaries through conductor 16 and switch 27. This is a condition suitable for refining, wherein the low voltage is employed, and at which time the electrodes are lowered for the short arcs. During this operation a rectified current passes from the three electrodes in multiple through the slag, molten metal, and furnace bottom, to the neutral point of the secondary system. If it is desired to increase the current flow through the furnace bottom, switch 29 is thrown so as to reverse the direction of the current flow through secondary 29.

For melting with higher voltage and longer arcs, switch 26 will be thrown to the right to connect the primaries in delta formation, and switch 28 thrown to the right to connect the secondaries in star or Y formation. hen this is done. switch 27 is also shifted to the right to disconnect conductor 16 from the neutral points of the secondary windings. Switch 16 may be provided in the circuit of conductor 16 whereby when switch 28 is thrown to the right to connect the secondaries in star formation in melting, the conducting casing 5 may be disconnected from the neutral of the secondary system.

By means of switches 28, 2t", and 28, and 30, 30 and 30 the current 'ariation may be further adjusted by connecting the subsections of the transformer windings in series or multiple, as above stated. For example, during melting these may be connected in multiple. and during refining they may be connected in series, or the subsections of the primary alone maybe so varied; or the subsections of the secondary alone may be so 'aried. Obviously. if it is desired to vary the voltage by changing from delta to star formation. or vice versa alone, the series multiple switches may be dispensed with, and if the series multiple 'ariation is desired alone. the delta-star switches may be dispensed with. The combined arrangement shown, however,

The change in voltage from delta to Y of course is in the proportion of 1 to-,/3.

It will be understood, while the various switches in Fig. 2 are indicated in a more or less separated way, that the operating mechanism for these switches may be interconnected so as to operate them in various combinations. This is purely a mechanical matter, however, and may be effected in any desired way.

It should also be understood that while in Figs. 1 and 2 I have shown furnaces provided with four and three arcing electrodes respectively, and with the transformer subsections in groups of two for connection in series or, multiple, still other numbers of electrodes and transformer secondaries may be used without departing from the spirit of my invention. In Fig. 3, for example, I have indicated a form of my invention in which the furnace is provided with six arc- 'maries provided with four subsections, in-

stead of 2 as illustrated in the preceding views. The transformers A, B and C, in this case receive current from a three phase circuit, each pair of electrodes corresponding to a different phase. In this diagram, I have merely indicated certain parts without showing the completed electrical connections, as the connections for the added electrodes 8 and 9 to the secondary subsections 15 and 15 are the same as the connections of either of the pairs of electrodes 8*. 9 or 8". 9 and the connections for the latter are fully shown in Fig. 1. The switching connections for the primaries 18 18 and 18, whereby the subsections of these primaries may be connected in series or multiple, are the same as in Fig. 1, with the two extra coils added to each primary, and allowing for the added primary C.

As the three phase circuit is the most common form of commercial power circuit for alternating currents, it is desirable to be able to operate a two or four phase furnace such, for example, as illustrated in Fig. 1, from such three phase circuit. In Fig. 4, I have shown an arrangement for effecting this by means of the well known Scotts connection, wherein this connection is applied to the case in which the transformer primaries are each composed of twoor more sections arranged to be connected In series or multiple for varying thearc voltage. In

Fig. 4, 31 31*, 31 indicate the three phase power mains; 32 and 32 the two phase transformer primaries, and switches 33 and 34 are so connected to these supply mains and primaries as to connect the sections of the latter in series or multiple.

It is sometimes the practice to commence the melting down of the scrap with some molten metal already in the furnace, so that it is not to be understood that my invention is limited to the cases in which the melting is started with cold scrap alone. It should be understood also that my invention applies in cases where there may be no scrap in the furnace. For example, it is sometimes the practice to charge furnaces with molten metal and put this through a refining or other process without the addition of scrap or unmolten metal. My invention in so far as it relates to the operation of the furnace in bringing the metal to a condition to be refined is therefore not limited to melting down the charge. but applies broadly speaking to the preliminary heating of the metal. 7

It should also be understood that my invention is not necessarily limited to the refining of metals, as the operation herein described as refining may be supplemented by any other operation involving the heating of the metal, or the heating of the metal while covered by a layer of slag or other refractory material.

Also while I have herein shown the electrodes raised out of contact or above the slag in the refining operatiomit should be understood that during this operation, or when there is molten slag over the metal, the electrodes may be lowered so as to extend more .or less into the slag.

It should also be understood that while I have herein shown a few modifications of the apparatus embodying my invention, other modifications may be effected without exceeding the scope of what I claim.

lVhat I claim is 1. In the manufacture of steel and other metals in an electric furnace, the method which consists in passing electric current through a plurality of electrodes in series with each other through the metal in one operation of thefurnace, and passing said current through said electrodes in multiple with each other through a slag and the metal, when molten, in another operation of the furnace. t

2. In the manufacture of steel and other metals in which metal is first melted or preheated and then refined in an electric furnace, the method which consists in passing electric current through a plurality of electrodes in series with each other through the metal in melting or preheating and passing said current through said electrodes in multiple with each other through .the molten slag and metal in refining. r

3. In the manufacture of steel and other metals in an electric furnace, the method which consists in playing electric arcs in series with each other through the furnace charge in one stage of the manufacture, and playing said arcs in multiple through the furnace charge in another stage of said manufacture.

4. In the melting and refining of steel and other metals in an electric furnace, the method which consists in producing a melt of the metal by means of a high voltage and long arc, and refining the melt with substantially the same current with reduced voltage and shorter arc.

5. In the 'manufacture of steel and other metals in an arc type electric furnace, the method which consists in operating the furnace at-the beginning of the treatment of the metal therein at one voltage and varying the voltage inversely with the formation of slag while maintaining the current substantially constant.

6. In the manufacture of steel and other metals in an electric furnace, the method which consists in supplying currentto a metal bath from a plurality of electrodes, and varying the amount of current flowing through the metal bath by varying the resistance between one or more of the electrodes less in number than the whole number of electrodes in circuit and the metal bath.

7. In the manufacture of steel and other metals in an arc type electric furnace, the method which consists in supplying current to a metal bath from a plurality of arcing electrodes, and varying the'amount of current through the metal bath by varying the lengths of one or more of said arcs with respect to others.

8. In the manufacture of steel and other metals in an electric furnace having pairs of electrodes in which the current as between the several pairs difi'ers in phasefbut as between the electrodes of the same pair is of the same phase, the method which consists in operating the individual pairs in series with each other at one stage of said manufacture, and operating said electrodes electrodes through the molten bath and furnace bottom, and varying the amount of said current by varying'the direction of the current flow through one or more of said electrodes.

11. In the manufacture of steel and other metals in an electric furnace having a plurality of arcing electrodes and a bottom susceptible of conducting electricity, the method which consists in varying the proportion of current flowing through the furnace bottom to that which flows from one electrode to another, in accordance with operating conditions.

12. The method of operating electric furnaces for the manufacture of steel and other metals in which the electrical energy is supplied from one or more transformers, which consists in connecting sections of the transformer windings in multiple to produce a relatively high voltage for melting or heating the metal to refining temperature, and connecting said sections 1n series to produce a lower voltage for refining.

13. In the manufacture of steel and other metals in an electric furnace in which the electrical energy is supplied from one or more transformers, the method which consists in operating with the transformer primaries connected delta and the secondaries connected star for melting or heatin the metal to refining temperature, and wit the primaries connected star and the secondaries connected delta for refining the metal.

14. In the manufacture of steel and other metals in an electric furnace in which the electrical energy is supplied from one or more transformers, the method which consists in operating with the transformer pri maries connected delta and the secondaries connected star for melting or heating the metal to refining temperature, and with the primaries connected star and the secondaries connected delta for refining the metal, and connecting subsections of the transformer primaries or secondaries, or both, in series or multiple to further vary the volta e as between the heating or melting and re ning operations.

15. An electric furnace having a plurality of electrodes and a bottom susceptible of conducting electricity, a transformer or 4 transformers for supplying electrical energy to said electrodes, and an electrical connec-, tion from the furnace bottom to a point in the transformer secondary windings, and forming with said furnace ottom a common return, and a switch in circuit with said secondary winding and adapted to reverse the direction of current therethrough for creating .an increased flow of current through the'furnace bottom.

' 16. An electric furnace having three arcing electrodes connected in a three phasecircuit, and a bottom susceptible of conducting electricity, conducting means forming a path for electric current from the furnace charge and furnace bottom, around the electrodes, to a neutral point in the three phase system, and a reversing switch arranged to unbalance the phases of the currents passing from said'electrodes.

17. An electric furnace having three arcing electrodes connected in a three phase circuit, and a bottom susceptible of conducting 'electricity conducting means forming a path fof electric current from the furnace charge and furnace bottom, around the electrodes, toa neutral oint in the three phase system, and meansm said three phase circuit for unbalan'cing'the phase of the currents assing from said electrodes. 18. 11 an electric furnace having a plurality of electrodes, and a bottom susceptible of conducting electricity, a transformer secondary connected to said electrodes and having its windings divided into sections, and means to effect an electrical connection around the electrodes from the molten bath through the furnace bottom to a point in the said secondary intermediate of said sections, and means to change the direction of the current flow in one of said sections with relation to that in. the other of said sections 19. In an electric furnace having an electrically conducting bottom, in combination with 'a plurality of transformer primaries, and means to change. the connections of the same to vary the voltage supplied to the furnace, a plurality of transformer secondaries inductively associated with said primaries, and having their windings divided into sections, furnace electrodes connected to said secondaries, means to effect electrical connection around the electrodes from the furnace charge to points in said secondaries. intermediate of the sections thereof, and means to vary the direction of the current flow in certain of the sections of said secondaries with respect to other sections thereof to cause the entire current from the electrodes to flow through the furformation or vice versa, and means to conduct current from the molten charge through the furnace bottom and around the electrodes to a neutral point in the transformer system. c

21. In an electric furnace having a bot. tom susceptible 9f conducting electricity, and three arcing electrodes supplied with current from a three phase transformer system, in combination .with switching means to connect windings of the transformer systemin series or multiple, and means to effect electrical connection from the furnace bottom around the electrodes to a neutral point in the trans ormer secondary system.

22. In an electric furnace having a bottom susceptible of conducting electricity, three arcing electrodes, a three phase transformer system connected to said electrodes, switching means for changing the primary connections of said transformer system from delta to -Y formation or vice' versa, a d

switching means for changing the seconda y connections of said transformer system from delta'to Y formation or vice versa,

windings of said transformer system in series or multiple, means to connect sections of switching means for changing the secondary connections of said transformer system from delta to Y formation or vice versa, means to connect sections of the primary WlIldlIlgS. of said transformer system 1n series or multiple, means to connect sections of the transformer secondaries of said system in series or multiple, means to effect electrical connection from the fuma-ce bottom around the electrodes to a neutral point in the transformer secondary system, and means for reversing the direction of the current in one of the transformer secondary windings.

In testimony whereof I aflix signature in the presence of two witnesses."

v WILLIAM E. MOORE. Witnesses:

L. C. PATIERSON, A. HrBAUGHMAN.

35 means to connect sections of the primary

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