US1036996A - Electric induction-furnace. - Google Patents

Description

A. E. GREENE.

ELECTRIC INDUCTION FURNACE.

APPLICATION FILED FEB.12,1912.

1,036,996, Patented Aug. 27, 1912.

y Z SHEET$SHEET 1. Elihu A. E. GREENE.

ELECTRIC INDUCTION FURNACE.

APPLICATION FILED FEB. 12,1912.

1,036,996. P ented Aug. 27, 1912.

2 SHEETS-SHEET 2.

UNITED STATES PATENT OFFICE.

ALBERT E. GREENE, OF CHICAGO, ILIJINOIS, ASSIGNOR '10 AIERICAN ELECTRIC SMELTING AND ENGINEERING COMPANY, 01 ST. LOUIS, MISSOURI, A CORPORA- 'IION OF MISSOURI.

ELECTRIC INDUCTION-FURNACE.

Specification of Letters ratent.

Patented Aug. 27, 1912.

To all whom it may concern:

'Be it known that I, ALBERT E. GREENE, citizen of the United States, residin at Chicago, in the county of Cook and tate of Illinois, have invented a certain new and useful Improvement in Electric Induction- Furnaces, of which the following is a full, clear, concise, and exact description.

My present invention relates to induction furnaces operating on poly-phase power.

In the operation of an induction furnace the fewer the number of channels used the less is the lining and repair cost. Heretofore to operate an induction furnace off a three-phase line, either the use of three separate channels has been resorted to with three corresponding primary circuits, or it has been suggested to use special transformers for transforming three-phase current into two-phase current, and supplying this latter to the primary coils of the furnace. It has also been customary to control the power by varying the voltage supplied to the primary coils of the furnace.

My present invention provides a means of operating induction furnaces directly from three-phase power lines of ordinary voltages, only two phases operating in" the furnace; and also combines a means of operating without unbalancing the three-phase I power supply and without the use of intervoltage or variable voltage.

mediary transformers for providing low For example, my invention provides a simple meansfof operating a two-channel induction furnace from a three-phase, sixty-six hundred volt, power line.

One feature of my invention relates to the use of two cores with interconnected primary windings thereon so arranged as to take three-phase power and transform it in the furnace to two-phase poWer,-Without undesirable unbalancing of the three-phase supply lines; and another feature relates to the use of constant voltage supply power and means of regulating the power in the furnace proper from such a constant voltage supply.

I will now describe in detail certain types of furnaces embodying my invention, and for the sake of clearness will refer to the accompanying drawings, in which Figure 1 is a sectional elevation of a two channel induction furnace embodying my invention; Fig. 2 shows diagrammatically a plan view of another embodiment of my invention. Fig. 3 shows diagrammatically a plan View of a two-channel furnace having a common leg for completing both magnetic circuits; Fig. 4. is a detail plan view of the yoke forming partof the magnetic circuit of the core shown in Fig. 3.

The type of furnace shown in Fig. l is suitable for capacities up to four or five tons. It consists essentially of two magnetic cores 1 and 2, supported upon suitable frame-work 3 preferably tilting, primary coils 4 and 5 on each of the cores, a shell 6 containing the refractory lining 7 with channels 8 and 9 for holding metal forming secondary circuits, these channels connecting with a main central chamber 10. The two cores 1 and 2 are located on opposite ends of the furnace and the central chamber 10, extending across the furnace, has a roof 11 elevated above the channel covers. This construction makes it possible to pile considerable quantities of scrap intothe central chamber.

The lining of the crucible is made of any refractory material suited to the particular kind of metal to be treated.

The use of two cores together with the interconnected primary coils thereon, and the arrangement of taps and switches in connection therewith, make possible the direct operation of the apparatus on threephase lines without use of intermediary transformers. My arrangement has, therefore, the special advantage of such direct operation from three-phase lines without unbalancing of the power and yet with a minimum number of secondary channels, and furthermore with a saving of the three per cent. or thereabout of power which is ordinarily lost in the transforming of power outside the furnace.

The arrangement of primary coils is shown in the fi ures diagrammatically.

Referring to ig. 1, one primary coil 5 is located on the core 2 and the corresponding primary coil 4: is located on the other core 1, One terminal of the primary. coil 5 is connected to one wire 13 of the. three-phase supply line, suitable switches and breakers bein installed on that line; and by meansof a-suitable switch 15 any one of the three taps 16, 17 or 18, constituting the other terminals of coil 5, may be connected, one at a time, to another phase 12 of the three-phase supply line. On the primary coil 5, taps 19, 20 and 21 are taken out at points approximately half the number of turns included by the tap; 16, 17 and 18 res ectively; that is, if tap 16 is taken out 0 the one-hundredth turu, then tap 19 would be taken out on the fiftieth turn; and accordingly if tap 17 were taken out on the eightieth turn of the winding, tap 20 would be taken out on the fortieth turn; likewise if tap 16 be taken out on the. sixtieth turn, tap 21 would be taken out from the thirtieth turn. These central taps 19, 20 and 21 on the winding 5 are connected to a terminal of the other primary winding 1 on the other core through suitable switching apparatus described below. The other primary coil 4 is designed to operate on a voltage equal to about 86 per cent. of the voltage supplied to coil 5, this latter coil taking the line voltage, and in order that the same amount of power may be developed in'each channel, the carrying capacity of the copper in coil 4 is increased accordingly. The coil 4 has taps 22, 23 and 24 at one end and a terminal 25,'at'the other and these taps are taken out at such points as to develop, when operated in combination with the other coil 5, equal voltages in both of the secondary circuits. That is, if tap 16 on coil 5 be on the one-hundredth turn, then tap 22 would be taken out on approximately the eighty-six h turn of coil 4; and if the second tap on coil 5 be taken out from the' eightieth turn, then tap 23 would be taken out on about 56 per cent. of eighty turns or the sixtyeighth turn: and tap 2-1 accordingly on about 86 per cent. of sixty or about the fifty-first turn corresponding to thetap on the sixtieth turn on the coil 5. Any of the taps 22, or 21 can be connected to a corresponding tap 19. 20 or 21 respectively by means of the switch 26. The terminal 25 goes, of course, to the other phase 14 of the three-phase supply line.

As many taps may be taken out as desired for the particular use to which the furnace is to be put, three taps having been chosen for clearnese.

Fig. 2 shows a method of embodying my invention in a furnace presumably of large size and in which more channels are required in order not to undesirably lower the power factor of the furnace as a whole. ()ne core 50 is encircled by two channels 52 and 53, these channels being made in the refractory lining 4.9. Likewise the other core 51 is surrounded by two other channels 54 and 55. Primary coils 56 and 57, forming one continuous'winding, are located on core 50 and similarly coils 58 and 59 are located on core 51. Each winding is divided into two parts having approximately the same number of turns, but each part located in close prox imity to a separate channel. Six taps, three on each part of the Winding, are taken out on each of the coils 57 and 56. The taps on coil 57 are 60, 61 and 62 and on 56 the taps are 63, 64 and 65. Any one of these taps on each coil can be connected by means of switches 67 and 68 with its particular wire of the three phase supply line 69. By this arrangement of taps on both ends of this primary winding on core 50, the junction 70 of the two coils 56 and 57 is always approximately the center of the winding on that core. This junction is connected electrically to a terminal 71 of the winding on the other core 51. At the other end of the winding on core 51 taps 72, 73 and 74 are taken out and any one of these can be connected by means of the switch 75 to the third wire of the threephase supply line. The continuous winding constituting co ls 56 and 57 corresponds to the coil 5 of Fig. 1, and the continuous winding constituting coils 58 and 59 corresponds to the coil 4 of Fig. 1. The taps 72, 7 3 and 74 correspond in function to the taps 22, 23 and24 of Fig. 1. In other Words the furnace shown in Fig. 2 operates on the same general principleas the 1 with the difference that the cores 1" and 2 of Fig. 3 extend to a common portion 3* instead of completing the magnetic circuit separately. The yoke 6 is removable and rests upon the upper end of the vertical legs 1, 2 and 3 and completes the two magnetic circuits. The windings 4 and 5 and the terminals .22 and 25 and also 13 and 16 aresimilar to the correspondin ones in Fig. 1. I/Vhere power is availab le from a variable voltage supply so that no taps on the furnace coils are required, the connection would be made to the outside terminals of the coils, but the arrangement need not be ditlcrent otherwise from the description herein.

It is understood that I do not limit myself to the location or number of the taps or to the point at which one coil is interconnected with the other coil. For example, where unbalancing of the three-phase supply is of no consequence I may connect one coil across one phase and the other across another phase, the two primaries then having one common terminal connection. In such case the number of taps required might be considerably lessened. In other cases where a small unbalancing is permissible I may permanently connect a terminal of the short coil to the approximate center of the other coil, and not allow for the variation of the neutral point with the variation of taps used on the long coil.

I claim 1. In an electric induction furnace, the combination of two magnetic cores, two channels in refractory material surrounding said cores and connectin with a main chamber, primary coils on eac of said cores, means of connecting a variable number of turns of one coil to one phase of a threephase supply, and means of connecting corresponding percentages of the second primary winding between the third wire of the three-phase supply and the approximate center of the other coil.

2. In an induction furnace, the combina tion with two channels connecting in a main chamber, or a magnetic core through each of said channels, a primary winding on each of said cores, means of connecting one primary winding between two wires of a threehase circuit, and means of connecting a suitable number of turns of the other primary winding between the third wire of said circuit and the approximate center of the first primary winding to give equal voltages on the two metal circuits.

3. In an induct-ion furnace, the combination with two separate channels connecting with a main chamber, of magnetic cores extending through each of said channels, primary windings on said cores provided with taps, means or" connecting a terminal to one coil to the approximate center of the other coil, and means of connecting the desired number of turns of each coil to the three wires of a three-phase system to give approximately equal power in each secondary.

4. In an electric induction furnace, the combination with two separate magnetic cores, channels surrounding each of these cores for forming single turn secondary circuits, and primary windings upon each of these cores, said primary windings being interconnected for taking three-phase current.

5. In a three-phase induction furnace, the combination of two magnetic cores, two separate channels around different legs of each core, all of said channels connecting in a main. central chamber, a primary winding on each core consisting of two coils in series, one coil located in proximity to each channel; taps on each primary winding, means of connecting the requisite number of turns of one winding between one conduc tor of a three-phase system and the approximate center of the other Winding, and means of connecting the corresponding number of turns of this other winding between the other two wires of said three-phase circuit to develop approximately equal voltages in all the secondary metallic circuits.

In witness whereof, I hereunto subscribe my name this ninth day of February, A. D.,

ALBERT E. GREENE.

Witnesses AL RED H. Moore, MCCLELLAND YouNo.

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