US1927894A - Fused stack arrester - Google Patents

Description

Sept. 26, 1933. Q. E. KRAU$E FUSED STACK ARRESTER Filed Dec. 5, 1929 INVENTOR Charles E. 706056.

A'TTORNEY Patented Sept. 26, 1933 PATENT OFFICE 1,927,894 Fuss!) STACK AimEs'rEa Charles E. Krause, Greensburg, Pia,

assignor to Westinghouse Electric & Manufacturing Company, a corporation of Pennsylvania Application December 5, 1929; Serial No. 411,916

9 Claims.

My invention relates to the construction and method of manufacture of a specific embodiment of the porous-block-arrester invention which is generically described and claimed in an application filed by Slepian, Tanberg and myself, Serial No. 379,899, filed July 22, 1929 and assigned to Westinghouse Electric and Manufacturing Company.

My present invention has more particular relation to a fused stack arrester composed of a plurality of discs separated by porous layers, as will be subsequently described and claimed with reference to the accompanying drawing, wherein Figure 1 is a perspective view of a lightningarrester element constructed in accordance with my invention, a part of the insulating covering being removed from its side walls;

Fig. 2 is a curve diagrahn subsequently referred to;

Fig. 3 is a perspective view, on a reduced scale,

illustrative of a step in the process of manufacture; I

Fig. 4 is an elevational view, partly in section, illustrating a complete lightning arrester em bodying my invention, and

Fig. 5 is a side elevational view of a modified arrester-element.

My lightning-arrester element 6 is a composite high-resistance fused solid body composed of a I plurality of layers '7 of molded material separated by layers 8 of powdered high-resistance material fused into a solid mass therewith.

The molded layers 7 are discs of about 5 thickness and about 2" in diameter, composed of the following ingredients:-

Percent Carborundum 70 Klingenberg clay ,7 Kaolin 23 The carborundum is in finely powdered form, such that not more than about 2 percent of it will fail to pass through a 270-mesh screen. These ingredients aremixed first in a dry state and then in a wet state. The mixture is then put through a granulating process, and the granules are poured into molds where the discs are pressed, which is readily done in an automatic machine r (not shown).

The molded discs, while still wet or damp, are then laid out on a table, and a dry mixture 8 of 80% powdered calcined clay and 20% of the same kind of powdered carborundum is sifted over the r entire surfaces of most of the molded discs, to a depth of approximately of an inch. The calcined clay, or grog, as I usually call it, is formed by heating kaolin clay to about cone 9, or about 1300 C., in a kiln, as described in the application referred to hereinabove.

The coated discs are then stacked in columns of any convenient height. I prefer to utilize a column of 6 coated discs surmounted by one plain disc to form a single arrester-element.

The stacks thus formed sire then placed in a suitable perforation 10 in a carbon sagger 11 (Fig. 3), a plurality of stacks being piled to= gether, with graphite spacer discs 12 disposed between the several stacks or elements, in order to keep them from fusing together in the sagger. The opening or openings in the sagger, after being filled as just described, are closed by means of a cap or caps 14, screwed in tightly against the stacks of discs, so as to hold the same under a firm mechanical pressure.

The saggers containing the stacks of arresterelements are then fired by being passed through a furnace having a maximum temperature of 1360 0., taking about 13 hours to go through the furnace, with something around 2 hours, perhaps, spent in the hottest part of the furnace. When the arrester elements are taken out of the sagger, they will be found to be fused into a solid integral mass, as a result of the firing operation under pressure. My striated block, as it comes from the sagg'er, is a black body having not more 35 than a trace of carbon which may have been absorbed from the sagger, thus insuring that the block is normally substantially an insulator, when it is not discharging an excess voltage surge.

After the firing operation, the end faces of the. stack are preferably plated with a copper plating 16 (Fig. 1), as by an electrolytic process, leaving about a of uncoated surface around the periphery in order to avoid any risk of getting copper on the lateral surfaces of the arresterelement. The copper coating is used in order to decrease the contact resistance and possibly to prolong the life of the arrester.

The lateral surfaces of each arrester-stack is 1 also treated with an insulating cement 18, as 00 described in the above-mentioned application, in order to prevent flashover along the side walls, of the arrester-element.

A 7-dlsc column, prepared as, above, having discs 7 of about V," thickness separated by layers 8 which have shrunk, during the firing operation, to about 20 inils each, thus having an overall height of about 1 inch and a diameter of about 2 inches, will have a maximum discharge-voltage of about 10,000 volts and a cut-oil 10 I voltage of about 4,000 volts, the cut-off current being only of the order of a few milliamperes, if that much, thus indicating that the arrester is normally substantially an insulator, when it is clean and in good condition. The break-down voltage is usually around 9,000 volts. Such an arrester-element easily handles repeated discharges of about 1000 amperes each without impairing its life.

A characteristic volt-ampere diagram of its operation during discharges is shown in Fig. 2, wherein the maximum voltage is indicated at Emax, its break-down voltage is indicated at EBD and its cut-off voltage is indicated at Eco. The peak value of the maximum line voltage to be expected at times when there is no excess voltage to be discharged therefrom, is indicated by the broken line 18 in Fig. 2.

A fused stack of discs, as hereinabove described, has been found to give very good protection, as just indicated, with long life. From certain tests which have been made, it is my present belief that the layers 8, of comparatively loosely pressed powdered material rich in clay, have a steeply drooping volt-ampere characteristic, with a very sharp cutoff, whereas the molded discs '7, of a mixture rich in carborundum, has a decidedly rising volt-ampere characteristic, with a relative- 1y, poorly defined cutoff. The two materials thus complement each other. I believe, also, that my stratified construction of dissimilar high-resistance porous-discharge materials serves to keep the discharges well distributed in the pores, and also serves to break the continuity of the edge" surface conditions, so as to check fiashovers along the sides of the arrester.

My arrester-element, prepared as described above, is then mounted, as shown in Fig. 4, in a suitable porcelain housing or casing 20, preferably one having a frangible drop-out bottom 21 characterized by having a thin wall-portion 22 which breaks when the arrester fails and overheats, so as to drop 0 it and clear the arrester from the line, as described in a patent of Golladay and Smith, No. 1,728,559, granted September 17, 1929, to the Westinghouse Electric and Manufacturing Company. i In the shipment of such drop-out-bottom arresters, with my solid fused arrester-element therein, difficulty has been experienced, during shipment, by reason of the pounding or jostling of the arrester-element, which is much more pronounced than when the arrester-element consisted of a plurality of separate stacked discs, as in the Golladay and Smith patent, presumably because of the greater cushioning effect of the pile of loose discs.

To overcome the difliculty resulting from the use of a single solid arrester-element in an arrester-casing having a frangible drop-out bottom, I have embedded the arrester-element 6 in a suitable insulating wax 23, which is applied hot, so as to come up about the top of the arresterelement, thereby eifectually curtailing its movement and cushioning the same during transit, besides providing effective insulation.

As will be seen from Fig. 4 of my drawing, the complete arrester preferably includes a series spark-gap 24 for the purpose of insuring its disconnection from the line and preventing the possibility of any leakage-current following a discharge, for any cause whatsoever.

. A modified form of the arrester-element is indicated in Fig. 5. consists of a thick molded porous disc orblock 30, which may have a thickness of of an inch, when molded, and which has the same composition as the dry powdered mixture 8 which has been described above for use in making the thin fused powdered layers 8 of my preferred embodiment, except that, in making the porous block 30, water is added and the block is molded as hereinabove described for the molded discs '7. On both the top and the bottom of the thick block 30 is disposed of the porous discs '7 hereinabove described, the same being separated from the porous block 30 by means of layers 31 consisting of a dry mixture of 60% grog or kaolin and 40% powdered carborundum applied to the damp'surfaces of the green discs as soon as they have been molded, the whole being fired under pressure, and then coppercoated at its ends and furnished with a lateral insulating coating, in accordance with the processes already described.

While I have described certain preferred constructions and operations and certain specific ingredients and proportions, it is to be understood that this description is only illustrative, and that I do not desire to be strictly limited thereto except as set forth in the appended claims when read in the light of the prior art.

I claim as my invention:

1. The method of making a composite highresistance fused article comprising making a wet mixture of insulating and binding materials, molding a plurality of pressed discs therefrom, applying an unmolded powdered material over the surfaces of a plurality of said discs while the latter are still damp, stacking the same so that the discs are separated by said powdered material and firing the same under sufficient mechanical pressure to cause the whole to adhere together.

2. A lightning-arrester element comprising a plurality of layers of powdered carborundum and a small percentage of binding material, characterized by at least one pair of said layers being separated by a layer of carborundum and a large percentage of binding material, all adhering together in a solid mass.

'3. The invention, as specified in claim 2, characterized by the fact that said binding material is powdered calcined clay.

4. The invention, as specified in claim 2, characterized by the fact that said binding material is powdered calcined clay and characterized further by the fact that the second-mentioned layers are relatively thin, as compared with the thickness of the first-mentioned layers.

5. The method of making a lightning-arrester element comprising making a wet mixture of insulating and binding materials, molding a plurality of pressed discs therefrom, applying an unmolded powdered mixture of dry powdered carborundum and dry powdered clay material over the surfaces of a plurality of said discs while the latter are still damp, stacking the same, so that the discs are separated by said powdered material, and firing the same under sufficient mechanical pressure to cause the whole to adhere together.

6. A porous solid lightning-arrester element operative by restricted discharges through the pores thereof, characterized by the fact that at least a portion of said element, through which the discharge passes, consists of fused powdered carborundum, over 80% of which will pass through a 2'70-mesh screen, and clay, and being further characterized by the fact that said lightningarrester element has strata of a material rich in clay sandwiched between strata of a material rich in carborundum.

' 7. A lightning-arrester element comprising a stratified solid structure of dissimilar high-resistance porous-discharge materials in superposed strata, characterized by the fact that said lightning-arrester element has one or .more strata of a black-body material rich in clay sandwiched between strata of a black-body material rich in carborundum.

8. A- lightning-arrester element comprising a Stratified solid structure of dissimilar high-resistance porous-discharge materials in superposed strata, characterized by the fact that said lightning-arrester element has one or more strata of a material rich in clay sandwiched between CHARLES E. KRAUSE.

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