US 3265841 A
Description (OCR text may contain errors)
Aug. 9, 1966 H. GREBER 3,265,841
I ELECTRICAL FUSE WITH FORCED CURRENT INTERRUPTION Filed Oct. 22, 1963 INVENTOR United States Patent 3,265,841 ELECTRICAL FUSE WITH FORCED CURRENT INTERRUPTION Henry Greber, 225 W. 80th St, Apt. 8]), New York, N.Y. Filed Oct. 22, 1963, Ser. No. 317,973 4 Claims. (Cl. 200-132) The purpose of this invention is to provide a rapid, current limiting electrical fuse, particularly applicable for high and extra-high voltages of alternating and direct currents, and also for high frequency currents, and adaptable for renewable fuse elements. Though many kinds of current limiting fuses are known, they all function by extinction of the are that interposes itself in place of the burned out part of the fuse element. This is valid even if the arc is interrupted in liquids such as oil and tetrachloride, or in sand. Though the current limiting fuses available at present are large, complex and expensive their performance is not precisely predictable, and the tolerances to which they are manufactured are rather wide, which constitutes an impediment in their application and coordination with other fuses and breakers. Their current interrupting capacity is limited.
It is the primary purpose of this invention to provide a fuse of great current interrupting capacity, which is accurately determinable. Another purpose of this invention is to limit the current in the circuit to the let-through value, at which the circuit will be opened, without letting the current attain its crest value. A further objective of this invention is to provide a simple, inexpensive, renewable fuse of small dimensions, but of great current interrupting capacity. A still further objective is to provide a fuse which can be manufactured simply and inexpensively by known production methods, by virtue of its being composed of only a few simple parts, which can -be readily assembled.
These objectives are attained by a novel method of forced current interruption. The method consists in insertion of a solid, insulating body into the gap created in the fuse element partly burned out. It has been known for a long time that the respective electric breakdown voltages for gaseous, liquid and solid insulating materials are in proportion of 1: 100: 1000. A thousand times greater voltage is needed to break down an insulating solid material than it is necessary for an air gap of the same thickness. In spite of this fact, fuses available at present are based on current interruption in air, or much less frequently in an insulating liquid such as oil. The fact that in the majority of fuses the fuse element is embedded in sand, does not change the above described situation, for even fuses with sand filling depend on their functioning on the dielectric strength of the air gap between the two separated parts of their blown fuse elements. In the here presented fuse the current is not interrupted in an arc, in contrast to the prior art, but after melting of the fuse element, the arc space is immediately filled with a solid dielectric. This prevents formation of an arc, and speeds up to the process of current interruption, since the melting time is not'followed by an about equally long arcing time.
Other objectives, features and advantages of this invention will be evident from the following detailed description and from the accompanying drawing. In this drawing FIG. 1 shows a longitudinal sectional view of the fuse, whose cross sectional view, along the line 2-2 is shown in FIG. 2. FIG. 3 presents a perspective view of the insulating body, serving for separation of the sections of the burned through fuse elements, and in FIG. 4 can be seen the perspective view of the spring working in conjunction with said insulating body. FIG. 5 shows a perspective view of said spring wrapped around with insulating tape. In FIG. 6 is represented a perspective mediary of the porcelain body 5. The fuse element 3, I
is also tensioned by two springs 6 and 7, which press at the bottoms 8 and 9, of ferrules 21 and 22. One end of fuse element 3, is fastened to the connector consisting of plates 11 and 12, which are pressed by means of bolts 13 and 14. The other end of said fuse element 3, is fastened to the connector consisting of plates 15 and 16, which are pressed by the bolts 17 and 18. Tube sections 19 and 20, serve as spacers, fixing the position of discs 8 and 9, Within the ferrules 21 and 22, respectively. Tube 1 serving as fuse enclosure, is made of insulating material, such as fiber.
FIG. 2 shows a cross sectional view taken along line 22, of the fuse presented in FIG. 1. Component parts shown in both figures are designated with the same numerals respectively. The porcelain body 5, is separately shown in the perspective view in FIG. 3. The elliptical spring 4 is presented separately in perspective view in FIG. 4. It is understandable that the spring can be reliably insulated with glass or asbestos tape. Such insulation can be used as a substitute for the insulating body 5, which wouldthen become unnecessary. A spring 4, provided with insulating tape 23, capable of functioning without the insulating body 5, is demonstrated in perspective view in FIG. 5.
In FIG. 6- is drawn the perspective view of a fuse enclosure 34, containing the fuse element 28, looped through two heavy insulating beads 29 and 30, which can be made of glass. The fuse element 28 is metallically connected to ferrules 23 and 27. The fuse enclosure 34 contains also two porcelain half-discs 31, and 32, which are held together by a circular coiled spring 33.
The insulating body 5, shown in FIG. 1 and FIG. 2 is made of porcelain, but can be also made of glass or steatite. It can be provided with a de-ion grid. In this case metallic conductors, or semi-conductors, separated from each other, would be embedded in said insulating body. Since the application of a de-ion grid'is not considered necessary in the majority of cases, and may be of advantage for fuses of very large current interrupting capacities, it is not shown in the drawing.
The fuse element of a fuse of large rating is thick. To shorten the time necessary for its interruption, it may be provided with one or more notches. On the contrary, fuse elements rated for small currents are too thin to sustain the tension of the two longitudinally acting springs, and of the transverse spring. To strengthen mechanically such thin fuse element, it is reinforced with threads of cotton or plastic. These threads are non-conducting, and when the metallic fuse element burns through these threads either burn through, as the case is with cotton,
' wool, etc., or they melt as is the case with plastics, such as nylon for example. Obviously cords and tapes of such materials can be used. Thus the fusible element 3 shown in FIG. 1, FIG. 2 and the fuse element 28 shown in FIG. 6 are combined fuse elements consisting of metallic wires and non-metallic threads woven together. All fuse elements have a tendency to blow in their middle, because of the cooling effect of the terminals, be it ferrules or blades. For the here described fuse, blowing of its fuse element somewhere near its center is important, though not essential. To make sure that the fuse element will actually blow near its center, the metallic wires constituting it can be notched at their centers, or corresponding incisions can be made in case of used metallic tapes, applied in parallel with tapes of fabrics.
In operation of the described fuse, the longitudinally is used in horizontal or vertical position.
acting springs exert a continuous tension on the fuse ele-.
ment. In case of an overcurrent, as soon as the fuse element is heated to such temperature that it loses its mechanical strength, the two tensioning springs tear it apart, and the transverse spring introduces the insulating block into the gap formed by the two separated sections of the blown fuse element. Thus the melting time, defined as the time necessary for the fuse element to melt and to open the circuit, is substantially reduced. In addition there is no arcing time following the melting time, often called the pre-arcing time of the fuse. The space in which an arc could be formed and stay for a short while, is filled with the insulating body, which thus forces the interruption of the current. In result of this, the fuse of this invention is capable of ultra-rapid operation, at a speed unobtainable with any other fuse of the prior art. Its current interrupting capacity and clearing time can be predicted with an accuracy which cannot be attained for any other fuse available at present.
As stated, two powerful springs pull the two sections of the burned through fuse element apart, while another spring acting in the transverse direction, pushes the insulating block into the gap between the two sections of the burned through fuse element. But while the springs tensioning the fuse element along its axis are strong, the spring pushing the insulating body is a weak one. In consequence the first, longitudinally acting springs will always pull the ends of the interrupted fuse element out of the middle of the fuse, before the insulating body will reach the Wall of the fuse enclosure. The longitudinally acting springs are able to pull the ends of the burned through fuse elements even if these ends were jammed and pressed by the insulating body towards the wall.
In departure from the standard designs, the fuse described and illustrated here is based on the principle of insertion of a solid insulating body into what would constitute an arc space in fuses of other designs. By this measure the entire process of current interruption is enforced and put under control. This fuse, whose function does not depend on the passage of the interrupted current through zero, is therefore Well suitable for opening not only alternating current circuits of commercial frequencies, but also of high frequencies and of direct current. The gap between the two separated sections of a burned through fuse element can be filled by the insulating body pushed in by force of gravity, regardless whether the fuse This possibility, shown in FIG. 6, can be used for inexpensive fuses. When the fuse element 28, having at least one notch at its center, is burned through, or rather before that, when it is only softened due to its elevated temperature, both beads 29 and 30 (if the fuse is used in horizontal position), or one of them (if the fuse is used in vertical position), pull the fuse element sections or section respectively from in between the insulating blocks 31 and 32. As soon as one of both sections of the burned through fuse element are pulled from the space between said two insulating blocks, these come in contact which each other, at least at one of their sides, because of the action of the coiled spring 33.
There is nothing to prevent the enclosure of this fuse to be filled with an insulating liquid such as oil, silicon liquid, tetrachloride, or with a slurry made of an insulating liquid mixed with dust of consistency of a powder or porcelain, glass, mica, asbestos and the like. This is advantageous for fuses of large current interrupting capacities. For the same purpose the transverse spring (4), can be covered with any of the materials, such as fiber, known to emanate arc extinguishing gas when in contact with an arc.
While only two embodiments of this invention are described and drawn in details, it is to be understood that these details are only illustrative, and not limiting the scope of the invention. There will be now obvious that many modifications, variations, and changes are possible, all in the spirit of this invention and within the scope of the following claims.
1. An electrical fuse with forced current interruption comprising: a housing, a fuse element in said housing which is conductively connected to the terminals of said fuse, said fuse element being exposed to a tensile stress exerted by at least one spring attached to one end of said fuse element, said fuse element being exposed simultaneously also to a force perpendicular to its axis exerted by at least one spring acting in a plane transverse to the fuse axis, said transverse spring acting through the intermediary of a segmented insulating body separating said transversely acting spring from said fuse element, said body being inserted into the gap created by the two sections of the fuse element separated from each other when the fuse is blown.
2. An electrical fuse with forced current interruption consisting of a fuse element conductively connected to the terminals of said fuse, said fuse element being exposed to a tensile stress exerted by at least one spring attached to one end of said fuse element, said fuse element being exposed also to the pressure perpendicular to its axis exerted by at least one elliptical spring contiguous with the concave side of a spoon-shaped concave-convex insulator which separates the elliptical spring from said fuse element, with said concave-convex insulator body being in contact with the fuse element, and said elliptical spring being in contact with the concave-convex insulator body and with the housing of said fuse.
3. An electrical fuse with forced current interruption as in claim 1 with said insulating body consisting of one of the group of ceramic materials, such as porcelain or glass.
4. An electrical .use with forced current interruption as in claim 1, with said transversely acting spring being covered with electro-insulating and heat-resistant tape of asbestos.
References Cited by the Examiner UNITED STATES PATENTS 975,421 11/1910 Harris 200- 982,281 1/1911 Lincoln et a1 200-117 1,934,243 11/1933 Steinmayer 200135 2,615,107 10/1952 Zito. 2,915,609 12/ 1959 Johnston 1. 200135 BERNARD A. GILHEANY, Primary Examiner.
H. B. GILSON, Assistant Examiner.