US2777033A

US2777033A - Power fuses with tubular links and pressure-type link connections

Info

Publication number: US2777033A
Application number: US436398A
Authority: US
Inventors: Frederick J Kozacka
Original assignee: Chase Shawmut Co
Current assignee: Chase Shawmut Co
Priority date: 1954-06-14
Filing date: 1954-06-14
Publication date: 1957-01-08
Anticipated expiration: 1974-01-08

Description

Jan. 8, 1957 F. J. KOZACKA 2,777,033

POWER FUSES WITH TUBULAR LINKS AND PRESSURE-TYPE LINK CONNECTIONS 2 Sheets-Sheet 1 Filed June 14, 1954 illlll-IJ Jan. 8, 1957 F. J. KOZACKA POWER FUSES WITH TUBULAR LINKS AND PRESSURE-TYPE LINK CONNECTIONS 2 Sheets-Sheet 2 Filed June 14', 1954 United States Patent POWER FUSES WITH TUBULAR LINKS AND PRESSURE-TYPE LINK CONNECTIONS Frederick J. Kozacka, Ameshury, Mass, assignor to The Chase-Shawmut Company, Newhuryport, Mass.

Application June 14, 1954, Serial No. 436,398

12 Claims. (Cl. 200-420)- This invention relates to the protection of electric circuits by means of high-capacity fuses, and more particularly to improved high-capacity fuse structures for lowvoltage circuits.

High-capacity fuses are preferably current-limiting, i. e. they are preferably designed to limit the let-through current below the peak of the available short-circuit current which the system is capable of supplying; Where the current normally carried by the fuse is relatively large andwhere it is desired'to achieve a drastic current-limiting action, the current path through the link must be made up of a plurality of fusible conductors adapted to be connectedin parallel into the electric circuit to be protected by' the fuse and these conductors must be surrounded by an arc-quenchcing filler, preferably a silicious pulverul'ent material. Fuses of this type offer a high degree ofshortcircuit protection at relatively moderate cost but are subject to a number of limitations. The magnetic energy inherent in the electric system under interruption at the time a majorfault occurs-must in-part be absorbed by' the arc-quenching filler within the casing; of the fuse. To

this end the fusible conductors within the fuse intended to be connected in parallel into the electric circuit ought to be arranged in such a way that each of the conductors issurrounded by a substantially equal amount of" filler; Generally all of the conductors which are connected" in parallel are substantially identical andsupposed to fuse simultaneously by'the heat generated by any major fault current. Manufacturing tolerances are of no consequence only as long as these tolerances are extremely small. Relatively small and absolutely unavoidable differences. between theparallel' fusible conductors have a tendency to result in improper operation of the fuse. Considering a pair of parallelconductors of which one fuses before the other, a small break will form at the. first fused conductor'by reason of the fusion thereof; however, sincethe first fused conductor is shunted by the second" conductor the voltage across the small fusion break. will be close to, zero andmay beinsufiicient'to kindle an arc across the fusion gap and to cause gap growth on account of-backburning by the arc.. When theother conductor fuses an arc gap will form and that arcgap will grow by virtue of back-burning. However, the small break formed in. the first fused'conductor will not grow and the arc-quenching filler surrounding that conductor willnotbe utilized in. the interrupting process, i. e. for absorbing. a portion of the magnetic energy inherentin the electric system at the time of the occurrence of the fault. In other words, the arc-quenching filler surrounding the first fused conductor. is not being used at all in the process of circuit. interruption. I

In a fuse having many conductors in parallel, a substan tial portion of the arc-quenching filler withinthe casing may remain unused, or inoperative as an energy absorber. during interruption ofja faulted. circuit by the fuse. Because of'this phenomenon, the interrupting efiieiencyof, the arc-quenching filiermay be small. As a' result, highcapacity' current-limiting fuses comprising a plurality of Patented Jan. 8, i957 fusible conductors in parallel are generally provided with larger numbers of fusible conductors, larger quantities of arc-quenching filler and casings of larger size than actually necessary if each element of the fuse assumed an approximately equal share in the total interrupting duty of the fuse upon occurrence of a major fault.

Providing a plurality of fusible conductors in a fuse intended to be connected in parallel into the circuit to be protected by the fuse results also in the relatively difiicult problem of conductively connecting the ends of the conductors to theterminals of the fuse. Spot-welding is one possible answer to the problem but spot-Welds have a tendency to come off if not carefully made by highly skilled labor. Spot welds are particularly difficult to achieve if the mass of the terminals of the fuse is large, as is widely adopted" practice in this country. Soldering with soft solder is another possibility of securing fuse links to terminal elements. Since terminal elements of high capacity fuses involve frequently a very large mass, it may be difficul't to heat the mass up to the temperature required for soldering.

Another drawback of high-capacity multiple fusible conductor fuses having ribbon type fusible conductors adapted to be connected in parallel into the electric circuit which the fuse is to protect resides in the fact that an additional spacer is genera-11y required to maintain the terminal elements in the proper spaced relation if the terminal elements involve a substantial mass, as is frequently the case, as mentioned before.

It is the primary object ofthis invention. to provide high-capacity fuses which are entirely free from all the above referred-to drawbacks and/ or limitations.

Another object of this invention is to provide currentlimiting fuses which are less expensive to manufacture and which have. a higher interrupting efiiciency than comparable prior art high-capacity fuses.

Still another object of this invention is to provide current-limiting fuses having tubular fuse links yet not' being subject to the limitations and/ or drawbacks of prior,

art fuses having fuse links of this type.

A further object of this invention is to provide highcapacity fuses the links of which can readily be removed and replaced upon blowing of the fuses.

A further object of this invention is to modify and improve the structure disclosed and claimed in my United StatesfPa'tent 2,665,348, January. 5, 1954, Current-Limiting Fuse, assigned to the same assignee as the present invention.

The foregoing and other general and special objects of the invention and advantages thereof will more clearly appear from the ensuing particular description of the invention, as illustrated in'the accompanying drawings wherein:

Fig. 1 is a perspective view of a portion of a fuse embodying my invention;

Fig. 2 is. a front view of a fuse link of sheet metal for a fuse embodying my invention;

,Fig. 3 is a longitudinal section along 3-3 of Fig. 4 showing, a fuse embodying my invention;

Fig. 4 is a cross-section. taken along 4-4 of Fig. 3;

Fig- 5 is a longitudinal section along 55 of Fig; 6 showing: another embodiment of the invention;

Fig. 6' is. a cross-section taken along 6-6 of Fig. 5;

Fig. 7 is. a. longitudinal section of a third embodiment of. my invention taken along 7-7 of Fig. 8, and

Fig. 8 is a cross-section of the structureshown in Fig. 7 taken, along 8-8 of Fig. 7.

Referringnow to the drawings, and more particularly to Figs. 1: to 4, inclusive, reference numeral 1 has been applied; to indicate. a tubular fuse link. Fuse link 1 is formed by Winding the stamping shownin'Fig; 2 into the" shape ofa cylinder, as clearly shown in Figs. 1, 3 and 4.

Fuse link 1 extends between a pair of spaced massive terminal elements 2 of copper, of which each comprises a substantially cylindrical block of copper. Each ter minal element 2 is provided with a blade contact 3 inserted into a groove 2a in the respective terminal element. Casing 4 of insulating material is slipped over terminal elements 2 and pinned to the latter by means of steel pins 5.

Casing 4 may either consist of a ceramic substance, or of a glass-cloth-laminate including a plastic fairly heat resisting material. Each terminal element 2 is provided with a shoulder s, subdividing the terminal element into a portion 212 of relatively small diameter and into a portion 20 of relatively large diameter. The portion of relatively large diameter 20 supports casing 4. The portion of relatively small diameter 2b of each terminal element 2 forms a cylindrical clamping surface for securing link 1 to, and conductively connecting link 1 with, the respective terminal element 2. To this end a split clamping ring 6 is mounted on each of the axially outer ends of link 1 and split rings 6 engage under pressure link 1 and press link 1 against the clamping surfaces 2b of the terminal elements 2. The outer non-split or continuous rings 7 are mounted under pressure upon the inner or split rings 6, and establish a firm mechanical connection between link 1 and terminal elements 2 having a very small electric interface resistance.

Ribbon type fuse link 1 is wound cylindrically to fit upon the cylindrical clamping surface 2b on each terminal element 2 and arranged within casing 4 in coaxial rela tion thereto. Link 1 is provided with a plurality of groups G1, G2, G3 of perforations 1a and intermediate current-carrying elements 1b. Each of said groups G1, G2, G3 comprises a plurality of narrowly spaced perforations 1a having a predetermined width and a plurality of intermediate current-carrying elements 1b arranged in circular relation in a plane at right angles to the axis of the cylindrical surface defined by link 1.

Upon occurrence of a fault current of major proportions, all the intermediate current-carrying elements 1b fuse substantially simultaneously. Each group of perforations G1, G2, G3 comprises 10 square perforations 1a and 10 intermediate current carrying elements 1b, and therefore the link behaves basically in the same fashion 1b immediately adjacent thereto. The stippled area in electric circuit, and of which each has three serially related necks, or points of reduced cross-sectional area. As in any fuse having a plurality of fuse links connected in parallel, some of the necks, or portions of reduced cross-sectional area, or current-carrying elements 1b, will fuse relatively soon and others relatively late. The first fused elements 1b form mere fusion gaps across of which there is virtually no voltage at the time of gap formation. Hence no arc is kindled and no back-burning takes place at these gaps. A voltage will prevail across the last formed gaps and cause kindling of arclets at these gaps, which arclets will burn back, resulting in progressive growth of the arc gaps and progressive increase of the arc voltage.

Referring now to Fig. 2, and more particularly to the two current-carrying elements 1!) at the left end of group G1; assuming that the element 1b way to the left fuses after the element in group G1 which is second from the left edge of link 1. An extremely narrow gap may be formed in the first fused element 117, which gap may be already relatively cool at the time the element 1b which fuses last fuses, and gives rise to the formation of an arclet. The Width W1 of the perforations 1a is sufficiently small to cause vaporization of the element 112 second from the left edge of link 1, i. e. of the first fused element 1b, by back-burning of the arclet formed at the element 115 way to the left of group G1, i. e. the element 1b to fuse last. Thus substantially the entire pulverulent arcquenching filler surrounding the link will be used as an energy absorber, irrespective of whether or not an are gap is initially formed at all points of break, or at all current-carrying elements 111. In other words, the width M of the perforations 1a is sufiiciently small to cause vaporization of any of the plurality of current-carrying elements 1b by back-burning of the are formed at a major fault at one of said plurality of current-carrying elements 112 immediately adjacent thereto. The stippled area in Fig. 2 is indicative of the amount of back-burning oc curring when a mere fusion break without arcing is formed at the current-carrying element 112 second from the left in group G1, and an arc is kindled upon fusion of the current-carrying element 1b way to the left of group G1.

The number of perforations la in each group G1, G2, G3, their width W1, and the dimensions of the currentcarrying elements 1b depend upon a number of factors. These parameters must be determined separately for each design. The number of perforations 1a required in each case may readily be determined experimentally from the above back-burning condition. As a general rule, the number of perforations in each group G1, G2, G3 should be larger than five. The number of groups G1, G2, G3 depends upon the arc voltage which it is desired to obtain and upon the desired rate of rise of the arc voltage. Where the circuit voltage is low and the current-limiting action which it is desired to achieve not very high, one single group of perforations la and intermediate currentcarrying elements 1b may be sufficient. Generally several groups G1, G2, G3 etc. of perforations 1a and intermediate current-carrying elements 1b should be provided, provision of each additional group increasing by one the number of serially related arclets forming during the process of interruption. As clearly shown in Fig. 2, each perforation 1a is rectangular and has a pair of relatively narrow sides and a pair of relatively wide sides. The narrow sides of perforations 1a extend parallel to the axis of the cylindrical surface defined by link 1, as can best be seen in Figs. 1 and 3. Reference character W2 indicates the Width of the current-carrying elements 1b. The length w of the wide sides is a multiple of the length W3 of the narrow sides. The ratio of the sum total of the lengths w of said wide series to the sum total of the widths wz of current-carrying elements 1b should be smaller than 10:1. This enables to achieve a considerable bending strength without sacrificing arc voltage. A number of serially related groups G1, G2, G3, etc. of perforations la and current-carrying elements 1b enables to build-up arc voltage to exactly the amount required. The ratio of ws/wl should preferably be in the order of Winding of a link of sheet metal in the shape of a cylinder greatly increases the mechanical strength, and more particularly the bending strength, of the link. It is thus possible to impart sufficient mechanical strength to the link to enable the link when clamped to the clamping surfaces 2b of the pair of terminal elements 2 to form jointly with the pair of terminal elements 2 a selfsustained structural unit, i. e. a unit which does not require a spacer, or mechanical tie, in addition to link 1, for maintaining the terminal elements 2 in the proper spaced relation thereof. The mechanical strength of tubular link 1 is not seriously impaired by the groups G1, G2, G3 of perforations 1a, i. e. link 1 does not lose its ability because of perforations 1a to tie the two terminal elements 2 mechanically into a structural unit that does not require an additional insulating spacer. The relatively shortlength W3 of current-carrying elements 112 is mainly responsible for the ability of link 1 to operate as a spacer for the

heavy masses

2, 3 attached to the ends thereof. While theshort length W3 of current-carrying elements 1b increases the bending strength of the terminal-elementlink-unit 1, 2, the shortness of their length W3 imposes a limitation with regard to the magnitude of the arc voltage which can be produced at each single point of reduced cross-sectional area, or at each break. As mentioned above, the arc voltage required in any particular instance can be readily produced by providing several serially related groups G1, G2, G3 of perforations 1a and currentcarrying elements 1b of reduced cross-sectional area.

As mentioned before, the axially outer ends of link 1 are each surrounded by a split ring 6, and an outer nonsplit or continuous ring 7 is mounted under pressure upon each split ring 6. The radial pressure of rings 7 upon rings 6 ought to be considerable to compress split rings 6, as required to minimize the voltage drop between link 1 and clamping surfaces 2b, thus minimizing heat losses occurring within the fuse. This considerable amount of pressure should preferably be achieved without resorting to heating, or cooling, of any part of the structure. In the embodiment of the invention shown in Figs. 3 and 4 the requisite pressure is being achieved by chamfering slightly the axially outer ends of rings 7. The degree of chamfering is so slight that this feature does not appear in the drawing. The difference between the outer diameter of split rings 6 in the compressed position thereof and the inner diameter of continuous rings 7 should be as small as possible.

In the process of manufacturing the fuse a subassembly is first produced comprising link 1', terminal elements 2, including blade contacts 3, and rings 6 and 7, all joined together to form a self-sustained structural unit. This unit is then shoved into casing 4 in such a way as to leave a small gap between casing 4' and one of the copper blocks of terminal elements 2. This small gap is used as filling gap for introducing the arc-quenching filler, or quartz sand 8, into the casing 4. The two edges 1 of link 1' define a gap 1d extending in a direction longitudinally of the link. When the fuse is being filled with quartz sand, or an equivalent pulverulent filler, the. sand penetrates through gap 1d into the space inside of link 1. Thus link 1 is ultimately surrounded both on the outside and on the inside thereof by the arc-extinguishing filler 8. When the space within casing 1 is completely filled with sand, the casing 4 is shoved into the position shown in Fig. 3 and the fuse is subjected to vibrations which cause the filler 8 within casing 4 to settle, resulting in a more dense packing of link 1 in the filler 8. Thereupon casing 4 is re-opened, some filler added, and pins 5 are inserted to preclude the casing 4 from coming off the terminal elements 2. If desired, several vibrating and re-filling operations may be included in the manufacturing process of the fuse.

The fuse link structure shown in Figs. 1, 3 and 4 is adapted to rapidly interrupt major fault currents. Where it is desirable to interrupt protracted overload currents, in addition to major fault currents, a small rivet 12 of tin, tin-indium alloy, or other suitable low fusing point metal is arranged immediately adjacent one end of eachcurrentcarrying element. As clearly shown in Fig. 1, two lines of rivets made of a low fusing point metal are arranged on opposite ends of current-carrying elements 111 each out of registry with the other. On occurrence of overloads of inadmissible duration rivets 12 melt, and the metal of which they are made forms an alloy with the metal of which the link proper is made. The link proper is made of a metal which has a relatively high fusing point and a relatively small heat-current integral, preferably silver. The alloys of silver and tin, or silver and indium, have a relatively high resistance, resulting in increased i -r losses at the points where rivets 12 are located. As a result, heat generation is stepped up at these points, and this is conducive to the rapid formation of interrupting breaks. Upon fusion of rivets 12 the fused low-melting point metal tends to fiow toward the current-carrying elements 1b and these are, therefore, the points where alloy-formation, increase of resistance, and formation of circuit interrupting gaps tend to take place. Interruption of all the current-carrying elements 1b in the group G2 forms a circular break, or; gap-,.which precludes continued flow of current.

Rivets 12 do not significantlythrough the fuse structure.

6 affect the mechanicalstrength oflink. 1 and do not deprive it of its character as a unitary sheet metal structure.

The fuselinkshown in Figs. 5 to 8, inclusive, is identical with the fuse link shown in Figs. 1 to- 4, inclusive, and therefore does not need to be described again hereinafter.

According to Figs. 5 and 6 the terminal copper blocks have a portion 20 the diameter of which is relatively large and a portion 217 the diameter of which is relatively small. Portion 2c supports the tubular insulating casing d and portion 2b supports the tubular fuse link 1. A pair of clamping rings 9 comprising the tightening screws 10 firmly clamp the axially outer ends of link 1 against the portions 2b of the terminal blocks. Pins 5 of steel provide a solid mechanical connection betwen the termiblocks and casing4.

Referring now to Figs; 7 and 8, each of the two cylindri'cal terminal blocks is provided with a coaxial groove A pair of slotted rings Il a and 11b is accommodated in each groove 2g. The radially inner rings 11b are in physical engagement with the surface of tubular link 1 and the radially outer rings are mounted upon the radially inner rings 11b. The radially outer rings 11a are wedge shaped and compress the radially inner rings 11b when driven into the grooves 2g, thus causing rings 11b to exert considerable pressure upon link 1 and terminal. blocks and minimizing interface resistance between link i and copper blocks 2. The slot in

rings

11a, 116 as well as the slots of rings 6 in Fig. 1 greatly increases the flexibility thereof.

It will be understood that I have illustrated and de scribed herein preferred embodiments only of the invention and that various alterations may be made in thedetails thereof without departing from the spirit" and scope of the invention as defined in the appended claims.

I claim as my invention:

1. A high-capacity fuse comprising a casing of insulating material, a pair of terminal elements one at each end of said casing, each of said pair of terminal elements having a cylindrical surface of relatively large diameter supporting said casing and a coaxial cylindrical clamping surface of relatively small diameter on the side thereof adjacent the inside of said casing, a ribbon-type fuse link of silver cylindrically wound to fit upon said cylindrical clamping surface on each of said pair of terminal elements arranged within said casing and maintained in coaxial relation thereto by engagement' with said clamping surface on each of said pair of terminal elements, said link being provided with a plurality of groups of perforations and intermediate current-carrying elements, each of said groups comprising a plurality of narrowly spaced perforations having a predetermined length substantially less than the overall length of said link and a predeter mined width and a plurality of intermediate currentcarrying elements arranged in circular relation in a plane at right angles to the axis of the cylindrical surface defined by said link, said predetermined width of each of said plurality of perforations being sufiiciently small to cause vaporization of any of said plurality of currentcarrying elements by back-burning of the arc formed at a major fault at one of said plurality of current-carrying elements immediately adjacent thereto, said link consisting of a unitary sheet of metal having sufiicient mechanical strength to form jointly with said pair of terminal elements a self-sustained structural unit when clamped to said clamping surface of each of said pair of terminal elements, a pair of clamping rings clamping each end of said link to said clamping surface of one of said pair of terminal elements and a pulverulent silicious filler in the space between said casing and said link and in the space inside of said link.

2. A high-capacity fuse comprising a casing of insulat ing material, a silicious arc-quenching filler within said casing, a pair of terminal elements one on each end ofv said casing, each of said'pair of terminal elements having a cylindrical clamping surface on the side thereof adjacent the center of said casing, a ribbon-type fuse link of silver wound cylindrically to fit upon said cylindrical clamping surface on each of said pair of terminal elements arranged within said casing and maintained in coaxial relation thereto by engagement with said clamping surface on each of said pair of terminal elements, said link being provided with a group of narrowly spaced perforations having a predetermined length substantially less than the overall length of said link and a predetermined width and a plurality of intermediate current-carrying elements arranged in circular relation in a plane at right angles to the axis of the cylindrical surface defined by said link, said predetermined width of each of said plurality of perforations being sufficiently small to cause vaporization of any of said plurality of current-carrying elements by back-burning of the are formed at a major fault at one of said plurality of current-carrying elements immediately adjacent thereto, said link having sufiicient mechanical strength to form a self-sustained structural unit jointly with said pair of terminal elements when clamped to said clamping surface of each of said pair of terminal elements, a pair of clamping rings clamping each end of said link to said clamping surface of one of said pair of terminal elements, and a filler of quartz sand in the space between said casing and said link and in the space inside said link.

3. A high-capacity fuse comprising a casing of insulating material, a pulverulent filler within said casing, a pair of terminal elements one at each end of said casing, each of said pair of terminal elements having'a cylindrical surface of relatively large diameter supporting said casing and a coaxial cylindrical clamping surface of relatively small diameter on the side thereof adjacent the inside of said casing, a ribbon-type fuse link of silver wound cylindrically to fit upon said cylindrical clamping surface on each of said pair of terminal elements arranged Within said casing and maintained in coaxial relation thereto by engagement with said clamping surface on each of said pair of terminal elements, said link being provided with a plurality of groups of perforations and intermediate currentcarrying elements, each of said groups comprising more than five narrowly spaced rectangular perforations and intermediate current-carrying elements arranged in circular relation in a plane at right angles to the axis of the cylindrical surface defined by said link, each of said perforations having a pair of relatively narrow sides and a pair of relatively wide sides, said narrow sides of each of said perforations extending parallel to the axis of the cylindrical surface defined by said link and the length of said Wide sides of each of said perforations being a multiple of the length of said narrow sides thereof, a pair of clamping rings clamping each end of said link to said clamping surface of one of said pair of terminal elements, a body of quartz sand in engagement with the radially inner surface of said link and a body of quartz sand in engagement with the radially outer surface of said link.

4. A high-capacity fuse comprising a casing of insulating material, a pulverulent arc-quenching filler Within said casing, a pair of terminal elements one at each end of said casing, each of said pair of terminal elements having a cylindrical surface of relatively large diameter supporting said casing and a coaxial cylindrical clamping surface of relatively small diameter on the sidc thcreof adjacent the inside of said casing, a ribbon-type fuse link wound cylindrically to fit upon said cylindrical clamping surface on each of said pair of terminal elements arranged within said casing and maintained in coaxial relation thereto by engagement with said clamping surface on each of said pair of terminal elements, said link being provided with a plurality of groups of perforations and intermediate current-carrying elements, each of said group comprising a plurality of narrowly spaced perforations having a predetermined Width and a plurality of intermediate currentcarrying elements arranged in circular relation in a plane at right angles to the axis of the cylindrical surface defined by said link, said predetermined width of each of said plurality of perforations being sufiiciently small to cause vaporization of any of said plurality of current-carrying elements by back-burning of the are formed at a major fault at one of said plurality of current-carrying elements immediately adjacent thereto, said link consisting of a unitary sheet metal having a sufficient mechanical strength to form jointly with said pair of terminal elements a selfsustained structural unit when clamped to said clamping surface of each of said pair of terminal elements, and an nular clamping means for clamping each end of said link to said clamping surface of each said pair of terminal elements, said annular clamping means comprising a pair of rings arranged on each end of said link, at least one of said pair of rings being radially split for increased flexibility.

5. A high-capacity fuse comprising a casing of insulating material, a pulvemlent arc-quenching filler within said casing, a pair of terminal elements one at each end of said casing, each of said pair of terminal elements having a cylindrical clamping surface on the side thereof adjacent the inside of said casing, the diameter of each said clamping surface being smaller than the diameter of said casing and each said clamping surface being situated within said casing, a ribbon-type fuse link cylindrically wound to fit upon said cylindrical clamping surface on each of said pair of terminal elements arranged Within said casing and maintained in coaxial relation thereto by engagement with said clamping surface on each of said pair of terminal elements, said link being provided with a plurality of groups of perforations and intermediate current-carrying elements, each of said groups comprising more than five narrowly spaced rectangular perforations and intermediate current-carrying elements arranged in circular relation in a plane at right angles to the axis of the cylindrical surface defined by said link, each of said perforations having a pair of relatively narrow sides and a pair of relatively wide sides, said narrow sides of each of said perforations extending parallel to the axis of the cylindrical surface defined by said link and the length of said wide sides of each of said perforations being a multiple-of the length of said narrow sides thereof, the ratio of the sum total of the lengths of said wide sides to the sum total of the width of said intermediate current-carrying elements being smaller than 10:1, said link consisting of a sheet metal having sufficient mechanical strength to form a self-sustained structural unit jointly with said pair of terminal elements when clamped to said clamping surface of each said pair of terminal elements, and annular clamping means for clamping each end of said link to said clamping surface of each of said pair of terminal elements, said annular clamping means comprising a pair of rings arranged on each end of said link, at least one of said pair of rings being radially split for increased flexibility.

6. A high-capacity fuse comprising a casing of insulating material, a pair of terminal elements one at each end of said casing, each of said pair of terminal elements having a cylindrical clamping surface on the side thereof adjacent .the inside of said casing, the diameter of each said clam-ping surface being smaller than the diameter of said casing and, each said clamping surface being situated within said casing, a rib'bontype fuse link cylindrioally wound to fit upon said cylindrical clamping surface on each of said pair of terminal elements arranged Within said casing and maintained in co'axia l relation thereto 'by said clamping surface on each of said pair of terminal elements, said link having a plurality of groups of perforations and intermediate current-carrying elements, each of said groups comprising a plurality of narrowly spaced perforations having a predetermined width and a plurality of intermediate current-carrying elements arranged in circular relation in a plane at right angles to the axis of the cylindrical surface defined by said link, said predetermined width of each of said plurality of perforations being sufficiently small to cause vaporization of any of said plurality of current-carrying elements by, back-burning ofthe are formed at a major fault at one of said plurality of current-carrying elements immediately adjacent thereto, said link consisting of one single stamped, out piece of sheet metal providing sulficient mechanical strength to cause said link to form a structural unit jointly with said pair of terminal elements when clamped to said clamping surface of each said pair of terminal elements, a plurality of rivets of a low melting point metal arranged in said link immediately adjacent =to one of said plurality of current ca-rrying elements, and a pair of clamping rings clamping each end of said link to said clamping surface on one of said pair .of terminal elements.

7. A high-capacity fuse comprising a casing of insulating material, a pulverulent arc-quenching filler within said casing, a pair of terminal elements one at each end of said casing, each of said pair of terminal elements comprising a copper block being substantially cylindrical and having a portion of relatively large diameter at the end thereof remote from the center of said casing and a portion of relatively small diameter at the end thereof adjacent to the center of said casing, said portion of relatively large diameter of said copper block of each of said pair of terminal elements fitting into and supporting said casing, a fuse link of sheet metal bent substantially in the shape of a cylinder engaged at the inside thereof by said portion of relatively small diameter of said copper block of each of said pair of terminal elements, a pair of split rings one at each end of said link, and a pair of continuous rings each mounted upon one of said pair of split rings to press said one of said pair of split rings against one of the ends of said link and against said portion of relatively small diameter of said copper block of each of said pair of terminal elements.

8. A high-capacity fuse comprising :a casing of insulating material, a pair of terminal elements one at each end of said casing, each of said pair of terminal elements comprising a substantially cylindrical block of metal having a portion of relatively large diameter at the end thereof remote from the center of said casing and a portion of relatively small diameter at the end thereof adjacent the center of said casing, said portion of relatively large diameter fitting into and supporting said casing, a fuse link of sheet metal bent substantially in the shape of a cylinder engaged at the inside thereof by said portion of relatively small diameter of said block of metal of each of said pair of terminal elements, said link being provided with a plurality of groups of perforations each arranged in circular relation in a separate plane at right angles to the axis of the cylindrical surface defined by said link, said link having suflicient mechanical strength to form jointly with said pair of terminal elements a self-sustained structural unit when clamped to said portion of relatively small diameter of said block of metal of each of said pair of terminal elements, and a pair of annular clamping means for clamping the portions of said link engaged by said portions of relatively small diameter of said block of metal of each of said pair of terminal elements to said portion of relatively small diameter of said block of metal of each of said pair of terminal elements.

9. A high-capacity fuse comprising a casing of insul-ating material, .a pulverulent arc-quenching filler within said casing, a pair of terminal elements one at each end of said casing, each of said pair of terminal elements having a portion of relatively large diameter at the end thereof remote from the center of said casing and a portion of relatively small diameter at the end thereof adjacent the center of said casing, said portion of relat-ively large diameter fitting into and supporting said casing, a fuse link of sheet metal bent substantially in the shape of a cylinder fitted upon and supported by said portion of relatively small diameter of each of said pair of terminal elements, said link being provided with a plurality of groups of perforations each arranged in circular relation, in a separate plane at right angles to the axis of the cylindrical surface defined by said link, said link having sufiicient mechanical strength to form jointly with said pair of. terminal elements. a self-sustained structural unit when clamped to said portion of relatively small di ameter of each, of said pair of terminal elements, a pair of split rings one at each end of said link, and a pair of continuous rings each mounted under pressure upon one of said pair of split rings to press said one of said pair of split rings against one of the ends of said link and against said portion of relatively small diameter of each of said pair of terminal elements.

1.0. A. high-capacity fuse comprising a casing of insu-v lating material, a pulverulent arc-quenching filler within said casing, a pair of terminal elements one at each end of said casing, each of said pair of terminal elements having a portion of relatively large diameter at the end thereof remote from the center of said casing and a portion of relatively small diameter at the end thereof adjacent the center of said casing, said portion of relatively large diameter fitting into and supporting said casing, a fuse link of sheet metal bent substantially in the shape of a cylinder fitted upon and supported by said portion of relatively small diameter of each of said pair of terminal elements, said link being provided with a plurality of groups of perforations and intermediate current-carrying elements, each of said group comprising a plurality of narrowly spaced perforations having a predetermined width and a plurality of intermediate current-carrying elements arranged in circular relation in a plane at right angles to the axis of the cylindrical surface defined by said link, said predetermined width of each of said plurality of perforations being sufiiciently small to cause vaporization of any of said plurality of current-carrying elements by back-burning of the are formed at a major fault at one said plurality of current-carrying elements immediately adjacent thereto, said link having sufficient mechanical strength to form jointly with said pair of terminal elements a self-sustained structural unit when clamped to said portion of relatively small diameter of each of said pair of terminal elements, a pair of split rings one at each end of said link, and a pair of continuous rings each mounted under pressure upon one of said pair of split rings to press said one of said pair of split rings against one of the ends of said link and against said portion of relatively small diameter of each of said pair of terminal elements.

1'1. A high-capacity fuse comprising a casing of insulating material, a pair of metal blocks circular in crosssection having the same diameter as the inside diameter of said casing each fitted into one of the ends of said casing, a pair of blade contacts each projecting trom one of said pair of metal blocks in a direction away from said casing, a pair of cylindrical link-supports circular in cross-section having a smaller diameter than said inside diameter of said casing, each of said pair of link-supports forming an integral coaxial part of one of said pair of metal blocks projecting therefrom toward and into said casing, a ribbon-type fuse link substantially in the shape of a cylinder having the same inside diameter as the diameter of said pair of link-supports mounted on and held by said pair of link-supports in coaxial relation with respect .to said casing, said link consisting of a stamping of sheet silver adapted to provide a continuous current path from one of said pair of link-supports to the other of said pair of link-supports, clamping ring means for clamping said link to said pair of link-supports, a first body of quartz sand inside said fuse link and a second body of quartz sand in the space between said fuse link and said casing.

:12. A high-capacity fuse comprising a casing of insulating material, a pair of metal block-s circular in crosssection having the same diameter as the inside of said casing each fitted into one of the ends of said casing, a pair of blade contacts each projecting from one of said pair of metal blocks in a direction away from said casing, a pair of cylindricallink-supports circular in crosssection having a smaller diameter than the inside diameter of said casing, each of said pair of link-supports forming an integral coaxial part of one of said pair of metal blocks projecting therefrom toward and into said casing, a ribbon-type fuse link substantially in the shape of a cylinder having the same inside diameter as the diameter of said pair of link-supports mounted on and held 'by said pair of link-supports in coaxial relation with respect to said casing, said link consisting essentially of a stamping of high conductivity high fusing point sheet metal adapted to provide a continuous current path within said metal from one of said pair of link-supports to the other of said pair of link-supports, said stamping having a plurality of stamped-out portions providing a plurality of points of reduced cross-sectional area, said link further having sufiicicnt bending-strength in spite of said plurality of points of reduced cross-sectional area to form jointly with said pair of metal blocks a self-sustained structural unit when clamped to said pair of link-supports, and clamping ring means for clamping said link to said pair of link supports.

References Cited in the file of this patent UNITED STATES PATENTS 1,207,351 Wake Dec. 5, 1916 1,215,999 Schweitzer Feb. 13, 1917 1,716,884 Goss June 11, 1929 1,828,277 Bennett Oct. 20, 1931 2,287,553 'Floten June 23, 1942 2,625,626 Matthysse Jan. 13, 1953 FOREIGN PATENTS 20,483 Great Britain Sept. 19, 1902