US3571775A

US3571775A - High-voltage fuse having a plurality of helically wound ribbon fuse links

Info

Publication number: US3571775A
Application number: US16116A
Authority: US
Inventors: Frederick J Kozacka; Richard A Belcher
Original assignee: Chase Shawmut Co
Current assignee: GOLUD INC A DE CORP; Chase Shawmut Co; Gould Inc
Priority date: 1970-03-03
Filing date: 1970-03-03
Publication date: 1971-03-23
Anticipated expiration: 1988-03-23

Abstract

A high-voltage fuse having a plurality of helically wound ribbon fuse links forming extension-springlike structures arranged in a cylindrical pattern. The ribbon fuse links are entirely selfsupporting, not requiring any support between the ends thereof other than a pulverulent arc-quenching filler.

Description

United States Patent inventors Frederick J. Kozacka South Hampton;

Richard A. Belcher, Hampton Falls, N11. Appl. No. 16,116 Filed Mar. 3, 1970 Patented Mar. 23, 1971 Assignee The Chase-Shawmut Company Newburyport, Mass.

Continuation-impart of application Ser. No.

879,990, Nov 24, 19 69 HIGH-VOLTAGE FUSE HAVING A PLURALITY OE HELICALLY WOUND RIBBON FUSE LINKS 24 Claims, 14 Drawing Figs.

US. Cl 337/ 161, 337/231, 337/291:

Int. Cl H01h 85/08,

HOlh 85/12 [50] Field of Search 337/158, 159,160,161, 231, 238, 239, 240, 290, 293, 295

[56] References Cited UNITED STATES PATENTS 3,460,085 8/ 1969 MCAllister et a1. 337/295(X) 3,374,328 3/1968 Cameron 337/293(X) 2,740,187 4/1956 Jacobs, Jr.,et a1 337/159(X) FOREIGN PATENTS 807,347 l/ 1959 Great Britain 337/295 Primary ExaminerBemard A. Gilheany Assistant Examiner-Dewitt M. Morgan Attorney-Erwin Salzer ABSTRACT: A high-voltage fuse having a plurality of helically wound ribbon fuse links forming extension-springlike structures arranged in a cylindrical pattern. The ribbon fuse links are entirely self-supporting, not requiring any support between the ends thereof other than a pulverulent arcquenching filler.

PATENTEUMARZBISYI 3571.775

sum

1 or 3 FIG. I

7 7g 20% F|G.6 FIG] F|G.8-

mvsmons: FREDERICK J., KOZACKA CHARD BELCHER BY WW 2% ATTY.

PATENTEU MAR23 ISTI FIG. l3

SHEET 3 0F 3 FIG. l4

mvemons: FREDERICK J. KOZACKA RICHARD A. BELCHER BY M/WW WWW ATTY.

ll-illGlill-VQLTAGE lFllJE ll'lAVlNG A PLUllAlLllTY (ill llZlElLlllAluLY WQUND ldllllllf fllN FUSE LlNllfS BACKGROUND OF lNVENTlON This is a continuation-in-part of our copending Pat. application Ser. No. 879,690, filed Nov. 24, 1969 for l-llGl-l VOLT- AGE FUSE ll-lAVlNG HEUCALLY WQUND RlBBON FUSE LlNli.

ilighvoltage fuses often call for fusible elements whose length exceeds that of the casing of the fuse or fuse tube. in such instances the fusible elements may be wound helically around a mandrel of ceramic or other heat resistant material, the mandrel being generally substantially star-shaped in cross section. This conventional design is subject to many drawbacks and limitations, and it has, therefore, for many years been the desire of designers of high-voltage fuses to provide high-voltage fuses which do not require a mandrel for supporting helically wound fusible elements.

The problem of providing high-voltage fuses having a helically wound fusible element, or several helically wound fusible elements, differs depending upon whether the fusible element, or elements, are formed of a silver wire, or a silver ribbon, or of a material other than silverfln this context consideration will be given only to the use of ribbon fuse links of sheet silver whose use is indicated as far as current-limiting high-voltage fuses for higher current ratings are concerned.

it is possible to wind a ribbon fuse link of silver helically around a temporary mandrel and remove, or withdraw, the mandrel from the casing of the fuse during the process of filling the casing of the fuse with a pulverulent arc-quenching filler. in that particular instance the arc-quenching filler provides a gradually extending, or gradually rising, lateral support for those portions of the helically wound fuse link from which the temporary, link-supporting mandrel is being gradually withdrawn. This process of making high-voltage fuses whose helically wound ribbon fuse links do not require a supporting mandrel when the fuse is fully assembled calls for a great deal of manual dexterity, and the cost of manufacture of such fuses are, therefore, relatively high.

British Pat. No. 307,347 refers to one of the early attempts to design high-voltage fuses whose ribbon fuse links are wound helically and do not require a link-supporting mandrel. The helically wound fuse link disclosed in the above patent is channel-shaped in cross section, or has a similar shape, tending to greatly increase its rigidity. This avoids, or is supposed to avoid, serious distortions of the helically wound fuse link or fusible element by the impact of pulverulent arc-quenching filler that occurs in the process of filling such fuses.

The configuration of a fusible element of silver as disclosed in the above British patent is relatively complex and tends to increase the required amount of silver. Such an increase of the required amount of silver without a concomitant increase of the interface between the silver and the surrounding pulverulent arc-quenching medium tends to adversely affect the operating characteristics of fuses designed according to the above British patent, and reduces their cost-effectiveness to impracticability.

it is possible to design high-voltage fuses having helically wound ribbon fuse links which are laterally supported at a few discrete points, particularly the center thereof, rather than at a larger number of points, as in case of use of a link-supporting mandrel arranged inside of a helically wound ribbon fuse link. The above is a step in the right direction, but still far away from the ultimate goal of dispensing entirely with additional structures providing lateral support for helically wound fuse links.

TECl-lNlCAL BACKGROUND We have found that it is possible to make helical ribbon fuse links of silver of critically small diameter which form extension-springlike structures and do not require any lateral support to prevent serious distortions thereof during the process of filling the fuses with a pulverulent arc-quenching filler.

A helically wound ribbon fuse link of critically small diameter such as three sixteenths inch to one-half inch has inherently a relatively small current-carrying capacity. The current-carrying capacity of fuses with such fuse links of critically small diameter can, however, be increased to comply with all existing requirements in regard to current-carrying capacity by paralleling several fuse links. Such a multiple fuse whose fuse links are arranged in a cylindrical pattern compares in many respects favorably with conventional high-voltage fuses including a common insulating mandrel of relatively large diameter supporting a plurality of spaced helically wound ribbon fuse links. One of these favorable distinctions resides in the relative increase of space inside the casing available for pulverulent arc-quenching filler which relative increase is due to the absence of the link-supporting mandrel. Another favorable distinction relates to the L/ 1 ratio, wherein L is the length of the helically wound ribbon fuse link and l the useful length of the casing of the fuse. In high-voltage fuses including a common insulating mandrel of relatively large diameter supporting a plurality of spaced helically wound ribbon fuse links the L/ 1 ratio decreases as the number of fuse links on the common mandrel increases. This is due to the fact that there must be a minimum axial spacing between adjacent turns of fuse links on the common insulating mandrel, as a result of which requirement the angular pitch of each fuse link must be increased as the number of fuse links is increased, this increase of angular pitch resulting in a decrease of the L/ 1 ratio. Under such circumstances the L/l' ratio may be increased, or improved, by arranging inside of a common casing a plurality of helically wound fuse links of critically small diameter in a cylindrical pattern.

For the purpose of this invention helically wound fuse links must have certain elastic properties, i.e. they must operate like extension springs and have a certain dimensional stability when suitably loaded. To this end they must be made of sheet silver having a high elastic or Youngs modulus. This, in other words, is relatively hard silver. Silver known as hard silver is preferred. it is, however, possible to wind ribbons of half hard silver into coil springs satisfactory for the purposes of this invention, particularly since the process of coil winding involves word hardening.

As used in this context the term helical fuse link of critically small diameter means a helically wound fuse link whose diameter ranges from about three sixteenths of an inch to about one-half inch. For reasons underlying the process of winding extension springs of hard silver their diameter can hardly be significantly less than three sixteenths of an inch, but the latitude in regard to an increase of diameter is larger than in regard to a decrease in diameter.

The silver ribbons to be wound helically ought to be rectangular in cross section and have serially related points of reduced cross-sectional area. Such ribbons are wound with the wide side thereof parallel to the axis of the helix, or spring axis. The silver ribbon is originally wound upon a temporary mandrel. Contiguous turns of the winding should be narrowly spaced, e.g. one thirty-second of an inch, or their spacing may even be virtually reduced to zero (closed winding). When arranged within the casing of the fuse the helically wound ribbon fuse links of silver are stretched, preferably to such a degree that the deflection per turn exceeds the diameter of the helix. When a helically wound ribbon fuse link of relatively hard sheet silver having a diameter of about three sixteenths to about one-half inch is loaded, or axially stretched, preferably to such a degree that the deflection per turn exceeds significantly the diameter of the helix, e.g. is twice the diameter of the helix, the helically wound silver link is rendered capable of carrying predetermined relatively small lateral loads without buckling, or losing its helical shape. To be more specific, the process of filling of a cartridge fuse having an extensionspring-type ribbon fuse link with a pulverulent arc-quenching filler generally involves some lateral loading of the fuse link tending to cause buckling and more or less serious distortions of the fuse link. The danger of buckling under relatively small lateral loads to which extension springs of silver are subjected can be decreased by limiting the diameter of such springs and by axially loading, or preloading, such springs to preferably such an extent that the deflection per turn exceeds significantly the diameter of the helix. To avoid buckling of extension-springlike fuse links it is also necessary and desirable to provide the fuse with means for minimizing lateral loading of the fuse links by the impact of pulverulent arc-quenching filler during the fuse filling process.

The aforementioned degree of stretching, or deflection, is not only desired for mechanical reasons, i.e. for the purpose of rendering the fuse links fully self-supporting and of preventing buckling or distortion under small lateral loads occurring in the process of filling the fuse casing with a pulverulent arcquenching filler, but also for electrical reasons. There would be a tendency upon blowing of the fuse of short-circuiting of contiguous turns of the hot helical fulguriteswhich take the place of contiguous turns of helical ribbon fuse links, considering ribbon fuse links, considering ribbon fuse links whose diameter is as little as about three sixteenths to one-half of an inch, unless the deflection, or spacing, between contiguous turns of the helical ribbon fuse links were not rendered suffrciently large by adequate stretching of the helical ribbon fuse links.

The silver ribbon fuse links used for embodying this invention and formed into a helical extension-springlike structure have overcenter ends at the ends of their helical portions to avoid undue stresses at the ends of their helical portions In fuses according to the above referred-to Pat. application Ser. No. 879,090 there are two principal reasons which account for the fact that their helical fuse links are not subject to buckling, or distortion, during the process of filling.

a. One of these reasons is the fact that the helically wound fuse links are entirely self-supporting (and thus are not distorted prior to filling) and have the capability of carrying relatively limited lateral loads without distortion (and thus are nor distorted by small lateral loads occurring incident to filling), and

b. the other of these reasons is the arrangement of helically wound fuse links in cylindrical coaxial passages which surround the helical fuse links relatively closely and thus limit the magnitude of lateral loads to which the fuse links may be subjected in the process of filling the casing with pulverulent arcquenching fillers.

It has been found that it is not necessary to arrange each helically wound fuse link in a separate passage narrowly surrounding the fuse link in order to avoid its distortion during the filling process. This will be explained below more in detail.

SUMMARY OF INVENTION If a plurality of helically wound ribbon fuse links which are not supported between the ends thereof is arranged in any random pattern inside of a relatively wide tubular casing parallel to the axis of the latter the danger that such fuse links will buckle, or be distorted, during the process of filling the casing with a pulverulent arc-quenching filler is very large.

This danger is decreased by imparting to the helically wound ribbon fuse links the above referred-to physical characteristics which make it permissible to subject the fuse links to relatively small lateral loads.

Buckling and distortion of helically wound ribbon fuse links having the above referred-to physical characteristics can be safely avoided during the filling process even in the absence of coaxial cylindrical passages whose boundary walls surround the fuse links relatively closely. This end can be achieved by arranging a plurality of helically wound ribbon fuse links having the above physical characteristics'in a cylindrical pattern, or circular pattern, respectively, coaxial with the casing of the fuse and by providing means for introducing the pulverulent arc-quenching filler strictly parallel to the axis of the cylindrical pattern, or circular pattern, respectively, preferably along the axis thereof, If the casing of the fuse is closed by a pair of terminal plugs and a filling hole in one of the tenninal plugs of the fuse is arranged parallel to the common axis of the casing and the terminal plugs (preferably at the center of one terminal plug) and if a plurality of relatively distortion resistant helically wound ribbon fuse links is arranged in a cylindrical pattern around the filling hole, the pulverulent filler filled through said hole does not directly impinge upon the helically wound fuse links. The pulverulent filler drops all the way down to the end of the casing opposite to the filling hole and rises inside the casing substantially as the level of water rises in a container, i.e. forming substantially horizontal surfaces of progressively increasing height. The aforementioned filling hole aims the particles of pulverulent filler with a sufficient degree of precision so that almost none of them impinges upon the lateral surfaces of the helical fuse links while the particles have a significant kinetic energy capable of exerting a linkdeforming lateral pressure or lateral load upon the helical fuse links. This, in other words, minimizes the lateral load to which the helically wound ribbon fuse links are subjected during filling operations and they can withstand such minimized lateral loads without distortion or buckling, provided that they are particularly designed to withstand limited lateral loads without buckling and without distortion and in the absence of any lateral supporting means therefor.

BRIEF DESCRIPTION OF DRAWINGS FIG. I is substantially a vertical section of a fuse embodying this invention taken along I[ of FIG. 2, some parts being shown in side elevation rather than in section and the center portion of the fuse structure being broken away to shorten the length of FIG. I;

FIG. 2 is a section taken along [H] of FIG. I;

FIGS. 3-5 are side elevations of three modifications of the fusible element structure shown in FIG. I drawn on a larger scale than FIG. I;

FIGS. 6-8 are sections along VI-VI of FIG. 3; along VII-VII of FIG. 4 and along VIII-VIII of FIG. 5;

FIG. 9 is a vertical section of a combination of a fuse holder and of a fuse according to FIGS. I and 2;

FIG. I0 is a side elevation of the structure of FIG. 9;

FIG. II is a diagrammatic vertical section of the structure of FIGS. 1 and 2 illustrating the filling process thereof;

FIG. 12 is a section along XII-XII of FIG. II;

FIG. I3 shows partly in side elevationand partly in longitudinal section a detail of FIG. I and is drawn on a much larger scale than FIG. l; and

FIG. I4 shows the structure shown in FIG. l3 drawn on the same scale as FIG. 13 as seen at an angle of relative to the direction of view of FIG. I3.

DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION Referring to FIGS. 1 and 2, numeral I has been applied to indicate a tubular casing of electric insulating material housing six helically wound fusible elements 2. Casing l is closed on the ends thereof by electroconductive terminal plugs 3. The axially inner end surfaces of terminal plugs 3 have been indicated by the reference character 3'. Each terminal plug 3 has a coaxial cylindrical projection 3" situated outside of casing I. Plugs 3 and their projections 3 define passageways 3a extending parallel to the common axis of easing I and plugs 33. Passageways 3a are closed by screw threaded plugs 3b. Terminal plugs 3 are secured to casing l. by transverse steel pins 4 and the space inside casing I between fuse links or fusible elements 2 is filled with a body of quartz sand 5.

Each fuse link 2 is a helical extension-springlike structure formed by a ribbon of relatively hard silver having a rectangular cross section. The aforementioned ribbon 2 has serially re lated points of reduced cross-sectional area formed by spaced circular perforations 2. The ribbons 2 forming the extensionspringlike structure are wound with the wide side thereof parallel to the spring axis along a helical path of about three sixteenths inch diameter. To be more specific, thirty-second the silver ribbon of which each winding 2 is formed is initially wound on a mandrel having a diameter of less than three sixteenths of an inch and expands to a diameter of about three sixteenths or" an inch when the helical winding 2 is removed form its cylindrical forming mandrel. Helical windings 2 have an initial deflection per turn which is very small. It may be virtually zero and should hardly ever exceed one thirty-second of an inch. When placed inside casing ll windings 2 are stretched out axially, preferably to such an extent that the deflection n per turn significantly exceeds the diameter d (FIGS. 1 and 2). The ratio of the diameter d of each winding 2 to the deflection n between contiguous turns may be about 1:2. This degree of axial loading of windings 2 allows them to be subjected to some transverse loading without buckling or distortion Windings 2 have axially outer overcenter ends 2b affixed by low thermalconductivity filler. Bothfillers must be sufficiently compacted to avoid interrnixing at their interface. The portions of windings 2 embedded in the low thermal conductivity arc-quenching fillers may be provided with a link-severing overlay (not shown in FlG. ll) of a metal having a considerably lower fusing point than silver, e.g. tin. The low thermal conductivity arc-quenching filler is preferably a mixture including aboutSO percent of silica, and 20 of iron oxide and aluminum oxide. The merits of such a composite pulverulent low thermal conductivity arc-quenching filler are set forth in greater detail in the copending patent application of Frederick J. Kozacka, filed Nov. 13, 1969, Ser. No. 876,445 for HIGH- VOLTAGE FUSE. As shown in FlG. ll quartz sand may be substituted for the body of low thermal conductivity filler.

it is apparent from FlG. i that tiller 5 inside casing 1 submerses windings 2, and that filler 5 is the only lateral support of windings 2 between terminal elements or terminal plugs 3.

As clearly shown in FIG. 2 windings are arranged in a cylindrical pattern, i.e. the axis thereof are arranged in a cylindrical surface coaxial with casing ll and passageways 3.

Euses according to H68. 1 and 2 have been'manufactured for a wide variety of voltage ratings having windings 2 and casings l of widely varying length. These fuses were X-rayed prior to performing electrical tests thereon. No significant distortion could ever be observed of the helical fuse links 2 though some of the fuses were of considerable length, e.g. 15 inches, and though the spring fuse links 2 were not supported between the ends thereof by any other means than bodies of pulverulent arceuenching filler 5.

Very satisfactory tests results were obtained with hard silver ribbons 0.0035 inches thick and 0.086 inches wide. The points of reduced cross-sectional area were established by circular perforations 2 having a diameter of 0.046 inches spaced 0.203 inches (HG. ll). This material was wound upon a mandrel having a diameter of one-eighth inches, and a clearance of three thirty-seconds inches was left between juxtaposed edges of the helically wound silver ribbon. Upon removal of each winding 2 from its forming mandrel the diameter of the former expanded to three sixteenths inch. The ends 2b of each winding 2 are arranged overcenter and the periphery of the heads of clamping screws 6 intersect the centers of winding 2 (PEG. 2). The overcenter ends 212 of windings 2 are not perforated since the would adversely affect the mechanical strength or integrity of the windings 2.

The ratio of the length of the unloaded windings 2 to the length of the loaded and extended or deflected windings 2 is about 1:2 which accounts for the magnitude of the ultimate deflection is per time.

The above figures or data are guidelines. They can be varied within limits, but a drastic departure therefrom is not feasible. For instance, a drastic reduction of the cross section of the ribbon fuse links would adversely affect their current-carrying capacity. A drastic reduction of the cross section of the ribbon fuse links is also incompatible with the required spring action thereof.

in another fuse similar to that shown in FIGS. l and 2 helical windings were used formed of hard silver ribbons 0.0l5 inches thick and 0.086 inches wide. The circular perforations had a diameter of 0.046 inches and their centers were spaced thirteen sixty-fourths inches. The material was wound upon a mandrel having a diameter of seven sixteenths inches without spacing between contiguous turns (closed helix). Upon removal of the windings from their forming mandrels their diameter expanded to seventeen thirty-seconds inches. These windings were stretched to obtain a deflection of three eighths inches per turn. When so stretched and stretched to span a length l of 10 inches between the axially inner end surfaces 3' and plugs 3 these winding were self-supporting; but they were not as capable of withstanding transverse forces without distortion as the windings whose parameters were specified above. It became apparent from tests conducted with these particular windings that the diameter should not exceed the range of one-half inch. Another cause for the relatively limited ability of these particular windings to withstand transverse forces without distortion is their relatively limited deflection per turn which is less than the diameter of a turn.

As a matter of principle, the points of reduced cross-sectional area of the ribbons of which windings are made may be formed either by notches extending from the edges toward the center lines of the ribbons, or by perforations arranged along the center lines of the ribbons. As shown in FIG. 1 the serially related points of reduced cross-sectional area of ribbon fuse links 2 are formed by serially related circular perforations 2 arranged along the center lines of helically wound ribbons 2, the longitudinal edges of the helically wound ribbon 2 being not interrupted by notches. This type of helical ribbons is capable of exerting stronger elastic forces and is less likely to be damaged by handling than helically wound ribbons whose points of reduced cross-sectional area are formed by notches extending from the edges toward the center lines of the ribbons.

lFiGS. 3& inclusive, refer to a structure as shown in'FIGS. i and 2 wherein each extension-springlike winding 2 includes a pair of coaxial helically wound sections 2a conductively interconnected at the spaced axially inner ends 2a thereof by conductor means 7,7 and '7 respectively.

According to FIGS. 3 and 6 the conductor means 7 are three straight round wires of silver whose axially outer ends are spot-welded to the axially inner overcenter turned ends of helical fuse link sections 2a. The axially outer ends (not shown) of coaxial helical fuse link sections 2a are secured to terminal plugs as shown in FIG. l at 2b and described in connection with this figure. The three wires 7 are arranged in a plane extending diametrically across the helical fuse link sections 2a which they conductively interconnect. in cases requiring but a relatively small current-carrying capacity the radially outer straight wires 7 may be deleted. The remaining center wire 7 being arranged overcenter relative to helical winding sections 2a is subjected to stresses resulting from the spring action of winding sections 20. These stresses would tend to distort wire 7 if it were helical rather than straight and arranged over the centers of winding sections 2b.

Referring now to FTGS. d and 7, the axially inner ends 2a of coaxial winding sections 2a are bent over the centers of the helical winding sections 2a and secured to a block or plate 7a of heat resistant insulating material, preferably a ceramic material. Any desired fastener means may be used to achieve this mechanical connection as, for instance, the pair of eyelets shown in MG. The block or plate 7a of insulating material supports a helical winding 7' of round silver wire. The axially outer ends of silver wire winding 7 are conductively connected to the axially inner ends 211 of coaxial winding sections 2a, preferably by spot welding. i-ielical wire winding '7' is not subjected to the spring action of winding sections 2a since the elastic forces exerted by winding sections 2a are received by insulating block or insulating plate 70. The axially outer ends (not shown) of helical winding sections 20 are affixed overce'nter to axially inner end surfaces 3 of terminal blocks as shown at 21) in FIG. 1, and all pairs of coaxial winding sections 2a according to FIG. 1, and all pairs of coaxial winding sections 2a according to FIGS. 4 and 7 are arranged in a circular pattern around an axial passageway 3a defined by one of a pair of casing-closing terminal elements 3.

The structure of FIGS. 5 and 8 is made up of a helically wound ribbon fuse link of silver including axially outer sections 2a having relatively short points of reduced cross-sectional area formed by circular perforations 2 and an axially inner section 7" forming a relatively long point of reduced cross-sectional area and conductively interconnecting the axially inner ends 2a of the axially outer sections 2a. As mentioned above the axially inner section 7" establishes a point or region of reduced cross-sectional area of considerably greater length than the length of each of the relatively short points or regions of reduced cross sectional area formed by circular perforations 2. The axially outer helically wound sections 2a exert a spring action on the straight axially inner section 7 which is arranged overcenter, tending to stretch the axially inner section 7" to keep it straight. The axially outer sections 2a and the axially inner section 7" may be fonned of a unitary stamping. The cross section of the axially inner section 7 is selected in such a way that it generates more heat per unit of length than the heat generated per unit of length of the axially outer sections 2a when both sections 7" and 2a carry the same current. This applies also in regard to the straight wire sections 7 of FIG. 3 and to the helical wire section 7' of FIG. 4.

A pair of silver-severing overlays 8 is arranged at the axially outer ends of the axially

inner sections

7, 7' and 7" of the structures of FIGS. 3, 4 and 5, or the axially inner ends 2a of the axially outer helical windings 2a. The presence of overlays 8 results in the formation of double breaks, or two series breaks on the occurrence of overloads of inadmissible duration. Overlays 8 are of a metal having a fusing point substantially lower than silver, e.g. tin. Upon fusion of overlays 8 the aforementioned breaks are formed by a process of metal interdiffusion.

The structures shown in FIGS. 38 when arranged in a cylindrical pattern as shown in FIGS. 1 and 2 make it possible to achieve a wide spectrum of E ratings without resorting to two pulverulent arc-quenching fillers, i.e. quartz sand and an additional arc-quenching filler having a smaller heat conductivity than quartz sand. As a general rule a large E rating calls for link severing overlays of tin or the like low fusing point metal embedded in a pulverulent arc-quenching filler having a smaller heat conductivity than quartz sand, e.g. gypsum. The use of two different filler materials is a considerable complication in the manufacture of high-voltage fuses which can be avoided by resorting to the fuse link structures of FIGS. 3-8 in the cylindrical pattern configuration shown in FIGS. 1 and The table below refers to fuses of the type having relatively long

narrow necks

7, 7, 7" between coaxial helical ribbon sections 2a.

In FIGS. 9 and 10 reference character 9 has been applied to indicate three parallel superimposed substantially tubular structures of which each houses a fuse structure 10 of the general character shown in FIGS. 1 and 2 and described in connection therewith. The tubular elbow 11 forms a multiple bushing for three conductors R,S,T connected to a three phase circuit. Conductors R,S,T include disconnect switch means 11' and their ends are conductively connected to three right fuse holders 12. Fuses 10 connect right fuse holders 12 with left fuse holders 13. The latter may be conductively connected to a load by conductors not shown. The right ends of tubular structures 9 are closed by pullcovers 14. Each pullcover 14 has an insulating insert 14' projecting into one of tubular structures 9. A pullhandle 15 is pivotally supported by each of covers 14. The right-hand fuse holders 12 are affixed to covers 14. Therefore pulling handles 14 from the position shown in FIG. 9 to the right results in removal of covers 14, fuse holders 12 and fuses 10 from tubular structures 9 and simultaneously opening of disconnect switch means 11'. The right terminals of fuses 10 are firmly affixed to fuse holders 12 while the left terminals of fuses 10 are readily slidable in a direction longitudinally of fuses 10 in left fuse holders 13. Therefore pulling of handles 15 from left to right results in removal of fuses 10 from tubular structures 9 preparatory to replacement of fuses 10.

High-voltage fuse gear of the general character shown in FIGS. 9 and 10 and described above is particularly desirable for indoor applications on account of its great compactness. In the past such switchgear could only be applied for relatively small current ratings because the heat generated in fuses 11) resulted in intolerably high temperatures inside of tubular structures 9 if the current rating fuses 10 was relatively high. In other words, the watt losses in conventional high-voltage fuses having a relatively high current rating are so high as to preclude the use of such high voltage fuses in ultra compact high-voltage fuse gear.

In high-voltage fuses according to FIGS. 1 and 2 the ration of the aggregate area of the interface between the silver ribbons 2 and the pulverulent arc-quenching filler 5 to the aggregate cross-sectional area of silver ribbons 2 can be maximized. This means that the arc-quenching ability of pulverulent arc-quenching filler 5 is utilized to a very high degree. Consequently the ribbon fuse links 2 must form but a relatively small number of series breaks to generate a required arc voltage incident to blowing of the fuse, i.e. and are voltage which will bring the current down to zero within a given interval of time. Since fuses as shown in FIGS. 1 and 2 include a large number of parallel-connected fuse links each of which calls for a relatively small number of points of reduced crosssectional area because each fuse link must establish but a relatively small number of series breaks incident to blowing, the voltage drop or resistance between the terminals of the fuse is minimized. Therefore f 'r losses are minimized. Consequently fuses according to FIGS. 1 and 2 may be housed in extremely compact fuse gear of the type shown in FIGS. 9 and 10 even if the current rating of the fuses is high.

FIGS. 11 and 12 illustrate diagrammatically the process of filling fuses embodying this invention with a pulverulent arcquenching filler such as quartz sand. The same reference characters have been applied in FIGS. 11 and 12 as in previous FIGS. to designate like parts, yet these parts are shown in FIGS. 11 and 12 in a more diagrammatic fashion. Casing 1 is closed by a pair of terminal plugs 3 having coaxial cylindrical projections 3" situated outside of casing 1. Terminal plugs 3 and projections 3 define a passageway 3a extending substantially parallel to the common axis of casing 1 and plugs 3. The spacing of the axially inner end surfaces of plugs 3 is 1. Reference character 2a has been applied to indicate six pairs of coaxial windings arranged in a cylindrical pattern, e.i. the axes of windings 2a are arranged in a cylindrical surface. The axially outer ends of windings 2a are affixed to the axially inner end surfaces of plugs 3 in the way shown in FIG. 1 at 2b and described in connection with this FIG. The length of each pair of coaxial windings 2a in their stretched or elongated state is 2, 0, and the spacing between the axially inner ends 2a of each pair of coaxial windings 2a is m. The axially inner ends 2a of coaxial windings 2a are conductively interconnected by fusible conductor means as shown in FIGS. 3 to 8 more in detail, and designated in FIG. ill by reference character 7. These fusible conductor means 7 have an axial length m and may be formed by round silver wires arranged as shown in FIGS. 3 and 6.

The process of filling the casing ofthe fuse with a pulverulent arc-quenching filler has been investigated by high speed photography which investigation revealed the following facts:

When quartz sand is filled into a passageway 3a which is relatively long any nonaxial force component which may have acted upon the constituent particles of quartz sand is rendered ineffective, and the constituent particles of quartz sand are accelerated by the action of gravity in a direction which is in cssence strictly parallel to the axes of the pairs of coaxial windings 2a. The same is true if windings 20 extend from one axially inner end surface of one plug 3 to the axially inner end surface of the opposite plug 3 without the presence of a relatively long neck portion 7, or'7', or 7" (see FIGS. 3 to 8) between axially outer coaxial fuse link windings 2a. The quartz sand having a velocity'strictly in the direction of the axis of coaxial windings 2a and lacking any significant transverse velocity component streams downward in form of a jet without exerting any significant transverse force upon extension-springlike windings 2a. The impact of that jet of sand occurs at the center of the cylindrical pattern formed by the arrangement of the coaxial pairs of windings 2a, i.e. relatively remote from windings 2a. Thus no transverse force component is exerted upon windings 2a as the result of the impact of quartz sand. Quartz sand is relatively nonelastic and, therefore, the number of particles which rebound from the point of impact is relatively small. The quartz sand tends to form a cone at the point of impact, but due to the physical properties of quartz sand the angle of that cone is relatively wide or, in other words, not much less than l80. FIG. ll indicates some of the

levels

5 and 5" of quartz sand successively formed during the process of filling the casing of the fuse with quartz sand. The radial arrows in FIG. 12 show how the sand spreads radially upon its impact in the center of the cylindrical pattern formed by windings 2a. Neglecting the small cone-shaped mound in the center of the body of quartz sand (FIG. ill), the filling process with sand is very much like that of the filling of a vessel with a liquid inasmuch as the level to the sand rises as that of a liquid, i.e. it forms sequentially horizontal relatively flat surfaces and the sand, as it rises, tends to support the windings 2a around their entire periphery rather than exerting a transverse force component upon windings 2a.

The success of the filling operation depends primarily upon three factors:

a. the arrangement of the windings 2a in a cylindrical pattern;

b. the orientation of the jet of sand filled into the fuse strictly in the direction of the axis of that pattern; and

c. the ability of the windings 2a to withstand limited transverse forces without undergoing any significant distortion.

The grater the ability of windings 2a to withstand limited transverse forces without significant distortion thereof in the absence of any lateral support therefor other than the quartz sand itself, the less rigid the requirement to orient the jet of quartz sand strictly in the direction of the axis of the cylindrical pattern formed by windings 2a must be enforced. On the other hand, if the ability of windings 2a to withstand small lateral forces without distortion is relatively limited, then the requirement of proper sand jet orientation must be met rigorously. This means in terms of structure that the length of passageway 3a may be short if the windings 2a have a sufficiently high capability to withstand without distortion relatively small transverse forces, and that the length of passageway 34;. ought to be relatively long if the windings 2a have a relatively limited ability to withstand without distortion relatively small transverse forces.

The required spring characteristic of the pairs of windings 2a and of the windings 2 of HG. l may also be expressed in terms of the natural frequency thereof. if the windings 2 of Till FIG. l. are plucked prior to filling of the fuse with quartz sand as strings of a string instrument, the windings 2 will vibrate at a natural frequency, and resonate if driven at that frequency. windings which were stretched as shown in FIG. 1 so that their deflection per turn exceeds considerably their diameter had natural frequencies of about 15 cycles per second. windings which were not stretched to such an extent had lower frequencies. Windings having frequencies of 9 cycles per second were more apt to be distorted by small transverse forces, yet still resulted in fuses which performed satisfactorily. It appears that windings 2 should not have a lower natural frequency than 9 cycles per second.

The success of the filling operation with quartz sand depends also to some extent on the given size of the quartz sand which is being used. Quartz sand having grain sizes corresponding to 2070'U.S. Standard Sieve Number may be used. Best results were obtained with quart sand having grain sizes corresponding to 2030 US. Standard Sieve Number.

It will be apparent from FIG. 11 that:

The length of both windings 2a in their unloaded or unstretched condition is considerably less than m, or less than 20. Upon being stretched, or loaded, the length of windings 2a is l-m.

Referring now to FIGS. 13 and 14, these FIGS. show more in detail the means for connecting mechanically and electrically the overcenter ends 2b ofwindings 2 to the axially inner end surfaces 3 of terminal plugs 3. Since windings 2 are in effect extension springs it is necessary to firmly anchor their overcenter ends to terminal plugs 3. This is achieved by screws 6. The outer circular periphery of the heads of each registering pair of screws 6 is intersected-at right angles by the axis of the particular winding 2 whose ends are affixed to plugs 3 by that particular pair of screws. In other words, the outer circular periphery of each of the heads of screws 6 engages tangentially the cylindrical surface defined by the axes of windings 2. This is clearly shown in FIG. 2. This way of securing windings 2 to plugs 3 minimizes stresses at the ends of windings 2. The shanks of screws 6 are parallel to the common axis of casing I and plugs 3. Each screw 6 clamps by means of its head the overcenter end 2a on one winding 2 against one of the axially inner end surfaces 3' on one of the pair of plugs 3. In order to minimize the electrical resistance between the axially outer overcenter ends 2b of windings 2 and the axially inner end surfaces 3 of plugs 3 both are conductively connected by solder joints 6a. The latter are dual function solder joints inasmuch as they minimize the resistance between the axially outer overcenter ends 2 b of windings 2 and the axially inner end surfaces 3 of plugs 3 and, in addition thereto they lock screws 6 firmly in position, i.e. prevent screws 6 from loosening. Since the overcenter ends 2b of windings 2 have a definite thickness, a small gap is formed between the inner end surface of each of the heads of screws 6 and the axially inner end surfaces 3 of plugs 3. This gap has a capillary action, as a result of which the solder used to solder the overcenter ends 2b of windings 2 to the axially inner end surfaces 3' of plugs 3 flows into said gap and forms a relatively strong bond between the heads of screws 6 and the end surfaces 3' upon solidification of the solder. This bond safely precludes loosening of screws 6 under the action of vibrations to which the fuse may be subjected either in transit, or when in service.

FIG. 13 shows clearly that one point of the periphery of the head of screw 6 is intersected at right angles by the axis of fuse link winding 2 or, in other words, that the heads of screws 6 tangentially engage the cylindrical surface in which according to FlGS. l and 2 the axes of windings 2 are arranged. Both FIGS. 13 and i4) show the gap formed between the axially inner end surfaces 3 of one of plugs 3 and the axially outer end surface of one of the heads of one of screws 6, and the dual function solder joint 6a formed by the influx of soft solder into said gap.

in all FIGS. and particularly FlGS. ll, 3, A, 5, l3 and 14 the spacing between perforations 2' has been shown to be equal to 180 of the windings 2. and 2a, respectively. The actual spacing of perforation 2 may be larger or smaller than the spacing shown in the drawing and must be determined empirically considering the electrical parameters of each particular instance.

The performance of fuses embodying this invention tends to improve the larger the number of windings 2, or the number of coaxial pairs of windings 20 arranged in a cylindrical pattern, or a cylindrical configuration. The fact that the diameter of the windings cannot be significantly less than three-sixteenths of an inch and that high-voltage fuses are subject to dimensional standards compels to limit the number of windings 2 and the number of coaxial pairs of windings 2a, respectively. It is, however, generally possible toprovide a fuse with six windings 2 or coaxial pairs of windings 2a, and there are instances when that number can readily be increased to eight.

We claim:

l. A current-limiting high-voltage fuse including:

a. a tubular casing of insulating material;

b. a pair of cylindrical terminal plugs inserted into the ends of said casing and closing said casing and having axially inner end surfaces having a predetermined axial spacing, one of said pair of plugs defining a passageway extending substantially parallel to the common axis of said casing and said pair of plugs;

c. a plurality of fusible elements inside said casing conductively interconnecting said pair of plugs, said plurality of fusible elements including ribbons of relatively hard resilient sheet silver of rectangular cross section each having a plurality of serially related points of reduced cross-sectional area, said ribbons forming a plurality of helical extension-springlihe windings having a diameter ranging from about three-sixteenths of an inch to about one-half of an inch and having when in unloaded condition an axial length substantially less than said axial spacing between said axially inner end surfaces of said pair of plugs, each of said plurality of windings having axially outer overcenter ends affixed to said axially inner surfaces of said pair of plugs and being arranged to form a cylindrical pattern around the axis of said passageway and being axially stretched to such a degree as to be self-supporting and having an extended length approximately equal to said axial spacing between said axially inner end surfaces of plugs; and

d. a body of pulverulent arc-quenching filler inside said casing submersing each of said plurality of windings, being in immediate physical engagement with each of said plurality of windings, and being the only lateral support of each of said plurality of windings.

2. A current-limiting high-voltage fuse as specified in claim ll including at least six helical extension-springlike windings having equal angular spacings.

3. A current-limiting high-voltage fuse as specified in claim 2 wherein said windings are stretched to such an extent that the deflection per turn exceeds the diameter thereof.

t. A current-limiting high-voltage fuse as specified in claim 1 wherein the spacing between contiguous turns of said plurality of windings ranges from near zero to one thirty-secondth of an inch in the nonloaded and unstretched condition thereof.

5. A current-limiting high-voltage fuse as specified in claim 3 wherein the deflection per turn is about twice the diameter thereof.

b. A current-limiting high-voltage fuse as specified in claim E wherein said plurality of serially related points of reduced crosssectional area is formed by a plurality of serially related circular perforations arranged along the centerline of said ribbons, and wherein the longitudinal edges of said ribbons are uninterrupted by notches.

7. A current-limiting high-voltage fuse as specified in claim l wherein each of said plurality of windings is formed by a pair of coaxial winding sections each having axially inner spaced overcenter ends conductively interconnected by a substantially straight fusible conductor means.

8. A current-limiting high-voltage fuse as specified in claim 8 wherein said straight fusible conductor means is formed by a length of round silver wire spotwelded at the axially outer end thereof to said axially inner spaced overcenter ends of one pair of coaxial winding sections.

9. A current-limiting fuse as specified in claim 8 wherein a silver-severing overlay of a metal having a lower fusing point than silver is arranged at each end of said length of round silver wire to form double breaks at the occurrence of overloads of inadmissible duration.

ii). A current-limitinghigh-voltage fuse including:

a. a tubular casing of insulating material;

b. a pair of cylindrical terminal plugs inserted into the ends of said casing and closing said casing and having inner end surfaces having a predetermined axial spacing, one of said pair of plugs defining a passageway extending substantially parallel to the common axis of said casing and said pair of plugs;

. A plurality of fusible elements inside said casing conductively interconnecting said pair of plugs, said plurality of fusible elements including ribbons of relatively hard resilient sheet silver of rectangular cross section each having a plurality of circular perforations arranged along the centerline thereof, the longitudinal edges of said rib bons being uninterrupted by notches, said ribbons forming a plurality of helical extension-springlike windings having a diameter less than one-half of an inch and having when in unloaded condition a length less than said axial spacing between said axially inner end surfaces of said pair of plugs, .said plurality of windings having axially outer overcenter ends affixed to said axially inner end surfaces of said pair of plugs and being arranged to form a cylindrical pattern around the axis of said passageway, said plurality of windings being axially stretched to such a degree as to be self-supporting, having an extended length approximately equal to said axial spacing between said axially inner end surfaces of said pair of plugs and having a deflection per turn exceedingthe diameter of each of said plurality of windings; and

. a body of quartz sand inside said casing submersing each of said plurality of windings, being in immediate physical engagement with each of said plurality of windings, being composed of particles ranging from 20 to 70 U.S. Standard Sieve Number, and being the only lateral support of each of said plurality of windings between said axially outer overcenter ends thereof.

11. A current-limiting high-voltage fuse as specified in claim 10 including at least six extension-springlike windings having equal angular springs.

32. A current-limiting high-voltage fuse including:

a. a tubular casing of insulating material;

b. a pair of terminal elements having a predetermined axial spacing closing the ends of said casing;

c. a plurality of pairs of coaxial helically wound ribbon fuse links inside said casing forming at least six pairs of coaxial helical extension-springlike windings arranged parallel to the axis of said casing and forming a cylindrical pattern coaxial with said casing, the constituent ribbon fuse links of said pairs of windings being of relatively hard resilient sheet silver and of rectangular cross section and having circular perforations arranged along the centerlines thereof, the longitudinal edges of said ribbon fuse link being uninterrupted by notching, each of said pairs of windings having a diameter ranging from about three-sixteenths of an inch to about one-half of an inch, and each of said pairs of windings having axially outer overcenter ends affixed to one of said pair of terminai elements, and each of said pairs of windings having axially inner ends, a plurality of fusible conductor means of silver, each of said plurality of fusible conductor means conductively interconnecting said axially inner ends of one pair of said pairs of windings, and each of said plurality of fusible conductor means having a shorter axial length than each winding of said pairs of windings, each of said plurality of fusible conductor means having a sufficiently small cross-sectional area to generate when carrying current larger amount of heat per unit of length than the same unit of length of said ribbon fuse links when carrying the same current, each pair of said pairs of windings having when in unloaded condition an aggregate length less than the difference of said predetermined axial spacing between said pair of terminal elements and the axial length of each of said plurality of fusible conductor means, each of said pairs of windings being axially stretched to such an extent as to be self-supporting, to have a deflection per turn exceeding the diameter thereof and to have an extended length substantially equal to the difference of said axial spacing between said pair of terminal elements and said axial length of each of said plurality of fusible conductor means; and

d. A body of pulverulent arc-quenching filler inside said casing submersing said pairs of windings and said plurality of conductor means, being in immediate physical engagement with said pairs of windings and said plurality of fusible conductor means and being the only lateral support provided for said pairs of windings and said plurality of conductor means inside all of the space bounded by said casing and said pair of terminal elements.

13. A current-limiting high-voltage fuse as specified in claim 112 wherein said pairs of windings have equal angular spacings.

14. A current-limiting high-voltage fuse as specified in claim 12 wherein said pair of terminal elements is formed by a pair of terminal plugs inserted into the ends of said casing, wherein each of said pair of terminal plugs is provided with an axially outer cylindrical coaxial projection of reduced diameter, and wherein one of said pair of terminal plugs and said projection thereof jointly define a passageway substantially coaxial with said cylindrical pattern.

115. A current-limiting high-voltage fuse as specified in claim l2 wherein a silver-severing overlay of a metal having a lower fusing point than silver is arranged adjacent one of the ends of each of said plurality of fusible conductor means, and wherein said pulverulent arc-quenching filler is a body of quartz sand and excludes other pulverulent arc-quenching filler means having a smaller heat conductivity than quartz sand.

116. A current-limiting high-voltage fuse as specified in claim 12 wherein a silver-severing overlay of a metal having a lower fusing point than silver is arranged adjacent each of the axially outer ends of each of said plurality of fusible conductor means, and wherein said pulverulent arc-quenching filler is a body of quartz sand and excludes pulverulent arc-quenching filler means having a smaller heat conductivity than quartz sand.

17. A current-limiting high-voltage fuse as specified in claim 12 wherein each of said plurality of fusible conductor means is formed by one of a plurality of straight lengths of round silver wire each spot-welded to said axially inner ends of one pair of said pairs of windings and arranged over the center of said one pair of said pairs of windings, wherein a silver-severing overlay of a metal having a lower fusing'point than silver is arranged adjacent each of the spot-welds attaching one of said lengths of silver wire to said axially inner ends of one pair of said pairs of windings, and wherein said pulverulent arcquenching filler is a body of quartz sand and excludes pulverulent arcquenching tiller means having a smaller heat conductivity than quartz sand.

llii. A current-limiting high-voltage fuse as specified in claim i2 wherein each of said plurality of fiisible conductor means is formed by one of a plurality of straight lengths of round silver wire spot-welded to said axially inner ends of one pair of said pairs of windings and arranged in a common plane extending diametrically across the center of said one pair of said pairs of windings, wherein a silver-severing overlay of a metal having a lower fusing point than silver is arranged adjacent each of the axially outer ends of each of said plurality of lengths of silver wire, and wherein said pulverulent arc-quenching filler is a body of quartz sand and excludes other pulverulent arcquenching filler means having a smaller heat conductivity than quartz sand.

it". A current-limiting high-voltage fuse as specified in claim 12 wherein each of said plurality of fusible conductor means is formed by one of a plurality of helically wound lengths of round silver wire mounted on an insulating core and having ends conductively connected to said axially inner ends of one pair of said pairs of windings, wherein said insulating core of each of said plurality of helically wound lengths of silver wire is affixed to said axially inner ends of one pair of said pairs of windings, wherein a silver-severing overlay of a metal having a lower fusing point than silver is arranged adjacent each of the axially outer ends of one of said plurality of helically wound lengths of round silver wire, and wherein said pulverulent arcquenching filler is a body of quartz sand and excludes other pulverulent arc-quenching filler means having a smaller heat conductivity than quartz sand.

20. A current-limiting high-voltage fuse including:

a. a tubular casing of insulating material;

b. a pair of cylindrical terminal plugs inserted into the ends of said casing and closing said casing, said pair of terminal plugs havingaxially inner end surfaces having a predetermined spacing, one of said pair of terminal plugs defining a passageway substantially parallel to the common axis of said casing and said pair of terminal plugs;

c. A plurality of fusible elements inside said casing conductively interconnecting said pair of terminal plugs, each of said plurality of fusible elements including a pair of axially outer sections having serially related relatively short points of reduced cross-sectional area and an axially inner section conductively interconnecting the axially inner ends of said pair of axially outer sections and establishing a region of reduced cross-sectional area of considerable greater length than the length of each of said relatively short points of reduced cross-sectional area, said axially outer sections being formed by coaxial pairs of extensionspringlike windings of ribbons of relatively hard sheet silver rectangular in cross section having circular perforations along the centerlines thereof forming said relatively short points of reduced cross-sectional area, the longitudinal edges of said ribbons being uninterrupted by notching, each of said coaxial pairs of windings having a diameter ranging from less then three-sixteenths of an inch to about one-half of an inch and being arranged in a cylindrical pattern around the axis of said passageway defined by said one of said terminal plugs, each pair of said pairs of windings having when in unloaded condition a shorter aggregate length than the difference of said spacing between said axially inner end surfaces of said pair of terminal plugs and the axial length of said axially inner section of each of said plurality of fusible elements, and each of said pairs of windings being stretched to such an extent as to be self-supporting, to cause the deflection per turn to exceed the diameter thereof and to have an aggregate length substantially equal to the difference of said spacing between said axially inner end surfaces of said pair of terminal plugs and the length of said axially inner section of each of said plurality of fusible elements;

d. a plurality of pairs of silver-severing overlays of a metal having a lower fusing point than silver, each pair of overlays being arranged adjacent the axially inner ends of one of said pairs of windings to establish two breaks in series upon fusion of each pair of saidplurality of pairs of overlays; and

e. a body of pulverulent arc-quenching filler inside said casing submersing said pairs of windings and said axially inner section of each of said plurality of fusible elements and being in immediate physical engagement with said pairs of windings and said axially inner section of each of including at least six coaxial pairs of windings having equal angular spacings,

22. A current-limiting high-voltage fuse including: 10

a. a tubular casing of insulating material;

b. a pair of cylindrical terminal plugs inserted into the ends of said casing and closing said casing, said pair of plugs having axially inner end surfaces having a predetermined axial spacing, one of said pair of plugs defining a passageway extending substantially parallel to the common axis of said casing and said pair of plugs;

c. a plurality of fusible elements inside said casing conductively interconnecting said pair of plugs, said plurality of fusible elements including ribbons of relatively hard resilient sheet silver rectangular in cross section each having a plurality of serially related points of reduced crosssectional area, said ribbons forming helical extensionspringlike windings having a diameter ranging from about three-sixteenths of an inch to about one-half of an inch, having axially outer overcenter ends and having when in unloaded condition a length substantially less than said axial spacing between said axially inner end surfaces of said pair of fuses, said windings being arranged in a cylindrical pattern around said passageway defined by said one of said pair of plugs, and said windings being stretched to such an extent that said axially outer overcenter ends thereof are coextensive with said axially inner end surfaces of said pair of plugs; 3 5

d. a plurality of screws having shanks parallel to the common axis of plugs screwed into said axially inner end surfaces of said pair of plugs to clamp said axially outer overcenter ends of said windings against said axially inner end surfaces of said pair of plugs;

e. a plurality of solder joints adjacent said plurality of screws conductively connecting said axially outer overcenter ends of said windings to said axially inner end surfaces of said pair of plugs and securing said plurality of screws in the position thereof; and

f. a body of pulverulent arc-quenching filler inside said casing submersing said plurality of fusible elements.

23. A current-limiting high-voltage fuse as specified in claim plurality of screws intersects at right angles the axis of one of said helical windings.

24. An electric high-voltage fuse gear including:

a. a tubular fusereceiving structure having a predetermined inner diameter;

b. a pullcover for closing one of the ends of said fuse-receiving structure, said pullover being provided with a pullhandle;

. a pair of fuse holders, one of said pair of fuse holders being arranged adjacent one of the ends of said fusereceiving structure remote from said pullcover and affixed to said fuse-receiving structure, and the other of said pair of fuse holders being arranged inside said pullcover and affixed to said pullcover; and

d. a high-voltage fuse arranged in said fuse-receiving structure, said fuse including a tubular casing of insulating material arranged in substantially coaxial relation inside of said fuse-receiving structure and having an outer diameter but slightly less than said inner diameter of said fuse-receiving structure, said high-voltage fuse further including a pair of cylindrical terminal plugs inserted into the ends of said casing and closing said casing and having axially inner end surfaces having a predetermined axial spacing, one of said pair of plugs defining a passageway extending substantially parallel to the commonaxis of said casing and said pair of plugs, a plurality of fusible elements inside said casing conductively interconnecting said pair of plugs, said plurality of fusible elements including ribbons of relatively hard resilient sheet silver of rectangular cross section each having a plurality of serially related points of reduced cross-sectional area, said ribbons forming helical extension-springlike windings having a diameter ranging from about three-sixteenths of an inch to about one-half of an inch and having when in unloaded condition a length less than said axial spacing between said axially inner end surfaces of said pair of plugs, said windings have axially outer overcenter ends affixed to said axially inner end surfaces of said pair of plugs and being arranged to form a cylindrical pattern around the axis of said passageway defined by one of said pair of plugs and said winding being stretched to such a degree as to be self-supporting, to have an extended length approximately equal to said axial spacing between said axially inner end surfaces of said pair or plugs, and a body of pulverulent arc-quenching filler inside said casing submersing each of said windings, being in immediate physical engagement with each of said windings, and being the only lateral support of each of said windings.

Claims

1. A current-limiting high-voltage fuse including: a. a tubular casing of insulating material; b. a pair of cylindrical terminal plugs inserted into the ends of said casing and closing said casing and having axially inner end surfaces having a predetermined axial spacing, one of said pair of plugs defining a passageway extending substantially parallel to the common axis of said casing and said pair of plugs; c. a plurality of fusible elements inside said casing conductively interconnecting said pair of plugs, said plurality of fusible elements including ribbons of relatively hard resilient sheet silver of rectangular cross section each having a plurality of serially related points of reduced crosssectional area, said ribbons forming a plurality of helical extension-springlike windings having a diameter ranging from about three-sixteenths of an inch to about one-half of an inch and having when in unloaded condition an axial length substantially less than said axial spacing between said axially inner end surfaces of said pair of plugs, each of said plurality of windings having axially outer overcenter ends affixed to said axially inner surfaces of said pair of plugs and being arranged to form a cylindrical pattern around the axis of said passageway and being axially stretched to such a degree as to be self-supporting and having an extended length approximately equal to said axial spacing between said axially inner end surfaces of plugs; and d. a body of pulverulent arc-quenching filler inside said casing submersing each of said plurality of windings, being in immediate physical engagement with each of said plurality of windings, and being the only lateral support of each of said plurality of windings.

2. A current-limiting high-voltage fuse as specified in claim 1 including at least six helical extension-springlike windings having equal angular spacings.

4. A current-limiting high-voltage fuse as specified in claim 1 wherein the spacing between contiguous turns of said plurality of windings ranges from near zero to one thirty-secondth of an inch in the nonloaded and unstretched condition thereof.

6. A current-limiting high-voltage fuse as specified in claim 1 wherein said plurality of serially related points of reduced cross-sectional area is formed by a plurality of serially related circular perforations arranged along the centerline of said ribbons, and wherein the longitudinal edges of said ribbons are uninterrupted by notches.

7. A current-limiting high-voltage fuse as spEcified in claim 1 wherein each of said plurality of windings is formed by a pair of coaxial winding sections each having axially inner spaced overcenter ends conductively interconnected by a substantially straight fusible conductor means.

10. A current-limiting high-voltage fuse including: a. a tubular casing of insulating material; b. a pair of cylindrical terminal plugs inserted into the ends of said casing and closing said casing and having inner end surfaces having a predetermined axial spacing, one of said pair of plugs defining a passageway extending substantially parallel to the common axis of said casing and said pair of plugs; c. A plurality of fusible elements inside said casing conductively interconnecting said pair of plugs, said plurality of fusible elements including ribbons of relatively hard resilient sheet silver of rectangular cross section each having a plurality of circular perforations arranged along the centerline thereof, the longitudinal edges of said ribbons being uninterrupted by notches, said ribbons forming a plurality of helical extension-springlike windings having a diameter less than one-half of an inch and having when in unloaded condition a length less than said axial spacing between said axially inner end surfaces of said pair of plugs, said plurality of windings having axially outer overcenter ends affixed to said axially inner end surfaces of said pair of plugs and being arranged to form a cylindrical pattern around the axis of said passageway, said plurality of windings being axially stretched to such a degree as to be self-supporting, having an extended length approximately equal to said axial spacing between said axially inner end surfaces of said pair of plugs and having a deflection per turn exceeding the diameter of each of said plurality of windings; and e. a body of quartz sand inside said casing submersing each of said plurality of windings, being in immediate physical engagement with each of said plurality of windings, being composed of particles ranging from 20 to 70 U.S. Standard Sieve Number, and being the only lateral support of each of said plurality of windings between said axially outer overcenter ends thereof.

12. A current-limiting high-voltage fuse including: a. a tubular casing of insulating material; b. a pair of terminal elements having a predetermined axial spacing closing the ends of said casing; c. a plurality of pairs of coaxial helically wound ribbon fuse links inside said casing forming at least six pairs of coaxial helical extension-springlike windings arranged parallel to the axis of said casing and forming a cylindrical pattern coaxial with said casing, the constituent ribbon fuse links of said pairs of windings being of relatively hard resilient sheet silver and of rectangular cross section and having circular perforations arranged along the centerlines thereof, the longitudinal edges of said ribbon fuse link being uninterrupted by notching, each of said pairs of windings having a diameter ranging from about three-sixteenths of an inch to about one-half of an inch, and each of said pairs of windings having axially outer overcenter ends affixed to one of said pair of terminal elements, and each of said pairs of windings having axially inner ends, a pluRality of fusible conductor means of silver, each of said plurality of fusible conductor means conductively interconnecting said axially inner ends of one pair of said pairs of windings, and each of said plurality of fusible conductor means having a shorter axial length than each winding of said pairs of windings, each of said plurality of fusible conductor means having a sufficiently small cross-sectional area to generate when carrying current larger amount of heat per unit of length than the same unit of length of said ribbon fuse links when carrying the same current, each pair of said pairs of windings having when in unloaded condition an aggregate length less than the difference of said predetermined axial spacing between said pair of terminal elements and the axial length of each of said plurality of fusible conductor means, each of said pairs of windings being axially stretched to such an extent as to be self-supporting, to have a deflection per turn exceeding the diameter thereof and to have an extended length substantially equal to the difference of said axial spacing between said pair of terminal elements and said axial length of each of said plurality of fusible conductor means; and d. A body of pulverulent arc-quenching filler inside said casing submersing said pairs of windings and said plurality of conductor means, being in immediate physical engagement with said pairs of windings and said plurality of fusible conductor means and being the only lateral support provided for said pairs of windings and said plurality of conductor means inside all of the space bounded by said casing and said pair of terminal elements.

13. A current-limiting high-voltage fuse as specified in claim 12 wherein said pairs of windings have equal angular spacings.

15. A current-limiting high-voltage fuse as specified in claim 12 wherein a silver-severing overlay of a metal having a lower fusing point than silver is arranged adjacent one of the ends of each of said plurality of fusible conductor means, and wherein said pulverulent arc-quenching filler is a body of quartz sand and excludes other pulverulent arc-quenching filler means having a smaller heat conductivity than quartz sand.

16. A current-limiting high-voltage fuse as specified in claim 12 wherein a silver-severing overlay of a metal having a lower fusing point than silver is arranged adjacent each of the axially outer ends of each of said plurality of fusible conductor means, and wherein said pulverulent arc-quenching filler is a body of quartz sand and excludes pulverulent arc-quenching filler means having a smaller heat conductivity than quartz sand.

17. A current-limiting high-voltage fuse as specified in claim 12 wherein each of said plurality of fusible conductor means is formed by one of a plurality of straight lengths of round silver wire each spot-welded to said axially inner ends of one pair of said pairs of windings and arranged over the center of said one pair of said pairs of windings, wherein a silver-severing overlay of a metal having a lower fusing point than silver is arranged adjacent each of the spot-welds attaching one of said lengths of silver wire to said axially inner ends of one pair of said pairs of windings, and wherein said pulverulent arc-quenching filler is a body of quartz sand and excludes pulverulent arc-quenching filler means having a smaller heat conductivity than quartz sand.

18. A current-limiting high-voltage fuse as specified in claim 12 wherein each of said plurality of fusible conductor means is formed by one of a plurality of straight lengths of round silver wire spot-welded to said axially inner ends of one pair of said pairs of windings and arranged in a common plane extending diametrically across the center of said one pair of said pairs of windings, wherein a silver-severing overlay of a metal having a lower fusing point than silver is arranged adjacent each of the axially outer ends of each of said plurality of lengths of silver wire, and wherein said pulverulent arc-quenching filler is a body of quartz sand and excludes other pulverulent arc-quenching filler means having a smaller heat conductivity than quartz sand.

19. A current-limiting high-voltage fuse as specified in claim 12 wherein each of said plurality of fusible conductor means is formed by one of a plurality of helically wound lengths of round silver wire mounted on an insulating core and having ends conductively connected to said axially inner ends of one pair of said pairs of windings, wherein said insulating core of each of said plurality of helically wound lengths of silver wire is affixed to said axially inner ends of one pair of said pairs of windings, wherein a silver-severing overlay of a metal having a lower fusing point than silver is arranged adjacent each of the axially outer ends of one of said plurality of helically wound lengths of round silver wire, and wherein said pulverulent arc-quenching filler is a body of quartz sand and excludes other pulverulent arc-quenching filler means having a smaller heat conductivity than quartz sand.

20. A current-limiting high-voltage fuse including: a. a tubular casing of insulating material; b. a pair of cylindrical terminal plugs inserted into the ends of said casing and closing said casing, said pair of terminal plugs having axially inner end surfaces having a predetermined spacing, one of said pair of terminal plugs defining a passageway substantially parallel to the common axis of said casing and said pair of terminal plugs; c. A plurality of fusible elements inside said casing conductively interconnecting said pair of terminal plugs, each of said plurality of fusible elements including a pair of axially outer sections having serially related relatively short points of reduced cross-sectional area and an axially inner section conductively interconnecting the axially inner ends of said pair of axially outer sections and establishing a region of reduced cross-sectional area of considerable greater length than the length of each of said relatively short points of reduced cross-sectional area, said axially outer sections being formed by coaxial pairs of extension-springlike windings of ribbons of relatively hard sheet silver rectangular in cross section having circular perforations along the centerlines thereof forming said relatively short points of reduced cross-sectional area, the longitudinal edges of said ribbons being uninterrupted by notching, each of said coaxial pairs of windings having a diameter ranging from less then three-sixteenths of an inch to about one-half of an inch and being arranged in a cylindrical pattern around the axis of said passageway defined by said one of said terminal plugs, each pair of said pairs of windings having when in unloaded condition a shorter aggregate length than the difference of said spacing between said axially inner end surfaces of said pair of terminal plugs and the axial length of said axially inner section of each of said plurality of fusible elements, and each of said pairs of windings being stretched to such an extent as to be self-supporting, to cause the deflection per turn to exceed the diameter thereof and to have an aggregate length substantially equal to the difference of said spacing between said axially inner end surfaces of said pair of terminal plugs and the length of said axially inner section of each of said plurality of fusible elements; d. a plurality of pairs of silver-severing overlays of a metal having a lower fusing point than silver, each pair of overlays being arranged adjacEnt the axially inner ends of one of said pairs of windings to establish two breaks in series upon fusion of each pair of said plurality of pairs of overlays; and e. a body of pulverulent arc-quenching filler inside said casing submersing said pairs of windings and said axially inner section of each of said plurality of fusible elements and being in immediate physical engagement with said pairs of windings and said axially inner section of each of said plurality of fusible elements, and said body of pulverulent arc-quenching filler being the only lateral support provided for said pairs of windings and said axially inner section of each of said plurality of fusible elements inside of all of the space bounded by said casing and said pair of terminal plugs.

21. A current-limiting high-voltage fuse as specified in claim 20 including at least six coaxial pairs of windings having equal angular spacings.

22. A current-limiting high-voltage fuse including: a. a tubular casing of insulating material; b. a pair of cylindrical terminal plugs inserted into the ends of said casing and closing said casing, said pair of plugs having axially inner end surfaces having a predetermined axial spacing, one of said pair of plugs defining a passageway extending substantially parallel to the common axis of said casing and said pair of plugs; c. a plurality of fusible elements inside said casing conductively interconnecting said pair of plugs, said plurality of fusible elements including ribbons of relatively hard resilient sheet silver rectangular in cross section each having a plurality of serially related points of reduced cross-sectional area, said ribbons forming helical extension-springlike windings having a diameter ranging from about three-sixteenths of an inch to about one-half of an inch, having axially outer overcenter ends and having when in unloaded condition a length substantially less than said axial spacing between said axially inner end surfaces of said pair of fuses, said windings being arranged in a cylindrical pattern around said passageway defined by said one of said pair of plugs, and said windings being stretched to such an extent that said axially outer overcenter ends thereof are coextensive with said axially inner end surfaces of said pair of plugs; d. a plurality of screws having shanks parallel to the common axis of plugs screwed into said axially inner end surfaces of said pair of plugs to clamp said axially outer overcenter ends of said windings against said axially inner end surfaces of said pair of plugs; e. a plurality of solder joints adjacent said plurality of screws conductively connecting said axially outer overcenter ends of said windings to said axially inner end surfaces of said pair of plugs and securing said plurality of screws in the position thereof; and f. a body of pulverulent arc-quenching filler inside said casing submersing said plurality of fusible elements.

23. A current-limiting high-voltage fuse as specified in claim 22 wherein the outer periphery of the heads of each of said plurality of screws intersects at right angles the axis of one of said helical windings.

24. An electric high-voltage fuse gear including: a. a tubular fuse-receiving structure having a predetermined inner diameter; b. a pullcover for closing one of the ends of said fuse-receiving structure, said pullover being provided with a pullhandle; c. a pair of fuse holders, one of said pair of fuse holders being arranged adjacent one of the ends of said fuse-receiving structure remote from said pullcover and affixed to said fuse-receiving structure, and the other of said pair of fuse holders being arranged inside said pullcover and affixed to said pullcover; and d. a high-voltage fuse arranged in said fuse-receiving structure, said fuse including a tubular casing of insulating material arranged in substantially coaxial relation inside of said fuse-receiving structure and having an outer diameter but slightly less than said inner diameter of said fuse-receiving structure, said high-voltage fuse further including a pair of cylindrical terminal plugs inserted into the ends of said casing and closing said casing and having axially inner end surfaces having a predetermined axial spacing, one of said pair of plugs defining a passageway extending substantially parallel to the common axis of said casing and said pair of plugs, a plurality of fusible elements inside said casing conductively interconnecting said pair of plugs, said plurality of fusible elements including ribbons of relatively hard resilient sheet silver of rectangular cross section each having a plurality of serially related points of reduced cross-sectional area, said ribbons forming helical extension-springlike windings having a diameter ranging from about three-sixteenths of an inch to about one-half of an inch and having when in unloaded condition a length less than said axial spacing between said axially inner end surfaces of said pair of plugs, said windings have axially outer overcenter ends affixed to said axially inner end surfaces of said pair of plugs and being arranged to form a cylindrical pattern around the axis of said passageway defined by one of said pair of plugs and said winding being stretched to such a degree as to be self-supporting, to have an extended length approximately equal to said axial spacing between said axially inner end surfaces of said pair or plugs, and a body of pulverulent arc-quenching filler inside said casing submersing each of said windings, being in immediate physical engagement with each of said windings, and being the only lateral support of each of said windings.