US3671909A

US3671909A - High-voltage fuse with one piece fuse links

Info

Publication number: US3671909A
Application number: US116037A
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: 1971-02-17
Filing date: 1971-02-17
Publication date: 1972-06-20
Anticipated expiration: 1989-06-20

Abstract

A high-voltage fuse for interrupting both protracted overload currents and major fault currents and operating as a currentlimiting fuse when interrupting major fault currents. The fuse includes one or more fusible elements each operating in the fashion of a composite fusible element including serially connected ribbon sections and a wire section interposed between, and spot-welded to, the ribbon sections. In fuses according to this invention one single stamping, i.e. one single length of sheet silver stock takes the plate of a spot-welded composite of ribbon sections and a wire section. The wire like effect is achieved by providing an oblong hole, or window, in the center region of the ribbon fuse link, resulting in the formation of two wire-like strips of small cross-sectional area to both sides of the oblong hole or window.

Description

United States Patent Kozacka et al. 1 June 20, 1972 s41 HIGH-VOLTAGE FUSE WITH ONE FOREIGN PATENTS OR APPLICATIONS PIECE FUSE LINKS 864,943 5/1941 France ..337/229 [72] Inventors: Frederick J. Kozaeka, South Hampton;

Richard Belch", Hampton Falls, both Primary Examiner-Bernard A. Gilheany of Assistant Examiner-Dewitt M. Morgan Attorney-Erwin Salzer [73] Assignee: The Chase-Shawmut Company, Newbuyp MaSS- [57] ABSTRACT [22] Filed: Feb. 17, 1971 A high-voltage fuse for interrupting both protracted overload currents and major fault currents and operating as a current- [2]] Appl' N l16o37 limiting fuse when interrupting major fault currents. The fuse includes one or more fusible elements each operating in the 52 us. (:1 ..337/160, 337/292, 337/295 fashion of a composite fusible element including serially 5 Int c mflmh 35/10, 011 5 12 nected ribbon sections and a wire section interposed between, 581 Field of Search ..337/159, 160, 161, 162, 166, and spot-welded the ribbon sections In fuses according I9 337/229, 292 293, 295 296 this invention one single stamping, i.e. one single length of sheet silver stock takes the plate of a spot-welded composite of ribbon sections and a wire section. The wire like effect is [56] Reemnces Cited achieved by providing an oblong hole, or window, in the UNITED STATES PATENTS center region of the ribbon fuse link, resulting in the formation of two wire-like strips of small cross-sectional area to both 3,386,062 5/1968 Kozacka 8! al. ..337/160 Sides of the oblong hole or window 3,471,818 10/1969 Koch ...337/295 X 3,571,775 3/1971 Kozacka et a] ..337[295 X 12 Claims, 7 Drawing Figures PATENYEDJUHZO I872 3,671,909

FIG.|

INVENTORS:

FREDERICK J. KOZACKA RICHARD A. BELCHER BY WWW WW ATTY.

HIGH-VOLTAGE FUSE WITH ONE PIECE FUSE LINKS BACKGROUND OF THE INVENTION It is an old onerous problem in the fuse art to provide fuses which are capable of effectively interrupting both major fault currents, or short circuit currents, as well as overload currents of inadmissible duration. US Pat. No, 3,386,062 to Frederick J. Kozacka et al., May 28, 1969 for ELECTRIC CARTRIDGE FUSE FOR INTERRUPTING PROTRACT ED OVERLOAD CURRENTS AND MAJOR FAULT CURRENTS discloses a fuse that performs particularly well the aforementioned two functions. This is primarily due to the particular geometry of its ribbon fuse link of silver. The fuse link includes a plurality of serially related necks, or points of reduced cross-sectional area, which are relatively short, and one neck, or point of reduced cross-sectional area, which is relatively long, and arranged in series with the aforementioned plurality of relatively short necks. It is desirable to adapt the aforementioned geometry to fuses having a relatively high voltage rating, e.g. a voltage rating from about 2.5 kV to kV. This calls for a substantial increase of the total length, and of the length of the relatively long neck, of the fuse link structure of U.S. Pat. No. 3,386,062. The necessary increase in the length of the neck renders the fuse link structure extremely fragile, and makes it very difficult to handle the same. It can only be handled by particularly skilled labor, and even if handled by skilled labor with reasonable care the rate of damage to such fuse links is relatively high. This is particularly troublesome since the damage to such a fuse link cannot normally be detected by visual inspection thereof, but can only be discovered by conducting electrical tests after the fuse has been assembled. The fact that quality control can only discover slightly damaged yet unacceptable fuse links upon assembly of a fuse greatly increases the cost of production, particularly since the cost of production of each'high-voltage fuse unit are relatively high.

Because of the difficulties involved in forming and in processing ribbon fuse links having long neck portions intended for the interruption of protracted overload currents, a type of high-voltage fuses has been developed wherein the long neck portions of the fuse link are formed by silver wires. The wires interconnect conductively ribbon sections of the fuse link which form a plurality of serially related relatively short necks or points of reduced cross-sectional area. The latter form series breaks upon occurrence of major fault currents. Such high-voltage fuses are disclosed and claimed in the copending patent application of Frederick J. Kozacka et al., Ser. No. 016,116, filed Mar. 30, 1970 for HIGH-VOLTAGE FUSE HAVING A PLURALITY OF HELICALLY WOUND RIBBON FUSE LINKS now US. Pat. No. 3,571,775 issued Mar. 23, 1971 While the performance of high-voltage fuses of the aforementioned character including fusible elements having wire sections forming relatively long overload current interrupting necks and having ribbon sections forming relatively short major fault current interrupting necks is satisfactory, the process of affixing the wire sections to the ribbon sections involves considerable difficulties. Affixing the wire sections to the ribbon section calls for spot-welding operations which are, in essence, manual operations calling for a certain skill and also requiring manual handling of fragile ribbon fuse links which may result in damage to the latter. A spot-weld may result in sufficient mechanical strength of the joint without reducing the contact resistance as much as necessary and/or desirable. In such instances the spot weld. must be covered by a solder joint to minimize contact resistance, and this means an additional operation which is not simple by any means, and further increases the cost of production.

The principal object of this invention is to provide high-voltage fuses which perform substantially in the same way as the fuses disclosed in the above referred-to U.S. Pat. No. 3,386,062, and which can be manufactured at reasonable or lower cost, its fuse link being a relatively rugged one-piece structure rather than a fabricated, spot-welded structure.

SUMMARY OF THE INVENTION High-voltage fuses embodying this invention include a tubular casing of electric insulating material and a pair of terminal elements arranged at the ends of the casing and closing the latter. The casing is filled with quartz sand. A ribbonfuse link of silver conductively interconnecting the pair of terminal elements is submersed in the filler of quartz sand. The fuse link has a plurality of serially related relatively short necks arranged in relatively long axially outer portions thereof, and the fuse link has a relatively long neck arranged between the axially outer portions thereof. Each of the plurality of short necks is formed by a circular perforation positioned in the center of the fuse link and having a predetermined diameter. The aforementioned relatively long neck is formed by an oblong perforation in the center of the fuse link. The width of said oblong perforation is equal to the diameter of each of said circular perforations. This oblong perforation results in the formation by the stock of the fuse link of a pair of parallel narrow strips of silver conductively interconnecting said axially outer portions thereof. An overlay of a silver-severing metal having a lower fusing point than silver is arranged on said narrow strips of silver.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is in substance a vertical section of a fuse embodying this invention taken along [-1 of FIG. 2;

FIG. 2 is a transverse section of the fuse shown in FIG. 1 taken along IIII of FIG. 1;

FIG. 3 shows in side elevation a modification of the fuse link structure of FIG. 1 intended to be arranged in the general assembly shown in FIG. 1, and described in connection therewith;

FIG. 3a is a front elevation of a portion of the fuse link structure of FIG. 3;

FIG. 4 shows in elevation a portion of another fuse embodying this invention;

FIG. 5 shows in side elevation another modification of the fuse link structure of FIG. I intended to be arranged in the general assembly shown in FIG. 1 and described in connection therewith; and

FIG. 5a is a front elevation of a portion of the fuse structure of FIG. 5.

' DESCRIPTION OF PREFERRED EMBODIMENTS Referring now to FIGS. 1 and 2, numeral 1 has been applied to indicate a tubular casing of electric insulating material, preferably a laminate of melamine and glass cloth. A pair of terminal elements is arranged at the ends of casing 1, closing the latter. The terminal elements are preferably formed by metal plugs 2, press-fitted into the ends of casing 1, and maintained in position by steel pins 3 projecting transversely through casing 1 into plugs 2. Terminal caps or ferrules 4 are mounted on the ends of casing l, and their axially inner surfaces are clamped by means of hexagonal screws 5 projecting through caps or ferrules 4 into plugs 2 against the axially outer end surfaces of plugs 2. Casing 1 contains a body of quartz sand 6, the volume of which is substantially equal to the volume of casing 1. Four ribbon fuse links 7 of sheet silver interconnect conductively the pair of terminal elements or terminal plugs 2, and are submersed in the quartz sand filler 6. Each fuse link 7 has a plurality of serially related relatively short necks arranged in the axially outer portions thereof. The letter E has been applied to indicate the length of the axially outer portions of fuse links 7. Each of the relatively short necks of fuse link 7 is formed by a circular perforation 7a positioned in the center line of the respective fuse link 7. The neck proper is the portion of fuse link metal situated to both sides of a circular perforation 7a, and the length of each short neck is equal to the diameter of each perforation 7a. Perforations 7a are spaced equidistantly and have equal diameters. The letter X indicates the length of the axially inner portion of fuse link 7 which is considerably less than the length L of the axially outer portions thereof. The axially inner portion of fuse link 7 is formed by a relatively long neck which, in turn, is formed by an oblong perforation or elongated window 7b. Oblong perforation or elongated window 7b is laterally bounded by a pair of parallel narrow strips 70 of silver conductively interconnecting the axially outer portions of fuse link 7. An overlay 8 of a silver-severing metal having a lower fusing point than silver is operatively related to strips 70 to sever the latter upon fusion of the overlay 8. An overlay 8 is preferably arranged in the center of each of strips 70, but may be arranged at other points thereof, e.g. near the ends thereof, as long as it effects a break in strips 7c incident to its fusion. The ends of ribbon fuse links 7 are bent 90 and abut against the axially inner end surfaces of terminal plugs 2, and are firmly clamped against the latter by screws 10 projecting at right angles into the axially inner end surfaces of terminal plugs 2.

Upon occurrence of relatively small overloads of inadmissible duration the overlays 8 on silver strips 7c melt and sever the latter, thus initiating arcing. The bumback length x of strip 70 may be sufficient to cause extinction of low current arcs, but if sufficient low currents arcs may be further elongated and quenched by burning into the axially outer portions of ribbon fuse link 7. It has been found that the larger the number of parallel current paths, the more effective the operation of the fuse on occurrence of small overload currents. This is one of the reasons why the low overload current interrupting performance of a fuse link such as shown in FIG. 1 is superior to the low current-interrupting performance of a fuse having a fuse link which has the geometry shown in the above referredto US. Pat. No. 3,386,062.

Upon occurrence of major fault currents melting is initiated at the points of smallest cross-sectional area of the ribbon fuse link 7. The process of manufacturing fuse links 7 is simplified if the diameter of circular perforations 7a and the width w of the oblong perforation 7b are equal. This calls for certain precautions in regard to the selection of this particular parameter. To be more specific, the diameter of the circular perforations 7a must be at least in the order of 60 percent of the width W of ribbon fuse links 7. Particularly good performance in regard to limiting surge voltage incident to inter ruption of major fault currents was achieved with fuse links having circular holes, or perforations, 7a whose diameter was 60-70 percent of the width W of the fuse links 7, and whose oblong perforation has a width w of 60-70 percent of the width W of fuse links 7. Excellent results were obtained with fuse links wherein the cross-sectional area of the short necks formed by perforations 7a at the narrowest points of the necks and the cross-sectional area of the long necks formed by perforation 7b was about 36 percent of the cross-sectional area of ribbon fuse links 7, the thickness of the latter being uniform throughout the entire length thereof. A reduction of the diameter of holes 70 and of the width w of perforation 7b to 53 percent of the width of fuse links 7 resulted in excessive surge voltages incident to interruption of major fault currents.

The criticality of the aforementioned parameters can be readily explained. If the cross-section of the short necks and of the long neck is equal, both kinds of necks fuse simultaneously on major fault currents, tending to result in excessive surge voltages. This tendency can be minimized by imparting a relatively large diameter to the circular perforations 7a, i.e. a diameter of at least 60 percent of the width W of fuse links 7. The larger the diameter of perforations 7a in relation to the width W of link 7, the smaller the ratio of the smallest crosssectional area of the necks formed by perforations 7a to the length of the necks formed by perforations 7a (which length is equal to the diameter of perforations 7a). The smaller the aforementioned ratio, the larger the rate of change of crosssectional area along each neck, and the smaller the rate of change of current di/dt incident to bumback of a neck formed by a circular perforation from the point of smallest cross-sectional area of the neck to its point of largest cross-sectional area where the neck ends, and where its cross-sectional area becomes equal to the cross-sectional area of fuse links 7 at the points of largest cross-sectional area thereof.

FIGS. 3,3a and 5 and 5a refer to fuse link structures having axially outer portions of relatively hard resilient silver bent to form a pair of loaded, self-supporting extension springs 9',9". The pair of narrow strips 7c',7c" formed by oblong windows or perforations 7b',7b" are arranged over centers of the axially outer portions of fuse links 7',7" forming extension springs 9',9". The axially inner portions of fuse links 7',7 having

windows

7b,7b" are substantially planar.

In FIGS. 3 and 3a the reference character 7a has been applied to indicate the circular perforations forming relatively short necks and reference character 8' has been applied to indicate overlays of tin, or a like low fusing point silver-severing metal, arranged in the centers of narrow silver strips 7!). The axially outer portions of fuse link 7 which form loaded extension springs 9 are bent transversely at a lurality of serially related equidistant points so as to assume a zig-zag shape. Strips 7c are arranged over the centers of springs 9' and are, therefore, under tension in a direction longitudinally thereof by the action of loaded springs 9. The axially outer ends of springs 9 may be screwed against a pair of terminal plugs as shown in FIG. 1, and explained more in detail in connection with FIG. 1. Each bend in fuse link 7 is arranged at a point where one of the perforations 7a forming relatively short necks is located, and one or more perforations 7a are arranged between each bend in fuse link 7'.

According to FIG. 4 a ribbon fuse link 7 having the same geometry as the fuse link 7 of FIG. 1 is wound helically around a mandrel 10" of insulating material. Link-supporting mandrel 10" may form a spacer between terminal plugs of the kind shown in FIG. 1, and may consist of a plurality of angularly displaced insulating plates having radially outer edges engaging grooves provided in the axially inner end surfaces of the terminal plugs of the structure of FIG. 1. A fuse of this character has been disclosed in detail in the cO-pending patent application of Frederick J. Kozacka for HIGH-VOLTAGE FUSE, filed Nov. 13, 1969, Ser. No. 876,445, now US Pat. No. 3,599,138 issued Aug. 10, 1971. Reference may be had to this patent for more detailed information in regard to the structure of FIG. 4 which has only diagrammatically been shown therein. The fuse of FIG. 4 differs from the fuse disclosed in U.S. Pat. No. 3,599, l 38 only inasmuch as the former includes a fuse link whose geometry differs from the geometry of the ribbon fuse link of US. Pat. No. 3,599,138.

Referring now more particularly to FIGS. 5 and 5a, these figures show another ribbon type of fuse link which may be substituted for the ribbon fuse link of FIG. I. The fuse link of FIGS. 5 and 5a includes two axially outer portions of relatively hard silver which are wound helically to form a pair of loaded extension springs. The axially outer portions of fuse links 7" are provided with circular perforations which are arranged equidistantly and form necks of relatively short length. A planar portion of fuse link 7" is arranged over the centers of helical spring windings 9", and provided with an oblong perforation 7b" forming a relatively long neck consisting of two parallel strips 70'' of silver. The latter support near the center thereof an overlay 8" of tin, or the like low fusing point silversevering metal in form of a solidified droplet. The length of the neck formed by oblong perforation 7b" is a large multiple of the length of the necks formed by perforations 7a", or a large multiple of the diameter of perforations 7a".

The above may be illustrated by some numerical examples. The development and successful testing of fuses embodying this invention included fuses having a voltage rating of 2.5, 5 and 8.3 kV. The width of the ribbon fuse link was 0.086 inch and its thickness was 0.0060.0ll inch, depending upon desired current-carrying capacity. The spacing between circular perforations was 0.203 inch and the length of the oblong perforation in the axially inner portion of the ribbon fuse link was 1% inches. The diameter of the circular perforations was 0.055 inch. In the fuse link for the 8.3 kV voltage rating there were 60 circular perforations to each side of the oblong perforation of 1% inches.

We claim as our invention:

1. A high-voltage fuse including a. a tubular casing of electric insulating material;

b. a pair of terminal elements arranged at the ends of said casing and closing said casing;

c. a filler of quartz sand inside said casing;

d. a ribbon fuse link of silver conductively interconnecting said pair of terminal elements and submersed in said filler, said fuse link having a-plurality of serially related relatively short necks arranged in relatively long axially outer portions thereof, and said fuse link having a relatively long neck arranged between said axially outer portions thereof, each of said plurality of relatively short necks being formed by a circular perforation positioned in the center of said fuse link and having a predetermined diameter, and said relatively long neck being formed by an oblong perforation having a width equal to said predetemiined diameter and arranged in the center of said fuse link and resulting in the formation by the stock of which said fuse link is made of a pair of parallel narrow strips of silver having a spacing equal to said predetermined diameter conductively interconnecting said axially outer portions of said fuse link; and

e. overlay means of a silver-severing metal having a lower fusing point than silver on said narrow strips of silver.

2. A high-voltage fuse as specified in claim 1 wherein said predetermined diameter of said circular perforation is at least in the order of 60% of the width of said fuse link.

3. A high-voltage fuse as specified in claim 1 wherein said axially outer portions of said fuse link are of relatively hard resilient silver and are bent to form a pair of loaded extension springs, and wherein said pair of narrow strips is arranged over centers of said axially outer portions of said fuse link.

4. A high-voltage fuse as specified in claim 1 wherein said axially outer portions of said fu'se link are of relatively hard resilient silver and are helically wound to form a pair of loaded extension springs, and wherein said narrow pair of strips is arranged over centers of said axially outer portions.

5. A high-voltage fuse as specified in claim 1 wherein said axially outer portions of said fuse link are of relatively hard resilient silver and are bent transversely at a plurality of serially related points to form a pair of zig-zag shaped loaded extension springs, and wherein said narrow pair of strips is arranged over centers of said axially outer portions of said fuse link.

6. A high-voltage fuse as specified in claim 1 wherein each of said pair of narrow strips has substantially midway between the ends thereof an overlay of a silver-severing metal having a lower fusing point than silver.

7. A ribbon fuse link as specified in claim 6 wherein each of said pair of axially outer portions is bent helically to form a helical extension spring.

8. A ribbon fuse link for high-voltage fuses including a ribbon of relatively hard sheet silver having an axially inner portion of relatively short length and a pair of axially outer portions being relatively long in comparison to said axially inner portion, each of said pair of axially outer portions being bent to form an extension spring, and each of said pair of axially outer portions having a plurality of serially related points of reduced cross-sectional area and predcten'nined length, each of said serially related points of reduced cross-sectional area being formed by a circular perforation having a predetermined diameter, said axially inner portion being substantially planar, arranged over the centers of said pair of axially outer portions and formed by a pair of parallel strips which are much longer than said length of each of said plurality of points of reduced cross-sectional area, said pair of parallel strips being separated by an oblong gap having a width equal to said predetermined diameter of said circular perforations, said pair of parallel strips being formed by the same ribbon of sheet silver as said pair of axially outer portions of said ribbon fuse link and said pair of parallel strips being provided with overlay means of a silver-severing metal having a lower fusing point than silver.

9. A ribbon fuse link as specified in claim 8 wherein each said circular perforation has a diameter of at least 60 percent of the width of said ribbon of relatively hard silver.

10. A ribbon fuse link as specified in claim 8 wherein said diameter of each of said circular perforation is 60 to 70 percent of the width of said ribbon of relatively hard silver.

11. A ribbon fuse link as specified in claim 8 wherein each of said pair of axially outer portions is bent transversely at a plurality of serially related points to form a zig-zag shaped extension spring.

12. In a high-voltage fuse the combination of a. an elongated mandrel of electric insulating material; and

b. a ribbon fuse link of silver wound helically around said mandrel, said ribbon fuse link having an axially inner portion of relatively short length and a pair of axially outer portions being relatively long in comparison to said axially inner portion, each of said pair of axially outer portions having a plurality of serially related circular perforations having a diameter at least in the order of 60 percent of the width of said ribbon fuse link, said axially inner portion having an oblong perforation having a width equal to said diameter of said circular perforations, the length of said oblong perforation being a large multiple of said diameter of said circular perforations, said oblong perforation being bounded laterally by a pair of parallel narrow strips each formed by the same ribbon as any other portion of said ribbon fuse link, and each of said pair of parallel narrow strips being provided with overlay means of a silver-severing metal having a lower fusing point than silver.

Claims

1. A high-voltage fuse including a. a tubular casing of electric insulating material; b. a pair of terminal elements arranged at the ends of said casing and closing said casing; c. a filler of quartz sand inside said casing; d. a ribbon fuse link of silver conductively interconnecting said pair of terminal elements and submersed in said filler, said fuse link having a plurality of serially related relatively short necks arranged in relatively long axially outer portions thereof, and said fuse link having a relatively long neck arranged between said axially outer portions thereof, each of said plurality of relatively short necks being foRmed by a circular perforation positioned in the center of said fuse link and having a predetermined diameter, and said relatively long neck being formed by an oblong perforation having a width equal to said predetermined diameter and arranged in the center of said fuse link and resulting in the formation by the stock of which said fuse link is made of a pair of parallel narrow strips of silver having a spacing equal to said predetermined diameter conductively interconnecting said axially outer portions of said fuse link; and e. overlay means of a silver-severing metal having a lower fusing point than silver on said narrow strips of silver.

2. A high-voltage fuse as specified in claim 1 wherein said predetermined diameter of said circular perforation is at least in the order of 60 percent of the width of said fuse link.

4. A high-voltage fuse as specified in claim 1 wherein said axially outer portions of said fuse link are of relatively hard resilient silver and are helically wound to form a pair of loaded extension springs, and wherein said narrow pair of strips is arranged over centers of said axially outer portions.

8. A ribbon fuse link for high-voltage fuses including a ribbon of relatively hard sheet silver having an axially inner portion of relatively short length and a pair of axially outer portions being relatively long in comparison to said axially inner portion, each of said pair of axially outer portions being bent to form an extension spring, and each of said pair of axially outer portions having a plurality of serially related points of reduced cross-sectional area and predetermined length, each of said serially related points of reduced cross-sectional area being formed by a circular perforation having a predetermined diameter, said axially inner portion being substantially planar, arranged over the centers of said pair of axially outer portions and formed by a pair of parallel strips which are much longer than said length of each of said plurality of points of reduced cross-sectional area, said pair of parallel strips being separated by an oblong gap having a width equal to said predetermined diameter of said circular perforations, said pair of parallel strips being formed by the same ribbon of sheet silver as said pair of axially outer portions of said ribbon fuse link and said pair of parallel strips being provided with overlay means of a silver-severing metal having a lower fusing point than silver.

12. In a high-voltage fuse the combination of a. an elongated mandrel of electric insulating material; and b. a ribbon fuse link of silver wound helically around said mandrel, said ribbon fuse link having an axially inner portion of relatively short length and a pair of axially outer portions being relatively long in comparison to said axially inner portion, each of said pair of axially outer portions having a plurality of serially related circular perforations having a diameter at least in the order of 60 percent of the width of said ribbon fuse link, said axially inner portion having an oblong perforation having a width equal to said diameter of said circular perforations, the length of said oblong perforation being a large multiple of said diameter of said circular perforations, said oblong perforation being bounded laterally by a pair of parallel narrow strips each formed by the same ribbon as any other portion of said ribbon fuse link, and each of said pair of parallel narrow strips being provided with overlay means of a silver-severing metal having a lower fusing point than silver.