US2662140A - Supercurrent fuse - Google Patents

Description

Dec. 8, 1953 F. J. KOZACKA 2,662,140

SUPERCURRENT FUSE Filed Aug. 15, 1952 3 Sheets-Sheet l .1.-/ /0AA/FF Ma 55 0 34 //0 /8 Dec. 8, 1953 F. J. KOZACKA SUPERCURRENT FUSE Filed Aug. 15, 1952 3 Sheets-Sheet 2 Ma b Fi' J K024101391,

1953 F. J. KOZACKA 2,662,140

SUPERCURRENT FUSE Filed Aug. 15, 1952 3 Sheets-Sheet 3 Patented Dec. 8, 1953 SUPERGURRENT FUSE Frederick J. Kozacka, Aniesbury, Mass., assignor to The Chase-Shawmut Company, a corporation of Massachusetts Application August 15, 1952, Serial No. 304,585

7 Claims.

This invention relates to high capacity fuses, i. e. fuses which have a high current-carrying capacity, e. g. a current-carrying capacity in the order of several thousand amperes.

A general object of the invention is to provide a fuse having the aforementioned order of current-carrying capacity and capable of effecting interruption of short-circuit currents before the short-circuit currents reach the peak of the maximum available short-circuit current of the circuit which is to be protected.

Such current limiting action can be effectively achieved by composite fuse structure comprising a great number of integrated fuse units adapted to be arranged in parallel in the circuit to be protected. If a relatively high current-carrying capacity and a relatively low maximum letthrough current are required, the number of fuse units which must be integrated into a composite fuse structure may be very large. It has been found desirable, for instance, to integrate between 200 and 300 single fuse units into a composite fuse structure designed for a currentcarrying capacity of 5000 amperes at a circuit voltage in the order of 750 volts if the available short-circuit current is in the order of 100,000 R. M. S. amps. The composite fuse structures of the prior art do not lend themselves to integration into them of such large numbers of single fuse units.

It is therefore a special object of the invention to provide composite fuse structures which lend themselves to integration into them of considerably larger numbers of fuse units than could be integrated into composite fuse structures which were known heretofore.

Another special object of this invention is to provide a composite fuse structure enabling to readily assemble a very large number of fuse units by subdividing the total number of fuse units into groups of use units and integrating each group of fuse units into a subassembly unit.

Still another special object of the invention is to provide a composite fuse structure which is made up of a very large number of separate fuse units and wherein means having great mechanical strength are provided for the lateral support of the casing of each separate fuse unit to increase the ability of said casing to withstand the high pressures which may be generated therein.

Another object of the invention is to provide a composite fuse structure comprising a large number of single fuse units which are tied together by a common insulating support to form a self-sustained structural unit, the casings of said single fuse units being pressed into said common support with a press fit to greatly increase the mechanical strength of said casings.

Very high pressures must be applied when mounting on a composite fuse structure comprising a plurality of identical fuse units if the contacts of said fuse units and said common terminal elements are to be joined by pressure only, i. e. without solder or brazing joint or spot weld. While it is very desirable to join contact elements by pressure only, yet the application of very high pressures entails generally the danger of fracturing the casings of the fuse units when mounting common terminal elements or common terminal blocks thereon.

It is therefore another special object of the invention to provide a composite fuse structure comprising a plurality of identical fuse units which have common terminal elements applied under considerable pressure and wherein the casings of the fuse units are not subjected to the danger of fracture when the terminal elements are being secured in place by the action of pressure.

Another special object of the invention is to provide a composite fuse comprising a very large number of single fuse units which are combined in such a way as to limit space requirements and the peak of the let-through current but as to obtain an optimum of current carrying ability.

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

Fig. 1 is substantially a longitudinal section of a single fuse unit;

Fig. 2 is substantially a longitudinal section of a composite fuse structure comprising a very large number of fuse units combined to form a plurality of smaller groups of which each group forms a self-sustained subassembly unit;

Fig. 3 is a cross-section along 33 of Fig. 2;

Fig. 4 is substantially a longitudinal section of one of the subassembly units of Fig. 2, shown on a larger scale;

Fig. 5 is a cross-section along 55 of Fig. 4;

Fig. 6 is an elevation of one of the terminal elements of the subassembly unit shown in Figs. 4 and 5;

Fig. '7 is a section along 1-! of Fig. 6;

Fig. 8 is an elevation of the insulating structure used for tying together a plurality of fuse units to form the subassembly unit of the kind shown in Figs. 4 and Fig. 9 is a section along 9-9 of Fig. 8, and

Fig. is a perspective view of the structure shown in Figs. 2 and 3 associated with a system of bus bars.

Referring now to the drawing and more particularly to Fig. 1 thereof, showing one single fuse unit, reference numeral II) has been applied to the casing of the fuse unit and reference numeral II to the fuse link thereof. Fuse link ll consists preferably of silver or copper. The casing I0 is filled with an arc-quenching filler l2, such as clean quartz sand. If desired, an additional filler I3 may be provided in casing I0. The additional filler I3, may consist of a pulverulent substance which does not fuse under the action of the heat of the arc, forming an insulating barrier effective during the time the quartz sand filler I2 is fused and hot and forming a good conductor of electricity. Filler I3 may consist of chalk which evolves gases under the heat of the are, thus requiring a casing of considerable mechanical strength. Casings I0 of glass-cloth laminates impregnated with suitable synthetic resins have sufiicient mechanical strength to permit the use of limited quantities of gas evolving fillers therein. Where different kinds of fillers are provided within one casing the fillers should be separated by a washer M or like partition means. Fuse link I I is provided with a plurality of substantially equidistant perforations Ila defining a plurality of restricted cross-section portions. An additional restricted cross-section portion is formed by a neck llb having a smaller cross-sectional area than the cross-sectional area of link I I at the points where the perforations Ila are situated. The purpose of neck Ilb is to limit the let-through current which is allowed to flow through link II to a predetermined relatively small value without change in rating of the device. A rivet llc of tin is inserted into one of the perforations Ila. The perforation Ila receiving tin rivet He is situated Within the portion of the casing I0 accommodating the non-fusing gas-evolving filler I3. Rivet llc fuses on the occurrence of small protracted overloads, thus initiating interruption of the circuit. At the occurrence of short-circuit currents, interruption of the circuit is initiated at the neck I lb. A pair of terminal caps Ma, l4-b is arranged at the ends of easing l0 and conductively interconnected by link I I. Terminal caps Ida, Nb are mounted on casing I0 by application of considerable pressure to provide a structure capable of withstanding internal pressures of large magnitude. A circular pressed-in portion [5a, [5b, respectively, provided in each cap l4a, Nb and projecting into the casing l0 tends to greatly increase the mechanical strength of the fuse unit thus precluding destruction thereof by internal excess pressure. Fuse link II is conductively connected to the terminal caps Ma, Mb by appropriate solder joints as generally applied in the fuse art for this purpose.

The structure shown in Fig. 1 is substantially the same as that disclosed in United States Patent 2,592,399 to W. S. Edsall et al., Current-Limiting Fuse, issued April 8, 1952, and in United States patent application Ser. No. 208,548, Frederick J. Kozacka, Current-Limiting Fuses, filled January 30, 1951, both assigned to the assignee of the present invention.

The composite structure shown in Figs. 2 and 3 is designed to have a current-carrying capacity Cir of 5000 amps. and a voltage rating of 750 volts. It comprises thirty-one subassembly units and each of these subassembly units comprises seven current-limiting fuse units of the type shown in Fig. 1. In other words, the composite fuse structure shown in Figs. 2 and 3 comprises thirtyone times seven fuse units, i. e. two-hundredseventeen fuse units. In spite of this large number of fuse units integrated into one single highcapacity fuse structure the assembly of the fuse units does not involve particular difficulties. This is due to the formation of a number of subassembly units, as will be described below in greater detail.

The subassembly units comprised in the struc ture shown in Figs. 2 and 3 each include a pair of spaced subassembly terminals IS, an insulating structure I! arranged in the space between the pair of subassembly terminals l6 and a plurality of fuse units I8 mechanically tied together by said insulating structure.

The insulating structures H are substantially in the shape of cylindrical bodies each having seven parallel passageways or bores I'Ia of which each is adapted to receive one fuse unit Ill. The geometry of insulating structures IT can best be seen from Figs. 8 and 9. Structures l'l consist preferably of a glass cloth laminate which is impregnated with a synthetic resin as, for instance, a melamine resin. The laminations of structures I1 and the fuse-unit-receiving cylindrical passageways or bores l'la provided therein are arranged at right angles, which makes for considerable mechanical strength in a direction radially of the cylindrical passageways or bores As shown in Figs. 2 and 3, the composite fuse structure is provided with a pair of spaced main terminals I9, each having an electrical connector in the shape of a multiple blade contact 20. The main terminals consist each of a solid disc of copper and both main terminals are enclosed within a shell 2l of fiber-reinforced insulating material. Shell 2| encloses all the subassembly units by which the composite fuse structure is formed and is secured to the main terminals [9 by means of a plurality of substantially radially arranged steel pins 22. If desired a pulverulent filler 30, as, for instance, quartz sand may be arranged within shell 2| in the interstices formed between the subassembly units arranged therein. Each pair of subassembly terminals I6 is in immediate electrical contact with one of said pairs of main terminals l9. To this end each sub-- assembly terminal is provided with a projection Ilia engaging a juxtaposed recess lBa in the main terminals l9. The terminal caps I4a, llb of each set of fuse units included in a subassembly unit are in immediate electrical contact with one pair of subassembly terminals l6. To this end subassembly terminals l6 are provided with aplurality of recesses IBb each adapted to receive one terminal cap Ila or Nb of one fuse unit. Caps 23 of thin sheet metal close the axially outer ends of the composite fuse structure.

As indicated in Figs. 1 and 2, blade contacts are provided with transverse bores 20a for inserting the composite fuse structure according to this invention into an electrical circuit comprising a bus structure.

In Fig. 10 reference numeral 24 has been applied generally to the composite fuse structure according to this invention and reference numeral 25 indicates a bus bar system. The blade contacts 20 of the composite fus structure are arranged in interleaving relation with the bus bars of the bus bar system 25 and both are clamped together by means of screws 26, providing the amount of contact pressure required to minimize I 1 losses.

In Fig. 10 some of the subassembly units I1 have been shown to be cut by a transversal plane which has been indicated in a general way by cross-hatching without illustrating the structural details of the different parts situated within this transversal plane.

Let n be the number of fuse units which are integrated into the composite fuse structure and p be the number of subassembly units Which form integral parts of said structure. p is an integral number and n a multiple of p. The insulating block I! forming part of each subassembly unit has n/p parallel passageways or bores Ila, each substantially equal in diameter to the outer diameter of the casing ID of each said 12 fuse units. Each of the n fuse units aocomodated in one passageway or bore Il'a projects with its terminal caps Ma, Mb beyond the passageway in which its casing I is held.

As can best be seen in Fig. 4, the subassembly terminals l6 rest with their axially inner ends on the insulating block ll which thus forms an abutment precluding terminals l6 to be pressed too far in a direction longitudinally of casing when subassembly terminal elements 16- are being mounted on caps Ma, [4b or when the main terminal elements l9 are being mounted on subassemb y terminal elements It under considerable pressure by means of a hydraulic press.

The number of pairs of subassembly terminal elements 16 is equal to the number of subassemblies, i. e. equal to p, and each subassembly terminal element I6 is common to n/p fuse units and in immediate contact with n/p terminal caps I la, Mb. Each main terminal element I9 is common to p subassembly terminal elements and in immediate electrical contact therewith.

Both the subassembly terminal elements I6 and the main terminal elements [9 have a considerable heat absorbing and heat dissipating ability which is required for achieving a drastic limitation of fault currents, i. e. for maintaining the let-through currents well below the peaks of the available short-circuit currents.

A single composite fuse structure of the kind shown requires considerably less space than a number of non-integrated fuse structures arranged side by side and connected in parallel in the circuit to be protected and having a com bined current carrying capacity equal to the current carrying capacity of the integrated fuse structure shown.

The lateral casing support provided by the insulating blocks i6 is stronger than the lateral casing support provided in any prior art composite fuse structure of which I am aware and enables therefore to admit higher internal gas pressures within the casings Ill than in any prior art composite fuse design.

Because the number of fuse units comprised in each subassembly unit is relatively limited, no mechanical difficulties are involved in assembling the parts which go into a subassembly unit. The limitations as to the number of subassemblies which go into a composite fuse structure tends to greatly reduce the mechanical difficulties involved in assembling all the parts which go into a complete composite fuse structure.

It will be understood that I have illustrated and described herein a preferred embodiment of the invention and that various alterations" bly terminals, an insulating structure arranged in the space between said pair of subassembly terminals, a plurality of fuse units, and joint tie means of insulating material for integrating said plurality of fuse units into a composite self-sus-.

tained structural unit, each of said pair of subassembly terminals being in immediate electrical contact with one of said pair of main terminal elements, each fuse unit of each said plurality of fuse units including a casing, a pulverulent arcquenching filler within said casing, a fuse link.

within said filler, and a pair of terminal caps arranged at the ends of said casing and conductively interconnected by said link; each of the terminal caps of each said plurality of fuse units included in each said subassembly units being in immediate electrical contact with one said pair of subassembly terminals.

2. In a high capacity fuse the combination of a pair of spaced main terminal elements each having an electrical connector and each being provided with a plurality of main terminal recesses on juxtaposed surfaces thereof, a plurality of self-sustained subassembly units each including a pair of spaced subassembly terminals, each of said pair of subassembly terminals projecting into one of said pair of main terminal recesses and each of said pair of subassembly terminals being provided with a plurality of subassembly terminal recesses on juxtaposed surfaces thereof, each said subassembly units comprising a plurality of fuse units, each said plurality of fuse units including a casing, a pulverulent arc-quenching filler within said casing, a fuse link within said filler and a pair of terminal .-caps arranged at the ends of said casing and conductively interconnected by said link, said pair of terminal caps of each of said plurality of fuse I units projecting into one juxtaposed pair of said subassembly terminal recesses.

3. A high capacity fuse comprising n fuse units each including a tubular casing, a pulverulent arc-extinguishing filler within said casing, a fuse link within said filler and a pair of terminal caps arranged at the ends of said casing and conductively interconnected by said link, 11 subassembly units each comprising a block of insulating material defining n/p parallel passageways each substantially equal in diameter to the outer diameter of said casing of each said 12 fuse units, each of said 11 fuse units being accommodated in one of said passageways and projecting with said pair of terminal caps thereof beyond said one of said passageways, p pairs of spaced subassembly terminal elements, each said subassembly terminal elements common to n/p said fuse units and each in immediate electrical contact with n/p of said terminal caps, and one pair of spaced main terminal elements, each of said pair of main terminal elements common to 11 said subassembly terminal elements and in immediate electrical contact therewith, 11 being an integral number and n a multiple of p.

4. A high capacity fuse comprising n fuse units each including a tubular casing, a pulverulent arc-quenching filler within said casing, a fuse 7. linkwithin-sai'd filler and a pair of terminal-heaps arranged at the ends =of said casing and conductively interconnected by said link, p subassembly units each "comprising a cylindrical block made of a glass cloth base synthetic resin laminate having n/p parallel bores extending in a direction transversally of the Jlaminations of "said block, each said bores being substantially equal in diameter to the outer diameter of said casing of each said 11. fuse units, each of said n fuse units being accommodated in one of said bores and projecting with said pair of terminal caps thereof beyond said one of said bores, 13 pairs of spaced subassembly terminal elements, each of said pairs of subassembly terminal elements being common to n/p of said fuse units and each in immediate electrical contact with n/p of said terminal caps, and one :pair of spaced main terminal elements, each of said pair of main terminal elements being common to p said subassembly terminal elements and each in immediate electrical contact therewith, p being an integral number and n a multiple of p.

5. A high capacity fuse comprising n fuse units each including a tubular casing, a pulverulent arc-extinguishing filler Within said casing, a fuse link within said filler and a pair of terminal caps arranged at the ends of said casing and conductively interconnected 'by said link, p. subassemb-ly units each comprising a cylindrical block of solid insulating material defining n/p parallel passages each substantially equal in diameter to the external diameter of said casing of each said n fusesunits, each of said n fuse units being accommodated :in one of said passages and projecting with said pair of terminal caps thereof beyond said one of :said passages, 17 pairs .of spaced subassembly terminal elements, each of said pairs of subassembly terminals being provided on juxtaposed surfaces thereof with n/p subassembly terminal recesses and each said recesses being engaged by one of said terminalcaps, and one pair of spaced main terminal elements, each or said'pair of main terminal elements being provided on ,juxtaposedsurfaces thereof with p main terminal recesses each being engaged by one :of said subassembly terminal elements, 10 being an integral number and n a multiple of p.

6. A multiple time structure comprising m hree units each including -a tubular casing, a pu'lverulent rarc-extinguishing filler w-ithinsaid casing, a

fuse link within-said filler and a pair of terminal caps arranged at the end of said-casingand-con ductively interconnected by said link, a cylindrical block of solid insulating material defining mpara-llel passages each substantially equal in diameter to the external diameter of said casingo'f each said m fuse units, each of said m fuse being accommodated in one of said passages and projecting with said pair ofterminal'ca-ps thereof beyond said one :of said passages, and a pair 'of spaced terminal elements, each of said pair 'ofterminal elements being common to said m ruse units and each in immediate electrical contact with m 2 of said terminal-caps,-m being an integrail number.

7. a highcapacity fuse the-combination of-a pair of spaced termina'l elements each havinga 'n' electrical connector and each being provided with a plurality of :main terminal recesses on flux-ta posed surfaces thereof, a plurality of 'subassembly units each includinga pair ofspacedsu-bassem'bly terminals, an insulating structure arranged Wit-hin the space between said subassembly terminals and :defin-ing -'a plurality of parallel passages and a pluralityor fuse units each arranged in one of: said passages and supported 'by said insulating structure, each of said subassembly terminals within said filler and a pair-of terminal capsarranged at the ends "or said casing and conducti-vely interconnected by said link, said pair of terminal caps of each of said plurality of fuse units projecting into one i-u-xtaposed pair ofsaid subassem'bly recesses.

FREDERICK J.. KOZACKA.

No references cited.

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