US2414344A

US2414344A - Current limiting fuse

Info

Publication number: US2414344A
Application number: US465206A
Authority: US
Inventors: Chauncey G Suits
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1942-11-11
Filing date: 1942-11-11
Publication date: 1947-01-14
Anticipated expiration: 1964-01-14

Description

Jan. 14, 1.9.47. Q Gl? sun-5 2,414,344

CURRENT LIMITING FUSE Filed NOV. 1l, 1942 Inventor* Chauncey G. Suit 5 b /VWTMH tdHis-:y Attorneg.

'Patented Jan. 14, 19.47

CURRENT LIMITING FSE .Chauncey G. Suits, Schenectady, N. Y., assigner to General Electric Company, a corporation of New York Application November 1,1, 1942, serial No. 465,206

y 7 Claims.

My invention relates to fuses and more particularly to fuses ofthe current limiting type.

Current limiting fuses arevknown'which con# sist in the main of a fusible Aelement in the form of one or more cnductorsof suitable metal such 5 as silver or zinc embedded in an inert granular or refractory arc-extinguishing material of high dielectric strength such` as sand, or relatively finely divided quartz, the conductor or conductors in some instances being wound on a supporting core of high temperature resistant ceramic material.I To these parts are added an enclosing housing and terminals for the conductors.

Upon subjection of such fuse to currents of large magnitude, suchasfupon short circuit, the 15 fusible element attains fusing temperature and dissipation only at a point of reduced crosssec tion, whereupon arcing occurs and the metal va 2o pors rapidly expand to many timesy the volume originally occupied by the fusible element itself. The force of this expansion throws the metal vapors outof the arc path and into the spaces between the granules of inert ller material.

These vapors condense upon the surfaces of the relatively cool granules and no longer are available for current conduction so that arcing is'conf lined to the small space previously occupied by the fusible element. The intimate' physical con- 30 tact between the hot arc column and the relatively cool granules causes an exceedingly rapid transfer of heat from the arc to the granules res sulting in a very high voltage gradient or a high voltage drop per unit length of arc column. The

form a hollow shell or fulguritel consisting 01.4.0 fused quartz if the Aarc-extinguishing material is granular quartz, and a small percentage of metal from which the fusible conductor is made.l This fused shell has the properties of an insulator and in' the normal operation of the fuse doesnot con- 45 stltute a currenteconducting element in the current path.

As` a result of the actions referred toin` the preceding paragraph there is in eect suddenly inserted into the path of the current at the in-V 5o stant of melting of the fusible element, the high l resistance formed by the arc column which initially limits the current to a magnitude which is only a small fraction of the current lwhich the associated is capable of producing. The inserted resistance causes rapid current decay and subsequent interruption of the current flow with negligible mechanical disturbance,there being no gassing or discharge of vapors or particles and practically no noise. Y

I have discovered that if, instead of an arc quenching Jmeans Acomprising an inert granular material, an arc quenching means comprising a pair of flat-spaced surfaces of insulating material such as fused quartz or the like, is used around the fusible element sothat the fusible element is mounted between the plates, the current limiting action of the fuse is increased by a relatively large factor. It is my belief that the reason fog` this higher interrupting ability is dissipates or vaporizes throughout a fusible section of considerable length as distinguished from based upon the following theory. It should be understood that this theory is presented by way of explanation only and I do not desire to be bound by this theory in the event that it is not the true explanation for the greater interruptingv ability of current limitingy fuses embodying my invention. It is believed that the space between the flat surfaces forms a reservoir for the hot gases developed by the arc whereby a large amount of the heat developed is removed by conduction and convection from the immediate vicinitytofthe arc. This action is believed to produce a very satisfactory current limit/ingl action.

It is an object of my invention toprovide a new and improved currentvlimiting fuse having a greater current interrupting ability than curgrent limiting fusesA known heretofore. Further objects and vadvantages of my inven-ll tion will become apparent as the following de scription proceeds and the features of novelty A which-characterize my invention will be pointed Y out with particularity in the claims annexed to and forming a part of this specification.

Referring, now to the drawing, Fig. 1 is a crosssectlonal view of a current limiting fuse embodying my invention in which the fusible element, for the purpose of simplifying the disclosure, has been shown as a straight conductor extending from end to end ofthe fuse enclosure and Figs. 2 and 3 are partial views of modifications embodying'th'e teachingsk of my invention.

'I'he current limiting fuse of Fig. 1 is illustrated as comprising an enclosing Vtubular casing lll of insulating` material such as fiber or glass upon the opposite ends of which are mounted terminals Il as by means of a suitable sal l2. If case; y ing I0 is constructed of glass, then I2 is a suitable glass-to-metalseal. system with which the current limiting fuse is The ends of casing I0 are preferably closed by suitable sealing members I3 upon which vindicia giving infomation concerning the 'fuse can be impressed. The fusible element illustrated at I4 is shown simply as a long conductor such as silver or zinc or the like,

interconnecting two fuse-supporting members I5 f of conducting material which in turn are electrically connected with terminals I I. Fusible element I4 has been illustrated as a single straight conducting member but it should be understood that depending upon the current rating it may comprise one or more parallel conducting members and as will become apparent from the modications shown in Figs. 2 and 3, it may extend by means of a tortuous path from one end of the enclosing casing Ill to the other. Instead of a silver wire, a flat silver foil might also be advantageously used with my invention as will become apparent from the following description.

The arc quenching means of my invention, which I have found to greatly increase the current interrupting ability and current limiting action of the current limiting fuse of my invention, is illustrated in Fig. 1 las comprising a pair of flat plates I6 and I 1 which are mounted in parallel planes along the axis of the fuse casing Ill. For highest current limiting action it may be desirable to limit the space I8 between plates I6 and Il to the diameter of the fusible element Ill so that the plates I6 and Il are actually pressed against the fusible element.` It will be understood that plates vi6 and il are mounted in this position in any-suitable manner as by being suitably clamped between fuse supporting members I5. The volts per centimeter, or voltage gradient, which is indicative of the current limiting action may be decreased somewhat by increasing the sparing I8 between the plates I6 and Il to a valve somewhat greater than the diameter of the fusible element. With this arrangement the voltage-surges produced on the system by virtue of the current'ilimiting action are somewhatl reduced but it is believed to be more satisfactory to obtain the highest voltage gradient possible for the maximum current limiting action, by decreasing the spacing I8 to a minimum and using a stepped wire construction,

Y for example, such as is disclosed in Lohausen Patent 2.157,907`to limit the voltage surges produced due to the very high current limiting action. With the arrangement described the arc The plates I6 and I"I should preferably be constructed from insulating material such as fused quartz', high resistivity glass, fused alumina, opaque fused silica, lava, magnesium oxide, thorium oxide or possibly from other high icsistivity ceramics.

Although I have found that the current limiting'action of the fuse of Fig. 1 is considerably better than current limiting fuses using an inert granular arc extinguishing ller material,- I have found that the addition of such liller material to the disclosure described thusfar, operates as satisfactorily as without such ller and under certain cases it may be desirable to include .such filler material in the space remaining in casing l0.

Normally itis necessary for the fusible elements in a'current limiting fuse to be consid- -erafbly longer than the practicable Alength of the like, around which the fusible element is spirall wound. In Figs. 2 and 3 two such constructions are shown which embody `.the features of the present invention and permit the properties of .the fiat-plate type of arc extinguishing structure.

Referring now to Fig. 2 I have illustrated a ceramic core I9 which may have an H-cros'ssection. The fusible elementI I4 is spirally wound around the ceramic core in the well-knownimanner. Plates and 2i are then placed adjacent the flat surfaces of the core I9 so as to provide for successive portions of' the fusible element the fiat plate geometry described in connection with Fig. l. Flat plates 20 and 2i may be pressed against the fiat surfaces of the core I9 if desired, to obtain the highest voltage gradient. It will be understood that with this type of construction mounted in a suitable enclosing casing I0 and embedded in a filler of an inert granular arc extinguishing materia1 such as sand indicated at-22, a sort of a composite current limiting fuse is obtained having the llat plate geometry for a portion thereof and the well-known construction of a fusible element embedded in sand v or the like for the other portion. The dileren- I arrangement to the composite fuse construction of Fig. 2 in which a ceramic core in the form of a hollow square 23 is provided upon which the fusible element comprising one or more parallel conductors is spirally wound. In this case a plurality of flat plates 2t are provided which are respectively mounted adjacent the flat surfaces of the hollow square core 23. ment disclosed in Fig. 3 a relatively large portion of the fuse would employ the Ilat plate properties described above as contrasted with Fig. 2.

From the above discussion i-t willbe obvious that I have provided a new and improved current limiting fuse which is simple in construction and which has a higher current interrupting ability and current limiting action than similar fuses used heretofore. r

While I have disclosed certain particularernbodiments of my invention, it will be apparent to those skilled in the art that my invention is not limited to the particular constructions shown but that changes and modifications may be made without departing from the spirit and scope of my invention and I aim in the appended lclaims to cover all such changes and modifications.

What I claim as new and desire to secure by Letters Patent of the United States is:

l. In a high tension fuse of the current linuting type, an enclosing casing, an insulating support mounted in said casing,la conductor spirally wound on said insulating support, said insulating support having at least one flat surface, and a flat plate of insulating materia1 disposed adjacent to and parallel with said flat surface to enclose portions of said spirally wound conductor between said flat surface and said flat plate, said conductor'being adapted to dissipate throughout a fusible section of considerable length as distinguished from dissipation only at a point of reduced cross section upon subjection of said fu.- sible section to excess current of large magnitude, said flat surface and at plate providing an arc With the arrange-v spirally wound conductor between said fiat plates and fiat surfaces, said conductor being adapted to dissipate throughout a. fusible section of con` siderable length as distinguished from dissipation only ata pointof reduced cross section upon subjectionY of said fusible section to excess cur-4 rent of large magnitude, said. fiat surfaces providing an arc quenching means, capable yof pro-l ducing a very high voltage 4gradient upon operation of said fuse so as toexert a high current limiting action.

3. In a high tension fuse of the current limiting type comprising an enclosing casing, a longitudinally ribbed H-shaped insulating support having two fiat surfaces mounted in said casing, a conductor spirally wound on -said insulating support, said conductor being adapted to dis.-y sipate throughout a fusible section of considerable length as distinguished from dissipation only at a point of reduced cross section upon subjection of said fusible section to excess current of large magnitude, and aflat plate of insulating mate: rial associated with each of the flat surfaces of said insulating support disposed adjacent' to and parallel with said flat surfaces to enclose portions of said spirally wound conductor between said ilat surfaces and said fiat plates, said fiat surfaces and plates providing anlarc quenching means capable of producing a very high voltage gradient upon operation of said fuse so as to exert a high current limiting action.

4. In a high tension fuse of the current limiting type comprising an enclosing casing, an in-I sulating support in the shape of a hollow square having a plurality of flat surfaces mounted in said casing, a conductor spirally wound on said insulating support, said conductor being adapted to dissipate throughout a fusible section of considerable length as distinguished from dissipation only at a point of reduced cross section upon subjection of said fusible section to excess current of vlarge magnitude, and a plurality of fiat plates of insulating material one associated with each of the fiat surfaces of said insulating support and disposed adjacent toand parallel with -said fiat surfaces to enclose portions of said spiport having at least one flat surface mounted in said casing, a conductor spirally wound on said insulating support said conductor being 'adaptedv y plate. f

' 6. A high tension fuse of the current limiting type `including in combination a cylindrical casing `of insulatingv material, a conductor mounted within said casing and adapted to dissipate throughout a fusible section of considerable length as distinguished from dissipation only at a point of reduced cross-section uponv subjection of the fusible section to excess current of large magnitude, and arc quenching means comprising two members of insulating material I mounted within said casing so as to extend longirally wound conductor between said fiatsurfaces and said flat plates.

5. In a high tension fuse of the current limiting type. an enclosing casing, an insulating suptudinally'thereof, each of said members having a flat surface extending throughout substantially the whole length of said casing and said members being positioned in said casing with said fiat surfaces on opposite sides of and adjacent the conductor whereby to exert s, high current limiting action upon subjection of said conductor to excess current of large magnitude.

7. A high tension fuse of the current limiting type `including in combination a cylindrical casing of insulating material, two terminals respectively mounted at the ends of said casing, two fuse supports respectively mounted-at the ends of said casing in current conducting relationship with the terminals at the respective ends, a conductor mounted within said casing and interconnectingsaid fuse supports, said conductor being adapted' to dissipate throughout a fusible section oi' considerable length as distinguished from dissipation only at a-point of reduced cross-section upon subjection of the fusible section to excess current of large magnitude, and arc quenchingI means comprising two members of fused quartz mounted within said casing so as to extend longitudinally thereof, each of said members having a flat surface extending from one of said fuse supports to the other and said members being positioned with said flat surfaces closely spaced and pressing against the fusible section of said conductor from opposite sides thereof whereby to exert a high current limiting action upon subiection yof the conductor to` excess current of large magnitude.

. CHAUNCEY G. SUITS.