US2245346A - Electric fuse - Google Patents

Description

June 10, 1941. F. s. KLEIN ELECTRIC FUSE Original Filed Aug. 6, 1937 IN V EN TOR.

Patented June 10, 1941 UNITED STATE PATENT FFIQ Substituted for abandoned application Serial No. 157,288, August 6, 1937. This application May 15, 1939, Serial No. 273,383

10 Claims.

This invention relates to fuses which form a fusible link in an electric circuit; when such fuses are opened, an electric are usually occurs and often is maintained long enough to damage open fuse gaps, or fuse casings; and while a destructive arc endures, serious damage, even personal injury progresses very swiftly where an accidental short circuit takes place.

It is generally understood that the ideal fuse is one in which the melting or volatilization of the link, i. e. a disruption, is prompt, brief, and with the minimum of violence; and such is the object of this invention.

In prior fuses many devices have been employed to limit an electric arc, and this seems to be the solution of the problem; such devices include, holding the link under tension, chemicals, parts which move to interrupt the arc, but an electric arc is swifter than any of these. Other devices are pulverized material to smothe'r an are, or to crush a disrupting link between two broad surfaces, but it is very often the nature of an electric arc to persist in spite of such treatment; even in enclosures providing an indirect passageway for the link, an arc is prolonged through metallic vapor; but my new fuse is not to be confused with any of the aforementioned nor with any device which utilizes the force of a disruption to break a once established arc, for I have provided a partition which stationarily blocks the path of an electric arc, before and during a disruption of the fuse link, without the least hindrance to a necessary disruption.

In this new fuse I use a link which may have end portions or other members of any description, but, at least one intermediate longitudinal section which is a relatively short and more fusible part of the link, the purposes of that arrangement are well known and include localizing a disruption, which frequently is not realized because, by an inductive overload or short circuit between heavy metal bodies in slight contact, a very persistent are often consumes the entire link.

But I insure all the advantages of a short and particularly fusible section in a fuse link, by having an arc barrier of dielectric material in the form of a plate, partition or substantially the same thing, secured transversely to the link, and tightly clamping and tightly confining only the middle part of said short section, which is the part most susceptible to heat and the initiation of volatilization; and by having an end part of said short section extending from or clear of each side of said Partition.

By this arrangement, fusing is retarded at the middle cross-section of the fusible section of the link, which prevents an electric are through the partition and allows only the end parts of that section to be destroyed. Thereby resulting in an important feature of this invention, that is, the partition causes, simultaneously, two relatively small and well separated ruptures in the fuse link, and prevents an are between the remaining portions of the link.

The advantage of those two ruptures in the link is equal to the well known advantage of opening an electric circuit in two well separated places simultaneously, that is, the damage that would result from a single opening in that circuit is importantly reduced.

When my invention is made-up substantially as shown and described, the damage and violence resulting in the link or the external circuit is such as would scarcely be less with any other fusible device having the same current carrying capacity.

The herein described partition, where it contacts the fuse link, is as thin, with respect to its breadth and the associated fuse gap, as is possible for withstanding and preventing an arc, so as to leave a great part of the fuse link as free to be acted upon by excess current as any fuse may be, and the partition may be of uniform thickness as the word partition usually implies; but I add thickness to parts of my partition, to provide body and surface for support or heat dissipation.

The invention above described can be used in any fuse gap whether open or inclosed, it is economical, simple, stationary, and constantly blocking the path of an electric arc; only two end portions of the purposely provided short section of my fuse link can be destroyed; while that short section may show incandescence when disrupted, such is not what I term an arc because it is necessary; the herein mentioned arc is to be understood as that unessential and destructive accompaniment of a disruption in a fuse which many have tried to eliminate.

In the instance of standard N. E. C. fuse gaps, open, or in casings, that part of my partition which grips a ten ampere link, need not be more than one eighth of an inch in thickness, or, less than 15% of the one inch fuse gap, and 15% is also a suitable thickness for a partition in a six inch six hundred ampere fuse gap. However, the spirit of this invention will be carried out if my partition is considerable thicker than indicated,

providing the fusible section of my fuse link is correspondingly lengthened.

Much depends on the material used for the partition and a heat conducting material such as porcelain is preferred for absorbing heat from the link whereby a time lag is obtained to save a fuse link from disruption by an overload of current Which may subside; and to the same end, a support is provided where the link is most susceptible to weakness from heat.

In the accompanying drawing, Fig. 1 is a view of a partly broken cartridg fuse showing the invention which is a partition forming an arc barrier.

Fig. 2 is a view of the fuse link and separated parts of the arc barrier shown at Fig. 1.

Fig. 3 is a sectional view of the arc barrier at Figs. 1 and 2.

Fig. 4 is a view of an arc barrier for open fuse links.

Fig. 5 is a crosssectional view of a screw plug fuse including an economical modification of the arc barrier shown above.

Referring in detail to the drawing, the number I indicates a fuse link preferably flat, having end portions at 2 and 2, and a longitudinally extending intermediate section at 3 which, with respect to the end members, is short and more fusible.

At 4 is a partition forming an arc barrier which is clamped transversely to the link, and tightly clamped so as to tightly confine only the middle part of the fusible section 3 by means which provides a firm heat conducting contact with said middle part, whereby short portions of said fusible section as at 5 and 5 extend free and clear of each side of said partition, the partition extending sufficiently in lateral directions from the section 3 to block the usual path of an electric arc.

The partition may be composed of a plastic material and hardened on the link, or made separate from the link; I prefer a porcelain partition, for its economy, with a concave surface on each broadside as at E and 5, thereby defining a relatively thin midsection I in the partition 4 and edges 8 of greater thickness for dissipating heat absorbed from the link and for supporting th partition, furthermor said concave surfaces are for reflecting metallic vapor away from a disruption in the link.

The partition 4 has two halves 9 and I0 joined edgewise and therewith clamping the middle part of the fusible section 3 in coaxial relation with the partition. While the joined edges of the halves 9 and I I) may be plain, I prefer to have the link passing through the partition in an indirect arc bafiling manner and I have made the juncture of the two halves with a tongue and groove joint the tongue I! being on the half at 9 and the groove I2 on the other half at IO.

In thus joining the two halves of the partition,

a triangular transverse ridge at I3 is formed in the middle of fusible section 3 to correspond with said tongue and groove, and in fuse links composed of metal having insufficient pliability to be so deformed. it will be necessary to preform the ridge I3 on the link. By this arrangement the partition is readily secured in proper relation with the link and the fusible section 3 clamped close in a tortuous arc baffling passageway.

Fig. 1 shows a cartridge fuse comprising, a tubular dielectric casing I4, having at each end a contact terminal I5 and I5 which may be of any type, also a fuse link I attached to said terminals and a partition both of which are arranged as described above.

At Fig. l the partition conforms closely to the cylindrical inside walls of the casing so that the fuse link and partition as a unit can be gently forced into the casing to frictionally hold in the proper position and clamped securely to the fusible section 3, this arrangement divides the easing I4 into two combustion chambers at Iii and I6 with a very short length of the fusible section 3 on each side of the partition or in each chamher. At Figs. 2 and 3 the partition and fuse link are shown in more detail.

Fig. 4 shows a fuse link I and a partition I arranged substantially as described above, but for open fuse gaps; in this instance more porcelain is used in the partition, the better to dissipate heat especially when copper links are used as they very often are hot for long periods.

At Fig. 4 the partition is generally rectangular in outline having, an upper half H, a lower half I 8, on a base I9, with holes 20 and 20 for fastening screws, also two threaded bolts 2| and 2| which extend at right angles from the base I9 and are slipped through holes in the two halves of the barrier 4 to extend above the assembled whole and receive the wing nuts at 22 and, 22 for clamping all together so as to easily replace any parts of the fuse link.

As shown, the middle part of a short fusible section 3 of the link I is clamped between the tongue II and the groove 52 which are on the adjacent edges of the two halves of the partition, again a relatively short portion 5 of the fusible section 3 extends out from each side of the partition-but because of the perspective'view at Fig. 4 the opposite portion 5 does not show. This partition also has a concave surface 6 on each side which is well adapted to reflect conductive metallic vapors in opposite directions when a disruption occurs on both sides of the barrier.

Fig. 5 shows a screw plug fuse comprising, a dielectric casing I l which preferably is of porcelain or material which conducts heat well, the usual screw shell contact terminal 23, and bottom contact terminal 24, a combustion chamber I6 closed at the top by a cap 25 which includes a window 26 of transparent material, a fuse link I such as described above and connected to the terminals 23 and 24.

At Fig. 5 the partition consists of a porcelain disc 4 which is wedged in the combustion chamher so as to clamp only a middle part of the fusible section 3 of the link between the wall of the combustion chamber and the edge of the partition 4 and divide the combustion chamber into two consecutive compartments l6 and I 6 each of which contains a very short end portion of the fusible section of the link, and the two ends of that section is all that may be destroyed when the fuse blows.

With the invention described above, the factor of safety provided by an electric fuse is materially increased by the prevention of unnecessary destruction by an electric are when the fuse link is overloaded; and as has been pointed out, the fuse link can often be saved when the heat of an overload is only sufficient to weaken the link. Moreover the force of gravity will have no effect on the link whatever its position may be. and the object of this invention is attained without in anywise restricting a necessary disruption in the link, without strain on the link, and with no dependence on any sequence of an overload of current.

This application is filed as a substitute for application No, 157,288, filed August 6, 1937.

I claim:

1. In the combination of a fuse link and a partition composed of dielectric material stationed transverse to the fuse link; a fuse link having an intermediate portion which forms a relatively short and more fusible part of the link, a partition tightly clamping and tightly confining only the middle part of said more fusible part of the fuse link and preventing an electric arc thereat, each end part of said fusible part extending clear of said partition and therefore more readily fused than the middle of said fusible part, whereby, excess electric current is caused to produce, simultaneously, two separate and relatively small ruptures of the fuse link.

2. In the combination of a fuse link and a partition composed of insulating material stationed transverse to the fuse link; a fusible link having an intermediate portion which forms a relatively short and more fusible part of the link, a partition tightly clamping and tightly confining only a middle cross-section of said more fusible part of the fuse link, the thickness of the partition being such that each end part of said fusible part of the link extends from the partition into clear space and fusing of said clamped middle cross-section of the fusible part of the link is sufficiently retarded to prevent an electric arc thereat whereby, a disruption of the fuse link is limited substantially to the two end parts of said fusible section.

3. In the combination of a fuse link and a partition stationed transverse to the fuse link; a fuse link having end portions which form the greater part of the link and a more fusible longitudinal section intermediate said end portions, a partition composed of heat conducting dielectric material, said partition tightly clamping and tightly confining only a middle cross-section of said longitudinal fusible section, the thickness of the partition in contact with said middle crosssection of the fusible section being sufiicient to absorb heat from the cross-section and retard the fusing thereof While end portions of said fusible section are being fused.

4. In the combination of a fuse link and a partition stationed in coaxial relation to the link; a fuse link comprising a fusible strip having a relatively short intermediate portion thereof reduced in cross-section and forming a more fusible portion of the strip; a partition composed of heat conducting dielectric material, said partition tightly clamping and tightly confining only the middle cross-section of said more fusible portion to retard fusing thereat While end portions of said more fusible portion are being fused, the length of said more fusible portion being such that an end thereof extends clear of each side of said partition a sufficiently short distance to receive, when weakened by excess current, support from the partition.

5. In the combination of a fuse link and a partition stationed in coaxial relation to the fuse link; a fuse link having a relatively short and more fusible section intermediate less fusible longitudinal portions, a heat conducting dielectric partition comprising two parts, said two parts clamped edgewise together and therebetween tightly clamping and tightly confining only a middle cross-section of said more fusible section, each end portion of said fusible section ex tending clear of said partition.

6. In the combination of a fuse link and a partition stationed in coaxial relation to the fuse link; a fuse link comprising a fusible strip having a relatively short intermediate part thereof reduced in cross-section and forming a more fusible section of the strip, a partition comprising two parts composed of heat conducting dielectric material, said two parts tightly clamping and tightly confining only the middle cross-section of said fusible section, and means to hold said parts in position, the thickness of said two parts of the partition and the length of said more fusible section being such that, sufficient of the fusible section is confined by the partition to retard fusing and prevent an electric arc thereat, while, end portions of said fusible section extend from each side of said partition and may be simultaneously fused, said end portions of the fusible section having sufiiciently short length to receive, until melted by excess current, material support from said partition.

7. In the combination of a fuse link and a dielectric partition stationed in coaxial relation to the fuse link; a fuse link comprising a fiat strip of metal having a relatively short portion thereof reduced in cross-section and located intermediate the ends of the strip, and having a transverse ridge formed on the middle cross-section of said reduced portion of the strip; a partition comprising, a part having on an edge thereof a tongue, a part having on an edge thereof a groove corresponding with said tongue, said edges of the two parts having a thickness which is less than the length of said reduced portion of the strip, clamping means to tightly clamp said two parts edge- Wise across only the middle part of said reduced portion of the strip, and tightly confine said transverse ridge on the strip in a tortuous passage through the partition formed by the tongue and the groove, to prevent an electric are therethrough the partition, and permit the ends of said reduced portion of the strip to be fused simultaneously.

8. In the combination of a fuse link and a partition stationed in coaxial relation to the fuse link; a fuse link comprising a fiat fusible strip having a relatively short intermediate portion thereof reduced and forming a more fusible section of the link, a partition composed of heat conducting dielectric material, and having a relatively thin midsection defined by more thick edges on the partition for dissipating heat absorbed from the midsection, said partition comprising, two half parts having at the midsection of the partition a tongue on one part and a groove on the other part, means clamping said two parts together and therewith tightly confining only the middle cross-section of said fusible section between said tongue and groove, thereby forming a tortouous passage adapted to absorb heat from said fusible section, prevent an electric arc, and permit both ends of the fusible section to be fused.

9. In the combination of a fuse link, a casing therefor having contact terminal, and a partition stationed in the casing transverse to the fuse link; a fuse link comprising a fusible strip having a relatively short section thereof reduced in crosssection intermediate the ends of the strip, a partition composed of heat conducting dielectric material tightly clamping and confining only the middle cross-section of said short section of the strip, the thickness of said partition and the length of said short section being such that the ends of the short section extend from opposite sides of the partition, and may be ruptured simultaneously by excess current, and an electric arc prevented between the ruptures.

10. In the combination of a fuse link, a tubular casing for the link, contact terminals on the 0215- the other of said parts, said thick edges of the partition tightly holding to the inner sides of said casing, and thereby clamping and tightly confining between said tongue and said groove only :the middle cross-sectional portion of said relatively short reduced portion of the fuse link, each end of said reduced portion extending clear of said partition for a short distance to cause, simultaneously, two separated ruptures of the link.

FRANKLIN S. KLEIN.

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