Fuse with carbon fiber fusible element

A fuse includes a body, a first conductive terminal coupled with a first end of the body, and a second conductive terminal coupled with a second end of the body. The body, the first conductive terminal, and the second conductive terminal define an exterior of the fuse. The fuse also includes an interruption assembly including a fusible element. The fusible element includes carbon fiber, is disposed on a conductive path between the first conductive terminal and the second conductive terminal, and is configured to break when a current through the fusible element exceeds a predetermined current.

BACKGROUND

The disclosed concept pertains generally to fuses. The disclosed concept also pertains to expulsion type fuses.

2. Background Information

Fuses, such as for example, medium voltage fuses, have traditionally used silver or other metal conductors as fusible element material. The size of the cross-section of the fusible element determines the maximum current that can be passed through the fusible element before melting. When relatively low amperage rated fuses are needed, fusible elements with relatively smaller cross-sections are employed. As the cross-section of the fusible element is reduced, the strength of the fusible element is also reduced.

Some fuses also incorporate blown fuse indicators such as a mechanical spring indicator or a chemically activated indicator. In one prior fuse, which uses a mechanical spring indicator, a fusible element is used to bias a spring. When the fusible element breaks, the spring is released which in turn deploys an indicator to indicate that the fuse is blown. In another prior fuse, which uses a chemically activated indicator, a fusible element is used to bias a firing pin. When the fusible element breaks, the firing pin is released which in turn causes a small explosion that deploys an indicator to indicate that the fuse is blown. In both the mechanical spring indicator and the chemically activated indicator, tension is applied to the fusible element. However, as the amperage rating of the fuse is reduced, the strength of the fusible element is also reduced. At relatively low amperage ratings, the tension applied to the fusible element by the mechanical spring indicator or the chemically activated indicator can cause the fusible element to prematurely break.

Expulsion type fuses face a similar difficulty. In one prior expulsion type fuse, tension is applied to the fusible element by a spring such that when the fusible element breaks, the spring pulls the portions of the fusible element away from each other. However, as the amperage rating of the fuse is reduced, the strength of the fusible element is also reduced. When the amperage rating of the fuse becomes too low, the tension applied by the spring can cause the fusible element to prematurely break.

It thus would be desirable to provide an improved fuse that overcomes these and other shortcomings associated with the relevant art.

SUMMARY

These needs and others are met by embodiments of the disclosed concept in which a fuse includes a fusible element which includes carbon fiber.

In accordance with one aspect of the disclosed concept, a fuse comprises a body, a first conductive terminal coupled with a first end of the body, and a second conductive terminal coupled with a second end of the body. The body, the first conductive terminal, and the second conductive terminal define an exterior of the fuse. The fuse also comprises an interruption assembly including a fusible element. The fusible element includes carbon fiber, is disposed on a conductive path between the first conductive terminal and the second conductive terminal, and is configured to break when a current through the fusible element exceeds a predetermined current.

The interruption assembly may further include an indicator assembly including an indicator member structured to provide a visible indication when the fusible element breaks

In accordance with another aspect of the disclosed concept, an expulsion type fuse comprises a body, a first conductive terminal coupled with a first end of the body, and a second conductive terminal coupled with a second end of the body. The body, the first conductive terminal, and the second conductive terminal define an exterior of the fuse. The fuse also comprises a fusible element including carbon fiber. The fusible element is disposed on a conductive path between the first conductive terminal and the second conductive terminal, and is configured to break when a current through the fusible element exceeds a predetermined current. The fuse also comprises a spring structured to apply tension to the fusible element such that a first portion of the fusible element moves away from a second portion of the fusible element when the fusible element breaks.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As employed herein, the term “electrical conductor” shall mean a wire (e.g., solid; stranded; insulated; non-insulated), a copper conductor, an aluminum conductor, a suitable metal conductor, or other suitable material or object that permits an electric current to flow easily.

As employed herein, the statement that two or more parts are “connected” or “coupled” together shall mean that the parts are joined together either directly or joined through one or more intermediate parts. Further, as employed herein, the statement that two or more parts are “attached” shall mean that the parts are joined together directly.

As employed herein, the term “low voltage” shall mean any voltage that is less than about 1000 VRMS.

As employed herein, the term “medium voltage” shall mean any voltage greater than a low voltage and in the range from about 1000 VRMSto about 38 kVRMS.

As employed herein, the term “high voltage” shall mean any voltage that is greater than about 59 kVRMS.

FIG. 1shows an expulsion type fuse1according to an example embodiment of the disclosed concept. A hollow insulating body10having a first conductive terminal11coupled at one end and a second conductive terminal12coupled at the other opposite end define an exterior of the expulsion type fuse1. The conductive terminals11,12can be, for example and without limitation, ferrules or metallic caps. The conductive terminals11,12are electrically connected by a conductive path formed inside the body10.

FIG. 2shows an interior of the expulsion type fuse1. The interior of the expulsion type fuse1includes a fusible element13and an arcing rod14disposed on the conductive path between the conductive terminals11,12. The fusible element13includes carbon fiber, such as for example, a plurality of strands of carbon fiber. The fusible element13is electrically connected between the first conductive terminal11and the arcing rod14. The fusible element13is structured such that it breaks (e.g., melts) when a current therethrough exceeds a predetermined level, thus interrupting the flow of current through the expulsion type fuse1. The arcing rod14is electrically connected between the fusible element13and the second terminal12. The distal end of the arcing rod14is coupled with an indicator15.

The expulsion type fuse1further includes an indicator assembly. The indicator assembly includes the indicator15along with a housing16and a spring17. Together, the fusible element13, the arcing rod14, and the indicator assembly form an interruption assembly.

The spring17is included in the housing16and the housing16couples the spring17with the arcing rod14such that the arcing rod14moves in conjunction with compression and expansion of the spring17. When the expulsion type fuse1is assembled, the spring17is compressed to a non-relaxed state and the fusible element13is coupled between the arcing rod14and the first terminal11to maintain the spring17in the compressed state. When the fusible element13breaks, the spring17is released from its compressed state and expands.

The expansion of the spring17pushes the arcing rod14toward the second conductive terminal12. The indicator15moves in conjunction with the arcing rod14and, when the spring17has expanded, a portion of the indicator15extends through an opening the second terminal12to the exterior of the expulsion fuse1(as shown in phantom line inFIG. 2) to provide an indication that the expulsion type fuse1has blown.

The movement of the arcing rod14also causes the remaining portions of the fusible element13to move away from each other. This movement lengthens the arc that is created when the fusible element13breaks.

The interior of the expulsion type fuse1further includes a chamber18. An arc-extinguishing material19is included in the chamber18. The arc-extinguishing material19may be made of boric acid or any other material that emits an arc-extinguishing gas when exposed to an electric arc. The lengthening of the arc and the arc-extinguishing gas assist with quenching the arc.

Maintaining the spring17in the compressed position places the fusible element13under tension. As the amperage rating of the expulsion type fuse1is reduced, the cross-sectional area of the fusible element13is also reduced, thus increasing the possibility that the fusible element13will prematurely break due to the tension placed on it by the spring17. However, carbon fiber can withstand a comparatively larger tension than other typical fusible element materials such as silver alloy or nickel-chrome alloy. As such, the expulsion type fuse1employing the fusible element13which includes carbon fiber can achieve a relatively lower amperage rating.

FIG. 3shows a current limiting fuse2in accordance with another example embodiment of the disclosed concept. A hollow insulating body20having a first conductive terminal21coupled at one end and a second conductive terminal22coupled at the other opposite end define an exterior of the current limiting type fuse2. The conductive terminals21,22can be, for example and without limitation, ferrules or metallic caps. A conductive path through the current limiting type fuse2electrically connects the conductive terminals21,22. As shown inFIG. 3, the body20has an elongated form.

FIG. 4shows an interior of the current limiting type fuse2. A first fusible element23is electrically connected on a first conductive path between the conductive terminals21,22. The first fusible element23can be, for example and without limitation, a restraining element. Additionally, second fusible elements24are electrically connected on other conductive paths between the conductive terminals21,22. The second fusible elements24can be, for example and without limitation, main fusible elements. When the current flowing through the current limiting type fuse2exceeds a predetermined value, the second fusible elements24break (e.g., melt) and then the first fusible element23breaks (e.g., melts). The first fusible element23can have a relatively higher resistance than the second fusible elements24, thus causing the second fusible elements24to break first. When the second fusible elements24break, the current flowing through the current limiting type fuse2flows through the first fusible element23, thus causing it to break as well.

The current limiting type fuse2shown inFIGS. 3 and 4includes a chemically activated indicator. An indicator assembly is located at one end of the current limiting type fuse2. The indicator assembly includes a firing pin25, a primer26, an explosive27, and an indicator28. The first fusible element23is coupled to the firing pin25and restrains the firing pin25so it stays in the retracted position. When the first fusible element23breaks, the firing pin25is released, which in turn sets off the primer26and triggers the explosive27. The explosion pushes a portion of the indicator28(shown in phantom line drawing inFIG. 4) through an opening32in the first conductive terminal21to the exterior of the current limiting type fuse2as an indication that the current limiting type fuse2is blown. Together, the indicator assembly along with the first and second fusible elements23,24form an interruption assembly.

The interior of the current limiting type fuse2can also include a chamber29filled with an arc-quenching material30such as, for example and without limitation, sand. When the first or second fusible elements23,24break, the sand collapses on the broken portion of the fusible elements23,24, thus helping to quench the arc.

The first fusible element23includes carbon fiber, such as for example, a plurality of strands of carbon fiber. Restraining the firing pin25places tension on the first fusible element23. However, carbon fiber can withstand relatively high tensions. As such, the first fusible element23can employ a relatively small amount of carbon fiber and have a relatively small cross-section. Thus, the current limiting type fuse2can achieve relatively low amperage ratings.

Selected sections of the first fusible element23can use fewer strands than other sections of the first fusible element23. The sections which use fewer strands have a smaller cross-section, and thus will break at a relatively lower current than other sections. As such, the location or locations at which the first fusible element23breaks can be controlled based on the number of carbon fiber strands that are used in each section of the first fusible element23.

The second fusible elements24can also include carbon fiber, such as for example, a plurality of strands of carbon fiber. Selected sections of the second fusible elements24can use fewer strands than other sections of the second fusible elements24, thus allowing control of the location or locations at which the second fusible elements24break. For example, the second fusible elements24can be configured to break at multiple points that are relatively evenly spaced apart from each other.

FIG. 5Ashows a fusible element including a single wire such as, for example, a typical fusible element made of silver alloy or nickel-chrome alloy.FIG. 5Bshows a fusible element including a plurality of strands of carbon fiber in accordance with the disclosed concept. Using a plurality of strands of carbon fiber as a fusible element allows strands to be added or removed to change the size of the cross-section of the fusible element or a portion of the fusible element. For example and without limitation, one portion of the fusible element can have outer strands33and inner strands34, whereas another portion of the fusible element can a number of the outer strands34removed. As such, the portion of the fusible element having the number of the outer strands33removed will have a smaller cross-section and break before the portion where the outer strands33are not removed. It is contemplated that any number of strands may be added or removed from any portion or portions of the fusible element without departing from the scope of the disclosed concept. In a typical fusible element, which is a single wire, the entire fusible element may need to be replaced to change the cross-sectional area of the fusible element.

While the expulsion type fuse1shown inFIGS. 1 and 2includes a mechanical spring indicator and the current limiting type fuse2shown inFIGS. 3 and 4includes a chemically activated indicator, the disclosed concept is not limited to these examples. The expulsion type fuse1and the current limiting type fuse2can each include any suitable type indicator assembly. For example and without limitation, the expulsion type fuse1can include a chemically activated indicator and the current limiting type fuse2can include a mechanical spring indicator. Additionally, it is contemplated that the indicators can be omitted from the expulsion type fuse1or the current limiting type fuse2without departing from the scope of the disclosed concept.

The expulsion type fuse1or the current limiting type fuse2can be suitably employed as medium voltage fuses. However, the disclosed concept is not limited thereto. It is contemplated that the expulsion type fuse1or the current limiting type fuse2can be modified for use at any suitable voltage (e.g., without limitation, high voltage) without departing from the scope of the disclosed concept.

In both the expulsion type fuse1and the current limiting type fuse2, any known methods may be used to mechanically connect the fusible elements13,23to other components of the fuses1,2without departing from the scope of the invention. For example and without limitation, the fusible elements13,23can be mechanically connected to other components of the fuses1,2by crimping, pinching, knots, loops, or any other suitable connection method.