The technical field generally relates to interrupting equipment in power distribution systems, and more particularly relates to fuse cutouts used in connection with such systems.
Power distribution systems include a variety of subsystems designed to protect transformers and other components from overload conditions and current surges. One such system is the fuse cutout—a protection device that is part fuse, part switch, and which is often used in connection with overhead feeder lines.
Fuse cutouts typically include a fuse tube rotatably coupled, at its lower end, to the cutout body. A fuse link assembly, which includes the actual fusible element, is installed within the fuse tube and is mechanically and electrically coupled (via an interference fit) to the top of the fuse cutout body. During an overload event, the fusible element in the fuse link melts and then mechanically separates and the fuse tube disconnects the electrical circuit by dropping the top end of the fuse tube out of the cutout body in a rotational manner.
An acceptable design for fuse links must account for several factors. For example, the fault-interrupting capability is dependent on the fuse link sheath. The interrupting performance of the fuse links must extend across the full range of possible faults conditions—i.e., from potentially tens of amperes at the low end to about 10,000 amperes at the high end. The fuse link should stay intact for a first range of fault current values, e.g. from tens of amperes to about 1,100 amperes to interrupt faults within the fuse link sheath, but also burst at a sufficiently low pressure to minimize the arc energy during transformer primary faults, a second range of fault current values from about 1,100 to about 10,000 amperes. A particular sheath material which provides desirable interrupting performance may require specific design features to yield optimal performance.
Accordingly, there is a need for improved fuse links of the type used in conjunction with fuse cutout systems. Other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.
The exemplary embodiments will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and wherein:
and
A fuse link in accordance with one embodiment includes a conductive terminal component having a generally cylindrical insertion region, the generally cylindrical insertion region having a knurled region formed therein; a fusible element electrically coupled to the conductive terminal component; and a generally tubular sheath having a first end, a length, an inner radius, and a wall thickness. The first end of the generally tubular sheath is configured to form a press-fit connection with the knurled region of the conductive terminal component such that the generally tubular sheath substantially encloses the fusible element. The inner radius, the wall thickness, and the length of the generally tubular sheath are together configured such that (a) the generally tubular sheath remains substantially intact when the fusible link experiences a first overload event within a first range of fault current values; and (b) does not remain substantially intact when the fusible link experiences an overload event within a second range of fault current values that is greater than the first range. For example, the interrupting performance of the fuse link extends across the full range of possible faults conditions—i.e., from tens of amperes at the low end to about 10,000 amperes at the high end. In particular, the fuse link should stay intact for the first range of fault current values, e.g. from tens of amperes to about 1,100 amperes to interrupt faults within the fuse link sheath, but also burst at a sufficiently low pressure to minimize the arc energy during transformer the second range of fault current values, e.g. from about 1,100 to about 10,000 amperes.
A fuse link in accordance with one embodiment includes a conductive terminal component and a generally tubular polymeric sheath. The conductive terminal component has a generally cylindrical insertion region, the generally cylindrical insertion region having a knurled region formed therein such that the knurled region includes a fraction of the cylindrical insertion region. In one embodiment, the knurled region is formed on at least 50% of the cylindrical insertion regions, and more preferably about 60-75% of the cylindrical insert region. The generally tubular polymeric sheath has a first end, a length, an inner radius, and a wall thickness, wherein the first end of the generally tubular polymeric sheath is configured to form a press-fit connection with the knurled region of the conductive terminal component. The inner radius, the wall thickness, and the length of the generally tubular polymeric sheath are together configured such that (a) the generally tubular sheath remains substantially intact when the fusible link experiences a first overload event within a first range of fault current values; and (b) does not remain substantially intact when the fusible link experiences an overload event within a second range of fault current values that is greater than the first range. The polymeric sheath may be formed using an acetal homopolymer resin such as acetal polyoxymethylene or POM, commercially available as DuPont™ Delrin® 150 extrusion grade material.
A method of forming a fuse link in accordance with one embodiment includes providing conductive terminal component having a generally cylindrical insertion region, the generally cylindrical insertion region having a knurled region formed therein. The method further includes providing a generally tubular sheath having a first end, a length, an inner radius, and a wall thickness that are together configured such that the generally tubular sheath remains substantially intact when the fusible link experiences a first overload event within a first range of fault current values; and does not remain substantially intact when the fusible link experiences an overload event within a second range of fault current values that is greater than the first range. The method further includes inserting the first end of the generally tubular sheath over the generally cylindrical insertion region to form a press-fit connection with the knurled region of the conductive terminal component.
Terminal 300 includes a cylindrical surface region (or “insertion region”) 306 extending from a shoulder 310, which is formed by virtue of a region 311 having a greater outer diameter than region 306. In accordance with various embodiments, a portion of region 306—i.e., region 308—is knurled or otherwise textured to facilitate a press-fit connection with a sheath, as will be described in further detail below. Region 308 may be referred to without loss of generality herein as a “knurled region.” In this regard, a variety of knurling patterns may be used in connection with knurled region 308. Such patterns include, without limitation, “left hand”, “diamond”, “axial”, and “circumferential” knurling patterns. In one embodiment, knurled region 308 is approximately a left hand 40 teeth-per-inch (TPI) knurl.
The resulting structure 600 (i.e., the assembled fuse link, sans fusible element) is illustrated in
Having thus given an overview of a fuse link assembly in accordance with various embodiments, example physical dimensions will now be described in conjunction with
In accordance with a first example, dimensions for a fuse link rated in the range of 1-50 amperes (continuous) will now be described. Referring to
Continuing with the first example, and referring to
In accordance with a second example, dimensions for a fuse link rated between 60 amperes and 100 amperes (continuous) will now be described. Referring to
Continuing with the second example, and referring to
While at least one exemplary embodiment has been presented in the foregoing detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to be models or otherwise limit the scope, applicability, or configuration of the disclosure in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing the exemplary embodiment or exemplary embodiments. It should be understood that various changes can be made in the function and arrangement of elements without departing from the scope of the disclosure as set forth in the appended claims and the legal equivalents thereof.
This application is a continuation of U.S. patent application Ser. No. 14/682,247 filed Apr. 9, 2015, which application claims priority to U.S. Patent Application No. 61/978,528 filed on Apr. 11, 2014, the disclosures of which are hereby incorporated herein by reference in their entireties for all purposes.
Number | Date | Country | |
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61978528 | Apr 2014 | US |
Number | Date | Country | |
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Parent | 14682247 | Apr 2015 | US |
Child | 16677736 | US |