Patent Application
20150137934
The field of the invention relates generally to electrical circuit protection fuses, and more specifically to compact fuse assemblies for high voltage, direct current (DC) electrical power distribution systems.
Fuses are widely used as overcurrent protection devices to prevent costly damage to electrical circuits. Fuse terminals typically form an electrical connection between an electrical power source and an electrical component or a combination of components arranged in an electrical circuit. One or more fusible links or elements, or a fuse element assembly, is connected between the fuse terminals, so that when electrical current through the fuse exceeds a predetermined limit, the fusible elements melt and open one or more circuits through the fuse to prevent electrical component damage.
Certain types of fuse assemblies present ongoing challenges to fuse manufacturers. For example, fuse assemblies are now desired for direct current (DC) power system applications operating at higher voltages than conventional DC power systems. Existing electrical fuse assemblies are inadequate for the higher voltage DC power systems now proposed, and improvements are desired.
Non-limiting and non-exhaustive embodiments are described with reference to the following Figures, wherein like reference numerals refer to like parts throughout the various drawings unless otherwise specified.
As further introduction to the inventive concepts described herein, accommodating higher operating voltages for electrical fuse assemblies can be anything but simple. Achieving higher voltage ratings, for example, is not simply achieved by scaling some or all components of a fuse assembly. In particular, the electrical energy associated with electrical arcing conditions as the fuse element operates, sometimes referred to as arc flash energy, is much more severe at higher operating voltages than at lower voltages. This is especially so when the operating voltage is increased substantially.
Electrical power systems operable at 1500 VDC are now being proposed for certain applications, including but not limited to in-line fuse assemblies for photovoltaic power systems. Of course, circuit protectors such as fuses are desired for use with such 1500 VDC power systems, but the potential arc flash energy associated with such a high voltage DC application renders existing electrical fuse assemblies disadvantaged for use in a 1500 VDC power system. While fuses are known having a rating as high as 1000 VDC, the jump to 1500 VDC power systems is daunting. A 50% increase in operating voltage from 1000 VDC power systems to 1500 VDC provides a dramatic increase in potential arc flash energy when a fuse operates under a 1500 VDC load, and renders conventional fuses, even those rated for 1000 VDC applications, unsuitable for 1500 VDC applications.
A potential solution would be to design a new fuse specifically for use in a 1500 VDC system. In a well-designed fuse for such use, the arc flash energy associated with high voltage DC power systems could be safely managed, but likely only at considerable cost.
Conventionally, increased voltage ratings for DC power applications have been achieved using more expensive materials to fabricate the fuse elements, implementing additional inspection and quality control procedures into manufacturing processes, adopting specific care in handing procedures, and/or adopt larger body fuses which provide additional design margin. Larger bodied fuses, in turn, facilitate more arc absorbing or arc extinguishing filler to absorb are energy. In a high volume, competitive environment, however, the introduction of newer, more expensive fuses is a difficult proposition.
Introducing larger-bodied fuses presents other problems too that are of practical concern to those in the fuse industry. In the example discussed, namely providing a fuse assembly for a 1500 VDC power system, a larger-bodied fuse would be incompatible with existing in-line fuse holder components and accessories that may be desirable in a photovoltaic power system or perhaps other types of fuse holder components or accessories in other electrical power system applications. Larger-bodied fuses may therefor necessitate larger in-line fuse assemblies and fuse holders that must be designed and/or purchased at further expense to fuse manufactures, providers and users.
Also, and following a general trend in the industry, smaller fuse asssemblies are generally preferred over larger ones. Providing higher fuse protection ratings in smaller physical packages, or in some cases providing higher fuse protection ratings in physical packages of the same size as existing fuses, is much more attractive to end users than larger bodied fuses having larger physical packages. The larger physical packages require more space to install and use, and in today's competitive environment increased space requirements imposes still other costs to costs to electrical power system providers.
Considering the collective costs of providing new, larger fuses for 1500 VDC applications, the costs of providing new fuse holders and accessories, and the costs of increased space requirements for larger fuses and accessories, providing custom designed fuse assemblies by enlarging the fuse package to render it more capable of performing such an operating environment is an unattractive proposition. The costs of newer, more expensive fuses and newer, more expensive fuse holders and accessories accumulate rapidly for large power systems having a high number of fuses. Cost and size constraints for existing power distribution systems can even be an impediment to adoption of higher voltage power distribution systems.
Exemplary embodiments of fuse assemblies are described hereinbelow that address these and other problems in the art. Fuse assemblies are provided for high voltage DC power systems without providing custom designed, more expensive and larger-bodied fuses. The fuse assemblies are similar in size to existing fuse packages, and compatibility with existing fuse holders and accessories is preserved. No change in tooling or assembly methods for customers of who wish to adopt higher voltage power systems is required. Reliable fuse operation for high voltage power systems is provided at relatively low cost.
The above and other benefits are achieved at least in part by providing a reinforced fuse assembly with enhanced arc flash energy containment capability. Reinforcement material is applied to a fuse that enhances structural strength of the fuse package, such that even if a body of the fuse were to rupture or fail at one or more locations due to severe arc flash energy release, the arc flash energy will still be safely contained interior to the reinforcement material. As such, overcurrent protection for a higher voltage DC power system (e.g., 1500 VDC) can be effectively provided in a smaller package size at relatively low cost without having to custom design new and larger fuse components, including but not limited to the fuse body. Method aspects will be in part apparent and in part explicitly discussed in the description below.
While the inventive concepts are described in the context of 1500 VDC photovoltaic power systems, the concepts herein are not necessarily limited to photovoltaic systems, nor are they necessarily limited to 1500 VDC applications. The following description is provided for the sake of illustrating rather than limitation, and other power systems (e.g., non-photovoltaic power system) operating at different voltages higher and lower than 1500 VDC may benefit from the concepts described herein.
Referring now to the drawings,
As one example, the fuse 102 may be 10×38 mm photovoltaic fuse, Catalog number PV-XXA10F solar fuse, available from Bussmann by Eaton, St Louis Mo. (formerly known as Cooper Bussmann), Bussmann Datasheet #720110. The fuse 102 in this example, may have a current rating of 1-20 A and a voltage rating of 1000 VDC, and is sometimes referred to herein as a high voltage, low current fuse. While an exemplary fuse 102 having exemplary ratings is identified, other fuses may likewise be used in other embodiments.
The fuse 102 generally includes an elongated, nonconductive fuse body 120 and conductive fuse terminals 122, 124 coupled to opposing ends of the body 120. The body 120 in the example shown is generally cylindrical and may be fabricated from a nonconductive material known in the art, including but not limited to ceramic. Other non-cylindrical shapes and configurations of the fuse body are possible, however, in other embodiments. The terminals 122, 124 may be recognized as ferrule terminals, although it is recognized that in other embodiments other types of fuse terminals may be provided on the fuse 102.
A fuse element 126 (shown in phantom in
The circuit connecting terminals 104, 106 in the exemplary embodiment shown in the Figures are in-line wire crimp terminals such as A2650 crimp terminal fittings fabricated from brass or another conductive material. In one non-limiting example, the circuit connector terminals 104, 106 are configured for crimping, using a suitable crimping tool (e.g., Sta-Kon® Comfort Crimp® Compression Tool, Model ERG4002 by Thomas & Betts), to connect line and load-side wires 108, 110 of an electrical circuit to the connector terminals 104, 106. While specific connector terminals 104, 106 are described, it is understood that other connector terminals may be provided having other features and configurations without departing from the scope of the present invention. The wires 108, 110 may be 10-12AWG stranded solar PV wire in one example, or may alternatively be other types of wire in other embodiments.
In the assembly 100, the connector terminals 104, 106 are separately provided elements from the fuse 102, and are secured to the fuse terminals 122, 124 via a friction fit. The reinforcing sleeve element 108 is then applied over the exterior of the fuse body 102 and portions of the connector terminals 104, 106.
In one example, the reinforcing sleeve element 108 is 2A3185 adhesive heat shrink R/C (YDTU2.E157227), Catalog. No. EPS-300, ½″, Black adhesive-lined, heat shrink tubing available from the 3M Company of St., Paul, Minn. The reinforcing sleeve element 108 may be applied in a known manner and provides structural reinforcement for the fuse body 102 to better withstand increased arc flash severity when the fuse element 126 operates when under a 1500 VDC load. Especially when the fuse body 102 is fabricated from ceramic, cracks or ruptures may develop when the fuse operates under load at a 1500 VDC load. Recognizing that the fuse 102 in the example discussed has a rating of 1000 VDC at least in part because of the construction of the body 122 and its ability to withstand arc flash energy at 1000 VDC or below, the additional structural strength of the reinforcing sleeve element 108 allows arc flash energy under a 1500 VDC load to be safely contained. The reinforcing sleeve element 108 and its dimensions is accordingly selected in view of the potential arc flash energy and the ability of the fuse body 102 to withstand it.
The adhesive lining of the reinforcing sleeve element 108 provides additional structural strength as well as additional sealing of the ferrule/body joints of the fuse 102. If electrical arcing occurs at a location closer to the fuse terminals 122, 124, and specifically in the vicinity of the fuse ferrule/body seal of the fuse 102, electrical arcing and arc flash energy may otherwise cause rupture of the seal. Again considering that the fuse 102 in the example described was designed with a 1000 VDC rating, the ferrule/body joints of the fuse 102 may be susceptible to rupture when the fuse element 126 operates under higher load at 1500 VDC. With the reinforcing sleeve element 108, the fuse having a 1000 VDC rating may otherwise capably perform in a 1500 VDC power system. In other words, the reinforcing sleeve element 108 including the adhesive effectively allows the fuse 102 designed to provide a 1000 VDC rating to effectively function as a 1500 VDC rated fuse assembly.
Considering the exemplary fuse 102 described above, a 1500 VDC rated fuse assembly is provided in a physical package slightly larger than a convention 10×38 mm fuse package. A 50% increase in the voltage rating of the fuse 102 (e.g., 1000 VDC) to the voltage rating of the assembly 100 (e.g., 1500 VDC) is provided in a substantially similar package size. Because the package size change of the assembly 100 versus the fuse 102 alone is slight, the assembly 100 is operable with existing fuse holders, wiring harnesses, and accessories.
While the adhesive lined reinforcing sleeve element 108 is beneficial for the reasons noted above, and also simplifies assembly steps as the fuse assembly 100 is manufactured, the adhesive could in some embodiments be supplied separately from the reinforcing sleeve element 108. In other contemplated embodiments, the adhesive may be considered optional and may be omitted. Also, while specific reinforcement material has been identified for the element 108, it is exemplary only. Other reinforcing materials known in the art may be used, including but not limited to different types of heat shrink material. Non-heat shrink reinforcement materials may also be utilized to achieve at least some of the benefits described to some extent.
The fuse label 110 is applied to the outer surface of the reinforcing sleeve element 108 in a known manner and is provided with text, graphics or indicia conveying information to the user regarding the ratings of the assembly 100. The label 110 may also be color coded in whole or in part to identify the type of assembly 100 to a user tasked with installing or replacing the assembly 100 in an electrical power system. For example, the fuse label 100 may be provided with a color such as yellow, to be matched with a compatible fuse holder, wiring harness, or other accessory used in combination with the assembly 100 also marked with the same color. As such, matching color coding may convey that the fuse assembly 100 and the accessory are compatible. Other colors may be used on incompatible accessories or other types of fuse assemblies. In such a manner, confusion regarding compatibility or incompatibility of fuse assemblies and accessories may be avoided in the field. As one illustration, a photovoltaic fuse assembly 100 having a first color (e.g., yellow) can be distinguished from a non-photovoltaic fuse assembly having a label with a second color (e.g., red), and a photovoltaic fuse accessory can be distinguished from a non-photovoltaic fuse accessory via similar color coding provided on the accessories. Mismatching of incompatible fuse assemblies and accessories is therefore easily avoided by installers or maintenance personnel for an electrical power system.
The fuse assembly 100 is beneficial in at least the following aspects. The assembly 100 meets new and higher voltage requirements for 1500 VDC power distributions by virtue of the reinforcing sleeve element 108, without having to custom design and tool a new fuse having larger components. The fuse assembly 100 may be used with existing accessories such as fuse holders and the like, without having to custom design and tool new accessories. Power distribution system operators may therefore adopt higher voltage power distribution systems with minimal increased costs and without having to use fuse assemblies having larger package sizes.
By virtue of the additional arc absorbing material 202 provided on the exterior of the fuse body 102 and portions of the wire connector terminals 104 and 106, additional protection against a release of arc flash energy is provided at the sealed joints of the fuse ferrules and body of the fuse 102. While in the example of
Because of the additional arc absorbing material 202, the fuse assembly 200 may more capably handle arc flash energy occurring under a 1500 VDC load than the assembly 100 described above. The assembly 200 including the additional arc absorbing material 202 may likewise provide an effective voltage rating of more than 1500 VDC for the assembly 200.
Except as noted, the construction of the assembly 200 is similar to the construction of the assembly 100, and the assembly 200 provides similar advantages to the assembly 100.
At step 304, connector terminals such the terminals 104 and 106 are provided. At step 306 the connector terminals 104, 106 are attached to the respective first and second terminal elements of the fuse 102. As described above the attachment may be accomplished by friction fit or other attachment techniques known in the art.
At step 308, an arc absorbent material such as the material 202 described above is optionally applied to the exterior of the fuse 102 at desired locations, including but not limited to the fuse ferrule and body joints.
At step 310, the fuse body, and also an arc absorbent material applied at step 308, is covered with a reinforcement material such as the material 108 described above. As described above, the reinforcement material applied at step 310 contains arc energy when the fuse element opens to break the circuit path when the body of the fuse has ruptured under an electrical load at least about 1500 VDC, even though the fuse 102 described in the assembly, on its own, has a voltage rating of 1000 VDC.
At step 312, an accessory is also provided. The accessory may be a fuse holder, a wiring harness, or another accessory known in the art. At step 314, color coding may be applied to the fuse assembly and to the accessory for the convenience of an end user. The color coding may be applied using adhesive labels and the like, or may be applied using other techniques known in the art.
The benefits and advantages of the invention are now believed to have been amply illustrated in relation to the exemplary embodiments disclosed.
An embodiment of an electrical fuse assembly has been disclosed including: an electrical fuse comprising a fuse body, first and second fuse terminal elements coupled to the fuse body, and a fuse element establishing a circuit path between the first and second fuse terminals, the fuse configured to provide a first direct current voltage rating; and a reinforcement material covering at least the fuse body configured to contain arc flash energy if the fuse body fails, thereby effectively increasing the direct current voltage rating to a second voltage rating greater than the first voltage rating.
Optionally, the assembly may also include first and second connector terminals attached to the respective first and second fuse terminal elements. The first and second connector terminals may be wire crimp terminals, and the reinforcement material may also cover at least a portion of the first and second connector terminals.
As further options, the fuse may be a cylindrical, photovoltaic fuse. At least one of the first and second fuse terminal elements may be a ferrule. The fuse body may be fabricated from ceramic. The first voltage rating may be about 1000 VDC, and wherein the second voltage rating is about 1500 VDC.
The assembly may optionally include an arc absorbing material extending between the reinforcement material and the fuse body. The arc absorbing material may be one of silicone and Teflon tape.
The reinforcement material may optionally be a heat shrink material, and the heat shrink material may include an adhesive.
The assembly may also optionally include a label, with the label being color coded to identify a compatible fuse accessory. The compatible fuse accessory may be at least one of a fuse holder and a wiring harness.
Another embodiment of an electrical fuse assembly has been disclosed. The assembly includes: an electrical fuse comprising a fuse body having opposing ends, first and second fuse terminals elements on the respective opposing ends of the fuse body, and a fuse element establishing a circuit path between the first and second fuse terminal element, wherein the electrical fuse has a voltage rating of at least about 1000V; first and second in-line wire crimp connectors attached to the respective first and second fuse terminal elements; and a reinforcement material covering the fuse body, wherein the reinforcement material contains arc energy when the fuse element opens to break the circuit path when the body of the fuse has ruptured under a load of at least about 1500 VDC.
Optionally, the first and second in-line connectors are friction fit to the first and second fuse terminal elements. The fuse may be a photovoltaic fuse, and the fuse body may be fabricated from ceramic. The fuse body may be cylindrical.
The assembly may further include an arc absorbing material extending between the reinforcement material and the body. The arc absorbing material may be one of silicone and Teflon tape.
The reinforcement material may be a heat shrink material, and the heat shrink material may be an adhesive lined heat shrink sleeve material.
The assembly may also include a label, the label being color coded to identify a compatible fuse accessory. The compatible fuse accessory may include at least one of a fuse holder and a wiring harness.
An exemplary method has been disclosed of manufacturing an in-line fuse assembly including an electrical fuse having a body having opposing ends, a fuse element extending interior to the body, and first and second fuse terminal elements on the respective opposing ends of the fuse body and establishing a circuit path with the fuse element. The method includes: attaching first and second in-line wire connectors to the respective first and second terminal elements of the fuse; and covering the body of the electrical fuse with a reinforcement material, whereby the reinforcement material contains arc energy when the fuse element opens to break the circuit path when the body of the fuse has ruptured under an electrical load at least about 1500 VDC.
Optionally, attaching the first and second in-line connectors may include friction fitting the first and second in-line connectors to the first and second terminal elements of the fuse. The fuse may be a photovoltaic fuse, and the body may be fabricated from ceramic.
The method may include extending an arc absorbing material between the reinforcement material and the body. Extending an arc absorbing material may include extending one of silicone and Teflon tape.
Covering the body of the electrical fuse with a reinforcement material may include applying a heat shrink material to the body. Applying a heat shrink material to the body may include applying an adhesive heat shrink material.
The method may also include applying a color coding to the fuse assembly. The method may also include providing a fuse accessory, and color coding the fuse accessory to match the fuse assembly.
An embodiment of an electrical fuse system has also been disclosed including: a fuse assembly including a low overcurrent protection fuse and a reinforcement material applied to the fuse and configured to provide a fuse assembly rating of at least 1500 VDC; and an accessory accepting the fuse assembly.
Optionally, the fuse may be a photovoltaic fuse having a rating of 1000 VDC. The fuse reinforcing material may include a heat shrink reinforcing element. The fuse assembly may include an arc absorbing material applied external to the fuse and extending internal to the reinforcement material. The fuse assembly and the accessory may be color coded. The fuse assembly may defines an in-line fuse assembly. The fuse may have a current rating of 1 to 20 Amps.
This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.
