Patent Description:
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 flowing 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.

In order to complete electrical connections to external circuits, a variety of fuse blocks and fuse holders have been made available that define fuse receptacles or compartments to receive overcurrent protection fuses and are provided with line and load-side fuse contact members to establish electrical connection through the fusible elements in the fuse. Attention is drawn to <CIT>, which relates to a structure of a fuse used in a high voltage circuit. An arc-extinguish material is stuffed in a cylinder of an insulator as well as a fuse-element is held therein. The fuse-element is connected to metal caps provided on both ends of the cylinder. Terminals are connected to the outer side of the caps to constitute a fuse body. The fuse body is mounted in a case connected to members that connect the fuse body to a direct-current circuit through the terminals. On both sides of the case, magnets are fitted so that the fuse-element is sandwiched. When a current larger than a predetermined value passes through the direct-current circuit, the fuse-element is fused to interrupt the current. The arc that is ignited at the moment, when the current is interrupted, receives a magnetic force from the magnets to lenghten the arc. Further, <CIT> is related to an electrical apparatus with fuse cut-outs, designed to interrupt an electric circuit by melting a fusible conductor when the amperage on the line becomes excessive, in combination with an electromagnet embedded in the fuse-box, beneath the fuse and about midway between the ends thereof, wherein magnet is in series with the fuse and the fuse is exposed directly to the magnet.

In view of trends in electrical power systems to operate at increasingly greater system voltages, and also in view of industry preferences to maintain a size form factor equal to or smaller than existing fuse blocks and fuse holders, known fuse blocks and fuse holders are disadvantaged in some aspects and improvements are desired. In accordance with the present invention, a fuse assembly as set forth in claim <NUM> is provided. Further embodiments are inter alia disclosed in the dependent claims.

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 views unless otherwise specified.

As system voltages continue to increase in various industrial sectors such as renewable energy, data centers, and in the mining industry to name a few, practical challenges are presented to circuit protection manufactures, generally and to overcurrent protection fuse manufacturers specifically. Among the challenges presented is an increased desired in the market to provide fuses and fuse assemblies with increased performance capabilities while maintaining or reducing existing form factor (i.e. size) of fuse and fuse assemblies.

For example in state of the art photovoltaic (PV) applications, the operating electrical system voltage is being increased from 600VDC to <NUM> VDC, and in some cases to 1500VDC. Operation of overcurrent fuses to interrupt circuitry at such increased system voltages while maintaining the form factor of existing fuses and fuse assemblies in conventional manner is inadequate because electrical arc energy experienced within the fuse is much more severe than in the lower voltage systems for which fuses and fuse assemblies having existing form factors were designed. Effectively containing and dissipating the increased amount of arc energy without enlarging the size of the fuse or fuse assembly presents practical challenges beyond the capability of existing and conventional fuses and fuse assemblies.

One possible approach to addressing increased arc energy issues at higher system voltage, but within the form factor constraints of existing fuses, is to provide additional areas of reduced cross sectional area, , often referred to as "weak spots", in the fuse element construction. Electrical arcing, which occurs at the locations of the weak spots in short circuit conditions, can therefore be divided over a greater number of weak spots with higher arc voltages at each location to limit and interrupt the fault current. There are practical limitations, however, as to how many weak spots can be designed into a fuse element and hence expanding the number of weak spots is not an effective solution to achieve satisfactory fuse operation in response to short circuit conditions at higher system voltages of <NUM> VDC or <NUM> VDC.

For fuses designed to respond to electrical overload conditions, accommodating increased arc energy presents still further challenges that are not effectively resolved in existing fuse assemblies.

Exemplary embodiments of fuse assemblies such as fuse holders and fuse blocks are described hereinbelow that address the above problems in the art and facilitate higher power operation of overcurrent protection fuses without increasing the form factor from present levels. The fuse holders and fuse blocks achieve higher voltage operation in a compact size via the provision of a permanent magnet arc deflection system. The permanent magnet arc deflection system generates an external magnetic field across the body of the fuse when received in the fuse block or the fuse holder. The fusible element inside the body of the fuse is therefore subjected to the external magnetic field that combines with an internal magnetic field produced by electrical current flowing through the fuse. The combined external and internal magnetic fields produce a mechanical force in response that, in turn, causes the electrical arc to deflect or bend inside the fuse body as the fuse element operates or opens to interrupt the circuit. This increase the cooling of the arc. Enhanced arc suppression is therefore possible without altering the fuse construction.

More specifically, the bending and deflection of the electrical arc can be directed to extend electrical arcing into cooler arc extinguishing material than if the arc was not deflected or caused to bend, and consequently fuses of the same physical size can be operated at much higher voltages in fuse blocks and fuse holders also having the same physical size and form factor of existing fuse blocks and fuse holders. The magnets can be easily applied to a fuse holder or fuse block in a low cost manner without increasing the form factor of the fuse holder or fuse block either. Method aspects will be in part apparent and in part explicitly discussed in the description below.

<FIG> is top view of an exemplary fuse assembly <NUM> in the form of a fuse block <NUM> including an electrically nonconductive housing <NUM> formed with a base wall <NUM> and upstanding side walls <NUM>, <NUM> extending from opposed longitudinal edges of the base wall <NUM>. The side walls <NUM>, <NUM> extend generally parallel to one another and include a centrally located cutout portion <NUM> and barrier portions <NUM>, <NUM> extending on each side thereof to end respective end edges <NUM>, <NUM> of the base wall <NUM>. The side walls <NUM>, <NUM> in combination with the base wall <NUM> define a fuse receptacle <NUM> extending above the base wall <NUM> and between the side walls <NUM>, <NUM>. The fuse receptacle <NUM> is generally elongated and is open and accessible from the top as shown in <FIG> and also is open and accessible from end edges <NUM>, <NUM>. As such, the fuse block <NUM> may be recognized as an open style fuse block.

The base wall <NUM> is provided with a set of fuse contact terminals in the form of a first fuse contact terminal <NUM> on one side of the fuse receptacle <NUM> near the end edge <NUM> and a second fuse contact terminal <NUM> on another side of the fuse receptacle <NUM> near the end edge <NUM>. Line and load side terminals <NUM>, <NUM> are also provided adjacent the fuse contact terminals <NUM>, <NUM> and are configured for connection to external line and load-side circuitry. The fuse contact terminals <NUM>, <NUM> are configured as resilient fuse clips. In contemplated embodiments, the line and load-side terminals <NUM>, <NUM> are configured to receive a stripped end of a respective wire and secured in place with a screw clamp arrangement as shown. A variety of alternative terminal structures and configurations are known and may be utilized in further and/or alternative embodiments.

A removable overcurrent protection fuse <NUM> may be received in the fuse receptacle <NUM> between the side walls <NUM>, <NUM> as shown. In the illustrated example, the overcurrent protection fuse <NUM> includes an elongated and generally cylindrical housing <NUM> fabricated from an electrically nonconductive material, and conductive fuse terminal elements in the form of end caps or ferrules <NUM>, <NUM>. Internal to the fuse housing <NUM> is a fusible element (not shown in <FIG> but described further below) that is fabricated from an electrically conductive material and that is connected to and defines a current path between the fuse terminal elements <NUM>, <NUM> and by implication completes the circuit between the line and load-side terminals <NUM>, <NUM> when the fuse <NUM> is received in the fuse receptacle <NUM> with the respective end caps or ferrules <NUM>, <NUM> engaged with the fuse contact terminals <NUM>, <NUM>.

In contemplated embodiments, the fusible element may include a short circuit element and/or an overload fuse element that is calibrated to melt, disintegrate or otherwise structurally fail to conduct current in response to specified overcurrent conditions. The structural failure of the fusible element creates an open circuit between the fuse terminal elements <NUM>, <NUM> but otherwise withstands other electrical current conditions. This operation of the fusible element from an intact, current carrying state to a non-current carrying state or open state, desirably electrically isolates load-side circuitry connected through the fuse <NUM> and protects the load-side circuit from damage that may otherwise result from overcurrent conditions. Once the fuse <NUM> operates to open or interrupt the circuit between the line and load-side terminals <NUM>, <NUM> it must be replaced to restore the connection between the line and load-side terminal <NUM>, <NUM> and the associated line and load side circuitry.

An increase in system voltage from <NUM> VDC to <NUM> VDC or <NUM> VDC results in a substantial increase of arc voltage requirement in order to interrupt the circuit for electrical arc within the fuse housing <NUM> as the fusible element opens. Effectively suppressing electrical arcing as the fuse operates is a primary limitation to providing fusible circuit protection for higher voltage circuitry while maintaining the same form factor (e.g., physical size and dimension) of the fuse <NUM> as existing fuses designed for lower voltage systems, as well as maintaining the same form factor of the fuse block <NUM> as blocks designed for lower voltage systems. Unfortunately, conventional fuse blocks and conventional fuses are not equipped to solve the problems associated with increased arc intensity.

To more effectively address electrical arc interruption issues associated with higher voltage operation, the fuse block <NUM> is equipped with a magnetic arc suppression system including embedded magnet structure as further explained in the examples below.

According to the example of <FIG>, a portion of which is also shown in <FIG>, the magnetic arc suppression system <NUM> includes a first permanent magnet <NUM> extending along the side wall <NUM> of the fuse block housing <NUM> and a second permanent magnet <NUM> extending along the side wall <NUM> of the fuse block housing <NUM>. The permanent magnets <NUM>, <NUM> are spaced apart but extend parallel to one another alongside and on opposing lateral sides of the fuse <NUM>, and more specifically the center portion of the fuse housing <NUM> extending in between the permanent magnets <NUM>, <NUM>. As such, the permanent magnets <NUM>, <NUM> are diametrically opposed on either lateral side of the fuse <NUM> and impose a magnetic field B (<FIG>) between the magnets <NUM>, <NUM> and also extending transversely across the fuse receptacle <NUM>. The magnetic field B generated between the magnets <NUM>, <NUM> acts upon an electrical arc (or electrical arcs) inside the fuse housing <NUM> as the fusible element operates as further explained below. The transverse magnetic field B deflects and stretches electrical arcs as they occur so that they can be more effectively quenched.

The permanent magnets <NUM> and <NUM> may be attached to the housing side walls <NUM>, <NUM> or otherwise mounted to the housing <NUM> in any manner desired. While two magnets <NUM>, <NUM> are shown in <FIG>, it is understood that additional permanent magnets may be provided with similar effect. The magnets <NUM>, <NUM> are shown in approximately centered positions between the end edges <NUM>, <NUM> of the housing <NUM> and therefore are also approximately centered with respect to the fuse <NUM>. Other arrangements of magnets are possible, however, and may be utilized so long as magnetic fields can be directed transversely to corresponding locations of the electrical arc in the fuse as it operates. It is understood that the location of the electrical arc can be determined by the geometry and configuration of the fusible elements included in the fuses <NUM>.

<FIG> is top view of an exemplary fuse assembly <NUM> including the fuse block <NUM>, wherein the magnetic arc suppression system <NUM> (shown in end view in <FIG>) includes the first and second permanent magnets <NUM> and <NUM>, and a U-shaped ferromagnetic plate <NUM> that extends not only along the lateral sidewalls <NUM>, <NUM> of the fuse block housing <NUM>, but also beneath the fuse <NUM> as seen in <FIG>. The ferromagnetic plate <NUM> may be fabricated from steel in one example and may facilitate the mounting of the magnets <NUM> and <NUM> in the fuse receptacle <NUM>, as well as improve the effect of the transverse magnetic field produced between the magnets <NUM> and <NUM> to deflect and suppress the electrical arc in the fuse <NUM> as it occurs.

While one ferromagnetic plate <NUM> is shown in <FIG> having a particular shape, it is recognized that more than one ferromagnetic plate <NUM> may alternatively be provided proximate each magnet <NUM> and <NUM>. It is also contemplated that in an embodiment having additional magnets, additional ferromagnetic plates could be provided. Wherever utilized, the ferromagnetic plates may function to increase the magnetic field intensity beyond the value provided by the magnets themselves, or to reduce the size and strength of the magnets utilized while still generating a magnetic field of a desired strength.

<FIG> is an end view of another configuration of the magnetic arc suppression system <NUM> including only one permanent magnet <NUM> positioned beneath the fuse <NUM>. The magnet <NUM> may be mounted, for example, on the base wall <NUM> of the fuse block housing <NUM> and when the fuse <NUM> is received in the fuse block <NUM> the fuse <NUM> overlies and substantially covers the magnet <NUM>. The magnetic arc suppression system <NUM> shown including the single magnet <NUM> establishes, in the orientation shown in <FIG>, a magnetic field B extending upwardly or vertically rather than horizontally as in the arrangements shown in <FIG> and <FIG>. That is, in the arrangement of <FIG>, the magnetic field is established in a direction parallel to the side walls <NUM>, <NUM> of the fuse block housing <NUM> rather than perpendicular to the side walls <NUM>, <NUM> as in the arrangements of <FIG> and <FIG>. It should be realized, however, that if desired a single magnet may nonetheless generate a transverse magnetic field by placing the magnet <NUM> on the lateral side of the fuse <NUM> instead of beneath the fuse <NUM> as shown in <FIG>.

<FIG> is an end view of another configuration of the magnetic arc suppression system <NUM> including the single magnet <NUM> in combination with the ferromagnetic plate <NUM>. In the example of <FIG>, the single magnet <NUM> is located on the bottom of the U-shaped ferromagnetic plate <NUM> and the fuse <NUM> is also located interior to the U-shaped plate <NUM> for improved magnetic effect to suppress electrical arcing inside the fuse <NUM>. As discussed above, more than one ferromagnetic plate and also ferromagnetic plates of different shapes and configurations may utilized in further and/or alternative embodiments to produce similar effects.

<FIG> is a schematic view of the magnetic arc suppression system <NUM> that provides magnetic arc deflection and enhances performance capability of the fuses <NUM> in, for example, DC power systems operating at <NUM> VDC or <NUM> VDC. The magnetic arc suppression system <NUM> assists in quickly and effectively dissipating an increased amount of arc energy associated with electrical arcing, generating an arc voltage that is higher than 1000VDC or 1500VDC to interrupt the circuit as each fuse <NUM> operates. Using the principles of the magnetic arc suppression system <NUM> described below, fuse blocks and fuse holders such as those described further below may be realized that may safely and reliably operate in electrical power systems operating at <NUM> VDC or greater. The interrupting capability of the fuse <NUM> accordingly may greatly increase via the implementation of the magnetic arc suppression system <NUM>. Because the magnetic arc suppression system <NUM> is provided externally from the fuse <NUM>, enhanced performance capabilities may be achieved without modifying the fuse or its form factor and also without increasing the form factor of the fuse blocks or fuse holders.

As seen in <FIG>, the magnetic arc suppression system <NUM> includes a pair of permanent magnets <NUM>, <NUM> arranged on each side of a conductor <NUM> that may correspond to a fuse element in the fuse <NUM> described above. In contemplated embodiments, each magnet <NUM>, <NUM> is a permanent magnet that respectively imposes a magnetic field <NUM> having a first polarity between the pair of magnets <NUM>, <NUM>, and the conductor <NUM> is situated in the magnetic field <NUM>. As shown in <FIG>, the magnet <NUM> has opposing poles S and N and the magnet <NUM> also has opposing poles S and N. Between the pole N of magnet <NUM> and the pole S of magnet <NUM> the magnetic field B (also indicated as element <NUM>) is established and generally oriented in the direction extending from the magnet <NUM> to the magnet <NUM> as shown (i.e., from left to right in the drawing of <FIG>). The magnetic field B has a strength dependent on the properties and spacing of the magnets <NUM> and <NUM>. The magnetic field B may be established in a desired strength depending on the magnets <NUM> and <NUM> utilized. As noted above, the magnetic field B can be established by a single magnet instead of a pair of magnets. In contemplated embodiments, the strength of the magnetic field B should preferably be higher than about 30mT, although higher and lower limits are possible and may be utilized in other embodiments.

When electrical current I flows through the conductor <NUM> in a direction normal to the plane of the page of <FIG> and more specifically in a direction flowing out of the plane of the page of <FIG>, a separate magnetic field <NUM> is induced and as shown in <FIG> the magnetic field <NUM> extends circumferentially around the conductor <NUM>. The strength or intensity of the magnetic field <NUM> is, however, dependent on the magnitude of the current flowing through the conductor <NUM>. The greater the current magnitude I, the greater the strength of the magnetic field <NUM> that is induced. Likewise, when no current flows through the conductor <NUM>, no magnetic field <NUM> is established.

Above the conductor <NUM> in the example illustrated in <FIG>, the magnetic field <NUM> and the magnetic field <NUM> generally oppose one another and at least partly cancel one another, while below the conductor <NUM> as shown in <FIG>, the magnetic field <NUM> and the magnetic field <NUM> combine to create a magnetic field of increased strength and density. The concentrated magnetic field resulting from the combination of the magnetic fields <NUM>, <NUM> beneath the conductor <NUM> produces a mechanical force F acting on the conductor <NUM>. The force F extends upward or generally vertically in the drawing of <FIG> that is, in turn, directed normal to the magnetic field B <NUM>. The force F may be recognized as a Lorenz force having magnitude F determined by the following relationship: <MAT> It should now be evident that the magnitude of the force F can be varied by applying different magnetic fields, different amounts of current, and different lengths (L) of conductor <NUM>. The orientation of the force F is shown to extend in the vertical direction in the plane of the page of <FIG>, but in general can be oriented in any direction desired according to Fleming's Left Hand Rule, a known mnemonic in the field.

Briefly, Fleming's Left Hand Rule illustrates that when current flows in a wire (e.g., the conductor <NUM>) and when an external magnetic field (e.g., the magnetic field B illustrated by lines <NUM>) is applied across that flow of current, the wire experiences a force (e.g., the force F) that is oriented perpendicularly both to the magnetic field and also to the direction of the current flow. As such, the left hand can be held so as to represent three mutually orthogonal axes on the thumb, first finger and middle finger. Each finger represents one of the current I, the magnetic field B and the force F generated in response. As one illustrative example, and considering the example shown in <FIG>, the first finger may represent the direction of the magnetic field B (e.g., to the right in <FIG>), the middle finger may represent the direction of flow of the current I (e.g., out of the page in <FIG>), and the thumb represents the force F. Therefore, when the first finger of the left hand is pointed to the right and the middle finger is oriented out of the page in <FIG>, the position of the thumb reveals that the force F that results is pointed in the vertical direction shown (i.e., toward the top of the page in <FIG>).

By orienting the current flow I in different directions through the magnetic field B, and also by orienting the magnetic field B in different directions, forces F extending in directions other than the vertical direction can be generated. Within the fuse receptacle <NUM> of the fuse blocks described above, magnetic forces F can accordingly be directed in particular directions. For example, and according to Fleming's Left Hand Rule, if the current flow I was directed into the paper instead of out of the paper as previously described in relation to the <FIG> while keeping the magnetic field B oriented as shown in <FIG> (i.e., toward the right in <FIG>), the force F generated would be oriented in a direction opposite to that shown (i.e., in a direction toward the bottom of the page in <FIG>). Likewise, if the magnetic field B was oriented vertically instead of horizontally as illustrated in <FIG> (e.g., as in the arrangements shown in <FIG>, forces F could be generated in horizontal directions according to Fleming's Left Hand Rule instead of the vertically oriented forces of the preceding examples. As such, by varying the orientation of the magnets and direction of current flow, forces F can be generated that extend transversely to the axis of the fuse receptacles <NUM> and associated fuses <NUM>, or forces F can be generated that extend axially or longitudinally in the fuse receptacles upon associated fuses <NUM>. Alternatively stated, the force F can be generally to extend laterally or longitudinally with respect to the longitudinal axis of the fuse <NUM>. Regardless, when the conductor <NUM> corresponds to a location of an electrical arc when the fuse element operates, the force F can deflect the electrical arc <NUM> when it occurs and considerably reduce arcing time and severity.

In further embodiments, the force F can be applied to the conductor <NUM> of the fuse <NUM> to provide different effects. That is, multi-directional arc deflecting configurations are possible having forces F acting in various different directions relative to the conductor <NUM> of the fuse. Forces F may be generated in axial and radial directions relative to a fuse <NUM>, as well as planer and edge deflection configurations depending on the placement of the magnets <NUM>, <NUM> to produce magnetic fields and forces in the directions desired to accomplish such arc deflecting configurations. In a multiple pole fuse holder defining multiple fuse receptacles or compartments, multiple sets of magnets may be provided to provide the same or different arc deflection configurations for each respective fuse in each compartment.

In certain contemplated embodiments, parallel fuses and fuse holders can mutually share a single magnet place between them to establish magnetic fields in different fuse compartments or receptacles. For example, the arrangement of magnets and fuses set forth below may be utilized
S/N Fuse S/N Fuse S/N Fuse S/N
wherein S/N represents the south and north pole of a respective magnet and in which the middle magnets function as a south pole for a first magnetic field acting upon a first fuse situated on a first side of the magnet and simultaneously function as a north pole for a second magnetic field acting upon a second fuse situated on the opposite side. This effect may be accomplished in a multiple pole fuse holder or in single pole fuse holders that are placed side by side.

<FIG> is a perspective view of the fuse block <NUM> incorporating the first fuse and magnet assembly configuration shown in <FIG>. Additional fuse blocks <NUM> may be provided side-by-side as shown to form a three-pole fuse block. While the magnetic arc suppression system <NUM> is shown only in the first fuse block shown in <FIG>, it shall be understood to be present in the other fuse blocks as well. The fuse blocks <NUM> can be provided as modules that can be ganged together as desired. Alternatively, a multi-pole fuse block may be provided that is formed with a single housing and multiple sets of fuse contact members and line and load side terminals.

<FIG> is a perspective view of the fuse block <NUM> incorporating the first fuse and magnet assembly configuration shown in <FIG>. Additional fuse blocks <NUM> may be provided side-by-side as shown to form a three-pole fuse block. While the magnetic arc suppression system <NUM> is shown only in the first fuse block shown in <FIG> it shall be understood to be present in the other fuse blocks as well. The fuse blocks <NUM> can be provided as modules that can be ganged together as desired. Alternatively, a multi-pole fuse block may be provided that is formed with a single housing and multiple sets of fuse contact members and line and load side terminals.

<FIG> is a perspective view of an exemplary fuse assembly not covered by the claims, in the form of a fuse holder <NUM>. The fuse holder <NUM> includes an electrically nonconductive housing <NUM> formed as a split shell casing (only one of which is shown in <FIG>). When assembled, the split shell casing collectively surrounds and encloses the components shown. The housing <NUM> defines, among other things, a fuse receptacle <NUM> that receives the overcurrent protection fuse <NUM>. Unlike the fuse blocks <NUM> described above, the fuse receptacle <NUM> in the fuse holder housing <NUM> is enclosed in the housing <NUM>, and a cap <NUM> is provided to close the end of the fuse receptacle <NUM> through which the fuse <NUM> can be inserted or removed along an insertion axis <NUM>.

The fuse <NUM> as shown is vertically oriented in the fuse holder housing <NUM>, and the fuse receptacle <NUM> is provided with line and load-side fuse contact members that, in turn, are electrically connected to line and load-side terminals <NUM>, <NUM>. Optionally, a set of switch contacts <NUM> and a rotary switch actuator <NUM> are provided, with the switch contacts <NUM> providing for connection and disconnection of a circuit path, responsive to a position of the switch actuator <NUM>, between the line-side terminal <NUM> and the fuse <NUM>. When the switch contacts <NUM> are closed and when the fuse <NUM> is present and has not yet opened (i.e., the fusible element is in an intact, current carrying condition) electrical current may flow through the fuse holder <NUM> between the line and load side-terminals <NUM>, <NUM> and through the fuse <NUM>. When the switch contacts <NUM> are opened, an open circuit is established in the fuse holder <NUM> between the line-side terminal <NUM> and the fuse <NUM>. The fuse <NUM> provides overcurrent protection via operation of the fusible element when the switch contacts <NUM> are closed. The embodiment depicted in <FIG> as described thus far may generally be recognized as a Compact Circuit Protector Base (CCPB) device available from Bussmann by Eaton of St. Louis Missouri.

To address electrical arcing issues associated with higher system voltage of <NUM> VDC or <NUM> VDC, the magnetic arc suppression system <NUM> including the permanent magnet <NUM> is provided in the fuse holder <NUM>. In the example of <FIG>, the magnetic arc suppression system <NUM> includes a single permanent magnet <NUM> that applies a magnetic field B across the fuse <NUM> in the fuse receptacle <NUM> to deflect the electrical arc inside the fuse <NUM> as the fusible element therein operates. In the position and orientation shown, the permanent magnet <NUM> extends generally perpendicular to a major side surface of the housing <NUM> and accordingly establishes a magnetic field B extending parallel to the major side surface of the housing <NUM> within the fuse receptacle <NUM>. The magnetic field B extends transversely across the fuse receptacle <NUM> in a direction generally perpendicular to the fuse insertion axis <NUM>. A force F is generated in response to the magnetic field B and the current I flowing through the fuse <NUM> to influence electrical arcing conditions as described above and specifically illustrated in the examples below.

While a single magnet <NUM> is shown in the example of <FIG> in the arc suppression, more than one magnet may be provided and magnets may be placed in positions other than that shown while producing otherwise similar effects. Any of the magnetic arrangements shown in <FIG>, <FIG>, <FIG> may be accomplished in the fuse holder <NUM> and the magnets utilized may be coupled to the fuse holder <NUM> in any desired location or orientation to produce the intended magnetic field arc suppression and effect.

Also, in contemplated embodiments the switch contacts <NUM> and the switch actuator <NUM> may be omitted and the fuse holder may be provided in modular form without switching capability. The modules may be ganged together to provide multiple pole fuse holders, or alternative, the housing may define multiple fuse receptacles <NUM> and contact terminals to accommodate a plurality of fuses <NUM>. In accordance with known modular fuse holders, the fuse holder <NUM> in such scenarios may include a fuse insertion drawer or other alternative means of accepting the fuse in the fuse receptacle. Various adaptations are possible to provide numerous types of fuse holders having embedded magnetic arc suppression systems to facilitate fusible circuit protection of circuitry operating at a system voltage of <NUM> VDC or <NUM> VDC.

<FIG> is a perspective view of another example not covered by the claims, of the fuse holder <NUM> that is similar in most aspects to the fuse holder shown in <FIG>, but includes a differently configured magnetic arc suppression system <NUM>.

To address electrical arcing issues associated with higher system voltage of <NUM> VDC or <NUM> VDC, the magnetic arc suppression system <NUM> including the permanent magnet <NUM> according to the present invention is provided. Comparing <FIG> and <FIG>, in the fuse holder <NUM> of <FIG> the single permanent magnet <NUM> is moved <NUM>° from its position shown in <FIG>. As such, in the position and orientation shown in <FIG>, the permanent magnet <NUM> extends generally parallel to the major side surface of the housing <NUM> and accordingly establishes a magnetic field B extending perpendicular to the major side surface of the housing <NUM> within the fuse receptacle <NUM>. The magnetic field B extends transversely across the fuse receptacle <NUM> in a direction generally perpendicular to the fuse insertion axis <NUM>. A force F is generated in response to the magnetic field B and the current I flowing through the fuse <NUM> to influence electrical arcing conditions as described above and specifically illustrated in the examples below. Additional magnets and orientations of magnets may also be provided to establish magnetic fields in still other directions and with varying intensity.

<FIG> is a sectional view of the overcurrent protection fuse <NUM> showing an exemplary internal construction. The fuse housing <NUM> defines an internal bore or passageway that accommodates a fuse element assembly <NUM> that is connected to the conductive end caps or ferrules <NUM>, <NUM> at each opposing end of the fuse housing <NUM>. In the example shown, the fuse element assembly <NUM> includes a short circuit element <NUM> and an overload element <NUM> connected to one another in series and in combination establishing a current path between the conductive end caps or ferrules <NUM>, <NUM>. The construction and operation of the short circuit element <NUM> and an overload element <NUM> is conventional, but enhanced by the magnetic arc suppression system in the fuse blocks of fuse holders described above.

The short circuit element <NUM> is fabricated from a strip of electrically conductive material and is provided with a number of openings formed therethrough. In between the openings are areas of reduced cross sectional area, referred to in the art as "weak spots", that are subject to increased amounts of heat in a short circuit current condition. As such, the short circuit element <NUM> begins to melt and disintegrate at the location of the weak spots when subject to a short circuit current condition. <FIG> illustrates a number of electrical arcs <NUM> occurring at the locations of the weak spots in a short circuit operating condition. To suppress the electrical arcs <NUM> the fuse housing <NUM> may be filled with an arc extinguishing media <NUM> such as silica sand. The arc extinguishing <NUM> media immediately surrounding the location of the arcs <NUM> absorbs the arc energy via heat dissipation. Such techniques have been generally effective for fuse operation at system voltages of up to <NUM> VDC, but is problematic at higher system voltages of <NUM> VDC or <NUM> VDC. The cooling of the arcs <NUM> at higher system voltage is not strong enough to generate an arc voltage higher than the source voltage such as 1000VDC or 1500VDC with a conventional fuse and fuse holder or conventional fuse and fuse block.

<FIG> illustrates an arc cooling effect produced in the same fuse <NUM> by the magnetic arc suppression system <NUM> described above. In <FIG>, the magnetic arc suppression system <NUM> applies a magnetic field B extending out of the page in the drawing of <FIG>. When current I flows through the fuse element assembly <NUM> from the end cap <NUM> to the end cap <NUM> (i.e., from left to right in <FIG>), the force F is applied laterally, radially or diametrically across the fuse and fuse element in the direction shown. When the electrical arcs <NUM> (<FIG>) have commenced, the force F drives and stretches the arcs <NUM> into the arc extinguishing media <NUM> farther away from the short circuit element <NUM> wherein the arc extinguishing media <NUM> is relatively cooler than the arc extinguishing media <NUM> immediately surrounding the short circuit element <NUM>. Heat is more readily dissipated by the relatively cooler arc extinguishing media <NUM>, which leads to an arc voltage higher than the source voltage, and the arc can be more readily and easily extinguished. The cooling effect is shown in <FIG> wherein the arcs are effectively shifted upward inside the fuse <NUM>. The magnetic arc deflection greatly improves the interrupting capability of the fuse <NUM>, without affecting the construction of the fuse <NUM> and its form factor. Instead, the arc suppression magnet (or magnets) are applied to the fuse holder or fuse block at relative low cost, without increasing the form factor of the fuse holder or the fuse block.

While the exemplary overcurrent protection fuse <NUM> described above includes an arc quenching media such as silica sand, it is recognized that another known arc quenching media may be utilized inside the fuse for similar purposes, including but not limited compositions or compounds that generate an arc extinguishing gas. In contemplated embodiments of this type, the composition may be applied, for example, on the interior surface of the fuse housing <NUM> and the short circuit fuse element <NUM> may be surrounded by air. The force F may be generated by the permanent magnet(s) of the arc suppression system to stretch and deflect the electrical arc across the air until it reaches the composition that, in turn, releases the arc extinguishing gas. The release of the gas enables the cooling of the arc, increases the pressure inside the fuse housing <NUM> and helps to compress ionized gas associated with the electrical arcs. The increased pressure also increases the arc voltage quickly and drives the fault current to zero so that the arcs cease to exist. As one non-limiting example of this type, an arc extinguishing composition such as melamine and its related compounds may be utilized to fill the interior of the fuse housing <NUM> with arc extinguishing gas and suppress the electrical arc with reduced intensity in combination with the magnetic arc suppression system described.

In still other embodiments, the fuse housing <NUM> may be filled with air in the absence of an arc extinguishing compound. The magnetic arc suppression system still applies the force F that stretches and deflects the arc farther away from the short circuit fuse element <NUM> into the air inside the fuse housing <NUM> to increase arc voltage and reduce arc interruption duration. In certain embodiments of this type, the arcs could reach the interior wall of the fuse housing <NUM> and the relatively cooler wall could aid in dissipating arc energy. Care should be taken, however, to ensure that the arc energy does not penetrate the wall of the fuse housing <NUM>.

<FIG> is a sectional view of the overcurrent protection fuse <NUM> illustrating an operation of the overload element <NUM> in an overload operating condition wherein electrical arcing has commenced. In the example, illustrated, the overload element <NUM> includes three soldered connections in the locations <NUM>. Heating of the solder in an electrical overload conditions weakens the soldered connections, and the spring element <NUM> eventually forces release of the overload fuse element <NUM> and physically severs its connection to the short circuit fuse element <NUM> and breaks the electrical connection through the fuse <NUM> between the end caps <NUM>, <NUM>. As seen in <FIG>, as the mechanical and electrical connection between the overload element <NUM> and the short circuit element <NUM> is broken, an electrical arc commences between the ends of the short circuit element <NUM> and the overload element <NUM>. The spring-loaded overload element <NUM> is pushed away from the end of the short circuit element <NUM> as this occurs, eventually extending the arc length enough so the arc can no longer be sustained, but at high system voltage (e.g. <NUM> VDC or <NUM> VDC), the arc voltage may not be high enough and is still problematic.

To address arc interruption issues associated with higher system voltage as the fuse <NUM> operates, <FIG> illustrates an arc cooling effect produced by the magnetic arc suppression system according to the present invention. As seen in <FIG>, the force F generated by the permanent magnet(s) in the fuse holder or fuse block stretches the arc farther away from the initial location where the arc started and therefore the arc contacts a cooler portion of the arc extinguishing media <NUM> than it otherwise would to more quickly dissipate arc energy via heat transfer. The other arc extinguishing media techniques described above may likewise alternatively be utilized in combination with the magnetic arc suppression as desired to address overload current operation of the fuse <NUM>.

It is contemplated that in some embodiments wherein overload current protection is the primary concern of the fusible circuit protection, the magnetic arc suppression system could be configured to generate a force F (shown in phantom in <FIG>) that is directed longitudinally instead of radially as in the previously described examples. That is, the magnetic field may be established so as to provide the force F extending in a direction parallel to the longitudinal axis of the fuse instead of transversely across the fuse. A longitudinally directed force F may assist in the disconnection of the overload element <NUM> and/or its movement away from the short circuit fuse element <NUM>. Such an improved disconnection force via the combination of the force F produced by the magnet(s) and the bias force of the spring element <NUM> would facilitate a reduction in arc duration as the overload element <NUM> operates.

<FIG> is a sectional view of a fuse <NUM> including another alternative overcurrent protection fuse element <NUM> connected between the fuse end caps <NUM> and <NUM>. As shown the fuse element <NUM> may be configured as a strip of conductive material having a number of openings formed therethrough that define weak spots as discussed above. A portion of the overload fuse element <NUM>, however, includes a Metcalf effect (M-effect) coating <NUM> where pure tin (Sn) is applied to the fuse element <NUM>, fabricated from copper in this example, proximate selected ones of the weak spots in the fuse element <NUM> as shown. During overload heating the Sn and Cu diffuse together in an attempt to form a eutectic material. The result is a lower melting temperature somewhere between that of Cu and Sn or about <NUM> in contemplated embodiments. The overload fuse element <NUM> and in particular the portion or section thereof including the M-effect coating <NUM> will therefore respond to overload current conditions that will not affect the remainder of the fuse element <NUM>. As the fuse element begins to open at the location of the M-effect coating <NUM>, an electrical arc commences inside the fuse housing <NUM>. At higher system voltage (e.g. <NUM> VDC or <NUM> VDC), the arc extinguishing media <NUM> may itself not be sufficient to contain or dissipate the arc energy quick enough to generate an arc voltage higher than the system voltage for successful circuit interruption.

To address arc energy issues associated with higher system voltage as the fuse <NUM> operates, <FIG> illustrates an arc cooling effect produced by the magnetic arc suppression system according to the present invention. As seen in <FIG>, the force F generated by the permanent magnet(s) in the fuse holder or fuse block stretches the arc farther away from the fuse element <NUM> and therefore the arc contacts a cooler portion of the arc extinguishing media <NUM> than it otherwise would to more quickly dissipate arc energy via heat transfer. The other arc extinguishing media techniques described above may likewise alternatively be utilized in combination with the magnetic arc suppression as desired to address overload current operation of the fuse <NUM>.

While exemplary fuses and fuse elements have been described in relation to the fuse blocks and fuse holders of the present invention, still other types of fuses and fuse elements are possible and likewise may be utilized. Various types of alternative fuses and fuse elements are known and not described in detail herein, any of which would benefit from the magnetic arc suppression techniques described for similar reasons to those described above.

Also, while the embedded magnet arc suppression system is described in relation to exemplary fuse blocks and fuse holders, the magnetic arc suppression is not necessarily limited to the embodiments described and illustrated. The benefits of the magnetic arc suppression more broadly apply to fuse assembles other than those specifically described herein.

Finally, while the present invention has been described in the context of particular applications for higher voltage DC system voltage and circuitry, the invention is not limited to the particular application and voltage ranges described. The magnetic arc suppression system may be advantageously utilized in wider range of applications and system voltages, and accordingly the exemplary applications and system voltages referred to herein are set forth for purposed of illustration rather than limitation.

The benefits and advantages of the inventive concepts disclosed herein are now believed to have amply demonstrated in relation to the exemplary embodiments disclosed.

An embodiment of a fuse assembly has been disclosed including: a nonconductive housing defining at least one fuse receptacle dimensioned to receive an overcurrent protection fuse; at least one set of fuse contact terminals configured to establish electrical connection through the overcurrent protection fuse when received in the at least one fuse receptacle; and at least one permanent magnet coupled to the nonconductive housing and imposing a magnetic field in the fuse receptacle; wherein at least a portion of the overcurrent protection fuse is disposed in the magnetic field when received in the fuse receptacle.

Optionally, the at least one permanent magnet may include a first permanent magnet and a second permanent magnet spaced apart from the first magnet, the magnetic field being established between the first permanent magnet and the second permanent magnet. The first permanent magnet and the second permanent magnet may be situated on opposing sides of the fuse receptacle and at least a portion of the overcurrent protection fuse may be disposed between the first magnet and the second magnet when the overcurrent protection fuse is received in the fuse receptacle. The fuse assembly may further include a ferromagnetic plate proximate the first permanent magnet and the second permanent magnet. The ferromagnetic plate may be U-shaped.

Also optionally, the at least one permanent magnet may be substantially covered by the overcurrent protection fuse when the overcurrent protection fuse is received in the fuse receptacle. The fuse assembly may further include a ferromagnetic plate proximate the at least one permanent magnet. The ferromagnetic plate may be U-shaped.

The overcurrent protection fuse is received in the fuse receptacle along an insertion axis, with the at least one magnet imposing a magnetic field extending perpendicular to the insertion axis. The assembly may further include at least one switch contact provided in the nonconductive housing. The nonconductive housing includes a major side wall, with the at least one magnet extending parallel to the major side wall. Alternatively, the at least one magnet may extend perpendicular to the major side wall.

The overcurrent protection fuse may be enclosed in the at least one fuse receptacle. The nonconductive housing may be configured as an open style fuse block. The nonconductive housing may also be configured as a fuse holder. The fuse assembly may include a cap covering an end of the fuse receptacle.

The magnetic field may be oriented inside the fuse receptacle to provide one of a radial arc deflecting force and an axial arc deflecting force acting upon the overcurrent protection fuse when the overcurrent protection fuse is received in the fuse receptacle.

The first and second fuse contact terminals may include resilient spring clips. The resilient spring clips may be configured to receive respective end caps of the overcurrent protection fuse.

The fuse assembly may be in combination with the overcurrent protection fuse. The overcurrent protection fuse may include at least one of a short circuit fuse element and an overload fuse element.

An embodiment of a fuse assembly has also been disclosed including: a nonconductive housing defining at least one elongated fuse receptacle dimensioned to receive a cylindrical overcurrent protection fuse including opposing end caps and at least one fusible element; at least one set of fuse contact terminals configured to establish electrical connection through the opposing end caps and the at least one fusible element when received in the at least one fusible element; and at least one permanent magnet coupled to the nonconductive housing and imposing a magnetic field in the fuse receptacle and across the at least one fusible element.

Optionally, the elongated fuse receptacle is defined by opposing side walls, and the magnetic field may be oriented perpendicular to the opposing side walls. The elongated fuse receptacle is defined by opposing side walls, and the magnetic field is oriented parallel to the opposing side walls. The fuse assembly may also include at least one ferromagnetic plate proximate the at least one magnet. The magnetic field may be oriented in one of an axial direction and a radial direction relative to the cylindrical fuse. The nonconductive housing may define one of an open style fuse block and a fuse holder. The at least one permanent magnet may include a first permanent magnet and a second permanent magnet, the magnetic field imposed between the first magnet and the second magnet.

Another embodiment of a fuse assembly has also been disclosed including: a nonconductive housing defining at least one a fuse block and a fuse holder, the nonconductive housing including at least one pair of opposed side walls defining at least one elongated fuse receptacle therebetween, the at least one fuse receptacle dimensioned to receive a cylindrical overcurrent protection fuse including opposing end caps and at least one fusible element; at least one set of resilient fuse clips configured to receive the opposing end caps and establish electrical connection through the least one fusible element when received in the at least one fusible element; and at least one permanent magnet located in the fuse receptacle and imposing an external magnetic field across the at least one fusible element, whereby current flowing through the at least one fuse element and through the external magnetic field produces a mechanical arc deflection force when the at least one fuse element operates to interrupt the circuit connection; and wherein the mechanical arc deflection force is oriented in one of a radial direction relative to the cylindrical fuse and a longitudinal direction relative to the fuse.

Claim 1:
A fuse assembly (<NUM>) comprising:
a nonconductive housing (<NUM>) defining at least one fuse receptacle (<NUM>) dimensioned to receive an overcurrent protection fuse (<NUM>) including fuse terminal elements (<NUM>, <NUM>) in the form of end caps or ferrules;
at least one set of fuse contact terminals (<NUM>, <NUM>) provided on a base wall (<NUM>) in the nonconductive housing (<NUM>) and configured as resilient fuse clips, the at least one set of fuse contact terminals (<NUM>, <NUM>) configured to establish electrical connection through the fuse terminal elements (<NUM>, <NUM>) of the overcurrent protection fuse (<NUM>) when the overcurrent protection fuse (<NUM>) is received in the at least one fuse receptacle (<NUM>);
at least one permanent magnet (<NUM>, <NUM>) coupled to the nonconductive housing (<NUM>) and imposing a magnetic field in the at least one fuse receptacle (<NUM>); and
at least one set of line-side terminals (<NUM>, <NUM>) and load-side terminals (<NUM>, <NUM>) accessible from an exterior of the nonconductive housing (<NUM>) and configured to electrically connect the at least one set of fuse contact terminals (<NUM>, <NUM>) and the overcurrent protection fuse (<NUM>) to an external circuit in an electrical power system;
wherein at least a portion of the overcurrent protection fuse (<NUM>) is disposed in the magnetic field when the overcurrent protection fuse (<NUM>) is received in the at least one fuse receptacle (<NUM>); and
wherein the fuse assembly (<NUM>) is configured to operate in an electrical system having an operating system voltage of <NUM> VDC or above.