Fuse conduit for an expulsion fuse

Abstract

An apparatus includes: a fuse body that extends along an axis from a first end to a second end, the fuse body including an interior surface that defines a bore that extends from the first end to the second end, the bore including regions, and the interior surface including at least a first transition and a second transition. A radial thickness of the fuse body is greater at the first transition than at the second transition such that the bore has a greater internal diameter at the second transition than at the first transition; the regions include at least a sheath exhaust region between the first transition and the second transition, a first region between the first end and the first transition, and a second region between the second transition and the second end; and the sheath exhaust region has a greater extent along a direction that is parallel to the axis than any of the other regions.

Description

[0001] FUSE CONDUIT FOR AN EXPULSION FUSE

[0002] CROSS-REFERENCE TO RELATED APPLICATION

[0003] This application claims the benefit of U.S. Provisional Application No. 63 / 632,629, filed on April 11, 2024 and titled FUSE CONDUIT FOR AN EXPULSION FUSE, which is incorporated herein by reference in its entirety.

[0004] TECHNICAL FIELD

[0005] This disclosure relates to a fuse conduit for an expulsion fuse.

[0006] BACKGROUND

[0007] A fuse may be used to protect electrical equipment.

[0008] SUMMARY

[0009] In one aspect, an apparatus includes: a fuse body that extends along an axis from a first end to a second end, the fuse body including an interior surface that defines a bore that extends from the first end to the second end, the bore including regions, and the interior surface including at least a first transition and a second transition. A radial thickness of the fuse body is greater at the first transition than at the second transition such that the bore has a greater internal diameter at the second transition than at the first transition; the regions include at least a sheath exhaust region between the first transition and the second transition, a first region between the first end and the first transition, and a second region between the second transition and the second end; and the sheath exhaust region has a greater extent along a direction that is parallel to the axis than any of the other regions.

[0010] Implementations may include one or more of the following implementations.

[0011] The sheath exhaust region may have a larger volume than any of the other regions.

[0012] The interior surface may include an arc-quenching material.

[0013] The interior surface also may include a third transition, the radial thickness of the fuse body may be greater at the second transition than at the third transition such that the bore has a greater internal diameter at the third transition than at the second transition; the second region may be between the second transition and the third transition, and the regions also may include a third region between the third transition and the second end; and the sheath exhaust region may have a greater extent along a direction that is parallel to the axis than any of the other regions. The interior surface also may include a fourth transition, the radial thickness of the fuse body may be greater at the third transition than at the fourth transition such that the bore has a greater internal diameter at the fourth transition than at the third transition; the third region is between the third transition and the fourth transition, and the regions also may include a fourth region between the fourth transition and the second end; and the sheath exhaust region may have a greater extent along a direction that is parallel to the axis than any of the other regions. The interior surface also may include a fifth transition. In these implementations, the radial thickness of the fuse body is greater at the fourth transition than at the fifth transition such that the bore has a greater internal diameter at the fifth transition than at the fourth transition, and the regions also include a fifth region between the fifth transition and the second end. An end point on each of the third transition, the fourth transition, and the fifth transition may fall on a first straight line that intersects a central axis of the fuse body and each of the end points. An end point on the second transition and the end point on the third transition may fall on a second straight line that intersects the central axis of the fuse body, the end point on the second transition, and the end point on the third transition; and each of the first straight line and the second straight line may define a different angle relative to the central axis. An end point on the first transition and the end point on the second transition may fall on a third straight line that intersects the central axis of the fuse body, the end point on the first transition, and the end point on the second transition; and each of the first straight line, the second straight line, and the third straight line may define a different angle relative to the central axis.

[0014] At least one of the first transition and the second transition may include two or more substeps.

[0015] The first transition may be between the first end and the second transition, and the second transition may be between the first transition and the second end.

[0016] The interior surface may include an ablative material.

[0017] The radial thickness of the fuse body may vary between the first transition and the second transition.

[0018] The radial thickness of the fuse body may be substantially constant between the first transition and the second transition. In another aspect, a fuse tube includes: a body that extends from a first end to a second end along an axis, the body including an exterior surface and an interior surface, the interior surface defining a bore that extends from the first end to the second end, and the body including a plurality of step transitions of a radial thickness of the body. At least one of the step transitions is a multi-step transition that includes at least two sub-step portions.

[0019] Implementations may include one or more of the following features.

[0020] Each sub-step portion in any multi-step transition may be defined by a different radial thickness of the body.

[0021] In each sub-step portion, the most upstream sub-step may have the greatest radial thickness, and the most downstream sub-step may have the smallest radial thickness.

[0022] In another aspect, an expulsion fuse includes: a fuse body that extends along an axis from a first end to a second end, the fuse body including an interior surface that defines a bore that extends from the first end to the second end, the bore including regions, and the interior surface including at least a first transition and a second transition. A radial thickness of the fuse body is greater at the first transition than at the second transition such that the bore has a greater internal diameter at the second transition than at the first transition; the regions include at least a sheath exhaust region between the first transition and the second transition, a first region between the first end and the first transition, and a second region between the second transition and the second end; and the sheath exhaust region has a greater extent along a direction that is parallel to the axis than any of the other regions. The expulsion fuse also includes a fuse link in the bore, the fuse link including: a fusible element and a sheath that surrounds the fusible element, and the sheath including a sheath exhaust opening. The sheath exhaust opening is open to the sheath exhaust region.

[0023] Implementations may include one or more of the following features.

[0024] The expulsion fuse also may include: a housing that surrounds the fuse body, the housing extending from a first housing end to a second housing end; an electrically conductive contact assembly on the first housing end; and an electrically conductive element that extends through the second housing end and the second end of the fuse body. The electrically conductive contact assembly and the electrically conductive element may be electrically connected to the fusible element. The expulsion fuse also may include an arc shortening rod between the fuse link and the electrically conductive contact assembly. The sheath may include a tube, the tube including a plurality of concentric layers that surround an open interior region.

[0025] The sheath may include alumina trihydrate (ATH).

[0026] Implementations of any of the techniques described herein may include an apparatus, an expulsion fuse, a system, or a method. The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features will be apparent from the description and drawings, and from the claims.

[0027] DRAWING DESCRIPTION

[0028] FIG. 1 is a block diagram of an electrical power distribution system that includes a fuse.

[0029] FIG. 2A is a side cross-sectional view of a fuse conduit and a fuse link.

[0030] FIG. 2B is a cross-sectional view of a sheath of the fuse link of FIG. 2A.

[0031] FIG. 3 is a side perspective exterior view of a fuse.

[0032] FIG. 4 shows the fuse of FIG. 3 mounted to a mounting structure.

[0033] FIG. 5 A shows a fuse conduit with the fuse link of FIG. 2A positioned as a standard expulsion fuse.

[0034] FIGS. 5B-5D and FIGS. 5E-5G are partial cross-sectional views of a fuse body.

[0035] FIG. 6 is a side cross-sectional view of another fuse conduit.

[0036] FIG. 7 shows the fuse conduit of FIG. 5 A used as an extended expulsion fuse.

[0037] FIG. 8 is a side cross-sectional view of the fuse conduit of FIG. 6 used in an extended expulsion fuse.

[0038] FIG. 9 is a cross-sectional view of another fuse conduit.

[0039] DETAILED DESCRIPTION

[0040] FIG. 1 is a block diagram of an electrical power distribution system 100 that includes a fuse 110. The fuse 110 may be a standard expulsion fuse or an extended expulsion fuse. The standard expulsion fuse also may be referred to as a standard cap or a standard design. The extended expulsion fuse also may be referred to as an extender cap, an extended design, an arc shortening rod design, or an arc shortening rod equipped expulsion fuse. As compared to the standard expulsion fuse, the extended expulsion fuse includes an electrically conductive rod or element between an electrical terminal of the fuse 110 and a fusible element inside the fuse. For a given voltage rating, the extended expulsion fuse has a greater maximum interruption current than the standard expulsion fuse. Other implementations of the system 100 are possible. For example, the fuse 110 may be an open link cutout expulsion device or a zero-awaiting device.

[0041] FIG. 2A is a side cross-sectional view of a fuse conduit 111 and a fuse link 130 that are part of the expulsion fuse 110. The fuse conduit 111 extends along an axis 192 from a first end 112 to a second end 113. The second end 113 defines an exhaust opening 117 through which gases and fluids may flow. The first end 112 is attached to a contact assembly 150 and is closed to the flow of gas and fluids. The second end 113 is downstream of the first end 112, and the first end 112 is upstream of the second end 113. As discussed below, the configuration of the fuse conduit 111 provides more effective arc cooling, more effective current interruption, reduces the risk of the fuse link 130 breaking apart, and allows the fuse conduit 111 to be constructed with less material than a typical fuse tube.

[0042] Under ordinary operating conditions, the expulsion fuse 110 is part of a current path 106 (FIG. 1) that electrically connects a first external electrical device 101 and a second external electrical device 102. The expulsion fuse 110 has a current interruption rating and a voltage rating. For example, the expulsion fuse 110 may have a voltage rating of 14.4 to 15.5 kilovolts (kV) and a current interruption rating in the range of 10 kilo-amperes (kA) to 16kA. In another example, the expulsion fuse 110 may have a voltage rating of 25 to 27 kV and a current interruption rating in the range of 8kA to 12 kA. These voltage and interruption ratings are provided as examples. The expulsion fuse 110 may have other voltage and interruption current ratings, including other widely used voltages and interrupting currents. A voltage rating of 38 kV is an example of another widely used voltage rating. When subjected to a current that exceeds the nominal current rating (for example, during an overcurrent or overvoltage fault condition), the expulsion fuse 110 opens the current path 106 such that the electrical devices 101 and 102 are no longer electrically connected.

[0043] Referring also to FIG. 2 A, the fuse conduit 111 has a body 120 with an interior surface 119 that defines a bore 124. The body 120 also includes an exterior surface 128. The body 120 is a three-dimensional structure such as, for example, a cylindrical tube. Other configurations are possible. For example, the body 120 may have an elliptical or rectangular cross-section.

[0044] The body 120 includes an arc-quenching material. For example, the body 120 may include melamine, melamine polyphosphate, melamine phosphate, boric acid, vulcanized fiber, magnesium borate, cellulose impregnated with boric acid, and / or another ablative material. In some implementations, the arc-quenching material is a lining, coating, or deposit on the interior surface 119 and the exterior surface 128 of the body 120 is a hardened shell of an electrically insulating material that forms an exterior housing of the fuse 110.

[0045] The body 120 includes first, second, and third step transitions 121, 122, and 123, which together define a tapered section 129 of the bore 124. Each step transition 121, 122, 123 corresponds to a change in the radial thickness of the body 120. Each different radial thickness of the body 120 corresponds to a different internal diameter of the bore 124. In the example shown, the internal diameter of the bore 124 at the step transition 121 is smaller than the internal diameter of the bore 124 at the step transition 122, and the internal diameter of the bore 124 at the step transition 122 is smaller than the internal diameter of the bore 124 at the step transition 123. The tapered section 129 of bore 124 is generally diverging downstream, that is, toward the exhaust opening 117. As compared to legacy fuse bodies that include diverging sections, the tapered section 129 is longer.

[0046] Other implementations are possible. For example, the internal diameter of the bore 124 may be continuously variable instead of varying in a stepwise manner. Moreover, the step transitions 121, 122, 123 are not necessarily abrupt changes in the radial thickness of the body 120. For example, the step transitions 121, 122, and 123 may be ramp-like transitions. In some implementations, one or more of the step transitions 121, 122, and 123 include sub-steps, such as shown in FIGS. 6 and 8.

[0047] At least part of the fuse link 130 is in the bore 124. The fuse link 130 includes a fusible element 134 and a sheath 135 that surrounds the fusible element 134. The fusible element 134 is electrically conductive. For example, the fusible element 134 may be a tin, copper, silver, or gold wire or cable. The fuse link 130 also includes an electrically conductive element 132. The electrically conductive element 132 may be, for example, a wire or cable. The electrically conductive element 132 is electrically connected to the fusible element 134 and extends through the exhaust opening 117. The sheath 135 extends along the axis 192 of the body 120 from a first sheath end 136 to a second sheath end 137, with the sheath end 137 open to a sheath exhaust region 127 of the bore 124. The sheath 135 may be a composite tube of electrical grade arcquenching, arc-extinguishing, ablative material combined with polymer wraps. Other implementations are possible, for example, the sheath 135 may include an extruded plastic tube with arc-extinguishing material mixed into the plastic.

[0048] FIG. 2B is a cross-sectional view of the sheath 135 in a plane that is perpendicular to the axis 192. In the example shown in FIG. 2B, the sheath 135 includes layers 161, 162, 163, and 164. The layer 161 is the innermost layer and defines an opening 165. The opening 165 passes through the sheath 135 in a direction that is parallel to the axis 192. The fusible element 134 (FIG. 2 A) is in the opening 165. The layer 162 surrounds the layer 161, the layer 163 surrounds the layer 162, and the layer 164 surrounds the layer 163. The layer 161 may be, for example, mylar or mylar strips, the layer 162 may be kraft paper, the layer 163 may be vulcanized fiber fish paper, and the layer 164 may be acetate wrap. The layer 164 may be an acetate wrap having a radial thickness of 0.008 inch (0.02032 centimeters).

[0049] The sheath 135 also may include alumina trihydrate (ATH). For example, the sheath 135 may include 15% ATH by weight, 15 to 19% ATH by weight, up to 20% ATH by weight, or 10 to 20% ATH by weight. The ATH may help build a large volume of dielectric quickly during relatively lower fault currents (for example, fault currents near 160A).

[0050] In some implementations, the sheath 135 includes magnesium di-hydroxide (MDH) with zinc borate (ZB). The relative ratio of MDH to ZB may be, for example, 5: 1 and the overall percentage of flame retardant by weight may be less than 65%. The opening 165 may be lined with a flame-retarding or arc extinguishing material such as, for example, melamine or melamine polyphosphate (MPP).

[0051] The sheath 135 has a radial thickness labeled as 166. The value of the radial thickness 166 may be, for example, between 0.10 and 0.12 inches (0.254 to 0.305 centimeters). Of the layers 161, 162, 163, 164, the layer 163 has the greatest radial thickness. In some implementations, 79% of the total radial thickness 166 of the sheath 135 is in the layer 163, the layer 164 is 6% of the radial thickness 166, and each of the layers 162 and 161 accounts for 8% of the radial thickness 166. Other implementations are possible. For example, more than 79% of the radial thickness 166 may be in the layer 163, or more than 6% of the radial thickness 166 may be in layer 161 while layer 163 is reduced.

[0052] The sheath exhaust region 127 is the region of the bore 124 that is between the step transition 121 and the step transition 122. The sheath exhaust region 127 has an extent 108 in a direction that is parallel to the axis 192. The extent 108 is greater than an extent of any other region of the bore 124. For example, the extent 108 is longer along a direction parallel to the axis 192 than the region of the bore 124 that is between the end 112 and the first step transition 121. The extent 108 is also longer than the region of the bore 124 that is between the second step transition 122 and the third step transition 123 and is also longer than the region of the bore 124 that is between the third step transition 123 and the end 113. Moreover, the sheath exhaust region 127 may have the largest air volume or free volume of any region of the bore 124.

[0053] The dimensions of the sheath exhaust region 127 and the body 120 depend on the voltage rating of the fuse 110. For example, the diameter of the sheath exhaust region 127, the extent 108, the overall size of the body 120 and the placement of the step transitions 121, 122, 123 may be increased by a constant scaling factor to allow the body 120 to be used as part of a fuse with a higher voltage rating. Moreover, at a given voltage rating, the body 120 may be used in a standard expulsion fuse or an extended expulsion fuse without modification.

[0054] When the fuse 110 operates to interrupt the current path 106, the fusible element 134 melts or separates and an arc may form in the fuse link 130. The arc generates hot gases and debris that are exhausted through the opening 165 at the sheath end 137 and into the bore 124. The gases initially collect outside the sheath 135 in the region of the bore 124 that is between the ends 136 and 137. After this region is filled, sheath exhaust region 127 begins to fill. The gases and debris are cooled and / or extinguished in the sheath exhaust region 127 and may be exhausted out of the body 120 through the exhaust opening 117.

[0055] The configuration of the fuse conduit 111 enables the fuse 110 to more effectively interrupt the current path 106 and more effectively quench or extinguish the arc. In legacy standard expulsion fuse designs that include a diverging interior space, the most upstream step transition (the first step transition) is downstream of the end of the sheath. On the other hand, in the fuse 110, the step transition 121 (which is the most upstream transition in the body 120) is upstream of the end 137 of the sheath 135. The placement of the step transition 121 improves the overall performance of the body 120 and the fuse 110, as discussed below.

[0056] First, placing the step transition 121 further upstream decreases the volume of material in the body 120, making the fuse 110 lighter in weight and less expensive than a legacy standard expulsion fuse.

[0057] Second, the upstream placement of the step transition 121 also reduces the wall thickness of the body 120 and increases the free volume of the bore 124, which may reduce internal pressure during in high current tests, even when the fuse 110 uses an arc shortening rod. Examples of high current tests include, for example, the Institute of Electrical and Electronics Engineers (IEEE) C37.41 Series 1, 2, 3, 4 tests or transformer limited fault tests. Moreover, reducing the radial thickness of the body 120 may provide additional performance enhancements. For example, the interior surface 119 may ablate in the presence of an arc, and the vapor produced by the ablating may include components (such as hydrogen) that help to cool the arc and other components (such as carbon) that are electrically conductive and may cause restrike or enhancement of the arc. By reducing the radial thickness of the body 120, the interior surface 119 is still able to extinguish the arcs but production of carbon is minimized.

[0058] Third, the upstream placement of the step transition 121 induces and / or enhances turbulence in the sheath exhaust region 127 and in the bore 124. The presence of turbulence may cool gases that exit the end 137 of the sheath 135 more rapidly than a legacy design that does not intentionally induce and / or enhance turbulence. Additionally, the upstream placement of the first step transition 121 provides a volume of space with a constant diameter (the sheath exhaust region 127) at the end 137 of the sheath 135. This constant-diameter volume also provides performance improvements. The volume of the sheath exhaust region 127 (which is determined by the placement of the first and second step transitions 121, 122) is large enough that it allows a mass of dielectric (for example, air and / or ablation vapors) to move relatively slowly during a transformer limited fault and it helps mitigate the pressure differential along the sheath 135. The placement of the second step transition 122, which is the step transition that is immediately downstream of the step transition 121, also improves the performance of the fuse 110. The second step transition 122 is placed downstream of the end 137 of the sheath 135. The gases that exit through the end 137 may be sonic or supersonic. The pressure differential along the sheath 135 (between the end 136 and the end 137) translates to a higher Mach number (a greater velocity) of the gases that exit through the end 137. The end 137 is free, whereas the end 136 is mounted to another element in the fuse 110. A pressure differential between the ends 136 and 137 can cause the end 137 to vibrate, with the amplitude of the vibrations increasing with the pressure differential. The vibrations can lead to the rupture of the sheath 135. However, by placing the second step transition 122 downstream from the end 137, the velocity of the gases leaving the end 137 may be reduced, thereby reducing the contribution of the flow of gases exiting the end 137 to the rupture of the sheath 135. Fourth, the upstream placement of the step transition 121 increases the volume of dielectric material (air), possibly improving the dielectric recovery of the overall gas mixture (air and / or ablated vapors and gases) in the bore 124.

[0059] Before discussing various examples of the fuse conduit 111, an overview of the system 100 is provided.

[0060] The electrical power distribution system 100 may be part of a power grid or power system that has an operating voltage of, for example, at least 1 kilovolt (kV), up to 34.5 kV, up to 38 kV, up to 69 kV, or 69 kV or higher. The electrical power distribution system 100 is an alternating current (AC) electrical network and may operate at a fundamental frequency of, for example, 50 or 60 Hertz (Hz). Each of the external electrical devices 101 and 102 is any device or devices that utilizes electricity and may include electrical equipment that receives and transfers or distributes electricity to other equipment in the distribution system 100. Examples of devices 101 and 102 include, without limitation, transformers, switchgear, energy storage systems, computer and communication equipment, lighting, heating and air conditioning, motors and electrical machinery in a manufacturing facility, electrical appliances and systems in a residential building. The device 101 and / or 102 may be a source of electricity such as, for example, a power plant that generates electricity from fossil fuel or from thermal energy, or an electrical substation, one or more distributed energy resources, such as, for example, a solar energy system that includes an array of photovoltaic (PV) devices that convert sunlight into electricity or a wind-based energy system.

[0061] FIG. 3 is a side perspective exterior view of the fuse 110. The fuse 110 includes a housing 155 that extends along the axis 192 from a first housing end 156 to a second housing end 157. The housing 155 surrounds the body 120 and may be concentric with the body 120. For example, the body 120 may be a shell, lining, or deposit that is inside the housing 155. In some implementations, the exterior surface 128 of the body 120 is the housing 155. The housing 155 is a high-strength and electrically insulating material, such as, for example, fiberglass and / or an epoxy resin.

[0062] The fuse 110 also includes an electrically conductive contact assembly 150, which is attached to the first housing end 156. The contact assembly 150 is electrically conductive and is electrically connected to the fusible element 134 (FIG. 2A). The contact assembly 150 is made of any electrically conductive material. For example, the contact assembly 150 may be made of a metal such as silver, gold, bronze, or copper. The housing 155 is open at the housing end 157. The exhaust opening 117 aligns with the housing end 157 such that gases and debris that may form when the fuse 110 operates to interrupt current are exhausted through the exhaust opening 117.

[0063] FIG. 4 shows the fuse 110 mounted to a mounting structure 470. The mounting structure 470 may be, for example, an insulated mounting bracket, which may be a fused cutout, a cutout without a fuse, an insulating bracket, or a visible break mounting bracket.

[0064] In the example shown in FIG. 4, a lower portion of the housing 155 (near the housing end 157) is mechanically connected to a lower portion 471 of the mounting structure 470 by a first mounting assembly 472. An upper portion of the body 120 (near the housing end 156) is mechanically connected to an upper portion 473 of the mounting structure 470 by a second mounting assembly 474.

[0065] The electrically conductive contact assembly 150 is electrically connected to the first external electrical device 101. The electrically conductive element 132 is electrically connected to an electrical connection point 476, which is electrically connected to the second external electrical device 102. Under normal and expected operating conditions, current flows into the electrically conductive contact assembly 150, into the fuse 110 and the electrically conductive element 132, and into the electrical connection point 476 such that the devices 101 and 102 are electrically connected by the current path 106. In the presence of a fault condition, the fuse 110 opens to interrupt the current path between the device 101 and 102.

[0066] The first and second mounting assemblies 472, 474 may have any configuration known in the art. For example, the mounting structure 470 may be configured to allow the fuse 110 to rotate about the first mounting assembly 472 after the fuse 110 operates. When the fuse 110 operates to interrupt the current path, the fusible element 134 melts or disintegrates, and the conductive element 132 is pulled out of the exhaust opening 117. An arc is established in the fuse 110. As the arc forms, the arc-extinguishing materials of the sheath 135 decompose and high quantities of de-ionizing, turbulent, and cooling gases are rapidly evolved. The loss of the tension on the conductive element 132 permits the second mounting assembly 474 to disengage from the contact assembly 150, allowing the fuse 110 to rotate about the first mounting assembly 472 into a “drop out” or “drop down” position. Other implementations of the mounting structure 470 are possible. FIGS. 5 A and 7 are side cross-sectional views of a fuse conduit 511. The fuse conduit

[0067] 511 may be used as a standard expulsion fuse 510 (FIG. 5 A) or as an extended expulsion fuse 710 (FIG. 7).

[0068] FIG. 5 A shows the fuse conduit 511 with the fuse link 130 positioned as a standard expulsion fuse 510. That is, the fuse 510 does not include an additional electrically conductive arc shortening rod between the fuse link 130 and the electrically conductive contact assembly 150. Instead, the fuse link 130 is directly connected to the electrically conductive contact assembly 150, such as shown in FIG. 2A.

[0069] The fuse conduit 511 includes a body 520 that extends along an axis 592 from a first end

[0070] 512 to a second end 513. The body 520 includes an interior surface 519 and an exterior surface 528. The body 520 includes an arc-quenching material. The interior surface 519 defines a bore 524 that has an exhaust opening 517 at the end 513. The body 520 has a variable radial thickness, and the interior surface 519 defines step transitions 521, 522, 523, 525, and 526. The radial thickness of the body 520 is greater at the step transition 521 than at the step transition 522, the radial thickness of the body 520 is greater at the step transition 522 than at the step transition 523, the radial thickness of the body 520 is greater at the step transition 523 than at the step transition 525, and the radial thickness of the body 520 is greater at the step transition 525 than at the step transition 526. In other words, the internal diameter of the bore 524 generally diverges or increases in the downstream direction toward the exhaust opening 517.

[0071] The fuse link 130 is in the bore 524, with the end 137 of the sheath 135 extending into a sheath exhaust region 527. The sheath exhaust region 527 is the portion of the bore 524 that is between the step transitions 521 and 522. A conductive sleeve 538 extends into the bore 524 from the end 512 and surrounds part of the sheath 135. The conductive sleeve 538 may be, for example, a metal tube such as a copper tube.

[0072] In legacy standard expulsion fuse designs that include a stepwise diverging interior space, the first step transition (the most upstream step transition) is downstream of the end of the sheath. On the other hand, in the fuse 510, the step transition 521 (which is the most upstream transition) is upstream of the end 137 of the sheath 135. Placing the step transition 521 further upstream decreases the volume of material in the body 520, making the fuse 510 lighter in weight and less expensive than a legacy standard expulsion fuse that lacks the body 520. The placement of the step transition 521 also reduces the wall thickness of the body 520 and increases the free volume of the bore 524, thereby reducing internal pressures in high current tests (for example, during Series 1 and 2 tests). Furthermore, the upstream placement of the step transition 521 enhances and / or induces turbulence in the sheath exhaust region 527 (and the bore 524), thereby cooling gases that are exhausted through the end 137 of the sheath 135 more quickly.

[0073] FIGS. 5B-5D and FIGS. 5E-5G are partial cross-sectional views of the fuse body 520. FIGS. 5B and 5E show the portion of the fuse body 520 that includes the step transitions 523, 525, and 526. FIGS. 5C and 5F show the portion of the fuse body 520 that includes the step transitions 522 and 523. FIGS. 5D and 5G show the portion of the fuse body 520 that includes the step transitions 521 and 522. The positions of the step transitions 521, 522, 523, 525, and 526 may be defined by three angles 582_1, 582_2, 582_3 and / or three angles 583 1 , 583_2, 583 3. Referring to FIGS. 5B-5D, the angle 582 1 is the angle defined by two lines (shown in short dash line style in FIG. 5B) that extend from a point on the axis 592 and intersect the beginning (or most upstream point) of each step transition 523, 525, 526. The angle 582_2 is the angle defined by two lines (shown in short dash line style in FIG. 5C) that extend from a point on the axis 592 and intersect the beginning (or most upstream point) of each step transition 522, 523. The angle 582_3 is the angle defined by two lines (shown in short dash line style in FIG. 5D) that extend from a point on the axis 592 and intersect the beginning (or most upstream point) of each step transition 521, 522.

[0074] The angle 583 1 (FIG. 5E) is defined by two lines that extend from a point on the axis 592 and intersect the end (or most downstream point) of the step transitions 523, 525, 526. The angle 583 2 (FIG. 5F) is defined by two lines that extend from a point on the axis 592 and intersect the end (or most downstream point) of the step transitions 522, 523. The angle 583 3 (FIG. 5G) is defined by two lines that extend from a point on the axis 592 and intersect the end (or most downstream point) of the step transitions 521, 522. The trio of angles 582_1, 582_2 and 582_3 do not have the same values. Likewise, the trio of angles 583 1 , 583_2 and 583_3 have different values. In other words, and unlike some prior fuse tube designs, all of the step transitions 521, 522, 523, 525, 526 do not fall on a single straight line that intersects the axis 592 and a single angle value is insufficient to define the placement of the step transitions 521, 522, 523, 525, 526. In some implementations, the inner diameter of the bore 524 in the sheath exhaust region 527 is 0.520 to 0.550 inches (in) (or 1.32 to 1.39 cm) and the length of the sheath exhaust region 527 along the axis 592 is 4.10 to 4.20 in (10.41 to 10.66 cm), the inner diameter of the bore 524 between the step transitions 522 and 523 is 0.550 to 0.580 in (or 1.39 to 1.47 cm) and the length of this portion is 1.3 to 1.4 in (3.30 to 3.55 cm), the inner diameter of the bore 524 between the step transitions 523 and 525 is 0.580 to 0.610 in (or 1.47 cm to 1.55 cm) and the length of this portion is 0.35 to 0.45 in (0.90 to 1.14 cm), the inner diameter of the bore 524 between the step transition 525 and the step transition 526 is 0.610 to 0.640 in (or 1.47 to 1.62 cm) and the length of this portion is 0.35 to 0.45 in (0.90 to 1.14 cm), and the inner diameter of the bore 524 between the step transition 526 and the exhaust opening 517 is 0.64 to 0.67 in (1.62 to 1.70 cm) and the length of this portion is 0.35 to 0.45 in (0.90 to 1.14 cm).

[0075] These dimensions are provided as an example, and other dimensions are possible. Moreover, for a particular voltage rating the same body 520 may be used in an extended expulsion fuse or in a standard expulsion fuse. Additionally, the inner diameters and the lengths of the various portions of the body 520 may be scaled (increased or decreased) by a constant amount and used in a standard expulsion fuse or an extended expulsion fuse of a different voltage rating. For example, the dimensions provided above may be an example for a fuse having a voltage rating of 15.5 V, and a body having diameters and lengths that are 1.1 to 1.5 times larger may be used in a fuse having a voltage rating of 27 kV.

[0076] FIG. 6 is a side cross-sectional view of another fuse conduit 611 that may be used in a standard expulsion fuse 610 (FIG. 6) or an extended expulsion fuse 810 (FIG. 8). The fuse conduit 611 includes a body 620 that extends from a first end 612 to a second end 613. The body 620 includes an interior surface 619 and an exterior surface 628. The body 620 includes an arc-quenching material. The interior surface 619 defines a bore 624 that has an exhaust opening 617 at the end 613. The body 620 has a variable radial thickness and defines step transitions 621, 622, 623, and 625. The radial thickness of the body 620 is greater at the step transition 621 than at the step transition 622, the radial thickness of the body 620 is greater at the step transition 622 than at the step transition 623, and the radial thickness of the body 620 is greater at the step transition 623 that at the step transition 625. In other words, the internal diameter of the bore 624 generally diverges or increases toward the exhaust opening 617. The fuse link 130 is in the bore 624, with the end 137 of the sheath 135 being upstream of or aligned with an opening of a sheath exhaust region 627 that is between the step transition 621 and the step transition 622. The body 620 is different from the body 520. First, the transition 621 is closer to the exhaust opening 617 than the step transition 521 is to the exhaust opening 517. Because of the placement of the transition 621, when the fuse link 130 is loaded into the bore 624, the sheath end 137 is upstream of or is substantially aligned with the opening of the sheath exhaust region 627. This is in contrast to the body 520, in which the sheath end 137 extends into the sheath exhaust region 527 when the fuse link 130 is loaded into the bore 524.

[0077] Second, the step transition 621 includes a plurality of sub-step portions instead of a single-step transition. The inset labeled 699 shows the step transition 621 in greater detail. As shown in the inset 699, the step transition 621 includes two sub-steps 621a and 621b that are separated by a relatively flat section 621c. The sub-step 621a corresponds to a portion of the body 620 that has a radial thickness 629a that decreases until reaching the portion of the body 620 that corresponds to the flat section 621c. The body 620 has a substantially constant radial thickness 629c in the flat section 621c until decreasing again in the portion of the body 620 that corresponds to the sub-step 621b. The flat section 621c may be, for example, about 0.25 to 2 millimeters (mm) such that the sub-step 621a and 621b are 0.5-4mm apart along a direction parallel to an axis 692 of the body 620.

[0078] As compared to a step transition that includes one step change in the radial thickness of the body, the step transition 621 (which includes the sub-steps 621a and 621b) increases the turbulence of gases that are exhausted from the sheath 135. The increased turbulence results in quicker cooling of the exhaust gases created downstream of the steps.

[0079] Other implementations are possible. For example, the step transition 621 may include more than two sub-steps. Additionally, the other step transitions 622, 623, 625 may include two or more sub-steps or may be implemented as single-step transitions.

[0080] FIG. 7 shows the fuse conduit 511 used as an extended expulsion fuse 710. As compared to the configuration shown in FIG. 5 A, which shows the fuse conduit 511 used as part of the standard expulsion fuse 510, the extended expulsion fuse 710 lacks the conductive sleeve 538 and instead includes an arc shortening rod 780. The arc shortening rod 780 is an electrically conductive element, such as a metal rod. The arc shortening rod 780 is between the fuse link 130 and the contact assembly 150 (not shown in FIG. 7). The arc shortening rod 780 is electrically connected to the contact assembly 150 and the fusible element 134. Under normal operating conditions, electrical current flows into the contact assembly 150, into the arc shortening rod 780, into the fusible element 134, and into the conductive element 132.

[0081] The sheath end 137 extends into the sheath exhaust region 527. As compared to the standard expulsion fuse 510 (FIG. 5 A), the sheath end 137 is closer to the exhaust opening 517 in the extended expulsion fuse 710 because the arc shortening rod 780 is placed between the contact assembly 150 and the fuse link 130. Placing the sheath end 137 closer to the exhaust opening 517 may cause the gases that are exhausted from the sheath end 137 to exit the body 520 more rapidly than they do in a standard expulsion fuse that lacks the arc shortening rod 780. The gases may exit the sheath end 137 at sonic or supersonic speed. Gases at sonic speeds or greater that exit from a diverging nozzle decrease the pressure at the exiting end as compared to the other end of the nozzle. If the fuse 710 used a legacy fuse tube instead of the body 520, the rapidly exiting gases could cause the pressure at the sheath end 137 to drop compared to the pressure at the sheath end 136. Because the sheath end 137 is substantially unsupported, this pressure differential could cause the sheath 135 to vibrate at the sheath end 137, which can result in rupture of the sheath 135.

[0082] On the other hand, the fuse 710 uses the body 520. In the body 520, the step transition 521 is positioned such that, when the fuse link 130 and arc shortening rod 780 are in the bore 524, the sheath exhaust region 527 has a larger volume than the exhaust region of fuse tubes used in legacy expulsion fuses. The larger volume allows a mass of dielectric (for example, air and / or vapor produced during ablation) to move relatively slowly toward the exhaust opening 517, thereby mitigating the pressure differential along the sheath 135. This allows the fuse 710 to interrupt higher transformer limited fault currents without the sheath 135 rupturing. For example, tests performed on the fuse 710 measured the absolute value of the average pressure differential along the sheath 135 at 6 pounds per square inch (PSI) as compared to an average measured pressure differential of 198 PSI for the legacy fuse that did not include the body 520.

[0083] FIG. 8 is a side cross-sectional view of the fuse conduit 611 used in an extended expulsion fuse 810. In the extended expulsion fuse 810, the sheath end 137 is in the sheath exhaust region 627. The expulsion fuse 810 uses the same fuse conduit 611 as the standard expulsion fuse 610, but the arc shortening rod 780 is between the end 612 and the fuse link 130. Due to the inclusion of the arc shortening rod 780, the end 137 of the sheath 135 closer to the exhaust opening 617 in the extended expulsion fuse 810 than in the standard expulsion fuse 610.

[0084] The addition of the arc shortening rod 780 allows the extended expulsion fuse 810 to interrupt higher maximum current ratings than the standard expulsion fuse 610. For example, without the arc shortening rod, an expulsion fuse with a voltage rating of 14.4 kV interrupts a maximum current of 10 kA. When the arc shortening rod 780 is added, the maximum interrupting capability increases to 16 kA. Interruptions with this high current value (for example, 16 kA) are typical of a line fault. A line fault is typical when an electrical line contacts another electrical line or contacts ground. The placement of the step transitions 621 and 622, which increase the volume of the sheath exhaust region 627 as compared to legacy designs, allow the extended expulsion fuse 810 to interrupt transformer limited faults (which are between about 160A and 1200A regardless of voltage). The free space volume of the sheath exhaust region 627 is large enough to allow a mass of dielectric to move relatively slowly during a transformer limited fault, and this helps prevent or mitigate a pressure differential along the sheath 135. This allows the fuse 810 to interrupt higher transformer limited fault currents without the sheath 135 rupturing. Additionally, the multi-step transition 621 increases the turbulence of the gases in the sheath exhaust region 627, providing further arc cooling.

[0085] FIG. 9 is a side cross-sectional view of another fuse conduit 911. The fuse conduit 911 may be used as a standard expulsion fuse (as shown in FIG. 9) or as an extended expulsion fuse. FIG. 9 shows the fuse conduit 911 with the fuse link 130 positioned as a standard expulsion fuse 910. That is, the fuse 910 does not include an additional electrically conductive arc shortening rod between the fuse link 130 and the electrically conductive contact assembly 150. Instead, the fuse link 130 is directly connected to the electrically conductive contact assembly 150, such as shown in FIG. 2A.

[0086] The fuse conduit 911 is similar to the fuse conduit 511, except the fuse conduit 911 has a bore 924 with an inner diameter that varies based on tapering instead of discrete steps. In greater detail, the fuse conduit 911 includes a body 920 that extends along an axis 992 from a first end 912 to a second end 913. The body 920 includes an interior surface 919 and an exterior surface 928. The body 920 includes an arc-quenching material. The bore 924 has an exhaust opening 917 at the end 913. The body 920 has a variable radial thickness, and the interior surface 919 defines slope transitions 921, 922, and 923. The radial thickness of the body 920 decreases linearly with a first slope between the transitions 921 and 922, decreases linearly with a second slope between transitions 922 and 923, and decreases linearly with a third slope between the transition 923 and the end 913. The first, second, and third slopes have different values such that the rate of decreasing radial thickness of the body 920 varies among the different regions. However, the inner diameter of the bore 924 generally increases or diverges from the slope transition 921 to the end 913.

[0087] The fuse link 130 is in the bore 924, with the end 137 of the sheath 135 extending into a sheath exhaust region 927. The sheath exhaust region 927 is the portion of the bore 924 that is between the slope transitions 921 and 922. A conductive sleeve 538 extends into the bore 924 from the end 912 and surrounds part of the sheath 135. The conductive sleeve 538 may be, for example, a metal tube such as a copper tube.

[0088] In the fuse 910, the slope transition 921 (which is the most upstream transition) is upstream of the end 137 of the sheath 135. Placing the step transition 921 upstream of the end 137 decreases the volume of material in the body 920, making the fuse 910 lighter in weight and less expensive than a legacy standard expulsion fuse. The placement of the slope transition 921 also reduces the wall thickness of the body 920 and increases the free volume of the bore 924, thereby reducing internal pressures in high current tests (for example, during Series 1 and 2 tests).

[0089] Other implementations of the fuse conduit 911 are possible. For example, although three slope transitions 921, 922, 923 are shown in FIG. 9, the fuse conduit 911 may include more or fewer slope transitions.

[0090] These and other implementations are within the scope of the claims.

Claims

WHAT IS CLAIMED IS:

1. An apparatus comprising: a fuse body that extends along an axis from a first end to a second end, the fuse body comprising an interior surface that defines a bore that extends from the first end to the second end, the bore comprising regions, and the interior surface comprising at least a first transition and a second transition, wherein a radial thickness of the fuse body is greater at the first transition than at the second transition such that the bore has a greater internal diameter at the second transition than at the first transition; the regions comprise at least a sheath exhaust region between the first transition and the second transition, a first region between the first end and the first transition, and a second region between the second transition and the second end; and the sheath exhaust region has a greater extent along a direction that is parallel to the axis than any of the other regions.

2. The apparatus of claim 1 , wherein the sheath exhaust region has a larger volume than any of the other regions.

3. The apparatus of claim 1, wherein the interior surface comprises an arc-quenching material.

4. The apparatus of claim 1 , wherein the interior surface further comprises a third transition, the radial thickness of the fuse body is greater at the second transition than at the third transition such that the bore has a greater internal diameter at the third transition than at the second transition; the second region is between the second transition and the third transition, and the regions further comprise a third region between the third transition and the second end; and the sheath exhaust region has a greater extent along a direction that is parallel to the axis than any of the other regions.

5. The apparatus of claim 4, wherein the interior surface further comprises a fourth transition, the radial thickness of the fuse body is greater at the third transition than at the fourth transition such that the bore has a greater internal diameter at the fourth transition than at the third transition; the third region is between the third transition and the fourth transition, and the regions further comprise a fourth region between the fourth transition and the second end; and the sheath exhaust region has a greater extent along a direction that is parallel to the axis than any of the other regions.

6. The apparatus of claim 5, wherein the interior surface further comprises a fifth transition, the radial thickness of the fuse body is greater at the fourth transition than at the fifth transition such that the bore has a greater internal diameter at the fifth transition than at the fourth transition, and the regions further comprise a fifth region between the fifth transition and the second end.

7. The apparatus of claim 6, wherein an end point on each of the third transition, the fourth transition, and the fifth transition fall on a first straight line that intersects a central axis of the fuse body and each of the end points.

8. The apparatus of claim 7, wherein an end point on the second transition and the end point on the third transition fall on a second straight line that intersects the central axis of the fuse body, the end point on the second transition, and the end point on the third transition; and wherein each of the first straight line and the second straight line defines a different angle relative to the central axis.

9. The apparatus of claim 8, wherein an end point on the first transition and the end point on the second transition fall on a third straight line that intersects the central axis of the fuse body, the end point on the first transition, and the end point on the second transition; and wherein each of the first straight line, the second straight line, and the third straight line defines a different angle relative to the central axis.

10. The apparatus of claim 1, wherein at least one of the first transition and the second transition comprises two or more sub-steps.

11. The apparatus of claim 1 , wherein the first transition is between the first end and the second transition, and the second transition is between the first transition and the second end.

12. The apparatus of claim 1, wherein the interior surface comprises an ablative material.

13. The apparatus of claim 1, wherein the radial thickness of the fuse body varies between the first transition and the second transition.

14. The apparatus of claim 1, wherein the radial thickness of the fuse body is substantially constant between the first transition and the second transition.

15. A fuse tube comprising: a body that extends from a first end to a second end along an axis, the body comprising an exterior surface and an interior surface, the interior surface defining a bore that extends from the first end to the second end, and the body comprising plurality of step transitions of a radial thickness of the body, wherein at least one of the step transitions is a multi-step transition that comprises at least two sub-step portions.

16. The fuse tube of claim 15, wherein each sub-step portion in any multi-step transition is defined by a different radial thickness of the body.

17. The fuse tube of claim 15, wherein, in each sub-step portion, the most upstream sub-step has the greatest radial thickness, and the most downstream sub-step has the smallest radial thickness.

18. An expulsion fuse comprising: a fuse body that extends along an axis from a first end to a second end, the fuse body comprising an interior surface that defines a bore that extends from the first end to the secondend, the bore comprising regions, and the interior surface comprising at least a first transition and a second transition, wherein a radial thickness of the fuse body is greater at the first transition than at the second transition such that the bore has a greater internal diameter at the second transition than at the first transition; the regions comprise at least a sheath exhaust region between the first transition and the second transition, a first region between the first end and the first transition, and a second region between the second transition and the second end; and the sheath exhaust region has a greater extent along a direction that is parallel to the axis than any of the other regions; and a fuse link in the bore, the fuse link comprising a fusible element and a sheath that surrounds the fusible element, the sheath comprising a sheath exhaust opening, and wherein the sheath exhaust opening is open to the sheath exhaust region.

19. The expulsion fuse of claim 18, further comprising: a housing that surrounds the fuse body, the housing extending from a first housing end to a second housing end; an electrically conductive contact assembly on the first housing end; and an electrically conductive element that extends through the second housing end and the second end of the fuse body, wherein the electrically conductive contact assembly and the electrically conductive element are electrically connected to the fusible element.

20. The expulsion fuse of claim 19, further comprising an arc shortening rod between the fuse link and the electrically conductive contact assembly.

21. The expulsion fuse of claim 18, wherein the sheath comprises a tube, the tube comprising a plurality of concentric layers that surround an open interior region.

22. The expulsion fuse of claim 18, wherein the sheath comprises alumina trihydrate (ATH).

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