Compact fuse support

Method and apparatus for mounting fuses in switchgear and similar electrical isolation equipment provide a nonconductive fuse support that allows the fuses to be mounted separately from the transformers. Two such fuse supports may be used to support a fuse, one fuse support for each fuse terminal. Each fuse support may support two fuse terminals so dual fuses may be supported by the same pair of fuse supports. The fuse supports substantially surround the fuse terminals to provide an insulating barrier that helps prevent electrical discharge and also ensure sufficient spacing between the fuse terminals and ground or other conductors in the switchgear. Such an arrangement allows the fuses and transformers to fit within a reduced space in the switchgear and similar electrical isolation equipment while complying with industry-standard performance requirements. The fuse supports are preferably noncontiguous, thereby leaving the nonconductive portion of the fuse physically unsurrounded.

FIELD OF THE INVENTION

The disclosed embodiments relate generally to switchgear and similar electrical isolation equipment, and particularly to methods and apparatuses for reducing the amount of space required to mount fuses and similar current-limiting devices in such isolation equipment.

BACKGROUND OF THE INVENTION

Switchgear and similar electrical isolation equipment are highly regulated by industry standards (e.g., IEEE, ANSI, etc.). Among other things, these standards require line-side (upstream) current-limiting fuses for voltage transformers (“VT”) used as sensors to monitor the condition and quality of power in medium voltage switchgear. Such fuses frequently resemble a tube having conductive terminals on each end and are typically mounted directly onto the voltage transformers in the switchgear cabinet. The industry standards also define the minimum clearance or spacing required in the absence of substantiating test documentation between exposed portions of adjacent conductors, such as adjacent electrical power buses, as well as from those conductors to ground for various voltage levels. The clearances are described in terms of direct or “strike” distances and linear surface or “tracking” distances.

Direct mounting of fuses onto the voltage transformers requires space in the switchgear. However, customer preferences for smaller and less expensive switchgear continue to push manufacturers toward ever smaller switchgear. As an example, for mature switchgear like the Masterclad™ series of medium voltage metal-clad switchgear from Schneider Electric USA, Inc., the voltage transformers and tubular fuses reside within a compartment that measures roughly 36 inches wide by 42 inches tall. On the other hand, smaller switchgear like the HVL/cb™ series of metal-enclosed switchgear from Schneider Electric USA require the voltage transformer and tubular fuse to fit within a compartment that is about half the size. This makes it difficult, if not impractical, to mount fuses directly onto voltage transformer in small footprint switchgears.

Similar challenges exist for other types of transformers in small footprint switchgears. For example, control power for breaker controls (e.g., relays, controllers, etc.) is often derived from the medium voltage switchgear primary circuit. The devices that convert power from the switchgear are commonly called control power transformers (“CPT”) and are generally larger than voltage transformers. As a result, it is especially difficult to mount fuses directly onto CPTs in small footprint switchgears. The above difficulty is compounded by the imperative also to comply with industry-standard clearance or performance requirements.

Thus, a need exists for a way to mount transformer fuses in small footprint switchgear and similar electrical isolation equipment where the space allocated for the fuses and transformers is limited while also complying with industry-standard performance requirements.

SUMMARY OF THE DISCLOSED EMBODIMENTS

The embodiments disclosed herein are directed to a method and apparatus for mounting fuses that protect transformers in switchgear and similar electrical isolation equipment. The method and apparatus provide a nonconductive fuse support that allows the tubular fuses to be mounted separately from, instead of directly on, the transformers. Two such fuse supports may be used to support a fuse, each fuse support supporting one fuse terminal. Alternatively, each fuse support may support two fuse terminals so dual fuses may be supported by the same pair of fuse supports. The fuse supports substantially surround the fuse terminals to provide an insulating barrier that helps prevent electrical discharge and also ensure sufficient spacing between the fuse terminals and ground or other conductors in the switchgear. Such an arrangement allows the fuses and transformers to fit within a reduced space in the switchgear and similar electrical isolation equipment while complying with industry-standard performance requirements.

In some embodiments, each nonconductive fuse support includes an open-ended housing made of a plastic or similar nonconductive material having a top wall, a bottom wall, and two side walls that form a generally rectangular tube. The housing has an elongated, generally cylindrical support structure also made of plastic or similar nonconductive material extending away from an exterior surface of the bottom wall substantially perpendicularly thereto. The elongated support structure helps keep the housing and the fuse terminal therein separated from any live or grounded components, such as a panel or wall in the switchgear, by a predefined strike distance when the fuse support is installed in the switchgear.

In some embodiments, the elongated support structure may include a neck portion and a base portion extending from the neck portion. The base portion is designed to be attached or otherwise fastened to a panel or wall within the switchgear and may have a larger diameter than the neck portion for greater stability. Either or both the base portion and the neck portion may have coaxial, radially extending insulating discs or sheds disposed thereon that function to increase the tracking distance along the outer surface of the elongated support structure. A first set of screw holes may be drilled or otherwise provided on an underside of the base portion to facilitate attaching it to the panel or wall in the switchgear.

A second set of screw holes may similarly be drilled or otherwise provided in the bottom wall of the housing on an interior surface thereof in some embodiments for screwing or otherwise attaching a bracket to the housing. The screw holes extend into, but do not pass through, a screw receiving channel integrally disposed on the exterior surface of the bottom wall at or near the point where the elongated support structure meets the bottom wall. The screw receiving channel helps prevent any screws or fasteners in the screw holes from breaking through so no potentially conductive components are exposed on the exterior surface of the housing, thereby maintaining the structural and insulating integrity of the fuse support.

The bracket may be part of a mounting assembly that helps hold a fuse between the fuse supports. The mounting assembly includes a pair of brackets, one bracket for each fuse support, and two conductive end caps, one end cap on each bracket, for receiving the fuse terminals of the fuse. One of the end caps may be fixed to one of the brackets while the other end cap be releasably attached to the second bracket via a suitable locking mechanism, such as a quarter-turn locking mechanism. The end caps may be field-shaping end caps that have mostly or only smooth and rounded surfaces so there are no hard or sharp edges or corners from which electrical discharge from/to ground or other conductors may occur. This use of smooth and rounded surfaces allows the end caps and thus the fuse terminals to be located nearer to ground or other conductors than would conventionally be the case.

In general operation, to mount a fuse, a pair of fuse supports is attached or otherwise fastened to the panel or wall in the switchgear so their respective brackets line up opposite from each other. One fuse terminal is then inserted in the fixed end cap on one of the bracket while the non-fixed end cap is placed over the opposite fuse terminal. The non-fixed end cap is then inserted in the second bracket and locked, for example, by a quarter-turn twist to secure the fuse between the two fuse supports. It is also possible to secure the fuse between the pair of fuse supports first and then attach or otherwise fasten the fuse supports to the panel or wall in the switchgear.

In general, in one aspect, the disclosed embodiments relate to a fuse support for mounting a tubular fuse in electrical isolation equipment. The fuse support comprises, among other things, an open-ended housing having a top wall, a bottom wall, and two side walls forming a generally rectangular tube and an elongated support structure extending from an exterior surface of the bottom wall of the housing substantially perpendicular thereto. The fuse support further comprises a terminal bracket attached to the bottom wall of the housing on an interior surface thereof over the elongated support structure and a cup shaped end cap attached to the bracket for receiving a fuse terminal of the tubular fuse, the cup shaped end cap having smooth and rounded surfaces that minimize or prevent electrical discharge through the end cap.

In general, in another aspect, the disclosed embodiments relate to a switchgear module. The switchgear module comprises, among other things, a panel, a fuse assembly attached to the panel, a mounting assembly disposed in the fuse assembly, and a fuse having a fuse terminal at each opposing end thereof, the fuse secured to the mounting assembly such that said fuse is mounted separately from any transformer attached to the panel.

DETAILED DESCRIPTION OF THE DISCLOSED EMBODIMENTS

As an initial matter, it will be appreciated that the development of an actual, real commercial application incorporating aspects of the disclosed embodiments will require many implementation specific decisions to achieve the developer's ultimate goal for the commercial embodiment. Such implementation specific decisions may include, and likely are not limited to, compliance with system related, business related, government related and other constraints, which may vary by specific implementation, location and from time to time. While a developer's efforts might be complex and time consuming in an absolute sense, such efforts would nevertheless be a routine undertaking for those of skill in this art having the benefit of this disclosure.

It should also be understood that the embodiments disclosed and taught herein are susceptible to numerous and various modifications and alternative forms. Thus, the use of a singular term, such as, but not limited to, “a” and the like, is not intended as limiting of the number of items. Similarly, any relational terms, such as, but not limited to, “top,” “bottom,” “left,” “right,” “upper,” “lower,” “down,” “up,” “side,” and the like, used in the written description are for clarity in specific reference to the drawings and are not intended to limit the scope of the invention.

Referring first toFIG. 1A, a side view of an exemplary module for a medium voltage switchgear (not expressly shown) according to the disclosed embodiments is shown. The switchgear module100comprises a grounded panel102on which a transformer unit104having one or more voltage transformers (not expressly shown) therein is attached or otherwise fastened along with other medium voltage switchgear equipment106. It should be understood that any reference to medium voltage switchgear, that is, switchgear with voltage ratings generally between 1 kV-35 kV, is illustrative only and that the principles and concepts discussed herein are also applicable to low and high voltage ratings.

One or more exemplary fuse assemblies, one of which is indicated at108a, are also attached or otherwise fastened on the panel102in accordance with the disclosed embodiments. The fuse assembly108aincludes a pair of exemplary fuse supports200a&200bthat hold or otherwise secure at least one current-limiting fuse110therebetween. As can be seen, the nonconductive fuse supports200a&200bare located separately from the transformer unit104so the fuse110is not mounted directly on a transformer within the transformer unit104. The mounting of the fuse110separately from the transformer allows the overall size of the switchgear module100to be reduced, making it possible or at least easier for the switchgear module100to fit within a smaller compartment compared to existing solutions. For example, the exemplary switchgear module100shown here may fit within a compartment that measures only 17 inches wide by 45 inches tall, such as may be found in the HVL/cb™ series of metal-enclosed switchgear from Schneider Electric USA, Inc., or similar metal-enclosed and metal-clad switchgear.

FIG. 1Bdepicts the switchgear module100looking down from the top of the panel102, with the transformer unit104and other electrical equipment106removed from the panel102for clarity. As this view shows, there are three fuse assemblies108a,108b, and108con the panel102, each fuse assembly comprising a pair of virtually identical fuse supports200a&200b. Each fuse support200a&200bhouses a fuse terminal for at least one tubular fuse110to secure the fuse therebetween. Only the nonconductive middle portions of the fuses110are visible, the conductive fuse terminals being hidden from view by the fuse supports200a&200b. In the example shown, the left fuse assembly108aand the right fuse assembly108ceach support two fuses110while the middle fuse assembly108bsupports a single fuse110. An alternative number of fuse assemblies and/or fuses per fuse assembly may of course be deployed depending on the needs of the particular switchgear application without departing from the scope of the disclosed embodiments.

FIG. 1Cshows a view of the switchgear module100as seen from the front of the panel102such that only one fuse support200afrom each of the fuse assemblies108a,108b, and108cis visible. From this angle, it can be seen that each fuse assembly108a,108b, and108cfurther comprises at least one mounting assembly300therein to which a fuse110(not visible here) may be physically and electrically connected. As will be more readily discerned fromFIG. 4, the fuse supports200a&200bsubstantially surround the fuse terminals (not visible here) to provide an insulating barrier that helps prevent electrical discharge and also ensure sufficient spacing between the fuse terminals and ground or other conductors in the switchgear. Where two fuses110and hence two mounting assemblies300are employed in a given fuse assembly108a,108b, or108c, a conductive plate112may be used to connect the dual mounting assemblies together and thus electrically connect the fuses110together in the fuse assembly.

Turning now toFIGS. 2A and 2B, perspective views of an exemplary fuse support200are shown according to the disclosed embodiments. The fuse support200includes two main sections, an open-ended housing202and an elongated, generally cylindrical support structure204extending perpendicularly away from the housing202. The housing202may resemble a generally rectangular tube having a top wall206, a bottom wall208, and two side walls210and212and may be made of a plastic or similar nonconductive material. The elongated support structure204, which may be made of the same nonconductive material, extends from an exterior surface208aof the bottom wall208near the center thereof and helps keep the housing202(and the fuse terminal therein) separated from the panel102and other conductors in the switchgear by a predefined clearance or strike distance.

In some embodiments, the elongated support structure204may also include two main sections, a neck portion214and a base portion216extending coaxially from the neck portion214. The base portion216is designed to be attached or otherwise fastened to the panel102and in some embodiments may have a larger diameter than the neck portion214for better stability. Either or both the base portion216and the neck portion214may have coaxial, radially extending insulating discs or sheds218disposed thereon that function to increase the tracking distance along the outer surface of the elongated support structure204. A first set of screw holes220may be drilled or otherwise provided on an underside216aof the base portion216to facilitate screwing or otherwise attaching it to the panel102.

A second set of screw holes222may also be drilled or otherwise provided in the bottom wall208of the housing202on an interior surface208bthereof in some embodiments for screwing or otherwise attaching a terminal bracket (302and304, discussed inFIG. 3) to the housing202. The screw holes222extend into, but do not go through, a bar shaped screw receiving channel224formed or otherwise integrally disposed on the exterior surface208aof the bottom wall208at or near the point where the elongated support structure204meets the bottom wall208. The screw receiving channel224helps prevent any screws or fasteners from breaking through the housing202so no potentially conductive components are exposed on the exterior surface208aof the housing202, thus preserving the structural and insulating integrity of the fuse support200.

The terminal bracket mentioned above may be part of a mounting assembly300, depicted inFIG. 3, that helps hold the fuse110between two fuse supports200a&200b(as shown inFIG. 4). The mounting assembly300includes two generally L-shaped terminal brackets302and304, one for each fuse terminal, and two generally cup-shaped end caps306and308, one end cap on each bracket302and304, respectively, for receiving the fuse terminals of the fuse110. The conductive end caps306and308may be field-shaping end caps that have mostly or only smooth and rounded surfaces so there are no hard or sharp edges or corners from which through-air electrical discharge from/to ground or other conductors may occur. This use of smooth and rounded surfaces allows the end caps and thus the fuse terminals therein to be located nearer to ground or other conductors than would otherwise be the case.

Each terminal bracket302and304has a generally flat base310and312, respectively, that may be fastened to the housing202of the fuse support200and a generally flat mounting plate314and316, respectively, extending perpendicularly from the base310and312for supporting the end caps306and308. One of the end caps, for example, the right end cap306, may be fixedly attached (e.g., welded, etc.) to the first terminal bracket, for example, the right bracket302, on the mounting plate314thereof. The mounting plate316of the second terminal bracket306may have a circular opening formed therein (not expressly labeled) for receiving the non-fixed end cap308. A locking mechanism, such as a quarter-turn locking mechanism, may be used to releasably attach the non-fixed end cap308to it its respective terminal bracket304. For example, the second terminal bracket304may have a notch318formed in the opening in the mounting plate316thereof and the non-fixed end cap308may have a tab320protruding therefrom that corresponds to the notch318. Inserting the non-fixed end cap308so the tab320passes through the notch318and rotating it a quarter turn locks the non-fixed end cap308in the second terminal bracket304.

In general operation, to mount a fuse110, a pair of discrete, noncontiguous fuse supports200(seeFIGS. 2A and 2B) is attached or otherwise fastened to the panel102in the switchgear so their brackets302and304line up opposite one another. One fuse terminal110aof the fuse110is then inserted in the fixed end cap306as indicated by the arrow “A.” The non-fixed end cap308is placed over the opposite fuse terminal110band inserted in the bracket304having the notch318therein. This non-fixed end cap308is then turned a quarter turn as indicated by the arrow “B” to lock it to the notched bracket304and thereby secure the fuse110between the two fuse supports. Alternatively, the fuse110may be secured between a pair of fuse supports first before attaching or otherwise fastening the fuse supports to the panel102. One or more screws322and324may be used to secure the brackets302and304to their respective fuse supports. The screws322and324may also be used to attach a cable lug or similar connector326to each one of the terminal brackets302and304to establish an electrical connection to the fuse110. An insulated conductor cable or the like (not expressly shown) may then be attached to the lug326for each terminal bracket302and304to carry current through the fuse110.

FIG. 4shows the exemplary fuse assembly108afromFIG. 1A, but with portions of the fuse supports200a&200bremoved in order better to see the mounting assembly300. In the example shown, each fuse support housing202may have a length “C” of about 6.5 inches, a height “D” of about 4.0 inches, and a width of about 5.0 inches for a fiberglass or ceramic ferrule-mounted, current-limiting protection type fuse in a 15 kV rated system. The height “E” of the elongated support structure204may be about 4.0 inches, with the height and outer diameter of the neck portion214(e.g., 2.25 inches and 2.11 inches, respectively) and the height and outer diameter of the base portion216(e.g., 1.17 inches and 3.50 inches, respectively) being selected as needed for a particular switchgear application. The clearance “F” between each end cap306and308and the walls of the housing202may be about 1.0 inch in some embodiment.

The embodiments disclosed herein provide a number of advantages and benefits. Among other things, the field-shaping end caps306and308have been observed to limit the electric fields around the fuse terminals to about 2 kV/mm, which allows a clearance of about 1.0 inch (25 mm) between the fuse terminals110aand110b(seeFIG. 3) and the housing202(seeFIG. 2) of the fuse support for a 15 kV-rated switchgear. This clearance along with the shape of the fuse support ensures that the 2 kV/mm threshold is not exceeded when the fuse support is placed at least 1.0 inch away from a live conductor or ground. By capping only the fuse terminals and taking advantage of the nonconductive middle portion of the fuse110, which is typically made of glass, ceramic, or fiberglass, the disclosed embodiments provide a way to protect fuses from undesirable electrical discharges as well as providing ease of physical access to the fuses. Additionally, the generally hollow rectangular shape of the fuse support also provides a barrier around the fuse terminal to avoid an arc event resulting from inadequate strike distance to ground or live conductors.

While particular aspects, implementations, and applications of the present disclosure have been illustrated and described, it is to be understood that the present disclosure is not limited to the precise construction and compositions disclosed herein and that various modifications, changes, and variations may be apparent from the foregoing descriptions without departing from the spirit and scope of the disclosed embodiments as defined in the appended claims.