Patent Application
20160268090
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.
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.
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.
The foregoing and other advantages of the disclosed embodiments will become apparent upon reading the following detailed description and upon reference to the drawings, wherein:
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 to
One or more exemplary fuse assemblies, one of which is indicated at 108a, are also attached or otherwise fastened on the panel 102 in accordance with the disclosed embodiments. The fuse assembly 108a includes a pair of exemplary fuse supports 200a & 200b that hold or otherwise secure at least one current-limiting fuse 110 therebetween. As can be seen, the nonconductive fuse supports 200a & 200b are located separately from the transformer unit 104 so the fuse 110 is not mounted directly on a transformer within the transformer unit 104. The mounting of the fuse 110 separately from the transformer allows the overall size of the switchgear module 100 to be reduced, making it possible or at least easier for the switchgear module 100 to fit within a smaller compartment compared to existing solutions. For example, the exemplary switchgear module 100 shown 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.
Turning now to
In some embodiments, the elongated support structure 204 may also include two main sections, a neck portion 214 and a base portion 216 extending coaxially from the neck portion 214. The base portion 216 is designed to be attached or otherwise fastened to the panel 102 and in some embodiments may have a larger diameter than the neck portion 214 for better stability. Either or both the base portion 216 and the neck portion 214 may have coaxial, radially extending insulating discs or sheds 218 disposed thereon that function to increase the tracking distance along the outer surface of the elongated support structure 204. A first set of screw holes 220 may be drilled or otherwise provided on an underside 216a of the base portion 216 to facilitate screwing or otherwise attaching it to the panel 102.
A second set of screw holes 222 may also be drilled or otherwise provided in the bottom wall 208 of the housing 202 on an interior surface 208b thereof in some embodiments for screwing or otherwise attaching a terminal bracket (302 and 304, discussed in
The terminal bracket mentioned above may be part of a mounting assembly 300, depicted in
Each terminal bracket 302 and 304 has a generally flat base 310 and 312, respectively, that may be fastened to the housing 202 of the fuse support 200 and a generally flat mounting plate 314 and 316, respectively, extending perpendicularly from the base 310 and 312 for supporting the end caps 306 and 308. One of the end caps, for example, the right end cap 306, may be fixedly attached (e.g., welded, etc.) to the first terminal bracket, for example, the right bracket 302, on the mounting plate 314 thereof. The mounting plate 316 of the second terminal bracket 306 may have a circular opening formed therein (not expressly labeled) for receiving the non-fixed end cap 308. A locking mechanism, such as a quarter-turn locking mechanism, may be used to releasably attach the non-fixed end cap 308 to it its respective terminal bracket 304. For example, the second terminal bracket 304 may have a notch 318 formed in the opening in the mounting plate 316 thereof and the non-fixed end cap 308 may have a tab 320 protruding therefrom that corresponds to the notch 318. Inserting the non-fixed end cap 308 so the tab 320 passes through the notch 318 and rotating it a quarter turn locks the non-fixed end cap 308 in the second terminal bracket 304.
In general operation, to mount a fuse 110, a pair of discrete, noncontiguous fuse supports 200 (see
The embodiments disclosed herein provide a number of advantages and benefits. Among other things, the field-shaping end caps 306 and 308 have 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 terminals 110a and 110b (see
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.
