Patent Publication Number: US-6710696-B2

Title: Fuse housing for network protector

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to power distribution equipment and, more particularly, to circuit interrupters with fuse protection. 
     2. Description of the Related Art 
     Two primary objectives of the electric utility industry in the delivery of electrical power are safety and reliability. Since the late 1920s, AC secondary network systems have been used in certain locations such as downtown business districts and commercial areas in order to provide a high degree of service continuity. In such an AC secondary network system, a plurality of secondary mains surround the area being served, such as a city block, and are connected with one another to form a secondary network grid at low voltage to which the customer loads are connected. 
     Electrical power is supplied to the secondary network by a plurality of high voltage transmission lines. Each high voltage transmission line delivers power to the network through network transformers. The transformers reduce the high voltage from the transmission lines to a lower voltage suitable for distribution to the customers. 
     In such secondary network systems, a failure of any one transmission line will not result in an interruption of service to the customers since electrical power will be supplied to the customers over the remaining transmission lines. When a failure or fault occurs in a high voltage transmission line or in one of its associated network transformers, the station end of the transmission line, that is, the end of the transmission line closest to the generating station, is disconnected from the system by opening a feeder circuit breaker. In addition, it is necessary that all of the network transformers on the failed transmission line be disconnected from the secondary network by some type of protective device to prevent power from the secondary network from being fed back through the network transformers to the fault. The protective device used for such purpose is the network protector. 
     The network protector consists of a specially designed circuit breaker with a closing and opening mechanism that is controlled by a relay. When the network protector is closed, the relay operates to trip the network protector upon a reversal of power flow. The relay acts to close the network protector when, and only when, the proper voltage conditions exist across the network protector. 
     Network protectors typically have been located outdoors either above ground or below ground and thus have been protected by a sealed enclosure. When a network protector is approached for maintenance, testing, or repair, the network protector must be electrically and physically disconnected from the power distribution equipment on both the network transformer side and the secondary network side. Historically, this consideration dictated the use of a rollout-type or draw-out-type circuit breaker which could be disconnected and rolled out of its enclosure for maintenance, testing, and repair. 
     Network protectors typically have additionally included fuses on each phase between the circuit breaker and the network transformer or between the circuit breaker and the network. Such fuses have been provided as a backup current interruption device that operates in the event of a failure of the circuit breaker. The fuses extending between the circuit breaker and the secondary network typically have either each been disposed in separate fuse housings that are disposed at the exterior of the sealed enclosure or been disposed internally within the sealed enclosure within which the circuit breaker is disposed. Such fuse housings typically have been molded out of an insulative material such as epoxy and include a cover which, when in place, seals the fuse within the fuse housing. While such fuse housings have been generally effective for their intended purposes, such fuse housings have not, however, been without limitations. 
     It is known that fuses generate heat during operation, and such heat must be dissipated through the fuse housing to the surrounding atmosphere. It is known that the heat generated by a fuse increases quadratically with the current passing through the fuse. As such, the heat dissipation characteristics of the fuse housings have limited the current-carrying capability of the fuses disposed within the housings. It is thus desired to provide an improved fuse housing having improved heat dissipation characteristics which permits a fuse disposed within the improved fuse housing to be employed in relatively higher current carrying applications than was previously possible. 
     Previously known fuse housings have included a pair of conductors extending from the interior of the fuse housing to the exterior thereof to permit the fuse to be connected between the circuit breaker and the network. At elevated current levels, particularly at fault current levels, the magnetic fields generated around such conductors can result in significant forces being applied to the conductors when the conductors of different phases are disposed closely adjacent one another. Such forces on the conductors have been known to fracture the fuse housings. It is thus desired to provide an improved fuse housing that is resistant to such fracturing due to forces from the conductors. 
     SUMMARY OF THE INVENTION 
     Accordingly, an improved fuse housing includes a main body and a cover and is configured to receive a fuse therein. The main body includes a plurality of fins that are configured to increase the surface area of the fuse housing in order to enhance the heat dissipative characteristics of the fuse housing. The main body is formed with a cavity within which the fuse can be disposed, and further includes a pair of conductors extending between the interior of the fuse housing and the exterior thereof that are connectable with the fuse. The cavity is configured to minimize the quantity of insulative air between the fuse and the fuse housing, which facilitates the transfer of heat from the fuse to the fuse housing and thus to the atmosphere. Each of the conductors includes an excess quantity of studs for connection with the fuse in order to enhance the conduction of heat away from the fuse. The cover is fastened to the main body with a sufficient number of fasteners to permit the cover to be a stressed member and to help resist fracturing of the fuse housing due to magnetic and other forces applied by the conductors. 
     As such, an aspect of the present invention is to provide an improved fuse housing that can be employed in conjunction with a network protector or other electrical device. 
     Another aspect of the present invention is to provide an improved fuse housing having enhanced heat dissipation characteristics. 
     Another aspect of the present invention is to provide an improved fuse housing having a plurality of fins formed thereon. 
     Another aspect of the present invention is to provide an improved fuse housing having a main body that is formed to include a cavity that is configured to receive a fuse therein, with the cavity being configured to minimize the quantity of insulative air between the fuse and the main body. 
     Another aspect of the present invention is to provide an improved fuse housing having a pair of conductors, wherein the conductors each include an excess number of fasteners for connection with a fuse to enhance the conduction of heat from the fuse to the conductors. 
     Another aspect of the present invention is to provide an improved fuse housing having a main body and a cover, in which the cover is securely fastened to the main body with a sufficient number of fasteners that the cover can become a stressed member and resist the fuse housing from fracture upon the application of forces thereto. 
     Accordingly, an aspect of the present invention is to provide a fuse housing that is structured to receive a fuse, in which the general nature of the fuse housing can be stated as including a main body, the main body including at least a first fin, the at least first fin being structured to dissipate heat from the fuse housing to the atmosphere, the main body being formed with a cavity, a first conductor, a second conductor, a cover, the cover being disposed over the cavity, and the cavity being structured to receive therein the fuse in electrically conductive engagement with the first and second conductors. 
     Another aspect of the present invention is to provide a current interrupter, the general nature of which can be stated as including a fuse housing, the fuse housing including a main body, the main body including at least a first fin, the at least first fin being structured to dissipate heat from the fuse housing to the atmosphere, the main body being formed with a cavity, a first conductor, a second conductor, a fuse, the fuse being disposed in the cavity, the fuse being electrically conductively engaged with the first conductor, the fuse being electrically conductively engaged with the second conductor, a cover, and the cover being disposed over the cavity. 
     Another aspect of the present invention is to provide a network protector, the general nature of which can be stated as including an enclosure, first current interruption means disposed internally within the enclosure, second current interruption means disposed externally to the enclosure, the second current interruption means including a fuse, the second current interruption means including a fuse housing, the fuse housing including a main body, the main body including at least a first fin, the at least first fin being structured to dissipate heat from the fuse housing to the atmosphere, the fuse housing including a first conductor, the fuse housing including a second conductor, the fuse being electrically conductively engaged with the first conductor, the fuse being electrically conductively engaged with the second conductor, the main body being formed with a cavity, the fuse being disposed in the cavity, the fuse housing including a cover, and the cover being disposed over the cavity. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A further understanding of the invention can be gained from the following description of the preferred embodiment when read in conjunction with the accompanying drawings in which: 
     FIG. 1 is an isometric view of an improved network protector in accordance with the present invention that includes an improved current interruption device in accordance with the present invention; 
     FIG. 2 is an isometric view of a portion of the current interruption device; 
     FIG. 3 is a front elevational view of a portion of the current interruption device; and 
     FIG. 4 is a sectional view as taken along line  4 — 4  of FIG.  3 . 
     Similar numerals refer similar to parts throughout the specification. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     An improved network protector  4  is indicated generally in FIG.  1 . The network protector  4  generally includes an enclosure  8 , a circuit breaker  12 , and a plurality of current interrupters  16 . The network protector  4  extends between a bank of network transformers (not shown) that are connected with a transmission line (not shown) and a secondary network grid (not shown) that is connected with a plurality of consumer electrical loads (not shown). The network protector  4  is configured to resist the transmission of excess quantities of electrical power therethrough in the event of a fault. The circuit breaker  12  and the current interrupters  16  each function as current interruption means which are configured to interrupt current flowing therethrough under certain specified circumstances. 
     The enclosure  8  is a substantially waterproof container that can receive the circuit breaker  12  therein. The circuit breaker  12  is a specially configured device that is electrically connected with other electrical components including a master relay (not specifically shown) and a phase relay (not specifically shown) that control the operation of the circuit breaker  12  in a known fashion. The circuit breaker  12  is of a rollout design but may be of other designs without departing from the concept of the present invention. While the circuit breaker  12  is disposed internally within the enclosure  8 , the current interrupters  16  are disposed externally to the enclosure  8 . 
     As can be understood from FIGS. 1 and 2, the current interrupter  16  includes an improved fuse housing  20  in accordance with the present invention and a fuse  24 . The fuse housing  20  includes a main body  28 , a cover  32  (FIG.  1 ), a first conductor  36  (FIGS.  3  and  4 ), and a second conductor  40  (FIGS.  3  and  4 ). The main body  28  and the cover  32  are molded out of an insulative material such as plastic or epoxy, although other formation techniques and materials may be employed. The first and second conductors  36  and  40  are molded into the material of the main body  28 , meaning that the first and second conductors  36  and  40  are pre-formed and are initially held in a given position in the mold from which the main body  28  is formed. The material out of which the main body  28  is to be formed is then injected into the mold and flows around the first and second conductors  36  and  40  and hardens with the first and second conductors  36  and  40  being retained in such position. 
     The main body  28  includes a cavity  44  formed therein. The cavity  44  is configured to receive the fuse  24  therein. As can be understood from FIGS. 3 and 4, the ends of the first and second conductors  36  and  40  protrude into the cavity  44  for connection with the fuse  24 . The cavity  44  includes a main region  46  and a void region  48 , with the main region  46  being in communication with the atmosphere when the cover  32  is removed from the main body  28 . The void region  48  is in communication with the main region  46 . 
     As can be seen from FIGS. 3 and 4, the void region  48  includes a base surface  52  opposite the main region  46 , plus a top lateral surface  56  (FIG.  4 ), a bottom lateral surface  60  (FIG.  4 ), a left lateral surface  64  (FIG.  3 ), and a right lateral surface  68  (FIG.  3 ). It can be seen that the top, bottom, left, and right lateral surfaces  56 ,  60 ,  64 , and  68  each extend between the base surface  52  and the main region  46 . It can also be seen that the base surface  52  and the top, bottom, left, and right lateral surfaces  56 ,  60 ,  64 , and  68  together generally define the void region  48 . 
     The main body  28  also includes a plurality of sockets  72  for fastening the cover  32  to the main body  28 . The sockets  72  may be any of a wide variety of structures that enable the cover  32  to be attached to the main body  28 . In this regard, the sockets  72  may each be threaded nuts that are embedded in the main body  28  and that are co-operable with a plurality of threaded fasteners such as screws or bolts. It is understood, however, that the sockets  72  may be of other configurations such as female bayonet fittings, or may simply be holes that are cooperable with self-tapping screws. Additionally, the sockets  72  may be formed in the cover  32  instead of the main body  28 . The sockets  72  are depicted in FIG. 3 in a schematic form, meaning that they can be of numerous different configurations depending upon the specific needs of the particular application. 
     It can be seen that the main body  28  includes a total of twelve sockets  72  for use in connecting the cover  32  with the main body  28 . It can further be seen that some of the sockets  72  are disposed in lugs  76  formed in the main body  28 . The lugs  76  are configured to permit forces to be transmitted from the main body  28  to the cover  32  without fracturing the main body  28 . 
     As can be understood from FIGS. 3 and 4, the first conductor  36  includes a first bus  80  and a plurality of studs  84 . The first bus  80  extends between the void region  48  and the exterior of the fuse housing  20  and is configured to be connected with the fuse  24  via the studs  84 . In the present embodiment, the studs  84  are fixedly mounted to the first bus  80  such as by casting the material of the first bus  80  around the studs  84 , although other attachment methodologies and degrees of fixation may be employed. 
     The studs  84  are, in the present embodiment, threaded conductive members that can be mounted to the fuse  24  with cooperative nuts. It is understood, however, that the studs  84  may be other types of fasteners, such as non-threaded fasteners, without departing from the concept of the present invention. As is best shown in FIG. 3, the first conductor  36  includes six of the studs  84  mounted on the first bus  80 . The studs  84  are all disposed within the cavity  44 . Although not specifically shown in the accompanying drawings, the first bus  80  connects between the fuse  24  and the load terminals of the circuit breaker  12 . 
     The second conductor  40  includes a second bus  88  and a plurality of studs  92 . The second conductor  40  is generally T-shaped, and the studs  92  are fixedly mounted on the second bus  88 . The second conductor  40  includes six of the studs  92  mounted on the second bus  88 . The studs  92  are virtually identical to the studs  84  of the first conductor  36 . The studs  92  are all disposed within the cavity  44  and are configured to be connectable with the fuse  24 . Although not specifically shown in the accompanying figures, the second bus  88  is configured to connect between the fuse  24  and a conduction member (not shown) that extends to the network. As with the first conductor  36 , the studs  92  may be fixedly mounted in the second bus  88  by casting the material of the second bus  88  around the studs  92 , although other attachment methodologies and degrees of fixation may be employed without departing from the concept of the present invention. 
     As can be seen in FIGS. 3 and 4, the main body  28  includes a base  96  defined thereon including a plurality of mounting holes  100 . Appropriate fasteners protrude outwardly from the enclosure  8  and extend through the mounting holes  100  for cooperation with appropriately configured nuts or other fasteners. The base  96  serves as a mount for mounting the fuse housing  20  to another structure, such as the enclosure  8 . It is understood, however, that different attachment methodologies may be employed to mount the base  96  of the main body  28  onto the enclosure  8 . It is further understood that in other embodiments (not shown) of the present invention, the fuse housing  20  may be mounted to a structure other than the enclosure  8 , such as a wall of a containment vessel, and potentially may not be mounted to any structure at all, and rather be floatingly mounted between the first and second conductors  36  and  40 . 
     As is best shown in FIG. 4, the main body  28  includes a plurality of fins  104  formed thereon. While in the present embodiment of the fuse housing  20  of the present invention the fins  104  are monolithically formed as a single-piece member with the main body  28 , it is understood that in other embodiments (not shown) the fins  104  potentially may be separately manufactured and attached to the main body  28 . In this regard, it is understood that the term “monolithically” and variations thereof refers to a construction that is substantially free of joint. 
     The fins  104  advantageously promote the transfer of heat from the main body  28  to the surrounding atmosphere by increasing the surface area of the main body  28  and thus enhancing heat transfer therefrom, including convective heat transfer to the surrounding atmosphere. 
     As can further be seen from FIG. 4, the main body  28  includes a first depression  108  that is disposed generally between the base  96  and the set of fins  104 . Similarly, the main body  28  further includes a second depression  112  on the opposite side of the fins  104  from the first depression  108 . The first and second depressions  108  and  112  serve to further increase the surface area of the main body  28  and thus promote heat transfer from the main body  28 , including convective heat transfer to the surrounding atmosphere. 
     It can be seen that the main body  28  forms a projection  114  between the first and second depressions  108  and  112 , and that the fins  104  are disposed on a free end  118  of the projection  114 . The projection  114  extends laterally outward from a side wall  122  (FIG. 4) of the main body  28 . In the embodiment of the main body  28  depicted herein, the side wall  122  is defined by the first and second depressions  108  and  112 . The projection  114  is generally wedge-shaped or tapered, and the void region  48  extends partially into the projection  114 . By forming the void region  48  in the projection  114 , the quantity of material of the main body  28  that is interposed between the fuse  24  and the exterior atmosphere is less than that of previously known fuse housings, which advantageously increases the rate at which heat is transferred away from the fuse  24 . 
     It thus can be seen that the fins  104  and the first and second depressions  108  and  112  together increase the surface area of the main body  28  and thus enhance the transfer of heat from the fuse housing  20  such as by convective heat transfer to the surrounding atmosphere, which helps to dissipate the heat generated by current passing through the fuse  24 . As such, the fins  104  and the first and second depressions  108  and  112  permit the current interrupter  16  to handle relatively greater current levels. 
     The fuse  24  can be seen to include a substantially cylindrical fuse body  116  and a pair of connection plates  120 . The connection plates  120  are generally coplanar and extend from the opposite circular end surfaces of the fuse body  116 . Each of the connection plates  120  is formed with a plurality of holes  124  that are configured to receive either the studs  84  or the studs  92 . 
     The relatively large number of holes  124  for connection with the studs  84  or the studs  92  provide an enhanced mechanical connection between the connection plates  120  and the first and second buses  80  and  88 , which promotes conduction of heat from the fuse body  116  to the first and second buses  80  and  88  and thence to the main body  28  for enhanced dissipation via the fins  104  and the first and second depressions  108  and  112 . While in many application the connection plates  120  might not necessarily each require six mechanical connections in order to form an electrically conductive connection, the large number of mechanical connections therebetween afforded by the holes  124  and the first and second buses  80  and  88  advantageously promotes an enhanced thermally conductive connection between the connection plates  120  and the first and second buses  80  and  88 . As such, the configuration of the holes  124  and the first and second buses  80  and  88  provides an additional level of heat dissipation from the fuse  24 , which further increases the current carrying capacity of the current interrupter  16 . 
     It can be seen that at least a portion of the fuse body  116  protrudes into the void region  48  of the cavity  44 . It can further be seen that the fuse body  16  is disposed substantially closer to the top and bottom lateral surfaces  56  and  60  than to the base surface  52 . It is known in the relevant art that air between the fuse body  116  and the main body  28  serves as an insulator which resists the transfer of heat therebetween. As such, by minimizing the distance between the fuse body  116  and the top and bottom lateral surfaces  56  and  60 , the amount of insulative air therebetween is likewise reduced, which enhances the transfer of heat from the fuse body  116  to the main body  28 , after which the heat is dissipated by the fins  104  and the first and second depressions  108  and  112 . In fuses  24  having different current ratings, the distance of the fuse body  116  to the base surface  52  may vary, but the space between the fuse body  116  and the top and bottom lateral surfaces  56  and  60  generally will remain unchanged, which allows for a consistent and predictable level of heat transfer between the fuse body  116  and the top and bottom lateral surfaces  56  and  60  to the main body  28 . 
     The close spacing of the fuse body  116  to the top and bottom lateral surfaces  56  and  60 , the distance which is less than the distance from the fuse body  116  to the base surface  52 , increases the heat transfer from the fuse body  116  to the main body  28 , which correspondingly enhances the current-carrying capacity of the current interrupter  16 . It is understood that since the surface of the fuse body  116  that faces the base surface  52  is generally arcuate and thus faces also toward the left and right lateral surfaces  64  and  68 . As such, heat from the arcuate surface will be transferred to the base surface  52  as well as the left and right lateral surfaces  64  and  68 . Accordingly, reference herein to the distance between the fuse body  116  and the base surface  52  refers more particularly to an aggregate distance, i.e., an average distance between the arcuate surface and the generally planar base surface  52  and the left and right lateral surfaces  64  and  68 . 
     As can be understood from the accompanying figures, the cover  32  is fastened to the main body  28  by employing twelve fasteners that are cooperable with the sockets  72 . It is understood that in most applications of the current interrupter  16 , twelve such fasteners and sockets  72  may not be strictly necessary to simply seal the fuse  24  within the cavity  44 . Nevertheless, by providing such a relatively large number of mechanical connections between the cover  32  and the main body  28 , the cover  32  is substantially transformed into a covering member that also functions as a structural member of the fuse housing  20 . In this regard, by securely fastening the cover  32  to the main body  28  with the fasteners that cooperate with the sockets  72 , forces or torques that are applied to the main body  28  will be, in turn, transmitted to the cover  32 , whereby any such forces and torques are distributed throughout the fuse housing  20  instead of being concentrated in the main body  28 . In such fashion, the fuse housing  20  is able to withstand greater levels of forces and torques than if the cover  32  were mounted to the main body  28  with only a minimal number of fasteners and sockets  72 . Accordingly, the current interrupter  16  is capable of structurally handling relatively greater current loads since it is advantageously capable of withstanding forces and torques that may be induced in the first and second conductors  36  and  40  as a result of such elevated current loads. 
     It thus can be seen that the improved fuse housing  20  that is employed in the improved current interrupter  16  is generally capable of handling a greater current load than previously known systems, which accordingly increases the current capacity of the improved network protector  4  that incorporates the current interrupter  16 . As set forth above, the fuse housing  20  includes various improvements which both thermally and structurally enable the current interrupter  16  to carry greater current loads. 
     While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of the invention which is to be given the full breadth of the claims appended and any and all equivalents thereof.