Title of Invention

"A DISCONNECTION SECTION BUSHING"

Abstract

A disconnection section bushing comprising: an insulation cylinder having a cylindrical shape with a bottom, for supporting a connection conductor of the disconnection section at a bottom surface thereof, and covering an outside of the connection conductor; and characterized by flange circumferentially provided around the insulation cylinder at an opening end thereof and having a curved portion which is curved toward the bottom surface in the axial cross section at a circumference edge portion.

Full Text

TITLE OF THE INVENTION ENCLOSED SWITCHQEAR AND DISCONNECTION SECTION BUSHING BACKGROUND OF THE INVENTION The present invention relates to a disconnection section bushing for supporting a connection conductor of a drawer type electric apparatus, such as a breaker, in a disconnection section of an enclosed switchgear, and to an enclosed switchgear equipped with such a disconnection section bushing. In order to make the maintenance and inspection easier, a breaker housed in an enclosed switchgear may be assembled to be of a drawer type, so that the breaker is allowed to engage with/disengage from the disconnection section provided behind each housing chamber when pushed in/pulled out at the front of the housing chamber. FIG. 1 is a side cross sectional view schematically showing an example enclosed switchgear equipped with a drawer type breaker. The enclosed switchgear illustrated in the drawing comprises an outer case 1 of a rectangular box made of grounding metal, inside of which is partitioned by partition walls made of grounding metal or an insulation material, and it is arranged in such a manner that a breaker chamber 3a housing a drawer type breaker 3 is provided at the lower front portion of the outer case 1, a bus chamber 6a furnished with a bus-side branched conductor 6 is provided at the upper rear portion of the breaker chamber 3a, and a cable chamber 7a furnished with a load-side conductor 5 for establishing a connection with a power cable 7 is provided at the lower rear portion of the breaker chamber 3a. The breaker 3 can be pulled out forward and pushed in backward on the bottom plate of the breaker chamber 3a. Connection conductors 14, each of which is connected to a connection terminal provided protrudently at the rear end of the breaker chamber 3a when the breaker 3 is pushed in and disconnected when the breaker 3 is pulled out, are provided to the rear wall 2 of the breaker chamber 3a while being supported by a bushing 40. The rear ends of the connection conductors 14 protrude towards the inside of the bus chamber 6a, and they are connected to bus-side branched conductors 6 respectively corresponding to the three phases. Further, another bushing 40 arranged in the same manner is provided below the firstly mentioned bushing 40. The rear ends of unillustrated connection conductors supported by the secondly mentioned bushing 40 are connected to load~side conductors 5 respectively corresponding to the three phases in the cable chamber 7a. Thus, a pair of the bushings 40 provided vertically form a disconnection section which disconnects the bus-side branched conductors 6 and the load-side conductors 5 when the breaker 3 is pulled out. FIG. 2 is an enlarged side cross sectional view showing the bushing 40 forming the disconnection section, and FIG, 3 is a front view taken on line VII - VII of FIG. 2. As shown in FIG. 2, the bushing 40 supports each connection conductor 14 fit through its bottom surface, and has a cylindrical shape with an opening at the other end. The bushing 40 comprises insulation cylinders 10 made of an insulation material, such as epoxy resin, and a flange 11 provided around the insulation cylinders 10 at its opening end in such a manner to overhang outward. As shown in FIG. 3, the insulation cylinders 10 have a front shape, in which three cylinders, respectively covering the outside of the connection conductors 14 respectively corresponding to the three phases while keeping a predetermined insulation distance, are aligned along the radius direction, and the flange 11 is provided around the outside of the insulation cylinders 10 to have a rectangular front shape. As shown in FIG. 2, the bushing 40 thus arranged is inserted through a mounting hole 2a made through the rear wall 2 of the breaker chamber 3a at an adequate position with the bottom end of the insulation cylinders 10 pointing outward, and mounted to the rear wall 2 by being fastened fixedly to the vicinity of the inner edge of the mounting hole 2a with set screws 9 at more than one point along the circumference edge of the flange 11. In FIG. 3, numeral references 9a represent screw holes provided for tightening the set screws 9. Under the above mounted state, protruding collars lla and lib, each having their respective diameters, are provided at the opening portion of the insulation cylinders 10 facing to the inside of the breaker chamber 3a, and a space 12 is formed between the protruding collars lla and lib. Consequently, as indicated by a two-dot chain line in FIG. 2, an insulation creeping distance with respect to a shutter plate S closing the front surface of the opening portion is secured in the disconnection state. Also, a protruding collar lie is provided protrudently at the bottom of the insulation cylinders 10, so that an insulation creeping distance with respect to a bushing terminal 13 provided adjacently at the rear end of each connection conductor 14 is secured. However, in the above-arranged conventional busing 40, when an external force along the axial longitudinal direction is applied to the connection conductors 14 each time the breaker 3 is pulled out or pushed in, a bending force acts on the flange 11 provided around the outside of the insulation cylinders 10. Thus, the flange 11 must be made sufficiently thick to have a predetermined strength against the bending force. However, this becomes a factor that makes the weight reduction of the bushing 40 impossible. Further, in order to attain a high voltage withstand performance by securing a predetermined surface leakage length with respect to the connection conductors 14 and bushing terminals 13 to which a high voltage is applied, the front surface size of the flange 11 must be increased. In particular, when the bushing terminals 13 are upsized in response to an increase of a rated current, it becomes difficult to secure the surface leakage length by the protruding collar lie provided protrudently at the bottom of the insulation cylinders 10. Accordingly, the front surface size of the flange 11 is further increased, which raises a problem that not only the weight reduction of the bushing 40 becomes impossible, but also the enclosed switchgear as a whole is undesirably upsized to secure a mounting area for the flange 11. BRIEF SUMMARY OF THE INVENTION The present invention is devised to solve the above problems, and it is therefore an object of the present invention to provide a disconnection section bushing which can obtain sufficient strength against an external force without thickening a flaftge and secure a sufficient surface leakage length with respect to a connection conductor and a bushing terminal without increasing the front surface size of the flange, while exhibiting an excellent voltage withstand performance regardless of its small size and light weight, and to provide an enclosed switchgear equipped with such a disconnection section bushing. The disconnection section bushing of the present invention is furnished with a curved portion which is formed on the circumference edge portion of the flange provided around an insulation cylinder at its opening end in such a manner to curve toward the bottom surface of the insulation cylinder on the axial cross section. Also, the enclosed switchgear of the present invention is furnished with the above-described disconnection section bushing on a wall at a push-in end of an electric apparatus, that is, a rear wall of an electric apparatus chamber for housing a drawer type electric apparatus. Therefore, the curved portion is provided at the circumference edge portion of the flange, and a surface leakage length with respect to the connection conductor and bushing terminal can be secured by increasing a surface length along the curved portion. Also, sufficient strength can be secured without thickening the flange exceedingly by having an external force applied under the mounted state act on the flange as tensile strength. Another enclosed switchgear and another disconnection section bushing of the present invention are furnished with an overhang portion overhung outwardly in a portion close to the outer circumference of the insulation cylinder on the side of the flange having a rectangular shape when seen from the opening end of the insulation cylinder. Therefore, a sufficient surface leakage length can be secured without upsizing the flange as a whole by providing the overhang portion locally on the side of the flange close to the outer circumference of the insulation cylinder, that is, on the side where it is difficult to secure the surface leakage length. Still another enclosed switchgear of the present invention is arranged in such a manner that the electric • apparatus is a drawer type breaker. Therefore, the drawer type breaker can be employed as the electric apparatus of the aforementioned enclosed switchgear. The above and further objects and features of the invention will more fully be apparent from the following detailed description with accompanying drawings. Accordingly there is provided a disconnection section bushing comprising: an insulation cylinder having a cylindrical shape with a bottom, for supporting a connection conductor of the disconnection section at a Dottom surface thereof, and covering an outside of the connection conductor; and a flange circumferentially provided around the insulation cylinder at an opening i end thereof and having a curved portion which is curved toward the bottom surface in the axial cross section at a circumference edge portion. • BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE^ DRAWINGS FIG. 1 is a side cross sectional view showing an {: -•-„••$• example of a conventional enclosed switchgear; FIG. 2 is a longitudinal sectional view of a conventional disconnection section bushing; FIG. 3 is a front view taken on line VII-VII of FIG. 2; . FIG. 4 is a side cross sectional view showing a disconnection section bushing in accordance with Embodiment 1 of the present invention; FIG. 5 is a front view taken on line II-II of FIG. 4; FIG. 6 is a front view showing a disconnection section bushing in accordance with Embodiment 2 of the present invention; and FIG. 7 is a cross sectional view taken on line IV - IV of Figure 6. DETAILED DESCRIPTION OF THE INVENTION f In the following, example embodiments of the present invention will be detailed with reference to the accompanying drawings. Embodiment 1 FIG. 4 is a side cross sectional view showing a disconnection section bushing in accordance with Embodiment 1 of the present invention, and FIG. 5 is a front view taken on line II - II of FIG. 4. A bushing 4 shown in these drawings is, like the conventional bushing 40 shown in FIGS. 2 and 3, used for the disconnection section which is disconnected when a drawer type breaker 3 is pulled out in an enclosed switchgear equipped with the drawer type breaker 3. In the drawing, numeral reference 2 indicates the rear wall of a breaker chamber 3a. The bushing 4 of the present invention comprises insulation cylinders 10 which support the connection conductors 14 fit through its bottom surface and have a cylindrical shape with an opening at the other end, and a flange 8 provided around the insulation cylinders 10 at its opening end in such a manner to overhang outward. The insulation cylinders 10 are members made of an insulation material, such as epoxy resin, and as shown in FIG. 5, the insulation cylinders 10 have a front shape, in which three cylinders, respectively covering the outside of the connection conductors 14 respectively corresponding to the three phases while keeping a predetermined insulation distance, are aligned along the radius direction while keeping a predetermined space from each other. Like the conventional bushing 40 shown in FIG. 2, protruding collars lla and lib, each having their respective diameters, are provided at the opening portion of the insulation cylinders 10 facing to the inside of the breaker chamber 3a, and a space 12 is formed between the protruding collars lla and lib, so that an insulation creeping distance with respect to a shutter plate S closing the front end of the opening portion is secured also in the bushing 4 of the present invention. The characteristics of the bushing 4 of the present invention is the shape of the flange 8 provided around the outside of the insulation cylinders 10. FIG. 5 is a front view of the bushing 4 seen from the opening end of the insulation cylinders 10. The flange 8, having a rectangular front surface shape, is provided around the outside of the insulation cylinders 10 having the aforementioned front surface shape, and as shown in FIG. 4, curved portions 8a, which are curved in arc toward an end of the bottom surface of the insulation cylinders 10, are provided on the axial cross section of the insulation cylinders 10 all along the circumference edge portion of the flange 8. The bushing 4 thus arranged is inserted through a mounting hole 2a made through the rear wall 2 of the breaker chamber 3a at an adequate position with the bottom end of the insulation cylinders 10 pointing outward, and mounted to the rear wall 2 by being fastened fixedly to the vicinity of the inner edge of the mounting hole 2a with set screws 9 at more than one point along the circumference edge portion of the flange 8. Here, the flange 8 having the aforementioned axial cross section shape touches the front surface of the inner edge of the mounting hole 2a at the extension ends, which are extended backward, of the curved portions 8a provided along the circumference edge. Thus, as shown in FIG. 5, the flange 8 is fixed with the set screws 9 at eight concavities 8b formed at the four corners of the rectangle and four points between each two cylinders out of three cylinders forming the insulation cylinders 10 by denting the extension end portions inward. As has been described above, in the busing 4 having the flange 8 under the mounted state of FIG. 4, an external force in the axial longitudinal direction applied to the connection conductors 14 each time the breaker 3 (see FIG. 1) is pulled out or pushed in changes its direction along the curved portions 8a. Thus, such an external force acts on the flange 8 as positive or negative tensile force. Therefore, as shown in the drawing, sufficient strength can be secured by the substantially uniformly thin flange 8. Consequently, a significant weight reduction of the bushing 4 including the flange 8 can be attained. In addition, the surface leakage length with respect to the connection conductors 14 and the bushing terminals 13 provided adjacently to the rear ends of the connection conductors 14 extends along the curved portions 8a in the flange 8. Thus, a sufficient surface leakage length can be readily secured without increasing the front surface size of the flange 8. Consequently, not only a high voltage withstand performance can be obtained, but also a further weight reduction of the bushing 4 can be attained. Also, unlike the prior art, it is no longer necessary to provide the protruding collar lie on the outside of the bottom surface of the insulation cylinders 10 to secure the surface leakage length with respect to the bushing terminals 13, thereby making it possible to employ large-sized bushing terminals 13 for a large current. Embodiment 2 FIG. 6 is a front view showing a disconnection section bushing in accordance with Embodiment 2 of the present invention, and FIG. 7 is a cross sectional view taken on line IV - IV of FIG. 6. As shown in FIG. 6, a flange 8 of the present embodiment has a rectangular shape when seen from the front of the opening end of the insulation cylinders 10, and includes overhang portions 15 overhung outwardly at the portions close to the outer circumference of the insulation cylinders 10 on its sides, that is, at the center portions of the two short sides in the drawing. The overhang portions 15 are provided in such a manner to increase the lengths at the portions close to the outer circumferences of the insulation cylinders 10 where the flat portions before reaching the curved portions 8a are short, so that a sufficient surface leakage with respect to the connection conductors 14 and bushing terminals 13 is secured. The front surface size of the other portions of the flange 8, where the lengths of the flat portions can be readily secured, can be made relatively smaller by providing the above overhang portions 15. Consequently, a further weight reduction of the bushing 4 can be attained by downsizing the flange 8 as a whole. As this invention may be embodied in several forms without departing from the spirit of essential characteristics thereof, the present embodiments are therefore illustrative and not restrictive, since the scope of the invention is defined by the appended claims rather than by the description preceding them, and all changes that fall within metes and bounds of the claims, or equivalence of such metes and bounds thereof are therefore intended to be embraced by the claims. WE CLAIM:- 1. A disconnection section bushing comprising: an insulation cylinder having a cylindrical shape with a bottom, for supporting a connection conductor of the disconnection section at a bottom surface thereof, and covering an outside of the connection conductor; and characterized by flange circumferentially provided around the insulation cylinder at an opening end thereof and having a curved portion which is curved toward the bottom surface in the axial cross section at a circumference edge portion. 2. The disconnection section bushing as claimed in claim 1, wherein the flange has a rectangular shape as seen from the opening end of the insulation cylinder and has an overhang portion that overhangs at a portion close to a circumference of the insulation cylinder in a direction away from the circumference. 3. A disconnection section bushing substantially as herein described with reference to the accompanying drawings.

Documents:

2864-del-1998-abstract.pdf

2864-del-1998-claims.pdf

2864-del-1998-correspondence-others.pdf

2864-del-1998-correspondence-po.pdf

2864-del-1998-description (complete).pdf

2864-del-1998-drawings.pdf

2864-del-1998-form-1.pdf

2864-del-1998-form-13.pdf

2864-del-1998-form-19.pdf

2864-del-1998-form-2.pdf

2864-del-1998-form-3.pdf

2864-del-1998-form-4.pdf

2864-del-1998-form-6.pdf

2864-del-1998-gpa.pdf

2864-del-1998-petition-137.pdf

2864-del-1998-petition-138.pdf

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