JP3149790B2 - Shield for reducing electric field of bushing - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a shield for reducing an electric field of a bushing.

[0002]

2. Description of the Related Art A shield for alleviating an electric field of a bushing is generally provided inside a bushing 10 as shown in a sectional view of the bushing in FIG. FIG. 4 is an enlarged cross-sectional view of a central portion of the bushing. The bushing 10 is composed of a main circuit conductor 1, a shield 2, and an epoxy resin 3 as an insulating medium. Flange 1 of bushing 10
Reference numeral 0a is fixed to an outer box of an electric device (not shown) by a holding plate 4 with bolts (not shown). The outer box, the bolt and the holding plate 4 are grounded, and a grounded shield 2 is provided to reduce the electric field inside the bushing 10 and the outer box. The shield 2 includes a shield body 21 and a shield ring 22 at an end 21a of the shield body 21. The shield ring 22 reduces the electric field at the end 21a of the shield body 21. The shield main body 21 is a punched metal having a hole for improving the adhesion to the epoxy resin 3. The shield ring 22 is a ring having a circular cross section, and is fixed to an end 21 a of the shield main body 21 by welding, brazing, or the like, and is set to the same potential as the shield main body 21.

[0003]

SUMMARY OF THE INVENTION Shield ring 2
When fixing the shield ring 2 to the shield body 21, the shield ring 2
A jig must be used to align the shield body 2 with the shield body 21. Further, in the case of welding, welding spatter jumps to the shield ring 22 and the shield main body 21, and the welding spatter reduces the effect of alleviating the electric field, so that it is necessary to remove the welding spatter. Further, in the case of brazing, since the shield body 21 is made of punched metal, there is a possibility that the brazing may not enter well between the shield ring 22 and the shield body 21. Therefore, it is a task that requires advanced skills. Then, this invention provides the shield which can perform assembly work easily and reliably.

[0004]

Means for Solving the Problems An end portion of a shield main body which is formed of a conductor is covered with a concave portion of a conductive rubber having a cross-sectional shape having a concave portion and having no corners except for the concave portion. By doing so, since the end of the shield main body is covered with the conductive rubber, the electric field at the end of the shield main body can be reduced.

[0005]

1 to 3 show an embodiment of the present invention.
Will be described. FIG. 3 is a cross-sectional view of a bushing that pulls in or pulls out the charged part from the outer case of a switch or transformer that is made of metal and grounded. FIG. 1 is an enlarged cross-sectional view of the center of the bushing. The bushing 10 includes a main circuit conductor 1, a shield 5, and an epoxy resin 3 as an insulating medium. The bushing 10 is fixed to an outer box such as a switch or a transformer (not shown) by a bolt and a holding plate 4 (not shown) via a flange 10a. The outer box, the bolts, and the holding plate 4 are at the ground potential, and the shield 5 is grounded by a method not shown to reduce the electric field inside and outside the bushing 10 by the outer box and the holding plate 4. .

The shield 5 includes a shield body 51 and shield rings 5 provided at both ends 51a of the shield body 51.
2 is comprised. The shield body 51 is a cylindrical punched metal conductor that covers the main circuit conductor 1 and is positioned inside the epoxy resin 3 by a support (not shown). The support is provided with a terminal on the surface of the bushing 3 and grounded. Connection to the member is possible. Recess 52 in cross section
The shield ring 52 is formed by a conductive rubber ring or band having a, and is covered over the entire upper and lower end surfaces 51 of the cylindrical shield body 51. The shield ring 52
The cross section has no corners except for the concave portion 52a. Recess 52
The width of “a” is smaller than the thickness of the conductor forming the shield body 51. Thus, when the concave portion 52a is put on the end portion 51a of the shield main body 51, the elasticity of the rubber makes it possible to obtain a contact that ensures that the shield main body 51 and the shield ring 52 are kept at the same potential without easily coming off. Also,
Since the shield ring 52 is made of rubber and has flexibility, it can freely correspond to the end 51a of the cylindrical shield body 51.

[0007] Except for the concave portion 52a of the shield ring 52, the cross-sectional shape has no corners. Fig. 2 shows an example of the cross section.
Shown in FIG. 2A shows a configuration in which a concave portion 52a is provided in a part of a circular cross section. FIG. 2 (b) has a substantially square cross section, in which four corners are rounded. FIG.
(C) is a shape in which the tip is rounded and the other end is squared, and the squared side is rounded. FIG. 2 (d) shows a shape in which the tip is R and the other end is tapered. Although the embodiment has been described with reference to the cylindrical shield, the present invention can also be applied to an end portion of a shield forming a surface including a shield on a flat plate. Although the shield 5 provided inside the bushing 10 has been described as forming a ground potential inside the bushing, the shield 5 can also be applied to a voltage detection sensor using electrostatic induction. This is a capacitor using the epoxy resin 3 as a dielectric as a dielectric by using the shield 5 as a floating electrode. A current detection sensor is provided in the middle of a connection line that connects the shield 5 to the outside, and the presence or absence of a voltage can be determined based on the presence or absence of a leakage current. Also, by connecting the shield 5 to the ground via a capacitor,
It is also possible to divide a capacitor.

[0008]

The positioning between the shield body and the conductive rubber serving as the shield ring can be easily and reliably performed only by fitting the conductive rubber into the concave portion of the conductive rubber and the end of the shield body. Also, even if the shield body is a punched metal, the assembling work can be performed reliably and easily without any problem, and can function as a shield without the work of soldering or welding the metal material. Furthermore, epoxy resins as insulating media generally shrink when cured. Due to this shrinkage, local internal stress is likely to be generated at the end of the shield, which causes cracks and partial discharge. However, since the shield ring is made of rubber having elasticity, it also helps to alleviate the internal stress. Further, even if the end of the shield main body has a ring shape, a circular shape, or a square shape, it can be freely handled by the elasticity of the rubber.

[Brief description of the drawings]

FIG. 1 is an enlarged cross-sectional view of a central portion of a bushing using a shield of the present invention.

FIG. 2 is an example of a cross-sectional shape of a rubber covering a shield end according to the present invention.

FIG. 3 is a cross-sectional view of the entire bushing having a shield for explaining the present invention and a conventional example.

FIG. 4 is an enlarged cross-sectional view of a central portion of a bushing using a conventional shield.

[Description of Signs] 1 Main circuit conductor 3 Epoxy resin 4 Holding plate 5 Shield 51 Shield body 51a End 52 Shield ring 52a Recess

Claims (1)

(57) [Claims] 1. A bushing electric field alleviating shield comprising a surface formed by a conductor provided at an arbitrary distance from a main circuit conductor, wherein the cross-sectional shape of the bushing has a concave portion and has no corners except for the concave portion. A bushing electric field alleviating shield, wherein a concave portion of the conductive rubber is covered on an end of the shield.