JPH09326319A - Electric field moderating shield of bushing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To securely and easily achieve an assembling work, and shield a metal material without soldering or welding and further moderate internal stress by covering on an end of a shield a recessed part of conductive rubber with a cross sectional configuration having the recessed part and not having any corner part at portions excepting the recessed part. SOLUTION: A shield 5 comprises a shield body 51 and a shield ring 52 provided on opposite ends 51a of the shield body 51. The shield ring 52 is formed as a ring of conductive rubber having a recessed part 52a in a cross section thereof, which is adapted to cover the entire peripheries of upper and lower opposite end surfaces 51 of the cylindrical shield body 51. The shield ring 52 is adapted such that it provides a cross section not having any corner part excepting the recessed part 52a, and the width of the recessed part 52a is made smaller than the thickness of a conductor constituting the shield body 51. Hereby, the recessed part 52a can be covered on the end part 51a of the shield body 51, and hence ensures a contact with the aid of rubber resiliency that securely keeps the shield body and the shield ring 52 at the same electric potential without being easlily disengaged from them.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art A bushing electric field relaxation shield is conventionally provided inside a bushing 10 as shown in the cross-sectional view of the bushing in FIG. Further, FIG. 4 is an enlarged cross-sectional view of the central portion of the bushing. The bushing 10 is composed of a main circuit conductor 1, a shield 2 and an epoxy resin 3 which is an insulating medium. Flange 1 of bushing 10
0a is fixed to the outer box of an electric device (not shown) by a holding plate 4 with a bolt (not shown). The outer box, bolts, and holding plate 4 are grounded, and the grounded shield 2 is provided to alleviate the electric field inside the bushing 10 and the outer box. The shield 2 is composed of a shield body 21 and a shield ring 22 at an end 21 a of the shield body 21, and the shield ring 22 serves to relieve the electric field at the end 21 a of the shield body 21. The shield body 21 is a punching metal having a hole for enhancing the adhesiveness with the epoxy resin 3. The shield ring 22 is a ring having a circular cross section, and is fixed to the end portion 21a of the shield body 21 by welding, brazing or the like, and has the same potential as the shield body 21.

[0003]

PROBLEM TO BE SOLVED BY THE INVENTION Shield ring 2
When fixing 2 to the shield body 21, the shield ring 2
A jig must be used to align 2 with the shield body 21. Further, in the case of welding, welding spatters fly to the shield ring 22 and the shield body 21, and the welding spatters reduce the effect of relaxing the electric field, so that it is necessary to remove the welding spatters. Further, in the case of brazing, since the shield body 21 is made of punching metal, there is a risk that the braze will not enter properly between the shield ring 22 and the shield body 21. Therefore, it is a work that requires a high degree of skill. Therefore, the present invention provides a shield that can be easily and surely assembled.

[0004]

A shield main body having a surface formed of a conductor is covered with a conductive rubber recess having a cross-sectional shape having a recess and no corners except the recess. By doing so, since the end of the shield body is covered with the conductive rubber, the electric field at the end of the shield body can be relaxed.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described with reference to FIGS.
Will be described. FIG. 3 shows a cross-sectional view of a bushing that pulls in and pulls out a charging part from an outer box of a switch and a transformer made of metal and grounded. An enlarged sectional view of the central portion of the bushing is shown in FIG. The bushing 10 is composed of a main circuit conductor 1, a shield 5 and an epoxy resin 3 as an insulating medium. Further, the bushing 10 is fixed to an outer box such as a switch or a transformer (not shown) with a bolt (not shown) and a holding plate 4 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, so that the electric field inside and outside the bushing 10 is relaxed by the outer box and the holding plate 4. .

The shield 5 includes a shield body 51 and a shield ring 5 provided at both ends 51a of the shield body 51.
2 is comprised. The shield body 51 is a cylindrical punching 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 is grounded. It can be connected to a member. Recess 52 in cross section
The shield ring 52 is formed of a conductive rubber ring or band having a and is covered on the entire circumference of the upper and lower end surfaces 51 of the cylindrical shield body 51. The shield ring 52 is
It is a cross section having no corners except for the recess 52a. Recess 52
The width of a is made smaller than the plate thickness of the conductor forming the shield body 51. As a result, when the recessed portion 52a is covered on the end portion 51a of the shield body 51, the elasticity of the rubber prevents the shield body 51 and the shield ring 52 from coming off easily, so that contact can be ensured at the same potential. Also,
Since the shield ring 52 is made of rubber and has flexibility, it can freely correspond to the end portion 51a of the cylindrical shield body 51.

The shield ring 52 is described as having a cross-sectional shape without corners except the recess 52a. An example of the cross section is shown in FIG.
Shown in In FIG. 2A, a concave portion 52a is provided in a part of the circular cross section. FIG. 2B shows an approximately square cross section in which four corner portions are rounded. FIG.
In (c), the tip has an R shape and the other end has a square shape, and the square side is rounded. In FIG. 2 (d), the tip portion is R and the other end is recessed. Although the cylindrical shield has been described as an example, the invention can be applied to the end portion of the shield that constitutes the surface including the shield on the flat plate. Further, although the shield 5 provided inside the bushing 10 is described as forming the ground potential inside the bushing, it can be applied to a voltage detection sensor using electrostatic induction. By using the shield 5 as a floating electrode, this becomes a capacitor having the epoxy resin 3 as an insulating medium as a dielectric. A current detection sensor is provided in the middle of the connection line that grounds the shield 5 outside, and the presence or absence of voltage can be determined by the presence or absence of leakage current. Also, by connecting the shield 5 to the ground via a capacitor,
It is also possible to divide the voltage in the condenser.

[0008]

The positioning of the shield main body and the conductive rubber to be the shield ring can be easily and surely performed only by fitting them into the recess of the conductive rubber and the end of the shield main body. Further, even if the shield body is made of punching metal, there is no problem, the assembly work can be performed reliably and easily, and the shield body can serve as the shield without the work of soldering or welding the metal material. Furthermore, epoxy resins as insulating media generally shrink when cured. Due to this contraction, a local internal stress is likely to occur at the end of the shield, causing cracks and partial discharges. However, since the shield ring is a rubber having elasticity, it also helps to alleviate the internal stress. Even if the end of the shield body has a ring shape, a circular shape, or a square shape, the elasticity of the rubber can be used to deal with it.

[Brief description of 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 rubber to be put on the shield end portion of the present invention.

FIG. 3 is a 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.

[Explanation of symbols]

 1 Main Circuit Conductor 3 Epoxy Resin 4 Holding Plate 5 Shield 51 Shield Body 51a End 52 Shield Ring 52a Recess

Claims (1)

[Claims] 1. A shield for electric field relaxation of a bushing, the surface of which is formed by a conductor provided at a position having an arbitrary distance from a main circuit conductor, which has a concave portion and a cross-sectional shape having no corner portion except the concave portion. 2. A shield for electric field relaxation of a bushing, characterized in that the end portion of the shield is covered with a rubber recess having conductivity.