Resin molded bushing and switchgear

An object of the present invention is to obtain a resin molded bushing which can easily perform positioning of an electric field relaxation shield in a switchgear. The resin molded bushing includes: an electric field relaxation shield which concentrically surrounds the outer periphery of an internal conductor made of conductor; a cast resin which covers the internal conductor and the electric field relaxation shield; and an elastic member which is disposed on the outer periphery of the electric field relaxation shield and is embedded in the cast resin. The height of the elastic member is equal to the thickness of the cast resin which covers the electric field relaxation shield.

TECHNICAL FIELD

The present invention relates to a resin molded bushing and a switchgear and, more particularly, relates to the structure of positioning between an internal conductor and an electric field relaxation shield in a resin molded bushing equipped in a switchgear.

BACKGROUND ART

A switchgear is equipped with a resin molded bushing. The resin molded bushing includes an internal conductor (metal conductor) and a cylindrical electric field relaxation shield disposed around the internal conductor. In a method of positioning between the internal conductor and the electric field relaxation shield, there are known a method of mounting an embedded metal on an electric field relaxation shield and fixing by the embedded metal in a mold tool (for example, Patent Document 1), a method of providing a flange on the inner surface of a mold tool (for example, Patent Document 2), and the like.

There is also conceivable a method of fixing a plastic spacer made of the same material as a cast resin in the radial direction of an electric field relaxation shield. Radially extended fixing plates are provided at several places on the outer peripheral surface of the electric field relaxation shield to fix the axial direction of the electric field relaxation shield via intervening fixing plates and plastic spacers.

PRIOR ART DOCUMENT

Patent Document

Patent Document 1: Japanese Unexamined Utility Model Publication No. S59-143213Patent Document 2: Japanese Unexamined Utility Model Publication No. S63-190221

SUMMARY OF THE INVENTION

Problems to be Solved by the Invention

When the whole length of the electric field relaxation shield is elongated, a fixing interval of the plastic spacers is also elongated; and accordingly, the longer the resin molded bushing is, the more a center deviation (coaxiality misalignment) between the internal conductor and the electric field relaxation shield is likely to be generated. In the case of applying plastic spacers to fixing the electric field relaxation shield, an issue is raised on the weakness of the plastic spacer for holding in the mold tool. When the resin molded bushing produces a center deviation in the electric field relaxation shield, the distribution of an electric field becomes non-uniform to generate a local electric field concentration.

In the case of fixing the electric field relaxation shield by the embedded metal and the plastic spacer, processing at the mounting position of the mold tool needs to be previously made; and accordingly, locating more fixing places is difficult. More particularly, in the case of fixing the electric field relaxation shield by the embedded metal, the embedded metal has to be fixed by bolts from the outside of the mold tool when the embedded metal is disposed on the electric field relaxation shield; and accordingly, there arises an extra work in assembling and disassembling of the mold tool.

The present invention has been made to solve the problem described above, and an object of the present invention is to obtain a resin molded bushing which can easily perform positioning between an electric field relaxation shield and an internal conductor.

Means for Solving the Problems

A resin molded bushing according to the present invention includes: an electric field relaxation shield which concentrically surrounds the outer periphery of an internal conductor made of conductor; a cast resin which covers the internal conductor and the electric field relaxation shield; and an elastic member which is disposed on the outer periphery of the electric field relaxation shield and is embedded in the cast resin. The height of the elastic member is equal to the thickness of the cast resin which covers the electric field relaxation shield.

Advantageous Effect of the Invention

The present invention exhibits the following effects. A center deviation can be prevented without increasing special processing to a mold tool, adjustment work in assembling of the mold tool, and extra disassembling work of the mold tool. Furthermore, a coil spring is merely disposed on the electric field relaxation shield, whereby mounting work can be made in a short time.

MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of a switchgear according to the present invention will be described in detail with reference to drawings. Incidentally, the present invention is not limited to the following description, but can be appropriately changed without departing from the spirit or scope of the present invention.

FIG. 1is a sectional view showing the schematic whole configuration of a switchgear including a circuit breaker. A switchgear100includes: a resin molded bushing11, a porcelain tube12, a vacuum interrupter15, an electromagnetic operating mechanism16, a housing (case)17, and the like. The inside of the housing17is filled with insulating gas14, such as sulfur hexafluoride (SF6) or dry air. The switchgear100includes a porcelain tube12aand a porcelain tube12b. A resin molded bushing11aand a resin molded bushing11bare inserted in the porcelain tube12aand the porcelain tube12b, respectively. An internal conductor (metal conductor)1aof the resin molded bushing11ais connected to a terminal conductor4aof the vacuum interrupter15. An internal conductor (metal conductor)1bof the resin molded bushing11bis connected to a terminal conductor4bof the vacuum interrupter15. The electromagnetic operating mechanism16performs switching control of a conductive state of the terminal conductor4aand the terminal conductor4b. The electromagnetic operating mechanism16operates by a switching control signal from the outside.

FIG. 2shows the structure of the resin molded bushing. The resin molded bushing11includes: an internal conductor1, an insulating layer2, an electric field relaxation shield5, a spiral ring7, a mounting flange9, and the like. The internal conductor1having a columnar shape is made of copper or aluminum alloy. The insulating layer2made of insulating resin is casted so as to concentrically surround the internal conductor1. A packing groove19is formed in an annular shape concentric with the internal conductor1on one surface (mounting surface to the housing) of the disk-shaped mounting flange9. The packing groove19places a packing which is for sealing by maintaining airtight between the inside and the outside of the housing17in the radial direction of the resin molded bushing11. The electric field relaxation shield5is embedded in the insulating layer2. The insulating layer2is formed by casting resin, in which mold resin is injected in a mold tool. An embedded metal8aand an embedded metal8b, both of which are formed with fixing holes of the resin molded bushing11, are fixed to outer peripheral portions near both side end portions of the electric field relaxation shield5. The embedded metal8bon the mounting flange side relates to joining to the housing17together with positioning of the electric field relaxation shield5. The spiral ring (coil spring)7formed in a ring shape is fixed at a predetermined position by soldering on the outer periphery of the electric field relaxation shield5.

A high voltage is applied to the internal conductor laand the internal conductor lb. A triple junction portion6which comes in contact with three different types of materials (metal, solid insulating material, and gas) of the internal conductor1, the insulating layer2, and the insulating gas14is formed on a longitudinal end portion of the resin molded bushing11. Local electric field concentration is generated near the triple junction portion6and accordingly insulation performance tends to deteriorate. An annular electric field relaxation ring3is mounted on the outer periphery of the internal conductor1for the purpose of achieving electric field relaxation near the triple junction portion6. A garter spring is suitably used in the electric field relaxation ring3. The garter spring is formed in a ring shape by connecting a continuation portion (nib portion). Normally, the outer diameter of the nib portion is finished slightly larger than the inner diameter of a body portion of the garter spring; and therefore, disengagement is not easily generated after assembly.

The structure of the electric field relaxation shield is shown inFIG. 3. The electric field relaxation shield5is made of copper or stainless steel mesh and controls the electric field inside the insulating layer2and outside the resin molded bushing11. The electric field relaxation shield5is disposed, concentrically with the internal conductor1, on the outer periphery of the internal conductor1. The embedded metal8ais directly joined to the electric field relaxation shield5. The embedded metal8bis joined to a tip end of a support bar18which is radially extended from the outer peripheral surface of the electric field relaxation shield5. The spiral ring7is fixed to the outer periphery of the electric field relaxation shield5. The position of the spiral ring7is preferable to be disposed at the center between the embedded metal8aand the embedded metal8b;however, in Embodiment 1, the position of the spiral ring7is located nearer to the mounting flange side in which a core deviation is likely to be generated due to the structure of a product.

FIG. 4shows the structure of the ring-shaped spiral ring7. The spiral ring7is formed in the ring shape (annular shape) by closing both ends of a contact coil spring. The ring-shaped spiral ring7is a spring body, thereby having elasticity in the radial direction or the longitudinal direction of the cross section of the spiral ring. In casting resin, in which the mold resin is injected, there is used a mold tool having an inner surface that is the same shape as the outer peripheral surface of the insulating layer2. The spiral ring7comes in contact with the inner surface of the mold tool on an outer peripheral end portion thereof and comes in contact with an outer peripheral end of the electric field relaxation shield5on an inner peripheral end portion thereof to bias in the radial direction of the internal conductor1; and thus, positioning of the electric field relaxation shield can be made. Positioning between the internal conductor1of the resin molded bushing and the electric field relaxation shield5is made by two embedded metals8and one spiral ring7; and therefore, a structure is made such that the center deviation is not likely to be generated while absorbing a slight dimensional error in each direction or a dimensional error due to thermal expansion. Even if the spiral ring7is disposed on the electric field relaxation shield5, special processing to the mold tool, adjustment work in assembling of the mold tool, and extra disassembling work of the mold tool are not needed. The spiral ring is merely disposed on the electric field relaxation shield; and therefore, mounting work can be made in a short time. Incidentally, the contact coil spring does not need to be completely closed to be the ring shape.

FIG. 5shows the relationship between the insulating layer and the spiral ring. The left side of the mounting flange9is of a nesting structure. A difference in level is formed in the thickness of resin on the left side of the spiral ring7; and thus, the surface of the product is not damaged in drawing the nesting. In a method of mounting the spiral ring7on the electric field relaxation shield, there is also conceivable a method in which both ends of the contact coil spring are joined (welding, brazing, soldering, or the like) or a method of using the garter spring. It is preferable to select the coil diameter of the spiral ring7substantially corresponding to the resin thickness (that is, the distance between the inner surface of the mold tool and the outer peripheral surface of the electric field relaxation shield5) of the insulating layer2. Incidentally, in this case, the spiral ring7is fixed on the outer periphery of the electric field relaxation shield5by soldering. However, the ring-shaped spiral ring7is not fixed by soldering or the like, but may be made to come in contact with the outer periphery of the electric field relaxation shield5to perform positioning by the contraction force of the spiral ring7.

FIG. 6shows Embodiment 2 of the present invention. Two ring-shaped spiral rings7are disposed keeping intervals on an electric field relaxation shield. The spiral rings7are disposed at plural places according to the structure of a resin molded bushing; and thus, fixing places are increased to be a structure in which a center deviation is not further likely to be generated. Combination use with the conventional fixing method is also easy and it can deal with various fixing methods by combining methods.

Embodiment 3 according to the present invention will be described with reference toFIG. 7andFIG. 8. In Embodiment 3, circular arc-shaped and short spiral rings7ato7care disposed in a ring shape on the outer periphery of an electric field relaxation shield5. A plurality of the spiral rings7ato7cwhich are disposed in the circular arc-like shape exhibit a function equivalent to that of a ring-shaped spiral ring. Three spiral rings are disposed in the circular arc-like shape on the outer periphery of the electric field relaxation shield5; and thus, a structure is made such that the spiral rings are not disposed at places corresponding to an upper portion of a cast mold tool.

The short spiral ring uses, for example, a contact coil spring having a length about one-sixth as long as the outer peripheral length of the electric field relaxation shield. Respective both ends of the spiral rings7ato7care fixed to the electric field relaxation shield5by a method such as welding. According to Embodiment 3, the contact coil springs are disposed so that the spiral rings do not come in contact with the upper surface of the mold tool for use in casting; and thus, air (void) is not remained in a spiral ring portion when resin is injected in the mold tool by casting.

In the aforementioned embodiments, the description has been made on examples of using the spiral ring7whose coil spring is formed in the annular shape. However, even when there intervenes an elastic member like extending in a waveform in the circumferential direction of the electric field relaxation shield5while alternately coming in contact with the inner peripheral surface of the mold tool and the outer peripheral surface of the electric field relaxation shield5, an effect equivalent to that of the aforementioned embodiments can be obtained. Other than those above, there can be obtained an effect equivalent to that of the aforementioned embodiments, even when there intervenes a heat resistant elastic member which is resistant to resin cast temperature and can apply a biasing force between the inner surface of the mold tool and the outer peripheral surface of the electric field relaxation shield5in the radial direction of an internal conductor. Furthermore, the description has been made on examples of the electric field relaxation shield5as an object to be retained; however, if the object to be retained is a member required to be retained at a predetermined position concentric with the internal conductor, an effect equivalent to that of the aforementioned embodiments can be obtained.

Incidentally, the present invention can freely combine the embodiments and appropriately change or omit the respective embodiments, within the scope of the present invention.

INDUSTRIAL APPLICABILITY

The present invention relates to an electric field relaxation shield of a resin molded bushing to be equipped in a switchgear and/or a circuit breaker.

DESCRIPTION OF REFERENCE NUMERALS