EP1821320A1

EP1821320A1 - Arrestor and method of measuring leakage current of arrestor

Info

Publication number: EP1821320A1
Application number: EP05814184A
Authority: EP
Inventors: Atsushi Ito; Satoshi Watahiki; Kazuhiro Saito; Takeshi Iwaida; Masatoshi Nakajima; Shinan Wan; Kazuhisa Adachi; Nobuyuki Sema; Jyunichi Sinagawa
Original assignee: Japan AE Power Systems Corp; SWCC Showa Cable Systems Co Ltd
Current assignee: Hitachi Ltd; SWCC Corp
Priority date: 2004-12-10
Filing date: 2005-12-08
Publication date: 2007-08-22
Also published as: EP1821320A4; TW200632949A; TWI378475B; KR100929906B1; CN101116156A; CN101116156B; KR20070088686A; WO2006062168A1

Abstract

An arrestor provides a bushing (2) installed in an opened section (1a) of an equipment case (1) hermetically, and a molded arrestor elements stack (6) of this invention is installed in the bushing (2) removably. The bushing (2) provides a rigid, insulated bushing body (3) and a high-voltage shielding electrode (4) embedded in the tip of the bushing body (3) concentrically with the bushing body (3). The bushing body (3) provides an intermediate cylindrical section (53) having a tapered insertion hole (53a) and the high-voltage shielding electrode (4) provides a shielding body (41). The molded arrestor elements stack (6) provides an arrestor elements stack (61) comprising a layer stack of a plurality of arrestor elements (61a) containing zinc oxide as the main component, and a molded rubber (67) comprising silicone rubber and so on is provided at the circumference of the arrestor elements stack (61).

Description

TECHNICAL FIELD

The present invention relates to an arrestor. In particular, the present invention relates to an arrestor having layered body (hereinafter called "arrestor elements stack") of two or more nonlinear resistance element (hereinafter called "arrestor element") containing zinc oxide as the main component.

BACKGROUND ART

In general, in gas insulated switchgear installed in the power plant or the substation and so on, an arrestor is installed to protect electric equipment such as switchgears or transformers from abnormal voltage which invades through the power cable line at the time of the thunderbolt and so on.
Heretofore, as the arrestor of this type, as shown in Fig. 16, the arrestor that the arrestor elements stack 100 is placed vertically on the bottom 110a of the tank 110 filled insulation gas, and is supported by the insulation supporting tube 120 is known (for example, refer to non-patent document No.1), or as shown in Fig. 17, the arrestor to which the bushing 220 is installed in the inner wall of the equipment case 210 hermetically, and the arrestor elements stack 230 is installed removaly in the bushing 220 is known (for example, refer to patent document No.1). Meanwhile, in Fig. 16, reference number 140 shows eccentric shield of high-voltage side, reference number 150 shows insulation spacer, reference number 160 shows instrumentation box and reference number 170 shows adsorbent.
However, in the former arrestor, it is necessary to set large-scale shield 130 on a high-voltage side of the arrestor elements stack 100 in order to equalize the voltage distribution of the arrestor element which constitutes the arrestor elements stack 100. Therefore, there is a difficult point that the equipment itself enlarges. And, when the withstand voltage test of the gas insulated switchgear (hereinafter called "GIS") having the arrestor elements stack 100 is done, because the arrestor elements stack 100 must be separated from the main circuit conductor (not shown), it is necessary to provide the separating device (not shown). Therefore, there is a difficult point that the structure of the equipment becomes complex.
On the one hand, in the latter arrestor, because it is not necessary to provide the separating device, the structure of the equipment becomes simple. And, when the withstand voltage test of the GIS is done, it is not necessary to do the work of collecting or filling insulation gas in the equipment case 210. But, the latter arrestor has following difficult points.
First, because the equipment case 210 as an earthed electrode exists in a part of the circumference of the arrester element layered body 230, it is difficult to equalize the voltage distribution of the arrestor element 230a. Therefore, There is a difficult point that the application is restricted to the power cable line for the medium voltage of 22/33kV.
Second, regarding the arrestor of this kind of plug-in-type, it is necessary to prevent the dielectric breakdown in the boundary by providing the molded body 240 comprising the insulated resin in circumference of the arrestor elements stack 230, and by making the outer surface of the molded body 240 adhere to the inner surface of the insertion hole of the bushing 220, and by ensuring the surface pressure between the outer surface of the molded body 240 and the inner surface of the insertion hole of the bushing 220.
Third, as the method to ensure the surface pressure between the aforementioned outer surface of the molded body 240 and the inner surface of the insertion hole of the bushing 220, the method of making the outer surface shape of the molded body 240 comprising the insulated resin fit in the inner surface shape of the insertion hole of the bushing 220 is known. But, only, by the structure that the outer surface shape of the molded body 240 comprising the insulated resin is merely fitted in the inner surface shape of the insertion hole of the bushing 220, and the molded body 240 comprising the insulated resin is inserted to the insertion hole of the bushing 220, it is difficult to give the effective surface pressure to the boundary between the outer surface of the molded body 240 and the insertion hole of the bushing 220.
Fourth, regarding the arrestor of this kind of plug-in-type, when the withstand voltage test of the equipment is done, because the voltage which exceeds the operational starting voltage of the arrestor elements stack 230 is impressed to the aforementioned arrestor elements stack 230, it is necessary to perform the withstand voltage test in the state of removing the arrestor elements stack 230 from the bushing 220. Therefore, in the case of removing the arrestor elements stack 230 from the bushing 220, it is necessary to insulate the inside of the bushing 220 by SF₆ gas or solid insulator and so on.
Fifth, as the method to insulate the inside of the aforementioned bushing 220, as shown in Fig. 18, the method that installs the insulation cap 310 of the same shape as the molded body 240 removably in the insertion hole of the bushing 220 is known. However, regarding the insulation cap 310 of this kind of structure, it is necessary to fit in the outer surface shape of the insulation cap 310 to the inner surface shape of the insertion hole of the bushing 220 so that the gap does not exist at the boundary between the inner surface of the insertion hole of the bushing 220 and the outer surface of the insulation cap 310. Therefore, there is a difficult point that the insulation cap 310 is enlarged beyond necessity. In addition, only by the structure that the outer surface shape of the insulation cap 310 is fitted in the inner surface shape of the insertion hole of the bushing 220, it is difficult to give the effective surface pressure to the boundary between the inner surface of the bushing 220 and the insulation cap 310 as well as the aforementioned molded body 240.
Non-patent document No. 1: The Institute of Electrical Engineers Japan, Technical Report, No.851, 7(Fig.2.10)
Patent document No. 1: Japanese Patent PublicationNo. Hei01-232681 (Fig. 1)

DISCLOSURE OF THE INVENTION

PROBLEM TO BE SOLVED BY THE INVENTION

This invention was done to solve the aforementioned difficult points. This invention has objects to provide the following arrestor. First, because it is not necessary to install the separating device in the hitherto known gas-insulated-tank-type arrestor, the simplification, miniaturization, weight-saving and cost reduction of the structure of the equipment can be attempted.
Second, when the withstand voltage test is done, it is not necessary to do the work of collecting or filling insulation gas in the equipment case. Third, because it is possible to equalize the voltage distribution, it is possible to adapt the arrestor of this invention to the high-voltage power cable line of 66/77kV grade.
Fourth, it is possible to prevent the dielectric breakdown in the boundary by ensuring the surface pressure between the inner surface of the insertion hole of the bushing and the outer surface of the molded rubber.
Fifth, it is possible to give the predefined surface pressure between the arrestor elements when the arrestor elements stack is installed, and it is possible to remove the arrestor elements stack easily when the withstand voltage test and so on are done.
Sixth, it is possible to separate the arrestor elements stack from the main circuit conductor easily.
Seventh, when the ground-fault current that greatly exceeds the nominal discharge current flows through the arrestor, it is possible to make the shock wave generated on the inside composition body of the bushing hard to propagate to the bushing and thereby to prevent scattering of the zinc oxide element or the bushing.
Eighth, it is possible to provide the arrestor which is able to measure the leakage current easily, and it is possible to provide the method of measuring leakage current of the arrestor.

MEANS FOR SOLVING THE PROBLEMS

The arrestor as the first feature of this invention, in an opened section of an equipment case housing electrical equipments, provides a bushing installed to cover the opened section hermetically and a molded arrestor elements stack installed in an insertion hole of the bushing removably from outside of the equipment case, and the molded arrestor elements stack provides an arrestor elements stack comprising a layer stack of a plurality of arrestor elements and a molded insulator provided around circumference of the arrestor elements stack, and the molded arrestor elements stack is housed inside of the insertion hole of the bushing throughout its length.
In the second feature of this invention according to the arrestor of the first feature, the molded arrestor elements stack is sealed by a sealing cover in a state housed inside of the insertion hole of the bushing.
In the third feature of this invention according to the arrestor of the first feature, the molded insulator is formed by a molded body of insulated rubber.
In the fourth feature of this invention according to the arrestor of the first feature, the bushing is formed by rigid plastic resin.
In the fifth feature of this invention according to the arrestor of the first feature, a main circuit connection terminal connected to a main circuit conductor of the electrical equipment is provided on the tip of said bushing, and a joint conductor connected to the main circuit connection terminal is provided with the molded arrestor elements stack integrally on the tip of the molded arrestor elements stack.
In the sixth feature of this invention according to the arrestor of the first feature, the molded arrestor elements stack provides the arrestor elements stack comprising a layer stack of a plurality of the arrestor elements containing zinc oxide as the main component, a joint conductor connected to high-voltage side of the arrestor elements stack, a pressure metal fitting connected to low-voltage side of the arrestor elements stack, and the molded insulator provided around circumference of the arrestor elements stack.
In the seventh feature of this invention according to the arrestor of the sixth feature, the molded arrestor elements stack is integrated by the molded insulator provided around circumference of the arrestor elements stack.
In the eighth feature of this invention according to the arrestor of the third feature, the molded arrestor elements stack is pressed toward the tip of the bushing in the inside of the insertion hole of the bushing.
In the ninth feature of this invention according to the arrestor of the eighth feature, a back-end side spring to which the spring force by pressing force of axial direction is given is installed at the back-end of the molded arrestor elements stack.
In the tenth feature of this invention according to the arrestor of the eighth feature, a inner surface of the insertion hole of the bushing has a tapered inner surface which extends conically from the tip toward the back-end of the bushing, and an outer surface of the molded insulator has a tapered outer surface to fit in the tapered inner surface.
In the eleventh feature of this invention according to the arrestor of the eighth feature, a tip side spring to which the spring force by pressing force toward axial direction is given is installed in the tip of the molded arrestor elements stack, and a back-end side spring to which the spring force by pressing force toward axial direction is given is installed in the back-end of the molded arrestor elements stack.
In the twelfth feature of this invention according to the arrestor of the eleventh feature, the spring constant of the tip side spring is set lower than entire spring constant of the back-end side spring.
In the thirteenth feature of this invention according to the arrestor of the first feature, in the insertion hole of the bushing, an insulation cap is removably installed instead of the molded arrestor elements stack exchangeably from outside of said equipment case.
In the fourteenth feature of this invention according to the arrestor of the thirteenth feature, the insulation cap provides an insulation cap body installed in the insertion hole of the bushing and having a tapered outer surface to fit in the tapered inner surface of the bushing in the outer surface, a contact component installed in the insertion hole of the bushing and making the high-voltage shielding electrode contact electrically with high-voltage side electrode of the insulation cap body, and a pressure component installed in the insertion hole of the bushing and pressing the insulation cap body toward the tip side of the bushing.
In the fifteenth feature of this invention according to the arrestor of the thirteenth feature, a spring is installed between back-end surface of the insulation cap body and tip surface of the pressure component, and given to the spring is spring force by pressing force toward tip direction of the bushing of the pressure component.
In the sixteenth feature of this invention according to the arrestor of the first feature, the circumference of tip of the molded arrestor elements stack is covered with a high-voltage shielding electrode.
In the seventeenth feature of this invention according to the arrestor of the sixteenth feature, the back-end of the bushing is led to the outside of the equipment case through the opened section of the equipment case.
In the eighteenth feature of this invention according to the arrestor of the seventeenth feature, the electric field of an intermediate section of the arrestor elements stack is controlled by adjustment of the interval between the back-end of the high-voltage shielding electrode and the inner surface of the equipment case.
In the nineteenth feature of this invention according to the arrestor of the sixteenth feature, the circumference of the high-voltage shielding electrode is covered by insulation barrier.
In the twentieth feature of this invention according to the sixteenth feature, the high-voltage shielding electrode has an almost same shaped metal fitting as the shape of tip of the bushing, and the metal fitting is embedded in the tip of the bushing concentrically with the bushing.
In the twenty-first feature of this invention according to the arrestor of the sixteenth feature, the high-voltage molded body is formed by conductive coating layer coated around circumference of the tip of the bushing.
In the twenty-second feature of this invention according to the arrestor of the sixteenth feature, the high-voltage shielding electrode has a cylindrical metal fitting, and the metal fitting is installed around the tip of the bushing to surround the tip of the bushing.
In the twenty-third feature of this invention according to the arrestor of the sixteenth feature, a solid insulated layer is provided around the circumference of the high-voltage shielding electrode.
In the twenty-fourth feature of this invention according to the arrestor of the first feature, the back-end of said bushing is led to the outside of the equipment case through the opened section of the equipment case.
In the twenty-fifth feature of this invention according to the arrestor of the twenty-fourth feature, at the back-end of the bushing, a cutoff area of current is provided in the section which extends from an end surface of the back-end of the bushing to the outer wall of the equipment case.
In the twenty-sixth feature of this invention according to the twenty-fifth feature, the back-end of the bushing is formed by an insulated cylindrical component.
The method of measuring leakage current of arrestor in the twenty-seventh feature of this invention has the steps of providing the arrestor in any one of twenty-fourth feature to twenty-sixth feature, installing an earthing conductor between the equipment case forming the arrestor and the low-voltage side of the arrestor elements stack forming the arrestor, and measuring current flowing through the earthing conductor.
In the twenty-eighth feature of this invention according to the arrestor in any one of the first feature to twenty-sixth feature, gas layer is provided between the molded arrestor elements stack and the insertion hole of the bushing.

EFFECT OF THE INVENTION

According to the arrestor and the method of measuring leakage current of the arrestor from first feature to twenty-eighth feature of this invention, there are following effects.
First, because it is possible to install the molded arrestor elements stack including the arrestor elements stack removably into the bushing which is installed hermetically at the opened section of the equipment case from the outside of the equipment case, it is not necessary to provide the separation device in hitherto known gas-insulated-tank-type arrestor. Therefore, the simplification, the miniaturization, the weight-saving, and the cost reduction can be attempted. Furthermore, when the withstand voltage test is done, it is not necessary to collect or fill insulation gas of the inside of the equipment case.
Second, by leading the back-end of the bushing to the outside of the equipment case hermetically, it is possible to lead a part of the arrestor elements stack (low-voltage side) to the outside of the equipment case. Therefore, the simplification, the miniaturization and the weight-saving of structure of the equipment can be attempted.
Third, because the molded arrestor elements stack including the arrestor elements stack is installed in the bushing, and the circumference of the upper end side (high-voltage side) of the arrestor elements stack is covered by shielding body embedded in the upper cylindrical section, the equalization of the voltage distribution of the arrestor element can be attempted, and consequently, it is possible to adapt the arrestor to the high-voltage power cable line of the 66/77kV grade.
Fourth, by pressing the molded rubber toward the tip of the bushing, it is possible to ensure the surface pressure between the inner surface of the insertion hole of the bushing and the outer surface of the molded rubber, and to prevent the dielectric breakdown at the boundary.
Fifth, by installing the back-end side spring at the back-end of the molded arrestor elements stack, and by giving the spring force to the aforementionedback-end side spring, it is possible to press the molded arrestor elements stack toward the tip of the bushing.
Sixth, by setting the spring constant of the tip side spring lower than entire spring constant of the back-end side spring, it is possible to press the molded arrestor elements stack toward the tip of the bushing by the entire suppress strength of the back-end side spring when the molded arrestor elements stack is installed. And, in the case of removal of arrester molded body, it is possible to push out the molded arrestor elements stack toward the back-end side of the bushing by the spring force of the tip side spring due to the release of the suppress strength of the back-end side spring.
Seventh, by fitting in the tapered outer surface of the molded rubber to the tapered inner surface of the bushing, it is possible to make the suppress strength of axial direction operate as a surface pressure effectively, and it is possible to make the insulation performance at the boundary between the tapered outer surface of the molded rubber and the tapered inner surface of the bushing improve.
Eighth, by the synergic effect of the spring force of the back-end side spring and the spring force of the tip side spring, it is possible to give the predefined surface pressure between the arrestor elements and the joint conductor, between the arrestor elements, and between the arrestor elements and the pressing section.
Ninth, by removing the sealing cover when the withstand voltage test and so on of the equipment is performed, because the molded arrestor elements stack is pushed out toward the back-end side of the bushing by the spring force of the tip side spring, it is possible to remove the molded arrestor elements stack easily.
Tenth, because the back-end of the bushing which is led to the outside of the equipment case is formed by the insulating component of epoxy resin and so on, and because the molded arrestor elements stack including the arrestor elements stack is installed in the bushing, it is possible to provide the cutoff area of current between the outside wall section of the equipment case and the low-voltage side of the arrestor elements stack.
Eleventh, by providing the gas layer such as air and nitrogen and so on between the molded insulator and the insertion hole of the bushing, it is possible to release (discharge pressure) the shock wave which generates when the arrestor element is broken by multiple flows of the ground-fault current that greatly exceeds the nominal discharge current from the gap and so on of the sealing section of the bushing through the gas layer. Consequently, because the aforementioned shock wave becomes difficult to propagate to the bushing, it is possible to prevent the scattering of the arrestor element.
Twelfth, when the withstand voltage test and so on is performed, by installing the insulation cap of predefined structure which is exchangeable for the molded arrestor elements stack in the insertion hole of the bushing, it is possible to ensure the insulation in the insertion hole of the bushing in the state of removing the molded arrestor elements stack. In addition, by locating the insulation cap inside of the end of the back-end side of the high-voltage shielding electrode that the electric field concentrates, it is possible to control the electric field effectively in the state of installing the insulation cap. Furthermore, because the insulation in the insertion hole of the bushing can be ensured by sealing only the inside in the vicinity of the end of the back-end side of the high-voltage shielding electrode, the miniaturization of the insulation cap can be attempted.
Thirteenth, by providing the conductive coating layer instead of the high-voltage shielding electrode comprising metal fitting, the weight-saving and the cost reduction of the arrestor can be attempted.
Fourteenth, by providing the insulation barrier component around the cylindrical metal fitting, it is possible to shorten the insulation distance between the phases, or the insulation distance between the arrestor and the equipment case. Consequently, the miniaturization of the equipment can be attempted.
Fifteenth, by providing the tapered inner surface that the surface pressure operates effectively inside the end of the back-end side of the high-voltage shielding electrode that the electric field concentrates, it is possible to prevent the dielectric breakdown at the boundary.
Sixteenth, by providing the cylindrical section on the joint conductor which is provided on the tip of the molded arrestor elements stack integrally, it is possible to install the tip side spring in the aforementioned cylindrical section easily. In addition, by providing the joint conductor insertion section at the main circuit connection terminal, it is possible to connect the cylindrical section that the tip side spring is provided in the aforementioned joint conductor insertion section by the plug-in connection easily.
Further, according to the method of measuring leakage current of arrestor of the twenty-seventh feature of this invention, because it is possible to provide the cutoff area of current between the outer wall of the equipment case and the low-voltage side of the arrestor elements stack, in the outside of the equipment case, by installing the earthing conductor between the insulated outer wall of the equipment case and the low-voltage side of the arrestor elements stack, it is possible to measure the leakage current of the arrestor elements stack easily. Consequently, it is not necessary to collect or fill insulation gas in the inside of the equipment case when the leakage current is measured. In addition, because it is not necessary to install the insulator in the equipment case, the miniaturization, the simplification, the weight-saving, and the cost reduction can be attempted.

BRIEF DESCRIPTION OF THE FIGURES

[Fig.1] The partial sectional view of the arrestor in the first embodiment of this invention.
[Fig. 2] The partial sectional view of the molded arrestor elements stack in the first embodiment of this invention.
[Fig. 3] The equipotential distribution figure of the arrestor in the first embodiment of this invention.
[Fig. 4] The partial sectional view of the arrestor in the second embodiment of this invention.
[Fig. 5] The partial sectional view of the arrestor in the third embodiment of this invention.
[Fig. 6 The equipotential distribution figure of the arrestor in the third embodiment of this invention.
[Fig.7] The partial sectional view of the insulation cap in the fourth embodiment of this invention.
[Fig.8] The equipotential distribution figure of the insulation cap in the fourth embodiment of this invention.
[Fig.9] The partial sectional view of the arrestor in the fifth embodiment of this invention.
[Fig. 10] The equipotential distribution figure of the arrestor in the fifth embodiment of this invention.
[Fig .11] The partial sectional view of the arrestor in the sixth embodiment of this invention.
[Fig. 12] The equipotential distribution figure of the arrestor in the sixth embodiment of this invention.
[Fig. 13] The partial sectional view of the arrestor in the seventh embodiment of this invention.
[Fig. 14] The equipotential distribution figure of the arrestor in the seventh embodiment of this invention.
[Fig.15] The partial sectional view of the arrestor in the eighth embodiment of this invention.
[Fig .16] The partial sectional view of the arrestor in the prior art. [Fig. 17] The partial sectional view of the arrestor in the prior art.
[Fig. 18] The partial sectional view of the insulation cap in the prior art.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the preferred modes of embodiment which is applicable to the arrestor of this invention will be explained with reference to the figures. Meanwhile, in the following explanation, "tip" of the molded arrestor elements stack, "tip" of the arrestor elements stack and "tip" of the bushing is the end of the high-voltage side of the molded arrestor elements stack, the arrestor elements stack and the bushing respectively, and these correspond to the upper direction in the figures. Furthermore, "back-end" of the molded arrestor elements stack, "back-end" of the arrestor elements stack and "back-end" of the bushing is the opposite end of the tip, and these correspond to the lower direction in the figures.

[Embodiment 1]

Fig.1 is the partial sectional view that shows an example of the arrestor of the 66/77kV grade of this invention.
In this figure, the electrical equipment having the arrestor of this invention provides the equipment case 1 which houses the electrical equipment (not shown) such as the switch and so on hermetically. And the insulated gas, for example, such as SF₆ gas and so on is filled in the equipment case 1. In addition, the opened section 1a is provided at the bottom of the equipment case 1, and in this opened section 1a, the bushing 2 is installed to make the tip of the bushing 2 itself locate in the inside of the equipment case 1 and to cover the opened section 1a in the back-end of the bushing 2 itself hermetically. And the molded arrestor elements stack 6 including the after-mentioned arrestor elements stack 61 is installed in this bushing 2 removably.
The bushing 2 provides the hard and insulated bushing body 3 comprising the molded body and so on which is formed by the epoxy resin, and the high-voltage shielding electrode 4 embedded together with the bushing body 3 concentrically at the tip of the bushing body 3.
The bushing body 3 provides the cylindrical section (hereinafter called "upper cylindrical section") 51 of upper end closing which has the insertion hole (hereinafter called "upper insertion hole") 51a to house the upper section of the molded arrestor elements stack 6, and the cylindrical section (hereinafter called "lower cylindrical section") 52 which has the insertion hole (hereinafter called "lower insertion hole") 52a to house the lower section of the molded arrestor elements stack 6, and the cylindrical section, (hereinafter called "intermediate cylindrical section") 53 which has the insertion hole (hereinafter called "tapered insertion hole") 53a to house the after-mentioned conically-shaped section 67b of the molded arrestor elements stack 6. And the annular mounting flange 52b which protrudes in the direction of a diameter is continuously installed in the circumference of the upper position of the lower cylindrical section 52. Here, the diameter of the lower insertion hole 52a is larger than the diameter of the upper insertion hole 51a, in addition, the tapered insertion hole 53a has the tapered inner surface 53b which extends conically from the tip toward the back-end of the bushing 2, and the upper insertion hole 51a continues to the lower insertion hole 52a through this tapered inner surface 53b. Furthermore, the outside diameter of the lower cylindrical section 52 is nearly equal or slightly small to the diameter of the opened section 1a of the equipment case 1 and the outside diameter of the mounting flange 52b is larger than the diameter of the opened section 1a of the equipment case 1.
The high-voltage shielding electrode 4 provides a bell shaped shielding body 41 which is embedded in the upper cylindrical section 51 concentrically astride the closed section 51b and the back-end of the upper cylindrical section 51, and the tubular section (hereinafter called "joint conductor insertion section") 42 which protrudes to the upper direction of the closed section 51b in the center of the horizontal section of the shielding body 41, and the main circuit connection terminal 43 which is formed continuously in the upper section of the joint conductor insertion section 42 and is connected to the main circuit conductor (not shown).
Here, the side wall section 41a of the shielding body 41 is formed so as to extend conically from the tip toward the back-end, and the length of the axial direction is the length from the closed section 51b of the upper cylindrical section 51 to the neighborhood of tip of the intermediate cylindrical section 53. Namely, the length of the axial direction is the length for making the tip of the aforementioned tapered inner surface 53b locate in the inside of the end of the back-end side of the side wall section 41a of the shielding body 41. Meanwhile, the joint conductor insertion section 42 has the function as the insertion hole of the after-mentioned joint conductor 62 of the molded arrestor elements stack 6, and the main circuit connection terminal 43 which is formed at the tip of the joint conductor insertion section 42 has also the function as the stopper of the after-mentioned coiled spring 63 of the molded arrestor elements stack 6.
Regarding the high-voltage shielding electrode 4 of this kind of structure, as shown in the figure, the main circuit connection terminal 43 protrudes from the closed section 51b of the upper cylindrical section 51, and is embedded in the upper cylindrical section 51 concentrically so that the side wall section 41a is located in the side wall section 51b of the upper cylindrical section 51.
Regarding the bushing 2 of this kind of structure, because the upper cylindrical section 51 and the intermediate cylindrical section 53 of the bushing 2 are located in the equipment case 1, and the lower cylindrical section 52 is led to the outside of the equipment case 1 through the opened section 1a, the upper surface of the mounting flange 52b comes in contact with the under surface of the peripheral section of the opened section 1a of the equipment case 1. Therefore, by placing the O-ring P1 in the annular concave groove 1b which is provided in the peripheral section of the opened section 1a of the equipment case 1, and by clenching the bolt V1 which is provided in the mounting flange 52b, it is possible to install the bushing 2 in the opened section 1a of the equipment case 1 hermetically.
The molded arrestor elements stack 6, as shown in Fig. 2, provides the arrestor elements stack 61 which stacked multiple arrestor elements 61a containing zinc oxide as the main component, and the joint conductor 62 which is installed at the tip side (high-voltage side) of the arrestor elements stack 61, and the coiled spring (hereinafter called "tip side spring") 63 which is installed at the tip side (high-voltage side) of the joint conductor 62, and the pressure metal fitting 64 which is installed at the back-end side (low-voltage side) of the arrestor elements stack 61, and the coiled spring (hereinafter called "back-end side spring") 66 which is installed under the pressure metal fitting 64, and the molded rubber 67 comprising silicone rubber and so on which is molded integrally astride the joint conductor 62 and the pressure metal fitting 64 in the circumference of the arrestor elements stack 61.
Here, the shape of the outer surface of the molded rubber 67 is formed so that it may correspond to the shape of inner surface of the insertion hole (the upper insertion hole 51a, the lower insertion hole 52a, the tapered insertion hole 53a) of the bushing 2. Specifically, the small diameter section 67a which comes in contact with the inner surface of the upper insertion hole 51a is provided in the tip side (high-voltage side) of the molded rubber 67, and the conically-shaped section 67b which has the tapered outer surface 67c which comes in contact with the tapered inner surface 53b of the tapered insertion hole 53a is provided in the intermediate section of the molded rubber 67, and the large diameter section 67d which comes in contact with the inner surface of the lower insertion hole 52a is provided in the back-end side (low-voltage side) of the molded rubber 67, respectively. In addition, the spring constant of the tip side spring 63 is set lower than entire spring constant of the back-end side spring 66 (the total spring constant of the multiple back-end side spring 66). Meanwhile, the number of arrestor elements 61a corresponding to the system voltage is determined in consideration of the predefined varistor voltage. This embodiment applies to the high voltage power cable line of 77kV.
The joint conductor 62 provides the circular plate section 62a which is the almost same shape as the arrestor element 61a which comes in contact with the high-voltage side of the arrestor elements stack 61, and the cylindrical section 62b which protrudes toward upper direction in the central section of the upper surface of this circular plate 62a. And the annular concave groove 62c is provided in the circumference of the cylindrical section 62b in order to set the tape-like electrical contact (multi-contact) which is not shown in the figure.
The pressure metal fitting 64 provides the circular component 65a which has slightly smaller diameter than the outside diameter of the back-end side (low-voltage side) of the molded rubber 67, and the plate-shaped pressing section 65b which is the almost same shape as the arrestor element 61a is provided in the central section of the upper surface of this circular component 65a, and, for example, the twelve concave groove sections 65c are provided so that these are placed along the circumference at regular interval in the neighborhood of circumference of the lower surface side. Meanwhile, the reference number 65d in the figure is, for example, four tapped holes which are placed along the circumference at regular interval in the inner periphery of the circular component 65a, and the reference number 65e is the large diameter concave groove section which is provided in the central section of the lower surface side of the circular component 65a.
In the circumference of the arrestor elements stack 61 of this kind of structure, the molded rubber 67 comprising silicone rubber and so on is provided in the state of contacting to the lower surface of the circular plate section 62a of the joint conductor 62 in the tip, and in the state of contacting to the pressing section 65b of the pressure metal fitting 64 in the back-end, and astride the upper surface section of the circular plate section 62a of the joint conductor 62 and the circumference of the pressure metal fitting 64. And, according to this molded rubber 67, the arrestor elements stack 61 is integrated together with the joint conductor 62 and the pressure metal fitting 64.
Next, the method of installing the molded arrestor elements stack 6 removably in the bushing 2 is explained.
First, the tip side spring 63 is installed in the cylindrical section 62b of the joint conductor 62 so that the upper section of the tip side spring 63 may protrude from the cylindrical section 62b, and the back-end side spring 66 is installed in the concave groove section 65c of the pressure metal fitting 64 so that the lower section of the back-end side spring 66 may protrude from the concave groove section 65c. And, in the state of not giving the spring force to the tip side spring 63 and the back-end side spring 66, as shown in Fig. 1, the tip (high-voltage side) of the molded arrestor elements stack 6 is inserted in the bushing 2, and the tip of the molded arrestor elements stack 6 is pushed until the tip of the tip side spring 63 comes in contact with the inner wall surface of the main circuit connection terminal 43. Herewith, the individual piece (not shown) which constitutes the electrical contact (multi-contact) which is installed in the cylindrical section 62b comes in contact with the inner peripheral surface of the joint conductor insertion section 42 electrically, furthermore, the small diameter section 67a of the molded rubber 67 comes in contact with the inner peripheral surface of the upper insertion hole 51a of the bushing 2, and the conically-shaped section 67b of the molded rubber 67 comes in contact with the inner peripheral surface of the tapered insertion hole 53c, and the large diameter section 67c of the molded rubber 67 comes in contact with the inner peripheral surface of the lower insertion hole 52a.
Here, the outside diameter of the tip side spring 63 is almost same diameter as the inner diameter of the cylindrical section 62b of the joint conductor 62, and the outside diameter of the back-end side spring 66 is almost same as the inner diameter of the concave groove section 65c of the pressure metal fitting 64.
Next, the sealing cover F comprising the plate-shapedmetal fitting is made to come in contact with the under surface of the lower cylindrical section 52 of the bushing 2, and is clenched at the under surface of the lower cylindrical section 52 by multiple bolts V2 which is placed along the circumference direction in the neighborhood of circumference of the sealing cover F. Herewith, the back-end side spring 66 is compressed between the back section of the concave groove section 65c and the upper surface of the sealing cover F, and the spring force of the axial direction is given to the back-end side spring 66. After this, the molded arrestor elements stack 6 is pushed further toward the tip of the bushing 2 by the spring force of the back-end side spring 66, and herewith, the predefined surface pressure is given between the conically-shaped section 67b of the molded rubber 67 and the surface of the inner periphery of the tapered insertion hole 53c, and the tip side spring 63 is compressed between the closed section of the cylindrical section 62b (the upper surface of the joint conductor 62) and the inner wall surface of the main circuit connection terminal 43, and the spring force of the axial direction (the reactive force toward the molded arrestor elements stack 6) is given to the tip side spring 63. Meanwhile, in Fig. 1, the mark N shows the tapped hole which is embedded in the lower surface of the lower cylindrical section 52 of the bushing 2, and the tip of the bolts V2 is screwed in this tapped holes N.
Fig. 3 shows the equipotential distribution figure of the arrestor in this embodiment. From this figure, it is clear that because the tip of the arrestor elements stack 61 is shielded by the high-voltage shielding electrode 4, the electric field does not concentrate to the aforementioned tip of the arrestor elements stack 61, and because the back-end of the arrestor elements stack 61 is installed at the outside of the equipment case 1 as the earthed electrode, the electric field does not also concentrate to the aforementioned back-end of the arrestor elements stack 61, and furthermore, in the intermediate section of the arrestor elements stack 61, because the electric field is controlled appropriately by adjustment of the interval between the high-voltage shielding electrode 4 and the equipment case 1 as the earthed electrode, the electric field does not also concentrate to the aforementioned intermediate section of the arrestor elements stack 61.
Here, the influence that the shielding body 41 and the equipment case 1 as the earthed electrode give to the arrestor elements stack 61 is explained. First, when the interval between the back-end of the shielding body 41 and the upper surface of the equipment case 1 is short, there is a relation that the electric field in the intermediate section of the arrestor elements stack 61 becomes dense by the influence of the shielding body 41 and the equipment case 1, and, on the contrary, when the interval of both is long, there is a relation that the electric field in the aforementioned intermediate section of the arrestor elements stack 61 becomes coarse. Therefore, even if arrangedmerely to have the structure which expands the interval of the both results, it is difficult to equalize the voltage distribution of the arrestor element 61a. On this point, in this embodiment, because the tip (length of about 1/3 of the arrestor elements stack 61) and the intermediate section (length of about 1/3 of the arrestor elements stack 61) of the arrestor elements stack 61 is located in the equipment case 1, and the back-end (length of about 1/3 of the arrestor elements stack 61) of the arrestor elements stack 61 is located outside the equipment case 1, the interval between the high-voltage shielding electrode 4 and the equipment case 1 as the earthed electrode is adjusted appropriately, and it is possible to control the electric field appropriately in the intermediate section of the arrestor elements stack 61. Consequently, the equalization of the voltage distribution of the arrestor element 61a can be attempted.
As described above, regarding the arrestor of this kind of structure, first, because it is possible to install the arrestor elements stack 61 removably from the outside of the equipment case 1 into the bushing 2 which is installed hermetically at the opened section 1a of the equipment case 1, it is not necessary to install the separation device in hitherto known gas-insulated-tank-type arrestor, and it is possible to simplify the structure of the equipment. Second, when the withstand voltage test is done, it is possible to make collecting or filling operation of the insulation gas of the inside of the equipment case 1 unnecessary. Third, by leading a part (low-voltage side) of the arrestor elements stack 61 outside of the equipment case 1, the miniaturization of the equipment can be attempted. Fourth, by installing the molded arrestor elements stack 6 including the arrestor elements stack 61 in the bushing 2, because the circumstance of the upper end side (high-voltage side) of the arrestor elements stack 61 is covered by the shielding body 41 embedded in the upper cylindrical section 51, the equalization of the voltage distribution of the arrestor element 61a can be attempted, and consequently, it is possible to adapt to the high voltage power cable line of the 66/77kV grade. Fifth, by pressing the molded rubber toward the tip of the bushing, it is possible to ensure the surface pressure between the inner surface of the insertion hole of the bushing and the outer surface of the molded rubber, and it is possible to prevent the dielectric breakdown at the boundary. Sixth, by installing the back-end side spring 66 at the back-end of the molded arrestor elements stack 6, and by giving the spring force to the aforementioned back-end side spring 66, it is possible to press the molded arrestor elements stack 6 toward the tip of the bushing 2 . Seventh, by fitting in the tapered outer surface of the molded rubber 67 to the tapered inner surface of the bushing 2, it is possible to make the suppress strength of axial direction as a surface pressure operate effectively. Namely, by giving the predefined surface pressure to the boundary between the conically-shaped section 67b of the molded rubber 67 and the inner peripheral surface of the tapered insertion hole 53c, it is possible to make the insulation performance of the boundary of both progress. Eighth, by the synergic effect of the spring force of the back-end side spring 66 and the spring force of the tip side spring 63, it is possible to give the predefined surface pressure between the arrestor elements 61a and the joint conductor 62, between the arrestor elements 61a, and between the arrestor element 61a and the pressing section 65b. Ninth, by removing the sealing cover F when the withstand voltage test of the equipment is performed, because the molded arrestor elements stack 6 is pushed out toward the back-end side of the bushing 2 by the spring force of the tip side spring 63, it is possible to remove the molded arrestor elements stack 6 easily.

[Embodiment 2]

Fig . 4 shows the partial sectional view of the arrestor in the second embodiment of this invention. Meanwhile, in this figure, the same reference numbers are given to the portions which are common to Fig.1, and detailed explanation is omitted.
In this embodiment, by forming the bushing 2 with the insulated material such as the epoxy resin and so on, the cutoff area of current Z is formed at the back-end of the bushing 2 which is led to the outside of the equipment case 1. Specifically, the cutoff area of current Z is formed in the section which extends from the end surface of the back-end of the lower cylindrical section 52 as the insulated cylindrical component to the outer wall of the equipment case 1.
Regarding the arrestor of this kind of structure, in the outside of the equipment case 1, by installing the earthing conductor E in the cutoff area of current Z which is provided in the back-end of the bushing 2, that is, by installing the earthing conductor E between the outer wall of the equipment case 1 and the low-voltage side of the arrestor elements stack 61, it is possible to measure the leakage current of the arrestor elements stack 61 easily. Specifically, by installing the one end side of the earthing conductor E in the bolt V1 of the same electric potential as the equipment case 1, and by installing the another end side of the earthing conductor E in the bolt V2 of the same electric potential as the low-voltage side of the arrestor elements stack 61 through the pressure metal fitting 64 and the sealing cover F, and by detecting the current that flows through the ground conductor E by the current transformer H, it is possible to measure the leakage current of the arrestor elements stack 61.
As mentioned above, regarding the arrestor of this kind of structure, because the back-end (the lower cylindrical section 52) of the bushing 2 which is led outside of the equipment case 1 is formed with the insulated material such as the epoxy resin, and because the molded arrestor elements stack 6 including the arrestor elements stack 61 is installed in the bushing 2, it is possible to provide the cutoff area of current Z between the outer wall of the equipment case 1 and the low-voltage side of the arrestor elements stack 61. And in the outside of the equipment case 1, by installing the earthing conductor E between the outer wall of the equipment case 1 which cuts off the current and the low-voltage side of the arrestor elements stack 61, it is possible to measure the leakage current of the arrestor elements stack 61 easily. Therefore, regarding the arrestor of this kind of structure, it is not necessary to collect or fill insulation gas in the inside of the equipment case 1 while measuring the leakage current, in addition, because it is not necessary to install the insulator in the equipment case 1, the miniaturization, the simplification, the weight-saving, and the cost reduction of the equipment can be attempted.

[Embodiment 3]

Fig. (a) shows the partial sectional view of the arrestor in the third embodiment of this invention, and Fig. 5 (b) shows the plane view of the sealing cover in the same embodiment. Meanwhile, in this figure, the same reference numbers are given to the portions which are common to Fig.1, and detailed explanation is omitted.
In Fig. 5 (a), the molded arrestor elements stack 6 provides the arrestor elements stack 61 stacking multiple arrestor elements 61a containing zinc oxide as the main component, and the joint conductor 62 which is installed in the tip side (high-voltage side) of the arrestor elements stack 61, and the columnar pressure metal fitting 64 which is installed in the back-end side (low-voltage side) of the arrestor elements stack 61, and the molded insulator 67d comprising silicone rubber and so on which is molded integrally astride the joint conductor 62 and the pressure metal fitting 64 in the circumference of the arrestor elements stack 61. And the gas layer G is provided between the molded insulator 67d and the insertion hole of the bushing 2.
The aforementioned molded insulator 67d has enough thickness to integrate the arrestor elements stack 61, the joint conductor 62 and the pressure metal fitting 64, and by thinning the aforementioned thickness as much as possible, in the state of housing the molded arrestor elements stack 6 in the bushing 2, the gas layer G is formed between the molded arrestor elements stack 6 and the insertion hole of the bushing 2 (the tip insertion hole 51a, the intermediate insertion hole 53a, the lower insertion hole 52a) . Furthermore, by providing suchlike molded insulator 67d in the circumference of the arrestor elements stack 61, it is possible to ease the electric field of the outer surface of the arrestor elements stack 61.
Here, the molded insulator 67d can be formed by molded body comprising the rubber, the plastic resin of the epoxy resin and so on in place of the molded body comprising the silicone rubber. Meanwhile, in Fig. 5, the reference number 68 shows the plate-shaped sealing cover which is installed in the under surface of the lower cylindrical section 52 of the bushing 2 to close the lower insertion hole 52a, and the aforementioned sealing cover 68 is formed with the metal fitting of the aluminum metal fitting and so on. In addition, the circular concave groove section 68a which is almost same shape as the pressure metal fitting 64 is provided in the center of the upper surface of this sealing cover 68, and in the neighborhood of circumference, as shown in Fig. 5 (b), for example, four bolt insertion holes H3 are provided so that these are placed along the circumference at regular interval. Furthermore, in the under surface side of the lower cylindrical section 52 of the bushing 2, the embedded metal fitting N having tapped holes is embedded in the place corresponding to the bolt insertion holes H3 of the sealing cover 68. Meanwhile, the mark H4 in Fig. 5 (b) shows the bolt insertion hole to insert the earthed electrode terminal.
Also in this embodiment, the coiled tip side spring 63 which is almost same diameter as the inner diameter of the cylindrical section 62b of the joint conductor 62 is installed in the cylindrical section 62b of the joint conductor 62 so that the upper section of the tip side spring 63 protrudes, and in this state, the tip (high-voltage side) of the molded arrestor elements stack 6 is inserted in the bushing 2, and the tip of the tip side spring 63 is pushed until it comes in contact with the inner wall surface 43a of the main circuit connection terminal 43. Herewith, the individual piece (not shown) constituting the electrical contact (multi-contact) which is installed in the annular concave groove 62c of the joint conductor 62 comes in contact with the inner peripheral surface of the joint conductor insertion section 42 electrically, furthermore, the arrestor elements stack 6 is inserted into the insertion hole of the bushing 2 removally.
Next, by installing the lower section of the pressure metal fitting 64 in the concave groove section 68a of the sealing cover 68, and by making the upper surface side of the aforementioned sealing cover 68 come in contact with the under surface of the lower cylindrical section 52 of the bushing 2, and by screwing the tip of the clenching bolts V1 into the tapped holes of the embedded metal fitting N of the bushing 2 through the under surface side of the sealing cover 68, namely, by making the sealing cover 68 come in contact with the under surface of the lower cylindrical section 52 and fixing the sealing cover 68 to the under surface of the lower cylindrical section 52, the arrestor elements stack 6 is pressed toward the tip of the bushing 2, and the tip side spring 63 which is installed in the tip of the arrestor elements stack 6 is pressed toward the axial direction, and the predefined spring force is given to the aforementioned tip side spring 63. Herewith, because the predefined surface pressure is given between the arrestor elements 61a and the joint conductor 62, between the arrestor elements 61a, and between the arrestor elements 61a and the pressure metal fitting 64, these components come in contact with each other certainly.
Fig. 6 shows the equipotential distribution figure of the arrestor in this embodiment. From this figure, it is clear that because the tip of the arrestor elements stack 6 is shielded by the high-voltage shielding electrode 4, the electric field does not concentrate to the aforementioned tip, and because the back-end of the arrestor elements stack 6 is installed in the outside of the equipment case 1 as the earthed electrode, the electric field does not also concentrate to the aforementioned back-end, and furthermore, in the intermediate section of the arrestor elements stack 6, because the electric field is controlled appropriately by adjustment of the interval between the high-voltage shielding electrode 4 and the equipment case 1 as the earthed electrode, the electric field does not also concentrate to the aforementioned intermediate section.
As described above, regarding the arrestor of this kind of structure, it provides the gas layer G between the molded insulator 67d and the insertion hole of the bushing 2. The shock wave which generates when the ground-fault current that greatly exceeds the nominal discharge current flows through the arrestor is released (discharged pressure) from the gap and so on of the sealing section of the bushing 2 through the gas layer G. Namely, the O-ring P2 for sealing which is installed between the under surface of the lower cylindrical section 52 of the bushing 2 and the sealing cover 68, and the sealing cover 68 itself transform by momentary rise of internal pressure of the bushing 2 when the breakdown of the arrestor element occurred. The shock wave is released (discharged pressure) from the gap which occurs by aforementioned transformation between the under surface of the lower cylindrical section 52 of the bushing 2 and the sealing cover 68. Therefore, the aforementioned shock wave becomes difficult to propagate to the bushing. Consequently, it is possible to prevent the scattering of the arrestor element.

[Embodiment 4]

Fig. 7 shows the partial sectional view of the insulation cap which is installed in the bushing removably instead of the aforementioned molded arrestor elements stack 6. Meanwhile, in this figure, the same reference numbers are given to the portions which are common to Fig.1 and Fig. 2 , and detailed explanation is omitted.
In Fig. 7, the insulation cap 20 of this invention provides the insulation cap body 21 which is installed in the tapered insertion hole 53a of the bushing 2, and the cylindrical contact component 22 which is located above the insulation cap body 21 and is installed with the upper cylindrical section 51 concentrically in the upper insertion hole 51a of the bushing 2, and the upper end closing cylindrical pressure component 23 which is located under the insulation cap body 21 and is installed with the lower cylindrical section 52 concentrically in the lower insertion hole 52a of the bushing 2. Here, the contact component 22 is formed by the metal fitting of the aluminum alloy and so on, and that diameter is smaller than the diameter of the upper insertion hole of the bushing, in addition, the length of the axial direction is equal to the interval between the top of inner wall 41b of the high-voltage shielding electrode 4 and the after-mentioned upper wall 27b of the high-voltage side electrode 27. Specifically, in the state of installing the insulation cap 20 in the bushing 2 at a right position, the length of the axial direction of the contact component 22 is the length that the tip of the contact component 22 comes in contact with the top of inner wall 41b of the high-voltage shielding electrode 4 electrically, and back-end of the contact component 22 comes in contact with the upper wall 27b of the high-voltage side electrode 27 electrically. Furthermore, the pressure component 23 is formed by the metal fitting such as the aluminum alloy, and thick wall section 23a is provided along the axial direction in a part of the cylindrical section. In addition, the multiple bolt insertion holes 23c are provided in the closed section 23b of the pressure component 23 so that these are placed along the circumference at regular interval and, if necessary, the tapped holes 23d are provided at the back-end surface of the thick wall section 23a.
The insulation cap body 21 provides the columnar section 24 which has the almost same outside diameter as the diameter of the lower insertion hole 52a of the bushing 2, and the conically-shaped section 25 which is connected to the tip of the aforementioned columnar section 24 continuously and is installed in the tapered insertion hole 53a of the bushing 2, and the hemispherical low-voltage side electrode 26 which is embedded in the back-end of the columnar section 24 so that the spherical salient 26a turns to the tip, and the hemispherical high-voltage side electrode 27 which is embedded in the tip of the conically-shaped section 25 so that the spherical salient 27a faces to the low-voltage side electrode 26.
Here, the outer surface of the conically-shaped section 25 has the tapered outer surface 25a which fits in the tapered inner surface 53b of the bushing 2, and the diameter of the low-voltage side electrode 26 is slightly smaller than the diameter of the columnar section 24. Furthermore, the under surface of the low-voltage side electrode 26 is embedded so as to become the state of the same level surface as the under surface of the columnar section 24, and the multiple spring housing holes 26b and the multiple tapped holes 26c are provided so that these are placed along the circumference at regular interval in the under surface of the aforementioned low-voltage side electrode 26.
The columnar section 24 and the conically-shaped section 25 are formed by the insulated material such as the ethylene-propylene rubber, and these are molded integrally together with the low-voltage side electrode 26 and the high-voltage side electrode 27.
Next, the method of installing the insulation cap 20 of such a structure removably in the bushing 2 is explained.
First, the bolt V2 shown in Fig.1 is removed and the sealing cover F is removed from the lower cylindrical section 52 of the bushing 2 and the molded arrestor elements stack 6 is removed from the bushing 2.
Next, as shown in Fig.7, the spring 28 is set in the spring housing holes 26b of the low-voltage side electrode 26 so that it's lower section protrudes from the spring housing hole 26b, and after that, the bolt 29 is inserted in the bolt insertion holes 23c and it's tip is set in the tapped holes 26c of the low-voltage side electrode 26. Herewith, the pressure component 23 is installed in the low-voltage side electrode 26 through the axial section 29a of the bolt 29 so as to advance and retreat freely. And in the state of not giving the spring force to the spring 28, the contact component 22, the insulation cap body 21 and the pressure component 23 are inserted in the bushing 2, and the tip of the contact component 22 is pushed until it comes in contact with the top section of inner wall 41b of the high-voltage shield. Herewith, the tapered outer surface 25a of the conically-shaped section 25 of the insulation cap body 21 comes in contact with the tapered inner surface 53b of the bushing 2.
After that, as well as the abovementioned, the sealing cover F comes in contact with the under surface of the lower cylindrical section 52 of the bushing 2. And the sealing cover F is clenched at under surface of the lower cylindrical section 52 by multiple bolts V2. Herewith, the surface of the upper-end of the pressure component 23 is pushed until it comes in contact with the surface of the lower-end of the low-voltage side electrode 26 through the axial section 2 9a of the bolt 29, and herewith, the spring 28 is pushed toward axial direction and the spring force of the axial direction is given to the aforementioned spring 28.
In addition, when the spring force of the axial direction is given to the spring 28, because the pressure component 23 which constitutes the insulation cap 20 is pushed toward the tip of the bushing 2, the predefined surface pressure is given to the fitted section of the tapered outer surface 25a of the insulation cap body 21 and the tapered inner surface 53b of the bushing 2.
Fig.8 shows the equipotential distribution figure of the insulation cap in this embodiment. From this figure, by installing the insulation cap 20 at the right position in the bushing 2, because the circumference of the tip of the insulation cap body 21 which constitutes the insulation cap 20 is covered by the high-voltage shielding electrode 4, it is clear that the electric field in the insulation cap body 21 is controlled appropriately.
As mentioned above, regarding the insulation cap of this kind of structure, when the withstand voltage test and so on are performed, by installing the insulation cap 20 which is exchangeable for the molded arrestor elements stack 6 in the insertion hole of the bushing 2, it is possible to ensure the insulation of the inside of the insertion hole of the bushing 2 in the state of removing the molded arrestor elements stack 6. In addition, by providing the insulation cap 20 in the inside of the end of the back-end side of the high-voltage shielding electrode 4 that the electric field concentrates, it is possible to control the electric field effectively in the state of installing the insulation cap 20. Furthermore, because the insulation of the inside of the insertion hole of the bushing 2 can be ensured by sealing only the inside in the vicinity of the end of the back-end side of the high-voltage shielding electrode 4, the miniaturization of the insulation cap 2 0 can be attempted.

[Embodiment 5]

Fig. 9 shows the partial sectional view of the arrestor in the fifth embodiment of this invention. Meanwhile, in this figure, the same reference numbers are given to the portions which are common to Fig. 1, and detailed explanation is omitted.
In Fig. 9, in this embodiment, the conductive coating layer 75 is provided on the peripheral surface of the tip of the bushing 7 as shown with the dotted line.
Here, the bushing 7 in the fifth embodiment provides the intermediate cylindrical section 71 that the circular concave groove section 71a is provided at the neighborhood of circumference of the upper surface of itself, and the upper cylindrical section 72 which is connected to the intermediate cylindrical section 71 concentrically and continuously at the upper end of the intermediate cylindrical section 71 and which has smaller diameter than the outside diameter of the intermediate cylindrical section 71 and which has the dwindled. conically-shaped section 72a whose upper end is closed, and the lower cylindrical section 73 which is connected to the intermediate cylindrical section 71 concentrically and continuously at the neighborhood of circumference of the under surface of the intermediate cylindrical section 71 and which has smaller diameter than the outside diameter of the intermediate cylindrical section 71, and the main circuit connection terminal 74 which is embedded in the center of the closed section 72b of the upper cylindrical section 72 so that the tip of itself protrudes from the closed section 72b. Meanwhile, in the bushing 7 in this embodiment, the outside diameter of the lower cylindrical section 73 is larger than the diameter of the opened section 1a of the equipment case 1 and the under surface of the circumference of the lower cylindrical section 73 is put on the upper surface of the equipment case 1 and is fixed hermetically.
The reference number 75 shows the conductive coating layer (for example, the coating layer comprising silver paint) as the high-voltage shielding electrode. And this conductive coating layer 75 is coated astride the outside circumference surface of the closed section 72b of the upper cylindrical section 72, the outside circumference surface of the conically-shaped section 72a and the outside circumference surface of the semicircular section 71b which constitutes the concave groove section 71a of the intermediate cylindrical section 71.
Fig. 10 shows the equipotential distribution figure of the arrestor in the fifth embodiment. From this figure, also in this embodiment, as well as the arrestor of the first embodiment, it is clear that because the tip of the arrestor elements stack 61 is shielded by the conductive coating layer 75 as the high-voltage shielding electrode, the electric field does not concentrate to the aforementioned tip, and because the back-end of the arrestor elements stack 61 is installed at the outside of the equipment case 1 as the earthed electrode, the electric field does not also concentrate to the aforementioned back-end, and furthermore, in the intermediate section of the arrestor elements stack 61, because the electric field is controlled by adjustment of the interval between the conductive coating layer 75 and the equipment case 1 as the earthed electrode, the electric field does not also concentrate to the aforementioned intermediate section.
As described above, also in the arrestor of the fifth embodiment, it is possible to equalize the voltage distribution of the arrestor element 61a. And in this embodiment, because the conductive coating layer 75 is provided instead of the high-voltage shielding electrode 4 comprising metal fitting, weight-saving and cost reduction can be attempted than the arrestor in the first embodiment. Meanwhile, the arrestor in this embodiment is suitable for the gas insulated type electric equipment or for the air insulated type electric equipment.

[Embodiment 6]

Fig. 11 shows the partial sectional view of the arrestor in the sixth embodiment of this invention. Meanwhile, in this figure, the same reference numbers are given to the portions which are common to Fig. 1, and detailed explanation is omitted.
In Fig. 11, in this embodiment, other high-voltage shielding electrode 10 is put on the tip of the bushing 8 and is fixed.
Here, the bushing 8 in the sixth embodiment provides the dwindled intermediate cylindrical section 81, and the upper cylindrical section 82 which is connected to the intermediate cylindrical section 81 concentrically and continuously at the upper end of the intermediate cylindrical section 81 and which has smaller diameter than the outside diameter of the intermediate cylindrical section 81, and the lower cylindrical section 83 which is connected to the intermediate cylindrical section 81 concentrically and continuously at the lower end of the intermediate cylindrical section 81 and which has almost same diameter as the outside diameter of the lower end of the intermediate cylindrical section 81. And the circular mounting flange 83a is provided continuously at the circumference of the tip of the lower cylindrical section 83.
The high-voltage shielding electrode 10 provides the cylindrical metal fitting 11 whose upper end is closed, and the main circuit connection terminal 13 which is installed toward the upper direction from the closed section 12 on the center of the closed section 12 of the metal fitting 11.
Regarding the high-voltage shielding electrode 10 of this kind of structure, as shown in the figure, the main circuit connection terminal 13 is installed on the upper position of the upper cylindrical section 82 and the side wall section 14 of the metal fitting 11 is put on the tip of the upper cylindrical section 82 concentrically so as to be located around the side wall section 82a of the upper cylindrical section 82 and is fixed.
Fig. 12 shows the equipotential distribution figure of the arrestor in the sixth embodiment of this invention. From this figure, also in this embodiment, as well as the arrestor of the first embodiment, it is clear that because the tip of the arrestor elements stack 61 is shielded by the cylindrical metal fitting 11 which constitutes the high-voltage shielding electrode 10, the electric field does not concentrate to the aforementioned tip, and because the back-end of the arrestor elements stack 61 is installed in the outside of the equipment case 1 as the earthed electrode, the electric field does not also concentrate to the aforementioned back-end, and furthermore, in the intermediate section of the arrestor elements stack 61, because the electric field is controlled by adjustment of the interval between the cylindrical metal fitting 11 and the equipment case 1 as the earthed electrode, the electric field does not also concentrate to the aforementioned intermediate section.
As described above, also in the arrestor of the sixth embodiment, it is possible to equalize the voltage distribution of the arrestor element 61a. Meanwhile, the arrestor in this embodiment is suitable for the oil insulated type electric equipment, for the gas insulated type electric equipment or for the air insulated type electric equipment.

[Embodiment 7]

Fig. 13 shows the partial sectional view of the arrestor in the seventh embodiment of this invention. Meanwhile, in this figure, the same reference numbers are given to the portions which are common to Fig. 1 and Fig. 11, and detailed explanation is omitted.
In Fig. 13, in this embodiment, the high-voltage shielding electrode 10 which is shown in Fig. 11 is put on the tip of the bushing 9 and is fixed, and the circumference of the high-voltage shielding electrode 10 is covered by the insulation barrier 91b as follows.
Here, the bushing 9 in the seventh embodiment provides the upper cylindrical section 91 that the circular concave groove section 91a is provided at the neighborhood of circumference of the upper surface of itself, and the lower cylindrical section 92 which is connected to the upper cylindrical section 91 concentrically and continuously at the lower end of the upper cylindrical section 91 and which has smaller diameter than the outside diameter of the upper cylindrical section 91. In addition, in the high-voltage shielding electrode 10 of the same structure shown in Fig. 11, that side wall section 14 is installed concentrically so as to be located in the concave groove section 91a of the upper cylindrical section 91. Meanwhile, in the bushing 9 in this embodiment, the outside diameter of the upper cylindrical section 91 is larger than the diameter of the opened section 1a of the equipment case 1 and the under surface of the circumference of the upper cylindrical section 91 is put on the inner surface of the equipment case 1 and is fixed hermetically.
Fig. 14 shows the equipotential distribution figure of the arrestor in the seventh embodiment. From this figure, also in this embodiment, as well as the arrestor of the first embodiment, it is clear that because the tip of the arrestor elements stack 61 is shielded by the cylindrical metal fitting 11 as the high-voltage shielding electrode, the electric field does not concentrate to the aforementioned tip, and because the back-end of the arrestor elements stack 61 is installed at the outside of the equipment case 1 as the earthed electrode, the electric field does not also concentrate to the aforementioned back-end, and furthermore, in the intermediate section of the arrestor elements stack 61, because the electric field is controlled by adjustment of the interval between the cylindrical metal fitting 11 and the equipment case 1 as the earthed electrode, the electric field does not also concentrate to the aforementioned intermediate section.
As described above, also in the arrestor of the seventh embodiment, it is possible to equalize the voltage distribution of the arrestor element 61a as a whole. And in the arrestor of this embodiment, by installing the side wall section 14 of the high-voltage shielding electrode 10 in the concave groove section 91a of the upper cylindrical section 91, because the insulation barrier component 91b is located around the cylindrical metal fitting 11, it is possible to shorten the insulating distance between phases or the insulating distance with equipment case 1, and consequently, the miniaturization of the equipment can be attempted. Meanwhile, the arrestor in this embodiment is suitable for the oil insulated type electric equipment, for the gas insulated type electric equipment or for the air insulated type electric equipment.

[Embodiment 8]

Fig. 15 shows the partial sectional view of the arrestor in the eighth embodiment of this invention. Meanwhile, in this figure, the same reference numbers are given to the portions which are common to Fig.1 and Fig.2, and detailed explanation is omitted.
In Fig. 15, in this embodiment, the high-voltage shielding electrode 20 is embedded in the tip of the molded arrestor elements stack 6 as follows.
Here, in the bushing 30 of the eighth embodiment, the joint conductor insertion section 42 shown in Fig.1 is embedded in the center of the closed section 51b of the upper cylindrical section 51, and the main circuit connection terminal 43 shown in Fig.1 is provided continuously on the tip of the joint conductor insertion section 42. In addition, the tapered hole 31 which extends conically toward the lower end section from the closed section 51b is provided in the inner circumference of the upper cylindrical section 51, and this tapered hole 31 is leading to the intermediate insertion hole 32 which is the same diameter as the lower insertion hole 52a shown in Fig.1 continuously.
The high-voltage shielding electrode 20 provides the plate-shaped horizontal section 21a, and the reverse-cup-like shielding body 21 which has the side wall section 21b which is provided vertically so as to extend conically from the circumference of the horizontal section 21. And the cylindrical section 62b shown in Fig. 2 is installed at the center of the upper section of the horizontal section 21a of this shielding body 21 so that it protrudes .
Regarding the high-voltage shielding electrode 20 of this kind of structure, as shown in the figure, the horizontal section 21a comes in contact with the tip side (high-voltage side) of the arrestor elements stack 61, and in this state, it is integrated by the molded rubber 67 which is provided at the circumference of the arrestor elements stack 61. Meanwhile, the conical section 67d which comes in contact with the inner circumference surface of the tapered hole 31 is provided at the circumference of the tip of the molded rubber 67.
As described above, also in this embodiment, because the circumference of the tip of the arrestor elements stack 61 is covered by high-voltage shielding electrode 20, it is possible to equalize the voltage distribution of the arrestor element 61a.
Meanwhile, in the eighth embodiment, although the case that the high-voltage shielding electrode 20 is embedded in the molded rubber 67 is explained, it is possible to install the aforementioned high-voltage shielding electrode 20 at the circumference of the molded rubber 67.

INDUSTRIAL APPLICABILITY

In this invention, it is possible to modify or revise the invention within the scope of claims as follows.
First, in the aforementioned embodiment, although the case that the bushing is installed at the bottom of the equipment case 1 is explained, also it is possible to install the bushing at the side wall of the equipment case 1.
Second, in the aforementioned embodiment, although the case that the arrestor of this invention is applied to the high voltage cable line of 66/77 kV is explained, also it is possible to apply the arrestor of this invention.to the cable line of less than 66 kV or to the high voltage cable line that exceeds 77 KV.

Claims

An arrestor providing, in an opened section of an equipment case which houses electrical equipments,
a bushing installed to cover said opened section hermetically, and
a molded arrestor elements stack installed in an insertion hole of said bushing removably from outside of said equipment case, in which
said molded arrestor elements stack has an arrestor elements stack comprising a layer stack of a plurality of arrestor elements, and a molded insulator provided around circumference of said arrestor elements stack, characterized in that:
said molded arrestor elements stack is housed inside of said insertion hole of the bushing throughout its length.
The arrestor as claimed in claim 1, characterized in that said molded arrestor elements stack is sealed by a sealing cover in a state housed inside of said insertion hole of the bushing.
The arrestor as claimed in claim 1, characterized in that said molded insulator is formed by a molded body of insulated rubber.
The arrestor as claimed in claim 1, characterized in that said bushing is formed by rigid plastic resin.
The arrestor as claimed in claim 1, characterized in that a main circuit connection terminal connected to a main circuit conductor of said electrical equipment is provided on the tip of said bushing, and
a joint conductor connected to said main circuit connection terminal is provided with said molded arrestor elements stack integrally on the tip of said molded arrestor elements stack.
The arrestor as claimed in claim 1, characterized in that said molded arrestor elements stack provides the arrestor elements stack comprising a layer stack of a plurality of the arrestor elements containing zinc oxide as the main component, a joint conductor connected to high-voltage side of said arrestor elements stack, a pressure metal fitting connected to low-voltage side of said arrestor elements stack, and the molded insulator provided around circumference of said arrestor elements stack.
The arrestor as claimed in claim 6, characterized in that said molded arrestor elements stack is integrated by the molded insulator provided around circumference of said arrestor elements stack.
The arrestor as claimed in claim 3, characterized in that said molded arrestor elements stack is pressed toward the tip of said bushing in the inside of said insertion hole of the bushing.
The arrestor as claimed in claim 8, characterized in that a back-end side spring to which the spring force by pressing force of axial direction is given is installed at the back-end of said molded arrestor elements stack.
The arrestor as claimed in claim 8, characterized in that a inner surface of said insertion hole of the bushing has a tapered inner surface which extends conically from the tip toward the back-end of said bushing, and an outer surface of said molded insulator has a tapered outer surface to fit in said tapered inner surface.
The arrestor as claimed in claim 8, characterized in that a tip side spring to which the spring force by pressing force toward axial direction is given is installed in the tip of said molded arrestor elements stack,
a back-end side spring to which the spring force by pressing force toward axial direction is given is installed in the back-end of said molded arrestor elements stack.
The arrestor as claimed in claim 11, characterized in that spring constant of said tip side spring is set lower than entire spring constant of said back-end side spring.
The arrestor as claimed in claim 1, characterized in that, in said insertion hole of the bushing, an insulation cap is removably installed instead of said molded arrestor elements stack exchangeably from outside of said equipment case.
The arrestor as claimed in claim 13, characterized in that said insulation cap provides:
an insulation cap body installed in said insertion hole of the bushing and having a tapered outer surface to fit in the tapered inner surface of said bushing in the outer surface,

a contact component installed in said insertion hole of the bushing and making a high-voltage shielding electrode contact electrically with high-voltage side electrode of said insulation cap body, and

a pressure component installed in said insertion hole of the bushing and pressing said insulation cap body toward the tip side of said bushing.
The arrestor as claimed in claim 13, characterized in that a spring is installed between back-end surface of said insulation cap body and tip surface of said pressure component, and
given to said spring is spring force by pressing force toward tip direction of said bushing of said pressure component.
The arrestor as claimed in claim 1, characterized in that the circumference of tip of said molded arrestor elements stack is covered with a high-voltage shielding electrode.
The arrestor as claimed in claim 16, characterized in that the back-end of said bushing is led to the outside of said equipment case through the opened section of said equipment case.
The arrestor as claimed in claim 17, characterized in that electric field of an intermediate section of said arrestor elements stack is controlled by adjustment of the interval between the back-end of said high-voltage shielding electrode and the inner surface of said equipment case.
The arrestor as claimed in claim 16, characterized in that the circumference of said high-voltage shielding electrode is covered with insulation barrier.
The arrestor as claimed in claim 16, characterized in that said high-voltage shielding electrode has an almost same shaped metal fitting as the shape of tip of said bushing, and
said metal fitting is embedded in the tip of said bushing concentrically with said bushing.
The arrestor as claimed in claim 16, characterized in that said high-voltage molded body is formed by conductive coating layer coated around circumference of the tip of said bushing.
The arrestor as claimed in claim 16, characterized in that said high-voltage shielding electrode has a cylindrical metal fitting, and
said metal fitting is installed around the tip of said bushing to surround the tip of said bushing.
The arrestor as claimed in claim 16, characterized in that a solid insulated layer is provided around the circumference of said high-voltage shielding electrode.
The arrestor as claimed in claim 1, characterized in that the back-end of said bushing is led to the outside of said equipment case through the opened section of said equipment case.
The arrestor as claimed in claim 24, characterized in that, at the back-end of said bushing, a cutoff area of current is provided in the section which extends from an end surface of the back-end of said bushing to the outer wall of said equipment case.
The arrestor as claimed in claim 25, characterized in that the back-end of said bushing is formed by an insulated cylindrical component.
A method of measuring leakage current of arrestor,
characterized by:
providing an arrestor as claimed in any one of claim 24 to claim 26,

installing an earthing conductor between a equipment case forming said arrestor and a low-voltage side of an arrestor elements stack forming said arrestor, and

measuring current flowing through said earthing conductor.
The arrestor as claimed in any one of claim 1 to claim 26, characterized in that gas layer is provided between said molded arrestor elements stack and said insertion hole of the bushing.