JPH083969B2 - Center clamp bushing - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an improvement of a center clamp bushing in which each member is clamped by a pulling force of a center conductor.

(Prior Art) A bushing is one in which a center conductor is attached to the inside of a porcelain outer shell, but temperature changes occur due to temperature changes and Joule loss during operation. It is unavoidable that a difference in thermal expansion occurs due to a difference in temperature and a difference in material. Therefore, in order to absorb this, a structure in which a spring (5) having a sufficiently low spring constant is provided between the central conductor (1) and the head metal fitting (2) is generally adopted. Such types are known.

For example, as shown in FIGS. 21 and 22, the central conductor (1)
There is a type in which the upper end of the is protruded to the outside from the head metal fitting (2) of the bushing. In this case, the thermal expansion causes a relative coordinate change of the central conductor (1) with respect to the head metal fitting (2), so that the shaft seal structure using a simple gasket has poor long-term reliability. So metal bellows (3)
Is mounted between the expansion chamber (6) and the central conductor (1), but it has the drawback that the sealing structure becomes very complicated.

Further, as shown in FIG. 23, there is also a type in which the upper end of the central conductor (1) is connected to the head metal fitting (2) through a flexible conductor (4). In this case, the above-mentioned problem of the shaft seal is solved, but since one end of the flexible conductor (4) needs to be attached to the top of the expansion chamber (6), the seal structure becomes complicated and the assembly is not easy. There are drawbacks. 22 and 23
In any of the types shown in the figure, the lid (7) of the expansion chamber (6) needs to be fixed and sealed by bolting, welding, etc., but in the case of bolting, it is sealed by creeping of the gasket (8). In the case of welding, assembly is complicated in order to avoid thermal deterioration of the insulating material, and an insulating material that does not like moisture is exposed to the outside air for a long time, which is not preferable.

Further, as shown in FIG. 24, there is also a type in which the center clamping force is applied only by the spring property of the center conductor (1) itself without using the spring (5). In this case, since the center clamping force is applied to the gasket (8) and the seal portion does not move, there is an advantage of high reliability, and it is also necessary to fix and seal the lid (7) by bolting or welding. Absent. However, since the spring constant of the central conductor (1) is several tens of times larger than that of the spring (5) described above, there are many drawbacks as follows.

That is, there is a large variation in the center clamping force due to a slight change in the tightening force during assembly, and a slight creep of the gasket (8) greatly reduces the center clamping force. Even if a high center clamping force is applied, the center clamping force will decrease significantly due to the temperature rise during operation, and the bending breaking load (bending load when oil leaks) will also decrease significantly (aluminum conductor, copper). In the case of bushings that use conductors, the bending fracture load has dropped to 50% or less at room temperature), the center clamp force fluctuates greatly due to temperature changes, and the center conductor (1) is easily fatigued. However, there are drawbacks such as decrease.

Further, as shown in FIG. 26, in order to reduce the difference in thermal expansion,
There is a type in which a plurality of pipes (9) and (10) having different thermal expansion coefficients are concentrically arranged and a center clamp load acts in series on them to lower an equivalent thermal expansion coefficient. This type of bushing itself is widely known to those skilled in the art, for example, from US Pat. No. 3973077. However, the spring constant cannot be made sufficiently low, the internal structure of the central conductor (1) becomes complicated, and even if dust enters inside, it is difficult to clean and there is a problem in quality control, and the pipe (9) Since the insulating oil inside (10) cannot convect, heat dissipation is poor, and the bushing becomes thick and heavy as a whole.

(Problems to be Solved by the Invention) The present invention solves the above-mentioned drawbacks of the prior art, and the fluctuation of the center clamping force is small, the assembly is easy and the sealing property is good, and the internal cooling property is excellent and large energization is performed. It was completed in order to provide a center clamp bushing capable of obtaining performance.

(Means for Solving the Problems) The present invention made to solve the above problems is a center clamp bushing in which each member is clamped by applying a compressive force to a gasket between each member by a tensile force of a central conductor. , The central conductor is divided into two in the axial direction, and the divided central conductors A and B are elastically connected by an elastic body that exerts a spring force in a direction to attract each other, and one central conductor B is tightened by a tightening nut. It is characterized in that it is fixed to the lid of the expansion chamber and the lid is pressed against the expansion chamber by the center clamping force.

(Operation) Since the center clamp bushing of the present invention configured as described above can reduce the equivalent spring constant of the center conductor by the action of the elastic body, it is possible to reduce the fluctuation of the center clamp force due to thermal expansion. it can. As a result, the stability of the seal and the mechanical strength of the bushing can be maintained, and the structure can be simplified to facilitate the assembly. Further, in the center clamp bushing of the present invention, there is no restriction on the position of the spring, and the upper end portion of the center conductor and the like can be immersed in insulating oil and cooled to improve the current-carrying performance. Furthermore, since one center conductor B is fixed to the lid of the expansion chamber by a tightening nut and the lid is crimped to the expansion chamber by the center clamping force, it is not necessary to fix the lid of the expansion chamber by bolting or welding. The center clamp force of the center conductor can securely fix the conductor.

In the center clamp bushing according to claim 2, the center conductor is replaced with a center pipe, the upper end is immersed in insulating oil, and a hole or notch (1
By providing 6), not only the same effects as above can be obtained, but also by circulating the insulating oil heated by the heat generation during energization by natural convection using the chimney effect of the pipe. , Sufficient cooling can be performed, and the current-carrying capacity can be significantly increased.

(Example) Hereinafter, the present invention will be described in more detail with reference to the illustrated examples.

In FIG. 1, (6) is an expansion chamber of the bushing head, and the central conductor (1) therein is divided into two parts A and B in the axial direction. Each part of the central conductor (1) divided into these two parts is elastically connected by an assembly of an elastic body (11) such as a spring and a flexible conductor (13). The upper central conductor (1) is fixed to the lid (7) of the expansion chamber (6) by the tightening nut (12).

As shown in FIG. 2, this assembly comprises a flexible conductor (13) and a tension spring that connects the two parts A and B of the central conductor (1) so as to attract each other. Since one central conductor B is fixed to the lid (7) of the expansion chamber (6) by the tightening nut (12) as described above, the lid (7) is pressed to the expansion chamber (6) by the center clamping force. Has been done. As shown in FIG. 3, a nut (14) may be used at the connecting portion between the assembly and the central conductor (1) to facilitate the assembling work.

FIGS. 4 and 5 show an example in which a compression spring having a more stable performance than a tension spring is used as the elastic body (11) and is housed inside the box-shaped load transmission member (15) together with the flexible conductor (13). Is shown. However, even in this embodiment, the elastic body (1
The spring force of 1) acts so as to attract the two parts of the central conductors A and B to each other. Load transfer member (15)
Does not necessarily have to be box-shaped,
It may be composed of a flange and a rod as shown in the figure.

FIG. 10 shows a pipe-shaped portion of the lower central conductor (1) at A. In the center conductor (1), the upper end of the portion A of the central conductor (1) is immersed in insulating oil, and a hole or notch (16) for circulating the insulating oil is provided near the lower end thereof. It is possible to circulate the heated insulating oil by natural convection by utilizing the chimney effect of the pipe as shown by the arrow, and to perform sufficient cooling. As a result, the energization performance can be increased, and the bushing can be reduced in diameter and weight.

FIG. 11 is an enlarged view of the portion of the expansion chamber (6) in the present invention, in which the flexible conductor (13) is immersed in insulating oil to improve the current-carrying performance, and the central conductor (1) The part B is fixed to the lid (7) of the expansion chamber (6) by the tightening nut (12), and the lid (7) is fixed by the center clamping force.
It shows the state where is closely attached to the expansion chamber (6). Thereby, as described above, the structure can be simplified and the assembling can be facilitated. However, the structures of the expansion chamber (6) and the lid (7) are not limited to those shown in FIG.
Various variations as shown are possible.

15 to 17 show an embodiment of a lead wire pull-up type center clamp bushing in which each member is clamped by a central pipe (18) into which a lead wire (17) is inserted. In the present invention, the central pipe (18) is used in place of the above-mentioned central conductor (1), and the flexible pipe (19) is used in place of the flexible conductor (13). It is the same as that described so far. A tension spring is used as the elastic body (11) in FIG. 15, and a compression spring is used as the elastic body (11) in FIGS. 16 and 17. Further, (20) is an annular seal member.

(Effect of the invention) As described above, the present invention can reduce the equivalent spring constant of the center conductor by the action of the elastic body, and can reduce the fluctuation of the center clamping force due to thermal expansion.
It is possible to obtain the stability of the seal between each member including the space between the lid and the expansion chamber.

Explaining this with concrete data, 10 gaskets with a thickness of 6 mm having creep characteristics as shown in FIG. 18 were incorporated into the bushing of the present invention, and the average surface pressure was 1 kgf / mm ² ,
2 kgf / mm ^2, performs tightening so that three kinds of 3 kgf / mm ^2, investigating changes in the thickness of the gasket was disassembled after heating corresponding time duration of exposure for 5 years. The result is No. 19
As shown in the figure, the creep amount of the gasket was small enough to be ignored in any of the cases where the surface pressure was applied. Further, FIG. 20 is a graph showing the relationship between the exposure period and the average amount of creep per sheet of gasket, and it can be seen that in the bushing of the present invention, there is no possibility of deterioration of the sealing property due to creep of the gasket.

Further, in the invention of claim 2, at least the lower central conductor is formed into a pipe shape, the upper end thereof is immersed in insulating oil, and a hole or a notch is provided in the vicinity of the lower end thereof so that the heated insulating oil is naturally contained therein. It can be cooled by circulating it by convection, and the current-carrying performance can be improved. When this is shown by concrete data, the bushing of the present invention using the center conductor of the same size and the same material and the conventional bushing (both 500 KV class) were subjected to a temperature rise test by energization. There was a temperature rise of 34.5 ° C in the central conductor when 2000A was energized, but the bushing of the present invention was 20.6 ° C, 600 ° C when 4000A was energized.
Only a temperature rise of 36.6 ° C occurred when 0 A was energized. Therefore, the bushing of the present invention has about three times the current carrying capacity when the center conductor is the same as the conventional one. The standard JEC-183 “Bushing” specifies that the temperature rise of the central conductor when energized is 65 ° C or less.

As described above, according to the present invention, the fluctuation of the center clamp force is small, the sealing property is excellent, the assembly is easy, the cooling property is excellent, and the energizing performance is large. As a solution to the problem of bushing, it contributes significantly to the development of industry.

[Brief description of drawings]

FIG. 1 is a partial sectional view showing an essential part of an embodiment of the present invention, and FIG.
FIG. 9 to FIG. 9 show various modified examples of an assembly of elastic bodies and flexible conductors. FIGS. 2 to 6 are sectional views and FIG.
Fig. 8 is a plan view, Fig. 8 is a sectional view, Fig. 9 is a plan view of Fig. 8, Fig. 10 is a sectional view showing an embodiment in which a pipe is used as a central conductor, and Fig. 11 is a sectional view of an expansion chamber portion. FIGS. 12 to 14 are cross-sectional views showing modified examples thereof, and FIGS. 15 to 17 show various modified examples of an elastic body and an assembly of flexible conductors in a lead wire pull-up type center clamp bushing. Cross section, 18th
The figure is a graph showing the creep characteristics of the gasket used in the performance test, FIG. 19 is a graph showing the creep amount of the gasket after disassembly, and FIG. 20 is a graph showing the relationship between the exposure period and the gasket creep amount. Further, FIG. 21 is a partial cross-sectional view showing a conventional center clamp bushing, FIG. 22 is an enlarged cross-sectional view of a main part thereof, and FIGS. 23 and 24 are enlarged views of a main part of another conventional center clamp bushing. FIG. 25 is a cross-sectional view, FIG. 25 is a graph showing a change in center clamp force in a conventional example, and FIG. 26 is a cross-sectional view of still another conventional center clamp bushing. (1): central conductor, (6): expansion chamber, (7): lid, (1
1): Elastic body, (13): Flexible conductor, (18): Center pipe, (12): Tightening nut, (16): Hole or notch

Claims (2)

[Claims] 1. A center clamp bushing in which each member is clamped by applying a compressive force to a gasket (8) between each member by a tensile force of the center conductor (1), and two center conductors (1) are axially arranged. The central conductors A and B are elastically connected by an elastic body (11) that exerts a spring force in a direction to attract each other, and one central conductor B is expanded by a tightening nut (12). 6)
The center clamp bushing is characterized in that it is fixed to the lid (7) and the lid (7) is pressed against the expansion chamber (6) by the center clamping force. 2. At least the lower central conductor A is formed into a pipe shape, the upper end of which is immersed in insulating oil, and a hole or notch (16) is provided near the lower end thereof, so that heated insulating oil is supplied to a pipe chimney. The center clamp bushing according to claim 1, wherein the center clamp bushing is circulated by natural convection utilizing the effect.