JP3112336B2 - Evaluation method for internal stress of stress cone - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for evaluating the internal stress of a stress cone for evaluating the internal stress applied to a stress cone attached to a power cable at the end of the power cable in order to reduce the electrical stress. About the method.

[0002]

2. Description of the Related Art A stress cone is used at a connection portion between a power cable and a device or at a straight line connection or a branch connection portion between power cables to relieve an electric stress. FIG. 6 is a diagram illustrating the configuration of a conventional general stress cone. In the figure, (a) is a longitudinal sectional view of a terminal portion of a cable to which a stress cone is attached, (b) is a perspective view of the stress cone, (c) is a longitudinal sectional view of a blind plug which is a kind of stress cone, and (d) is It is a perspective view of a blind plug. (A) of the figure
In the cable 1, the sheath 2, the shielding layer 3, the semiconductive layer 4, and the insulator 5 are sequentially peeled off to expose the conductor 6, and the compression terminal 7 is connected to the conductor 6. Such a terminal portion of the cable 1 is inserted into the bushing 8. A stress cone 9 is attached to alleviate the electrical stress between the terminal of the cable 1 and the bushing 8 to enhance the insulation.

[0005] The stress cone 9 has a semiconductive portion 9 A electrically connected to the semiconductive layer 4 of the cable 1, and an insulating member which is fitted on the outer periphery of the insulator 5 of the cable 1 and pressed against the inner wall surface of the bushing 8. 9B. The stress cone 9 is applied with a constant pressure in the direction of arrow 10 by a spring or other pressing mechanism (not shown) to maintain the pressure between the insulating portion 9B and the inner wall surface of the bushing 8 at a certain level or more. Improves insulation properties. The stress cone 9 has an appearance as shown in FIG. When the terminal portion of the cable 1 is not attached to such a bushing 8, the blind plug 11 having a sectional structure as shown in FIG. Is inserted. The blind plug 11 has an insulating portion 11C provided between a high-voltage electrode 11A and a low-voltage electrode 11B. In addition,
Also in this blind plug 11, the insulating portion 11C is made of EP rubber or the like similar to the stress cone 9. FIG. 4D shows a perspective view of the blind plug 11.

[0004]

However, as described above, the stress cone 9 and the blind plug 11 must be pressed against the inner wall surface of the bushing 8 with a certain pressure or more.
Further, it is desired that the pressure at the interface be constant or higher at any part. However, stress corn 9
6 in the direction of arrow 10 shown in FIG.
(C) Mechanism for pressing blind plug 11 and its electrode 1
Due to the structure of 1A or 11B, the distribution of the internal stress applied to the insulating portions 9B and 11C becomes very complicated. Therefore, it is necessary to design the shape of the stress cone 9 and the configuration of the electrodes 11A and 11B of the blind plug 11 while taking such internal stress into account in advance. For this purpose, analysis by computer simulation has conventionally been performed, and a design has been made based on such an analysis result. However, specific experiments are required to prove the validity of the analysis results of computer simulation.

For this reason, as shown in FIG. 6, for example, a pressure sensor 12 is attached to the inner wall surface of the bushing 8, and its output signal is taken out to the outside using a lead wire 13, and actually applied to the insulating portion 9B of the stress cone 9. The pressure was to be measured. Also, stress cone 9 and cable 1
In order to measure the pressure applied between the insulators 5 of the cable 1, for example, a rod having the same diameter as the insulator 5 of the cable 1 is used, a pressure sensor 12 is attached to the outer peripheral surface thereof, and the output is output using a lead wire 13. I was trying to extract the signal.

However, such a surface pressure sensor 12
In the case of measuring a high surface pressure, an error becomes relatively large. Further, the rubber used for the insulating portions 9B and 11C is not a complete fluid, but is a moving system combining a spring and a damper. Therefore, the influence of the shape is extremely large. Further, the surface pressure applied to the bushing 8 of the stress cone 9 does not always have to be constant as a whole,
A design that applies a higher pressure to a place where the electric field is largely concentrated is preferable. Therefore, the stress cone 9 and the blind plug 1
It is preferable to accurately analyze how the force of pressing 1 by a pressing mechanism using a spring or the like is distributed to these insulators and transmitted to the interface thereof. A stress cone or the like with a distribution can be designed. Therefore, a detailed analysis of the surface pressure is an essential element in designing a stress cone or the like. The present invention has been made in view of the above points, and an object of the present invention is to provide a method for evaluating the internal stress of a stress cone capable of accurately and precisely analyzing and evaluating the internal stress of the stress cone by a simpler method. It is assumed that.

[0007]

According to the method for evaluating the internal stress of a stress cone of the present invention, a stress cone to be evaluated is sliced along a plane passing through its axis to produce a plate-shaped evaluation sample, and the evaluation sample is used as the evaluation sample. After drawing a grid-like striped pattern,
Applying the same pressure as that applied when using the stress cone to the evaluation sample, and comparing the degree of deformation of the striped pattern before and after pressing, to estimate the internal stress distribution of the stress cone. Is what you do.

[0008]

In this method, a plane model having a sectional shape obtained by slicing an actual stress cone along a plane passing through its axis is used as an evaluation sample. A lattice stripe pattern is drawn on this plane model. When pressure is applied to an evaluation sample having an appropriate thickness, the evaluation sample is deformed similarly to the case where pressure is applied to an actual stress cone, and the stripe pattern is deformed. By analyzing the degree of deformation of the stripe pattern, the internal stress distribution of the stress cone can be estimated.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the embodiments shown in the drawings. FIG. 1 is an explanatory view showing an embodiment of a stress cone internal stress evaluation method according to the present invention. In the example of the figure, a method for evaluating the internal stress of the blind plug 11 described above with reference to FIG. 6 as a kind of stress cone will be described. First,
It is assumed that a sample corresponding to an angle dθ is cut out along a plane passing through the axis of the blind plug 11. As shown in the figure, the high-voltage side electrode 11A, the insulator 11C, and the low-voltage side electrode 11B
Is provided. When calculating and analyzing the internal stress distribution by computer simulation, the thickness of such a sample is extended to infinity as shown in the center part of the figure, and the stress distribution is calculated based on a so-called two-dimensional model. Therefore, such an experimental sample cannot be actually manufactured, and a model having the same shape as the real thing is used when performing an experiment for verifying the results of computer simulation.

However, the EP rubber used for the insulator 11C is a relatively hard material, and by setting a certain thickness, the cross section passing through the axis even if the force in the thickness direction is ignored. From the viewpoint, it was found that almost the same deformation as the real thing was performed. In the present invention, based on the principle described above, an evaluation sample 12 having a cross-sectional shape obtained by slicing a stress cone to be evaluated along a plane passing through its axis is prepared, and the same as that applied to an actual stress cone when it is used. Was applied to evaluate the stress distribution.

As shown in the drawing, the evaluation sample 12 has a high-voltage side electrode 12A, a low-voltage side electrode 12B, and an insulating portion 12C made of the same material as the actual product. Also, a grid-like striped pattern 13 is drawn on the surface of the insulating portion 12C. The lattice-shaped striped pattern 13 is used to evaluate the degree of deformation when pressure is applied to the insulating portion 12C. In addition, actually, the thickness of this evaluation sample is, for example,
It was found that the internal stress distribution can be estimated in a state very close to the actual product by selecting about 30 mm.

An example of actual stress distribution measurement will be described with reference to FIGS. FIG. 2 shows a first example, in which a pressure is applied to an evaluation sample 12 having the same cross-sectional shape as shown in FIG. The evaluation sample 12 has a grid-like striped pattern 13 similar to that described above. In this case, the lattice-shaped striped pattern 13 after the deformation faithfully expresses the internal stress distribution such that a portion where a stress is strongly applied becomes finer and a portion where the stress is applied from the lateral direction is curved. Note that, for such analysis, the grid-like striped pattern 13 is drawn, for example, vertically and horizontally at 1 mm intervals. The front view of the actual evaluation sample shown in FIG. 3 shows that deformation of the side surface can be easily understood by bringing the ruler 15 along the side surface. In other words, the stress cone having such a cross-sectional shape is designed so that the low-pressure portion swells more and a high surface pressure is applied to the low-pressure portion. Note that the blind line having such a configuration can be said to be a design in which the electric field formed between the low-voltage side electrode 12B and the high-voltage side electrode 12A is relatively uniform, and the internal electric field distribution is particularly important.

FIG. 4 shows an example in which electrodes having shapes different from those shown in FIG. 2 are used. That is, the low-voltage side electrode 14A of this stress cone has the same cross-sectional shape as that shown in FIG. 2, but the cross-sectional shape of the high-voltage side electrode 14B is designed to be convex downward. On the other hand, when pressure is applied in the direction of arrow 10 shown in FIG. 4, the insulating portion 14C is deformed. The degree of the deformation is such that the bulge increases on the high pressure side. Further, as can be seen from the lattice-shaped striped pattern 13, the deformation of the insulating portion 14C tends to be outward from the center. Therefore, the example shown in the figure is designed so that surface pressure is emphasized rather than electric field distribution. FIG.
When the ruler 15 is brought into contact with the side surface of the evaluation sample 14 as shown in FIG. Further, even when the striped patterns 13 are compared with each other, it can be clearly understood that the manner in which the surface pressure is applied is greatly different. The present invention is not limited to the above embodiments. In the above-described embodiment, an example in which the grid-like stripe pattern is drawn in the vertical and horizontal directions is shown, but this may be drawn in an oblique direction, and the pitch of the stripe pattern is partially changed as necessary. You can do it. The evaluation of the stress cone as shown in FIG. 6B can be performed in the same manner.

[0014]

As described above, according to the method for evaluating the internal stress of a stress cone according to the present invention, an evaluation sample having a sectional shape obtained by slicing a stress cone to be evaluated along a plane passing through its axis is prepared. After drawing a grid-like striped pattern on the evaluation sample, apply the same pressure to the evaluation sample when applying a stress cone, compare the degree of deformation of the striped pattern, and measure the internal stress distribution of the stress cone As a result, the error distribution is smaller than when measuring the stress distribution using a surface pressure sensor or the like using an actual stress cone, and the stress distribution is evaluated directly and in detail by the naked eye. be able to. This makes it possible to relatively easily design a stress cone having a stress distribution that is closer to the ideal than in the past.

[Brief description of the drawings]

FIG. 1 is a principle explanatory diagram for explaining an internal stress evaluation method of a stress cone according to the present invention.

FIG. 2 is a front view showing an actual evaluation sample in a pressurized state.

FIG. 3 is a front view of the evaluation sample of FIG. 2 showing the degree of deformation after pressing.

FIG. 4 is a front view showing a pressurized state of another evaluation sample.

5 is a front view of the evaluation sample of FIG. 4 showing the degree of deformation after pressing.

6A and 6B illustrate a configuration of a conventional stress cone. FIG. 6A is a longitudinal sectional view of a cable end portion, FIG. 6B is a perspective view of the stress cone, and FIG. FIG. 4 is a longitudinal sectional view, and FIG.

[Explanation of symbols]

 Reference Signs List 12 Evaluation sample 12A High voltage side electrode 12B Low voltage side electrode 12C Insulation part 13 Lattice stripe pattern

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G01L 1/00 G01N 3/08

Claims (1)

(57) [Claims] 1. An evaluation sample having a plate-like cross section obtained by slicing a stress cone to be evaluated along a plane passing through the axis thereof is prepared, and a grid-like striped pattern is drawn on the evaluation sample. Applying the same pressure as that applied when using the cone, and estimating the internal stress distribution of the stress cone by comparing the degree of deformation of the striped pattern before and after pressurization. Evaluation methods.