JPH05240720A - Evaluating method for internal stress of stress cone - Google Patents

Abstract

PURPOSE:To estimate the internal stress distribution of a stress cone by analyzing the degree of deformation of a striped pattern. CONSTITUTION:A plane model of a cross section formed by slicing an actual stress cone on a plane passing its axis is used as a sample 12 for evaluation. A checked pattern 13 is traced on the plane model. When pressure is applied to the sample 12 for evaluation which has proper thickness, the sample 12 for evaluation is deformed in the same manner as when pressure is applied to the actual stress cone, and the checked pattern is deformed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an internal stress evaluation of a stress cone for evaluating the internal stress received by a stress cone mounted at the end of a power cable for relieving electrical stress during its use. Regarding the method.

[0002]

2. Description of the Related Art A stress cone is used at a connecting portion between a power cable and a device, or at a straight connecting portion or a branch connecting portion between the power cables in order to relieve the electric stress. FIG. 6 shows an explanatory diagram of the structure of a conventional general stress cone. In the figure, (a) is a longitudinal sectional view of a terminal portion of a cable equipped with a stress cone, (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. Figure (a)
In the cable 1, the sheath 2, the shielding layer 3, the semiconductive layer 4, and the insulator 5 are stepped off in order to expose the conductor 6, and the compression terminal 7 is connected to the conductor 6. The terminal portion of such a cable 1 is inserted into the bushing 8. A stress cone 9 is attached to relieve electrical stress between the end of the cable 1 and the bushing 8 and enhance insulation.

The stress cone 9 is fitted around the semiconductive portion 9A electrically connected to the semiconductive layer 4 of the cable 1 and the outer periphery of the insulator 5 of the cable 1 and is pressed against the inner wall surface of the bushing 8. It is composed of a section 9B. A constant pressure is applied to the stress cone 9 in the direction of the 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 higher. Improves insulation properties. The stress cone 9 has an appearance as shown in FIG. Further, when the end portion of the cable 1 is not attached to the bushing 8 as described above, a blind plug 11 having a cross-sectional structure as shown in (c) is provided in order to relieve electrical stress at the open portion of the bushing 8 and ensure insulation. Is fitted. This blind plug 11 is provided with an insulating portion 11C between the high voltage side electrode 11A and the low voltage side electrode 11B. In addition,
In the blind plug 11, the insulating portion 11C is also made of EP rubber or the like similar to the stress cone 9. A perspective view of the blind plug 11 is shown in FIG.

[0004]

By the way, 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 is above a certain level in any part. However, stress cone 9
6 and a pressing mechanism for pushing in the direction of arrow 10 shown in FIG.
A mechanism for pressing the blind plug 11 shown in (c) and its electrode 1
The structure of 1A and 11B makes the distribution of internal stress applied to the insulating portions 9B and 11C 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 in consideration of such internal stress in advance. For this purpose, analysis by computer simulation has conventionally been performed, and design has been made based on the result of such analysis. However, concrete experiments are required to prove the validity of the computer simulation results.

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

However, such a surface pressure sensor 12
Has a relatively large error when measuring a high surface pressure. Further, the rubber used for the insulating portions 9B and 11C is not a perfect fluid but a moving system in which a spring and a damper are combined. 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 necessarily have to be constant as a whole,
A design that applies higher pressure to the place where the electric field is largely concentrated is preferable. Therefore, stress cone 9 and 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 is transmitted to the interface, and the ideal surface pressure depends on the analysis results. You can design a stress cone for distribution. Therefore, detailed analysis of the surface pressure is an essential element for designing a stress cone or the like. The present invention has been made in view of the above points, and an object thereof is to provide a stress cone internal stress evaluation method capable of accurately and precisely analyzing and evaluating the internal stress of a stress cone by a simpler method. Is to

[0007]

The internal stress evaluation method for a stress cone of the present invention is to prepare an evaluation sample having a cross-section plate shape obtained by slicing a stress cone to be evaluated along a plane passing through the axis, and After drawing a grid-like striped pattern,
The same stress as that applied when using the stress cone is applied to the evaluation sample, and the internal stress distribution of the stress cone is estimated by comparing the degree of deformation of the striped pattern before and after pressurization. To do.

[0008]

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

[0009]

The present invention will be described in detail below with reference to the embodiments shown in the drawings. FIG. 1 is an explanatory view showing an embodiment of an internal stress evaluation method of a stress cone of 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 will be described as a kind of stress cone. First,
It is assumed that a sample corresponding to the angle dθ is cut along the surface passing through the axis of the blind plug 11. This sample includes a high voltage side electrode 11A, an insulator 11C, and a low voltage side electrode 11B as shown in the figure.
Is provided. When the internal stress distribution is calculated and analyzed by computer simulation, the thickness of such a sample is extended to infinity as shown in the central part of the figure, and the stress distribution is calculated by the so-called two-dimensional model. Therefore, such an experimental sample cannot be actually manufactured, and a model having the same shape as the actual product is used when an experiment for demonstrating the result of computer simulation is performed.

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

In this evaluation sample 12, a high voltage side electrode 12A, a low voltage side electrode 12B and an insulating portion 12C are formed of the same material as the actual product, as shown in the figure. Further, a grid-shaped striped pattern 13 is drawn on the surface of the insulating portion 12C. This grid-shaped striped pattern 13 is used to evaluate the degree of deformation when pressure is applied to the insulating portion 12C. In addition, in practice, 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 one by selecting about 30 mm.

An example of actual stress distribution measurement will be described with reference to FIGS. 2 to 5. FIG. 2 shows a first example of the deformation state of the evaluation sample 12 having the same sectional shape as that shown in FIG. 1 when pressure is applied in the direction of arrow 10. 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 the portion to which the stress is strongly applied becomes fine and is curved when the stress is applied from the lateral direction. For such an analysis, the grid-shaped striped pattern 13 was drawn vertically and horizontally at intervals of 1 millimeter, for example. The front view of the actual evaluation sample shown in FIG. 3 shows that the deformation of the side surface can be easily understood by placing the ruler 15 along the side surface. That is, 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. It should be noted that the blind wire having such a configuration has a relatively uniform electric field formed between the low-voltage side electrode 12B and the high-voltage side electrode 12A, and can be said to be a design that emphasizes the internal electric field distribution.

FIG. 4 shows an example in which an electrode having a shape different from that shown in FIG. 2 is 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 high-voltage side electrode 14B is designed so that the cross-sectional shape is 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 deformation is such that the bulge increases on the high pressure side. Further, as can be seen from the grid-like striped pattern 13, the deformation of the insulating portion 14C has a tendency to go outward from the center. Therefore, the example in the figure is designed with emphasis on surface pressure rather than electric field distribution. Figure 5
When the ruler 15 is applied to the side surface of the evaluation sample 14 as shown in FIG. 3, it is well understood that the degree of deformation thereof is significantly different from that shown in FIG. Further, it can be clearly understood that even when the striped patterns 13 are compared with each other, how the surface pressure is applied is greatly different. The present invention is not limited to the above embodiments. In the above embodiment, an example in which a grid-like striped pattern is drawn vertically and horizontally is shown, but this may be drawn diagonally, and the pitch of the striped pattern may be partially changed if necessary. There is no problem in doing so. In addition, the stress cone as shown in FIG. 6B can be evaluated in the same manner.

[0014]

As described above, according to the stress cone internal stress evaluation method of the present invention, an evaluation sample having a cross-sectional shape is prepared by slicing a stress cone to be evaluated by a plane passing through the axis, and After drawing a grid-shaped stripe pattern on the evaluation sample, apply the same pressure as that applied when using the stress cone to the evaluation sample and compare the degree of deformation of the stripe pattern to measure the internal stress distribution of the stress cone. Since this is done, there is less error than when measuring the stress distribution using a surface pressure sensor etc. using an actual stress cone, and the stress distribution can be evaluated directly and in detail with the naked eye. be able to. As a result, it becomes possible to design a stress cone having a stress distribution that is closer to the ideal than the conventional one, relatively easily.

[Brief description of drawings]

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

FIG. 2 is a front view showing a pressed state of an actual evaluation sample.

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

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

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

6A and 6B are views for explaining the structure of a conventional stress cone, where FIG. 6A is a vertical cross-sectional view of a cable end portion, FIG. 6B is a perspective view of the stress cone, and FIG. 6C is a blind plug as a type of stress cone. A longitudinal sectional view, (d) is a perspective view of a blind plug.

[Explanation of symbols]

 12 Evaluation sample 12A High-voltage side electrode 12B Low-voltage side electrode 12C Insulation part 13 Lattice-shaped striped pattern

Claims (1)

[Claims] 1. A stress cone to be evaluated is sliced along a plane passing through its axis to prepare a cross-sectional plate-shaped evaluation sample, and a grid-shaped striped pattern is drawn on the evaluation sample. The internal stress of the stress cone is characterized by estimating the internal stress distribution of the stress cone by applying the same pressure as that applied when using the cone and comparing the degree of deformation of the striped pattern before and after pressurization. Evaluation methods.