JPH06308000A - Deterioration diagnostic method for dielectric material - Google Patents

Abstract

PURPOSE:To diagnose the deterioration of a dielectric material easily and positively by comparing the tensile strength of the dielectric material under initial condition and that after deterioration for a predetermined, time or comparing the water content under initial condition with that after deterioration for a predetermined time. CONSTITUTION:The tensile strength of a dielectric material, especially of a laminated dielectric material, lowers as the material deteriorates wherein the fluctuation is constant up to some value and thereby the maximum and minimum value, as well as the average value, can be estimated. But the fluctuation increases abruptly at some value. In particular, exfoliation takes place in a laminated material at some value and a decision is made that the service life is close to the end while taking account of the worst case. When the some value is recognized as the end of service life and the time thereof is estimated, deterioration of material can be diagnosed positively. A definite correlation exists between the tensile strength and the water absorbing capacity, and the deterioration of dielectric material is diagnosed by setting the time when the fluctuation of tensile force increases at the time when the water absorbing capacity decreases below some value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for diagnosing deterioration of insulating material.

[0002]

2. Description of the Related Art Insulating materials such as phenol resin laminates are widely used as insulating materials for electric conductive parts such as power receiving and distribution boards. These insulating materials may have poor electrical insulation characteristics over a long period of use, resulting in poor insulation, which may eventually lead to an accident. This deterioration of the insulation characteristics is due to the deterioration of the insulating material over time, and the operating conditions are affected by the temperature, humidity, gas, etc. as the usage environment, and particularly the temperature accelerates the progress of deterioration over time.

Generally, the deterioration diagnosis of the insulating material is judged by the presence / absence of cracks, dimensional change and discoloration state by visual inspection, and by conducting many tests such as mechanical property test and electrical property test by sample investigation. ing. Most of the data obtained here summarizes the relationship with the number of years of use, including temperature.

The electrical insulation characteristics of the insulating material are deteriorated due to long-term use, and when the physical characteristics are deteriorated and the structural material cannot withstand, or the withstand voltage characteristics are below a reference value, the insulating material is Cannot be used as
That is, it is determined that the insulation is defective. The time when the insulation failure occurs depends on the use environment as the deterioration condition, and the insulation failure occurs early in an atmosphere such as a high temperature and high humidity atmosphere where the deterioration progresses at a high speed. Since poor insulation may eventually lead to an accident, it is important to estimate poor insulation before an accident.

[0005]

However, it is necessary to comprehensively judge deterioration diagnosis of the conventional insulating material by measuring many characteristics. Furthermore, the measured characteristic values often have many variations, and it is not easy to make a reliable diagnosis. Also, even if the number of years elapsed is the same,
When the degree of deterioration is different due to different history due to high power load, it is difficult to diagnose deterioration and estimate the remaining life until insulation failure. As described above, it is necessary to have a lot of empirical knowledge to measure various characteristics of insulating materials used in different atmospheres and to comprehensively judge the degree of deterioration including variations in data. An object of the present invention is to provide a method of diagnosing an insulating material, which can reliably and easily diagnose deterioration of the insulating material.

[0006]

In order to achieve the above object, a first aspect of the present invention relates to a process of setting a tensile strength of an insulating material in an initial state and a tensile strength of the insulating material after deterioration for a predetermined time. Since the point is to have a process of setting and a process of diagnosing the deterioration of the insulating material by comparing these tensile strengths, it is not necessary to measure various characteristics.

In the second aspect of the invention, the process of setting the water absorption rate of the insulating material in the initial state, the process of setting the water absorption rate of the insulating material after deterioration for a predetermined time, and comparing these water absorption rates, the insulating material is compared. Therefore, it is not necessary to measure various characteristics as in the first aspect of the invention, since it has a process of diagnosing the deterioration of.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below.
The tensile strength of an insulating material, particularly a laminated insulating material, is recognized to decrease due to accelerated deterioration, and the variation is constant up to a certain value, so that the tensile strength against deterioration can be estimated. That is, not only the average value but also the maximum value and the minimum value can be estimated, which is confirmed by experiments.

However, when the value is less than a certain value, the variation rapidly increases, and although it is possible to estimate the average value for deterioration, it is difficult to estimate the minimum value. In the case of an insulating material, especially a laminated material, it is appropriate to judge that the tensile strength will be drastically decreased, but it will be judged that the tensile strength is close to the life, although it depends on the actual use conditions. Therefore, in the case of an insulating material, particularly a laminated material, the deterioration of the insulating material can be reliably diagnosed by assuming a certain value here as the life and estimating the time when this value is reached.

Here, the time when the variation in tensile strength becomes large is defined as the life, and the reason will be described. In the case of insulating materials, especially laminated insulating materials, it has been confirmed by experiments that when peeling occurs between laminated materials, the tensile strength changes depending on the degree of peeling.

In insulating materials, especially laminated insulating materials,
The fact that peeling occurred inside the layers means that peeling proceeds from this peeled portion even with a slight stress, and it is considered that even a slight peeling will be the starting point for the life.

The tensile test is effective for detecting this peeling, and since a uniform force is applied between the test jigs holding the test sample in the tensile test, the test sample sandwiched between the jigs is also uniformly applied. Power is added. Therefore, if peeling occurs, the tensile strength will decrease.

It is also possible to detect this peeling by a bending test or the like. In the bending test, for example, in the case of a three-point bending test based on JIS, it is impossible to detect the peeling unless a test sample having the peeling is arranged on the opposite side of the central jig in the bending test. This is because the maximum force is applied to the opposite side of the central jig, and the bending strength does not change even if peeling occurs in other places.

In the case of insulating materials, especially laminated materials,
It was found by experiments by the present inventors that there is a clear correlation between the water absorption rate and the tensile strength, and it was considered that the tensile strength can be estimated by measuring the water absorption rate. In other words, when the water absorption rate is below a certain value, the variation in tensile strength becomes large, and the relationship between water absorption rate and tensile strength is obtained in advance to diagnose deterioration of insulating materials, especially laminated insulating materials. can do.

On the other hand, if the time when insulation of the insulating material becomes poor, that is, the time when the variation in tensile strength spreads is converted and set in advance to the water absorption rate, the deterioration of the insulating material can be diagnosed by measuring the water absorption rate. The remaining life can be estimated.

[0016] According to the above, by measuring the water absorption rate and the tensile strength of the insulating material in the initial stage and after aging under various power load conditions, deterioration of the insulating material can be achieved without measuring various characteristics. The degree and life span can be diagnosed. In addition, it is possible to clarify the process that reaches the end of life by using a test sample that has been deteriorated in advance, for example, by accelerating temperature etc. and added and using a database in which deterioration factors and degree of deterioration are filled in as a matrix. Therefore, it is possible to estimate the time to reach the end of life, that is, the remaining life.

Next, a more specific description will be given with reference to the drawings. Fig. 1 shows a test sample cut out from a laminated insulating material that supports a conductor of a test switchboard operated under a certain power load condition at regular intervals over a long period of about 30 years, and the tensile strength and water absorption are measured and plotted. It is a graph. The tensile strength and water absorption were measured according to JIS K6911.

In the graph (a), the horizontal axis represents the logarithm of time and the vertical axis represents the tensile strength. When the time is t (hour) and the tensile strength is y (MPa), the following regression linear equation is obtained.

[0019]

## EQU1 ## y = 112.17-0.146 × log (t) Here, the dotted line 5 represents the confidence limit of entering 99.9% of the regression line obtained by performing the same evaluation and the same analysis.

As is apparent from this figure, the confidence limit of the regression line is very narrow, and the tensile strength can be linearly regressed with respect to the deterioration time. Also, when looking at the actually measured data plotted, values with almost no variation are obtained up to a certain time, but the variation of the data becomes extremely large after a certain time. In addition, although the Weibull distribution 6 is used as the variation here, the variation is almost the same even when arranged by the normal distribution. From such a viewpoint, the Weibull distribution 6
Looking at the laminated insulators evaluated this time in terms of the fact that the shape parameters that are related to the dispersion of the values greatly change, it was possible to obtain time equivalent to 25 years.

On the other hand, in the graph (b), the horizontal axis represents the logarithm of time and the vertical axis represents the water absorption rate. When the time is t (hour) and the water absorption rate is y (%), the following regression linear equation is obtained.

[0022]

[Formula 2] y = 0.501 −0.106 × log (t) Also, the dotted line 5 shows the 99.9% confidence limit of the regression linear equation, but the interval is narrow in parallel with the regression linear equation, and the deterioration time and water absorption rate Can regress with a straight line. Moreover, although the actually plotted data are arranged by the normal distribution 7, the range of variation is almost constant and the reliability is high. If such a relationship can be clarified, for example, we have determined that the tensile strength is 25 years,
Substituting this for 25 years in the formula for water absorption yields a water absorption of 0.35
%was gotten. Therefore, for example, in the insulating material used under the same conditions as the test sample, the deterioration degree and the remaining life can be estimated only by measuring the water absorption.

By the way, although the slope (deterioration rate) of the graph varies depending on the history of use of the insulating material, the power load condition can be examined by recording. Therefore, various tensile strengths and water absorption rates according to the power load condition can be obtained. It is also possible to estimate the life of the insulating material by constructing a database that assumes the secular change of, using test samples, and measuring the water absorption rate regularly.

The above is the tensile strength and water absorption of the laminated insulating material used in the actual plant. Separately from this, the test results were prepared by intentionally accelerating the deterioration by making a test sample. Shown in FIG. There are many acceleration factors,
When simulating the actual usage situation, the largest deterioration factor is the thermal factor. Here, according to the temperature table of IEC Publ 216, deterioration was accelerated at temperatures of 220 ° C and 200 ° C.

The test sample was taken out at regular intervals and the water absorption rate and the tensile strength were measured. Although the deterioration condition is different in the test switchboard, the tendency of the plotted data is the same, and in the case of the water absorption rate, although it decreases due to deterioration, its variation is almost unchanged. Also, the slope of the regression line changes depending on the degree of acceleration.

On the other hand, the tensile strength also tends to decrease due to deterioration, and the average value can be estimated from the regression linear equation. However, the degree of the variation became extremely large after a certain time, and it became impossible to estimate the lowest value after a certain time.

[0027]

As described above, according to the first aspect of the present invention, the deterioration of the insulating material is diagnosed by comparing the initial state of the insulating material with the tensile strength after deterioration for a predetermined time. The deterioration of material can be diagnosed.

Also according to the second aspect of the invention, since the deterioration of the insulating material is diagnosed by comparing the initial state of the insulating material with the water absorption after deterioration for a predetermined time, the deterioration of the insulating material can be reliably and easily diagnosed.

[Brief description of drawings]

FIG. 1 is a characteristic diagram showing an embodiment of the present invention.

FIG. 2 is a characteristic diagram when the deterioration according to the present invention is accelerated.

[Explanation of symbols]

 1 ... A line showing a change in water absorption rate with respect to time. 2 ... A threshold value of the absorption rate that causes electrical insulation deterioration. 3 ... Time to cause electrical insulation deterioration. 4 ... A line showing a change in tensile strength with respect to elapsed time. 5 ... Regression line confidence limit. 6 ... Weibull distribution. 7 ... Normal distribution.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Isao Jinchi 1st in Toshiba Fuchu, Tokyo Fuchu-shi, Toshiba Fuchu factory (72) Inventor Kenichi Sato 1st in Toshiba Fuchu, Tokyo, Fuchu factory

Claims (3)

[Claims] 1. A method of setting a tensile strength of an insulating material in an initial state, a step of setting a tensile strength of the insulating material after deterioration for a predetermined time, and comparing the tensile strengths of the insulating material with each other. And a method of diagnosing deterioration of an insulating material, the method comprising: 2. A process of setting a water absorption rate of an insulating material in an initial state, a process of setting a water absorption rate of the insulating material after deterioration for a predetermined time, and comparing these water absorption rates with each other to prevent deterioration of the insulating material. A method of diagnosing deterioration of an insulating material, the method comprising: diagnosing. 3. A relationship between a change in tensile strength of the insulating material and a change in water absorption rate is set in advance, and deterioration of the insulating material is diagnosed from this relationship. 2. A method of diagnosing deterioration of an insulating material according to 2.