JPS62163954A - Detection of thermal deterioration - Google Patents

Abstract

PURPOSE:To enable the detection of the degree of thermal deterioration an extensive range, by determining the degree of thermal deterioration of material to be measured as function of temperature and/or time from changes in a melting heat curve of a sample sampled from material to be measured previously thermally deteriorated beforehand to detect the degree of thermal deterioration of an actual equipment by comparing the results to the melting heat curve obtained by a differential scanning calorific measurement of the material being measured sampled from the actual equipment. CONSTITUTION:An insulating material the same as a sample is used as insulating coil of an electric equipment and after the electric equipment is operated for a required time, a very small amount of the insulating material is sampled from the insulating coil. Based on a melting heat curve obtained by a differential scanning calorific measurement, the depth Cb of the peak newly generated owing to a deterioration is determined and to obtain conver sion time thetab from the coordinate of the point crossing between Cb on the vertical axis and a master curve A. The conversion time thetab is a function of temperature and time. Therefore, the average temperature (equivalent temperature) during the period can be calculated if the operating time of the electric equipment is determined or the operating time can be calculated if the temperature at the operating is determined. Thus, it is possible to calculate the degree of thermal deterioration.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for detecting thermal deterioration of insulating materials used for electrical equipment insulation.

[Conventional technology]

Fixed insulating materials, liquid insulating materials, and gas insulating materials are commonly used alone or in combination to insulate electrical equipment.

In the case of liquid insulation in oil-immersed transformers and gas insulation in gas-insulated switchgear, methods have been proposed to determine insulation deterioration using physicochemical methods such as decomposition gas analysis, and some of them have been put into practical use. has been made into However, when it comes to solid insulation in rotating machines and the like, electrical testing methods, so-called "insulation diagnostic methods" are the main method of determination.

[Problem that the invention seeks to solve]

However, with current insulation diagnostic methods such as DC test method, AC test method, dielectric loss tangent test method, and partial discharge test method using electrical tests, it is not possible to apply a test voltage exceeding the rated voltage of the device under test. Therefore, the changes in the obtained properties are small, and the test results are influenced by the environmental conditions at the time of the test, especially humidity. For this reason, it is not possible to take stable measures against insulation deterioration, and the state of deterioration can only be estimated empirically.

In addition, physical science methods include changes in the dynamic viscoelastic properties of insulating materials, such as changes in mechanical tan δ expressed as the ratio of dynamic elastic modulus to loss elastic modulus, or infrared absorption spectra in infrared spectroscopy. A method for determining the degree of deterioration that uses changes in the deterioration level as a criterion has been proposed, and some of it has been put into practical use.

However, in the deterioration degree determination method that uses the change in mechanical tan δ as a criterion, film materials are the main applicable samples, and even with film materials, in the high deterioration region where the material is significantly brittle, , the sample is easily destroyed during measurement, making it impossible to determine the degree of deterioration. On the other hand, in the deterioration degree determination method that uses changes in the infrared absorption spectrum of infrared spectroscopy as a criterion, materials with low brightness, such as black materials or materials that have turned black due to deterioration, have a high infrared absorption rate, which indicates that the degree of deterioration is high. Difficult to judge.

The present invention was devised to eliminate such drawbacks, and is based on the reliability of data regarding the degree of thermal deterioration determined in advance based on samples when performing repairs, updates, etc. during the maintenance of electrical equipment, etc. The purpose is to detect the degree of thermal deterioration over a wide range so that it can be carried out with high precision.

[Means for solving problems]

In order to achieve the object, the present invention calculates the degree of thermal deterioration of a measured substance as a function of temperature and/or time from the change in the heat of fusion curve of a sample taken from a measured substance that has been thermally degraded in advance, and It is characterized by detecting the degree of thermal deterioration of the actual equipment by comparing it with the heat of fusion curve obtained by differential scanning calorimetry of the substance to be measured taken from the equipment.

[Effect]

Generally, changes in the chemical structure of insulating materials of electrical equipment due to thermal degradation follow chemical reaction kinetics. On the other hand, the viscosity of a solution at a given concentration is primarily determined by its chemical structure. That is, assuming that the change in crystal structure due to thermal deterioration of the crystalline polymer follows reaction kinetics, the change in the amount of crystal structure X is expressed by the following formula (1).

dx/dt=A-exp(-ΔE/RT)-
g (xl ・---------(D, however, t: deterioration time.

A: Frequency factor ΔE: Activation energy R: Gas constant T: Absolute temperature of deterioration g
If we integrate equation (1) assuming that it changes from to Xt, we get
The following equation (2) is obtained.

Here, since the integral on the right side is in the time dimension, it is called the converted time θ. That is, the converted time θ is expressed by the following equation (3).

Therefore, equation (2) is converted to the following equation (4).

In a deterioration region where the function g (X) indicating the deterioration mechanism and the frequency factor A are constant, even if deterioration occurs under various temperature conditions, if the converted time θ is the same, the changes in the amount of crystal structure will be the same. That is, the relationship between the two is expressed by the following equation (5).

θ-f txt −・・・−・・・・・・・
・・・・・・−・・−・・・・・・・−・+51 Furthermore, assuming that the melting energy Q in the heat of fusion curve determined by differential scanning calorimetry is uniquely determined by the amount of crystal structure,
The melting energy Q is calculated using the following formula% formula% In other words, between the conversion time θ and the melting energy Q,
The following equation (7) holds true.

θtsur (h-' (Q) l −・−・−・・−
...(7) Therefore, the conversion time θ of thermal deterioration is calculated by the formula (7)
), it can be determined from the change in melting energy Q.

〔Example〕

The features of the present invention will be specifically explained below using examples using polyethylene terephthalate, which is widely used as an electrical insulating material, as a sample.

FIG. 1 shows an example of a heat of fusion curve obtained by differential scanning calorimetry of a sample deteriorated in a hot air circulation constant temperature bath with an internal temperature of 160° C., 180° C., and 1200° C. Polyethylene terephthalate melts with a temperature width T, -''rz that corresponds to the distribution of crystals with different melting temperatures.As a result of deterioration, a new melting peak appears on the slightly lower temperature side of the main melting peak. The beeping becomes deeper as the deterioration progresses.

Figure 2 shows these deterioration temperatures of 160°C, 180°C, and 200°C.
It shows the relationship between the deterioration time at °C and the depth of the melting peak newly generated due to deterioration. The depth of the peak is
It can be seen that the depth increases linearly in proportion to the logarithm of the deterioration time.

Next, a master curve is created using the conversion time θ of deterioration from the increasing straight line of the melting peak newly generated due to deterioration using the deterioration temperature shown in FIG. 2 as a parameter. First, the depth of the melting peak determined from the regression line in Figure 2 is 0.5 m.
The relationship between the deterioration temperature and deterioration time up to 1 mJ/mg-sec and 1 mJ/mg-sec is represented by a coordinate point plot based on the Arrhenius equation shown in FIG. The activation energy ΔE is determined from the slope ΔE/R of the relationship diagram shown in FIG. 3, and the activation energy ΔE is substituted into equation (3). In this way, the converted time θ is calculated. Then, as shown in Fig. 4, the horizontal axis represents the converted time θ and the degree of deterioration, and the vertical axis represents the depth of the newly generated melting peak.
A master curve A regarding the depth of the melting peak newly generated due to thermal deterioration of the sample was obtained.

As is clear from FIG. 4, each of the illustrated deterioration temperatures 160
The depths of newly generated melting peaks at °C, 180 °C, and 200 °C are on the same line. That is, it can be seen that there is a very strong correlation between the depth of the newly generated melting peak and the converted time θ of deterioration.

For example, if the heat-resistant life of an electrical equipment insulated wire ring is 20,000 hours in an atmosphere at a temperature of 130°C, then the formula (
From 3), the converted time θ of the life point is 3×10−19, and this converted time θ is shown as the life point on the horizontal axis of deterioration degree with a scale of 1.0. Next, an insulating material made of polyethylene terephthalate, like the sample, is used for an insulated wire ring (not shown) of an electrical device, and after the electrical device has been operated for a required time, a small amount of the insulating material is collected from the insulated wire ring. do. Then, based on the heat of fusion curve obtained by differential scanning calorimetry, the depth C5 of the peak newly generated due to deterioration is determined, and the converted time is calculated from the coordinates of the point where C1 and master curve A intersect on the vertical axis in FIG. Obtain θ. This converted time θ is a function of temperature and time. Therefore, if the operating time of the electrical equipment is known, the average temperature (equivalent temperature) during that time can be calculated, or if the temperature during operation is known, the operating time can be calculated using equation (3). In this way, it becomes possible to calculate the degree of thermal deterioration. Furthermore, by making the converted time θ correspond to the scale of the degree of deterioration on the horizontal axis, the remaining life of the electrical equipment insulating wire can be known.

In the above embodiment, polyethylene terephthalate was described, but other crystalline polymers such as polyethylene, which are often used in cable insulation, can be used.

It goes without saying that the thermal deterioration detection method of the present invention is not limited to electrical equipment insulators, but can also be applied to thermal deterioration detection of crystalline polymers used in other fields.

〔Effect of the invention〕

As explained above, in the thermal deterioration detection method of the present invention, the amount of thermal deterioration of the substance to be measured is determined as a function of temperature and time from the change in the heat of fusion curve obtained by differential scanning calorimetry of a minute sample. By comparing the heat of fusion curve with the suggested scanning calorimetry of the substance to be measured taken from the equipment,
This is designed to detect the degree of thermal deterioration of the actual equipment. Therefore, repairs, updates, and other maintenance procedures for electrical equipment can be carried out with high reliability based on a pre-stored database, and the insulation design of electrical equipment can be directly verified. This has the effect of improving the reliability of electrical equipment by providing feedback to insulation design.

[Brief explanation of drawings]

Fig. 1 shows an example of a heat of fusion curve obtained by differential scanning calorimetry of a degraded sample, Fig. 2 shows the relationship between the depth of the melting peak and the deterioration time, and Fig. 3 shows the relationship between the deterioration temperature and the deterioration time. The relationship is expressed by a coordinate point plot based on the Arrhenius equation, and FIG. 4 is a diagram showing the relationship between the depth of the melting peak, the converted time, and the degree of deterioration.

Claims (1)

[Claims] 1. Determine the degree of thermal deterioration of the measured substance as a function of temperature and/or time from the change in the heat of fusion curve of a sample taken from the measured substance that has been thermally degraded in advance, and calculate the difference between the measured substances sampled from the actual equipment. A thermal deterioration detection method characterized by detecting the degree of thermal deterioration of a device in actual use by comparing it with a heat of fusion curve obtained by scanning calorimetry.