JPH068793B2 - Thermal deterioration detection method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for detecting thermal deterioration of an insulating material or the like used for insulating an electric device.

[Conventional technology]

For insulation of electric devices, solid insulating materials, liquid insulating materials and gas insulating materials are usually used alone or in combination.

In the case of liquid insulation in oil-immersed transformers and gas insulation in gas-insulated switchgear, etc., a method for determining insulation deterioration by a physicochemical method such as decomposition gas analysis has been proposed, and it is partially used. Has been converted. However, in solid insulation in rotating machines and the like, a method based on an electrical test, a so-called “insulation diagnosis method”, is the center of determination method.

[Problems to be solved by the invention]

However, it is not possible to apply a test voltage exceeding the rated voltage of the device under test by the current insulation test methods such as a DC test method, an AC test method, a dielectric loss tangent test method, and a partial discharge test method based on an electrical test. Therefore, changes in the obtained characteristics are small, and the test results are affected by the environmental conditions during the test, particularly the humidity temperature. For this reason, it is empirical to estimate the deterioration state without being able to take stable measures against insulation deterioration.

Further, as a physics-based method, a change in dynamic viscoelastic property of an insulating material, for example, a change in mechanical-tan δ represented by a ratio of a dynamic elastic modulus and a loss elastic modulus, or an infrared absorption spectrum of infrared spectroscopic analysis A deterioration degree judgment method using the change of is used as a judgment criterion has been proposed and partially put into practical use.

However, in the deterioration degree judgment method using the change of mechanical-tan δ as a judgment criterion, a film material is mainly applicable as a sample, and even in the case of a film material, in a high deterioration degree region where material embrittlement is remarkable, , The sample is easily broken during the measurement, and the degree of deterioration cannot be determined. On the other hand, in the deterioration degree judgment method using the change in the infrared absorption spectrum of the infrared spectroscopic analysis as a judgment standard, a material having a low lightness such as a black material or a material which is blackened due to deterioration has a high infrared absorption rate and a deterioration degree of It is difficult to judge.

The present invention has been devised in order to eliminate such drawbacks, and makes it possible to perform reliable measures such as repairs and renewals in maintenance of electrical equipment with respect to data on the degree of thermal deterioration previously obtained based on a sample. The purpose is to detect the extent of thermal degradation over a wide range so that it can be performed with high accuracy.

[Means for solving problems]

In order to achieve the object, the present invention deteriorates a sample of the same material as the substance to be measured at various temperatures, and based on the change of the melting peak of the melting heat curve with respect to the deterioration temperature and deterioration time of the sample, The degree of thermal degradation of the substance to be measured is obtained as a function of temperature and time obtained from the Arrhenius reaction rate equation, and by comparing it with the melting peak of the melting heat curve by differential scanning calorimetry of the substance to be measured collected from the device, It is characterized in that the degree of thermal deterioration is detected.

[Action]

Generally, a chemical structural change of an insulating material of an electric device due to heat deterioration follows a chemical reaction kinetics. On the other hand, the viscosity of a solution at a constant concentration is uniquely determined by its chemical structure. That is, assuming that the change in the crystal structure due to the thermal deterioration of the crystalline polymer follows the reaction kinetics, the change in the crystal structure amount X is represented by the following formula (1).

dx / dt = A * exp (-[Delta] E / RT) * g (x) ... (1) where t: deterioration time, A: frequency factor [Delta] E: activation energy R: gas constant T: absolute temperature of deterioration g (x): function indicating deterioration mechanism Deterioration of material progresses from time 0 to t, and crystal structure amount is x ₀
Integrating equation (1) as varied from x _t from the following equation
It becomes (2).

Here, since the integration on the right side has a dimension of time, it is called a conversion time θ. That is, the conversion time θ is expressed by the following equation (3).

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

In the deterioration region where the function g (x) indicating the deterioration mechanism and the frequency factor A are constant, even if the deterioration occurs under various temperature conditions, if the conversion times θ are equal, the changes in the crystal structure amount are also equal. That is, the relationship between the two is expressed by the following equation (5).

θ = f (x) (5) Further, assuming that the melting energy Q in the melting heat curve by differential scanning calorimetry is uniquely determined by the crystal structure amount, the melting energy Q is It is represented by.

Q = h (x) ………… (6) That is, between the conversion time θ and the melting energy Q,
The following equation (7) holds.

θ = f {h ⁻¹ (Q)} ... (7) Therefore, the conversion time θ of thermal deterioration can be obtained from the change of the melting energy Q as shown in the equation (7).

〔Example〕

Hereinafter, the features of the present invention will be specifically described with reference to examples in which polyethylene terephthalate, which is widely used as an electric insulating material, is used as a sample.

Fig. 1 shows an example of a melting heat curve by differential scanning calorimetry of a sample of the same material as the substance to be measured which has been deteriorated in a hot air circulation type constant temperature bath whose temperature inside the bath is 160 ° C, 180 ° C and 200 ° C. Polyethylene terephthalate melts with a temperature width T _{1 to} T ₂ corresponding to the distribution of crystals with different melting temperatures. Then, due to the deterioration, a new melting peak appears on the slightly lower temperature side of the main melting peak, and the peak becomes deeper as the deterioration progresses.

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

Next, a master carp using the deterioration conversion time θ is created from the increasing line of the melting peak newly generated by the deterioration using the deterioration temperature of FIG. 2 as a parameter. First, the melting peak depth obtained from the regression line in Fig. 2 is 0.5 mJ / m.
The relationship between the deterioration temperature and the deterioration time up to g · sec, 1 mJ / mg · sec is represented by a coordinate point plot based on the Arrhenius equation shown in FIG. The activation energy ΔE is obtained from the gradient ΔE / R of the relationship diagram shown in FIG. 3, and the activation energy ΔE is substituted into the equation (3). In this way
The conversion time θ is calculated. Then, as shown in FIG.
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, to obtain a master curve A relating to the depth of the melting peak newly generated by the thermal deterioration of the sample.

As is apparent from FIG. 4, the deterioration temperatures of 160 ° C.
The depths of newly generated melting peaks at 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 conversion time θ of deterioration.

For example, assuming that the heat-resistant life of the insulated loop of electrical equipment is 20,000 hours in a temperature atmosphere of 130 ° C, the converted time θ _a of the life point from Equation (3) becomes 3 × 10 ^-19 , and this converted time θ
_A is shown as a life point by grading 1.0 on the deterioration degree axis on the horizontal axis. Next, the same insulating material made of polyethylene terephthalate as that of the sample is used for an insulating wire ring (not shown) of an electric device, and after the electric device is operated for a required time, a small amount of the insulating material is sampled from the insulating wire ring. To do. And
Based on the heat of fusion curve by differential scanning calorimetry, determined the depth C _b of the peak newly generated by the degradation, in terms of time from the C _b and the coordinates of the point of intersection between the master curve A on the vertical axis of FIG. 4 Obtain θ _b . This conversion time θ _b is a function of temperature and time. Therefore, if the operating time of the electric device is known, the average temperature (equivalent temperature) during that time can be calculated, or if the operating temperature is known, the operating time can be calculated by the formula (3). In this way, the degree of thermal deterioration can be calculated. Further, when the converted time θ _b is made to correspond to the scale of deterioration degree on the horizontal axis, it is possible to know the remaining life of the electric device insulating coil.

In the above embodiments, polyethylene terephthalate was described, but in addition to this, it can be applied to a crystalline polymer such as polyethylene that is often used for cable insulation.

Further, it goes without saying that the heat deterioration detection method of the present invention is not limited to electrical equipment insulators and can be applied to heat deterioration detection of crystalline polymers used in other fields.

〔The invention's effect〕

As described above, in the method for detecting thermal deterioration of the present invention, from the change in the depth of the melting peak of the melting heat curve by the differential scanning calorimetry of a minute amount sample, the thermal deterioration amount of the substance to be measured can be measured with respect to temperature and time. The heat deterioration degree of the actual equipment is detected by comparing it with the depth of the melting peak of the melting heat curve by differential scanning calorimetry of the substance to be measured collected from the actual equipment. Therefore,
Measures such as repairs and renewals for the maintenance of electrical equipment can be performed with high reliability based on a database that has been stored in advance, and the insulation design of electrical equipment can be directly verified and insulation design can be performed. The effect of improving the reliability of the electric device can be achieved by feeding back to.

[Brief description of drawings]

FIG. 1 shows an example of the melting heat curve of a deteriorated sample by differential scanning calorimetry, FIG. 2 shows the relationship between the melting peak depth and deterioration time, and FIG. 3 shows the deterioration temperature and deterioration time. The relationship is represented by a coordinate point plot based on the Arrhenius equation, and FIG. 4 is a view showing the relationship between the depth of the melting peak and the conversion time and deterioration degree.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-54-113398 (JP, A) JP-A-54-32388 (JP, A) JP-A-61-117441 (JP, A) Kanbara, ed. Molecular Materials Testing Method ▲ I ▼ -High Molecular Experiments Course 7- ", first edition, published January 5, 1958, Kyoritsu Publishing, P. 307 ~ P309

Claims (1)

[Claims] 1. A sample of the same material as the substance to be measured is deteriorated at various temperatures, and the degree of thermal deterioration of the substance to be measured is based on the change of the melting peak of the melting heat curve with respect to the change of the deterioration temperature and deterioration time of the sample. Is calculated as a function of temperature and time obtained from the Arrhenius reaction rate equation, and the degree of thermal deterioration of the actual equipment is detected by comparing it with the melting peak of the melting heat curve by differential scanning calorimetry of the measured substance collected from the actual equipment. A thermal deterioration detection method characterized by the above.