JP2024018007A - How to diagnose molded transformer - Google Patents

Abstract

To diagnose characteristics of a molded resin inside a winding, such as near a conductor.SOLUTION: A diagnostic method of a mold transformer including a winding and a resin covering the winding includes a first measurement step of measuring reflective absorbance of a surface of the resin, a second measurement step of polishing the surface of the resin and measuring reflective absorbance of an exposed internal surface of the resin, and a step of estimating bending rupture strength of the resin near a conductor of the winding from measurement data of the first measurement step and measurement data of the second measurement step.SELECTED DRAWING: Figure 6

Description

The present invention relates to a technique for diagnosing a molded transformer.

Resin materials are used in electrical equipment as insulating materials and structural materials. For example, in a molded transformer, the windings of the transformer are impregnated with resin and molded. Resin has excellent moldability, is lightweight, and has high insulation performance. On the other hand, resin, which is an organic material, generally deteriorates more easily over time than metal or ceramic materials. For this reason, resin materials are considered to control the lifespan of electrical equipment, and techniques for diagnosing the remaining lifespan of electrical equipment have been developed by evaluating the aging state of resin materials used in electrical equipment.

Patent Document 1 describes that a molded transformer is diagnosed for deterioration by irradiating it with light or X-rays, and by measuring reflected absorbance. It is also described that a resin member covering the outer circumferential side of the coil is provided with a non-painted area for light irradiation and a covering member covering this, and when diagnosing deterioration, the covering member is peeled off and light is irradiated to diagnose deterioration.

Patent Document 2 describes that deterioration diagnosis is performed by irradiating an electrical device equipped with a molded resin with X-rays or the like. Further, it is described that the physical quantity measuring means for the surface layer portion of the mold resin measures an unpainted area of the mold resin.

Japanese Patent Application Publication No. 2018-166164 JP 2019-7806 Publication

As the molding resin of the molded transformer, for example, an epoxy resin filled with inorganic filler is used. The mold resin deteriorates due to heat generated during operation, electrical and mechanical stress, and surrounding environmental factors, and its physical properties deteriorate. In general, epoxy resins and unsaturated polyester resins that constitute mold resins are organic materials and are subject to thermal deterioration. In thermal deterioration of epoxy resin, changes in the dielectric and insulating properties of the resin itself are small, but changes in mechanical properties and reduction in mechanical strength are significant. Due to the decrease in the mechanical strength of the epoxy resin, cracks are generated or the adhesive interface between the resin and the coil peels off, resulting in a significant decrease in insulation performance. For this reason, it is believed that the decrease in mechanical strength due to thermal deterioration of epoxy resin governs the lifespan of molded transformers, and deterioration diagnosis techniques have been developed that focus on the thermal deterioration behavior of epoxy resin.

The physical and chemical structure of epoxy resin changes due to thermal deterioration, resulting in changes in physical properties and mechanical properties. Therefore, by evaluating changes in the physical properties of epoxy resins due to thermal deterioration, it is possible to diagnose changes in mechanical properties and decreases in mechanical strength.

It is thought that epoxy resin deteriorates due to heat mainly through the following mechanism.
(1) The chemical structure of the resin changes, resulting in changes in the resin surface color, glass transition temperature, elastic modulus, bending strength, etc.
(2) The resin decomposes to produce low-molecular-weight compounds, which are released and lose weight.
(3) Stress relaxation due to aging is accelerated.

Simple non-destructive measurements are preferable for diagnosing molded transformers on-site, but the mechanical strength of epoxy resin, which is thought to control the lifespan of molded transformers, cannot be measured non-destructively. difficult. Furthermore, in a molded transformer, if cracks or peeling occur in the molded resin near the conductor of the winding, the insulation performance may deteriorate. During operation, the temperature of the conductor of the winding increases, so the mold resin near the conductor is susceptible to thermal deterioration.When diagnosing deterioration, it is preferable to evaluate the mechanical strength of the mold resin near the conductor. Therefore, it is difficult to nondestructively evaluate the deterioration state of the molding resin inside the winding near the conductor. Furthermore, in molded transformers, the surface of the molded resin is often painted, and the paint is usually made of a material different from the resin used for the mold.

For this reason, there has been a problem in that it is difficult to easily and non-destructively measure the mechanical strength of the molded resin inside near the conductor of the winding with respect to epoxy resin, which is thought to control the lifespan of a molded transformer.

Patent Document 1 and Patent Document 2 describe that deterioration diagnosis is performed by irradiating a molded resin with light or X-rays. Furthermore, Patent Document 1 discloses that a non-painted area for light irradiation and a coating member covering this are provided in a resin member covering the outer peripheral side of the coil, and when diagnosing deterioration, the coating member is peeled off and light is irradiated to diagnose deterioration. Are listed. Furthermore, in Patent Document 2, a deterioration diagnosis is performed by irradiating an electrical device equipped with a molded resin with X-rays, etc., and a means for measuring a physical quantity of the surface layer of the molded resin measures an unpainted area of the molded resin. It is stated that However, all of these methods measure the characteristics of the surface of the molded resin, and do not directly measure the characteristics of the molded resin inside, such as in the vicinity of the conductor of the winding.

An object of the present invention is to diagnose the characteristics of the molded resin inside the winding, such as in the vicinity of the conductor.

An example of the present invention is a method for diagnosing a molded transformer having a winding and a resin covering the winding,
a first measurement step of measuring the reflective absorbance of the surface of the resin;
a second measurement step of measuring the reflective absorbance of the exposed inner surface of the resin by polishing the surface of the resin;
The method of diagnosing a molded transformer includes the step of estimating the bending rupture strength of the resin near the conductor of the winding from the measurement data of the first measurement step and the measurement data of the second measurement step.

According to the present invention, it is possible to diagnose the characteristics of the molded resin inside the winding, such as in the vicinity of the conductor.

A diagram showing a master curve A. A diagram showing a master curve B. A diagram showing a master curve C. A schematic diagram of a winding cross section when there is no coating on the mold resin surface. 1 is a block diagram of a molded transformer diagnostic system according to a first embodiment; FIG. Flowchart of processing in Example 1. A schematic diagram of the reflection absorbance measurement points of the molded resin of the winding wire. A diagram showing a master curve A'. A diagram showing a master curve B'. A diagram showing a master curve C'. A schematic diagram of a winding cross section when the mold resin surface is coated. Flowchart of processing in Example 2.

Embodiments of the present invention will be described below with reference to the drawings. In each figure for explaining the embodiment, the same names and symbols are given to the same components as much as possible, and repeated explanations thereof will be omitted.

In order to understand the thermal deterioration behavior of mold resin, which is the target of diagnosis, we prepared a sample of cured mold resin, cut the sample of cured mold resin into a predetermined shape, and heated it in a constant temperature oven at various temperatures. accelerated deterioration. In order to quantitatively evaluate the color change on the mold resin surface, a reflection absorbance spectrum was measured. Further, the mold resin surface was polished and the reflected absorbance of the exposed inner surface of the mold resin was measured. A probe-type portable spectral reflectometer was used to measure the reflected absorbance. In addition, bending rupture strength was evaluated as the mechanical strength of the resin.

The procedure for diagnosing the deterioration of a molded transformer when there is no coating on the surface of the molded resin will be described as Scheme 1. Scheme 1 includes the following steps: ``creation of a master curve regarding the deterioration of mold resin properties,'' ``creation of temperature distribution data of the mold resin in the winding during operation,'' and ``measurement of the average temperature of the mold resin by measuring reflective absorbance.'' ``Estimation'' and ``Estimation of bending rupture strength of mold resin.''

Based on the idea proposed by Dakin, it is assumed that all changes in various properties of an insulating material due to thermal deterioration are caused by the amount x of change in chemical structure. Assuming that the amount x of change in chemical structure follows chemical reaction kinetics, it is expressed as equation (1) with respect to time t.
dx/dt=a・exp(−ΔE/RT)・g(x) (1)
a: Frequency factor ΔE: Apparent activation energy R: Gas constant T: Absolute temperature g(x): Function expressing thermal deterioration reaction Also, generalized time (degradation degree) with unit of time in the following formula (2) θ is defined.
θ=t・exp(−ΔE/RT) (2)

Regarding "Creating a master curve related to deterioration of properties of mold resin", a master curve related to deterioration can be created using the following procedure.
First, the sample is thermally degraded by changing the heating temperature, the characteristics after thermal degradation are measured, and the measured characteristics are plotted against the heating time. Next, find the heating time (t) until the characteristic reaches a certain value for each test temperature, and plot the logarithm of that heating time against the reciprocal (1/T) of each test temperature (absolute temperature). From the slope, (ΔE/R) of equation (1) is obtained, and the activation energy ΔE can be calculated (Arrhenius method). Furthermore, by converting the heating time t into a generalized time θ using equation (2) and replotting it, each data is superimposed and a master curve regarding deterioration can be created.

Select two wavelengths, λ1, where the reflection absorbance of the mold resin surface changes significantly due to thermal deterioration, and wavelength λ2, where the change is small, and evaluate the difference ΔA between the reflection absorbance A(λ1) and A(λ2) at each wavelength. did. Assuming that changes in the reflected absorbance difference ΔA follow Arrhenius law, a master curve regarding the reflected absorbance difference ΔA can be created. FIG. 1 shows a schematic diagram of a master curve A regarding the difference ΔA in reflected absorbance on the mold resin surface.

Next, the mold resin surface is polished to select two wavelengths, the wavelength λ3 at which the reflection absorbance of the exposed inner surface of the mold resin changes significantly, and the wavelength λ4 at which the change is small, and the reflection absorbance B(λ3) at each wavelength is calculated. The difference ΔB from B(λ4) was evaluated. Assuming that the change in the reflected absorbance difference ΔB follows Arrhenius law, a master curve B regarding the reflected absorbance difference ΔB can be similarly created. A schematic diagram of master curve B regarding the difference ΔB in reflected absorbance is shown in FIG. 2.

From FIG. 1 and FIG. 2, the generalized time θ until the difference in reflected absorbance reaches a certain value can be obtained. From the obtained θ, the operating temperature at which the difference in reflected absorbance reaches a certain value after t hours of use, that is, the heat-resistant temperature T, can be determined from equation (2). Conversely, once the operating temperature T is determined, θ is converted to real time t using equation (2), and the change behavior of the difference in reflected absorbance due to thermal deterioration at real time t can be obtained. FIG. 3 shows a schematic diagram of master curve C regarding bending breaking strength, which was created using the same procedure.

The temperature distribution data of the mold resin inside the winding during operation is created by analyzing the "Creation of temperature distribution data of the mold resin inside the winding during operation" and by actually measuring the temperature during operation of the molded transformer. FIG. 4 shows a schematic diagram of a winding cross section when there is no coating on the mold resin surface. In order to be able to evaluate the temperatures during operation at the mold resin surface 4a on which reflective absorbance is to be measured, the mold resin inner surface 5a exposed by polishing the surface of the mold resin 1, and the mold resin 6a near the conductor 2 of the winding, we Obtain temperature distribution data of the mold resin inside the winding at the time.

FIG. 5 shows a block diagram of the molded transformer diagnostic system of this embodiment. The molded transformer diagnostic system of this embodiment includes a measuring device 10 and a diagnostic device 11. The measuring device 10 is a device that measures the reflected light absorbance of a molded resin surface of a molded transformer having a winding and a resin covering the winding.

The diagnostic device 11 includes a mold resin average temperature estimation section 12 , a mold resin bending breaking strength estimation section 13 , and a display section 14 . The diagnostic device may include a processing device such as a processor, a recording unit storing a program, etc., and the processing device may call the program to realize the function. The display unit 14 may display the estimated result of the bending breaking strength of the diagnosed molded resin, or the deterioration state such as the remaining life of the molded transformer evaluated from the estimated result.

FIG. 6 shows a flowchart of the processing of the diagnostic system. "Estimating the average temperature of the mold resin by measuring reflected absorbance" and "Estimating the bending rupture strength of the mold resin" in Scheme 1 will be explained using FIG. 6.

The measuring device 10 measures the reflected absorbance of the mold resin surface of the molded transformer during the operating time t (S601).

The average temperature estimation unit 13 of the mold resin calculates the generalization time θ _A from the difference in reflection absorbance at two different wavelengths λ ₁ and λ ₂ obtained by measurement and the master curve A (see FIG. 1). From the generalized time θ _A and the operating time t, the average temperature T ₁ of the mold resin surface during operation is determined from equation (2) (S602).

The measuring device 10 measures the reflection absorbance inside the mold resin at the location where the mold resin surface of the molded transformer during the operating time t has been polished (S603). Here, it is sufficient to polish the surface of the mold resin, which is effective for easily and non-destructively measuring the mechanical strength of the mold resin inside the vicinity of the conductor of the winding.

The average temperature estimating unit 13 of the mold resin calculates the generalized time θ _B from the master curve B and the difference in internal reflection absorbance at two different wavelengths λ ₃ and λ ₄ obtained through measurement (see FIG. 2). From the generalized time θ _B and the operating time t, the average temperature T ₂ inside the mold resin during operation is determined from equation (2) (S604).

The average temperature estimation unit 13 of the mold resin calculates the average temperature T ₁ of the surface of the mold resin during operation, the average temperature T ₂ inside the mold resin, and the temperature of the mold resin inside the winding during operation that has been created. From the distribution data, the average temperature _T3 of the mold resin near the conductor is obtained (S605).

The estimator 13 of the bending rupture strength of the mold resin calculates the generalized time θ _C from the operating time t, the average temperature T ₃ of the mold resin near the conductor during operation, and equation (2). The bending rupture strength estimating unit 13 of the mold resin calculates the bending of the resin when the average temperature during operation of the mold resin near the conductor 6a is T ₃ from the generalized time θ _C and the master curve C shown in FIG. 3. The breaking strength is estimated (S606). In addition, in order to obtain the generalization time from the difference in reflection absorbance, record the correspondence between the difference in reflection absorbance on the vertical axis and the generalization time on the horizontal axis in the master curve in a recording section such as a database, and check the correspondence. From the relationship, the generalization time can be determined based on the difference in reflected absorbance.

Here, it can be seen that the change in the difference in reflected absorbance due to deterioration is larger in FIG. 1 than in FIG. 2. This is because thermal decomposition reactions and crosslinking reactions mainly occur inside the mold resin, whereas oxidation and hydrolysis reactions mainly occur on the mold resin surface that is in contact with the atmosphere, resulting in changes in the chemical structure. This is thought to be due to the large change in reflected absorbance. Therefore, by using the master curve A in Figure 1 obtained by measuring the reflective absorbance of a surface that is highly sensitive to heat, it is possible to estimate with high accuracy the average temperature _T1 of the mold resin surface during operation. Become. Furthermore, by using T _{1 and T 2 respectively, the average temperature during operation of the mold resin surface 4a and the mold resin inner surface 5a exposed by polishing the mold resin surface is T 1} and T ₂ respectively, so that the average temperature during operation of the mold resin near the conductor 6a is The average temperature T ₃ of can be estimated with higher accuracy.

The chemical structure of the mold resin after deterioration is different between the interior of the mold resin, where decomposition reactions and crosslinking reactions mainly occur due to heat, and the mold resin surface, where oxidation reactions and hydrolysis reactions mainly occur. The absorbance spectra are also different. Therefore, when evaluating the thermal deterioration of the mold resin surface 4a and the mold resin inner surface 5a exposed by polishing the mold resin surface by reflection absorbance, the combinations of the two wavelengths λ1 and λ2 and the two wavelengths λ3 and λ4 to be selected are , may be the same, but it is preferable to select appropriate wavelengths so that changes in ΔA and ΔB are large in each reflection absorbance spectrum.

Further, in evaluating the inside of the mold resin, it is preferable to polish it by about 50 to 100 μm from the surface. Since oxygen or water in the air slowly diffuses into the mold resin, it is thought that deterioration due to oxidation reactions and hydrolysis reactions occurs to some extent even within the mold resin, which is not in direct contact with the outside air. The color change of the mold resin due to thermal deterioration is noticeable from about 50 to 100 μm from the mold resin surface, so by polishing and removing the part where the color change is significant due to thermal deterioration, the mold resin near the conductor can be removed. The thermal deterioration state of deteriorated mold resin can be evaluated using the same mechanism.

FIG. 7 shows a schematic diagram of the locations where the reflection absorbance of the molded resin of the winding was measured. Normally, the air around the winding 7 whose temperature increases due to Joule heat cools the winding 7 through natural convection, so that the temperature of the upper part of the winding 7 is higher than that of the lower part. Therefore, for example, by measuring the temperature of the upper surface of the wire-wound mold resin 8a in FIG. 7, thermal deterioration of the mold resin 1 can be evaluated with higher sensitivity. Alternatively, the side surface of the upper part of the winding mold resin shown in 8b or 8c in FIG. 7 may be measured.

It is thought that the temperature of the mold resin surface varies depending on the structure of the winding, the thickness of the mold resin, the distance from the conductor surface to the mold resin surface, etc. For this reason, thermal deterioration of the mold resin can be evaluated with higher sensitivity by selecting a high-temperature portion from previously acquired temperature distribution data and measuring the reflected absorbance.

According to the procedure shown in Scheme 1 above, in the molded resin of the winding, from the reflection absorbance measurement results of the molded resin surface and the internal surface of the molded resin exposed by polishing the molded resin surface, it was found that the inside of the winding near the conductor It becomes possible to non-destructively evaluate the bending rupture strength of molded resin.

In order to understand the thermal deterioration behavior of a molded resin whose surface is coated to be diagnosed, we prepared a sample with the surface of the cured molded resin coated, and then shaped the sample of the cured molded resin into a predetermined shape. They were cut out and heated in a constant temperature bath at varying temperatures to accelerate deterioration. In order to quantitatively evaluate the color change of the painted surface, the reflection absorbance spectrum was measured. Furthermore, the coating on the mold resin surface was polished and the reflected absorbance of the exposed mold resin surface was measured. A probe-type portable spectral reflectometer was used to measure the reflected absorbance. In addition, the bending strength at break was evaluated as the mechanical strength of the resin.

The procedure for diagnosing the deterioration of a molded transformer in Example 2, in which there is paint on the surface of the molded resin, will be described as Scheme 2. Also in this example, a master curve regarding deterioration can be created using the following procedure similar to that in Example 1.

Regarding "creating a master curve regarding deterioration of properties of mold resin", first, the sample is thermally degraded by changing the heating temperature, the properties after the thermal degradation are measured, and the measured properties are plotted against the heating time. Next, find the heating time (t) until the characteristic reaches a certain value for each test temperature, and plot the logarithm of that heating time against the reciprocal (1/T) of each test temperature (absolute temperature). From the slope, (ΔE/R) of equation (1) is obtained, and the activation energy ΔE can be calculated (Arrhenius method). Furthermore, by converting the heating time t into a generalized time θ using equation (2) and replotting it, each data is superimposed and a master curve regarding deterioration can be created.

Two wavelengths, λ5, where the reflective absorbance of the painted surface changes significantly due to thermal deterioration, and wavelength λ6, where the change is small, are selected, and the difference ΔA' between the reflective absorbance A'(λ5) and A'(λ6) at each wavelength is calculated. was evaluated. Assuming that the change in the reflected absorbance difference ΔA' follows the Arrhenius law, a master curve A' regarding the reflected absorbance difference ΔA' can be created. FIG. 8 shows a schematic diagram of the master curve A' regarding the difference ΔA' in the reflection absorbance of the mold resin surface.

Next, the mold resin surface is polished to select two wavelengths, λ7, where the reflection absorbance of the exposed inner surface of the mold resin changes significantly, and wavelength λ8, where the change is small, and the reflection absorbance B'(λ7) at each wavelength is selected. The difference ΔB' between and B'(λ8) was evaluated. Assuming that the change in the difference ΔB' in reflected absorbance follows the Arrhenius law, a master curve B' regarding the difference ΔB' in reflected absorbance can be similarly created. FIG. 9 shows a schematic diagram of the master curve B' regarding the difference ΔB' in reflected absorbance.

From FIG. 8 and FIG. 9, the generalized time θ until the difference in reflected absorbance reaches a certain value can be obtained. From the obtained θ, the operating temperature at which the difference in reflected absorbance reaches a certain value after t hours of use, that is, the heat-resistant temperature T, can be determined from equation (2). Conversely, once the operating temperature T is determined, θ is converted to real time t using equation (2), and the change behavior of the difference in reflected absorbance due to thermal deterioration at real time t can be obtained. FIG. 10 shows a schematic diagram of a master curve C' regarding bending breaking strength, which was created using the same procedure.

Regarding "Creation of temperature distribution data of the molded resin inside the winding during operation", we also created temperature distribution data of the molded resin inside the winding during operation through analysis and actual measurement of the temperature during operation of the molded transformer. do. FIG. 11 shows a schematic diagram of a winding cross section when the mold resin surface is coated. In order to be able to evaluate the temperature during operation of the painted surface 4b on which reflective absorbance is to be measured, the surface 5b of the internal molded resin 1 exposed by polishing the painted surface, and the molded resin 6b near the conductor 2 of the winding, Obtain temperature distribution data of the mold resin inside the winding.

FIG. 12 shows a flowchart regarding processing in the diagnostic system. "Estimating the average temperature of the mold resin by measuring reflected absorbance" and "Estimating the bending rupture strength of the mold resin" in Scheme 2 will be explained using FIG. 12. Descriptions similar to those in Example 1 may be omitted. Regarding the second embodiment, the system configuration diagram of the diagnostic system is the same as that shown in FIG. 5.

The measuring device 10 measures the reflective absorbance of the coated surface of the molded transformer during operation time t (S1201).

The average temperature estimating unit 12 of the mold resin in the diagnostic device 11 calculates the generalization time θ _A ′ from the difference in reflection absorbance at two different wavelengths λ ₇ and λ ₈ obtained by measurement and the master curve A′ (FIG. 8 ). Then, from θ _A ′ and the operating time t, the average temperature T ₁ ′ of the painted surface of the mold resin during operation is determined from equation (2) (S1202).

The measuring device 10 measures the reflective absorbance of the internal mold resin at the location where the coating of the mold resin in the molded transformer during operation time t has been polished (S1203).

The average temperature estimation unit 12 of the mold resin calculates θ _B ′ from the difference in reflection absorbance at two different wavelengths λ ₇ and λ ₈ obtained through measurement and the master curve B′ (see FIG. 9). Then, from θ _B ′ and the operating time t, the average temperature T ₂ ′ inside the mold resin during operation is determined from equation (2) (S1204).

The average temperature estimating unit 12 of the mold resin calculates the average temperature T1' of the coated surface of the mold resin during operation, the average temperature _T2 ' inside the mold resin, and the created mold inside the winding during operation. From the temperature distribution data of the resin, the average temperature T ₃ ' of the molded resin near the winding conductor is obtained (S1205).

The estimator 13 of the bending rupture strength of the mold resin calculates the generalized time θ _C ′ from the operating time t, the average temperature T ₃ ′ of the mold resin near the conductor during operation, and equation (2). Then, from the generalized time θ _C ' and _the master curve C' in FIG. The bending breaking strength of the resin is estimated (S1206).

Here, it can be seen that the change in the difference in reflected absorbance due to deterioration is slightly larger in FIG. 8 than in FIG. 9. This is because thermal decomposition reactions and crosslinking reactions mainly occur inside the mold resin, whereas oxidation and hydrolysis reactions mainly occur on the mold resin surface that is in contact with the atmosphere, resulting in changes in the chemical structure. This is thought to be due to the large change in reflected absorbance. Therefore, by using the master curve A' in Figure 8 obtained by measuring the reflective absorbance of a surface that is highly sensitive to heat, it is possible to estimate the average temperature T ₁ ' of the painted surface during operation with high accuracy. becomes. Furthermore, by using T ₁ ' and T ₂ ', respectively, the average temperatures during operation of the painted surface 4b and the mold resin inner surface b exposed by polishing the mold resin surface, the operation of the mold resin near the conductor 6b is The average temperature _T3 at the time can be estimated with higher accuracy.

The reflective absorbance spectra obtained during measurement differ between the mold resin and the paint, which have different constituent materials and chemical structures. In addition, the chemical structure of the mold resin after deterioration is different between the inside of the mold resin, where thermal decomposition reactions and crosslinking reactions occur, and the painted surface, where oxidation reactions and hydrolysis reactions mainly occur, so the chemical structure obtained by measurement is different. The reflection absorbance spectra are also different. Therefore, when evaluating the thermal deterioration of the coated surface 4b and the mold resin inner surface 5b exposed by polishing the mold resin surface by reflection absorbance, the combinations of the two wavelengths λ5 and λ6 and the two wavelengths λ7 and λ8 to be selected are as follows. Although they may be the same, it is preferable to select appropriate wavelengths so that changes in ΔA' and ΔB' are large in each reflection absorbance spectrum.

Further, since the thickness of the coating is usually about 50 to 100 μm, it is sufficient to remove this coating when evaluating the inside of the mold resin, and it is preferable to polish the surface by about 50 to 100 μm. Since oxygen or water in the air slowly diffuses into the mold resin through the mold coating, it is thought that some degree of deterioration due to oxidation and hydrolysis reactions will occur even inside the mold resin, which is not in direct contact with the outside air. The color change of the mold resin due to thermal deterioration is noticeable up to approximately 50 to 100 μm from the painted surface, so by polishing and removing the painted area where the color change is significant due to thermal deterioration, the mold resin near the conductor can be removed. The thermal deterioration state of deteriorated mold resin can be evaluated using the same mechanism.

FIG. 7 shows a schematic diagram of the locations where the reflection absorbance of the molded resin of the winding was measured. Normally, the air around the winding, whose temperature increases due to Joule heat, cools the winding 7 through natural convection, so that the temperature of the upper part of the winding is higher than that of the lower part. Therefore, for example, by measuring the temperature of the upper surface of the wire-wound mold resin 8a in FIG. 7, thermal deterioration of the mold resin 1 can be evaluated with higher sensitivity. Alternatively, the side surface of the upper part of the winding mold resin 8b or 8c in FIG. 7 may be measured.

It is thought that the temperature of the mold resin surface varies depending on the structure of the winding, the thickness of the mold resin, the distance from the conductor surface to the mold resin surface, etc. For this reason, thermal deterioration of the mold resin can be evaluated with higher sensitivity by selecting a high-temperature portion from previously acquired temperature distribution data and measuring the reflected absorbance.

By the procedure shown in Scheme 2 above, in the molded resin on which the surface of the winding is painted, from the reflection absorbance measurement results of the painted surface and the surface of the internal molded resin exposed by polishing the painted surface, It becomes possible to non-destructively evaluate the bending rupture strength of the molded resin inside the wire near the conductor.

In Examples 1 and 2 described above, an example was explained in which diagnosis was made using a master curve based on changes in reflection absorbance at two wavelengths, but the diagnosis is not limited thereto. Diagnosis can also be made using a master curve.

1...Mold resin 2...Conductor 3...Painting 4a...Mold resin surface 4b...Painted surface 5a...Surface inside the mold resin exposed by polishing the surface 5b...Surface 6a of the internal mold resin exposed by polishing the painted surface , 6b...Mold resin 7 near the conductor...Winding 8a, 8b, 8c...Reflection absorbance measurement position

Claims (7)

A method for diagnosing a molded transformer having a winding and a resin covering the winding, the method comprising:
a first measurement step of measuring the reflective absorbance of the surface of the resin;
a second measurement step of measuring the reflective absorbance of the exposed inner surface of the resin by polishing the surface of the resin;
A method for diagnosing a molded transformer, comprising the step of estimating the bending rupture strength of the resin near the conductor of the winding from the measurement data of the first measurement step and the measurement data of the second measurement step. The method for diagnosing a molded transformer according to claim 1,
The step of estimating the bending rupture strength of the resin includes:
A method for diagnosing a molded transformer, comprising the step of estimating an average temperature of the resin, and estimating the bending rupture strength of the resin from the estimated average temperature. The method for diagnosing a molded transformer according to claim 2,
In the first measurement step,
Measure the reflected absorbance at two different wavelengths,
In the second measurement step,
A diagnostic method for molded transformers that measures reflected absorbance at two different wavelengths. The method for diagnosing a molded transformer according to claim 3,
The step of estimating the average temperature of the resin includes:
Determining a first generalization time from the difference in reflection absorbance of the two wavelengths in the first measurement step and the first master curve,
Determining a first average temperature of the surface of the resin from the first generalization time and the operating time of the molded transformer,
Determining the second generalization time from the difference in reflection absorbance of the two wavelengths in the second measurement step and the second master curve,
Determining a second average temperature of the inner surface of the resin from the second generalization time and the operating time of the molded transformer;
A method for diagnosing a molded transformer, in which a third average temperature near a winding conductor is determined from a first average temperature, a second average temperature, and temperature distribution data of resin in the winding. The method for diagnosing a molded transformer according to claim 4,
The step of estimating the bending rupture strength of the resin includes:
Determining a third generalized time from the third average temperature and the operating time of the molded transformer,
A method for diagnosing a molded transformer, estimating the bending rupture strength of the resin from a third generalized time and a third master curve. The method for diagnosing a molded transformer according to claim 1,
A method for diagnosing a molded transformer, comprising the step of displaying the estimated bending breaking strength. A method for diagnosing a molded transformer having a winding and a resin covering the winding, the surface of which is coated,
a first measurement step of measuring the reflective absorbance of the painted surface;
a second measurement step of polishing the painted surface to remove the paint and measuring the reflective absorbance of the exposed internal surface of the resin;
A method for diagnosing a molded transformer, comprising the step of estimating the bending rupture strength of the resin near the conductor of the winding from the measurement data of the first measurement step and the measurement data of the second measurement step.

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