Diagnosis method for molded transformers

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

[Technical Field]

[0001] The present invention relates to a technique for diagnosing a molded transformer. [Background technology]

[0002] Resin materials are used in electrical equipment as insulating and structural materials. For example, in molded transformers, the windings of the transformer are impregnated with resin and then molded. Resin has excellent moldability, is lightweight, and has high insulating properties. However, as an organic material, resin generally deteriorates more easily over time than metal or ceramic materials. For this reason, resin materials are thought to determine the lifespan of electrical equipment, and technologies for assessing the remaining lifespan of electrical equipment by evaluating the deterioration state of the resin materials used in electrical equipment have been developed.

[0003] Patent Document 1 describes a method for diagnosing deterioration of a molded transformer by irradiating it with light or X-rays and measuring the reflected light absorbance. It also describes a method for diagnosing deterioration by providing a non-painted area for light irradiation on a resin member covering the outer periphery of the coil and a covering member covering this, and by peeling off the covering member and irradiating it with light during deterioration diagnosis.

[0004] Patent Document 2 describes a method for diagnosing deterioration of electrical equipment that includes a molded resin by irradiating it with X-rays or the like. It also describes that the physical quantity measuring means for the surface layer of the molded resin measures an unpainted area of ​​the molded resin. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2018-166164 [Patent Document 2] Japanese Patent Application Publication No. 2019-7806 Summary of the Invention [Problem to be solved by the invention]

[0006] Molded transformers typically use epoxy resins filled with inorganic fillers as their molding resins. Molded resins deteriorate due to heat generation during operation, electrical and mechanical stress, and environmental factors, resulting in a decline in their physical properties. Generally, the epoxy and unsaturated polyester resins that make up these molding resins are organic materials and are subject to thermal degradation. Thermal degradation of epoxy resins results in only minor changes in the dielectric and insulating properties of the resin itself, but significant changes in mechanical properties and a decline in mechanical strength. A decline in the mechanical strength of epoxy resins can lead to cracks or peeling at the adhesive interface between the resin and the coil, significantly reducing their insulating performance. Therefore, it is believed that the decline in mechanical strength associated with thermal degradation of epoxy resins determines the lifespan of molded transformers. Therefore, degradation diagnosis techniques focusing on the thermal degradation behavior of epoxy resins have been developed.

[0007] Thermal degradation of epoxy resins causes changes in their physical and chemical structure, resulting in changes in their physical properties and mechanical properties. Therefore, by evaluating the changes in the physical properties of epoxy resins that accompany thermal degradation, it is possible to diagnose changes in mechanical properties and a decrease in mechanical strength.

[0008] It is believed that epoxy resins deteriorate due to heat mainly through the following mechanism. (1) The chemical structure of the resin changes, and the color of the resin surface, glass transition temperature, elastic modulus, bending strength, etc. change. (2) The resin decomposes to produce low molecular weight compounds, which are released and result in a loss of weight. (3) Stress relaxation due to aging is accelerated.

[0009] While simple, nondestructive measurements are desirable for on-site diagnosis of molded transformers, the mechanical strength of epoxy resin, which is believed to determine the lifespan of a molded transformer, is difficult to measure nondestructively. Furthermore, cracks or peeling in the molded resin near the winding conductors of a molded transformer can lead to a deterioration in insulation performance. During operation, the temperature of the winding conductors rises, making the molded resin near the conductors susceptible to thermal degradation. Therefore, while it is desirable to evaluate the mechanical strength of the molded resin near the conductors in a deterioration diagnosis, it is difficult to nondestructively evaluate the deterioration state of the molded resin inside the winding conductors from the surface of the molded resin. Furthermore, the surface of the molded resin in molded transformers is often painted, and the paint is typically made of a different material than the resin used for the mold.

[0010] Therefore, there was a problem in that it was difficult to easily and non-destructively measure the mechanical strength of the internal molding resin near the winding conductor, which is thought to determine the lifespan of a molded transformer.

[0011] Patent Documents 1 and 2 describe a method for diagnosing deterioration by irradiating molded resin with light or X-rays. Patent Document 1 also describes a method for diagnosing deterioration by providing a resin member covering the outer periphery of a coil with an unpainted area for light irradiation and a covering member covering the unpainted area, and for diagnosing deterioration by removing the covering member and irradiating light. Patent Document 2 also describes a method for diagnosing deterioration by irradiating an electrical device with molded resin with X-rays or the like, and for measuring the physical quantity of the surface layer of the molded resin to measure an unpainted area of ​​the molded resin. However, both methods measure the surface characteristics of the molded resin, and do not directly measure the characteristics of the internal molded resin, such as near the conductor of the winding.

[0012] An object of the present invention is to diagnose the characteristics of the internal molding compound, such as that near the conductor of a winding. [Means for solving the problem]

[0013] One example of the present invention is a diagnostic method for a molded transformer having a winding and a resin covering the winding, comprising: a first measurement step of measuring the reflection absorbance of the surface of the resin; a second measuring step of polishing the surface of the resin to measure the reflection absorbance of the internal surface of the resin exposed; and estimating the bending fracture 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. [Effects of the Invention]

[0014] According to the present invention, it is possible to diagnose the characteristics of the internal molding resin, such as that near the conductor of the winding. [Brief explanation of the drawings]

[0015] [Figure 1] Graph showing master curve A. [Figure 2] A diagram showing master curve B. [Figure 3] A diagram showing master curve C. [Figure 4] Schematic diagram of a winding cross section when there is no paint on the mold resin surface. [Figure 5] FIG. 1 is a block diagram of a molded transformer diagnostic system according to a first embodiment. [Figure 6] 1 is a flowchart of a process according to the first embodiment. [Figure 7] Schematic diagram of the measurement points for the reflection and absorbance of the winding molding resin. [Figure 8] A diagram showing master curve A'. [Figure 9] Graph showing master curve B'. [Figure 10] Graph showing master curve C'. [Figure 11] Schematic diagram of a winding cross section when the mold resin surface is painted. [Figure 12] 10 is a flowchart of a process according to a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In each drawing for explaining the embodiments, the same components are denoted by the same names and reference numerals as much as possible, and repeated description thereof will be omitted. [Example]

[0017] To understand the thermal degradation behavior of the molded resin to be diagnosed, samples of the cured molded resin were prepared, cut into specified shapes, and heated in a thermostatic chamber at different temperatures to accelerate degradation. Reflection / absorbance spectra were measured to quantitatively evaluate the color change on the molded resin surface. Furthermore, the molded resin surface was polished to measure the reflection / absorbance of the exposed inner surface of the molded resin. A probe-type portable spectroreflectometer was used to measure the reflection / absorbance. The mechanical strength of the resin was also evaluated by its flexural strength.

[0018] The procedure for diagnosing deterioration of a molded transformer when there is no paint on the molded resin surface is explained as Scheme 1. Scheme 1 consists of the following steps: "Creating a master curve for deterioration of molded resin characteristics," "Creating temperature distribution data of molded resin inside the winding during operation," "Estimating average temperature of molded resin by measuring reflection absorbance," and "Estimating bending fracture strength of molded resin."

[0019] Based on the idea proposed by Dakin, we assume that all changes in the properties of insulating materials due to thermal degradation are caused by the amount of change x in their chemical structure. If we assume that the amount of change x in their chemical structure follows chemical reaction kinetics, it can be 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 that represents the thermal degradation reaction Furthermore, a generalized time (deterioration level) θ having a unit of time is defined by the following equation (2). θ=t·exp(-ΔE / RT) (2)

[0020] Regarding "Creating a master curve for deterioration of mold resin properties," a master curve for deterioration can be created by the following procedure. First, the sample is thermally degraded by changing the heating temperature, the properties after thermal degradation are measured, and the measured properties are plotted against the heating time. Next, the heating time (t) until the property reaches a certain value is determined for each test temperature, and the logarithm of that heating time is plotted against the reciprocal (1 / T) of each test temperature (absolute temperature). From the slope, (ΔE / R) in equation (1) can be obtained, and the activation energy ΔE can be calculated (Arrhenius method). Furthermore, by converting the heating time t to a generalized time θ using equation (2) and replotting, each data can be overlaid to create a master curve for degradation.

[0021] Two wavelengths were selected: λ1, where the reflection absorbance of the molded resin surface changes significantly due to thermal degradation, and λ2, where the change is small, and the difference ΔA between the reflection absorbance A(λ1) and A(λ2) at each wavelength was evaluated. Assuming that the change in the reflection absorbance difference ΔA follows the Arrhenius law, a master curve for the reflection absorbance difference ΔA can be created. A schematic diagram of the master curve A for the reflection absorbance difference ΔA of the molded resin surface is shown in Figure 1.

[0022] Next, the surface of the molded resin was polished, and two wavelengths were selected: wavelength λ3, at which the reflected absorbance of the exposed inner surface of the molded resin changed significantly, and wavelength λ4, at which the change was small. The difference ΔB between the reflected absorbance B(λ3) and B(λ4) at each wavelength was evaluated. Assuming that the change in the reflected absorbance difference ΔB follows the Arrhenius law, a master curve B for the reflected absorbance difference ΔB can be created in the same way. A schematic diagram of the master curve B for the reflected absorbance difference ΔB is shown in Figure 2.

[0023] From Figures 1 and 2, the generalized time θ required for the difference in reflection absorbance to reach a certain value can be obtained. From the obtained θ, the operating temperature at which the difference in reflection absorbance reaches a certain value after use for t hours, i.e., the heat resistance temperature T, can be calculated using equation (2). Conversely, once the operating temperature T is determined, θ can be converted to actual time t using equation (2), and the behavior of the change in the difference in reflection absorbance due to thermal degradation at actual time t can be obtained. Figure 3 shows a schematic diagram of the master curve C for flexural breaking strength, created using a similar procedure.

[0024] Regarding "Creating temperature distribution data for mold resin inside windings during operation" Temperature distribution data for the molded resin inside the windings during operation is created through analysis and actual temperature measurements during operation of the molded transformer. Figure 4 shows a schematic diagram of a cross section of a winding when the molded resin surface is uncoated. Temperature distribution data for the molded resin inside the windings during operation is acquired in advance so that temperatures during operation can be evaluated for molded resin surface 4a, where reflective absorbance is measured, molded resin inner surface 5a exposed by polishing the surface of molded resin 1, and molded resin 6a near winding conductor 2.

[0025] Figure 5 shows a block diagram of the molded transformer diagnostic system of this embodiment. The molded transformer diagnostic system of this embodiment is composed of a measuring device 10 and a diagnostic device 11. The measuring device 10 is a device that measures the reflection and absorbance of the surface of the molded resin of a molded transformer that has windings and resin covering the windings.

[0026] The diagnostic device 11 comprises a molded resin average temperature estimation unit 12, a molded resin bending rupture strength estimation unit 13, and a display unit 14. The diagnostic device may have a processing device such as a processor and a recording unit storing a program, and the processing device may call up the program to implement its functions. The display unit 14 may display the estimated results of the diagnosed molded resin bending rupture strength, or the deterioration state of the molded transformer, such as the remaining lifespan, evaluated from the estimated results.

[0027] Fig. 6 shows a flowchart of the processing of the diagnostic system. "Estimation of the average temperature of the molded resin by measuring the reflection absorbance" and "Estimation of the bending breaking strength of the molded resin" in Scheme 1 will be explained using Fig. 6.

[0028] The measuring device 10 measures the reflection absorbance of the surface of the molding resin of the molded transformer for the operating time t (S601).

[0029] The average temperature estimation unit 13 of the mold resin calculates the generalized time θ from the difference in the reflection absorbance at two different wavelengths λ1 and λ2 obtained by the measurement and the master curve A. A (See Figure 1.) Generalized time θ A and the operation time t, the average temperature T1 of the mold resin surface during operation is calculated using equation (2) (S602).

[0030] At the point where the surface of the molded resin in the molded transformer has been polished during operation time t, the measuring device 10 measures the reflected light absorbance inside the molded resin (S603). Here, polishing the surface of the molded resin is sufficient, which is effective for easily and non-destructively measuring the mechanical strength of the molded resin inside near the conductor of the winding.

[0031] The average temperature estimation unit 13 of the mold resin calculates the generalized time θ from the difference in the internal reflection absorbance at two different wavelengths λ3 and λ4 obtained by the measurement and the master curve B. B (See Figure 2.) Generalized time θ B From the operating time t, the average temperature T2 inside the mold resin during operation is calculated using equation (2) (S604).

[0032] The mold resin average temperature estimation unit 13 obtains the average temperature T3 of the mold resin near the conductor from the average temperature T1 of the mold resin surface during operation, the average temperature T2 inside the mold resin, and the temperature distribution data of the mold resin inside the winding during operation that has been created (S605).

[0033] The mold resin bending breaking strength estimation unit 13 calculates the generalized time θ from the operating time t, the average temperature T3 of the mold resin near the conductor during operation, and the formula (2). C The molding resin bending breaking strength estimation unit 13 calculates the generalized time θ C From the master curve C, the bending breaking strength of the resin at the average temperature T3 during operation of the molding resin in the vicinity of the conductor 6a is estimated (S606). Note that, to find the generalized time from the difference in reflection absorbance, the correspondence between the difference in reflection absorbance on the vertical axis and the generalized time on the horizontal axis of the master curve is recorded in a recording unit such as a database, and the generalized time can be found from that correspondence based on the difference in reflection absorbance.

[0034] It can be seen that the difference in reflection absorbance due to deterioration is greater in Figure 1 than in Figure 2. This is thought to be because, while thermal decomposition and crosslinking reactions occur primarily inside the molded resin, oxidation and hydrolysis reactions primarily occur on the surface of the molded resin in contact with the atmosphere, resulting in a larger change in reflection absorbance due to changes in chemical structure. Therefore, by using master curve A in Figure 1, obtained by measuring the reflection absorbance of a surface that is highly sensitive to heat, it is possible to estimate with high accuracy the average temperature T1 of the molded resin surface during operation. Furthermore, by using the average temperatures T1 and T2 of the molded resin surface 4a and the molded resin inner surface 5a exposed by polishing the molded resin surface, respectively, it is possible to more accurately estimate the average temperature T3 of the molded resin near the conductor 6a during operation.

[0035] The chemical structure of the molded resin after deterioration differs between the interior of the molded resin, where thermal decomposition and crosslinking reactions occur primarily, and the surface of the molded resin, where oxidation and hydrolysis reactions occur primarily, and therefore the reflection-absorbance spectra obtained by measurement also differ. Therefore, when evaluating the thermal degradation of molded resin surface 4a and molded resin inner surface 5a exposed by polishing the molded resin surface using reflection-absorbance, the combinations of the two wavelengths λ1 and λ2 and the two wavelengths λ3 and λ4 selected may be the same, but it is preferable to select appropriate wavelengths so that the changes in ΔA and ΔB in each reflection-absorbance spectrum are large.

[0036] Furthermore, when evaluating the interior of the molded resin, it is preferable to polish off approximately 50 to 100 μm from the surface. Because oxygen and water in the air diffuse slowly into the interior of the molded resin, it is thought that some degree of degradation due to oxidation and hydrolysis reactions will occur even inside the molded resin that is not directly exposed to the outside air. Since the color change of the molded resin due to thermal degradation is most noticeable from the surface to approximately 50 to 100 μm, by polishing off the areas where the color change due to thermal degradation is most noticeable, it is possible to evaluate the state of thermal degradation of the molded resin, which has deteriorated by the same mechanism as the molded resin near the conductor.

[0037] Figure 7 shows a schematic diagram of the measurement points for the reflection and absorbance of the winding's molding resin. Normally, the air surrounding the winding 7, whose temperature rises due to Joule heat, cools the winding 7 through natural convection, making the upper part of the winding 7 hotter than the lower part. For this reason, for example, by measuring the temperature of the top surface of the winding molding resin 1, indicated by 8a in Figure 7, it is possible to evaluate the thermal degradation of the molding resin 1 with greater sensitivity. It is also possible to measure the side surface of the top of the winding molding resin, indicated by 8b or 8c in Figure 7.

[0038] It is believed that the temperature of the mold resin surface varies depending on the winding structure, the thickness of the mold resin, the distance from the conductor surface to the mold resin surface, etc. For this reason, by selecting high-temperature areas from pre-acquired temperature distribution data and measuring the reflected light absorbance, it is possible to evaluate thermal degradation of the mold resin with greater sensitivity.

[0039] The procedure shown in Scheme 1 above makes it possible to nondestructively evaluate the bending fracture strength of the internal molding resin near the conductor of the winding from the reflection-absorbance measurement results of the molding resin surface and the internal surface of the molding resin exposed by polishing the molding resin surface. [Example]

[0040] To understand the thermal degradation behavior of mold resins with painted surfaces, we prepared samples by painting the surfaces of the cured mold resins we had prepared. We then cut these samples into predetermined shapes and heated them in a thermostatic chamber at various temperatures to accelerate degradation. To quantitatively evaluate the color change of the painted surface, we measured the reflection / absorbance spectrum. Furthermore, we polished the paint off the mold resin surface to measure the reflection / absorbance of the exposed mold resin surface. A probe-type portable spectroreflectometer was used to measure the reflection / absorbance. Furthermore, we evaluated the flexural strength of the resin as a measure of its mechanical strength.

[0041] The procedure for diagnosing deterioration of a molded transformer in Example 2, in which the molded resin surface is painted, is explained as Scheme 2. In this example, too, a master curve for deterioration can be created by the following procedure similar to that in Example 1.

[0042] "Creating a master curve for deterioration of mold resin properties" First, the sample is thermally degraded by changing the heating temperature, the properties after thermal degradation are measured, and the measured properties are plotted against the heating time. Next, the heating time (t) until the property reaches a certain value is determined for each test temperature, and the logarithm of that heating time is plotted against the reciprocal (1 / T) of each test temperature (absolute temperature). From the slope, (ΔE / R) in equation (1) can be obtained, and the activation energy ΔE can be calculated (Arrhenius method). Furthermore, by converting the heating time t to a generalized time θ using equation (2) and replotting, each data can be overlaid to create a master curve for degradation.

[0043] Two wavelengths were selected: λ5, where the reflection absorbance of the painted surface changes significantly due to thermal degradation, and λ6, where the change is small. The difference ΔA' between the reflection absorbance A'(λ5) and A'(λ6) at each wavelength was evaluated. Assuming that the change in the reflection absorbance difference ΔA' follows the Arrhenius law, a master curve A' for the reflection absorbance difference ΔA' can be created. A schematic diagram of the master curve A' for the reflection absorbance difference ΔA' of the molded resin surface is shown in Figure 8.

[0044] Next, the surface of the molded resin was polished, and two wavelengths were selected: λ7, at which the reflected absorbance of the exposed inner surface of the molded resin changed significantly, and λ8, at which the change was small. The difference ΔB' between the reflected absorbance B'(λ7) and B'(λ8) at each wavelength was evaluated. Assuming that the change in the reflected absorbance difference ΔB' follows the Arrhenius law, a master curve B' for the reflected absorbance difference ΔB' can be created in the same way. A schematic diagram of the master curve B' for the reflected absorbance difference ΔB' is shown in Figure 9.

[0045] From Figures 8 and 9, the generalized time θ required for the difference in reflection absorbance to reach a certain value can be obtained. From the obtained θ, the operating temperature at which the difference in reflection absorbance reaches a certain value after use for t hours, i.e., the heat resistance temperature T, can be calculated using equation (2). Conversely, once the operating temperature T is determined, θ can be converted to actual time t using equation (2), and the behavior of the change in the difference in reflection absorbance due to thermal degradation at actual time t can be obtained. A schematic diagram of the master curve C' for flexural breaking strength, created using a similar procedure, is shown in Figure 10.

[0046] Regarding "Creating temperature distribution data for mold resin inside windings during operation" Furthermore, temperature distribution data for the molded resin inside the windings during operation is created through analysis and actual temperature measurements during operation of the molded transformer. Figure 11 shows a schematic diagram of a cross section of a winding when the molded resin surface is painted. Temperature distribution data for the molded resin inside the windings during operation is acquired in advance so that temperatures during operation can be evaluated for the painted surface 4b where the reflective absorbance is measured, the surface 5b of the internal molded resin 1 exposed by polishing the painted surface, and the molded resin 6b near the winding conductor 2.

[0047] FIG. 12 shows a flowchart of the processing in the diagnostic system. Using FIG. 12, "estimation of average temperature of molded resin by measuring reflection absorbance" and "estimation of bending breaking strength of molded resin" in Scheme 2 will be explained. Explanations similar to those in Example 1 may be omitted. In Example 2 as well, the system configuration diagram of the diagnostic system is similar to that in FIG. 5.

[0048] The measuring device 10 measures the reflective absorbance of the painted surface of the molded transformer for the operating time t (S1201).

[0049] The average temperature estimation unit 12 of the mold resin in the diagnostic device 11 calculates the generalized time θ from the difference in the reflection absorbance at two different wavelengths λ7 and λ8 obtained by the measurement and the master curve A'. A ' is calculated (see Figure 8). Then, θ A From the temperature T1′ and the operating time t, the average temperature T1′ of the coating surface of the mold resin during operation is calculated using equation (2) (S1202).

[0050] At the point where the molding resin coating of the molded transformer has been polished during the operating time t, the measuring device 10 measures the reflection absorbance of the molding resin inside (S1203).

[0051] The average temperature estimation unit 12 of the mold resin calculates θ from the difference in the reflection absorbance at two different wavelengths λ7 and λ8 obtained by measurement and the master curve B'. B ' is calculated (see Figure 9). Then, θ B From the temperature T' and the operating time t, the average temperature T2' inside the mold resin during operation is calculated using equation (2) (S1204).

[0052] The molding resin average temperature estimation unit 12 obtains the average temperature T3' of the molding resin near the winding conductor from the average temperature T1' of the coating surface of the molding resin during operation, the average temperature T2' inside the molding resin, and the temperature distribution data of the molding resin inside the winding during operation that has been prepared (S1205).

[0053] The mold resin bending breaking strength estimation unit 13 calculates the generalized time θ from the operating time t, the average temperature T3′ of the mold resin near the conductor during operation, and the formula (2). C Then, the resin bending breaking strength estimation unit 13 calculates the generalized time θ C 10, the bending breaking strength of the molding resin in the vicinity of the conductor 6b at the average temperature T3' during operation is estimated (S1206).

[0054] Here, we can see that the change in the difference in reflection absorbance due to deterioration is slightly larger in Figure 8 than in Figure 9. This is thought to be because, while thermal decomposition and crosslinking reactions occur primarily inside the molded resin, oxidation and hydrolysis reactions primarily occur on the molded resin surface in contact with the atmosphere, resulting in a larger change in reflection absorbance due to changes in chemical structure. Therefore, by using master curve A' in Figure 8, obtained by measuring the reflection absorbance of a surface that is highly sensitive to heat, it is possible to estimate with high accuracy the average temperature T1' of the painted surface during operation. Furthermore, by using the average temperatures T1' and T2' of the painted surface 4b and the inner surface b of the molded resin exposed by polishing the molded resin surface, respectively, the average temperature T3 of the molded resin near the conductor 6b during operation can be estimated with even greater accuracy.

[0055] The reflection-absorbance spectra obtained by measurement differ between the mold resin and the paint, which differ in their constituent materials and chemical structures. Furthermore, the chemical structure of the mold resin after deterioration differs between the interior of the mold resin, where thermal decomposition and crosslinking reactions primarily occur, and the painted surface, where oxidation and hydrolysis reactions primarily occur, resulting in different reflection-absorbance spectra. Therefore, when evaluating the thermal degradation of painted surface 4b and the mold resin inner surface 5b exposed by polishing the mold resin surface using reflection-absorbance, the combinations of the two wavelengths λ5 and λ6 and the two wavelengths λ7 and λ8 selected may be the same, but it is preferable to select appropriate wavelengths so that the changes in ΔA' and ΔB' are large in each reflection-absorbance spectrum.

[0056] Furthermore, because the coating is typically approximately 50 to 100 μm thick, evaluation of the interior of the molded resin requires only the removal of this coating, preferably by polishing approximately 50 to 100 μm from the surface. Because oxygen or water in the air slowly diffuses through the molded coating into the interior of the molded resin, even inside the molded resin that is not directly exposed to the outside air, some degree of degradation due to oxidation and hydrolysis reactions is likely to occur. Because color changes in molded resins due to thermal degradation are most pronounced within the first 50 to 100 μm of the coating, polishing and removing the areas of the coating where color change due to thermal degradation is most pronounced allows evaluation of the state of thermal degradation of molded resins that have deteriorated through the same mechanism as the molded resin near the conductor.

[0057] Figure 7 shows a schematic diagram of the measurement points for the reflection and absorbance of the winding's mold resin. Normally, the air surrounding the winding, which rises in temperature due to Joule heat, cools the winding 7 through natural convection, making the temperature higher at the top of the winding compared to the bottom. For this reason, for example, by measuring the temperature of the top surface of the winding mold resin 1 (8a in Figure 7), it is possible to evaluate the thermal degradation of the mold resin 1 with greater sensitivity. It is also possible to measure the side surface of the top of the winding mold resin 1 (8b or 8c in Figure 7).

[0058] It is believed that the temperature of the mold resin surface varies depending on the winding structure, the thickness of the mold resin, the distance from the conductor surface to the mold resin surface, etc. For this reason, by selecting high-temperature areas from pre-acquired temperature distribution data and measuring the reflected light absorbance, it is possible to evaluate thermal degradation of the mold resin with greater sensitivity.

[0059] The procedure shown in Scheme 2 above makes it possible to nondestructively evaluate the bending fracture strength of the internal molding resin near the conductor of a winding, when the surface of the molding resin is coated on the winding, from the reflection / absorbance measurement results of the coated surface and the surface of the internal molding resin exposed by polishing the coated surface.

[0060] In the above-described first and second embodiments, examples have been described in which a master curve based on changes in reflection-absorbance at two wavelengths is used for diagnosis, but the present invention is not limited to this, and diagnosis may also be performed using a master curve based on changes in reflection-absorbance spectrum due to deterioration. [Explanation of symbols]

[0061] 1...Mold resin 2...conductor 3...Painting 4a…Mold resin surface 4b...painted surface 5a: The surface inside the mold resin exposed by polishing the surface 5b...The surface of the internal mold resin exposed by grinding away the painted surface 6a, 6b...Mold resin near the conductor 7...Winding 8a, 8b, 8c...Measurement positions of reflection absorbance

Claims

1. A diagnostic method for a molded transformer having a winding and a resin covering the winding, comprising: a first measuring step of measuring the reflection absorbance of the surface of the resin; a second measuring step of polishing the surface of the resin to measure the reflection absorbance of the internal surface of the resin exposed; and estimating the bending fracture 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.

2. The method for diagnosing a molded transformer according to claim 1, The step of estimating the flexural strength of the resin includes: A diagnostic method for a molded transformer, comprising a step of estimating an average temperature of the resin, and estimating the bending fracture strength of the resin from the estimated average temperature.

3. The method for diagnosing a molded transformer according to claim 2, In the first measurement step, Measure the reflection absorbance at two different wavelengths, In the second measurement step, A diagnostic method for molded transformers that measures the reflection absorbance at two different wavelengths.

4. 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 generalized time from the difference in reflection absorbance at 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 generalized time and the operating time of the molded transformer; A second generalized time is calculated from the difference in the reflection absorbance at the two wavelengths in the second measurement step and the second master curve; A second average temperature of the inner surface of the resin is calculated from the second generalized time and the operating time of the molded transformer; A diagnostic method for a molded transformer, which determines a third average temperature near a winding conductor from the first average temperature, the second average temperature, and temperature distribution data of the resin in the winding.

5. The method for diagnosing a molded transformer according to claim 4, The step of estimating the flexural strength of the resin includes: A third generalized time is calculated from the third average temperature and the operating time of the molded transformer. A molded transformer diagnosis method for estimating the bending fracture strength of the resin from a third generalized time and a third master curve.

6. The method for diagnosing a molded transformer according to claim 1, A diagnostic method for a molded transformer, comprising a step of displaying the estimated bending fracture strength.

7. A diagnostic method for a molded transformer having a winding and a resin covering the winding, the surface of which is painted, comprising: a first measuring step of measuring the reflective absorbance of the painted surface; a second measuring step of polishing the coated surface to remove the coating and measuring the reflective absorbance of the exposed inner surface of the resin; and estimating the bending fracture 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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