JP5407480B2 - Internal diagnosis method of transformer - Google Patents

Description

  The present invention relates to a transformer internal diagnosis method for diagnosing whether an abnormality has occurred inside a transformer.

  For example, the life of oil-filled transformers has been evaluated from the deterioration characteristics of insulating paper and the temperature rise characteristics of transformers, and gas analysis in oil and various electrical tests have been widely implemented as transformer diagnostic techniques. Yes. In the oil-in-gas analysis, oil is collected in the state of operation of the transformer, the abnormal level is determined based on the amount of gas components in the oil, and overheating, partial discharge, and arc discharge are diagnosed based on an abnormality diagnosis diagram based on a combination of gas composition ratios.

  On the other hand, as various electrical tests, an insulation resistance measurement, a winding resistance measurement, an impedance test, an excitation current measurement, a transformation ratio test, and the like are used to determine the internal abnormality of the transformer and whether or not to continue the operation. At present, these diagnostic methods are combined as appropriate to diagnose transformers. However, it is difficult to detect changes in transformer windings even in impedance tests. At present, no effective diagnostic method has been established other than the status check by open inspection.

  Using frequency response analysis FRA, the first measurement area where changes occur when the iron core deforms and the second measurement where changes occur when the winding is abnormal are used to identify the abnormal state of the iron core and windings inside the transformer. For the region, measure the transfer function of the high voltage winding with the low voltage winding open and shorted, and measure the transfer function of the low voltage winding with the high voltage winding opened and shorted. There is one in which an abnormal aspect of a transformer is identified based on a combination of measurement regions that appear (see, for example, Patent Document 1).

JP 2009-25153 A

  However, in Patent Document 1, it can be determined that the iron core is deformed, the winding is misaligned, or the winding is deformed. For example, even if the winding is deformed, the primary Whether it is eccentric with the secondary winding or buckling deformation of the secondary winding, or further, whether it is a combined state of eccentricity and buckling deformation cannot be determined in detail.

  As a result of recent research, it has been found that when oil-filled transformers are used for a long period of time, gaps are generated due to the death of insulators such as press boards and the windings are easily deformed. Therefore, in order to judge the life and use limit of the transformer, it is required to establish a technique for capturing such a minute deformation of the winding.

  In conventional gas analysis in oil and impedance measurement, it is necessary to establish a diagnostic method for minute deformation of the winding because accurate evaluation cannot be performed for the minute deformation of the winding. The number of oil-filled transformers that have exceeded 30 years of age is on the rise, and since it is approaching the expected life of transformers, it is necessary to ensure thorough use of existing facilities while ensuring reliability. It is in.

  An object of the present invention is to provide an internal diagnosis method for a transformer that can determine in detail a minute deformation of the winding without performing an internal open inspection of the transformer.

  In the transformer internal diagnosis method according to the first aspect of the present invention, either the primary winding or the secondary winding of the transformer is short-circuited to ground, and a variable frequency voltage is applied to the opposite-side winding that is short-circuited to ground. The current flowing through the winding is measured, the variable frequency voltage is divided by the current to obtain the impedance, the eccentricity of the primary and secondary windings of the transformer based on the impedance frequency characteristics, the secondary winding Whether the buckling deformation of the wire, the combined state of the eccentricity and the buckling deformation, the axial displacement of the primary winding and the secondary winding, or the combined state of the buckling deformation and the axial displacement It is characterized by diagnosing.

  According to a second aspect of the present invention, there is provided a transformer internal diagnosis method according to the first aspect of the present invention, wherein the secondary winding of the transformer is short-circuited to ground and the variable frequency voltage is applied to the primary winding. In the characteristics, the first resonance point of the impedance frequency characteristic shifts to the higher frequency side than the impedance frequency characteristic in the normal state, and the impedance frequency characteristic in the frequency region higher than the first resonance point shifts to the lower frequency side than the impedance frequency characteristic in the normal state. In this case, it is diagnosed that the primary winding and the secondary winding of the transformer are eccentric.

The transformer internal diagnosis method according to the invention of claim 3 is the impedance frequency when the secondary winding of the transformer is short-circuited to ground and a variable frequency voltage is applied to the primary winding. In the characteristics, when the impedance frequency characteristic is shifted to a lower frequency side than the impedance frequency characteristic in a normal state in a region higher than a predetermined high frequency, and the primary winding of the transformer is short-circuited to ground and variable to the secondary winding In the impedance frequency characteristics when a frequency voltage is applied, if the impedance frequency characteristics shift to a lower frequency side than the impedance frequency characteristics in the normal state in a region above a predetermined high frequency, the buckling of the secondary winding of the transformer It is characterized by diagnosing the deformation.

  According to a fourth aspect of the present invention, there is provided a transformer internal diagnosis method according to the first aspect of the present invention, wherein the secondary winding of the transformer is short-circuited to ground, and the impedance frequency when a variable frequency voltage is applied to the primary winding. In the characteristic, the impedance frequency characteristic shifts to a lower frequency side than the normal impedance frequency characteristic in a region above a predetermined high frequency, and the minimum impedance value between the first resonance point and the second resonance point is the normal state impedance. The impedance frequency characteristic between the minimum value and the second resonance point is larger than the minimum value of the frequency characteristic, and shifts to a lower frequency side than the impedance frequency characteristic of the normal state, and the impedance value of the second resonance point is the impedance of the normal state When the impedance value is smaller than the frequency characteristic impedance value, it is diagnosed that the eccentricity and the buckling deformation are combined. And features.

  The transformer internal diagnosis method according to the invention of claim 5 is the impedance frequency when the secondary winding of the transformer is short-circuited to ground and a variable frequency voltage is applied to the primary winding. In the characteristic, the minimum value of the impedance between the first resonance point and the second resonance point is larger than the minimum value of the impedance frequency characteristic in the normal state, and the impedance frequency characteristic between the minimum value and the second resonance point is normal. If the impedance frequency characteristic shifts to the low frequency side beyond the predetermined frequency width, and the impedance at the sixth resonance point is equal to or higher than the predetermined value, it is diagnosed as an axial displacement between the primary winding and the secondary winding. It is characterized by that.

  According to a sixth aspect of the present invention, there is provided a transformer internal diagnosis method according to the first aspect of the present invention, wherein the secondary winding of the transformer is short-circuited to ground, and the impedance frequency when a variable frequency voltage is applied to the primary winding. In the characteristic, the impedance frequency characteristic between the minimum value of the impedance between the first resonance point and the second resonance point and the second resonance point is shifted to a lower frequency side than the impedance frequency characteristic in the normal state, and the second When the impedance is shifted to a lower frequency side than the impedance frequency characteristic in the normal state in the high frequency range from the resonance point, and the impedance at the sixth resonance point is a predetermined value or more, the combined state of the buckling deformation and the axial displacement is It is characterized by making a diagnosis.

  According to the present invention, either the primary winding or the secondary winding of the transformer is short-circuited to ground, the variable frequency voltage is applied to the opposite-side winding that is short-circuited, and the current flowing through the winding is measured. Dividing the variable frequency voltage by the current to obtain the impedance, and based on the impedance frequency characteristics, the transformer primary and secondary windings eccentricity, secondary winding buckling deformation, eccentricity and buckling Diagnose whether the combined state of deformation, axial displacement of primary and secondary windings, or combined state of buckling deformation and axial displacement, so check the internal opening of the transformer. Therefore, the minute deformation of the winding can be judged in detail. This makes it possible to determine the usage limit of the transformer and improve the accuracy of diagnosis of the oil-filled transformer in the actual field, so that the secular transformation aimed at thorough use of existing facilities while maintaining the reliability of the oil-filled transformer. It can be used for container maintenance measures.

The flowchart which shows an example of the internal diagnostic method of the transformer concerning embodiment of this invention. Explanatory drawing of the micro deformation | transformation of the coil | winding made into object by this invention. The wave form diagram which shows the impedance frequency characteristic when the primary winding and secondary winding of a transformer are eccentric. The wave form diagram which shows an impedance frequency characteristic in case a secondary winding of a transformer has buckling deformation. The wave form diagram which shows the impedance frequency characteristic in case eccentricity and buckling deformation have generate | occur | produced in the secondary winding of a transformer. The wave form diagram which shows an impedance frequency characteristic in case there is an axial displacement in the secondary winding of a transformer. The wave form diagram which shows the impedance frequency characteristic in case buckling deformation and axial direction displacement have generate | occur | produced in the secondary winding of the transformer.

  Embodiments of the present invention will be described below. FIG. 1 is a flowchart showing an example of an internal diagnosis method for a transformer according to an embodiment of the present invention. First, either the primary winding or the secondary winding of the transformer to be diagnosed is short-circuited to ground (S1), and a variable frequency voltage is applied to the opposite winding that is short-circuited to ground (S2). Then, the impedance is obtained (S3), and the minute deformation of the winding is judged in detail from the obtained impedance frequency characteristic (S4). The impedance is obtained by measuring the current flowing through the winding when a variable frequency voltage is applied and dividing the variable frequency voltage by the current. Also, the minute deformation of the winding is based on the impedance frequency characteristics, the eccentricity of the primary and secondary windings of the transformer, the buckling deformation of the secondary winding, the combined state of eccentricity and buckling deformation, This is performed by diagnosing whether the primary winding and the secondary winding are in the axial displacement or the combined state of buckling deformation and axial displacement.

  That is, in the present invention, an FRA (Frequency Response Analysis: frequency) in which a variable frequency voltage is applied to a winding of a transformer to obtain an impedance frequency characteristic and a winding fault of the transformer is diagnosed based on the impedance frequency characteristic. Diagnosis using response analysis. That is, according to the present invention, the frequency response of the impedance of the transformer is determined by the inductance and the capacitance of the winding, and when the winding is deformed, the inductance and the capacitance change to correspond to the deformed portion. The focus is on the change in the frequency and amplitude of the resonance point. Hereinafter, in the actual transformer single-phase winding model, the FRA characteristic change due to the displacement and deformation of the winding will be measured, and the physical change at the time of winding deformation and the frequency change region of the FRA characteristic will be explained. .

  FIG. 2 is an explanatory view of a minute deformation of the winding subject to the present invention. 2A shows the eccentricity between the primary winding 11 and the secondary winding 12 of the transformer, FIG. 2B shows the buckling deformation of the secondary winding 12, and FIG. 2C shows the eccentricity and buckling deformation. FIG. 2D shows the axial displacement of the primary winding 11 and the secondary winding 12. In addition, although illustration is abbreviate | omitted, the compound state of buckling deformation and axial displacement is also made into object in this invention.

  In FIG. 2A, the primary winding 11 and the secondary winding 12 are formed in a concentric cylindrical shape and held together by a wedge in a normal state, but the primary winding 11 and the secondary winding 12 When the wedge is shifted, the center A1 of the primary winding 11 and the center A2 of the secondary winding 12 are shifted, and the secondary winding 12 is eccentric. FIG. 2A shows a case where the secondary winding 12 is decentered and a shift Δx occurs between the center A1 of the primary winding 11 and the center A2 of the secondary winding 12. FIG. 2B shows a case where the inner secondary winding 12 is buckled and deformed, and a case where the buckling deformed portion 13 is generated.

  2C, when the eccentricity of the primary winding 11 and the secondary winding 12 in FIG. 2A and the buckling deformation of the secondary winding 12 in FIG. 2B occur simultaneously. FIG. 2D shows a case where the axial position B2 of the inner secondary winding 12 is shifted in the axial direction by Δy from the axial position B1 of the primary winding 11. Although not shown in the drawings, the present invention also deals with the case where the buckling deformation of the secondary winding 12 shown in FIG. 2 (b) occurs simultaneously with the axial deviation of FIG. 2 (d).

  FIG. 3 is a waveform diagram showing impedance frequency characteristics when the primary winding 11 and the secondary winding 12 are decentered. FIG. 3A shows a short circuit grounding of the secondary winding of the transformer to form the primary winding. FIG. 3B is an impedance frequency characteristic diagram when a variable frequency voltage is applied, and FIG. 3B is an impedance frequency characteristic diagram when the transformer primary winding is shorted to ground and a variable frequency voltage is applied to the secondary winding. 3A and 3B, curve S1 is a waveform in a normal state, curve S2 is a waveform when the amount of eccentricity Δx is relatively small, and curve S3 is when the amount of eccentricity Δx is relatively large. It is a waveform.

  As can be seen from FIG. 3A, when a variable frequency voltage is applied to the primary winding, the curves S2 and S3 are such that the first resonance point Q1 of the impedance frequency characteristic is shifted to the higher frequency side than the curve S1 in the normal state. In the frequency region higher than the first minimum value between the first resonance point Q1 and the second resonance point, the frequency shifts to the lower frequency side than the curve S1 in the normal state. On the other hand, as can be seen from FIG. 3B, when a variable frequency voltage is applied to the secondary winding, the curves S1, S2, and S3 have substantially the same characteristics, and there is almost no change in the frequency characteristics due to eccentricity. Accordingly, in the radial eccentricity of the secondary winding of the transformer, the impedance frequency characteristic when the variable frequency voltage is applied to the primary winding is higher than the first resonance point Q1, and the impedance frequency characteristic is low frequency. Diagnosis is possible by moving to the side.

  In order to improve the accuracy of the eccentricity diagnosis of the secondary winding of the transformer, the diagnosis should be made with both waveforms when the variable frequency voltage is applied to the primary winding and when the variable frequency voltage is applied to the secondary winding. It may be. That is, the impedance frequency characteristic when a variable frequency voltage is applied to the primary winding moves to the low frequency side in a frequency region higher than the first resonance point Q1 from the normal characteristic, and is variable to the secondary winding. When the impedance frequency characteristic when the frequency voltage is applied is almost the same as the normal characteristic, it can be diagnosed as the eccentricity of the secondary winding of the transformer.

  Next, FIG. 4 is a waveform diagram showing impedance frequency characteristics when the secondary winding 12 is buckled and deformed. FIG. 4A is a diagram illustrating a case where the secondary winding of the transformer is short-circuited to the primary winding. FIG. 4B is an impedance frequency characteristic diagram when a variable frequency voltage is applied, and FIG. 4B is an impedance frequency characteristic diagram when a variable frequency voltage is applied to the secondary winding with the primary winding of the transformer short-circuited to ground. 4A and 4B, the curve S4 is a waveform in a normal state, the curve S5 is a waveform when the buckling deformation is relatively small, and the curve S6 is a relatively large buckling deformation. It is a waveform.

  As can be seen from FIG. 4A, when a variable frequency voltage is applied to the primary winding, the curves S5 and S6 are in a region of a predetermined high frequency (50 kHz) or higher than the curve S4 in a normal state of impedance frequency characteristics. The characteristics are shifted to the low frequency side. On the other hand, as can be seen from FIG. 4 (b), when a variable frequency voltage is applied to the secondary winding, the curves S5 and S6 show the normal state of the impedance frequency characteristic in the region of a predetermined high frequency (400 kHz) or higher. The characteristic is shifted to the lower frequency side than the curve S4.

  Therefore, in the buckling deformation of the secondary winding 12, the diagnosis is made because the impedance frequency characteristic moves to the low frequency side in a predetermined high frequency region when a variable frequency voltage is applied to the primary winding or the secondary winding. Is possible. In particular, when a variable frequency voltage is applied to the secondary winding, a characteristic waveform in the case of buckling deformation can be obtained in a region of a predetermined high frequency (400 kHz) or more, so that the buckling deformation of the transformer can be easily performed. Can be diagnosed.

In order to improve the accuracy of buckling deformation diagnosis of the secondary winding of the transformer, diagnosis is performed with both waveforms when a variable frequency voltage is applied to the primary winding and when a variable frequency voltage is applied to the secondary winding. You may make it do. That is, the impedance frequency characteristic when a variable frequency voltage is applied to the primary winding is a characteristic shifted from the normal characteristic to the low frequency side in a region higher than a predetermined high frequency (50 kHz), and two When the impedance frequency characteristic when a variable frequency voltage is applied to the secondary winding is a characteristic shifted to a lower frequency side than the normal state characteristic in a region of a predetermined high frequency (400 kHz) or more, the secondary of the transformer It can be diagnosed as a buckling deformation of the winding.

  Next, FIG. 5 is a waveform diagram showing impedance frequency characteristics when eccentricity and buckling deformation occur in the secondary winding 12, and FIG. 5 (a) is a short circuit of the secondary winding of the transformer. Fig. 5 (b) shows the impedance frequency when the primary winding of the transformer is short-circuited and the variable frequency voltage is applied to the secondary winding when the variable frequency voltage is applied to the primary winding. FIG. 5 (a) and 5 (b), the curve S7 is a waveform in a normal state, the curve S8 is a waveform in the case of relatively buckling deformation only, and the curve S9 is in the case of eccentricity and buckling deformation. It is a waveform.

  As can be seen from FIG. 5 (a), when a variable frequency voltage is applied to the primary winding, the curve S9 is a curve S7 having a normal impedance frequency characteristic in a region of a predetermined high frequency (50 kHz) or a buckling deformation. Shift to the lower frequency side than the curve S8. Further, the minimum value m1 of the impedance value between the first resonance point Q1 and the second resonance point Q2 is larger than the minimum value m2 of the impedance value in the normal state, and between the minimum point m1 and the second resonance point Q2. The impedance frequency characteristic is shifted to the lower frequency side than the curve S7 in the normal state and the curve S8 in the case of only buckling deformation. Furthermore, the impedance value M1 of the second resonance point Q2 is smaller than the impedance value M2 in the normal state.

  On the other hand, as can be seen from FIG. 5B, when a variable frequency voltage is applied to the secondary winding, the curve S9 is a curve S7 in a normal state of impedance frequency characteristics in a region of a predetermined high frequency (400 kHz) or more. The characteristics are shifted to the lower frequency side. In this case, the curve S9 has substantially the same characteristics as the curve S8 in the case of only buckling deformation.

  Therefore, in the combined state of the eccentricity and buckling deformation of the secondary winding of the transformer, the impedance frequency characteristic when a variable frequency voltage is applied to the primary winding is an impedance frequency in a region of a predetermined high frequency (50 kHz) or more. The characteristic is shifted to the lower frequency side than the curve S7 in the normal state and the curve S8 in the case of only buckling deformation, and the minimum value m1 of the impedance value between the first resonance point Q1 and the second resonance point Q2 is in the normal state. The impedance frequency characteristic is larger than the minimum value m2 of the impedance value, and the impedance frequency characteristic between the minimum point m1 and the second resonance point Q2 is shifted to a lower frequency side than the curve S7 in the normal state or the curve S8 in the case of only buckling deformation. Furthermore, when the impedance value of the second resonance point Q2 is smaller than the curve S7 in the normal state or the curve S8 in the case of only buckling deformation, the eccentricity and buckling deformation of the transformer It is diagnosed with a focus state.

  Even in this case, in order to improve the accuracy of diagnosis of the combined state of the eccentricity and buckling deformation of the secondary winding of the transformer, it is possible to apply a variable frequency voltage to the primary winding and to change the secondary winding. You may make it diagnose with both waveforms when a frequency voltage is applied.

  Next, FIG. 6 is a waveform diagram showing impedance frequency characteristics when the secondary winding has an axial displacement, and FIG. 6A is a short circuit grounding the secondary winding of the transformer and changing it to the primary winding. FIG. 6B is an impedance frequency characteristic diagram when a frequency voltage is applied, and FIG. 6B is an impedance frequency characteristic diagram when a variable frequency voltage is applied to the secondary winding by short-circuiting the primary winding of the transformer. 6 (a) and 6 (b), the curve S10 is a waveform in a normal state, the curve S11 is a waveform when the axial displacement is relatively small, and the curve S12 is when the axial displacement is relatively large. It is a waveform.

  6A, when a variable frequency voltage is applied to the primary winding, when there is axial displacement, the curves S11 and S12 are compared with the curve 10 in the normal state, and the first resonance point Q1 and the second resonance point are compared. The minimum values m11 and m12 of the impedance between Q2 are larger than the minimum value m2 of the impedance frequency characteristic in the normal state. Further, the impedance frequency characteristic between the minimum values m11 and m12 and the second resonance point Q is shifted to the low frequency side by a predetermined frequency width Δf or more from the impedance frequency characteristic in the normal state. Furthermore, the impedance at the sixth resonance point is larger than the waveform at the normal state.

  On the other hand, as can be seen from FIG. 6B, when a variable frequency voltage is applied to the secondary winding, the curves S10, S11, and S12 have substantially the same characteristics, and there is almost no change in the frequency characteristics due to axial displacement. Therefore, the axial displacement of the secondary winding of the transformer is the axial displacement of the primary winding and the secondary winding from the characteristic point of the impedance frequency characteristic when a variable frequency voltage is applied to the primary winding. Can be diagnosed. Even in this case, in order to improve the accuracy of the diagnosis of the combined state of the eccentricity and buckling deformation of the secondary winding of the transformer, when the variable frequency voltage is applied to the primary winding and the variable frequency is applied to the secondary winding. You may make it diagnose with both waveforms when a voltage is applied.

  Next, FIG. 7 is a waveform diagram showing impedance frequency characteristics when buckling deformation and axial displacement occur in the secondary winding 12, and FIG. 7 (a) shows the secondary winding of the transformer. Fig. 7 (b) is a diagram of when the transformer primary winding is shorted to ground and the variable frequency voltage is applied to the secondary winding. It is an impedance frequency characteristic figure. 7A and 7B, a curve S13 is a waveform in a normal state, and a curve S14 is a waveform in a case where buckling deformation and axial displacement occur and the axial displacement is relatively small. Curve S15 is a waveform when buckling deformation and axial displacement occur and the axial displacement is relatively large.

  In FIG. 7A, when a variable frequency voltage is applied to the primary winding, attention is focused on impedance frequency characteristics between a predetermined high frequency range of 50 kHz to 70 kHz and a sixth resonance point to 700 kHz. That is, first, in a predetermined high frequency range (50 kHz to 70 kHz), a minimum value (first minimum value) m between the first resonance point Q1 and the second resonance point Q2 of the curves S14 and S15, and a second resonance point. Pay attention to the impedance frequency characteristics between Q2. That is, the impedance frequency characteristic between the first minimum value m and the second resonance point Q2 is such that the curves S14 and S15 are shifted to the lower frequency side than the curve S13 in the normal state, and normal in the high frequency range from the second resonance point Q2. The state is shifted to the low frequency side from the curve S13. Further, between the sixth resonance point and 700 kHz, the impedance value of the sixth resonance point Q6 is a predetermined value or more. On the other hand, as can be seen from FIG. 7B, when a variable frequency voltage is applied to the secondary winding, as shown in FIG. A characteristic almost similar to the impedance frequency characteristic in the composite state can be obtained.

  Therefore, in the combined state of buckling deformation and axial displacement, the impedance frequency characteristic between the first minimum value m when the variable frequency voltage is applied to the primary winding and the second resonance point is in the axially displaced state. When the impedance frequency characteristic shifts to a higher frequency side and the impedance at the sixth resonance point is equal to or greater than a predetermined value, it can be diagnosed that the state is a combination of buckling deformation and axial displacement.

  Even in this case, in order to improve the accuracy of the diagnosis of the combined state of buckling deformation and axial displacement of the secondary winding of the transformer, the variable frequency voltage is applied to the primary winding and to the secondary winding. You may make it diagnose with both waveforms when a variable frequency voltage is applied.

  According to the embodiment of the present invention, either the primary winding or the secondary winding of the transformer is short-circuited to ground, the variable frequency voltage is applied to the opposite-side winding that is short-circuited, and flows to the winding. The current is measured, the variable frequency voltage is divided by the current to obtain the impedance, and the waveform characteristic of the impedance frequency characteristic is examined. And from the characteristics of the waveform, the eccentricity of the primary and secondary windings of the transformer, the buckling deformation of the secondary winding, the combined state of the eccentricity and buckling deformation, the primary and secondary windings Therefore, it is possible to determine in detail the minute deformation of the winding without checking the internal opening of the transformer.

11 ... Primary winding, 12 ... Secondary winding, 13 ... Buckling deformation part

Claims (6)

Either one of the primary winding or secondary winding of the transformer is short-circuited to ground, a variable frequency voltage is applied to the opposite winding short-circuited to ground, the current flowing through the winding is measured, and the variable frequency voltage is measured. The current is divided by the current to obtain the impedance, and based on the impedance frequency characteristics, the eccentricity of the primary and secondary windings of the transformer, the buckling deformation of the secondary winding, the eccentricity and the buckling deformation An internal diagnosis method for a transformer characterized by diagnosing a composite state, an axial displacement of a primary winding and a secondary winding, or a composite state of the buckling deformation and the axial displacement. In the impedance frequency characteristic when the secondary winding of the transformer is short-circuited and a variable frequency voltage is applied to the primary winding, the first resonance point of the impedance frequency characteristic is on the higher frequency side than the impedance frequency characteristic in a normal state. When the impedance frequency characteristic of the frequency region higher than the first resonance point is shifted to a lower frequency side than the impedance frequency characteristic in the normal state, the primary winding and the secondary winding of the transformer are eccentric. The internal diagnosis method for a transformer according to claim 1, wherein diagnosis is performed. In the impedance frequency characteristic when the secondary winding of the transformer is short-circuited to ground and a variable frequency voltage is applied to the primary winding, the impedance frequency characteristic is lower than the impedance frequency characteristic in a normal state in a region above a predetermined high frequency. In the impedance frequency characteristic when shifted to the frequency side, and when the primary winding of the transformer is short-circuited to ground and the variable frequency voltage is applied to the secondary winding, the impedance frequency characteristic in a region above a predetermined high frequency 2. The internal diagnosis of a transformer according to claim 1, wherein when the voltage is shifted to a lower frequency side than the impedance frequency characteristic in a normal state, it is diagnosed as buckling deformation of the secondary winding of the transformer. Method. In the impedance frequency characteristic when the secondary winding of the transformer is short-circuited to ground and a variable frequency voltage is applied to the primary winding, the impedance frequency characteristic is lower than the impedance frequency characteristic in a normal state in a region above a predetermined high frequency. The minimum value of impedance between the first resonance point and the second resonance point is larger than the minimum value of the impedance frequency characteristic in the normal state, and the impedance frequency between the minimum value and the second resonance point is shifted to the frequency side. When the characteristic shifts to a lower frequency side than the impedance frequency characteristic in the normal state and the impedance value of the second resonance point is smaller than the impedance value of the impedance frequency characteristic in the normal state, the combined state of the eccentricity and the buckling deformation The internal diagnosis method for a transformer according to claim 1, wherein diagnosis is performed. The impedance minimum value between the first resonance point and the second resonance point is normal in the impedance frequency characteristics when the secondary winding of the transformer is shorted to ground and a variable frequency voltage is applied to the primary winding. The impedance frequency characteristic is larger than the minimum value of the impedance frequency characteristic in the state, and the impedance frequency characteristic between the minimum value and the second resonance point is shifted to the lower frequency side by a predetermined frequency width or more than the impedance frequency characteristic in the normal state. 2. The transformer internal diagnosis method according to claim 1, wherein when the impedance of the transformer is greater than or equal to a predetermined value, the axial displacement between the primary winding and the secondary winding is diagnosed. In the impedance frequency characteristic when the secondary winding of the transformer is short-circuited to ground and a variable frequency voltage is applied to the primary winding, a minimum value of the impedance between the first resonance point and the second resonance point; The impedance frequency characteristic between the second resonance point shifts to a lower frequency side than the impedance frequency characteristic in a normal state, shifts to a lower frequency side than the impedance frequency characteristic in a normal state in a high frequency region from the second resonance point, 2. The transformer internal diagnosis method according to claim 1, wherein when the impedance at the resonance point is equal to or greater than a predetermined value, diagnosis is made as a composite state of the buckling deformation and the axial displacement.

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