JP2017106893A - Method and device for diagnosing abnormality and deterioration in transformer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and a device capable of diagnosing abnormality in a transformer and a service life thereof.SOLUTION: A method for diagnosing a transformer analyzes oscillation response of the transformer in operation in a manner that obtains, using an oscillation detector with sensitivity for detecting oscillation of the transformer in operation in a range from low-frequency wave to audible sound (1 Hz to 20 kHz), either or both of character frequency of a several types of oscillation generated from the transformer during operation thereof due to electromagnetic force caused by electric current applied thereto through signal processing means using an electronic circuit or software and a mechanical oscillation phase with reference to a phase of excitation force due to the electric current applied to the transformer.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method and an apparatus capable of easily diagnosing a transformer internal abnormality and deterioration without stopping an operating transformer.

  Transformers are important equipment for power facilities. Since its service life is as long as several tens of years, it is important to diagnose whether the transformer is operating without problems during the period of use and to perform appropriate repairs before failure. In addition, it is important to ensure the reliability of the equipment by taking measures such as deterioration diagnosis and establishing a renewal plan to determine how long the equipment can be used in the future. Is desired.

Measuring the magnitude of vibration generated by a machine and judging the condition of the machine is a common means of machine equipment diagnosis, and “experimental mode analysis” is known as a means of analyzing machine vibration. (See Non-Patent Document 1).
In the experimental mode analysis, the test object is struck with a hammer to apply an impact, or a device called a vibrator is used to place it on a table that can be constantly excited at a single frequency, or contact. The method of letting it vibrate is adopted. The former method can be used to test how the DUT vibrates at the natural frequency and attenuates. In the latter method, the vibration test (frequency sweep excitation experiment) is performed with the frequency changed arbitrarily. Data related to excitation force and response (frequency response function) is obtained, and the natural frequency, natural mode, magnitude of damping ratio, etc. mixed in the data in a hidden form can be analyzed.

  Modeling the structure of a machine, creating a motion equation based on force balance and energy principle, and solving it to find the natural frequency and natural mode are called "theoretical mode analysis". However, in the theoretical mode analysis, it is difficult to solve the equation of motion analytically in a system with a large degree of freedom, and it is often analyzed using a finite element method.

In manufacturing a mechanical device, it is first to design the device so that it has the required functions. However, when a new device is operated, unexpected vibration and noise may be generated, and unexpected vibration and noise may make the device user uncomfortable. Therefore, in the business, improving the vibration and noise characteristics will differentiate the product from competitors. Therefore, in the transformer, devise measures to prevent vibration and noise from the design stage, Efforts are being made to measure vibration noise characteristics and reduce vibration and noise.
For transformers, each transformer manufacturer and each steel manufacturer have introduced measures to reduce noise in order to meet social demands for environmental protection and differentiation from other companies. For example, as shown in Non-Patent Documents 2 to 5, natural frequencies of iron cores, windings, tanks, etc. are analyzed from both experimental and theoretical viewpoints, and the natural frequency of the machine is close to twice the power supply frequency and resonates. Researches have been made to reduce noise by contriving to avoid this and by designing the shape of the core joint.

It is possible to hit the structure inside the transformer with a hammer or vibrate with a vibrator at the design and manufacturing stage of the transformer, but such a vibration test cannot be applied to a transformer in operation. . In view of this, a method has been proposed in which a current flowing through a transformer applies electromagnetic force to the iron core and winding in the transformer, and the inside of the transformer is diagnosed from vibration and sound generated from the iron core and winding.
In Patent Document 1, instead of hitting the transformer with a hammer, a magnetizing inrush current (several times the rated current) is passed through the transformer, an impact force is applied using the electromagnetic mechanical force generated thereby, and diagnosis based on the generated sound Has proposed.
Further, Patent Document 2 describes a method for measuring the natural frequency of a transformer by exciting an iron core and a winding by changing an excitation frequency stepwise in a predetermined frequency range instead of using a vibrator. . In this case, the transformer noise level for each excitation frequency is measured to obtain a frequency response function.

Japanese Patent No. 569298 JP 2008-82778 A Japanese Patent No. 2550066 JP 2010-271073 A JP-A-4-318905

Edited by Akio Nagamatsu, "Sound / Vibration Modal Analysis and Control", Corona Publishing, (1996) Masaaki Maejima, Minoru Kanai “Recent Transformer Noise Reduction Technology”, Hitachi review, vol.67 No.2 (1985) Kiyoto Hiraishi, Yashiro Hori, Shigeru Shida “Short-circuit strength of large-capacity transformer windings” Hitachi review, vol.51 No.6 (1969) Atsushi Katayanagi "Transformer tank vibration analysis" Takadake review, vol.56 No.1 (2011) Masato Mizogami and Yosuke Kurosaki “Changes in Noise and Magnetostriction due to Transformer Core Type” Electrical Theory, vol.134 No.5 (2014) IEEJ Technical Report, No. 1336 “Latest Trends in Transformer Abnormality Diagnosis Technology Using Electrical and Acoustic Techniques” (2015) Supervised by Motohachiro Tanaka and Yasuo Hori “Electromagnetic Vibration and Noise Design Method” Science Information Publishing Co., Ltd. (2015) Hirotaka Hanaomote, Tetsumi Takano, Noboru Urabe, Kenji Watanabe “Optical Epoxy Resin Degradation Diagnosis Technology for Mold Transformers”, Electronics Theory, Vol. 132 no. 11 (2012)

  In the prior art, the flow of the excitation inrush current and the excitation frequency in stages is caused by causing the transformer to generate multiple natural vibration modes and their natural frequencies (hereinafter referred to as mechanical system natural frequencies). This is because an excitation force having a plurality of frequency components is applied to the iron core and windings in the transformer in order to diagnose the transformer by obtaining the frequency). However, since such a test for passing a special current cannot be applied to an operating transformer, there is a problem that the operating transformer must be stopped for the test.

  Accordingly, an object of the present invention is to provide a method for diagnosing a transformer by analyzing a vibration response of the transformer in an operating state.

  The method for diagnosing internal abnormality and deterioration of a transformer of the present invention uses a vibration detector having a detection sensitivity from a low frequency region to an audible sound region (1 Hz to 20 kHz) for an operating transformer vibration, and an electronic circuit or software. The natural frequency of various vibrations generated from the operating transformer due to the electromagnetic force generated by the energizing current applied to the operating transformer is directly measured using signal processing means using Or the phase of the transformer vibration based on the phase of the excitation force due to the current applied to the transformer, or both, and the vibration response of the operating transformer is analyzed.

The present invention is characterized in that the state of the transformer in operation is analyzed by comparing the natural frequency and / or phase of the transformer vibration obtained previously with the vibration characteristics of the healthy transformer.
The present invention is characterized in that the state of the transformer in operation is analyzed by obtaining the natural frequency of the transformer component from the vibration phase of the power supply system obtained previously.
The present invention is characterized by analyzing the state of an operating transformer by capturing that a specific frequency component determined for each transformer changes from time to time in a vibration spectrum detected from the operating transformer. And
In the present invention, the transformer includes a winding that constitutes a coil body, an iron core, and a tank that accommodates them, and winding vibration generated by the winding due to an energization current during operation, and iron core vibration generated by the iron core, The tank vibration generated by the tank is separated and individually detected, and the vibration response of the transformer is analyzed.

  The transformer internal abnormality / deterioration diagnosis device according to the present invention has a detection sensitivity for vibrations from a low frequency region generated by the transformer to an audible sound region (1 Hz to 20 kHz) attached to the transformer in operation. A vibration detector having, an analyzer for receiving a detection signal from the vibration detector, an analyzer for obtaining a phase of mechanical vibration based on a phase of an excitation force caused by an energizing current to an operating transformer, and the analyzer And a calculation means for calculating the obtained data.

In the present invention, information on the natural frequency and / or phase of a healthy transformer is recorded in the calculation means, and the ability to compare the vibration information detected by the vibration detector with the vibration information of the healthy transformer. The configuration provided in the calculation means can be adopted.
In the present invention, the calculation means includes the capability of analyzing the state of the transformer in operation by obtaining the natural frequency of the transformer component from the phase of mechanical vibration obtained by the vibration detector. Can be adopted.
In the present invention, the vibration spectrum detected from the operating transformer by the vibration detector captures that the specific frequency component determined for each transformer changes over time, and changes the state of the operating transformer. A configuration in which the computing means has the ability to analyze can be adopted.
In the present invention, the transformer includes a winding constituting a coil body, an iron core, and a tank for housing them, and the vibration detector is caused by winding vibration generated by the winding due to an energization current during operation, and the iron core The iron core vibration generated by the tank and the tank vibration generated by the tank are separated and individually detected, and the arithmetic means has a function of analyzing the vibration response of the transformer.

According to the diagnostic method of the present invention, it is possible to externally diagnose internal abnormalities and deterioration without stopping the operating transformer.
Further, in the frequency response analysis in the electric vibration, the abnormality is diagnosed after the iron core and the coil are actually displaced, but the diagnosis method according to the present invention can diagnose the decrease in the tightening force of the coil winding. Therefore, it is a method that can grasp an abnormality before a deviation actually occurs, and is an excellent diagnostic method as a preventive maintenance method for a transformer.

The block diagram which shows 1st Embodiment of the apparatus which diagnoses the abnormality and deterioration of the transformer which concern on this invention. BRIEF DESCRIPTION OF THE DRAWINGS The example structure of the transformer made into a measuring object by this invention is shown, (A) is the perspective schematic diagram which fractured | ruptured one part, (B) is an expanded sectional view of a coil part. The block diagram of the 1 degree-of-freedom dynamic model used as a reference when approximating the vibration of a transformer winding and establishing a motion equation. The graph which shows an example of the vibration detection waveform by the laser displacement meter measured from the wall center vicinity of the transformer tank in operation. The graph which shows an example of the waveform obtained by Fourier-transforming the waveform shown in FIG. The graph which shows the waveform of the result of having extracted the 2nd harmonic (100 Hz component) of the power supply frequency from the waveform shown in FIG. The graph which shows the phase difference of the waveform which squared the power supply current waveform of the transformer, and normalized the 100Hz component, and the waveform shown in FIG. The figure which shows an example of the method of calculating | requiring the coefficient of a viscosity term using a high frequency component. The graph which shows an example of the waveform which carried out the Fourier transform of the output waveform of the AE sensor measured in the center of the wall surface of a tank in the transformer which is operating with a load factor of 60%. The graph which displayed the vertical axis | shaft on the logarithmic scale about the waveform shown in FIG. The graph which shows an example of the waveform which carried out the Fourier-transform of the output waveform of the AE sensor measured in the 65-cm downward position from the tank center when calculating | requiring the waveform shown in FIG. The graph which shows an example of the waveform which carried out the Fourier transformation of the output waveform of the AE sensor measured in the center of the wall surface of a tank in the transformer which is operating with a load factor of 30%. The figure explaining an example of the measurement by a compensation method. The perspective view which shows the outline | summary of the transformer tank applied to the test in an Example. 14A and 14B show vibration modes of the iron core housed in the transformer tank shown in FIG. 14, wherein FIG. 14A is a perspective view showing a torsion mode, FIG. 14B is a perspective view showing a bending mode 1, and FIG. FIG. Explanatory drawing which shows the position which attached the sensor to the upper right side wall of a transformer tank in an Example. The graph which shows the value which carried out the Fourier-transform of the vibration measurement result at the time of the actual operation of the transformer tank obtained in the Example, and at the time of vibration.

<First Embodiment>
Hereinafter, a first embodiment of a transformer abnormality and deterioration diagnosis method and diagnosis apparatus according to the present invention will be described with reference to the drawings, taking an oil-filled transformer as an example.
FIG. 1 is a configuration diagram showing a first embodiment of a device for diagnosing abnormality and deterioration of a transformer. A diagnosis device A of this embodiment is an example of an abnormality of an oil-filled transformer 1 having a structure shown in FIG. It is a device that diagnoses deterioration.
In the oil-filled transformer 1 of this example, a plurality of winding-type coil bodies 3 are accommodated in a tank 2 with their central axes facing up and down, and the tank 2 is filled with insulating oil. An iron core 5 made of a magnetic material such as a silicon steel plate is inserted through the center of each coil body 3, and each iron core 5 is integrated with a rod-shaped yoke portion 6 made of a magnetic material such as a silicon steel plate at the upper and lower ends. ing.
A frame-shaped clamp part 7 is provided so as to surround both ends of each iron core 5 and the periphery of the yoke part 6, and a clamp 8 is extended and formed on the upper and lower clamp parts 7 as shown in FIG. Then, the coil bodies 3 are sandwiched from above and below by the upper and lower fastening fittings 8, and a tightening force is applied to each coil body 3.

In this embodiment, the coil body 3 includes an outer coil 9 and an inner coil 10 as shown in FIG. 2B, and the outer coil (primary coil) 9 has an outer winding (primary winding) 11 and an insulating spacer. A laminated body in which (solid insulator) 12 is vertically stacked is sandwiched between an upper insulator 13 and a lower insulator 15. The inner coil (secondary coil) 10 is configured by sandwiching a laminated body in which an inner winding (secondary winding) 16 and an insulating spacer (solid insulator) 17 are vertically stacked between an upper insulator 18 and a lower insulator 19. Has been.
By sandwiching the upper insulators 13 and 18 and the lower insulators 15 and 19 with the upper and lower clamping brackets 8, a clamping force is applied to each coil body 3 from above and below, and in this state, the coil bodies 3 are immersed in insulating oil. ing.
Further, a bushing (not shown) for inputting / outputting electric power is formed on the ceiling or the side surface of the tank 2.

Since the transformer 1 having the above-described configuration is used for the purpose of stepping down a high voltage sent from a transmission line or the like near a power user, a current is always passed through the windings 11 and 16. Since an electromagnetic force acts by passing a current through the windings 11 and 16, the electromagnetic force acts on the coil body 3 and the iron core 5, and these vibrate. This vibration is transmitted to the entire transformer 1, and is also transmitted to the side wall 2A, the bottom wall 2B, and the ceiling wall 2C of the tank 2.
In addition, when a short circuit accident or a ground fault occurs in the transmission line, a large current that reaches 10 to several tens of times the rated load current may flow through the windings 11 and 16 of the transformer 1. Force and vibration may act on the transformer 1.
Due to these various factors, the insulating oil of the transformer 1 gradually deteriorates with time. In addition, since the insulating spacers 12 and 17 on which the tightening force and vibration always act are made of cellulose fiber, there is a risk of deterioration, and the windings 11 and 16 are also subject to unexpected deterioration due to a short circuit accident or a ground fault. May occur.
As described above, the transformer 1 may be deteriorated in each part when used for a long period of time.

  A diagnosis apparatus A for abnormality and deterioration of a transformer 1 shown in FIG. 1 receives and amplifies a vibration detector (vibration sensor) 22 disposed along the transformer 1 and an output signal from the vibration detector 22. An amplifier (vibration sensor amplifier) 25, a signal analyzer (phase difference detector) 26 that receives an output from the amplifier 25, and an arithmetic unit 27 connected to the signal analyzer 26 are mainly configured. In the diagnostic apparatus A, a voltmeter (energized voltmeter) 23 for measuring a voltage for energizing the transformer 1 and a signal analyzer 26 are connected to the voltmeter 23 via an amplifier (energized voltage amplifier) 24.

The vibration of the transformer 1 is analyzed by the procedure described below using the diagnostic device A shown in FIG. 1, but the basic theory according to the experimental mode analysis used when the diagnostic device A of the present embodiment diagnoses abnormality and deterioration. Is described below.
First, an equation of motion is established by approximating the vibration of the transformer winding to a forced vibration with damping in a one-degree-of-freedom system. The mass of the winding is represented by m, the stiffness is represented by k, and the viscosity is represented by c (attenuation coefficient). When the stiffness k is displayed with a spring and the viscosity c is displayed with a damper, it is as shown in FIG. This degree of freedom dynamic model is described in Non-Patent Document 1.
The displacement at time t is expressed as x (t), and the equation of motion in the case of applying a harmonic excitation force of magnitude F and angular frequency ω can be expressed by the following equation (1).

  When the displacement x in the above equation (1) is solved by assuming the following equation (2), the following equations (3) and (4) are obtained.

Here, in the equations (3) and (4), Ω = (k / m) ^1/2 represents the unattenuated natural angular frequency, and β = ω / Ω represents the angular frequency of the external force and the unattenuated natural angular vibration. Number ratio, c _c = 2 (m / k) ^1/2 represents a critical damping coefficient, and ζ = c / c _c represents a damping ratio (ratio of viscous damping to critical damping coefficient).
The equation (4) can be developed into the following equations (5) to (9) as a vibration equation of an angular frequency ω whose phase is delayed from the harmonic excitation force.

  In the equation (9), the phase difference φ is given by the following equation (10).

  Therefore, the displacement X assumed in the equation (2) is given by the following equation (11).

  The equation (1) is a non-homogeneous linear differential equation because the right side is not zero. The general solution of the inhomogeneous linear differential equation can be written as the sum of the general solution of the linear homogeneous equation and one special solution that satisfies the inhomogeneous equation. The equation (4) is one special solution that satisfies the equation (1) of the inhomogeneous equation. Here, the linear homogeneous equation is given by the following equation (12).

  When the general solution of the equation (12) is obtained, the following equation (13) is obtained.

  In the formula (13), there is a relationship of the following formula (14).

The equation (14) has a square root, and a different phenomenon appears depending on whether the contents are positive or negative.
In the case of ζ ≧ 1, both λ ₁ and λ ₂ are negative real numbers, and become non-periodic motion that decreases in size with time and approaches zero. Therefore, in this case, the general solution of the equation (1) is expressed as the sum of the vibration at the angular frequency ω of the harmonic excitation force given by the equation (11) and the aperiodic motion given by the equation (13). Is done.
When ζ <1, σ = Ωζ: damping rate, ω _D = Ω (1-ζ ² ) ^1/2 : when the damped natural angular frequency is introduced, the above equation (13) is expressed by the following equation (15): be able to.

Therefore, in this case, the general solution of the equation (1) has two angular frequencies ω _D of the harmonic excitation force given by the equation (11) and the damped natural angular frequency ω _D given by the equation (15). It becomes a vibration with a component.
On the other hand, the equation of motion when the external force {f} acts on the N degrees of freedom system is expressed by the following equation (16).

However, in the above equation (16), [M] represents a mass matrix, [C] represents an attenuation matrix, and [K] represents a stiffness matrix, each of which is an N-dimensional square matrix.
In general, if there are _N mutually independent vector groups {φ ₁ } to {φ _N } in an N-dimensional space, a coordinate system based on them can be formed, thereby expressing an arbitrary N-dimensional vector. The expression is expressed by the following equations (17) and (18).

If the N-degree-of-freedom system is considered to form an N-dimensional space, it is an N-dimensional vector group having general orthogonality with respect to the mass matrix [M], the damping matrix [C], and the stiffness matrix [K]. A coordinate system serving as a reference vector can be formed.
Then, the equation of motion (16) of the N-degree-of-freedom system results in the following equation of motion (19) of the one-degree-of-freedom system regarding the r-th eigenmode.

In the equation (19), m _r = {φ _r } ^T [M] {φ _r }: mode mass, c _r = {φ _r } ^T [C] {φ _r }: mode damping coefficient, k _r = { ψ _r } ^T [K] {ψ _r }: Mode rigidity.
When a harmonic excitation force having an angular frequency ω and an amplitude Fi acts only on the degree of freedom i in the multi-degree-of-freedom system, the external force vector {f} is F _i e ^jωt in the _i- th row and all other terms. Becomes zero. Substituting this into the equation (19) yields the following equation (20).

In the equation (20), ψ _ri is a term in the i-th row of the _r-th eigenmode {ψ _r }.
The equation (20) has the same format as the equation (1) in the one-degree-of-freedom system.
Assuming that the solution ξ _r is expressed by a harmonic function, the solution for the r-th eigenmode is expressed by the following equation (21).

  By substituting this into the equation (18) and taking the sum for all eigenmodes, the following equation (22) can be obtained as a solution on spatial coordinates.

  The equation (16) is an asymmetric linear differential equation because the right side is not zero. The general solution of the equation (16) can also be described as the sum of one special solution that satisfies the general solution of the linear homogeneous equation and the inhomogeneous equation. The equation (22) is one special solution that satisfies the equation (16), which is an inhomogeneous equation. Here, the linear homogeneous equation is given by the following equation (23).

  A general solution of the equation (23) is obtained. The case where the attenuation matrix [C] is proportional viscosity attenuation as expressed by the following equation (24) can be considered as follows.

  Here, the displacement is assumed to be the following equation (25).

  Then, the equation (23) can be expressed by the following equation (26).

  Here, if the formula (24) is substituted into the formula (26) and the following formula (27) is substituted, the formula (23) becomes the following formula (28).

  Here, by substituting p obtained by solving equation (28) into equation (27), r-order λr is obtained as in the following equation (29).

  Here, the natural angular frequency is expressed by the following equation (30), the mode damping rate is expressed by the following equation (31), the damped natural angular frequency is expressed by the following equation (32), and the r th order: The mode damping ratio is expressed by the following equation (33).

From the above, the general solution of the equation (16) is the damping angle natural angular frequency appearing in the equation (32) showing the angular frequency ω of the harmonic excitation force given by the equation (22) and the damping natural angular frequency. This is a vibration having a component of ω _rd .

On the other hand, the propagation path of vibration and noise generated by the transformer in the operating state is described in Non-Patent Document 2 described above.
The primary causes of vibration and noise are the vibration of the iron core and the vibration of the winding, and both vibrations propagate to the tank and others. Therefore, the vibration of the transformer tank is a combination of the iron core vibration, the winding vibration and the vibration of the tank itself. When diagnosing the state of the iron core, the iron core vibration component of the energized noise vibration is evaluated, and when diagnosing the state of the winding, the winding vibration component is evaluated. Each of the iron core vibration and the winding vibration has a natural frequency.
A resonance phenomenon occurs when the natural frequency is close to the frequency of the power supply system. The excitation force has the largest component of twice the power supply frequency, but there is also an excitation force that is an odd or even multiple of the power supply frequency, and the natural frequency of iron core vibration, winding vibration or tank vibration is other than twice the power supply frequency. May be larger than the vibration of the double component of the power supply frequency. By measuring the natural frequency of the mechanical system with respect to the excitation force of the power supply system, it is possible to diagnose abnormality inside the transformer and deterioration. Further, when it is difficult to directly measure the natural frequency because the natural vibration amplitude of the mechanical system is small, etc., the natural frequency of the mechanical system is obtained by analyzing the phase difference of the forced vibration. As described in 3, the internal abnormality and deterioration diagnosis of the transformer can be performed.
That is, it is possible to analyze the state of the transformer in operation by obtaining the natural frequencies of the transformer components (the natural frequencies of the iron core vibration, the winding vibration, and the vibration of the tank itself).

Basically, the excitation force is a component twice the power frequency. However, it is considered that vibrations having various natural frequencies are induced due to distortion of power supply voltage, distortion of generated magnetic force, distortion of transmitted force, and the like.
A procedure for dividing the vibration of the tank 2 in the transformer 1 into three components of iron core vibration, winding vibration and tank vibration will be described. It is assumed that the principle of superposition holds for three-component vibration.
When vibration is measured at the center of the tank wall, the tank vibration having an even number of antinodes in the vertical direction or the horizontal direction becomes a node of vibration, and only the tank vibration component having an odd number of antinodes in both the vertical and horizontal directions. Therefore, when vibration is measured at the center of the tank wall surface, the vibration waveform is a superposition of the tank vibration component having the odd antinodes in both the vertical and horizontal directions, the iron core vibration and the winding vibration. Next, if vibration is measured at a position slightly below the center of the tank, tank vibration with an even number of antinodes in the vertical direction or horizontal direction, which has disappeared in the center of the tank, is measured, and tank vibrations with odd antinodes in both the vertical and horizontal directions are measured. The component has a small amplitude.

On the other hand, the magnitudes of iron core vibration and winding vibration do not change. By measuring by changing the position of the tank surface in this way, the natural vibration component can be grasped for all the tank vibrations, and the remaining is the separation of the iron core vibration and the winding vibration.
The magnetic flux in the iron core does not change depending on the presence or absence of the load current, so the iron core vibration does not change, but it is described on page 87 of Non-Patent Document 6 that the vibration of the winding changes in proportion to the square of the current. ing. Therefore, if the vibration is measured by changing the load current and the load dependency is used, it is possible to separate the iron core vibration and the winding vibration and measure each vibration waveform.

"Analysis of winding vibration"
Next, an analysis example of winding vibration will be described.
The life of a general oil-filled transformer is considered to be a state in which the insulating paper of the coil cannot withstand the electromagnetic mechanical force applied to the transformer coil winding when a short circuit failure occurs outside the transformer.
On the other hand, an electromagnetic force (external thrust) repelling the primary winding (outer winding) and the secondary winding (inner winding) also acts in the axial direction of the winding when a short circuit failure occurs. When the insulator inserted in the winding part shrinks in size due to aging and the tightening force of the winding decreases, the axial winding structure may be damaged by the external thrust. Such a state is also considered the life of the transformer. When the tightening force is reduced and the winding is loosened, the noise from the winding increases.
According to the description in Patent Document 4, it is explained that when the tightening torque value of each part of the transformer becomes smaller than a specified value, the level of each frequency component in the normal state is greatly deviated from the distribution range.

Next, the excitation force applied to the winding of the transformer will be described.
Current flows in the opposite direction in the inner winding 16 and the outer winding 11 of the transformer winding, thereby forming a leakage magnetic field. The electromagnetic force applied to the winding is a Lorentz force and acts on the current and the magnetic field in directions perpendicular to each other. The axial electromagnetic force is a compressive force in both the inner winding 16 and the outer winding 11, and the electromagnetic force is proportional to the square of the current. Therefore, the frequency of the axial excitation force is twice the frequency of the current (that is, the power supply frequency).
A decrease in the tightening force of the windings 11 and 16 appears as a change in the natural frequency of the windings. Therefore, the vibration component included in the winding vibration may be clarified by the experimental mode analysis directly or using a compensation method described later. Direct means that the vibration component is clarified by Fourier transforming the raw waveform of the AE sensor or the acceleration sensor.

Next, the natural frequency of the winding can be obtained with respect to the frequency of the power source from the phase difference φ (the difference in phase of the transformer vibration based on the phase of the exciting force due to the energizing current). It is assumed that a vibration mode having a large signal intensity due to twice the power supply frequency or the influence of resonance is the r-th mode. When the phase difference with respect to the r-th mode is φr, the r-th natural frequency Ω _r of the winding can be calculated by the following equation (34) using the above-described equation (10). At that time, the attenuation coefficient _cr is obtained from another experiment.

Although the amplitude of the vibration of the transformer is small, free vibration can be obtained directly or by measurement using a compensation method and a lock-in amplifier described later.
The method for obtaining the damping coefficient c is a method for measuring a mode i having a natural frequency several times larger than the frequency of the excitation force. Although the value of the damping coefficient c is considered to be different for each mode, the frequency of the excitation force can be approximated by that value.
In this case, the damping coefficient c _i is obtained from the damping motion of several cycles that appear before the excitation force passes one cycle. FIG. 8 is an explanation of the waveform.
In general, the amplitude of a damped free vibration waveform attenuates exponentially. Therefore, it is considered that the logarithm of the ratio of adjacent amplitudes always takes a constant value, and the natural logarithm of the ratio of adjacent amplitudes is called a logarithmic attenuation rate δ _i . When the n-th amplitude at time t _n is a _n , and similarly n + 1,..., N + m-th amplitude is a _{n + l} ,..., _{An + m} , the logarithmic decay rate δ _i is defined by the following equation (35).

If it is approximated that δ _r is equal to δ _i , the r-th order mode damping ratio ζ _r is obtained by the following equation (36).

Thereby, the attenuation coefficient _cr is obtained by the following equation (37).

  Incidentally, the relationship between the natural frequency of the winding and the tightening force is given by the following equation (38).

  Here, L represents the length of the winding in the axial direction, and ρ represents the linear density when the winding is regarded as a distributed constant system. Further, the tightening force T can be obtained by the following equation (39) from the equations (34) and (38).

The natural frequency of the winding can also be obtained by dividing the damped natural angular frequency of the equation (32) in free vibration by 2π using the mode damping ratio.
However, when the transformer is relatively close to a new one, the winding tightening force is sufficiently large and vibration is less likely to occur. That is, it is considered that the damping coefficient c is larger than the critical damping coefficient c _c and the damping ratio ζ is larger than 1. In that case, vibration related to the natural frequency does not occur, and a non-periodic damping motion occurs. As a result, even if forced vibration is applied, vibration components other than the frequency of forced vibration are not generated. Even in such a case, if the method measures the phase delay, information on the natural frequency can be obtained.

When the tightening force T obtained by the equation (39) is equal to or higher than the design lower limit value of the transformer, it is diagnosed that the degree of deterioration of the transformer is healthy, and when it falls below the design lower limit value, the probability of destruction due to external thrust increases. Therefore, it can be diagnosed that the degree of deterioration of the transformer has reached the end of its life.
As an example, the analyzer 26 and the computing device 27 shown in FIG. 1 are composed of a personal computer, the computing device 27 is a CPU, and a storage device such as a memory or a hard disk is mounted on the analyzer 26. The information on the tightening force T of the transformer in a healthy initial state is stored. Each of the above equations is recorded in the storage device of the analyzer 26, and information such as the natural frequency of the winding obtained from the measurement result is recorded in the storage device of the analyzer 26. Contrast with clamping force is made.
A comparison table is recorded in the storage device of the analyzer 26 according to a healthy initial state of the transformer clamping force and how much reduction is observed with respect to the clamping force. When it is found that the decrease in the tightening force actually measured and calculated by the arithmetic device 27 is lower than the initial state, it is diagnosed whether the deterioration degree of the transformer has reached the end of its life. . The diagnostic reference value is set individually for each transformer. The diagnosis reference value is recorded in the storage device of the analyzer 26, and the life of the transformer can be diagnosed by comparing the measurement result of the arithmetic unit 27 with the table.

When obtaining the natural frequency of the mechanical system from the phase difference, if the deterioration of the insulator used in the winding is minor, the main transformer vibration is twice the vibration of the power supply frequency (double vibration). It is better to analyze by focusing on the phase difference of the double vibration.
However, if the natural frequency of the mechanical system is close to a frequency that is an integer multiple different from the frequency that is twice the power supply frequency, a larger vibration amplitude may be given due to the effect of resonance. It may be better to analyze the frequency component of.

  If the tightening force is reduced, it is thought that vibration due to the electromagnetic force acting in the radial direction of the winding will occur in addition to the electromagnetic force acting in the axial direction of the winding. It is thought that the amplitude of increases. Therefore, it is effective to analyze a transformer that has deteriorated by paying attention to the amplitude of higher-order vibration components.

The transient vibration due to the higher-order natural vibration mode is considered to be a vibration component added to the steady vibration shown by the equation (22), and is given by the equation (25).
In this embodiment, the Lorentz force generated by energization of the transformer is used as the excitation force. However, the excitation force is only one frequency component and cannot be an efficient excitation force for all vibration modes. there is a possibility. However, when the winding tightening force becomes weak in a transformer that has deteriorated, the winding will loosen, and the excitation force of simple vibration will be distorted and transmitted, and various modes of vibration will be induced. Conceivable.
Therefore, it can be diagnosed that the insulator used in the winding portion is deteriorated by grasping that the amplitude of the higher-order vibration component becomes larger than the double vibration amplitude. In this case, it is considered that the higher-order vibration component has a phase lag determined by the oscillating force transmitted in a distorted manner.
Therefore, by removing background noise whose phase is not constant, it is possible to grasp high-order vibration components that cause a phase lag determined by the distorted transmitted vibration force, and to use the insulator used in the winding section. It is possible to capture the increase in amplitude of higher-order vibration components related to the deterioration of.
However, the internal stress in the transformer manufacturing stage may be eased over time, and the higher-order vibration amplitude may be reduced. The cause of the change must be interpreted to diagnose the transformer. Therefore, the fact that the specific frequency component determined for each transformer changes with time is captured, and the state of the operating transformer is analyzed and diagnosed. The diagnostic reference value is set individually for each transformer.
As an example, if the analyzer 26 shown in FIG. 1 analyzes the graph of the measurement result and recognizes an increase in high-order natural vibration, the degree of deterioration of the transformer 1 is calculated. The increase rate of higher-order natural vibration is recorded in advance in the storage device of the analyzer 26 according to the degree of deterioration, and how much is the deterioration degree of the transformer according to the increase rate calculated by the arithmetic unit 27? In addition, it is diagnosed whether the life as a transformer has been reached.

An AE (acoustic emission) sensor having a wide frequency characteristic can be used to widely analyze from a low-order double vibration component to a high-order natural vibration component. Alternatively, low frequency and high frequency can be used in combination with high sensitivity AE sensors. Alternatively, a highly sensitive AE sensor can be used in combination for each specific frequency.
Moreover, if it is a sensor which measures a vibration, it is not limited to an AE sensor, and it is analyzed by an acceleration sensor, a method of measuring vibration with a sound wave, or a method of directly measuring vibration of a transformer tank wall surface with a laser displacement meter. Is also possible.

"Analysis of iron core vibration"
Next, an analysis example of iron core vibration will be described.
The iron core is vibrated by the magnetostriction of the electrical steel sheet. Magnetostriction generates vibration twice each time the direction of the magnetic field changes, that is, for one cycle of the energizing current. The iron core of the transformer is screwed or tightened with a band. If a transformer is used for many years, the screw may loosen due to repeated vibrations and temperature changes, and the tightening force may be reduced.
Due to the magnetostriction of the electromagnetic steel sheet, the yoke (yoke) and the leg (core) of the iron core are shaken and vibrated (see Non-Patent Document 6). When the tightening force of the iron core is reduced, vibration occurs and noise increases.
A slight air layer is present at the joint of the iron core, and the magnetic flux passes through the steel plates avoiding the air portion, so that an attractive force acts between the steel plates. The laminated steel plates are not completely flat but are in partial contact, and act as a spring as a whole in the lamination direction. The spring constant varies depending on the tightening force. Further, when the tightening force becomes weak, slip occurs between the steel plates, and the damping coefficient becomes small.
Therefore, when the tightening force changes, the natural frequency changes as a change in the spring constant or damping coefficient. By detecting changes in the natural frequency and damping coefficient, it is possible to diagnose abnormalities and deterioration such as a decrease in the tightening force of the iron core.
As an example, if the analyzer 26 shown in FIG. 1 analyzes the graph of the measurement result and recognizes the degree of decrease in the clamping force, the degree of deterioration of the transformer 1 is calculated. The decreasing rate of the clamping force is recorded in advance in the storage device of the analyzer 26 according to the decreasing rate, the degree of deterioration of the transformer according to the decreasing rate, and the life as the transformer Diagnosed whether or not
The diagnostic reference value is set individually for each transformer.

"Analysis in case of dry transformer"
Next, diagnosis by vibration analysis of a dry transformer will be described.
The dry type transformer is also called a molded transformer, and is obtained by immersing the inside of the transformer with an epoxy resin of insulation instead of insulating oil and curing it. Therefore, the main deterioration factor of the dry transformer is thermal deterioration of the epoxy resin (see Non-Patent Document 8).
When the epoxy resin is thermally deteriorated, the mechanical strength is lowered, and when a crack is generated by an external force such as a short circuit current or an earthquake, there is a possibility of causing a dielectric breakdown. When the epoxy resin is thermally deteriorated, the natural frequency of the transformer changes due to the evaporation of the epoxy resin and a decrease in mass.
Therefore, it is possible to diagnose abnormalities and deterioration of dry transformers by vibration analysis. In the case of a mold transformer in which the core and winding are combined and cured with resin, the vibration of the container surface is measured.
In the case of a mold transformer in which the core and winding are separately resin-cured, or a mold transformer in which only the winding is resin-cured, the iron core and the winding vibrate separately, so the surface of the iron core and the winding It is possible to measure vibration individually and to diagnose abnormality and deterioration of iron core and winding as well as oil-filled transformer.
As an example, record the initial vibration state of the transformer core and winding individually in the storage device of the analyzer 26 shown in FIG. 1 and compare it with the actual measurement results in accordance with the changed ratio. Thus, it is possible to diagnose the degree of deterioration of the transformer and whether or not the lifetime of the transformer has been reached.

In order to solve the above-mentioned conventional problems, in this embodiment, in the transformer in the operating state, the amplitude and phase of the vibration are measured and compared with the amplitude and phase of the power supply voltage. It is a method of diagnosis. There is no need to pass a special current for diagnosis.
In the present embodiment, only the electromagnetic force generated by energization of the transformer in the operating state is used as the source of the excitation force that vibrates the iron core or winding of the transformer. Therefore, in Patent Document 2, the excitation frequency is equal to the commercial frequency only, and the diagnosis method of this embodiment is partially similar to the method described in Patent Document 2, but in Patent Document 2, This is a method of analyzing the natural frequency by combining the measurement results for each frequency obtained by changing the frequency step by step.
On the other hand, in the diagnosis method of the present embodiment, the energization frequency causing vibration is basically only one that is twice the power supply frequency, which is a major difference. Paying attention to this excitation force, it is important to capture various vibrations generated according to the tightening state of the iron core and windings and the state of thermal deterioration of the epoxy resin and compare it with the energization frequency.

In this embodiment, the power supply current that causes vibration is only one frequency component, but various modes are involved due to distortion of power supply voltage, distortion of generated magnetic force, distortion of transmitted force, etc. It is thought that the vibration of is induced.
The power supply voltage is ideally a sine wave, but it is conceivable that the sine wave is distorted and the excitation force itself includes harmonics depending on the power supply stage and the content of the load side connected device.
For iron core vibration, the magnetic field generated by the excitation current is the source of the iron core vibration, but the magnetic flux density includes harmonics due to the nonlinearity of the magnetic saturation curve of the iron core. In addition, there is nonlinearity between the magnetization and magnetostriction of the iron core, and an excitation force having a frequency component different from the power supply voltage is also induced.
In the case of winding vibration, Lorentz force is generated from the leakage flux of the winding and the current flowing in the winding, but the leakage flux is distorted from sinusoidal changes due to the wiring and bias of the winding method, An excitation force having a frequency component different from the power supply voltage is also induced.

In a general transformer, the iron core is laminated with thin electromagnetic steel plates and screwed or fastened with a band. Further, the winding is tightened through a tightening screw. The iron core or winding that receives the tightening force is equivalent to a kind of spring, and its spring constant varies depending on the tightening force, and due to non-uniformity of the tightening force, the tightening force is distorted and transmitted, which is different from the excitation force. Induces frequency component vibration. Therefore, it is possible to obtain information on the natural vibration mode of a frequency component different from twice the power supply frequency without passing a special current for diagnosis.
In that case, the main frequency component of the excitation force is an integer multiple of the power supply frequency (referred to as the natural frequency of the power supply system), and the even multiple component is larger than the odd multiple component, and in many cases in a healthy transformer Has the largest double component. In addition, the frequency component is small but includes any frequency component other than an integral multiple of the power supply frequency, and excites free vibration of the iron core and windings.

Further, as the transformer deteriorates, the tightening force is weakened, and the vibration component having a frequency different from the excitation frequency is increased. Therefore, if the insulator used in the winding part is deteriorated by grasping that the vibration amplitude of other vibration components becomes larger than the double vibration amplitude (100 Hz when the power supply frequency is 50 Hz). Can be diagnosed.
In this case, it is considered that other natural vibrations have a phase lag determined by the oscillating force transmitted in a distorted manner. Therefore, by analyzing in pairs with the phase information, it is possible to remove the background noise whose phase is not constant and capture the increase in the amplitude of other vibration components limited to the vibration generated by the energized current.
Captures the fact that the amplitude of other vibration components in the audible sound region of the vibration spectrum detected from the operating transformer increases with respect to the magnitude of the frequency component of the excitation force due to the energized current. Analyzing the state of the transformer is a method of diagnosing abnormalities and deterioration inside the transformer as described above.

  A method for diagnosing abnormalities and deterioration inside a transformer by simply measuring noise during operation of the transformer without supplying a special current for diagnosis has been proposed. Patent Document 3 discloses a method of diagnosing a machine abnormality by detecting the sound pressure of the machine and comparing it with a preset reference spectrum. Further, in Patent Document 4, when an abnormality occurs due to, for example, an iron core or a bolt tightening a winding being loosened in a transformer, the sound produced by the device changes, and the sound pressure level of each frequency component is within the normal range. It is described that it will deviate significantly. These diagnosis methods are methods for diagnosing abnormality or deterioration when the difference between the acoustic pattern at normal time and the acoustic pattern at abnormal time is large, and is completely different from the mode analysis.

  The method for comparing the normal and abnormal acoustic patterns is to set the upper and lower thresholds of the sound pressure level as described in Patent Document 4, and to diagnose by the ratio of data exceeding the range. In this case, there is a possibility that background noise is superimposed and erroneous determination occurs, and there is a problem that the accuracy of diagnosis is lowered because it is necessary to increase the width of the upper and lower thresholds.

In the case of this embodiment, since the phase of the excitation force due to the energizing current is used as a reference, it is possible to eliminate background noise unrelated to the energizing current and prevent a decrease in diagnostic accuracy. Moreover, the phase difference φ of the forced vibration can be easily estimated by comparing the amplitude information that changes depending on the amplification of the measurement system and the phase of the energized power source.
Furthermore, if the state of the operating transformer is analyzed by comparing the mechanical vibration phase obtained above with the healthy transformer vibration phase, the phase difference is compared with the initial transformer data. If there is a change, it can be diagnosed that some internal abnormality or aging has occurred. However, the initial data needs to measure the load current dependency and to check the balance between the iron core vibration and the winding vibration. It is also possible to collect initial data at a later date using the same type of transformer.

Non-Patent Document 6 describes a technique for diagnosing abnormality of a transformer by an acoustic method. When partial discharge occurs inside the transformer, it detects ultrasonic waves that are generated at the same time by the AE sensor, which is different from the method described in the previous section for determining the state of the machine by the experimental mode analysis in mechanical vibration. .
Non-Patent Document 6 describes a transformer diagnostic technique based on frequency response analysis (FRA). The frequency response referred to in Non-Patent Document 6 is a method of measuring a transfer function by applying a sinusoidal voltage and sweeping the frequency. When the transformer core or coil is displaced due to a decrease in the tightening force or due to external force, or when the ground is disconnected, the electrical impedance changes, so the short-circuit impedance or winding leakage inductance changes. This is a focused diagnostic method, which is also different from the method of determining the state of the machine by the experimental mode analysis in the mechanical vibration described above.

Example 1
Laser displacement meter near the center of tank wall of oil-filled transformer (3-phase, rated capacity 200kVA, rated current 550A, operation 9 years, Mitsubishi Electric RA-TN type) operating at 50Hz (load factor 10%) The output waveform of Keyence Corporation LK-G5000) was measured. The wall surface of this transformer tank is about 80 cm in height, and the region where the vibration is the smallest is the central portion of the tank wall surface, which is considered as a tank vibration node.
FIG. 4 shows an example of the output waveform of the laser displacement meter. The waveform shown in FIG. 4 shows a waveform in which a waveform having a frequency of 100 Hz, which is twice the power supply frequency, is superimposed on a basic waveform of about 10 Hz.
An example of a waveform obtained by Fourier transforming the waveform shown in FIG. 4 is shown in FIG. In FIG. 5, the large peak waveform appearing in the portion of about 10 Hz was judged as noise due to the influence of the wind hitting the transformer, and was deleted in the following analysis.
The power supply frequency of the transformer is 50 Hz, and has a peak at an integral multiple of the frequency. The 100 Hz component that is twice the power supply frequency is the basis of the excitation force, and the component that is an integral multiple of 100 Hz is forced vibration by the power supply system. Although a large vibration of about 10 Hz is also seen in FIG. 5, this vibration is a forced vibration due to a wind at the time of measurement other than the power supply system, so this vibration was excluded from the future analysis.

  Next, a waveform obtained by extracting a double wave (100 Hz component) of the power frequency from the laser displacement meter output waveform of FIG. 4 using a lock-in amplifier is the waveform of FIG. The amplitude is normalized to 1. This transformer vibration includes iron core vibration in addition to winding vibration. The load factor at the time of measurement was about 10%.

  Next, FIG. 7 shows the phase difference between the waveform (dotted line) obtained by squaring the power supply current waveform and standardizing the amplitude of the 100 Hz component to ± 1, and the transformer vibration (solid line). The numerical value of the phase difference can also be obtained using a two-phase lock-in amplifier. If there is a change with respect to the phase difference compared to the initial data with a load factor of 10%, it can be diagnosed that some internal abnormality or aging has occurred.

(Example 2)
Output waveform of AE sensor near the center of tank wall of oil-filled transformer (3-phase, rated capacity 12MVA, primary side 11kV, secondary voltage 3.45kV, operation 33 years) operating at 50Hz (load factor 60%) FIG. 9 shows a result obtained by plotting the frequency with a frequency scale on the horizontal axis and the amplitude on the vertical axis with a linear scale. A peak that is an integral multiple of the power supply frequency appears.
As the transformer deteriorates, the proportion of high-frequency components increases, so the amplitude of higher-order vibration components within the audible band of the vibration spectrum of the transformer tank is the frequency of the excitation force due to the energized current ( If it is understood that it becomes larger with respect to the magnitude of the component (twice the power supply frequency), the internal abnormality diagnosis and deterioration diagnosis of the transformer can be performed.

FIG. 10 shows the result of redisplaying the measured waveform shown in the graph of FIG. 9 with the vertical axis as a logarithmic scale. In addition, FIG. 11 shows the result of measuring the tank sidewall measurement position by the AE sensor by about 65 cm lower than the center position of the tank sidewall (height 260 cm), and the measurement result with the load on the transformer set to 30%. As shown in FIG.
As shown in FIG. 10, the one-dot chain line peak indicates the peak due to the iron core vibration, the chain line peak indicates the tank vibration peak, and the two-dot chain line peak indicates the winding vibration peak. In the measurement results, it is unclear which part is in the vibration mode.
When the power supply frequency is 50 Hz, a peak appears at a frequency that is an integral multiple of 50 Hz, as shown in FIG. The 100 Hz component that is twice the power supply frequency is the basis of the excitation force, and the component that is an integral multiple of 100 Hz is forced vibration by the power supply system. In FIG. 9 in which the amplitude is plotted on a linear scale, a conspicuous peak can be seen only by forced vibration by the power supply system. However, in FIG. 10 showing the logarithm of the amplitude, a peak is seen in addition to the frequency that is an integral multiple of 50 Hz, which is considered to be mechanical vibration.
The vibration of the mechanical system shown in FIG. 10 mainly consists of three components of iron core vibration, winding vibration, and tank vibration, but the measurement result at this stage is unclear on which part the vibration mode is.

  Table 2 below summarizes the measured natural vibrations of the mechanical system and their vibration strengths for two measurement results (graphs of FIGS. 10 and 11) with different measurement positions at a load factor of 60%. In Tables 1 and 2 below,-means that the amplitude could not be observed, and the number of + was increased according to the amplitude.

  The vibration mode in which the vibration intensity is changed by changing the measurement position is considered to be tank vibration, and the rest is considered to be iron core vibration and winding vibration. From the comparison between the result shown in FIG. 11 and the result shown in FIG. 10, each vibration of 37 Hz, 62 Hz, 99 Hz, 137 Hz, 174 Hz, 268 Hz, 329 Hz, 398 Hz, 478 Hz, and 566 Hz is a tank vibration, and the remaining vibration components are It can be seen that the vibration is related to the iron core and windings.

  Table 2 below shows the vibration strengths related to the measured iron core vibration and winding vibration for two measurement results (graphs of FIGS. 10 and 12) with the load position varied with the measurement position at the center of the tank wall surface.

The vibration mode in which the vibration intensity is changed by changing the load factor is considered to be winding vibration, and the rest is considered to be iron core vibration. From the results shown in FIG. 12, it can be seen that 23 Hz, 78 Hz, and 97 Hz are iron cores, and 141 Hz and 582 Hz are winding vibrations.
This embodiment is a measurement using a sensor (one-dimensional sensor) that measures vibration in one direction, but the same measurement and analysis can be performed when a three-dimensional sensor is used.

The frequency for higher order vibration modes can be estimated by Fourier transforming the vibration waveform. However, high-order vibration modes are difficult to detect because the amplitude is small, especially in transformers that have not progressed much. Therefore, it is preferable to perform signal processing in synchronization with the power supply phase, called a compensation method.
When a noise component of a plurality of factors is included in addition to the target physical quantity, it is removed using a measurement system having a main sensitivity to the noise component that cannot be removed by the differential method. Measurement accuracy can be improved by subtracting a certain amount from the measurement amount within a range not exceeding the measurement amount and measuring the remaining portion by the displacement method or the zero method.

In the frequency measurement, as shown in FIG. 13, the measurement frequency f is subtracted from the standard frequency f _s by frequency mixing (beat method) using a mixer 30, and the difference frequency f _B is measured. The frequency f _B is called the intermediate frequency f _IF, the frequency to be amplified decreases, together with the measurement accuracy becomes easy amplification increases to facilitate the measurement of high frequency. The standard frequency used here is referred to as a local oscillation frequency f _LO .
When the frequency f _s included in the signal and the local oscillation frequency f _LO are matched, the difference becomes zero. That is, a method of selecting f _LO so that f _s and f _LO coincide from the beginning and dropping the original signal directly to the baseband frequency of zero is called homodyne.
Further, the local transmission frequency f _LO can be selected so that the intermediate frequency f _IF of the sum or difference of the frequency f _s and the local transmission frequency f _LO included in the signal is constant. Signal processing for converting a signal to an intermediate frequency is called heterodyne.

If Miidasere frequency f _s that is included in the signal in the above manner, it is possible to measure the raw waveform of the small target signal buried in large noise using a lock-in amplifier.
In addition, since the standard frequency is variable from mHz to 100 kHz, it can be analyzed using a technique called PLL (phase locked loop) in which the resonance point is found by sweeping the frequency.
Furthermore, the phase information of the measurement frequency can be analyzed by adjusting the phase of the standard frequency with a phase shifter.

(Example 3)
Oil-filled transformer (3-phase, rated capacity 10 MVA, primary rated voltage 11 kV, secondary rated voltage 3.45 kV, insulation oil volume 5300 liters, operating oil 1975, operating at a rated frequency of 60 Hz (load factor about 10%) The vibration sensor was installed at various positions on the wall of the transformer tank, and the vibration of the transformer tank was measured. A three-axis accelerometer (356A17) manufactured by PCB (Toyo Technica Co., Ltd.) was used for the vibration sensor, a clamp ammeter was used for current measurement, and an FFT analyzer (OR38V3-32 manufactured by Oros Co., Ltd.) was used for the data logger.

An outline of the transformer tank is shown in FIG. However, the bushing and wiring for inputting / outputting electric power to / from the transformer are omitted in FIG.
The transformer tank 31 is a rectangular parallelepiped hollow container made of a steel plate having a width of 2200 mm, a height of 2000 mm, and a depth of 800 mm, and is made of metal waist-wrapped at two upper and lower positions that divide the height into three equal parts. Reinforcing stays 32 and 33 are provided.
A portion of the peripheral wall of the transformer tank 31 above the reinforcing stay 32 is constituted by the upper peripheral wall 31a, and a portion of the peripheral wall of the transformer tank 31 below the reinforcing stay 32 is constituted by the middle peripheral wall 31b. The lower part of the reinforcing stay 33 is composed of a lower peripheral wall 31c.
Since the portions of the reinforcing stays 32 and 33 in the transformer 31 are positions where vibrations are restricted, the following 18 positions are candidates as positions where vibrations are attached and vibrations are measured.

  In this transformer tank 31, vibrations can be measured by attaching a vibration sensor to each of the positions surrounded by the circles 1 to 16 in FIG. 14. The position of the numeral 1 surrounded by a circle indicates the left wall surface of the upper peripheral wall 31a, and the position of the numeral 2 surrounded by a circle is a position corresponding to the left end side of the front wall of the upper peripheral wall 31a (about 40 cm from the left end of the front wall). The position of the numeral 3 surrounded by circles indicates a position corresponding to the right end side of the front wall of the upper peripheral wall 31a (near the position about 40 cm away from the right end of the front wall). The position of the numeral 4 surrounded by a circle indicates the right wall surface of the upper peripheral wall 31a, and the position of the numeral 5 surrounded by a circle is a position corresponding to the right end side of the back wall of the upper peripheral wall 31a (about 40 cm from the right end of the back wall). The position of the numeral 6 surrounded by a circle indicates the position corresponding to the left end side of the back wall of the upper peripheral wall 31a (the vicinity of the position about 40 cm away from the left end of the back wall).

As illustrated here, the vibration sensor is attached at the positions of numerals 7, 8, 9, 10 surrounded by circles on the middle peripheral wall 31 b below the reinforcing stay 32 and on the lower peripheral wall 31 c below the reinforcing stay 33. The position may be any of the numbers 13, 14, 15, and 16 surrounded by a circle. Note that the attachment position on the back wall side of the middle peripheral wall 31b and the attachment position on the back wall side of the lower peripheral wall 31c are omitted because they are not shown in FIG. 14, but correspond to the attachment positions surrounding the numerals 5 and 6 with circles. They are set on the back wall side of the middle peripheral wall 31b and on the back wall side of the lower peripheral wall 31c, respectively.
In these vibration sensor attachment candidate positions, vibrations were measured by installing a vibration sensor on the upper right wall corresponding to the position surrounding the numeral 4 with a circle in the following tests.

The transformer tested in this example accommodates an iron core 38 having a cross-girder structure in which three leg portions 35 are connected by upper and lower yoke portions 36 and 37 as shown in FIG. In FIG. 15, the description of the primary side winding and the secondary side winding wound around the leg portion 35 is omitted.
It is assumed that the iron core 38 takes three types of vibration modes: a torsion mode shown in FIG. 15 (A), a bending mode 1 shown in FIG. 15 (B), and a bending mode 2 shown in FIG. 15 (C). Can do. The mode analysis shown in FIG. 15 is based on “Natural vibration characteristics of transformer core” (2013, IEEJ National Conference 5-195) by Sueyoshi Mizuno et al.
In the case of the torsional mode transformer shown in FIG. 15 (A), the vibration of the iron core is captured on the tank wall surface by installing a vibration sensor at a position surrounding the numbers 2, 3, 5, and 6 shown in FIG. It is thought that you can. In this case, the numbers 2 and 3 are in the opposite direction, the numbers 5 and 6 are in the opposite direction, the numbers 2 and 6 are in the same direction, and the numbers 3 and 5 are in the same direction. If it can confirm that it has displaced, it will be understood that the iron core vibrates in the torsion mode. Similarly, as shown in FIG. 15B, if a vibration sensor is installed at the positions of numbers 8, 9, 11, and 12 to confirm the displacement, it can be seen that the vibration is generated in mode 1. Similarly, as shown in FIG. 15C, if a vibration sensor is installed at positions 7 and 10 and the displacement is confirmed, it can be seen that the vibration is in mode 2.
If the vibration mode can be identified by the natural frequency of the iron core, the tightening force of the iron core can be calculated from the natural frequency. However, if the tightening force of the iron core varies, the peak of natural vibration spreads. Conversely, it is also possible to evaluate the variation in the tightening force from the spread of the natural frequency, for example, the half width. The same evaluation can be performed when the natural vibration peak of the winding has a broadening. The widening of the peak width is related to the deterioration of the iron core or winding, but how much the peak width becomes the threshold value for deterioration diagnosis depends on the design of each transformer, so it is necessary to decide for each transformer.

In this example, in the right side wall of the upper peripheral wall of the transformer tank, the right and left direction of the right side wall is divided and divided as 1A, 2A,... 15A, and the right side wall has a vertical direction of 1A, 1B,. Thus, an impact test was performed in which one vibration sensor was installed at a position of 3C, for example, and the position of 4C on the right side was struck with a hammer to apply vibration.
Moreover, it is good also as a test which installs a vibration sensor in the position of 13F, and strikes the position of 13E with a hammer. Note that the position where the vibration sensor is attached and the position where the hammer is hit can be any position as long as the vibration of the transformer tank can be satisfactorily picked up, and is not limited to the position shown in FIG.

FIG. 17 shows a waveform (waveform during actual operation) on the lower side of FIG. 17 by measuring the vibration of the operating transformer tank with the vibration sensor installed at the position of 3C and Fourier transforming the measurement result.
The waveform of the result of Fourier transform of the vibration measurement result obtained when an impact test is performed in which the position of 4C is hit with a hammer while the transformer is operating while the vibration sensor is installed at the position of 3C is shown on the upper side of FIG. (Waveform during excitation).

  In the waveform indicating the vibration measurement result during actual operation, a large peak is seen at an integer multiple of 60 Hz (120, 180, 240, 300, 360, 420 Hz), and a plurality of weak peaks are also seen. In the vibration measurement result at the time of excitation, there are some peaks at frequency positions (142, 217, 334 Hz, etc.) indicated by vertical dotted lines (black chain lines) other than an integral multiple of 60 Hz. Of the peaks during actual operation, the ones that overlap with the peaks during vibration are considered to be natural vibration components of the tank wall surface. However, whether the peak during vibration is the natural vibration component of the tank wall is confirmed by confirming the change in the phase component to be measured at the same time, and further repeating the measurement by changing the sensor installation position and the point of hitting. It is preferable to do.

As described above in paragraph 0079, the peak due to winding vibration is preferably identified by changing the load factor and changing the intensity. Of the transformer vibrations, when the tank vibration and the winding vibration are separated as described above, the remainder is considered to be iron core vibration.
However, the area around the transformer in operation is an environment with large electromagnetic noise. It is conceivable that electromagnetic noise affects the vibration sensor, the amplifier, the analyzer, the cable connecting them, and the measurement device drive power supply. There is also the possibility that the building or ground where the transformer is installed is shaking. It is also important to improve the accuracy of diagnosis by devising to reduce or reduce the influence of such noise.

It is desirable to perform the above-mentioned test using a device such as a device that is susceptible to electromagnetic noise covered with a metal foil, a device can sufficiently grounded, and a device that uses a battery drive system.
If it is possible to simultaneously measure the vibration of the building or ground at the place where the test is performed, or if it is possible to periodically repair the transformer, measure the background noise in advance to check it, and check the transformer vibration. It is desirable to perform a process such as subtracting from.

  A ... diagnostic device, 1 ... transformer, 2 ... tank, 3 ... coil body, 5 ... iron core, 8 ... fastening fitting, 9 ... outer coil (primary coil), 10 ... inner coil (secondary coil), 11 ... Outer winding (primary winding), 12 ... Insulating spacer, 16 ... Inner winding (secondary winding), 22 ... Vibration detector (vibration sensor), 23 ... Voltmeter, 24, 25 ... Amplifier, 26 ... Analyzer, 27 ... arithmetic device.

Claims (10)

  With respect to the transformer vibration in the operating state, a vibration detector having a detection sensitivity from a low frequency region to an audible sound region (1 Hz to 20 kHz) is used, and the operating state is measured by means of signal processing using an electronic circuit or software. Directly measure the natural frequency of various vibrations generated from the operating transformer due to the electromagnetic force generated by the current applied to the transformer, or the phase of the excitation force due to the current applied to the transformer A method for diagnosing a transformer internal abnormality and deterioration, wherein a phase of a transformer vibration or both of them is obtained as a reference, and a vibration response of an operating transformer is analyzed.   2. The state of the operating transformer is analyzed by comparing the natural frequency and / or phase of the mechanical vibration obtained in claim 1 with the vibration characteristics of a healthy transformer. Diagnosis method for internal abnormalities and deterioration of transformers.   2. The transformer internal abnormality according to claim 1, wherein the state of the operating transformer is analyzed by obtaining the natural frequency of the transformer component from the vibration phase of the power supply system obtained in claim 1. And diagnostic methods for degradation.   The vibration spectrum detected from the operating transformer is characterized in that a specific frequency component determined for each transformer is changed over time and the state of the operating transformer is analyzed. 2. A method for diagnosing transformer internal abnormality and deterioration according to 1.   The transformer includes a winding and an iron core that constitute a coil body, and a tank that accommodates the coil body. Winding vibration generated by the winding due to an energization current during operation, iron core vibration generated by the iron core, and the tank The generated tank vibration is separately detected and individually detected, and the vibration response of the operating transformer is analyzed based on each of the vibrations. Diagnosis method of transformer internal abnormality and deterioration.   A vibration detector that is attached to an operating transformer and has detection sensitivity for vibrations from a low frequency region generated by the transformer to an audible sound region (1 Hz to 20 kHz), and a detection signal from the vibration detector Receiving an analyzer for obtaining a phase of mechanical vibration based on a phase of an exciting force caused by an energizing current to a transformer in operation, and a calculation means for calculating data obtained from the analyzer. A diagnostic device for internal abnormalities and deterioration of transformers.   Information on the natural frequency and / or phase of the healthy transformer is recorded in the calculation means, and the calculation means has the ability to compare the vibration information detected by the vibration detector with the vibration information of the healthy transformer. The diagnostic device for internal abnormality and deterioration of a transformer according to claim 6, comprising:   The arithmetic means has the ability to analyze the state of the transformer in operation by obtaining the natural frequency of the transformer component from the phase of mechanical vibration obtained by the vibration detector. The diagnostic device for internal abnormality and deterioration of the transformer according to claim 6 or 7.   Ability to analyze the state of the operating transformer by capturing that the specific frequency component determined for each transformer changes from time to time in the vibration spectrum detected from the operating transformer by the vibration detector. The diagnostic device for internal abnormality and deterioration of a transformer according to any one of claims 6 to 8, wherein the arithmetic means is provided.   The transformer includes a winding that constitutes a coil body, an iron core, and a tank that accommodates them, and the vibration detector generates winding vibration caused by the winding due to an energization current during operation, and iron core vibration caused by the iron core. 10. The tank vibration generated by the tank is separated and individually detected, and the arithmetic means has a function of analyzing the vibration response of the transformer. The diagnostic apparatus for internal abnormality and deterioration of the transformer according to any one of the above.

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