TRANSFORMER NOISE LEVEL DIAGNOSTIC METHOD AND NOISE REDUCTION METHOD

Abstract

A method for diagnosing the noise level of a transformer comprises: a step of acquiring a frequency spectrum of noise from a stacked iron core 21 contained in a transformer, the stacked iron core 21 being formed by stacking electrical steel laminations; a step in which, for the calculation of the excitation vibration of the stacked iron core 21, the transverse moduli of elasticity are determined in two planes, each including a stacking direction of the stacked iron core 21; a step in which the excitation vibration for the stacked iron core 21 is calculated using a constitutive equation that includes an elasticity matrix comprising the determined transverse moduli of elasticity as elements, and a frequency spectrum of an excitation vibration of the stacked iron core 21 is acquired;a calculation stage of the difference between the excitation noise spectrum of the stacked iron core 21 and the excitation vibration frequency spectrum of the stacked iron core 21 as a differential spectrum; and a transformer noise level diagnostic stage based on the differential spectrum.

Description

Transformer noise performance diagnosis method and noise reduction method

[0001] The present disclosure relates to a method for diagnosing noise performance and a method for reducing noise of a transformer.

[0002] Conventionally, noise reduction structures for transformers have been known. For example, Patent Document 1 discloses a noise reduction structure for a transformer having a soundproof wall surrounding the transformer body, in which a resonance-type sound-absorbing structure that resonates with a specific frequency of noise generated when the transformer is operating is provided on the floor of a closed space formed by the outer surface of the transformer and the inner surface of the soundproof wall. Also, Patent Document 2 discloses a configuration in which a noise-reducing weight is attached to part of a reinforcing member attached to the side of the transformer tank, thereby reducing noise by shifting the frequency of the noise from the resonant frequency of the reinforcing member.

[0003] JP 2013-21035 A JP 2020-170797 A

[0004] Countermeasures for reducing transformer noise, such as those disclosed in Patent Document 1, which involve installing soundproof walls and resonance-type sound-absorbing structures, increase the cost of the transformer. Furthermore, countermeasures for reducing noise by attaching weights to reinforcing members, such as those disclosed in Patent Document 2, are limited in the frequencies of noise that can be reduced. Furthermore, if the main noise source is not identified, costs are unnecessarily increased by attaching weights to members that do not require weights. There is a need to reduce transformer noise efficiently and at low cost.

[0005] Therefore, an object of the present disclosure is to provide a method for diagnosing noise performance of a transformer and a method for reducing noise, which can reduce the noise of the transformer efficiently or at low cost.

[0006] A method for diagnosing noise performance of a transformer according to one embodiment of the present disclosure includes: a first step of measuring excitation noise of a laminated core formed by laminating electromagnetic steel sheets to obtain a frequency spectrum of the noise, a second step of determining transverse elastic moduli in two planes including the lamination direction of the laminated core of the transformer, the transverse elastic moduli being included as elements of an elastic matrix that expresses the relationship between stress and strain in the laminated core in matrix form, in order to calculate excitation vibration of the laminated core of the transformer, using a constitutive equation including an elastic matrix that expresses the relationship between stress and strain in the laminated core in matrix form, a third step of calculating excitation vibration of the laminated core of the transformer using a constitutive equation including the elastic matrix that includes the transverse elastic moduli determined in the second step as elements, to obtain a frequency spectrum of excitation vibration of the laminated core of the transformer, and a fourth step of calculating a difference spectrum between the excitation noise spectrum of the laminated core of the transformer obtained in the first step and the frequency spectrum of excitation vibration of the laminated core of the transformer obtained in the third step. and a fifth step of diagnosing the noise performance of the transformer based on the difference spectrum calculated in the fourth step.

[0007] A method for reducing noise in a transformer according to one embodiment of the present disclosure includes a step of identifying components that are increasing the noise of the transformer based on a diagnostic result of the noise performance of the transformer obtained by executing the method for diagnosing noise performance of the transformer, and generating and notifying a diagnostic result that encourages noise reduction measures for the identified components.

[0008] According to the transformer noise performance diagnosis method and noise reduction method of the present disclosure, the noise of a transformer can be reduced efficiently or at low cost.

[0009] 1 is a diagram showing an example of the configuration of a laminated core of a transformer that is to be diagnosed by a noise performance diagnosis method according to an embodiment; FIG. 2 is a block diagram showing an example of the configuration of a noise performance diagnosis device according to an embodiment; FIG. 3 is a flowchart showing an example of the procedure of a determination method according to an embodiment; FIG. 4 is a graph showing an example of the frequency spectrum of noise from a transformer; FIG. 5 is a diagram explaining normal stress in the lamination direction (Z-axis direction) acting on a laminated core; FIG. 6 is a diagram explaining normal stress in a direction orthogonal to the lamination direction (X-axis direction) acting on a laminated core; FIG. 7 is a diagram explaining normal stress in a direction orthogonal to the lamination direction (Y-axis direction) acting on a laminated core; FIG. 8 is a diagram explaining shear stress in the ZX plane acting on a laminated core; FIG. 9 is a diagram explaining shear stress in the XY plane acting on a laminated core; and FIG. 10 is a diagram explaining shear stress in the YZ plane acting on a laminated core. 10 is a graph showing an example of a difference spectrum between a frequency spectrum of excitation vibration and a frequency spectrum of excitation noise of a laminated iron core of a transformer.

[0010] Transformers such as power distribution transformers are constructed by winding a coil around a laminated core made of laminated electromagnetic steel sheets. Important performance characteristics of transformers include, for example, iron loss (no-load loss) characteristics, excitation current characteristics, and noise characteristics.

[0011] Distribution transformers are installed in a variety of locations. Low noise levels are especially important for transformers installed in urban areas. Considering the impact of transformers on the surrounding environment, noise reduction is becoming increasingly important as a required performance feature for transformers.

[0012] Grain-oriented electrical steel sheets, which are often used as the iron core material for transformers, vibrate due to material expansion and contraction caused by magnetization. Material expansion and contraction caused by magnetization is also called magnetostriction. Vibration caused by magnetostriction is also called magnetostrictive vibration. Magnetostrictive vibration is one of the main causes of noise in transformers. Therefore, the noise performance of a transformer can be strongly dependent on the magnetostrictive properties of the electrical steel sheets used as the iron core material. To reduce transformer noise, electrical steel sheets with low magnetostrictive properties can be used as the iron core material for transformers.

[0013] However, even when electromagnetic steel sheets with excellent magnetostrictive properties are used as the core material, the noise of transformers is often not sufficiently reduced. One possible cause of this insufficient noise reduction is the occurrence of resonance phenomena in the auxiliary parts other than the iron core, such as the fixing brackets or tank of the transformer iron core. Therefore, when designing and manufacturing transformers, it is extremely important to reduce the noise caused by mechanical vibrations of the auxiliary parts other than the iron core.

[0014] Various techniques for reducing the excitation noise of transformers are conceivable. For example, a method of installing a soundproof wall made of steel plates or concrete around the transformer body is conceivable. While this method may reduce noise due to the sound-insulating effect of the soundproof wall, it may not be possible to sufficiently reduce noise due to resonance within the soundproof wall. As disclosed in the above-mentioned Patent Document 1 (JP 2013-21035 A), it is also conceivable to reduce noise caused by resonance within the soundproof wall by installing a resonance-type sound-absorbing structure within the soundproof wall. However, the cost of the transformer increases not only due to the installation of the soundproof wall alone, but also due to the installation of the resonance-type sound-absorbing structure.

[0015] Alternatively, as disclosed in the aforementioned Patent Document 2 (JP 2020-170797 A), it is possible to reduce transformer noise without installing a soundproof wall by attaching a reinforcing member to the side of the transformer tank and attaching a weight to a portion of the reinforcing member. However, measures that use weights limit the noise frequencies that can be reduced. For example, in Patent Document 2, the noise frequencies that can be reduced are limited to twice the excitation frequency. Furthermore, if the noise generated by the reinforcing member with the attached weight is not the main source of transformer noise, the noise reduction effect of attaching the weight is negligible. If the noise reduction effect is negligible, attaching the weight is wasteful and simply incurs additional costs.

[0016] Hereinafter, a method for diagnosing noise performance of a transformer according to this embodiment will be described, which is a method for easily identifying the main noise sources of the transformer. Also, a method for reducing noise of a transformer according to this embodiment will be described, which is a method for efficiently and inexpensively implementing countermeasures against the noise sources identified by the noise performance diagnosis method.

[0017] Hereinafter, embodiments of a transformer noise performance diagnosis method and a noise reduction method according to the present disclosure will be described with reference to the drawings. The drawings are schematic and may differ from the actual product. Furthermore, the following embodiments exemplify devices or methods for embodying the technical concept of the present invention, and are not intended to limit the configuration to those described below. In other words, the technical concept of the present disclosure can be modified in various ways within the technical scope described in the claims.

[0018] (Embodiment) The laminated core 21 to be analyzed in this embodiment is assumed to be a laminated core for a three-phase, three-limbed transformer used, for example, as a distribution transformer. As shown in Fig. 1 , the laminated core 21 may be configured by laminating a plurality of grain-oriented electromagnetic steel sheets 22 having a predetermined thickness, each of which has three legs 22c connected between an upper yoke 22a and a lower yoke 22b. The laminated grain-oriented electromagnetic steel sheets 22 are fixed by wrapping glass tape around them. The laminated core 21 to be analyzed in this embodiment is not limited to the laminated core for a three-phase, three-limbed transformer illustrated in Fig. 1 .

[0019] The steps of the transformer noise performance diagnosis method according to this embodiment may be executed by a noise performance diagnosis device 40 illustrated in Fig. 2. The noise performance diagnosis device 40 includes a control unit 42, a storage unit 44, and an interface 46.

[0020] The control unit 42 controls and manages each functional unit constituting the noise performance diagnosis device 40 and the entire noise performance diagnosis device 40. The control unit 42 may be configured to include at least one processor, such as a CPU (Central Processing Unit), in order to control and manage various functions. The control unit 42 may be configured with one processor or multiple processors. The processor constituting the control unit 42 may implement the functions of the noise performance diagnosis device 40 by reading and executing programs stored in the storage unit 44.

[0021] The storage unit 44 may function as a memory that stores various types of information. The storage unit 44 may store, for example, a program executed by the control unit 42, or data or processing results used in processing executed by the control unit 42. The storage unit 44 may also function as a work memory for the control unit 42. The storage unit 44 may be configured, for example, by a semiconductor memory or the like, but is not limited to this, and may be configured to include any storage device. For example, the storage unit 44 may be configured as an internal memory of a processor used as the control unit 42, or may be configured as a hard disk drive (HDD) accessible from the control unit 42.

[0022] The interface 46 may include a communication interface for communicating with other devices via a wired or wireless connection. The interface 46 may include an input / output port for inputting and outputting data to and from other devices. The interface 46 transmits and receives necessary data and signals to and from a process computer or a higher-level system. The interface 46 may communicate based on a wired communication standard or a wireless communication standard. For example, the wireless communication standard may include cellular phone communication standards such as 3G, 4G, and 5G. Furthermore, for example, the wireless communication standard may include IEEE 802.11, Bluetooth (registered trademark), and the like. The interface 46 may support one or more of these communication standards. The interface 46 is not limited to these examples and may communicate with other devices or input and output data based on various standards.

[0023] The noise performance diagnosis method according to this embodiment will be described below assuming that each step in the flowchart illustrated in Fig. 3 is executed by the control unit 42 of the noise performance diagnosis device 40. Each step in the noise performance diagnosis method may be executed by another device or by a person.

[0024] First, in step S1 (first step), the control unit 42 acquires the measurement results of the frequency spectrum of the excitation noise of the laminated core 21 of the transformer shown in FIG. 1 , which is the target of vibration analysis. Specifically, the excitation noise is measured by setting the excitation frequency of the laminated core 21 to 50 Hz. Generally, the frequency spectrum of the excitation noise of a transformer is composed of frequency components that are integer multiples of twice the excitation frequency (even-number multiples of the excitation frequency). Therefore, the excitation noise spectrum at each frequency in 100-Hz increments within the range of 100 Hz to 1000 Hz is acquired as the noise frequency spectrum. At transformer manufacturing sites, the excitation noise characteristics of transformers are widely measured as a quality control item for shipped products. Therefore, there is no particular difficulty in measuring the excitation noise. The excitation frequency may be set to 60 Hz. When the excitation frequency is set to 60 Hz, the excitation noise spectrum is acquired at 120-Hz increments from 120 Hz to 1200 Hz.

[0025] The following describes the case where the excitation frequency is set to 50 Hz. An example of the frequency spectrum of noise acquired when the excitation frequency is set to 50 Hz is shown as a graph in Fig. 4. In the graph of Fig. 4, the horizontal axis represents frequency, and the vertical axis represents the magnitude of the excitation noise.

[0026] Next, in step S2 (second step), the control unit 42 determines the transverse elastic coefficient to be included as an element in the elastic matrix in order to perform an excitation vibration calculation of the laminated core 21 to obtain the frequency spectrum of the excitation vibration in step S4, which will be described later. The excitation vibration calculation of the laminated core 21 is made possible by accurately estimating the mechanical property values ​​of the laminated core 21, which is created by stacking a large number of thin steel plates. The mechanical property values ​​of the laminated core 21 can be accurately estimated based on the technology disclosed in Japanese Patent No. 6729837, for example. In this embodiment, the excitation vibration calculation of the laminated core 21 is basically performed using the technology disclosed in Japanese Patent No. 6729837.

[0027] In this embodiment, in order to perform a numerical analysis of the vibration of the laminated core 21 of the three-phase, three-limbed transformer illustrated in Fig. 1, a constitutive equation showing the relationship between stress and strain is used as the governing equation for elastic structural analysis. The constitutive equation is expressed as the following equation (1) by replacing the laminated material with an equivalent homogeneous body and expressing the influence of the lamination in terms of matrix physical properties: [σ] = [C][ε] (1) [σ] is the stress matrix. [C] is the elasticity matrix (stiffness matrix) as a response function. [ε] is the strain matrix.

[0028] 1, the directions of the laminated core 21 are represented by the X-axis, Y-axis, and Z-axis of an XYZ Cartesian coordinate system. The grain-oriented electrical steel sheets 22 extend along the XY plane and are laminated along the Z-axis direction.

[0029] The stress acting on the laminated core 21 includes a normal component acting in a direction normal to the laminated core 21 (compression or tension direction) and a shear component acting in the shear direction of the laminated core 21. Figures 5A, 5B, and 5C illustrate normal stresses acting in the Z-axis, X-axis, and Y-axis directions, respectively. The normal stresses acting in the Z-axis, X-axis, and Y-axis directions are represented by σz, σx, and σy, respectively. Figures 5D, 5E, and 5F illustrate shear stresses acting in the ZX-plane, XY-plane, and YZ-plane, respectively. The shear stresses acting in the ZX-plane, XY-plane, and YZ-plane are represented by τzx, τxy, and τyz, respectively. The stress matrix [σ] has normal stress and shear stress as components.

[0030] The strain of the laminated core 21 includes a component that distorts the laminated core 21 in the vertical direction (compression or tension direction) and a component that distorts the laminated core 21 in the shear direction. The vertical strains in the Z-axis, X-axis, and Y-axis directions are represented by εz, εx, and εy, respectively. The shear strains in the ZX plane, XY plane, and YZ plane are represented by γzx, γxy, and γyz, respectively.

[0031] The elasticity matrix [C] has 6 x 6 = 36 elements that specify the relationship between the six components of stress and the six components of strain. The 36 elements are represented by elastic coefficients Cij (i = 1 to 6, j = 1 to 6). The relationship between stress and strain is expressed by the elasticity matrix as shown in the following equation (2).

[0032] Since the laminated core 21 is formed by stacking grain-oriented electromagnetic steel sheets 22, it has mechanical symmetry within the laminated core 21, and also has 180-degree symmetry in the longitudinal direction of the laminated grain-oriented electromagnetic steel sheets 22 and in the direction perpendicular to the longitudinal direction. Therefore, the laminated core 21 can be said to have orthotropy in terms of anisotropy classification. The elastic matrix of an object having orthogonal anisotropy is basically expressed by a total of nine elastic coefficients: C11, C12, C13, C22, C23, C33, C44, C55, and C66, as shown in the following equation (3).

[0033] Of these nine elastic coefficients, the elastic coefficients C11, C12, C13, C22, C23, and C33 are calculated using the following formulas (4) to (10) based on the longitudinal elastic moduli Ex, Ey, and Ez and the Poisson's ratios νxy, νyx, νyz, νzy, νzx, and νxz.

[0034] As shown in the following equations (11), (12), and (13), the elastic modulus C44 corresponds to the transverse elastic modulus Gyz in the YZ plane, the elastic modulus C55 corresponds to the transverse elastic modulus Gzx in the ZX plane, and the elastic modulus C66 corresponds to the transverse elastic modulus Gxy in the XY plane.

[0035] Here, Ex, Ey, and Ez respectively represent the X-direction longitudinal elastic modulus (Young's modulus), the Y-direction longitudinal elastic modulus (Young's modulus), and the Z-direction longitudinal elastic modulus (Young's modulus). νxy, νyx, νyz, νzy, νzx, and νxz respectively represent the Poisson's ratio of the XY plane (the ratio of the X-direction longitudinal strain to the Y-direction lateral strain), the Poisson's ratio of the YX plane, the Poisson's ratio of the YZ plane, the Poisson's ratio of the ZY plane, the Poisson's ratio of the ZX plane, and the Poisson's ratio of the XZ plane. The relationship between the longitudinal elastic modulus and the Poisson's ratio, expressed by the following equation (14), known as the reciprocity theorem, holds true.

[0036] By the reciprocity theorem, the Poisson's ratio νyx in the YX plane is expressed using Ex, Ey, and νxy. The Poisson's ratio νzy in the ZY plane is expressed using Ez, Ey, and νyz. The Poisson's ratio νxz in the XZ plane is expressed using Ez, Ex, and νzx.

[0037] In this way, the values ​​of the nine elastic coefficients C11, C12, C13, C22, C23, C33, C44, C55, and C66 that represent the elastic matrix of an orthogonally anisotropic object are expressed using nine mechanical property values: the longitudinal elastic moduli Ex, Ey, and Ez, the transverse elastic moduli Gyz, Gzx, and Gxy, and the Poisson's ratios vxy, vyz, and vzx. Therefore, determining these nine mechanical property values ​​is equivalent to determining the nine elastic coefficients that represent the elastic matrix. Below, methods for determining the longitudinal elastic moduli, transverse elastic moduli, and Poisson's ratios will be described.

[0038] First, regarding the longitudinal elastic modulus of the orthogonally anisotropic laminated core 21, the longitudinal elastic modulus Ex and Ey can be set to values ​​equal to the longitudinal elastic modulus Ex0 and Ey0 of a single steel plate. On the other hand, the longitudinal elastic modulus Ez cannot be set to a value equal to the longitudinal elastic modulus Ez0 of a single steel plate because there are small gaps between the stacked steel plates. Therefore, in this embodiment, an experiment is conducted to determine the relationship between the load and displacement in the stacking direction of the laminated steel plates, and the longitudinal elastic modulus Ez is set based on the experimental results. In this embodiment, Ez = 10 GPa based on the experimental results. Note that the magnitude of the longitudinal elastic modulus in the stacking direction has little effect on the vibration calculation results. Therefore, even if Ez is set to a value equal to the longitudinal elastic modulus Ez0 of a single steel plate, the error in the vibration calculation results will not be large.

[0039] Furthermore, with regard to the Poisson's ratio of the orthogonally anisotropic laminated core 21, the Poisson's ratio vxy in the XY plane can be set to a value equal to the Poisson's ratio vxy0 of a single steel plate. On the other hand, the Poisson's ratio vyz in the YZ plane and the Poisson's ratio vzx in the ZX plane cannot be set to the Poisson's ratios vyz0 and vzx0 of a single steel plate. This is because, in the laminated core 21, the mechanical coupling between the strain in the lamination direction and the strain in the direction perpendicular to the lamination direction is considered to be extremely weak. Here, it is extremely difficult to actually measure vyz and vzx. However, based on the above considerations, vyz and vzx are expected to be extremely small values. Therefore, in this embodiment, vyz and vzx are both assumed to be zero.

[0040] Furthermore, regarding the transverse elastic modulus of the laminated core 21, the transverse elastic modulus Gxy in the XY plane can be set to a value equal to the transverse elastic modulus Gxy0 of a single steel plate. On the other hand, the transverse elastic modulus of two planes including the lamination direction, i.e., the transverse elastic modulus Gzx in the ZX plane and the transverse elastic modulus Gyz in the YZ plane, cannot be set to the transverse elastic modulus Gxz0 and Gyz0 of a single steel plate. This is because the transverse elastic modulus Gzx and Gyz must reflect the influence of slippage between the steel plates in the X and Y directions, which are perpendicular to the lamination direction, at the interface between the laminated steel plates. Therefore, in order to perform vibration analysis using a constitutive equation that expresses the relationship between stress and strain in the laminated core 21 in a matrix representation, it is important to determine the transverse elastic modulus of two planes including the lamination direction of the transformer laminated core 21, i.e., the transverse elastic modulus Gzx in the ZX plane and the transverse elastic modulus Gyz in the YZ plane, which are included in the elasticity matrix of the constitutive equation.

[0041] Therefore, in this embodiment, the transverse elastic moduli Gzx and Gyz in two planes including the stacking direction are determined based on the method disclosed in Patent No. 6729837 for the value of the clamping pressure in the stacking direction when creating the laminated core 21.

[0042] Next, in step S3, the control unit 42 acquires frequency spectrum data of excitation magnetostriction to be used in the excitation vibration calculation of the laminated iron core 21 of the transformer in step S4, which will be described later. The control unit 42 acquires frequency spectrum data of excitation magnetostriction of an electromagnetic steel sheet that is the same as the grain-oriented electromagnetic steel sheet 22 that constitutes the laminated iron core 21 of the transformer that is the target of vibration analysis shown in FIG. 1. The control unit 42 acquires spectrum data of excitation magnetostriction amplitude at each frequency in 100-Hz increments within a range from 100 Hz to 1000 Hz as the frequency spectrum data of excitation magnetostriction. The control unit 42 can acquire the frequency spectrum data of excitation magnetostriction by measuring the excitation magnetostriction of the electromagnetic steel sheet or by obtaining it from the manufacturer of the electromagnetic steel sheet. An example of the acquired frequency spectrum data of excitation magnetostriction is shown as a graph in FIG. 6. In the graph of FIG. 6, the horizontal axis represents frequency, and the vertical axis represents the magnitude of the magnetostriction amplitude. The magnitude of the magnetostriction amplitude at each frequency is expressed in dB by dividing the normalized value by the value of the magnetostriction amplitude at a frequency of 100 Hz. The dB expression corresponds to the value obtained by multiplying the common logarithm of the displayed value by 10.

[0043] Next, in step S4, the control unit 42 performs numerical calculations of the excitation vibration of the laminated core 21 of the target transformer shown in FIG.

[0044] Specifically, the control unit 42 uses structural analysis software to perform a vibration response analysis on the laminated core 21 of the transformer that is the target of the vibration analysis. Of the nine mechanical property values ​​of the laminated core 21, namely the longitudinal elastic moduli Ex, Ey, and Ez, the transverse elastic moduli Gyz, Gzx, and Gxy, and the Poisson's ratios vxy, vyz, and vzx, the seven values ​​excluding the transverse elastic moduli Gyz and Gzx are set as follows, as described above: Ex=Ex0, Ey=Ey0, Ez=10 GPa Gxy=Gxy0 vxy=vxy0, vyz=vzx=0

[0045] Then, for the remaining two transverse elastic moduli Gyz and Gzx in two planes including the lamination direction, the control unit 42 performs vibration calculations by applying the transverse elastic moduli Gzx and Gyz in two planes including the lamination direction, which were determined based on the method disclosed in Japanese Patent No. 6729837 to the value of the clamping pressure in the lamination direction when the iron core was fabricated as described above, and calculates the frequency spectrum of the vibration response function of the laminated iron core 21 of the transformer. An example of the frequency spectrum of the vibration response function of the laminated iron core 21 of the transformer calculated in step S4 is shown as a graph in FIG. 7. In the graph of FIG. 7, the horizontal axis represents frequency, and the vertical axis represents the magnitude of the response function. The magnitude of the response function is displayed normalized so that the vibration response value at a frequency of 100 Hz is 0 dB.

[0046] Next, in step S5, the control unit 42 calculates the frequency spectrum of the excitation vibration of the transformer laminated core 21 based on the frequency spectrum data of the excitation magnetostriction of the electromagnetic steel sheets acquired in step S3 and the frequency spectrum of the vibration response function of the transformer laminated core 21 calculated in step S4. Specifically, the control unit 42 calculates the frequency spectrum of the excitation vibration of the transformer laminated core 21 as the product of the frequency spectrum data of the excitation magnetostriction of the electromagnetic steel sheets and the frequency spectrum of the vibration response function of the transformer laminated core 21. When the frequency spectrum is displayed in dB, the control unit 42 calculates the frequency spectrum of the excitation vibration of the transformer laminated core 21 as the sum of the frequency spectrum of the excitation magnetostriction of the electromagnetic steel sheets and the frequency spectrum of the vibration response function of the transformer laminated core 21.

[0047] An example of the frequency spectrum of the excitation vibration of the laminated core 21 of the transformer calculated in this manner is shown as a graph in Figure 8. In the graph of Figure 8, the horizontal axis represents frequency, and the vertical axis represents the calculated value of the magnitude of the excitation vibration. The magnitude of the excitation vibration is displayed in dB.

[0048] In the noise performance diagnosis method according to this embodiment, the procedure from steps S3 to S5 in FIG. 3 is defined as the third step, in which excitation vibration calculation is performed on laminated core 21 of the target transformer shown in FIG. 1 to obtain the frequency spectrum of the excitation vibration.

[0049] Next, in step S6 (fourth step), the control unit 42 calculates the difference between the frequency spectrum of the excitation noise of the transformer laminated core 21 acquired in the first step (step S1) and the frequency spectrum of the excitation vibration of the transformer laminated core 21 calculated in the second step (steps S2 to S5). An example of the frequency spectrum of the difference between the excitation noise spectrum (actually measured value) of the transformer laminated core 21 and the frequency spectrum (calculated value) of the excitation vibration is shown as a graph in FIG.

[0050] Next, in step S7 (fifth step), the control unit 42 diagnoses the noise performance of the transformer based on the difference spectrum calculated in step S6. The frequency spectrum (calculated value) of excitation vibration of the transformer's laminated core 21 shown as an example in Fig. 8 represents a predicted value of excitation vibration noise emitted only by the iron core made of electromagnetic steel sheets. On the other hand, the frequency spectrum (measured value) of excitation noise of the transformer's laminated core 21 shown as an example in Fig. 4 represents the excitation vibration noise of the entire transformer, including not only the iron core made of electromagnetic steel sheets but also accessory parts other than the electromagnetic steel sheets, such as metal fittings that secure the iron core. In consideration of the meaning of each frequency spectrum, the difference spectrum between the excitation noise spectrum (actual measurement value) and the excitation vibration frequency spectrum (calculated value) of the transformer laminated core 21 shown as an example in Figure 9 can be interpreted as corresponding to the increase in transformer noise due to noise emitted as a noise source by accessory parts in parts other than the electromagnetic steel plates of the transformer in question. Therefore, by interpreting the physical meaning of the difference spectrum between the excitation noise spectrum (actual measurement value) and the excitation vibration frequency spectrum (calculated value) of the transformer laminated core 21 shown as an example in Figure 9 as described above, the control unit 42 can easily identify the frequency of noise generated by accessory parts in parts other than the electromagnetic steel plates of the transformer.

[0051] For example, in the difference spectrum illustrated in Figure 9, the component with a frequency of 400 Hz is large. From this, the control unit 42 can easily diagnose that one of the accessory parts of the transformer is vibrating at 400 Hz, causing an increase in the noise of the entire transformer. Each component of the difference spectrum is also referred to as a difference value. The frequency at which the difference value is maximum is also referred to as a peak frequency. The control unit 42 may determine the frequency at which the difference value is maximum as the peak frequency based on the difference spectrum.

[0052] The control unit 42 acquires the measurement results of the vibration frequency of the accessory part. The vibration frequency of the accessory part can be measured by attaching an acceleration sensor to the accessory part and exciting it, or by measuring the vibration frequency of the accessory part with a laser Doppler vibrometer while the transformer is excited.

[0053] The control unit 42 may then extract accessory parts having vibration frequencies corresponding to the frequencies with large values ​​in the difference spectrum, and generate and notify diagnostic results urging noise reduction measures for those parts. The control unit 42 may also extract parts whose vibration frequencies are the same as the peak frequency of the difference spectrum, or parts whose vibration frequencies differ by a predetermined value or less, and generate and notify diagnostic results urging noise reduction measures for those extracted parts. Parts extracted based on the difference spectrum can also be considered identified as parts that increase the noise of the transformer. For example, if the difference spectrum is calculated as shown in the graph of FIG. 9 , a part with a vibration frequency of 400 Hz can be extracted from the accessory parts, and noise reduction measures can be taken for that part. In this way, transformer noise reduction can be achieved efficiently and at low cost.

[0054] EXAMPLES Hereinafter, verification of the effects obtained by implementing the transformer noise performance diagnosis method and noise reduction method according to the present embodiment will be described as examples.

[0055] First, grain-oriented electromagnetic steel sheets 22 with a thickness of 0.23 mm were prepared. Next, the prepared grain-oriented electromagnetic steel sheets 22 were stacked to produce a laminated core 21 for a three-phase, three-limbed transformer to be subjected to vibration analysis, as illustrated in FIG. 1 . The steel sheet lamination thickness of the laminated core 21 was 100 mm. The upper yoke 22a and the lower yoke 22b each had a width of 100 mm and a length of 500 mm. The three legs 22c each had a width of 100 mm and a core window length of 300 mm. The legs 22c were connected between the upper yoke 22a and the lower yoke 22b with a 100 mm gap between them. An IV wire was then wound around each of the three legs 22c of the laminated core 21 to form an excitation coil.

[0056] A 50 Hz three-phase current was passed through the coil, and the power supply voltage was adjusted so that the iron core magnetic flux density was exactly 1.7 T. In this state, the excitation noise was measured using a sound level meter, similar to the procedure in step S1 of Figure 3, to obtain the noise frequency spectrum. The measurement results of the noise frequency spectrum in the example are assumed to be similar to the graph shown in Figure 6. Of the components of the noise frequency spectrum measured in the example, the magnitude of the 100 Hz component is assumed to be approximately 23 dBA.

[0057] Next, the magnetostriction frequency spectrum was obtained by measuring the magnetostriction of the prepared grain-oriented electrical steel sheet 22 using a magnetostriction measurement device when the sheet was excited at an excitation frequency of 50 Hz and a magnetic flux density of 1.7 T. The frequency spectrum of magnetostriction in the example is assumed to be similar to the graph shown in Fig. 6. Of the components of the frequency spectrum of magnetostriction in the example, the magnitude of the component at a frequency of 100 Hz is assumed to be approximately 1.5E-7.

[0058] Next, a vibration response analysis was performed using structural analysis software on the laminated core 21 of the transformer, which was the subject of the vibration analysis. Here, seven of the nine mechanical property values ​​of the laminated core 21, namely the longitudinal elastic moduli Ex, Ey, and Ez, the transverse elastic moduli Gyz, Gzx, and Gxy, and the Poisson's ratios vxy, vyz, and vzx, were set as follows: Ex = 132 GPa, Ey = 220 GPa, Ez = 10 GPa, Gxy = 116 GPa, vxy = 0.37, vyz = vzx = 0, where x corresponds to the steel sheet rolling direction, y corresponds to the direction perpendicular to x, and z corresponds to the steel sheet lamination direction.

[0059] The transverse elastic moduli Gyz and Gzx in the two planes including the remaining two lamination directions are assumed to be determined using the technology disclosed in Japanese Patent No. 6729837, as described above. The clamping pressure in the lamination direction of the laminated core 21 for the three-phase, three-limbed transformer shown in FIG. 1 was set to 0.1 MPa when the core was fabricated. Therefore, the transverse elastic moduli of the laminated core 21 were determined to be Gyz = Gzx = 0.09 GPa. The frequency spectrum of the vibration response function of the laminated core 21 calculated in the example is assumed to be similar to the graph shown in FIG. 7. Among the components of the frequency spectrum of the vibration response function calculated in the example, the magnitude of the component at a frequency of 1000 Hz is assumed to be approximately 13 dB.

[0060] Next, the frequency spectrum of the excitation vibration of the laminated core 21 of the transformer was calculated based on the frequency spectrum data of the excitation magnetostriction of the electromagnetic steel sheets and the frequency spectrum of the vibration response function of the laminated core 21 of the transformer. The frequency spectrum of the excitation vibration of the laminated core 21 calculated in the example is assumed to be similar to the graph shown in Fig. 8. Of the components of the frequency spectrum of the excitation vibration calculated in the example, the magnitude of the component with a frequency of 100 Hz is assumed to be approximately 22 dBA.

[0061] Next, a difference spectrum was calculated between the frequency spectrum of the excitation noise of the laminated iron core 21 of the transformer illustrated in Fig. 4 and the frequency spectrum of the excitation vibration of the laminated iron core 21 of the transformer illustrated in Fig. 8. The difference spectrum calculated in the example is assumed to be similar to the graph illustrated in Fig. 9. Of the components of the difference spectrum calculated in the example, the magnitude of the component with a frequency of 400 Hz is assumed to be approximately 10 dB.

[0062] Next, the noise performance of the transformer is diagnosed based on the difference spectrum illustrated in Fig. 9. In this example, the transformer to be diagnosed has an auxiliary component that vibrates at 400 Hz, and it is diagnosed that the noise generated by the vibration of this component is increasing the noise of the transformer.

[0063] Therefore, the vibration frequency of the transformer's accessory parts was measured using a laser vibrometer while the transformer to be diagnosed was excited at a frequency of 50 Hz and a magnetic flux density of 1.7 T. As a result, it was found that the end of the metal fitting tightening the upper yoke 22a of the transformer's laminated core 21 was vibrating at 400 Hz.

[0064] Therefore, an additional bolt was added to the end of the metal fitting that fastens the upper yoke 22a of the transformer's laminated core 21, further tightening the metal fitting to increase its rigidity, resulting in an overall reduction of the transformer's excitation noise by 3.5 dB.

[0065] As described above, in this embodiment, it is possible to identify the accessory parts that are causing the increase in noise of the transformer, and to easily take measures to reduce noise from the identified parts.

[0066] Although the embodiments of the present disclosure have been described based on the drawings and examples, it should be noted that those skilled in the art could make various modifications or alterations based on the present disclosure. Therefore, it should be noted that these modifications and alterations are included within the scope of the present disclosure. For example, the functions included in each component or step can be rearranged so as not to cause logical inconsistencies, and multiple components or steps can be combined or divided into one. The embodiments of the present disclosure can also be realized as a program executed by a processor included in an apparatus or a storage medium on which a program is recorded. It should be understood that these are also included within the scope of the present disclosure.

[0067] Furthermore, in the above embodiment, the noise performance diagnosis for a three-phase, three-limbed transformer has been described, but the present disclosure is not limited to this and can also be applied to the noise performance diagnosis of the laminated core 21 in a three-phase, five-limbed transformer or other transformers.

[0068] 21 Laminated iron core 22 Grain-oriented electromagnetic steel sheet (22a: upper yoke, 22b: lower yoke, 22c: legs) 40 Noise performance diagnostic device (42: control unit, 44: memory unit, 46: interface)

Claims

1. In a transformer having a laminated core formed by laminating electromagnetic steel sheets, a first step is to measure the excitation noise of the laminated core to obtain a frequency spectrum of the noise; a second step is to determine transverse elastic moduli in two planes including the lamination direction of the laminated core of the transformer, which are included as elements of an elastic matrix in order to perform an excitation vibration calculation of the laminated core of the transformer using a constitutive equation including an elastic matrix that expresses the relationship between stress and strain in the laminated core in a matrix representation; a third step is to perform an excitation vibration calculation of the laminated core of the transformer using a constitutive equation including the elastic matrix that includes the transverse elastic moduli determined in the second step as an element to obtain a frequency spectrum of the excitation vibration of the laminated core of the transformer; a fourth step is to calculate the difference between the excitation noise spectrum of the laminated core of the transformer obtained in the first step and the frequency spectrum of the excitation vibration of the laminated core of the transformer obtained in the third step as a difference spectrum; and a fifth step is to diagnose the noise performance of the transformer based on the difference spectrum calculated in the fourth step. A method for diagnosing noise performance of a transformer, comprising:

2. A method for diagnosing noise performance of a transformer as set forth in claim 1, wherein in said fifth step, the frequency at which the difference value of said difference spectrum is maximum is determined as the peak frequency.

3. A method for reducing noise in a transformer, comprising a step of identifying components that are increasing the noise of the transformer based on the diagnostic results of the noise performance of the transformer obtained by executing the noise performance diagnostic method for a transformer as claimed in claim 1 or 2, and generating and notifying a diagnostic result that encourages noise reduction measures for the identified components.

4. A method for reducing noise in a transformer as described in claim 3, further comprising a step of identifying, among components other than the laminated core of the transformer, components whose vibration frequency when the transformer is excited is the same as the frequency at which the difference value of the difference spectrum is maximum, or components whose vibration frequency and the peak frequency have a difference within a predetermined value, as components that are increasing the noise of the transformer.

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