JP2008082778A - Method and apparatus for measuring natural frequency of iron core of transformer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable the natural frequency of an iron core of a transformer to be measured simply, and to enable a relation with a transformer noise to be clarified. <P>SOLUTION: A method includes: a step S1 of exciting the transformer 10 while changing an excitation frequency step-by-step in a prescribed frequency range, and measuring the noise of the transformer at respective steps; a step S2 of applying a frequency analysis to the measured noise and obtaining noise components each having the frequency being N times the excitation frequency of each step (N is an even number); and a step S3 of determining a peak value of the noise components as the natural frequency of the iron core of the transformer, based on the relation between frequencies (analysis frequencies) being N times the excitation frequency and the noise components having the N-times frequencies. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method and apparatus for measuring the natural frequency of a transformer core, and more particularly to the natural vibration of a transformer core that is suitable for application to a transformer using an electromagnetic steel sheet that generates magnetostrictive vibration upon excitation as an iron core. The present invention relates to a number measuring method and apparatus.

  Transformers are installed in various places, but a low noise level is strongly required especially for transformers installed in urban areas. Electrical steel sheets are mainly used as transformer core materials. This electromagnetic steel sheet has magnetostriction accompanying excitation, and this magnetostrictive vibration is said to be the cause of transformer noise.

  When manufacturing a transformer with low noise, an electromagnetic steel sheet having a small magnetostriction is generally used as a core material. However, there are cases where the transformer noise cannot meet the required specifications in spite of the use of an electromagnetic steel sheet having a small magnetostriction. When the cause is investigated, it is very often the resonance phenomenon of the natural frequency of the transformer core and the magnetostrictive vibration of the electrical steel sheet. For this reason, grasping the natural frequency of the transformer core is extremely important in designing and manufacturing the transformer.

  As a method for testing the natural frequency, for example, as described in Patent Documents 1 and 2, a method using a vibrometer (accelerometer) is common. This is a method for obtaining a natural frequency of a measurement target by exciting a measurement target with an acceleration sensor by a technique such as hammering and measuring a vibration response of the measurement target.

JP-A-62-288534 JP 7-294327 A

  However, Patent Document 1 measures the natural frequency of an auxiliary machine fixed to the engine body via a stay or the like, and Patent Document 2 measures the natural frequency of an electric motor, both of which are transformer iron cores. The natural frequency of was not measured.

  In general, since an iron core has a plurality of vibration modes, the method using an acceleration vibrometer as in Patent Documents 1 and 2 must pay close attention to the installation of the acceleration sensor. For example, if an acceleration sensor is installed at a node position in a certain vibration mode, vibration in that mode cannot be detected. In addition, for example, since the acceleration sensor cannot sense vibration in a direction perpendicular to the sensing direction, in order to sense three-dimensional vibration, three acceleration sensors are installed for sensing each of the x, y, and z directions, or three axes. It is necessary to install a sensor.

  Also, as for the vibration position of the iron core, it is not always possible to excite all the vibration modes that exist in one place, so it is necessary to vibrate multiple positions of the iron core and measure the vibration response each time. There is.

  As described above, the method using the acceleration vibrometer requires a plurality of sensors and a plurality of vibration / response measurements, is complicated and complicated, and in order to actually obtain accurate iron core natural frequency data, Experience and know-how are required.

  Further, depending on the vibration mode of the iron core, even if the amount of vibration is large, the amount of noise is not necessarily large. That is, the radiation efficiency of sound waves differs depending on the vibration mode. Therefore, in the above method, even if the natural vibration mode can be known, any of the vibration modes that exist is actually increased in the transformer noise accompanied by the generation of sound. The problem was that it was not possible to determine whether it was the cause of the problem.

  The present invention has been made to solve the above-described conventional problems, and it is an object of the present invention to be able to easily measure the natural frequency of a transformer core and to clarify the relationship with transformer noise. .

  As a method of measuring the natural frequency of the transformer core in order to solve the above-mentioned problems, the present inventors do not measure the vibration of the iron core, but measure the resulting noise to obtain the natural frequency of the iron core. Investigate whether it is possible to know. As a result, the magnetostrictive vibration of the iron core material (for example, an electromagnetic steel sheet) that causes transformer noise is a superposition of N frequency components (N is an even number of 2, 4, 6, 8, 10,...) Of the excitation frequency. It was found that the natural frequency of the iron core can be known by measuring the noise by using the frequency multiplex vibration.

  The present invention has been made based on such knowledge. When measuring the natural frequency of the transformer core, the excitation frequency is changed stepwise in a predetermined frequency range, and the transformer is excited. A step of measuring the noise of the transformer, a frequency analysis of the measured noise, a step of obtaining a noise component of N times the excitation frequency (where N is an even number), and a step of N times the excitation frequency The problem is solved by including the step of setting the peak value of the noise component in the relationship between the frequency (analysis frequency) and the noise component of each N-fold frequency to the natural frequency of the transformer core.

  The present invention also performs means for exciting the transformer by changing the excitation frequency stepwise within a predetermined frequency range, means for measuring the noise of the transformer at each stage, and frequency analysis of the measured noise. In the relationship between the means for obtaining the N-frequency (N is an even number) noise component of the excitation frequency at each stage and the N-frequency frequency (analysis frequency) of the excitation frequency and the N-frequency noise component, Means for setting the peak value of the noise component to the natural frequency of the transformer core, and a device for measuring the natural frequency of the transformer core are provided.

  In the present invention, since the vibration of the iron core is not measured but the noise is measured, the natural frequency of the iron core can be easily and easily compared with a method using an acceleration vibrometer even without experience. Can be measured.

  In addition, since the natural frequency of the iron core is known by measuring the noise generated as a result of vibration, the relationship between the natural frequency mode of the iron core and the transformer noise can be clearly understood, which vibration mode If it is suppressed, it can be immediately known whether the transformer is most effective for noise reduction.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  In the present embodiment, as shown in FIG. 1, while changing the excitation frequency stepwise, the first step S1 for measuring the transformer noise each time, and the frequency analysis of the measured noise is performed to obtain N times the excitation frequency. In the second step S2 for obtaining the noise component (N is an even number) and the relationship between the N-frequency frequency (analysis frequency) of the excitation frequency and the noise component of each N-frequency frequency, the peak value of the noise component is determined as the transformer core. And a third step S3 having the natural frequency.

  Hereinafter, further detailed description will be given with reference to the embodiment of the measuring apparatus shown in FIG.

  First, in the first step S1, transformer noise is measured by the sound collecting microphone 22 disposed in the vicinity of the transformer 10 each time the excitation frequency applied from the excitation circuit 20 to the transformer 10 is changed stepwise.

The frequency of excitation by the excitation circuit 20 is not particularly defined. However, if the excitation frequency range is f ₁ Hz to f ₂ Hz, f ₂ = 2 × f ₁ is preferable. For example, if the lowest excitation frequency is 50 Hz, the frequency range is 50 Hz to 100 Hz, and if the lowest excitation frequency is 60 Hz, the frequency range is 60 Hz to 120 Hz. The frequency pitch may be appropriately selected according to the analysis accuracy of the natural frequency, but may be approximately 1 Hz to 2 Hz. The excitation magnetic flux density may be performed in the constant excitation magnetic flux density mode in which the excitation voltage is changed according to the excitation frequency so that the excitation magnetic flux density is always constant. However, the excitation magnetic flux density may be performed in the constant voltage mode in which the excitation frequency is changed and the excitation frequency is changed. Simpler and better.

  The noise measurement position and the measurement location by the sound collecting microphone 22 are not particularly limited, but basically the position is beyond the near sound field and the measurement location may be one, but when the measurement location is close to the iron core, the measurement location It is more preferable to use a plurality. Also in the case of a large transformer, it is preferable to have a plurality of measurement points.

  The collected data at the time of noise measurement is data that can be subjected to frequency analysis next. Rough data with a frequency pitch of about the octave band, which is made by conventional noise measurement, is insufficient. The result data obtained by frequency analysis of the time waveform of noise with an FFT analyzer or the like may be simple. However, the time waveform data of noise may be collected and stored, and frequency analysis may be performed later.

  In the second step S2, the frequency analysis of the signal from the sound collecting microphone 22 converted into a voltage signal through, for example, the charge amplifier 24 is performed by, for example, the FFT analyzer 26, and the Nth order (N is an even number) of the excitation frequency. ) Noise component. In the case where the frequency range in which the noise measurement is performed is 50 Hz to 100 Hz and the pitch is 1 Hz, as shown in Table 1, for each excitation frequency, the value of the frequency component of the noise, that is, a frequency N times the excitation frequency. Obtain the noise value at.

  In the third step S3, the harmonic frequency dependence of the N-frequency noise value of the excitation frequency is obtained from the output of the FFT analyzer 26 using, for example, the personal computer 28. As an example of the double frequency data processing method in the case where the frequency range of the noise measurement is 50 Hz to 100 Hz and the pitch is 1 Hz, as shown in the double frequency section of Table 1, in the case of 50 Hz excitation. The 100 Hz component of noise, the 102 Hz component of noise in the case of 51 Hz excitation,..., And the 200 Hz component of noise in the case of 100 Hz excitation are plotted as responses to each frequency as illustrated in FIG. FIG. 3 also plots a processing example for quadruple frequency data. In the same manner, when plotting as 6 times frequency, 8 times frequency,..., The result as shown in FIG.

  In this way, the natural frequency of the transformer core over a wide band can be determined clearly and simply by performing data processing as described above only by performing noise measurement in an extremely narrow frequency band. Moreover, since it is the result of direct measurement of noise, it can be easily understood that the cause of the increase in transformer noise is the highest peak, that is, the natural vibration of 312 Hz, in the example of FIG. Can do.

  A directional electromagnetic steel sheet hoop material having a width of 150 mm was prepared, cut at an oblique angle, and laminated to prepare a three-layer three-leg test transformer having a leg width and a yoke width of 150 mm and a stacking thickness of 50 mm. The stacking direction was alternately stacked. Next, 60 turns of exciting windings were applied to the three legs of the test transformer. Thereafter, in order to reduce noise caused by flapping of the steel plate, the yoke portion was fixed with a jig at an average surface pressure of 2 kgf / cm.

  The sound collecting microphone 22 for noise measurement was installed at a position 30 cm away from the center leg, and the excitation voltage was fixed at 100 V, and the noise was measured while changing the excitation frequency from 50 Hz to 100 Hz in increments of 1 Hz.

  The signal from the sound collecting microphone 22 for noise measurement was converted into a voltage signal via the charge amplifier 24 and then input to the FFT analyzer 26 to collect noise frequency component data. FIG. 4 was obtained by obtaining and plotting the noise components of the double frequency, quadruple frequency,... In FIG. 4, in order to make the graph easy to see, data points are omitted. For example, 10-times frequency data has data points from 500 Hz to 1000 Hz, but data points below 750 Hz are omitted.

  When the method of the present invention is used, as shown in FIG. 4, the natural frequency of the iron core over a wide band can be obtained very simply and easily only by performing noise measurement in a very narrow frequency band of 50 Hz to 100 Hz. It was. It was also easy to grasp that the cause of the increase in transformer noise was the highest peak, that is, the natural vibration of 312 Hz.

  For comparison, when the natural frequency of the test transformer was measured using an acceleration sensor, it was confirmed that it had a resonance peak in the vicinity of 310 Hz.

  In the above description, the present invention has been described with respect to a transformer having an electromagnetic steel sheet as an iron core, but the application target of the present invention is not limited to this.

The flowchart which shows the procedure of embodiment of the measuring method which concerns on this invention The block diagram which shows the structure of embodiment of the measuring apparatus which concerns on this invention The figure which shows the example of a process of 2nd frequency and 4th frequency data in case the frequency range in embodiment of this invention is 50Hz-100Hz and a pitch is 1Hz. The figure which shows the example of a natural vibration analysis of the test transformer in the Example of this invention

Explanation of symbols

10 ... Transformer 20 ... Excitation circuit 22 ... Sound collecting microphone 26 ... FFT analyzer 28 ... PC

Claims (2)

In a predetermined frequency range, exciting the transformer by changing the excitation frequency step by step, and measuring the noise of the transformer at each step;
Performing a frequency analysis of the measured noise and obtaining a noise component of N times the excitation frequency of each stage (where N is an even number);
A step of setting the peak value of the noise component in the relationship between the N-frequency frequency of the excitation frequency and the noise component of each N-frequency to the natural frequency of the transformer core;
A method for measuring the natural frequency of a transformer core, comprising: Means for exciting the transformer by changing the excitation frequency stepwise within a predetermined frequency range;
Means for measuring the noise of the transformer at each stage;
Means for performing a frequency analysis of the measured noise and obtaining a noise component of N times the excitation frequency of each stage (where N is an even number);
Means for setting the peak value of the noise component in the relationship between the N-frequency frequency of the excitation frequency and the noise component of each N-frequency to the natural frequency of the transformer core;
An apparatus for measuring the natural frequency of a transformer core, comprising:

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