JPH07111217A - Method of estimating noise level of transformer - Google Patents

Abstract

PURPOSE:To get accurate evaluation method by bringing the conventional magnetic distortion measurement for evaluation of noise close to the actual use condition. CONSTITUTION:Magnetic distortion is measured by exciting a magnetic material in audible frequency range. Acoustic pressure is fround from this value. Hereby, the magnetic distortion of a steel plate is measured, whereby the noise caused from excitation including harmonic components can be evaluated by making use of A-characteristic.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a noise level predicting method used industrially for power and distribution transformers.

[0002]

2. Description of the Related Art In magnetic materials widely used in electric and electronic devices, the change in length when excited is one of the material characteristics and one of the evaluation items in quality control. The length ratio before and after excitation is called magnetostriction. Magnetostriction is one of the causes of transformer noise. Another cause of transformer noise is electromagnetic force, but this is due to the transformer manufacturing method, which can be seen in the gaps between steel sheets, loose windings, etc. We decided to study the effect of magnetic materials.

Conventionally, there are a method using a strain gauge, a method using a differential transformer, and a method using a laser Doppler vibrometer in recent years as a method for measuring magnetostriction of a magnetic material. In the strain gauge method, a strain gauge of about 5 mm is attached to the material, and the change in length is converted into an electric signal to measure magnetostriction. In the differential transformer method, vibration due to magnetostriction is transmitted to a differential transformer by a vibration transmission jig and converted into an electrical signal for measurement. In the conventional method, the measurement was difficult because the vibration speed due to magnetostriction was high at frequencies higher than the commercial frequency.

In recent years, control devices using electronic circuits have been developed,
Excitation current containing harmonics flows through the transformer, and harmonics due to distorted waves are generated in transformers with a high magnetic flux density design, so noise from the transformer also contains harmonic components. This harmonic is caused by magnetostriction with a high excitation frequency.

Conventional evaluation of magnetostriction has been carried out by adding a magnetic flux density at a commercial frequency to a magnetic material. If this value is large, noise is predicted to be large. However, the higher the magnetic flux density is, the more distorted magnetic flux flows in the magnetic material, and it is difficult to know the actual state by measuring only commercial frequency excitation. Also, for transformers used at commercial frequencies and above, there is little data on magnetostriction at the frequencies used, and evaluation cannot be done without measuring the noise of the assembled transformer.

Further, pulse excitation or the like in which the excitation waveform is controlled contains many harmonics, and the transformer used in this environment has a small amount of magnetostrictive data including harmonics. The noise cannot be evaluated unless the noise of the assembled transformer is measured.

As described above, the measurement of magnetostriction is a fundamentally important quality evaluation item for magnetic materials in industry, but the magnetostriction evaluation of harmonic components has not been conventionally performed. In addition, it was difficult to evaluate the noise of transformers used at higher frequencies than commercial frequencies.

[0008]

An object of the present invention is to predict the noise level of a transformer constructed using the magnetic material based on the magnetostriction data of the magnetic material for the transformer. The present invention also provides a noise level prediction method for a transformer that performs frequency analysis on a magnetostrictive waveform of arbitrary waveform excitation, converts the magnitude into sound pressure, and performs auditory correction.

[0009]

The first gist of the present invention is as follows.
A method of predicting a noise level of a transformer is characterized in that the magnetostriction of a magnetic material for a transformer is measured in an audible frequency range, the obtained magnetostriction is converted into a sound pressure, and then the audibility is corrected.

The second gist of the present invention is to perform a frequency analysis on the magnetostrictive waveform of the magnetic material for a transformer excited by an arbitrary waveform, convert the magnetostriction at each frequency into sound pressure, and further perform auditory correction. It is a method of predicting noise level of a transformer, which is characterized by applying it.

In order to improve the conventional magnetostrictive evaluation method,
A magnetostriction measuring device using a laser Doppler vibrometer is used. This device can measure the magnetostriction of high frequency excitation as compared with the differential transformer method used conventionally.
This device is used to measure magnetostriction from 50Hz to 2kHz. The obtained magnetostriction is time-differentiated to calculate the displacement velocity v. Here, it is assumed that the surrounding air particles are moved at the same displacement velocity v that is caused by magnetostriction.
Applying the formula expressing sound pressure to the displacement velocity, the magnetostriction is expressed by sound pressure. The formula used here is shown below. p = ρcv where p: sound pressure, ρ: density of medium, c: speed of sound, v:
The velocity of air particles (magnetostrictive displacement velocity). In air, ρc = 413 (Kg / m ² s). This is audibly corrected to obtain a sound pressure level of A characteristic obtained from magnetostriction (JEM-1117; method of measuring noise level of transformer).

[0012]

[Function] By this method, magnetostriction from commercial frequency up to 2 kHz, which has not been obtained as clear knowledge in the past, can be measured. This is because it is possible to measure even high-frequency magnetostrictive vibration by using the laser Doppler vibrometer.

Further, the sound pressure (noise) actually perceived by the human ear can be predicted by performing the auditory sense correction, and it has been difficult to find the correlation between the magnetostriction and the noise in the past. By inserting it, it is possible to predict the noise closer to the actual noise.

For the above reasons, it is possible to predict the noise level of a transformer constructed using the magnetic material only by measuring the magnetostriction of the magnetic material for the transformer without manufacturing the transformer.

[0015]

【Example】

[Embodiment 1] FIG. 1 shows an example of measuring magnetostriction at each excitation frequency. It can be seen that the magnetostriction decreases at high frequencies.

As an example, electromagnetic steel sheets of grade (JIS) G13 and G9H were measured. At high frequencies, G9H having a high grade has a smaller magnetostriction than G13 having a low grade. Furthermore, when the magnetostriction is converted into sound pressure, the audibility correction is applied, and the sound pressure is converted into the A characteristic,
It becomes the curve shown in FIG. High frequency range (1-2kHz
), G13 shows a large sound pressure, and it is easily predicted that a large noise is generated in the magnetic field on which the distorted waveform is superimposed.

[Embodiment 2] FIGS. 3 and 4 show examples in which magnetostriction was measured by sinusoidal excitation at frequencies of 50 Hz and 60 Hz. The excitation waveform is arbitrary and may be one that matches the usage condition. The magnetostriction was obtained by frequency analysis, and each frequency component was obtained by an FFT waveform analysis program. The frequency component may be directly obtained by a spectrum analyzer. The sound pressure at each frequency is obtained by performing the above operation, and the audibility is corrected. It can be seen that the harmonics have higher sound pressure than the fundamental wave.

As an example, the grade (JIS) is 27G1
Magnetic steel sheets of 30 and 27P95 were measured. High grade at high frequency 27P95 low grade 2
Sound pressure is low as a whole compared to 7G130. This is 5
This is true for both 0 and 60 Hz (Figs. 5 and 6).

When this is a waveform containing harmonics, it can be evaluated that the sound pressure becomes high at a high frequency portion. Excitation at 1.9T, which is close to this, is a distorted waveform and the magnitude of the harmonic component is It can be understood from the figure that it is large.

[0020]

As described above, according to the present invention, by measuring the magnetostriction of the magnetic material used for the transformer, the noise generated from the excitation including the harmonic component is utilized as the A characteristic sound pressure. It can be evaluated by doing. In addition, by installing a device for measuring A-weighted sound pressure in the audible frequency range on the manufacturing line based on this prediction method, quality control for manufacturing low noise materials can be performed, and further, for the present noise problem It gives clear guidelines for material development, and the industrial benefits are extremely large.

[Brief description of drawings]

FIG. 1 is data comparing the frequency dependence of magnetostriction.

FIG. 2 is a diagram in which the characteristics shown in FIG. 1 are converted into A characteristic sound pressure and compared.

FIG. 3 is a diagram in which a magnetostriction in an electromagnetic steel sheet having a grade (JIS) of 27G130 is subjected to frequency analysis and converted into A characteristic sound pressure.

FIG. 4 is a diagram in which magnetostriction is subjected to frequency analysis using the same steel plate as in FIG. 3 and converted into A characteristic sound pressure.

FIG. 5 is a diagram in which magnetostriction in an electromagnetic steel sheet having a grade (JIS) of 27P95 is frequency analyzed and converted into A characteristic sound pressure.

FIG. 6 is a diagram in which magnetostriction is subjected to frequency analysis using the same steel plate as in FIG. 5 and converted into A characteristic sound pressure.

Claims (2)

[Claims] 1. A noise level predicting method for a transformer, comprising: measuring magnetostriction of a magnetic material for a transformer in an audible frequency range; converting the obtained magnetostriction into sound pressure; 2. A transformer which is characterized in that a magnetostriction waveform of a magnetic material for a transformer excited by an arbitrary waveform is subjected to frequency analysis, magnetostriction at each frequency is converted into sound pressure, and further auditory sensation correction is performed. Noise level prediction method.