JP2567067B2 - Low noise dry type transformer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention (Field of Industrial Application) The present invention relates to a low noise dry type transformer capable of sufficiently reducing noise in a low frequency band.

(Prior Art) When a transformer is excited, a vibration occurs, and the energy of this vibration is propagated to the outside through a case (container) and becomes noise. The causes of this vibration are mainly the magnetostrictive vibration of the iron core and the magnetic attraction force between the laminated layers of the silicon steel strips or at the joint portion.

Techniques for reducing such transformer noise have been reported. For example, as described in the document "Ohmsha Publishing: Sakae Morita," Noise and Noise Prevention ", pages 266 to 267, a means to make a transformer case into a double wall, porous plastic, glass wool on the inner surface of the case, There is a means for attaching a sound absorbing member made of felt or the like.

(Problems to be Solved by the Invention) However, there are the following problems in applying the above noise reducing means to a self-cooling dry type transformer that cools the transformer main body in the case by natural convection. That is, a double wall having a completely sealed structure cannot be constructed because of the necessity of preventing the temperature rise and easiness of operation and maintenance. Generally, due to the above-mentioned necessity, a double wall provided with a ventilation window or the like is used, but the leakage noise from the ventilation window is large and the noise reduction effect is low.

In addition, there is a problem that the double wall is economically disadvantageous and requires a large space. In this case, if the space between the double walls is narrowed to save space,
After all, it is not effective because the sound attenuation cannot be obtained.

Therefore, a configuration in which the above-mentioned means using the sound absorbing member is applied to a double-walled means can be considered. That is, a sound absorbing material is put in the gap between the double walls to attenuate the sound. With this configuration, the sound pressure rises and falls in the space (gap),
Since the air particles do not move much, no sound absorbing effect can be obtained. Further, the frequency of the noise generated by the transformer is, for example, if the power supply frequency is 50 Hz, 100 Hz, 200 Hz, and 300 Hz are the main components and belong to the low frequency band, so even if the sound absorbing member described above is used, noise in the low frequency band Could not be reduced, and as a whole, sufficient noise reduction could not be achieved.

On the other hand, the case itself has a natural frequency as a sound field characteristic, becomes a muffled sound in the case in agreement with the frequency generated by the transformer, and conversely increases noise and becomes a large noise.

Therefore, an object of the present invention is to provide a low noise dry type transformer that can sufficiently reduce noise in a low frequency band.

[Structure of the Invention] (Means for Solving the Problems) The present invention has the following structures in order to solve the above problems and achieve the objects.

In a low noise dry type transformer in which a ventilation window is provided in a case for accommodating the main body of the dry type transformer, the lengths of the three sides of the case are combined in an integral multiple of each other, or the same, and
It is characterized in that the wavelength of the noise generated by the dry-type transformer main body or the integral multiple or 1 / integer multiple of the wavelength does not match the length dimension of the three sides of the case.

(Operation) The natural frequency of the room inside the transformer case is the sound velocity c in the air.
As Given in. Here, l _x , l _y , l _z are long dimensions of three sides of the case, n _x , n _y , n _z are 0 and any positive integer multiple, and a set of n _x , n _y , n There is one eigenmode for _z .

At this time, the number N (f) of natural frequencies included between frequencies 0 and f is _{Here, V = l x · l y} · l z, given by _{S = 2 (l x l y} + l y · l z + l z l x) L = 4 (l x + l y + l z). The natural frequency equation is rewritten as follows.

This is equivalent to the distance between the point (cn _x / 2l _x , cn _y / 2l _y , cn _z / 2l _z ) and the origin in the orthogonal three-dimensional frequency space (f _x , f _y , f _z ). To do. That is, the spacing c / 2l _x , in the f _x , f _y , f _z axis direction
If you make a cubic lattice divided by c / 2l _y and c / 2l _z , each lattice corresponds to one natural frequency. Here, the length dimensions l _x , l _y , and l _z of the three sides in the case are the same or
When the combined size is an integral multiple, the same natural frequency is frequently generated, and the number of natural frequencies in the case is substantially reduced. Also, an integral multiple of the wavelength of the frequency generated by the dry transformer body, or an integral multiple and the length dimension of the three sides of the case l _x , l _y ,
Since it does not match l _z , the natural frequency in the case is small, and the frequency generated by the dry transformer main body does not match the natural frequency in the case, so
Noise inside the case is reduced, and radiated noise outside the case is also reduced.

(Embodiment) An embodiment of the present invention will be described below with reference to FIG. 1 and FIG. 1 is a case, and this case 1 is a side plate 2
And a bottom plate 3 and a ceiling plate 4. The length dimensions in the case 1 are l _x , l _y and l _z . Reference numeral 5 is a transformer body, and 6 is a coil portion of the transformer body 5. The transformer body 5 is housed inside the case 1. The case 1 has an upper window 7 and a lower window 8, and the cooling air enters and leaves the case 1 through the windows 7 and 8. Further, a vibration proof rubber 9 is provided between the transformer body 5 and the bottom plate 3 of the case 1. The entire case 1 is installed on the foundation base 11 via the channel steel 10. In this case, the noise of the transformer is, for example, when excited at the power frequency f _o = 50 Hz,
2f _o = 100 Hz, 4f _o = 200 Hz, 6f _o = 300 Hz ... and are generated at even multiples of f _o . The generated noise frequency f and the wavelength λ of the sound wave have the following relationship.

As shown in FIGS. 1 and 2, the lengths l _x , l _y , and l _z of the three sides of the case 1 are half wavelengths of the frequency of noise generated by the transformer body 5, or integers of half wavelengths. It does not match the multiple or 1 / integer multiple. For example, if the power supply frequency f _o is 50 Hz, then 2f _o = 100Hz, 4f _o = 200Hz, 6f _o = 300Hz ... And a half wavelength Becomes Therefore, the lengths l _x , l _y , and l _z of the three sides shown in FIGS. 1 and 2 are set to l _x = ly _y = l _z = 2.0 m. Table 1 shows the calculated natural frequencies.

According to Table 1, the same numerical value of natural frequency appears, and the number of orders decreases. This order is the number of natural frequencies. In addition, since the half-wavelength of the noise generation frequency from the transformer or the integral multiple of the half-wavelength or 1 / integer multiple does not match l _x , l _y , and l _z , the natural frequency and the noise generation from the transformer match. There is nothing to do.

Further, for example, as in the conventional case, the lengths l _x , l _y , and l _z of three sides shown in FIG. 1 and FIG. 2 are represented by l _x = 2.2 m, l _y = 1.3 m, l _z =
Assuming 1.9 m, the natural frequency will be as shown in Table 2.

According to Table 2, there are many natural frequencies, and the natural frequency and the generation frequency of the transformer are the same in some cases.

Next, the operation of the above configuration will be described. When the transformer body 5 is excited, it is radiated as noise due to magnetostrictive vibration or the like. Since the three side lengths l _x , l _y , and l _z of the case 1 are the same, the number of natural frequencies in the case 1 is small. In addition, since l _x , l _y , and l _z do not match the half-wavelength of the noise generation frequency from the transformer, or an integral multiple or 1 / integer multiple of the half-wavelength, the natural frequency and the transformer in Case 1 Since it does not match the noise generation frequency from the container, noise is greatly reduced. That is, the noise inside the case 1 is reduced, so that the noise outside the case 1 is reduced.

EFFECTS OF THE INVENTION As described above, in the present invention, the lengths of the three sides of the case that houses the transformer main body are set to a combination of integer multiples or the same size, and a half wavelength of the noise frequency of the transformer or By not matching the size of the case to an integer multiple or 1 / integer multiple of half-wavelength, the number of natural frequencies in the case decreases, and since it does not match the natural frequency, This has the excellent effect of reducing the noise and effectively reducing the noise in the low frequency band.

[Brief description of drawings]

FIG. 1 is a cross-sectional front view showing an embodiment of the present invention, and FIG. 2 is a vertical cross-sectional view of FIG. 1 ... Case, 2 ... Case side plate, 3 ... Case bottom plate, 4 ... Case ceiling plate, 5 ... Transformer body, 6 ...
Coil, 7 ... upper window, 8 ... lower window, 9 ... anti-vibration rubber, 10
…… Channel steel, 11 …… Foundation foundation.

Claims (1)

(57) [Claims] 1. A low noise dry type transformer in which a ventilation window is provided in a case for accommodating a dry type transformer body, wherein the lengths of the three sides of the case are combined with each other by an integral multiple or the same. Low noise dry type transformer characterized in that the half-wavelength of the frequency of the noise generated by the transformer main body or an integer multiple or 1 / integer multiple of the half-wavelength does not match the length dimensions of the three sides of the case. .