JPS6112362B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic shielding device made of a magnetic material that reduces eddy current loss in a box housing a transformer, etc. and prevents local temperature rise.

Generally, the leakage magnetic flux generated by the load current flowing through the transformer windings flows into the iron box housing the windings (hereinafter referred to as the tank) as part of its magnetic path, creating eddy currents in the tank and causing a local temperature rise. . In order to reduce the local temperature rise of the box, a plurality of magnetic shields made of magnetic material are placed in front of the inner wall of the tank as shown in FIG. FIG. 1 is a perspective view of a conventional magnetic shielding device, and FIG. 2 is a sectional view taken along line A-A. In the figure, 1 is a transformer tank, and 2 is a magnetic shield made of a magnetic material placed on the inner wall of this tank with a gap 3 in between.

The conventional magnetic shielding device is constructed as described above, and since the magnetic shield 2 is placed inside the tank 1 and is generally made of laminated silicon steel plates, the magnetic shield 2 is placed inside the tank 1 and is generally made of laminated silicon steel plates. Of the leakage magnetic flux, most of the magnetic flux 4 that uses the tank 1 as a magnetic path does not enter the tank, suppressing a local temperature rise. However, the length of the magnetic shield 2 is limited due to manufacturing restrictions or restrictions when installing it to the tank 1.
Since the joints 3 are placed apart from each other and the magnetic resistance of the joint portion 3 is high, a portion of the passing magnetic flux 4 enters the tank as shown in FIG. Magnetic flux 4 that entered this tank 1
As a result, an eddy current 5 is generated locally as shown in FIG. 3, and this eddy current loss causes a local temperature rise. In order to suppress this local temperature rise, it is conceivable to use a non-magnetic metal such as stainless steel for the tank wall 6 near the joint 3 of the magnetic shield 2 as shown in Figure 4, but it is difficult to construct and economically difficult. It is also expensive.

In addition, in order to suppress the leakage of magnetic flux to the magnetized shield 1, it is necessary to make the joint 3 as small as possible.
Ideally, it would be good to eliminate the seam 3, that is, just make the magnetic shields 2 contact each other, but on the other hand, if the magnetic shields 2 are brought into contact with each other, or due to excitation vibrations when using the device, the magnetic shields 2 This causes the inconvenience that the metal parts of the joints rub against each other, and the management of the seams 3 has become an important issue in manufacturing.

This invention has been made in view of the above-mentioned problems, and by arranging a magnetic flux bypass magnetic shield in parallel with the magnetic shield at a predetermined distance between the magnetic shields facing each other across the joint, it is possible to improve the efficiency of transformers, etc. To provide a magnetic shielding device that can perform magnetic shielding without causing a local temperature rise in a box and can provide sufficient space between joints.

An embodiment of the present invention shown in FIGS. 5 and 6 will be described below. FIG. 5 is a perspective view, and FIG. 6 is a sectional view taken along the line B-B in FIG.
The same reference numerals as those in the figures and FIG. 2 indicate the same or corresponding parts. Reference numeral 1 designates a magnetic shield 2, which is made of a magnetic material and is attached via a mounting piece 8 between the magnetic shield 2 and the tank wall 1 so as to bridge the seam 3.

In the magnetic shielding device configured as described above, the joint 3 of the magnetic shield 2 is closer to the magnetic shield 2 than the tank 1, and the third magnetic shield 7 is attached so as to be a continuous bridge. In FIG. 6, the magnetic resistance of the magnetic path from the left magnetic shield 2 to the magnetic shield 2 is much smaller than that of the magnetic path from the left magnetic shield 2 to the tank 1 to the right magnetic shield 2. From this, most of the magnetic flux leaking from the magnetic shield 2 to the tank side 1 in the continuation portion of the magnetic shield 2 passes through the magnetic shield 7 and does not enter the tank 1. Therefore, the eddy current loss generated in the tank 1 is reduced in this portion, and if the magnetic shield 7 is made of laminated silicon steel plates, almost no loss will occur in the magnetic shield 7. In other words, local temperature rise is suppressed. In addition, since the third magnetic shield 7 is arranged in parallel with the magnetic shield 2 at a predetermined distance, adverse effects caused by excitation vibration and the like are also prevented.

In the above embodiment, the third magnetic shield 7 is installed between the magnetic shield 2 and the tank 1 at the connection part of the magnetic shield 2 so as to bridge the joint 3 of the magnetic shield 2. Similarly, when the third magnetic shield is attached to the side opposite to the tank 1 so as to bridge the joint 3 of the magnetic shield 2, it can be expected that the eddy current loss of the tank 1 will be similarly reduced. In other words, the magnetic resistance of the air gap 3 is R ₁ , and the magnetic resistance from the left magnetic shield 2 to the tank 1 and from the tank 1 to the right magnetic shield 2 is R 1 .
R ₂ , tank 1 in the case of the conventional system as shown in Figure 2
Let _R3 be the magnetic characteristic of the space between the magnetic shield 2 on the opposite side and the magnetic shield 2 on the left side as shown in Fig. 7.
If the magnetic resistance from the magnetic shield 7 to the magnetic shield 2 on the right side is R ₄ and the total amount of magnetic flux passing through the magnetic shield 2 is φ ₀ , then
The leakage magnetic flux φ ₁ to the tank 1 in the case of the conventional system shown in FIG. 2 is given by equation (1), and the leakage magnetic flux φ ₂ to the tank 1 in the case of FIG. 7 is given by equation (2). i.e. Since R ₃ >> R ₄ in equations (1) and (2), φ ₁ > φ
₂ , further magnetic shield 2 and magnetic shield 3
If the gap between R ₁ and R 2 is made smaller, R 1 , R ₂ >> R ₄ can be set, and from equation (2), φ ₂ ≒ R ₄ /R ₂ φ ₀ ...(3), and (3 ), _φ2 becomes very small. That is, by attaching the third magnetic shield 7 as shown in FIG. 7, leakage magnetic flux to the tank 1 is reduced, so that local temperature rise is suppressed.

FIG. 8 shows another embodiment of the present invention.
The difference from FIG. 7 is that one magnetic shield 7 is arranged for each pair of magnetic shields 2, and the operation and effect are the same as those described above, so a description thereof will be omitted.

As described above, according to the present invention, the third magnetic shield is arranged in parallel with the magnetic shield at a predetermined distance between the ends of the magnetic shield, which is arranged in front of the magnetized shield with the ends facing each other. By doing so, most of the leakage magnetic flux at the end is passed through the third magnetic shield, preventing magnetic flux from penetrating into the magnetized shield or shield, so that the local temperature of the magnetized shield or shield is reduced. Magnetism and shielding can be performed without raising the magnetism, and the magnetized shield, such as a transformer box, can be formed from a structural rolled steel plate that is inexpensive and easy to manufacture;
Adverse effects due to excitation vibration etc. are also prevented.

[Brief explanation of drawings]

Figure 1 is a perspective view of a conventional magnetic shielding device, Figure 2 is a perspective view of a conventional magnetic shielding device;
The figure is a sectional view taken along the line A-A in Fig. 1, Fig. 3 is a view showing the eddy current flowing through the tank wall, Fig. 4 is a sectional view showing another conventional example, and Figs. FIGS. 7 and 8 are a perspective view and a BB sectional view showing one embodiment of the magnetic shielding device, and a sectional view and a perspective view showing other embodiments of the present invention. In the figure, 2 is a magnetic shield, 3 is a connecting joint of the magnetic shield 2, and 7 is a magnetic shield.
Note that the same reference numerals in each figure indicate the same or corresponding parts.

Claims (1)

[Scope of Claims] 1. A plurality of magnetic shields of a predetermined length made of a magnetic material are formed on the front surface of a magnetized shield, with their ends facing each other with an air gap interposed therebetween, and the magnetized shield is and a third magnetic shield is arranged in parallel with the magnetic shield at a predetermined interval between adjacent ends of the magnetic shield. Device. 2. The magnetic shielding device according to claim 1, wherein the third magnetic shield is disposed on the side of the magnetic shield facing the magnetized shielding body. 3. The magnetic shield device according to claim 1, wherein the third magnetic shield is disposed on the opposite side of the magnetic shield to the surface facing the magnetized shield.