JPS5823726B2 - Box magnetic shielding device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic shielding device for a box housing equipment that generates leakage magnetic flux, and more particularly to a magnetic shielding device in which an electromagnetic shield is provided near the inner wall of the box.

In an earthen transformer box, leakage magnetic flux generated by the load current of the transformer winding housed in the box flows into the box as part of the magnetic path, causing eddy current loss and local There is a risk of causing a temperature rise.

Figures 1 and 2 show a conventional magnetic shielding device for a transformer box body to prevent this.A thin iron plate or a silicon steel plate is installed near the inner wall of a transformer box body 1 made of ordinary structural rolled steel plate. Laminated electromagnetic shields 2 are arranged along the magnetic flux of the leakage magnetic flux to deflect the leakage magnetic flux from the box body 1.

However, the electromagnetic shield 2 is not a continuous piece because its length is limited due to manufacturing or structural reasons, and the corner portions of the box 1 must guide the magnetic flux at right angles. A plurality of electromagnetic shields 2 are connected via gaps 3.

The end portions of the electromagnetic shields 2 that face each other with the gap 3 interposed therebetween are planar and perpendicular to the longitudinal direction of the electromagnetic shields 2.

However, due to the existence of the air gap 3, the magnetic resistance of the air gap 3 becomes extremely large compared to the continuous part of the electromagnetic shield 2, and a part of the leakage magnetic flux passing through the shield 2 is transmitted through the air gap as shown by arrow 4 in Fig. 2. 2, and some of it bypassed the magnetic box 1 wall as a magnetic path as shown by arrow 5.

Therefore, in this bypass section, the possibility of eddy current loss and local temperature rise occurring in the wall of the box body remained.

FIG. 3 shows an example of a conventional measure to prevent this, in which the wall of the box 1 near the gap 3 is welded with non-magnetic steel 6.

By replacing the wall of the box 1 near the air gap 3 with non-magnetic steel 6, the magnetic resistance on the side of the box 1 wall in the air gap 3 can be made comparable to that on the opposite side. The magnetic flux that was bypassed in the wall of the box body 1 as shown by the mark 5 is transferred to the arrow 7.
It can be pulled back to the magnetic shield 2 side as shown in FIG.

Even if this pullback is not complete and some of the magnetic flux reaches the first wall of the box, the eddy current product generated can be sufficiently reduced because the wall of the first box in that part is made of non-magnetic steel. .

However, the structure shown in FIG. 3 has the disadvantage that the number of welded parts of the box body 1 increases, making the work complicated, and that the non-magnetic steel 6 is expensive, making it uneconomical.

The present invention has been made to eliminate the above-mentioned conventional drawbacks, and provides a box-shaped magnetic shielding device that can effectively prevent the occurrence of eddy current loss and local temperature rise, and is excellent in workability and economy. The purpose is to

A magnetic shielding device for a box according to the present invention includes a plurality of electromagnetic shields made of laminated thin magnetic plates near the inner wall of a box housing equipment that generates leakage magnetic flux, each longitudinal end of which has an air gap. In a box-like magnetic shielding device arranged so as to face each other through the magnetic shields, each end of the electromagnetic shields facing each other may have a stepped surface or an inclined surface. Thin plates in bundles or one
Each sheet is laminated and sequentially shifted in the longitudinal direction.

The present invention will be explained below based on embodiments shown in the drawings.

As shown at noon in FIG. 4, an electromagnetic shield 2 made of laminated thin iron plates or silicon steel plates is arranged near the inner wall of a transformer box 1 made of ordinary structural rolled steel plates.

The longitudinal ends of each electromagnetic shield 2 are step-shaped in the thickness direction, so that the gap 3 formed between the ends of each electromagnetic shield 2 is crank-shaped.

In this example, the thickness of the electromagnetic shield is 1 and 4.
Each dimension shown in the figure is D2. D3, the opposing area between the two ends of each electromagnetic shield is (D1+D2)/D, or (D1+D3)/D1 compared to the conventional structure shown in FIG.
(1) Increase twice.

On the other hand, when the distance between the air gaps 3 is small, the magnetic resistance of the air gaps 3 changes approximately in inverse proportion to the facing area of the electromagnetic shield 20, so the magnetic resistance of the air gaps 3 is expressed by the equation (]) compared to Fig. 2. decreases by the reciprocal of

Therefore, the amount of magnetic flux leaking out of the air gap 3 can be suppressed, and eddy current loss in the box body 1 near the air gap 3 can be reduced.

FIG. 5 shows another embodiment of the present invention, in which each end of the electromagnetic shield 2 has an inclined surface in the thickness direction.

In this embodiment as well, the opposing area of the magnetic shield 2 is
Compared to the figure, the distance is D4/D1 (D4=v'2D1 in angle) (
2) The magnetic resistance is increased by a factor of two, and the magnetic resistance can be reduced to the reciprocal of this, thereby reducing eddy current loss.

6 and 7 respectively show still other embodiments of the present invention, which differ from FIGS. 4 and 5 in that the ends of the electromagnetic shield 2 are stepped or inclined in the width direction. .

In the embodiment shown in FIGS. 6 and 7, the fourth and fifth
The same effect as in the case shown in the figure can be obtained, but considering that the thin iron plates or silicon steel plates constituting the electromagnetic shield 2 are stacked perpendicularly to the wall of the box body 1, the cases shown in Figs. 6 and 7 are better. Workability is even better than in the cases shown in FIGS. 4 and 5.

However, the opening length of the air gap 3 facing the wall of the box body 1 is longer in the cases shown in FIGS. 6 and 7, which is disadvantageous in that the magnetic flux is widely dispersed and leaks.

In each of the above embodiments, the present invention is applied to a transformer box, but it goes without saying that the present invention can also be applied to a box housing a beam drill or other stationary induction equipment.

As described above, the magnetic shielding device for a box body according to the present invention changes the shape of the end of the electromagnetic shield to increase the opposing area of each electromagnetic shield, so that the magnetic shielding device for the box body according to the present invention can be used without deteriorating workability or economical efficiency. It has the excellent effect of effectively preventing eddy current loss in the body and local temperature increases based on this.

[Brief explanation of drawings]

Fig. 1 is a perspective view showing a conventional magnetic shielding device for a transformer box, Fig. 2 is a sectional view showing the same conventional device, and Fig. 3 is a sectional view showing another conventional magnetic shielding device for a transformer box. 4 is a cross-sectional view showing one embodiment of the box-like magnetic shielding device of the present invention, FIG. 5 is a cross-sectional view showing another embodiment of the box-like magnetic shielding device of the present invention, and FIG. FIG. 7 is a perspective view showing still another embodiment of the box magnetic shielding device of the present invention, and FIG. 7 is a perspective view showing still another embodiment of the box magnetic shielding device of the present invention. Note that the same reference numerals in the drawings indicate the same or equivalent parts; in the drawings, reference numeral 1 is a box, and 2 is a magnetic shield 3, which is an air gap.

Claims (1)

[Claims] 1 A plurality of electromagnetic shields made of thin plates of magnetic material are arranged near the inner wall of a box housing equipment that generates leakage magnetic flux so that the longitudinal ends of each are joined facing each other with an air gap between them. In the box-shaped magnetic shielding device, a plurality of thin plates of magnetic material forming each electromagnetic shield are arranged in bundles in order to make each end joint surface of the electromagnetic shield facing each other a stepped surface or an inclined surface. Alternatively, a box-shaped magnetic shielding device characterized in that each sheet is laminated and sequentially shifted in the longitudinal direction.