JP2007149822A - Magnetic shield device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a support structure which does not degrade magnetic characteristics of a magnetic shield device for shielding an AC cable. <P>SOLUTION: A magnetic body 10 is housed in an aluminum case 15. The magnetic body 10 covered with the aluminum case 15 is prepared in a plurality of numbers to enclose a three-phase AC cable 20 in the plane orthogonal to the cable 20, so that the magnetism leaking from the cable 20 is shielded. The aluminum case 15 comprises a gap for enclosing the cable 20, with an insulator 32 arranged in the gap. An insulator case can be used instead of the aluminum case. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a magnetic shield device that shields a magnetic field leaking from a cable through which a current flows, and more particularly to a magnetic shield device that shields a magnetic field leaking from a cable through which a single-phase or three-phase alternating current flows.

  For example, an electrical room in which a three-phase AC cable for power is laid is conventionally located in the basement of a building and isolated from other rooms. Therefore, magnetic leakage from such a three-phase AC cable is prevented. There was little need to consider. Substations were also installed in suburbs with low population density, and it was not necessary to take measures to prevent magnetic leakage from power cables.

  However, in recent years, in high-rise buildings and the like, there are many designs in which the electric room is arranged from the basement to the middle floor in consideration of the wiring length and water discharge. There are also cases where substations with private power generation facilities are provided in urban areas. The three-phase AC cable has little magnetic leakage if the cables are arranged so that the three phases are balanced, but the three cables form one plane from the transformer to other devices. Side by side, the connection is often unbalanced and the leakage of the magnetic field increases. As a result, it is becoming impossible to ignore the influence of the leakage magnetic field on a human body, particularly a pacemaker, which is susceptible to the influence of a magnetic field, and on other equipment, particularly information equipment. In particular, in hospitals and other places, there is an increase in the number of medical devices and high-performance measuring devices that require a large amount of power, and there are voices concerned that the effects of leakage magnetic fields from AC cables may affect other devices such as high-performance measuring devices. is there. In addition, due to sophistication of social life, there is a concern that malfunctions may occur with respect to leakage magnetic fields in high-function devices such as IT devices.

  As a countermeasure against the leakage magnetic field from such a power cable or the like, an open shield structure has been proposed in which a magnetic frame in which electromagnetic steel plates are laminated is arranged around the power cable at a predetermined interval and magnetically shielded (Patent Document 1). reference). However, no specific study has been made on how to support the magnetic frame. For example, when a hole is made in the steel plate of the magnetic body frame in order to support the magnetic body frame, the magnetic flux turns there and the leakage magnetic field increases. Further, when the steel plate is point-supported, the steel plate bends at the fulcrum, and stress acts on the steel plate, thereby deteriorating the soft magnetic properties of the steel plate due to the inverse magnetostrictive effect and also increasing the leakage magnetic field.

International Publication No. 2004/084603 Pamphlet

  An object of this invention is to provide the magnetic shielding apparatus which has a magnetic body support structure which does not cause the deterioration of the magnetic characteristic of the magnetic body of a magnetic shielding apparatus in view of the said problem.

  In order to achieve the above object, a magnetic shield device for shielding a magnetic field leaking from a cable through which a current flows according to the present invention is a plurality of magnetic bodies surrounding the cable, arranged at predetermined intervals in the longitudinal direction of the cable. A plurality of magnetic frames are each covered with a conductor case, and the conductor case is provided with at least one gap surrounding the cable.

  An insulator may be disposed in this gap, and it may be provided on the surface of the conductor case close to the cable and the surface far from the cable. Further, the conductor case can be made of an aluminum material, a copper material, a magnetic steel material, or a nonmagnetic stainless material, which is a metal building member.

  The plurality of magnetic frames are each covered with an insulator case. The material is an architectural resin member or wood.

  According to the present invention, each of the plurality of magnetic frames is covered with the insulator case or the conductor case having at least one gap surrounding the cable, so that the magnetic body in the cover is maintained while maintaining the magnetic shielding performance. Therefore, the magnetic frame can be supported without causing soft magnetic deterioration due to the inverse magnetostrictive effect.

Embodiments of the present invention will be described below with reference to the drawings.
1A, 1B, and 2 show a magnetic shield device according to a first embodiment of the present invention. As shown in FIG. 1 (a), the magnetic shield device according to the present embodiment magnetically shields a three-phase AC cable 20 having three cables 20U, 20V, and 20W. A plurality of aluminum cases 15 accommodating the frame 10 are arranged at predetermined intervals in the longitudinal direction of the cable. In order to facilitate understanding, only the aluminum case 15-1 housing the magnetic body frame 10-1 is shown in an exploded perspective view. In the present embodiment, the aluminum case 15 is configured by providing a gap between the upper and lower cases and disposing an insulator in the gap. The insulators 32-2 and 32-3 arranged in the gap between the aluminum cases 15-2 and 15-3 are shown.

  FIG. 1B is a partial cross-sectional view of the magnetic shield device shown in FIG. 1A, and shows a cross section of the magnetic frame 10-1 covered with the cable 20U and the aluminum case 15-1 near the cable 20U. ing. The insulator 31-1 is disposed in the gap (front gap) on the surface close to the cable 20 to be magnetically shielded, and the insulator 32-1 is disposed in the gap (rear gap) on the far surface. In this embodiment, such a configuration is common to all aluminum cases. In the figure, three sets of magnetic body frames 10 and their aluminum cases 15 are shown, but the number can be appropriately increased or decreased depending on the length of the cable and the arrangement interval of the magnetic body frames.

  FIG. 2 shows only the magnetic body frame 10 that performs the magnetic shielding action, with the aluminum case 15 removed. The magnetic body frame 10 is a magnetic plate-like member, and it is desirable to align the plate surfaces in a direction perpendicular to the cable 20. Each of the magnetic body frames 10-1 to 10-3 is formed in a rectangular shape by attaching two long and short sets of laminated directional electromagnetic steel sheets to each other. Electrical steel sheets are suitable as magnetic shielding materials because they have good magnetic properties and low iron loss. In addition, using directional electrical steel sheets, four sets of directional electrical steel sheets are combined so that the longitudinal direction of the four sides of the rectangle is the easy magnetization direction, so the magnetic field generated by the current flowing in the cable is supplemented. It has become easier. Furthermore, since the directional electrical steel sheets are laminated to form the magnetic body frame 10, no eddy current flows in the longitudinal direction of the cable. This is because the electromagnetic steel sheet is usually provided with an insulating coating, and therefore does not have conductivity in the stacking direction even when stacked.

  However, although the magnetic steel sheet is excellent in magnetic properties, it is also expensive, so that a general thin steel plate material may be used. As a general thin steel plate, the Si content may be reduced so that it is easy to cold-roll, and the saturation magnetic flux density may be increased by reducing the carbon content. Insulation is not applied to the surface of general sheet steel, so when using it in layers, apply an insulator to the surface so that it does not have conductivity in the direction parallel to the cable. Must be.

  The present embodiment has one technical feature in that the magnetic body frame 10 is accommodated in the aluminum case 15. That is, the aluminum case 15 firmly supports the magnetic frames 10-1 to 10-3 on which directional electromagnetic steel plates are laminated, and even if the aluminum case 15 is point-supported, the aluminum case 15 has no surface. It is a support and prevents the magnetic properties from being deteriorated due to stress applied to the electrical steel sheet. In addition, when the magnetic shield device of the present embodiment is applied to a cable in a place where it can be touched by human eyes, there is an effect that it looks good.

  Another technical feature of the present embodiment is a gap provided in the aluminum case 15. As described above, the aluminum case 15 has two gaps: a front gap near the cable 20 on which the insulator 31 is disposed and a rear gap far from the cable 20 on which the insulator 32 is disposed. Since the aluminum case 15 is a conductor, when an eddy current flows due to a changing magnetic field, the magnetic field by the cable 20 does not reach the magnetic frame 10 in the aluminum case 15, so that the magnetic shield effect by the magnetic frame 10 is effective. Decrease. Therefore, in this embodiment, the aforementioned gap is provided to prevent the generation of eddy current.

  Of course, in order to divide the current path of the aluminum case 15, the slit may be provided at one place, and a gap can be provided at an arbitrary place. However, according to the simulation results shown below, it is more effective to provide two gaps at a location close to and far from the cable 20 as in this embodiment. Note that a copper or steel case may be used instead of the aluminum case, and other conductive materials may be used. In addition, an insulator disposed in the gap is not necessarily required when it functions as a case that covers the magnetic frame even if the gap is open.

  Hereinafter, an analysis model and an analysis result of the magnetic shield device will be described with reference to FIGS. 3 to 5 show analysis models. FIG. 3 is a top view of a magnetic shield device for shielding a magnetic field by a three-phase cable, and FIG. 4 is a front view thereof. FIG. 6 is a cross-sectional view taken along the line AA in FIG. 4 and shows a cross section of the aluminum case 15-1 that houses the magnetic body frame 10-1.

The magnetic shield device as an analysis model is a cable 20U, 20V, 20W in which two magnetic body frames 15-1, 15-2 are housed in aluminum cases 15-1, 15-2, respectively, and a three-phase current of 50 Hz flows. Encloses a three-phase cable consisting of The exciting current is three-phase 50 Hz, and the magnetomotive force is 15,700 ATrms ( ² ATrms / mm ² ).

  As shown in FIG. 3, the cables 20U, 20V, and 20W have a diameter of 100 mm and are arranged in the X direction. The distance L1 between the centers of the cables 20U and 20V, 20V and 20W is 200 mm, and the X-direction distance L2 between the cables 20U and 20W and the aluminum case is 10 mm. The aluminum case is made by combining a member having a width L3 of 85 mm and a length L4 of 200 mm and a member having a width L3 of 85 mm and a length L5 of 770 mm.

  As shown in FIG. 4, the thickness L6 of the aluminum case is 42 mm, and the distance between the centers of the aluminum cases 15-1 and 15-2 is 150 mm.

  As shown in FIG. 5, in the analysis model, 20 electromagnetic steel plates 35ZG having a width M1 of 50 mm are stacked to form a magnetic frame plate 10-1 having a thickness M2 of 7 mm, and an aluminum case 15- 1 is made of an aluminum material having a thickness L7 of 15 mm, and the cross section of the space in the case is 55 mm × 12 mm.

  FIG. 6 shows a table of physical property values of electromagnetic steel sheets and aluminum materials used in the analysis model. The electrical steel sheet of this example is a grain-oriented electrical steel sheet, and has a relative permeability of 80,000 in the easy axis direction and a relative permeability of 5,000 in the hard axis direction.

FIG. 7 is a graph showing the results of the simulation performed on the magnetic shield device of FIGS. 4 to 6, and FIG. 8 is a diagram showing the horizontal axis of the graph of FIG. 7 in association with the analysis model. As shown in FIG. 8, the graph of FIG. 7 shows the center of the cable 20V arranged at the center of the magnetic shield device as the origin and the horizontal axis on the center line in the thickness direction (z direction) of the aluminum case 15-1. The vertical axis represents the magnetic flux density at each point in the x direction. It showed the point of _x 1 ~x ₇ for each 100mm to reference. The range from 300 mm (x ₁ ) to 385 mm from the center is an aluminum case, and if it exceeds 385 mm, it becomes the outside of the magnetic shield device according to the present invention.

  The one-dot chain line in FIG. 7 is the case without the shield device, and the broken line is the gap before the eddy current is cut when the electromagnetic steel sheet housed in the aluminum case without the gap to cut off the eddy current is used. When using an electromagnetic steel sheet housed in an aluminum case with a thick line, a thick line indicates a case of using an electromagnetic steel sheet housed in an aluminum case having a front-rear gap that blocks eddy current.

  As is apparent from the figure, when a magnetic steel sheet simply contained in an aluminum case is used, it is almost indistinguishable from the case where magnetic shielding is not performed. On the other hand, when an electrical steel sheet housed in an aluminum case with a gap that blocks eddy current is used, the effect of magnetic shielding appears, and electrical steel sheet housed in an aluminum case that has two gaps at the front and rear to block eddy current Is used, the magnetic shielding effect is larger than that of one gap.

  In this way, by covering the magnetic frame that acts as a magnetic shield with the aluminum case having a gap, it is possible to realize a support structure that prevents stress concentration on the magnetic frame while maintaining the magnetic shielding effect. Further, since the magnetic shield device has an open structure, it is superior in heat dissipation effect and advantageous for maintenance and inspection as compared with a shield device having a sealed structure. Note that the outer shape of the magnetic frame or the outer shape of the aluminum case is not limited to a rectangle. Furthermore, although the example which shields the magnetic field produced | generated by the electric current of three-phase alternating current 50Hz was demonstrated as embodiment, it is not limited to this, This invention is effective in the range of several Hz to several kHz.

  Further, as a second embodiment of the present invention, a case where the case for housing the magnetic frame is an insulator will be described. The shielding effect of the magnetic frame is the same as that of the first embodiment. Further, since the magnetic frame is surface-supported, soft magnetism deterioration due to the inverse magnetostriction effect is small. At this time, phenol resin or wood is used as the insulator. In this case, the above gap is naturally unnecessary. In addition, a resin-based member such as a fiber reinforced resin may be used.

(A) is a figure which shows one Embodiment of the magnetic shielding apparatus of this invention, (b) is a figure which shows the partial cross section. It is a figure which removes an aluminum case from the magnetic shielding apparatus of one Embodiment of this invention, and shows a magnetic body frame. It is a figure which shows the upper surface of the analysis model of the magnetic shield apparatus of this embodiment. It is a figure which shows the front of the analysis model of the magnetic shielding apparatus of this embodiment. It is a figure which shows the cross section of the aluminum case of an analysis model. It is a figure which shows the physical-property value of the material used for an analysis model. It is a figure which shows the graph of the simulation result of an analysis model. It is a figure which shows the relationship between the horizontal axis of the graph of FIG. 7, and an analysis model.

Explanation of symbols

10 Magnetic body frame 15 Aluminum case 20 Three-phase AC cable 31, 32 Insulator

Claims (11)

A magnetic shield device for shielding a magnetic field leaking from a cable through which a current flows,
A plurality of magnetic frames surrounding the cable, arranged at predetermined intervals in the longitudinal direction of the cable;
The plurality of magnetic frames are each covered with a conductor case, and the conductor case is provided with at least one gap surrounding the cable.   The magnetic shield device according to claim 1, wherein an insulator is disposed in the gap.   The magnetic shield device according to claim 1 or 2, wherein the magnetic frame is a laminated steel plate in which a plurality of steel plates insulated from each other are laminated in the longitudinal direction of the cable.   The magnetic shield device according to claim 3, wherein the steel plate is an electromagnetic steel plate.   5. The magnetic shield device according to claim 4, wherein the electromagnetic steel sheet is a directional electromagnetic steel sheet having an easy magnetization axis aligned in a direction surrounding the cable.   The magnetic shield device according to claim 1, wherein the gap is provided on a surface of the conductor case close to the cable.   The magnetic shield device according to claim 1, wherein the gap is provided on a surface near and far from the cable of the conductor case.   The magnetic shield device according to claim 1, wherein the conductor case is made of a conductive metal building member.   9. The magnetic shield device according to claim 8, wherein the metal building member is an aluminum material, a copper material, a magnetic steel material, or a nonmagnetic stainless material.   The magnetic shield device according to claim 1, wherein each of the plurality of magnetic frames is covered with an insulator case.   The magnetic shield device according to claim 10, wherein the insulator case is an architectural resin member or wood.

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