JP2007179888A - Direct current high voltage vacuum apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a direct current high voltage vacuum apparatus capable of operating without impairing withstand voltage performance even in the case where dust remains or enters in a vacuum container. <P>SOLUTION: The direct current high voltage vacuum apparatus has a casing formed by an insulation wall, an evacuated sealed space formed in the casing, electrodes provided in the sealed space to which direct current is applied and a dust capture container for capturing dust in the sealed space; and the dust capturing container is provided at a position free from effect of an electric field formed by the electrodes. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a direct-current high-voltage vacuum apparatus configured to apply a direct-current high voltage to an electrode provided in a vacuum vessel.

  Generally, in a vacuum vessel, it is possible to insulate against a high voltage as compared with the atmosphere. In vacuum, the withstand voltage per mm between the electrodes is 10 kV or more, but in the atmosphere, the withstand voltage per mm between the electrodes is about 3 kV. Utilizing this property, vacuum containers are used in many high voltage devices. For example, there are power devices such as a vacuum circuit breaker and a vacuum disconnector, a cathode ray tube, and the like. Recently, it is also used for measurement electron microscopes and medical X-ray tubes. In a cathode ray tube, a measuring electron microscope, and a medical X-ray tube, a vacuum container is used for insulation of a DC voltage.

  Insulation using a vacuum significantly reduces the withstand voltage performance when there is local concentration of the electric field. If there is a protrusion on the electrode, local concentration of the electric field is caused, and the withstand voltage performance is reduced due to electron emission from the electric field. Therefore, electrode protrusions should be avoided. In particular, when a DC voltage is applied, the polarity of the electrode does not change. Therefore, if there is a projection on the anode, there is a high risk that electrons will be emitted continuously and an insulation failure will occur immediately. In order to prevent local concentration of the electric field, it is not necessary to provide a protrusion on the electrode. For this purpose, so-called mirror polishing, in which the electrode is polished so that the surface becomes a mirror surface, is thoroughly performed.

  When a vacuum container is manufactured, fine dust may remain inside. When this dust adheres to the electrode surface, it becomes the same as a projection formed on the electrode surface. Accordingly, electron emission occurs due to local electric field concentration, and the withstand voltage performance between the electrodes is lowered. It is ideal to eliminate the dust remaining in the vacuum vessel, but it is difficult to eliminate the dust at all in the industrial mass production process. Although vacuum containers are manufactured in a clean environment such as a clean room, it is possible to eliminate dust residue in the manufacturing process as much as possible, but fine dust is generated due to sliding of metals during operation as a product. Sometimes. Furthermore, if repair is required after a long period of operation, the vacuum vessel must be disassembled. Even in such a case, dust may be mixed in the vacuum container.

  The dust in the vacuum container reciprocates between the high voltage electrode and the low voltage electrode. When dust comes into contact with one electrode, an electric charge is instantaneously injected from the electrode into the dust, and the dust has the same potential as that electrode. Thus, an electrostatic force acts between the dust having the same potential as one of the electrodes and the counter electrode. Dust flies to the counter electrode by the resultant force of this force and gravity. Since gravity acts on the dust, a large electrostatic force is required for the dust to fly from the lower electrode to the upper electrode. This electrostatic force is generated by the electric field between the electrodes.

  When the strength of the electric field is small, a phenomenon such as dust does not fly up and rises on the electrode surface occurs. When the strength of the electric field increases, the dust also jumps from the lower electrode and reaches the upper electrode. In this way, it will fly repeatedly between electrodes. Such reciprocation of dust between electrodes is a phenomenon peculiar to DC voltage. Moreover, since it is in a vacuum, dust reciprocates between electrodes without receiving air resistance. The phenomenon so far is not a big problem because dust only flies inside the vacuum vessel. However, when the strength of the electric field is further increased, the projection is formed on the electrode at the moment when dust contacts the positive electrode. Electrons are emitted from the tip of the dust by an electric field. When electron emission becomes active, a short circuit occurs between the electrodes.

  Therefore, it is only necessary to prevent dust generated due to residual, generation, or mixing in the DC high-voltage vacuum vessel from becoming protrusions on the electrode surface.

  An object of the present invention is to provide a direct-current high-voltage vacuum apparatus that can be operated without impairing the withstand voltage performance even if dust remains or enters the vacuum container.

  A direct current high voltage vacuum apparatus according to the present invention includes a casing formed by an insulating wall, a vacuum exhausted sealed space formed in the casing, an electrode disposed in the sealed space to which direct current is applied, and A dust trapping container for trapping dust in the sealed space, and the dust trapping container is disposed at a position not affected by the electric field formed by the electrode.

  According to the present invention, operation can be performed without impairing the withstand voltage performance even if dust remains or enters the vacuum container.

  FIG. 1 shows an embodiment of a DC high voltage vacuum vessel according to the present invention. FIG. 1 schematically shows a direct-current high-voltage vacuum vessel, with electrodes highlighted. Other components are provided in the actual DC high-voltage vacuum vessel, but are omitted here.

  The DC high-voltage vacuum vessel has a casing 3, a pair of electrodes 1 and 2, and a ring-shaped dust trapping vessel 5. The direction of gravity is assumed to be a direction from top to bottom in FIG. Therefore, the electrode 1 is on the ceiling side and the electrode 2 is on the bottom side.

  The casing 3 is formed of an insulating wall such as glass or ceramics. The inside of the casing 3 is a sealed space 4 that is evacuated. The outer side 6 of the casing 3 is filled with air, insulating oil, insulating gas and the like.

  The electrodes 1 and 2 are disposed so as to face each other. A high voltage is applied to one electrode and a low voltage is applied to the other electrode. The electrodes 1 and 2, respectively, have inner end portions 1-a and 2-a at radially inner ends, support posts 1-b and 2-b that support the end portions, and external terminals 1-c connected to the support posts, 2-c. The outer ends of the external terminals 1-c and 2-c are arranged outside the casing 3.

  The dust container 5 is disposed on the bottom surface of the sealed space 4. In this example, the dust trapping container 5 is disposed so as to be embedded in the external terminal 2-c of the electrode 2 on the bottom surface side.

  When a DC high voltage is applied between the electrodes 1 and 2, an electric field is generated in the sealed space 4. The dust in the casing 3 reciprocates between the high voltage electrode 1 and the low voltage electrode 2. Such a flight between dust electrodes is a phenomenon that occurs in a vacuum vessel to which a DC high voltage is applied, as described above.

  When dust comes into contact with the positive electrode, there is a risk that electrons are emitted from the tip of the dust instantly. However, in this example, the dust capturing container 5 is provided on the bottom surface of the casing 3. Dust flying between the electrodes is captured by the dust capturing container 5 by gravity. The electric field in the dust trapping container 5 is almost negligible. Once the dust enters the dust capturing container 5, it does not fly again between the electrodes.

  The structure of the dust trapping container 5 according to the present invention will be described with reference to FIG. FIG. 2 a shows a cross-sectional configuration of the dust trapping container 5, and FIG. 2 b shows a plan configuration of the dust trapping container 5. The dust trapping container 5 includes an inner cylindrical portion 5-a, an outer cylindrical portion 5-b, and a ring-shaped bottom plate 5-c, and a ring-shaped groove 5-e is formed by these three members. . A through hole 5-f for arranging the electrode 2 is formed in the center of the ring-shaped groove.

  At the upper end of the ring-shaped groove 5-e, a plurality of rods 5-d are arranged at predetermined intervals along the radial direction. As shown in FIG. 2b, the opening of the ring-shaped groove 5-e is partially closed by the rod 5-d. A window 5-g is formed between the bars.

  The cross section of the rod 5-d may have any shape as long as a flat surface is not formed on the upper surface, and may be, for example, a circle or a convex triangle.

  Of the dust that has fallen from above, the dust that has fallen between the rods 5-d falls down as it is and is deposited on the bottom plate 5-c. Of the dust that has fallen from above, the dust that collides with the rod 5-d slides on the surface of the rod 5-d, falls between the rods 5-d, and accumulates on the bottom plate 5-c. Thus, the dust deposited on the bottom plate 5-c does not jump out of the dust catching container 5.

  If the window 5-g is small, the function of capturing dust by the dust capturing container 5 is lowered, but the function of preventing the captured dust from jumping out is enhanced. When the window 5-g is large, the function of capturing dust by the dust capturing container 5 is enhanced, but the function of preventing the captured dust from jumping out becomes low. The window 5-g is determined by the diameter and number of the rod 5-d.

  With reference to FIG. 3, the diameter and number of the rods 5-d will be described. Here, a case where a cylindrical bar is used as the bar 5-d will be described. The horizontal axis in FIG. 4 is the diameter of the cylindrical rod, and the vertical axis is the number of short circuits per thousand hours. As shown in the figure, when the diameter of the cylindrical bar is larger than 13 mm, the number of occurrences of short circuit increases. This is because when the diameter of the cylindrical rod is larger than 13 mm, dust adheres to the upper surface of the cylindrical rod and does not slide and fall. Therefore, the diameter of the cylindrical rod needs to be 12 mm or less.

Next, the number of cylindrical bars is calculated. The diameter of the cylindrical rod is d, the outer diameter of the inner cylindrical portion 5-a is D, and the number of cylindrical rods is n. n must satisfy the following equation.
n <π × D / d

When it is necessary to provide at least 6 cylindrical rods, the diameter d of the cylindrical rods needs to satisfy the following formula.
d <π × D / 6

  When the outer diameter D of the inner cylindrical portion 5-a is constant, the diameter d and the number n of the columnar bars are in a reciprocal relationship with each other. As the diameter d of the cylindrical rod increases, the number n decreases, and as the number n increases, the diameter d decreases.

  An example in which a dust trapping container is provided in an electron gun of an electron microscope will be described with reference to FIG. An electron gun 11 and an electrode 12 are arranged in a vacuum vessel 13 made of an insulating wall. The electron gun 11 is disposed on the upper side, and the electrode 12 is disposed on the lower side. The electron gun 11 has an electron gun part 11-a and an electron gun shield 11-b, and a positive high voltage is applied thereto. The electrode 12 has an electron introduction cylinder 12-a and an outer wall 12-b. A high DC voltage is applied between the electron gun 11 and the electrode 12. Electrons from the electron gun unit 11-a are guided downward through the electron introduction cylinder 12-a.

  A dust trapping container 14 is disposed around the electron introduction cylinder 12-a of the electrode 12. The dust trapping container 14 may be the same as that shown in FIG.

  The dust in the vacuum container 13 falls downward by its own weight and is captured by the dust capturing container 14. When an electric field is generated in the vacuum container 13, the dust falls downward and is captured by the dust capturing container 14. The dust once trapped in the dust trapping container 14 does not jump out of it.

  Thus, since the dust in the vacuum container 13 is captured by the dust capturing container 14, a short circuit due to the dust can be prevented.

  An example in which a dust trapping container is provided in a CT X-ray tube will be described with reference to FIG. The CT X-ray tube includes a glass vacuum vessel 23, a rotating anode 21 disposed therein, and a cathode 22 including an electron gun. A plurality of dust capturing containers 24 are provided around the vacuum container 23. The CT X-ray tube is installed inside a rotating donut-shaped tube and rotates at a high speed in the same cycle as the rotation of the donut-shaped tube. The CT X-ray tube rotates around a horizontal axis. The dust in the CT X-ray tube jumps radially outward from the rotation axis by centrifugal force and is captured by the dust capturing container 24 disposed around the vacuum container 23.

  With reference to FIG. 6, the detail of the structure of the dust capture container 24 provided in the X-ray tube for CT is demonstrated. As shown in the figure, the dust capturing container 24 has a rotating bottom plate 24-a, two side plates 24-b, 24-c, and an upper cover plate 24-d, and a space 26 is formed by these members. The The rotating bottom plate 24-a and the two side plates 24-b and 24-c are connected to the vacuum vessel 23 and rotate together with the vacuum vessel 23. The lid plate 24-d and the side plates 24-b and 24-c are separated from each other. Therefore, even when the vacuum vessel 23 rotates, the lid plate 24-d does not rotate. The dust in the vacuum vessel 23 moves radially outward by centrifugal force, and is trapped in the space 26 through the gap between the lid plate 24-d and the side plates 24-b, 24-c as indicated by arrows. Is done. The dust once trapped in the space 26 does not jump out from there.

  A glass 25 is provided in part of the rotating bottom plate 24-a and the lid plate 24-d to extract X-rays. Even with such a configuration, dust can be sufficiently captured, but in this example, a lid plate weight 24-g is further provided on the lid plate 24-d, and a lid plate rail is provided at the tip of the lid plate weight 24-g. 24-f is provided. On the other hand, a cover plate sliding wheel 24-e is provided on the rotating bottom plate 24-a. The protrusion of the cover plate sliding wheel 24-e is disposed in the recess of the cover plate rail 24-f. However, the lid sliding wheel 24-e rotates together with the vacuum vessel 23, but the rotary lid rail 24-f is stationary. Therefore, the cover plate sliding wheel 24-e and the rotary cover plate rail 24-f are separated from each other. Thus, in this example, the lid plate 24-d of the dust trapping container 24 does not rotate even when the CT X-ray tube rotates, so that dust can be trapped stably.

  Although the example of the present invention has been described above, the present invention is not limited to the above-described example, and various modifications can be easily made by those skilled in the art within the scope of the invention described in the claims. It will be understood.

It is sectional drawing which shows the direct current | flow high voltage vacuum vessel which becomes one Example of this invention. It is a figure which shows the structure of the dust collection container by this invention. It is a characteristic view which shows the diameter of a cylindrical rod, and the frequency | count of a short circuit occurrence. It is sectional drawing which shows the example which applied the direct-current high voltage vacuum vessel which becomes one Example of this invention to the electron gun of an electron microscope. It is sectional drawing which shows the example which applied the DC high voltage vacuum vessel which becomes one Example of this invention to the X-ray tube for CT. It is sectional drawing which shows the example which applied the dust trapping container of the DC high voltage vacuum container which becomes one Example of this invention to the X-ray tube for CT.

Explanation of symbols

1, 2 ... Electrode, 3 ... Casing, 4 ... Sealed space, 5 ... Dust trap, 6 ... Outside

Claims (6)

  A casing formed by an insulating wall, an evacuated sealed space formed in the casing, an electrode disposed in the sealed space to which direct current is applied, and a dust trap for trapping dust in the sealed space A direct current high voltage vacuum apparatus, wherein the dust trapping container is disposed at a position not affected by an electric field formed by the electrode.   2. The DC high-voltage vacuum apparatus according to claim 1, wherein the electrode has an upper electrode and a lower electrode, and the dust trapping container is provided around the lower electrode and at the bottom of the casing. A DC high-pressure vacuum apparatus characterized by that.   The DC high-voltage vacuum apparatus according to claim 2, wherein the dust trapping container has an inner cylindrical portion, an outer cylindrical portion, and a ring-shaped bottom plate, and a ring-shaped groove is formed by these three members, A through-hole for arranging the lower electrode is formed in the center of the ring-shaped groove, and a plurality of bars are arranged at predetermined intervals along the radial direction at the upper end of the ring-shaped groove. DC high voltage vacuum apparatus characterized by being made.   2. The DC high-voltage vacuum apparatus according to claim 1, wherein one of the electrodes is an electron gun, the other of the electrodes is a cylindrical electrode, and the dust trapping container is disposed around the cylindrical electrode. A DC high-voltage vacuum apparatus characterized by   2. The DC high-voltage vacuum apparatus according to claim 1, wherein the casing is a tube that can rotate around a horizontal axis, and the dust trapping container is provided around the tube. High voltage vacuum equipment.   6. The DC high-voltage vacuum apparatus according to claim 5, wherein the dust trapping container includes an outer peripheral surface member provided on the tube and rotating together with the tube, side members on both sides of the outer peripheral surface, the outer peripheral surface member and the side surface. An inner peripheral surface member provided and fixed so as to cover a container formed by the member, and an opening formed between the inner peripheral surface member and the side surface member, and dust in the tube A direct-current high-voltage vacuum apparatus configured to enter the dust trapping container through the opening by centrifugal force.

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