JP3504985B2 - High voltage bushing of X-ray tube - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high voltage bushing mounted on the wall of an X-ray tube for supplying a high voltage to a filament (cathode) of an electron gun of the X-ray tube.

[0002]

2. Description of the Related Art The inside of an X-ray tube is evacuated to a vacuum,
A high negative voltage with respect to ground is applied to the filament of the X-ray tube. Therefore, it is necessary to electrically insulate the conductor for supplying high voltage to the tube wall of the X-ray tube with high withstand voltage and hermetically seal the tube wall. High voltage bushings are used for this purpose. As a high voltage bushing for an X-ray tube, a high voltage bushing that employs an oil insulation method is commonly used to increase the withstand voltage.

[0003]

In the process of technological development for miniaturizing the outer dimensions of the X-ray tube, there is a demand for making the outer diameter of the generally cylindrical high-voltage bushing as small as possible. In this case, in the conventional oil-insulated high-voltage bushing,
There are the following problems. When the temperature of the high-voltage bushing rises, the temperature of the oil enclosed inside also rises and the oil thermally expands. Since oil is an incompressible fluid, if this thermal expansion is not properly absorbed, the pressure of the oil will become very high and the bushing may be destroyed. Therefore, it is necessary to provide the bushing with a mechanism for absorbing the thermal expansion of oil. Further, the volume of oil cannot be extremely reduced in order to effectively absorb the thermal expansion of oil. For this reason, there is a limit to downsizing the bushing.

By the way, in a technical field other than the X-ray tube, it is known to use an insulating gas as an insulating method for a high voltage bushing. Therefore, as a high voltage bushing for the X-ray tube, it is conceivable to adopt a gas insulation method in order to solve the above-mentioned problems of the oil insulation method.
However, the gas-insulated high-voltage bushing used for other than X-ray tubes does not have a structure that can be directly adopted for the X-ray tube, and a new gas-insulated high-voltage bushing for X-ray tube is not available. Had to develop.

The present invention was developed in such a situation, and an object thereof is to provide a gas insulation type high voltage bushing having a structure suitable for an X-ray tube.
Another object of the present invention is to provide a high voltage bushing for an X-ray tube, which can have a small outer diameter.

[0006]

In the high voltage bushing of the present invention, a space is formed between the vacuum side insulating member and the atmosphere side insulating member, and the insulating gas is sealed in this space. Further, the atmosphere side insulating member is formed of a molding resin, and the discharge suppressing circuit is embedded inside the molding resin. By adopting such a configuration, the outer diameter dimension of the high voltage bushing can be reduced.

The material of the mold resin forming the atmosphere side insulating member is preferably an epoxy resin containing fine particles of alumina ceramics. Alumina ceramics is an insulating material having good heat conduction, so that the heat transmitted from the electron gun to the vacuum side terminal can be released through the mold resin. Further, if the vacuum side insulating member is made of alumina ceramics, heat can be similarly released through the vacuum side insulating member. By molding the atmosphere side insulating member integrally with a metal holder and cooling this holder with cooling water, the heat transmitted through the atmosphere side insulating member can be released from this holder to the cooling water. You can With such a configuration, the temperature rise of the high voltage bushing can be suppressed. Therefore, the vacuum side terminal can directly mechanically support the electron gun, and in that case, the heat transmitted to the vacuum side terminal can be effectively released.

[0008]

1 is a longitudinal sectional view of an embodiment of a high voltage bushing according to the present invention. This bushing forms a narrow space 14 between the insulator 10 as a vacuum side insulating member and the cable post 12 as an atmosphere side insulating member,
The space 14 is filled with insulating gas. Sulfur hexafluoride is used as the insulating gas. The insulator 10 is made of alumina ceramics and has a substantially cylindrical shape with a bottom, and the cylindrical portion is slightly tapered. A vacuum side terminal 18 is provided at the tip of the insulator 10.
Is pierced through and is fixed to the insulator 10 in an airtight manner by brazing. The cable post 12 is made of molding resin. This mold resin is an epoxy resin, and is mixed with alumina powder having a particle size of 5 to 8 μm. The weight ratio of epoxy resin and alumina powder is 9:
It is 4. When the cable post 12 is molded, the inner wall surface of the brass holder 32 is used as a part of the molding die, whereby the cable post 12 is molded so as to be integrated with the holder 32. The cable post 12 has a discharge suppressing circuit 16 embedded therein, and the connection terminal 20 and the atmosphere-side terminal 22 are exposed to the outside. The connection terminal 20 exposed from the cable post 12 is the vacuum-side terminal 1 penetrating the insulator 10.
8 is connected.

The discharge suppressing circuit 16 includes a discharge suppressing coil, an arrester and a capacitor. In the X-ray tube, electric discharge may occur between the electron gun and the tube wall of the X-ray tube or between the electron gun and the target. When this first discharge occurs, discharges are likely to be induced one after another. The discharge suppression circuit 16 is for suppressing this secondary discharge. Further, the discharge suppression circuit 16 also plays a role of protecting the high voltage power source located at the end of the high voltage cable. If the discharge suppressing circuit 16 is molded inside the molding resin, inside the insulator 10 having a reduced diameter,
The position of the discharge suppressing circuit 16 can be reliably positioned, and the risk that the components of the discharge suppressing circuit 16 touch the insulator 10 is eliminated.

This bushing is attached to the tube wall 26 of the X-ray tube by a mounting flange 24. Insulator 10
The flange portion 28 at the base of is fixed by being sandwiched between the mounting flange 24 and the flange portion 34 of the holder 32.
The flange portion 34 of the holder 32 is fixed to the mounting flange 24 with a bolt 36.

The electrical path from the vacuum side terminal 18 to the atmosphere side terminal 22 will be described. The vacuum side terminal 18 is connected to the discharge suppression circuit 16 via the connection terminal 20 and the conductor inside the cable post 12. Connected. The discharge suppressing circuit 16 is connected to the atmosphere-side terminal 22 via another conductor inside the cable post 12. Therefore, the connecting conductor between the vacuum side terminal 18 and the atmosphere side terminal 22 is composed of the conductor in the cable post 12 and the discharge suppressing circuit 16. Also, the vacuum side terminal 18 and the atmosphere side terminal 2
The conductor consisting of 2 and the connecting conductor between them is the insulator 1
0 and the cable post 12 allow the mounting flange 24
Is electrically insulated so that it can be hermetically sealed.

The holder 32 is provided with a supply valve 38 for supplying the insulating gas to the space 14. This supply valve 38
The mounting screw portion 40 is screwed into the screw portion of the holder 32 and then fixed to the holder 32 with an adhesive. This seals the insulating gas. Inside the supply valve 38 is a spring-biased check valve, and on the atmosphere side of this check valve there is also an O-ring sealed plug. This plug is held from the outside by a screw-in type cap 42. Holder 3
A groove 44 for passing cooling water is formed on the outer peripheral surface of 2, and the groove 44 is covered with a water cooling jacket plate 46. The water cooling jacket plate 46 is brazed to the outer peripheral surface of the holder 32. The water cooling jacket plate 46 is electrically grounded.

In FIG. 1, the upper side of the tube wall 26 is the inside of the X-ray tube, that is, the vacuum side, and the lower side of the tube wall 26 is the atmosphere side. A vacuum seal is made between the tube wall 26 and the mounting flange 24 by an O-ring 48, and the mounting flange 24 and the insulator 1
A vacuum seal is made between 0 and O ring 50. The insulating gas is sealed between the insulator 10 and the holder 32 by the O-ring 52.

FIG. 2 is a bottom view seen from below in FIG.
The above-mentioned FIG. 1 is a sectional view taken along the line II of FIG. The holder 32 is provided with a pressure sensor 54 that detects a pressure drop of the insulating gas. The insulating gas is filled at a pressure of 1.5 atm, but the pressure sensor 54 detects this when the pressure drops to 0.4 atm. When the pressure drop of the gas is detected, the insulating gas can be supplied from the supply valve 38. It should be noted that if the insulating gas has a pressure equal to or higher than the atmospheric pressure, there is no problem with the insulating performance, but for safety, 0.4 atmospheric pressure is set as the lower limit value as described above.

The water cooling jacket plate 46 is provided with an inlet 53 and an outlet 55 of cooling water. The flange portion 34 of the holder 32 has notches 35 equally arranged in four portions, and bolt holes 37 are formed at corresponding portions of the mounting flange 24. By passing a bolt through the bolt hole 37, the mounting flange 24 can be fixed to the tube wall 26 (see FIG. 1) of the X-ray tube.

FIG. 3 is a plan view seen from above in FIG.
The vacuum-side terminal 18 fixed to the end face of the insulator 10 is 2
It is composed of one filament terminal 56, 58 and two bias terminals 60, 62. Filament terminals 56, 58
Is connected to the filament of the electron gun of the X-ray tube. The bias terminals 60 and 62 are short-circuited to each other and connected to a Wehnelt electrode for focusing an electron beam. A female screw is cut at the tip of each of these terminals 56, 58, 60 and 62, and a connecting wire can be connected to this female screw. As an example of the potential of each terminal, −60 kV is applied to the filament terminals 56 and 58 with respect to the ground, and the filament terminal 5
A voltage of 26 V is applied between the terminals 6 and 58, and the bias terminals 60 and 62 have a voltage of −
A bias voltage of 760V is applied.

FIG. 4 shows a vertical cross-sectional view of the cable post on the cable insertion side and a front view of the connection portion of the high-voltage cable side by side. The cable post 12 is formed with a receiving hole 64 for receiving the connection portion 80 of the high voltage cable, and a terminal space 66 following the receiving hole 64. The receiving hole 64 is tapered. In the terminal space 66,
As the atmosphere side terminals, three types of terminals 70, 72, 74 are exposed. The center terminal 70 is a bias terminal, and the outer two annular terminals 72 and 74 are filament terminals. The annular terminals 72 and 74 are equally spaced and formed with slits. A groove 78 is formed on the outer peripheral surface of the cable post 12 to serve as an insulating gas supply passage.

An annular corona ring 76 is embedded in the cable post 12 so as to surround the terminal space 66. The corona ring 76 prevents corona discharge. Without this corona ring 76, corona discharge may occur between the exposed edge portions of the terminals 72, 74 and the like and the edge portion of the tube wall of the X-ray tube. As shown in FIG. 1, the corona ring 76 extends in the axial direction of the cable post 12 so as to also surround the discharge suppressing circuit 16.
The corona ring 76 has a filament potential.

The connection 80 of the high voltage cable is inserted into the cable post 12. The tapered surface 82 of the connecting portion 80 is
It is made of ethylene / propylene rubber and conforms to the tapered shape of the receiving hole 64 of the cable post 12. The tapered surface 82 of the connecting portion 80 is formed into the receiving hole 6 of the cable post 12.
When the taper surface 82 is inserted, silicone grease is applied to the taper surface 82 so that no air remains between the taper surface 82 and the inner surface of the receiving hole 64 when the taper surface 82 is inserted.

The tip portion 81 of the connecting portion 80 is made of phenolic resin, and the two electrodes 86 and 88 are axially separated from each other and are exposed on the outer periphery thereof. These electrodes 8
Reference numerals 6 and 88 are brass plated with silver and are in contact with the annular terminals 72 and 74 of the cable post 12, respectively. Further, a terminal hole 90 is formed on the end surface of the tip portion 81 of the connecting portion 80, and the terminal 70 at the center of the cable post 12 is inserted into the terminal hole 90. Electrode 8
8 is formed with a step 84, and the step 84 contacts the axial end surface of the corona ring 76 of the cable post 12. Three conductors extend inside the cable wire 92, and these conductors are connected to the electrodes 86 and 88 of the tip portion 81 and the terminal hole 90. This high-voltage cable is made by passing a screw through a hole 96 formed in the flange 94 to the holder 3
Screw to the end face of 2 (see FIG. 1). The other end of this high voltage cable is connected to a high voltage power supply.

Next, returning to FIG. 1, the function of the high voltage bushing will be described. The vacuum-side terminal 18 and the connection terminal 20 connected to the vacuum-side terminal 18 are insulated from the mounting flange 24 by the insulator 10. Since the outer surface of the insulator 10 is exposed to the vacuum space, the withstand voltage on the outer surface is very high. Further, since the inner surface of the insulator 10 is covered with the insulating gas, the withstand voltage on this inner surface is also very high.

This high voltage bushing is heated by the conduction heat from the electron gun being transmitted through the vacuum side terminal 18. An example of temperature rise when the electron gun is mechanically supported by the vacuum-side terminal 18 is as follows.
0 ℃, 120 ℃ at the connection terminal 20, holder 32
The flange portion 34 has a temperature of 50 ° C. Since this high voltage bushing uses an insulating gas as an insulating fluid between the insulator 10 and the cable post 12 without using oil, there is little problem with the temperature rise of the insulating fluid. That is, since the gas is a compressive fluid, even if the temperature of the insulating gas rises and the insulating gas thermally expands, it only replaces the rise in pressure of the gas, and the rise in pressure is not great. Therefore,
It is not necessary to increase the volume as in the case of oil, and the enclosed volume of insulating gas can be small. Also, there is no need for a thermal expansion absorber as with oil. Therefore, the use of the insulating gas greatly contributes to downsizing of the high pressure bushing. In this embodiment, the thickness of the insulating gas filled space 14 is about 2 mm.

In this high voltage bushing, the heat conduction is improved so that the heat transmitted from the electron gun is released to the cooling water through the holder 32. That is, since the mold resin of the cable post 12 contains fine particles of alumina ceramics having good electric insulation and good heat conduction, the heat transmitted to the vacuum side terminal 18 is transmitted through the cable post 12. It is easy to reach the holder 32. Further, since the insulator 10 is made of alumina ceramic having good heat conductivity, heat can be released to the holder 32 also through the insulator 10. With such a configuration, the temperature rise of the high voltage bushing can be suppressed. If the temperature rise becomes large without such measures, it will adversely affect the mold resin of the bushing, the rubber and grease of the high-voltage cable, and the like. As described above, since the cooling capacity of the high voltage bushing is increased, it is possible to directly mechanically support the electron gun assembly by the vacuum side terminal 18.

[0024]

According to the high voltage bushing of the X-ray tube of the present invention, an insulating gas is filled between the vacuum side insulating member and the atmosphere side insulating member, and the atmosphere side insulating member is formed of a mold resin. Since the discharge suppressing circuit is embedded in the mold resin, the outer diameter of the high voltage bushing can be reduced. Further, the atmosphere side insulating member is formed of a mold resin containing fine particles of alumina ceramics, the vacuum side insulating member is formed of alumina ceramics, and the atmosphere side insulating member is molded integrally with a metal holder. , Since I tried to cool this holder with cooling water,
The temperature rise of the high voltage bushing can be suppressed. This allows the vacuum side terminal to directly mechanically support the electron gun, in which case the heat transmitted from the vacuum side terminal can be effectively released.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of an embodiment of a high voltage bushing of the present invention.

FIG. 2 is a bottom view seen from below in FIG.

3 is a plan view seen from above in FIG. 1. FIG.

FIG. 4 is a vertical cross-sectional view of a cable post on a cable insertion side and a front view of a connection portion of a high-voltage cable.

[Explanation of symbols]

10 Insulator (vacuum side insulation member) 12 cable posts (atmosphere side insulation member) 14 space 16 Discharge suppression circuit 18 Vacuum side terminal 20 connection terminals 22 Air side terminal 24 mounting flange 26 X-ray tube wall 32 holder 44 groove 46 Water-cooled jacket plate 54 Pressure sensor 76 Corona ring

Claims (9)

(57) [Claims] 1. A mounting portion for mounting on an X-ray tube, and X
A vacuum side terminal electrically connected to the electron gun of the wire tube, and an atmosphere side terminal electrically connected to the electrode of the high voltage cable,
A connection conductor that electrically connects the vacuum-side terminal and the atmosphere-side terminal, and a conductor consisting of the vacuum-side terminal, the connection conductor, and the atmosphere-side terminal are electrically insulated so that they can be hermetically sealed to the mounting portion. In a high-voltage bushing for an X-ray tube, the insulating member is a vacuum-side insulating member exposed to the vacuum side,
An atmosphere side insulating member exposed to the atmosphere side is provided, an insulating gas is filled in a space between the vacuum side insulating member and the atmosphere side insulating member, and the atmosphere side insulating member is formed of a mold resin, A high-voltage bushing in which a discharge suppression circuit is embedded inside the molding resin. 2. The high voltage bushing according to claim 1, wherein the mold resin contains fine particles of ceramics. 3. The high voltage bushing according to claim 2, wherein the mold resin is an epoxy resin containing fine particles of alumina ceramics. 4. The high voltage bushing according to claim 1, wherein a corona ring is embedded in the molding resin, and the corona ring surrounds the atmosphere side terminal. 5. The high-voltage bushing according to claim 1, wherein the vacuum-side insulating member is made of alumina ceramics. 6. The high-voltage bushing according to claim 1, wherein the atmosphere-side insulating member is molded integrally with a metal holder. 7. The high voltage bushing according to claim 6, wherein the metal holder is cooled by a refrigerant. 8. The high voltage bushing according to claim 6, wherein the metal holder includes a pressure sensor that detects the pressure of the insulating gas. 9. The high voltage bushing according to claim 6, wherein the vacuum side insulating member is sandwiched and fixed between the metal holder and the mounting portion.