Method and device for the reduction of flashover-related transient electrical signals between the acceleration section of an X-ray tube and a high-voltage source

Abstract

A high-voltage resistant cable for connecting a high-voltage source and an acceleration section of an X-ray tube that each have a respective socket and a flange. The cable includes an inner conductor, a surrounding electrical insulator, an enveloping shielding made of an electrically conductive material, and plugs at each respective end. Each plug includes a plug flange for cooperating with the respective flange and having a hollow interior, and an electrical insulator that includes a conic-shape portion for extending into the respective socket, and a cylindrical portion extending within the hollow interior of the plug flange. The cable including absorber elements at each of the two ends of the cable for absorbing the energy of high-voltage discharge-related transients. Each absorber element is configured as a ring-shape, the ring-shape absorber element encircling the cylindrical portion and being located within the hollow interior of the plug flange.

Claims

1. A high-voltage resistant cable for connecting a high-voltage source and an acceleration section of an X-ray tube, each of the high-voltage source and the acceleration section of the X-ray tube, having a respective socket and a respective flange that receive a respective end of the cable, the cable comprising: an inner conductor; an electrical insulator surrounding the inner conductor; a shielding made of an electrically conductive material and enveloping the inner conductor and the insulator; plugs at each of two respective ends of the cable for receipt at the respective sockets and the respective flanges of the high-voltage source and the acceleration section of the X-ray tube, each plug comprising: a plug flange for cooperating with the respective flange, the plug flange having a hollow interior; and an electrical insulator insulating the inner conductor, the electrical insulator comprising a conic-shape portion for extending into the respective socket, and the electrical insulator comprising a cylindrical portion extending within the hollow interior of the plug flange; and absorber elements at each of the two ends of the cable for absorbing the energy of high-voltage discharge-related transients, each absorber element being configured as a ring-shape, the ring-shape absorber element encircling the cylindrical portion and being located within the hollow interior of the plug flange.

2. The cable according to claim 1 wherein the absorber elements are made of a soft magnetic material.

3. The cable according to claim 2, wherein permeability of the soft magnetic material is above 50.

4. The cable according to claim 3, wherein permeability of the soft magnetic material is above 500.

5. The cable according to claim 4, wherein permeability of the soft magnetic material is above 1000.

6. The cable according to claim 2, wherein the absorber elements are comprised of at least one of the following materials: iron, cobalt, alloys of NiFe, ferritic materials, amorphous metals, nanocrystalline metals and ferrofluids.

7. The cable according to claim 1, wherein the insulator has a round cross section in whose center the inner conductor is disposed, and the absorber elements enclose the insulator in a ring-shaped manner at each of the two ends of the cable.

8. The cable according to claim 7, wherein a gap width between an inner surface of the absorber element and an outer surface of the insulator is less than 1 mm.

9. The cable according to claim 8, wherein the gap width between the inner surface of the absorber element and the outer surface of the insulator is less than 0.5 mm.

10. The cable according to claim 9, wherein the gap width between the inner surface of the absorber element and the outer surface of the insulator is less than 0.1 mm.

11. The cable according to claim 1, wherein each absorber element encircling only the inner conductor and the electrical insulator of the respective plug.

12. The cable according to claim 1, further including a metal sleeve at each plug, each metal sleeve encircling the inner conductor and the electrical insulator of the respective plug.

13. The cable according to claim 12, wherein each metal sleeve encircling only the inner conductor and the electrical insulator of the respective plug.

14. The cable according to claim 1, wherein each absorber element is configured to be pushed on to the electrical insulator of the respective plug.

15. The cable according to claim 1, wherein each absorber element is press fit on to the electrical insulator of the respective plug.

16. The cable according to claim 15, wherein each absorber element is press fit on to the electrical insulator of the respective plug during connection of the respective plug to the respective socket.

17. The cable according to claim 16, wherein each absorber element is configured to be pushed on to the conic-shape portion of the electrical insulator.

18. The cable according to claim 1, wherein each absorber element is disposed between the inner conductor and the shielding.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a schematic representation of a testing assembly according to the invention for the non-destructive material testing by means of X-radiation,

(2) FIG. 2 shows a sectional view of a high-voltage resistant cable used for an HV connecting cable according to the invention,

(3) FIG. 3 shows a partial sectional view of a high-voltage resistant plug used for an HV connecting cable according to the invention,

(4) FIG. 4 shows a partial sectional view of a high-voltage resistant socket used for an HV connecting cable according to the invention,

(5) FIG. 5 shows a three-dimensional representation of a damping body according to the invention,

(6) FIG. 6 shows a partial sectional view of a high-voltage resistant plug-and-socket combination used for an HV connecting cable according to the invention,

(7) FIG. 7 shows the frequency distribution of the flashovers observed during the assembly of a ventilated microfocus X-ray tube depending on the flashover voltage and the strength of the observed transient oscillations on the inner conductor of an HV connecting cable between the high-voltage source and the X-ray tube according to the prior art,

(8) FIG. 8 as FIG. 7, using an HV connecting cable according to the invention with a damping body made of ferromagnetic iron,

(9) FIG. 9 as FIG. 7, using an HV connecting cable according to the invention with a damping body made of a ferritic material, and

(10) FIG. 10 shows the curve over time of the power in an HV connecting cable between a high-voltage source 20 and a microfocus X-ray tube 10 immediately after a flashover has occurred.

DETAILED DESCRIPTION

(11) FIG. 1 shows a testing assembly 1 for the non-destructive material testing by means of X-radiation. The assembly comprises a microfocus X-ray tube 10 with an acceleration section and a high-voltage source 20 formed separate from the X-ray tube. Further, the testing assembly 1 comprises a high-voltage resistant HV connecting cable 40 for electrically connecting the acceleration section with the high-voltage source.

(12) The HV connecting cable 40 comprises a high-voltage resistant cable 50 according to FIG. 2 with an inner conductor 52, an electrical insulator 58 surrounding the latter, and a shielding 62 made of an electrically conductive material and enveloping the inner conductor 52 and the insulator 58.

(13) The inner conductor 52 and the shielding 62 are made from an alloy of Cu and Sn, with the inner conductor 52 having a three-core configuration.

(14) The three cores 54 of the inner conductor 52 are embedded in a sheath 56 made from semi-conductive ERP.

(15) The sheath 56 itself is surrounded by an electrical insulator 58 with a round cross section made from non-conductive ERP. On its outer surface, the insulator 58 is covered with a thin sheath layer 60 made from semi-conductive ERP, on which the electrically conductive shielding 62 is, in turn, disposed. On the outer side, the assembly comprised of the inner conductor 52, the insulator 58 and the shielding 62 is wrapped in a cable sheath 64 of PVC.

(16) On its two ends, the HV connecting cable 40 is provided with a high-voltage resistant plug 70 according to FIG. 3 for forming an electrical plug-and-socket connection of the high-voltage source 20 with the acceleration section of the X-ray tube 10. The plugs 70 also each comprise an inner conductor 72 which is made from an electrically conductive material, in particular a metallic material, which, if necessary, is surface-treated, and which is embedded in the center of an electrical insulator 74 with a round cross section that tapers towards the end of the plug on the side of the socket. The inner conductor 72 and the insulator 74 are encased over a part of their length by a shielding 76 made of a material that is also electrically conductive. In the exemplary embodiment shown, the shielding 76 is configured as a metallic sleeve 78 to whose outer surface 80 a flange part 82 is screwed. The flange part is configured for mechanically fixing the plug 70 in a complementarily formed high-voltage resistant socket 90 according to FIG. 4, e.g. by means of a screw connection with a corresponding flange part of the socket 90.

(17) The high-voltage resistant socket 90 according to FIG. 4 also has an inner conductor 92 and an electrical insulator 94 surrounding the latter, which forms a conical recess 95 for accommodating the conically tapering end 74 of the plug 70 in the exemplary embodiment shown. The shielding 96 of the socket 90 is formed as a metallic flange part 98, which, on the one hand, is made from an electrically conductive material, such as a metal sheet, for the purpose of being screw-connected to a surrounding housing, and, on the other hand, has threaded bores 99 that serve for a screw-connection to the flange part 82 of the plug 70. If necessary, the shielding can also comprise an electrically conductive layer, e.g. made from a copper-tin alloy, which is applied to the outside of the insulator 94 (not shown). Such an electrically conductive layer can be configured, for example, as a cylindrical socket housing in which the insulator 94 and the inner conductor 92 are disposed.

(18) FIG. 5 shows an absorber element 100 for absorbing the energy of high-voltage discharge-related transients, which is configured to be pushed on to the conically tapering end of the plug 70 until this results in a press fit in the cylindrical portion 75 indicated in FIG. 3. The absorber element 100 has a ring-shaped geometry, with the diameter of the inner recess being adapted to the outer diameter of the cylindrical portion 75, so that a press fit of the absorber element 100 on the cylindrical portion 75 is obtained. In this position, the absorber element 100 encloses the inner conductor 72 of the plug 70 in a ring-shaped manner

(19) The inner diameter of the absorber element 100 is typically a few millimeters to a few tens of millimeters; the wall thickness of the ring is typically a few millimeters. The longitudinal extent of the ring along its axis of symmetry is also typically a few millimeters. Both the wall thickness as well as the longitudinal extent are primarily limited by the geometry of the plug-and-socket combination used. However, it was found that a larger volume of the absorber element 100 improves its efficiency according to the invention. Furthermore, it was found that the efficiency of the absorber element 100 is improved if the gap width between the cylindrical inner surface 102 of the absorber element 100 and the cylindrical outer surface 75 of the insulator 74 of the plug 70 is minimal. In the exemplary embodiment shown, the gap width is virtually zero, due to the press fit of the absorber element 100, and is determined substantially by the machining precision of the surfaces 102 and 75.

(20) The absorber element 100 is made of a soft magnetic material whose permeability in an embodiment is above 500 and particularly above 1000. Iron in a ferromagnetic crystal structure and soft magnetic ferrites have proved to be particularly suitable materials that permit a cost-effective production of sufficiently efficient absorber elements 100. Manganese-zinc ferrites and nickel-zinc ferrites are suitable ferrites.

(21) FIG. 6 shows a high-voltage resistant plug-and-socket assembly or combination 110 according to the invention, i.e. the plug 70 from FIG. 3 inserted into a socket 90, which in turn is screwed with its flange part 96 to the wall of a housing 12/22 of an X-ray tube 10 or a high-voltage source 20 while forming an electrically conductive connection.

(22) FIGS. 7, 8 and 9 each show the frequency distribution of the flashovers observed during the assembly of a ventilated microfocus X-ray tube depending on the flashover voltage and the power contained in the observed transient oscillations on the inner conductor of the HV cable between the high-voltage source and the X-ray tube. FIG. 7 shows the frequency distribution with an HV cable according to the prior art, FIG. 8 shows the frequency distribution with an HV cable according to the exemplary embodiment discussed above with an absorber element made of ferromagnetic iron, and FIG. 9 shows the frequency distribution with an HV cable according to the exemplary embodiment discussed above with an absorber element made of a ferritic material. The average strength of the oscillations can be reduced from a value of 0.0148(2) (arbitrary units) of the undamped system to a value of 0.0141(1) (arbitrary units) with the damping element of ferromagnetic iron and to a value of 0.0111(2) (arbitrary units) with the damping element of a ferritic material.

(23) FIG. 10 shows the curve over time of the power in an HV connecting cable 40 between a high-voltage source 20 and a microfocus X-ray tube 10 immediately after a flashover has occurred. It shows the power curve in the case of the use of an undamped HV connecting cable 40 according to the prior art and an HV connecting cable 40 according to the exemplary embodiment discussed above. Just as in FIG. 9, a ferritic material was used as the material for the damping body 100. The strong transient damping obtained becomes apparent from FIG. 10, which is sufficient for reliably preventing damage both to the HV connecting cable 40 as well as the high-voltage source 20.