Method for detecting high-voltage flashovers in an X-ray device and X-ray device

Abstract

Method for detecting high-voltage flashovers in an X-ray device (2) comprising an X-ray source (6) and a high-voltage supply (4), wherein the X-ray source (6) comprises an X-ray tube (10) and the high-voltage supply (4) comprises a high-voltage generator (7) and at least one cable (14), wherein the at least one cable (14) is at least part of a connecting path (VS) between the high-voltage generator (7) and the X-ray tube (10), characterized in that during normal operation of the X-ray device (2), a disturbance pulse (I) is detected and evaluated, which occurs due to the high-voltage flashover in the connecting path (VS), and that different flashover classes are determined based on the evaluated disturbance pulse (I), in particular on - Breakovers in the vacuum of the X-ray tube (10) - Flashovers in an insulating material - Partial discharges.

Description

[0001] The invention relates to a method for detecting high-voltage flashovers in an X-ray device with the features of the preamble of claim 1. The invention further relates to an X-ray device with the features of the preamble of claim 10.

[0002] X-rays are generated in an X-ray tube. An applied high voltage accelerates electrons to nearly the speed of light. After acceleration, they are decelerated to preferably 30% to 70% of their speed. This deceleration produces X-rays. The X-ray tube has a cathode as the electron source and an anode. Additionally, the X-ray tube contains a vacuum in which the cathode and anode are located. The vacuum serves as high-voltage insulation. The X-ray tube is located inside an X-ray source and is often surrounded by an insulating medium, such as insulating oil or a solid insulator. The X-ray source is further enclosed in a housing. A detailed description of the construction of an X-ray tube and an X-ray source can be found in "Imaging Systems for Medical Diagnostics," edited by Heinz Morneburg, 3rd edition, 1995, Publicis MCD Verlag, pp. 230 ff.

[0003] Generating X-rays requires, firstly, a current in the range of preferably a few milliamperes up to about 6 A, and secondly, a voltage of several hundred kilovolts. The radiation quality, also called radiation hardness, is determined by the applied voltage, and the radiation intensity by the selected current.

[0004] A high-voltage generator, typically a high-frequency generator, is used to generate the high voltage. The high-voltage generator and the X-ray tube are often electrically connected via at least one cable, particularly in a single-pole configuration, or via several cables, e.g., two cables, particularly in a two-pole configuration. The at least one cable is typically a coaxial cable. In the single-pole configuration, the high voltage, or rather, one forward and one return conductor of the X-ray tube current, is carried through the single coaxial cable. The two-pole configuration of the X-ray device has one cable each as the forward and return conductors of the X-ray tube current. This consequently halves the current load per cable; however, this configuration often requires more space compared to the single-pole configuration.

[0005] A coaxial cable for the electrical connection of the high-voltage generator and the X-ray tube is described in DE 42 43 360 C2. In the known coaxial cable, the X-ray tube current is supplied via an inner conductor of the coaxial cable. The return of the X-ray tube current to the high-voltage generator is via an outer conductor of the coaxial cable, an inner conductor of a second coaxial cable, or via a housing connection. A housing connection in this context refers, for example, to a common ground connection between the housing of the high-voltage generator and the housing of the X-ray tube.

[0006] The applied high voltage often leads to unintended high-voltage flashovers within the X-ray device during operation. These flashovers can occur at different locations with varying effects.

[0007] High-voltage flashovers within the vacuum of the X-ray tube are largely self-healing; however, high-voltage flashovers into the insulating medium can lead to irreversible changes in the insulating medium and thus to the loss of the intended insulating effect. Furthermore, high-voltage flashovers into the tube housing can lead to the destruction of the X-ray tube.

[0008] In an X-ray tube, so-called dummy plugs or dummy sockets can be used to detect defective components caused by high-voltage flashovers. The X-ray tube is disconnected from the X-ray apparatus and replaced with a dummy socket. If no further high-voltage flashover occurs during restarting the operation, it can be assumed that the flashover was caused by a defective X-ray tube. The use of dummy sockets or dummy plugs is costly and results in the X-ray apparatus being shut down.

[0009] The high-voltage generator typically incorporates integrated electronics designed to detect high-voltage flashovers. These electronics typically serve to protect both the generator and the X-ray tube, for example, by means of a short-circuit contactor. Alternatively or additionally, the output voltage of the generator is measured. This measurement is typically achieved using a voltage divider, often with a ratio of several kV to several volts, for example, 100 kV to 5 V. Due to the positioning of this electronics at the generator and the inherently slow measurement speed (e.g., by a factor of 100) inherent to the voltage divider, these electronics alone are insufficient for detecting high-voltage flashovers in the X-ray tube.

[0010] US patent 4,768,215 A describes an X-ray device with a high-voltage power supply and an X-ray tube. The high-voltage power supply and the X-ray tube are electrically connected by two high-voltage lines. To determine the X-ray tube current, one of the two high-voltage lines has a magnetic sensor element that detects the X-ray tube current flowing through the respective high-voltage line, taking current losses into account.

[0011] US Patent 5,055,828 A describes an electrical system with two components electrically connected by a conductor. A current-sensing element is arranged around the conductor, which detects parasitic (interference) currents within the conductor and, depending on the detected parasitic (interference) currents, emits a warning signal, preferably an audible one.

[0012] US patent 2015 / 0137795 A1 discloses a measuring system for detecting voltages and currents in an X-ray system, as well as various arrangements of conductors and cables for connecting a high-voltage supply to an X-ray source.

[0013] Based on this, the invention aims to provide a method for detecting high-voltage flashovers.

[0014] The problem is solved according to the invention by a method for detecting high-voltage flashovers in an X-ray device with the features of claim 1. Advantageous embodiments, further developments and variants are the subject of the dependent claims.

[0015] The X-ray device comprises an X-ray source and a high-voltage power supply. The X-ray source includes an X-ray tube, and the high-voltage power supply includes a high-voltage generator and a cable. The cable is preferably a coaxial cable and forms at least part of a connection between the high-voltage generator and the X-ray tube. A connection is defined as an electrical link between the output of the high-voltage generator and the input of the X-ray tube. A high-voltage generator is understood here to be, in particular, a high-frequency generator, for example, as described in "Imaging Systems for Medical Diagnostics," edited by Heinz Morneburg, 3rd edition, 1995, Publicis MCD Verlag, pp. 277 ff., which includes integrated electronics for detecting high-voltage discharges at an output or within the high-voltage generator itself.

[0016] High-voltage flashovers within an X-ray tube are frequently accompanied by interference pulses. These interference pulses are, for example, flashover currents flowing due to parasitic properties, which occur particularly in the form of common-mode currents. The interference pulses typically flow through multiple current paths, such as the X-ray tube housing, a current path into the insulating medium, or the connecting path. Common-mode currents are defined as currents that are present at different inputs—in this case, the different current paths—simultaneously and with the same phase. For example, an interference pulse flowing through the connecting path has the same phase as the total current at the arc of the high-voltage flashover. Thus, the interference pulses are correlated with the high-voltage flashovers.

[0017] The detection of high-voltage flashovers relies on capturing and analyzing the interference pulse. This interference pulse occurs, among other places, in the connecting path due to the high-voltage flashover. This interference pulse, occurring in the connecting path, is detected and subsequently analyzed during normal operation of the X-ray device.

[0018] Based on the analysis of the detected interference pulse, different flashover classes are determined. Flashover classes refer to the types of flashover and the location where the flashover occurs. For example, high-voltage flashovers in - Flashovers into the vacuum of the X-ray tube, - Flashovers into a solid of the X-ray source and - Partial discharges due to partially defective insulation gaps within the insulating medium.

[0019] Flashovers into the vacuum of the X-ray tube are largely self-healing, meaning they do not pose a concrete danger to the X-ray tube or the X-ray source. They are caused by a faulty vacuum and are unavoidable, as residual air remains in the X-ray tube during manufacturing.

[0020] Flashovers into a solid component of the X-ray tube, such as a potting compound or the tube's insulating medium, as well as into a cable or the insulating medium of the high-voltage generator, usually result in a tube defect. Firstly, a high-voltage flashover alters the chemical composition of the insulating oil, thus reducing or even completely eliminating its insulating properties. Secondly, the high, albeit brief, thermal stress of a high-voltage flashover damages or destroys the housing of an affected component or part, potentially leading to damage or destruction of the component or part itself.

[0021] Partial discharges represent a special case. These partial discharges arise from slight differences in the dielectric strength of a material. For example, if small, low-energy partial discharges occur on the housing of the X-ray tube, the dielectric strength at these points of partial discharge will be lower than in other parts of the housing. Alternatively, partial discharges can be interpreted as so-called pre-discharges preceding the actual high-voltage flashover. In this case, either the applied voltage is not yet sufficient for a breakdown to occur, or the dielectric strength is just sufficient to prevent a high-voltage flashover. Both properties of partial discharges can be used for the early detection of high-voltage flashovers and thus damage to the X-ray tube. The evaluated interference pulse is preferably used to assess the condition of the X-ray tube.

[0022] This evaluation has the advantage that a physical quantity is recorded which is directly correlated with the high-voltage flashover.

[0023] It has proven advantageous to detect the interference pulse locally along the connecting path. "Local" here refers to a measurement position along the connecting path.

[0024] Preferably, the interference pulse is detected along the cable. Detection along the cable is based on the consideration that a significant portion of the high-voltage flashover flows through the cable between the high-voltage generator and the X-ray tube. Furthermore, detection at a local measurement point along the cable is advantageous because it ensures easy access to the cable and thus simple and cost-effective measurement. Since the interference pulse is detected at a functioning X-ray device, this design is particularly advantageous because the detection of the interference pulse occurs during normal operation of the X-ray device. Alternatively, the interference pulse is detected within the X-ray tube itself.

[0025] In a further development, a measuring device designed to detect high-voltage flashovers includes a measuring element for detecting the interference pulses. Preferably, this is a measuring element for detecting an electric current or for detecting a physical quantity from which an electric current is derived.

[0026] The current waveform resulting from a high-voltage flashover is typically no longer accurately detectable after traveling a distance of approximately one meter in the cable. This is due to the cable's attenuation. Because of this attenuation, a near-field of the X-ray source is defined over the last half, and especially the last quarter, of the cable (viewed in the direction of the X-ray source). For example, the near field is defined by the last 30 cm, and particularly the last 10 cm, of the cable before the X-ray source connects to the cable. Preferably, the interference pulse is detected in this near field. This has the advantage that the interference pulse is detected with virtually no attenuation.

[0027] High-voltage flashovers through the insulating medium typically occur over time intervals of, for example, a few microseconds. However, high-voltage flashovers in a vacuum often exhibit transients corresponding to values ​​in the range of 1 kV to 30 kV per nanosecond. The duration of high-voltage flashovers that, for example, flash into the insulating medium can sometimes be several microseconds, for example, times in the range of 5 µs to 10 µs. Therefore, a "fast" measurement technique is required for detecting the fault pulse, one that can capture signals with a duration preferably in the range of 2 ns to 10 µs, and particularly in the range of 10 ns to 100 ns.

[0028] To differentiate between the types of flashover relevant to the procedure, the distinct profiles of the flashover voltage and the associated flashover current are used. By comparing the recorded profile of the fault pulse with, for example, reference profiles stored in a database, a specific flashover class is determined.

[0029] The advantage of categorizing high-voltage flashovers and assessing the condition of the X-ray tube lies in the timely procurement of replacement parts when necessary. In particular, detecting partial discharges ensures early detection of damage to the X-ray tube, allowing for pinpointing the location of the faulty component and determining the severity of the defect. This enables timely decisions regarding follow-up measures, such as whether the defective component can be replaced or repaired. Consequently, downtime and associated costs are reduced.

[0030] In preferred training methods, the evaluation of the interference pulse is carried out using remote diagnostics. This training has the advantage that the evaluation of the recorded measurement is location-independent. Specifically, the diagnosis is performed by the device manufacturer, for example, via remote access.

[0031] The problem is further solved according to the invention by an X-ray device with the features of claim 10.

[0032] The X-ray device includes an X-ray tube and a high-voltage power supply. Furthermore, the X-ray-

Claims

[1] Method for detecting high-voltage flashovers in an X-ray device (2) comprising an X-ray source (6) and a high-voltage supply (4), wherein the X-ray source (6) comprises an X-ray tube (10) and the high-voltage supply (4) comprises a high-voltage generator (7) and at least one cable (14), wherein the at least one cable (14) is at least part of a connecting path (VS) between the high-voltage generator (7) and the X-ray tube (10), characterized by , that during normal operation of the X-ray device (2) a disturbance pulse (I) is detected and evaluated, which occurs due to the high-voltage flashover in the connecting path (VS), and that different flashover classes are determined based on the evaluated disturbance pulse (I), in particular on - Breakovers in the vacuum of the X-ray tube (10) - Flashovers in an insulating material - Partial discharges. [2] Method according to the preceding claim, characterized by , that the disturbance pulse (I) is detected at a measurement position (21) located along the connecting path (VS). [3] Method according to any one of the preceding claims, characterized by , that a current flowing due to the high-voltage flashover in the connecting path (VS) is evaluated. [4] Method according to the preceding claim, characterized by , that the interference pulse (I) is detected at a measurement position (21) located along the cable (14). [5] Method according to any one of the preceding claims, characterized by , that the interference pulse (I) is detected in a near range (N) of the X-ray source (6). [6] Method according to one of the two preceding claims, characterized by , that disturbance pulses (I) with a pulse duration (τ) with values ​​in a range of 1ns to 10µs are detected and evaluated. [7] Method according to any one of the preceding claims, characterized by , that an assessment of the state of preservation of the X-ray device (2) or its components is carried out on the basis of the evaluated interference impulse (I). [8] Method according to any one of the preceding claims, characterized by , that the evaluation of the interference impulse (I) is carried out using remote diagnostics. [9] Method according to any one of the preceding claims, characterized by , that the high voltage generator (7) additionally has a voltage measuring device (7c) which is used additionally for the detection of high voltage flashovers. [10] X-ray apparatus (2), which - an X-ray tube (6) and - has a high-voltage supply (4), wherein the X-ray source (6) has an X-ray tube (10) and the high-voltage supply (4) has a high-voltage - a voltage generator (7) and a cable (14), wherein the cable (14) is at least part of a connecting path (VS) between the high voltage generator (7) and the X-ray tube (10), characterized by , that the X-ray device (2) has a measuring device (18) with a measuring element (20) which is configured in operation to detect a disturbance pulse (I) which occurs due to the high-voltage flashover in the connecting path (VS), wherein the measuring device (18) is configured for evaluating the disturbance pulse (I) such that different flashover classes are determined on the basis of the evaluated disturbance pulse (I), in particular -Eruptions in the vacuum of the X-ray tube (10) -Flashovers in an insulating material -Partial discharges. [11] X-ray device (2) according to the preceding claim, characterized by, that the measuring device (18) is designed such that it detects the disturbance pulse (I) at a measuring position (21) along the cable (14). [12] X-ray device (2) according to one of claims 10 or 11, characterized by , that the measuring device (18) is positioned in a near range (N) of the X-ray source (6). [13] X-ray device (2) according to any one of claims 10 to 12, characterized by , that the measuring element (20) has a coil (22). [14] X-ray device (2) according to the preceding claim, characterized by , that the coil (22) is designed as a Rogowski coil. [15] X-ray device (2) according to one of claims 13 to 14, characterized by , that the coil (22) has a differential structure

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