EP0497169A2 - X-ray line - Google Patents

Abstract

2.1. An X-ray line has the following construction: inner conductor (1) or line core with a plurality of inner conductors, and concentrically around it: inner conducting sleeve, high-voltage insulation (3), outer conducting sleeve, outer conductor or screen (5) and sheath (6). During X-ray operation, transient overvoltages can occur and lead to disturbances. In the past, such overvoltages were rendered safe by means of attenuating elements which are connected in the line circuit. …<??>2.2. A further remedy is to construct the line such that it has an attenuation which increases greatly with frequency above 1 MHz, without the use of attenuating elements. To this end, each inner conductor (1) consists of one or more wires having a thickness between 0.6 and 0.1 mm, of which at least one wire consists of a ferromagnetic material, preferably a nickel/iron alloy. If required, a small portion of the wires consist of copper or silver. …<??>2.3. Use as an X-ray line with high attenuation. …<IMAGE>…

Description

The invention relates to an x-ray line which is constructed in accordance with the preamble of claim 1. Its purpose is to make any transient overvoltages that occur during X-ray operation harmless.

For a long time, the structure of an X-ray line, as described for example in DE-PS 972 701, looks as follows: inside the high-voltage conductor, above it the inner conductive layer (conductive sheath), high-voltage insulation and outer conductive layer, above it the screen (concentric outer conductor) and finally the coat.

• a) Im Kern der Röntgenleitung sind neben dem blanken Hochspannungsleiter zwei isolierte Heizleiter angeordnet, wobei der runde, feindrähtige Hochspannungsleiter aus Symmetriegründen in zwei halbe, ebenfalls runde Leiter geteilt ist, so daß im Leitungskern vier Elemente miteinander verseilt sind (F&G-Prospekt "Elektrotechnik" 12.72, S. 23).
• b) Im Kern der Röntgenleitung sind die beiden isolierten Heizleiter mit einem isolierten Gittersteuerleiter verseilt, darum liegt eine leitfähige Umhüllung, und darum ist der konzentrische Hochspannungsleiter geseilt (DE-GM 85 26 448).
• c) Konzentrischer Aufbau: Heizleiter 1, Isolierung, Heizleiter 2, Isolierung, Hochspannungsleiter als Geflecht (F&G-Prospekt "Röntgenleitungen" 04.89).

Over time, the line core (the inner conductor arrangement) received various training, while the rest of the line structure remained the same. Of the usual conductor arrangements today are listed:

• a) In the core of the X-ray line, two insulated heating conductors are arranged next to the bare high-voltage conductor, the round, finely stranded high-voltage conductor being divided into two half, also round conductors for reasons of symmetry, so that four elements are stranded together in the core (F&G brochure "Electrical engineering" 12.72, p. 23).
• b) In the core of the X-ray line, the two insulated heating conductors are stranded with an insulated grid control conductor, which is why there is a conductive sheath, and therefore the concentric high-voltage conductor is roped (DE-GM 85 26 448).
• c) Concentric structure: heating conductor 1, insulation, heating conductor 2, insulation, high-voltage conductor as braid (F&G brochure "X-ray lines" 04.89).

In all cases, the further structure is the same: inner conductive layer, high-voltage insulation, outer conductive layer, shield and jacket.

The following are commonly used as materials: a) strands made of thin, tinned copper wires for the inner conductor, which can be reinforced by galvanized steel wires for tensile strength in the core, b) semiconducting rubber or plastic mixtures (compounds), tapes or foils for the guide sleeves, c) for the high-voltage insulation cross-linked rubber or plastic mixtures (elastomers such as EPR), d) for the outer conductor roping or braid made of copper wires and e) for the sheath rubber or plastic mixtures (such as PVC) or glass yarn braid.

During X-ray operation, electrical discharges (short circuits) can occur in the X-ray tubes, during which transient overvoltages (traveling waves) occur, which are dissipated via the X-ray line. These high-frequency overvoltages can lead to faults and failures in electronic devices and components that are close to the source of interference (X-ray tube and line).

In order to avoid such interference, measures are known to shield the interference source electrically and to reduce or prevent the propagation of the transient overvoltages via the X-ray line by means of attenuators which are connected into the line circuit.

With regard to shielding, DE-A-1 540 232 describes a cable sheath for shielding electromagnetic interference signals, in which two braids are arranged between the cable core and the sheath, the wires of which are made of pure iron in one braid and in an iron braid in the other. Nickel alloy exist with a relatively high permeability, the first-mentioned braid facing the respective (radiating or radiating) source of interference. The purpose of such shielding is to suppress spurious signals across the entire electromagnetic spectrum, from direct current to the microwave frequencies. For the cable it is only stated that it consists of a group of wires or lines, the shielding causes star signals to be attenuated in the transverse but not in the longitudinal direction of the cable, and the problem of transient overvoltages which arises with x-ray lines continues to exist.

In order to solve this problem with X-ray lines, attenuators that are connected to the line circuit are known in various designs and arrangements. DE-A-2 010 143 describes a high-voltage cable for an X-ray tube, in which a damping resistor is vulcanized into the high-voltage connector that connects the cable to the tube. The resistor can be designed as an ohmic resistor (resistance wire), as an inductive resistor (conductor coil on a core of high magnetic permeability) or a combination of both.

And in DE-A1-39 29 402 an X-ray device is described in which an attenuation impedance which is effective only in terms of radio frequency is arranged in the high-voltage cable or at the output of the high-voltage generator. In the first arrangement it consists of a ferrite core, which surrounds the cable in a hollow cylinder shape, in the second in a resistor (including diode or capacitor), which is connected in parallel to the generator output.

On the one hand, these additional attenuators require considerable effort, and on the other hand, their effectiveness could still be improved.

The invention is therefore based on the object of specifying a further measure in order to largely reduce the propagation of the transient overvoltages via the X-ray line.

The solution to this problem is, according to the invention, that the X-ray line, without the use of attenuators, has an attenuation of the transient overvoltages which increases sharply with the frequency above 1 MHz. For this purpose, each inner conductor consists of several between 0.1 and 0.4 mm thick wires or from a between 0.2 and 0.6 mm thick wire, each or at least one wire made of a ferromagnetic material, e.g. B. of iron or a nickel-iron alloy with high permeability at frequencies above 1 MHz, and optionally the remaining wires consist of a material with high electrical conductivity. The multiplication factor of the attenuation values based on 1 kHz is when using wires of a nickel-iron alloy at 3 MHz over 190 and at 6 MHz over 360, and the DC resistance of each inner conductor is below 20 Ω / m.

It is advantageous to use a nickel-iron alloy of the composition 75% Ni, 5% Cu, 2% Cr, 0.5% Mn, 0.2% Si, 0.02% C, the rest Fe, as they do is sold under the name Magnifer® 75. - In order not to exceed the limit value of the DC resistance for the inner conductor, the core wire or the smaller part of the wires can be made of copper, more rarely silver, and the remaining wires can be made of iron or the Ni-Fe alloy.

The advantage achieved with the X-ray line according to the invention is, in particular, that the attenuators previously required in the X-ray system for surge protection are eliminated, which on the one hand saves space in the system and on the other saves system costs.

The invention makes use of the theory of electrical lines as follows: One can attribute four lines through which alternating current flows: resistance, inductance, capacitance and dissipation (dielectric losses). In relation to a line section, one speaks of the corresponding covering. Inductance coating L 'and capacitance coating C' are less, resistance coating R '(skin effect) and derivative covering G' are more frequency-dependent.

• (1) für hinreichend niedrige Frequenzen ${\text{α = (½ ω C' R')}}^{\text{½}}$
  
  und
• (2) für höhere Frequenzen ${\text{α = R'/2 (C'/L')}}^{\text{½}}{\text{+ G'/2 (L'/C')}}^{\text{½}}$
  
  .

The damping coating α indicates how large the relative decrease in the effective values (of voltage and current in a progressing wave) is based on the cable length. The damping is caused by the energy losses in the line, which arise partly in the line wires and partly in the insulation. The following approximate equations are obtained for α (with the angular frequency ω = 2 π f):

• (1) for sufficiently low frequencies ${\text{α = (½ ω C 'R')}}^{\text{½}}$
  
  and
• (2) for higher frequencies ${\text{α = R '/ 2 (C' / L ')}}^{\text{½}}{\text{+ G '/ 2 (L' / C ')}}^{\text{½}}$
  
  .

Accordingly, the damping coating increases more at sufficiently low frequencies (Eq. 1) than at higher ones (Eq. 2). At higher frequencies, it increases as a result of the skin effect and attenuation. With normal cables, the loss is usually small compared to the resistance loss. Increasing the inductance reduces (according to Eq. 2) the resistance damping and increases the derivative damping, thus reducing the total damping, as long as the resistance damping is greater than the derivative damping. (For more see Küpfmüller "Introduction to theoretical electrical engineering" Springer-Verlag 1984 p. 404/10/15.)

The inductance of the X-ray line is determined by the permeability of the conductor materials used. - The skin effect, which is based on the current displacement in a cylindrical conductor, causes the resistance to increase with frequency and permeability. For very high frequencies one obtains R = ω L _i .

While the lowest possible attenuation is required for lines for the transmission of high-frequency data and signals, considerable attenuation is required for X-ray lines in the frequency range above 1 MHz, in order to make disturbing transient overvoltages harmless.

• Fig. 1 eine 110 kV-Röntgenleitung mit einem Innenleiter und einem dazu konzentrischen Außenleiter (Hier wird die Heizleitung getrennt von der Hochspannungsleitung geführt.) und
• Fig. 2 eine 75 kV-Röntgenleitung mit 4 Innenleitern (2 Hochspannungs- und 2 Heizleiter) im Leitungskern, beide Leitungen ausgebildet zur Dämpfung von transienten Überspannungen. Dazu sind in der Zeichnung die Meßergebnisse an drei Prüflingen des in Fig. 1 gezeigten Leitungstyps mit unterschiedlichen Innenleitern dargestellt. Es zeigen
• Fig. 3 das zeitliche Abklingen der transienten Überspannung U_o (im Verhältnis zur anliegenden Spannung U) im Kurzschlußfall und
• Fig. 4 den relativen Anstieg der Leitungsdämpfung mit der Frequenz.

Two embodiments of the invention are shown in the drawing and are described in more detail below. They show a side view and a top view

• Fig. 1 shows a 110 kV X-ray line with an inner conductor and an concentric outer conductor (here the heating line is routed separately from the high-voltage line) and
• Fig. 2 is a 75 kV X-ray line with 4 inner conductors (2 high voltage and 2 heating conductors) in the core, both lines designed to damp transient overvoltages. For this purpose, the measurement results on three test specimens of the line type shown in FIG. 1 with different inner conductors are shown in the drawing. Show it
• 3 shows the temporal decay of the transient overvoltage U _o (in relation to the applied voltage U) in the event of a short circuit and
• Fig. 4 shows the relative increase in line loss with frequency.

• Beispiel A: Kern ein Kunststoffstrang und darum eine Lage von 6 Verseilelementen aus einem Kerndraht und einer Lage von 6 Drähten, alle 42 Drähte 0,15 mm starke Stahldrähte, zu einer Litze verseilt, und
• Beispiel B: Kern ein 0,2 mm starker Cu-Draht und darum eine Lage von sechs 0,2 mm starken Ni-Fe-Legierung-Drähten. und wie üblich um den Innenleiter konzentrisch angeordnet:
• innere Leithülle 2 aus halbleitendem Gummi mit 5 mm ∅,
• Hochspannungsisolierung 3 aus EPR (Ethylen-Propylen-Rubber) mit 15 mm ∅,
• äußere Leithülle 4 aus halbleitendem Gummi,
• Außenleiter 5 Geflecht aus Cu-Drähten mit 95 % Bedeckung und
• Außenmantel 6 aus PVC mit 19 mm ∅.

1, the 110 kV x-ray line has the following structure: according to the invention, the inner conductor 1

• Example A: core a plastic strand and therefore a layer of 6 stranding elements made of a core wire and a layer of 6 wires, every 42 wires 0.15 mm thick steel wires, stranded into a strand, and
• Example B: The core is a 0.2 mm thick Cu wire and therefore a layer of six 0.2 mm thick Ni-Fe alloy wires. and, as usual, arranged concentrically around the inner conductor:
• inner sleeve 2 made of semiconducting rubber with 5 mm ∅,
• High-voltage insulation 3 made of EPR (ethylene-propylene rubber) with 15 mm ∅,
• outer guide sleeve 4 made of semiconducting rubber,
• Outer conductor 5 braid made of Cu wires with 95% coverage and
• Outer jacket 6 made of PVC with 19 mm ∅.

• erfindungsgemäß: im Leitungskern 1' zwei blanke Hochspannungsleiter 7 aus Ni-Fe-Legierung-Drähten und zwei isolierte Heizleiter 8 auch aus Ni-Fe-Legierung-Drähten mit einer Leiterisolierung 9 aus Tefzel (Handelsname). Die Hochspannungsleiter 7 und die Heizleitungen 8-9 sind miteinander zum Leitungskern verseilt.
• und darum wie üblich: innere Leithülle 2 aus halbleitendem Gummi, Hochspannungsisolierung 3 aus EPR, äußere Leithülle 4' aus einem halbleitend beschichteten Band, Schirmgeflecht 5 aus Cu-Drähten, und Außenmantel 6 aus PVC.

In Fig. 2, the 75 kV X-ray line has the following structure:

• According to the invention: in the core 1 'two bare high-voltage conductors 7 made of Ni-Fe alloy wires and two insulated heating conductors 8 also made of Ni-Fe alloy wires with a conductor insulation 9 made of Tefzel (trade name). The high-voltage conductor 7 and the heating lines 8-9 are stranded together to form the core.
• and therefore as usual: inner guiding sleeve 2 made of semiconducting rubber, high-voltage insulation 3 made of EPR, outer guiding sleeve 4 'made of a semiconducting coated tape, braided screen 5 made of Cu wires, and outer jacket 6 made of PVC.

As indicated above in the prior art under b) and c), there are various other designs of the line core. The further structure of the X-ray lines (high-voltage insulation, shield and sheath) is however the same. In all cases, according to the invention, all conductors of the line core (inner conductor) are designed as strands or as ropes made solely of ferromagnetic wires or in combination with copper wires, more rarely with silver wires.

The behavior of traveling waves in X-ray lines has been investigated by short-circuit studies on test leads. 3 and 4 show the measurement results on three test specimens of the line type shown in FIG. 1 with the following different structure of the inner conductor:
N) (1 + 6) x 0.11 mm Cu,
A) Plastic core + 6 x (1 + 6) x 0.15 mm Fe and
B) 1 x 0.2 mm Cu + 6 x 0.2 mm NiFeLeg.

As can be seen from the circuit diagram of FIG. 3, the test object is connected at one end of the line to the direct current source U _o via a series resistor, whereas the other end is short-circuited. The voltage curve in this circuit is tapped between the series resistor and the device under test and recorded using a digital storage oscilloscope. In Fig. 3 the temporal decay of the transient overvoltage U _o in relation to the applied voltage U in the event of a short circuit is shown graphically. It is striking that the test leads A and B according to the invention have a have stronger or much stronger damping of the transient overvoltage than the usual test object N.

Furthermore, the line constants in relation to the frequency were measured on these test objects, from which the respective line loss was determined with the help of an impedance analyzer. 4 shows the relative increase in the line attenuation for the three test objects, based on the attenuation values at 1 kHz, with the frequency. From this it can be seen that the multiplication of the relative attenuation values with the usual use of copper wires (test specimen O) at 3 MHz only achieves a factor of 30 and at 6 MHz a factor of 65, whereas when using iron wires (test specimen A) according to the invention they reach a factor of 70 or . 120 and when using Ni-Fe alloy wires (test specimen B) even exceeds the factor 190 or 360.

Claims (5)

X-ray line with the following structure, concentric from the inside to the outside: inner conductor (1) or core (1 ') with several inner conductors, inner sleeve (2), high-voltage insulation (3), outer sleeve (4), shield (outer conductor 5) and sheath ( 6),
characterized, that the X-ray line, without the use of attenuators, has an attenuation of the occurring transient overvoltages which increases sharply with the frequency above 1 MHz, - For this purpose, each inner conductor (1) consists of several between 0.1 and 0.4 mm thick wires or one between 0.2 and 0.6 mm thick wire, each or at least one wire made of a ferromagnetic material, e.g. B. made of iron or a nickel-iron alloy with high permeability at frequencies above 1 MHz, and optionally the remaining wires consist of a material with high electrical conductivity, - And that the multiplication factor of the attenuation values related to 1 kHz when using wires of a nickel-iron alloy is 3 MHz over 190 and 6 MHz over 360, and the DC resistance of each inner conductor is below 20 Ω / m. X-ray line according to claim 1, characterized in - That all wires of the inner conductor (1) made of iron or a nickel-iron alloy of the composition 75%, Ni, 5% Cu, 2% Cr, 0.5% Mn, 0.2% Si, 0.02% C, rest Fe exist, - Or that at least the core wire made of copper or silver and the remaining wires made of iron or the Ni-Fe alloy. X-ray line according to claim 2 characterized by the following structure of the inner conductor: core is a plastic strand and therefore a layer of 6 stranding elements made of a core wire and a layer of 6 wires, all 42 wires 0.15 mm thick steel wires, stranded into a strand. X-ray line according to claim 2 characterized by the following structure of the inner conductor; Core of a copper or silver wire and therefore at least one layer of iron or Ni-Fe alloy wires stranded to form a strand, - Preferably core a 0.2 mm thick copper wire and therefore a layer of six 0.2 mm thick Ni-Fe alloy wires. X-ray line according to one of Claims 1 to 4 with the following structure of the line core: a) concentric without heating conductor: high-voltage conductor (Fig. 1) or b) concentric with heating conductor: heating conductor, insulation, heating conductor, insulation, high voltage conductor or c) 2 high-voltage conductors (7) and 2 heating cables (8-9) stranded together (Fig. 2) or d) 2 heating cables and 1 grid control cable stranded together, therefore guiding sleeve and concentric high-voltage conductor,
characterized in that all conductors (inner conductors) are formed as strands (1, 7, 8) or as ropes made solely of ferromagnetic wires or in combination with copper or silver wires.

Images