Current measuring resistor and associated manufacturing process

Abstract

The invention relates to a current-sensing resistor (1) for measuring an electric current, particularly in the kA range in a high-voltage network. The current-sensing resistor (1) according to the invention comprises two connection parts (2, 3) for introducing and discharging the electric current, respectively, and a resistance element (4) made of a low-resistance resistive material. The resistance element (4) is arranged in the current-flow direction between the two connection parts (2, 3) and joined with the two connection parts (2, 3) so that the electric current to be measured flows through the resistance element (4) during operation and generates a voltage drop across the resistance element (4).The invention provides that at least one coil (23, 24) is provided for energy harvesting from the magnetic field of the current measuring resistor (1), and that the coil (23, 24) supplies the electrical energy required to operate a measuring circuit, in particular alone or with an additional power supply.

Description

[0001] The invention relates to a current-sensing resistor for measuring an electric current, particularly in the kA range in a high-voltage network. The invention further relates to a corresponding manufacturing process for such a network resistor.

[0002] Low-resistance current-sensing resistors are known from the prior art (e.g., EP 0 605 800 A1) that enable current measurement according to the known four-wire technique. In this method, the current to be measured is passed through the low-resistance current-sensing resistor, and the voltage drop across the resistor is measured. According to Ohm's law, the voltage drop across the resistor is a measure of the electric current flowing through it. The known current-sensing resistors according to EP 0 605 800 A1 are typically cut from a composite material strip and therefore have a rectangular cross-section in a section perpendicular to the current flow direction. However, these known current-sensing resistors are not suitable for measuring alternating currents in the kA range in a high-voltage network.The rectangular shape of the resistor leads, especially with alternating currents, to strongly location- and frequency-dependent distributions of amplitudes and phase positions.

[0003] Current measuring resistors according to the preamble of claim 1, which contain a coil, are known from DE 195 35 551 A1 and DE 11 2012 003 086 T5. These documents also disclose a manufacturing method according to the preamble of claim 12. However, in this case, the coil does not serve to supply power to a measuring circuit.

[0004] The invention is therefore based on the objective of providing a correspondingly improved current measuring resistor and a manufacturing method for it.

[0005] This problem is solved by a current measuring resistor according to the invention and a corresponding manufacturing method according to the independent claims.

[0006] The current measuring resistor according to the invention initially has, in accordance with the known current measuring resistors described at the outset, two connection parts made of a conductor material (e.g. copper) in order to introduce the electric current to be measured into the current measuring resistor or to direct it out of the current measuring resistor.

[0007] Furthermore, the current measuring resistor according to the invention, in accordance with the prior art, has a resistive element made of a low-resistance resistive material (e.g., Noventin). ® , i.e. CuMnNi 25-10 ) consists of the resistive element being arranged in the direction of current flow between the two terminal parts and joined together with the two terminal parts, so that the electric current to be measured flows through the resistive element during operation and produces a voltage drop across the resistive element which forms a measure of the electric current to be measured.

[0008] The current-sensing resistor according to the invention differs from the known current-sensing resistor described above, preferably in that the two connection parts and the resistance element each have a substantially round cross-section, in particular a substantially circular cross-section, in a section plane perpendicular to the direction of flow of the electric current. This advantageously enables a design of the current-sensing resistor for measuring high alternating currents in the kA range in a high-voltage network.

[0009] The term "round cross-section" used within the scope of the invention is not limited to a cross-section that is exactly circular in the mathematical-geometric sense. Rather, the cross-section can also be represented by a polygon with a plurality of vertices, such as 16 vertices. In any case, however, the current-sensing resistor according to the invention differs from the known current-sensing resistors with a square or rectangular cross-section described above. In a preferred embodiment, the cross-section of the connecting parts and the resistance element is essentially circular and has only flattened sections that facilitate the manufacturing process or enable the mounting of a circuit board, as will be described in detail below.

[0010] In the preferred embodiment of the invention, the round resistive element has a larger outer diameter than the two round terminal parts, and is arranged centrally between the two terminal parts with respect to the current flow direction. The current-sensing resistor between the two outer terminal parts with the smaller outer diameter and the central resistive element with the larger outer diameter has a transition contour, which can be smooth and free of kinks to achieve a homogeneous current distribution. For example, the transition contour can also have a concave section.

[0011] Furthermore, it should be noted that the transition contour is preferably located exclusively in the connecting parts, while the outer diameter of the resistive element remains essentially constant along its length. Alternatively, however, the transition contour may also extend into the resistive element or be located entirely within the resistive element.

[0012] It has already been mentioned above that the connecting parts are joined together with the resistance element, as is basically the case with the known current-measuring resistors described at the beginning.

[0013] In one embodiment of the invention, this connection between the resistive element on the one hand and the connecting part on the other is made by electron beam welding, as is also known from the aforementioned patent application EP 0 605 800 A1. However, in producing such an electron beam weld, the electron beam must extend from the outer surface of the cladding to the center of the current-sensing resistor. This is relatively difficult due to the relatively large outer diameter of the current-sensing resistor according to the invention, which is why an electron beam weld is not optimal.

[0014] In another, preferred embodiment of the invention, the connection between the resistance element on the one hand and the connecting parts on the other hand is therefore made by brazing (e.g., vacuum brazing), which is preferably carried out in a furnace capable of heating the workpieces (resistance element and connecting parts) homogeneously and subjecting them to a specific temperature profile over time. The cooling gradients and cooling times also contribute to the quality of the brazed joint. Brazing generally requires a certain pressure on the joint. However, the workpieces to be joined (resistance element and connecting parts) have a relatively high weight in the current-sensing resistor according to the invention, so that additional external pressure on the workpieces is generally not necessary.

[0015] Preferably, brazing is carried out as part of a vacuum brazing process, such processes being known from the prior art and therefore need not be described again.

[0016] Furthermore, it should be noted that the resistive material of the resistor element may contain manganese, which makes a good solder joint more difficult. Therefore, the mating surfaces of the resistor element are preferably coated with a layered surface finish before joining (brazing). This finish may contain, for example, nickel, nickel-phosphorus (NiP), gold, or silver. The composition of the alloy, or the additions to the nickel, are crucial for the solder joint. The more noble the nickel alloy, the faster it forms a passivation layer, which in turn makes soldering more difficult. This surface finish enables a good solder joint despite the presence of manganese in the resistive material.

[0017] In the current-sensing resistor according to the invention, a printed circuit board is preferably mounted on the outer surface of the resistor in order to measure the voltage drop across the resistive element. This printed circuit board is preferably a flexible printed circuit board (flex circuit board) which may be curved or bent in the circumferential direction according to the outer contour of the current-sensing resistor.

[0018] The printed circuit board (PCB) is preferably connected to the current-sensing resistor by a weld, for example, by ultrasonic or laser welding. The weld can be located, for instance, only in the area of ​​the terminals to electrically and mechanically connect voltage taps on the inside of the PCB to these terminals. Alternatively, the weld between the PCB and the current-sensing resistor can be located only in the area of ​​the resistor element itself, allowing the voltage taps to be positioned within the resistor element.

[0019] Furthermore, the weld connection can extend across both the connection parts and the resistor element. Alternatively, the circuit board can be connected to the current-sensing resistor via a soldered connection.

[0020] Regarding the printed circuit board, it should also be mentioned that the circuit board is preferably designed with at least two layers in order to be accessible from both sides.

[0021] Furthermore, the circuit board can also incorporate a temperature sensor to measure the temperature of the resistive element, in particular an NTC resistor (NTC: negative temperature coefficient) or a PTC resistor (PTC: positive temperature coefficient). Alternatively, chip temperature sensors (Pt100, Pt1000, Ptx, 1-Wire, etc.) can also be used.

[0022] In a preferred embodiment of the invention, not just a single pair of voltage taps is provided to measure the voltage drop across the resistive element. Rather, several pairs of voltage taps are preferably provided, arranged at different locations on the current-sensing resistor, each providing a corresponding voltage measurement. The pairs of voltage taps are preferably distributed around the circumference of the current-sensing resistor, preferably equidistantly. For example, the number of pairs of voltage taps can be greater than 2, 4, 8, 12, or 14, with exactly 16 pairs of voltage taps being provided in the preferred embodiment of the invention.

[0023] For example, the voltage taps can be mounted directly on the circuit board and make direct contact with the outer surface of the terminals. The voltage taps can then be located on the side of the circuit board facing the current-sensing resistor and make contact with the terminals after the circuit board has been welded on. Preferably, however, the voltage taps are accessible via through-hole plating on both sides of the circuit board.

[0024] As mentioned briefly above, each pair of voltage taps provides a voltage measurement. An average value can then be calculated from these individual voltage measurements, which then represents the measure of the electric current flowing through the current-sensing resistor. Preferably, however, weighting resistors are provided to weight the individual voltage measurements, and a resulting measured value is then determined from the weighted voltage measurements. These weighting resistors can also be arranged on the circuit board.

[0025] The pairs of voltage taps are preferably connected to a measuring circuit that determines the voltage drop across the resistive element, wherein the measuring circuit preferably calculates the voltage drop across the resistive element from the weighted voltage measurements. The measuring circuit is preferably not arranged on the circuit board itself, but on at least one separate measurement card, which is connected to the circuit board by a wire.

[0026] The measuring circuit can also be connected to a data interface to transmit voltage drop measurements to an external evaluation unit. Preferably, this data interface is an electro-optical data interface that transmits the measurements to the external evaluation unit via an optical fiber.

[0027] To create redundancy in the measurement, preferably at least two measurement cards are provided, each having a measurement circuit, wherein the two measurement circuits are connected to the circuit board on the input side and record the voltage measurements of the individual pairs of voltage taps.

[0028] Each individual measurement circuit can have at least two or at least three measurement paths, with each path acquiring the measured values ​​for the voltage drop across the resistive element from the circuit board. With three measurement paths, the first two paths can, for example, have the same signal gain, while the third path has a lower signal gain.

[0029] It has already been briefly mentioned above that the outer contour of the current-sensing resistor does not have to be exactly round, but can have flattened areas in the outer surface in order to mount the circuit board parallel to the flattened area.

[0030] In a preferred embodiment of the invention, several flattened sections are arranged around the circumference of the current-sensing resistor, preferably more than 2, 4, 6, 8, 10, 12, or 14 flattened sections. In this preferred embodiment, the current-sensing resistor has a polygonal cross-section with 16 flattened sections. The printed circuit board (PCB) is folded multiple times, corresponding to the number of flattened sections in the current-sensing resistor, and contains flat PCB sections between each fold, each of which is mounted parallel to one of the flattened sections. In the embodiment of the current-sensing resistor according to the invention with 16 flattened sections in its outer surface, the PCB has 16 flat PCB sections, each of which rests parallel to one of the flattened sections.

[0031] It should be noted that the flattening in the axial direction preferably extends from the area of ​​the resistance element into the areas of the adjacent connection parts.

[0032] The measuring circuit described above and other electronic components of the current-sensing resistor require a power supply during operation. According to the invention, the current-sensing resistor has at least one coil for energy harvesting from its magnetic field. During operation, the electric current flowing through the current-sensing resistor generates a magnetic field that permeates the energy-harvesting coil, thereby enabling energy harvesting. This coil can then supply the electrical energy required to operate the measuring circuit, either on its own or with an additional power supply. Preferably, the coil has at least 20, 50, 100, or 140 turns, with exactly 150 turns being provided in the preferred embodiment of the invention. Furthermore, the coil preferably includes a magnetic core that surrounds the terminals in a ring-like fashion and is wound with the coil.In the preferred embodiment of the invention, several coils are provided, each of which surrounds one of the two connection parts in a ring shape.

[0033] Furthermore, a current storage device can also be integrated into the current measuring resistor, in particular at least one so-called power cap with a capacity of at least 10 mF, 50 mF, 100 mF, 500 mF or at least 1,000 mF.

[0034] A photocell can also be integrated into the current measuring resistor to provide supplementary power.

[0035] The conductor material is preferably copper or a copper alloy; however, other conductor materials are also possible within the scope of the invention. The conductor material of the connecting parts should, however, have a lower specific electrical resistance than the resistive material of the resistive element.

[0036] For example, the resistive material of the resistive element may be a copper-manganese-nickel alloy, in particular with 25 wt% manganese, 10 wt% nickel and the remainder copper or with 12 wt% manganese, 2 wt% nickel and the remainder copper.

[0037] The resistive material of the resistive element preferably has a specific electrical resistance that is less than 1,000 µΩcm, 500 µΩcm, 250 µΩcm, 100 µΩcm or 50 µΩcm.

[0038] In contrast, the conductor material of the connecting parts preferably has a specific electrical resistance that is less than 20 µΩcm, 10 µΩcm, 5 µΩcm or 2 µΩcm.

[0039] Furthermore, it should be mentioned that the resistive element, the first connection part, and / or the second connection part are preferably solid and without cavities. This is advantageous because cavities in the current-sensing resistor could allow water to penetrate. Moreover, the solid construction of the current-sensing resistor is also advantageous because, for sufficient short-circuit withstand capability, the current-sensing resistor according to the invention must have a large mass so that it can buffer the thermal power loss generated during a short circuit without a significant change in its resistance value.

[0040] Furthermore, it should be mentioned that the connecting parts can each have an axially extending longitudinal groove in their outer surface, originating from the end face of the connecting parts. These longitudinal grooves advantageously provide anti-rotation protection.

[0041] Furthermore, each of the two connecting parts can have an axially extending blind bore in its end face, in particular with an internal thread, wherein the blind bore is preferably arranged centrally and coaxially. This blind bore enables, for example, the connection of cables.

[0042] Furthermore, the connecting parts can each have at least one radially extending blind hole for housing mounting in their outer surface, whereby this blind hole can be located, for example, in the transition contour of the current measuring resistor.

[0043] As mentioned above, the current-sensing resistor in the area of ​​the resistive element forms a polygonal cross-section to allow for the mounting of the multiply folded printed circuit board. Therefore, the connection parts preferably contain corresponding annular grooves with a similarly polygonal cross-section and the same circumferential orientation. These annular grooves with the polygonal cross-section then serve as manufacturing aids during the automated assembly of the printed circuit board.

[0044] The current-sensing resistor according to the invention differs from the known current-sensing resistors described above also in its significantly larger dimensions, which are adapted for current measurement in the kA range. The outer diameter of the round resistance element can therefore be at least 6 cm, 7 cm, 8 cm, or 9 cm, with the outer diameter of the round resistance element being essentially 10 cm in the preferred embodiment of the invention. The outer diameter of the round connection parts, on the other hand, is preferably at least 2 cm, 3 cm, 4 cm, or 5 cm and is thus significantly smaller than the outer diameter of the round resistance element.

[0045] In the axial direction, the current measuring resistor according to the invention preferably has a relatively large length of at least 10 cm, 20 cm, 30 cm, 40 cm, 50 cm or 60 cm, wherein the length of the current measuring resistor in the preferred embodiment is essentially 64 cm.

[0046] In contrast, the individual resistance element preferably has an axial length of at least 1 cm, 2 cm, 3 cm, 4 cm, 5 cm or 6 cm in the direction of current flow, with the length of the resistance element in the preferred embodiment being essentially 7 cm.

[0047] The individual connection parts preferably have an axial length of at least 10 cm, 20 cm, 25 cm or 30 cm in the direction of current flow, with the axial length of the individual connection parts being essentially 31 cm in the preferred embodiment of the invention.

[0048] The mass of the connecting parts and the resistance element in the current-sensing resistor according to the invention is also preferably significantly larger than in the known current-sensing resistors described above, in order to ensure sufficient current-carrying capacity and short-circuit withstand capability. Thus, the connecting parts preferably each have a mass of at least 1 kg, 2 kg, 5 kg, 10 kg, 15 kg, or 20 kg, and in the preferred embodiment, substantially 22 kg. The resistance element, on the other hand, preferably has a mass of at least 0.5 kg, 1 kg, 1.5 kg, or 2 kg, with the mass in the preferred embodiment being substantially 2 kg.

[0049] The current measuring resistor according to the invention differs from known current measuring resistors also by a very high continuous current carrying capacity, which is at least 1 kA, 5 kA, 10 kA, 15 kA, 50 kA, 75 kA, 95 kA or even at least 100 kA for alternating current.

[0050] Furthermore, the current measuring resistor is also designed for a relatively high voltage level and is suitable for alternating current voltages of at least 1 kV, 5 kV, 10 kV, 50 kV, 110 kV, 220 kV or at least 380 kV.

[0051] Furthermore, it should be mentioned that the invention does not only claim protection for the current-measuring resistor according to the invention as a single component. Rather, the invention also claims protection for a corresponding manufacturing process. The individual process steps of the manufacturing process according to the invention are already evident from the preceding description, so that a separate description of the manufacturing process according to the invention can be omitted.

[0052] Other advantageous embodiments of the invention are characterized in the dependent claims or are explained in more detail below together with the description of the preferred embodiment of the invention with reference to the figures. The figures show: Fig. 1 a side view of a current measuring resistor according to the invention, Fig. 2 another side view of the current measuring resistor according to the invention Fig. 1, Fig. 3 a section view according to section line AA in Fig. 2, Fig. 4 a detailed view of detail area Z in Fig. 3, Fig. 5 a detailed view of detail area X in Fig. 3, Fig. 6 a perspective exploded view of the current measuring resistor according to the invention, Fig. 7 the manufacturing process according to the invention in the form of a flowchart.

[0053] The drawings show an embodiment of a current measuring resistor 1 according to the invention, which can be used in high-voltage networks of, for example, 220 kV alternating current for current measurement in the kA range.

[0054] The current measuring resistor 1 initially has two copper connection parts 2, 3, which serve to measure an electric current I AC to introduce into or extract from the current measuring resistor 1.

[0055] In the direction of current flow between the two terminal parts 2, 3 there is a resistive element 4 made of a resistive material (e.g. Noventin). ® , i.e. CuMnNi 25-10 ).

[0056] The resistive element 4 is connected to the two terminal parts 2, 3 at its two end faces by a brazing connection. To enable this brazing process despite the otherwise interfering manganese content of the resistive material, the resistive element 4 has a layered surface finish 5, 6 made of nickel-phosphorus (NiP) on both joining surfaces. The surface finishes 5, 6 are applied before the brazing connection is made in order to enable or facilitate the subsequent brazing process despite the manganese content of the resistive element 4.

[0057] The terminal parts 2, 3 and the resistive element 4 generally have a substantially circular cross-section, with a smaller diameter d1 in the region of the terminal parts 2, 3 and a larger outer diameter d2 in the region of the resistive element 4. To accommodate the diameter change between the two outer diameters d1, d2, terminal part 2 has a transition contour 7, while the other terminal part 3 has a corresponding transition contour 8. The two transition contours 7, 8 form the transition from the smaller outer diameter d1 of the terminal parts 2, 3 to the larger outer diameter d2 of the resistive element 4. It should be noted that both transition contours 7, 8 have a concave section to ensure a more homogeneous current density within the transition contours 7, 8.

[0058] In the end faces of the two connection parts 2,3 there is each a coaxial, central blind bore 9, 10 with an internal thread, wherein the two blind bores 9, 10 each enable the connection of cables.

[0059] Furthermore, the two connecting parts 2, 3 each have a longitudinal groove 11, 12 in their outer surface, which enables anti-rotation protection.

[0060] In the transition contours 7, 8 of the two connection parts 2, 3 there are also several radially extending blind bores 13, 14, 15 and 16, which enable housing mounting, as will be explained in detail below.

[0061] The cross-section of the resistive element 4 and the adjacent areas of the two terminal parts 2, 3 is not exactly circular. Rather, the current-sensing resistor 1 has a total of sixteen flats 17 in its center, which are arranged equidistantly around its circumference. Thus, the resistive element 4 has a polygonal cross-section with sixteen vertices in a cross-section perpendicular to the direction of current flow. The flats 17 serve to mount a flexible printed circuit board 18, which is folded multiple times according to the number of flats 17. Between each fold of the printed circuit board 18 are flat circuit board sections, each of which lies parallel to one of the flats 17.

[0062] The circuit board 18 has on its inner side facing the connection parts 2, 3 sixteen pairs of voltage taps 19, 20 which are plated through and rest on the connection parts 2, 3 and therefore each measure the voltage drop across the resistor element 4 in pairs.

[0063] The circuit board 18 with the voltage taps 19, 20 is connected to the connection parts 2, 3 by an ultrasonic welding connection.

[0064] The two connection parts 2, 3 also contain two annular grooves 21, 22, which likewise have a polygonal cross-section with sixteen sides. This polygonal cross-section of the annular grooves 21, 22 enables precise angular alignment during automated manufacturing and serves as a manufacturing aid during the assembly of the printed circuit board 18.

[0065] As mentioned above, the current-sensing resistor 1 is used for high-current measurement in a high-voltage network. To achieve sufficient current-carrying capacity and correspondingly high short-circuit withstand capability, the current-sensing resistor 1 has large dimensions and relatively large masses. The total axial length of the current-sensing resistor 1 is 640 mm. The connection parts 2 and 3 each have a mass of approximately 18–22 kg, while the mass of the resistance element 4 is approximately 2.5 kg. The outer diameter d2 is approximately 10 cm, while the outer diameter d1 of the connection parts 2 and 3 is correspondingly smaller.

[0066] From the exploded view in Fig. Figure 6 shows that the connecting parts 2, 3 are each surrounded by an energy harvesting coil 23, 24, which obtains electrical energy from the magnetic field of the current measuring resistor 1 for the operation of measuring circuits.

[0067] The measuring circuits are redundantly arranged on two measuring cards 25, 26, which are connected to the circuit board 18 by a cable.

[0068] Furthermore, it should be mentioned that the circuit board 18, in addition to the voltage taps 19 and 20, also carries weighting resistors to weight the voltage measurements of the individual pairs of voltage taps 19 and 20. The weighted voltage measurements are then transmitted from the circuit board 18 via the line to the two measurement cards 25 and 26 and processed there.

[0069] The measurement cards 25, 26 also have an electro-optical data interface to transmit measurement data via an optical fiber to an external evaluation unit.

[0070] Furthermore, the exploded view shows that the current measuring resistor 1 has two housing parts 27, 28 which can be attached to the blind holes 13-16 in the current measuring resistor 1.

[0071] The housing part 28 forms a slot 29 for the two measuring cards 25, 26, the slot 29 being able to be closed by a cover 30.

[0072] The following will now be described with reference to the flowchart according to Fig. 7 the manufacturing process according to the invention is described.

[0073] In a first step S1, the two connecting parts 2, 3 made of copper and the resistive element 4 made of noventin are first ® provided as round blanks.

[0074] In a further step S2, the blanks are then turned and / or milled.

[0075] In the next step S3, the surface finishing of the resistance element at the joining surfaces is carried out in order to apply the surface finishing 5, 6.

[0076] After this surface finishing, the brazing process can then begin in step S4 to join the resistance element 4 with the connection parts 2, 3.

[0077] In the next step S5, the current measuring resistor 1 is then stabilized and cleaned.

[0078] Subsequently, the current measuring resistor 1 is turned down in a step S6 to achieve the desired outer contour with the outer diameters d1, d2.

[0079] In a further step S7, the flattened areas 17 are milled into the round outer surface of the current measuring resistor 1.

[0080] Then, in step S8, the circuit board 18 is attached to the outer surface of the current measuring resistor 1 by ultrasonic welding.

[0081] In step S9, a housing is then assembled, consisting of the two housing parts 27, 28.

[0082] Then, in step S10, the two measurement cards 25, 26 are inserted into the slot 29.

[0083] In step S11, the energy harvesting coils 23 and 24 are then assembled.

[0084] Finally, in step S12, the housing cover is mounted.

[0085] For example, many aspects of the invention are also conceivable for current measuring resistors that do not have a round cross-section. Reference symbol list: 1 current measuring resistor 2, 3 connection parts for introducing or diverting the current to be measured 4 resistance element 5, 6 Surface finishing on the joining surfaces of the resistance element 7, 8 Transition contour between connection parts and resistance element 9, 10 Axial blind holes in the end faces of the connecting parts 11, 12 longitudinal grooves in the connecting parts 13-16 blind holes for housing mounting 17 flattenings 18 Flexible printed circuit boards 19, 20 voltage taps 21, 22 Ring grooves in the connecting parts 23, 24 Energy harvesting coil for energy generation through energy harvesting 25, 26 measurement cards 27, 28 Housing parts 29 Slot for the measurement cards 30 Lid of the insert compartment d1 diameter in the area of ​​the connection parts d2 diameter in the area of ​​the resistance element

Claims

[1] Current measuring resistor (1) for measuring an electric current (I AC ), with a) a first connecting part (2) made of a conductor material for introducing the electric current (I AC ) into the current measuring resistor (1), b) a second connecting part (3) made of a conductor material for conducting the electric current (I AC ) from the current-sensing resistor (1), and c) a resistive element (4) made of a low-resistance resistive material, wherein the resistive element (4) is arranged in the direction of current flow between the first terminal part (2) and the second terminal part (3) and is joined with the two terminal parts (2, 3) so that the electric current to be measured (I AC ) during operation through the resistance element (4) and a voltage drop (U) MESS ) generated above the resistance element (4), and d) at least one coil (23, 24), characterized by , e) that the coil (23, 24) is designed for energy harvesting from the magnetic field of the current-sensing resistor (1), and f) that the coil (23, 24) supplies the electrical energy required to operate a measuring circuit. [2] Current measuring resistor (1) according to claim 1, characterized by , that the first terminal part (2), the second terminal part (3) and the resistance element (4) are each in a section plane perpendicular to the direction of flow of the electric current (I) AC ) have an essentially round cross-section. [3] Current measuring resistor (1) according to claim 2, characterized by , a) that the round resistive element (4) has an outer diameter (d2) that is larger than the outer diameter (d1) of the two round connecting parts (2, 3), and b) that the resistive element (4) is arranged centrally between the two terminal parts (2, 3) with respect to the direction of current flow, and c) that the current measuring resistor (1) has a transition contour (7, 8) between the two outer connection parts (2, 3) with the smaller outer diameter (d1) and the central resistance element (4) with the larger outer diameter (d2), d) that the transition contour (7, 8) is smooth and free of kinks in order to achieve a homogeneous current distribution, e) that the transition contour (7, 8) is located exclusively in the connecting parts (2, 3), and f) that the transition contour (7, 8) is at least partially concave. [4] Current measuring resistor (1) according to any one of the preceding claims, characterized by , that the resistive element (4) is joined to the first terminal part (2) and to the second terminal part (3) by one of the following connection types: a) Soldered joint, b) Welded joint. [5] Current measuring resistor (1) according to any one of the preceding claims, characterized by, that the resistance element (4) has a layered surface finish (5, 6) at the joints to the two connecting parts (2, 3). [6] Current measuring resistor (1) according to any one of the preceding claims, characterized by , a) that a circuit board (18) is attached to the outer surface of the current-sensing resistor (1) in order to measure the voltage drop (U MESS ) above the resistance element (4), and b) that the circuit board (18) is arranged in the axial direction in the area of ​​the resistive element (4) and extends in the axial direction on both sides beyond the outer surface of the two terminal parts (2, 3), and c) that the circuit board (18) is a flexible circuit board (18) which is curved or bent in the circumferential direction according to the outer contour of the current-sensing resistor (1), and d) that the circuit board (18) is connected to the current-sensing resistor (1) by a soldered or welded connection. [7] Current measuring resistor (1) according to claim 6, characterized by , a) that several pairs of voltage taps (19, 20) are provided, each pair of voltage taps (19, 20) measuring the voltage drop (U) MESS ) measures across the resistive element (4) and provides a corresponding voltage measurement value, and b) that the pairs of voltage taps (19, 20) are arranged distributed over the circumference of the current-sensing resistor (1) to minimize the voltage drop (U) MESS ) above the resistance element (4) at several different points distributed over the circumference of the current-sensing resistor (1), c) that the number of pairs of voltage taps (19, 20) is greater than 2, 4, 8, 12, 14, and d) that the voltage taps are attached directly to the circuit board (18) and rest directly on the outer surface of the terminal parts (2, 3), and e) that the pairs of voltage taps (19, 20) are each connected to weighting resistors in order to weight the individual voltage measurements according to the resistance value of the weighting resistors, and f) that the weighting resistors are arranged on the circuit board (18). [8] Current measuring resistor (1) according to claim 7, characterized by , a) that the pairs of voltage taps (19, 20) are connected to the measuring circuit which calculates the voltage drop (U) from the measured values MESS ) determined above the resistance element (4), and / or b) that the measuring circuit detects the voltage drop (U MESS ) calculated over the resistance element (4) from the weighted voltage measurements, and / or c) that the measuring circuit is not arranged on the printed circuit board (18), but on at least one separate measuring card (25, 26) which is connected to the printed circuit board (18) by a line, and / or d) that the measuring circuit is connected to a data interface to receive measured values ​​of the voltage drop (U) MESS ) to transfer to an external evaluation unit, e) that the data interface is an electro-optical data interface which transmits the measured values ​​to the external evaluation unit via an optical fiber, and / or f) that, to create redundancy in the measurement, two measurement cards (25, 26) are provided, each having a measurement circuit, and / or g) that the measuring circuit has at least two or at least three measuring paths, wherein each measuring path receives the measured values ​​for the voltage drop across the resistive element (4) from the printed circuit board (18), and h) that the first measurement path and the second measurement path have the same signal gain, while the third measurement path has a lower signal gain. [9] Current measuring resistor (1) according to any one of claims 6 to 8, characterized by , a) that the substantially round outer contour of the current-sensing resistor (1) has at least one flat flattened surface (17) in the outer surface of the current-sensing resistor (1) in order to mount the printed circuit board (18) parallel to the flattened surface (17), and b) that several flattened areas (17) are arranged in the outer surface of the current-sensing resistor (1) distributed around its circumference, and / or c) that the flattened areas (17) are located in the lateral surface of the resistive element (4), and / or d) that the flattened sections (17) extend on both sides in the direction of current flow into the terminal parts (2, 3), and / or e) that the printed circuit board (18) is folded multiple times according to the number of flattened sections (17) and has several flat printed circuit board sections, each of which is mounted parallel to one of the flattened sections (17). [10] Current measuring resistor (1) according to any one of the preceding claims, characterized by , a) that the coil (23, 24) has at least 20, 50, 100 or 140 turns, and / or b) that the coil (23, 24) contains a magnetic core, and / or c) that several coils (23, 24) are provided for energy harvesting, each of which surrounds one of the two connection parts (2, 3) in a ring shape, and / or d) that an energy storage device is integrated into the current measuring resistor (1), and / or e) that a photocell is integrated into the current measuring resistor (1) for the purpose of providing a supplementary power supply. [11] Current measuring resistor (1) according to any one of the preceding claims, characterized by , a) that the conductor material is copper or a copper alloy, and / or b) that the conductor material of the connecting parts (2, 3) has a lower specific electrical resistance than the resistive material of the resistive element (4), and / or c) that the resistive material of the resistive element (4) is a copper-manganese-nickel alloy, and / or d) that the resistive material of the resistive element (4) has a specific electrical resistance of less than 1000 µΩcm, 500 µΩcm, 250 µΩcm, 100 µΩcm or 50 µΩcm, and / or e) that the conductor material has a specific electrical resistance of less than 20 µΩcm, 10 µΩcm, 5 µΩcm or 2 µΩcm, and / or f) that the resistive element (4), the first terminal part and / or the second terminal part are solid and without cavities, and / or g) that the connecting parts (2, 3) each have an axially extending longitudinal groove (11, 12) in their outer surface, which extends from the end face of the connecting parts (2, 3), and / or h) that the two connecting parts (2, 3) each have at least one radially extending blind hole (13-16) in their outer surface for housing mounting, and / or i) that the two connecting parts (2, 3) each have an axially extending blind bore (9, 10) in their end face, and / or j) that the two connecting parts (2, 3) each have a circumferential annular groove (21, 22) with a polygonal cross-section in their outer surface, which serves as a manufacturing aid, and / or k) that the outer diameter (d2) of the round resistance element (4) is at least 6cm, 7cm, 8cm or 9cm, and / or I) that the outer diameter (d1) of the round connecting parts (2, 3) is at least 2 cm, 3 cm, 4 cm or 5 cm, and / or m) that the current-sensing resistor (1) has an axial length of at least 10 cm, 20 cm, 30 cm, 40 cm, 50 cm or 60 cm in the direction of current flow, and / or n) that the resistive element (4) has an axial length of at least 1 cm, 2 cm, 3 cm, 4 cm, 5 cm or 6 cm in the direction of current flow, and / or o) that the two connecting parts (2, 3) each have an axial length of at least 10 cm, 20 cm, 25 cm or 30 cm in the direction of current flow, and / or p) that the two connecting parts (2, 3) each have a mass of at least 1kg, 2kg, 5kg, 10kg, 15kg or 20kg, and / or q) that the resistance element (4) has a mass of at least 0.5 kg, 1 kg, 1.5 kg or 2 kg, and / or r) that the current measuring resistor (1) has a continuous current carrying capacity of at least 1 kA, 5 kA, 10 kA, 25 kA, 50 kA, 75 kA, 95 kA or at least 100 kA when operating on alternating current, and / or s) that the current-sensing resistor (1) is suitable for alternating current at a voltage level of at least 1 kV, 5 kV, 10 kV, 50 kV, 110 kV, 220 kV or at least 380 kV, and / or t) that the first terminal part, the second terminal part and / or the resistive element (4) are each in a section plane perpendicular to the direction of flow of the electric current (I AC ) have a polygonal cross-section with at least 12, 14 or 16 corners to form the substantially round cross-section. [12] Manufacturing process for a current-sensing resistor (1), comprising the following steps: a) Provision of a first connection part (2) made of a conductor material for introducing the electric current (I AC ) into the current measuring resistor (1), b) Provision of a second connection part (3) made of a conductor material for conducting the electric current (I AC ) from the current measuring resistor (1), c) Provision of a resistive element (4) made of a low-resistance resistive material, d) Assembling the resistive element (4) with the two terminal parts (2, 3) to form the current-measuring resistor (1), such that the resistive element (4) is arranged in the direction of current flow between the first terminal part (2) and the second terminal part (3) and the electric current to be measured (I) AC ) during operation through the resistance element (4) and a voltage drop (U) MESS ) above the resistance element (4) generated, characterized by , e) that at least one coil (23, 24) is mounted to harvest energy from the magnetic field of the current-measuring resistor (1) by means of energy harvesting, and f) that the coil (23, 24) supplies the electrical energy required to operate a measuring circuit. [13] Manufacturing process according to claim 12, characterized by, that the first terminal part (2), the second terminal part (3) and the resistive element (4) each have a substantially round cross-section in a section plane perpendicular to the direction of current flow. [14] Manufacturing process according to claim 13, characterized by , that the joining of the resistive element (4) with the two connecting parts (2, 3) is carried out by one of the following joining methods: a) Soldering, b) Welding. [15] Manufacturing process according to claim 14, characterized by the following step before joining the resistor element (4) with the two connection parts (2, 3): Surface finishing of the joining surface. [16] Manufacturing process according to any one of claims 13 to 15, characterized by The following steps are taken after joining the resistor element (4) with the two connection parts (2, 3): a) Shaping the outer contour of the current-sensing resistor (1), in particular by turning or milling, and / or b) Forming planar flattenings (17) in the lateral surface of the current-sensing resistor (1) for the plane-parallel mounting of a printed circuit board (18) on the flattenings (17), wherein numerous flattenings (17) are formed distributed over the circumference of the current-sensing resistor (1) in the lateral surface of the current-sensing resistor (1). [17] Manufacturing process according to claim 16, characterized by the following steps: a) Attaching a printed circuit board (18) for measuring the voltage drop across the resistive element (4) to the outer surface of the resistive element (4), wherein the printed circuit board (18) is folded multiple times according to the number of plates (17) and has several flat printed circuit board sections, and the individual flat printed circuit board sections are each mounted parallel to one of the plates (17) of the current-sensing resistor (1), and / or b) Mounting a housing (27, 28) on the current-sensing resistor (1), wherein the housing encloses the resistive element (4), and / or c) Inserting at least one measuring card (25, 26) into the housing (27, 28), wherein the measuring card (25, 26) measures the voltage drop (U MESS ) measures above the resistance element (4), and / or d) Mounting a housing cover on the current measuring resistor (1).

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