Resonance testing system and resonant circuit comprising a superconductor

Abstract

The disclosure relates to a resonant circuit (100) comprising: an electrical coil (110) having a variable inductance for setting a resonant frequency in an oscillating circuit; a magnetic core (120), which is arranged at least partially within the coil (110) and is designed to form a magnetic field together with the coil (110); a superconductor (140), which is arranged at least partially around the magnetic core (120); and an excitation device (130, 150), which is designed to excite the superconductor (140) to transition from a superconducting state, in which the magnetic field within the magnetic core (120) is at least partially displaced, into a normal-conducting state, in which the magnetic field within the magnetic core (120) is at least partially restored, and thereby to change an inductance of the coil (110).

Description

[0001] 2025PF00001

[0002] 1

[0003] RESONANCE TESTING SYSTEM AND RESONANCE CIRCUIT WITH SUPRACONDUCTOR

[0004] Technical field

[0005] The present invention relates to the field of electrical testing of the capacitance of test objects, in particular high-voltage devices such as cables, gas-insulated switchgear, switches, disconnectors and isolators, transformers and other network components, using electrical resonant circuits for resonance testing. The invention relates to a resonant test system and a resonant circuit with a superconductor, a corresponding test method, and a coil with adjustable inductance. The invention further relates to a choke with variable inductance and variable frequency.

[0006] State of the art

[0007] Resonance test systems rely on the transfer effect of the energy stored in the resonant circuit, which is then transferred to the magnetic circuit in the test system's inductor. To tune the resonant circuit, either the frequency of the power source is adjusted or the inductance of the inductor is changed. Currently, the inductance is changed by mechanically adjusting the core of the inductor. When testing the capacitance of electrical lines intended for transmission from power generators to distribution or consumer networks, inductors or coils with magnetic cores are used. These cores are correspondingly heavy, sometimes weighing several tons. Therefore, mechanically adjusting the core is complex and time-consuming.Gears as well as hydraulic or pneumatic mechanisms are used to move the magnetic core; these must be manufactured with high precision to ensure the necessary accuracy in setting the choke's inductance. The mechanical adjustment of the core therefore represents a potential source of error and also limits the flexibility of the test system when test specimens with different capacitances or test voltages are to be tested with the same system. 2025PF00001.

[0008] 2

[0009] Description of the invention

[0010] One object of the invention is therefore to create a new technological concept for a resonance testing system in which the disadvantages described above do not occur, i.e., in which the inductance of the coil can be adjusted with high flexibility without the need for a complex mechanical adjustment of the core.

[0011] The problem is solved by the subject matter of the independent claims. Advantageous embodiments of the invention are specified in the dependent claims, the description, and the accompanying figures.

[0012] The inventive solution is based on the idea of ​​combining the coil with a superconductor or integrating a superconductor into the coil, which makes it possible to easily change the magnetic properties of the coil and thus the inductance of the coil or the magnetic flux in the core.

[0013] Superconductors or superconducting materials are metallic conductive materials that, when cooled at a critical temperature, the so-called transition temperature T, c, transitioning into a state with zero DC resistance. The transition temperature is the temperature at which the transition from the normal-conducting to the superconducting phase occurs. For elemental metals, it is generally below 10 K; in compounds, it can assume higher values, reaching over 100 K for special materials known as high-temperature superconductors.

[0014] To change the core's inductance, a fundamental property of a superconductor is exploited. No magnetic field appears in the envelope of a direct current-carrying superconductor. If a corresponding number of independent, superconducting turns (for example, n = 1 to 3) are placed around the end of the choke core, each of which can be individually switched on and off or supplied with a current using a current source, this results in a corresponding number of combinations of virtual, freely switchable air gaps in the choke core, through which the magnetic flux is expelled from the core. This then results in a correspondingly variable inductance. Due to the superconductivity, the required current is very low and flows almost without loss in the superconductor.

[0015] 3

[0016] According to one embodiment, with appropriate design of the individual superconductors, the switching on or off of the virtual air gap can also be regulated via the critical current. For this purpose, the current is driven so high that the critical current density of the superconductor is reached and it transitions into the normal conducting state. By appropriately designing the cross-sections of the superconductors, an alternative control level for the variable inductance can thus be realized.

[0017] In a particularly preferred embodiment of the invention, the variable inductance is combined with the variable frequency of a conventional power supply. This is currently difficult to achieve because simultaneously adjusting the core and the supply frequency mechanically makes it virtually impossible to find the resonance point of the respective test setup without stressing the mechanically adjustable core. However, if the inductance can be arbitrarily adjusted in real time within the control range using the superconductor(s), finding the resonance point for the conventional power supply becomes possible, thus enabling the combination of variable inductance and variable frequency in a single test circuit.

[0018] The same result can also be achieved with a counter-current source, which, for example, uses a power electronically controlled source to create a counter-magnetic field.

[0019] Furthermore, excitation does not necessarily have to be achieved by injecting a DC or AC current into the superconductor. Changing the temperature of the superconductor, for example using a controllable cryostat, also allows the magnetic properties of the coil and the core, and thus the inductance of the coil, to be altered.

[0020] The concept presented here can also be used in filters and compensation chokes in network operation by distribution network operators (DNOs) and transmission system operators (TSOs).

[0021] According to one aspect, the problem described above is solved by a resonant circuit with: an electrical coil with a variable inductance for setting a resonant frequency in a resonant circuit; a magnetic core, which 2025PF00001

[0022] 4

[0023] a superconductor that is at least partially arranged within the coil and is configured to form a magnetic field together with the coil; a superconductor that is at least partially arranged around the magnetic core; and an excitation device configured to excite the superconductor to transition from a superconducting state in which the magnetic field within the magnetic core is at least partially displaced to a normal-conducting state in which the magnetic field within the magnetic core is at least partially restored, thereby changing an inductance of the coil.

[0024] The resonant circuit presented here is based on a novel technological concept in which the disadvantages described at the beginning do not occur, i.e., in which the inductance of the coil can be adjusted with high flexibility without the need for a complex mechanical adjustment of the core.

[0025] The resonant circuit described here combines or integrates a coil with a superconductor, which makes it possible to easily change the magnetic properties of the coil and thus the inductance of the coil or core.

[0026] In the superconducting effect of perfect diamagnetism, the magnetic field is expelled from the interior of the material or ring in the superconducting state. This effect was described by Meissner and Ochsenfeld and is used in the resonant circuit described here to change the inductance of the coil.

[0027] An electrical resonant circuit, as described herein, also called a resonant circuit, is a resonant electrical circuit consisting of a coil and a capacitor that can perform electrical oscillations.

[0028] According to an exemplary embodiment of the resonant circuit, the excitation device comprises a current source configured to supply a current for flowing through the superconductor; wherein the superconductor is configured to transition from the superconducting state to the normal conducting state when a current flows through the superconductor, thereby changing the inductance of the coil.

[0029] The excitation of the superconductor can be achieved in essentially two ways: firstly, by excitation using a current source, and secondly, by changing the temperature. Je2025PF00001

[0030] 5

[0031] Depending on the magnitude of the current flowing through the superconductor, the superconductor can be switched to the superconducting state or the normal conducting state, so that a simple change can be achieved by controlling the current flow through the superconductor.

[0032] The power source can be a direct current (DC) or an alternating current (AC) source. A change in the magnetic field is observed when the superconductor is excited by either DC or AC current.

[0033] The same result can also be achieved with a counter-current source, which generates a counter-magnetic field using a power electronically controlled source.

[0034] According to an exemplary embodiment of the resonant circuit, the excitation device comprises a cryostat configured to cool the superconductor; wherein the superconductor is configured to transition from the superconducting state to the normal conducting state upon a reduction in cooling, which is associated with an increase in the temperature of the superconductor above a critical temperature, and thereby to change the inductance of the coil.

[0035] As described above, the excitation of the superconductor can be achieved in essentially two ways. Firstly, by excitation using a current source, and secondly, by excitation using a cryostat to change the temperature of the superconductor. Depending on the cooling of the superconductor and the resulting temperature, the superconductor can be brought into either the superconducting or the normal conducting state, so that a simple change can be achieved by controlling the temperature of the superconductor using a cryostat.

[0036] According to an exemplary embodiment of the resonant circuit, the superconductor comprises one or more superconducting windings arranged around the magnetic core, each of which can be independently supplied with current and / or cooling by the excitation device. 2025PF00001

[0037] 6

[0038] This offers the advantage that the superconductor essentially consists of a multitude of individual superconductors, namely the superconducting windings, which can be controlled separately and independently of each other, in order to realize a multitude of inductance settings.

[0039] According to an exemplary embodiment of the resonant circuit, the one or more superconducting windings arranged around the magnetic core are arranged axially to the magnetic core and / or the multiple superconducting windings are arranged parallel to each other.

[0040] In such an axial arrangement, the magnetic field lines run longitudinally through the core in the normal conducting state and are largely expelled from the core in the superconducting state. This allows for the greatest possible change in the coil's inductance. The same advantage applies to the parallel arrangement of the superconducting windings. Here, individual superconducting windings, and thus virtual air gaps, can also be easily switched on or off, enabling the coil's inductance to be adjusted flexibly and according to requirements.

[0041] According to an exemplary embodiment of the resonant circuit, the one or more superconducting windings are shaped in a ring-shaped, disc-shaped or coil-shaped form.

[0042] This type of winding ensures that sufficiently high currents can flow through the superconducting windings.

[0043] According to an exemplary embodiment of the resonant circuit, the inductance of the coil is adjustable in steps depending on the number of superconducting turns.

[0044] This achieves the advantage that an inductance can be easily set at which the associated resonant circuit is in resonance.

[0045] According to an exemplary embodiment of the resonant circuit, the inductance of the coil is adjustable based on a combination of superconducting windings in a normal conducting state and superconducting windings in a superconducting state. 2025PF00001

[0046] 7

[0047] By combining windings in a normal conducting state with superconducting windings in a superconducting state, a large number of inductance values ​​can be set.

[0048] The respective windings can be switched between the normal conducting state and the superconducting state by applying current and / or cooling or temperature.

[0049] According to an exemplary embodiment of the resonant circuit, the resonant circuit comprises: one or more cooling lines for cooling the superconductor, wherein the one or more cooling lines can be supplied with coolant from the cryostat.

[0050] As described above, this makes it possible to flexibly adjust the inductance of the coil, firstly by changing the current flow through the superconductor, and secondly by changing the cooling of the superconductor, which can be easily achieved by one or more cooling lines.

[0051] According to an exemplary embodiment of the resonant circuit, the magnetic core is shaped according to a closed or open magnetic contour and includes a leg around which the superconductor is arranged.

[0052] The shape of the magnetic core can therefore be manufactured flexibly. The magnetic field can be determined based on the shape of the magnetic core. Preliminary investigations can be used to determine the optimal core shape for a specific application.

[0053] The contour in question can be rectangular, square, or U-shaped, for example. Other geometric shapes are also possible.

[0054] According to an exemplary embodiment of the resonant circuit, the superconductor is configured to restore the magnetic field within the magnetic core when the current of the power source is switched on or increased, and to at least partially displace the magnetic field within the magnetic core when the current of the power source is switched off or decreased, thereby changing the inductance of the coil. 2025PF00001

[0055] 8

[0056] This offers the advantage that the inductance of the coil can be easily adjusted simply by switching on or off, or increasing or decreasing (or generally changing) the current of the power source.

[0057] According to an exemplary embodiment of the resonant circuit, the superconductor is designed to cancel the displacement of the magnetic field from the magnetic core when the current is driven above a threshold value corresponding to a critical current density of the superconductor at which the superconductor transitions into the normal conducting state, thereby changing the inductance of the coil.

[0058] This offers the advantage that the inductance of the coil can be easily adjusted simply by moving the superconductor into the normal conducting state or the superconducting state.

[0059] According to an exemplary embodiment of the resonant circuit, the superconductor is designed to restore the magnetic field within the magnetic core when the cooling of the superconductor is switched off, and to at least partially displace the magnetic field within the magnetic core when the cooling by the cryostat is switched on, thereby changing the inductance of the coil.

[0060] This offers the advantage that the inductance of the coil can be easily adjusted simply by switching the cooling of the superconductor on or off (or generally changing it) using the cryostat.

[0061] According to an exemplary embodiment of the resonant circuit, the superconductor is designed to cancel the displacement of the magnetic field from the magnetic core when the cooling is switched off after reaching the critical temperature at which the superconductor transitions into the normal conducting state, thereby changing the inductance of the coil.

[0062] This offers the advantage that the coil's inductance can be easily adjusted simply by switching the superconductor between its normal conducting and superconducting states by controlling the cooling. 2025PF00001

[0063] 9

[0064] According to an exemplary embodiment of the resonant circuit, the magnetic core is fixed or firmly anchored in a fixed position relative to the coil.

[0065] This achieves the advantage that the resonant circuit can be built as a compact unit, requiring no special precautions for transport, since the magnetic core is fixed or firmly anchored in a fixed position relative to the coil and therefore cannot fall out or detach itself.

[0066] According to a second aspect, the problem described above is solved by a resonant test system for testing the electrical capacitance of a test object in electrical resonance; wherein the resonant test system comprises the resonant circuit according to the first aspect described above; and wherein the electrical coil is configured to form an electrical resonant circuit with the electrical capacitance of the test object.

[0067] The resonance test system presented here is based on a novel technological concept that avoids the disadvantages described earlier; that is, the coil's inductance can be adjusted with high flexibility without requiring complex mechanical adjustments to the core. This resonance test system combines or integrates a coil with a superconductor, allowing for easy modification of the coil's magnetic properties and thus its inductance or core.

[0068] According to an exemplary embodiment of the resonance test system, the electrical resonant circuit can be excited via an alternating current supply with variable frequency, so that a resonance point of the resonant circuit can be set based on the variable frequency and the changeable inductance of the coil, in particular via a control signal.

[0069] This offers the advantage that the resonant frequency can be adjusted very precisely and very quickly, since two parameters can be adjusted for this purpose: the frequency of the AC power supply and the inductance of the coil.

[0070] According to an exemplary embodiment of the resonance test system, the electrical resonant circuit can be excited via an alternating current supply with a fixed frequency, so that a2025PF00001

[0071] 10

[0072] The resonance point of the resonant circuit can be adjusted based on the fixed frequency and the variable inductance of the coil, which can be changed, in particular, via a control signal.

[0073] This offers the advantage that the resonant frequency is easily adjustable. Only a fixed-frequency oscillation excitation is required. The resonant circuit can be easily brought into resonance by adjusting the inductance of the coil.

[0074] According to an exemplary embodiment, the resonance test system is designed to test the electrical capacitance of an electrical device, in particular a cable, for an electrical transmission network, especially at a high-voltage or medium-voltage network level.

[0075] This offers the advantage that the inductance can be changed without mechanically adjusting the core of the choke. A complex and time-consuming mechanical adjustment of the core is therefore unnecessary, thus eliminating potential sources of error. The resonant test system allows for the flexible testing of specimens with varying capacitances or test voltages without the need for multiple such systems.

[0076] According to a third aspect, the problem described above is solved by a method for testing the electrical capacitance of a test object, wherein the method comprises: coupling the capacitance of the test object with an inductance of the coil of a resonant test system according to the second aspect described above to form an electrical resonant circuit; and controlling the excitation device of the resonant test system to set an inductance of the coil at which the electrical resonant circuit can be operated in resonance.

[0077] The method presented here is based on a novel technological concept, as described above, in which the inductance of the coil can be adjusted with high flexibility without the need for complex mechanical adjustment of the core.

[0078] According to a fourth aspect, the task described above is solved by a coil with adjustable inductance, comprising: a coil former; a magnetic core, which 2025PF00001

[0079] 11

[0080] a superconductor that is at least partially arranged within the coil body and is designed to form a magnetic field together with the coil body; and a superconductor that is at least partially arranged around the magnetic core and is designed, when the superconductor is excited, to transition from a superconducting state in which the magnetic field within the magnetic core is at least partially displaced to a normal-conducting state in which the magnetic field within the magnetic core is at least partially restored, and thereby to change an inductance of the coil.

[0081] The coil described here incorporates a superconductor, which allows the magnetic properties of the coil, and thus the inductance of the coil or core, to be easily changed. In the superconducting effect of perfect diamagnetism, the magnetic field is expelled from the interior of the material or ring in the superconducting state. This effect was described by Meissner and Ochsenfeld and is used in the coil described here to adjust its inductance.

[0082] According to an exemplary embodiment of the coil, the excitation of the superconductor is based on a temperature change of the superconductor and / or a change in the current flow through the superconductor.

[0083] Switching the superconductor between its superconducting and normal conducting states can be achieved in various ways, firstly by changing the current flow through the superconductor and secondly by changing its temperature. The coil presented here can therefore adjust its inductance in a simple and flexible manner.

[0084] Brief character description

[0085] The invention will now be described in more detail with reference to exemplary embodiments and the figures. The figures show:

[0086] Fig. 1 shows an illustration of a resonant circuit 100 according to the invention in an exemplary embodiment; 2025PF00001

[0087] 12

[0088] Fig. 2 shows an illustration of a test arrangement 200 according to an exemplary embodiment of the invention, which includes the resonance circuit 100 from Figure 1; and

[0089] Fig. 3 is a schematic illustration of a method 300 for testing the electrical capacitance of a test object.

[0090] The figures are merely schematic representations and serve only to illustrate the invention. Identical or equivalent elements are consistently identified by the same reference numerals.

[0091] The following detailed description refers to the accompanying drawings, which form part thereof and illustrate specific embodiments in which the invention can be implemented. It is understood that other embodiments can also be used and structural or logical modifications can be made without deviating from the concept of the present invention. Therefore, the following detailed description is not to be understood as limiting. Furthermore, it is understood that the features of the various embodiments described herein can be combined with one another, unless specifically stated otherwise.

[0092] The aspects and embodiments are described with reference to the drawings, where the same reference numerals generally refer to the same elements. For explanatory purposes, numerous specific details are set forth in the following description to provide a thorough understanding of one or more aspects of the invention. However, it may be obvious to a person skilled in the art that one or more aspects or embodiments can be implemented with a lesser degree of specific detail. In other cases, known structures and elements are shown schematically to facilitate the description of one or more aspects or embodiments. It is understood that other embodiments may be used and structural or logical modifications may be made without departing from the concept of the present invention. 2025PF00001

[0093] 13

[0094] Fig. 1 shows an illustration of a resonant circuit 100 according to the invention in an exemplary embodiment.

[0095] The resonant circuit 100 comprised an electrical coil 110 with a variable inductance for setting a resonant frequency in a resonant circuit; a magnetic core 120, which is arranged at least partially inside the coil 110 and is configured to form a magnetic field together with the coil 110; a superconductor 140, which is arranged at least partially around the magnetic core 120; and an excitation device 130, 150. This excitation device 130, 150 is configured to excite the superconductor 140 to transition from a superconducting state, in which the magnetic field inside the magnetic core 120 is at least partially displaced, to a normal-conducting state, in which the magnetic field inside the magnetic core 120 is at least partially restored, and thereby to change the inductance of the coil 110.

[0096] This utilizes the superconducting effect of perfect diamagnetism, in which the magnetic field is expelled from the interior of the material or a ring in the superconducting state. This effect was described by Meissner and Ochsenfeld.

[0097] The Meissner-Ochsenfeld effect is a very characteristic property of superconductors. The external magnetic field penetrates approximately 100 nm into the material; deeper layers are field-free. This "pushing out" of the magnetic field is independent of whether the sample was already superconducting before the magnetic field was applied or is made superconducting only after the magnetic field has been switched on.

[0098] The use of this superconducting effect for the construction of inductively shielded superconducting fault current limiters (iSFCL) and the two states "normally conducting" and "superconducting" are explained in more detail, for example, in the publication: "U. Kaltenborn et al., Inductive shielded superconducting fault current limiter - an enabler of smarter grids, 21st International Conference on Electricity Distribution, Paper 0955, Frankfurt, 6-9 June 2011".

[0099] The excitation device 130, 150 can, for example, comprise a current source 130 configured to supply a current for flowing through the superconductor 140. The2025PF00001

[0100] 14

[0101] Superconductor 140 is designed to transition from the superconducting state to the normal conducting state when a current flows through the superconductor 140, as described above with regard to the Meissner-Ochsenfeld effect, and thereby change the inductance of the coil 110.

[0102] The current source 130 can be a direct current source or an alternating current source. Both can cause a change in the magnetic field and thus in the inductance of the coil.

[0103] The excitation device 130, 150 can, for example, also or alternatively include a cryostat 150 configured to cool the superconductor 140. The superconductor 140 is also configured to transition from the superconducting state to the normal conducting state when the cooling is reduced, which occurs when the temperature of the superconductor 140 rises above a critical temperature, thereby changing the inductance of the coil 110.

[0104] The superconductor 140 can, for example, comprise one or more superconducting turns 141 arranged around the magnetic core 120, each of which can be independently supplied with current and / or cooling by the excitation device 130, 150. Figure 1 shows an exemplary number of six superconducting turns 141.

[0105] These one or more superconducting windings 141 arranged around the magnetic core 120 are arranged axially to the magnetic core 120, as shown in Figure 1. The multiple superconducting windings 141 can be arranged parallel to each other, as illustrated by way of example in Figure 1.

[0106] The superconducting windings 141 can, for example, be shaped like rings, discs, or coils. Other geometric shapes are also possible.

[0107] The inductance of coil 110 can be adjusted in steps depending on the number of superconducting turns 141. 2025PF00001

[0108] 15

[0109] For example, the inductance of the coil 110 can be adjusted based on a combination of superconducting windings 141 that are in a normal conducting state and those that are in a superconducting state.

[0110] The respective windings can be switched between the normal conducting state and the superconducting state by applying current and / or cooling or temperature.

[0111] The resonant circuit 100 can have one or more cooling lines 151 for cooling the superconductor 140. The cooling lines 151 can be supplied with coolant from a cryostat 150, as shown in Figure 1.

[0112] The magnetic core 120 can be shaped according to a closed or open magnetic contour (not shown in Figure 1) and comprise a leg around which the superconductor 140 is arranged.

[0113] The contour in question can be rectangular, square, or U-shaped, for example. Other geometric shapes are also possible.

[0114] For example, when the current 131 of the power source 130 is switched on, the superconductor 140 can restore the magnetic field within the magnetic core 120, and when the current 131 of the power source 130 is switched off, it can at least partially displace the magnetic field within the magnetic core 120, thus changing the inductance of the coil 110.

[0115] For example, when the current 131 is applied above a threshold value corresponding to a critical current density of the superconductor 140, at which the superconductor 140 transitions into the normal conducting state, the superconductor 140 can cancel the displacement of the magnetic field from the magnetic core 120 and thus change the inductance of the coil 110.

[0116] The critical current density or critical current of a superconductor can be defined as the current density that eliminates the resistance-free state of the superconductor. In first-order superconductors, this occurs when the critical field arises at the surface of the superconductor due to the magnetic effect of the current. (See also: Superconductors 2025PF00001)

[0117] 16

[0118] The second type of critical current corresponds to the transition to the resistive superconducting state, in which flux motion occurs.

[0119] When the cooling of the superconductor 140 is switched off, it can restore the magnetic field within the magnetic core 120, and when the cooling is switched on by the cryostat 150, it can at least partially displace the magnetic field within the magnetic core 120, thus changing the inductance of the coil 110.

[0120] When the cooling is switched off after reaching the critical temperature at which the superconductor 140 transitions into the normal conducting state, the superconductor 140 can cancel the displacement of the magnetic field from the magnetic core 120 and thus change the inductance of the coil 110.

[0121] The magnetic core 120 can, for example, be fixed in a fixed position relative to the coil 110 or be firmly anchored. The core 120 and the coil 110 can be manufactured as a single unit that can be moved or transported together. Therefore, no relative movement between the core 120 and the coil 110 is necessary to change the inductance of the coil 110.

[0122] In addition to the resonant circuit 100 described above, Figure 1 also shows a coil 110 with adjustable inductance, which comprises: a coil former 110a (which essentially corresponds to the coil 110 described above); a magnetic core 120, which is arranged at least partially within the coil former 110a and is designed to form a magnetic field together with the coil former 110a; and a superconductor 140, which is arranged at least partially around the magnetic core (120).

[0123] The superconductor 140 is designed, upon excitation, to transition from a superconducting state, in which the magnetic field within the magnetic core 120 is at least partially displaced, to a normal conducting state, in which the magnetic field within the magnetic core 120 is at least partially restored, thereby changing the inductance of the coil 110. 2025PF00001

[0124] 17

[0125] The excitation of the superconductor 140 is based, for example, on a temperature change of the superconductor 140 and / or a change in the current flow through the superconductor 140, as described above.

[0126] Fig. 2 shows an illustration of a test arrangement 200 according to the invention in an exemplary embodiment, which includes the resonance circuit 100 from Figure 1.

[0127] The resonance test system 200 is used to test the electrical capacitance 210 of a test specimen in electrical resonance. The resonance test system 200 comprises the resonance circuit 100 described above in Figure 1. The electrical coil 110 is configured to form an electrical resonant circuit 220 with the electrical capacitance 210 of the test specimen.

[0128] The resonance test system 200 is based on the charging effect of the energy stored in the resonant circuit 220 in the (test specimen) capacitance 210 to the magnetic circuit in the choke or coil 110 of the test system 200. To tune the resonant circuit 220, the frequency of the supply source 240 can be adjusted or the inductance of the choke or coil 110.

[0129] The electrical resonant circuit 220 can be excited via an alternating current supply 240 with variable frequency, so that a resonance point of the resonant circuit 220 can be set based on the variable frequency and the changeable inductance of the coil 110.

[0130] The setting can be made, for example, via a control signal 231 from a controller 230, which controls the excitation device 130, 150 to excite the coil 110. For example, the control signal 231 can control the current source 130, determining the current flowing through the superconductor 140 or the individual superconducting turns 131 of the superconductor 140. For example, the control signal 231 can control the cryostat 150 (not explicitly shown here in Figure 2), determining the amount of coolant used to cool the superconductor 140 or the individual superconducting turns 131 of the superconductor 140, and thus the temperature at which the superconductor 140 or the individual superconducting turns 141 reach.

[0131] The electrical resonant circuit 220 can also be excited via an alternating current supply 240 with a fixed frequency, so that a resonance point of the resonant circuit 220 based on 2025PF00001

[0132] 18

[0133] The inductance of the coil 110 can be adjusted on the fixed frequency and the variable inductance of the coil 110, in particular via the control signal 231, as described above.

[0134] The test setup 200 can therefore be operated with variable frequency and variable inductance or with fixed frequency and variable inductance.

[0135] The resonance test system 200 can thus test the electrical capacitance 210 of, for example, an electrical cable for an electrical transmission network, for example at a high-voltage or medium-voltage network level.

[0136] Fig. 3 shows a schematic illustration of a method 300 for testing the electrical capacitance of a test specimen.

[0137] The method 300 comprises coupling 301 of the capacitance of the test object with an inductance of the coil 110 of a resonant test system 200 as described above in Figure 2 to form an electrical resonant circuit 220.

[0138] The method 300 also includes controlling 302 of the excitation device 130, 150, as described above for Figure 1, of the resonance test system 200 for setting an inductance of the coil 110 at which the electrical resonant circuit can be operated in resonance.

[0139] The procedure can be executed by a computer program with program code, provided the program code is executed on a computer. 2025PF00001

[0140] 19

[0141] REFERENCE MARK LIST

[0142] 100 resonance circuits according to the invention

[0143] 110 electrical coil or choke

[0144] 120 magnetic core (of the coil)

[0145] 140 superconductors

[0146] 141 superconducting turns (of the superconductor) 130 power source as part of the excitation device 150 cryostat as part of the excitation device 131 electric current

[0147] 151 cooling lines for cooling the superconductor

[0148] 200 Resonance test system according to the invention 210 Electrical capacitance

[0149] 220 electrical resonant circuit

[0150] 230 control

[0151] 231 Control signal

[0152] 240 AC power supply

[0153] 300 method according to the invention

[0154] 301 First step: Coupling

[0155] 302 second step: Target

Claims

2025PF00001 20 PATENT CLAIMS 1. Resonance circuit (100), with: an electrical coil (110) with a variable inductance for setting a resonant frequency in a resonant circuit; a magnetic core (120) which is at least partially arranged inside the coil (110) and is designed to form a magnetic field together with the coil (110); a superconductor (140) which is arranged at least partially around the magnetic core (120); and an excitation device (130, 150) configured to excite the superconductor (140) to transition from a superconducting state in which the magnetic field within the magnetic core (120) is at least partially displaced to a normal conducting state in which the magnetic field within the magnetic core (120) is at least partially restored, and thereby to change an inductance of the coil (110).

2. Resonance circuit (100) according to claim 1, wherein the excitation device (130, 150) comprises a current source (130) configured to supply a current for flowing through the superconductor (140); wherein the superconductor (140) is designed to transition from the superconducting state to the normal conducting state when a current flows through the superconductor (140) and thereby change the inductance of the coil (110).

3. Resonance circuit (100) according to claim 1 or 2, wherein the excitation device (130, 150) comprises a cryostat (150) configured to cool the superconductor (140); wherein the superconductor (140) is designed to transition from the superconducting state to the normal conducting state upon a reduction in cooling, which is associated with an increase in the temperature of the superconductor (140) above a critical temperature, and thereby to change the inductance of the coil (110).

4. Resonance circuit (100) according to one of the preceding claims, 2025PF00001 21 wherein the superconductor (140) comprises one or more superconducting windings (141) arranged around the magnetic core (120), each of which can be independently supplied with current and / or cooling by the excitation device (130, 150).

5. Resonance circuit (100) according to claim 4, wherein the one or more superconducting turns (141) arranged around the magnetic core (120) are arranged axially to the magnetic core (120) and / or the multiple superconducting turns (141) are arranged parallel to each other.

6. Resonance circuit (100) according to claim 4 or 5, wherein the one or more superconducting windings (141) are shaped in a ring-shaped, disc-shaped or coil-shaped form.

7. Resonance circuit (100) according to one of claims 4 to 6, wherein the inductance of the coil (110) is adjustable in steps depending on the number of superconducting turns (141).

8. Resonance circuit (100) according to claim 7, wherein the inductance of the coil (110) is adjustable based on a combination of superconducting windings (141) in a normal conducting state and in a superconducting state.

9. Resonance circuit (100) according to one of the preceding claims, comprising: one or more cooling lines (151) for cooling the superconductor (140), wherein the one or more cooling lines (151) can be supplied with coolant from a cryostat (150).

10. Resonance circuit (100) according to one of the preceding claims, wherein the magnetic core (120) is shaped according to a closed or open magnetic contour and comprises a leg around which the superconductor (140) is arranged.

11. Resonance circuit (100) according to claim 2,2025PF00001 22 wherein the superconductor (140) is configured to restore the magnetic field within the magnetic core (120) when the current (131) of the power source (130) is switched on, and to at least partially displace the magnetic field within the magnetic core (120) when the current (131) of the power source (130) is switched off, thereby changing the inductance of the coil (110).

12. Resonance circuit (100) according to claim 11, wherein the superconductor (140) is designed, when the current (131) is applied above a threshold value corresponding to a critical current density of the superconductor (140), at which the superconductor (140) transitions into the normal conducting state, to eliminate the displacement of the magnetic field from the magnetic core (120) and thus to change the inductance of the coil (110).

13. Resonance circuit (100) according to claim 3, wherein the superconductor (140) is configured to restore the magnetic field within the magnetic core (120) when the cooling of the superconductor (140) is switched off, and to at least partially displace the magnetic field within the magnetic core (120) when the cooling by the cryostat (150) is switched on, thereby changing the inductance of the coil (110).

14. Resonance circuit (100) according to claim 13, wherein the superconductor (140) is designed to cancel the displacement of the magnetic field from the magnetic core (120) and thus change the inductance of the coil (110) when the cooling is switched off after reaching the critical temperature at which the superconductor (140) transitions into the normal conducting state.

15. Resonance circuit (100) according to one of the preceding claims, wherein the magnetic core (120) is fixed or firmly anchored in a fixed position relative to the coil (110).

16. Resonance test system (200) for testing an electrical capacitance (210) of a test specimen in electrical resonance; 2025PF00001 23 wherein the resonance test system (200) comprises the resonance circuit (100) according to one of the preceding claims; and wherein the electrical coil (110) is designed to form an electrical resonant circuit (220) with the electrical capacitance (210) of the test specimen.

17. Resonance test system (200) according to claim 16, wherein the electrical resonant circuit (220) can be excited via an alternating current supply (240) with variable frequency, so that a resonance point of the resonant circuit (220) can be set based on the variable frequency and the changeable inductance of the coil (110), in particular via a control signal (231).

18. Method (300) for testing an electrical capacitance of a test object, wherein the method (300) comprises the following: Coupling (301) the capacitance of the test specimen with an inductance of the coil (110) of a resonant test system (200) according to one of claims 16 or 17 for forming an electrical resonant circuit; and Controlling (302) the excitation device (130, 150) of the resonance test system (200) to adjust an inductance of the coil (110) at which the electrical resonant circuit (220) can be operated in resonance.

19. Coil (110) with adjustable inductance, comprising: a coil former (110a); a magnetic core (120) which is at least partially arranged within the coil body (110a) and is designed to form a magnetic field together with the coil body (110a); and a superconductor (140), which is at least partially arranged around the magnetic core (120) and is designed to transition, upon excitation of the superconductor (140), from a superconducting state in which the magnetic field within the magnetic core (120) is at least partially displaced, to a normal conducting state in which the magnetic field within the magnetic core (120) is at least partially restored, and thereby to change an inductance of the coil (110).

20. Coil (110) according to claim 19,2025PF00001 24 in which the excitation of the superconductor (140) is based on a temperature change of the superconductor (140) and / or a change in the current flow through the superconductor (140).

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