JP5696941B2 - Measuring method of critical current - Google Patents

Description

  The present invention relates to a method for measuring critical current. In particular, the present invention relates to a critical current measuring method capable of accurately measuring the critical current of the entire length of a cable core used for a component of a superconducting cable.

  Superconducting cables are being developed as power cables constituting power supply paths. A superconducting cable typically includes a cable core having a superconducting layer, and a heat insulating tube that houses the cable core and is filled with a refrigerant such as liquid nitrogen. The superconducting layer typically includes a superconducting conductor layer and an outer superconducting layer provided on the outer periphery of the superconducting conductor layer via an electrical insulating layer, and is typically configured by winding a superconducting wire. The outer superconducting layer functions as a shield in AC power transmission, for example.

  For normal conducting cables such as OF cables and CV cables, a full length test (frame test) is performed on the full length before shipping to the factory to investigate the electrical characteristics. On the other hand, when examining the electrical characteristics of a superconducting cable, it is necessary to cool the superconducting conductor layer to bring it into a superconducting state. Therefore, if a full-length test of a superconducting cable is performed, it takes time to fill a thin heat insulating tube with a refrigerant. Therefore, a superconducting cable is subjected to a sampling test using a short sample.

  On the other hand, in Patent Document 1, after laying the superconducting cable, when measuring the critical current of the superconducting cable, connect one cable core to be measured to another cable core and perform reciprocal energization. Measuring the critical current of an object is disclosed.

JP 2006-329838

  It is desired to perform a full length test on a cable core used for a superconducting cable.

  The measurement method proposed in Patent Document 1 targets a superconducting cable in a state where a cable core is housed in a heat insulating tube. Since the electrical characteristics of the superconducting cable are essentially the characteristics of the cable core, if the characteristics of the cable core itself are not good before storage in the heat insulation tube, the result of the full-length test of the superconducting cable using this cable core Of course not good. In addition, when the cable core is shipped alone, the object of the shipping test is the cable core. Therefore, it is desired to perform a full length test on the cable core before being housed in the heat insulating tube.

  However, conventionally, an appropriate full length test method has not been proposed for a cable core for a superconducting cable.

  For example, since the cable core used for the superconducting cable is long, it is conceivable that the cable core is wound around a drum and cooled in this state so as to be easy to handle. In this case, the cable core wound around the drum may be housed in a container, and the container may be filled with a refrigerant. For example, compared with the case where the heat insulation pipe is filled with a refrigerant and circulated and cooled, a simple cooling facility is used. The test can be conducted. In addition, since both ends of the cable core are arranged close to each other when wound on the drum, for example, it is possible to easily attach a power source used for examining electrical characteristics. However, in this case, it is difficult to accurately measure the critical current.

  Here, the critical current of the superconducting wire constituting the superconducting layer such as the superconducting conductor layer depends on the magnetic field, and the critical current tends to be lower than the critical current under zero magnetic field by applying the magnetic field. As the critical current of the superconducting wire decreases, the critical current of the superconducting layer also decreases.

  The turns formed by the cable core wound around the drum are close to each other, and magnetic fields based on the currents flowing through the turns leak out of the turns, and the leakage magnetic fields interfere with each other. Therefore, even when the critical current is measured by attaching both ends of the cable core to the power source as described above, the measured value becomes lower than the original value (design value) due to the interference of the magnetic field between the turns. In particular, in the case of a cable core having a high design value, a critical current is measured by supplying a large current. However, the magnetic field is likely to increase as the applied current increases, and the measured critical current can be further reduced.

  Accordingly, an object of the present invention is to provide a critical current measuring method capable of accurately measuring the critical current of the entire length of the cable core for a superconducting cable.

  In measuring the critical current over the entire length of the cable core, the present invention achieves the above-mentioned object by causing the opposite currents to flow through the superconducting conductor layer and the outer superconducting layer.

  The method for measuring the critical current of the present invention, as a test object, preparing a superconducting conductor layer and a cable core comprising an outer superconducting layer on the outer periphery of the superconducting conductor layer, passing a direct current through the superconducting conductor layer, A critical current of the entire length of the cable core is measured with the outer superconducting layer in a state in which a current opposite to the current flowing in the superconducting conductor layer flows.

  In the present invention, when measuring the critical current over the entire length of the cable core, the outer superconducting layer provided in the same cable core is not used only in the superconducting conductor layer provided in the cable core. In addition, it is assumed that a specific current, specifically, a current in the direction opposite to the current flowing in the superconducting conductor layer (hereinafter referred to as a conductor current) flows. The magnetic field based on the reverse current can cancel the magnetic field based on the conductor current to some extent and reduce the magnetic field leaking out of the cable core. Therefore, the present invention can suppress a decrease in critical current due to the influence of the magnetic field described above, and can measure a value close to the original value (design value). Therefore, the present invention can accurately measure the critical current of the entire length of the cable core, and can be suitably used as a full length test of the cable core.

  As one form of this invention, the form by which the said cable core was wound up by the drum is mentioned. Moreover, the form by which this drum was comprised with the nonmagnetic material is mentioned.

  The above-mentioned form in which the cable core wound around the drum is the test target is (1) easy to handle the test target, (2) the test can be performed with a simple cooling facility omitting the refrigerator and the circulation pump, (3) There is an advantage that the power supply can be easily attached. Further, according to the present invention, as described above, the cable core is wound around the drum by causing the opposite currents to flow in both the superconducting conductor layer and the outer superconducting layer, and each turn made by the cable core is The critical current can be measured with high accuracy even in close proximity. When the drum is made of a nonmagnetic material, the magnetic field based on the conductor current and the magnetic field disturbance based on the reverse current can be suppressed.

  As one aspect of the present invention, at one end of the cable core, the superconducting conductor layer and the outer superconducting layer are electrically connected to form a reciprocal current path by the superconducting conductor layer and the outer superconducting layer, At the other end of the cable core, the superconducting conductor layer and the outer superconducting layer are connected to a DC power source, and a DC current is supplied to the reciprocating current path.

  In the above embodiment, one end of the superconducting conductor layer and one end of the outer superconducting layer provided in the same cable core are short-circuited, that is, the adjacent constituent members are short-circuited. Moreover, since the said form connects the other end of the adjacent structural member to the same DC power supply, the lead member for connecting DC power supply can be shortened, connection work is easy, and the resistance component of the lead member can be reduced. The increase in the output voltage of the power supply accompanying the increase can be reduced. Therefore, in the above-described embodiment, when measuring the critical current of the entire length of the cable core, the workability of measurement preparation is excellent, and a DC power source having a small output capacity can be used as a DC power source used for the test. In particular, when the cable core wound around the drum in the above embodiment is used as a test object, the short-circuiting operation and the connection operation described above can be performed more easily because both ends of the cable core are close.

  As one form of the present invention, the outer superconducting layer is electrically connected by a short-circuit connecting portion at both ends of the cable core to form a closed loop, and the superconducting conductor layer is connected to a DC power source at both ends of the cable core. In the closed loop including the outer superconducting layer, a direct current is passed through the superconducting conductor layer, and an induced current based on the current flowing in the superconducting conductor layer is supplied as the reverse current.

  Since only the superconducting conductor layer is an object to be measured, the above form can be suitably used for measuring the critical current of the superconducting conductor layer. In the above embodiment, in particular, when a cable core wound in multiple layers such as two layers on a drum is used as a test object, the closed end of the cable core and the power supply connection work can be more easily performed because the ends of the cable core are close.

  As one form of the present invention, a form in which a plurality of the above-described cable cores are wound together on one drum is a test object. In this form, the outer superconducting layers provided in the two cable cores of the co-wound cable cores are electrically connected by a short-circuit connection portion to form one closed loop, and the two cables At one end of the core, the superconducting conductor layers provided in each cable core are electrically connected to each other to form a reciprocating current path by these superconducting conductor layers, and at the other end, the superconducting conductor layer provided in each cable core. Is connected to a direct current power source, a direct current is passed through the reciprocating current path, and an inductive current based on the current flowing in the superconducting conductor layer is supplied as a reverse current to the closed loop including the outer superconducting layer. Is mentioned.

  In the above configuration, when a plurality of cable cores are to be tested, the critical current of the superconducting conductor layer can be accurately measured, and the cable cores are wound on one drum, so that each cable core Therefore, the closed loop and the reciprocating current path can be formed and the power supply can be easily connected.

  As a form including the short-circuit connection portion, a form in which the measured critical current is corrected can be employed. More specifically, a Rogowski coil is attached to the short-circuit connection part, or the short-circuit connection part has a shunt resistance, and the induced current is measured using the Rogowski coil or the shunt resistance, From the difference between the energization current to the superconducting conductor layer and the actually measured induced current, the amount by which the critical current of the superconducting conductor layer is reduced due to the leakage magnetic field leaking outside the cable core is obtained, and the measured critical current is calculated. The structure correct | amended based on the said reduced amount is mentioned.

  As a result of investigations by the present inventors, when a direct current is applied to the superconducting conductor layer at a constant change rate, the induced current changes according to the change rate. Specifically, if the change rate is low, the induced current is small. I got the knowledge that. When the induced current is small, the leakage magnetic field based on the difference between the conductor current and the induced current becomes large, and the critical current measured by the leakage magnetic field decreases. In the above embodiment, the critical current can be accurately measured in order to correct this decrease. In the above-mentioned form, the leakage magnetic field can be obtained with high accuracy by using the actually measured value of the induced current, and hence the amount of decrease in critical current due to the leakage magnetic field can be obtained accurately. Often required. Furthermore, in the above embodiment, since the generation of a leakage magnetic field is allowed, the rate of change of current to the superconducting conductor layer can be reduced, so that a small capacity power source can be used. That is, it is not necessary to use a large-capacity power supply that can cope with a large induced voltage accompanying an increase in the change rate. In addition, in the form using the Rogowski coil, it can be easily attached to the short-circuited connection portion and excellent in workability, and can be easily removed after use. In the form using the shunt resistor, the induced current can be obtained with high accuracy, so that the critical current can be measured with higher accuracy.

  As one aspect of the present invention, the superconducting conductor layer is connected to a DC power source at both ends of the cable core, a DC current is passed through the superconducting conductor layer, and the outer superconducting layer is connected to another DC at both ends of the cable core. There is a mode in which a current opposite to the current flowing in the superconducting conductor layer is passed through the outer superconducting layer by connecting to a power source.

  In the above configuration, even when the design value of the critical current of the superconducting conductor layer and the design value of the critical current of the outer superconducting layer are greatly different, the current should flow sufficiently in a range not exceeding the smaller one of the above design values. Therefore, the influence of the magnetic field can be minimized. In other words, the above configuration can easily reduce the leakage magnetic field based on the difference between the conductor current and the current flowing in the outer superconducting layer, and can substantially eliminate the leakage magnetic field. Therefore, the said form can reduce the fall of the critical current by the influence of a magnetic field, for example, can measure a critical current accurately, without performing the above correction | amendments. Moreover, since the current value flowing through each of the superconducting conductor layer and the outer superconducting layer is controlled by the power source, the above-described configuration can accurately measure the difference even when there is a difference in the current flowing through each layer.

  The method for measuring the critical current of the present invention can accurately measure the critical current of the entire length of the cable core used in the superconducting cable.

3 is an explanatory diagram for explaining a method for measuring a critical current according to Embodiment 1. FIG. 5 is an explanatory diagram for explaining a method for measuring a critical current according to Embodiment 2. FIG. 6 is an explanatory diagram for explaining a method for measuring a critical current according to Embodiment 3. FIG. 5 is an explanatory diagram for explaining a method for measuring a critical current according to Embodiment 4. FIG. FIG. 3 is an explanatory diagram for explaining a state in which a cable core is wound around a drum, which is a critical current measuring method according to the first embodiment. It is a cross-sectional view which shows the cable core for superconducting cables typically.

  Hereinafter, the present invention will be described in more detail with reference to the drawings. In the figure, the same reference numeral indicates the same name object. First, a cable core for a superconducting cable to be measured will be described, then a more specific method for measuring the critical current will be described, and then a more specific form of the test object will be described.

[Cable core]
As shown in FIG. 6, the cable core 100 includes, for example, a former 101, a superconducting conductor layer 102, an electrical insulating layer 103, an outer superconducting layer 104, and a protective layer 105 in order from the center.

  The former 101 is a support member for the superconducting conductor layer 102 and also functions as a tensile material for the cable core 100. In addition, the former 101 is used for an energization path that diverts an accident current in the event of an accident such as a short circuit or a ground fault. When used in the current path, the former 101 can be preferably a solid body or hollow body (tubular body) made of a normal conducting material such as copper, aluminum, or an alloy thereof. More specifically, for example, a stranded wire material obtained by twisting a plurality of copper wires having an insulation coating such as polyvinyl formal (PVF) or enamel. A cushion layer can be provided by winding an insulating tape material such as kraft paper or PPLP (registered trademark of Sumitomo Electric Industries, Ltd.) around the outer periphery of the former 101.

Examples of the superconducting conductor layer 102 and the outer superconducting layer 104 include a single layer or a multilayer including a wire layer in which a superconducting wire is spirally wound. Superconducting wire is a wire comprising an oxide superconducting phase, specifically, REBa ₂ Cu ₃ O _x (RE123: RE is a rare earth element), for example, a thin film comprising a rare earth oxide superconducting phase such as YBCO, HoBCO, GdBCO. There are high-temperature superconducting wires that comprise a wire and a Bi-based oxide superconducting phase such as Bi ₂ Sr ₂ Ca ₂ Cu ₃ O _{10 + δ} (Bi2223) and Ag or an alloy thereof as a metal matrix. In the case of a multilayer structure, an interlayer insulating layer in which insulating paper such as kraft paper is wound can be formed between the layers of the wire layers. An inner semiconductive layer can be provided by winding carbon paper or the like directly on the superconducting conductor layer 102. Note that when a magnetic field is applied perpendicularly to the surface of each of the thin film wire and the Bi-based oxide superconducting wire (when a magnetic field is applied in the thickness direction of the superconducting wire), the magnetic field is parallel to the surface. As compared with the case where is applied, the critical current tends to decrease.

  For example, the outer superconducting layer 104 is used as a magnetic shield in the case of AC power transmission, and is used as a return conductor or a neutral wire in the case of DC power transmission. The number of superconducting wires constituting the superconducting conductor layer 102 and the outer superconducting layer 104 and the number of wire layers are designed according to the desired power supply capacity.

  The electrical insulating layer 103 can be formed by winding an insulating tape material such as semi-synthetic insulating paper such as kraft paper or PPLP (registered trademark) on the superconducting conductor layer 102 (or inner semiconductive layer). . An outer semiconductive layer can be provided by winding carbon paper or the like directly on the electrical insulating layer 103.

  A normal conducting shield layer can be provided on the outer periphery of the outer superconducting layer 104 to be used for the above-described accident current induced current passage. The normal conductive shield layer can be formed, for example, by winding a metal tape material made of a normal conductive material such as copper.

  In order to mechanically protect the outer superconducting layer 104 by winding an insulating tape material such as semi-synthetic insulating paper such as kraft paper or PPLP (registered trademark) around the outer periphery of the outer superconducting layer 104 (or normal conducting shield layer) A protective layer 105 can be provided.

  The above-described cable core 100 is used as a constituent member of a superconducting cable. A superconducting cable is manufactured by housing one or a plurality of (typically three) cores 100 in one heat insulating tube (not shown). The heat insulation pipe is typically composed of a double pipe of an inner pipe and an outer pipe, and a vacuum heat insulation structure in which a vacuum is drawn between the inner pipe and the outer pipe. A superconducting cable is used in a power supply path by filling a heat insulating pipe with a refrigerant (for example, a liquid refrigerant such as liquid nitrogen or liquid helium), cooling the superconducting conductor layer 102 or the outer superconducting layer 104 with this refrigerant, and making it into a superconducting state. The

[Measurement method of critical current]
In the present invention, in measuring the critical current of the entire length of the cable core 100 described above, a direct current is passed through the superconducting conductor layer 102, and a current in the direction opposite to the conductor current flows through the outer superconducting layer 104. . Specific embodiments include the following Embodiments 1 to 4.

(Embodiment 1)
In the first embodiment, as shown in FIG. 1, the superconducting conductor layer 102 provided in the cable core 100 and the outer superconducting layer 104 are short-circuited to perform reciprocal energization. For example, the superconducting conductor layer 102 has a forward current and an outer superconducting layer. A return current is passed through.

  More specifically, for example, one end of the cable core 100 is stripped to expose the superconducting conductor layer 102 and the outer superconducting layer 104, and one end of each of the layers 102, 104 is electrically connected by the short-circuit connecting portion 20. Thus, a reciprocating current path is formed. The short-circuit connection portion 20 can be formed by appropriately combining superconducting wires similar to the superconducting wires constituting the superconducting layer such as the superconducting layer such as the superconducting layer such as a superconducting layer such as a superconducting conductor layer 102. The same material can be used for the short-circuit connection portions 21 to 24 of Embodiments 2 and 3 described later. The members attached to the core 100 for measuring the critical current, such as the short-circuit connections 20 to 24, are appropriately removed after the measurement, and the core 100 is shipped or used for manufacturing a superconducting cable. .

  In measuring the critical current, the superconducting conductor layer 102 and the outer superconducting layer 104 are connected to the DC power source 50 at the other end of the cable core 100 in order to supply a DC current to the reciprocating current path. As the DC power source 50, an appropriate one that secures an induced voltage generated according to the rate of change of current can be used, and a commercially available product can be used. In addition, the DC power supply 50 may be one having a mechanism capable of controlling the change speed, or a commercially available sweeper device (not shown) capable of controlling the change speed may be provided in the DC power supply 50. it can.

  Furthermore, it has storage means for recording various measurement data (signals such as energization current and voltage between the end of the superconducting conductor layer 102 and the end of the outer superconducting layer 104) from the DC power supply 50, the cable core 100, etc. When the recording device 51 is connected to the DC power supply 50 or the end of the core 100, the operator can easily grasp the measurement result.

  When the reciprocal energization path is formed by the superconducting conductor layer 102 and the outer superconducting layer 104 as described above, a direct current is supplied to the reciprocal energization path at a constant change rate by the DC power source 50, and the critical current is measured.

  In the first embodiment, the voltage signal (potential difference) between the superconducting conductor layer 102 and the outer superconducting layer 104 is measured, the relationship between the current and the voltage is recorded in the recording device 51, and the obtained current-voltage characteristics are used. A current with an electric field of 1 μV / cm (= 0.1 mV / m) is obtained, and this current is set as a critical current of at least one of the superconducting conductor layer 102 and the outer superconducting layer 104. In the first embodiment, when the design value of the critical current of the superconducting conductor layer 102 and the design value of the critical current of the outer superconducting layer 104 are extremely large, the critical current with the lower design value can be measured. Further, it is preferable to attach voltage taps to each of the superconducting conductor layer 102 and the outer superconducting layer 104 and measure the respective voltages, because the critical currents of the respective layers 102 and 104 can be measured with higher accuracy. In Embodiments 2 and 4 to be described later, the potential difference between both ends of the superconducting conductor layer 102 was measured, and the “current that generated an electric field of 1 μV / cm” obtained from the obtained current-voltage characteristics was determined as the critical current of the superconducting conductor layer 102. In Embodiment 3, the potential difference between the ends of the superconducting conductor layers 102A and 102B provided in the two cable cores 100A and 100B is measured, and the electric field of 1 μV / cm obtained from the obtained current-voltage characteristics is obtained. Is the critical current of the superconducting conductor layer. In Embodiment 4 to be described later, by measuring separately the potential difference between both ends of the superconducting conductor layer 102 and the potential difference between both ends of the outer superconducting layer 104, the critical current of the superconducting conductor layer 102, the critical current of the outer superconducting layer 104 Each can also be measured separately.

  In the first embodiment, substantially all of the current flowing through the superconducting conductor layer 102: the magnetic field created by the conductor current can be canceled out by the magnetic field created by the current flowing in the outer superconducting layer 104: the current opposite to the conductor current. Therefore, Embodiment 1 can reduce the leakage magnetic field from each turn even when the turns that the cable core 100 is wound around the drum 10 and the core 100 creates are close to each other as will be described later. Therefore, the first embodiment can reduce the amount by which the critical current of the superconducting conductor layer 102 or the outer superconducting layer 104 that is the measurement target is reduced by the leakage magnetic field, and can accurately measure the critical current of the measurement target.

(Embodiment 2)
In the second embodiment, as shown in FIG. 2, the outer superconducting layer 104 provided in the cable core 100 is short-circuited to form a closed loop, and an induced current based on the conductor current flowing in the superconducting conductor layer 102 is passed through the closed loop.

  More specifically, the ends of the outer superconducting layer 104 are electrically connected by the short-circuit connecting portion 21 at both ends of the cable core 100. Further, at both ends of the cable core 100, the ends of the superconducting conductor layer 102 are connected to the DC power source 50, and a DC current is supplied at a constant change rate to measure the critical current of the superconducting conductor layer 102.

  In the second embodiment, an induced current opposite to the conductor current flows through the closed loop mainly composed of the outer superconducting layer 104, and the magnetic field based on the conductor current can be canceled to some extent by the magnetic field generated by the induced current. Therefore, Embodiment 2 can reduce the leakage magnetic field based on the difference between the conductor current and the induced current in each turn even when the cable core 100 is wound around a drum as described later and the turns are close to each other. Therefore, Embodiment 2 can reduce the amount by which the critical current of the superconducting conductor layer 102 to be measured decreases due to the leakage magnetic field, and can accurately measure the critical current.

  In particular, in the second embodiment, by sufficiently increasing the rate of change of the current supplied to the superconducting conductor layer 102, it is possible to generate an induced current having substantially the same magnitude as the conductor current, and the above-described leakage magnetic field does not substantially occur. That is, a decrease in critical current due to a leakage magnetic field can be suppressed. By adjusting the rate of change so that the induced current is 75% or more of the conductor current, the leakage magnetic field can be effectively reduced.

  Alternatively, in the second embodiment, the magnitude of the induced current is measured to obtain a leakage magnetic field based on the difference between the conductor current and the induced current, and further, the amount of decrease in the critical current that is reduced by the leakage magnetic field is obtained and measured. The reduced amount can be corrected for the critical current.

  Specifically, for example, the Rogowski coil 30 is attached to the short-circuit connection portion 21, and the measurement data from the Rogowski coil 30 (for example, the integrated value of the generated voltage) is used to induce an induced current (for example, the outer superconducting layer 104) , The integral value × calibration coefficient). If the measurement data is stored in the storage means of the recording device 51, the measurement data can be easily used. The Rogowski coil 30 is easy to attach and detach and has excellent workability during measurement. Instead of the Rogowski coil 30, the induced current may be measured using a shunt resistor. In this case, a short-circuit connection portion 21 having a shunt resistor (not shown) is constructed. Since the shunt resistor is directly connected to the components of the short-circuit connection portion 21, the measurement error is small and the measurement accuracy of the induced current is high.

  The difference between the measured critical current and the induced current is obtained, and the amount of decrease in the critical current according to the leakage magnetic field based on the difference between the two currents is obtained. As the change rate α of the energization current increases, the induced current increases and the difference between the two currents decreases. Then, since the leakage magnetic field is reduced, the amount of decrease in critical current is also reduced, and the error due to correction is reduced. The amount of decrease in critical current is obtained by previously obtaining correlation data between leakage magnetic fields of various magnitudes and the amount of decrease in critical current when each leakage magnetic field is applied, and referring to this correlation data. Sought easily. If this correlation data is also stored in the storage means of the recording device 51 described above, the amount of decrease in critical current can be obtained more easily.

  Alternatively, the amount of decrease in critical current can be obtained by calculation using electromagnetic field analysis. Specifically, when a direct current is passed through the superconducting conductor layer at a change rate α, a current waveform of an induced current induced in the outer superconducting layer is obtained according to the change rate α, and based on the difference between the conductor current and the induced current. Magnetic field distribution and time change are calculated by electromagnetic field analysis (2D or 3D). Moreover, the magnetic field applied to each superconducting wire forming the superconducting layer is calculated. In advance, a critical current maintenance factor when a magnetic field is applied to the superconducting wire is experimentally determined, and a decrease in the critical current of each superconducting wire constituting the superconducting layer is determined by the magnetic field. For example, the reduction rate of the critical current of the superconducting conductor layer is obtained using this reduction amount. Commercially available analysis software can be used for the electromagnetic field analysis. For example, when the superconducting wire is a Bi-based oxide superconducting wire, the critical current tends to decrease as described above when the applied magnetic field is a vertical magnetic field, so that the applied magnetic field can be analyzed as a vertical magnetic field. Can be mentioned.

  Then, the measured critical current is corrected by adding the obtained decrease amount, and an appropriate critical current (ideally, the original critical current when there is no decrease due to the leakage magnetic field) is obtained. Here, as the recording device 51, in addition to the storage unit described above, a correction amount calculation unit that calculates a correction amount for correcting a decrease in the critical current that has been decreased due to the leakage magnetic field using data called from the storage unit; It is possible to use a device including critical current calculation means for correcting a measured value using the obtained correction amount and calculating an appropriate critical current. If the arithmetic means is made to perform correction, the critical current can be obtained more easily and automatically. Alternatively, a calculation device including the calculation means can be separately prepared and used.

  Note that the voltage at both ends of the superconducting conductor layer 102 becomes very large as the current change rate increases. Assuming that the change rate of the energizing current is α (A / sec), the induced voltage is defined by L · (dI / dt) = Lα, and as the change rate α is increased, the generated induced voltage is increased. Therefore, for example, when the cable core 100 becomes longer, a power source that secures the induced voltage in addition to the voltage of the resistance component, that is, a large-capacity power source that can handle a large current and a large voltage is required. However, in the form of correcting the measurement value, the case where the induced current is small is allowed, so that the change speed can be reduced (slow). Therefore, in the embodiment in which the measured value is corrected, the critical current can be obtained with higher accuracy, and a small-capacity DC power supply 50 can be used.

  Further, in this form, when correcting the measured value, the induced current is actually measured, and the correction amount is determined based on the actually measured value.Therefore, when the resistance of the short-circuit connection portion 21 is different from the design value due to a manufacturing error or the like, Even when the gap width between the cable cores 100 wound around the drum is different from the predetermined value, the critical current can be measured with high accuracy and the reliability is high.

(Embodiment 3)
In the third embodiment, as shown in FIG. 3, the superconducting conductor layers 102A and 102B provided in the two cable cores 100A and 100B are reciprocally energized, and the outer superconducting layers 104A and 104B provided in the cores 100A and 100B are provided. A short circuit is formed into one closed loop, and an induced current based on the conductor current flowing in the superconducting conductor layers 102A and 102B is passed through the closed loop. The configuration and material of the two cores 100A and 100B are the same as those of the cable core 100.

  More specifically, at one end of both cable cores 100A and 100B, the superconducting conductor layers 102A and 102B are electrically connected to each other by the short-circuit connecting portion 22 to form a reciprocal energization path by the superconducting conductor layers 102A and 102B. Further, the end portions of the outer superconducting layers 104A and 104B provided in both the cores 100A and 100B are electrically connected by the short-circuit connecting portions 23 and 24, respectively. Then, at the other end of each core 100A, 100B, the ends of the superconducting conductor layers 102A, 102B are connected to the DC power supply 50, and a DC current is supplied to the reciprocating current path at a constant change speed, so that the superconducting conductor layers 102A, 102B, Measure the critical current of 102B.

  In the third embodiment, similarly to the second embodiment, an induced current in the direction opposite to the conductor current flowing in the reciprocating current path flows in the closed loop mainly composed of the outer superconducting layers 104A and 104B, and a magnetic field generated by the induced current is generated. Thus, the magnetic field based on the conductor current can be canceled to some extent. Therefore, the third embodiment can also reduce the leakage magnetic field based on the difference between the conductor current and the induced current in each of the cores 100A and 100B even when the cable cores 100A and 100B are wound around the drum as will be described later. Therefore, Embodiment 3 can reduce the amount by which the critical current of the superconducting conductor layer to be measured decreases due to the leakage magnetic field, and can accurately measure the critical current.

  Similarly to the second embodiment, the third embodiment can suppress the decrease in the critical current due to the influence of the magnetic field by sufficiently increasing the rate of change of the current to the reciprocating current path by the superconducting conductor layers 102A and 102B. As in the second embodiment, the third embodiment is also configured to correct the decrease in the critical current due to the leakage magnetic field based on the difference between the conductor current and the induced current, even when a small capacity power source is used. Current can be measured with high accuracy. When this correction is performed, the Rogowski coil 30 is attached to one of the short-circuit connection portions 23 and 24 (the short-circuit connection portion 23 in FIG. 3) or a short-circuit connection portion having a shunt resistance is constructed as in the second embodiment. When the induced current is actually measured using the Rogowski coil 30 or the like, the induced current can be measured with high accuracy, and the correction amount can be obtained with high accuracy, and the critical current can be measured with higher accuracy.

  In Embodiments 2 and 3, the above-described correction is performed by a cable core used for a superconducting cable for use in large-capacity power supply such as a setting value of the critical current of the superconducting conductor layer of 4 kA or more, further 5 kA or more, Can be suitably used when it is difficult to induce an induced current. Of course, the form of performing this correction is that the set value of the critical current is less than 4 kA, for example, a superconducting cable core for power supply applications of about 3 kA, and the critical current of the entire length of a long cable core such as the kilometer order. It can also be used for measurement.

(Embodiment 4)
In the fourth embodiment, as shown in FIG. 4, separate DC power supplies 50C and 50S are attached to the superconducting conductor layer 102 and the outer superconducting layer 104 included in the cable core 100, and currents in opposite directions are passed. As the DC power supplies 50C and 50S, the same DC power supply 50 as described above can be used. The capacity of the power source can be changed as appropriate.

  More specifically, at both ends of the cable core 100, the end of the superconducting conductor layer 102 is connected to the DC power supply 50C, and the end of the outer superconducting layer 104 is connected to the DC power supply 50S. Then, a direct current is supplied at a constant change rate, and the critical current of the superconducting conductor layer 102 or the outer superconducting layer 104 is measured. The current value to be passed through the superconducting conductor layer 102 and the outer superconducting layer 104 is selected within a range that does not exceed the lower design value between the critical current design value of the superconducting conductor layer 102 and the critical current design value of the outer superconducting layer 104. To do.

  In the fourth embodiment, since the rate of change of the current flowing through the superconducting conductor layer 102 and the outer superconducting layer 104 can be easily adjusted, the magnitude of the current flowing through each of the layers 102 and 104 can be easily made the same. Accordingly, the magnetic field based on the conductor current flowing in the superconducting conductor layer 102 can be canceled to some extent, preferably substantially all by the magnetic field based on the current flowing in the outer superconducting layer 104 = the current opposite to the conductor current. Therefore, even when the cable core 100 is wound around a drum as will be described later, the fourth embodiment can reduce the interference of the magnetic field in each turn, and the superconducting conductor layer that is the measurement target without performing the above correction The critical current of 102 or the outer superconducting layer 104 can be accurately measured. Further, in this embodiment, since the current flowing in the superconducting conductor layer 102 and the current flowing in the outer superconducting layer 104 can be adjusted by power supply control, the leakage magnetic field can be accurately grasped. That is, in this embodiment, since the decrease in the critical current based on the leakage magnetic field is also accurately obtained, the critical current can be accurately measured by correcting the decrease as described above. In addition, this form can be suitably used for the above-described large-capacity power supply application or when measuring the critical current of the entire length of a short cable core.

[Test target form]
When carrying out the above-described first to fourth embodiments, for example, the cable core 100 is wound around the drum 10 as shown in FIG. 5 (in the third embodiment, the cores 100A and 100B (FIG. 3) are wound together. When the object is a test object, the long core 100 is easy to handle. FIG. 5 shows the first embodiment.

  By being wound around the drum 10, the cable core 100 (cable cores 100A and 100B in the third embodiment) is close to both ends of the cores 100, 100A, and 100B, and the short-circuit connection portions 20 to 24 (see FIG. 2, Fig. 3) and lead electrodes 25, 26 (Fig. 5) for connecting DC power supplies 50, 50C (Fig. 3), 50S (Fig. 3) can be easily attached, and workability is excellent. As the lead electrodes 25 and 26, those having an appropriate shape and length made of an appropriate conductive material such as copper or a copper alloy can be used so that energization is possible.

  The test object in which the above-described reciprocating current path and closed loop are formed and the lead electrodes 25 and 26 are attached while being wound around the drum 10 is stored in the cooling container 1 and the liquid refrigerant 2L (typical) filled in the container 1 is stored. Specifically, the superconducting conductor layer 102 and the outer superconducting layer 104 are cooled by liquid nitrogen), and the critical current is measured in a superconducting state.

  Examples of the drum 10 include a drum having a cylindrical winding drum 11 and annular flanges 12A and 12B protruding from the peripheral edges of the winding drum 11 to the outside of the winding drum 11, respectively. Examples of the constituent material of the drum include materials having resistance to the refrigerant, for example, high-strength metal materials such as high carbon steel and stainless steel. The collar parts 12A and 12B are typically in a form of being integrally held by the winding drum 11, but one of the collar parts 12A can be attached to and detached from the winding drum 11, and the container 1 with the collar part 12A removed. When it is housed, the lead electrodes 25, 26 and the like can be easily pulled out.

  The cooling container 1 includes a main body 2 that is a box-like body that is open on one side, and a lid 3 that closes the opening of the main body 2. The main body 2 has a vacuum heat insulating structure including a vacuum layer 2a, and has a volume that can sufficiently accommodate a test object. The main body portion 2 includes an attachment portion 2f for attaching the lid portion 3 to the opening side. Examples of the constituent material of the main body 2 include a material having excellent resistance to a refrigerant temperature (for example, about 77K in the case of liquid nitrogen) such as stainless steel. The lid 3 is a member for sealing the refrigerant in the cooling container 1 (here, the liquid refrigerant 2L and the gas phase formed above the liquid refrigerant 2L). Here, the lid 3 is a solid body (for example, a plate material made of stainless steel), and includes a through-hole through which the lead electrodes 25 and 26 are drawn out. When the drum 10 is housed so that the axis of the drum 10 is orthogonal to the bottom surface of the cooling container 1, the core 100 can be in a uniform state and the characteristics of the entire length of the core 100 can be measured. The drum 10 can also be stored such that the axis of the drum 10 is parallel to the bottom surface of the cooling container 1.

  The present invention is not limited to the above-described embodiment, and can be modified as appropriate without departing from the gist of the present invention. For example, the material / configuration of the drum and the material / configuration / shape of the cooling container can be appropriately changed.

  The method for measuring the critical current of the present invention can be suitably used when measuring the critical current of the entire length of the cable core at any time, such as a shipping test of the cable core, an intermediate test during the production of the superconducting cable, and the like.

1 Cooling vessel 2 Body 2a Vacuum layer 2L Liquid refrigerant 2f Mounting part 3 Lid
10 drum 11 roll 12A, 12B buttocks
20, 21, 22, 23, 24 Short circuit connection 25, 26 Lead electrode 30 Rogowski coil
50, 50C, 50S DC power supply 51 Recording device
100,100A, 100B Cable core 101 former
102,102A, 102B Superconducting conductor layer 103 Electrical insulation layer
104,104A, 104B Outer superconducting layer 105 Protective layer

Claims (4)

As a test object, a superconducting conductor layer, and a cable core comprising an outer superconducting layer on the outer periphery of the superconducting conductor layer, prepared in a state not accommodated in a heat insulating tube ,
Electrically connecting the outer superconducting layer at both ends of the cable core by a short-circuit connection to form a closed loop;
Connecting the superconducting conductor layer to a DC power source at both ends of the cable core, passing a DC current through the superconducting conductor layer,
In the closed loop including the outer superconducting layer , an inductive current based on the current flowing in the superconducting conductor layer flows as a current opposite to the current flowing in the superconducting conductor layer. current was measured,
A Rogowski coil is attached to the short-circuit connection part, or the short-circuit connection part comprises a shunt resistor, and the induced current is measured using the Rogowski coil or the shunt resistor,
From the difference between the energization current to the superconducting conductor layer and the measured induced current, the amount by which the critical current of the superconducting conductor layer decreases due to the leakage magnetic field leaking outside the cable core,
A method for measuring a critical current, wherein the measured critical current is corrected based on the reduced amount . As a test object, a superconducting conductor layer and a plurality of cable cores comprising an outer superconducting layer on the outer periphery of the superconducting conductor layer are prepared so that they are wound together in one drum in a state where they are not housed in a heat insulating tube ,
Of the co-wound cable cores, the outer superconducting layers provided in two cable cores are electrically connected by a short-circuit connection part to form one closed loop,
At one end of the two cable cores, the superconducting conductor layers provided in the cable cores are electrically connected to each other to form a reciprocal current path by the superconducting conductor layers, and at the other end, the cable cores are provided with the cable cores. Connecting the superconducting conductor layer to a DC power source, and applying a DC current to the reciprocating current path ,
In the closed loop including the outer superconducting layer , an inductive current based on the current flowing in the superconducting conductor layer flows as a current opposite to the current flowing in the superconducting conductor layer. current was measured,
A Rogowski coil is attached to the short-circuit connection part, or the short-circuit connection part comprises a shunt resistor, and the induced current is measured using the Rogowski coil or the shunt resistor,
From the difference between the energization current to the superconducting conductor layer and the measured induced current, the amount by which the critical current of the superconducting conductor layer decreases due to the leakage magnetic field leaking outside the cable core,
A method for measuring a critical current, wherein the measured critical current is corrected based on the reduced amount . Said cable core, method of measuring the critical current according to 請 Motomeko 1 that has been wound on the drum. The drum, method of measuring the critical current according to 請 Motomeko 2 or claim 3 that is composed of a nonmagnetic material.

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