JP2006108560A - Current leads for superconducting equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a current lead for a superconducting device capable of preventing a deterioration of a sealing material such as an O-ring, and thereby preventing a decrease in vacuum degree and a dielectric strength in a vacuum heat insulating tube and capable of a safe and stable continuous operation.
To a superconducting device installed in a cryogenic container, a conductor for supplying power from a power source installed in a room temperature environment, and a refrigerant pipe for forming a refrigerant flow path for cooling the conductor. And a vacuum heat insulating tube 3 that insulates the periphery of the refrigerant pipe in a vacuum atmosphere, and a vacuum port 7 for drawing out a measuring lead is provided in a part of the vacuum heat insulating tube 3. The port is a superconducting device current lead in which a lid portion 8 having a sealing device (12) is provided in a measurement lead lead portion, and the lid portion 8 includes a heater 13 on the outer peripheral portion thereof.
[Selection] Figure 1

Description

  The present invention supplies power from a power source at room temperature to a superconducting device cooled to a cryogenic temperature in a superconducting device such as a superconducting coil for storing superconducting energy, a superconducting current limiter, a superconducting cable, a superconducting generator, or a superconducting transformer. Regarding current leads. In particular, the present invention relates to a configuration of a current lead for a superconducting device provided with a vacuum port for drawing out a measurement lead such as temperature and voltage.

  Superconducting devices such as superconducting coils for superconducting energy storage, superconducting fault current limiters, superconducting cables, superconducting generators, and superconducting transformers have features such as small size and high efficiency compared to conventional normal conducting devices. Expectations are rising. FIG. 3 shows an example of a schematic configuration of a superconducting device provided with the current lead. The superconducting device shown in FIG. 3 includes a superconducting coil 21 cooled to a cryogenic temperature, a cryogenic container 22 that houses the superconducting coil 21, a power source 24 at room temperature, and a current lead 23 that supplies power from the power source 24 to the superconducting coil 21. It consists of.

  Superconducting wires and superconducting coils used in superconducting devices cannot be used at room temperature, and only show their performance when cooled to cryogenic temperatures and become superconducting. Therefore, it is necessary to maintain cryogenic cooling. There are two types of cooling methods for superconducting coils: immersion cooling and conduction cooling.In the case of immersion cooling, the cryogenic container is filled with the refrigerant liquid and its evaporated gas. The refrigerant piping is in thermal contact, and the inside of the cryogenic container is a vacuum space.

  The current lead is used for supplying electric power from the power source at room temperature to the superconducting wire and the superconducting coil, and is indispensable for the superconducting device. In the longitudinal direction of the current lead, the power supply side is at room temperature, and the extremely low temperature side is approximately 4.2K to 80K, depending on the operating environment of the superconducting device and the cooling method of the current lead. Therefore, a temperature distribution is created along the longitudinal direction of the current lead, and heat enters from the room temperature end of the current lead toward the low temperature end of the superconducting device.

  As the material of the current lead, a highly conductive material such as copper is used. However, the electrical conductivity is excellent and the thermal conductivity is large, and the amount of heat penetration into the low temperature end of the current lead is large. If the current lead has a large amount of heat penetration, the thermal load at cryogenic temperatures will increase, reducing the operating efficiency, or the penetration heat will be transmitted through the connection between the current lead and the superconducting coil, causing the coil to rise in temperature and lowering the critical current, etc. May affect the coil characteristics. As a measure for reducing the Joule loss of the current lead itself in addition to the reduction of the heat penetration amount, a high-temperature superconducting wire made of an oxide superconducting material may be used in the current path on the low temperature side of the current lead (Patent Document 1). reference).

  Next, the cooling method of the current leads, the heat insulation configuration, etc. will be described. Current lead cooling methods include (1) a cooling method using a superconducting device or a liquid refrigerant for coil cooling or its evaporative gas (liquid refrigerant cooling method), and (2) a cooling method using a dedicated refrigerant gas. (Refrigerant gas cooling method), (3) a method of cooling by connecting a cooling head of a refrigerator (refrigerator connection method), and the like.

  Among the above three cooling methods, the liquid refrigerant cooling method (1) is disclosed in, for example, Patent Document 2, and the low temperature end of the current lead is immersed in liquid helium or liquid nitrogen and cooled by its heat conduction. It is a method to do. Furthermore, cooling along the longitudinal direction of the current lead is also performed using the cold heat of the evaporation gas of the liquid refrigerant. The configuration of this method will be described later with reference to FIG.

  Next, although the refrigerant gas cooling method (2) is also disclosed in FIG. 2 of Patent Document 3, as shown in FIG. 3, a refrigerant path is provided along the longitudinal direction of the conductor, It has a configuration in which a refrigerant gas is flowed to cool the entire conductor. In large superconducting devices such as superconducting energy storage devices and nuclear fusion superconducting devices, the cooled gas is collected, re-cooled, and recycled. FIG. 3 will be described later, including other configurations related to the present invention.

  Finally, the refrigerator connection method (3) is a method in which the cooling head of the refrigerator cooled to 4.2K to 80K is thermally connected to the low temperature end of the current lead and cooled by its heat conduction. Yes, illustration is omitted. In any of the above three methods, a refrigeration capacity equal to or higher than the heat load is required at the low temperature end of the current lead with respect to the heat load that combines the Joule heat due to the energized current and the intrusion heat from the outside due to heat conduction.

  Next, FIG. 7 will be described. FIG. 7 is an explanatory diagram of the structure of the liquid refrigerant cooling type current lead disclosed in Patent Document 2. FIGS. 7 (a) and 7 (b) show FIGS. 1 and 2 of Patent Document 2, respectively. Show. However, in FIG. 7, for the sake of convenience, each part number is given a suffix a, and the part number of Patent Document 2 is changed.

  In FIG. 7, 1a is a current lead, 2a is a superconducting coil, 3a is a liquid helium storage tank, 4a is a power source, 5a is an electrically insulating material, 6a is a vacuum vessel, and 7a is helium gas. The low-temperature end of the current lead 1a in FIG. 7 is immersed in liquid helium and cooled by heat conduction, and is cooled along the longitudinal direction of the current lead by using an evaporation gas of liquid helium. In the case of FIG. 7B, liquid helium is separately supplied to the low temperature end of the current lead separately from the cooling of the superconducting coil. In FIG. 7, the current lead 1a and the vacuum vessel 6a are configured to be electrically insulated by an electrically insulating material 5a.

  Next, FIG. 3 will be described. Since the outline of the overall configuration of FIG. 3 has been described above, a redundant description will be omitted, and a detailed configuration of the current lead 23 will be mainly described below. In FIG. 3, a vacuum heat insulating tube 3 that provides a vacuum atmosphere 23 around the refrigerant pipe 2 is provided as means for suppressing the amount of heat entering from the outside into the current lead. As a material of the vacuum heat insulating tube 3, a stainless steel tube is generally used from the viewpoint of mechanical strength, workability, and corrosion resistance.

  3, the illustration of the electrical insulation configuration between the current lead and the vacuum vessel as disclosed in FIG. 7 is omitted, but in the case of FIG. An electrically insulating structure is provided between the cryogenic container 22 having a vacuum heat insulating layer (not shown). Moreover, in FIG. 3, the path | route of the flow of the refrigerant | coolant in the refrigerant | coolant piping 2 is shown by the flow direction 4 of the refrigerant | coolant shown with an arrow line.

  Furthermore, FIG. 4 shows an explanatory diagram of only a current lead portion including a measuring element and a measuring port which will be described in detail later. 4, the same members as those shown in FIG. 3 are denoted by the same reference numerals. In FIG. 4, part number 1 is a conductor, 5 is a low temperature end, 6 is a room temperature end, 9 is a measurement line terminal, and 11 is a measurement element.

  Next, another detailed configuration of the current lead 23 will be further described based on FIGS. 3 and 4. A measurement line is often provided on the current lead for the purpose of R & D and operation monitoring. It is mainly used for measuring and monitoring the temperature and generated voltage at the cold end of the current lead and at the connection part. In particular, in the high-temperature superconducting current lead, it is important to monitor the high-temperature end temperature so that the high-temperature superconducting member does not become normal conducting. Therefore, as shown in FIG. 4, a measurement line 10 for taking out a signal from the measurement element 11 such as a voltage tap or a temperature element passes through the vacuum insulation tube 3, and the measurement line from the sealed vacuum insulation tube 3. A vacuum port 7 for taking out 10 to the outside is provided in a part of the vacuum heat insulating tube 3.

A lid 8 is attached to the vacuum port 7 via a sealing material such as an O-ring 12 and is bolted so that it can be removed and opened. The measurement line 10 is hermetically connected at the lid 8 by, for example, a measurement line terminal 9 having a hermetic seal, and is electrically connected to a terminal provided outside.
Japanese Patent Laid-Open No. 10-188691 (page 4-5, FIG. 1) JP 63-299217 A (page 1-3, FIG. 1-2) JP-A-4-94105 (page 3-4, FIG. 2)

  The conventional current lead as described above has the following problems. The current lead is designed according to the rated energization of the superconducting device, and the conductor shape and cooling conditions are determined. In particular, in the case of the refrigerant gas cooling system shown in FIG. 3, the flow rate and pressure of the refrigerant gas, the temperature of the refrigerant gas inlet supplied to the current lead, and the like are determined. It is designed not to run away but to settle down.

  By the way, in the case of a superconducting device such as a superconducting energy storage device that is normally in a standby state and momentarily energizes the rated current, a sufficient amount of refrigerant gas flows in the standby state, so the temperature at the end of the room temperature decreases. There are too many problems. Also, other superconducting devices have the same problem that the temperature at the room temperature end is too low, although the coolant flow rate is somewhat reduced during the initial cooling or when the nighttime energization is stopped.

  FIG. 5 is a schematic diagram showing a comparison of temperature distributions when the current lead is rated and not energized. Note that X on the horizontal axis in FIG. 5 is the distance from the low temperature end shown in FIG. 4, where X = 0 indicates the low temperature end and X = L indicates the room temperature end. FIG. 5 shows a case where the room temperature end is 300K during rated energization, but drops to 200K when no power is supplied.

  When the temperature at the room temperature end becomes zero degrees or less, the surrounding moisture freezes, and so-called condensation occurs on the room temperature side of the current lead. FIG. 6 is a diagram for explaining the dew condensation state of the current lead. In FIG. As described above, the temperature of the current lead in the dewed portion may reach close to 200K. When this state reaches the port for the measurement line, the vacuum port 7 and the O-ring 12 of the lid 8 are cold resistant. Even if it is used, the sealing material may cool and condense and harden, or cracks may occur, and sufficient sealing performance cannot be obtained. As a result, the degree of vacuum in the vacuum heat insulating tube 3 is lowered, and as a result, the intrusion heat from the outside is increased, which adversely affects the cooling system and the superconducting coil. Moreover, when the vacuum heat insulation part of a current lead is a part of a superconducting device, the vacuum degree of the whole superconducting device may be lowered, and the insulation withstand voltage may be lowered.

  The present invention has been made in order to solve the above-described problems, and an object of the present invention is to prevent the deterioration of a sealing material such as an O-ring. As a result, the vacuum degree in the vacuum heat insulating tube is reduced and the dielectric strength is reduced. It is an object of the present invention to provide a current lead for a superconducting device capable of preventing a decrease in the temperature and enabling safe and stable continuous operation.

  In order to solve the above-described problems, the present invention is directed to a superconducting device installed in a cryogenic container, a conductor supplying power from a power source installed in a room temperature environment, and a flow of a refrigerant that cools the conductor. A current lead comprising a refrigerant pipe forming a passage and a vacuum heat insulation pipe for insulating the circumference of the refrigerant pipe in a vacuum atmosphere, wherein a vacuum port for drawing out a measurement lead is provided in a part of the vacuum heat insulation pipe The vacuum port is a current lead for a superconducting device in which a lid portion having a sealing device is provided in a measurement lead lead portion, and the lid portion includes a heater on an outer peripheral portion thereof (Invention of Claim 1) ). According to this invention, the problem that the temperature at the room temperature end side is excessively lowered due to heating by the heater is solved, and the deterioration of the sealing material such as the O-ring is prevented. As a result, the degree of vacuum in the vacuum heat insulating tube is reduced and the dielectric strength is reduced. It is possible to prevent the decrease and to perform safe and stable continuous operation.

  Further, in the current lead for a superconducting device according to claim 1, an insulating joint made of an electrically insulating material is provided between the vacuum port and the lid, and the heater is replaced with the outer periphery of the lid, It shall be provided in the outer peripheral part of the said insulation coupling (invention of Claim 2). Thereby, the insulation of a heater part can further be improved.

  According to the present invention, it is possible to provide a current lead for a superconducting device capable of preventing a decrease in the degree of vacuum and a decrease in dielectric strength in a vacuum heat insulating tube and capable of safe and stable continuous operation.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a diagram showing a schematic configuration of a current lead for a superconducting device showing an embodiment of the present invention. The same members as those shown in FIG. 3 and FIG. Is omitted. 1 is different from that shown in FIG. 4 in that the heater 13 is wound around a cylindrical outer peripheral portion protruding from the flange of the lid portion 8.

  The heater 13 shown in FIG. 1 is preferably one that can easily change its shape, such as a silicone rubber heater. In addition, a bar heater may be embedded in a hole provided in the lid portion 8. Further, a non-contact heater such as a far infrared heater can be used. By providing a heater, even if the superconducting device is on standby or not energized, the room temperature end of the current lead is cooled by the refrigerant gas and condensation occurs. Temperature drop can be prevented. The heater may be controlled to be turned on / off by an external power supply, but may be turned on / off in a standby state or in a non-energized state in conjunction with an operation state such as an energization current. Further, a temperature element can be attached in the vicinity of the heater, and on / off switching and heating value control can be performed by monitoring the temperature.

  Next, an embodiment different from FIG. 1 will be described based on FIG. The current lead shown in FIG. 2 has a configuration in which an insulating joint 14 made of an electrically insulating material such as glass fiber reinforced plastic is disposed between the vacuum port 7 and the lid 8. Further, a sealing material such as an O-ring 12 is provided between the vacuum port 7 and the insulating joint 14 and between the insulating joint 14 and the lid portion 8.

  According to the above configuration, even when the room temperature end of the current lead is below room temperature when no current is applied, the insulating joint 14 acts as a heat insulating member, so the lid 8 side is relatively difficult to cool. Further, by winding a heater 13 (for example, a silicone rubber heater) around the outer periphery of the insulating joint 14, the O-ring 12 between the vacuum port 7 and the insulating joint 14 and in direct contact with the insulating joint is also warmed by the heater. The sealing performance can be maintained in a state close to room temperature. Furthermore, since the insulating joint 14 is an electrically insulating material, the insulation of the heater portion is maintained even in a high voltage environment, no new insulation measures are required, and it can be applied to a current lead having a high withstand voltage specification.

  According to the above embodiment, it is possible to provide a current lead for a superconducting device capable of safe and stable continuous energization without degrading a seal portion such as an O-ring and lowering the degree of vacuum.

The typical block diagram of the current lead for superconducting devices which shows embodiment of this invention. The typical block diagram of the current lead for superconducting devices which shows embodiment different from FIG. The figure which shows an example of the typical structure of the superconducting apparatus provided with the conventional electric current lead. FIG. 4 is a detailed explanatory diagram of a current lead portion in FIG. 3. The schematic diagram which compared the temperature distribution at the time of the rated electricity supply of the conventional current lead, and the time of no electricity supply. The figure explaining the dew condensation state of an electric current lead. Explanatory drawing of the structure of the current lead of a liquid refrigerant cooling system disclosed by patent document 2. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Conductor 2 Refrigerant piping 3 Vacuum insulation pipe 7 Vacuum port 8 Cover part 9 Measuring line terminal 10 Measuring line 11 Measuring element 12 O-ring 13 Heater 14 Insulating joint 21 Superconducting coil 22 Cryogenic container 23 Current lead 24 Power supply

Claims (2)

For a superconducting device installed in a cryogenic container, a conductor that supplies power from a power source installed in a room temperature environment, a refrigerant pipe that forms a refrigerant flow path for cooling the conductor, and a refrigerant pipe A current lead provided with a vacuum heat insulating tube that insulates the surroundings in a vacuum atmosphere, and a vacuum port for drawing out a measurement lead is provided in a part of the vacuum heat insulating tube, and this vacuum port is connected to the measurement lead drawing portion. A superconducting device current lead comprising a lid portion having a sealing device, wherein the lid portion includes a heater on an outer peripheral portion thereof. The current lead for a superconducting device according to claim 1, wherein an insulating joint made of an electrically insulating material is provided between the vacuum port and the lid portion, and the heater is replaced with the outer peripheral portion of the lid portion, and the insulating joint is provided. A current lead for a superconducting device, characterized in that it is provided on the outer periphery of the current.

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