AU2021355610B2 - Current lead for high-temperature superconducting (hts) cable and design method thereof - Google Patents
Current lead for high-temperature superconducting (hts) cable and design method thereof Download PDFInfo
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- 238000000034 method Methods 0.000 title claims abstract description 21
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims abstract description 76
- 229910052757 nitrogen Inorganic materials 0.000 claims abstract description 38
- 239000007788 liquid Substances 0.000 claims abstract description 36
- 239000004593 Epoxy Substances 0.000 claims abstract description 33
- 229910052751 metal Inorganic materials 0.000 claims abstract description 16
- 239000002184 metal Substances 0.000 claims abstract description 16
- 238000004088 simulation Methods 0.000 claims abstract description 13
- 230000005684 electric field Effects 0.000 claims abstract description 11
- 230000008878 coupling Effects 0.000 claims abstract description 5
- 238000010168 coupling process Methods 0.000 claims abstract description 5
- 238000005859 coupling reaction Methods 0.000 claims abstract description 5
- 238000005457 optimization Methods 0.000 claims abstract description 5
- 239000007787 solid Substances 0.000 claims abstract description 4
- 239000000463 material Substances 0.000 claims description 27
- 238000009835 boiling Methods 0.000 claims description 8
- 230000004907 flux Effects 0.000 claims description 7
- 239000012530 fluid Substances 0.000 claims description 4
- 238000009826 distribution Methods 0.000 abstract description 21
- 238000004519 manufacturing process Methods 0.000 abstract description 3
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 6
- 229910052782 aluminium Inorganic materials 0.000 description 6
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 6
- 230000008859 change Effects 0.000 description 6
- 229910052802 copper Inorganic materials 0.000 description 6
- 239000010949 copper Substances 0.000 description 6
- 238000004364 calculation method Methods 0.000 description 4
- 239000000110 cooling liquid Substances 0.000 description 3
- 229910000881 Cu alloy Inorganic materials 0.000 description 2
- 230000009286 beneficial effect Effects 0.000 description 2
- 229910052797 bismuth Inorganic materials 0.000 description 2
- JCXGWMGPZLAOME-UHFFFAOYSA-N bismuth atom Chemical compound [Bi] JCXGWMGPZLAOME-UHFFFAOYSA-N 0.000 description 2
- 239000004020 conductor Substances 0.000 description 2
- 238000001816 cooling Methods 0.000 description 2
- 239000000112 cooling gas Substances 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- XSOKHXFFCGXDJZ-UHFFFAOYSA-N telluride(2-) Chemical compound [Te-2] XSOKHXFFCGXDJZ-UHFFFAOYSA-N 0.000 description 2
- 230000007704 transition Effects 0.000 description 2
- 230000005540 biological transmission Effects 0.000 description 1
- 229910010293 ceramic material Inorganic materials 0.000 description 1
- 239000002131 composite material Substances 0.000 description 1
- 230000007812 deficiency Effects 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 238000001704 evaporation Methods 0.000 description 1
- 230000008020 evaporation Effects 0.000 description 1
- 230000006872 improvement Effects 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000008569 process Effects 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
- H01B12/00—Superconductive or hyperconductive conductors, cables, or transmission lines
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
- H01B12/00—Superconductive or hyperconductive conductors, cables, or transmission lines
- H01B12/02—Superconductive or hyperconductive conductors, cables, or transmission lines characterised by their form
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01R—ELECTRICALLY-CONDUCTIVE CONNECTIONS; STRUCTURAL ASSOCIATIONS OF A PLURALITY OF MUTUALLY-INSULATED ELECTRICAL CONNECTING ELEMENTS; COUPLING DEVICES; CURRENT COLLECTORS
- H01R4/00—Electrically-conductive connections between two or more conductive members in direct contact, i.e. touching one another; Means for effecting or maintaining such contact; Electrically-conductive connections having two or more spaced connecting locations for conductors and using contact members penetrating insulation
- H01R4/58—Electrically-conductive connections between two or more conductive members in direct contact, i.e. touching one another; Means for effecting or maintaining such contact; Electrically-conductive connections having two or more spaced connecting locations for conductors and using contact members penetrating insulation characterised by the form or material of the contacting members
- H01R4/68—Connections to or between superconductive connectors
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
- Y02E40/60—Superconducting electric elements or equipment; Power systems integrating superconducting elements or equipment
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- Physics & Mathematics (AREA)
- Condensed Matter Physics & Semiconductors (AREA)
- General Physics & Mathematics (AREA)
- Containers, Films, And Cooling For Superconductive Devices (AREA)
Abstract
The present disclosure provides a current lead structure for a high-temperature
superconducting (HTS) cable and a design method thereof. The current lead structure includes a
plurality of metal rods arranged in parallel at a preset interval along an axial direction of a
current lead, where the metal rod includes a first lead segment, a second lead segment, and a
third lead segment; a bottom end of the first lead segment is in contact with a liquid nitrogen
level, and a top end of the first lead segment is connected to a bottom end of the second lead
segment; a top end of the second lead segment is connected to a bottom end of the third lead
segment, and a top end of the third lead segment is connected to a room-temperature wiring
terminal; the first lead segment and the third lead segment are solid metal rods, and the second
lead segment is a hollow metal rod; and the top end of the second lead segment is not higher than
a position of an epoxy board. A hollow groove is formed inside to form a simple structure, which
significantly optimizes a thermal field distribution, reduces a heat leakage of the current lead,
and provides a reliable support for the subsequent design of the current lead. A current lead with
the structure is easy to manufacture, install, and maintain, which is conducive to engineering
promotion and application.
Step 1: measure a distance between the liquid nitrogen level in a terminal of the HTS
cable and the room-temperature wiring terminal, and a distance between the liquid
nitrogen level and the epoxy board; and determine lengths of the first lead segment,
the second lead segment, and the third lead segment ofthe current lead separately
Step 2: measure an outer diameter of the current lead, and set an initial value of an
inner diameter ofthe second lead segment of the current lead based on a rated current
ofthe current lead
Step 3: measure a temperature of the liquid nitrogen level, a temperature of the
position of the epoxy board, and a temperature of the room-temperature wiring
terminal
Step 4: based on a coupling model of a thermal field and an electric field ofthe
current lead, and with a minimum heat leakage ofthe current lead as an objective
function, use a simulation method to optimize the length and the inner diameter of the
second lead segment starting from the initial value of the inner diameter of the second
lead segment
Step 5: re-determine the lengths of the first lead segment and the third lead segment of
the current lead based on optimization results of the length and the inner diameter of
the second lead segment
Description
[0001] The present disclosure relates to a technical field of current leads for high-temperature superconducting (HTS) cables, and particularly to a current lead for an HTS cable and a design method thereof.
[0002] High-temperature superconducting (HTS) cables have advantages such as high transmission power, high current density, low loss, and environmental friendliness. An HTS current lead is a composite current lead, which adopts an HTS material in a low-temperature segment, a conventional conductive material in a room-temperature segment, and a conductive material such as copper or copper alloy in a transition segment. A high-temperature oxide superconducting material as a ceramic material has very low thermal conductivity and produces no heat during normal operation, such that a very small amount of heat is injected into a liquid nitrogen container. A temperature difference between two ends of a conventional part of the current lead is reduced, and a heat leakage of the current lead is reduced accordingly.
[0003] However, the current lead itself has a specified resistance and thus will produce heat when transmitting a current, and a part of the heat is transferred to a cryogenic container from a tail end of the current lead. Small superconducting cables have a small operating current, and thus no special consideration needs to be given to current leads. However, in large superconducting cables, the heat leakage of the current leads largely determines a cooling capacity required by the superconducting cables during normal operation. Therefore, in a design of the large superconducting cables, a design of a current lead is very particular, where the design of all parts of a current lead must be carefully considered. The design of the current lead should reduce an amount of heat flowing into the cryogenic container as much as possible under the premise of meeting operating current requirements of the superconducting cable.
[0004] Through research, it is found that, at a specified current, the heat leakage of the current lead is related to a material of the current lead. Once the material of the current lead is determined, the heat leakage of the current lead is closely related to a size and a shape of the current lead. Therefore, an optimization of the size and the shape of the lead is very important. Heat leakage introduced into the cryogenic container by the current lead includes conductive heat and Joule heat. An increase in a cross-sectional area of the current lead can reduce Joule heat, but will increase heat leakage caused by conductive heat; and a decrease in the cross-sectional area of the current lead results in just the opposite. Therefore, when various parameters of the current lead are known, there is a length-to-cross-sectional area ratio L/A (namely, a ratio of a length to a cross-sectional area of the current lead) with a minimum heat loss, such that the amount of heat flowing into the cryogenic container of the superconducting cable is minimal from the tail end of the current lead.
[0005] In the prior art, Chinese patent application (CN110323325) discloses a Peltier current lead device, where a current lead formed of a thermoelectric material (bismuth telluride) is inserted into an existing copper or copper alloy lead, such that heat at a low-temperature end of the current lead can be transferred to a room-temperature end when a current flows through the current lead; and because a thermal conductivity of the bismuth telluride material is only 0.4% of a thermal conductivity of the copper material, a heat leakage caused by the current lead can be reduced when no current flows.
[0006] In the prior art, a current lead is often designed into a form of a heat exchanger to reduce a heat leakage to a cryogenic container through the current lead as possible. Current leads made of different materials have different minimum heat leakages. On the basis of a given material, a size of the current lead is further optimized to make a heat leakage of the current lead close to a minimum value. Cooling gas evaporated from cooling liquid in a cryogenic cooling liquid container is used to take away conductive heat and Joule heat on the current lead, that is, an air-cooled current lead is adopted, and making full use of sensible heat of the cooling gas will greatly reduce the heat leakage of the current lead, thereby reducing the evaporation of the cooling liquid.
[0007] Chinese patent (CN110994534) discloses a multi-segment current lead based on evaporative cooling, where a first lead segment wraps a superconducting cable and the lead; a second lead segment increases a heat exchange area between the lead and liquid nitrogen and strengthens the heat exchange between the lead and liquid nitrogen; a third lead segment increases a heat exchange area between the lead and evaporated nitrogen, strengthens the heat exchange between the lead and the evaporated nitrogen, reduces a temperature of the lead, and reduces a heat leakage of the lead; a fourth lead segment realizes the temperature transition from the third lead segment to a room-temperature end; and the third lead segment includes a plurality of copper bars arranged in parallel at a preset interval along two mutually-perpendicular directions on a cross section of the lead. Chinese patent (CN107068324) discloses a 6 kA HTS current lead, where a copper heat exchanger segment is composed of 30 copper rods, with a diameter of 6 mm, 10 of which are arranged in an inner layer and 20 of which are arranged in an outer layer.
[0008] In conclusion, a current lead needs to be further optimized to reduce a heat leakage of a current lead caused by Joule heat and external heat.
[0009] In order to solve the deficiencies in the prior art, the present disclosure is intended to provide a current lead for an HTS cable, and a design method thereof, where a heat leakage of the current lead can be reduced by optimizing the current lead.
[0010] The present disclosure adopts the following technical solutions.
[0011] A current lead for an HTS cable is provided, including a plurality of metal rods arranged in parallel at a preset interval along an axial direction of a current lead, where
[0012] the metal rod includes a first lead segment, a second lead segment, and a third lead segment; a bottom end of the first lead segment is in contact with a liquid nitrogen level, and a top end of the first lead segment is connected to a bottom end of the second lead segment; a top end of the second lead segment is connected to a bottom end of the third lead segment, and a top end of the third lead segment is connected to a room-temperature wiring terminal; and the top end of the second lead segment is not higher than a position of an epoxy board.
[0013] The first lead segment and the third lead segment may be solid metal rods, and the second lead segment may be a hollow metal rod.
[0014] A design method of the current lead for an HTS cable is provided, including steps of:
[0015] step 1: measuring a distance between a liquid nitrogen level in a terminal of the HTS cable and the room-temperature wiring terminal, and a distance between the liquid nitrogen level and the epoxy board; and determining lengths of the first lead segment, the second lead segment, and the third lead segment of the current lead separately;
[0016] step 2: measuring an outer diameter of the current lead, and setting an initial value of an inner diameter of the second lead segment of the current lead based on a rated current of the current lead;
[0017] step 3: measuring a temperature of the liquid nitrogen level, a temperature of the position of the epoxy board, and a temperature of the room-temperature wiring terminal;
[0018] step 4: based on a coupling model of a thermal field and an electric field of the current lead and with a minimum heat leakage of the current lead as an objective function, using a simulation method to optimize the length and the inner diameter of the second lead segment starting from the initial value of the inner diameter of the second lead segment; and
[0019] step 5: re-determining the lengths of the first lead segment and the third lead segment of the current lead based on optimization results of the length and the inner diameter of the second lead segment.
[0020] Preferably, the step 1 may include:
[0021] step 1.1: taking the distance between the liquid nitrogen level and the room-temperature wiring terminal as a total length of the first lead segment, the second lead segment, and the third lead segment of the current lead;
[0022] step 1.2: with the liquid nitrogen level as the bottom end of thefirst lead segment, determining the top end of the first lead segment accordingly;
[0023] step 1.3: with the top end of the first lead segment as the bottom end of the second lead segment and with the top end of the second lead segment not higher than the position of the epoxy board, determining the length of the second lead segment accordingly; and
[0024] step 1.4: with the top end of the second lead segment as the bottom end of the third lead segment and with a position of the room-temperature wiring terminal as the top end of the third lead segment, determining the length of the third lead segment accordingly.
[0025] Further, in the step 1.2, the length of the first lead segment may be not less than 200 mm.
[0026] Further, in the step 2, an outer diameter of the first lead segment, an outer diameter of the second lead segment, and an outer diameter of the third lead segment of the current lead may be the same, and the inner diameter of the second lead segment may satisfy 30mm ! d <
56mm < D, where d represents the inner diameter of the second lead segment and D represents the outer diameter of the second lead segment.
[0027] Further, in the step 4, a thermal field model of the current lead may satisfy relationship equations of:
[0028] pCpu -VT + V - q= Qe
[0029] q = -kVT
[0030] where p represents a density of a material of the current lead, C, represents a heat capacity at constant pressure of the material of the current lead, I represents a flow rate of fluid outside the current lead, q represents a heat flux of the current lead, k represents a thermal conductivity coefficient of the material of the current lead, V represents a gradient operator, T represents a temperature of the current lead, and Qe represents a Joule heat loss of the current lead.
[0031] Further, in the step 4, an electric field model of the current lead may satisfy relationship equations of:
[0032] = Z +,fe
[0033] E -VV
[00341 Q, -- . E
[0035] where J represents a current density of the current lead, Je represents a ratio of a current flowing through the current lead to a cross-sectional area of the current lead, E represents an electric field intensity of the current lead, V represents a potential of the current lead, o represents an electrical conductivity of the material of the current lead, Qe represents a Joule heat loss of the current lead, and V represents a gradient operator.
[0036] Further, in the step 4, a constraint condition for taking a minimum heat leakage of the current lead as an objective function may be that the temperature of the position of the epoxy board is closest to the temperature of the room-temperature wiring terminal.
[0037] Further, in the step 4, boundary conditions for taking a minimum heat leakage of the current lead as an objective function may include: a temperature of a top end of the current lead is an ambient temperature, a temperature of a bottom end of the current lead is a boiling temperature of liquid nitrogen, and boundaries of the current lead other than the top end and the bottom end are all thermally-insulated.
[0038] Compared with the prior art, the present disclosure has the following beneficial effects: Based on the existing current lead and shape, a hollow groove is formed inside to form a simple structure, which significantly optimizes a thermal field distribution, reduces a heat leakage of the current lead, and provides a reliable support for the subsequent design of the current lead. A current lead with the structure is easy to manufacture, install, and maintain, which is conducive to engineering promotion and application.
[0039] FIG. 1 is a schematic diagram of an axisymmetric model of the current lead for an HTS cable according to the present disclosure;
[0040] FIG. 2 is a flow chart of the design method of the current lead for an HTS cable according to the present disclosure;
[0041] FIG. 3 is a curve graph illustrating an epoxy board temperature distribution under different lengths of the second lead segment when the current lead for an HTS cable of the present disclosure is used in Example 1;
[0042] FIG. 4 is a curve graph illustrating a heat leakage distribution at the bottom of the current lead under different lengths of the second lead segment when the current lead for an HTS cable of the present disclosure is used in Example 1;
[0043] FIG. 5 is a curve graph illustrating an epoxy board temperature distribution under different inner diameters of the second lead segment when the current lead for an HTS cable of the present disclosure is used in Example 1;
[0044] FIG. 6 is a curve graph illustrating a heat leakage distribution at the bottom of the current lead under different inner diameters of the second lead segment when the current lead for an HTS cable of the present disclosure is used in Example 1;
[0045] FIG. 7 is a curve graph illustrating an epoxy board temperature distribution under different lengths of the second lead segment when the current lead for an HTS cable of the present disclosure is used in Example 2;
[0046] FIG. 8 is a curve graph illustrating a heat leakage distribution at the bottom of the current lead under different lengths of the second lead segment when the current lead for an HTS cable of the present disclosure is used in Example 2;
[0047] FIG. 9 is a curve graph illustrating an epoxy board temperature distribution under different inner diameters of the second lead segment when the current lead for an HTS cable of the present disclosure is used in Example 2; and
[0048] FIG. 10 is a curve graph illustrating a heat leakage distribution at the bottom of the current lead under different inner diameters of the second lead segment when the current lead for an HTS cable of the present disclosure is used in Example 2.
[0049] The prevent application is further described below with reference to the accompanying drawings. The following embodiments are only used for describing the technical solutions of the present disclosure more clearly, and are not intended to limit the protection scope of the present disclosure.
[0050] A current lead is a component connecting a transformer (room temperature 293 K) and a superconducting cable (liquid nitrogen 77 K) in a terminal, and Joule heat generated during its operation and heat from the outside will be introduced into liquid nitrogen through the current lead, which causes some heat loss and increases a burden on a refrigerator. Therefore, in the case of ensuring a flow capacity of the current lead, reducing the heat loss of the current lead as much as possible is a key point to be considered in the design of the current lead.
[0051] The current lead for an HTS cable provided by the present disclosure includes a plurality of metal rods arranged in parallel at a preset interval along an axial direction of a current lead.
[0052] For the heat loss caused by Joule heat and externally-transferred heat, the heat loss of the current lead for an HTS cable can be reduced as much as possible through reasonable structural design. An optimized design idea is usually to adopt a hollow design, that is, the current lead is partially hollowed inside and a hollowed part is presented as a cylinder, such as to optimize a thermal field distribution and reduce the heat leakage of the current lead. Generally, the optimal size of the cylindrical hollow groove can be given through simulation calculation, which provides a basis for the design of the subsequent current lead.
[0053] Considering the uniformity, both the current lead and the hollowed part thereof adopt a cylindrical structure. Therefore, in the simulation calculation, an axisymmetric model is adopted for geometric modeling, which is convenient for simplifying the model. FIG. 1 is a schematic diagram of the axisymmetric model of the current lead for an HTS cable according to the present disclosure.
[0054] As shown in FIG. 1, the metal rod includes afirst lead segment 1, a second lead segment 2, and a third lead segment 3, where
[0055] a bottom end of the first lead segment 1 is in contact with a liquid nitrogen level, and a top end of the first lead segment 1 is connected to a bottom end of the second lead segment 2; a top end of the second lead segment 2 is connected to a bottom end of the third lead segment 3, and a top end of the third lead segment 3 is connected to a room-temperature wiring terminal; and the top end of the second lead segment 2 is not higher than a position of an epoxy board.
[0056] The first lead segment 1 and the third lead segment 3 may be solid metal rods, and the second lead segment 2 may be a hollow metal rod.
[0057] In a preferred embodiment of the present disclosure, the current lead adopts a hollow design, where a groove is formed inside. The groove is formed such that a bottom of the groove is 201 mm from a bottom of the current lead.
[0058] As shown in FIG. 2, the design method of the current lead for an HTS cable includes steps of:
[0059] Step 1: A distance between a liquid nitrogen level in a terminal of the HTS cable and the room-temperature wiring terminal and a distance between the liquid nitrogen level and the epoxy board are measured; and lengths of the first lead segment, the second lead segment, and the third lead segment of the current lead are determined separately.
[0060] Specifically, the step 1 may include steps of:
[0061] step 1.1: taking the distance between the liquid nitrogen level and the room-temperature wiring terminal as a total length of the first lead segment, the second lead segment, and the third lead segment of the current lead;
[0062] step 1.2: with the liquid nitrogen level as the bottom end of the first lead segment and with a length of the first lead segment no less than 200 mm, determining the top end of the first lead segment accordingly;
[0063] step 1.3: with the top end of the first lead segment as the bottom end of the second lead segment and with the top end of the second lead segment not higher than the position of the epoxy board, determining the length of the second lead segment accordingly; and
[0064] step 1.4: with the top end of the second lead segment as the bottom end of the third lead segment and with a position of the room-temperature wiring terminal as the top end of the third lead segment, determining the length of the third lead segment accordingly.
[0065] In a preferred embodiment of the present disclosure, it can be seen from FIG. 1 that when the liquid nitrogen level is set as a starting point of the axial coordinate (namely, x = 0), a length of the first lead segment is 201 mm and the position of the epoxy board is x = 811 mm.
[0066] Step 2: An outer diameter of the current lead is measured, and an initial value of an inner diameter of the second lead segment of the current lead is set based on a rated current of the current lead.
[0067] Specifically, in the step 2, an outer diameter of the first lead segment, an outer diameter of the second lead segment, and an outer diameter of the third lead segment of the current lead may be the same, and the inner diameter of the second lead segment may satisfy 30mm ! d < 56mm < D, where d represents the inner diameter of the second lead segment and D represents the outer diameter of the second lead segment.
[0068] Step 3: A temperature of the liquid nitrogen level, a temperature of the position of the epoxy board, and a temperature of the room-temperature wiring terminal are measured.
[0069] In a preferred embodiment of the present disclosure, under normal operating conditions, a pressure inside the terminal is about 0.4 MPa, and the bottom end of the current lead is in contact with the liquid nitrogen level. Boiling temperatures of liquid nitrogen under different pressures are shown in Table 1.
[0070] Table 1 Boiling temperatures of liquid nitrogen under different pressures Absolute pressure (MPA) Boiling point (°C) Thermodynamic temperature (K) 0.015 -209 64.15 0.02 -207.3 65.85 0.03 -204.8 68.35 0.04 -202.9 70.25 0.05 -201.3 71.85 0.1 -196.9 76.25 0.2 -189.5 83.65 0.3 -185.243 87.9073 0.4 -181.917 91.2327 0.5 -179.155 93.995 0.6 -176.77 96.3805 0.7 -174.657 98.4934 0.8 -172.751 100.3987
Absolute pressure (MPA) Boiling point (°C) Thermodynamic temperature (K) 0.9 -171.01 102.1397 1 -169.403 103.7469 1.1 -167.907 105.2427 1.2 -166.506 106.6439 1.3 -165.186 107.9638 1.4 -163.937 109.2127 1.5 -162.751 110.399 2 -157.552 115.5985 3 -149.534 123.6162
[0071] It can be seen from Table 1 that liquid nitrogen has a boiling temperature of about 90 K at 0.4 MPa, and thus a temperature at the bottom end of the current lead is the temperature of the liquid nitrogen level, which is 90 K; the top end of the current lead is at room temperature, namely, a temperature of the room-temperature wiring terminal, which is 293.15 K; and the rest boundaries are thermally-insulated.
[0072] Step 4: Based on a coupling model of a thermal field and an electric field of the current lead and with a minimum heat leakage of the current lead as an objective function, a simulation method is used to optimize the length and the inner diameter of the second lead segment starting from the initial value of the inner diameter of the second lead segment.
[0073] Specifically, in the step 4, a coupling model of a thermal field and an electric field of the current lead may satisfy relationship equations of:
[0074] thermal field model:
[0075] pCpu -VT +V - q= Qe
[0076] q = -kVT
[0077] electric field model:
[0078] = -Z +Je
[00791 E -VV
[0080] Qe =J- E
[0081] where
[0082] p represents a density of a material of the current lead,
[0083] C, represents a heat capacity at constant pressure of the material of the current lead,
[0084] u represents a flow rate of fluid outside the current lead,
[0085] q represents a heat flux of the current lead,
[0086] k represents a thermal conductivity coefficient of the material of the current lead,
[0087] T represents a temperature of the current lead,
[0088] J represents a current density of the current lead,
[0089] Je represents a ratio of a current flowing through the current lead to a cross-sectional area of the current lead,
[0090] I represents an electric field intensity of the current lead,
[0091] V represents a potential of the current lead,
[0092] u represents an electrical conductivity of the material of the current lead,
[0093] Q, represents a Joule heat loss of the current lead, and
[0094] V represents a gradient operator.
[0095] In a preferred embodiment of the present disclosure, a material of the current lead is aluminum, and a density of aluminum does not change much at different temperatures and thus can be regarded as a constant. Main material property parameters of the current lead are set as follows:
[0096] an overall flow rate of fluid outside the current lead is 0, that is, u is 0, and thus the influence of the change of a heat capacity at constant pressure with a temperature cannot be considered in the thermal field model; and the heat capacity at constant pressure can be given a constant value, and the heat capacity at constant pressure C, of the current lead material can be set as 900 J/(kg - K).
[0097] The thermal conductivity coefficient and electrical conductivity vary with temperature. Values of the thermal conductivity coefficient k of aluminum at different temperatures are shown in Table 2:
[0098] Table 2 Thermal conductivity coefficient k of aluminum at different temperatures (unit: W/(m - K)) Temperature (K) 4.2 29 76 273 373
k 3200 5700 420 238 230
[0099] It can be seen from Table 2 that a change of thermal conductivity coefficient between 76 K and 273 K can be regarded as a linear change, and a linear expression of the change of the thermal conductivity coefficient k with temperature can be given through fitting. It is known that a temperature coefficient of resistance (TCR) of aluminum is 0.0043/K, and at T = 293.15 K, an electrical conductivity u of aluminum is 3.44828e7S/m, from which a linear expression of the change of the electrical conductivity u with temperature can be obtained. Therefore, the thermal conductivity coefficient k of the current lead material is set as 491.5 + (420 238)/(77[K] - 273[K]) x T, in unit W/(m•K), and the electrical conductivity U of the current lead material is set as 3.44828e7 * (1 + 0.0043[1/K] x (293.15[K] - T)), inunit S/m.
[0100] A density p of the current lead material is set as 2,700 kg/m 3 .
[0101] Specifically, in the step 4, a constraint condition for taking a minimum heat leakage of the current lead as an objective function may be that the temperature of the position of the epoxy board is closest to the temperature of the room-temperature wiring terminal.
[0102] In the step 4, boundary conditions for taking a minimum heat leakage of the current lead as an objective function may include: a temperature of a top end of the current lead is an ambient temperature, a temperature of a bottom end of the current lead is a boiling temperature of liquid nitrogen, and boundaries of the current lead other than the top end and the bottom end are all thermally-insulated.
[0103] Step 5: The lengths of the first lead segment and the third lead segment of the current lead are re-determined based on optimization results of the length and the inner diameter of the second lead segment.
[0104] When the current lead design method provided by the present disclosure is adopted, a simulation process includes:
[0105] (1) Simulated working conditions: A calculation working condition of Example 1 is set as current I = 1 kA, and a calculation working condition of Example 2 is set as current I = 2 kA.
[0106] (2) During simulation, the inner diameter of the second lead segment is first fixed, and the influence of different lengths of the second lead segment on the heat leakage of the current lead is then simulated; and in the case of fixing the length of the second lead segment, the influence of the inner diameter of the second lead segment on the heat leakage of the current lead is then simulated.
[0107] (3) Results are compared to obtain the optimal parameters.
[0108] Example 1
[0109] FIG. 3 and FIG. 4 are curve graphs respectively illustrating an epoxy board temperature distribution and a heat leakage distribution at the bottom of the current lead under different lengths of the second lead segment when the current lead for an HTS cable of the present disclosure is used in Example 1.
[0110] It can be seen from the simulation curve graphs that, at a current I = 1 kA, when the inner diameter of the second lead segment is fixed, the longer the second lead segment, the smaller the heat flux at the bottom of the current lead, that is, the smaller the heat leakage of the current lead. However, given that the temperature at the epoxy board should be as close to room temperature as possible, from the actual conditions, the second lead segment should be as long as possible when the top end of the second lead segment is not higher than the epoxy board, namely, L = 610 mm.
[0111] FIG. 5 and FIG. 6 are curve graphs respectively illustrating an epoxy board temperature distribution and a heat leakage distribution at the bottom of the current lead under different inner diameters of the second lead segment when the current lead for an HTS cable of the present disclosure is used in Example 1.
[0112] It can be seen from the simulation curve graphs that, when the length of the second lead segment is fixed, the heat leakage at the bottom of the current lead is the smallest as the inner diameter of the second lead segment is d = 56 mm.
[0113] Example 2
[0114] FIG. 7 and FIG. 8 are curve graphs respectively illustrating an epoxy board temperature distribution and a heat leakage distribution at the bottom of the current lead under different lengths of the second lead segment when the current lead for an HTS cable of the present disclosure is used in Example 2.
[0115] It can be seen from the simulation curve graphs that, at a current I = 2 kA, when the inner diameter of the second lead segment is fixed, the longer the second lead segment, the smaller the heat flux at the bottom of the current lead, that is, the smaller the heat leakage of the current lead. However, given that the temperature at the epoxy board should be as close to room temperature as possible, from the actual conditions, the second lead segment should be as long as possible when the top end of the second lead segment is not higher than the epoxy board, namely, L = 610 mm.
[0116] FIG. 9 and FIG. 10 are curve graphs respectively illustrating an epoxy board temperature distribution, a heat leakage distribution at the bottom of the current lead, and an axial temperature distribution of the current lead under different inner diameters of the second lead segment when the current lead for an HTS cable of the present disclosure is used in Example 2.
[0117] It can be seen from the simulation curve graphs that, when the length of the second lead segment is fixed, the heat leakage at the bottom of the current lead is the smallest as the inner diameter of the second lead segment is d = 50 mm.
[0118] In summary, it can be known according to the simulation results of Example 1 and Example 2 that, in order to make the heat leakage at the bottom of the current lead as small as possible and make the temperature at the epoxy board as close to room temperature as possible, the top end of the second lead segment should not be higher than the position of the epoxy board, and under this premise, the second lead segment should be as long as possible. At the current I = 1 kA, when the inner diameter d of the second lead segment is 56 mm, the heat flux at the bottom of the current lead is the smallest; and at the current I = 2 kA, when the inner diameter d of the second lead segment is 50 mm, the heat flux at the bottom of the current lead is the smallest. It can be seen that the inner diameter of the second lead segment should not be greater than 50 mm. From the perspective of mechanical strength, it is not recommended that a wall thickness of the current lead is too small. Therefore, optimized parameters of the second lead segment are as follows: length: 610 mm, and inner diameter: 40 mm.
[0119] Compared with the prior art, the present disclosure has the following beneficial effects: Based on the existing current lead and shape, a hollow groove is formed inside to form a simple structure, which significantly optimizes a thermal field distribution, reduces a heat leakage of the current lead, and provides a reliable support for the subsequent design of the current lead. A current lead with the structure is easy to manufacture, install, and maintain, which is conducive to engineering promotion and application.
[0120] The implementation examples of the present disclosure are described in detail by the applicants of the present disclosure with reference to the accompanying drawings in the specification. However, those skilled in the art should understand that the above implementation examples are only preferred embodiments of the present disclosure, and the detailed description is only to help readers better understand the spirit of the present disclosure, rather than to limit the protection scope of the present disclosure. On the contrary, any improvement or modification based on the spirit of the present disclosure shall fall within the protection scope of the present disclosure.
[0121] The reference to any prior art in this specification is not, and should not be taken as, an acknowledgement or any form of suggestion that such prior art forms part of the common general knowledge.
[0122] It will be understood that the terms "comprise" and "include" and any of their derivatives (e.g. comprises, comprising, includes, including) as used in this specification, and the claims that follow, is to be taken to be inclusive of features to which the term refers, and is not meant to exclude the presence of any additional features unless otherwise stated or implied.
Claims (8)
1. A design method of a current lead for a high-temperature superconducting (HTS) cable, comprising steps of: step 1: measuring a distance between a liquid nitrogen level in a terminal of the HTS cable and a room-temperature wiring terminal, and a distance between the liquid nitrogen level and an epoxy board; and determining lengths of a first lead segment, a second lead segment, and a third lead segment of a current lead separately; step 2: measuring an outer diameter of the current lead, and setting an initial value of an inner diameter of the second lead segment of the current lead based on a rated current of the current lead; step 3: measuring a temperature of the liquid nitrogen level, a temperature of a position of the epoxy board, and a temperature of the room-temperature wiring terminal; step 4: based on a coupling model of a thermal field and an electric field of the current lead, and with a minimum heat leakage of the current lead as an objective function, using a simulation method to optimize the length and the inner diameter of the second lead segment starting from the initial value of the inner diameter of the second lead segment; and step 5: re-determining the lengths of the first lead segment and the third lead segment of the current lead based on optimization results of the length and the inner diameter of the second lead segment; wherein in the step 4, a thermal field model of the current lead satisfies relationship equations of: pCu- VT + V - Qe q = -kVT and an electric field model of the current lead satisfies relationship equations of: J= uE +J, E = -VV Qe =J- E wherein p represents a density of a material of the current lead,
C, represents a heat capacity at constant pressure of the material of the current lead, u represents a flow rate of fluid outside the current lead, represents a heat flux of the current lead, k represents a thermal conductivity coefficient of the material of the current lead,
T represents a temperature of the current lead, J represents a current density of the current lead, Je represents a ratio of a current flowing through the current lead to a cross-sectional area of the current lead, E represents an electric field intensity of the current lead, V represents a potential of the current lead, - represents an electrical conductivity of a material of the current lead, Qe represents a Joule heat loss of the current lead, and V represents a gradient operator.
2. The design method of the current lead for an HTS cable according to claim 1, wherein the step 1 comprises: step 1.1: taking the distance between the liquid nitrogen level and the room-temperature wiring terminal as a total length of the first lead segment, the second lead segment, and the third lead segment of the current lead; step 1.2: with the liquid nitrogen level as a bottom end of thefirst lead segment, determining a top end of the first lead segment accordingly; step 1.3: with the top end of the first lead segment as a bottom end of the second lead segment and with a top end of the second lead segment not higher than the position of the epoxy board, determining the length of the second lead segment accordingly; and step 1.4: with the top end of the second lead segment as a bottom end of the third lead segment and with a position of the room-temperature wiring terminal as a top end of the third lead segment, determining the length of the third lead segment accordingly.
3. The design method of the current lead for an HTS cable according to claim 2, wherein in the step 1.2, the length of the first lead segment is not less than 200 mm.
4. The design method of the current lead for an HTS cable according to claim 1, wherein in the step 2, an outer diameter of thefirst lead segment, an outer diameter of the second lead segment, and an outer diameter of the third lead segment of the current lead are the same, and the inner diameter of the second lead segment satisfies 30mm ! d 56mm < D, wherein d represents the inner diameter of the second lead segment and D represents the outer diameter of the second lead segment.
5. The design method of the current lead for an HTS cable according to claim 1, wherein in the step 4, a constraint condition for taking the minimum heat leakage of the current lead as the objective function is that the temperature of the position of the epoxy board is closest to the temperature of the room-temperature wiring terminal.
6. The design method of the current lead for an HTS cable according to claim 5, wherein in the step 4, boundary conditions for taking the minimum heat leakage of the current lead
as the objective function comprising: a temperature of a top end of the current lead is an ambient
temperature, a temperature of a bottom end of the current lead is a boiling temperature of liquid
nitrogen, and boundaries of the current lead other than the top end and the bottom end of the
current lead are all thermally-insulated.
7. A current lead for an HTS cable obtained by using the method according to any one of claims 1 to 6, comprising a plurality of metal rods arranged in parallel at a preset interval along an axial direction of the current lead, wherein the metal rod comprises the first lead segment, the second lead segment, and the third lead segment; and the bottom end of the first lead segment is in contact with the liquid nitrogen level, and the top end of the first lead segment is connected to the bottom end of the second lead segment; the top end of the second lead segment is connected to the bottom end of the third lead segment, and the top end of the third lead segment is connected to the room-temperature wiring terminal; and the top end of the second lead segment is not higher than the position of the epoxy board.
8. The current lead for an HTS cable according to claim 7, wherein the first lead segment and the third lead segment are solid metal rods, and the second lead
segment is a hollow metal rod.
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|---|---|---|---|
| CN202121414937.5 | 2021-06-24 | ||
| CN202121414937.5U CN215070460U (en) | 2021-06-24 | 2021-06-24 | High-temperature superconducting cable current lead structure |
| CN202110704661.2 | 2021-06-24 | ||
| CN202110704661.2A CN113300130B (en) | 2021-06-24 | 2021-06-24 | Current lead structure of high-temperature superconductive cable and design method thereof |
| PCT/CN2021/143426 WO2022267431A1 (en) | 2021-06-24 | 2021-12-30 | High-temperature superconductive cable current lead structure and design method therefor |
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Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102867610A (en) * | 2012-09-03 | 2013-01-09 | 中国科学院电工研究所 | Binary pluggable vapor cooled current lead device |
| CN106450992A (en) * | 2016-09-19 | 2017-02-22 | 中国科学院合肥物质科学研究院 | Liquid-nitrogen conducting cooling type high-temperature superconducting current lead structure |
| US20190181326A1 (en) * | 2017-12-12 | 2019-06-13 | Guy Deutscher | Superconductive lead |
| CN110994534A (en) * | 2019-12-13 | 2020-04-10 | 华中科技大学 | Multi-section current lead based on evaporative cooling |
Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113300130B (en) * | 2021-06-24 | 2023-04-28 | 国网上海市电力公司 | Current lead structure of high-temperature superconductive cable and design method thereof |
| CN215070460U (en) * | 2021-06-24 | 2021-12-07 | 国网上海市电力公司 | High-temperature superconducting cable current lead structure |
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2021
- 2021-12-30 WO PCT/CN2021/143426 patent/WO2022267431A1/en unknown
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102867610A (en) * | 2012-09-03 | 2013-01-09 | 中国科学院电工研究所 | Binary pluggable vapor cooled current lead device |
| CN106450992A (en) * | 2016-09-19 | 2017-02-22 | 中国科学院合肥物质科学研究院 | Liquid-nitrogen conducting cooling type high-temperature superconducting current lead structure |
| US20190181326A1 (en) * | 2017-12-12 | 2019-06-13 | Guy Deutscher | Superconductive lead |
| CN110994534A (en) * | 2019-12-13 | 2020-04-10 | 华中科技大学 | Multi-section current lead based on evaporative cooling |
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