WO2022267431A1 - High-temperature superconductive cable current lead structure and design method therefor - Google Patents

Abstract

A high-temperature superconductive cable current lead structure and a design method therefor. The high-temperature superconductive cable current lead structure comprises a plurality of metal bars, which are arranged in parallel along a lead axis, the metal bars keeping a preset distance therebetween, and each metal bar comprising a first lead section, a second lead section and a third lead section, wherein a bottom end of the first lead section is in contact with a liquid nitrogen surface, and a top end of the first lead section is connected to a bottom end of the second lead section; a top end of the second lead section is connected to a bottom end of the third lead section, and a top end of the third lead section is connected to a room-temperature wiring terminal; and the first lead section and the third lead section are both a solid metal bar, the second lead section is a hollow metal bar, and the top end of the second lead section is not beyond the position of an epoxy plate. By means of providing an internal hollow channel, the structure is simple, significantly optimizes the distribution of a thermal field, reduces the heat leakage of a current lead, and provides a reliable support for a subsequent current lead design. A current lead which uses this structure is easy to process and manufacture, is convenient for installation and maintenance, and facilitates the popularization and application of a project.

Description

High temperature superconducting cable current lead structure and its design method technical field

The invention relates to the technical field of high-temperature superconducting cable current leads, and more particularly, to the structure and design method of the high-temperature superconducting cable current leads.

Background technique

High-temperature superconducting cables have the advantages of high transmission power, high current density, low loss and environmental friendliness. The high-temperature superconducting current lead is a composite current lead. It uses high-temperature superconducting materials in the low-temperature section, and uses conductive materials such as copper or copper alloys between room temperature and high-temperature superconducting materials. It is used as a high-temperature oxide superconducting material for ceramic materials. The thermal conductivity is very low, and no heat is generated during normal operation, so the heat injected into the liquid nitrogen container is very small. In the conventional current lead part, because the temperature difference between the two ends of the lead is reduced, the heat leakage of the lead is also reduced accordingly.

However, the current lead itself has a certain resistance, so heat is generated when the current is transmitted, and part of the heat is transferred to the cryogenic container from the end of the lead. The operating current of small superconducting cables is small, so there is no special consideration for the current leads; however, in large superconducting cables, the heat leakage of the current leads largely determines the cooling capacity required by the superconducting cables during normal operation. Therefore, in the design of a large superconducting cable, the design of the current lead is very particular, and the design method of each part of the lead must be carefully considered. The design of the current lead is to reduce the heat flowing into the cryogenic container as much as possible under the premise of meeting the operating current requirements of the superconducting cable.

Through research, it is found that under a certain current, the heat leakage of the current lead is related to the material of the lead. Once the material of the lead is determined, the heat leakage of the lead is closely related to the size and shape of the lead. Therefore, the optimization of the size and shape of the lead is very important. important. The leakage heat transferred from the current leads to the cryogenic container includes conduction heat and Joule heat. Increasing the cross-sectional area of the current lead can reduce Joule heat, but it will increase the heat leakage caused by conduction heat; while reducing the cross-sectional area of the current lead, the situation is just the opposite. Therefore, when the parameters of the lead wire are known, there is a length balance ratio L/A with the minimum heat loss, that is, the ratio of the lead wire length to the cross-sectional area, so that the heat flowing into the cryogenic container of the superconducting cable at the end of the lead wire is the smallest.

In the prior art, the Chinese invention patent (CN110323325) discloses a Peltier current lead device. By inserting a current lead formed of thermoelectric material bismuth telluride into the existing copper or copper alloy lead, the current lead can be passed through the current lead. The heat from the low temperature end of the current lead is transferred to the room temperature end, and since the thermal conductivity of the bismuth telluride material is only 0.4% of that of the copper material, the heat leakage caused by the current lead can be reduced when no current passes.

In the prior art, the current leads are often designed in the form of a heat exchanger to minimize the heat leakage through the current leads to the cryogenic container. The current leads made of different materials have different minimum heat leakage. On the basis of determining the material, further optimize the size of the current lead to make the heat leakage of the lead close to the minimum value; use the cooling gas evaporated from the coolant in the low-temperature coolant container to take away the conduction heat and Joule heat on the current lead, that is, use air cooling The current lead structure, making full use of the sensible heat of the cooling gas will greatly reduce the heat leakage of the current lead, thereby reducing the evaporation of the cooling liquid.

Chinese invention patent (CN110994534) discloses a multi-section current lead based on evaporative cooling. The first lead segment wraps the superconducting cable and the lead, and the second lead segment increases the heat exchange area between the lead and liquid nitrogen, and strengthens the connection between the lead and the liquid nitrogen. For heat exchange between liquid nitrogen, the third lead section increases the heat exchange area between the lead and evaporated nitrogen, strengthens the heat exchange between the lead and evaporated nitrogen, reduces the temperature of the lead, and reduces the heat leakage of the lead. The temperature transition is realized from the lead segment to the room temperature end; the third lead segment adopts the arrangement of multiple copper bars arranged in parallel in two directions perpendicular to each other on the lead cross section, and a preset distance is maintained between each copper bar. Chinese invention patent (CN107068324) discloses a 6kA high-temperature superconducting current lead, in which 30 copper rods with a diameter of 6 mm are used in the copper heat exchanger section, and are arranged in an arrangement of 10 inner layers and 20 outer layers.

To sum up, it is necessary to further optimize the lead structure to reduce the heat leakage of the current lead caused by Joule heat and external heat.

Contents of the invention

In order to solve the deficiencies in the prior art, the object of the present invention is to provide a high-temperature superconducting cable current lead structure and a design method thereof, by optimizing the current lead structure, the heat leakage of the current lead can be reduced.

The present invention adopts the following technical solutions.

The current lead structure of the high-temperature superconducting cable adopts a plurality of metal rods arranged in parallel along the direction of the lead wire axis, and a preset distance is maintained between each metal rod.

The metal rod comprises a first lead segment, a second lead segment and a third lead segment; wherein, the bottom end of the first lead segment contacts the liquid nitrogen liquid level, and the top of the first lead segment connects to the bottom end of the second lead segment; The top of the lead segment is connected to the bottom of the third lead segment, and the top of the third lead segment is connected to the room temperature terminal; the top of the second lead segment does not exceed the position of the epoxy board.

Wherein, the first lead segment and the third lead segment are solid metal rods, and the second lead segment is a hollow metal rod.

The steps of the design method of the high temperature superconducting cable current lead structure are as follows:

Step 1, measure the distance between the liquid nitrogen liquid surface in the high-temperature superconducting cable terminal and the room temperature terminal, and the distance between the liquid nitrogen liquid surface and the epoxy board; respectively determine the first lead segment and the second lead segment in the current lead and the length of the third lead segment;

Step 2, measure the outer diameter of the current lead, and set the initial value of the inner diameter of the second lead segment in the current lead according to the rated current of the current lead;

Step 3, measure liquid nitrogen liquid surface temperature, epoxy board position temperature and room temperature wiring terminal temperature;

Step 4, based on the coupling model of the thermal field and the electric field of the current lead, using simulation means, with the minimum heat leakage of the current lead as the objective function, starting from the initial value of the inner diameter of the second lead segment, optimizing the length and inner diameter of the second lead segment;

Step 5, according to the optimization results of the length and inner diameter of the second lead segment, re-determine the lengths of the first lead segment and the third lead segment in the current lead.

Preferably, step 1 includes:

Step 1.1, taking the distance between the liquid nitrogen liquid level and the room temperature terminal as the total length of the first lead segment, the second lead segment and the third lead segment in the current lead;

Step 1.2, taking the liquid nitrogen liquid level as the bottom end of the first lead segment, and determining the top of the first lead segment accordingly;

Step 1.3, taking the top of the first lead segment as the bottom end of the second lead segment, and the top of the second lead segment does not exceed the position of the epoxy board, thereby determining the length of the second lead segment;

Step 1.4, taking the top of the second lead segment as the bottom end of the third lead segment, taking the position of the room temperature terminal as the top of the third lead segment, and determining the length of the third lead segment accordingly.

Further, in step 1.2, the length of the first lead segment is not less than 200mm.

Further, in step 2, the outer diameters of the first lead segment, the second lead segment and the third lead segment in the current lead are the same, and the inner diameter of the second lead segment satisfies 30mm≤d≤56mm<D, where d represents the second lead The inner diameter of the segment, D represents the outer diameter of the second lead segment.

Further, in step 4, the thermal field model of the current lead satisfies the following relationship:

In the formula, ρ represents the density of the current lead material, C _p represents the constant pressure heat capacity of the current lead material,

Indicates the flow velocity of the fluid outside the current lead,

represents the heat flux of the current lead, k represents the thermal conductivity of the current lead material,

Represents the gradient operator, T represents the temperature of the current lead, and Q _e represents the Joule heat loss of the current lead.

Further, in step 4, the electric field model of the current lead satisfies the following relationship:

In the formula,

represents the current density of the current lead,

Indicates the ratio of the current flowing through the current lead to the cross section of the lead,

represents the electric field density of the current lead, V represents the electric potential of the current lead, σ represents the electrical conductivity of the current lead material, Q _e represents the Joule heat loss of the current lead,

Represents the gradient operator.

Further, in step 4, the minimum heat leakage of the current lead is the constraint condition of the objective function that the temperature at the position of the epoxy board is closest to the temperature of the terminal at room temperature.

Further, in step 4, the boundary conditions where the minimum heat leakage of the current lead is the objective function include: the temperature at the top of the current lead is the ambient temperature, the temperature at the bottom of the current lead is the boiling temperature of liquid nitrogen, and the boundaries of the current lead except the top and bottom are uniform For thermal insulation.

The beneficial effect of the present invention is that, compared with the prior art, the structure and shape of the existing current leads adopt the method of opening hollow slots inside, the structure is simple, the thermal field distribution is significantly optimized, and the heat leakage of the current leads is reduced. The design of the current lead wire provides reliable support; the current lead wire adopting this structure is easy to process and manufacture, easy to install and maintain, and is beneficial to engineering popularization and application.

Description of drawings

Fig. 1 is a schematic diagram of an axisymmetric model of a high temperature superconducting cable current lead structure of the present invention;

Fig. 2 is the flow chart of the design method of high temperature superconducting cable current lead structure of the present invention;

Fig. 3 is a temperature distribution curve of the epoxy board under different lengths of the second lead segment when the current lead structure of the high temperature superconducting cable of the present invention is applied in Embodiment 1;

Fig. 4 is a curve diagram of heat leakage heat distribution at the bottom of the current lead when the current lead structure of the high temperature superconducting cable of the present invention is applied in Embodiment 1 under different lengths of the second lead segment;

Fig. 5 is a graph showing the temperature distribution curve of the epoxy board under different inner diameters of the second lead section when the current lead structure of the high temperature superconducting cable of the present invention is applied in Embodiment 1;

Fig. 6 is a curve diagram of heat leakage heat distribution at the bottom of the current lead when the current lead structure of the high temperature superconducting cable of the present invention is applied in Embodiment 1 under different inner diameters of the second lead segment;

Fig. 7 is a temperature distribution curve of the epoxy board under different lengths of the second lead segment when the current lead structure of the high temperature superconducting cable of the present invention is applied in Embodiment 2;

Fig. 8 is a curve diagram of heat leakage heat distribution at the bottom of the current lead when the current lead structure of the high temperature superconducting cable of the present invention is applied in Embodiment 2 under different lengths of the second lead segment;

Fig. 9 is a curve diagram of the temperature distribution of the epoxy board under different inner diameters of the second lead section when the current lead structure of the high temperature superconducting cable of the present invention is applied in Embodiment 2;

Fig. 10 is a curve diagram of heat leakage heat distribution at the bottom of the current lead under different inner diameters of the second lead segment when the current lead structure of the high temperature superconducting cable of the present invention is applied in Embodiment 2.

detailed description

The application will be further described below in conjunction with the accompanying drawings. The following examples are only used to illustrate the technical solutions of the present invention more clearly, but not to limit the protection scope of the present application.

The current lead is used as a part connecting the transformer (normal temperature 293K) and the superconducting cable (liquid nitrogen 77K) in the terminal, and the Joule heat generated by itself and the heat from the outside will be introduced into the liquid nitrogen through it, causing part of the heat loss , increasing the burden on the refrigerator. Therefore, in the case of ensuring the current flow capacity of the current lead, minimizing the heat loss of the current lead is the key point to be considered in the design of the current lead structure.

The high-temperature superconducting cable current lead structure proposed by the present invention adopts a plurality of metal rods arranged in parallel along the direction of the lead wire axis, and a preset distance is maintained between each metal rod.

In view of the heat loss caused by Joule heat and external heat, the heat loss of the current lead of the high-temperature superconducting cable can be reduced as much as possible through reasonable structural design. The optimization design idea is usually to adopt a hollow design, that is, to hollow out a part inside the current lead, and the hollowed out part appears as a cylinder, so as to optimize the thermal field distribution and reduce the heat leakage of the current lead. Generally, the optimal size of the hollow slot of the cylinder can be given through simulation calculation, which provides a basis for the design of the subsequent current lead.

Considering the uniformity, the current lead and its internal hollowed out part adopt a cylindrical structure. Therefore, in the simulation calculation, the geometric modeling adopts an axisymmetric model, which facilitates the simplification of the model. Fig. 1 is a schematic diagram of the axisymmetric model of the high temperature superconducting cable current lead structure of the present invention.

As shown in Figure 1, the metal rod includes a first lead segment 1, a second lead segment 2 and a third lead segment 3; wherein,

The bottom end of the first lead segment 1 contacts the liquid nitrogen liquid level, and the top of the first lead segment 1 connects the bottom end of the second lead segment 2; the top end of the second lead segment 2 connects the bottom end of the third lead segment 3, and the third The top of the lead segment 3 is connected to the room temperature terminal; the top of the second lead segment 2 does not exceed the position of the epoxy board.

The first lead segment 1 and the third lead segment 3 are solid metal rods, and the second lead segment 2 is a hollow metal rod.

In a preferred embodiment of the present invention, the current lead adopts a hollow design, and grooves are dug inside it. When digging the groove, the bottom of the groove is 201mm away from the bottom of the current lead.

As shown in Figure 2, the steps of the design method for the current lead of the high-temperature superconducting cable are as follows:

Step 1, measure the distance between the liquid nitrogen liquid surface in the high-temperature superconducting cable terminal and the room temperature terminal, and the distance between the liquid nitrogen liquid surface and the epoxy board; respectively determine the first lead segment and the second lead segment in the current lead and the length of the third lead segment.

Specifically, step 1 includes:

Step 1.1, taking the distance between the liquid nitrogen liquid level and the room temperature terminal as the total length of the first lead segment, the second lead segment and the third lead segment in the current lead;

Step 1.2, take the liquid nitrogen liquid level as the bottom end of the first lead segment, and set the length of the first lead segment to be not less than 200mm, and determine the top of the first lead segment accordingly;

Step 1.3, taking the top of the first lead segment as the bottom end of the second lead segment, and the top of the second lead segment does not exceed the position of the epoxy board, thereby determining the length of the second lead segment;

Step 1.4, taking the top of the second lead segment as the bottom end of the third lead segment, taking the position of the room temperature terminal as the top of the third lead segment, and determining the length of the third lead segment accordingly.

In the preferred embodiment of the present invention, as can be seen from Fig. 1, take the liquid nitrogen liquid level as the starting point of the axial coordinates, that is, x=0, then the length of the first lead segment is 201mm, and the position of the epoxy board is x=811mm .

Step 2, measure the outer diameter of the current lead, and set the initial value of the inner diameter of the second lead segment in the current lead according to the rated current of the current lead.

Specifically, in step 2, the outer diameters of the first lead segment, the second lead segment, and the third lead segment in the current lead are the same, and the inner diameter of the second lead segment satisfies 30mm≤d≤56mm<D, where d represents the second The inner diameter of the lead segment, D represents the outer diameter of the second lead segment.

Step 3, measure the temperature of the liquid nitrogen liquid surface, the temperature of the epoxy board position and the temperature of the terminal at room temperature.

In a preferred embodiment of the present invention, under normal operating conditions, the pressure inside the terminal is about 0.4 MPa, and the bottom end of the current lead is in contact with the liquid nitrogen surface. The boiling temperatures of liquid nitrogen at different pressures are shown in Table 1.

Table 1 Boiling temperature 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

Absolute pressure (MPA)	Boiling point (°C)	Thermodynamic temperature (K)
0.5	-179.155	93.995
0.6	-176.77	96.3805
0.7	-174.657	98.4934
0.8	-172.751	100.3987
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

It can be seen from Table 1 that the boiling temperature of liquid nitrogen at 0.4MPa is about 90K, so the temperature at the bottom of the current lead, that is, the liquid nitrogen liquid surface temperature, is 90K; the top of the current lead is at normal temperature, that is, the temperature of the room temperature terminal is 293.15K; The remaining boundaries are thermally insulated.

Step 4: Based on the coupling model of the thermal field and electric field of the current lead, using simulation means, taking the minimum heat leakage of the current lead as the objective function, starting from the initial value of the inner diameter of the second lead segment, optimizing the length and inner diameter of the second lead segment.

Specifically, in step 4, the coupling model of the thermal field and electric field of the current lead satisfies the following relationship:

Thermal field model:

Electric field model:

In the formula,

ρ denotes the density of the current lead material,

C _p represents the constant pressure heat capacity of the current lead material,

Indicates the flow velocity of the fluid outside the current lead,

represents the heat flux in the current leads,

k represents the thermal conductivity of the current lead material,

T represents the temperature of the current lead,

represents the current density of the current lead,

Indicates the ratio of the current flowing through the current lead to the cross section of the lead,

represents the electric field density of the current lead,

V represents the potential of the current lead,

σ denotes the electrical conductivity of the current lead material,

_Qe represents the Joule heat loss in the current leads,

Represents the gradient operator.

In a preferred embodiment of the present invention, the material of the current leads is aluminum, and the density of aluminum does not change much at different temperatures, so it can be regarded as a constant. The main material property parameters for the current leads are set as follows:

The overall flow velocity of the fluid outside the current lead is 0, that is

is 0, so the thermal field model does not need to consider the influence of constant pressure heat capacity with temperature change, the constant pressure heat capacity can be given a constant value, and the constant pressure heat capacity C _p of the current lead material is set to 900J/(kg K) .

The thermal conductivity and electrical conductivity change with the temperature. At different temperatures, the values of the thermal conductivity k of aluminum are shown in Table 2:

Table 2 Thermal conductivity k of aluminum at different temperatures (unit: W/(m K))

temperature (K)	4.2	29	76	273	373
k	3200	5700	420	238	230

It can be seen from Table 2 that the thermal conductivity between 76K-273K can be regarded as a linear change, and the linear expression of the thermal conductivity k changing with temperature can be given by fitting; it is known that the temperature coefficient of resistance of aluminum is 0.0043/K. When T=293.15K, the electrical conductivity σ of aluminum is 3.44828e7S/m, from which the linear expression of the electrical conductivity σ changing with temperature can be obtained; therefore, the thermal conductivity k of the current lead material is set to 491.5+(420-238)/ (77[K]-273[K])×T, the unit is W/(m K), the conductivity σ of the current lead material is 3.44828e7*(1+0.0043[1/K]×(293.15[K] -T)), the unit is S/m.

The density ρ of the current lead material is set to be 2700 kg/m ³ .

Specifically, in step 4, the minimum heat leakage of the current lead is the constraint condition of the objective function that the temperature at the position of the epoxy board is closest to the temperature of the terminal at room temperature.

In step 4, the boundary conditions where the minimum heat leakage of the current lead is the objective function include: the temperature at the top of the current lead is the ambient temperature, the temperature at the bottom of the current lead is the boiling temperature of liquid nitrogen, and the boundaries of the current lead except the top and bottom are heat insulation.

Step 5, according to the optimization results of the length and inner diameter of the second lead segment, re-determine the lengths of the first lead segment and the third lead segment in the current lead.

Adopt the current lead design method that the present invention proposes, simulation process comprises:

(1) Simulated working conditions: the calculated working conditions of embodiment 1 are set to current I=1kA, and the calculated working conditions of embodiment 2 are set to current I=2kA.

(2) During simulation, first fix the inner diameter of the second lead segment, and simulate the influence of different lengths of the second lead segment on the leakage heat of the current lead; in the case of determining the length of the second lead segment, then simulate the second lead segment Effect of inner diameter on heat leakage of current leads;

(3) The optimal parameters are obtained by comparing the results.

Example 1.

Fig. 3 and Fig. 4 respectively show the temperature distribution curve of the epoxy board and the heat leakage heat distribution curve at the bottom of the current lead when the current lead structure of the high temperature superconducting cable of the present invention is applied in Example 1 under different lengths of the second lead segment.

It can be seen from the simulation graph that under the condition of current I=1kA, when the inner diameter of the second lead segment is determined, the longer the length of 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 is. small; but considering that the temperature at the epoxy board should be as close to room temperature as possible, therefore, from the actual situation, the length of the second lead segment should be as long as possible under the condition that the top of the second lead segment does not exceed the epoxy board. Possible length, namely L=610mm.

Fig. 5 and Fig. 6 respectively show the temperature distribution curve of the epoxy board and the heat leakage heat distribution curve at the bottom of the current lead when the current lead structure of the high temperature superconducting cable of the present invention is applied in Example 1 under different inner diameters of the second lead segment.

It can be seen from the simulation graph that when the length of the second lead segment is determined and the inner diameter of the second lead segment is d=56mm, the heat leakage at the bottom of the current lead is the smallest.

Example 2.

Fig. 7 and Fig. 8 respectively show the temperature distribution curve of the epoxy board and the heat leakage heat distribution curve at the bottom of the current lead when the current lead structure of the high temperature superconducting cable of the present invention is applied in Example 2, under different lengths of the second lead segment.

Seen from the simulation graph, under the situation of electric current I=2kA, when the inner diameter of the second lead wire section is determined, the length of the second lead wire segment is longer, and the heat flux at the bottom of the current lead wire is smaller, that is, the leakage heat of the current lead wire is smaller. However, considering that the temperature at the epoxy board should be as close to room temperature as possible, therefore, from the actual situation, the length of the second lead segment should be as long as possible under the condition that the top of the second lead segment does not exceed the epoxy board. Possible length, namely L=610mm.

Fig. 9 and Fig. 10 are the temperature distribution curve of the epoxy board, the heat leakage heat distribution curve and the current at the bottom of the current lead when the current lead structure of the high temperature superconducting cable of the present invention is applied in Embodiment 2, under different inner diameters of the second lead segment. Lead axial temperature distribution curve.

It can be seen from the simulation graph that when the length of the second lead segment is determined and the inner diameter of the second lead segment is d=50mm, the heat leakage at the bottom of the current lead is the smallest.

In summary, according to the simulation results of Embodiment 1 and Embodiment 2, in order to keep the heat leakage at the bottom of the current lead as small as possible, and to make the temperature at the epoxy board as close to room temperature as possible, the second It is difficult for the top of the lead segment to exceed the position of the epoxy board. On this premise, the length of the second lead segment should be as long as possible. Secondly, when the current I=1kA and the inner diameter d of the second lead segment is 56mm, the heat flow at the bottom of the current lead is the smallest; when the current I=2kA and the inner diameter d of the second lead segment is 50mm, the heat flow 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 larger than 50mm. Considering the mechanical strength, it is not recommended that the wall thickness of the current lead is too small. Therefore, the optimized parameters of the second lead segment are: length 610mm, inner diameter 40mm.

The beneficial effect of the present invention is that, compared with the prior art, the structure and shape of the existing current leads adopt the method of opening hollow slots inside, the structure is simple, the thermal field distribution is significantly optimized, and the heat leakage of the current leads is reduced. The design of the current lead wire provides reliable support; the current lead wire adopting this structure is easy to process and manufacture, easy to install and maintain, and is beneficial to engineering popularization and application.

The applicant of the present invention has made a detailed description and description of the implementation examples of the present invention in conjunction with the accompanying drawings, but those skilled in the art should understand that the above implementation examples are only preferred implementations of the present invention, and the detailed description is only to help readers better To understand the spirit of the present invention rather than limit the protection scope of the present invention, on the contrary, any improvement or modification made based on the spirit of the present invention shall fall within the protection scope of the present invention.

Claims (10)

1. The high temperature superconducting cable current lead structure adopts a plurality of metal rods arranged in parallel along the direction of the lead wire axis, and maintains a preset distance between each metal rod, and is characterized in that,

   The metal rod includes a first lead segment, a second lead segment and a third lead segment;

   The bottom end of the first lead segment is in contact with the liquid nitrogen liquid surface, 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 Room temperature terminal; the top of the second lead segment does not exceed the position of the epoxy board.
2. The high temperature superconducting cable current lead structure according to claim 1, characterized in that,

   The first lead segment and the third lead segment are solid metal rods, and the second lead segment is a hollow metal rod.
3. The method for designing the high temperature superconducting cable current lead structure applicable to the high temperature superconducting cable current lead structure described in claim 1 or 2, characterized in that,

   The steps of the design method are as follows:

   Step 1, measure the distance between the liquid nitrogen liquid surface in the high-temperature superconducting cable terminal and the room temperature terminal, and the distance between the liquid nitrogen liquid surface and the epoxy board; respectively determine the first lead segment and the second lead segment in the current lead and the length of the third lead segment;

   Step 2, measure the outer diameter of the current lead, and set the initial value of the inner diameter of the second lead segment in the current lead according to the rated current of the current lead;

   Step 3, measure liquid nitrogen liquid surface temperature, epoxy board position temperature and room temperature wiring terminal temperature;

   Step 4, based on the coupling model of the thermal field and the electric field of the current lead, using simulation means, with the minimum heat leakage of the current lead as the objective function, starting from the initial value of the inner diameter of the second lead segment, optimizing the length and inner diameter of the second lead segment;

   Step 5, according to the optimization results of the length and inner diameter of the second lead segment, re-determine the lengths of the first lead segment and the third lead segment in the current lead.
4. The design method of the high temperature superconducting cable current lead structure according to claim 3, characterized in that,

   Step 1 includes:

   Step 1.1, taking the distance between the liquid nitrogen liquid level and the room temperature terminal as the total length of the first lead segment, the second lead segment and the third lead segment in the current lead;

   Step 1.2, taking the liquid nitrogen liquid level as the bottom end of the first lead segment, and determining the top of the first lead segment accordingly;

   Step 1.3, taking the top of the first lead segment as the bottom end of the second lead segment, and the top of the second lead segment does not exceed the position of the epoxy board, thereby determining the length of the second lead segment;

   Step 1.4, taking the top of the second lead segment as the bottom end of the third lead segment, taking the position of the room temperature terminal as the top of the third lead segment, and determining the length of the third lead segment accordingly.
5. The design method of the high temperature superconducting cable current lead structure according to claim 4, characterized in that,

   In step 1.2, the length of the first lead segment is not less than 200mm.
6. The design method of the high temperature superconducting cable current lead structure according to claim 3, characterized in that,

   In step 2, the outer diameters of the first lead segment, the second lead segment and the third lead segment in the current lead are the same, and the inner diameter of the second lead segment satisfies 30mm≤d≤56mm<D, where d represents the diameter of the second lead segment Inner diameter, D represents the outer diameter of the second lead segment.
7. The design method of the high temperature superconducting cable current lead structure according to claim 3, characterized in that,

   In step 4, the thermal field model of the current lead satisfies the following relationship:

   

   

   In the formula,

   ρ denotes the density of the current lead material,

   C _p represents the constant pressure heat capacity of the current lead material,

   

   Indicates the flow velocity of the fluid outside the current lead,

   

   represents the heat flux in the current leads,

   k represents the thermal conductivity of the current lead material,

   

   Represents the gradient operator,

   T represents the temperature of the current lead,

   Q _e represents the Joule heat loss in the current leads.
8. The design method of the high temperature superconducting cable current lead structure according to claim 3, characterized in that,

   In step 4, the electric field model of the current lead satisfies the following relationship:

   

   

   

   In the formula,

   

   represents the current density of the current lead,

   

   Indicates the ratio of the current flowing through the current lead to the cross section of the lead,

   

   represents the electric field density of the current lead,

   V represents the potential of the current lead,

   σ denotes the electrical conductivity of the current lead material,

   _Qe represents the Joule heat loss in the current leads,

   

   Represents the gradient operator.
9. The design method of the high temperature superconducting cable current lead structure according to claim 3, characterized in that,

   In step 4, the minimum heat leakage of the current leads is the constraint condition of the objective function that the temperature at the position of the epoxy board is closest to the temperature of the terminal at room temperature.
10. The design method of the high temperature superconducting cable current lead structure according to claim 9, characterized in that,

    In step 4, the boundary conditions where the minimum heat leakage of the current lead is the objective function include: the temperature at the top of the current lead is the ambient temperature, the temperature at the bottom of the current lead is the boiling temperature of liquid nitrogen, and the boundaries of the current lead except the top and bottom are heat insulation.

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