CN215070460U - High temperature superconducting cable current lead structure - Google Patents

Abstract

The high-temperature superconducting cable current lead structure adopts the method of arranging a plurality of metal rods in parallel along the lead axis, maintaining a preset distance between the metal rods, and the metal rods include a first lead segment, a second lead segment and a third lead segment; The bottom end of a lead segment is in contact with the liquid nitrogen level, 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 first lead segment and the third lead segment are solid metal bars, the second lead segment is a hollow metal bar, and the top of the second lead segment does not exceed the position of the epoxy board. The internal hollow groove is adopted, the structure is simple, the thermal field distribution is significantly optimized, the heat leakage of the current lead is reduced, and a reliable support is provided for the subsequent design of the current lead; the current lead with this structure is easy to process and manufacture, easy to install and maintain, and has Conducive to engineering promotion and application.

Description

High temperature superconducting cable current lead structure

technical field

The utility model relates to the technical field of high-temperature superconducting cable current leads, in particular to a high-temperature superconducting cable current lead structure.

Background technique

High-temperature superconducting cables have the advantages of large transmission power, high current density, low loss and environmental friendliness. The high-temperature superconducting current lead is a composite current lead, which uses high-temperature superconducting material in the low temperature section, and uses conductive materials such as copper or copper alloy between the room temperature and the high-temperature superconducting material. 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 part of the conventional current lead, due to the reduction of the temperature difference between the two ends of the lead, 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 a part of this heat is transferred to the cryogenic container from the end of the lead. The operating current of small superconducting cables is small, so no special consideration should be given to the current leads; however, in large superconducting cables, the heat leakage of the current leads largely determines the cooling capacity required for the superconducting cable in normal operation. Therefore, in the design of large-scale superconducting cables, 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 lead material 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. Leakage heat introduced into the cryocontainer by the current leads includes conduction heat and Joule heat. Increasing the cross-sectional area of the current lead can reduce the 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 are known, there is a length-to-balance ratio L/A with the minimum heat loss, that is, the ratio of the length of the lead to the cross-sectional area, so that the end of the lead flows into the superconducting cable cryogenic container with the smallest heat.

In the prior art, Chinese utility model patent (CN110323325) discloses a Peltier current lead device, by inserting a current lead formed of a thermoelectric material bismuth telluride into an existing copper or copper alloy lead, the current lead can pass through the current lead. The heat from the low temperature end of the current lead is transferred to the room temperature end when the current is flowing, 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 flows.

In the prior art, the current leads are often designed in the form of a heat exchanger to minimize the heat leakage to the cryogenic container through the current leads. The current leads made of different materials have different minimum heat leakage. On the basis of the fixed material, the size of the current lead is further optimized to make the heat leakage of the lead close to the minimum value; the cooling gas evaporated from the cooling liquid in the low-temperature coolant container is used to take away the conduction heat and Joule heat on the current lead, that is, air cooling is adopted. The structure of the current lead, 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 utility model patent (CN110994534) discloses a multi-segment 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 the liquid nitrogen, strengthens the lead For heat exchange with 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 the evaporated nitrogen, reduces the temperature of the lead, and reduces the heat leakage of the lead. The three lead segments realize temperature transition to the room temperature end; the third lead segment adopts an arrangement in which two directions on the lead cross section are perpendicular to each other and are arranged in parallel with a plurality of copper bars, and each copper bar maintains a preset spacing. Chinese utility model patent (CN107068324) discloses a 6kA high-temperature superconducting current lead, wherein the copper heat exchanger section adopts 30 copper rods with a diameter of 6mm, and is arranged in an inner layer of 10 and an outer layer of 20.

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

Utility model content

In order to solve the deficiencies in the prior art, the purpose of the present invention is to provide a high temperature superconducting cable current lead structure, which can reduce the leakage heat of the current lead by optimizing the current lead structure.

The utility model adopts the following technical scheme.

In the current lead structure of the high temperature superconducting cable, the bottom end of the current lead contacts the liquid nitrogen level, the top end of the current lead is connected to the room temperature terminal, and the current lead passes through the epoxy board.

The current lead adopts a plurality of metal rods arranged in parallel along the direction of the lead axis, and a preset distance is maintained between each metal rod.

The metal rod includes a first lead segment, a second lead segment and a third lead segment; the distance between the liquid nitrogen liquid level and the room temperature terminal is taken as the distance between the first lead segment, the second lead segment and the third lead segment in the current lead. total length.

The bottom end of the first lead segment is in contact with the liquid nitrogen level, 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 end of the second lead segment does not exceed the epoxy board position.

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

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

Further, the distance between the bottom of the hollow groove of the second lead segment and the bottom end of the second lead segment is not less than 1 mm.

Further, 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 inner diameter of the second lead segment, D Indicates the outer diameter of the second lead segment.

Preferably, the temperature of the bottom end of the current lead is the boiling temperature of liquid nitrogen; the temperature of the top end of the current lead is the temperature of the terminal at room temperature; the remaining boundaries of the current lead are in the thermal insulation structure.

Preferably, the constant pressure heat capacity of the current lead does not change with temperature changes, and the thermal conductivity and electrical conductivity change with temperature changes.

Preferably, the material of the current leads is aluminium.

The beneficial effect of the utility model is that, compared with the prior art, the structure and shape of the current lead wire adopts the method of opening a hollow groove inside, the structure is simple, the thermal field distribution is significantly optimized, the heat leakage of the current lead wire is reduced, and the The subsequent current lead design provides reliable support; the current lead with this structure is easy to process and manufacture, easy to install and maintain, and is conducive to engineering popularization and application.

Description of drawings

Fig. 1 is the axisymmetric model schematic diagram of the high-temperature superconducting cable current lead structure of the utility model;

Fig. 2 is the flow chart of the design method of the high-temperature superconducting cable current lead structure of the utility model;

3 is a graph showing the temperature distribution of the epoxy board under different lengths of the second lead segment when the high-temperature superconducting cable current lead structure of the present invention is applied in Example 1;

4 is a graph showing the distribution of heat leakage at the bottom of the current lead 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;

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

6 is a graph showing the distribution curve of heat leakage 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 1;

7 is a graph showing the temperature distribution of the epoxy board under different lengths of the second lead segment when the high-temperature superconducting cable current lead structure of the present invention is applied in Example 2;

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

9 is a graph showing the temperature distribution of the epoxy plate under different inner diameters of the second lead section when the high-temperature superconducting cable current lead structure of the present invention is applied in Example 2;

10 is a graph showing the distribution of heat leakage 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 Example 2.

Detailed ways

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

The current lead is used as the part connecting the transformer (room temperature 293K) and the superconducting cable (liquid nitrogen 77K) in the terminal. The Joule heat generated by its own operation and the heat from the outside will be introduced into the liquid nitrogen through it, causing some heat loss. , increasing the burden on the refrigerator. Therefore, in the case of ensuring the current flow capacity of the current lead, reducing the heat loss of the current lead as much as possible 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 utility model adopts a plurality of metal rods arranged in parallel along the direction of the lead axis, and a preset spacing is maintained between the metal rods.

For the heat loss caused by Joule heat and external incoming 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 optimal design idea is usually to adopt a hollow design, that is, a part of the current lead is hollowed out, and the hollowed part is presented 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 by simulation calculation, which can provide a basis for the design of the subsequent current lead.

Considering the uniformity, the current lead and its hollowed-out part all adopt a cylindrical structure. Therefore, in the simulation calculation, the geometric modeling adopts an axisymmetric model, which is convenient for simplifying the model. FIG. 1 is a schematic diagram of the axisymmetric model of the current lead structure of the high-temperature superconducting cable of the present invention.

As shown in Figure 1, the metal bar 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 is in contact with the liquid nitrogen surface, the top end of the first lead segment 1 is connected to the bottom end of the second lead segment 2; the top end of the second lead segment 2 is connected to the bottom end of the third lead segment 3, and the third lead segment The top end of the lead segment 3 is connected to the room temperature terminal; the top end 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 bars, and the second lead segment 2 is a hollow metal bar.

In the preferred embodiment of the present utility model, the current lead adopts a hollow design, and a groove is cut in the inside thereof. When digging the slot, the bottom of the hollow slot is 201mm away from the bottom of the current lead.

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

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

Specifically, step 1 includes:

Step 1.1, take 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 level as the bottom end of the first lead segment, and set the length of the first lead segment to be no less than 200mm, and determine the top of the first lead segment accordingly;

Step 1.3, take 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, and determine the length of the second lead segment accordingly;

In step 1.4, the top end of the second lead segment is taken as the bottom end of the third lead segment, and the position of the room temperature terminal is taken as the top end of the third lead segment, and the length of the third lead segment is determined accordingly.

In the preferred embodiment of the present utility model, it can be seen from FIG. 1 that the liquid nitrogen level is taken as the starting point of the axial coordinate, 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, and D represents the outer diameter of the second lead segment.

Step 3, measure the liquid nitrogen liquid surface temperature, the epoxy board position temperature and the room temperature terminal 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 surface of liquid nitrogen. The boiling temperature of liquid nitrogen under different pressures is shown in Table 1.

Table 1 Boiling temperature of liquid nitrogen under different pressures

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 temperature of the liquid nitrogen surface, is 90K; the top of the current lead is at room temperature, that is, the temperature of the terminal at room temperature, which is 293.15K; The rest of the boundaries are thermally insulated.

Step 4: Based on the coupling model of the thermal field and the electric field of the current lead, the length and the inner diameter of the second lead segment are optimized starting from the initial value of the inner diameter of the second lead segment, using the simulation method to minimize the heat leakage of the current lead as the objective function.

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

Thermal field model:

Electric field model:

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,

表示电流引线外部流体的流速，

represents the flow rate of the fluid outside the current lead,

表示电流引线的热通量，

represents the heat flux of the current lead,

k is the thermal conductivity of the current lead material,

T is the temperature of the current lead,

表示电流引线的电流密度，

represents the current density of the current lead,

表示流过电流引线的电流与引线截面的比值，

represents the ratio of the current flowing through the current lead to the cross-section of the lead,

表示电流引线的电场密度，

represents the electric field density of the current lead,

V represents the potential of the current lead,

σ represents the conductivity of the current lead material,

Q _e represents the Joule heat loss of the current lead,

表示梯度算子。

represents the gradient operator.

In the preferred embodiment of the present invention, the material of the current lead is aluminum, and the density of aluminum changes little at different temperatures, so it can be regarded as a constant. The main material property parameters of the current lead are set as follows:

为0，因此热场模型中可不考虑恒压热容随温度变化的影响，恒压热容可给定一个常值，设置电流引线材料的恒压热容C_p为900J/(kg·K)。The overall flow rate of the fluid outside the current lead is 0, i.e.

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

The thermal conductivity and electrical conductivity change with the change of temperature. At different temperatures, the value of the thermal conductivity k of aluminum is 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 the standard 2 that the thermal conductivity between 76K-273K can be regarded as a linear change, and the linear expression of the thermal conductivity k with temperature can be given by fitting; the known temperature coefficient of resistance of aluminum is 0.0043/K, in When T=293.15K, the conductivity σ of aluminum is 3.44828e7S/m, from which a linear expression of the conductivity σ with temperature can be obtained; therefore, the thermal conductivity k of the current lead material is set as 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)) in S/m.

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

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

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

Step 5: Determine the lengths of the first lead segment and the third lead segment in the current lead according to the optimized results of the length and inner diameter of the second lead segment.

Using the current lead design method proposed by the utility model, the simulation process includes:

(1) Simulation working condition: The calculation working condition of Example 1 is set as current I=1kA, and the calculation working condition of Embodiment 2 is set as current I=2kA.

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

(3) Obtain the optimal parameters by comparing the results.

Example 1.

3 and 4 are respectively the temperature distribution curve of the epoxy plate and the heat leakage distribution curve of the bottom of the current lead under different lengths of the second lead section when the high-temperature superconducting cable current lead structure of the present invention is applied in Example 1.

It can be seen from the simulation graph that in the case 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. However, considering that the temperature at the epoxy board should be as close to room temperature as possible, from the actual situation, the length of the second lead segment should be as long as possible when the top of the second lead segment does not exceed the epoxy board. Possible length, ie L=610mm.

5 and 6 are respectively the temperature distribution curve of the epoxy plate and the heat leakage distribution curve of the bottom of the current lead under different inner diameters of the second lead section when the high-temperature superconducting cable current lead structure of the present invention is applied in Example 1.

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=56 mm, the heat leakage at the bottom of the current lead is the smallest.

Example 2.

7 and 8 are respectively the temperature distribution curve of the epoxy plate and the leakage heat distribution curve of the bottom of the current lead under different lengths of the second lead section when the high-temperature superconducting cable current lead structure of the present invention is applied in Example 2.

It can be seen from the simulation graph that in the case of current I=2kA, 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. However, considering that the temperature at the epoxy board should be as close to room temperature as possible, from the actual situation, the length of the second lead segment should be as long as possible when the top of the second lead segment does not exceed the epoxy board. Possible length, ie L=610mm.

Fig. 9, Fig. 10 are respectively when the utility model high-temperature superconducting cable current lead structure is applied in embodiment 2, under the different inner diameters of the second lead segment, the temperature distribution curve of the epoxy plate, the leakage heat distribution curve of the bottom of the current lead and Graph of the axial temperature distribution of the current lead.

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.

To sum up, according to the simulation results of Example 1 and Example 2, in order to make the heat leakage at the bottom of the current lead as small as possible, the temperature at the epoxy board should be as close to room temperature as possible, so the second The top of the lead segment is not easy to exceed the position of the epoxy board. Under 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 size of the inner diameter of the second lead segment should not be greater than 50mm. From the point of view of 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: a length of 610 mm and an inner diameter of 40 mm.

The beneficial effect of the utility model is that, compared with the prior art, the structure and shape of the current lead wire adopts the method of opening a hollow groove inside, the structure is simple, the thermal field distribution is significantly optimized, the heat leakage of the current lead wire is reduced, and the The subsequent current lead design provides reliable support; the current lead with this structure is easy to process and manufacture, easy to install and maintain, and is conducive to engineering popularization and application.

The applicant of the present invention has made a detailed description and description of the embodiments of the present invention in conjunction with the accompanying drawings, but those skilled in the art should understand that the above embodiments are only preferred embodiments of the present invention, and the detailed description is only for the purpose of helping Readers better understand the spirit of the present invention, rather than limiting the scope of protection of the present invention, on the contrary, any improvement or modification made based on the spirit of the present invention should fall within the scope of protection of the present invention.

Claims (10)

1. High-temperature superconducting cable current lead structure, the bottom end of the current lead contacts the liquid nitrogen level, the top of the current lead connects room temperature terminals, and the current lead passes through the epoxy plate, it is characterized in that: The current lead adopts a plurality of metal rods arranged in parallel along the axis of the lead wire, and maintains a preset distance between the metal rods. 2. high temperature superconducting cable current lead structure according to claim 1, is characterized in that, The metal rod includes a first lead segment, a second lead segment and a third lead segment; the distance between the liquid nitrogen liquid level and the room temperature terminal is taken as the first lead segment, the second lead segment and the third lead in the current lead The total length of the segment. 3. high temperature superconducting cable current lead structure according to claim 2, is characterized in that, The bottom end of the first lead segment contacts the liquid nitrogen level, 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 bottom end of the third lead segment. The top end is connected to the room temperature terminal; the top end of the second lead segment does not exceed the position of the epoxy board. 4. The high-temperature superconducting cable current lead structure according to claim 2 or 3, characterized in that, The length of the first lead segment is not less than 200mm. 5. The high-temperature superconducting cable current lead structure according to claim 3, 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. 6. The high-temperature superconducting cable current lead structure according to claim 5, characterized in that, The distance between the bottom of the hollow groove of the second lead segment and the bottom end of the second lead segment is not less than 1 mm. 7. The high-temperature superconducting cable current lead structure according to claim 1, characterized in that, In the current lead, the outer diameter of the first lead segment, the second lead segment and the third lead segment are the same, and the inner diameter of the second lead segment satisfies 30mm≤d≤56mm<D, where d represents the inner diameter of the second lead segment, D Indicates the outer diameter of the second lead segment. 8. The high temperature superconducting cable current lead structure according to claim 1, characterized in that, The temperature of the bottom end of the current lead is the boiling temperature of liquid nitrogen; the temperature of the top of the current lead is the temperature of the terminal at room temperature; the remaining boundaries of the current lead are in the thermal insulation structure. 9. The high temperature superconducting cable current lead structure according to claim 1, characterized in that, The constant pressure heat capacity of the current lead does not change with the temperature change, and the thermal conductivity and the electrical conductivity change with the temperature change. 10. The high temperature superconducting cable current lead structure according to claim 9, characterized in that, The material of the current lead is aluminum.

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