CN101446598B - Variable-cross-section current lead wire - Google Patents

Abstract

The invention relates to a variable-cross-section current lead wire which is applicable to a system for testing critical current properties of a high-temperature superconducting tape and belongs to the field of applications of superconducting technology. The variable-cross-section current lead wire comprises the straight copper bar variable-cross-section current lead wire which uses the improved gas-cooled current lead wire segmented calculation method to carry out the optimized design of geometric parameters of the variable-cross-section current lead wire; and a mixed lead wire section which is formed by welding a copper stranded wire and a BSCCO tape in parallel and is used for connecting the tail end of the straight copper bar variable-cross-section current lead wire with a YBCO tape. The variable-cross-section current lead wire designed by the invention has the advantages of small heat leakage, high cooling efficiency and ability of saving lead wire materials and refrigeration cost.

Description

A kind of variable-cross-section current lead wire

Technical field

The present invention relates to a kind of variable-cross-section current lead wire of superconduction belt material critical current characteristic test system, belong to the superconductor technology application.

Background technology

The critical characteristic test experiments of high-temperature superconductor is described as one of experiment the most classical on the modern physics history.Critical current properties is one of three critical characteristics of superconductor.The critical current properties experiment of high-temperature superconductor is soaked in belt material of high temperature superconduct in the cryogenic liquid (as liquid nitrogen, liquid helium) usually, records different critical electric current values by changing magnetic field size and magnetic direction.

Current feed plays crucial effect in measuring the critical current properties experiment, be used for connecting room temperature power supply and superconducting tape, and apply electric current to the latter.During this, lead-in wire low temperature end face passes out the evaporation that the heat that comes causes cooling liquid, and the cold air that evaporates continues to cool off current feed again.Under overfreezing liquid nitrogen temperature 64K, yttrium is the critical current density of oxide YBCO band even can reaches tens thousand of ampere/square centimeters.Joule heat that high-current leading rises and the conductive heat leakage of bringing owing to the temperature difference at lead-in wire two ends will cause a large amount of evaporations of cooling liquid, thereby increase cooling cost greatly.Therefore the optimal design of current feed just seems extremely important.

Because lead-in wire is in the temperature difference of room temperature and cryogenic liquid, lead-in wire is the closer to the low-temperature end position, thermal conductivity is big more, and resistivity is more little, thereby causes conductive heat leakage bigger, Joule heat is less, the refrigerating gas temperature of bottom of going between simultaneously is minimum, and cooling power is higher, and traditional uniform cross section current feed does not utilize these characteristics that go up current feed, cause the waste of refrigerating gas, increased cooling cost indirectly.The optimal design of current feed geometrical structure parameter is exactly will be by finding the solution of current feed thermal balance equation being realized to the length of current feed and the computation optimization of sectional area size, the heat minimum that feasible lead-in wire low temperature end face spills, reduce the consumption of heat eliminating medium, reduce cooling cost.Publish first piece of relevant superconducting magnet in nearly 50 years with current feed optimal design article from nineteen fifty-nine scientist McFee R. at " Review of Scientific Instruments " magazine, scientific worker and engineering technical personnel that various countries are engaged in superconductor applications research have done a large amount of work on the current feed optimum Design of Parameters, thereby a variety of computing method have appearred, the pure analytic solution of partial differential equation for example, the segmentation computing method are based on numerical computation method of finite element software etc.Some can be common to most GAS-COOLED CURRENT LEAD design in these methods, and some is then only at some special operating modes.Generally speaking these computing method all are to be based upon on the basis that the current feed thermal balance equation is found the solution, in conjunction with concrete operating mode, to some calculating parameters (as the rerum natura of lead material, lead-in wire and the heat exchanger effectiveness of refrigerating gas etc.) do some rational hypothesis, thus obtain one comparatively near the parameters optimization of actual conditions.

Summary of the invention

The objective of the invention is to design a kind of yttrium that is applicable to is the air cooling variable-cross-section current lead wire that oxide YBCO band measuring critical current properties is used, the GAS-COOLED CURRENT LEAD segmentation computing method of application enhancements has been done optimal design to the geometrical structure parameter of variable-cross-section current lead wire, and content of the present invention comprises:

A kind of variable-cross-section current lead wire, it is characterized in that, this current feed has goes up the structure that cross-sectional area changes along its length, the variation pattern of described cross-sectional area uses GAS-COOLED CURRENT LEAD segmentation computing method to calculate, and is connected between described current feed end and the YBCO band by the lead segments of mixing that bismuth system oxide BSCCO superconducting tape and copper stranded conductor are formed in parallel.

It is characterized in that according to variable-cross-section current lead wire of the present invention described current feed is straight copper rod.

It is characterized in that according to variable-cross-section current lead wire of the present invention described GAS-COOLED CURRENT LEAD segmentation computing method may further comprise the steps:

(1) determines to calculate initial value according to the practical structures of superconducting apparatus and the working environment of current feed, comprise lead-in wire indoor temperature end section radius R, lead-in wire indoor temperature end, low-temperature end temperature T h, T1, lead-in wire indoor temperature end hot-fluid Q0, liquid nitrogen vaporization rate optimal value m, the segments n that the lead-in wire segmentation is calculated, wherein n is a positive integer;

(2) set lead-in wire section radius change step Δ r, make the lead-in wire sectional area reduce piecemeal, make up the variable-cross-section current lead wire function, the sectional area Si=π (R-i Δ r) 2 of i section lead-in wire, wherein i is a positive integer;

(3) from the 1st section of the lead-in wire indoor temperature end,, carry out iterative computation piecemeal, obtain the optimal shape factors Δ X1/S1 of each section lead-in wire by the numerical solution of GAS-COOLED CURRENT LEAD thermal balance equation, Δ X2/S2 ..., the end of Δ Xn/Sn and each section lead-in wire leaks calorific value Q1, Q2 ..., Qn;

(4) Si and Δ Xi/Si are multiplied each other can obtain the optimum length of each section lead-in wire, can obtain the optimum length X of whole lead-in wire to its addition, the sectional area that can get the variable-cross-section current lead wire low-temperature end thus is Sn, and optimizing the back lead terminal, to leak heat be Qn.

The air cooling variable-cross-section current lead wire that is applicable to the experiment of YBCO band measuring critical current properties of the present invention's design has following effect and advantage:

(1) takes into full account the lower characteristics of lead-in wire bottom refrigerating gas temperature,, increase the heat of lead-in wire bottom, improve lead-in wire bottom refrigerating gas heat exchange efficiency, reduce heat eliminating medium consumption by using variable section structure.

(2), can obtain shorter wire length under the condition of identical leakage heat, to satisfy the superconducting device characteristics of miniaturization day by day in the same material amount.

(3) by straight copper rod terminal with the YBCO band between one section of welding mix lead-in wire by what copper stranded conductor and BSCCO band were formed in parallel, can further reduce to be in the heating of the lead segments in the cooling liquid, the consumption of minimizing heat eliminating medium.

Description of drawings

Fig. 1 shows the current down-lead structure analysis and calculation model;

Fig. 2 shows current feed segmentation computation model synoptic diagram;

Fig. 3 shows current feed and leaks heat and liquid nitrogen vaporization rate relation curve;

Fig. 4 shows variable cross section GAS-COOLED CURRENT LEAD computing method process flow diagram;

Fig. 5 shows current feed Temperature Distribution simulation result;

Fig. 6 shows current feed design physical dimension parameter, wherein, and 1, straight copper rod variable-cross-section current lead wire; 2, the BSCCO band mixes lead segments with copper stranded conductor.

Embodiment

The present invention is further described below in conjunction with accompanying drawing.Be to describe design concept of the present invention in detail, Fig. 1 is the heat flux distribution figure of a typical GAS-COOLED CURRENT LEAD, according to classical thermal conduction study law, can analyze that to obtain the each several part hot-fluid as follows:

(1), can get the heat that passes through in cross section, x place, current feed optional position and be according to Fourier heat equation

$Q=-\mathrm{KA}\frac{\mathrm{dT}}{\mathrm{dx}}---\left(1\right)$

In the formula, Q is a heat flux, refers to pass through in the unit interval heat of a certain area of section, and unit is W; K is coefficient of heat conductivity or thermal conductivity, and the capacity of heat transmission of its reflection object is often recorded by experiment, and unit is W/ (mK); A is the lead-in wire sectional area, and promptly perpendicular to the area of section of heat conduction direction, unit is m ²DT/dx is the thermograde of lead-in wire section; Negative sign represents that the heat transferred direction is opposite with the thermograde direction.

(2) cool off according to newton that formula obtains refrigerating gas and current feed convection heat transfer amount is

$Q=\mathrm{hA\ΔT}=m{C}_p\frac{d{T}_g}{\mathrm{dx}}---\left(2\right)$

In the formula

It is the absolute value of the difference of lead-in wire wall surface temperature and refrigerating gas temperature; A is the convection heat transfer area; H is a convection transfer rate

The Joule heat size that produces when (3) current feed is by electric current I is

$Q={\mathrm{<figure-callout\; id="2"\; label="I"\; filenames="H2008102271854E00042.png"\; state="\{\{state\}\}">I</figure-callout>}}^2\mathrm{\&rho;}\frac{L}{A}---\left(3\right)$

ρ is the resistivity of lead material in the formula, and L is a wire length, and A is the lead-in wire sectional area.

According to law of conservation of energy, it is as follows that we can obtain the thermal balance equation of GAS-COOLED CURRENT LEAD

$\frac{d(k\left(T\right)\mathrm{SdT}/\mathrm{dx})}{\mathrm{dx}}-\mathrm{fm}{C}_P\frac{\mathrm{dT}}{\mathrm{dx}}+\mathrm{\&rho;}\left(T\right){\mathrm{<figure-callout\; id="2"\; label="I"\; filenames="H2008102271854E00042.png"\; state="\{\{state\}\}">I</figure-callout>}}^2/S=0---\left(4\right)$

Fig. 2 is a GAS-COOLED CURRENT LEAD segmentation computing method infitesimal analysis synoptic diagram, establishes lead-in wire is divided into the n section, and the temperature difference at every section lead-in wire two ends is all equated, make the T into △, and it is equal to establish lead-in wire sectional area everywhere, so

$\mathrm{\&Delta;T}=\frac{1}{n}(t_1-t_{n+1})---\left(5\right)$

If segments is enough big, for the electricalresistivity of each section lead material _i, thermal conductivity k _iSpecific heat C with refrigerating gas _iWhat can be similar to thinks constant.So i section lead-in wire satisfies the differential equation with downstream condition

$\left\{\begin{array}{c}{Q}_{\mathrm{ci}}=k_{i}S\frac{\mathrm{dT}}{\mathrm{dx}}+\frac{I^2}{S}{\mathrm{\&rho;}}_{i}x-\mathrm{fm}{C}_{\mathrm{pi}}(T-t_{n+1})\\ x=X_i,T=t_i,x=X_i+\mathrm{\&Delta;}{X}_i,T=t_{i+1}\end{array}\right.---\left(6\right)$

It is found the solution the Temperature Distribution function that can obtain i section lead-in wire is

$T_i\left(x\right)=e^{\frac{\mathrm{fm}{C}_{\mathrm{Pi}}}{S{k}_i}x}\{\&Integral;\frac{\mathrm{fm}{C}_{\mathrm{Pi}}}{S{k}_i}x[\frac{Q_{\mathrm{ci}}}{S{k}_i}-\frac{\mathrm{fm}{C}_{\mathrm{Pi}}{t}_i}{S{k}_i}-\frac{{\mathrm{<figure-callout\; id="2"\; label="I"\; filenames="H2008102271854E00042.png"\; state="\{\{state\}\}">I</figure-callout>}}^2{\mathrm{\&rho;}}_i}{S^2{k}_i}x]\mathrm{dx}+B\}---\left(7\right)$

Put in order

$T_i\left(x\right)=-\frac{Q_{\mathrm{ci}}}{\mathrm{fm}{C}_{\mathrm{Pi}}}+t_i+\frac{{\mathrm{<figure-callout\; id="2"\; label="I"\; filenames="H2008102271854E00042.png"\; state="\{\{state\}\}">I</figure-callout>}}^2\mathrm{\&rho;}}{\mathrm{Sfm}{C}_{\mathrm{Pi}}}x+\frac{I^2{k}_i\mathrm{\&rho;}}{f^2{m}^2{C}_{\mathrm{Pi}}^2}+B{e}^{\frac{\mathrm{fm}{C}_{\mathrm{Pi}}}{S{k}_i}x}---\left(8\right)$

Boundary condition is brought into, can be solved

$B=\frac{Q_{\mathrm{Ci}}}{\mathrm{fm}{C}_{\mathrm{Pi}}}-\frac{I^2{k}_i\mathrm{\&rho;}}{f^2{m}^2{\mathrm{<figure-callout\; id="2"\; label="C\; Pi"\; filenames="H2008102271854E00042.png"\; state="\{\{state\}\}">C</figure-callout>}}_{\mathrm{Pi}}^{}}$

$t_{i+1}-t_i=(\frac{Q_{\mathrm{Ci}}}{\mathrm{fm}{C}_{\mathrm{Pi}}}-\frac{I^2{k}_i\mathrm{\&rho;}}{f^2{m}^2{C}_{\mathrm{Pi}}^2})(e^{\frac{\mathrm{fm}{C}_{\mathrm{Pi}}{X}_i}{S{k}_i}}-1)+\frac{{\mathrm{<figure-callout\; id="2"\; label="I"\; filenames="H2008102271854E00042.png"\; state="\{\{state\}\}">I</figure-callout>}}^2{\mathrm{\&rho;}}_i\mathrm{\&Delta;}{X}_i}{\mathrm{fm}{C}_{\mathrm{Pi}}S}---\left(9\right)$

Formula (9) arrangement is obtained from the heat Q of i section lead terminal outflow _Ci

$Q_{\mathrm{ci}}=\frac{\mathrm{fm}{C}_{\mathrm{pi}}(t_i-t_{i+1})-{\mathrm{<figure-callout\; id="2"\; label="I"\; filenames="H2008102271854E00042.png"\; state="\{\{state\}\}">I</figure-callout>}}^2{\mathrm{\&rho;}}_i\frac{\mathrm{\&Delta;}{X}_i}{S}}{e^{\frac{\mathrm{fm}{C}_{\mathrm{pi}}}{k_i}\frac{\mathrm{\&Delta;}{X}_i}{S}}-1}+\frac{I^2{k}_i{\mathrm{\&rho;}}_i}{\mathrm{fm}{C}_{\mathrm{pi}}}---\left(10\right)$

△ Xi is the length of i section lead-in wire in the formula.In addition, for i section lead-in wire,, establish an equation under should satisfying according to law of conservation of energy

$Q_i=Q_{i-1}+{\mathrm{<figure-callout\; id="2"\; label="I"\; filenames="H2008102271854E00042.png"\; state="\{\{state\}\}">I</figure-callout>}}^2{\mathrm{\&rho;}}_i\frac{\mathrm{\&Delta;}{X}_i}{S}-\mathrm{fm}{C}_{\mathrm{pi}}\mathrm{\&Delta;T}---\left(11\right)$

Cancellation Qi, put in order

$[\frac{f^2{m}^2{C}_{\mathrm{pi}}^2}{I^2{k}_i{\mathrm{\&rho;}}_i}(t_i-t_{i+1})-\frac{\mathrm{fm}{C}_p}{k_i}\frac{\mathrm{\&Delta;}{X}_i}{S}+1]\exp \left(\frac{\mathrm{fm}{C}_{\mathrm{pi}}}{k_i}\frac{\mathrm{\&Delta;}{X}_i}{S}\right)-1=0---\left(12\right)$

By the iterative computation that goes between piecemeal, just can be in the hope of the horizontal ratio of the length of each section lead-in wire

$\frac{\mathrm{\&Delta;}{X}_1}{S},\frac{\mathrm{\&Delta;}{X}_2}{S},\frac{\mathrm{\&Delta;}{X}_3}{S},...,\frac{\mathrm{\&Delta;}{X}_n}{S}$

Leakage heat with each section lead-in wire

Q ₁，Q ₂，Q ₃，...，Q _n

Wherein Qn is exactly the minimum heat that flows into Cryo Equipment from the current feed lower end, promptly

Q _min＝Q _n (13)

The long horizontal ratio of the best of whole current feed is that each section lead-in wire is long horizontal than sum, promptly

${\left(\frac{X}{A}\right)}_{\mathrm{opt}}=\underset{i=1}{\overset{n}{\mathrm{\&Sigma;}}}\frac{\mathrm{\&Delta;}{X}_i}{S}---\left(14\right)$

Self cooling variable-cross-section current lead wire computing method are to add a sectional area tapering function in the segmentation of lead-in wire is calculated, and make the sectional area of lead-in wire reduce to reach the purpose that makes up the variable cross section lead-in wire piecemeal.

Want the form factor of calculating optimum lead-in wire, the liquid helium rate of evaporation that causes by the heat of the terminal inflow of current feed low-temperature (low temperature) vessel when at first needing to obtain lead-in wire size the best.Desirable a series of nitrogen flow value is calculated the heat that flows out from lead terminal, then can draw the curve of a Q=f (m) according to these group data.For self cooling current feed, satisfy linear functional relation Q=m*C between liquid nitrogen vaporization rate and the liquid nitrogen latent heat simultaneously _L, can make a curve again, the horizontal ordinate m value of two intersections of complex curve place correspondences is the liquid nitrogen vaporization rate value of self cooling optimization lead-in wire.Fig. 3 this two curves that drawn, intersection point is the liquid nitrogen vaporization rate of being asked.

After trying to achieve the liquid nitrogen vaporization rate value of optimizing lead-in wire, can begin to calculate the Q of each section of sectional leading wires according to the segmentation computing method _iWith

X _i/ S.Set a lead-in wire indoor temperature end sectional area radius initial value R simultaneously, lead-in wire sectional area change in radius step-length

, then

, S _iWith

Multiply each other and to obtain the length of every section lead-in wire

, the total length X that addition can be optimized and go between.Fig. 4 is the process flow diagram of computing method.

Use these computing method to the system design of the second generation YBCO measuring critical current properties of high-temperature superconducting tape variable-cross-section current lead wire.Fig. 5 is the Temperature Distribution simulation calculation result of current feed current feed under the 500A rated current for this reason.

In addition, mix lead segments one section of the terminal welding of straight copper rod by what copper stranded conductor and the parallel connection of BSCCO superconducting tape were welded.Among the BSCCO superconducting tape was soaked in liquid nitrogen, when working in superconducting state, electric current will be among BSCCO superconduction band flows into the YBCO band, thereby does not produce Joule heat.Be connected current feed with simple use copper stranded conductor and compare, further reduced the leakage heat of current feed with YBCO band situation.

Optimal design size according to the computation optimization gained has been manufactured variable-cross-section current lead wire, as shown in Figure 6.

Invention has been described according to specific exemplary embodiment herein.It will be conspicuous carrying out suitable replacement to one skilled in the art or revise under not departing from the scope of the present invention.Exemplary embodiment only is illustrative, rather than to the restriction of scope of the present invention, scope of the present invention is by appended claim definition.

Claims (2)

1. variable-cross-section current lead wire, it is characterized in that, this current feed has goes up the structure that cross-sectional area changes along its length, the variation pattern of described cross-sectional area uses GAS-COOLED CURRENT LEAD segmentation computing method to calculate, and lead segments is connected in described current feed end and yttrium is between the oxide YBCO band by mixing of being formed in parallel of bismuth system oxide BSCCO superconducting tape and copper stranded conductor; Described GAS-COOLED CURRENT LEAD segmentation computing method may further comprise the steps:

(1) determines to calculate initial value according to the practical structures of superconducting apparatus and the working environment of current feed, comprise lead-in wire indoor temperature end section radius R, lead-in wire indoor temperature end, low-temperature end temperature T _h, T _l, lead-in wire indoor temperature end hot-fluid Q ₀, liquid nitrogen vaporization rate optimal value m, the segments n that the lead-in wire segmentation is calculated, wherein n is a positive integer;

(2) set lead-in wire section radius change step Δ r, make the lead-in wire sectional area reduce piecemeal, make up the variable-cross-section current lead wire function, the sectional area S of i section lead-in wire _i=π (R-i Δ r) ², wherein i is a positive integer;

(3) from the 1st section of the lead-in wire indoor temperature end,, carry out iterative computation piecemeal, obtain the optimal shape factors Δ X of each section lead-in wire by the numerical solution of GAS-COOLED CURRENT LEAD thermal balance equation ₁/ S ₁, Δ X ₂/ S ₂..., Δ X _n/ S _nLeak calorific value Q with the end of each section lead-in wire ₁, Q ₂..., Q _n

(4) with S _iWith Δ X _i/ S _iMultiplying each other to obtain the optimum length of each section lead-in wire, can obtain the optimum length X of whole lead-in wire to its addition, and the sectional area that can get the variable-cross-section current lead wire low-temperature end thus is S _n, optimizing back lead terminal leakage heat is Q _n

2. variable-cross-section current lead wire as claimed in claim 1 is characterized in that described current feed is straight copper rod.

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