CN105184003A - Calculating method for power-cable magnetic-thermal coupling field - Google Patents

Abstract

The invention provides a calculating method for a power-cable magnetic-thermal coupling field. The method comprises the steps that 1, a power-cable electromagnetic field physical model and a power-cable temperature field physical model are built; 2, power-cable physical simulation models are built, and calculating parameters and boundary conditions are determined; 3, the corresponding calculating parameters are obtained by measuring a power cable; 4, an electromagnetic field and a temperature field of the power cable are solved according to the electromagnetic field physical simulation model and the temperature field physical simulation model; 5, if calculating results are convergent, the electromagnetic field and the temperature field of the power cable are obtained, magnetic-thermal coupling analysis is achieved, and if the calculating results are not convergent, iterative analysis is performed by returning to the step 4 until the calculating results are convergent. The calculating method is flexible in solving mode and very suitable for the magnetic-thermal coupling problems of processing cable loss and temperature rising.

Description

A kind of computing method of power cable magnetic-thermal coupling field

Technical field

The invention belongs to power cable field, be specifically related to the computing method of a kind of power cable based on ANSYS magnetic-thermal coupling field.

Background technology

Power cable is in operation and will inevitably produces loss, thus causes heating, and cable temperature raises, therefore cable lay the heat dissipation problem needing to consider cable, ensureing that cable is in operation will cause insulation ag(e)ing to be accelerated because of overtemperature, and cable life shortens, and even cable destroys at once.And the factor affecting cable temperature field is complicated and changeable, the current-carrying capacity of cable is also difficult to determine exactly.

In recent years, the maturation of Fibre Optical Sensor thermometry, becomes the important measurement means of power equipment on-line temperature monitoring.Its application on cable, if the temperature of monitoring core and epidermis, cannot embody the actual value of optical fiber distributed type thermometric.The destruction of cable insulation material is often along with the heating process of positive feedback, and thermal process is just for distributed optical fiber temperature measuring monitoring technology provides useful information, if these information can be gone out by on-line monitoring, once insulation is broken down, local cable temperature rise is high, and it accurately and is timely located is possible.Cable insulation internal electrical heat integration fault causes local overheating to make original Temperature Distribution distortion, and the Temperature Distribution of this distortion of accurate analysis, has important Research Significance to the cable insulation On-line Fault monitoring technology based on distributed optical fiber temperature measurement.

Cables manufacturing enterprise and operation power department receive much concern to the loss of cable and temperature rise.For different construction conditions, generally all to test.Experimental study is limited by the factors such as expense, time, experiment condition and environment, obviously studies the loss under different situations, temperature and current-carrying capacity by experiment and there is a lot of troubles, and appearing as it and open the floodgates wide with Mathematic calculation method.Adopt the analysis means research loss of power cable and the temperature rise of mathematics, improve the capacity utilization of cable and assess state of insulation accurately, to reliable, the safety of cable, economical operation, there is important practical significance.

Summary of the invention

Technical matters to be solved by this invention is: the computing method providing a kind of power cable magnetic-thermal coupling field, the method carries out the calculating of magnetic-thermal coupling field to power cable, again each field order is desirably analyzed one by one, coupling analysis process be using the analysis result of previous field as dynamic changes process to the mode analyzed in a rear field.It is flexible that the method solves mode, very applicable to this kind of magnetic-thermal coupling problem of process cable loss and temperature rise.

The technical solution adopted in the present invention is: a kind of computing method of power cable magnetic-thermal coupling field, comprising:

S1) power cable electromagnetic field and temperature field physical model is set up;

S2) set up power cable physical phantom, specify calculating parameter and boundary condition;

S3) corresponding calculating parameter is obtained to power cable measurement;

S4) according to electromagnetic field and temperature field physical phantom and corresponding calculating parameter, the electromagnetic field of power cable and temperature field are solved;

S5) if numerical convergence, then obtain magnetic field and the thermal field of power cable, realize magnetic-Thermal couple analysis; As result of calculation does not restrain, then turn back to step S4 and carry out iterative analysis, until convergence.

Described computing method, the method that step S1 sets up physical model comprises:

When power cable normally runs under power frequency condition, the calculating of magnetic-thermal coupling field need be supposed as follows:

1) cable length is very large, is far longer than the diameter of cable, therefore only considering the thermo parameters method of cable radial direction when calculating, carrying out two dimensional surface calculating;

2) impact of space charge and displacement current is ignored;

3) magnetic permeability of cable and earth materials is all linear;

4) only have insulation course between cable conductor and metallic sheath, conductor shield is ignored, and namely the cross-section of cable from inside to outside comprises conductor, insulation course, metallic sheath, oversheath, soil successively;

Under coulomb specification, the magnetic vector of each Rotating fields of cable is analyzed, obtains power cable each region vector magnetic potential equation:

Cable conductor region,

▽ ²A ₁＝-μ ₀J _s

In above formula, J _sthe current density of conductive region, A ₁represent the vector magnetic potential of conductor layer, μ 0 represents permeability of vacuum;

Cable insulation layer region,

▽ ²A ₂＝0

In above formula, A ₂represent insulation course vector magnetic potential;

Cable metal cover region,

▽ ²A ₃＝-μ ₀J _e

In above formula, J _erepresent metallic sheath vortex flow density, A ₃represent insulation course and metallic sheath vector magnetic potential;

Cable jacket region,

▽ ²A ₄＝0

In above formula, A ₄represent oversheath vector magnetic potential;

Soil region,

▽ ²A ₅＝0

In above formula, A ₅represent the vector magnetic potential of soil region;

In addition, the continuity equation above the border of each layer of cable and soil is:

$\left\{\begin{array}{c}{A}_i=A_j\\ {\mathrm{\μ}}_i^{-1}\▿A_i={\mathrm{\μ}}_j^{-1}\▿A_j\\ {\mathrm{\μ}}_i^{-1}\▿\×A_i\×n={\mathrm{\μ}}_j^{-1}\▿\×A_j\×n\end{array}\right.$

In above formula, i and j represents the numbering (i, j value is corresponding with the subscript of A1-A5 before) of adjacent area, and n is unit normal vector, μ _i, μ _jrepresent i-th respectively, the magnetic permeability in j region;

The eddy current loss computing formula of metal screen layer inside is:

$\left\{\begin{array}{c}{J}_e=-{\mathrm{j\ω\γ}}_3{A}_3\\ P_e={\mathrm{\γ}}_3^{-1}\∫J_e^{2}dV\\ P_e={\mathrm{\γ}}_3^{-1}\Σ\left({\left(J_{e\left(i\right)}\right)}^{2}2{\mathrm{\πr}}_i{S}_i\right)={\mathrm{\γ}}_3^{-1}\Σ{\left({\mathrm{\ω\γ}}_3{A}_{3,i}\right)}^{2}2{\mathrm{\πr}}_i{S}_i)\end{array}\right.$

In formula, Je represents metallic sheath induced current density, and A3 represents the vector magnetic potential of metal screen layer, and Pe is unit length eddy current loss power, and γ 3 is the conductivity of metallic sheath material, and ri represents the distance of each unit to axle center, and Si represents each cellar area.

The temperature field of cable is analyzed by equivalent Re Lufa, Re Lu and heat flow field corresponding to the physical quantity in circuit or current field, that is:

According to the theory of thermal conduction study, calculate the thermal resistance T of cable insulation, inner liner (between metallic sheath and oversheath), serving (oversheath) and surrounding media (soil or air) respectively ₁~ T ₄, computing formula is as follows:

$T_1=\frac{{\mathrm{\ρ}}_{T_1}}{2\mathrm{\π}}ln\frac{D_i}{D_c}$

$T_2=\frac{{\mathrm{\ρ}}_{T_2}}{2\mathrm{\π}}ln\frac{D_a}{D_s^{\′}}$

$T_3=\frac{{\mathrm{\ρ}}_{T_3}}{2\mathrm{\π}}ln\frac{D_e}{D_a^{\′}}$

$T_4=\frac{{\mathrm{\ρ}}_{T_4}}{2\mathrm{\π}}ln\frac{4L}{D_e}$

In formula, be respectively the coefficient of heat conductivity of insulation course, inner liner, serving and soil, D _iand D _cbe respectively insulation course internal diameter and external diameter, D _aand D' _sbe respectively inner liner internal diameter and external diameter, D _eand D' _abe respectively serving internal diameter and external diameter, L is the cable laying degree of depth.Cable thermal field (as calculated by ANSYS) is calculated again by Finite Element Method.

Described computing method, the method that step S2 sets up cable physical phantom comprises: establish cable to be axisymmetric cylindrical shape, and its electromagnetic field produced is two dimensional surface field, the conduction of thermal field also negligible axial hot-fluid, and this calculated field is also two dimensional field; Then set threephase cable be laid in the infinitely-great soil of scope, three cables are positioned at the centre position of model, the left side be A phase, centre be B phase, the right be C phase; The coboundary of model is convection boundary condition, and lower boundary is arranged forces steady temperature (25 degrees Celsius), and both sides are natural boundary conditions; The power cable ANSYS physical phantom of magnetic-thermal coupling field is finally set up according to these settings.

Described method, the calculating parameter of step S2 comprises the correlation parameters such as the conductivity of cable copper conductor layer, insulation course, semi-conductive non-woven fabric layer, metal sheath layer, PVC external sheath layer and soil, relative dielectric constant, coefficient of heat conductivity, density and normal pressure thermal capacitance.

Described method, the material property parameter of soil and each Rotating fields of power cable can be consulted power cable product manual and be learnt.

Described computing method, the method that step S4 solves comprises: utilize ANSYS software to set up magnetic-thermal coupling field physical model, in physical model, three-phase current (current value of the size of about 1000A can be applied) is applied to cable core, setting cable laying spacing (being generally 0.5m), obtains the current-carrying capacity of the Temperature Distribution of whole domain, the loss value of cable and temperature value and cable as calculated afterwards.

Described method, the method obtaining Temperature Distribution, the loss value of cable and the current-carrying capacity of temperature value and cable specifically comprises: use sense answers heating physical field to carry out Temperature of Power Cables field and current-carrying capacity numerical evaluation; In computation process, first determine a preliminary current-carrying capacity, according to formulae discovery loss, obtain cable and ambient temperature field distribution thereof, if the maximum temperature of cable conductor is lower than 90 DEG C, then increase size of current, re-start calculating; If the conductor maximum temperature of power cable is higher than 90 DEG C, then reduces size of current, recalculate; Finally obtain electric current when cable conductor temperature is 90 DEG C, be required current-carrying capacity; And by the analysis result to Temperature of Power Cables value and current-carrying capacity, solve loss value and Temperature Distribution that difference lays power cable under spacing.

Described method, the method for step S5 magnetic-Thermal couple analysis comprises: analyze the influence factor of core temperature and calculate maximum carrying capacity.

Advantage of the present invention: the computing method that the invention provides a kind of power cable based on ANSYS magnetic-thermal coupling field, the method can solve the problem of cable magnetic-thermal coupling aspect in power cable temperature rise and loss analysis.The method is all very flexible in model foundation, unit selection and stress and strain model, has solving speed faster, have stronger engineering practicability compared with other classic methods.Meanwhile, the method applied in the present invention can improve the capacity utilization of cable and assess state of insulation accurately, has important practical significance to reliable, the safety of cable, economical operation.

Accompanying drawing explanation

Accompanying drawing 1 is the computing method of a kind of power cable based on ANSYS magnetic-thermal coupling field;

Fig. 2 two-circuit cable laying schematic diagram (A, B, C represent three-phase);

Fig. 3 single loop in-line lays schematic diagram (S represents spacing).

Embodiment

The invention provides the computing method of a kind of power cable based on ANSYS magnetic-thermal coupling field, comprising: S1) set up power cable physical phantom, set up electromagnetic field and temperature field physical model; S2) clear and definite Electromagnetic Calculation parameter and solve type; S3) electromagnetic field analysis file is write, then clear and definite temperature field analysis data; S4) write temperature field analysis file, start to calculate; S5) if numerical convergence, then can calculate magnetic field and the thermal field of cable, realize magnetic-Thermal couple analysis; As result of calculation does not restrain, then re-write electromagnetic field and temperature field file, iterative analysis, until convergence.The method can be used in power cable temperature rise and loss analysis, is well-adapted for cable magnetic-thermal coupling case study.The method is all very flexible in model foundation, unit selection and stress and strain model, has solving speed faster, have stronger engineering practicability compared with other classic methods.

The solution of the present invention comprises:

S1) set up power cable physical phantom, set up electromagnetic field and temperature field physical model;

S2) clear and definite Electromagnetic Calculation parameter, mesh generation and solve type;

S3) write electromagnetic field analysis file, then clear and definite temperature field analysis data, and write temperature field file;

S4) if numerical convergence, then can calculate magnetic field and the thermal field of cable, realize magnetic-Thermal couple analysis; As result of calculation does not restrain, then re-write electromagnetic field and temperature field file, iterative analysis, until convergence;

Described method, in step S1, in step S1, sets up power cable electromagnetic field and temperature field physical model based on ANSYS.

When power cable normally runs under power frequency condition, magnetic-thermal coupling model accounting temperature field and current-carrying capacity is adopted to suppose as follows:

1) cable length is very large, is far longer than the diameter of cable, therefore only considering the thermo parameters method of cable radial direction when calculating, carrying out two dimensional surface calculating;

2) impact of space charge and displacement current is ignored;

3) magnetic permeability of cable and earth materials is all linear;

4) only have insulation course between cable conductor and metallic sheath, conductor shield is ignored.

Generally be regarded as stable state for power frequency electromagnetic field, ignore the impact of displacement current, the maxwell equation group of power cable vortex field is:

$\left\{\begin{array}{c}\▿\×H=J_c+J_s\\ \▿\×E=-\frac{\∂B}{\∂t}\\ \▿\·B=0\\ \▿\·D=0\end{array}\right.$

Wherein J _erepresent vortex flow density, J _sexpression source current density.

Under electromagnetic field effect, the macroscopic property of these parameters can be represented by following formula:

$\left\{\begin{array}{c}B=\mathrm{\μ}H\\ J=\mathrm{\γ}E\\ D=\mathrm{\ϵ}E\end{array}\right.$

In formula, μ represents permeability of vacuum, and B is magnetic flux density vector, and H is magnetic intensity vector; J represents current density vectors, and γ represents the conductivity of medium; ε represents the permittivity of insulating medium, and E represents electric field intensity, and D represents electric displacement vector.

Under coulomb specification, the magnetic vector of each Rotating fields of cable is analyzed, vector magnetic potential equation can be obtained.

Cable conductor region,

▽ ²A ₁＝-μ ₀J _s

In formula, J _sthe current density of conductive region, A ₁represent the vector magnetic potential of conductor layer.

Cable insulation layer region,

▽ ²A ₂＝0

Cable metal cover region,

▽ ²A ₃＝-μ ₀J _e

In above formula, J _erepresent metallic sheath vortex flow density, A ₂, A ₃represent insulation course and metallic sheath vector magnetic potential respectively.

Cable jacket region,

▽ ²A ₄＝0

Soil region,

▽ ²A ₅＝0

In formula, A ₄, A ₅represent the vector magnetic potential of oversheath and soil region.

In addition, the continuity equation above the border of each layer of cable and soil is:

$\left\{\begin{array}{c}{A}_i=A_j\\ {\mathrm{\μ}}_i^{-1}\▿A_i={\mathrm{\μ}}_j^{-1}\▿A_j\\ {\mathrm{\μ}}_i^{-1}\▿\×A_i\×n={\mathrm{\μ}}_j^{-1}\▿\×A_j\×n\end{array}\right.$

In formula, i and j represents the numbering of adjacent area.

The eddy current loss computing formula of metal screen layer inside is:

$\left\{\begin{array}{c}{J}_e=-{\mathrm{j\ω\γ}}_3{A}_3\\ P_e={\mathrm{\γ}}_3^{-1}\∫J_e^{2}dV\\ P_e={\mathrm{\γ}}_3^{-1}\Σ\left({\left(J_{e\left(i\right)}\right)}^{2}2{\mathrm{\πr}}_i{S}_i\right)={\mathrm{\γ}}_3^{-1}\Σ{\left({\mathrm{\ω\γ}}_3{A}_{3,i}\right)}^{2}2{\mathrm{\πr}}_i{S}_i)\end{array}\right.$

In formula, Je represents metallic sheath induced current density, and A3 represents the vector magnetic potential of metal screen layer, and Pe is unit length eddy current loss power, and γ 3 is the conductivity of metallic sheath material, and ri represents the distance of each unit to axle center, and Si represents each cellar area.

Because cable is axisymmetric cylindrical shape, its electromagnetic field produced is two dimensional surface field, and therefore calculate with two dimensional field, computing unit selects PLANE53 unit.Setting threephase cable be laid in the infinitely-great soil of scope, be the electromagnetic field physical model of magnetic-thermal coupling field, three cables are positioned at the centre position of model, the left side be A phase, centre be B phase, the right be C phase.The circle surrounding cable is soil, and radius is 2m, and the territory, 4 faces of outermost forms an annulus (external diameter is 4m), is the unlimited far field of model, for solving the far field dissipation issues of electromagnetic field.Apply the identical electric current of size respectively at the core of three cables, phase angle difference 120 °, setting unit degree of freedom is AZVOLT, and coupled voltages degree of freedom.Cable metal sheath is ground connection single-end earthed, and aspergillus ficuum exists, and be arranged to open-circuit condition, the magnetic potential of infinite boundary is set to 0.

The conduction of negligible axial hot-fluid on thermal field, this calculated field is also two dimensional field.From cable more away from, the soil moisture is more unaffected.General distance cable 1.2m place soil be affected hardly, its temperature level and environment temperature basically identical.Therefore the nearest cable 2m of left and right frontier distance is got, the nearest cable 1.2m of lower boundary.The coboundary of model be convection boundary condition, environment temperature is 40 DEG C, and natural convection air coefficient is 6.52W/mK, and lower boundary is arranged forces steady temperature 25 DEG C, and both sides are natural boundary conditions.

Use sense answers heating physical field to carry out Temperature of Power Cables field and current-carrying capacity numerical evaluation, by the cable data that above-mentioned formulae discovery is relevant, environmental parameter can arrange relevant soil conductivity and relative medium parameter according to actual needs, then can set up power cable magnetic-ermal physics model at ANSYS.

Described method, in step S2, sets up power cable physical model according to step 1, in physical model, applies three-phase current, and arranges cable according to actual conditions and apply spacing, obtain the temperature profile of whole domain as calculated afterwards to cable core.

Described method, in step S4, by the analysis result to Temperature of Power Cables and current-carrying capacity, can solve loss and Temperature Distribution that difference lays power cable under spacing, analyze the influence factor of core temperature and calculate maximum carrying capacity.

The present invention is described in further detail below in conjunction with accompanying drawing.

The invention provides the computing method that a kind of power cable based on ANSYS magnetic-thermal coupling field is provided, the method can utilize ANSYS to carry out the calculating of magnetic-thermal coupling field to power cable, each field order desirably can be analyzed one by one, coupling analysis process be using the analysis result of previous field as dynamic changes process to the mode analyzed in a rear field.

Based on computing method for the power cable magnetic-thermal coupling field of ANSYS, mainly comprise following steps:

S1) set up power cable physical phantom, set up electromagnetic field and temperature field physical model;

S2) clear and definite Electromagnetic Calculation parameter, mesh generation and solve type;

S3) write electromagnetic field analysis file, then clear and definite temperature field analysis data, and write temperature field file;

S4) if numerical convergence, then can calculate magnetic field and the thermal field of cable, realize magnetic-Thermal couple analysis; As result of calculation does not restrain, then re-write electromagnetic field and temperature field file, iterative analysis, until convergence;

Described method, in step S1, in step S1, sets up power cable electromagnetic field and temperature field physical model based on ANSYS.

When power cable normally runs under power frequency condition, magnetic-thermal coupling model accounting temperature field and current-carrying capacity is adopted to suppose as follows:

1) cable length is very large, is far longer than the diameter of cable, therefore only considering the thermo parameters method of cable radial direction when calculating, carrying out two dimensional surface calculating;

2) impact of space charge and displacement current is ignored;

3) magnetic permeability of cable and earth materials is all linear;

4) only have insulation course between cable conductor and metallic sheath, conductor shield is ignored.

Generally be regarded as stable state for power frequency electromagnetic field, ignore the impact of displacement current, the maxwell equation group of power cable vortex field is:

$\left\{\begin{array}{c}\▿\×H=J_c+J_s\\ \▿\×E=-\frac{\∂B}{\∂t}\\ \▿\·B=0\\ \▿\·D=0\end{array}\right.$

Wherein J _erepresent vortex flow density, J _sexpression source current density.

Under electromagnetic field effect, the macroscopic property of these parameters can be represented by following formula:

$\left\{\begin{array}{c}B=\mathrm{\μ}H\\ J=\mathrm{\γ}E\\ D=\mathrm{\ϵ}E\end{array}\right.$

In formula, μ represents permeability of vacuum, and B is magnetic flux density vector, and H is magnetic intensity vector; J represents current density vectors, and γ represents the conductivity of medium; ε represents the permittivity of insulating medium, and E represents electric field intensity, and D represents electric displacement vector.

Under coulomb specification, the magnetic vector of each Rotating fields of cable is analyzed, vector magnetic potential equation can be obtained.

Cable conductor region,

▽ ²A ₁＝-μ ₀J _s

In formula, J _sthe current density of conductive region, A ₁represent the vector magnetic potential of conductor layer.

Cable insulation layer region,

▽ ²A ₂＝0

Cable metal cover region,

▽ ²A ₃＝-μ ₀J _e

In above formula, J _erepresent metallic sheath vortex flow density, A ₂, A ₃represent insulation course and metallic sheath vector magnetic potential respectively.

Cable jacket region,

▽ ²A ₄＝0

Soil region,

▽ ²A ₅＝0

In formula, A ₄, A ₅represent the vector magnetic potential of oversheath and soil region.

In addition, the continuity equation above the border of each layer of cable and soil is:

$\left\{\begin{array}{c}{A}_i=A_j\\ {\mathrm{\μ}}_i^{-1}\▿A_i={\mathrm{\μ}}_j^{-1}\▿A_j\\ {\mathrm{\μ}}_i^{-1}\▿\×A_i\×n={\mathrm{\μ}}_j^{-1}\▿\×A_j\×n\end{array}\right.$

In formula, i and j represents the numbering of adjacent area.

The eddy current loss computing formula of metal screen layer inside is:

$\left\{\begin{array}{c}{J}_e=-{\mathrm{j\ω\γ}}_3{A}_3\\ P_e={\mathrm{\γ}}_3^{-1}\∫J_e^{2}dV\\ P_e={\mathrm{\γ}}_3^{-1}\Σ\left({\left(J_{e\left(i\right)}\right)}^{2}2{\mathrm{\πr}}_i{S}_i\right)={\mathrm{\γ}}_3^{-1}\Σ{\left({\mathrm{\ω\γ}}_3{A}_{3,i}\right)}^{2}2{\mathrm{\πr}}_i{S}_i)\end{array}\right.$

In formula, Je represents metallic sheath induced current density, and A3 represents the vector magnetic potential of metal screen layer, Pe is unit length eddy current loss power, and γ 3 is the conductivity of metallic sheath material, and ri represents the distance of each unit to axle center, Si represents each cellar area, and j is imaginary unit.

Because cable is axisymmetric cylindrical shape, its electromagnetic field produced is two dimensional surface field, therefore calculates with two dimensional field.Setting threephase cable be laid in the infinitely-great soil of scope, be the electromagnetic field physical model of magnetic-thermal coupling field, three cables are positioned at the centre position of model, the left side be A phase, centre be B phase, the right be C phase.The circle surrounding cable is soil, and radius is 2m, and the territory, 4 faces of outermost forms an annulus (external diameter is 4m), is the unlimited far field of model, for solving the far field dissipation issues of electromagnetic field.The identical electric current of size is applied respectively, phase angle difference 120 °, and coupled voltages degree of freedom at the core of three cables.Cable metal sheath is ground connection single-end earthed, and aspergillus ficuum exists, and is arranged to open-circuit condition.

The conduction of negligible axial hot-fluid on thermal field, this calculated field is also two dimensional field.From cable more away from, the soil moisture is more unaffected.General distance cable 1.2m place soil be affected hardly, its temperature level and environment temperature basically identical.Therefore the nearest cable 2m of left and right frontier distance is got, the nearest cable 1.2m of lower boundary.The coboundary of model be convection boundary condition, environment temperature is 40 DEG C, and natural convection air coefficient is 6.52W/mK, and lower boundary is arranged forces steady temperature 25 DEG C, and both sides are natural boundary conditions.

Model shown in Fig. 3 has three boundary conditions, is right boundary, lower boundary, coboundary respectively.For lower boundary, soil is buried underground deep, and the soil moisture keeps constant substantially, selects First Boundary Condition.Under general 20m, the soil moisture is 8 DEG C.In computation process, first determine a preliminary current-carrying capacity, according to formulae discovery loss, obtain cable and ambient temperature field distribution thereof.If the maximum temperature of cable conductor lower than 90 DEG C, then increases size of current, re-start calculating.If the conductor maximum temperature of power cable is higher than 90 DEG C, then reduces size of current, recalculate.Electric current when finally can to obtain cable conductor temperature be 90 DEG C, is required current-carrying capacity.

The models show that software the is set up image of cable region, and other region is uniform soil, without the need to providing.Cable data, lay environmental baseline and boundary condition and had above and introduce in detail.Whole model divides in order to many junior units by mesh generation, and for the more uniform region of physical material properties, as soil region, because the equation between grid is identical with parameter, grid comparatively speaking can be larger; And for cable body, the change comparison in difference of material is large, the thickness of different structure layer is also smaller, and mesh generation is smaller, to obtain result more accurately,

Use sense answers heating physical field to carry out Temperature of Power Cables field and current-carrying capacity numerical evaluation, by the cable data that above-mentioned formulae discovery is relevant, environmental parameter can arrange relevant soil conductivity and relative medium parameter according to actual needs, then can set up power cable magnetic-ermal physics model at ANSYS.

Described method, in step S2, sets up power cable physical model according to step 1, in physical model, applies three-phase current, and arranges cable according to actual conditions and apply spacing, obtain the temperature profile of whole domain as calculated afterwards to cable core.

Described method, in step S4, by the analysis result to Temperature of Power Cables and current-carrying capacity, can solve loss and Temperature Distribution that difference lays power cable under spacing, analyze the influence factor of core temperature and calculate maximum carrying capacity.

Concrete implementation step is as follows:

1, utilize ANSYS to set up power cable physical phantom, set up electromagnetic field and temperature field physical model

2, clear and definite Electromagnetic Calculation parameter, mesh generation and solve type;

3, write electromagnetic field analysis file, then clear and definite temperature field analysis data, and write temperature field file;

4, utilize model to carry out magnetic-thermal coupling field to calculate, if numerical convergence, then can calculate magnetic field and the thermal field of cable, realize magnetic-Thermal couple analysis; As result of calculation does not restrain, then re-write electromagnetic field and temperature field file, iterative analysis, until convergence.

Claims (7)

1. computing method for power cable magnetic-thermal coupling field, is characterized in that comprising:

S1) power cable electromagnetic field and temperature field physical model is set up;

S2) set up power cable physical phantom, specify calculating parameter and boundary condition;

S3) corresponding calculating parameter is obtained to power cable measurement;

S4) according to electromagnetic field and temperature field physical phantom and corresponding calculating parameter, the electromagnetic field of power cable and temperature field are solved;

S5) if numerical convergence, then obtain magnetic field and the thermal field of power cable, realize magnetic-Thermal couple analysis; As result of calculation does not restrain, then turn back to step S4 and carry out iterative analysis, until convergence.

2. computing method according to claim 1, is characterized in that, the method that step S1 sets up physical model comprises:

When power cable normally runs under power frequency condition, under coulomb specification, the magnetic vector of each Rotating fields of cable is analyzed, obtains power cable each region vector magnetic potential equation:

Cable conductor region,

${\▿}^2{A}_1=-{\mathrm{\μ}}_0{J}_s$

In above formula, J _sthe current density of conductive region, A ₁represent the vector magnetic potential of conductor layer, μ ₀represent permeability of vacuum;

Cable insulation layer region,

${\▿}^2{A}_2=0$

In above formula, A ₂represent insulation course vector magnetic potential;

Cable metal cover region,

${\▿}^2{A}_3=-{\mathrm{\μ}}_0{J}_e$

In above formula, J _erepresent metallic sheath vortex flow density, A ₃represent insulation course and metallic sheath vector magnetic potential;

Cable jacket region,

${\▿}^2{A}_4=0$

In above formula, A ₄represent oversheath vector magnetic potential;

Soil region,

${\▿}^2{A}_5=0$

In above formula, A ₅represent the vector magnetic potential of soil region;

In addition, the continuity equation above the border of each layer of cable and soil is:

$\left\{\begin{array}{c}{A}_i=A_j\\ {\mathrm{\μ}}_i^{-1}\▿A_i={\mathrm{\μ}}_j^{-1}\▿A_j\\ {\mathrm{\μ}}_i^{-1}\▿\×A_i\×n={\mathrm{\μ}}_j^{-1}\▿\×A_j\×n\end{array}\right.$

In above formula, i and j represents the numbering of adjacent area, i, j value and A before ₁~ A ₅subscript corresponding, n is unit normal vector, μ _i, μ _jrepresent i-th respectively, the magnetic permeability in j region;

The eddy current loss computing formula of metal screen layer inside is:

$\left\{\begin{array}{c}{J}_e=-{\mathrm{j\ω\γ}}_3{A}_3\\ P_e={\mathrm{\γ}}_3^{-1}\∫J_e^{2}dV\\ P_e={\mathrm{\γ}}_3^{-1}\Σ\left({\left(J_{e\left(i\right)}\right)}^{2}2{\mathrm{\πr}}_i{S}_i\right)={\mathrm{\γ}}_3^{-1}\Σ{\left({\mathrm{\ω\γ}}_3{A}_{3,i}\right)}^{2}2{\mathrm{\πr}}_i{S}_i)\end{array}\right.$

In formula, J _erepresent metallic sheath induced current density, A ₃represent the vector magnetic potential of metal screen layer, P _efor unit length eddy current loss power, γ ₃for the conductivity of metallic sheath material, r _irepresent the distance of each unit to axle center, S _irepresent each cellar area.

The temperature field of cable is analyzed by equivalent Re Lufa, and Re Lu and heat flow field, corresponding to the physical quantity in circuit or current field, namely according to the theory of thermal conduction study, calculate the thermal resistance T of cable insulation, inner liner, serving and surrounding media respectively ₁~ T ₄, computing formula is as follows:

$T_1=\frac{{\mathrm{\ρ}}_{T_1}}{2\mathrm{\π}}ln\frac{D_i}{D_c}$

$T_2=\frac{{\mathrm{\ρ}}_{T_2}}{2\mathrm{\π}}ln\frac{D_a}{D_s^{\′}}$

$T_3=\frac{{\mathrm{\ρ}}_{T_3}}{2\mathrm{\π}}ln\frac{D_e}{D_a^{\′}}$

$T_4=\frac{{\mathrm{\ρ}}_{T_4}}{2\mathrm{\π}}ln\frac{4L}{D_e}$

In formula, be respectively the coefficient of heat conductivity of insulation course, inner liner, serving and soil, D _iand D _cbe respectively insulation course internal diameter and external diameter, D _aand D' _sbe respectively inner liner internal diameter and external diameter, D _eand D' _abe respectively serving internal diameter and external diameter, L is the cable laying degree of depth; Cable temperature field is calculated again by Finite Element Method.

3. computing method according to claim 2, it is characterized in that, the method that step S2 sets up cable physical phantom comprises: establish cable to be axisymmetric cylindrical shape, and its electromagnetic field produced is two dimensional surface field, the conduction of thermal field also negligible axial hot-fluid, this calculated field is also two dimensional field; Then set threephase cable be laid in the infinitely-great soil of scope, three cables are positioned at the centre position of model, the left side be A phase, centre be B phase, the right be C phase; The coboundary of model is convection boundary condition, and lower boundary is arranged forces steady temperature, and both sides are natural boundary conditions; The power cable physical phantom of magnetic-thermal coupling field is finally set up according to these settings.

4. method according to claim 3, is characterized in that: the calculating parameter of step S2 comprises the correlation parameters such as the conductivity of cable copper conductor layer, insulation course, semi-conductive non-woven fabric layer, metal sheath layer, PVC external sheath layer and soil, relative dielectric constant, coefficient of heat conductivity, density and normal pressure thermal capacitance.

5. computing method according to claim 3, it is characterized in that, the method that step S4 solves comprises: the magnetic-thermal coupling field physical model utilizing above-mentioned foundation, three-phase current is applied to cable core, setting cable laying spacing, obtains the current-carrying capacity of the Temperature Distribution of whole domain, the loss value of cable and temperature value and cable as calculated afterwards.

6. method according to claim 5, is characterized in that, the method obtaining Temperature Distribution, the loss value of cable and the current-carrying capacity of temperature value and cable specifically comprises: use sense answers heating physical field to carry out Temperature of Power Cables field and current-carrying capacity numerical evaluation; In computation process, first determine a preliminary current-carrying capacity, according to formulae discovery loss, obtain cable and ambient temperature field distribution thereof, if the maximum temperature of cable conductor is lower than 90 DEG C, then increase size of current, re-start calculating; If the conductor maximum temperature of power cable is higher than 90 DEG C, then reduces size of current, recalculate; Finally obtain electric current when cable conductor temperature is 90 DEG C, be required current-carrying capacity; And by the analysis result to Temperature of Power Cables value and current-carrying capacity, solve loss value and Temperature Distribution that difference lays power cable under spacing.

7. method according to claim 1, is characterized in that, the method for step S5 magnetic-Thermal couple analysis comprises: analyze the influence factor of core temperature and calculate maximum carrying capacity.