CN113971355A - Three-dimensional electric field calculation method for live-line operation tower of extra-high voltage direct current line - Google Patents
Three-dimensional electric field calculation method for live-line operation tower of extra-high voltage direct current line Download PDFInfo
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Abstract
The invention discloses a method for calculating a three-dimensional electric field of an extra-high voltage direct current line live-line operation tower, which is parallel to an extra-high voltage alternating current transmission line, and comprises the following steps: determining relevant parameter information of the extra-high voltage alternating current-direct current parallel section power transmission line, and constructing a three-dimensional hybrid electric field calculation model and a finite element human body model according to the relevant parameter information; according to the establishment of a three-dimensional mixed electric field calculation model and a finite element human body model, calculating the electric field intensity of a human body model body surface of a human body model near a pole tower line at each operation position under three working conditions of single-pole electrification, double-pole electrification and power failure maintenance of an extra-high voltage direct current line by using a finite element calculation method, changing the parallel distance between the direct current line and the alternating current line, and obtaining the electric field intensity of the human body model body surface under different parallel distances; and obtaining the current live working electromagnetic shielding protection mode and the design optimization reference of the line according to the influence degree of the three working conditions and different parallel distances of the direct current line on the electric field intensity.
Description
Technical Field
The invention relates to a method for calculating a three-dimensional electric field of an extra-high voltage direct current line live-line operation tower, in particular to a method for calculating a three-dimensional electric field of an extra-high voltage direct current line live-line operation tower considering a parallel alternating current line.
Background
With the western energy strategy of China, the development of energy in western regions such as Xinjiang and Tibet is further enhanced by China, the distance between large energy bases and the load center of the east is more than 2400 kilometers, and the development and application of an extra-high voltage direct-current transmission technology with a higher voltage level are urgently needed, and the +/-1100 kV extra-high voltage direct-current transmission technology has the advantages of long economic transmission distance, strong single-circuit line transmission capacity, low transmission loss, strong large-range resource allocation capacity, remarkable driving effect on the electrical equipment industry and the like.
The operation and maintenance work is an important means for mastering the operation condition of the power grid equipment and timely discovering and treating the defects of the equipment. In view of the core status of the ultra-high voltage power grid in the whole national power grid, the operation and maintenance work of the ultra-high voltage power grid has very important significance for ensuring the safe, stable and reliable operation of the ultra-high voltage power grid and even the whole national power grid. And due to the important position of the extra-high voltage power grid, once the system is put into operation, the system is difficult to overhaul by power failure. Therefore, live working is used as an important technical means for operation and maintenance of the extra-high voltage power grid, and has important significance for ensuring safe, stable and reliable operation of the extra-high voltage power grid.
The plus or minus 1100kV extra-high voltage direct current line live-line work puts higher demands on the protection of the electric field and the current of live-line workers. Especially, in a partial area (such as a Xuan city area in Anhui province), where the line passes through, the distance between a partial section and an AC line section is very close to 28 meters at the nearest position, and the multiple circuits are parallel, so that the electromagnetic environment is complex. In order to ensure the safety of live working, under the typical working conditions of bipolar power failure, unipolar power failure and live working, the electromagnetic environment and safety protection measures for line maintenance are urgently needed to be researched. At present, most of the existing technical methods aim at the live working electric field calculation when an extra-high voltage line is erected independently, and the live working related calculation of a parallel alternating current line is not considered yet. And the prior related technology is mostly used for calculating the electric field of the ground.
Disclosure of Invention
The invention aims to provide a method for calculating a three-dimensional electric field of an extra-high voltage direct current line live-line operation tower, which is a method for calculating a three-dimensional electric field of an extra-high voltage direct current line live-line operation tower considering a parallel alternating current line. And a certain reference basis is provided for the electromagnetic shielding protection mode and how to optimize the live working electromagnetic field environment during the design and construction of the line.
In order to achieve the purpose, the technical scheme of the invention is as follows:
a three-dimensional electric field calculation method for an extra-high voltage direct current line live-line operation tower is used for obtaining a live-line operation electromagnetic shielding protection mode and design optimization reference of a line, and parallel extra-high voltage alternating current transmission lines are arranged beside the extra-high voltage direct current line, and the method comprises the following steps:
a. determining relevant parameter information of the extra-high voltage alternating current-direct current parallel section power transmission line, and constructing a three-dimensional hybrid electric field calculation model and a finite element human body model according to the relevant parameter information;
b. according to the establishment of a three-dimensional mixed electric field calculation model and a finite element human body model, calculating the electric field intensity of a human body model body surface of a human body model near a pole tower line at each operation position under three working conditions of single-pole electrification, double-pole electrification and power failure maintenance of an extra-high voltage direct current line by using a finite element calculation method, changing the parallel distance between the direct current line and the alternating current line, and obtaining the electric field intensity of the human body model body surface under different parallel distances;
c. obtaining the current live working electromagnetic shielding protection mode and the design optimization reference of the line according to the influence degree of the three working conditions and different parallel distances of the direct current line on the electric field intensity;
wherein:
the related information comprises the voltage grade of the alternating current transmission line, the voltage grade of the direct current transmission line, the type and design drawing of a typical tower of the transmission line, the split distance of the transmission line, the split number of the conductor, the radius of the sub-conductor, the phase sequence arrangement, the height of the line from the ground, the parallel distance of the alternating current and direct current lines and the size parameter of the human body model.
The scheme is further as follows: each operation position comprises 5 types, namely: the operating personnel stand upright at the tower body, when the operating personnel are about to contact the line, the operating personnel stand on the power transmission line, the operating personnel stand at the cross arm of the tower and the operating personnel are at the ground wire.
The scheme is further as follows: the different parallel spacings are different spacings in the range of 28m-88 m.
The scheme is further as follows: the method comprises the steps of constructing a three-dimensional mixed electric field calculation model, wherein the three-dimensional mixed electric field calculation model comprises a line arrangement information graph, a human body model located at each position graph and a mixed electric field calculation model which are drawn according to relevant parameter information, and the mixed electric field calculation model comprises a Poisson equation and a charge conservation equation; the Poisson equation and the charge conservation equation are used for solving and calculating electric fields near the line and on the surface of the human body of an operator under three operation conditions of single-pole electrification and power failure maintenance of the direct-current line to obtain the mixed electric field intensity when extra-high voltage alternating current and direct current are parallel, and changing the parallel distance of the line to obtain the electric field intensity of the body model surface of the human body under different parallel distances; the poisson equation and the charge conservation equation are respectively as follows:
poisson equation:
conservation of charge equation:
the parameters are as follows:
is a space potential in (V); rho+And ρ-Respectively positive and negative space charge density (C/m)3)；ε0A value of 8.85X 10 for a vacuum dielectric constant-12F/m; r is the positive and negative ion recombination coefficient, (m)3/s)；K+And K-Is the positive and negative ion mobility, (m)2V · s)); e is the electron charge amount, and the value is 1.6X 10-19C; e is the space electric field intensity (V/m), and the parameters are obtained according to the related parameter information.
The scheme is further as follows: the finite element calculation method specifically comprises the following steps:
1) setting voltage boundary conditions, wherein the AC line and the DC line are operating voltages, and the voltage values of the tower, the ground wire and the ground are zero;
2) setting initial values of the surface charge densities of the circuit and the human body;
3) setting relative dielectric constant and conductivity parameter values of various materials in the calculation model;
4) constructing a control equation to be solved in an ABAQUS or ANSYS or MSC finite element calculation software multi-physical field module;
5) and (3) carrying out iterative solution coupling calculation by utilizing COMSOL Multiphysics finite element simulation software to determine the body surface electric field intensity of the direct-current line under different working conditions and different parallel distances.
The scheme is further as follows: the step of determining the body surface electric field intensity of the direct current line under different working conditions and different parallel distances by carrying out iterative solution coupling calculation is as follows:
1) solving a Poisson (Poisson) equation by using a finite element method, and solving a charge conservation equation by using a finite volume method; obtaining the initial distribution of the space electric field and the electric potential;
2) adjusting an initial value of the surface charge density of the wire, obtaining a space charge value through calculation, judging whether a convergence condition is met, and updating and distributing the surface charge density of the wire if the convergence condition is not met;
the updated charge values are:
where ρ isn+1Is the charge density value of one point in the space after the n +1 th iteration, Es is the surface electric field intensity of the wire, Ec is the corona field intensity of the wire, and can be calculated by a picogram formula;
3) if the charge density is converged, carrying out the next step, substituting the calculated space charge density of each node into the charge density for solving the Poisson equation so as to solve the potential and the electric field of each node, and solving a current continuity equation by taking the electric field as a condition so as to solve a new space charge density;
4) and (3) performing iterative calculation in a circulating manner until the electric field on the surface of the wire and the space charge density of the node satisfy the formula to judge whether the stable convergence condition is satisfied:
in the formula EmaxIs the maximum electric field strength, rho, of the wire surfacen(i) And ρn1(i) Space charge density, E, obtained for the nth and (n-1) th iterations of the ith node, respectivelyon＝EcAnd deltaEAnd deltaρRespectively, are relative error conditions for determining convergence.
The scheme is further as follows: in the step c, after the parallel distance between the direct current line and the alternating current line is repeatedly changed in the step b, the body model surface electric field strength of the body model near the pole tower line at each operation position under the three working conditions of single-pole electrification, double-pole electrification and power failure maintenance of the extra-high voltage direct current line is repeatedly calculated by using a finite element calculation method, and the calculation results of the electric field strength of the transmission line, the insulator, the ground wire and the body surface electric field strength of the operation body model under different conditions are obtained from the body model body surface electric field strengths under different parallel distances, so that the influence degrees of different variables on the electric field strength are obtained.
The invention has the beneficial effects that: the electric field intensity near the power transmission line and the human body surface electric field intensity of an operator at five typical operation positions of line maintenance live working are calculated, and the influence of the parallel distance of the alternating current and direct current lines on the electric field level is analyzed, so that a certain reference basis is provided for the electromagnetic shielding protection mode and how to optimize the live working electromagnetic field environment during line design and construction.
The invention is described in detail below with reference to the figures and examples.
Drawings
FIG. 1 is a diagram of the overall process of the calculation method of the present invention;
FIG. 2 is a layout diagram of the line arrangement of the + -1100 kV line and the AC coupling section according to the present invention;
FIG. 3 is a schematic diagram of five exemplary operating position distributions for hot-line operation according to the present invention;
FIG. 4 is a flow chart of finite element method electric field calculation according to the present invention;
FIG. 5 is a schematic diagram of a first order tetrahedral cell of the present invention.
Detailed Description
A method for calculating a three-dimensional electric field of an extra-high voltage direct current line live-line operation tower is used for obtaining a live-line operation electromagnetic shielding protection mode and a design optimization reference of a line, as shown in figure 2, a parallel ultra-high voltage alternating current transmission line 1100kV is arranged beside a +/-1100 kV extra-high voltage direct current line, as shown in figure 1, and the calculating method comprises the following steps:
a. determining relevant parameter information of the extra-high voltage alternating current-direct current parallel section power transmission line, and constructing a three-dimensional hybrid electric field calculation model and a finite element human body model according to the relevant parameter information;
b. according to the establishment of a three-dimensional mixed electric field calculation model and a finite element human body model, calculating the electric field intensity of a human body model body surface of a human body model near a pole tower line at each operation position under three working conditions of single-pole electrification, double-pole electrification and power failure maintenance of an extra-high voltage direct current line by using a finite element calculation method, changing the parallel distance between the direct current line and the alternating current line, and obtaining the electric field intensity of the human body model body surface under different parallel distances;
c. obtaining the current live working electromagnetic shielding protection mode and the design optimization reference of the line according to the influence degree of the three working conditions and different parallel distances of the direct current line on the electric field intensity;
wherein:
the related information comprises the voltage grade of the alternating current transmission line, the voltage grade of the direct current transmission line, the type and design drawing of a typical tower of the transmission line, the split distance of the transmission line, the split number of the conductor, the radius of the sub-conductor, the phase sequence arrangement, the height of the line from the ground, the parallel distance of the alternating current and direct current lines and the size parameter of the human body model.
Wherein: each operation position comprises 5 types, namely: as shown in fig. 3, the operator stands at position 1 at the tower, position 2 when the operator is about to touch the line, position 3 when the operator stands on the transmission line, position 4 when the operator stands at the tower cross arm, and position 5 when the operator is at the ground.
Wherein: the different parallel spacings are different spacings in the range of 28m-88 m.
In the examples: the construction of the three-dimensional hybrid electric field calculation model comprises drawing a line arrangement information graph, a human body model position graph and a hybrid electric field calculation model shown in figure 2 according to the related parameter information, wherein the hybrid electric field calculation model is a poisson equation and a charge conservation equation; the Poisson equation and the charge conservation equation are used for solving and calculating electric fields near the line and on the surface of the human body of an operator under three operation conditions of single-pole electrification and power failure maintenance of the direct-current line to obtain the mixed electric field intensity when extra-high voltage alternating current and direct current are parallel, and changing the parallel distance of the line to obtain the electric field intensity of the body model surface of the human body under different parallel distances; the poisson equation and the charge conservation equation are respectively as follows:
poisson equation:
conservation of charge equation:
the parameters are as follows:
is a space potential in (V); rho+And ρ-Respectively positive and negative space charge density (C/m)3)；ε0Is a vacuum dielectric mediumNumber, number 8.85X 10-12F/m; r is the positive and negative ion recombination coefficient, (m)3/s)；K+And K-Is the positive and negative ion mobility, (m)2V · s)); e is the electron charge amount, and the value is 1.6X 10-19C; e is the space electric field intensity (V/m), and the parameters are obtained according to the related parameter information.
In the examples: the finite element calculation method specifically comprises the following steps:
1) setting voltage boundary conditions, wherein the AC line and the DC line are operating voltages, and the voltage values of the tower, the ground wire and the ground are zero;
2) setting initial values of the surface charge densities of the circuit and the human body;
3) setting relative dielectric constant and conductivity parameter values of various materials in the calculation model;
4) constructing a control equation to be solved in an ABAQUS or ANSYS or MSC finite element calculation software multi-physical field module;
5) and (3) carrying out iterative solution coupling calculation by utilizing COMSOL Multiphysics finite element simulation software to determine the body surface electric field intensity of the direct-current line under different working conditions and different parallel distances.
Wherein: as shown in fig. 4, the step of determining the body surface electric field intensity of the direct current line under different working conditions and different parallel distances by performing iterative solution coupling calculation includes:
1) solving a Poisson (Poisson) equation by using a finite element method, and solving a charge conservation equation by using a finite volume method; obtaining the initial distribution of the space electric field and the electric potential;
2) adjusting an initial value of the surface charge density of the wire, obtaining a space charge value through calculation, judging whether a convergence condition is met, and updating and distributing the surface charge density of the wire if the convergence condition is not met;
the updated charge values are:
where ρ isn+1Is the charge at a point in space after the (n + 1) th iterationThe density value Es is the surface electric field intensity of the lead, Ec is the corona onset field intensity of the lead, and can be calculated by a picogram formula;
3) if the charge density is converged, carrying out the next step, substituting the calculated space charge density of each node into the charge density for solving the Poisson equation so as to solve the potential and the electric field of each node, and solving a current continuity equation by taking the electric field as a condition so as to solve a new space charge density;
4) and (3) performing iterative calculation in a circulating manner until the electric field on the surface of the wire and the space charge density of the node satisfy the formula to judge whether the stable convergence condition is satisfied:
in the formula EmaxIs the maximum electric field strength, rho, of the wire surfacen(i) And ρn-1(i) Space charge density, E, obtained for the nth and (n-1) th iterations of the ith node, respectivelyon＝EcAnd deltaEAnd deltaρRespectively, are relative error conditions for determining convergence.
In the examples: in the step c, after the parallel distance between the direct current line and the alternating current line is repeatedly changed in the step b, the body model surface electric field strength of the body model near the pole tower line at each operation position under the three working conditions of single-pole electrification, double-pole electrification and power failure maintenance of the extra-high voltage direct current line is repeatedly calculated by using a finite element calculation method, and the calculation results of the electric field strength of the transmission line, the insulator, the ground wire and the body surface electric field strength of the operation body model under different conditions are obtained from the body model body surface electric field strengths under different parallel distances, so that the influence degrees of different variables on the electric field strength are obtained.
The following is a more detailed description of the above method further taken in conjunction with the accompanying drawings:
FIG. 1 illustrates an overall computational process diagram:
the method comprises the steps of determining relevant parameter information of a high-voltage alternating current-direct current parallel section power transmission line, and constructing a three-dimensional finite element electric field calculation model according to the relevant parameter information, wherein the line arrangement information is shown in figure 2, and the unit of interval numbers in the figure is m.
The specific process comprises the steps of determining the voltage grade of the alternating-current transmission line, the voltage grade of the direct-current transmission line, the type and design drawing of a typical tower of the transmission line, the splitting distance of the transmission line, the splitting number of the conducting wire, the radius of the sub-conducting wire, the phase sequence arrangement, the line height from the ground, the parallel distance of the alternating-current and direct-current lines, the size parameter of a human body model and the like.
Secondly, as shown in fig. 3, aiming at the distance between the corresponding alternating current line and the corresponding direct current line, a finite element method is adopted to solve and calculate electric fields near the line and on the human body surface of an operator under three operation conditions of direct current line list, bipolar electrification and power failure maintenance at five typical operation positions during live working, so as to obtain the mixed electric field intensity when high voltage alternating current and direct current are parallel, and the parallel line distance of the line is changed to obtain the electric field level of the line under different parallel distances.
The method comprises the specific process that the finite element method belongs to the content of a numerical calculation method, wherein the calculation specifically applies an iterative solution based on radial basis interpolation, and finite element calculation software is required to be adopted. The change of the parallel distance of the lines is required to be searched between 28m and 88m within the range of data parameters provided by the relevant line construction section.
The main calculation is as follows:
i, calculating a control equation by using an electric field of the alternating current-direct current parallel line:
under consideration of the influence of the alternating current: the variation factor t becomes when the control equation is added:
poisson equation:
conservation of charge equation:
wherein
Is a space potential in (V); rho+And ρ-Respectively positive and negative space charge density (C/m)3)；ε0A value of 8.85X 10 for a vacuum dielectric constant-12F/m; r is the recombination coefficient (m) of positive and negative ions3/s)；K+And K-Is the positive and negative ion mobility (m)2V · s)); e is the electron charge amount, and the value is 1.6X 10-19C; e is the spatial electric field strength (V/m).
II, basic assumption of electric field calculation of AC/DC parallel line
As can be seen from the above mathematical equation of electric field calculation, the electrostatic field and the space charge are coupled with each other, so some reasonable assumptions must be introduced to decouple and calculate them. The basic assumptions adopted by the present embodiment are:
(1) neglecting the sag of the line, and adopting a straight wire model for calculation.
(2) Neglecting the diffusion effect of positive and negative charges, the positive and negative ion mobility is constant. Space charge is diffused around the dc transmission line, but has much smaller scale and influence than directional motion under the action of electric force, so its diffusion effect can be disregarded.
(3) Because of the extremely high and strong electric field in the vicinity of the line, the electric charges migrate rapidly under the influence of the electric field, so that the charge accumulation in the region very close to the line is neglected.
(4) Neglecting the thickness of the corona layer around the wire; after the high-voltage direct-current transmission line operates, the space around the positive and negative leads is filled with charges with two polarities, and the thickness of the ionized layer around the leads can be ignored because the thickness of the ionized layer and the radius of the leads are in the same order of magnitude and are far smaller than the interelectrode distance and the ground height of the leads.
III, boundary condition of mixed ion flow field of AC/DC parallel line
The boundary conditions in the electric field calculation mathematical model of the power transmission line are as follows:
(1) the surface voltage of the wire is the operating voltage:
d, direct current: u ± 1100kV, ac: u shape2Three-phase ac instantaneous expression (4)
(2) The ground and ground potentials are zero:
(3) artificial boundary:
on the basis of ensuring the calculation precision and the calculation efficiency, the artificial boundary is added, an infinite element calculation domain is arranged outside the artificial boundary, and the artificial boundary does not need to be added with a nominal boundary condition.
IV, finite element calculation:
as shown in fig. 4, a three-dimensional finite element calculation model is established based on the above control equation and the boundary conditions. Through the above basic assumptions, iterative solution can be performed on the electric field intensity near the tower and on the body surface of the operator, and referring to fig. 4, the solution process can be divided into the following steps:
1) solving a Poisson (Poisson) equation by using a finite element method and a charge conservation equation by using a finite volume method in combination with finite element calculation software; the initial distribution of the spatial electric field and potential is obtained.
2) And adjusting the initial value of the surface charge density of the wire, obtaining a space charge value through calculation, judging whether a convergence condition is met, and updating and distributing the surface charge density of the wire if the convergence condition is not met. The updated charge values are:
where ρ isn+1Is the charge density value, E, of a point in space after the (n + 1) th iterationsIs the electric field intensity on the surface of the wire, EcThe wire corona field strength can be calculated by a picogram formula.
3) And if the charge density is converged, carrying out the next step, substituting the calculated space charge density of each node into the charge density for solving the Poisson equation so as to solve the potential and the electric field of each node, and solving a current continuity equation by taking the electric field as a condition so as to solve the new space charge density.
4) And (3) performing iterative calculation in a circulating manner until the electric field on the surface of the wire and the space charge density of the node satisfy the formula to judge whether the stable convergence condition is satisfied:
in the formula EmaxIs the maximum electric field strength, rho, of the wire surfacen1(i) And ρn-1(i) The space charge density obtained by the nth iteration and the (n-1) th iteration of the ith node are respectively obtained. Eon＝EcAnd deltaEAnd deltaρRespectively, are relative error conditions for determining convergence.
The problem of electric field generated by three-dimensional space charge can be generally attributed to the following potential margin problem:
wherein omega is a space electric field calculation area,
the boundaries are calculated manually. For some arbitrary tetrahedral cell in the region Ω, the unknown function
Available at the unit node
The value is expressed as the coordinates of four nodes are (x) respectivelyi,yi),(xj,yj),(xm,ym),(xl,yl) The known potential value is
After the interpolation formula on each cell is obtained, the local coefficient matrix of each cell can be obtained
[K]：
Carrying out equivalent transformation on the Poisson equation by a variational principle:
since [ K ] is a symmetric matrix, so
Namely the potential satisfying the above formula
Is also a generalized solution of poisson's equation. For the right-hand vector [ f ] in equation (2.35)]It is equal to:
[f]＝[P][ρ] (12)
wherein [ P]For the elementary tetrahedral parameter synthesis matrix, [ rho ]]＝(ρ1ρ2ρ3…ρn)TIs a matrix of charge densities at points in space. To give out [ P]The potential values of the respective nodes are obtained.
The computational idea of the finite volume method is that the charge density of each node depends only on the cell above its velocity, which is the basic idea of the up-flow finite element method. If the charge density of node ilm is known to solve for the charge density of node j, as in the tetrahedron of FIG. 5, it must be determined whether the tetrahedron ijlm constitutes an upstream element of node j as shown in FIG. 5.
After the upstream node is determined, the nonlinear equation describing the space charge can be converted into a problem for solving a linear equation of two.
If the reverse extension line of the charge velocity vector at the node j passes through the tetrahedral unit ijlm, that is, the velocity vector of the charge density at the node j satisfies the following relationship, the tetrahedral unit is the upstream element of the node j, and the corresponding mathematical description is as follows:
bkVx+ckVy+dkVz≤0(k＝i,l,m) (13)
wherein Vx、Vy、VzThree coordinate components of the charge velocity vector at j.
The combined charge conservation equation yields:
when solving the charge conservation equation, interpolation of charge density is required. Similar to the potential interpolation method in the previous section, the interpolated charge density within triangle ijm can be expressed as:
ρ(x,y)＝Niρi+Njρj+Nmρm＝[N][ρ] (18)
the partial derivative of the above equation with respect to coordinates can be expressed as:
the following transformation forms can be obtained in combination:
A-ρi-2+B-ρi-+C-＝0 (21)
wherein A is-、B-、C-All of which are quadratic polynomials about V, rho, Delta, solving a quadratic equation of unity, each equation giving two solutions, the larger of which is taken as rhoiThe value of (c). It can be shown that for the upstream element the larger of the two solutions is always less than or equal to pjAnd ρmThis coincides with the physical fact that the space charge density at the point below the velocity is always less than the space charge density at the point above the velocity, ensuring convergence of the knowledge.
And thirdly, changing different operation conditions of five typical operation positions of live working and the parallel distance between the alternating current line and the +/-1100 kV direct current line, and acquiring the electric field calculation level under different conditions to make reference for electromagnetic shielding protection.
The method comprises the specific process that in solving operation of electric fields near the line and on the surface of the human body of an operator under three operation conditions of direct current line single, bipolar electrification and power failure maintenance at five typical operation positions, the bipolar electrification and power failure maintenance conditions and the parallel line spacing are changed, a finite element method is repeatedly applied to calculate a mixed electric field, calculation results of electric field intensities of the transmission line, an insulator, a ground wire and the like and the body surface of the operator under different conditions are obtained, and the influence degree of different variables on the electric field level is obtained.
According to the method for calculating the three-dimensional electric field of the live-line operation tower of the extra-high voltage direct current line, the electric field intensity near the power transmission line and the electric field intensity on the human body surface of an operator at five typical operation positions of line maintenance live-line operation is calculated, and the influence of the parallel distance of the alternating current line and the direct current line on the electric field level is analyzed, so that a certain reference basis is provided for the electromagnetic shielding protection mode and how to optimize the live-line operation electromagnetic field environment during line design and construction.
Claims (7)
1. A three-dimensional electric field calculation method for an extra-high voltage direct current line live-line operation tower is used for obtaining a live-line operation electromagnetic shielding protection mode and design optimization reference of a line, and parallel extra-high voltage alternating current transmission lines are arranged beside the extra-high voltage direct current line, and is characterized by comprising the following steps:
a. determining relevant parameter information of the extra-high voltage alternating current-direct current parallel section power transmission line, and constructing a three-dimensional hybrid electric field calculation model and a finite element human body model according to the relevant parameter information;
b. according to the establishment of a three-dimensional mixed electric field calculation model and a finite element human body model, calculating the electric field intensity of a human body model body surface of a human body model near a pole tower line at each operation position under three working conditions of single-pole electrification, double-pole electrification and power failure maintenance of an extra-high voltage direct current line by using a finite element calculation method, changing the parallel distance between the direct current line and the alternating current line, and obtaining the electric field intensity of the human body model body surface under different parallel distances;
c. obtaining the current live working electromagnetic shielding protection mode and the design optimization reference of the line according to the influence degree of the three working conditions and different parallel distances of the direct current line on the electric field intensity;
wherein:
the related information comprises the voltage grade of the alternating current transmission line, the voltage grade of the direct current transmission line, the type and design drawing of a typical tower of the transmission line, the split distance of the transmission line, the split number of the conductor, the radius of the sub-conductor, the phase sequence arrangement, the height of the line from the ground, the parallel distance of the alternating current and direct current lines and the size parameter of the human body model.
2. The method for calculating the three-dimensional electric field of the extra-high voltage direct current line live-wire operation tower according to claim 1, wherein each operation position comprises 5 types, namely: the operating personnel stand upright at the tower body, when the operating personnel are about to contact the line, the operating personnel stand on the power transmission line, the operating personnel stand at the cross arm of the tower and the operating personnel are at the ground wire.
3. The method for calculating the three-dimensional electric field of the extra-high voltage direct current line live working tower according to claim 1, wherein the different parallel distances are different distances within a range of 28m to 88 m.
4. The method for calculating the three-dimensional electric field of the extra-high voltage direct current line live-wire work tower according to claim 1, wherein the step of constructing the three-dimensional mixed electric field calculation model comprises a line arrangement information graph, a human body model located at each position graph and a mixed electric field calculation model which are drawn according to the related parameter information, wherein the mixed electric field calculation model is a Poisson equation and a charge conservation equation; the Poisson equation and the charge conservation equation are used for solving and calculating electric fields near the line and on the surface of the human body of an operator under three operation conditions of single-pole electrification and power failure maintenance of the direct-current line to obtain the mixed electric field intensity when extra-high voltage alternating current and direct current are parallel, and changing the parallel distance of the line to obtain the electric field intensity of the body model surface of the human body under different parallel distances; the poisson equation and the charge conservation equation are respectively as follows:
poisson equation:
conservation of charge equation:
the parameters are as follows:
is a space potential in (V); rho+And ρ-Respectively positive and negative space charge density (C/m)3)；ε0A value of 8.85X 10 for a vacuum dielectric constant-12F/m; r is the positive and negative ion recombination coefficient, (m)3/s)；K+And K-Is the positive and negative ion mobility, (m)2V · s)); e is the electron charge amount, and the value is 1.6X 10-19C; e is the space electric field intensity (V/m), and the parameters are obtained according to the related parameter information.
5. The method for calculating the three-dimensional electric field of the extra-high voltage direct current line live-wire operation tower according to claim 1, wherein the finite element calculation method specifically comprises the following steps:
1) setting voltage boundary conditions, wherein the AC line and the DC line are operating voltages, and the voltage values of the tower, the ground wire and the ground are zero;
2) setting initial values of the surface charge densities of the circuit and the human body;
3) setting relative dielectric constant and conductivity parameter values of various materials in the calculation model;
4) constructing a control equation to be solved in an ABAQUS or ANSYS or MSC finite element calculation software multi-physical field module;
5) and (3) carrying out iterative solution coupling calculation by utilizing COMSOL Multiphysics finite element simulation software to determine the body surface electric field intensity of the direct-current line under different working conditions and different parallel distances.
6. The method for calculating the three-dimensional electric field of the live-wire operation tower of the extra-high voltage direct current line according to claim 5, wherein the step of determining the body surface electric field intensity of the direct current line under different working conditions and different parallel distances by performing iterative solution coupling calculation comprises the following steps of:
1) solving a Poisson (Poisson) equation by using a finite element method, and solving a charge conservation equation by using a finite volume method; obtaining the initial distribution of the space electric field and the electric potential;
2) adjusting an initial value of the surface charge density of the wire, obtaining a space charge value through calculation, judging whether a convergence condition is met, and updating and distributing the surface charge density of the wire if the convergence condition is not met;
the updated charge values are:
where ρ isn-1Is the charge density value of one point in the space after the n +1 th iteration, Es is the surface electric field intensity of the wire, Ec is the corona field intensity of the wire, and can be calculated by a picogram formula;
3) if the charge density is converged, carrying out the next step, substituting the calculated space charge density of each node into the charge density for solving the Poisson equation so as to solve the potential and the electric field of each node, and solving a current continuity equation by taking the electric field as a condition so as to solve a new space charge density;
4) and (3) performing iterative calculation in a circulating manner until the electric field on the surface of the wire and the space charge density of the node satisfy the formula to judge whether the stable convergence condition is satisfied:
in the formula EmaxIs the maximum electric field strength, rho, of the wire surfacen(i) And ρn-1(i) Space charge density, E, obtained for the nth and (n-1) th iterations of the ith node, respectivelyon＝EcAnd deltaEAnd deltaρRespectively, are relative error conditions for determining convergence.
7. The method according to claim 1, wherein the three operating conditions of the extra-high voltage direct current line live working tower and the influence degrees of different parallel distances on the electric field strength in the step c are obtained by repeatedly calculating the electric field strength of the human body model body table of the extra-high voltage direct current line at each operating position of the human body model near the tower line under the three operating conditions of single-pole live working, bipolar live working and power failure maintenance by using a finite element calculation method after repeatedly changing the parallel distance between the direct current line and the alternating current line, and obtaining the calculation results of the electric field strength of the transmission line, the insulator, the ground wire and the operating human body model body table under different conditions from the electric field strength of the human body model body table under different parallel distances to obtain the influence degrees of different variables on the electric field strength.
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