CN113971355B - Three-dimensional electric field calculation method for pole tower of live working of extra-high voltage direct current line - Google Patents
Three-dimensional electric field calculation method for pole tower of live working of extra-high voltage direct current line Download PDFInfo
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Abstract
The invention discloses a three-dimensional electric field calculation method of an extra-high voltage direct current line live working tower, which is parallel to an extra-high voltage alternating current transmission line, and comprises the following steps: determining relevant parameter information of the ultra-high voltage alternating current/direct current parallel section power transmission line, and constructing a three-dimensional mixed electric field calculation model and a finite element human body model according to the relevant parameter information; according to the three-dimensional mixed electric field calculation model and the finite element human body model, calculating the human body model body surface electric field intensity of the ultra-high voltage direct current line at each operation position of the human body model near the pole tower line under three working conditions of single-pole, bipolar electrification and power failure maintenance by using a finite element calculation method, changing the parallel interval between the direct current line and the alternating current line, and obtaining the human body model body surface electric field intensity under different parallel intervals; and obtaining the current live working electromagnetic shielding protection mode and the design optimization reference of the line from the three working conditions of the direct current line and the influence degree of different parallel intervals on the electric field intensity.
Description
Technical Field
The invention relates to a three-dimensional electric field calculation method for an extra-high voltage direct current line live working tower, in particular to a three-dimensional electric field calculation method for an extra-high voltage direct current line live working tower considering a parallel alternating current line.
Background
With the strategic and western shift of energy resources in China, the development force of the China on energy resources in western areas such as Xinjiang, tibet and the like is further increased, the distance between the large-scale energy resource bases and the middle east load center exceeds 2400 km, the ultra-high voltage direct current transmission technology with higher voltage level is urgently required to be developed and applied, and the + -1100 kV ultra-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-scale resource allocation capacity, obvious driving effect on electrician equipment industry and the like.
The operation and maintenance work is an important means for grasping the operation condition of the power grid equipment and timely finding and processing the defects of the equipment. In view of the fact that the extra-high voltage power grid is in the core position in the whole national power grid, operation and maintenance work of the extra-high voltage power grid has very important significance for guaranteeing safe, stable and reliable operation of the extra-high voltage power grid and even the whole national power grid. And the method is also because of the importance of the extra-high voltage power grid, and the maintenance is difficult to be carried out by power failure once the extra-high voltage power grid is put into operation. Therefore, live working is an important technical means for operation and maintenance of the ultra-high voltage network, and has important significance for ensuring safe, stable and reliable operation of the ultra-high voltage network.
Live working of 1100kV extra-high voltage direct current circuits puts higher demands on protection of electric fields and currents of live working personnel. In particular, the partial area of the line (such as the urban area in the Anhui) is very close to the AC line, the distance between the partial area and the AC line is 28 meters at the nearest place, and the multiple lines 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 of a maintenance line are urgently needed to be researched. The existing technical method is mainly aimed at live working electric field calculation when the extra-high voltage line is singly erected, and live working related calculation of parallel alternating current lines is not considered yet. And the related art is mostly used for calculating the ground electric field.
Disclosure of Invention
The invention aims to provide a three-dimensional electric field calculation method for an extra-high voltage direct current line live working tower, which is a three-dimensional electric field calculation method for an extra-high voltage direct current line live working tower considering a parallel alternating current line. And a certain reference basis is provided for optimizing the electromagnetic field environment of live working when the electromagnetic shielding protection mode and the circuit are designed and built.
In order to achieve the above object, the technical scheme of the present invention is as follows:
The three-dimensional electric field calculation method of the live working pole tower of the extra-high voltage direct current line is used for obtaining an electromagnetic shielding protection mode of live working and design optimization reference of the line, and a parallel extra-high voltage alternating current transmission line is arranged beside the extra-high voltage direct current line, and the method comprises the following steps:
a. determining relevant parameter information of the ultra-high voltage alternating current/direct current parallel section power transmission line, and constructing a three-dimensional mixed electric field calculation model and a finite element human body model according to the relevant parameter information;
b. According to the three-dimensional mixed electric field calculation model and the finite element human body model, calculating the human body model body surface electric field intensity of the ultra-high voltage direct current line at each operation position of the human body model near the pole tower line under three working conditions of single-pole, bipolar electrification and power failure maintenance by using a finite element calculation method, changing the parallel interval between the direct current line and the alternating current line, and obtaining the human body model body surface electric field intensity under different parallel intervals;
c. Obtaining the current live working electromagnetic shielding protection mode and the design optimization reference of the line from the three working conditions of the direct current line and the influence degree of different parallel intervals on the electric field intensity;
wherein:
The related information comprises an alternating current transmission line voltage level, a direct current transmission line voltage level, a transmission line Lu Dian type tower model and a design drawing, a transmission line split distance, a wire split number, a sub-wire radius, a phase sequence arrangement, a line-to-ground height, an alternating current-to-direct current line parallel distance and a human model size parameter.
The scheme is further as follows: each operation position comprises 5 kinds of operation positions, namely: the operators stand at the tower body, when the operators are about to contact the line, the operators stand on the transmission line, the operators stand at the cross arm of the tower and the operators stand at the ground line.
The scheme is further as follows: the different parallel pitches are different pitches in the range of 28m-88 m.
The scheme is further as follows: the three-dimensional mixed electric field calculation model comprises a line arrangement information diagram drawn according to the related parameter information, a human body model positioned at each position diagram and a mixed electric field calculation model, 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 the electric fields near the line and on the surface of the human body of an operator under three operation conditions of single-pole, double-pole electrification and power failure maintenance of the direct-current line to obtain the mixed electric field intensity when the extra-high voltage alternating current and direct current are parallel, and changing the parallel spacing of the line to obtain the electric field intensity of the human body model body surface under different parallel spacing; the poisson equation and the charge conservation equation are respectively:
Poisson equation:
Charge conservation equation:
Wherein the parameters are as follows: The space potential is given by V; ρ + and ρ - are positive and negative space charge densities C/m 3;ε0, respectively, are vacuum dielectric constants, with values of 8.85×10 -12 F/m; r is positive and negative ion composite coefficient m 3/s;K+ and K - is positive and negative ion mobility m 2/(V.s); e is the electron charge quantity, and the value is 1.6X10 -19 C; 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 an alternating current line and a direct current line are running voltages, and the voltage values of a tower, a ground wire and the ground are zero;
2) Setting initial values of the circuit and the surface charge density of the human body;
3) Setting the 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 computing software multi-physical-field module;
5) And carrying out iterative solution coupling calculation by utilizing COMSOL Multiphysics finite element simulation software to determine the body surface electric field strength under different working conditions and different parallel distances of the direct current circuit.
The scheme is further as follows: the step of carrying out iterative solution coupling calculation to determine the body surface electric field strength of the direct current circuit under different working conditions and different parallel distances is as follows:
1) Solving a poisson equation by using a finite element method, and solving a charge conservation equation by using a finite volume method; obtaining initial distribution of a space electric field and electric potential;
2) Adjusting an initial value of the surface charge density of the lead, obtaining a space charge value through calculation, judging whether a convergence condition is met, and if the convergence condition is not met, updating and distributing the surface charge density of the lead;
the updated charge values are:
Wherein ρ n+1 is the charge density value of a point in space after the n+1th iteration, es is the electric field intensity of the surface of the wire, ec is the corona onset field intensity of the wire, and can be calculated by a Peak formula;
3) If the charge density converges, carrying out the next step, bringing the calculated space charge density of each node into the charge density for solving the poisson equation, solving the potential and the electric field of each node, and solving the current continuity equation by taking the electric field as a condition to solve the new space charge density;
4) And (3) carrying out iterative computation in a circulating way until the electric field on the surface of the lead and the space charge density of the node meet the condition of stable convergence:
Wherein E max is the maximum electric field intensity of the wire surface, ρ n (i) and ρ n-1 (i) are the space charge densities obtained by the nth and n-1 iterations of the ith node, E on＝Ec, and delta E and delta ρ are the relative error conditions for judging 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, the electric field intensity of the human body model body surface of the extra-high voltage direct current line, which is positioned at each operation position and is near the pole tower line under the three working conditions of single-pole electrification and bipolar electrification and power failure maintenance, is repeatedly calculated by a finite element calculation method, and the electric field intensity calculation results of the power transmission line, the insulator and the ground wire under different conditions and the electric field intensity of the operation human body model body surface are obtained from the electric field intensity of the human body model body surface under different parallel distances, so that the electric field intensity influence degree of different variables is obtained.
The beneficial effects of the invention are as follows: the electric field intensity near the power transmission line and on the surface of the human body of an operator at five typical working positions of line maintenance and live working is calculated, and meanwhile, the influence of parallel intervals of alternating current and direct current lines on the electric field level is analyzed, so that a certain reference basis is provided for optimizing the electromagnetic field environment of live working in an electromagnetic shielding protection mode and during line design and construction.
The present invention will be described in detail with reference to the accompanying drawings and examples.
Drawings
FIG. 1 is a diagram showing the overall process of the calculation method of the present invention;
FIG. 2 is a layout of the + -1100 kV line and AC coupling section line of the present invention;
FIG. 3 is a distribution of five typical job locations for live jobs according to the present invention;
FIG. 4 is a finite element method electric field flow diagram of the present invention;
FIG. 5 is a schematic diagram of a first order tetrahedral unit according to the present invention.
Detailed Description
The three-dimensional electric field calculation method for the live working pole tower of the extra-high voltage direct current line is used for obtaining a live working electromagnetic shielding protection mode and design optimization reference of the line, as shown in figure 2, 1100kV of a parallel extra-high voltage alternating current transmission line is arranged beside the + -1100 kV extra-high voltage direct current line, as shown in figure 1, and the steps of the calculation method comprise:
a. determining relevant parameter information of the ultra-high voltage alternating current/direct current parallel section power transmission line, and constructing a three-dimensional mixed electric field calculation model and a finite element human body model according to the relevant parameter information;
b. According to the three-dimensional mixed electric field calculation model and the finite element human body model, calculating the human body model body surface electric field intensity of the ultra-high voltage direct current line at each operation position of the human body model near the pole tower line under three working conditions of single-pole, bipolar electrification and power failure maintenance by using a finite element calculation method, changing the parallel interval between the direct current line and the alternating current line, and obtaining the human body model body surface electric field intensity under different parallel intervals;
c. Obtaining the current live working electromagnetic shielding protection mode and the design optimization reference of the line from the three working conditions of the direct current line and the influence degree of different parallel intervals on the electric field intensity;
wherein:
The related information comprises an alternating current transmission line voltage level, a direct current transmission line voltage level, a transmission line Lu Dian type tower model and a design drawing, a transmission line split distance, a wire split number, a sub-wire radius, a phase sequence arrangement, a line-to-ground height, an alternating current-to-direct current line parallel distance and a human model size parameter.
Wherein: each operation position comprises 5 kinds of operation positions, namely: as shown in fig. 3, the operator stands at a position 1 at the tower body, a position 2 when the operator is about to contact the line, a position 3 when the operator stands on the power transmission line, a position 4 when the operator stands on the tower cross arm, and a position 5 when the operator stands on the ground line.
Wherein: the different parallel pitches are different pitches in the range of 28m-88 m.
In the examples: the step of constructing a three-dimensional mixed electric field calculation model comprises the steps of drawing a circuit arrangement information diagram shown in figure 2, a human body model positioned in each position diagram and a mixed electric field calculation model 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 the electric fields near the line and on the surface of the human body of an operator under three operation conditions of single-pole, double-pole electrification and power failure maintenance of the direct-current line to obtain the mixed electric field intensity when the extra-high voltage alternating current and direct current are parallel, and changing the parallel spacing of the line to obtain the electric field intensity of the human body model body surface under different parallel spacing; the poisson equation and the charge conservation equation are respectively:
Poisson equation:
Charge conservation equation:
Wherein the parameters are as follows: The space potential is given by V; ρ + and ρ - are positive and negative space charge densities C/m 3;ε0, respectively, are vacuum dielectric constants, with values of 8.85×10 -12 F/m; r is positive and negative ion composite coefficient, m 3/s;K+ and K - are positive and negative ion mobility m 2/(V.s); e is the electron charge quantity, and the value is 1.6X10 -19 C; 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 an alternating current line and a direct current line are running voltages, and the voltage values of a tower, a ground wire and the ground are zero;
2) Setting initial values of the circuit and the surface charge density of the human body;
3) Setting the 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 computing software multi-physical-field module;
5) And carrying out iterative solution coupling calculation by utilizing COMSOL Multiphysics finite element simulation software to determine the body surface electric field strength under different working conditions and different parallel distances of the direct current circuit.
Wherein: as shown in fig. 4, the step of performing iterative solution coupling calculation to determine body surface electric field strengths of the direct current circuit under different working conditions and different parallel distances is as follows:
1) A deberthing pine (Poisson) equation is solved by a finite element method, and a charge conservation equation is solved by a finite volume method; obtaining initial distribution of a space electric field and electric potential;
2) Adjusting an initial value of the surface charge density of the lead, obtaining a space charge value through calculation, judging whether a convergence condition is met, and if the convergence condition is not met, updating and distributing the surface charge density of the lead;
the updated charge values are:
Wherein ρ n+1 is the charge density value of a point in space after the n+1th iteration, es is the electric field intensity of the surface of the wire, ec is the corona onset field intensity of the wire, and can be calculated by a Peak formula;
3) If the charge density converges, carrying out the next step, bringing the calculated space charge density of each node into the charge density for solving the poisson equation, solving the potential and the electric field of each node, and solving the current continuity equation by taking the electric field as a condition to solve the new space charge density;
4) And (3) carrying out iterative computation in a circulating way until the electric field on the surface of the lead and the space charge density of the node meet the condition of stable convergence:
Wherein E max is the maximum electric field intensity of the wire surface, ρ n (i) and ρ n-1 (i) are the space charge densities obtained by the nth and n-1 iterations of the ith node, E on＝Ec, and delta E and delta ρ are the relative error conditions for judging 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, the electric field intensity of the human body model body surface of the extra-high voltage direct current line, which is positioned at each operation position and is near the pole tower line under the three working conditions of single-pole electrification and bipolar electrification and power failure maintenance, is repeatedly calculated by a finite element calculation method, and the electric field intensity calculation results of the power transmission line, the insulator and the ground wire under different conditions and the electric field intensity of the operation human body model body surface are obtained from the electric field intensity of the human body model body surface under different parallel distances, so that the electric field intensity influence degree of different variables is obtained.
The following is a more detailed description of the above method, further in connection with the accompanying drawings:
FIG. 1 illustrates a global calculation process diagram:
1. And determining relevant parameter information of the 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 fig. 2, and the unit of interval numbers in the diagram is m.
The method comprises the steps of determining voltage levels of an alternating current transmission line, voltage levels of a direct current transmission line, model and design drawing of a transmission line Lu Dian type tower, split intervals of the transmission line, split numbers of the transmission line, radius of sub-wires, phase sequence arrangement, line height from the ground, parallel intervals of the alternating current and direct current lines, size parameters of a human body model and the like.
2. As shown in fig. 3, for the distance between the corresponding ac line and dc line, a finite element method is used to solve and calculate the electric fields near the line and on the surface of the human body of the operator under three operation conditions of single-pole, double-pole live and power-off maintenance of the dc line at five typical operation positions, so as to obtain the mixed electric field intensity when the ac and dc lines are parallel, change the parallel distance of the lines, and obtain the electric field level of the lines at different parallel distances.
The method comprises the specific process that the finite element method belongs to the content of a numerical value calculation method, wherein the calculation specifically applies an iterative solution based on radial basis interpolation, and finite element calculation software is needed. The changing of the line parallel pitch is required to be found between 28m and 88m within the data parameter range provided by the relevant line construction section.
The main calculation is as follows:
I, calculating a control equation of an alternating current-direct current parallel line electric field:
under consideration of the influence of communication: adding a time-varying factor t into a control equation to obtain:
Poisson equation:
Charge conservation equation:
Wherein the method comprises the steps of The space potential is given by V; ρ + and ρ - are positive and negative space charge densities C/m 3;ε0, respectively, are vacuum dielectric constants, with values of 8.85×10 -12 F/m; r is positive and negative ion composite coefficient m 3/s;K+ and K - is positive and negative ion mobility m 2/(V.s); e is the electron charge quantity, and the value is 1.6X10 -19 C; e is the spatial electric field strength V/m.
II, basic assumption of electric field calculation of AC/DC parallel lines
From the mathematical equation of the electric field calculation above, it can be seen that the electrostatic field and the space charge are coupled to each other, so that reasonable assumptions must be introduced to decouple and calculate them. The basic assumption adopted in this embodiment is that:
(1) Neglecting sag of the line, and calculating by adopting a straight wire model.
(2) Neglecting the diffusion of positive and negative charges, the mobility of positive and negative ions is constant. Space charges are spread around the dc transmission line but are much smaller in scale and influence than directional motion under the influence of electric field forces, so their spreading effect can be disregarded.
(3) Because of the extremely high strong electric field in the vicinity of the line, the charge migrates very rapidly under the force of the electric field, and charge accumulation in the very close vicinity of the line is therefore ignored.
(4) Neglecting the thickness of the corona layer around the wire; after the high-voltage direct-current transmission line runs, the space around the positive and negative electrode wires is filled with charges of two polarities, and the thickness of the ionized layer is in the same order of magnitude as the radius of the wires and is far smaller than the interelectrode distance and the height to the ground of the wires, so that the thickness of the ionized layer around the wires is negligible.
III, boundary condition of mixed ion flow field of AC/DC parallel line
Boundary conditions in the electric field calculation mathematical model of the power transmission line are as follows:
(1) The wire surface voltage is its operating voltage:
direct current: u= ±1100kV, ac: u 2 = three-phase ac transient expression, (4)
(2) The ground and ground potentials are zero:
(3) Manual boundary:
on the basis of ensuring the calculation precision and the calculation efficiency, adding the artificial boundary, and setting an infinite element calculation domain outside the artificial boundary, the artificial boundary can be free from adding the nominal boundary condition.
IV, finite element calculation:
As shown in fig. 4, a three-dimensional finite element calculation model is built according to the control equation and the boundary conditions described above. Through the basic assumption, the electric field intensity near the pole tower and on the body surface of the operator can be subjected to iterative solution, and the solution process can be divided into the following steps:
1) Combining finite element calculation software, solving deberthing Song (Poisson) equation by using a finite element method, and solving charge conservation equation by using a finite volume method; an initial distribution of the spatial electric field and potential is obtained.
2) And (3) adjusting an initial value of the surface charge density of the lead, obtaining a space charge value through calculation, judging whether a convergence condition is met, and if the convergence condition is not met, updating and distributing the surface charge density of the lead. The updated charge values are:
Where ρ n+1 is the charge density value of a point in space after the n+1th iteration, E s is the wire surface electric field strength, and E c is the wire corona onset field strength, which can be calculated by the picogram formula.
3) And if the charge density converges, carrying out the next step, bringing 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 the current continuity equation under the condition of the electric field so as to solve the new space charge density.
4) And (3) carrying out iterative computation in a circulating way until the electric field on the surface of the lead and the space charge density of the node meet the condition of stable convergence:
Wherein E max is the maximum electric field intensity of the wire surface, and ρ n (i) and ρ n-1 (i) are the space charge densities obtained by the nth and n-1 th iterations of the ith node, respectively. E on＝Ec, and δ E and δ ρ are relative error conditions for determining convergence.
The electric field problem generated by three-dimensional space charge can be generally summarized as the following potential edge problem:
Where Ω is the spatial electric field calculation region, Boundaries are calculated manually. For any tetrahedral element in region Ω, the function is unknownAt the unit node availableThe values represent the coordinates of four nodes (x i,yi),(xj,yj),(xm,ym),(xl,yl), respectively, and the known potential values are
After the interpolation formula on each cell is found, the local coefficient matrix [ K ] of each cell can be found:
the poisson equation is equivalently transformed by the variational principle:
since [ K ] is a symmetric matrix
I.e. a potential satisfying the aboveAnd is also a generalized solution to poisson's equation. For the right-hand vector [ f ] in equation (2.35), it is equal to:
[f]＝[P][ρ] (12)
wherein [ P ] is a unit tetrahedron parameter synthesis matrix, [ ρ ] = (ρ 1 ρ2 ρ3 … ρn)T is a charge density matrix of each point in space, and the potential value of each node is obtained by solving [ P ].
The idea behind the finite volume method is that the charge density of each node depends only on the unit 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 tetrahedron ijlm constitutes the upstream cell of node j as in fig. 5.
After determining the upstream node, the nonlinear equation describing the space charge can be converted into a problem solving a binary once-through equation.
If the reverse extension of the charge velocity vector at node j passes through tetrahedral unit ijlm, i.e., the velocity vector of the charge density at node j satisfies the following relationship, then the tetrahedral unit is the upflow element of node j, and the corresponding mathematical description is:
bkVx+ckVy+dkVz≤0(k＝i,l,m) (13)
Where V x、Vy、Vz is the three coordinate components of the charge velocity vector at j.
The combined charge conservation equation can be obtained:
In solving the charge conservation equation, interpolation of charge density is required. Similar to the potential interpolation method in the upper section, the charge density interpolation within triangle ijm can be expressed as:
ρ(x,y)＝Niρi+Njρj+Nmρm＝[N][ρ] (18)
the partial derivative of the above formula with respect to coordinates can be expressed as:
Simultaneous may give the following conversion forms:
A-ρi- 2+B-ρi-+C-＝0 (21)
Where A -、B-、C- is a homogeneous polynomial of V, ρ, Δ, solving a unitary quadratic equation, each of which yields two solutions, the larger of which is taken as the value of ρ i. It can be demonstrated that for the upstream element the larger of the two solutions is always equal to or smaller than the absolute values ρ j and ρ m, which coincides with the physical fact that the space charge density at the point below the velocity is always smaller than the space charge density at the point above the velocity, ensuring convergence of the knowledge.
3. The electric field calculation level under different conditions is obtained by changing different operation conditions of five typical operation positions of live working and parallel intervals between an alternating current circuit and a +/-1100 kV direct current circuit, and the electric field calculation level is used as a reference for electromagnetic shielding protection.
The method comprises the steps of changing the operation positions, single-double-pole live-line and power-off maintenance working conditions and repeatedly applying a finite element method to calculate a mixed electric field in the process of solving and calculating electric fields near a line and on the surface of a human body of an operator under three operation working conditions of single-pole, double-pole live-line and power-off maintenance of the five typical operation positions, and repeatedly applying a finite element method to the parallel intervals of the line, so as to obtain electric field intensity calculation results of power transmission lines, insulators, ground wires and the like and the surface of the operator under different conditions, and obtain the influence degree of different variables on the electric field level.
According to the three-dimensional electric field calculation method for the live working pole tower of the extra-high voltage direct current line, electric field intensities near the power transmission line and on the surface of the human body of an operator at five typical working positions of line maintenance live working are calculated, and meanwhile, influences of parallel intervals of the alternating current and direct current line on the electric field level are analyzed, so that a certain reference basis is provided for an electromagnetic shielding protection mode and how to optimize an electromagnetic field environment of the live working when the line is designed and built.
Claims (4)
1. The three-dimensional electric field calculation method of the live working pole tower of the extra-high voltage direct current line is used for obtaining an electromagnetic shielding protection mode of live working and design optimization reference of the line, and the extra-high voltage direct current line is provided with a parallel extra-high voltage alternating current transmission line, and is characterized by comprising the following steps:
a. determining relevant parameter information of the ultra-high voltage alternating current/direct current parallel section power transmission line, and constructing a three-dimensional mixed electric field calculation model and a finite element human body model according to the relevant parameter information;
b. According to the three-dimensional mixed electric field calculation model and the finite element human body model, calculating the human body model body surface electric field intensity of the ultra-high voltage direct current line at each operation position of the human body model near the pole tower line under three working conditions of single-pole, bipolar electrification and power failure maintenance by using a finite element calculation method, changing the parallel interval between the direct current line and the alternating current line, and obtaining the human body model body surface electric field intensity under different parallel intervals;
c. Obtaining the current live working electromagnetic shielding protection mode and the design optimization reference of the line from the three working conditions of the direct current line and the influence degree of different parallel intervals on the electric field intensity;
wherein:
The related information comprises an alternating current transmission line voltage level, a direct current transmission line voltage level, a transmission line Lu Dian type and design drawing of a pole tower, a transmission line split distance, a wire split number, a sub-wire radius, phase sequence arrangement, a line-to-ground height, an alternating current-to-direct current line parallel distance and a human model size parameter;
Each operation position comprises 5 kinds of operation positions, namely: the operation staff stands on the tower body, when the operation staff is about to contact the line, the operation staff stands on the transmission line, the operation staff stands on the tower cross arm and the operation staff stands on the ground wire;
The finite element calculation method specifically comprises the following steps:
1) Setting voltage boundary conditions, wherein an alternating current line and a direct current line are running voltages, and the voltage values of a tower, a ground wire and the ground are zero;
2) Setting initial values of the circuit and the surface charge density of the human body;
3) Setting the 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 computing software multi-physical-field module;
5) Carrying out iterative solution coupling calculation by utilizing COMSOL Multiphysics finite element simulation software to determine the body surface electric field strength under different working conditions and different parallel distances of the direct current circuit;
the step of carrying out iterative solution coupling calculation to determine the body surface electric field strength of the direct current circuit under different working conditions and different parallel distances is as follows:
1) Solving a poisson equation by using a finite element method, and solving a charge conservation equation by using a finite volume method; obtaining initial distribution of a space electric field and electric potential;
2) Adjusting an initial value of the surface charge density of the lead, obtaining a space charge value through calculation, judging whether a convergence condition is met, and if the convergence condition is not met, updating and distributing the surface charge density of the lead;
the updated charge values are:
Wherein ρ n+1 is the charge density value of a point in space after the n+1th iteration, es is the electric field intensity of the surface of the wire, ec is the corona onset field intensity of the wire, and can be calculated by a Peak formula;
3) If the charge density converges, carrying out the next step, bringing the calculated space charge density of each node into the charge density for solving the poisson equation, solving the potential and the electric field of each node, and solving the current continuity equation by taking the electric field as a condition to solve the new space charge density;
4) And (3) carrying out iterative computation in a circulating way until the electric field on the surface of the lead and the space charge density of the node meet the condition of stable convergence:
Wherein E max is the maximum electric field intensity of the wire surface, ρ n (i) and ρ n-1 (i) are the space charge densities obtained by the nth and n-1 iterations of the ith node, E on＝Ec, and delta E and delta ρ are the relative error conditions for judging convergence.
2. The method for calculating the three-dimensional electric field of the live working tower of the extra-high voltage direct current line according to claim 1, wherein the different parallel pitches are different pitches in the range of 28m-88 m.
3. The method for calculating the three-dimensional electric field of the pole tower for the live working of the extra-high voltage direct current line according to claim 1 is characterized in that the constructing of the three-dimensional mixed electric field calculation model comprises a line arrangement information graph drawn according to the related parameter information, a human body model positioned in each position graph and a mixed electric field calculation model, 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 the electric fields near the line and on the surface of the human body of an operator under three operation conditions of single-pole, double-pole electrification and power failure maintenance of the direct-current line to obtain the mixed electric field intensity when the extra-high voltage alternating current and direct current are parallel, and changing the parallel spacing of the line to obtain the electric field intensity of the human body model body surface under different parallel spacing; the poisson equation and the charge conservation equation are respectively:
Poisson equation:
Charge conservation equation:
Wherein the parameters are as follows: The space potential is given by V; ρ + and ρ - are positive and negative space charge densities C/m 3;ε0, respectively, are vacuum dielectric constants, with values of 8.85×10 -12 F/m; r is positive and negative ion composite coefficient m 3/s;K+ and K - is positive and negative ion mobility m 2/(V.s); e is the electron charge quantity, and the value is 1.6X10 -19 C; e is the space electric field intensity V/m, and the parameters are obtained according to the related parameter information.
4. The method for calculating the three-dimensional electric field of the live working tower of the extra-high voltage direct current line according to claim 1 is characterized in that the influence degree of the three working conditions and different parallel distances from the direct current line on the electric field intensity in the step c is that after the parallel distances between the direct current line and the alternating current line are repeatedly changed in the step b, the electric field intensity of the human body model body surface of the extra-high voltage direct current line, which is positioned at each working position, of a human body model near the tower line under three working conditions of single, bipolar electrification and power failure overhaul, is repeatedly calculated by a finite element calculation method, and the influence degree of different variables on the electric field intensity is obtained from the electric field intensity of the human body model body surface under different conditions of the power transmission line, the insulator, the ground wire and the working human body model body surface.
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