CN111929348B - Method for calculating surface potential of direct current grounding electrode in horizontal multilayer structure earth environment - Google Patents
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Abstract
The invention discloses a method for calculating the surface potential of a direct current grounding electrode in a horizontal multilayer structure earth environment. The method simplifies the Green function step of solving the DC grounding extremely fine earth model, does not need matrix decomposition operation, and has high solving efficiency; the linear filtering method has the outstanding advantages of intuition, simplicity and quickness, is very suitable for solving a fine geodetic model, and has great advantages for forming a software algorithm.
Description
Technical Field
The invention belongs to the field of research on influence analysis of a high-voltage direct-current transmission technology on the surrounding environment, and particularly relates to a numerical calculation method for solving a horizontal multilayer structure direct-current grounding extremely fine earth model by using a linear filtering method under two conditions of considering the embedding depth of a direct-current grounding electrode (based on a sign-algebraic equation method) and not considering the embedding depth (based on a transmission line model method).
Background
The resistivity model of the earth in the DC grounding electrode address is closely related to the problems of the grounding performance of the DC grounding electrode, the DC magnetic bias of the transformer and the like, and an accurate earth resistivity model needs to be obtained by inverting the measured data after the on-site exploration. The soil generally has heterogeneity and can be treated approximately as a horizontally stratified soil structure of several layers. Due to the difference in resistivity of the soil on both sides of the interface, the current field and the electric field change at the layered soil interface. In the traditional power system grounding calculation, because the area occupied by the transformer substation grounding grid is smaller, the model scale of the horizontal multilayer structure ground used in the grounding calculation is smaller, and the traditional theoretical and numerical methods can meet the solving requirement.
The long-distance direct current transmission project has a transmission distance of hundreds to three thousand kilometers, the current in the ground of direct current transmission has great propagation depth, the ground potential of a direct current grounding electrode relates to a large-scale ground surface coverage area, the used horizontal multi-layer structure ground far exceeds the existing traditional model in both layering number and depth coverage range, and the soil model numerical calculation process is complicated and the theoretical difficulty is high. And when the numerical values of the soil resistivities of the two adjacent layers are greatly different and the layer with large/small thickness exists, the numerical value singularity phenomenon exists when the fine horizontal layering earth model is solved by the pure numerical method. With the increase of the complexity of the direct current grounding electrode fine earth model, the traditional theoretical method cannot meet the solving precision and speed of the fine horizontal layered earth model calculation, so that a new theoretical method and a digital calculation means are required to solve the direct current grounding electrode earth surface potential in the fine horizontal multilayer structure earth environment.
The calculation of the direct current grounding pole fine earth model can be divided into two scenes: the method comprises the following steps of common grounding calculation and earth surface potential calculation of direct current magnetic bias, and inversion calculation of earth resistivity exploration data. Both involve a core algorithm, which is how to solve the algorithm of forming the space potential distribution by the known point current source, namely the green function problem of the fine earth model. The Green function analytic solution for the fine earth model can be written as follows:
formula (1) belongs to the generalized infinite integral, wherein: f and F are respectively a Hankel (Hankel) integral function and an integral kernel function;randposition parameters and integral variables respectively; j. the design is a square0Is a zero order bessel function of the first kind. Due to the complexity of the integral kernel function F, there is not necessarily an analytical solution for F. Therefore, the numerical calculation of the formula (1) becomes a basic problem in the fields of geology and grounding, and the current solving method mainly comprises the following four steps:
a numerical integration method such as a sinbose integration method and a Bessel function zero point interval integration method;
the classical mirror image method is only suitable for the condition that the Hankel integral kernel function f can be expanded into exponential series;
the linear filtering method belongs to a general method in the field of geology, and is less applied to the grounding of a power system;
the complex mirror image method is introduced from high-frequency computing electromagnetism and is widely applied to grounding computation of a power system at present.
The numerical integration method and the classical mirror image method have the problems of large calculated amount, low convergence rate and the like, and are rarely applied at present. Although the linear filtering method has a great deal of research results in the geological industry, the complex mirror image method is still used for most of the power system grounding calculation. With the development of a numerical calculation method, researchers have studied and used an improved complex mirror image method to solve the problem of a singular constant current field, and the accuracy of the algorithm is improved to a certain extent. In view of the above, aiming at the above limitations encountered in the current calculation method, the present invention provides a numerical calculation method for solving a horizontal multilayer structure dc ground pole fine earth model by a linear filtering method under two conditions of considering the dc ground pole burying depth (based on a sign-algebraic equation method) and not considering the burying depth (based on a transmission line model method), and makes the method become a good supplement of a complex mirror image method, so as to provide a new idea and a new means for calculating the dc ground pole surface potential in the fine horizontal multilayer structure earth environment.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a horizontal layered direct current grounding electrode grounding model solving method starting from a linear filtering method under the two conditions of considering the direct current grounding electrode embedding depth (based on a sign-algebraic equation method) and not considering the embedding depth (based on a transmission line model method),
the present invention employs the following solution. A high-efficiency fine geodetic model solving scheme is formed based on a linear filtering method, and the existing filtering weight coefficient is used for converting the Hankel infinite integral into a finite term summation form, so that the direct-current grounding extremely fine geodetic model is solved.
A method for calculating the earth surface potential of a direct current grounding electrode in a horizontal multilayer structure earth environment comprises the following specific steps:
in the formula, F and F are respectively a Hankel (Hankel) integral function and an integral kernel function;representing integral variables, e x The parameters of the position are represented by,;J0representing a first class of zero order bessel functions.
in the formula:H n is a filter coefficient; f is an integral kernel function in formula (1); n to be the position of the sampling point(s),nindicating the number of sample points.
Indicating that the point current source is at the secondiThe green's function of the layer of soil,ρ i resistivity of the source layer (omega ∙ m), z-z0To observe the horizontal distance from the point to the point current source, in equation (5),is a function of Kronecker-delta, if and only ifi=sTime of flight (i– s)=1Otherwise (i–s)=0;AAndBall relate to integral variablesThe function to be solved of (a) is,is an integral variable.
Further, a 61-point version of guptaasma-Singh is used in step 2 to solve equation (3):
wherein: log (log)10( n )=–5.199 138 304 + 0.116 638 304 n,n=1, 2, …, 61;H n The values are shown in Table 1.
Further, in step 3, horizontalmSimplest universal hankel integral kernel function meter for stratum soilThe calculation method comprises the following steps:
a. establishing a symbolic equation:
x and Y are both sparse matrixes/vectors, and the vector C = [ to be solved ]A 1, B 1, …, A m , B m ]T. X is 2m 2mDimension matrix, orderi = 1, …, m-1, having:
whereinK i Is undergroundiThe reflection coefficient of the boundary is determined,. Y is 2mDimension column vector, specific form and source layer numbersIt is related.s(ii) =1, case where a non-zero element of Y is represented by formula (14);s=mnon-zero elements of YThe extract is represented by formula (15); the non-zero element for the other cases Y is taken as formula (16):
b. will be described in detail n Solving the substituted symbol equation (6)ABThen using formula (5) to obtain the correspondingf i ( n );
Further, in step 3, by combining the engineering practice of the dc magnetic biasing problem, when a large-scale earth surface potential distribution is solved, the dc grounding electrode is simplified into a point source and the buried depth of the dc grounding electrode is ignored, that is, the grounding electrode is simplified into an earth surface point current source, and at this time, the hankel integral kernel function can be solved by adopting a transmission line model, so that the effect of simplifying analysis is achieved.
Solving earth surface potential from transmission line modelVThe calculation formula of (2) is as follows:
wherein the content of the first and second substances,rthe distance between the earth surface observation point and the point current source is taken as the distance; j. the design is a square0Is a first class zero order Bessel function;is an integral variable;R 1as a function of the form:
wherein R is obtained by the following recursion formula1:
Wherein the content of the first and second substances,in order to be the angular frequency of the frequency,are respectively the firstiThe thickness, resistivity and permeability of the layer soil, i is as followsiThe wave number of the layer soil is,r i is as followsiThe wave impedance of the layer of soil,R 1in order to represent the apparent impedance,R i (i = 2, …, ) In order to be a function of the impedance coefficient,mthe total number of layers of soil.
Compared with the prior art, the invention has the following beneficial effects: the Green function step of solving the direct current grounding extremely fine earth model is simplified, matrix decomposition operation is not needed, and the method has high solving efficiency; the linear filtering method has the outstanding advantages of intuition, simplicity and quickness, is very suitable for solving a fine geodetic model, and has great advantages for forming a software algorithm.
Drawings
Fig. 1 is a schematic diagram of a point current source in a horizontal multi-layer structure earth ground.
Fig. 2 is a schematic diagram of a transmission line model.
Detailed Description
It should be noted that, in the present application, the embodiments and features of the embodiments may be combined with each other, and the present invention will be described in detail with reference to the accompanying drawings and embodiments.
For better understanding of the present invention, the following examples are provided to further illustrate the present invention, and the examples described are only a part of the present invention, but the present invention is not limited to the following examples. Various changes or modifications may be effected therein by one skilled in the art and such equivalents are intended to be within the scope of the invention as defined by the claims appended hereto.
The invention provides a method for calculating the earth surface potential of a direct current grounding electrode in a horizontal multilayer structure earth environment, which comprises the following four steps:
H n is a filter coefficient; f is an integral kernel function in formula (1); n the position of the sampling point.
Step 2a, further, using a 61-point version of guptaasma-Singh to solve equation (23) in step 2:
wherein log10( n )=–5.199 138 304 + 0.116 638 304 n,n=1, 2, …, 61;H n The values are shown in Table 1.
In the formula (I), the compound is shown in the specification,is a function of Kronecker-delta, if and only ifi=sTime of flight (i–s) =1, otherwise (i–s)=0;AAndBare all the functions to be solved,is an integral variable.
Further, for step 3, the solution is performed in consideration of the burial depth, and the specific steps are as follows:
step 3a, establishing a symbolic equation of the following form:
wherein X and Y are both sparse matrices/vectors, and the vector C = [ is to be solved ]A 1, B 1, …, A m , B m ]T. X isDimension matrix, orderi = 1, …, m-1, having:
whereinK i Is underground in FIG. 1iThe reflection coefficient of the boundary is determined,. Y is 2mDimension column vector, specific form and source layer numbersIt is related.s(ii) =1, case where a non-zero element of Y is represented by formula (34);s=mthe non-zero element of Y is represented by formula (35); the non-zero elements for the other cases Y are taken as formula (36):
step 3b, mixing n Solving the substituted symbol equation (6)ABThen using formula (5) to obtain the correspondingf i ( n );
And 4, when the large-range ground surface potential distribution is solved, simplifying the direct current grounding electrode into a point source and neglecting the buried depth of the direct current grounding electrode, namely, the grounding electrode in the figure 1 is considered to be simplified into a ground surface point current source, and at the moment, the Hankel integral kernel function can be solved by adopting the transmission line model shown in the figure 2, so that the effect of simplifying analysis is achieved. Method for solving earth surface potential in FIG. 1 from model of FIG. 2VThe calculation formula of (2) is as follows:
wherein the content of the first and second substances,rthe distance between the earth surface observation point and the point current source is taken as the distance; j. the design is a square0Is a first class zero order Bessel function;is an integral variable;R 1as a function of the form:
r1 can be derived from the following recursion equation:
wherein the content of the first and second substances,in order to be the angular frequency of the frequency,andare respectively the firstiThe thickness, resistivity and permeability of the layer soil, i is as followsiThe wave number of the layer soil is,r i is as followsiThe wave impedance of the layer of soil,R 1in order to represent the apparent impedance,R i (i = 2, …, ) In order to be a function of the impedance coefficient,mthe total number of layers of soil.
Potential of earth's surfaceVThe calculation results are shown in Table 4
Details not described in this specification are within the skill of the art that are well known to those skilled in the art. It is within the spirit of the invention that conventional alternatives according to the prior art be made within the spirit of the invention.
Claims (3)
1. A method for calculating the earth surface potential of a direct current grounding electrode in a horizontal multilayer structure earth environment is characterized by comprising the following specific steps:
step 1, under the condition of considering the buried depth, orderResolving the Green function of the fine earth model by using a linear filtering method
The hankel transformation is rewritten as:
in the formula, F and F are a Hankel integral function and an integral kernel function respectively;representing integral variables, e x The parameters of the position are represented by,x, y ;J0representing a first class of zero order Bessel functions;
step 2, e in the formula (2) x y–According to the intervalSampling, sampling intervalLess than 0.5 times of the cut-off frequency, the discrete signal obtained by sampling can be recovered to a continuous signal without distortion, so equation (2) can be:
in the formula:H n is a filter coefficient; f is an integral kernel function in formula (1); n to be the position of the sampling point(s),na serial number representing a sampling point;
step 3, the analytic solution form of the horizontal multilayer geodesic Green function is
WhereinIndicating that the point current source is at the secondiThe green's function of the layer of soil,ρ i is the source layer resistivity, z-z0To observe the horizontal distance of the point-to-point current source,is a function of Kronecker-delta,s representsSource layer numbering,If and only ifi=sTime of flight (i–s) =1, otherwise (i–s)=0;Andare all aboutThe function to be solved of (a) is,is an integral variable.
2. The method for calculating the earth surface potential of the direct current grounding electrode in the horizontal multilayer structure earth environment according to claim 1, wherein a 61-point version of Guptaasma-Singh is used in the step 2 to solve the formula (3):
3. The method for calculating the earth surface potential of the direct current grounding electrode in the horizontal multilayer structure earth environment according to claim 1, wherein the engineering practice of the direct current magnetic biasing problem is combined in step 3, when the large-range earth surface potential distribution is solved, the direct current grounding electrode is simplified into a point source, the buried depth of the direct current grounding electrode is ignored, namely the grounding electrode is considered to be simplified into an earth surface point current source, and at the moment, the Hankel integral kernel function is solved by adopting a transmission line model;
solving earth surface potential from transmission line modelVThe calculation formula of (2) is as follows:
wherein the content of the first and second substances,rthe distance between the earth surface observation point and the point current source is taken as the distance; j. the design is a square0Is a first class zero order Bessel function;is an integral variable;R 1as a function of the form:
wherein, the formula is obtained by the following recursionR 1:
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