CN110119544B - Spiral grounding electrode size parameter design method suitable for complex environment area - Google Patents
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Abstract
The invention relates to a design method of a spiral grounding electrode size parameter suitable for a complex environment area, which solves the defect that the design method of the spiral grounding electrode size is not available in the prior art. The invention comprises the following steps: setting a grounding electrode finite element calculation method; measuring the soil resistivity of a complex environment area; measuring the ground resistance; designing the length of the spiral grounding electrode; designing the radius of the spiral grounding electrode; and (3) designing the screw pitch of the spiral grounding electrode. The invention provides a specific dimension parameter design method of a spiral grounding electrode, which can ensure that the spiral grounding electrode has good grounding performance in complex soil environments such as limited axial electrode distribution space, higher resistivity and the like through reasonable parameter design.
Description
Technical Field
The invention relates to the technical field of spiral grounding electrodes, in particular to a design method of size parameters of a spiral grounding electrode suitable for a complex environment area.
Background
In the grounding system of the power transmission network in China, common grounding electrode laying modes are horizontal laying and vertical laying, but the two laying modes have the defects of long laying distance or large burying depth for achieving the expected scattering effect, are easily restricted by uncertain factors such as pipelines, highways, geology and the like, and cause the increase of grounding resistance to influence the normal operation of the power transmission line.
At present, the research of a grounding structure is mainly focused on different laying modes of grounding poles in different complicated terrain areas, such as a wet area with soil resistivity rho less than or equal to 100 and an area with operation experience, and iron towers and reinforced concrete foundations can be utilized for natural grounding, and when a flexible foundation or a cast-in-place pile foundation is adopted for a tower foundation, foundation reinforcement grid is fully utilized as a natural grounding body; in residential areas, paddy fields and other areas where the laying of horizontal grounding bodies is limited, the grounding devices are preferably laid in a closed ring shape around the tower foundation, and when the grounding resistance cannot meet the requirement or the grounding excavation is limited by adopting the closed ring-shaped grounding devices, the closed ring-shaped grounding devices and the vertical grounding electrode can be used; in a wider area, the grounding device adopts a plurality of radial grounding electrodes with the total length not exceeding 500m or adopts continuous extension grounding electrodes to be connected in series or in parallel; in the western region with steep topography, a plane with a large area (suitable for embedding the grounding electrode) is difficult to find, and the grounding device adopts a plurality of copper bars, steel bars and angle steel as the grounding electrode and is vertically driven into the ground.
The conventional laying modes have corresponding defects, and the problem that current overflows and is difficult to reach the expected requirement exists in the natural grounding electrode; the closed annular grounding device has deeper burying depth and limited application range; the laying length of the horizontal grounding electrode is longer, so that the construction difficulty and cost are increased; the vertical grounding electrode has the problems of uneven current flow and overhigh soil temperature rise.
The spiral grounding electrode laying mode is based on the idea of expanding the contact area between the axial space grounding electrode and soil and effectively reducing the axial electrode arrangement distance, and the structure of the spiral grounding electrode laying mode is shown in figure 1. The grounding electrode and the down conductor are connected by 180 degrees, so that the transition of the ground entering current is facilitated, the resistance value of the grounding resistor can be effectively reduced, the purpose of maximizing the current overflow effect can be achieved in a complex soil environment, and the device has the advantages of being shallow in embedded depth, short in embedded length, even in current overflow and the like.
However, the spiral grounding electrode is used as a novel grounding structure, and specific parameters such as the length, radius and pitch of the grounding electrode are not randomly designed, and the corresponding calculation design should be performed according to the design requirement of the grounding system of the power transmission network. Therefore, how to propose a design method for the dimensional parameters of the spiral grounding electrode has become an urgent technical problem to be solved
Disclosure of Invention
The invention aims to solve the defect that a spiral grounding electrode size design method is not available in the prior art, and provides a spiral grounding electrode size parameter design method suitable for a complex environment area to solve the problems.
In order to achieve the above object, the technical scheme of the present invention is as follows:
a spiral grounding electrode size parameter design method suitable for a complex environment area comprises the following steps:
setting a grounding limit finite element calculation method: setting a grounding electrode finite element calculation method to obtain the surface potential of the grounding electrode with any structural parameter by the grounding electrode finite element calculation method;
measurement of soil resistivity in complex environmental areas: indirectly measuring the soil resistivity through the soil by using a quadrupole method;
measuring the ground resistance: measuring the grounding resistance of the grounding body by using a tripolar method;
design of the length of the spiral grounding electrode: analyzing and designing the laying length of the spiral grounding electrode when the axial electrode distribution space is smaller than 10m according to a finite element numerical value calculation method;
designing the radius of the spiral grounding electrode: analyzing and designing the radius size of the spiral grounding electrode according to the grounding resistance value;
design of screw grounding electrode pitch: and analyzing and designing the screw grounding electrode pitch according to the grounding resistance value.
The method for calculating the set grounding limit finite element comprises the following steps:
the grounding electrode is approximated as a group of point current sources, potential function
Satisfy differential equation
Wherein I is the size of the point current source in the field,
vectors representing the spatial position of the field point, +.>
Vectors representing the spatial position of the source point, +.>
As a Dike function ρ s Is soil resistivity;
listing the edge equation of the ground electrode in the electric field:
let Ω be the required field Γ 1 Is the interface of soil medium and air, Γ 2 To simulate an equivalent boundary at zero potential at infinity, boundary Γ=Γ 1 +Γ 2 ，Γ 3 The potential of the surface of the approximately spiral grounding electrode is constant by neglecting the voltage drop of the surface of the grounding electrode to be the interface between the surface of the grounding electrode and a soil medium
Listing the edge value problem:
converting the above edge equation into a variation problem:
according to the above description, the analysis process of the current overflow of the grounding electrode is the Poisson side value problem, and the conversion of the typical side value problem into the equivalent variation problem is as follows:
splitting and interpolating the three-dimensional field:
mesh subdivision and interpolation are carried out on the three-dimensional field, a first order tetrahedron unit is selected as a basic unit for subdivision of the three-dimensional field, and if the solved field is assumed to be subdivided into Z by tetrahedron 0 Units, get N 0 A plurality of discrete nodes; each node corresponds to a unique space potential equation, four vertexes of a first-order tetrahedron unit are taken as nodes, and the actual numbers of the nodes in the whole domain are i, j, l and m;
the linear interpolation is as follows:
the interpolation function is continuous in the unit tetrahedron e, and brings four vertex coordinates and corresponding bit values into the unit tetrahedron e respectively to obtain: alpha 1 +α 2 x i +α 3 y i +α 4 z i i＝(1,2,3,4)；
Simultaneous equation solving to obtain alpha 1 ,α 2 ,α 3 ,α 4 Each coefficient to be determined is put into an interpolation function, and is obtained after finishing:
the elements of the coefficient matrix in the rectangular coordinate system are required to form the finite element equation:
because of
So that
Unit analysis of unit tetrahedra:
after subdivision and interpolation, the unit tetrahedrons are subjected to unit analysis, unit analysis [ P ]] e Is a matrix element of (a):
the center of gravity point (x) c 、y c 、z c ) Substituting the coordinates into the above equation, assuming that the unit endogenous density is approximately unchanged, becomes:
and (3) obtaining a finite element equation:
integrating all parameters in a rectangular coordinate system comprehensively to obtain related parameters in a global range:
[k]＝∑[k] e ，[p]＝∑[p] e (9)
therefore, the finite element equation of the poisson field satisfying the second homogeneous boundary condition is
Wherein [ k ]]As a matrix of the energy coefficients of the total electric field,
the potential matrixes of all the nodes are obtained, the corresponding calculation program is called after the finite element equation is obtained,can obtain +.>
Is a value of (2).
The measurement of the soil resistivity of the complex environment area comprises the following steps:
measuring soil resistivity by indirect measurement of soil resistance using quadrupole method, let a be 1 、a 2 For the distance, a, between the current pole A and the potential poles C, D 3 、a 4 The distance between the current electrode B and the potential electrodes C and D;
driving four electrodes A, B, C, D into the ground, wherein the depth of the ground is uniform;
applying a current I to the electrodes A and B by using a regulated power supply E, enabling the current to flow in through the electrode A, and returning the current to the power supply by the electrode B, so that a current field generates a potential on the electrodes C and D, and measuring the potential difference between the electrodes C and D by using a potential difference meter or a high-resistance state voltmeter;
the four electrode bars are distributed on the same straight line, the spacing between the electrode bars is equal to a, and the depth of each electrode bar which is driven into the ground is not more than 1/20 of the spacing a of the electrode bars;
the soil resistivity was measured and the calculation formula was as follows:
wherein ρ is soil resistivity (Ω·m), R is measured resistance (Ω), a is distance (m) between the measured electrodes, and b is depth (m) of the measured electrodes driven into the ground;
when the test electrode is driven into the ground by a depth b not exceeding 0.2a, assuming b=0, the following formula is simplified:
ρ＝2πaR。 (12)
the measuring of the ground resistance comprises the steps of:
the method comprises the steps of measuring the grounding resistance of a grounding body by using a tripolar method, setting the grounding body G, the earth and a current pole C to form a current loop together, enabling measured current injected into the grounding body to flow out of the current pole after passing through soil with a certain distance, enabling the potential on the ground to be distorted, arranging a voltage pole at a potential compensation point at the moment, and enabling the potential difference between the measured voltage pole P and the grounding pole G to be equal to the voltage drop on a grounding resistor;
let the voltage U between the measuring voltage pole and the grounding pole divided by the input current I to obtain the grounding resistance R,
let the radius of hemispherical grounding body be a, the current injected into the grounding body be I, the distance between the grounding body and current pole be L GC The distance between the grounding body and the voltage pole is L GP The distance between the voltage pole and the current pole is L PC ；
The application of the superposition principle can result in a potential difference V' between the GPs due to the current I input from the ground electrode G:
the current I flowing from the current pole C makes the potential difference V' between GPs appear as:
the ground resistance R is calculated as:
while the actual grounding resistance R of the grounding electrode 0 The method comprises the following steps:
to make the measurement error
Is 0:
namely:
let L be PG ＝aL GC Because the grounding electrode G, the voltage electrode P and the current electrode C are on the same straight line, the distance between the voltage electrode and the current electrode is L PG ＝L GC -aL GC ；
Substituting formula (18) to obtain a=0.618;
arranging the voltage poles at zero potential point, i.e. L PG ＝0.618L GC In this case, the actual ground resistance is obtained.
The design of the length of the spiral grounding electrode comprises the following steps:
setting parameters: setting soil resistivity, grounding body down-lead length, section radius, radius of a spiral coil and screw pitch in the calculation process of the spiral grounding electrode;
according to a finite element analysis method, mesh subdivision and interpolation are firstly carried out on the grounding electrode, the magnitude of injection current is set, and the potential magnitude of any point on the surface of the grounding electrode can be obtained after calculation;
comparing the potential of the tail end of the grounding electrode with the injection current to obtain the value of the grounding resistance of the grounding electrode;
setting an initial value and a final value of the laying length to be 1m and 10m respectively, and setting the step length to be 1m to obtain the potential of any point on the horizontal linear grounding body and the spiral grounding body with the laying length from 1m to 10m, and comparing the potential with the injection current to obtain the grounding resistor;
and selecting a corresponding laying length according to the grounding resistance value.
The design of the radius of the spiral grounding electrode comprises the following steps:
setting parameters: setting a hemispherical soil pool radius, a soil resistivity, a grounding body down-lead length, a section radius, a screw pitch, a laying length and a coil radius to be 0.1m to 2.5m in the calculation process of the spiral grounding electrode;
calculating the grounding resistance values of different coil radiuses:
according to a control variable method, keeping other parameters unchanged, changing the coil radius of the spiral grounding electrode, and analyzing the influence rule of different coil radii on the grounding resistance of the spiral grounding electrode;
according to a finite element analysis method, mesh subdivision and interpolation are firstly carried out on a grounding electrode, the injection current is set to be 1A, and the potential of any point on the surface of the grounding electrode can be obtained after calculation; then comparing the potential of the tail end of the grounding electrode with the injection current to obtain the value of the grounding resistance of the grounding electrode;
and selecting a corresponding grounding electrode radius according to the numerical value requirement of the grounding resistance of the grounding electrode.
The design of the screw grounding electrode screw pitch comprises the following steps:
setting parameters: setting a hemispherical soil pool radius, a soil resistivity, a grounding body down-lead length, a section radius, a spiral coil radius and a laying length in the calculation process of the spiral grounding electrode;
calculating the grounding resistance value of the grounding electrode under different pitches:
according to a finite element analysis method, mesh subdivision and interpolation are firstly carried out on a grounding electrode, the magnitude of injection current is set to be 1A, the potential magnitude of any point on the surface of the grounding electrode is obtained after calculation, and then the potential magnitude of the tail end of the grounding electrode is compared with the injection current to obtain the grounding resistance of the spiral grounding electrode under different pitches;
according to the numerical requirement of the grounding resistance of the grounding electrode, the corresponding screw pitch is selected.
Advantageous effects
Compared with the prior art, the invention provides a specific size parameter design method of the spiral grounding electrode. The grounding performance of the spiral grounding electrode device can enlarge the contact area of the grounding electrode and soil to realize the maximization of current overflow when the axial grounding electrode is identical in length, so that the grounding resistance is reduced. Due to the structural advantages of the spiral grounding electrode, the spiral grounding electrode can be guaranteed to have good grounding performance under complex soil environments such as limited axial electrode distribution space and higher resistivity through reasonable parameter design. Along with the gradual shortage of future power transmission corridor resources and the high requirements of high-capacity power transmission on grounding performance, the design method of the spiral grounding electrode parameters provided by the invention realizes the optimal grounding performance and the maximized scattered flow in unit space and effectively improves the operation safety and reliability of power transmission and transformation equipment.
Drawings
FIG. 1 is a schematic view of a prior art spiral grounding electrode;
FIG. 2 is a process sequence diagram of the present invention;
FIG. 3 is a schematic diagram of the measurement of soil resistivity in the present invention;
FIG. 4 is a graph showing the comparison of the resistance reduction performance of the spiral grounding electrode and the horizontal grounding electrode in the present invention;
FIG. 5 is a graph showing the relationship between the grounding resistance of the spiral grounding electrode and the radius of the coil in the present invention;
FIG. 6 is a graph of the relationship between the grounding resistance of the spiral grounding electrode and the radius of the cross section in the invention.
Detailed Description
For a further understanding and appreciation of the structural features and advantages achieved by the present invention, the following description is provided in connection with the accompanying drawings, which are presently preferred embodiments and are incorporated in the accompanying drawings, in which:
as shown in fig. 2, the method for designing the size parameter of the spiral grounding electrode suitable for the complex environment area comprises the following steps:
first, a finite element calculation method is set. The finite element method is most widely applied to electromagnetic field numerical calculation, the traditional finite element method is based on a variation principle, the side value problem of a required solution is converted into a corresponding variation problem, and then the variation problem is discretized into an extremum problem of a common multiple function by utilizing subdivision interpolation. The method for calculating the finite element of the grounding electrode is firstly set so as to obtain the surface potential of the grounding electrode with any structural parameter by the method for calculating the finite element of the grounding electrode. The method comprises the following specific steps:
(1) To solve the potential at any point in the space of infinite ground, the ground is approximated as a set of point current sources, potentialsFunction of
Satisfy differential equation
Wherein I is the size of the point current source in the field,
vectors representing the spatial position of the field point, +.>
Vectors representing the spatial position of the source point, +.>
As a Dike function ρ s Is the resistivity of the soil.
(2) Listing the edge equation of the ground electrode in the electric field:
to simulate an infinitely distant point of zero potential, the radius of the hemispherical field of the simulated soil should be at least 5 times the axial length of the ground electrode. The method effectively avoids inconvenience brought by directly solving the open domain space, and greatly improves the solving efficiency.
Let Ω be the required field Γ 1 Is the interface of soil medium and air, Γ 2 To simulate an equivalent boundary at zero potential at infinity, boundary Γ=Γ 1 +Γ 2 ，Γ 3 The potential of the surface of the approximately spiral grounding electrode is constant by neglecting the voltage drop of the surface of the grounding electrode to be the interface between the surface of the grounding electrode and a soil medium
Listing the edge value problem: />
(3) Converting the above edge equation into a variation problem:
according to the above description, the analysis process of the current overflow of the grounding electrode is the Poisson side value problem, and the conversion of the typical side value problem into the equivalent variation problem is as follows:
(4) Splitting and interpolating the three-dimensional field:
mesh subdivision and interpolation are carried out on the three-dimensional field, a first order tetrahedron unit is selected as a basic unit for subdivision of the three-dimensional field, and if the solved field is assumed to be subdivided into Z by tetrahedron 0 Units, get N 0 A plurality of discrete nodes; each node corresponds to a unique space potential equation, four vertexes of a first-order tetrahedron unit are taken as nodes, and the actual numbers of the nodes in the whole domain are i, j, l and m;
the linear interpolation is as follows:
the interpolation function is continuous in the unit tetrahedron e, and brings four vertex coordinates and corresponding bit values into the unit tetrahedron e respectively to obtain: alpha 1 +α 2 x i +α 3 y i +α 4 z i i＝(1,2,3,4)；
Simultaneous equation solving to obtain alpha 1 ,α 2 ,α 3 ,α 4 Each coefficient to be determined is put into an interpolation function, and is obtained after finishing:
the elements of the coefficient matrix in the rectangular coordinate system are required to form the finite element equation:
because of
So that
(5) Unit analysis of unit tetrahedra:
after subdivision and interpolation, the unit tetrahedrons are subjected to unit analysis, unit analysis [ P ]] e Is a matrix element of (a):
the center of gravity point (x) c 、y c 、z c ) Substituting the coordinates into the above equation, assuming that the unit endogenous density is approximately unchanged, becomes:
(6) And (3) obtaining a finite element equation:
integrating all parameters in a rectangular coordinate system comprehensively to obtain related parameters in a global range:
[k]＝∑[k] e ，[p]＝∑[p] e (9)
therefore, the finite element equation of the poisson field satisfying the second homogeneous boundary condition is
Wherein [ k ]]As a matrix of the energy coefficients of the total electric field,
obtaining finite element equation for potential matrix of all nodes, and calling corresponding calculation program to obtain +.>
Is a value of (2).
The surface potential of the grounding electrode with any structural parameter can be obtained by the method, and the corresponding grounding resistance can be obtained by comparing the potential with the injection current of the grounding electrode. The subsequent calculation of the structural parameters of the spiral grounding electrode is researched and analyzed by the calculation method of the grounding resistance.
And secondly, measuring the soil resistivity in the complex environment area. In order to improve the accuracy of the calculation result and the definition of the conclusion of the grounding resistance, the invention provides a measurement scheme of the grounding resistance. The spiral earthing pole laying mode is shown in figure 1. The grounding electrode and the down lead adopt a 180-degree connection mode, so that the transition of the ground entering current is facilitated, the resistance value of the grounding resistor can be effectively reduced, and the purpose of maximizing the current overflow effect can be achieved in a complex soil environment. Prior to the design of the relevant parameters of the spiral earthing pole, the soil resistivity and the earthing resistance in different soil environments have to be measured, wherein the soil resistivity is measured indirectly through the soil by means of the quadrupole method. The method comprises the following specific steps:
(1) The soil resistivity is typically measured by indirect measurement of soil resistance using a quadrupole method in engineering practice. The soil resistivity is measured indirectly by a four-pole method through soil resistance measurement, and fig. 3 is a schematic diagram of the four-pole method for measuring the soil resistivity, and a is set 1 、a 2 For the distance, a, between the current pole A and the potential poles C, D 3 、a 4 The distance between the current electrode B and the potential electrodes C and D.
(2) Four electrodes A, B, C, D are driven into the ground, and the depth of the driven into the ground is uniform, so that the distance between the current electrodes is not too small to avoid the influence of mutual inductance between the leads on the measurement result.
(3) Applying a current I to the electrodes A and B by using a regulated power supply E, enabling the current to flow in through the electrode A, and returning the current to the power supply by the electrode B, so that a current field generates a potential on the electrodes C and D, and measuring the potential difference between the electrodes C and D by using a potential difference meter or a high-resistance state voltmeter;
the four electrode bars are distributed on the same straight line, the spacing between the electrode bars is equal to a, and the depth of each electrode bar which is driven into the ground is not more than 1/20 of the spacing a of the electrode bars;
(4) The soil resistivity was measured and the calculation formula was as follows:
wherein ρ is soil resistivity (Ω·m), R is measured resistance (Ω), a is distance (m) between the measured electrodes, and b is depth (m) of the measured electrodes driven into the ground;
when the test electrode is driven into the ground by a depth b not exceeding 0.2a, assuming b=0, the following formula is simplified:
ρ＝2πaR。 (12)
according to the soil resistivity measuring method, in a complex terrain area, particularly in a high resistivity area such as rock, rubble, sandy soil and the like, the horizontal grounding electrode is often not ideal in current scattering effect due to the fact that the horizontal grounding electrode cannot be paved for a long distance, the grounding performance is reduced, and the input cost and the operation and maintenance cost of the grounding electrode are greatly increased if resistance reducing measures are added. In order to improve the grounding performance of the grounding electrode in a complex terrain area, the spiral grounding electrode can be better suitable for a complex soil environment based on the idea of reducing the grounding resistance value by enlarging the contact area of the grounding electrode and soil in unit axial space.
Third, measuring the grounding resistance: and measuring the grounding resistance of the grounding body by using a tripolar method. The ground resistance of the ground body is measured by a tripolar method, as shown in fig. 3. The grounding body G, the earth and the current electrode C together form a current loop, the measured current injected into the grounding body flows out of the current electrode after passing through soil with a certain distance, the potential on the ground is distorted, at the moment, the voltage electrode can be arranged at a potential compensation point, the potential difference between the measured voltage electrode P and the grounding electrode G is equal to the voltage drop on the grounding resistor, and therefore the voltage U between the measured voltage electrode and the grounding electrode is divided by the input current I to obtain the grounding resistance R. The method comprises the following specific steps:
(1) The three-pole method is used for measuring the grounding resistance of the grounding body, the grounding body G, the earth and the current pole C are arranged to form a current loop together, the measured current injected into the grounding body flows out of the current pole after passing through soil with a certain distance, the potential on the ground is distorted, the voltage pole is arranged at a potential compensation point at the moment, and the measured potential difference between the voltage pole P and the grounding pole G is equal to the voltage drop on the grounding resistor.
(2) Let the voltage U between the measuring voltage pole and the grounding pole divided by the input current I to obtain the grounding resistance R,
let the radius of hemispherical grounding body be a, the current injected into the grounding body be I, the distance between the grounding body and current pole be L GC The distance between the grounding body and the voltage pole is L GP The distance between the voltage pole and the current pole is L PC 。
(3) The application of the superposition principle can result in a potential difference V' between the GPs due to the current I input from the ground electrode G:
(4) The current I flowing from the current pole C makes the potential difference V' between GPs appear as:
(5) The ground resistance R is calculated as:
while the actual grounding resistance R of the grounding electrode 0 The method comprises the following steps:
(6) To make the measurement error
Is 0:
namely:
(7) Let L be PG ＝aL GC Because the grounding electrode G, the voltage electrode P and the current electrode C are on the same straight line, the distance between the voltage electrode and the current electrode is L PG ＝L GC -aL GC ；
Substituting formula (18) to obtain a=0.618;
arranging the voltage poles at zero potential point, i.e. L PG ＝0.618L GC In this case, the actual ground resistance is obtained.
The effect of soil resistivity on grounding performance for complex areas is analyzed as follows;
the magnitude of the grounding resistance of the grounding electrode reflects the current overflow performance of the grounding electrode, and is one of important parameters for measuring the grounding performance of the grounding electrode.
a) Setting parameters and carrying out grouping research: the spiral grounding electrode, the 10m horizontal round steel grounding electrode and the 62.8m horizontal grounding electrode with the same soil contact area are selected at present and divided into 3 groups for comparison, the burying directions are all along the x-axis direction, the burying depths are all 0.8m, and the body parameters are shown in table 1.
TABLE 1 comparison table of grounding electrode structural parameters (unit: m)
The grounding resistance of the two grounding electrodes can be obtained by selecting 1 group and 3 groups of grounding electrodes for comparison analysis under the condition of the same axial electrode distribution distance; and selecting 2 groups and 3 groups of grounding electrodes for comparison analysis to obtain the grounding resistance of the two grounding electrodes under the condition that the contact areas of the grounding electrodes and soil are the same.
b) Calculating the grounding resistance of the grounding electrode: according to the finite element analysis method, mesh division and interpolation are carried out on the grounding electrode, the magnitude of injection current is set, and the potential magnitude of any point on the surface of the grounding electrode can be obtained after calculation. And comparing the potential of the tail end of the grounding electrode with the injection current to obtain the value of the grounding resistance of the grounding electrode. Setting the soil resistivity to be 100 omega-m and the step length to be 50, thereby obtaining the influence of the soil resistivity on the ground resistance. Fig. 4 shows that the ground resistance of all three sets of ground electrodes increases with increasing soil resistivity. From the slopes of the three curves, it can be seen that the horizontal grounding electrode with the length of 10m is maximally subjected to the soil environment, the grounding resistance in the soil with the resistivity of 100 omega-m is as high as 67.9 omega, and resistance reduction measures are required in the environment with higher soil resistivity. The grounding resistance of the horizontal grounding electrode of 62.8m is the smallest than that of the spiral grounding, but the horizontal grounding electrode of more than 60m is generally not adopted in practical engineering due to the construction cost, the operation maintenance cost and other angles.
c) Analysis results, conclusion: in the soil environment with different resistivity, the spiral grounding electrode has the advantages of small axial electrode distribution space and good grounding performance, and the grounding performance of the grounding electrode in the complex soil environment with the same electrode distribution space is greatly improved.
Fourth, designing the length of the spiral grounding electrode. The horizontal grounding electrode can basically meet most engineering requirements when the axial electrode distribution space is larger than 10m, and the design index of the laying length of the spiral grounding electrode when the axial electrode distribution space is smaller than 10m is mainly analyzed. And analyzing and designing the laying length of the spiral grounding electrode when the axial electrode distribution space is smaller than 10m according to a finite element numerical calculation method. The method comprises the following specific steps:
(1) Setting parameters: soil resistivity, grounding body down-lead length, section radius, radius of spiral coil and screw pitch are set in the calculation process of the spiral grounding electrode.
(2) According to the finite element analysis method, mesh division and interpolation are firstly carried out on the grounding electrode, the magnitude of injection current is set, and the potential magnitude of any point on the surface of the grounding electrode can be obtained after calculation.
(3) And comparing the potential of the tail end of the grounding electrode with the injection current to obtain the value of the grounding resistance of the grounding electrode.
(4) Setting the initial value and the final value of the laying length to be 1m and 10m respectively, and the step length to be 1m to obtain the potential of any point on the horizontal linear grounding body and the spiral grounding body with the laying length from 1m to 10m, and comparing the potential with the injection current to obtain the grounding resistor.
(5) And selecting a corresponding laying length according to the grounding resistance value.
Here, specific examples of providing spiral ground length designs are as follows:
(A) Setting parameters: soil resistivity is 100 omega-m, the length of a grounding body down-lead is 0.8m, the section is a circle with the radius of 0.006m, the radius of a spiral coil is 0.5m, and the pitch is 0.5m.
(B) Calculating the grounding resistance of the grounding electrode under different laying lengths: according to the control variable method, other parameters are kept unchanged, the laying length of the spiral grounding electrode is changed, and the influence rule of different laying lengths on the grounding resistance of the spiral grounding electrode is researched. According to the finite element analysis method, mesh division and interpolation are firstly carried out on the grounding electrode, the magnitude of injection current is set, and the potential magnitude of any point on the surface of the grounding electrode can be obtained after calculation. And then comparing the potential of the tail end of the grounding electrode with the injection current to obtain the value of the grounding resistance of the grounding electrode. Setting the initial value and the final value of the laying length to be 1m and 10m respectively, and the step length to be 1m, the potential of any point on the horizontal straight-line grounding body and the spiral grounding body with the laying length from 1m to 10m can be obtained, the potential and the injection current can be compared, and the grounding resistance can be obtained, and the calculation results are shown in table 2 and fig. 5.
TABLE 2 comparison of laying lengths of spiral grounding electrode and horizontal grounding electrode
(C) Analysis results, conclusion: the calculation result shows that the grounding resistance of the spiral grounding body is far smaller than that of the horizontal grounding electrode under the condition that the laying lengths are the same in the interval of 1m to 10m. When the laying length L is more than or equal to 5m, the grounding resistance of the spiral grounding electrode meets the requirement that the resistance is less than 10Ω, and in order to save materials, the laying length of the spiral grounding electrode can be set to be 5 to 8m.
Fifthly, designing the radius of the spiral grounding electrode: and analyzing and designing the radius size of the spiral grounding electrode according to the grounding resistance value. The method comprises the following specific steps:
(1) Setting parameters: setting a hemispherical soil pool radius, a soil resistivity, a grounding body down-lead length, a section radius, a screw pitch, a laying length and a coil radius to be 0.1m to 2.5m in the calculation process of the spiral grounding electrode;
(2) Calculating the grounding resistance values of different coil radiuses:
according to a control variable method, keeping other parameters unchanged, changing the coil radius of the spiral grounding electrode, and analyzing the influence rule of different coil radii on the grounding resistance of the spiral grounding electrode;
according to a finite element analysis method, mesh subdivision and interpolation are firstly carried out on a grounding electrode, the injection current is set to be 1A, and the potential of any point on the surface of the grounding electrode can be obtained after calculation; then comparing the potential of the tail end of the grounding electrode with the injection current to obtain the value of the grounding resistance of the grounding electrode;
(3) And selecting a corresponding grounding electrode radius according to the numerical value requirement of the grounding resistance of the grounding electrode.
Here, specific examples of providing spiral ground radius designs are as follows:
(A) Setting parameters: setting a hemispherical soil pool radius of 250m, a soil resistivity of 100 Ω & m, a grounding body down-lead length of 0.8m, a section of radius of 0.006m, a pitch of 0.5m, a laying length of 10m in a calculation model of a spiral grounding electrode, calculating by taking different coil radiuses, and setting the coil radius of 0.1m to 2.5m.
(B) Calculating the grounding resistance values of different coil radiuses: according to the control variable method, other parameters are kept unchanged, the coil radius of the spiral grounding electrode is changed, and the influence rule of different coil radii on the grounding resistance of the spiral grounding electrode is researched. According to the finite element analysis method, mesh subdivision and interpolation are firstly carried out on the grounding electrode, the injection current is set to be 1A, and the potential of any point on the surface of the grounding electrode can be obtained after calculation. The magnitude of the potential at the end of the ground electrode was then compared with the injection current to obtain the value of the ground resistance of the ground electrode, and the results are shown in table 3 and fig. 6.
Table 3 comparison table of ground resistance of spiral ground electrode under different coil radii
In connection with tables 3 and 6, it is shown that as the radius of the spiral earthing pole coil increases, the contact area between the conductors and the soil increases, the radial distance between the conductors increases, the shielding effect decreases, and the earthing resistance tends to decrease. According to the structural analysis of the spiral grounding electrode, the construction depth of the spiral grounding electrode is equal to the distribution depth plus the coil diameter, and the overlarge coil radius increases the construction cost and reduces the utilization rate of the grounding conductor material.
(C) And (3) analyzing rules to obtain conclusion: by further analyzing the law of influence of the coil radius on the grounding resistance in fig. 6, it is obtained that when the coil radius is larger than 1m, the resistance value of the grounding resistance tends to a constant value at a slow speed, and the grounding resistance does not change significantly with the increase of the coil radius. According to the analysis, the optimal coil radius of the spiral grounding electrode is between 0.5m and 1m, so that on one hand, the good renting effect of the spiral grounding electrode in a complex area is fully exerted, and on the other hand, the unnecessary construction and material cost is reduced.
(D) Calculating the grounding resistance values of different section radiuses: in order to analyze the influence of the section radius of the spiral grounding electrode on the grounding performance, other parameters are kept unchanged according to a control variable method, the section radius of the spiral grounding electrode is changed, and the influence rule of different section radii on the grounding resistance of the spiral grounding electrode is researched. And similarly, mesh dissection and interpolation are carried out on the grounding electrode according to a finite element analysis method, the injection current is set to be 1A, the potential of any point on the surface of the grounding electrode can be obtained after calculation, and then the potential of the tail end of the grounding electrode is compared with the injection current, so that the grounding resistance of the spiral grounding electrode with the section radius ranging from 0.005m to 0.03m can be obtained.
Table 4 ground resistance comparison table for spiral ground electrode at different section radii
As can be seen from table 4, the ground resistance decreases with increasing cross-sectional radius of the spiral ground electrode, but the ground resistance with a cross-sectional radius of 0.030m decreases by only 0.55Ω compared to the ground resistance with a cross-sectional radius of 0.005m, but the metal material increases significantly.
(E) And (3) analyzing rules to obtain conclusion: fig. 6 shows that the ground resistance reduction speed is large in the range of 0.005m to 0.020m, in which the section radius has a large influence on the ground resistance. If the section radius is more than 0.020m, the influence of the section radius on the grounding resistance is weak, and the reduction of the grounding resistance value is not obvious. From the above analysis, it is found that the selection of the cross-sectional radius of the spiral grounding electrode can select an optimal layout scheme between 0.005m and 0.020m according to the actual burying environment.
Sixth, designing the pitch of the spiral grounding electrode: and analyzing and designing the screw grounding electrode pitch according to the grounding resistance value. The method comprises the following specific steps:
(1) Setting parameters: setting a hemispherical soil pool radius, a soil resistivity, a grounding body down-lead length, a section radius, a spiral coil radius and a laying length in the calculation process of the spiral grounding electrode;
(2) Calculating the grounding resistance value of the grounding electrode under different pitches:
according to a finite element analysis method, mesh subdivision and interpolation are firstly carried out on a grounding electrode, the magnitude of injection current is set to be 1A, the potential magnitude of any point on the surface of the grounding electrode is obtained after calculation, and then the potential magnitude of the tail end of the grounding electrode is compared with the injection current to obtain the grounding resistance of the spiral grounding electrode under different pitches;
(3) According to the numerical requirement of the grounding resistance of the grounding electrode, the corresponding screw pitch is selected.
Here, a specific example of providing the helical ground pitch is as follows:
(A) Setting parameters: in order to study the influence of the screw pitch on the grounding resistance of the spiral grounding body, a hemispherical soil pool radius of 250m, a soil resistivity of 100 Ω & m, a grounding body down-lead length of 0.8m, a section of radius of 0.006m, a spiral coil radius of 0.5m and a laying length of 10m are arranged in a calculation model of the spiral grounding electrode.
(B) Calculating the grounding resistance value of the grounding electrode under different pitches: according to the finite element analysis method, mesh subdivision and interpolation are firstly carried out on the grounding electrode, the injection current is set to be 1A, the potential of any point on the surface of the grounding electrode can be obtained after calculation, then the potential of the tail end of the grounding electrode is compared with the injection current, and the grounding resistance of the spiral grounding electrode under different pitches can be obtained, and the results are shown in Table 5.
TABLE 5 comparison of spiral earthing pole earthing resistance under different axial distances (unit: omega)
(C) Analysis results, conclusion: the result is that the ground resistance of the spiral ground electrode at any turn spacing is far less than the horizontal ground electrode at the same L. At l=1, the ground resistance of the spiral ground electrode is most significantly affected by the inter-turn distance, which is less than half of that at 1m when the inter-turn distance is 0.1 m. As L increases, the amount of decrease in resistance of the ground electrode due to the change in the inter-turn distance decreases, but the material consumption of the ground electrode increases greatly.
(D) Comprehensively considering the service efficiency of the grounding material and the resistance-reducing performance of the grounding electrode: the utilization ratio of the spiral grounding electrode material is defined as the difference of grounding resistance with the turn spacing of 1 under a certain length of the cloth electrode minus the grounding resistance with the turn spacing of a certain length of the cloth electrode divided by the number of turns of the spiral grounding electrode under a corresponding size, and the result of the utilization ratio of the spiral grounding electrode material is as follows.
Table 6 comparison table of grounding electrode material utilization
(E) Analysis results, conclusion: table 6 shows that under the same axial cloth electrode distance, the utilization rate of the material is increased and then reduced along with the increase of the turn distance, and the optimal range of the turn distance is selected from 0.4m to 0.6m by comprehensively considering the utilization rate of the material and the size of the grounding resistance.
Comprehensively considering the construction cost, the material consumption, the grounding performance and other aspects of the spiral grounding electrode, wherein the laying length of the spiral grounding electrode is in the range of 5m to 8 m; the radius of the spiral grounding electrode coil is in the range of 0.3m to 0.5 m; the radius of the section is in the range of 0.005m to 0.020 m; the turn spacing is selected to be in the range of 0.4m to 0.6m, certain adjustment can be carried out according to the actual soil resistivity and working conditions, the turn spacing can be properly increased when the pole arrangement space is larger, and the turn spacing can be properly reduced when the pole arrangement space is smaller.
In summary, compared with a horizontal straight-line grounding body, the spiral grounding body can effectively reduce the grounding resistance under the condition of equal laying length, and can be more suitable for complex soil environments. And the laying length of the spiral grounding body has the greatest influence on the grounding resistance, the radius of the spiral coil has the secondary influence on the resistance, and the pitch has the least influence on the resistance. In the region with more complicated topography condition, can replace horizontal straight line grounding body with the spiral grounding body in order to reduce the earth resistance, improve the earth performance, reach the safety index.
The foregoing has shown and described the basic principles, principal features and advantages of the invention. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, and that the above embodiments and descriptions are merely illustrative of the principles of the present invention, and various changes and modifications may be made therein without departing from the spirit and scope of the invention, which is defined by the appended claims. The scope of the invention is defined by the appended claims and equivalents thereof.
Claims (6)
1. The design method of the spiral grounding electrode size parameter suitable for the complex environment area is characterized by comprising the following steps of:
11 Setting a grounding limit finite element calculation method: setting a grounding electrode finite element calculation method to obtain the surface potential of the grounding electrode with any structural parameter by the grounding electrode finite element calculation method;
the method for calculating the set grounding limit finite element comprises the following steps:
111 Approximating the ground electrode as a set of point current sources, potential function
Satisfy differential equation
Wherein I is the size of the point current source in the field,
vectors representing the spatial position of the field point, +.>
Vectors representing the spatial position of the source point, +.>
As a Dike function ρ s Is soil resistivity;
112 Listing the edge equation of the ground electrode in the electric field:
let Ω be the required field Γ 1 Is the interface of soil medium and air, Γ 2 To simulate an equivalent boundary at zero potential at infinity, boundary Γ=Γ 1 +Γ 2 ，Γ 3 The potential of the surface of the approximately spiral grounding electrode is constant by neglecting the voltage drop of the surface of the grounding electrode to be the interface between the surface of the grounding electrode and a soil medium
Listing the edge value problem:
113 Converting the above edge equations into a variation problem:
according to the above description, the analysis process of the current overflow of the grounding electrode is the Poisson side value problem, and the conversion of the typical side value problem into the equivalent variation problem is as follows:
114 Splitting and interpolating the three-dimensional field:
mesh subdivision and interpolation are carried out on the three-dimensional field, a first order tetrahedron unit is selected as a basic unit for subdivision of the three-dimensional field, and if the solved field is assumed to be subdivided into Z by tetrahedron 0 Units, get N 0 A plurality of discrete nodes; each node corresponds to a unique space potential equation, four vertexes of a first-order tetrahedron unit are taken as nodes, and the actual numbers of the nodes in the whole domain are i, j, l and m;
the linear interpolation is as follows:
/>
the interpolation function is continuous in the unit tetrahedron e, and brings four vertex coordinates and corresponding bits respectivelyValue, obtain: alpha 1 +α 2 x i +α 3 y i +α 4 z i i＝(1,2,3,4)；
Simultaneous equation solving to obtain alpha 1 ,α 2 ,α 3 ,α 4 Each coefficient to be determined is put into an interpolation function, and is obtained after finishing:
the elements of the coefficient matrix in the rectangular coordinate system are required to form the finite element equation:
because of
So that
115 Unit analysis of unit tetrahedrons):
after subdivision and interpolation, the unit tetrahedrons are subjected to unit analysis, unit analysis [ P ]] e Is a matrix element of (a):
the center of gravity point (x) c 、y c 、z c ) Substituting the coordinates into the above equation, assuming that the unit endogenous density is approximately unchanged, becomes:
116 Deriving a finite element equation:
integrating all parameters in a rectangular coordinate system comprehensively to obtain related parameters in a global range:
[k]＝∑[k] e ，[p]＝v[p] e (9)
therefore, the finite element equation of the poisson field satisfying the second homogeneous boundary condition is
Wherein [ k ]]As a matrix of the energy coefficients of the total electric field,
for the potential matrix of all nodes, after the finite element equation is obtained, the corresponding calculation program is called to obtain +.>
Is a value of (2);
12 Measurement of soil resistivity in complex environmental areas: indirectly measuring the soil resistivity through the soil by using a quadrupole method;
13 Measuring ground resistance): measuring the grounding resistance of the grounding body by using a tripolar method;
14 Design of the length of the spiral grounding electrode: analyzing and designing the laying length of the spiral grounding electrode when the axial electrode distribution space is smaller than 10m according to a finite element numerical value calculation method;
15 Design of spiral grounding electrode radius): analyzing and designing the radius size of the spiral grounding electrode according to the grounding resistance value;
16 Design of the screw grounding electrode pitch): and analyzing and designing the screw grounding electrode pitch according to the grounding resistance value.
2. The method for designing the size parameter of the spiral grounding electrode suitable for the complex environment area according to claim 1, wherein the measurement of the soil resistivity of the complex environment area comprises the following steps:
21 Measuring soil resistivity by indirect measurement of soil resistance using quadrupole method, let a be 1 、a 2 For the distance, a, between the current pole A and the potential poles C, D 3 、a 4 The distance between the current electrode B and the potential electrodes C and D;
22 Four electrodes A, B, C, D are driven into the ground, and the depth of the driven-in ground is uniform;
23 Applying a current I to the electrodes A and B by using a regulated power supply E, allowing the current to flow in through the electrode A, and returning the current to the power supply by the electrode B, so that a current field generates a potential on the electrodes C and D, and measuring the potential difference between the electrodes C and D by using a potential difference meter or a high-resistance state voltmeter;
the four electrode bars are distributed on the same straight line, the spacing between the electrode bars is equal to a, and the depth of each electrode bar which is driven into the ground is not more than 1/20 of the spacing a of the electrode bars;
24 Soil resistivity is measured, and the calculation formula is as follows:
wherein ρ is soil resistivity Ω·m, R is measured resistance Ω, a is distance m between the electrodes measured, and b is depth m of the electrodes measured into the ground;
when the test electrode is driven into the ground by a depth b not exceeding 0.2a, assuming b=0, the following formula is simplified:
ρ＝2πaR (12)。
3. a spiral earthing pole size parameter design method suitable for a complex environment area according to claim 1, wherein the measuring earthing resistance comprises the following steps:
31 The ground resistance of the grounding body is measured by a tripolar method, the grounding body G, the ground and the current electrode C are arranged to form a current loop together, the measured current injected into the grounding body flows out of the current electrode after passing through soil with a certain distance, the potential on the ground is distorted, the voltage electrode is arranged at a potential compensation point, and the potential difference between the measured voltage electrode P and the ground electrode G is equal to the voltage drop on the grounding resistor;
32 Setting the voltage U between the measuring voltage pole and the grounding pole divided by the input current I to obtain the grounding resistance R,
let the radius of hemispherical grounding body be a, the current injected into the grounding body be I, the distance between the grounding body and current pole be L GC The distance between the grounding body and the voltage pole is L GP The distance between the voltage pole and the current pole is L PC ；
33 By applying the superposition principle, the current I input from the ground electrode G causes a potential difference V' to occur between the GPs:
34 A current I flowing from the current pole C makes the potential difference V "present between the GP:
35 Calculating the ground resistance R as:
while the actual grounding resistance R of the grounding electrode 0 The method comprises the following steps:
36 Error of measurement
Is 0:
namely:
37 Set L PG ＝aL GC Because the grounding electrode G, the voltage electrode P and the current electrode C are on the same straight line, the distance between the voltage electrode and the current electrode is L PG ＝L GC -aL GC ；
Substituting formula (18) to obtain a=0.618;
arranging the voltage poles at zero potential point, i.e. L PG ＝0.618L GC In this case, the actual ground resistance is obtained.
4. A method of designing a size parameter of a spiral earthing pole suitable for a complex environment area according to claim 1, wherein the designing of the length of the spiral earthing pole comprises the steps of:
41 Setting parameters: setting soil resistivity, grounding body down-lead length, section radius, radius of a spiral coil and screw pitch in the calculation process of the spiral grounding electrode;
42 According to finite element analysis, mesh division and interpolation are firstly carried out on the grounding electrode, the magnitude of injection current is set, and the potential magnitude of any point on the surface of the grounding electrode can be obtained after calculation;
43 Comparing the potential of the end of the grounding electrode with the injection current to obtain the value of the grounding resistance of the grounding electrode;
44 Setting an initial value and a final value of the laying length to be 1m and 10m respectively, and setting the step length to be 1m to obtain the potential of any point on the horizontal linear grounding body and the spiral grounding body with the laying length from 1m to 10m, and comparing the potential with the injection current to obtain the grounding resistor;
45 According to the grounding resistance value, the corresponding laying length is selected.
5. A method of designing a spiral earthing pole size parameter for a complex environmental area according to claim 1, wherein the design of the spiral earthing pole radius comprises the steps of:
51 Setting parameters: setting a hemispherical soil pool radius, a soil resistivity, a grounding body down-lead length, a section radius, a screw pitch, a laying length and a coil radius to be 0.1m to 2.5m in the calculation process of the spiral grounding electrode;
52 Calculating the ground resistance values of different coil radii):
according to a control variable method, keeping other parameters unchanged, changing the coil radius of the spiral grounding electrode, and analyzing the influence rule of different coil radii on the grounding resistance of the spiral grounding electrode;
according to a finite element analysis method, mesh subdivision and interpolation are firstly carried out on a grounding electrode, the injection current is set to be 1A, and the potential of any point on the surface of the grounding electrode can be obtained after calculation; then comparing the potential of the tail end of the grounding electrode with the injection current to obtain the value of the grounding resistance of the grounding electrode;
53 According to the numerical value of the grounding resistance of the grounding electrode, selecting the corresponding grounding electrode radius.
6. The method for designing the size parameter of the spiral grounding electrode suitable for the complex environment area according to claim 1, wherein the design of the spiral grounding electrode pitch comprises the following steps:
61 Setting parameters: setting a hemispherical soil pool radius, a soil resistivity, a grounding body down-lead length, a section radius, a spiral coil radius and a laying length in the calculation process of the spiral grounding electrode;
62 Calculating the grounding resistance value of the grounding electrode under different pitches:
according to a finite element analysis method, mesh subdivision and interpolation are firstly carried out on a grounding electrode, the magnitude of injection current is set to be 1A, the potential magnitude of any point on the surface of the grounding electrode is obtained after calculation, and then the potential magnitude of the tail end of the grounding electrode is compared with the injection current to obtain the grounding resistance of the spiral grounding electrode under different pitches;
63 According to the value of the grounding resistance of the grounding electrode, selecting a corresponding screw pitch.
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