CN113504411B - Large-scale grounding grid grounding resistance multi-factor evaluation method - Google Patents
Large-scale grounding grid grounding resistance multi-factor evaluation method Download PDFInfo
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Abstract
The invention provides a multi-factor evaluation method for ground resistance of a large-scale grounding grid, and belongs to the technical field of transformer substation grounding grids. The method comprises the following steps: acquiring large-scale grounding grid parameters, establishing an original database, establishing a grounding grid simulation calculation model, acquiring evaluation values of the grounding resistance R under 11 influence element changes, and acquiring a grounding grid grounding resistance multi-element evaluation value set. Compared with the prior art, the method and the device have the advantages that the influence of multiple factors such as the horizontal grounding conductor structure parameters, the vertical grounding conductor structure parameters, the soil structure parameters and the like on the performance indexes is considered, and the power frequency characteristic evaluation of the large grounding grid is more comprehensive and accurate.
Description
Technical Field
The invention belongs to the technical field of transformer substation grounding networks, and particularly relates to a multi-factor evaluation method for grounding resistance of a large grounding network.
Background
The traction substation is an important component of a high-speed railway traction power supply system, and has the functions of converting high-voltage power-frequency alternating current acquired from a power system into single-phase power-frequency alternating current through an internal traction transformer and then transmitting the electric energy to a contact network through a feeder line to be supplied to a corresponding electric locomotive for use. The traction substation grounding grid is an important component for ensuring safe and stable operation of a substation, and when a power frequency grounding fault occurs in the substation, casualties and equipment loss can be caused if the grounding grid cannot normally operate. In order to avoid accidents, the safety performance of the grounding grid needs to be accurately evaluated, and the grounding resistance is an important index for evaluating the grounding grid.
At present, the design and evaluation of the grounding grid of the traction substation are generally completed by an empirical formula and the experience of technicians. Due to the few factors considered, there are the following problems:
1) in the traditional method, the grounding grid is equivalent to a circuit network based on an analysis method of a circuit theory, and the method has the advantages of clear concept but low calculation precision; the analysis method based on the transmission line theory ignores the electromagnetic coupling between the conductors of the grounding grid, and is not suitable for the analysis of the large-scale grounding grid.
2) The empirical formula considers few factors, does not consider factors such as unevenness of soil and distribution of conductors, and has defects when evaluating the large-scale grounding grid.
Disclosure of Invention
The invention aims to solve the technical problem that the ground grid evaluation is not totally inaccurate due to over dependence on an empirical formula and personal experience in the safety performance evaluation of the large-scale ground grid at present.
The invention aims to realize the purpose, and provides a large-scale grounding network grounding resistance multi-factor evaluation method, which comprises the following steps:
Step 1.1, determination of influencing factors
Marking a large grounding grid as a grounding grid, classifying influence elements influencing grounding resistance change of the grounding grid into three types, namely 11 types according to known statistical data, and marking any one of the 11 types of influence elements as an influence element MαβWhere α is the number of the influencing element class, α ═ α1，α2，α3，α1For horizontal ground conductor influencing element, α2For influencing elements of the vertical grounding conductor, α3Is a soil structure influencing element; beta is an influencing element MαβSerial No. in each category, β ═ 1, 2 …; specifically, the method comprises the following steps:
horizontal ground conductor influencing element
Mesh size
Horizontal ground conductor shape
Double-layer ground screen interval
And the distance between the external ground screen and the ground screen
Vertical ground conductor influencing element
Number of vertical grounding conductors on four sides and inside of grounding grid
Number of vertical grounding conductors at lightning rod
Number of vertical grounding conductors at gate-type structure
All vertical ground conductor lengths
Length of external vertical ground conductor
Vertical ground conductor profile
Soil structure influencing element
Soil stratification and resistivity of each layer of soil
Step 1.2, collecting original data and establishing an original database
Acquiring original data of each influence element according to the influence elements given in the step 1.1, specifically, acquiring the soil condition of the grounding grid on site, measuring the soil resistivity of the area where the grounding grid is located on site, and acquiring structural parameter information of the grounding grid according to a design drawing of the grounding grid;
establishing an original database of the grounding grid according to the acquired original data of each influence element;
in the original database, all the original data of each influence element are combined into a set, a set of 11 influence element original data is obtained, and the influence element M is combinedαβIs denoted as an original data set Mαβ', the set of influencing elements Mαβ' totally comprises E original data, E is a positive integer, and alpha is alpha1，α2，α3，β＝1，2…；
Step 2, establishing a grounding grid simulation calculation model
Step 2.1, constructing a soil layering model
The soil layering model is composed of T layers of soil, T is the number of soil layers, any one of the T layers of soil is marked as a soil layer j, j is 1, 2 … T, and the thickness of the soil layer j is HjAnd the resistivity of the soil layer j is rhoj；
Step 2.2, setting the topological structure of the grounding grid conductor
The topological structure of the grounding grid conductor comprises Q horizontal grounding conductors, W vertical grounding conductors and a current injection conductor; the Q horizontal grounding conductors have the same sectional area and the same buried depth, and the sectional area of the horizontal grounding conductor is expressed as S1And the buried depth of the horizontal grounding conductor is marked as S2(ii) a W vertical grounding conductors have the same cross-sectional area and the same length, and the cross-sectional area of the vertical grounding conductor is expressed as S3And the length of the vertical grounding conductor is recorded as S4(ii) a The cross-sectional area of the current-injected conductor is denoted as S5The length of the current-injecting conductor is denoted S6；
Simplifying the grounding grid into a rectangle, establishing a spatial three-dimensional rectangular coordinate system by taking any one of four corners of the grounding grid as a coordinate origin O, and recording any one of Q horizontal grounding conductors as a horizontal grounding conductor gammaAA is the serial number of the horizontal grounding conductor, A is 1, 2AStarting point coordinates and end point coordinates in a spatial three-dimensional rectangular coordinate systemIs (x)1A，y1A，z1A) And (x)2A，y2A，z2A) (ii) a Any one of the W vertical ground conductors is referred to as a vertical ground conductor ΨBB is the number of the vertical conductor, 1, 2BThe start coordinate and the end coordinate in the spatial three-dimensional rectangular coordinate system are respectively (x)3B，y3B，z3B) And (x)4B，y4B，z4B) (ii) a The initial coordinate and the end coordinate of the current injection conductor in the space three-dimensional rectangular coordinate system are respectively (x)5，y5，z5) And (0, 0, 0);
according to the soil layering model and the topological structure of the grounding grid conductor, and the 11 influence elements given in the step 1.1 are integrated, and the establishment of the grounding grid simulation calculation model is completed under the environment of simulation software CDEGS;
step 2.3, setting of evaluation index
Under the environment of simulation software CDEGS, recording a current injection conductor in a simulation calculation model of the grounding grid as a conductor He, recording the current value of the injection conductor He as an injection current I, recording the potential rise corresponding to the injection current I as a potential rise U, and recording the grounding resistance value of the grounding grid corresponding to the injection current I and the potential rise U as a grounding resistance R, wherein R is U/I;
the grounding resistance R is used as an evaluation index of a grounding network grounding resistance multi-factor evaluation method;
step 3, obtaining the evaluation value of the grounding resistance R under the change of 11 influencing factors
Step 3.1, determining simulation reference formula G
Each raw data set M obtained in step 1αβ' in this example, one original data is arbitrarily selected as a reference value Hαβ，α＝α1，α2，α3β ═ 1, 2 …, i.e. corresponding to 11 original data sets Mαβ' obtaining 11 reference values H of 11 influencing elements in totalαβThe 11 reference values HαβSubstituting the grounding grid simulation model into a simulation benchmark formula G;
step 3.2Calculating the influence factor MαβEvaluation of ground resistance value RαβThe specific process is as follows:
extracting an original data set Mαβ' and replacing the reference value H with E pieces of original dataαβSubstituting the simulation reference formula G for simulation to obtain potential rises U corresponding to the E original data, and recording the potential rise U with the maximum value as the maximum potential rise U1And calculating the grounding resistance value at this time and recording as an evaluation grounding resistance value Rαβ，Rαβ＝U1/I；
Step 3.3, sequentially simulating the 11 influence elements according to the method of the step 3.2 to obtain 11 evaluation grounding resistance values R corresponding to the 11 influence elementsαβ；
11 evaluation ground resistance values R corresponding to the 11 influence elements obtained in step 3.3αβThe set is recorded as a grounding grid grounding resistance multi-factor evaluation value set R0，
Preferably, the structural parameter information of the grounding grid in the step 1 includes a structure of the grounding grid, an area of the grounding grid, and a buried depth of the grounding grid; the distribution condition of the horizontal grounding conductors, the sectional area of the horizontal grounding conductors, the buried depth of the horizontal grounding conductors and the number of the horizontal grounding conductors; distribution of vertical grounding conductors, vertical grounding conductor cross-sectional area, vertical grounding conductor length, number of vertical grounding conductors, current injection conductor cross-sectional area, and current injection conductor length.
Preferably, the method for evaluating the grounding resistance of the large grounding network by multiple elements is characterized in that the step 1 further comprises the step of normalizing data in an original database after the original database is established, so that the data in the original database keeps uniform dimension.
Compared with the prior art, the invention has the following beneficial effects:
1. aiming at the characteristics of a large grounding grid, a CDEGS simulation software is used, a moment method is adopted for analysis, all electromagnetic coupling between grounding grid conductors is considered, and the calculation result of a grounding grid model is more accurate.
2. Various factors influencing the ground resistance evaluation, such as soil uniformity, double-layer grounding grids, conductor distribution conditions and the like, are considered, so that the safety performance evaluation of the grounding grid is more comprehensive and scientific.
Drawings
FIG. 1 is a flow chart of the evaluation method of the present invention;
FIG. 2 is a diagram showing a basic structure of a plurality of influencing elements in the evaluation method of the present invention;
FIG. 3 is a schematic diagram of a horizontal grounding conductor in a simulation calculation model of a grounding grid according to an embodiment of the present invention;
FIG. 4 is a schematic diagram of a vertical grounding conductor in a simulation calculation model of a grounding grid according to an embodiment of the present invention;
FIG. 5 is a schematic diagram of positions of a lightning rod and a door type framework in a simulation calculation model of a grounding grid according to an embodiment of the present invention;
fig. 6 is a schematic view of a soil structure in a simulation calculation model of a grounding grid in the embodiment of the invention.
Detailed Description
The evaluation method of the present invention will be discussed in detail below with reference to the drawings.
Fig. 1 is a flow chart of the evaluation method of the invention, and as can be seen from fig. 1, the method for evaluating the grounding resistance of the large-scale grounding grid comprises the following steps:
Step 1.1, determination of influencing factors
Marking a large grounding grid as a grounding grid, classifying influence elements influencing grounding resistance change of the grounding grid into three types, namely 11 types according to known statistical data, and marking any one of the 11 types of influence elements as an influence element MαβWhere α is the number of the influencing element class, α ═ α1，α2，α3，α1For horizontal ground conductor influencing element, α2For influencing elements of the vertical grounding conductor, α3Is a soil structure influencing element; beta is an influencing element MαβThe numbers in each class, β ═ 1, 2 …. Specifically, the method comprises the following steps:
horizontal ground conductor influencing element
Mesh size
Horizontal ground conductor shape
Double-layer ground screen interval
And the distance between the external ground screen and the ground screen
Vertical ground conductor influencing element
Number of vertical grounding conductors on four sides and inside of grounding grid
Number of vertical grounding conductors at lightning rod
Number of vertical grounding conductors at gate-type structure
All vertical ground conductor lengths
Length of external vertical ground conductor
Vertical grounding conductor branchCloth Condition
Soil structure influencing factors
Soil stratification and resistivity of each layer of soil
Fig. 2 shows the basic structure of the above influencing elements.
Step 1.2, collecting original data and establishing an original database
Acquiring original data of each influence element according to the influence elements given in the step 1.1, specifically, acquiring the soil condition of the grounding grid on site, measuring the soil resistivity of the area where the grounding grid is located on site, and acquiring structural parameter information of the grounding grid according to a design drawing of the grounding grid;
establishing an original database of the grounding grid according to the acquired original data of each influence element;
in the original database, all the original data of each influence element are combined into a set, a set of 11 influence element original data is obtained, and the influence element M is combinedαβIs denoted as an original data set Mαβ', the set of influencing elements Mαβ' totally comprises E original data, E is a positive integer, and alpha is alpha1，α2，α3，β＝1，2…；
In this embodiment, the structural parameter information of the ground net in step 1 includes a structure of the ground net, an area of the ground net, and a buried depth of the ground net; the distribution condition of the horizontal grounding conductors, the sectional area of the horizontal grounding conductors, the buried depth of the horizontal grounding conductors and the number of the horizontal grounding conductors; distribution of vertical grounding conductors, vertical grounding conductor cross-sectional area, vertical grounding conductor length, number of vertical grounding conductors, current injection conductor cross-sectional area, and current injection conductor length.
In this embodiment, the step 1 further includes performing normalization processing on the data in the original database after the original database is established, so that the data in the original database keeps uniform dimensions.
Step 2, establishing a grounding grid simulation calculation model
Step 2.1, constructing a soil layering model
The soil layering model is composed of T layers of soil, T is the number of soil layers, any one of the T layers of soil is marked as a soil layer j, j is 1, 2 … T, and the thickness of the soil layer j is HjAnd the resistivity of the soil layer j is rhoj。
Fig. 6 is a schematic diagram showing a soil structure in a simulation calculation model of the grounding grid in the embodiment.
Step 2.2, setting the topological structure of the grounding grid conductor
The topological structure of the grounding grid conductor comprises Q horizontal grounding conductors, W vertical grounding conductors and a current injection conductor; the Q horizontal grounding conductors have the same sectional area and the same buried depth, and the sectional area of the horizontal grounding conductor is expressed as S1And the buried depth of the horizontal grounding conductor is marked as S2(ii) a W vertical grounding conductors have the same cross-sectional area and the same length, and the cross-sectional area of the vertical grounding conductor is expressed as S3And the length of the vertical grounding conductor is recorded as S4(ii) a The cross-sectional area of the current-injected conductor is denoted as S5The length of the current-injecting conductor is denoted S6。
Simplifying the grounding grid into a rectangle, establishing a spatial three-dimensional rectangular coordinate system by taking any one of four corners of the grounding grid as a coordinate origin O, and recording any one of Q horizontal grounding conductors as a horizontal grounding conductor gammaAA is the number of the horizontal grounding conductor, A is 1, 2AThe start point coordinate and the end point coordinate in the spatial three-dimensional rectangular coordinate system are respectively (x)1A，y1A，z1A) And (x)2A，y2A，z2A) (ii) a Any one of the W vertical ground conductors is referred to as a vertical ground conductor ΨBB is the number of the vertical conductor, 1, 2BIn space three-dimensional right angleThe start and end coordinates in the coordinate system are respectively (x)3B，y3B，z3B) And (x)4B，y4B，z4B) (ii) a The initial coordinate and the end coordinate of the current injection conductor in the space three-dimensional rectangular coordinate system are respectively (x)5，y5，z5) And (0, 0, 0).
And (3) according to the soil layering model and the topological structure of the grounding grid conductor, and by integrating the 11 influence elements given in the step 1.1, establishing a grounding grid simulation calculation model under the environment of simulation software CDEGS.
Fig. 3 is a schematic diagram of a horizontal grounding conductor in the simulation calculation model of the grounding grid in this embodiment, fig. 4 is a schematic diagram of a vertical grounding conductor in the simulation calculation model of the grounding grid in this embodiment, and fig. 5 is a schematic diagram of positions of a lightning rod and a gate-type framework in the simulation calculation model of the grounding grid in this embodiment.
Step 2.3, setting of evaluation index
In the environment of simulation software CDEGS, a current injection conductor in a simulation calculation model of a grounding grid is denoted as a conductor He, the current value of the injection conductor He is denoted as an injection current I, a potential rise corresponding to the injection current I is denoted as a potential rise U, and the grounding resistance value of the grounding grid corresponding to the injection current I and the potential rise U is denoted as a grounding resistance R, wherein R is U/I.
And taking the grounding resistance R as an evaluation index of the grounding grid grounding resistance multi-factor evaluation method.
Step 3, obtaining the evaluation value of the grounding resistance R under the change of 11 influencing factors
Step 3.1, determining simulation reference formula G
Each raw data set M obtained in step 1αβ' in this example, one original data is arbitrarily selected as a reference value Hαβ，α＝α1，α2，α3β ═ 1, 2 …, i.e. corresponding to 11 original data sets Mαβ' obtaining 11 reference values H of 11 influencing elements in totalαβThe 11 reference values H are comparedαβSubstituting the grounding grid simulation model into a simulation benchmark formula G;
step 3.2, calculating the influencing factor MαβEvaluation of ground resistance value RαβThe specific process is as follows:
extracting an original data set Mαβ' and replacing the reference value H with E pieces of original dataαβSubstituting the simulation reference formula G for simulation to obtain potential rises U corresponding to the E original data, and recording the potential rise U with the maximum value as the maximum potential rise U1The ground resistance value at this time is calculated and recorded as an evaluation ground resistance value Rαβ，Rαβ＝U1/I；
Step 3.3, sequentially simulating the 11 influence elements according to the method of the step 3.2 to obtain 11 evaluation grounding resistance values R corresponding to the 11 influence elementsαβ；
11 evaluation ground resistance values R corresponding to the 11 influencing elements obtained in step 3.3αβThe set is recorded as a grounding grid grounding resistance multi-factor evaluation value set R0，
Taking the grounding grid of a traction substation in the Xuzhou section of the high-speed railway as an example, the grounding grid is subjected to multi-dimensional evaluation of grounding resistance according to the evaluation method of the invention.
The steps 1 and 2 are the same as above.
In the present embodiment, first, 11 kinds of influence elements of fig. 2 are determined. Secondly, acquiring the soil condition and the soil resistivity of the grounding grid of a certain traction substation in the Xuzhou section of the high-speed railway on site, acquiring the structural parameter information of the grounding grid according to a design drawing for calling the grounding grid, collecting the structural parameters of the grounding grid of the certain traction substation in the Xuzhou section of the high-speed railway, establishing an original database, and performing normalization processing.
Specifically, in this embodiment, the resistivity of the region where the grounding grid is located is 300 Ω m, and the floor area of the grounding grid is 7200m2Horizontal ground conductor cross-sectional area S1＝185mm2Horizontal ground conductor buried depth S20.8m, vertical ground conductor cross-sectional area S3＝250mm2Length S of vertical ground conductor42.5m, cross-sectional area S of current injection conductor5＝250mm2Length S of current injection conductor60.5 m. The number of horizontal ground conductors Q is 72, and the number of vertical ground conductors W is 84.
In addition, the simulation calculation of the invention is completed by using a software package CDEGS. CDEGS is software developed by canadian safety engineering services and technologies for accurate analysis of problems with grounding, electromagnetic fields, electromagnetic interference, etc. At present, the grounding problem at home and abroad is generally simulated and analyzed by the software, and the calculation principle is a moment method.
Step 3, inputting the original data of the 11 influence elements into the grounding grid simulation calculation model in the grounding grid simulation calculation model to obtain 11 evaluation grounding resistance values R corresponding to the 11 influence elementsαβ。
Step 3.1, determining simulation reference formula G
Each raw data set M obtained in step 1αβ' in this example, one original data is arbitrarily selected as a reference value Hαβ，α＝α1，α2，α3β ═ 1, 2 …, i.e. corresponding to 11 original data sets Mαβ' obtaining 11 reference values H of 11 influencing elements in totalαβThe 11 reference values HαβSubstituting the grounding grid simulation model into a simulation benchmark formula G;
specifically, in this embodiment, the following reference values are selected for 11 influencing elements in the ground grid simulation calculation model: mesh size 10X 10m2The horizontal grounding conductor is cylindrical, the distance between the double-layer grounding grids is 0m, the distance between the external grounding grids is 0m, the number of the four sides of the grounding grid and the number of the internal vertical grounding conductors are 50, the number of the vertical grounding conductors at the lightning rod is 4, the number of the vertical grounding conductors at the door-shaped framework is 0, the length of all the vertical grounding conductor is 2.5m, the length of the external vertical grounding conductor is 2.5m, the distribution condition of the vertical grounding conductors is shown in figure 4 of the specification, the soil is layered into a single layer, the single layer is formedThe soil resistivity was 200. omega. m.
Step 3.2, calculating the influencing factor MαβEvaluation of ground resistance value RαβThe specific process is as follows:
extracting an original data set Mαβ' and replacing the reference value H with E pieces of original dataαβSubstituting the simulation reference formula G for simulation to obtain potential rises U corresponding to the E original data, and recording the potential rise U with the maximum value as the maximum potential rise U1The ground resistance value at this time is calculated and recorded as an evaluation ground resistance value Rαβ，Rαβ＝U1/I；
Step 3.3, sequentially simulating the 11 influence elements according to the method of the step 3.2 to obtain 11 evaluation grounding resistance values R corresponding to the 11 influence elementsαβ；
Wherein the mesh size
Number of vertical grounding conductors at lightning rod
Number of vertical grounding conductors at gate-type structure
Soil stratification and each layer of soil resistivity
4 evaluation ground resistance values corresponding to the four influencing elements
The simulation of (c) is calculated as follows.
(1) The size of the mesh
Corresponding evaluation of the ground resistance
The length of the long edge of the mesh of the grounding grid is set as C1The length of the short side is C2. Mesh size extraction from raw data set
All the original data of (1) constitute an influence element
Set of raw data, denoted raw data set
CSAs to the number of the original data,
extracting raw data sets
And respectively replacing the reference value HαβCarrying out simulation by bringing in a simulation reference formula G to obtain potential rises U corresponding to each original data, and recording the potential rise U with the maximum value as the maximum potential rise U1And calculating the grounding resistance value at this time and recording as the evaluation grounding resistance value
Simulation result
(2) Number of conductors connected to the lightning rod perpendicularly
Corresponding evaluation of the ground resistance
The number of vertical conductors at the lightning rod, provided in the raw database, includes 4 cases. I.e. with influencing elements
Corresponding original data set
Including 4 original data, replacing the reference value H with the 4 original dataαβCarrying out simulation by bringing in a simulation reference formula G to obtain potential rises U corresponding to 4 original data, and recording the potential rise U with the maximum value as the maximum potential rise U1And calculating the grounding resistance value at this time and recording as the evaluation grounding resistance value
Simulation result
(3) Number of vertical ground conductors at gate-type structure
Corresponding evaluation of the ground resistance
The number of vertical conductors at the lightning rod includes 5 cases, provided in the raw database. I.e. with influencing elements
Corresponding original data set
Including 5 original data, and replacing the reference value H with the 5 original dataαβCarrying out simulation by substituting into a simulation reference formula G to obtain potential rises U corresponding to 5 original data, and recording the potential rise U with the maximum value as the maximum potential rise U1And calculating the grounding resistance value at this time and recording as the evaluation grounding resistance value
Simulation result
(4) Delamination from soil and resistivity of soil in each layer
Corresponding evaluation of the ground resistance
The soil structure of a ground grid of a traction substation in a Xuzhou section of a high-speed railway is complex. In an original database, soil structures are divided into 8 different cases, the number of soil layers in each soil structure is recorded as T, any one of the T soil layers is recorded as a soil layer j, j is 1, 2 … T, and the thickness of the soil layer j is recorded as HjAnd the resistivity of the soil layer j is rhojI.e. with influencing elements
Corresponding original data set
Including 8 × T groups of original data, and replacing the reference value H with the 8 × T groups of original dataαβCarrying out simulation by substituting into a simulation reference formula G to obtain 8 multiplied by T potential rise U corresponding to 8 multiplied by T group original data, and recording the potential rise U with the maximum value as the maximum potential rise U1And calculating the grounding resistance value at this time and recording as the evaluation grounding resistance value
Simulation result
The data obtained by the simulation are:
R0＝{1.622，18.311，0.933，0.713，1.631，1.083，1.082，1.644， 4.705，1.641，6.352}。
obviously, from the simulation result, the shape of the horizontal grounding conductor
Length of external vertical ground conductor
Soil stratification and resistivity of each layer of soil
The influence on the ground resistance is large.
According to the technical scheme, the simulation calculation model of the grounding grid is established based on CDEGS simulation software, and the moment method in the electromagnetic field theory is adopted for analysis. The influence of various factors such as horizontal grounding conductors, vertical grounding conductors, soil structure parameters and the like on the important index of the grounding resistance in the safety performance evaluation of the grounding grid is comprehensively considered, and the evaluation value of the grounding resistance under various conditions is obtained.
Claims (3)
1. A large-scale grounding grid grounding resistance multi-factor evaluation method is characterized by comprising the following steps:
step 1, obtaining parameters of a large-scale grounding grid and establishing an original database
Step 1.1, determination of influencing factors
Marking a large grounding grid as a grounding grid, classifying influence elements influencing grounding resistance change of the grounding grid into three types, namely 11 types according to known statistical data, and marking any one of the 11 types of influence elements as an influence element MαβWhere α is the number of the influencing element class, α ═ α1，α2，α3，α1For horizontal ground conductor influencing element, α2For influencing elements of the vertical grounding conductor, α3Is a soil structure influencing element; beta is an influencing element MαβSerial No. in each category, β ═ 1, 2 …; specifically, the method comprises the following steps:
horizontal ground conductor influencing element
Mesh size
Horizontal ground conductor shape
Double-layer ground screen interval
And the distance between the external ground screen and the ground screen
Vertical ground conductor influencing element
Number of vertical grounding conductors on four sides and inside of grounding grid
Number of vertical grounding conductors at lightning rod
Number of vertical grounding conductors at gate-type structure
All vertical ground conductor lengths
External vertical connectionLength of ground conductor
Vertical ground conductor profile
Soil structure influencing element
Soil stratification and resistivity of each layer of soil
Step 1.2, collecting original data and establishing an original database
Acquiring original data of each influence element according to the influence elements given in the step 1.1, specifically, acquiring the soil condition of the grounding grid on site, measuring the soil resistivity of the area where the grounding grid is located on site, and acquiring structural parameter information of the grounding grid according to a design drawing of the grounding grid;
establishing an original database of the grounding grid according to the acquired original data of each influence element;
in the original database, all the original data of each influence element are combined into a set, a set of 11 influence element original data is obtained, and the influence element M is combinedαβIs denoted as an original data set Mαβ', the set of influencing elements Mαβ' totally comprises E original data, E is a positive integer, and alpha is alpha1，α2，α3，β＝1，2…；
Step 2, establishing a grounding grid simulation calculation model
Step 2.1, constructing a soil layering model
The soil layering model is composed of T layers of soil, T is the number of soil layers, any one of the T layers of soil is marked as a soil layer j, j is 1, 2 … T, and the thickness of the soil layer j is HjThe resistance of the soil layer jA ratio of rhoj；
Step 2.2, setting the topological structure of the grounding grid conductor
The topological structure of the grounding grid conductor comprises Q horizontal grounding conductors, W vertical grounding conductors and a current injection conductor; the Q horizontal grounding conductors have the same sectional area and the same buried depth, and the sectional area of the horizontal grounding conductor is expressed as S1And the buried depth of the horizontal grounding conductor is marked as S2(ii) a W vertical grounding conductors have the same cross-sectional area and the same length, and the cross-sectional area of the vertical grounding conductor is expressed as S3And the length of the vertical grounding conductor is recorded as S4(ii) a The cross-sectional area of the current-injected conductor is denoted as S5The length of the current-injecting conductor is denoted S6；
Simplifying the grounding grid into a rectangle, establishing a spatial three-dimensional rectangular coordinate system by taking any one of four corners of the grounding grid as a coordinate origin O, and recording any one of Q horizontal grounding conductors as a horizontal grounding conductor gammaAA is the number of the horizontal grounding conductor, A is 1, 2AThe start point coordinate and the end point coordinate in the spatial three-dimensional rectangular coordinate system are respectively (x)1A，y1A，z1A) And (x)2A，y2A，z2A) (ii) a Any one of the W vertical ground conductors is referred to as a vertical ground conductor ΨBB is the number of the vertical conductor, 1, 2BThe start coordinate and the end coordinate in the spatial three-dimensional rectangular coordinate system are respectively (x)3B，y3B，z3B) And (x)4B，y4B，z4B) (ii) a The initial coordinate and the end coordinate of the current injection conductor in the space three-dimensional rectangular coordinate system are respectively (x)5，y5，z5) And (0, 0, 0);
according to the soil layering model and the topological structure of the grounding grid conductor, and the 11 influence elements given in the step 1.1 are integrated, and the establishment of the grounding grid simulation calculation model is completed under the environment of simulation software CDEGS;
step 2.3, setting of evaluation index
Under the environment of simulation software CDEGS, the system will be connected withThe current injection conductor in the simulation calculation model of the earth screen is marked as conductor HeIs to be injected into the conductor HeThe current value of (1) is recorded as injection current I, the potential rise corresponding to the injection current I is recorded as potential rise U, the grounding resistance value of the grounding grid corresponding to the injection current I and the potential rise U is recorded as grounding resistance R, and R is U/I;
the grounding resistance R is used as an evaluation index of a grounding network grounding resistance multi-factor evaluation method;
step 3, obtaining the evaluation value of the grounding resistance R under the change of 11 influencing factors
Step 3.1, determining simulation reference formula G
Each raw data set M obtained in step 1αβ' in this example, one original data is arbitrarily selected as a reference value Hαβ，α＝α1，α2，α3β ═ 1, 2 …, i.e. corresponding to 11 original data sets Maβ' obtaining 11 reference values H of 11 influencing elements in totalαβThe 11 reference values H are comparedαβSubstituting the grounding grid simulation model into a simulation benchmark formula G;
step 3.2, calculating the influencing factor MαβEvaluation of ground resistance value RαβThe specific process is as follows:
extracting an original data set Mαβ' and replacing the reference value H with E pieces of original dataαβSubstituting the simulation reference formula G for simulation to obtain potential rises U corresponding to the E original data, and recording the potential rise U with the maximum value as the maximum potential rise U1The ground resistance value at this time is calculated and recorded as an evaluation ground resistance value Rαβ，Rαβ＝U1/I；
Step 3.3, sequentially simulating the 11 influence elements according to the method of the step 3.2 to obtain 11 evaluation grounding resistance values R corresponding to the 11 influence elementsαβ；
Step 4, obtaining a grounding grid grounding resistance multi-factor evaluation value set
11 evaluation ground resistance values R corresponding to the 11 influencing elements obtained in step 3.3αβThe set is recorded as a grounding grid grounding resistance multi-factor evaluation value setR is a hydrogen atom0，
2. The method for evaluating the grounding resistance of the large grounding grid according to the claim 1, wherein the structural parameter information of the grounding grid in the step 1 comprises the structure of the grounding grid, the area of the grounding grid and the buried depth of the grounding grid; the distribution condition of the horizontal grounding conductors, the sectional area of the horizontal grounding conductors, the buried depth of the horizontal grounding conductors and the number of the horizontal grounding conductors; distribution of vertical ground conductors, vertical ground conductor cross-sectional area, vertical ground conductor length, number of vertical ground conductors, current injection conductor cross-sectional area, current injection conductor length.
3. The method for evaluating the grounding resistance of the large grounding network according to the claim 1 or 2, wherein the step 1 further comprises normalizing the data in the original database after the original database is established, so that the data in the original database keeps uniform dimension.
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