CN104007308A - Grounding grid branch current detecting method based on differential method - Google Patents

Abstract

The invention discloses a grounding network branch current detection method based on a differential method. According to the selected grounding network branch position and grounding network branch burial depth, a rectangular measurement area is selected, and the grounding network is used in the measurement area. Lead the ground body, inject current from one point and extract current from another point, measure the magnetic induction intensity of the ground surface in the direction perpendicular to the ground surface or the magnetic induction intensity in the direction parallel to the ground surface, and eliminate the noise interference after digital filtering of the magnetic induction intensity , through the differential method, first obtain the modulus of the 1st derivative of the magnetic induction in the direction perpendicular to the ground surface, the modulus of the 3rd derivative or the modulus of the 2nd derivative of the magnetic induction in the direction parallel to the ground surface, and then obtain the derivatives of each order The main peak value of the mode and the corresponding proportional coefficient are used to determine the magnitude of the grounding grid branch current in the measurement area. The whole detection process is simple and the calculation amount is small.

Description

A Differential-Based Detection Method for Grounding Grid Branch Current

technical field

The invention relates to a method for detecting the current of a branch circuit of a grounding grid, in particular to a method for detecting the magnitude of the current of a current-carrying conductor of the grounding grid based on a differential method.

Background technique

The grounding grid is an important guarantee for the safe operation of the substation, and its grounding performance has always been valued by the design and production operation departments. In the safe operation of the substation, the grounding grid not only provides a common potential reference ground for various electrical equipment in the substation, but also quickly discharges the fault current and reduces the ground potential of the substation when the grounding grid is struck by lightning or a short-circuit fault occurs in the power system Lift. The grounding performance of the grounding grid is directly related to the personal safety of the workers in the substation and the safety and normal operation of various electrical equipment. my country's grounding grid is generally made of flat steel, connected to each other into a grid shape, buried horizontally in the ground at a depth of about 0.3 to 2 meters, the grid spacing is usually 3 to 7 meters, and the ratio of the grids on both sides is usually 1:1 ~1:3. Since the grounding grid is prone to corrosion in long-term operation, it is necessary to detect the defects of the grounding grid in time and take repair measures.

At present, the main methods of grounding grid corrosion diagnosis are analysis methods based on circuit theory and analysis methods based on electromagnetic field theory. The former regards the grounding grid as a pure resistance network, uses the basic principles of circuit theory, establishes the corrosion diagnostic equation of the grounding grid through certain measurement methods and calculation methods, and obtains the actual resistance or resistance of each branch conductor by solving the diagnostic equation. Value change rate, and then judge the corrosion status of the grounding grid. This method needs to know all or part of the design drawings of the grounding grid in advance; the latter is mainly by injecting a certain frequency current into the grounding grid and measuring the grounding grid. , and finally diagnose the corrosion degree of the grounding grid according to the distribution of the magnetic field. Some scholars use the method of solving the magnetic field inverse problem to determine the topological structure of the grounding grid, but in the process of solving the magnetic field inverse problem, there will be ill-conditioned solutions, and the solution process is complicated.

The detection of the grounding network branch current can be used to indirectly detect the resistance of the grounding network branch, which provides a good basis for the later grounding network fault diagnosis and branch state evaluation.

Contents of the invention

In view of the deficiencies in the prior art above, the object of the present invention is to provide a grounding network branch current detection method based on a differential method with a simple detection process and a small amount of calculation. Technical scheme of the present invention is as follows:

A grounding grid branch current detection method based on a differential method, comprising the following steps:

101. Obtain the burial depth h of the grounding grid branch and the length L of the grounding grid branch, and arbitrarily select the upper grounding body A from several upper grounding bodies on the ground surface of the grounding grid branch to be tested as the injection current The grounding body B is used as the extraction current terminal, and A≠B; a measurement area S is selected between the grounding body A and the grounding body B;

102. Establish a right-handed rectangular coordinate system xyz for the measurement area S in step 101, specifically: take the midpoint of the selected grounding network branch as the coordinate origin, and take the upward direction perpendicular to the measurement area S as the positive direction of the z-axis, so that Select the direction of the ground grid branch current as the positive direction of the x-axis, and the direction passing through the origin of the coordinates and perpendicular to the ground grid branch is the y-axis, and complete the establishment of the right-handed rectangular coordinate system xyz, where the coordinate axes x-axis and y-axis are consistent with the measurement area S sides parallel or perpendicular;

103. Divide the measurement area S into M×N grids, the sides of the grid are parallel or perpendicular to the x-axis, the node P _ij of the grid is selected as the measurement point, and the position coordinates corresponding to the measurement point P _ij are (x _ij , y _ij ), inject current into the upper ground body A described in step 101, measure the magnetic induction intensity B along the positive direction of the z-axis on the measurement point P _ij and measure _z (x, y) along the positive direction of the y-axis The magnetic induction intensity B measures _y (x, y), where M is the number of rows of the grid, N is the number of columns of the grid, 1≤i≤M+1, 1≤j≤N+1; change the position of the measurement point to get The magnetic induction intensity B measures _z (x, y) and the magnetic induction intensity B measures _y (x, y) of several measurement points, and obtains the magnetic induction intensity function B _z (x, y) and the magnetic induction intensity function B _y (x, y ); here the statistical method adopts the linear fitting method;

104. Using the differential method to obtain the modulus of the first derivative of the magnetic induction intensity function B _z (x, y) obtained in step 103, the formula is as follows $\left|B_z^{\left(1\right)}(x,\mathrm{the\; y})\right|=\sqrt{{\left(\frac{\∂B_z(x,\mathrm{the\; y})}{\∂x}\right)}^2+{\left(\frac{\∂B_z(x,\mathrm{the\; y})}{\∂\mathrm{the\; y}}\right)}^2},$ Or use the differential method to obtain the modulus of the third derivative of the magnetic induction function B _z (x, y) $\left|B_z^{\left(3\right)}(x,\mathrm{the\; y})\right|=\sqrt{{\left(\frac{{\∂}^3{B}_z(x,\mathrm{the\; y})}{{\∂x}^3}\right)}^2+{\left(\frac{{\∂}^3{B}_z(x,\mathrm{the\; y})}{{\∂\mathrm{the\; y}}^3}\right)}^2};$ Or the magnetic induction intensity function B _y (x, y) obtained in step 103 adopts differential method to obtain the modulus of the second order derivative, and the formula is as follows:

$<span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; B</span>}}_{\mathrm{<span\; class="notranslate">\; the\; y</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; |</span><span\; class="notranslate">\; =</span>\sqrt{{<span\; class="notranslate">\; (</span>\frac{{<span\; class="notranslate">\; \&PartialD;</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; B</span>}}_{\mathrm{<span\; class="notranslate">\; the\; y</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; )</span>}{{<span\; class="notranslate">\; \&PartialD;</span>\mathrm{<span\; class="notranslate">\; x</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{<span\; class="notranslate">\; (</span>\frac{{<span\; class="notranslate">\; \&PartialD;</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; B</span>}}_{\mathrm{<span\; class="notranslate">\; the\; y</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; )</span>}{{<span\; class="notranslate">\; \&PartialD;</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; ;</span>$

105. According to the modulus of the first order derivative of B _z (x, y) obtained in step 104 Modulus of the 3rd derivative And the modulus of B _y (x,y) 2nd order derivative Calculated The peak value F of the main peak and the coordinate position (x ₀ , y ₀ ) corresponding to the peak value of the main peak, the F includes And according to the burial depth h of the grounding network branch obtained in step 101, the length L of the grounding network branch, obtain the proportional coefficient λ _z1 , the proportional coefficient λ _z3 and the proportional coefficient λ _y2 according to the formula, wherein λ _z1 represents the The scale coefficient corresponding to the main peak value of the modulus of the first derivative of the magnetic induction B _z (x, y) in the surface direction; λ _z3 represents the modulus of the third derivative of the magnetic induction B _z (x, y) in the direction perpendicular to the ground surface λ _y2 represents the proportional coefficient corresponding to the main peak value of the modulus of the second derivative of the magnetic induction intensity B _y (x, y) parallel to the direction of the ground surface; where ${\mathrm{\&lambda;}}_{z1}=\underset{i=1}{\overset{2}{\mathrm{\&Sigma;}}}\frac{{\mathrm{\&mu;L}}_i}{4\mathrm{\&pi;}{h}^2\sqrt{(L_i^2+h^2)}};$ ${\mathrm{\&lambda;}}_{z3}=\underset{i=1}{\overset{2}{\mathrm{\&Sigma;}}}\frac{3{\mathrm{\&mu;L}}_i({2L}_i^2+{3h}^2)}{4\mathrm{\&pi;}{h}^4(L_i^2+h^2)\sqrt{(L_i^2+h^2)}};$ ${\mathrm{\&lambda;}}_{\mathrm{the\; y}2}=\underset{i=1}{\overset{2}{\mathrm{\&Sigma;}}}\frac{\mathrm{\&mu;}}{4\mathrm{\&pi;}{h}^3}\frac{L_i({2L}_i^2+{3h}^2)}{(L_i^2+h^2)\sqrt{(L_i^2+h^2)}};$

106. According to the obtained in step 105 And proportional coefficient λ _z1 , proportional coefficient λ _z3 and proportional coefficient λ _y2 , according to the formula or or Obtain the branch current I of the grounding network branch.

Further, in step 103, the frequency of the current injected by the grounding body A is 0-2000 Hz, and the amplitude is 1A-30A.

Further, the M×N grid in step 103 has an equal interval Δx in the x-axis direction, and an equal interval Δy in the y-axis direction.

Further, before performing the calculation in step 104, the magnetic induction intensity B _z (x, y) in the direction perpendicular to the ground surface and/or the magnetic induction intensity B _y (x, y) in the direction parallel to the ground surface are digitally filtered .

Advantage of the present invention and beneficial effect are as follows:

This method selects a rectangular measurement area S according to the location of the selected grounding grid branch and the burial depth of the grounding grid branch. By using the grounding grid's upper ground body, the current is injected from one point and the current is extracted from another point to measure the grounding. The magnetic induction intensity B _z (x, y) of the net surface perpendicular to the ground surface or the magnetic induction intensity B _y (x, y) of the direction parallel to the ground surface, after the magnetic induction intensity B _z (x, y) or B _y ( x, y) is digitally filtered to eliminate noise interference, and first obtain the modulus of the first-order derivative of the magnetic induction B _z (x, y) by differential method Modulus of the 3rd derivative Or the modulus of the second derivative of the magnetic induction B _y (x,y) Secondly, the main peak peak value of the modulus of each order derivative is obtained separately And the corresponding proportional coefficients λ _z1 , λ _z3 , λ _y2 to determine the magnitude of the grounding network branch current I in the measurement area. The whole detection process is simple and the calculation amount is small.

Description of drawings

Fig. 1 is a schematic diagram of measuring point labeling in a preferred embodiment of the present invention;

figure 2 distribution map;

image 3 section diagram of

Figure 4 distribution map;

Figure 5 section diagram of

Figure 6 distribution map;

Figure 7 section diagram of

Figure 8 is the distribution diagram of the proportional coefficients λ _z1 , λ _z3 , and λ _y2 ;

Fig. 9 is a flow chart of detecting the ground grid branch current.

Detailed ways

A non-limiting embodiment is given below in conjunction with the accompanying drawings to further illustrate the present invention.

A grounding grid branch current detection method based on a differential method, comprising the following steps:

Step 1: Determine a measurement area S on the ground surface of the ground grid according to the location of the selected grounding grid branch and the burial depth h of the grounding grid branch, and obtain the magnetic induction of the measurement area S, including the magnetic induction perpendicular to the ground surface B _z (x,y) and/or magnetic induction B _y (x,y) parallel to the ground surface;

Step 2, respectively obtain the modulus of the first derivative of the magnetic induction intensity B _z (x, y) perpendicular to the ground surface Modulus of the 3rd derivative and/or the modulus of the second derivative of the magnetic induction B _y (x,y) parallel to the surface

Step 3, respectively obtain the peak value F of the main peak and the coordinate position (x ₀ , y ₀ ) corresponding to the peak value of the main peak of the modulus of each derivative described in step 2;

Step 4, according to the coordinate position (x ₀ , y ₀ ) of the selected main peak, the node coordinates at both ends of the selected grounding grid branch, the buried depth h of the grounding grid branch and the soil magnetic permeability μ, calculate the proportionality coefficient λ;

Step 5, according to the main peak value F of the modulus of each order derivative described in step 3 and the proportional coefficient λ described in step 4, determine the magnitude of the grounding network branch current in the measurement area S.

The step of obtaining the magnetic induction intensity of the measurement area described in the above step 1 includes:

AUsing the grounding body of the grounding grid, inject current from any one of the grounding bodies, and extract the current from another grounding body except the grounding body that injects the current; the frequency of the injected current is 0～ 2000Hz, amplitude 1A～30A;

B Determine a rectangular measurement area S on the ground surface of the ground grid according to the selected grounding grid branch position and the buried depth h of the grounding grid branch. The measurement area S is located between the injection current and the extraction current described in step A. Between the upward grounding bodies, the positive direction of the z-axis is perpendicular to the measurement area S, the selected grounding network branch is on the x-axis, the current direction of the selected grounding network branch is the same as the positive direction of the x-axis, and the selected grounding network branch is on the x-axis. The middle point of the network branch is the coordinate origin, and a right-handed rectangular coordinate system xyz is established, wherein the coordinate axes x and y are parallel or perpendicular to the sides of the measurement area S;

C divides the measurement area S into M×N grids, the sides of the grid are parallel or perpendicular to the x-axis, the node P _ij of the selected grid is the measurement point, and the corresponding position coordinates of the measurement point are (x _ij , y _ij ) , measure the magnetic induction intensity B _z (x, y) perpendicular to the ground surface at the measurement point P _ij and the magnetic induction intensity B _y (x, y) along the positive direction of the y-axis, where M is the number of rows of the grid, N is the number of columns in the grid, 1≤i≤M+1, 1≤j≤N+1.

The M×N grid has an equal pitch Δx in the x-axis direction and an equal pitch Δy in the y-axis direction.

The measurement area S of the ground surface of the ground grid is directly above the selected ground grid branch.

The main peak value F of the modulus of each order derivative described in the above-mentioned step 3 comprises:

The main peak of the modulus of the first derivative of the magnetic induction B _z (x, y) perpendicular to the ground surface is The main peak of the modulus of the third derivative of the magnetic induction B _z (x, y) perpendicular to the ground surface is And/or the main peak of the mode of the second derivative of the magnetic induction B _y (x,y) parallel to the direction of the ground surface is

The calculation steps for obtaining the proportional coefficient described in the above step 4 include:

a The length of the selected grounding grid branch is L, the midpoint of the selected grounding grid branch is the coordinate origin, and the coordinates of the nodes at both ends of the grounding grid branch are (L/2,0), (-L/2,0) , the distances between the coordinate position (x ₀ , y ₀ ) of the selected main peak and the nodes at both ends of the grounding network branch in the direction parallel to the x-axis are L ₁ =L/2-x ₀ , L ₂ =L/2 +x ₀ ;

b. The burial depth of the grounding network branch is h and the soil magnetic permeability is μ. The acquisition of the proportional coefficient λ described in step 4 includes: the first derivative of the magnetic induction intensity B _z (x, y) perpendicular to the ground surface direction The proportional coefficient corresponding to the main peak peak value of the mode is λ _z1 ; the proportional coefficient corresponding to the main peak peak value of the mode of the third-order derivative of the magnetic induction B _z (x, y) in the direction perpendicular to the ground surface is λ _z3 ; and/or parallel to the ground The proportional coefficient corresponding to the main peak of the mode of the 2nd order derivative of the magnetic induction intensity B _y (x, y) in the surface direction is λ _y2 ; where

${\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; z</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}\frac{{\mathrm{<span\; class="notranslate">\; \&mu;L</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}}{\mathrm{<span\; class="notranslate">\; 4</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}{\mathrm{<span\; class="notranslate">\; h</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\sqrt{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; h</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>}}<span\; class="notranslate">\; ;</span>$ ${\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; z</span>}\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}\frac{\mathrm{<span\; class="notranslate">\; 3</span>}{\mathrm{<span\; class="notranslate">\; \&mu;L</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; 3</span>}\mathrm{<span\; class="notranslate">\; h</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; 4</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}{\mathrm{<span\; class="notranslate">\; h</span>}}^{\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; h</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>\sqrt{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; h</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>}}<span\; class="notranslate">\; ;</span>$ ${\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; the\; y</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}\frac{\mathrm{<span\; class="notranslate">\; \&mu;</span>}}{\mathrm{<span\; class="notranslate">\; 4</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}{\mathrm{<span\; class="notranslate">\; h</span>}}^{\mathrm{<span\; class="notranslate">\; 3</span>}}}\frac{{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; 3</span>}\mathrm{<span\; class="notranslate">\; h</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>}{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; h</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>\sqrt{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; h</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>}}<span\; class="notranslate">\; .</span>$

The calculation steps of the grounding grid branch current described in the above step five include:

According to the main peak value of the modulus of the 1st derivative of the magnetic induction B _z (x, y) perpendicular to the surface and the corresponding proportional coefficient λ _z1 , the grounding network branch current I in the measurement area S is obtained as

$\mathrm{<span\; class="notranslate">\; I</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; z</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; /</span>{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; z</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; ;</span>$

According to the main peak value of the modulus of the 3rd derivative of the magnetic induction B _z (x, y) perpendicular to the surface and the corresponding proportional coefficient λ _z3 , the grounding network branch current I in the measurement area S is obtained as

$\mathrm{<span\; class="notranslate">\; I</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; z</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; /</span>{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; z</span>}\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; ;</span>$

According to the main peak peak value of the mode of the second derivative of the magnetic induction intensity B _y (x,y) parallel to the direction of the ground surface and the corresponding proportional coefficient λ _y2 , the grounding network branch current I in the measurement area S is obtained as

$\mathrm{<span\; class="notranslate">\; I</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; the\; y</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; /</span>{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; the\; y</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; .</span>$

When the method of the present invention detects, after step one and before the calculation of step two, the magnetic induction intensity B _z (x, y) perpendicular to the ground surface direction and/or the magnetic induction intensity B parallel to the ground surface direction can be first _y (x, y) is digitally filtered.

The specific steps to obtain the modulus of each derivative in step 2 are as follows:

Obtain the modulus of the 3rd derivative of the magnetic induction B _z (x,y) the process of:

Take the position variable x of the measuring point as the independent variable to obtain the first derivative of the magnetic induction B _z (x, y)

Take the position variable y of the measuring point as the independent variable, and obtain the first derivative of the magnetic induction B _z (x, y)

Take the position variable x of the measuring point as the independent variable to obtain the second derivative of the magnetic induction B _z (x, y)

Take the position variable y of the measuring point as the independent variable, and obtain the second derivative of the magnetic induction B _z (x, y)

Take the position variable x of the measuring point as the independent variable to obtain the third derivative of the magnetic induction B _z (x, y)

Taking the position variable y of the measuring point as the independent variable, calculate the third derivative of the magnetic induction B _z (x, y)

Obtain the modulus of the 3rd derivative of the magnetic induction B _z (x,y)

Obtain the modulus of the 1st derivative of the magnetic flux density B _z (x,y) the process of:

Take the position variable x of the measuring point as the independent variable to obtain the first derivative of the magnetic induction B _z (x, y)

Take the position variable y of the measuring point as the independent variable, and obtain the first derivative of the magnetic induction B _z (x, y)

Obtain the modulus of the 1st derivative of the magnetic flux density B _z (x,y)

Obtain the modulus of the 2nd derivative of the magnetic flux density B _y (x,y) the process of:

Take the position variable x of the measurement point as the independent variable, and obtain the first derivative of the magnetic induction intensity B _y (x,y)

Take the position variable y of the measuring point as the independent variable, and obtain the first derivative of the magnetic induction intensity B _y (x,y)

Taking the position variable x of the measuring point as the independent variable, find the second derivative of the magnetic induction intensity B _y (x,y)

Taking the position variable y of the measuring point as the independent variable, find the second derivative of the magnetic induction intensity B _y (x,y)

Obtain the modulus of the 2nd derivative of the magnetic flux density B _y (x,y)

See Fig. 1. In actual situation, the branch length of the substation grounding grid is fixed. A current-carrying conductor MN with a length L is horizontally buried in a single layer of uniform soil with a magnetic permeability μ. The conductor is placed in parallel on the x-axis, so that The midpoint of the selected grounding network branch is the coordinate origin, and a right-handed rectangular coordinate system xyz is established. The ground surface is parallel to the xoy plane and the distance is h. The current flowing in the conductor is I, and the direction of the current is along the positive direction of the x-axis. Assume that the bottom of the plane z=h is a single layer of uniform soil with a magnetic permeability μ, and the magnetic permeability of the soil is approximately taken as the magnetic permeability μ _o in vacuum. Neglect the leakage current of the conductor on the soil.

Select I=1A, h=1m, L=6m.

As shown in Figure 1, select a measurement surface S on the ground surface of the grounding grid, with an area of 12m×12m, and divide a 399×399 grid on the measurement surface S. The sides of the grid are parallel or perpendicular to the x-axis, and the grid is on the x-axis The direction has an equal spacing △x=3cm, the grid has an equal spacing △y=3cm in the y-axis direction, the node P _ij of the grid is the measurement point, and the measurement point has a corresponding position coordinate (x _ij , y _ij ) , measure the magnetic induction intensity B _z (x, y) perpendicular to the ground surface at the measurement point P _ij , and measure the magnetic induction intensity B _y (x, y) parallel to the positive direction of the y-axis at the measurement point P _ij , where M is The number of rows of the grid, N is the number of columns of the grid, 1≤i≤400, 1≤j≤400.

Obtain the modulus of the 1st derivative of the magnetic flux density B _z (x,y) See Figure 2;

Take the position variable x of the measuring point as the independent variable to obtain the first derivative of the magnetic induction B _z (x, y)

Take the position variable y of the measuring point as the independent variable, and obtain the first derivative of the magnetic induction B _z (x, y)

Obtain the modulus of the 1st derivative of the magnetic flux density B _z (x,y)

Referring to Figure 3, obtain the x=0m cross-section in Figure 2, and obtain from the x=0m cross-section The magnitude of the main peak peak of is The corresponding proportional coefficient λ _z1 = 1.89736×10 ^-7 H/m ³ , which can determine the current size of the branch circuit of the grounding grid

Obtain the modulus of the 3rd derivative of the magnetic induction B _z (x,y) See Figure 4;

Take the position variable x of the measuring point as the independent variable to obtain the third derivative of the magnetic induction B _z (x, y)

Taking the position variable y of the measuring point as the independent variable, calculate the third derivative of the magnetic induction B _z (x, y)

Obtain the modulus of the 3rd derivative of the magnetic induction B _z (x,y)

Referring to Fig. 5, obtain x=0m cross-section in Fig. 4, obtain from x=0m cross-section The magnitude of the main peak peak of is The corresponding proportional coefficient λ _z3 = 1.19535×10 ^-6 H/m ⁵ , which can determine the current size of the branch circuit of the grounding grid

Obtain the modulus of the 2nd derivative of the magnetic flux density B _y (x,y) See Figure 6;

Taking the position variable x of the measuring point as the independent variable, find the second derivative of the magnetic induction intensity B _y (x,y)

Taking the position variable y of the measuring point as the independent variable, find the second derivative of the magnetic induction intensity B _y (x,y)

Obtain the modulus of the 2nd derivative of the magnetic flux density B _y (x,y)

Referring to Fig. 7, obtain x=0m cross-section in Fig. 6, obtain from x=0m cross-section The magnitude of the main peak peak of is The corresponding proportional coefficient λ _y2 = 3.98448×10 ^-7 H/m ⁴ , can determine the magnitude of the grounding network branch current

Referring to Fig. 8, the distribution of proportional coefficients λ _z1 , λ _z3 , and λ _y2 when h=1m, L=6m, μ ₀ =4π×10 ^-7 H/m.

Fig. 9 is a flow chart of detecting the ground grid branch current.

The above embodiments should be understood as only for illustrating the present invention but not for limiting the protection scope of the present invention. After reading the content of the present invention, the skilled person can make various changes or modifications to the present invention, and these equivalent changes and modifications also fall into the scope of the present invention. scope.

Claims (4)

1. a grounding network branch current detection method based on differential method, is characterized in that comprising the following steps: 101. Obtain the burial depth h of the grounding grid branch and the length L of the grounding grid branch, and arbitrarily select the upper grounding body A from several upper grounding bodies on the ground surface of the grounding grid branch to be tested as the injection current The grounding body B is used as the extraction current terminal, and A≠B; a measurement area S is selected between the grounding body A and the grounding body B; 102. Establish a right-handed rectangular coordinate system xyz for the measurement area S in step 101, specifically: take the midpoint of the selected grounding network branch as the coordinate origin, and take the upward direction perpendicular to the measurement area S as the positive direction of the z-axis, so that Select the direction of the grounding grid branch current as the positive direction of the x-axis, and the direction passing through the origin of the coordinates and perpendicular to the grounding grid branch is the y-axis, and complete the establishment of a right-handed rectangular coordinate system xyz, where the coordinate axes x-axis and y-axis are in line with the measurement area S sides parallel or perpendicular; 103. Divide the measurement area S into M×N grids, the sides of the grid are parallel or perpendicular to the x-axis, the node P _ij of the grid is selected as the measurement point, and the position coordinates corresponding to the measurement point P _ij are (x _ij , y _ij ), inject current into the upper ground body A described in step 101, measure the magnetic induction intensity B along the positive direction of the z-axis on the measurement point P _ij and measure _z (x, y) along the positive direction of the y-axis The magnetic induction intensity B measures _y (x, y), where M is the number of rows of the grid, N is the number of columns of the grid, 1≤i≤M+1, 1≤j≤N+1; change the position of the measurement point to get The magnetic induction intensity B measures _z (x, y) and the magnetic induction intensity B measures _y (x, y) of several measurement points, and obtains the magnetic induction intensity function B _z (x, y) and the magnetic induction intensity function B _y (x, y ); 104. Using the differential method to obtain the modulus of the first derivative of the magnetic induction intensity function B _z (x, y) obtained in step 103, the formula is as follows $\left|B_z^{\left(1\right)}(x,\mathrm{the\; y})\right|=\sqrt{{\left(\frac{\&PartialD;B_z(x,\mathrm{the\; y})}{\&PartialD;x}\right)}^2+{\left(\frac{\&PartialD;B_z(x,\mathrm{the\; y})}{\&PartialD;\mathrm{the\; y}}\right)}^2},$ Or use the differential method to obtain the modulus of the third derivative of the magnetic induction function B _z (x, y) $\left|B_z^{\left(3\right)}(x,\mathrm{the\; y})\right|=\sqrt{{\left(\frac{{\&PartialD;}^3{B}_z(x,\mathrm{the\; y})}{{\&PartialD;x}^3}\right)}^2+{\left(\frac{{\&PartialD;}^3{B}_z(x,\mathrm{the\; y})}{{\&PartialD;\mathrm{the\; y}}^3}\right)}^2};$ Or the magnetic induction intensity function B _y (x, y) obtained in step 103 adopts differential method to obtain the modulus of the second order derivative, and the formula is as follows: $<span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; B</span>}}_{\mathrm{<span\; class="notranslate">\; the\; y</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; |</span><span\; class="notranslate">\; =</span>\sqrt{{<span\; class="notranslate">\; (</span>\frac{{<span\; class="notranslate">\; \&PartialD;</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; B</span>}}_{\mathrm{<span\; class="notranslate">\; the\; y</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; )</span>}{{<span\; class="notranslate">\; \&PartialD;</span>\mathrm{<span\; class="notranslate">\; x</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{<span\; class="notranslate">\; (</span>\frac{{<span\; class="notranslate">\; \&PartialD;</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; B</span>}}_{\mathrm{<span\; class="notranslate">\; the\; y</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; )</span>}{{<span\; class="notranslate">\; \&PartialD;</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; ;</span>$ 105. According to the modulus of the first order derivative of B _z (x, y) obtained in step 104 Modulus of the 3rd derivative And the modulus of B _y (x, y) 2nd order derivative Calculated The peak value F of the main peak and the coordinate position (x ₀ , y ₀ ) corresponding to the peak value of the main peak, the F includes And according to the burial depth h of the grounding network branch obtained in step 101, the length L of the grounding network branch, obtain the proportional coefficient λ _z1 , the proportional coefficient λ _z3 and the proportional coefficient λ _y2 according to the formula, wherein λ _z1 represents the The scale coefficient corresponding to the main peak value of the modulus of the first derivative of the magnetic induction B _z (x, y) in the surface direction; λ _z3 represents the modulus of the third derivative of the magnetic induction B _z (x, y) in the direction perpendicular to the ground surface λ _y2 represents the proportional coefficient corresponding to the main peak value of the modulus of the second derivative of the magnetic induction intensity B _y (x, y) parallel to the direction of the ground surface; where ${\mathrm{\&lambda;}}_{z1}=\underset{i=1}{\overset{2}{\mathrm{\&Sigma;}}}\frac{{\mathrm{\&mu;L}}_i}{4\mathrm{\&pi;}{h}^2\sqrt{(L_i^2+h^2)}};$ ${\mathrm{\&lambda;}}_{z3}=\underset{i=1}{\overset{2}{\mathrm{\&Sigma;}}}\frac{3{\mathrm{\&mu;L}}_i({2L}_i^2+{3h}^2)}{4\mathrm{\&pi;}{h}^4(L_i^2+h^2)\sqrt{(L_i^2+h^2)}};$ ${\mathrm{\&lambda;}}_{\mathrm{the\; y}2}=\underset{i=1}{\overset{2}{\mathrm{\&Sigma;}}}\frac{\mathrm{\&mu;}}{4\mathrm{\&pi;}{h}^3}\frac{L_i({2L}_i^2+{3h}^2)}{(L_i^2+h^2)\sqrt{(L_i^2+h^2)}};$ 106. According to the obtained in step 105 And proportional coefficient λ _z1 , proportional coefficient λ _z3 and proportional coefficient λ _y2 , according to the formula or or Obtain the branch current I of the grounding network branch. 2. The method for detecting the burial depth of grounding network branches based on differential method according to claim 1, characterized in that: in step 103, the frequency of the current injected by the grounding body A is 0-2000 Hz, and the amplitude is 1 A-30 A. 3. The grounding network branch burial depth detection method based on differential method according to claim 1, characterized in that: said M × N grid in step 103 has an equal spacing Δx in the x-axis direction, and Δx in the y-axis direction The directions have an equal spacing Δy. 4. the grounding network branch current detection method based on differential method according to claim 1, is characterized in that: before carrying out the calculation of step 104, first to the magnetic induction intensity B _z (x, y) perpendicular to the ground surface direction and/or the magnetic induction intensity B _y (x, y) parallel to the ground surface is subjected to digital filtering processing.