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

Abstract

The invention discloses a grounding grid branch current detecting method based on a differential method. The method comprises the steps that a rectangular measurement area is selected according to the position of a selected grounding grid branch and the buried depth of the grounding grid branch, an upper lead grounding body on a grounding grid is utilized in the measurement area, currents are injected to one point, the currents are pulled out of the other point, the magnetic induction intensity, perpendicular to the direction of the ground surface, of the ground surface of the grounding grid or the magnetic induction intensity, parallel to the direction of the ground surface, of the ground surface of the grounding grid is measured, digital filtering is carried out on the magnetic induction intensity, then noise interference is removed, a one-order derivative model and a three-order derivative model of the magnetic induction intensity perpendicular to the direction of the ground surface or a two-order derivative model of the magnetic induction intensity parallel to the direction of the ground surface is obtained through the differential method, and then main peak values and corresponding proportionality coefficients of all the orders of derivative models are obtained to determine the current of the grounding grid branch in the measurement area. The whole detecting process is simple, and the calculated amount is small.

Description

A kind of grounded screen branch current detection method based on the differential method

Technical field

The present invention relates to a kind of grounded screen branch current detection method, particularly a kind of method of the detection grounded screen current－carrying conductor size of current based on the differential method.

Background technology

Grounded screen is the important guarantee of substation safety operation, and its ground connection performance is subject to the attention of design and production run department always.Grounded screen is in service at substation safety, not only for various electrical equipments in transformer station provide a public potential reference ground, be struck by lightning or when electric system is short-circuited fault, can also drain rapidly fault current, and reduce the earth potential liter of transformer station in grounded screen.The quality of Grounding performance is directly connected to staff's personal safety and the safety of various electrical equipments and normally operation in transformer station.China's grounded screen generally adopts band steel to make, and is interconnected to mesh shape, and level is embedded in underground dark approximately 0.3～2 meter, common 3～7 meters of the spacing of grid, and the ratio of the grid of both sides is generally 1:1～1:3.Because grounded screen long-time running is easily corroded, need detect in time the defect of grounded screen and take reclamation activities.

The main method of corrosion diagnosis of grounding grid has the analytical approach based on Circuit theory and the analytical approach based on Theory of Electromagnetic Field at present.The former regards grounded screen as pure resistance network, utilize the ultimate principle of Circuit theory, set up the corrosion diagnosis equation of grounded screen by certain measurement means and computing method, and obtain actual resistance or the resistance change rate of each branch road conductor by solving diagnostic equation, and then the corrosion condition of grounded screen is differentiated, this method needs to understand in advance all or part of design drawing of grounded screen; The latter is mainly by inject the electric current of certain frequency to grounded screen, and measures grounded screen earth's surface magnetic field intensity, finally according to the distribution in magnetic field, ground net corrosion degree is diagnosed.There is scholar to adopt to solve the method for magnetic field inverse problem to determine the topological structure of grounded screen, there will be morbid state to separate but solve in the process of magnetic field inverse problem, solution procedure complexity.

The detection of grounded screen branch current size can be for indirect detection grounded screen branch road resistance sizes, for Fault Diagnosis for Grounding Grids and the branch road state estimation in later stage provide good basis.

Summary of the invention

For above deficiency of the prior art, the object of the present invention is to provide the grounded screen branch current detection method based on the differential method that a kind of testing process is simple, calculated amount is little.Technical scheme of the present invention is as follows:

A grounded screen branch current detection method based on the differential method, it comprises the following steps:

101, obtain the depth of burial h of grounded screen branch road, the length L of grounded screen branch road, and choose arbitrarily and draw grounding body A as Injection Current end in drawing grounding body on several on the ground surface of grounded screen branch road to be measured, on draw grounding body B as extracting current terminal, and A ≠ B out; Between grounding body A and grounding body B, select a measured zone S;

102, the measured zone S in step 101 is set up to right hand rectangular coordinate system xyz, be specially: taking selected grounded screen branch road mid point as true origin, taking perpendicular to measured zone S direction upwards as z axle positive dirction, taking the direction of selected grounded screen branch current as x axle positive dirction, cross true origin and be y axle perpendicular to the direction of grounded screen branch road, complete and set up right hand rectangular coordinate system xyz, wherein coordinate axis x axle is parallel or vertical with the limit of measured zone S with y axle;

103, measured zone S is divided into M × N grid, the limit of grid is parallel with x axle or vertical, the node P of selected grid _ijfor measurement point, measurement point P _ijcorresponding position coordinates is (x _ij, y _ij), on described in step 101, draw grounding body A Injection Current, measure at measurement point P _ijthe upper magnetic induction density B along z axle positive dirction is surveyed _z(x, y) and survey along the magnetic induction density B of y axle positive dirction _y(x, y), the line number that wherein M is grid, the columns that N is grid, 1≤i≤M+1,1≤j≤N+1; The position that changes measurement point obtains the magnetic induction density B survey of several measurement points _z(x, y) and magnetic induction density B are surveyed _y(x, y), and statistics obtains magnetic induction density function B _z(x, y) and magnetic induction density function B _y(x, y); Statistical method adopts linear fitting herein;

104, to the magnetic induction density function B obtaining in step 103 _z(x, y) adopts the differential method to obtain the mould of 1 order derivative, and formula is as follows $\left|B_z^{\left(1\right)}(x,y)\right|=\sqrt{{\left(\frac{\∂B_z(x,y)}{\∂x}\right)}^2+{\left(\frac{\∂B_z(x,y)}{\∂y}\right)}^2},$ Or adopt the differential method to obtain magnetic induction density function B _zthe mould of (x, y) 3 order derivatives $\left|B_z^{\left(3\right)}(x,y)\right|=\sqrt{{\left(\frac{{\∂}^3{B}_z(x,y)}{{\∂x}^3}\right)}^2+{\left(\frac{{\∂}^3{B}_z(x,y)}{{\∂y}^3}\right)}^2};$ Or to the magnetic induction density function B obtaining in step 103 _y(x, y) adopts the differential method to obtain the mould of 2 order derivatives, and formula is as follows:

$\left|B_y^{\left(2\right)}(x,y)\right|=\sqrt{{\left(\frac{{\∂}^2{B}_y(x,y)}{{\∂x}^2}\right)}^2+{\left(\frac{{\∂}^2{B}_y(x,y)}{{\∂y}^2}\right)}^2};$

105, according to obtaining B in step 104 _zthe mould of (x, y) 1 order derivative the mould of 3 order derivatives and B _ythe mould of (x, y) 2 order derivatives calculate main peak peak F and the coordinate position (x of corresponding main peak peak value ₀, y ₀), described F comprises and according to the length L of the depth of burial h of the grounded screen branch road obtaining in step 101, grounded screen branch road, try to achieve scale-up factor λ according to formula _z1, scale-up factor λ _z3and scale-up factor λ _y2, wherein λ _z1represent the magnetic induction density B perpendicular to ground surface direction _zthe scale-up factor corresponding to main peak peak value of the mould of 1 order derivative of (x, y); λ _z3represent the magnetic induction density B perpendicular to ground surface direction _zthe scale-up factor corresponding to main peak peak value of the mould of 3 order derivatives of (x, y); λ _y2represent to be parallel to the magnetic induction density B of ground surface direction _ythe scale-up factor corresponding to main peak peak value of the mould of 2 order derivatives of (x, y); Wherein ${\mathrm{\λ}}_{z1}=\underset{i=1}{\overset{2}{\mathrm{\Σ}}}\frac{{\mathrm{\μL}}_i}{4\mathrm{\π}{h}^2\sqrt{(L_i^2+h^2)}};$ ${\mathrm{\λ}}_{z3}=\underset{i=1}{\overset{2}{\mathrm{\Σ}}}\frac{3{\mathrm{\μL}}_i({2L}_i^2+{3h}^2)}{4\mathrm{\π}{h}^4(L_i^2+h^2)\sqrt{(L_i^2+h^2)}};$ ${\mathrm{\λ}}_{y2}=\underset{i=1}{\overset{2}{\mathrm{\Σ}}}\frac{\mathrm{\μ}}{4\mathrm{\π}{h}^3}\frac{L_i({2L}_i^2+{3h}^2)}{(L_i^2+h^2)\sqrt{(L_i^2+h^2)}};$

106, according to obtaining in step 105 with scale-up factor λ _z1, scale-up factor λ _z3and scale-up factor λ _y2, according to formula or or try to achieve grounded screen branch road branch current I.

The frequency of the electric current that further, in step 103, grounding body A injects is that 0～2000Hz, amplitude are 1A～30A.

Further, the grid of M × N described in step 103 has equal spacing △ x at x direction of principal axis, has equal spacing △ y at y direction of principal axis.

Further, before carrying out the calculating of step 104, first to the magnetic induction density B perpendicular to ground surface direction _z(x, y) and/or be parallel to the magnetic induction density B of ground surface direction _y(x, y) carries out digital filtering processing.

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

This method is according to according to selected grounded screen branch road position and grounded screen branch road depth of burial, a selected rectangle measured zone S, by utilize grounded screen on draw grounding body, extract electric current out from some Injection Currents and from another point, measure the grounded screen ground surface magnetic induction density B perpendicular to ground surface direction _z(x, y) or be parallel to the magnetic induction density B of ground surface direction _y(x, y), process is to magnetic induction density B _z(x, y) or B _y(x, y) carries out digital filtering and processes rear cancellation noise jamming, by the differential method, first asks for magnetic induction density B _zthe mould of 1 order derivative of (x, y) the mould of 3 order derivatives or magnetic induction density B _ythe mould of 2 order derivatives of (x, y) secondly obtain respectively the main peak peak value of the mould of all-order derivative with corresponding scale-up factor λ _z1, λ _z3, λ _y2, determine the grounded screen branch current I size in measured zone.Whole process testing process is simple, and calculated amount is little.

Brief description of the drawings

Fig. 1 preferred embodiment of the present invention measurement point mark schematic diagram;

Fig. 2 distribution plan;

Fig. 3 sectional drawing;

Fig. 4 distribution plan;

Fig. 5 sectional drawing;

Fig. 6 distribution plan;

Fig. 7 sectional drawing;

Fig. 8 scale-up factor λ _z1, λ _z3, λ _y2distribution plan;

Fig. 9 detects the process flow diagram of grounded screen branch current.

Embodiment

The invention will be further elaborated to provide the embodiment of an indefiniteness below in conjunction with accompanying drawing.

A grounded screen branch current detection method based on the differential method, comprises the following steps:

Step 1, according to selected grounded screen branch road position and grounded screen branch road depth of burial h, determines a measured zone S at grounded screen ground surface, obtains the magnetic induction density of described measured zone S, comprises the magnetic induction density B perpendicular to ground surface direction _z(x, y) and/or be parallel to the magnetic induction density B of ground surface direction _y(x, y);

Step 2, obtains respectively the magnetic induction density B perpendicular to ground surface direction _zthe mould of 1 order derivative of (x, y) the mould of 3 order derivatives and/or be parallel to the magnetic induction density B of ground surface direction _ythe mould of 2 order derivatives of (x, y)

Step 3, respectively the main peak peak F of mould and the coordinate position (x of corresponding main peak peak value of all-order derivative described in obtaining step two ₀, y ₀);

Step 4, according to the coordinate position (x of selected main peak peak value ₀, y ₀), selected grounded screen branch road two ends node coordinate, grounded screen branch road depth of burial h and soil magnetic permeability μ, calculate scale-up factor λ;

Step 5, according to the scale-up factor λ described in the main peak peak F of the mould of all-order derivative described in step 3 and step 4, determines the grounded screen branch current size in measured zone S.

The step of obtaining the magnetic induction density of described measured zone described in above-mentioned steps one comprises:

A utilize grounded screen on draw grounding body, draw grounding body Injection Current from any, and draw grounding body and extract electric current out from another outside grounding body of drawing of removing Injection Current; The frequency of this Injection Current is that 0～2000Hz, amplitude are 1A～30A;

B is according to selected grounded screen branch road position and grounded screen branch road depth of burial h, at grounded screen ground surface, determine the measured zone S of a rectangle, described measured zone S is at the Injection Current described in steps A and extract out on two, electric current and draw between grounding body, taking perpendicular to measured zone S upwards as z axle positive dirction, selected grounded screen branch road is on x axle, selected grounded screen branch current direction is identical with x axle positive dirction, taking selected grounded screen branch road mid point as true origin, set up right hand rectangular coordinate system xyz, wherein coordinate axis x axle is parallel or vertical with the limit of measured zone S with y axle;

Measured zone S is divided into M × N grid by C, and the limit of grid is parallel with x axle or vertical, the node P of selected grid _ijfor measurement point, the position coordinates that measurement point is corresponding is (x _ij, y _ij), measure at measurement point P _ijthe upper magnetic induction density B perpendicular to ground surface _z(x, y) and along the magnetic induction density B of y axle positive dirction _y(x, y), the line number that wherein M is grid, the columns that N is grid, 1≤i≤M+1,1≤j≤N+1.

Described M × N grid has equal spacing △ x at x direction of principal axis, has equal spacing △ y at y direction of principal axis.

The measured zone S of grounded screen ground surface is position directly over selected grounded screen branch road.

The main peak peak F of the mould of all-order derivative described in above-mentioned steps three comprises:

Perpendicular to the magnetic induction density B of ground surface direction _zthe main peak peak value of the mould of 1 order derivative of (x, y) is perpendicular to the magnetic induction density B of ground surface direction _zthe main peak peak value of the mould of 3 order derivatives of (x, y) is and/or be parallel to the magnetic induction density B of ground surface direction _ythe main peak peak value of the mould of 2 order derivatives of (x, y) is

The calculation procedure of obtaining described scale-up factor described in above-mentioned steps four comprises:

The selected grounded screen branch road of a length is L, and taking selected grounded screen branch road mid point as true origin, grounded screen branch road two ends node coordinate is respectively (L/2,0), (L/2,0), the coordinate position (x of selected main peak peak value ₀, y ₀) be respectively L with grounded screen branch road two end nodes in the distance being parallel on x direction of principal axis ₁=L/2-x ₀, L ₂=L/2+x ₀;

B grounded screen branch road depth of burial is that h and soil magnetic permeability are μ, obtains described scale-up factor λ and comprises: perpendicular to the magnetic induction density B of ground surface direction described in step 4 _zthe scale-up factor corresponding to main peak peak value of the mould of 1 order derivative of (x, y) is λ _z1; Perpendicular to the magnetic induction density B of ground surface direction _zthe scale-up factor corresponding to main peak peak value of the mould of 3 order derivatives of (x, y) is λ _z3; And/or be parallel to the magnetic induction density B of ground surface direction _ythe scale-up factor corresponding to main peak peak value of the mould of 2 order derivatives of (x, y) is λ _y2; Wherein

${\mathrm{\λ}}_{z1}=\underset{i=1}{\overset{2}{\mathrm{\Σ}}}\frac{{\mathrm{\μL}}_i}{4\mathrm{\π}{h}^2\sqrt{(L_i^2+h^2)}};$ ${\mathrm{\λ}}_{z3}=\underset{i=1}{\overset{2}{\mathrm{\Σ}}}\frac{3{\mathrm{\μL}}_i({2L}_i^2+{3h}^2)}{4\mathrm{\π}{h}^4(L_i^2+h^2)\sqrt{(L_i^2+h^2)}};$ ${\mathrm{\λ}}_{y2}=\underset{i=1}{\overset{2}{\mathrm{\Σ}}}\frac{\mathrm{\μ}}{4\mathrm{\π}{h}^3}\frac{L_i({2L}_i^2+{3h}^2)}{(L_i^2+h^2)\sqrt{(L_i^2+h^2)}}.$

Described in above-mentioned steps five, the calculation procedure of grounded screen branch current comprises:

According to the magnetic induction density B perpendicular to ground surface direction _zthe main peak peak value of the mould of 1 order derivative of (x, y) with corresponding scale-up factor λ _z1, the grounded screen branch current I obtaining in measured zone S is

$I=F_z^{\left(1\right)}/{\mathrm{\λ}}_{z1};$

According to the magnetic induction density B perpendicular to ground surface direction _zthe main peak peak value of the mould of 3 order derivatives of (x, y) with corresponding scale-up factor λ _z3, the grounded screen branch current I obtaining in measured zone S is

$I=F_z^{\left(3\right)}/{\mathrm{\λ}}_{z3};$

According to the magnetic induction density B that is parallel to ground surface direction _ythe main peak peak value of the mould of 2 order derivatives of (x, y) with corresponding scale-up factor λ _y2, the grounded screen branch current I obtaining in measured zone S is

$I=F_y^{\left(2\right)}/{\mathrm{\λ}}_{y2}.$

When method of the present invention detects, after step 1 and before carrying out the calculating of step 2, can be first to the magnetic induction density B perpendicular to ground surface direction _z(x, y) and/or be parallel to the magnetic induction density B of ground surface direction _y(x, y) carries out digital filtering processing.

In obtaining step two, the concrete steps of the mould of all-order derivative are as follows:

Obtain magnetic induction density B _zthe mould of 3 order derivatives of (x, y) process:

Taking measurement point location variable x as independent variable, ask for magnetic induction density B _z1 order derivative of (x, y)

Taking measurement point location variable y as independent variable, ask for magnetic induction density B _z1 order derivative of (x, y)

Taking measurement point location variable x as independent variable, ask for magnetic induction density B _z2 order derivatives of (x, y)

Taking measurement point location variable y as independent variable, ask for magnetic induction density B _z2 order derivatives of (x, y)

Taking measurement point location variable x as independent variable, ask for magnetic induction density B _z3 order derivatives of (x, y)

Taking measurement point location variable y as independent variable, ask for magnetic induction density B _z3 order derivatives of (x, y)

Obtain magnetic induction density B _zthe mould of 3 order derivatives of (x, y)

Obtain magnetic induction density B _zthe mould of 1 order derivative of (x, y) process:

Taking measurement point location variable x as independent variable, ask for magnetic induction density B _z1 order derivative of (x, y)

Taking measurement point location variable y as independent variable, ask for magnetic induction density B _z1 order derivative of (x, y)

Obtain magnetic induction density B _zthe mould of 1 order derivative of (x, y)

Obtain magnetic induction density B _ythe mould of 2 order derivatives of (x, y) process:

Taking measurement point location variable x as independent variable, ask for magnetic induction density B _y1 order derivative of (x, y)

Taking measurement point location variable y as independent variable, ask for magnetic induction density B _y1 order derivative of (x, y)

Taking measurement point location variable x as independent variable, ask for magnetic induction density B _y2 order derivatives of (x, y)

Taking measurement point location variable y as independent variable, ask for magnetic induction density B _y2 order derivatives of (x, y)

Obtain magnetic induction density B _ythe mould of 2 order derivatives of (x, y)

Referring to Fig. 1, under actual conditions, the branch road length of grounding net of transformer substation is fixed, the current－carrying conductor MN level of a length L is embedded in the individual layer uniform soil that magnetic permeability is μ, and conductor is parallel to be placed on x axle, taking selected grounded screen branch road mid point as true origin, set up right hand rectangular coordinate system xyz, ground surface is parallel to xoy plane and distance is h, and the electric current flowing through in conductor is I, and sense of current is along x axle positive dirction.The below of supposing plane z=h is that magnetic permeability is the individual layer uniform soil of μ, the approximate magnetic permeability μ getting in vacuum of magnetic permeability of soil _o.Ignore the leakage current of conductor on soil.

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

As Fig. 1, measure face S selected one of grounded screen ground surface, area is 12m × 12m, on the face of measurement S, divide 399 × 399 grids, the limit of grid is parallel with x axle or vertical, grid has equal spacing △ x=3cm at x direction of principal axis, and grid has equal spacing △ y=3cm at y direction of principal axis, the node P of grid _ijfor measurement point, it is (x that measurement point has corresponding position coordinates _ij, y _ij), measure at measurement point P _ijthe upper magnetic induction density B perpendicular to ground surface _z(x, y), measures at measurement point P _ijon be parallel to the magnetic induction density B of y axle positive dirction _y(x, y), the line number that wherein M is grid, the columns that N is grid, 1≤i≤400,1≤j≤400.

Obtain magnetic induction density B _zthe mould of 1 order derivative of (x, y) referring to Fig. 2;

Taking measurement point location variable x as independent variable, ask for magnetic induction density B _z1 order derivative of (x, y)

Taking measurement point location variable y as independent variable, ask for magnetic induction density B _z1 order derivative of (x, y)

Obtain magnetic induction density B _zthe mould of 1 order derivative of (x, y)

Referring to Fig. 3, obtain x=0m square section in Fig. 2, obtain from x=0m square section the size of main peak peak value be corresponding scale-up factor λ _z1=1.89736 × 10 ^-7h/m ³, can determine grounded screen branch current size

Obtain magnetic induction density B _zthe mould of 3 order derivatives of (x, y) referring to Fig. 4;

Taking measurement point location variable x as independent variable, ask for magnetic induction density B _z3 order derivatives of (x, y)

Taking measurement point location variable y as independent variable, ask for magnetic induction density B _z3 order derivatives of (x, y)

Obtain magnetic induction density B _zthe mould of 3 order derivatives of (x, y)

Referring to Fig. 5, obtain x=0m square section in Fig. 4, obtain from x=0m square section the size of main peak peak value be corresponding scale-up factor λ _z3=1.19535 × 10 ^-6h/m ⁵, can determine grounded screen branch current size

Obtain magnetic induction density B _ythe mould of 2 order derivatives of (x, y) referring to Fig. 6;

Taking measurement point location variable x as independent variable, ask for magnetic induction density B _y2 order derivatives of (x, y)

Taking measurement point location variable y as independent variable, ask for magnetic induction density B _y2 order derivatives of (x, y)

Obtain magnetic induction density B _ythe mould of 2 order derivatives of (x, y)

Referring to Fig. 7, obtain x=0m square section in Fig. 6, obtain from x=0m square section the size of main peak peak value be corresponding scale-up factor λ _y2=3.98448 × 10 ^-7h/m ⁴, can determine grounded screen branch current size

With reference to figure 8, h=1m, L=6m, μ ₀=4 π × 10 ^-7when H/m, scale-up factor λ _z1, λ _z3, λ _y2distribution situation.

Fig. 9 detects the process flow diagram of grounded screen branch current.

These embodiment are interpreted as being only not used in and limiting the scope of the invention for the present invention is described above.After having read the content of record of the present invention, technician can make various changes or modifications the present invention, and these equivalences change and modification falls into the grounded screen branch current detection method claim limited range that the present invention is based on the differential method equally.

Claims (4)

1. the grounded screen branch current detection method based on the differential method, is characterized in that comprising the following steps:

101, obtain the depth of burial h of grounded screen branch road, the length L of grounded screen branch road, and choose arbitrarily and draw grounding body A as Injection Current end in drawing grounding body on several on the ground surface of grounded screen branch road to be measured, on draw grounding body B as extracting current terminal, and A ≠ B out; Between grounding body A and grounding body B, select a measured zone S;

102, the measured zone S in step 101 is set up to right hand rectangular coordinate system xyz, be specially: taking selected grounded screen branch road mid point as true origin, taking perpendicular to measured zone S direction upwards as z axle positive dirction, taking the direction of selected grounded screen branch current as x axle positive dirction, cross true origin and be y axle perpendicular to the direction of grounded screen branch road, complete and set up right hand rectangular coordinate system xyz, wherein coordinate axis x axle is parallel or vertical with the limit of measured zone S with y axle;

103, measured zone S is divided into M × N grid, the limit of grid is parallel with x axle or vertical, the node P of selected grid _ijfor measurement point, measurement point P _ijcorresponding position coordinates is (x _ij, y _ij), on described in step 101, draw grounding body A Injection Current, measure at measurement point P _ijthe upper magnetic induction density B along z axle positive dirction is surveyed _z(x, y) and survey along the magnetic induction density B of y axle positive dirction _y(x, y), the line number that wherein M is grid, the columns that N is grid, 1≤i≤M+1,1≤j≤N+1; The position that changes measurement point obtains the magnetic induction density B survey of several measurement points _z(x, y) and magnetic induction density B are surveyed _y(x, y), and statistics obtains magnetic induction density function B _z(x, y) and magnetic induction density function B _y(x, y);

104, to the magnetic induction density function B obtaining in step 103 _z(x, y) adopts the differential method to obtain the mould of 1 order derivative, and formula is as follows $\left|B_z^{\left(1\right)}(x,y)\right|=\sqrt{{\left(\frac{\∂B_z(x,y)}{\∂x}\right)}^2+{\left(\frac{\∂B_z(x,y)}{\∂y}\right)}^2},$ Or adopt the differential method to obtain magnetic induction density function B _zthe mould of (x, y) 3 order derivatives $\left|B_z^{\left(3\right)}(x,y)\right|=\sqrt{{\left(\frac{{\∂}^3{B}_z(x,y)}{{\∂x}^3}\right)}^2+{\left(\frac{{\∂}^3{B}_z(x,y)}{{\∂y}^3}\right)}^2};$ Or to the magnetic induction density function B obtaining in step 103 _y(x, y) adopts the differential method to obtain the mould of 2 order derivatives, and formula is as follows:

$\left|B_y^{\left(2\right)}(x,y)\right|=\sqrt{{\left(\frac{{\∂}^2{B}_y(x,y)}{{\∂x}^2}\right)}^2+{\left(\frac{{\∂}^2{B}_y(x,y)}{{\∂y}^2}\right)}^2};$

105, according to obtaining B in step 104 _zthe mould of (x, y) 1 order derivative the mould of 3 order derivatives and B _ythe mould of (x, y) 2 order derivatives calculate main peak peak F and the coordinate position (x of corresponding main peak peak value ₀, y ₀), described F comprises and according to the length L of the depth of burial h of the grounded screen branch road obtaining in step 101, grounded screen branch road, try to achieve scale-up factor λ according to formula _z1, scale-up factor λ _z3and scale-up factor λ _y2, wherein λ _z1represent the magnetic induction density B perpendicular to ground surface direction _zthe scale-up factor corresponding to main peak peak value of the mould of 1 order derivative of (x, y); λ _z3represent the magnetic induction density B perpendicular to ground surface direction _zthe scale-up factor corresponding to main peak peak value of the mould of 3 order derivatives of (x, y); λ _y2represent to be parallel to the magnetic induction density B of ground surface direction _ythe scale-up factor corresponding to main peak peak value of the mould of 2 order derivatives of (x, y); Wherein ${\mathrm{\λ}}_{z1}=\underset{i=1}{\overset{2}{\mathrm{\Σ}}}\frac{{\mathrm{\μL}}_i}{4\mathrm{\π}{h}^2\sqrt{(L_i^2+h^2)}};$ ${\mathrm{\λ}}_{z3}=\underset{i=1}{\overset{2}{\mathrm{\Σ}}}\frac{3{\mathrm{\μL}}_i({2L}_i^2+{3h}^2)}{4\mathrm{\π}{h}^4(L_i^2+h^2)\sqrt{(L_i^2+h^2)}};$ ${\mathrm{\λ}}_{y2}=\underset{i=1}{\overset{2}{\mathrm{\Σ}}}\frac{\mathrm{\μ}}{4\mathrm{\π}{h}^3}\frac{L_i({2L}_i^2+{3h}^2)}{(L_i^2+h^2)\sqrt{(L_i^2+h^2)}};$

106, according to obtaining in step 105 with scale-up factor λ _z1, scale-up factor λ _z3and scale-up factor λ _y2, according to formula or or try to achieve grounded screen branch road branch current I.

2. the grounded screen branch road depth of burial detection method based on the differential method according to claim 1, is characterized in that: the frequency of the electric current that in step 103, grounding body A injects is that 0～2000Hz, amplitude are 1A～30A.

3. the grounded screen branch road depth of burial detection method based on the differential method according to claim 1, is characterized in that: the grid of M × N described in step 103 has equal spacing △ x at x direction of principal axis, has equal spacing △ y at y direction of principal axis.

4. the grounded screen branch current detection method based on the differential method according to claim 1, is characterized in that: before carrying out the calculating of step 104, first to the magnetic induction density B perpendicular to ground surface direction _z(x, y) and/or be parallel to the magnetic induction density B of ground surface direction _y(x, y) carries out digital filtering processing.