CN104007308B - 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 differentiation

Technical field

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

Background technology

Grounded screen is the important guarantee that substation safety runs, and its ground connection performance is constantly subjected to design and production run department Attention.In substation safety operation, only in transformer station, various electrical equipments do not provide a public current potential to grounded screen Reference ground, grounded screen be struck by lightning or power system be short-circuited fault when moreover it is possible to drain fault current rapidly, and reduce change The ground potential liter in power station.The quality of Grounding performance is directly connected in transformer station the personal safety of staff and various The safety of electrical equipment and normal operation.China's grounded screen is typically made using band steel, is interconnected to mesh shape, and level is buried Deep about 0.3～2 meter in underground, usual 3～7 meters of the spacing of grid, the ratio of the grid of both sides is usually 1:1～1:3.Due to connecing Earth mat longtime running is susceptible to corrode, and needs the defect of in time detection grounded screen and takes reclamation activitiess.

At present the main method of corrosion diagnosis of grounding grid has analysis method based on Circuit theory and is based on Theory of Electromagnetic Field Analysis method.The former is to regard grounded screen as pure resistance network, using the ultimate principle of Circuit theory, by certain measurement Means and computational methods set up the corrosion diagnosis equation of grounded screen, and obtain the reality of each branch conductor by solving diagnostic equation Resistance or resistance change rate, and then the corrosion condition of grounded screen is differentiated, this method needs to understand in advance grounded screen All or part of design drawing；The latter mainly passes through to inject the electric current of certain frequency to grounded screen, and measures ground connection entoilage Table magnetic field intensity, the distribution finally according to magnetic field diagnoses to ground net corrosion degree.Magnetic field is inverse to ask using solving scholar The topological structure to determine grounded screen for the method for topic, but morbid state solution, solution procedure during solving magnetic field inverse problem, occur Complicated.

The detection of grounded screen branch current size can be used for indirect detection grounded screen branch resistance size, is connecing of later stage Earth mat fault diagnosis and membership assessment provide good basis.

Content of the invention

For deficiency of the prior art above, it is an object of the invention to provide a kind of detection process is simple, amount of calculation The little grounded screen branch current detection method based on differentiation.Technical scheme is as follows:

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

101st, buried depth h, length l of grounded screen branch road of grounded screen branch road are obtained, and in grounded screen branch road to be measured Draw on several on ground surface arbitrarily to choose in grounding body and draw grounding body a as injection current end, above draw grounding body b conduct Extract current terminal out, and a ≠ b；Measured zone s is selected between grounding body a and grounding body b；

102nd, right hand rectangular coordinate system xyz is set up to measured zone s in step 101, particularly as follows: propping up with selected grounded screen Road midpoint be zero, with perpendicular to measured zone s upwardly direction for z-axis positive direction, with selected grounded screen branch current Direction be x-axis positive direction, cross zero and be y-axis perpendicular to the direction of grounded screen branch road, complete to set up right hand right angle and sit Mark system xyz, wherein coordinate axess x-axis are parallel with the side of measured zone s or vertical with y-axis；

103rd, measured zone s is divided into m × n grid, the side of grid is parallel with x-axis or vertical, the node of selected grid p_ijFor measurement point, measurement point p_ijCorresponding position coordinateses are (x_ij,y_ij), draw grounding body a injection on described in step 101 Electric current, measures in measurement point p_ijOn along z-axis positive direction magnetic induction b survey_z(x, y) and the magnetic induction along y-axis positive direction Intensity b is surveyed_y(x, y), wherein m are the line number of grid, and n is the columns of grid, 1≤i≤m+1,1≤j≤n+1；Change measurement point Position obtain several measurement points magnetic induction b survey_z(x, y) and magnetic induction b survey_y(x, y), and count and obtain magnetic Induction function b_z(x, y) and magnetic induction function b_y(x,y)；Statistical method adopts linear fitting herein；

104th, to the magnetic induction function b obtaining in step 103_z(x, y) obtains the mould of 1 order derivative using differentiation, Formula is as follows $\left|b_z^{\left(1\right)}(x,y)\right|=\sqrt{{\left(\frac{\&partiald;b_z(x,y)}{\&partiald;x}\right)}^2+{\left(\frac{\&partiald;b_z(x,y)}{\&partiald;y}\right)}^2},$ Or magnetic induction function b is obtained using differentiation_z(x,y)3 The mould of order derivative $\left|b_z^{\left(3\right)}(x,y)\right|=\sqrt{{\left(\frac{{\&partiald;}^3{b}_z(x,y)}{{\&partiald;x}^3}\right)}^2+{\left(\frac{{\&partiald;}^3{b}_z(x,y)}{{\&partiald;y}^3}\right)}^2};$ Or to the magnetic induction function b obtaining in step 103_y (x, y) obtains the mould of 2 order derivatives using differentiation, and formula is as follows:

$\left|b_y^{\left(2\right)}(x,y)\right|=\sqrt{{\left(\frac{{\&partiald;}^2{b}_y(x,y)}{{\&partiald;x}^2}\right)}^2+{\left(\frac{{\&partiald;}^2{b}_y(x,y)}{{\&partiald;y}^2}\right)}^2};$

105th, according to obtaining b in step 104_zThe mould of (x, y) 1 order derivativeThe mould of 3 order derivativesAnd b_yThe mould of (x, y) 2 order derivativeCalculateMain peak peak value f and right Answer the coordinate position (x of main peak peak value₀,y₀), described f includesAnd according to the ground connection obtaining in step 101 Buried depth h of net branch road, length l of grounded screen branch road, try to achieve proportionality coefficient λ according to formula_z1, proportionality coefficient λ_z3And ratio Coefficient lambda_y2, wherein λ_z1Represent the magnetic induction b perpendicular to ground surface direction_zThe main peak peak value pair of the mould of 1 order derivative of (x, y) The proportionality coefficient answered；λ_z3Represent the magnetic induction b perpendicular to ground surface direction_zThe main peak peak value of the mould of 3 order derivatives of (x, y) Corresponding proportionality coefficient；λ_y2Represent the magnetic induction b parallel to ground surface direction_yThe main peak peak of the mould of 2 order derivatives of (x, y) It is worth corresponding proportionality coefficient；Wherein ${\mathrm{\λ}}_{z1}=\underset{i=1}{\overset{2}{\mathrm{\σ}}}\frac{{\mathrm{\μl}}_i}{4\mathrm{\π}{h}^2\sqrt{(l_i^2+h^2)}};$ ${\mathrm{\λ}}_{z3}=\underset{i=1}{\overset{2}{\mathrm{\σ}}}\frac{3{\mathrm{\μl}}_i({2l}_i^2+{3h}^2)}{4\mathrm{\π}{h}^4(l_i^2+h^2)\sqrt{(l_i^2+h^2)}};$ ${\mathrm{\λ}}_{y2}=\underset{i=1}{\overset{2}{\mathrm{\σ}}}\frac{\mathrm{\μ}}{4\mathrm{\π}{h}^3}\frac{l_i({2l}_i^2+{3h}^2)}{(l_i^2+h^2)\sqrt{(l_i^2+h^2)}};$

106th, according to obtaining in step 105With proportionality coefficient λ_z1, proportionality coefficient λ_z3And ratio system Number λ_y2, according to formulaOrOrTry to achieve grounded screen branch road branch current i.

Further, in step 103 grounding body a injection electric current frequency be 0～2000hz, amplitude be 1a～30a.

Further, m × n grid described in step 103 has equal spacing △ x in x-axis direction, in y-axis direction tool There is equal spacing △ y.

Further, before carrying out the calculating of step 104, first to the magnetic induction b perpendicular to ground surface direction_z (x, y) and/or the magnetic induction b parallel to ground surface direction_y(x, y) carries out digital filtering process.

Advantages of the present invention and having the beneficial effect that:

This method, according to according to selected grounded screen bypass position and grounded screen branch road buried depth, selectes a rectangle measurement zone Domain s, draws grounding body by using in grounded screen, extracts electric current, measurement ground connection entoilage out from some injection currents and from another point Surface is perpendicular to the magnetic induction b in ground surface direction_z(x, y) or the magnetic induction b parallel to ground surface direction_y(x, y), Through to magnetic induction b_z(x, y) or b_y(x, y) carries out eliminating after digital filtering process noise jamming, by differentiation, first Ask for magnetic induction b_zThe mould of 1 order derivative of (x, y)The mould of 3 order derivativesOr magnetic induction b_y The mould of 2 order derivatives of (x, y)Secondly obtain the main peak peak value of the mould of all-order derivative respectively With corresponding proportionality coefficient λ_z1、λ_z3、λ_y2, to determine the grounded screen branch current i size in measured zone.Whole process detects Process is simple, and amount of calculation is little.

Brief description

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

Fig. 2Scattergram；

Fig. 3Sectional drawing；

Fig. 4Scattergram；

Fig. 5Sectional drawing；

Fig. 6Scattergram；

Fig. 7Sectional drawing；

Fig. 8 proportionality coefficient λ_z1、λ_z3、λ_y2Scattergram；

The flow chart that Fig. 9 detects grounded screen branch current.

Specific embodiment

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

A kind of grounded screen branch current detection method based on differentiation, comprises the following steps:

Step one, according to selected grounded screen bypass position and grounded screen branch road buried depth h, determines in grounded screen ground surface One measured zone s, obtains the magnetic induction of described measured zone s, including the magnetic induction perpendicular to ground surface direction b_z(x, y) and/or the magnetic induction b parallel to ground surface direction_y(x,y)；

Step 2, obtains the magnetic induction b perpendicular to ground surface direction respectively_zThe mould of 1 order derivative of (x, y)The mould of 3 order derivativesAnd/or the magnetic induction b parallel to ground surface direction_y2 order derivatives of (x, y) Mould

Step 3, the seat of the main peak peak value f of mould of all-order derivative described in obtaining step two and corresponding main peak peak value respectively Cursor position (x₀,y₀)；

Step 4, according to the coordinate position (x of selected main peak peak value₀,y₀), selected grounded screen branch road two ends node coordinate, connect Earth mat branch road buried depth h and soil magnetic permeability μ, calculate proportionality coefficient λ；

Step 5, the ratio system described in the main peak peak value f of the mould of all-order derivative according to step 3 and step 4 Number λ, determines the grounded screen branch current size in measured zone s.

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

A draws grounding body using in grounded screen, draws grounding body injection current from any one, and from removing injection current On draw outside grounding body another on draw grounding body and extract electric current out；The frequency of this injection current is 0～2000hz, amplitude is 1a ～30a；

B, according to selected grounded screen bypass position and grounded screen branch road buried depth h, in grounded screen ground surface, determines one Measured zone s of rectangle, described measured zone s is located on injection current and two, the electric current of extraction described in step a draws grounding body Between, so that perpendicular to measured zone s, upwards for z-axis positive direction, in x-axis, selected grounded screen branch road is electric for selected grounded screen branch road Stream direction is identical with x-axis positive direction, with selected grounded screen branch road midpoint as zero, sets up right hand rectangular coordinate system xyz, its Middle coordinate axess x-axis is parallel with the side of measured zone s or vertical with y-axis；

Measured zone s is divided into m × n grid by c, and the side of grid is parallel with x-axis or vertical, the node p of selected grid_ijFor Measurement point, the corresponding position coordinateses of measurement point are (x_ij,y_ij), measure in measurement point p_ijOn perpendicular to ground surface magnetic induction Intensity b_z(x, y) and the magnetic induction b along y-axis positive direction_y(x, y), wherein m are the line number of grid, and n is the columns of grid, 1 ≤ i≤m+1,1≤j≤n+1.

Described m × n grid has equal spacing △ x in x-axis direction, has equal spacing △ y in y-axis direction.

Measured zone s of grounded screen ground surface is in the position directly above of selected grounded screen branch road.

The main peak peak value f of the mould of all-order derivative described in above-mentioned steps three includes:

Magnetic induction b perpendicular to ground surface direction_zThe main peak peak value of the mould of 1 order derivative of (x, y) isVertically Magnetic induction b in ground surface direction_zThe main peak peak value of the mould of 3 order derivatives of (x, y) isAnd/or parallel to ground surface The magnetic induction b in direction_yThe main peak peak value of the mould of 2 order derivatives of (x, y) is

The calculation procedure obtaining described proportionality coefficient described in above-mentioned steps four includes:

Grounded screen leg length selected by a is l, with selected grounded screen branch road midpoint as zero, 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 value₀,y₀) and grounded screen branch road two end segment Point is being respectively l parallel to the distance on x-axis direction₁=l/2-x₀、l₂=l/2+x₀；

B grounded screen branch road buried depth is h and soil pcrmeability is μ, obtains described proportionality coefficient λ bag described in step 4 Include: perpendicular to the magnetic induction b in ground surface direction_zThe corresponding proportionality coefficient of main peak peak value of the mould of 1 order derivative of (x, y) is λ_z1；Magnetic induction b perpendicular to ground surface direction_zThe corresponding proportionality coefficient of main peak peak value of the mould of 3 order derivatives of (x, y) is λ_z3；And/or the magnetic induction b parallel to ground surface direction_yThe corresponding ratio of main peak peak value of the mould of 2 order derivatives of (x, y) Coefficient 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 includes:

According to the magnetic induction b perpendicular to ground surface direction_zThe main peak peak value of the mould of 1 order derivative of (x, y)With right The proportionality coefficient λ answering_z1, obtain measured zone s in grounded screen branch current i be

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

According to the magnetic induction b perpendicular to ground surface direction_zThe main peak peak value of the mould of 3 order derivatives of (x, y)With right The proportionality coefficient λ answering_z3, obtain measured zone s in grounded screen branch current i be

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

According to the magnetic induction b parallel to ground surface direction_yThe main peak peak value of the mould of 2 order derivatives of (x, y)With right The proportionality coefficient λ answering_y2, obtain measured zone s in grounded screen branch current i be

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

When the method for the present invention is detected, after step one and carry out step 2 calculating before, can be first to hanging down Directly in the magnetic induction b in ground surface direction_z(x, y) and/or the magnetic induction b parallel to ground surface direction_y(x, y) is carried out Digital filtering is processed.

In obtaining step two, the mould of all-order derivative specifically comprises the following steps that

Obtain magnetic induction b_zThe mould of 3 order derivatives of (x, y)Process:

With measurement point location variable x as independent variable, ask for magnetic induction b_z1 order derivative of (x, y)

With measurement point location variable y as independent variable, ask for magnetic induction b_z1 order derivative of (x, y)

With measurement point location variable x as independent variable, ask for magnetic induction b_z2 order derivatives of (x, y)

With measurement point location variable y as independent variable, ask for magnetic induction b_z2 order derivatives of (x, y)

With measurement point location variable x as independent variable, ask for magnetic induction b_z3 order derivatives of (x, y)

With measurement point location variable y as independent variable, ask for magnetic induction b_z3 order derivatives of (x, y)

Obtain magnetic induction b_zThe mould of 3 order derivatives of (x, y)

Obtain magnetic induction b_zThe mould of 1 order derivative of (x, y)Process:

With measurement point location variable x as independent variable, ask for magnetic induction b_z1 order derivative of (x, y)

With measurement point location variable y as independent variable, ask for magnetic induction b_z1 order derivative of (x, y)

Obtain magnetic induction b_zThe mould of 1 order derivative of (x, y)

Obtain magnetic induction b_yThe mould of 2 order derivatives of (x, y)Process:

With measurement point location variable x as independent variable, ask for magnetic induction b_y1 order derivative of (x, y)

With measurement point location variable y as independent variable, ask for magnetic induction b_y1 order derivative of (x, y)

With measurement point location variable x as independent variable, ask for magnetic induction b_y2 order derivatives of (x, y)

With measurement point location variable y as independent variable, ask for magnetic induction b_y2 order derivatives of (x, y)

Obtain magnetic induction b_yThe mould of 2 order derivatives of (x, y)

Referring to Fig. 1, under practical situation, the leg length of grounding net of transformer substation is fixed, the current－carrying conductor mn water of length l Put down and be embedded in the monolayer uniform soil that pcrmeability is μ, conductor is parallel to be placed in x-axis, with selected grounded screen branch road midpoint as coordinate Initial point, sets up right hand rectangular coordinate system xyz, and parallel to xoy plane and distance is h to ground surface, and the electric current flowing through in conductor is i, Sense of current is along x-axis positive direction.The lower section of hypothesis plane z=h is the monolayer uniform soil of μ for pcrmeability, the magnetic of soil Conductance approximately takes the magnetic permeability μ in vacuum_o.Ignore leakage current on soil for the conductor.

Choose i=1a, h=1m, l=6m.

As Fig. 1, select measuring surface s in grounded screen ground surface, area is 12m × 12m, measuring surface s divides 399 × 399 grids, the side of grid is parallel with x-axis or vertical, and grid has equal spacing △ x=3cm in x-axis direction, and grid is in y Direction of principal axis has equal spacing △ y=3cm, the node p of grid_ijFor measurement point, measurement point has corresponding position coordinateses and is (x_ij,y_ij), measurement is in measurement point p_ijOn perpendicular to ground surface magnetic induction b_z(x, y), measurement is in measurement point p_ijUpper parallel Magnetic induction b in y-axis positive direction_y(x, y), wherein m are the line number of grid, and n is the columns of grid, 1≤i≤400,1≤j ≤400.

Obtain magnetic induction b_zThe mould of 1 order derivative of (x, y)Referring to Fig. 2；

With measurement point location variable x as independent variable, ask for magnetic induction b_z1 order derivative of (x, y)

With measurement point location variable y as independent variable, ask for magnetic induction b_z1 order derivative of (x, y)

Obtain magnetic induction b_zThe mould of 1 order derivative of (x, y)

Referring to Fig. 3, obtain x=0m cross section in Fig. 2, obtain from x=0m cross sectionMain peak peak value size ForCorresponding proportionality coefficient λ_z1=1.89736 × 10^-7h/m³It may be determined that grounded screen is propped up Road size of current

Obtain magnetic induction b_zThe mould of 3 order derivatives of (x, y)Referring to Fig. 4；

With measurement point location variable x as independent variable, ask for magnetic induction b_z3 order derivatives of (x, y)

With measurement point location variable y as independent variable, ask for magnetic induction b_z3 order derivatives of (x, y)

Obtain magnetic induction b_zThe mould of 3 order derivatives of (x, y)

Referring to Fig. 5, obtain x=0m cross section in Fig. 4, obtain from x=0m cross sectionMain peak peak value big Little it isCorresponding proportionality coefficient λ_z3=1.19535 × 10^-6h/m⁵It may be determined that grounded screen Branch current size

Obtain magnetic induction b_yThe mould of 2 order derivatives of (x, y)Referring to Fig. 6；

With measurement point location variable x as independent variable, ask for magnetic induction b_y2 order derivatives of (x, y)

With measurement point location variable y as independent variable, ask for magnetic induction b_y2 order derivatives of (x, y)

Obtain magnetic induction b_yThe mould of 2 order derivatives of (x, y)

Referring to Fig. 7, obtain x=0m cross section in Fig. 6, obtain from x=0m cross sectionMain peak peak value big Little it isCorresponding proportionality coefficient λ_y2=3.98448 × 10^-7h/m⁴It may be determined that grounded screen Branch current size

With reference to Fig. 8, h=1m, l=6m, μ₀=4 π × 10^-7During h/m, proportionality coefficient λ_z1、λ_z3、λ_y2Distribution situation.

The flow chart that Fig. 9 detects grounded screen branch current.

The above embodiment is interpreted as being merely to illustrate the present invention rather than limits the scope of the invention.? After the content of the record having read the present invention, technical staff can make various changes or modifications to the present invention, these equivalent changes Change and modify and equally fall into the grounded screen branch current detection method claim limited range based on differentiation for the present invention.

Claims (4)

1. a kind of grounded screen branch current detection method based on differentiation is it is characterised in that comprise the following steps:

101st, buried depth h, length l of grounded screen branch road of grounded screen branch road are obtained, and the earth's surface in grounded screen branch road to be measured Draw on several on face arbitrarily to choose in grounding body and draw grounding body a as injection current end, above draw grounding body b as extraction Current terminal, and a ≠ b；Measured zone s is selected between grounding body a and grounding body b；

102nd, right hand rectangular coordinate system xyz is set up to measured zone s in step 101, particularly as follows: with selected grounded screen branch road Point be zero, with perpendicular to measured zone s upwardly direction for z-axis positive direction, with the side of selected grounded screen branch current To for x-axis positive direction, crossing zero and being y-axis perpendicular to the direction of grounded screen branch road, complete to set up right hand rectangular coordinate system Xyz, wherein coordinate axess x-axis are parallel with the side of measured zone s or vertical with y-axis；

103rd, measured zone s is divided into m × n grid, the side of grid is parallel with x-axis or vertical, the node p of selected grid_ijFor Measurement point, measurement point p_ijCorresponding position coordinateses are (x_ij, y_ij), draw grounding body a injection current on described in step 101, Measure in measurement point p_ijOn along z-axis positive direction magnetic induction b survey_z(x, y) and the magnetic induction b along y-axis positive direction Survey_y(x, y), wherein m are the line number of grid, and n is the columns of grid, 1≤i≤m+1,1≤j≤n+1；Change the position of measurement point The magnetic induction b obtaining several measurement points surveys_z(x, y) and magnetic induction b survey_y(x, y), and count that to obtain magnetic induction strong Degree function b_z(x, y) and magnetic induction function b_y(x,y)；

104th, to the magnetic induction function b obtaining in step 103_z(x, y) obtains the mould of 1 order derivative using differentiation, and formula is such as UnderOr magnetic induction function b is obtained using differentiation_z(x, y) 3 order derivative MouldOr to the magnetic induction function b obtaining in step 103_y(x,y) Obtain the mould of 2 order derivatives using differentiation, formula is as follows:

105th, according to obtaining b in step 104_zThe mould of (x, y) 1 order derivativeThe mould of 3 order derivativesAnd b_y(x, Y) mould of 2 order derivativesCalculateMain peak peak value f and corresponding main peak Coordinate position (the x of peak value₀, y₀), described f includesAnd according to the grounded screen branch road obtaining in step 101 Buried depth h, length l of grounded screen branch road, proportionality coefficient λ is tried to achieve according to formula_z1, proportionality coefficient λ_z3And proportionality coefficient λ_y2, Wherein λ_z1Represent the magnetic induction b perpendicular to ground surface direction_zThe corresponding ratio of main peak peak value of the mould of 1 order derivative of (x, y) Example coefficient；λ_z3Represent the magnetic induction b perpendicular to ground surface direction_zThe main peak peak value of the mould of 3 order derivatives of (x, y) is corresponding Proportionality coefficient；λ_y2Represent the magnetic induction b parallel to ground surface direction_yThe main peak peak value of the mould of 2 order derivatives of (x, y) corresponds to Proportionality coefficient；Wherein μ is soil pcrmeability, l_iPosition (x for selected main peak peak value₀, y₀) and grounded screen Branch road two end node is parallel to the distance on x-axis direction；

106th, according to obtaining in step 105With proportionality coefficient λ_z1, proportionality coefficient λ_z3And proportionality coefficient λ_y2, whereinIt is the magnetic induction b perpendicular to ground surface direction_zThe main peak peak value of the mould of 1 order derivative of (x, y),For Magnetic induction b perpendicular to ground surface direction_zThe main peak peak value of the mould of 3 order derivatives of (x, y),It is parallel to ground surface The magnetic induction b in direction_yThe main peak peak value of the mould of 2 order derivatives of (x, y)；According to formulaOr OrTry to achieve grounded screen branch road branch current i.

2. the grounded screen branch current detection method based on differentiation according to claim 1 it is characterised in that: step In 103 grounding body a injection electric current frequency be 0～2000hz, amplitude be 1a～30a.

3. the grounded screen branch current detection method based on differentiation according to claim 1 it is characterised in that: step M × n grid described in 103 has equal spacing δ x in x-axis direction, has equal spacing δ y in y-axis direction.

4. the grounded screen branch current detection method based on differentiation according to claim 1 it is characterised in that: carrying out Before the calculating of step 104, first to the magnetic induction b perpendicular to ground surface direction_z(x, y) and/or parallel to ground surface side To magnetic induction b_y(x, y) carries out digital filtering process.