CN101900767A - Visual method for utilizing short distance measuring method to measure ground resistance of analogue ground screen - Google Patents

Abstract

The invention relates to a visual method for utilizing short distance measuring method to measure ground resistance of analogue ground screen. The method includes of development of a transformer substation ground resistance measuring interface which adopts short distance method, a calculation method of ground resistance, a calculation method of ground potential and a method for calculating the obtained given voltage pole position according the interface and the two methods. The invention realizes visualization of transformer substation ground resistance measurement by adopting short distance method, the method is simple and visual, related interference factors in field test process can be inhibited or eliminated, massive manpower and material resources are saved, and the method has great engineering practical value.

Description

Use the method for visualizing of short distance measuring method to measure ground resistance of analogue ground screen

Technical field

The present invention relates to the High-Voltage Technology field, relate generally to a kind of method for visualizing when adopting short distance measuring method to measure substation grounding resistance.

Background technology

In order to work and security needs, some current-carrying part of the electric device in electric system or the buildings, facility is connected Here it is ground connection with earthing pole through ground wire.Stake resistance is one of important technology index that characterizes the earthing device electric property, refer to when the electric current I voltage U on the electrode and the ratio of electric current I when ground-electrode flows into the earth, it comprises the extremely electric resistance of soil of infinite distant place of the contact resistance of resistance, earthing pole and soil of resistance, earthing pole body of ground lead and electrode.

Because send out, the grounded screen of transformer station bearing the fault current of releasing, balanced ground potential and the task of stable reference current potential is being provided, therefore its stake resistance must satisfy following requirement, promptly the rising of ground potential can not surpass the limit value that equipment operation allowed when releasing fault current, can not constitute electrical impact to the person simultaneously.Therefore, new send out, transformer station, before it puts into operation, stake resistance is measured, whether the stake resistance that can check new grounded screen reaches designing requirement, and calculated value carried out verification, the correctness of checking computing method, thus foundation provided for applying of new computing method and module.Concerning the transformer station of operation, its stake resistance is measured, help to check monitoring equipment operation equipment, avoid the generation of fault.

The fall-of-potential method measure theory be by eighties of last century grow up the sixties so far still by the ground resistance measurement method of ANSI/IEEE standard recommendation, theoretically, this method can be measured very little stake resistance and not be subjected to the influence of auxiliary electrode resistance, therefore very popular, be still the ground resistance measurement method of standard recommendation so far.During concrete test, an electric current utmost point C and a potential pole P are set, or be triangularly arranged point-blank with earthing device G, the electric current utmost point and potential pole.As shown in Figure 1, electric current is injected earthing device, measure the voltage between this electric current and earthing pole and potential pole.Measure the apparent stake resistance of the different potentials utmost point position correspondence during measurement respectively, the change curve when making stake resistance with the potential pole position change, the stake resistance of curve flat sections correspondence is the stake resistance of earthing device.The position that potential electrode reasonably is set is the key of carrying out grounding resistance measurement.

The ground potential distribution curve of correspondence when Fig. 2 is the fall-of-potential method measurement of Grounding Resistance, the Potential distribution curve when wherein curve 1 scatters in ground for having only tested electrode individualism and having electric current I to pass through; Curve 2 is for having only the existence of the auxiliary current utmost point and having electric current I to flow back to the Potential distribution curve of electrode from ground; Curve 3 is the simultaneous combined potential distribution curve of tested electrode and auxiliary electrode, the i.e. algebraic sum of curve 1 and curve 2.

As seen from Figure 2, because the effect of the auxiliary current utmost point, the zero potential of infinite distant place has moved on to the O point position among the figure.During measurement, if with the voltage pole choice of location in the O at zero point point position owing to be subjected to the influence of the auxiliary current utmost point, the grounding body current potential is by U ₁₀Dropped to U ₁₀+ U ₂₀, measurement result also just becomes R=(U accordingly ₁₀+ U ₂₀)/I obviously has certain error.In order to compensate the error that influence caused of the auxiliary current utmost point, a segment distance must be moved again to electric current extreme direction in the voltage pole position, and promptly to move to current potential be U in the measuring position ₂₀The P point time, make U _P=U ₂₀, the measurement result of this moment is

R＝(U ₁₀+U ₂₀-U _P)/I＝(U ₁₀+U ₂₀-U ₂₀)/I＝U ₁₀/I

Identical with the true value of stake resistance.This shows that the impedance ground of zero-potential point correspondence is not actual impedance ground, and the position of corresponding actual impedance ground should be the compensation point of potential pole, promptly compensates the reduction of the impedance ground that causes owing to the extremely close earthed system of electric current, this is penalty method.

The similarities and differences of the position of arranging according to three potential electrode, earth resistance method commonly used at present mainly contains 0.618 method and 30 degree angle-off sets.

(1) 0.618 method

If three potential electrode shown in Figure 1 are linearly arranged, establish the distance that electric current utmost point C and voltage pole P leave the earthing device center and be respectively x and d, GP=x and GC=d are promptly arranged.If think that earthing device G and electric current utmost point C are semispheres, and its radius compares very for a short time with x and d, and then will make measuring error is 0, then need

$\frac{1}{d}+\frac{1}{x}-\frac{1}{d-x}=0---\left(1\right)$

Following formula is found the solution, can get x=0.618d.Promptly when three potential electrode are linearly arranged, only potential pole need be arranged in 0.618D apart from the earthing device center _GCThe place, just can make measuring error is zero.0.618 usually said method that Here it is.But when 0.618 method of use was carried out grounding resistance measurement, should meet the following conditions: (1) had very uniform soil; (2) enough big electrode separation is arranged, so that electrode can be regarded the structure of semicircle as.

(2) 30 degree angle-off sets

If earthing device G, electric current utmost point C and voltage pole P are isosceles triangle layout (as shown in Figure 3), i.e. D _GP=D _GCThe time, wanting to make measuring error is 0, then needs

$\frac{1}{\sqrt{D_{\mathrm{AC}}^2+D_{\mathrm{AB}}^2-2D_{\mathrm{AC}}^2\cos \mathrm{\θ}}}-\frac{1}{D_{\mathrm{AB}}}-\frac{1}{D_{\mathrm{AC}}}=0---\left(2\right)$

Following formula is found the solution, can get θ=29 °.When promptly adopting triangular-shaped electrodes to arrange, can eliminate measuring error when making the angle of the electric current utmost point and potential pole be 29 °, claim that usually this measuring method is 30 degree angle-off sets.But when using 30 degree angle-off sets to carry out grounding resistance measurement, should meet the following conditions equally: (1) has very uniform soil; (2) enough big electrode separation is arranged, so that electrode can be regarded the structure of semicircle as.

Increase along with the earth mat scale, the workload of using 0.618 method and 30 degree angle-off set measurement of Grounding Resistance is increasing, interference problem is also serious day by day, therefore press for the measuring method that can shorten electric current utmost point lead-in wire, especially in the city of generally hardening in mountain area and heavy traffic, the ground of landforms complexity.

Studies show that in the past, no matter the geometric configuration of tested earthing device and type are how, because the influence of the auxiliary current utmost point, its Potential distribution curve all is the curve that reduces to the negative potential dullness from positive potential.How long be not difficult to conclude not tube current wiring thus, always between the earthing device and the electric current utmost point exist a bit and have only a bit, its current potential just equals auxiliary current extremely to the current potential that influences of tested electrode, and the grounding resistance that measures when voltage pole is placed this equals the true grounding resistance of earthing device.That is to say that short distance is measured and set up in theory, as long as find out the Potential distribution rule on grounding body ground, by calculating and the analysis that the earth mat extrinsic current is distributed, just can solve correct measuring position.

As 0.618 method, the key issue of short distance measuring method is to determine compensation point.As long as determined compensation point, just can carry out short distance and measure according to the wiring of 0.618 method, not only can guarantee in theory the accuracy measured can also reduce workload, reduce and disturb.But 0.681 method and deriving method thereof all are that the earthed system equivalence is hemispheric computation model, and the computing formula that distributes according to semisphere grounding body ground potential calculates the distribution of the outer ground of earth mat current potential then, obtains corresponding measuring position point in view of the above.But the shape of actual earth mat is various, and with the difference of vertical junction ground body length difference.In addition, if place the nearer place of earth mat as near 1 times of catercorner length the time electric current utmost point position, the truth of earth mat can not be with the equivalence of hemisphere earthing pole.Therefore, carry out the short distance Measurement Study, at first must the Potential distribution rule of earth mat be summarized, rebulid the equivalent grounding network computation model that can when short distance, be suitable for, could calculate and derive according to measuring principle then, foundation is the short distance measure theory of measurement of Grounding Resistance accurately.

The current potential of any point is the outwards source of leakage current generation in the soil in the soil.Grounded screen is exactly the source of an outside leakage current, and the current potential of arbitrfary point is all produced by it near the transformer station, and the leakage current distribution of obtaining on the grounded screen just can be in the hope of the current potential of electric current decanting point, and simultaneously, the current potential of arbitrfary point also can be tried to achieve on the face of land.Therefore, want to search out the tram of voltage pole, key is the distribution that will obtain leakage current in the conductor.

Summary of the invention

The objective of the invention is to adopt a coupling method of moment that the stake resistance of grounded screen and the diffusing distributions of earth mat conductor are calculated, and model is determined the method for the reference position of voltage pole quickly and easily in actual measurement is used in view of the above, and realize that it is visual.May further comprise the steps and method:

Step 1 is set up visualization model, realizes the visual of short distance measuring method measurement of Grounding Resistance;

In order to improve the versatility of short distance measuring method, the present invention has realized the visualization model of short distance method measurement of Grounding Resistance.Specifically, this module can realize following several functions:

1, concerning a certain given grounding net of transformer substation, the position coordinates of each ingredient by the input grounding net can demonstrate the three-dimensional plot directly perceived of grounded screen in module;

2,,, calculate the Potential distribution of earth mat when the no current utmost point is arranged by the parameters such as position coordinates of input soil resistivity, subdivision number, the testing current utmost point according to the earth mat position coordinates;

3, on this basis, provide the recommendation test position of voltage pole according to the penalty method principle, for on-the-spot test provides reference;

Step 2, the leakage current that adopts some coupling method of moment to calculate the grounded screen conductor distributes and stake resistance;

Think that grounded screen is an equipotential body when step 2.1, calculating.The current potential of unit point current source in the arbitrfary point in the known infinitely great homogeneous conductive ature of coal is that Green function is:

$G=\frac{\mathrm{\ρ}}{4\mathrm{\πr}}---\left(3\right)$

In the formula, ρ is a resistivity of media, and r is show up a little a distance of source point.

Step 2.2, if a length is leakage current on the L conductor segment is I, the current potential of arbitrfary point can be found the solution by the integration on conductor segment so, is shown below:

Step 2.3, if the true value of j section conductive surface current potential be Current potential that must this section surface central point by numerical evaluation is

With Between certain error is generally arranged, with error

On j section conductive surface, carry out weighted mean, and be zero, the objective function that is shown below is then arranged:

j＝1～n

(5)

In the formula size of n by

Approach

Desired precision decision.

Can further obtain by following formula

In the formula, W _jBe called as weight function, this is the universal expression formula of method of moment.

If step 2.4 is got W _j=δ _j(r _i-r _j), δ _j(r _i-r _j) be Dirac function, and the field point is taken at the mid point of j section surface, then have

Following formula is a coupling method of moment, and it is considered as constant with the wandering electric current of each section conductor, and the current potential that the current potential of each section is gone up mid point with the surface is represented.

Step 2.5, grounded screen is divided into the n section after, can obtain n equation by following formula:

j＝1～n

(8)

In the formula,

$R_{\mathrm{ij}}=\frac{\mathrm{\ρ}}{4\mathrm{\π}{L}_i}\underset{L_i}{\∫}\frac{1}{r_i}{\mathrm{dl}}_i---\left(9\right)$

The form of step 2.6, the matrix of being write as has

In the formula, R is n * n matrix, is called two sections mutual resistance between conductor when i ≠ j, is called the mutual resistance of this section conductor when i=j; I=[I ₁, I ₂..., I _n] ^TBeing the n dimensional vector, is the leakage current of every section conductive surface;

Being the n dimensional vector, is every section surface of conductors current potential.

Step 2.7, when design factor matrix R, the coordinate of establishing unit i two-end-point is respectively (x _I1, y _I1, z _I1) and (x _I2, y _I2, z _I2); The coordinate of the two-end-point of unit j is (x _J1, y _J1, z _J1) and (x _J2, y _J2, z _J2); Match point P is the mid point of unit j, and its coordinate is (x _p, y _p, z _p).

Yi Zhi, x _p=(x _J1+ x _J2)/2, y _p=(y _J1+ y _J2)/2, z _p=(z _J1+ z _J2)/2; If the mirror image of the i of unit is i ', then its two-end-point coordinate is (x _I1, y _I1,-z _I1) and (x _I2, y _I2,-z _I2); The length of unit i is l _i, as can be known:

$l_i=\sqrt{{(x_{i2}-x_{i1})}^2+{(y_{i2}-y_{i1})}^2+{(z_{i2}-z_{i1})}^2}$

If moving point of integration and mirror image coordinate thereof be (x, y, z) and (x, y ,-z), corresponding differentiation element is dl, the distance of moving of integration and mirror image and match point is respectively R and R ', then has:

$R,R^{\′}=\sqrt{{(x-x_p)}^2+{(y-y_p)}^2+{\left(z\stackrel{\‾}{+}{z}_p\right)}^2}$

Get by formula (10):

$R_{\mathrm{ij}}=\frac{\mathrm{\ρ}}{4\mathrm{\π}{L}_i}{\∫}_{(x_{i1},y_{i1},z_{i1})}^{(x_{i2},y_{i2},z_{i2})}(\frac{1}{R}+\frac{1}{R^{\′}})\mathrm{dl}---\left(11\right)$

Introduce dimensionless coordinate k, the moving point of integration done as down conversion:

$x=\frac{{\mathrm{<figure-callout\; id="2"\; label="x\; i"\; filenames="H200910057320XE0000012.png,H200910057320XE0000042.png"\; state="\{\{state\}\}">x</figure-callout>}}_i+x_{i1}+k(x_{i2}-x_{i1})}{2}$ $y=\frac{y_{i2}+y_{i1}+k(y_{i2}-y_{i1})}{2}$ $z=\frac{z_{i2}+z_{i1}+k(z_{i2}-z_{i1})}{2}$

Promptly

$\mathrm{dl}=\sqrt{{\left(\mathrm{dx}\right)}^2+{\left(\mathrm{dy}\right)}^2+{\left(\mathrm{dz}\right)}^2}=\frac{1}{2}\sqrt{{(x_{i2}-x_{i1})}^2+{(y_{i2}-y_{i1})}^2+(z_{i2}-z_{i1})}\mathrm{dk}$

When k=-1, x=x is arranged _I1, y=y _I1, z=z _I1When k=1, x=x is arranged _I2, y=y _I2, z=z _I2, then formula (11) can turn to the integration to k, that is:

$R_{\mathrm{ij}}=\frac{\mathrm{\&rho;}}{8\mathrm{\&pi;}}{\&Integral;}_{-1}^1\frac{\mathrm{dk}}{\sqrt{L^2{\mathrm{<figure-callout\; id="2"\; label="k"\; filenames="H200910057320XE0000012.png,H200910057320XE0000042.png"\; state="\{\{state\}\}">k</figure-callout>}}^2+\mathrm{Mk}+{\mathrm{<figure-callout\; id="2"\; label="N"\; filenames="H200910057320XE0000012.png,H200910057320XE0000042.png"\; state="\{\{state\}\}">N</figure-callout>}}^2}}+{\&Integral;}_{-1}^1\frac{\mathrm{dk}}{\sqrt{L^2{\mathrm{<figure-callout\; id="2"\; label="k"\; filenames="H200910057320XE0000012.png,H200910057320XE0000042.png"\; state="\{\{state\}\}">k</figure-callout>}}^2+M^{\&prime;}k+N^{\&prime;2}}}---\left(12\right)$

In the formula:

$L=\sqrt{{(x_{i2}-x_{i1})}^2+{(y_{i2}-y_{i1})}^2+{(z_{i2}-z_{i1})}^2}$

M＝2[(x _i2-x _i1)·(x _i2+x _i1-2x _p)+(y _i2-y _i1)·(y _i2+y _i1-2y _p)+(z _i2-z _i1)·(z _i2+z _i1-2z _p)]

$N=\sqrt{{({\mathrm{<figure-callout\; id="2"\; label="x\; i"\; filenames="H200910057320XE0000012.png,H200910057320XE0000042.png"\; state="\{\{state\}\}">x</figure-callout>}}_i+x_{i1}-{2x}_p)}^2+{(y_{i2}+y_{i1}-{2y}_p)}^2+{({\mathrm{<figure-callout\; id="2"\; label="z\; i"\; filenames="H200910057320XE0000012.png,H200910057320XE0000042.png"\; state="\{\{state\}\}">z</figure-callout>}}_i+z_{i1}-{2z}_p)}^2}$

$W=2\sqrt{{(x_{i2}-x_p)}^2+{(y_{i2}-y_p)}^2+{(z_{i2}-z_p)}^2}$

M′＝2[(x _i2-x _i1)·(x _i2+x _i1-2x _p)+(y _i2-y _i1)·(y _i2+y _i1-2y _p)+(z _i2-z _i1)·(z _i2+z _i1+2z _p)]

$N^{\&prime;}=\sqrt{{({\mathrm{<figure-callout\; id="2"\; label="x\; i"\; filenames="H200910057320XE0000012.png,H200910057320XE0000042.png"\; state="\{\{state\}\}">x</figure-callout>}}_i+x_{i1}-{2x}_p)}^2+{(y_{i2}+y_{i1}-{2y}_p)}^2+{({\mathrm{<figure-callout\; id="2"\; label="z\; i"\; filenames="H200910057320XE0000012.png,H200910057320XE0000042.png"\; state="\{\{state\}\}">z</figure-callout>}}_i+z_{i1}+{2z}_p)}^2}$

$W^{\&prime;}=2\sqrt{{(x_{i2}-x_p)}^2+{(y_{i2}-y_p)}^2+{({\mathrm{<figure-callout\; id="2"\; label="z\; i"\; filenames="H200910057320XE0000012.png,H200910057320XE0000042.png"\; state="\{\{state\}\}">z</figure-callout>}}_i+z_p)}^2}$

Formula (12) is carried out integration to be had

$R_{\mathrm{ij}}=\frac{\mathrm{\&rho;}}{4\mathrm{\&pi;}}(\ln \frac{{2\mathrm{<figure-callout\; id="2"\; label="L"\; filenames="H200910057320XE0000012.png,H200910057320XE0000042.png"\; state="\{\{state\}\}">L</figure-callout>}}^2+M+2\mathrm{LW}}{M+2\mathrm{LN}}+\ln \frac{{2\mathrm{<figure-callout\; id="2"\; label="L"\; filenames="H200910057320XE0000012.png,H200910057320XE0000042.png"\; state="\{\{state\}\}">L</figure-callout>}}^2+M^{\&prime;}+2L{W}^{\&prime;}}{M^{\&prime;}+2L{N}^{\&prime;}})---\left(13\right)$

Should note when calculating: when match point P is on the extended line of unit i with following formula, 0/0 result may appear in first ln item in the formula (13), the coordinate that for this reason needs appropriate change P to order is as opposite side that the P point is moved on to unit i symmetry or the radius a that adds ground-electrode.

When match point P moves on on the unit i, when promptly unit i and unit j overlap, occurred denominator in the formula (13) and be zero situation, thereby needed to consider to add the equivalent redius a of grounded screen and the surface that match point P is moved on to unit i, promptly have:

$L=\sqrt{{\left(x{-x}_p\right)}^2+{(y-y_p)}^2+{(z-z_p)}^2+a^2}$

The substitution formula in like manner can obtain in (13):

$R_{\mathrm{ij}}=\frac{\mathrm{\&rho;}}{4\mathrm{\&pi;}}(\ln \frac{L+\sqrt{L+{4a}^2}}{-L+\sqrt{L+{4a}^2}}+\ln \frac{2{\mathrm{<figure-callout\; id="2"\; label="L"\; filenames="H200910057320XE0000012.png,H200910057320XE0000042.png"\; state="\{\{state\}\}">L</figure-callout>}}^2+M^{\&prime;}+2L{W}^{\&prime;}}{M^{\&prime;}+2{\mathrm{LN}}^{\&prime;}})---\left(14\right)$

Step 2.8, after having calculated matrix of coefficients R since this step process in the middle of think that grounded screen is equipotential, promptly

And order

Equal a certain constant, so after finding the solution the leakage current I that obtains every section conductor according to formula (8),

Step 2.9, can try to achieve stake resistance and be:

Step 3 is according to the leakage current Distribution calculation ground potential of earth mat conductor;

Step 3.1, the ground potential during the no current utmost point distributes;

Try to achieve after the distributions of loosing, the ground potential when using superposition principle conveniently to try to achieve the no current utmost point according to its current potential contribution at the ground each point distributes.

Step 3.2, the ground potential that calculates under the influence of the electric current utmost point distributes;

When calculating the ground potential distribution under the influence of the electric current utmost point,, just can calculate ground potential according to superposition principle as long as obtain the diffusing distributions that the electric current utmost point influences lower conductor.With infinite distant place is reference point, establishes the earth mat current potential and is upgraded to V, and the current potential of the electric current utmost point is V _c, the earth mat conductor is divided into the section into n, and the stream electric current that looses is followed successively by i _jThe electric current utmost point is divided into the m section, and the stream electric current that looses is i _Ck, then the diffusing stream current vector of system is:

$\stackrel{\&RightArrow;}{I}=\{i_1,{\mathrm{<figure-callout\; id="2"\; label="i"\; filenames="H200910057320XE0000012.png,H200910057320XE0000042.png"\; state="\{\{state\}\}">i</figure-callout>}}_2,...,i_n,i_{c1},i_{c2},...,i_{\mathrm{cm}}\}---\left(16\right)$

The current potential vector is:

$\stackrel{\&RightArrow;}{V}=\{V,V,...,V,V_c,...,V_c\}---\left(17\right)$

Mutual resistance matrix between each segmentation of computing system is A, and then fundamental equation remains:

Step 3.3, this equation have n+m+2 variable, but have only n+m equation.Because V and V _cUnequal, can not pass through extra current equation ∑ i _j=I and ∑ i _Ck=-I finds the solution, and this moment, matrix of coefficients can lose symmetry, influenced computing velocity and precision;

Fundamental equation is split as following two equations:

In the following formula

Element all equal V, then:

${\stackrel{\&RightArrow;}{V}}_2=\{\mathrm{0,0},...,0,V_c-V,...,V_c-V\}$

Establishing V arbitrarily is a constant C ₁, so in the formula (19)

Can find the solution by preceding method; Establish V simultaneously _c-V is arbitrary constant C ₂, the equation in the formula (20) then

Can separate too.Here two current vectors have been obtained

With

But then both and fict distribution of current must be used and concern ∑ i _j=I and ∑ i _Ck=-I just can obtain the electric current of diffusing distributions

$\left\{\begin{array}{c}{k}_1\underset{j=1}{\overset{n}{\mathrm{\&Sigma;}}}{\stackrel{\&RightArrow;}{I}}_1\left(j\right)+{\mathrm{<figure-callout\; id="2"\; label="k"\; filenames="H200910057320XE0000012.png,H200910057320XE0000042.png"\; state="\{\{state\}\}">k</figure-callout>}}_2\underset{j=1}{\overset{n}{\mathrm{\&Sigma;}}}{\stackrel{\&RightArrow;}{I}}_2\left(j\right)=-I\\ k_1\underset{j=n+1}{\overset{n+m}{\mathrm{\&Sigma;}}}{\stackrel{\&RightArrow;}{I}}_1\left(j\right)+{\mathrm{<figure-callout\; id="2"\; label="k"\; filenames="H200910057320XE0000012.png,H200910057320XE0000042.png"\; state="\{\{state\}\}">k</figure-callout>}}_2\underset{j=n+1}{\overset{n-m}{\mathrm{\&Sigma;}}}{\stackrel{\&RightArrow;}{I}}_2\left(j\right)=I\end{array}\right.---\left(21\right)$

Formula (21) found the solution obtain scale-up factor k ₁And k ₂Afterwards, can obtain current vector:

Step 3.4, can calculate ground potential according to superposition principle thereafter.

Step 4 is determined the test position of voltage pole according to the penalty method principle.

By calculating have, the Potential distribution of earth mat during the no current utmost point, can draw earth mat have, earth potential liter during the no current utmost point, and can get the changing value that earth potential rises thus.According to the penalty method principle, can between electric current utmost point position and ground network edge, intercept the identical position of Relative Zero current potential potential rise changing value when the electric current utmost point is arranged on the Potential distribution curve, just can draw the recommendation test position of voltage pole thus, for on-the-spot test provides reference.

Description of drawings

Fig. 1 is a fall-of-potential method measurement of Grounding Resistance schematic diagram.

Fig. 2 is the ground potential distribution curve that the fall-of-potential method measurement of Grounding Resistance is.

Fig. 3 is the triangular arrangement schematic diagram of in-site measurement stake resistance.

Fig. 4 is the described grounded screen synoptic diagram of embodiment.

Fig. 5 carries out the ground potential distribution curve that simulation calculation draws to grounded screen among the described embodiment.

Fig. 6 lays respectively at ground potential distribution curve when being respectively 15 meters, 20 meters, 25 meters and 30 meters apart from the earth mat center when the electric current utmost point among the described embodiment.

Fig. 7 is the synoptic diagram of the described embodiment electric current utmost point possible test position of voltage pole when being positioned at apart from 25 meters, earth mat center.

Fig. 8 is that substation grounding resistance short distance is measured schematic flow sheet.

Embodiment

Following according to Fig. 4～Fig. 8, specify preferred embodiment of the present invention:

When using short distance measuring method that the stake resistance of transformer station is tested, need be under the given situation in electric current utmost point position, use numerical computation method Potential distribution of earth mat when the no current utmost point is arranged to carry out simulation calculation according to the true form of grounding body, and then the position of definite compensation point is the placement location of voltage pole.But the shape of earth mat is of all kinds, almost do not have identical shaped earth mat to exist, and its concrete shape not all is regular also.So for the ease of calculating, usually with concrete earth mat equivalence for respectively along the axial some ground rods of x axle, y axle and z.

Present embodiment be Fig. 4 when shown in grounded screen.

This earth mat is that the vertical junction terrain that 10 meters horizontal conductor and length are 4 meters is formed by four length, and it is shaped as the square of 10m * 10m, and the buried depth of earth mat is 0.2 meter, and the conductor radius is 0.0071 meter.

According to the parameter and the described Calculating of Ground Resistance method of step 1 of this grounded screen, the stake resistance that can draw this grounded screen is R=0.7208 Ω.Think soil resistivity ρ=18 Ω m during calculating.

The stake resistance formula of the compound grounded screen of the arbitrary shape edge closure that the power industry standard of implementing in 1998 " ground connection of alternating-current electric device " is recommended is:

$R_n=\frac{\sqrt{S}}{L_0}(3\ln \frac{L_0}{\sqrt{S}}-0.2)(0.213\&times;\frac{\mathrm{\&rho;}}{\sqrt{S}}(1+\frac{1}{1+(4.6h/\sqrt{S})})$

$+\frac{\mathrm{\&rho;}}{2\mathrm{\&pi;}{L}_s}(\ln \frac{S}{9\mathrm{hd}}-5\frac{1}{1+(4.6h/\sqrt{S})}))---\left(23\right)$

In the formula, R _nThe stake resistance of the closed grounded screen in----arbitrary shape edge, Ω

ρ----soil resistivity, Ω m

The total area of S----grounded screen, m ²

The diameter or the equivalent diameter of the d----horizontal grounding utmost point, m

The depth of burying of the h----horizontal grounding utmost point, m

L ₀The peripheral sideline total length of----horizontal grounding net, m

L _sThe total length of----horizontal grounding utmost point, m

Correlation parameter substitution formula (23) with grounded screen can get R _n=0.7249 Ω.This shows that the result of calculation of some coupling method of moment and the result of calculation of experimental formula are comparatively approaching, the validity of the described method of this step 1 has been described.

According to the short distance basic principle of measurement, according to step 1 and the described method of step 2, the Potential distribution curve of the no current utmost point is arranged time simulation earth mat is carried out simulation calculation, come in view of the above to determine that compensation point is the test position of voltage pole.

Fig. 5 is for to carry out the ground potential distribution curve that simulation calculation draws to grounded screen.Wherein, the ground potential of earth mat distributed when solid line was introduced for the no current utmost point, that is the ground potential when at infinity measuring distributes, and the earth potential liter (GPR) of this moment is 74.9829V; Dot-and-dash line is that the ground potential when placing the electric current utmost point apart from 15 meters, earth mat center distributes, and this moment, injection current was 100A, and the earth potential of earth mat is upgraded to 43.1488V.Obviously, the earth potential liter of earth mat is changed to-31.8341V.In view of the above, the position that can find out potential compensation point from Potential distribution curve 2 is that the position of voltage pole is for apart from 10.6 meters at earth mat center.

As can be seen from Figure 5, the diffusing distributions on the earth mat conductor is uneven, and edge effect is apparent in view, and the diffusing stream in the end points place of conductor is bigger.

In addition, as seen from Figure 5, the electric potential gradient of earth mat edge is very big, gently descends gradually along with the increase of leaving the earth mat distance.When having the electric current utmost point to exist, electric current injects from the simulation earth mat, and is no longer wandering to infinite distant place, but gets back to power supply through the measuring current utmost point, and near the extremely current potential of electric current has severe distortion, and this is because resistance very big causing for earth mat resistance of the electric current utmost point.The electric potential gradient of zero potential between the earth mat electric current utmost point and grounded screen of this moment is bigger, and the position that should try one's best during therefore actual test exactly to voltage pole positions, to improve measuring accuracy.

Ground potential distribution curve when Fig. 6 is respectively 15 meters, 20 meters, 25 meters and 30 meters for the electric current utmost point lays respectively at apart from the earth mat center.As seen from the figure, along with the electric current utmost point leaves the increase of earth mat centre distance, near the electric potential gradient earth mat of earth mat Potential distribution curve slows down gradually, and is comparatively favourable to the actual measurement location of voltage pole, helps to improve measuring accuracy.

In fact, according to the potential compensation principle, the test position that current potential equals on the ground, the place of earth mat potential rise Δ u all should be voltage pole during the no current utmost point.Fig. 7 has provided the synoptic diagram of the possible test position of voltage pole when the electric current utmost point is positioned at apart from 25 meters, earth mat center.Concerning compact substation, the on-the-spot test that is calculated as of the possible test position of a plurality of voltage poles provides many convenience.In addition, when the test stake resistance electric current utmost point and voltage pole are placed with certain angle, the coupled interference between can reducing to go between improves measuring accuracy.

Fig. 8 measures flow process for the short distance of substation grounding resistance.

Claims (3)

1. method for visualizing that uses short distance measuring method to measure substation grounding resistance is characterized in that the method includes the steps of:

Step 1, set up visualization model, realize the visual of short distance measuring method measurement of Grounding Resistance;

Step 2, the leakage current that adopts some coupling method of moment to calculate the grounded screen conductor distribute and stake resistance;

Step 3, according to the leakage current Distribution calculation ground potential of grounded screen conductor;

Step 4, determine the test position of voltage pole according to the penalty method principle.

2. employing short distance measuring method as claimed in claim 1 is measured the method for visualizing of substation grounding resistance, it is characterized in that described step 2 comprises following steps:

Step 2.1, determine that unit point current source in the infinitely great homogeneous conductive ature of coal is at the current potential of arbitrfary point, i.e. Green function

Step 2.2, to establish length be that leakage current on the L conductor segment is I, can determine the current potential of arbitrfary point according to step 2.1

Step 2.3, if the true value of j section conductive surface current potential be Current potential that must this section surface central point by numerical evaluation is

With Between certain error is generally arranged, with error On j section conductive surface, carry out weighted mean, and be zero, can get objective function

J=1～n, and further obtain the universal expression formula of method of moment

Step 2.4, get W _j=δ _j(r _i-r _j), δ _j(r _i-r _j) be Dirac function, and the field point is taken at the mid point of j section surface, then obtain

This is a coupling method of moment expression formula, and the wandering electric current with each section conductor in the formula is considered as constant, and the current potential that the current potential of each section is gone up mid point with the surface is represented;

Step 2.5, grounded screen is divided into after the n section, can obtains n equation by following formula

J=1～n is in the formula

Step 2.6, above-mentioned equation is transformed to matrix form then has

Step 2.7, design factor matrix R;

Step 2.8, since computation process in the middle of think that grounded screen is equipotential, promptly

And order

Equal a certain constant, can find the solution the leakage current I that obtains every section conductor according to formula in the middle of the step 2.5;

Step 2.9, try to achieve stake resistance and be

3. employing short distance measuring method as claimed in claim 1 is measured the method for visualizing of grounding resistance of transformer substation grounding net, it is characterized in that described step 3 comprises following steps:

Ground potential when step 3.1, the no current utmost point distributes: the fundamental equation of solution point coupling method of moment

The leakage current that obtains the earth mat conductor distributes, and the ground potential when using superposition principle to try to achieve the no current utmost point according to its current potential contribution at the ground each point distributes;

Step 3.2, be reference point, establish the earth mat current potential and be upgraded to V that the current potential of the electric current utmost point is V with infinite distant place _c, the earth mat conductor is divided into the section into n, and the stream electric current that looses is followed successively by i _j, the electric current utmost point is divided into the m section, and the stream electric current that looses is i _CkThen the diffusing stream current vector of system is

The current potential vector is

Mutual resistance matrix between each segmentation is A, and then fundamental equation is

Step 3.3, fundamental equation is split as two equations

With

In the formula

Element all equal V, then

Establishing V arbitrarily is a constant C ₁, establish V simultaneously _c-V is arbitrary constant C ₂, find the solution and draw two current vectors

With

Use and concern ∑ i _j=I and ∑ i _Ck=-I obtains the electric current of diffusing distributions

After, calculate ground potential according to superposition principle.

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