CN101034129B - Method and device for online monitoring power station and substation grounding grid - Google Patents

Abstract

This invention discloses an on-line monitoring method of grounding net of power station and its device. The method includes following steps: bury state transmitter in soil where have station earthing net; survey electric resistance of transmitter electrode and self corrosion electric potential; add square wave signal to electrode of state transmitter, survey electric current; after smoothing surveyed data, deliver to microprocessor to compute corrosion rate of electrode, take it as corrosion rate of grounding electrode in corresponding area; use corrosion rate to compute corrosion deep and actual geometry size of grounding electrode of grounding net, and use computing method of grounding net numerus to compute electricity performance parameter of grounding net; compare computed electricity performance parameter and design value, judge safe performance of grounding net. This invention can do online monitoring to corrosion deep and electricity performance parameter of grounding net of power station. The invention provides a overall, effective, economic, real time solving method to survey and evaluate grounding net of power station.

Description

Transmission transformer station grounded screen on-line monitoring method and device thereof

Technical field

The present invention relates to a kind of grounded screen monitoring method, particularly a kind of transmission transformer station grounded screen on-line monitoring method and device thereof.

Background technology

Grounding net of transformer substation plays an important role for the reliability service of electric system and staff's personal safety.But the ubiquity of phenomenon because earthing device is corroded causes that the grounding body cross section reduces, electric property worsens, thereby directly jeopardizes the safe and stable operation of electrical network.Therefore, carry out the grounded screen state on_line monitoring, understand at any time ground-electrode in soil the corrosion situation and the electric property of grounded screen, pinpoint the problems early to take corresponding safeguard procedures, prevent trouble before it happens, this maintenance to earthing device seems very urgent and important.

Yet, electric system at present is big electric current by measuring direct injection grounded screen and the grounded screen voltage manual measurement that carries out the ground connection parameter to the detection of grounded screen or adopts excavation inspection to estimate the corrosion condition of grounded screen, facility is quite heavy, be difficult for moving, be not easy to regular detection, let alone on-line monitoring, simultaneously, with corrosion condition traditional, that inspection method that by virtue of experience excavate several places is difficult to accurately judge whole grounded screen.

Summary of the invention

For overcoming existing ground net corrosion checkout equipment heaviness, be not easy to regular detection, can't realize the technical matters of on-line monitoring, the invention provides a kind of precision transmission transformer station grounded screen on-line monitoring method and device thereof higher, easy to use.

The technical scheme that the present invention solves the problems of the technologies described above may further comprise the steps:

1) three electrode state sensors is embedded in the soil of grounded screen region;

2) measure the interelectrode in twos resistance R of three electrode state sensors _S1, R _S2, R _S3And corrosion potential U ₁₀

3) square-wave signal is added between three electrode state sensor auxiliary electrodes and the research electrode, measures the electric current that flows through between auxiliary electrode and the research electrode;

4) data of measuring are delivered to the corrosion rate that microprocessor calculates three electrode state sensor electrodes after bandreject filtering, low-pass filtering, with this corrosion rate as ground-electrode in the three electrode state sensor regions;

5) calculate the mean value of the corrosion depth of whole grounded screen and physical dimension and maximal value, minimum value according to the corrosion rate of each regional ground-electrode; Utilize the Numerical Calculation of Grounding Grids method to calculate the mean value of Resistance of Grounding Grids, maximum step voltage and maximum touch voltage and maximal value, minimum value;

6) mean value of the stake resistance of grounded screen, maximum step voltage and maximum touch voltage and the design load of maximal value, minimum value and relevant parameter are compared, judge the security performance of grounded screen.

A kind of device of realizing above-mentioned transmission transformer station grounded screen on-line monitoring method, comprise three electrode state sensors, signal source, first gauge tap, second gauge tap, comparison amplifier, first operational amplifier, power amplifier, second operational amplifier, the 3rd operational amplifier, four-operational amplifier, differential amplifier, electric resistance measuring apparatus, converter A/D1, converter A/D2, converter A/D3, converter A/D4, single-chip microcomputer, converter D/A1, converter D/A2, first wave filter, second wave filter, the 3rd wave filter, optoelectronic switch, it is characterized in that: the input end of signal source is through converter D/A1, converter D/A2 links to each other with single-chip microcomputer, the amplitude of the output control signal source output signal of converter D/A1, the output control signal source output signal frequency of converter D/A2, the output terminal of signal source links to each other with first gauge tap, the control end of first gauge tap links to each other with single-chip microcomputer, two output terminals of first gauge tap connect comparison amplifier respectively, the input end of first operational amplifier, comparison amplifier, the input end of the output termination power amplifier of first operational amplifier, the contrast electrode of the input termination three electrode state sensors of second operational amplifier, an input end of the output termination comparison amplifier of second operational amplifier, the input end of output termination second gauge tap of power amplifier, the control end of second gauge tap links to each other with single-chip microcomputer, the input end and sample resistance one end of the output terminal of second gauge tap and differential amplifier link to each other, the other end of sample resistance links to each other with another input end of differential amplifier and the auxiliary electrode of three electrode state sensors, the output of differential amplifier is through first wave filter, deliver to single-chip microcomputer behind the converter A/D1, an input end grounding of the 3rd operational amplifier, the auxiliary electrode of another input end and three electrode state sensors, electric resistance measuring apparatus links to each other, the output of the 3rd operational amplifier is through second wave filter, deliver to single-chip microcomputer behind the converter A/D2, the contrast electrode of input termination three electrode state sensors of four-operational amplifier, another input end is with the research electrode ground connection of three electrode state sensors, one tunnel output of four-operational amplifier is through the 3rd wave filter, deliver to single-chip microcomputer behind the converter A/D3, another road output is delivered to single-chip microcomputer through optoelectronic switch, and the output of electric resistance measuring apparatus is delivered to single-chip microcomputer through converter A/D4.

Technique effect of the present invention is: the present invention is embedded in the state sensor of some in the soil of grounded screen region, simulate the corrosion process of grounded screen ground-electrode in the respective regions with the corrosion process of state sensor electrode, monitor the corrosion situation of whole grounded screen electrode with this, workload was big during this monitoring method had not only overcome existing grounded screen detection and assessed, measurement facility heaviness, shortcomings such as inconvenient operation, and can carry out on-line monitoring to the corrosion depth and the electric property parameter of transmission transformer station grounded screen, real-time assessment is carried out in security to grounded screen, and can be grounded the inquiry of historical datas such as net corrosion rate and electric property parameter, for the detection of transmission transformer station grounded screen and assessment provide a kind of comprehensively, effectively, economical, real-time solution.In addition, the present invention uses methods such as bandreject filtering, low-pass filtering effectively to remove undesired signal in the soil to the authenticity of test signal with detect the influence of accuracy rate, thereby realizes the accurate measurement of sensor electrode corrosion rate, has improved the precision of on-line monitoring.

The present invention is further illustrated below in conjunction with accompanying drawing.

Description of drawings

Fig. 1 is a structural drawing of the present invention.

Fig. 2 is the structural drawing of state sensor among the present invention.

Fig. 3 is three electrode equivalent circuit diagrams of state sensor among the present invention.

Fig. 4 is three electrode equivalent electrical circuit after the state sensor charging finishes among the present invention.

Fig. 5 is a software systems block diagram of the present invention.

Fig. 6 is data acquisition subsystem block diagram among the present invention.

Fig. 7 is data process subsystem block diagram among the present invention.

Embodiment

Referring to Fig. 1, Fig. 1 is the structural drawing of transmission transformer station grounded screen on-Line Monitor Device of the present invention.This monitoring device comprises state sensor, signal source, gauge tap, comparison amplifier, operational amplifier 1, power amplifier, operational amplifier 2, operational amplifier 3, operational amplifier 4, differential amplifier, electric resistance measuring apparatus, converter A/D ₁, converter A/D ₂, converter A/D ₃, converter A/D ₄, single-chip microcomputer, converter D/A ₁, converter D/A ₂, wave filter, optoelectronic switch.Signal source adopts amplitude and all continuously adjustable square-wave generator of frequency, comparison amplifier, power amplifier, sample resistance, operational amplifier 2 and state sensor have constituted the steady state measurement part of system, operational amplifier 1, power amplifier, sample resistance and state sensor have constituted the transient measuring part of system, amplifier 3, amplifier 4 and filter circuit are finished the Filtering Processing to signal, converter A/D ₁, converter A/D ₂, converter A/D ₃, converter A/D ₄Finish the collection of data, single-chip microcomputer is finished functions such as data acquisition, computing, processing, converter D/A ₁, converter D/A ₂Finish control, the adjusting of system to signal source output signal frequency and amplitude.

The structure of state sensor as shown in Figure 2 among the present invention.State sensor adopts three electrode measurement systems, by research electrode t _y, auxiliary electrode t _fWith contrast electrode t _cForm.Three electrodes all adopt with the ground-electrode identical materials and constitute, and middle opposite face stays does electrode research face, and other aspect is fixed by organic material between the electrode by epoxy sealing, and lead is drawn in the electrode upper end, as signal connection end.During installation, three electrodes of sensor are embedded in the soil of grounded screen region, the depth of burying is identical with the grounded screen depth of burying.Like this, when three electrodes of sensor be in the soil with grounded screen ground-electrode same nature and on the ground-electrode wandering electric current also with the electric current of each sensor electrode near the time, the corrosion process of coming analogue ground net ground-electrode with regard to the corrosion process of available sensors electrode, that is the corrosion rate of ground-electrode is identical with the corrosion rate of sensor electrode.

Yet because wandering current's intensity difference on the unevenness of soil property and each ground-electrode, therefore, the degree that the ground-electrode of diverse location is corroded in soil is also different.Theoretically, should adopt sensor as much as possible could simulate the corrosion process of whole grounded screen truly, all sidedly.But consider that from the angle of Technological Economy the number of sensors in placing into the soil can not be too much.Therefore, how to determine the quantity and the distribution of sensor, promptly how to select the burial place of sensor in soil, just seem very important for the etch state of accurately monitoring whole grounded screen from limited check point.

At this, the quantity of following definite sensor and the method for distribution are proposed:

1. according to soil geological exploration report, according to its character subregion, the riding position of sensor should guarantee that different soils character can both be reflected the corrosive effect of ground-electrode, that is all is equiped with sensor in the zone of different soils character to soil;

2. use the Numerical Calculation of Grounding Grids method, determine wandering maximum with minimum zone of electric current and maximum with the minimum zone of surface potential gradient on the ground-electrode, the riding position of sensor should guarantee that the corrosion situation of ground-electrode in these zones can both be reflected, that is all is furnished with sensor in wandering maximum with minimum zone of electric current and maximum with the minimum zone of electric potential gradient;

3. from satisfying above-mentioned requirements, select minimum number and the corresponding region thereof that to bury sensor underground;

4. the choice of location of sensor installation should make the density degree that distributes at whole grounded screen region inner sensor as far as possible near even;

5. according to the condition of construction of the accuracy requirement of grounded screen monitoring, earth mat and sensor distribution density situation thereof etc., suitably increase 1-2 sensor again in can distributing at the sensor of minimum number.

When the earial drainage electric current of application Numerical Calculation of Grounding Grids method calculating grounded screen electrode and earth potential distribute, in order to improve the accuracy of calculating, the earth should be considered as two layers or multilayer model, and adopt the multiple method of images to handle multilayer the earth model, thereby reach higher computational accuracy with less calculated amount, its basic calculating principle is as follows.

Being provided with a steady current I and flowing into the electrode that is embedded in the soil that resistivity is ρ, according to the steady current field theory, use the principle of Green function, is reference point with the unlimited distance, obtains electrode earial drainage electric current and at the current potential that arbitrfary point P produces is:

In the formula, J (Q) is that electrode surface S goes up the earial drainage current density at some Q place, and (P Q) is green theorem corresponding to electrode geometry to G.Here, on behalf of unitary current, it flow through the current potential that electrode surface Q point produces at the P point.

Equal the injection current I of grounding body through total earial drainage electric current of earth mat inflow soil:

$I=\underset{s}{\∫}\∫J\left(Q\right)\mathrm{ds}---\left(2\right)$

Ignore the voltage drop on the conductor, then obtain boundary condition

If the electrode length overall is L, the total current by the L earial drainage is I, and L is divided into n little section, and the little segment length of j is L _j, its center is O _j, j section earial drainage electric current is I _jSo, have:

$L=\underset{j=1}{\overset{n}{\mathrm{\Σ}}}{L}_j---\left(4\right)$

$I=\underset{j=1}{\overset{n}{\mathrm{\Σ}}}{I}_j---\left(6\right)$

Respectively the P point is fixed on the little section I of electrode, then (i j) just represents i to G, and the mutual resistance between j is used R _IjExpression.When i=j, R _IjIt is i section self-resistance.Get by (5) formula:

By boundary condition (3), make electrode potential be

Then formula (7) becomes:

(6), (8) formula is formed (n+1) rank Simultaneous Equations:

$\underset{i=1}{\overset{n}{\mathrm{\Σ}}}{I}_i=I---\left(9\right)$

According to the definition of stake resistance, stake resistance is:

By resistance coefficient R _IjCalculate the mutual conductance matrix, calculate earial drainage distribution of current I by the total leakage current of known transformer station again along electrode _jAnd electrode potential liter With stake resistance R, just can calculate the current potential of every bit in the soil again according to formula (1).Then, above earth potential carries out the gradient computing, can try to achieve the surface potential gradient.

Fig. 3 is three electrode equivalent circuit diagrams of state sensor among the present invention.R among the figure _S1Be contrast electrode t _cWith research electrode t _yResistance between the surface; R _S2Be contrast electrode t _cWith auxiliary electrode t _fResistance between the surface; R _S3Be research electrode t _yWith auxiliary electrode t _fBetween resistance; R _pBe polarization resistance; C _dBe double-layer capacitance.

Measure the corrosion speed of metal electrode, need polarize, it is departed from from etch state, measure the response of the outer hyper polarization of this electrode pair, thereby obtain corrosion parameter the metal electrode that is corroded.According to the linear polarization theory, between near the polarization current corrosion potential and polarized potential, exist linear rule, so be on the basis of corrosion potential, to add ± 10mV when metal polarized, be in the linear polarization stage to guarantee metal.

Among the present invention square-wave signal is added on outward between auxiliary electrode and the research electrode.Enough big when the cycle of square-wave signal, in the time of can guaranteeing that the double-layer capacitance charging finishes, double-layer capacitance is equivalent to open-circuit condition, its equivalent-circuit model such as Fig. 4.

The frequency computation part method of square-wave signal is as follows:

Because electrostatic double layer (C _d) charge effects, all be in transient state process in the incipient stage of every half period, be through just reaching stable state after a while.Square wave frequency is too high, does not reach the steady-state polarization signal and has just commutated, the polarization resistance R that the result records _pOn the low side.On the contrary, frequency is too low, and the unidirectional polarization time is long, and the accumulation that electrode surface state and surrounding medium change can increase, and corrosion potential also may drift about.These all will bring measuring error, so the selection of frequency is wanted suitably will treat that the transient state waveform reaches stable state substantially and just samples and commutate.

For the electrode process of electrochemical reaction control, reaching the needed time of stable state depends on the time constant of electrode, decides with electrode system.The square wave semiperiod should be T _Half〉=5R _pC _d, so square wave frequency should be

$f\≤\frac{1}{10R_p{C}_d}.$

To sensor equivalent electrical circuit shown in Figure 3, when it being applied a constant potential pulse ε, the response current I of t time _tCan be expressed as:

I _t＝V _t/R＝ε(C ₀+C ₁e ^-t/τ)(11)

In the formula: R is a sample resistance

C ₀＝1/[(R _s1+R _s3)//R _s2+R _p](Ω ^-1)；

C ₁＝R _p/{[(R _s1+R _s3)//R _s2][(R _s1+R _s3)//R _s2+R _p]}(Ω ^-1)

$\mathrm{\τ}=\frac{C_d[(R_{s1}+R_{s3})//R_{s2}]R_p}{(R_{s1}+R_{s3})//R_{s2}+R_p}\left(s\right)$

Transient response L under constant potential pulse ε effect _t～t carries out curve fitting by above formula and obtains suitable R _p, C _dObtained R _p, C _dAfter, with its substitution formula

Can calculate square wave

Frequency.

The corrosion rate acquisition methods of sensor electrode is as follows:

Resistance R _S1, R _S2, R _S3And corrosion potential U ₁₀Before being recharged at every turn, electrode records; Current potential U between contrast electrode and the research electrode ₁, the electric current I between auxiliary electrode and the research electrode records in polarization process.According to these data, can calculate polarization resistance R _p, that is:

U ₁-U ₁₀＝I ₁R _s1+I _rR _p； $I_1=I_3=\frac{R_{s2}}{R_{s1}+R_{s2}+R_{s3}}\·I;$ I _r＝I；

Draw polarization resistance R by following formula _pExpression formula as follows:

$R_p=\frac{U_1-U_{10}}{I}-\frac{R_{s1}{R}_{s2}}{R_{s1}+R_{s2}+R_{s2}}---\left(12\right)$

According to the Stern-Geary formula, Wherein:

b _aIt is the Ta Feier constant of anode reaction; b _kIt is the Ta Feier constant of cathode reaction; b _a, b _kCan calculate according to electrochemical properties, also can try to achieve from the strong polarized area of polarization curve.

Like this by calculating R _p, can obtain corrosion current I _Corr, corrosion electric current density i then _Corr=I _Corr/ S (S is the electrode useful area) is according to i _CorrCan be converted into corrosion rate v, it is:

$v=3.73\×{10}^{-4}\·\frac{M}{Z}\·i_{\mathrm{corr}}---\left(13\right)$

In the following formula: v is corrosion rate (g/m ²H); M is the molal weight (g/mol) of metal; Z is an atomic valence of metal; i _CorrBe corrosion electric current density (μ A/cm ²).

The present invention is at first disconnected by the output and the sample resistance of gauge tap 2 with power amplifier, obtain parameters such as the resistance of state sensors and corrosion potential by electric resistance measuring apparatus and operational amplifier 3, operational amplifier 4, after these parameters process single-chip microcomputer calculation process, can draw signal source and answer the size of plus signal amplitude and frequency, Single Chip Microcomputer (SCM) system is determined converter D/A in line computation then ₁, converter D/A ₂Output valve, promptly determine the amplitude and the frequency of signal source output square wave, the square-wave signal of signal source output by gauge tap control its signal flow to, and then make the output of power amplifier be added to auxiliary electrode through sample resistance by gauge tap 2, carry out the Temporal Data of system and measure and the steady state data measurement.

The transient measuring workflow: the grounded screen on-line monitoring system belongs to the transient measuring course of work when state sensor double-layer capacitance charge and discharge process is measured.Detailed process is: gauge tap 1 is exported the input end that is connected to operational amplifier 1 with signal source, after signal process operational amplifier 1 and the power amplifier processing and amplifying, is added on the state sensor, finishes the response process that discharges and recharges of electric capacity.The time of transient measuring is very short, sampling, the processing that must finish data in the time discharging and recharging of electric capacity.Single Chip Microcomputer (SCM) system obtains to flow through the current signal of sensor and the electric potential signal of sensor by sample resistance and operational amplifier 3, and samples and data processing.

The steady state measurement workflow: the grounded screen on-line monitoring system belongs to the steady state measurement process to the DATA REASONING that the state sensor double-layer capacitance discharges and recharges after the end.Detailed process is: gauge tap 1 is connected to signal source output the input end of comparison amplifier, signal acts on the state sensor after comparison amplifier and power amplifier processing and amplifying, and feed back to comparison amplifier by operational amplifier 2, finish a closed-loop control, thereby the size of autoregulation signal on state sensor improves antijamming capability.Pumping signal is charged to the sensor double-layer capacitance after the end, by the current potential of measuring sample resistance obtain the to flow through current signal of state sensor, obtain state sensor electrode potential signal by operational amplifier 3 and operational amplifier 4, these signals are by after the filter process, through converter A/D ₁, converter A/D ₂, converter A/D ₃The sample circuit sampling is delivered to single-chip microcomputer and is carried out data processing.

Finish the DATA REASONING of just having finished one-period after transient state and steady state data are measured, its data can obtain the corrosion rate of sensor electrode after the single-chip microcomputer COMPREHENSIVE CALCULATING is handled.

But the obstacle that can run in the above measurement is: power current, dash current in the grounded screen of the flowing through soil can cause strong jamming to input.Therefore, must take corresponding method to remove and disturb, to guarantee the accuracy of measurement result.At this,, adopt the bandreject filtering method with its filtering for the 50HZ power current; For dash current, its amplitude may be very big, can cause soil discharge, but its equivalent frequency is again than high many of power frequency, so can adopt low-pass filtering method not only withstand voltage but also can the filtering impact noise effectively to remove power current, dash current etc. to interference that input caused.

In addition, before the computer system processor data, earlier sampled data is carried out smoothing processing, the stochastic error of bringing during with the elimination sampled data, promptly the one group of enough intensive data pointwise that collects in the constant duration is carried out smoothly according to the program of finishing in advance by computing machine, it derives smoothing formula according to the trend of data point development according to the principle of least square, for the time dependent signal of gathering, good many of the method that effect is averaged than observation experiment data repeatedly.

After the online corrosion rate that calculates sensor electrode of Single Chip Microcomputer (SCM) system, with this corrosion rate as ground-electrode in the respective regions, calculate corresponding with it grounded screen electric property parameter more in view of the above and grounded screen is carried out safety evaluation, concrete grammar and step are:

By the integration of corrosion rate to the time, try to achieve the corrosion depth of each regional grounding body, round the maximal value, mean value, minimum value of grounding body corrosion depth in the zone maximum corrosion depth, average corrosion depth and the minimal erosion degree of depth as grounded screen;

Go out maximal value, mean value, the minimum value of the actual geometry (being the length of the length of each ground-electrode and xsect and wide) of grounding body by the design geometric size calculation of maximum corrosion depth, average corrosion depth, the minimal erosion degree of depth and grounding body, calculate maximal value, mean value, the minimum value of each grounding body cross-sectional area thus, be respectively S _Amax, S _Aav, S _Amin

S according to each grounding body _Amax, S _Aav, S _Amin, ask for maximal value, mean value, the minimum value of each grounding body xsect equivalent redius, be respectively r _Amax, r _Aav, r _Amin

According to the physical length of each ground-electrode and maximal value, mean value, the minimum value of each grounding body xsect equivalent redius, utilizing the Numerical Calculation of Grounding Grids method to calculate the maximal value of Resistance of Grounding Grids, mean value, minimum value and corresponding surface potential distributes, by the definition of maximum step voltage of grounded screen and maximum touch voltage, calculate maximal value, mean value, the minimum value of maximum step voltage and maximum touch voltage again;

Design permissible value according to Resistance of Grounding Grids, maximum step voltage and maximum touch voltage, security performance to grounded screen is assessed: when the minimum value of every calculating electric property parameter all designed permissible value above it, the security performance of grounded screen was defective; When the mean value of the minimum value of partly calculating the electric property parameter and every calculating electric property parameter all designed permissible value above it, the security performance of grounded screen was defective; When the mean value of every calculating electric property parameter all less than its design permissible value, but the maximal value that part is calculated the electric property parameter is during greater than its design permissible value, the security of grounded screen is relatively poor, must start corresponding safeguard procedures; When the maximal value of every calculating electric property parameter all designed permissible value less than it, the security performance of grounded screen was qualified.

Software systems of the present invention are mainly by data acquisition subsystem, data process subsystem, data query

Five parts such as subsystem, man-machine interface subsystem, communication subsystem are formed, as shown in Figure 5.Wherein, data acquisition subsystem and data process subsystem are the core of whole software system, and it respectively as shown in Figure 6 and Figure 7.Data acquisition subsystem is used for determining square wave frequency, regulates square wave frequency and amplitude through D/A output, and the mode of control survey is simultaneously measured accordingly, and gathered corresponding data.Data process subsystem is read in CPU with the data of gathering, and chooses valid data, carries out the real-time assessment in line computation and grounded screen security of ground net corrosion speed, corrosion depth and electric property parameter.

Claims (5)

1. transmission transformer station grounded screen on-line monitoring method may further comprise the steps:

1) three electrode state sensors is embedded in the soil of grounded screen region;

2) measure the interelectrode in twos resistance R of three electrode state sensors _S1, R _S2, R _S3And corrosion potential U ₁₀

3) square-wave signal is added between three electrode state sensor auxiliary electrodes and the research electrode, measures the electric current that flows through between auxiliary electrode and the research electrode;

4) data of measuring are delivered to the corrosion rate that microprocessor calculates three electrode state sensor electrodes after bandreject filtering, low-pass filtering, with this corrosion rate as ground-electrode in the three electrode state sensor regions;

5) calculate the mean value of the corrosion depth of whole grounded screen and physical dimension and maximal value, minimum value according to the corrosion rate of each regional ground-electrode; Utilize the Numerical Calculation of Grounding Grids method to calculate the mean value of Resistance of Grounding Grids, maximum step voltage and maximum touch voltage and maximal value, minimum value;

6) mean value of the stake resistance of grounded screen, maximum step voltage and maximum touch voltage and the design load of maximal value, minimum value and relevant parameter are compared, judge the security performance of grounded screen.

2. transmission transformer station grounded screen on-line monitoring method according to claim 1, it is characterized in that: the depth of burying of three electrode state sensors is identical with grounded screen in the described step 1), and three electrode state number of sensors and burial place are according to the area dividing of soil property, surface potential gradient and ground-electrode earial drainage size of current is determined.

3. transmission transformer station grounded screen on-line monitoring method according to claim 1, it is characterized in that: described step 5) may further comprise the steps:

By the integration of corrosion rate to the time, try to achieve the corrosion depth of each regional grounding body, get the maximal value, mean value, minimum value of grounding body corrosion depth in the whole zone of grounded screen maximum corrosion depth, average corrosion depth and the minimal erosion degree of depth as grounded screen;

Go out maximal value, mean value, the minimum value of the actual geometry of grounding body by the design geometric size calculation of maximum corrosion depth, average corrosion depth, the minimal erosion degree of depth and grounding body, calculate maximal value, mean value, the minimum value of each grounding body cross-sectional area thus;

According to maximal value, mean value, the minimum value of each grounding body cross-sectional area, calculate maximal value, mean value, the minimum value of each grounding body xsect equivalent redius;

According to the physical length of each ground-electrode and maximal value, mean value, the minimum value of each grounding body xsect equivalent redius, utilizing the Numerical Calculation of Grounding Grids method to calculate the maximal value of Resistance of Grounding Grids, mean value, minimum value and corresponding surface potential distributes, by the definition of maximum step voltage of grounded screen and maximum touch voltage, calculate maximal value, mean value, the minimum value of maximum step voltage and maximum touch voltage again.

4. transmission transformer station grounded screen on-line monitoring method according to claim 1 is characterized in that:

The frequency of square-wave signal is determined by following formula in the described step 3):

Polarization resistance R in the formula _pWith double-layer capacitance C _dBy to the three transient response Is of electrode state sensor equivalent electrical circuit under the constant potential pulse action _t=V _t/ R=ε (C ₀+ C ₁e ^{-t/ τ}) carrying out curve fitting obtains, wherein: C ₀=1/[(R _S1+ R _S3The R of) // _S2+ R _p], C ₁=R _p/ { [(R _S1+ R _S3The R of) // _S2] [(R _S1+ R _S3The R of) // _S2+ R _p] (Ω ^-1),

R is a sample resistance.

5. a transmission transformer station grounded screen on-Line Monitor Device comprises three electrode state sensors, signal source, gauge tap, comparison amplifier, operational amplifier 1, power amplifier, operational amplifier 2, operational amplifier 3, operational amplifier 4, differential amplifier, electric resistance measuring apparatus, converter A/D ₁, converter A/D ₂, converter A/D ₃, converter A/D ₄, single-chip microcomputer, converter D/A ₁, converter D/A ₂, wave filter, optoelectronic switch, it is characterized in that: the input end of signal source is through converter D/A ₁, converter D/A ₂Link to each other converter D/A with single-chip microcomputer ₁The amplitude of output control signal source output signal, converter D/A ₂Output control signal source output signal frequency, the output terminal of signal source links to each other with gauge tap 1, the control end of gauge tap 1 links to each other with single-chip microcomputer, two output terminals of gauge tap 1 connect comparison amplifier respectively, the input end of operational amplifier 1, comparison amplifier, the input end of the output termination power amplifier of operational amplifier 1, the contrast electrode of the input termination three electrode state sensors of operational amplifier 2, an input end of the output termination comparison amplifier of operational amplifier 2, the input end of the output termination gauge tap 2 of power amplifier, the control end of gauge tap 2 links to each other with single-chip microcomputer, the input end and sample resistance one end of the output terminal of gauge tap 2 and differential amplifier link to each other, the other end of sample resistance links to each other with another input end of differential amplifier and the auxiliary electrode of three electrode state sensors, and the output of differential amplifier is through wave filter, converter A/D ₁After deliver to single-chip microcomputer, an input end grounding of operational amplifier 3, another input end links to each other with auxiliary electrode, the electric resistance measuring apparatus of three electrode state sensors, the output of operational amplifier 3 is through wave filter, converter A/D ₂After deliver to single-chip microcomputer, the contrast electrode of one of operational amplifier 4 input termination three electrode state sensor, another input end are with the research electrode ground connection of three electrode state sensors, one tunnel output of operational amplifier 4 is through wave filter, converter A/D ₃After deliver to single-chip microcomputer, the output of another road is delivered to single-chip microcomputer through optoelectronic switch, the output of electric resistance measuring apparatus is through converter A/D ₄Deliver to single-chip microcomputer.

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