CN104777400A - Three-dimensional digitalized monitoring device for substation grounding grid and evaluation method - Google Patents

Abstract

The invention discloses a three-dimensional digital monitoring device and evaluation method for a substation grounding network, including a microcontroller, an adjustable DC constant current source, a current channel switch module, a multi-channel wiring socket, a voltage channel switch module, a signal processing module, Data storage module, wireless communication module and upper computer; the present invention controls the output current size through the microcontroller, and then outputs the analog voltage signal through the built-in D/A module to enter the adjustable DC constant current source, and uses the current channel to switch the switch module , The multi-channel wiring socket and the voltage channel switch module store the obtained voltage signal through the file system and store it in the SD card; the collected data is sent to the host computer through the wireless device SX1212, and the host computer collects the data through the software Calculate the impedance of the branch, and perform three-dimensional imaging of the grounding grid conductor and the surrounding soil according to the topological structure of the grounding grid and the soil resistivity.

Description

A three-dimensional digital monitoring device and evaluation method for substation grounding grid

technical field

The invention relates to the technical field of fault detection of substation grounding grids, in particular to a three-dimensional digital monitoring device and evaluation method for substation grounding grids.

Background technique

The corrosion status of substation grounding grid is directly related to the safe and stable operation of various electrical equipment and facilities. Grounding equipment needs a low-impedance way to maintain electrical connection with the earth. The traditional grounding grid monitoring device only injects a large current into the grounding grid, and the current can reach tens or even hundreds of amperes. However, because the grounding grid itself has good conductivity and relatively small resistance, the measurement accuracy of the traditional detection device is often not good. It can meet the requirements, but there are serious errors in the analysis of the corrosion status of the grounding grid. At the same time, due to the relatively large current, the requirements for the device's own capacity and insulation performance are extremely high, resulting in a relatively large volume of the entire device and high requirements for the power supply capacity, which is not conducive to outdoor grounding grid testing. For operators, they must operate strictly in accordance with the regulations, and electric shock accidents may easily occur if they are not careful. At the same time, due to the harsh surface conditions of the grounding grid, it is difficult for traditional equipment to operate on site.

In terms of data analysis and processing, traditional equipment is limited to measuring N sets of voltage data, and only uses the relationship between current and voltage to calculate the size of grounding resistance. The amount of data information is too small, the calculation results have large errors, and there is no real There are ground grids for digital archiving, so it is difficult to make a more accurate life assessment.

Contents of the invention

The purpose of the present invention is to provide a three-dimensional digital monitoring device and evaluation method for the substation grounding grid, which can calculate and evaluate the impedance of the grounding grid, and can perform three-dimensional imaging, and can also establish a digital detection file for each detected grounding grid. Realize long-term tracking of grounding grid status.

The technical scheme adopted in the present invention is:

A three-dimensional digital monitoring device for a substation grounding network, including a microcontroller, an adjustable DC constant current source, a current channel switch module, a multi-channel wiring socket, a voltage channel switch module, a signal processing module, a data storage module, and a wireless communication module And the upper computer, the microcontroller controls the adjustable DC constant current source to output currents of different sizes through the digital signal output by its own peripheral D/A conversion unit; the current output terminal of the adjustable DC constant current source is connected to the current channel switch On the current injection channel switch of the module, the current output terminal of the current channel switch module is connected to the current injection interface of the multi-channel wiring socket. The current output interface of the wiring socket is connected to the voltage channel switch module, the controlled terminals of the current channel switch module and the voltage channel switch module are connected to the control terminal of the microprocessor, the current channel switch module and the voltage channel switch module The disconnection of the switch is controlled by the microcontroller; the voltage output terminal of the voltage channel switch module is connected to the signal input terminal of the signal processing module, and the signal output terminal of the signal processing module is connected to the signal input terminal of the microcontroller. The signal output terminal is connected to the data input terminal of the data storage module, and the second signal output terminal of the microcontroller is connected to the upper computer through the wireless communication module, and the three-dimensional imaging and the status evaluation of the grounding network are performed through the upper computer.

The adjustable DC constant current source includes a filter circuit for filtering the generated constant voltage signal output, a subtraction circuit for eliminating the interference of the power supply of each chip in the circuit on the output DC constant current source, and a circuit for increasing the output DC constant current Voltage feedback circuit for source stability, precision resistors for final DC constant current source current generation, operational amplifiers, power supplies for powering each chip, and current detection for DC constant current source calibration to ensure DC constant current source stability Resistor; the inverting input end of the subtraction circuit is connected to the digital signal output end of the microcontroller through the filter circuit, and the microcontroller is used to generate a constant voltage signal and adjust the output of the constant voltage signal through the feedback signal, and the inphase of the subtraction circuit The input end is connected to the positive power supply pin of the power supply for each chip, the output end of the subtraction circuit is connected to the inverting input end of the voltage feedback circuit; one end of the precision resistor is connected to the non-inverting input end of the voltage feedback circuit, and the other end of the precision resistor is simultaneously connected to each The positive power supply pin of the chip power supply is connected to one end of the current-sensing resistor, and the other end of the current-sensing resistor is connected to an output I/O pin of the microcontroller through an operational amplifier.

The current channel switching switch module includes a current injection channel switching control module, a multi-channel analog switch, a multi-channel transistor array and a multi-channel relay array, and the multi-channel analog switch, the multi-channel transistor array and the multi-channel relay array all pass through the current injection channel The switching control module is connected to the control terminal of the microcontroller, the current injection terminal of each analog switch in the multi-channel analog switch is connected to the current output terminal of the adjustable DC constant current source, and the output terminal of each analog switch is respectively connected to the multi-channel analog switch. The base of the corresponding triode in the multi-channel triode array, the collector of each triode is respectively connected to the control terminal of the corresponding relay in the multi-channel relay array, and the output end of each relay is connected to the current injection interface of the multi-channel wiring socket .

The constituent components of the voltage channel switch module are the same as those of the current channel switch module, and the connection relationship is symmetrical to that of the current channel switch module.

The signal processing module includes a voltage isolation circuit, a low-pass filter circuit and an A/D conversion circuit, the signal input end of the voltage isolation circuit is connected to the voltage channel switch module, and the signal output end of the voltage isolation circuit is connected to the voltage isolation circuit. The signal output terminal is connected to the signal input terminal of the low-pass filter circuit, and the signal output terminal of the low-pass filter circuit is connected to the microprocessor through the A/D conversion circuit.

Described data storage module adopts SD card memory.

The microcontroller adopts an ARM single-chip microcomputer, and the microprocessor is also connected with a display screen and keys.

A three-dimensional digital evaluation method for substation grounding grid based on the three-dimensional digital monitoring device for substation grounding grid described in claim 1, comprising the following steps:

Step A: First, collect the voltage values of some nodes of the grounding grid under test through the three-dimensional digital monitoring device of the substation grounding grid;

Step B: Send the measured voltage values of some nodes of the grounding grid to the host computer, and the host computer uses the grounding grid state evaluation system to solve the resistance value of each branch of the grounding grid under test; the grounding grid state evaluation system uses the grounding branch based on the inverse problem The calculation method of the conductor impedance of the grounding grid solves the state of each branch of the grounding network, and the solution process is as follows:

Step B1: Equivalent the measured grounding grid to a pure resistance network, assuming that the grounding grid has N nodes and B branches, then according to the electrical network theory, the equations are:

$\left\{\begin{array}{c}{\mathrm{<span\; class="notranslate">\; Y</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}\\ {\mathrm{<span\; class="notranslate">\; Y</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; AY</span>}}_{\mathrm{<span\; class="notranslate">\; b</span>}}{\mathrm{<span\; class="notranslate">\; A</span>}}^{\mathrm{<span\; class="notranslate">\; T</span>}}\\ {\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; b</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; A</span>}}^{\mathrm{<span\; class="notranslate">\; T</span>}}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}\\ {\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; b</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; Y</span>}}_{\mathrm{<span\; class="notranslate">\; b</span>}}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; b</span>}}\end{array}\right.<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

In the formula, A is the correlation matrix of the network; Y _b is the branch admittance matrix, Y _n is the node admittance matrix; U _b is the branch voltage vector; U _n is the node voltage vector; I _n is the node current vector; I _b is the branch current vector;

Step B2: Suppose U _n0 is the measured value of the node voltage of the grounding grid under test; U _n (R) is the theoretically calculated value of the node voltage of the grounding grid under test, where U _n (R) is a function of R, and R is Unknown quantity; then, minimize f(R), and obtain the variation that conforms to the measured value as:

$\mathrm{<span\; class="notranslate">\; min</span>}\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}{<span\; class="notranslate">\; |</span><span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; |</span><span\; class="notranslate">\; |</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; =</span>{<span\; class="notranslate">\; [</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; B</span>}}<span\; class="notranslate">\; ]</span>}^{\mathrm{<span\; class="notranslate">\; T</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

Step B3: According to the principle of the least square method, from the formula (2):

$\frac{<span\; class="notranslate">\; \&PartialD;</span>\mathrm{<span\; class="notranslate">\; f</span>}}{<span\; class="notranslate">\; \&PartialD;</span>\mathrm{<span\; class="notranslate">\; R</span>}}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; [</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; ]</span>\frac{{<span\; class="notranslate">\; \&PartialD;</span>\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; )</span>}{<span\; class="notranslate">\; \&PartialD;</span>\mathrm{<span\; class="notranslate">\; R</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

Step B4: Then the objective function f(R)=||U _n (R)-U _n0 || ² is approximated by Taylor series expansion at R ^(k) :

$\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; R</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\frac{<span\; class="notranslate">\; \&PartialD;</span>\mathrm{<span\; class="notranslate">\; f</span>}}{<span\; class="notranslate">\; \&PartialD;</span>\mathrm{<span\; class="notranslate">\; R</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; R</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; R</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; R</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; T</span>}}\frac{{<span\; class="notranslate">\; \&PartialD;</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; f</span>}}{{<span\; class="notranslate">\; \&PartialD;</span>\mathrm{<span\; class="notranslate">\; R</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; R</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; R</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>$

Step B5: Calculate the extremum of the series expansion of the Taylor function obtained by formula (4) to obtain the extremum point:

$\frac{<span\; class="notranslate">\; \&PartialD;</span>\mathrm{<span\; class="notranslate">\; f</span>}}{<span\; class="notranslate">\; \&PartialD;</span>\mathrm{<span\; class="notranslate">\; R</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; R</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{<span\; class="notranslate">\; \&PartialD;</span>\mathrm{<span\; class="notranslate">\; f</span>}}{<span\; class="notranslate">\; \&PartialD;</span>\mathrm{<span\; class="notranslate">\; R</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; R</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; R</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; R</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; T</span>}}\frac{{<span\; class="notranslate">\; \&PartialD;</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; f</span>}}{<span\; class="notranslate">\; \&PartialD;</span>{\mathrm{<span\; class="notranslate">\; R</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; R</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 5</span>}<span\; class="notranslate">\; )</span>$

Step B6: If reversible, we get:

${\mathrm{<span\; class="notranslate">\; R</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; R</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; -</span>{<span\; class="notranslate">\; (</span>\frac{{<span\; class="notranslate">\; \&PartialD;</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; f</span>}}{{<span\; class="notranslate">\; \&PartialD;</span>\mathrm{<span\; class="notranslate">\; R</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; R</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; )</span>}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}\frac{<span\; class="notranslate">\; \&PartialD;</span>\mathrm{<span\; class="notranslate">\; f</span>}}{<span\; class="notranslate">\; \&PartialD;</span>\mathrm{<span\; class="notranslate">\; R</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; R</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 6</span>}<span\; class="notranslate">\; )</span>$

Step B7: Align again Taking the derivative at R ^(k) yields:

$\frac{<span\; class="notranslate">\; \&PartialD;</span>\mathrm{<span\; class="notranslate">\; f</span>}}{<span\; class="notranslate">\; \&PartialD;</span>\mathrm{<span\; class="notranslate">\; R</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; R</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}{<span\; class="notranslate">\; (</span>\frac{{<span\; class="notranslate">\; \&PartialD;</span>\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}}{<span\; class="notranslate">\; \&PartialD;</span>\mathrm{<span\; class="notranslate">\; R</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; R</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; T</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; R</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 7</span>}<span\; class="notranslate">\; )</span>$

Step B8: Deriving from formula ⑺ and ignoring higher-order terms:

$\frac{{<span\; class="notranslate">\; \&PartialD;</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; f</span>}}{{<span\; class="notranslate">\; \&PartialD;</span>\mathrm{<span\; class="notranslate">\; R</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; R</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 2</span>}{<span\; class="notranslate">\; (</span>\frac{{<span\; class="notranslate">\; \&PartialD;</span>\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}}{<span\; class="notranslate">\; \&PartialD;</span>\mathrm{<span\; class="notranslate">\; R</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; R</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; T</span>}}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; R</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 8</span>}<span\; class="notranslate">\; )</span>$

and thus get: $R^{(k+1)}=R^{\left(k\right)}-{\left(J_k^T{J}_k\right)}^{-1}{J}_k^T(u_{\mathrm{no}}\left(R^{\left(k\right)}\right)-u_{\mathrm{no}0})---\left(9\right)$

in is the Jacobian matrix; formula (9) is the iterative formula of the NR method of the fault diagnosis equation of the grounding grid, so as to solve the unknown branch resistance value;

Step B8: According to the variation of ground grid branch resistance, compare with the branch resistance design value of each branch, and evaluate the ground grid corrosion status according to the ground grid corrosion degree discrimination standard.

Step C is also included: sending the grounding network branch resistance value data obtained in step B to the three-dimensional imaging system for three-dimensional imaging, the specific steps are as follows:

Step C1: Firstly, divide the entire computing field into a finite number of discrete units;

Step C2: Calculate the conductivity of each discrete unit according to the ground grid branch resistance value calculated in step B and the soil resistivity around the ground grid to be measured;

Step C3: According to the conductivity of each discrete unit provided in step C2, combined with the topological structure of the grounding grid to be tested, perform a three-dimensional imaging of the branch resistance of the grounding grid and the surrounding soil. The image includes the three-dimensional topology of the grounding grid and the branch resistance size.

In the present invention, the output current is controlled by the microcontroller, and then the analog voltage signal is output through the built-in D/A module to enter the adjustable DC constant current source, so as to ensure the accuracy of the current injected into the grounding grid, and measure the voltage on the corresponding branch. Use the current channel switch module, multi-channel wiring socket and voltage channel switch module to store the obtained voltage signal through the file system and store the data in the SD card, which can not only effectively buffer the data, so as to wirelessly communicate with the host computer and then transmit data, and can also directly read the data in the memory card to meet the actual needs of different users. The collected data is sent to the host computer through the wireless device SX1212, and the host computer calculates the impedance of the branch through the software based on the collected data, and performs three-dimensional imaging of the grounding grid conductor and the surrounding soil according to the topological structure of the grounding grid and the soil resistivity. The evaluation software calculates the corrosion rate of the branch circuit based on historical statistical data, measures the service life of the branch circuit of the grounding grid, and evaluates the state of the grounding grid.

Description of drawings

Fig. 1 is the block diagram of circuit principle of the present invention;

Fig. 2 is the schematic block diagram of the adjustable DC constant current source circuit of the present invention;

Fig. 3 is a block diagram of the connection relationship between the current channel switching module, the multi-channel wiring socket and the voltage channel switching module of the present invention.

Detailed ways

As shown in Figures 1, 2 and 3, the present invention includes a microcontroller, an adjustable DC constant current source, a current channel switch module, a multi-channel wiring socket, a voltage channel switch module, a signal processing module, a data storage module, a wireless The communication module and the upper computer, the microcontroller controls the adjustable DC constant current source to output currents of different sizes through the digital signal output by its own peripheral D/A conversion unit; the current output terminal of the adjustable DC constant current source is connected to the current channel On the current injection channel switch of the switch module, the current output terminal of the current channel switch module is connected to the current injection interface of the multi-channel wiring socket, and the current output terminal of the multi-channel wiring socket is used to connect to the node of the grounding grid under test. The current output interface of the multi-channel wiring socket is connected to the voltage channel switch module, the controlled terminals of the current channel switch module and the voltage channel switch module are connected to the control terminal of the microprocessor, the current channel switch module and the voltage channel switch The switching of the switch module is controlled by the microcontroller; the voltage output terminal of the voltage channel switch module is connected to the signal input terminal of the signal processing module, the signal output terminal of the signal processing module is connected to the signal input terminal of the microcontroller, and the signal output terminal of the microcontroller is connected to the signal input terminal of the microcontroller. The first signal output terminal is connected to the data input terminal of the data storage module, and the second signal output terminal of the microcontroller is connected to the host computer through the wireless communication module, and the host computer performs three-dimensional imaging and status evaluation of the grounding grid.

The adjustable DC constant current source includes a filter circuit for filtering the output of the generated constant voltage signal, a subtraction circuit for eliminating the interference of the power supply of each chip in the circuit on the output DC constant current source, and a circuit for increasing the output DC constant current Voltage feedback circuit for source stability, precision resistors for final DC constant current source current generation, operational amplifiers, power supplies for powering each chip, and current detection for DC constant current source calibration to ensure DC constant current source stability Resistor; the inverting input end of the subtraction circuit is connected to the digital signal output end of the microcontroller through the filter circuit, and the microcontroller is used to generate a constant voltage signal and adjust the output of the constant voltage signal through the feedback signal, and the inphase of the subtraction circuit The input end is connected to the positive power supply pin of the power supply for each chip, the output end of the subtraction circuit is connected to the inverting input end of the voltage feedback circuit; one end of the precision resistor is connected to the non-inverting input end of the voltage feedback circuit, and the other end of the precision resistor is simultaneously connected to each The positive power supply pin of the chip power supply is connected to one end of the current-sensing resistor, and the other end of the current-sensing resistor is connected to an output I/O pin of the microcontroller through an operational amplifier.

The microcontroller adopts ARM single-chip microcomputer with programmable function. The microprocessor also connects the display screen and keys. The DC constant current source is generated by programming the microcontroller; since the DC constant voltage generated by the microcontroller programming has good stability, the resulting DC constant current source also has good stability.

The filter circuit is a second-order low-pass filter circuit with a cutoff frequency of 10 Hz. The gain value of the subtraction circuit is 1. In order to eliminate power interference, the filter circuit ensures that the signal will not be amplified or reduced. The input voltage of the non-inverting input terminal and the inverting input terminal of the voltage feedback circuit are equal, so the voltage across the precision resistor is the constant voltage generated by the microcontroller programming. The precision resistor is a high-precision power resistor with a resistance value of 1Ω˜0.5Ω. Since the output voltage of the microcontroller is relatively small, the resistance needs to be selected to be relatively small.

The resistance value of the current-sensing resistor is 0.1Ω, and the voltage at both ends thereof is fed back to the microcontroller for calibration of the DC constant-current source current output.

The method for generating an adjustable DC constant current source based on a microcontroller includes the following steps:

A: Make an I/O port of the microcontroller generate and output a constant voltage signal through programming, and send the constant voltage signal to the filter circuit for processing to obtain a single frequency constant voltage signal;

B: Send the single-frequency constant-voltage signal after filtering to the inverting input of the subtraction circuit, and the non-inverting input of the subtraction circuit is connected to the positive power supply pin of each chip, and the power supply of each chip is eliminated by the subtraction circuit. Interference effect of constant current source;

C: Output the difference between the positive power supply and the constant voltage signal output by the microcontroller to the inverting input of the voltage feedback circuit through the output of the subtraction circuit; since the voltage of the inverting input of the voltage feedback circuit is equal to the voltage of the non-inverting input, It is equivalent to connecting the above difference to one end of the precision resistor, and the other end of the precision resistor is connected to the positive power supply, so that the constant voltage signal output by the microcontroller is indirectly loaded on the precision resistor, and DC is generated on the precision resistor through Ohm's law Constant current signal;

D: The current detection resistor first converts the DC constant current signal generated on the precision resistor into a voltage detection constant voltage signal, and then amplifies the voltage detection constant voltage signal through the operational amplifier to be equal to the output constant voltage signal of the microcontroller generated by the setting. Feedback the amplified voltage detection constant voltage signal to the microcontroller;

E: The microcontroller compares the amplified voltage detection constant voltage signal fed back by the current detection resistor with the value of the constant voltage signal output by the microcontroller. If the two are equal in size, the microcontroller will always output a different value. variable constant voltage source current; if the two are not equal, the microcontroller will adjust the value of the output constant voltage source current according to the size of the two until the two are equal to output a stable DC constant current.

The microcontroller realizes the generation of the DC constant current source through programming. Since the DC constant voltage generated by the microcontroller programming has good stability, the resulting DC constant current source also has good stability. The microcontroller is used to program to generate a constant voltage signal output, the filter circuit is used to filter the generated constant voltage signal, the subtraction circuit is used to eliminate the influence of the power supply on the output constant current source, and combine the power supply and the constant voltage signal The difference is output to the voltage feedback circuit. The voltage feedback circuit is used to increase the output stability of the DC constant current source. At the same time, the constant voltage signal generated by the microcontroller is indirectly loaded to both ends of the precision resistor, thereby generating a DC constant current source. The constant current source flows through the current detection resistor before the output to generate a feedback current detection voltage, and sends the feedback current detection voltage to the microcontroller, and the microcontroller adjusts its output constant voltage signal by detecting the magnitude of the current detection voltage size, so that a DC constant current source with adjustable amplitude can be generated to further ensure the output stability of the DC constant current source.

The current channel switching switch module includes a current injection channel switching control module, a multi-channel analog switch, a multi-channel transistor array and a multi-channel relay array, and the multi-channel analog switch, the multi-channel transistor array and the multi-channel relay array all pass through the current injection channel The switching control module is connected to the control terminal of the microcontroller, the current injection terminal of each analog switch in the multi-channel analog switch is connected to the current output terminal of the adjustable DC constant current source, and the output terminal of each analog switch is respectively connected to the multi-channel analog switch. The base of the corresponding triode in the multi-channel triode array, the collector of each triode is respectively connected to the control terminal of the corresponding relay in the multi-channel relay array, and the output end of each relay is connected to the current injection interface of the multi-channel wiring socket . The constituent components of the voltage channel switch module are the same as those of the current channel switch module, and the connection relationship is symmetrical to that of the current channel switch module. When it is necessary to control the opening or closing of the channel, the microprocessor only needs to write different signal values to the address lines of the analog switch to control the injection and outflow of current, which facilitates the realization of digital control. The above-mentioned multi-channel analog switch, multi-channel triode array and multi-channel relay array all use 16 components to form 16 channels.

The signal processing module voltage isolation circuit, low-pass filter circuit and A/D conversion circuit, the signal input end of the voltage isolation circuit is connected to the voltage channel switch module, and the signal output end of the voltage isolation circuit is connected to the signal of the voltage isolation circuit The output end is connected to the signal input end of the low-pass filter circuit, and the signal output end of the low-pass filter circuit is connected to the microprocessor through the A/D conversion circuit. The voltage isolation circuit is a voltage follower. The follower tracks and receives the voltage signal generated by the injection current from the 16-channel wiring socket on the grounding grid, and performs isolation and impedance matching on the input voltage signal and the output voltage signal to the low-pass filter. , The low-pass filter circuit filters out the interference of various high-frequency signal components in the grounding grid, and transmits the signal to the A/D converter, and the A/D converter transmits the converted digital signal to the microcontroller.

The data storage module adopts an SD card memory, which is composed of an SDIO circuit module of STM32 and an external SD card circuit. The FATFAS file system is built, and the data storage format is txt to facilitate long-term data storage and reading.

The wireless communication module is composed of a microcontroller peripheral USART interface connected with a wireless chip SX1212 to form a wireless transmitting circuit, and the SX1212 on the host computer is configured as a receiving circuit. By configuring the matching communication rate of the transceiver circuit, the SD card data is stored in the memory card of the upper computer, and the storage format is Excel or txt.

The working process of the whole device of the present invention is that the tester sets the size of the current to be injected through the button, the microcontroller outputs the analog voltage signal through the D/A module that comes with it and enters the adjustable DC constant current source, and the signal is filtered to Eliminate the high-frequency component signal in the output analog signal of the D/A module, enter the subtraction circuit to eliminate the interference of the front-end filter circuit and the back-end feedback circuit chip on the output current signal, and in order to achieve output signal stability, the signal from the subtraction circuit enters the feedback circuit , the generated dynamic and stable signal enters the constant current output circuit to output a constant current, and injects it into the grounding grid through the multi-channel wiring socket. The grounding grid generates a corresponding voltage because of the current flowing through it. The microcontroller selects the voltage of the corresponding grounding point on the grounding network by controlling the switching of the voltage switching module, and transmits the voltage signal to the signal processing circuit. The voltage signal first enters the voltage isolation circuit to realize the isolation of input and output. The output resistance value of the circuit is relatively large, and the output signal is transmitted to the filter circuit to achieve a good match. The low-pass filter circuit filters out the high-frequency components in the grounding grid and the circuit, and the voltage signal enters the high-precision A/D converter. Convert it into a digital signal and send it to the microcontroller, and the microcontroller will store the voltage data in txt format in the SD card through the peripheral module SDIO to the SD card with the FATFAS file system established in the circuit, and start the wireless data transmission mode by pressing the button and The data stored in the SD card will be transmitted to the upper computer wireless receiving chip SX1212 through the wireless chip SX1212 connected to the peripheral USART interface of the microcontroller in turn, and the upper computer will store the voltage data obtained in Excel format to realize the signal storage.

The following describes the three-dimensional digital evaluation method of the substation grounding grid, which is characterized in that it includes the following steps:

Step A: First, collect the voltage values of some nodes of the grounding grid under test through the three-dimensional digital monitoring device of the substation grounding grid;

Step B: Send the measured voltage values of some nodes of the grounding grid to the host computer, and the host computer uses the grounding grid state evaluation system to solve the resistance value of each branch of the grounding grid under test; the grounding grid state evaluation system uses the grounding branch based on the inverse problem The calculation method of the conductor impedance of the grounding grid solves the state of each branch of the grounding network, and the solution process is as follows:

Step B1: Equivalent the measured grounding grid to a pure resistance network, assuming that the grounding grid has N nodes and B branches, then according to the electrical network theory, the equations are:

$\left\{\begin{array}{c}{\mathrm{<span\; class="notranslate">\; Y</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}\\ {\mathrm{<span\; class="notranslate">\; Y</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; AY</span>}}_{\mathrm{<span\; class="notranslate">\; b</span>}}{\mathrm{<span\; class="notranslate">\; A</span>}}^{\mathrm{<span\; class="notranslate">\; T</span>}}\\ {\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; b</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; A</span>}}^{\mathrm{<span\; class="notranslate">\; T</span>}}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}\\ {\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; b</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; Y</span>}}_{\mathrm{<span\; class="notranslate">\; b</span>}}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; b</span>}}\end{array}\right.<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

In the formula, A is the correlation matrix of the network; Y _b is the branch admittance matrix, Y _n is the node admittance matrix; U _b is the branch voltage vector; U _n is the node voltage vector; I _n is the node current vector; I _b is the branch current vector;

Step B2: Suppose U _n0 is the measured value of the node voltage of the grounding grid under test; U _n (R) is the theoretically calculated value of the node voltage of the grounding grid under test, where U _n (R) is a function of R, and R is Unknown quantity; then, minimize f(R), and obtain the variation that conforms to the measured value as:

$\mathrm{<span\; class="notranslate">\; min</span>}\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}{<span\; class="notranslate">\; |</span><span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; |</span><span\; class="notranslate">\; |</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; =</span>{<span\; class="notranslate">\; [</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; B</span>}}<span\; class="notranslate">\; ]</span>}^{\mathrm{<span\; class="notranslate">\; T</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

Step B3: According to the principle of the least square method, from the formula (2):

$\frac{<span\; class="notranslate">\; \&PartialD;</span>\mathrm{<span\; class="notranslate">\; f</span>}}{<span\; class="notranslate">\; \&PartialD;</span>\mathrm{<span\; class="notranslate">\; R</span>}}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; [</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; ]</span>\frac{{<span\; class="notranslate">\; \&PartialD;</span>\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; )</span>}{<span\; class="notranslate">\; \&PartialD;</span>\mathrm{<span\; class="notranslate">\; R</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

Step B4: Then the objective function f(R)=||U _n (R)-U _n0 || ² is approximated by Taylor series expansion at R ^(k) :

$\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; R</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\frac{<span\; class="notranslate">\; \&PartialD;</span>\mathrm{<span\; class="notranslate">\; f</span>}}{<span\; class="notranslate">\; \&PartialD;</span>\mathrm{<span\; class="notranslate">\; R</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; R</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; R</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; R</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; T</span>}}\frac{{<span\; class="notranslate">\; \&PartialD;</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; f</span>}}{{<span\; class="notranslate">\; \&PartialD;</span>\mathrm{<span\; class="notranslate">\; R</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; R</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; R</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>$

Step B5: Calculate the extremum of the series expansion of the Taylor function obtained by formula (4) to obtain the extremum point:

$\frac{<span\; class="notranslate">\; \&PartialD;</span>\mathrm{<span\; class="notranslate">\; f</span>}}{<span\; class="notranslate">\; \&PartialD;</span>\mathrm{<span\; class="notranslate">\; R</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; R</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{<span\; class="notranslate">\; \&PartialD;</span>\mathrm{<span\; class="notranslate">\; f</span>}}{<span\; class="notranslate">\; \&PartialD;</span>\mathrm{<span\; class="notranslate">\; R</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; R</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; R</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; R</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; T</span>}}\frac{{<span\; class="notranslate">\; \&PartialD;</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; f</span>}}{<span\; class="notranslate">\; \&PartialD;</span>{\mathrm{<span\; class="notranslate">\; R</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; R</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 5</span>}<span\; class="notranslate">\; )</span>$

Step B6: If reversible, we get:

${\mathrm{<span\; class="notranslate">\; R</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; R</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; -</span>{<span\; class="notranslate">\; (</span>\frac{{<span\; class="notranslate">\; \&PartialD;</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; f</span>}}{{<span\; class="notranslate">\; \&PartialD;</span>\mathrm{<span\; class="notranslate">\; R</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; R</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; )</span>}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}\frac{<span\; class="notranslate">\; \&PartialD;</span>\mathrm{<span\; class="notranslate">\; f</span>}}{<span\; class="notranslate">\; \&PartialD;</span>\mathrm{<span\; class="notranslate">\; R</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; R</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 6</span>}<span\; class="notranslate">\; )</span>$

Step B7: Align again Taking the derivative at R ^(k) yields:

$\frac{<span\; class="notranslate">\; \&PartialD;</span>\mathrm{<span\; class="notranslate">\; f</span>}}{<span\; class="notranslate">\; \&PartialD;</span>\mathrm{<span\; class="notranslate">\; R</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; R</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}{<span\; class="notranslate">\; (</span>\frac{{<span\; class="notranslate">\; \&PartialD;</span>\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}}{<span\; class="notranslate">\; \&PartialD;</span>\mathrm{<span\; class="notranslate">\; R</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; R</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; T</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; R</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 7</span>}<span\; class="notranslate">\; )</span>$

Step B8: Deriving from formula ⑺ and ignoring higher-order terms:

$\frac{{<span\; class="notranslate">\; \&PartialD;</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; f</span>}}{{<span\; class="notranslate">\; \&PartialD;</span>\mathrm{<span\; class="notranslate">\; R</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; R</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 2</span>}{<span\; class="notranslate">\; (</span>\frac{{<span\; class="notranslate">\; \&PartialD;</span>\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}}{<span\; class="notranslate">\; \&PartialD;</span>\mathrm{<span\; class="notranslate">\; R</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; R</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; T</span>}}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; R</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 8</span>}<span\; class="notranslate">\; )</span>$

and thus get: $R^{(k+1)}=R^{\left(k\right)}-{\left(J_k^T{J}_k\right)}^{-1}{J}_k^T(u_{\mathrm{no}}\left(R^{\left(k\right)}\right)-u_{\mathrm{no}0})---\left(9\right)$

in is the Jacobian matrix; formula (9) is the iterative formula of the NR method of the fault diagnosis equation of the grounding grid, so as to solve the unknown branch resistance value;

Step B8: According to the variation of ground grid branch resistance, compare with the branch resistance design value of each branch, and evaluate the ground grid corrosion status according to the ground grid corrosion degree discrimination standard.

Step C: Send the grounding network branch resistance value data obtained in step B to the 3D imaging system for 3D imaging. The specific steps are as follows:

Step C1: Firstly, divide the entire computing field into a finite number of discrete units;

Step C2: Calculate the conductivity of each discrete unit according to the ground grid branch resistance value calculated in step B and the soil resistivity around the ground grid to be measured;

Step C3: According to the conductivity of each discrete unit provided in step C2, combined with the topological structure of the grounding grid to be tested, perform a three-dimensional imaging of the branch resistance of the grounding grid and the surrounding soil. The image includes the three-dimensional topology of the grounding grid and the branch resistance size.

Claims (9)

1. a grounding net of transformer substation three-dimensional digital supervising device, it is characterized in that: comprise microcontroller, adjustable DC constant current source, current channel change-over switch module, hyperchannel connector socket, voltage channel change-over switch module, signal processing module, data memory module, wireless communication module and host computer, microcontroller exports the electric current of different size by the Digital Signals adjustable DC constant current source that the D/A converting unit of self peripheral hardware exports, the current output terminal of adjustable DC constant current source is connected on the pulse current injectingt passage bridge switch of current channel change-over switch module, the current output terminal of current channel change-over switch module is connected on the pulse current injectingt interface of hyperchannel connector socket, the current output terminal of hyperchannel connector socket is for connecting the node of tested grounded screen, the current output interface of hyperchannel connector socket is connected in voltage channel change-over switch module, current channel change-over switch module is all connected microprocessor-based control end with the controlled end of voltage channel change-over switch module, current channel change-over switch module and voltage channel change-over switch module cut-off all by microprocessor controls, the signal input part of the voltage output end connection signal processing module of voltage channel change-over switch module, the signal output part of signal processing module connects the signal input part of microcontroller, the data input pin of the first signal output part connection data memory module of microcontroller, the secondary signal output terminal of microcontroller connects host computer by wireless communication module, is carried out the state estimation of three-dimensional imaging and grounded screen by host computer.

2. grounding net of transformer substation three-dimensional digital supervising device according to claim 1, it is characterized in that: described adjustable DC constant current source comprises the filtering circuit constant voltage signal output produced being carried out to filtering, for eliminating the subtraction circuit that in circuit, each chip power supply power supply disturbs output DC constant current power supply, for increasing the voltage feedback circuit exporting DC constant current power supply stability, for finally producing the precision resistance of DC constant current power supply electric current, operational amplifier, the power supply that each chip is powered and for DC constant current power supply calibration with the inspection leakage resistance guaranteeing DC constant current power supply stability, the inverting input of described subtraction circuit connects the digital signal output end of microcontroller by filtering circuit, microcontroller is for generation of a constant voltage signal and adjusted by the output of feedback signal to constant voltage signal, the in-phase input end of subtraction circuit connects the positive power pin to each chip power supply power supply, and the output terminal of subtraction circuit connects the inverting input of voltage feedback circuit, precision resistance one end connects the in-phase input end of voltage feedback circuit, the other end of precision resistance connects positive power pin to each chip power supply power supply and inspection leakage resistance one end simultaneously, and the other end of inspection leakage resistance exports I/O pin by operational amplifier and microcontroller one and is connected.

3. grounding net of transformer substation three-dimensional digital supervising device according to claim 2, it is characterized in that: described current channel change-over switch module comprises pulse current injectingt passage bridge control module, multichannel analog switch, multichannel triode array and multicircuit relay array, multichannel analog switch, multichannel triode array and multicircuit relay array are all connected the control end of microcontroller by pulse current injectingt passage bridge control module, the pulse current injectingt end of each analog switch in multichannel analog switch all connects the current output terminal of adjustable DC constant current source, the output terminal of each analog switch is connected respectively the base stage of the corresponding triode in multichannel triode array, the collector of each triode is connected respectively the control end of the corresponding relay in multicircuit relay array, the output terminal of each relay is connected on the pulse current injectingt interface of hyperchannel connector socket.

4. grounding net of transformer substation three-dimensional digital supervising device according to claim 3, it is characterized in that: the composition components and parts of described voltage channel change-over switch module and the identical of current channel change-over switch module, and the annexation of annexation and current channel change-over switch module is symmetrical.

5. grounding net of transformer substation three-dimensional digital supervising device according to claim 4, it is characterized in that: described signal processing module comprises voltage isolation circuit, low-pass filter circuit and A/D change-over circuit, the signal input part of voltage isolation circuit is connected in voltage channel change-over switch module, the signal output part of voltage isolation circuit connects the signal input part of the signal output part connection low-pass filter circuit of voltage isolation circuit, and the signal output part of low-pass filter circuit connects microprocessor by A/D change-over circuit.

6. grounding net of transformer substation three-dimensional digital supervising device according to claim 5, is characterized in that: described data memory module adopts SD card memory.

7. grounding net of transformer substation three-dimensional digital supervising device according to claim 6, is characterized in that: described microcontroller adopts ARM single-chip microcomputer, and microprocessor also connects display screen and button.

8., based on a grounding net of transformer substation three-dimensional digital appraisal procedure for grounding net of transformer substation three-dimensional digital supervising device according to claim 1, it is characterized in that: comprise the following steps:

Steps A: first, gathers the magnitude of voltage of the part of nodes of tested grounded screen by grounding net of transformer substation three-dimensional digital supervising device;

Step B: the magnitude of voltage of the grounded screen part of nodes measured is sent to host computer, host computer utilizes grounded screen status assessing system to solve each branch resistance value of tested grounded screen; Grounded screen status assessing system adopts the ground connection branch conductor impedance computation method based on inverse problem to solve each membership of grounded screen, solution procedure following steps:

Step B1: tested grounded screen is equivalent to pure resistance network, supposes that grounded screen has N number of node and B bar branch road, has then established an equation according to electric network theory:

In formula, A is the incidence matrix of network; Y _bfor branch admittance matrix, Y _nfor bus admittance matrix; U _bfor branch voltage vector; U _nfor node voltage vector; I _nfor node current vector; I _bfor branch current vector;

Step B2: suppose U _n0for the measured value of the node voltage of tested grounded screen; U _n(R) be the node voltage calculated value of tested grounded screen, wherein, U _n(R) be function about R, R is unknown quantity; Then, minimized by f (R), the variable quantity of trying to achieve coincidence measurement value is:

Step B3: according to principle of least square method, is (2) obtained by formula:

Step B4: again by objective function f (R)=|| U _n(R)-U _n0|| ²at R ^(k)place's Taylor series expansion is approximately:

Step B5: extreme value is asked for the series expansion of the Taylor function that (4) formula obtains and obtains extreme point:

Step B6: if reversible, then obtain:

Step B7: right again at R ^(k)differentiating in place, obtains:

Step B8: (7) being derived by formula and ignored higher order term obtains:

Therefore obtain:

Wherein for Jacobi matrix; Formula (9) is the NR method iterative formula of Fault Diagnosis for Grounding Grids equation, thus solves unknown branch resistance value;

Step B9: according to grounded screen branch resistance value situation of change, compared with the branch resistance design load of each branch road, according to ground net corrosion degree discrimination standard, thus carries out state estimation to ground net corrosion situation.

9. grounding net of transformer substation three-dimensional digital appraisal procedure according to claim 8, is characterized in that: also comprise step C: send to 3-D imaging system to carry out three-dimensional imaging the grounded screen branch resistance Value Data obtained in step B, concrete steps are as follows:

Whole calculating field domain subdivision is limited discrete unit by step C1: first;

Step C2: according to the soil resistivity around the grounded screen branch resistance value calculated in step step B and grounded screen to be measured, calculate the conductivity of each discrete unit;

Step C3: according to the conductivity of each discrete unit that step C2 provides, in conjunction with the topological structure of grounded screen to be measured, carry out three-dimensional imaging to grounded screen branch resistance and surrounding soil, image comprises three dimensional topology and the branch resistance size of grounded screen.