CN202453451U - Earth grid corrosion and broken point diagnosing system for large and medium-sized substations - Google Patents

Abstract

A system for diagnosing ground grid corrosion and breakpoints of large and medium-sized substations, including a mobile measurement port box, a port measurement device, a mobile computer host, and test clamps. The utility model proposes a new type of diagnosis system, that is, after wiring some points to be measured in the station once, all combinations of any two points to be measured that are wired to be measured can be measured at the mobile measurement port box, which saves the work of repeated wiring , After the data is measured by the port measuring device, it is transmitted to the mobile computer host through the high-speed serial port. Use the diagnostic software to analyze the data to get the specific situation of the defects of each branch of the grounding grid. The utility model can be widely used for corrosion fault detection of the ground grid of the substation that has been put into operation, and is especially suitable for large-scale substations that occupy a large area and have high safety requirements. In addition, it can also be used in other industries such as steel, chemical industry, and power plants. ground grid system.

Description

A system for diagnosing ground grid corrosion and breakpoints in large and medium-sized substations

technical field

The utility model relates to a system for diagnosing ground grid corrosion and breakpoints of large and medium-sized substations, in particular to a diagnostic system for quickly and easily measuring the ground grids of large and medium-sized substations, and locating corrosion and breakpoint faults. It belongs to the technical field of detection. the

Background technique

Grounding refers to the electrical connection between some nodes of the electrical system or some conductive parts of electrical facilities and the earth. The grounding of power plant substations is the unity of lightning protection grounding, working grounding and protective grounding. The grounding conductors of substation ground grids in my country are mainly made of ordinary carbon steel, which are generally laid horizontally with flat steel or round steel, arranged in long or square holes and buried underground, and their area is slightly larger than that of the substation. After the grounding grid is put into operation, the grounding grid buried in the soil will be corroded to varying degrees over time. In the weakly corrosive soil, the annual corrosion degree of the metal conductor of the grounding grid is 1mm. Medium up to 3mm. After many years of operation of the grounding grid, different degrees of corrosion will directly reduce the service life of the grounding grid and affect the safe operation of the grid. The corrosion of carbon steel is usually local corrosion, and after corrosion, it will become brittle, layered, and the corrosion site will gradually become thinner and thinner, or even fracture, resulting in grounding performance that cannot meet the requirements of thermal stability. As a result, in the event of a ground fault, ground short-circuit currents may cause local potentials to exceed specifications. Even the insulation of secondary equipment is damaged due to counterattack or cable sheath circulation, which expands the accident and endangers equipment and personal safety, thus bringing huge economic losses and adverse social impacts. the

Since the grounding grid is buried underground all the year round, the previous monitoring of the grounding grid was to find the electrical connection fault point or corrosion section of the grounding grid through excavation after the grounding resistance was found to be unqualified or faulty, so as to determine whether to carry out the whole station reconstruction. This method is extremely backward and unscientific. It can be seen that it is difficult for managers to understand the current situation conveniently and accurately by conventional means for corrosion or breakpoints of ground grid conductors. At present, some new diagnostic systems have also appeared. According to the topological structure of the ground network, certain incentives are injected into the ground network nodes, and the detected responses are analyzed by mathematical tools to obtain the ground network fault situation. For example, the patent application number 200710185685.1 is "Substation Grounding Grid Defect Diagnosis Method and Device", which measures the distribution of magnetic induction intensity on the ground surface by injecting excitation signals, and then compares the measurement results with the normal state data calculated by simulation to judge the grounding grid The specific location and extent of corrosion thinning or fracture defects. The main disadvantages of this patent are: due to the extremely complex electromagnetic environment in the switchyard of the substation, the detected magnetic induction intensity is greatly disturbed, the filter design is extremely complicated, and the accuracy is difficult to improve. Another example is the patent application number 201010586932.0 "a measuring device for diagnosing the connection state of the grounding grid", which includes a measuring circuit, a central processing control circuit, and a PC. The device takes the ground rod as the carrier, inputs the excitation signal to it, and obtains the local connection information of the ground grid through the subsequent processing of the output response signal. The main disadvantage of this patent is that the ground network of large substations often occupies a large area, and extremely long measurement leads are required to be pulled back and forth frequently and change measurement points frequently during on-site diagnosis and measurement. Larger, and there will be serious safety hazards in the long-term measurement operation in the switch yard of the live area of the substation. the

Contents of the invention

The purpose of the utility model is to solve the problems existing in the existing corrosion diagnosis, and provide a diagnosis system for large and medium-sized substation grounding grids that is quick and easy to operate, and can accurately detect corrosion or breakpoints without power failure and large-scale excavation. the

The technical scheme adopted by the utility model to solve the above-mentioned technical problems is: a system for diagnosing ground network corrosion and breakpoints of large and medium-sized substations, including a mobile measuring port box, a port measuring device, a mobile computer host and testing clamps. the

Wherein, one end of the test clamp clamped by the jaws on the lead wire of the ground network node is connected to the measurement terminal on the mobile measurement port box through the measurement wire, and several points to be measured are collected in the mobile measurement port box. the

The port measurement device includes a measurement module, a data conversion module and a communication module; the measurement module is connected to any pair of measurement terminals on the mobile measurement port box through the measurement current wire and the measurement voltage wire, and the measurement current wire Inject current excitation, measure the voltage value between the two measurement terminals by the measurement voltage line, and then obtain the resistance value between any two points to be measured corresponding to the pair of measurement terminals through the double-arm bridge of the measurement module; The data conversion module and the communication module are input to the mobile computer host, and the mobile computer host analyzes and calculates the data, and diagnoses the corrosion and breakpoint of the ground network according to the variation of the resistance value relative to the theoretical value. the

Analyzing the actual value of the grounding network branch resistance test data and the original resistance value of the grounding network branch in the mobile computer mainframe using diagnostic software compiled in the computer. The analysis principle is as follows:

Assuming that the grounding grid has n+1 nodes, b branches, and m grounding leads (that is, the lead wires of the grounding grid nodes), ignoring the influence of soil factors, the grounding grid can be regarded as a resistance network. Obtaining the port resistance of the original network: Assume that an I ₀ current source is added to the i and j ports of the network. Definition: A is the correlation matrix of the network after selecting a reference node; Y _b is the branch admittance matrix; Y _n is the node admittance matrix; I _b is the branch current matrix; U _n is the node voltage column vector; I _n is the current source column vector of the node (the current value of the non-excited joint is 0).

According to the circuit principle:

(1)

Can get:

                                (2)

(2)

Thus the port resistance R _ij is obtained:

                             (3)。

(3).

It can be seen from the circuit principle that for any N-terminal network, if the structure of the network, the resistance of the branch, and the excitation situation are known, then, according to the node analysis method, the port resistance can be obtained. But for fault diagnosis, the resistance R _k of the branch of the grounding network is calculated by R _ij , which can be seen as the inverse problem of circuit calculation.

，仍在其i，j端加电流源，电流值为I₀。求出R _ij ′；可知网络N和网络N^’拓扑结构相同，当网络支路K发生腐蚀或断裂时，此时网络的端口电阻R _ij 变为R _ij ′，即：  Consider the grounding grid model diagram before corrosion as a network N with b+1 branches and n+1 nodes. Among them, the b+1th branch is connected to the i and j terminals of the grounding grid. A current source is added to the i-th and j-th ports of the grounding grid, and its current value is I ₀ , and R _ij can be obtained according to the circuit principle; when the grounding grid is corroded, the model diagram is regarded as the network

, still adding a current source to its i and j terminals, and the current value is I ₀ . Calculate R _ij ′; it can be seen that the network N and network N ^′ have the same topological structure, when the network branch K is corroded or broken, the port resistance R _ij of the network becomes R _ij ′, namely:

                   (4)

(4)

According to Tellegen's theorem

(5)

                  (6)

(6)

From (5)-(6):

        (7)

(7)

thereby:

             (8)

(8)

            (9)。

(9).

In this way, the relationship between the change value of the port resistance and the change value of the branch resistance is obtained, but the change value of the branch resistance cannot be obtained directly from the change value of the port resistance, because there are b variables in the branch resistance, so a series of The port resistance leads to a set of equations:

            (10)

(10)

，方程组变成线性方程组，但方程组m＜b欠定，需用优化方法求解，用的是拟牛顿法求解。这样就求出△R_k和△R_k′，接着用△R_k′(0)计算出

；然后

计算

。重复上面的计算，直到求出的电阻增量满足要求，得到最后的计算结果，从而得到接地网各条支路缺陷的具体情况。 Among them, m is the number of ports measured, and I _k can be obtained from R _k . I _k ′ is determined by R _k ′, but R _k ′ is unknown. It can be seen from the above formula that the equations are nonlinear equations and cannot be solved directly. To solve the problem, an iterative method is introduced. First, make

, the system of equations becomes a system of linear equations, but the system of equations m<b is underdetermined and needs to be solved by an optimization method, which is solved by the quasi-Newton method. In this way, △R _k and △R _k ′ are obtained, and then △R _k ′(0) is used to calculate

;Then

calculate

. Repeat the above calculation until the calculated resistance increment meets the requirements, and the final calculation result is obtained, so as to obtain the specific conditions of the defects of each branch of the grounding grid.

After the conductor is corroded, the most intuitive performance is the change of the cross-sectional area of the conductor and the resistance value of the branch. The ratio of the large amount to the branch resistance value before corrosion is used as an index to measure the fault degree of the grounding grid conductor. See Table 1 for the specific division of the fault degree. the

≤1 1<

≤9

>9 导体等效直径 90%<

≤100% 10%<

≤90%

<10% Table 1 Division of grounding grid conductor fault degree Fault description Minor failure Moderate failure Serious failure (including fracture) The multiple of the conductor resistance increase 0<

≤1 1<

≤9

>9 Conductor Equivalent Diameter 90%<

≤100% 10%<

≤90%

<10%

The beneficial effects of the utility model are:

1) The composition of the system of the utility model is simple. By applying current excitation and measuring the voltage signal to calculate the port resistance, the anti-interference ability is strong, and the obtained signal is stable. After wiring multiple measurement points once, the port measurement device can quickly measure different measurement point pairs, which saves the time for rewiring to measure different measurement point pairs, and reduces safety risks by reducing measurement work. Port measuring devices of different sizes can be selected for grounding grids of different areas, and the application range is wide.

2) The utility model has the advantages of high pertinence, simple and portable equipment, strong mobility, and the power panel in the station can be used for real-time measurement in the substation, and the measurement data can be directly input into the mobile computer host for analysis and storage. the

3) The utility model can discover the corrosion fault of the grounding grid and the development of the fault in advance, make a location and safety assessment for the corrosion fault of the grounding grid, and realize the non-destructive detection and diagnosis of the substation. The method of breakpoint and corrosion section does not affect the normal operation of the power system, thus ensuring the safe operation of the power system and the reliability of power supply, and establishing a good image of the power system in various industries, resulting in indirect economic benefits and The social benefits are also huge. the

The utility model can be widely used for the corrosion fault detection of the ground network of the substation which has been put into operation, and is especially suitable for the large-scale substation which covers a large area and has high safety requirements. In addition, it can also be applied to other systems with ground grids such as steel, chemical industry and power plants. the

Description of drawings

Fig. 1 is a schematic diagram of the structure of the utility model;

Figure 2 is a structural diagram of the mobile measurement port box;

Fig. 3 is a functional block diagram of the port measuring device;

In the figure: 1-horizontal grounding grid buried in the ground; 2-leading wire of grounding grid node; 3-measurement wire; 4-mobile measurement port box; 5-port measurement device; 6-mobile computer host; 7-test clamp ; 9-round hole; 10-measuring current line; 11-measuring voltage line; 12-measuring terminal.

Detailed ways

Below in conjunction with accompanying drawing, the utility model is further described. the

Example 1

A system for diagnosing ground grid corrosion and breakpoints in large and medium-sized substations, as shown in Figures 1, 2, and 3, mainly includes a mobile measurement port box 4, a port measurement device 5, a mobile computer host 6, and a test clamp 7.

The mobile measurement port box 4 is composed of a measurement wire 3 and a measurement terminal 12 . The measuring wire 3 is a commercially available S-twisted two-core flexible wire, each core flexible wire has a nominal cross section of 1.5mm ² , and the two core wires in the measuring wire 3 are respectively connected to the test clamp 7 superior. One of the test clamps 7 is only connected to the lead wire 2 of a ground network node, and the measurement wires 3 converge in the mobile measurement port box 4 . The mobile measurement port box 4 is a cuboid box, and the box body material is made of engineering plastics, which can withstand a certain external force, and has good electrical insulation and dimensional stability, and can still maintain its shape at high and low temperatures. Excellent performance. The box is 3mm thick, 60mm high, 90mm long, and 90mm wide. There is a circular hole 9 with a diameter of 5mm on each side of the box for the measurement wire 3 to pass through. The measurement terminal 12 is a commercially available component, the panel waist hole is φ6.0mm, the withstand current is 10A, and the test withstand voltage is 3KV. It is embedded on the panel of the mobile measurement port box 4. The round holes 9 are equal and close in position. There are four round holes 9 and the measuring terminals 12 respectively, and each of the measuring terminals 12 is connected to one of the measuring wires 3 through the nearest The circular hole 9 leads out. The top of the measurement terminal 12 is located outside the mobile measurement port box 4, and the tail is embedded in the panel of the box and connected to a core of the measurement wire 3, marked with a symbol C, which is used to connect the measurement current during measurement Line 10; marked with the symbol P, which is used to connect the measuring voltage line 11 during measurement. Each of the measuring wires 3 passes through one of the circular holes 9 nearby, and the function of the mobile measurement port box 4 is to gather a plurality of the measuring wires 3 for one-time wiring and multiple measurements. By measuring the data of any two pairs of binding posts on the mobile measurement port box 4 , the port of the corresponding ground node connected to the measurement wire 3 is equivalently measured.

The test pliers 7 are commercially available electric power test pliers. The clamp frame is made of ABS material with high pressure resistance and high strength. The jaws are divided into upper and lower layers, which are insulated, and the current and voltage are separated. The jaws can move and make surface contact. The opening and length are 30mm and 180mm respectively, the test withstand voltage is greater than 3KV, and the contact resistance is less than 1MΩ. the

The port measuring device 5 is composed of a commercially available DC resistance tester, which is composed of a power supply module, a measurement module, a digital-to-analog conversion module (AD574D), an open circuit protection module, and a communication module. The power module is powered by AC 220V, 50Hz mains. The measurement module is a double-arm electric bridge based on the Kelvin connection principle, and its resistance element is made of manganese-copper wire with mature technology. The measured resistance (ground network port) is connected to the double-arm bridge by the four-terminal button method, 2A current is injected through the measurement current line 10, and the voltage is measured by the measurement voltage line 11 to calculate the corresponding port resistance. This wiring measurement method can transfer the wire resistance and contact resistance to the power circuit. Since the bridge arm resistance is much larger than the corresponding additional resistance, the additional resistance is ignored, and the difference between the wire resistance and the contact resistance to be measured is eliminated. Influence. The communication module adopts RS-232 communication interface, the frame mode is 8 data bits, 1 stop bit, and each group of data transmission has 11 bytes, wherein the measurement data is 5 bytes, and the decimal point is 1 byte. Space 1 or 2 bytes, unit symbol 4 or 3 bytes. The corresponding PC control code S is a single sending command, that is, the RS-232 interface only sends a set of data, and the control code C is a continuous sending data command. After the measurement module measures any pair of the binding posts, the resistance-voltage conversion is performed, and then converted into a digital signal by the digital-to-analog conversion module, which can directly communicate with the computer through the RS-232 communication interface; Communicate with the computer by means of wireless transmission. The port measurement device 5 can be a commercially available product, such as Shanghai Zhengyang ZY9858. the

Described mobile computer host computer 6 is a commercially available mobile computer, the memory of the computer is 4GB DDR3, the processor is the Intel Core Duo processor i5-2450M, adopts Windows7 operating system, hard disk is 500GB, the hard disk of large capacity and high-end memory are enough to guarantee Computers are capable of storing and analyzing data. the

A diagnostic method for diagnosing ground grid corrosion and breakpoints of large and medium-sized substations is as follows:

① Input the topological structure data of the actual ground network into the mobile computer host 6, and select a measurement plan according to the size of the ground network to measure the required ground network port data.

② Enter the switch yard of the substation, select 4 measurement points, and clamp the test clamp 7 on the 4 measurement wires in the mobile measurement port box 4 to the ground wires of the measurement points at various locations . the

③ Based on the four-terminal button access method of the double-arm bridge, connect the measurement current line 10 and the measurement voltage line 11 connected to the port measurement device 5 to a pair of binding posts 12 on the mobile measurement port box 4, and apply 2A Direct current excitation is used to measure the port resistance of the corresponding network node pair, and the measured resistance parameter signal is transmitted to the mobile computer host 6 through the RS-232 communication interface in the port measurement device 5 . the

④ After inputting into the analysis software, calculate according to the following principles: 

，方程组变成线性方程组，但方程组欠定，需用优化方法求解，本课题中用的是非负最小二乘法。这样就求出

和，接着用

计算出

；然后用

计算

。重复上面的计算，直到求出的电阻增量满足要求，得到最后的计算结果。 The equations in formula (10) are nonlinear equations, and an iterative method is introduced. First, make

, the system of equations becomes a system of linear equations, but The system of equations is underdetermined and needs to be solved by an optimization method. In this project, the non-negative least squares method is used. so find out

and , followed by

Calculate

; then use

calculate

. Repeat the above calculation until the calculated resistance increment meets the requirements, and the final calculation result is obtained.

The following are the detailed steps of the entire calculation process:

；根据电路原理计算出

，选取一些测量节点组求出理论节点间电阻(s＝1～m)； 1) Obtain the topological structure and branch resistance of the grounding network from the design diagram

; Calculated according to the circuit principle

, select some measurement node groups to find the theoretical inter-node resistance (s=1～m);

； 2) Measure port resistance , calculate the port resistance change value

;

； 3) order

;

； 4) Calculated by using the equation group (10) combined with the optimization method (t = 0, 1, ..., t is the number of iterations); then calculate

;

而且，那么停止迭代计算，认为

为最后结果，

为设定的常数；否则继续下一步； 5) If

and , then stop the iterative calculation and consider

for the final result,

is the set constant; otherwise, continue to the next step;

计算

；重复第4步。 6) with

calculate

; Repeat step 4.

Because the number of unknown quantities in equation group (10) is b, to get the exact values of these variables, the number of equations should be b, but the value of b is very large, because the number of grounding wires in general substations is less than that of the grounding grid It is impossible to complete these multiple measurements in engineering. In order to get better accurate values, optimization techniques need to be used:

                 (11)

(11)

 (k =1，2，...，b) st

(k=1,2,...,b)

After calculation and analysis of the measurement software, the corrosion fault situation is obtained, the corrosion fault branch is located, and the analysis results are output and stored for further research and maintenance.

Example 2

A system for diagnosing corrosion and breakpoints of ground grids in large and medium-sized substations, the same as in Embodiment 1, wherein the nominal cross-section of each core flexible wire is 2.5 mm ² , the junction box 8 is 7 mm thick, 100 mm high, 150 mm long, and 150 mm wide 150mm, measuring terminal 12 panel waist hole is φ8.0mm. There are 12 circular holes 9 and measuring terminals 12 respectively, and 3 circular holes 9 are respectively arranged on each side of the junction box 8 . The measurement current line 10 is injected with a current excitation of 5A.

Claims (2)

1. A system for diagnosing ground grid corrosion and breakpoints of large and medium-sized substations, characterized in that the system includes a mobile measurement port box (4), a port measurement device (5), a mobile computer host (6) and test clamps (7 ); Wherein, one end of the test clamp (7) clamped by the jaws on the lead wire (2) of the ground network node is connected to the measurement terminal (12) on the mobile measurement port box (4) through the measurement wire (3) , collecting several points to be measured in the mobile measurement port box (4); The port measurement device (5) includes a measurement module, a data conversion module and a communication module; the measurement module is connected to the mobile measurement port box (4) through a measurement current line (10) and a measurement voltage line (11) On any pair of measurement terminals (12), inject current excitation through the measurement current line (10), measure the voltage value between the two measurement terminals (12) through the measurement voltage line (11), and then pass through the dual measurement module. The arm bridge obtains the resistance value between any two points to be measured corresponding to the pair of measuring terminals (12); input the mobile computer host (6) through the data conversion module and the communication module, and the mobile computer host (6) compares the data Carry out analysis and calculation, and diagnose the corrosion and breakpoint of the ground network according to the change of the resistance value relative to the theoretical value. 2. A system for diagnosing ground grid corrosion and breakpoints of large and medium-sized substations according to claim 1, characterized in that: the measuring terminals (12) are composed of two terminals marked C and P, wherein C Connect the measurement current wire (10), and P connect the measurement voltage wire (11).

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