Method for monitoring and evaluating corrosion state of grounding grid

Abstract

NOT VISIBLE DUE TO STATUS OF PATENT

Description

A monitoring and evaluation method for the corrosion status of grounding grid Technical Field

[0001] The present invention relates to the technical field of electric power safety protection, and in particular to a method for monitoring and evaluating the corrosion state of a grounding grid. Background Art

[0002] In power systems, ensuring the operation and safety of the entire system often requires connecting certain parts of the system and its electrical equipment to the earth. This is known as grounding. Power system grounding has two functions: operational grounding and protective grounding. Protective grounding is categorized into three types: lightning protection grounding, anti-static grounding, and insulation breakdown or leakage grounding. Operational grounding primarily provides a stable potential reference point for the power system; protective grounding primarily provides a path for current leakage, preventing accidents involving personnel or power facilities.

[0003] The grounding system is the grounding carrier for the power system, connecting the power system or electrical equipment to the earth. It consists of a grounding grid that directly contacts the soil and grounding leads that connect the grid to the grounding terminals of the power system or electrical equipment. The metal conductors and grounding leads that make up the grounding grid are collectively called grounding systems or branches of the grounding grid. Grounding systems are categorized by size into general and large-scale grounding systems. The safety and compliance of grounding systems play a crucial role in the safe and stable operation of the entire power system.

[0004] Three factors generally influence the grounding performance of grounding devices: the size of the grounding device, the resistivity of the soil in its environment, and the conductivity of the materials it comprises. Currently, large-scale grounding devices in my country are primarily constructed of galvanized flat steel. After years of operation, some have begun to experience severe corrosion. Furthermore, the grounding grid that makes up these devices is located underground, making them concealed facilities. Corrosion defects are difficult to detect during routine maintenance and inspections, making corrosion a major hazard to the safe operation of power systems.

[0005] Over the years, with the expansion of my country's power sector and the operation of new substations and power plants, short-circuit current levels have varied across substations and are on an upward trend. Consequently, each power company requires annual thermal stability verification of the conductors in the grounding branch circuits. This verification requires collecting data on the corrosion rate of the grounding material in its environment, thereby accurately determining the current cross-sectional area of ​​the grounding branch circuit and the maximum short-circuit current level that can pass through it.

[0006] Grounding grid corrosion in soil can be categorized into three main types: electrochemical corrosion, stray current corrosion, and microbial corrosion. Electrochemical corrosion is the most prominent and predominant form of grounding grid corrosion. Corrosion rate measurement is a key aspect of grounding grid corrosion monitoring technology. Numerous methods exist for measuring corrosion rates. The most primitive and simplest is the weight loss method, which is similar in principle to the coupon method. In addition, there are resistance probe and electrochemical methods. Grounding grids are buried in the soil, creating a unique testing environment. Furthermore, corrosion occurs during operation, and measuring corrosion rates requires the grid to be shut down or removed from the soil. Therefore, weight loss, coupon, and resistance probe methods are not suitable. Electrochemical corrosion rate measurement is an in-situ measurement technique capable of real-time measurements. It offers high sensitivity and can measure instantaneous metal corrosion information. It can also provide long-term monitoring of metal electrode surface corrosion, thus meeting the requirements for long-term online monitoring of grounding grid corrosion rates.

[0007] However, judging the corrosion status of grounding grids based solely on a few parameters, such as corrosion rate, has been unsatisfactory and somewhat one-sided. Because the corrosion of grounding grid electrodes is much more complex than that of open systems, the measurement parameters are scattered and influenced by many factors. These factors are not only related to the corrosion potential and corrosion rate of the grounding electrodes, but also include soil pH, chloride ion concentration, and soil resistivity, which are also the most important parameters affecting buried grounding electrode corrosion. Therefore, how to further utilize electrochemical testing technology to improve the accuracy and comprehensiveness of grounding grid corrosion status judgment has become a technical challenge urgently needed to be addressed by those skilled in the art. Summary of the Invention

[0008] The purpose of the present invention is to provide a monitoring and evaluation method for the corrosion state of a grounding grid based on the above-mentioned deficiencies of the prior art. By monitoring the soil resistivity, pH value and Cl ion concentration in the on-site soil environment of the grounding grid, and combining the corrosion potential and corrosion rate, a judgment expression for the corrosion state of the grounding grid is established to achieve comprehensive, accurate and effective corrosion monitoring of the grounding electrode structure of the grounding grid.

[0009] The purpose of the present invention is achieved by the following technical solutions:

[0010] A method for monitoring and evaluating the corrosion state of a grounding grid, characterized in that it comprises the following steps:

[0011] Obtain soil resistivity, soil environmental pH value, soil Cl ion concentration, corrosion potential and corrosion rate in the grounding grid area;

[0012] An expression for judging the corrosion state of the grounding grid is established based on the soil resistivity, the soil environment pH value, the soil chloride ion concentration, the corrosion potential, and the corrosion rate. The expression is as follows:

[0013] E=40%A+30%B+10%C+20%D;

[0014] Wherein, E is the grounding grid corrosion state parameter, which is used to characterize the state of the grounding grid and is divided into unusable state, usable state, and normal state; A is the score value corresponding to the corrosion potential; B is the score value corresponding to the corrosion rate; C is the score value corresponding to the soil resistivity; D is the score value corresponding to the ratio between the soil chloride ion concentration and the hydroxide ion concentration calculated by combining the soil environment pH value;

[0015] The E value is calculated according to the expression, and the corrosion state of the grounding grid is judged according to the E value.

[0016] The judgment of the grounding grid corrosion state parameter E is divided into:

[0017] When E is greater than or equal to 2.7, it is determined that the grounding grid is in an unusable state;

[0018] When E is greater than 1.5 and less than 2.7, it is determined that the grounding grid is in a usable state;

[0019] When E is less than or equal to 1.5, it is determined that the grounding grid is in a normal state.

[0020] The scoring criteria include:

[0021] When the corrosion potential is greater than -500 mV, A=1; when the corrosion potential is between -500 mV and -850 mV, A=2; when the corrosion potential is less than -850 mV, A=3;

[0022] When the corrosion rate is less than 0.1 mm / a, B=1; when the corrosion rate is between 0.1 mm / a and 1 mm / a, B=2; when the corrosion rate is greater than 1 mm / a, B=3;

[0023] When the soil resistivity is greater than 100 kΩ·cm, C=1; when the soil resistivity is between 50 kΩ·cm and 100 kΩ·cm, C=2; when the soil resistivity is between 10 kΩ·cm and 50 kΩ·cm, C=3; when the soil resistivity is less than 10 kΩ·cm, C=4;

[0024] When the ratio between the soil chloride ion concentration and the hydroxide ion concentration is less than 0.6, D=1; when the ratio between the soil chloride ion concentration and the hydroxide ion concentration is greater than 0.6, D=2.

[0025] The soil resistivity is calculated by measuring the soil resistance in the grounding grid area, and the calculation formula is:

[0026] Where ρ is the soil resistivity, R is the measured soil resistance, L is the distance between the resistance electrodes, and S is the cross-sectional area of ​​the resistance electrodes.

[0027] The soil environment pH value is calculated by measuring the pH open circuit potential of the soil in the grounding grid area, and the calculation formula is:

[0028] Where η pH is the pH value of the soil environment, u pH is the pH open circuit potential value measured by the electrochemical corrosion probe, b pH is the intercept corresponding to the soil pH value, k pH is the slope corresponding to the soil pH value.

[0029] The soil chloride ion concentration is calculated by measuring the open circuit potential of Cl ions in the soil within the grounding grid area. The calculation formula is:

[0030] Where η Cl is the Cl ion concentration value of the soil environment, u Cl is the open circuit potential of Cl ion measured by the electrochemical corrosion probe, b Cl is the intercept corresponding to Cl ions in the soil environment, k Cl is the slope corresponding to the Cl ion concentration in the soil environment.

[0031] Based on the measured soil environment pH value η pH and Cl ion concentration η C l, first calculate the hydroxide ion concentration σ, then calculate the Cl chloride ion concentration η Cl The ratio λ between the concentration of hydroxide ions and the concentration of hydroxide ions is σ = 10 ηpH-14 , the corresponding ratio

[0032] The corrosion rate is calculated by measuring the corrosion current of the grounding electrode of the grounding grid. The calculation formula is:

[0033] Where V is the corrosion rate of the grounding electrode of the grounding grid, i corr is the grounding electrode corrosion current density, A is the atomic weight of the grounding electrode material, n is the number of electrons gained or lost by the grounding electrode material, is the density of the grounding electrode material.

[0034] The advantages of the present invention are: by introducing the judgment parameters of soil resistivity, soil environmental pH value and soil Cl ion concentration, and combining them with corrosion potential and corrosion rate, the corrosion state of the grounding grid can be judged more accurately, and the safety and service life of the substation grounding grid can be evaluated more effectively, thereby providing technical support for power operation and maintenance personnel to take more scientific and reasonable maintenance measures. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] FIG1 is a schematic diagram of a flow chart of an embodiment provided by the present invention;

[0036] Figure 2 is a schematic diagram of the potential-pH value of carbon steel in a water system. DETAILED DESCRIPTION

[0037] The features of the present invention and other related features are further described in detail below through embodiments in conjunction with the accompanying drawings to facilitate understanding by those skilled in the art:

[0038] Example: As shown in FIG1 , the method for monitoring and evaluating the corrosion state of the grounding grid in this embodiment includes the following steps:

[0039] S100: Obtain the soil resistivity of the grounding grid area.

[0040] S200: Obtaining the pH value of the soil environment in the grounding grid area.

[0041] S300: Obtaining soil Cl ion concentration in the grounding grid area.

[0042] S400: Obtaining the corrosion potential of the grounding grid area.

[0043] S500: Obtain the corrosion rate of the grounding grid area.

[0044] S600: Determine the corrosion status of the grounding grid based on soil resistivity, soil pH value, soil Cl ion concentration, corrosion potential and corrosion rate.

[0045] In step S100, soil resistivity is calculated by measuring the resistance of the soil. A resistance sensor can be installed in the soil at the grounding grid to obtain the soil resistance. Considering the following characteristics, the soil surrounding the grounding grid has: first, it is multiphase, primarily composed of soil particles, water, and air, with a complex multiphase structure. Second, it has capillary porosity, a corrosive electrolyte. Third, it is heterogeneous; the various physical and chemical properties of the soil, particularly the electrochemical properties related to corrosion, are unevenly distributed. Finally, it has relative stability. These properties determine the corrosion behavior of metals in the soil.

[0046] Soil resistivity reflects the conductivity of the soil medium and is an important indicator of soil corrosivity. It is also a comprehensive factor affecting soil corrosion. Soil salt content, moisture content, and temperature all affect soil resistivity. Generally, soil with low resistivity is more corrosive. Therefore, using soil resistivity to determine soil corrosivity, and therefore the corrosion status of the grounding grid, can improve accuracy.

[0047] The calculation formula for soil resistivity is: Where ρ is the soil resistivity (in Ω·cm), is the measured soil resistance (in Ω), R is the distance between the resistor electrodes (in cm), and L is the cross-sectional area of ​​the resistor electrodes (in cm). 2 ).

[0048] Usually when designing and manufacturing a multifunctional electrochemical corrosion probe, L and S are fixed values. For example, for a cylindrical grounding electrode of a traction substation grounding grid, the resistance electrode spacing L is set to 2 cm, and the resistance electrode diameter d is set to 0.6 cm, that is, the cross-sectional area is cm. 2 .

[0049] In step S200, the soil pH is calculated by measuring the soil's open-circuit potential. A pH open-circuit potential sensor can be installed in the soil at the grounding grid to measure the soil's open-circuit potential. Given that the grounding grid is buried in the soil, the surface contacts different soil physical and chemical properties, resulting in differences in electrode potential. This difference is one of the causes of grounding grid corrosion. Soil media exhibit varying pH levels due to varying moisture, oxygen, and salt content. Soils with a pH of 6.5-7.5 are generally classified as neutral. Most soils are neutral, but some alkaline sandy clays and saline-alkali soils have pH values ​​between 7.5-9.5, while others are acidic humus soils and marsh soils with pH values ​​between 3.0-6.0. Various metal materials exhibit the least corrosion in neutral soils. The electrochemical corrosion reaction of the grounding grid consists of at least one anodic reaction and one cathodic reaction. Generally, in acidic soils, the cathodic process is the dominant corrosion step, primarily controlled by oxygen diffusion.

[0050] The calculation formula for the pH value of the soil environment is: Among them, η pH is the pH value of the soil environment, u pH is the pH open circuit potential value measured by the electrochemical corrosion probe (in mV); b pH is the intercept corresponding to the soil pH value, k pH is the slope corresponding to the soil pH value.

[0051] The slope kpH and intercept b pH The pH value of the solution is measured and calibrated by using standard solutions of different pH values ​​at the factory. The specific operation is as follows: first, prepare standard solutions of different pH values, then use a pH meter to measure the pH value of the solution, and use a grounding grid electrochemical corrosion probe to measure the corresponding potential value u at this time. pH (mV). In general, it is necessary to measure the pH value η of at least two or more different standard solutions. pH and potential value u pH (mV), thereby obtaining the corresponding slope k pH and intercept b pH The parameter value is finally substituted into the above calculation formula to achieve the potential value u measured by the electrochemical corrosion probe pH Calculate the corresponding pH value η pH .

[0052] The pH value is an indicator of soil acidity and alkalinity, reflecting the salt content of the soil. Generally speaking, acidic soils are more corrosive, and the lower the pH value, the more corrosive it is. Metals corrode less in neutral and alkaline soils. However, when soil contains a large amount of organic acids, even though the pH value is close to neutral, it can still be highly corrosive.

[0053] The potential-pH relationship diagram for general metal materials in aqueous solutions is shown in Figure 2 (using carbon steel as an example). Figure 2(a) shows the relationship diagram without chloride ions, and Figure 2(b) shows the relationship diagram with chloride ions. As Figure 2 shows, maintaining the soil's high alkalinity and protecting it from chloride ion attack as much as possible, ensuring that carbon steel remains in the passivation zone or corrosion-free zone, is the fundamental guarantee for protecting it from corrosion. Maximizing the protective layer's ability to resist carbonization and penetration of aggressive media over a long period of time, while leveraging the concrete cover's inherent protective function, are the primary measures for preventing carbon steel corrosion.

[0054] At normal temperatures in nature, the pH value of water is generally between 4.3 and 10.0. In such aqueous solutions, a Fe(OH)2 film often forms on the surface of carbon steel. At this point, the corrosion rate of carbon steel is primarily determined by the diffusion rate of oxygen and is almost unrelated to pH. Between pH values ​​of 4 and 10, the corrosion rate remains almost constant. When the pH is above 10, the iron surface is passivated, and the corrosion rate continues to decrease. When the pH drops below 4.0, the protective film on the iron surface dissolves, the H+ concentration in the water increases, and hydrogen evolution occurs, causing the corrosion rate to increase dramatically.

[0055] In step S300, the soil Cl ion concentration is calculated by measuring the soil Cl ion open circuit potential. A Cl ion open circuit potential sensor can be installed in the soil at the grounding grid to obtain the soil Cl ion open circuit potential.

[0056] The calculation formula for Cl chloride ion concentration is: Among them, η Cl is the Cl ion concentration in the soil environment (in mol / L), u Cl b is the open circuit potential of Cl ions measured by the electrochemical corrosion probe (in mV); Cl is the intercept corresponding to Cl ions in the soil environment, k Cl is the slope corresponding to the Cl ion concentration in the soil environment.

[0057] The slope k Cl and intercept b Cl The chloride ion concentration is measured and calibrated by using standard solutions with different chloride ion concentrations at the factory. The specific operation is as follows: first, prepare standard solutions with different chloride ion concentrations, then use a chloride ion analyzer to measure the chloride ion concentration of the solution, and use a grounding grid electrochemical corrosion probe to measure the corresponding potential value u at this time. Cl (mV). In general, it is necessary to measure the chloride ion concentration and potential value u of at least two or more different standard solutions. Cl (mV), thereby obtaining the corresponding slope k Cl and intercept b Cl The parameter value is finally substituted into the above calculation formula to achieve the potential value u measured by the electrochemical corrosion probe Cl Convert the corresponding Cl ion concentration value η Cl .

[0058] The intrusion of chlorides is one of the important reasons for the corrosion of grounding electrodes in grounding grids. Chloride ions can destroy the passivation film on the surface of the grounding electrode and cause local corrosion of the grounding electrode, which has a catalytic effect on the corrosion process. Chloride ions are extremely strong depassivating agents. It is generally believed that in heterogeneous concrete, chloride ions can destroy the passivation film on the surface of metal materials and cause local corrosion of the metal. Iron corrodes in the anode area to generate iron ions. When chloride ions exist in the metal interface environment, under the action of the electric field generated by the corrosion cell, chloride ions continue to migrate to the anode area and enrich. Fe 2+ and Cl - The generated FeCl2 is soluble in water and then diffuses out of the anode area and reacts with the OH in the bulk solution or the cathode area. - The generated Fe(OH)2, commonly known as "brown rust", quickly transforms into other forms of rust, such as Fe(OH)3, when it encounters water and oxygen in the pore fluid. After FeCl2 generates Fe(OH)2, it also releases Cl - , "new" Cl - Under the electric field of the corrosion cell, it migrates to the anode area, bringing out more Fe 2+ .Cl -It does not constitute a corrosion product and is not consumed in the corrosion process. It catalyzes the corrosion repeatedly. - It plays an anode depolarization role in the corrosion of metal grounding electrodes, accelerates the anode reaction of the grounding electrodes, and promotes local corrosion of the grounding electrode metal.

[0059] Chloride ions corrode metal materials. They participate in the metal corrosion process, destroying the passivation film on the metal surface and accelerating the corrosion rate. Chloride ions have a destructive effect on metal materials in the soil structure, primarily corroding the metal. Chloride ions corrode the metal surface, reducing its strength. Chloride ion corrosion of grounding electrodes causes premature aging of the grounding grid, leading to premature instability and increased safety risks. In environments with high chloride ion concentrations, grounding electrode corrosion can damage the grounding grid structure, preventing it from maintaining its required safety and stability. When chloride ions damage the grounding grid structure, they compromise its durability and undermine its safe use. The impact of chloride ions on grounding grid durability is a significant issue, impacting its service life and causing premature aging, posing a safety hazard.

[0060] Further, according to the measured soil environment pH value η pH and Cl ion concentration η C l, first calculate the hydroxide ion concentration σ, then calculate the Cl chloride ion concentration η Cl The ratio λ to the hydroxide ion concentration σ. The hydroxide ion concentration is calculated as The unit is mol / L, then the corresponding ratio

[0061] In step S500, the corrosion rate is calculated by measuring the corrosion current of the grounding electrode of the grounding grid. The calculation formula is: Where V is the corrosion rate of the grounding electrode of the grounding grid (mm / a), i corr is the grounding electrode corrosion current density (mA / cm 2 ), A is the atomic weight of the grounding electrode material, n is the number of electrons gained or lost by the grounding electrode material, is the density of the grounding electrode material (g / cm 3 For example, when the grounding electrode is made of carbon steel, its corresponding density is About 7.85g / cm 3 Assuming that the number of electrons lost is 2, the main material is iron Fe, and the atomic weight A is about 56, the corrosion rate is 1mm / a≈85.736mA / cm 2Corrosion current density. For example, when the grounding electrode is made of pure copper, its corresponding density is About 8.96g / cm 3 Assuming that the number of electrons lost n is 2 and the atomic weight A is about 63.546, the corrosion rate is 1mm / a≈86.239mA / cm 2 Corrosion current density.

[0062] In step S600, the step of determining the corrosion state of the grounding grid includes:

[0063] When E is greater than or equal to 2.7, the grounding grid is judged to be in an unavailable state;

[0064] When E is greater than 1.5 and less than 2.7, the grounding grid is judged to be in a usable state;

[0065] When E is less than or equal to 1.5, the grounding grid is judged to be in normal state;

[0066] E=40%A+30%B+10%C+20%D;

[0067] Among them, A is the score corresponding to the currently measured corrosion potential, B is the score corresponding to the currently measured corrosion rate, C is the score corresponding to the currently measured soil resistivity, and D is the score corresponding to the ratio of the currently measured Cl chloride ion concentration to the hydroxide ion concentration.

[0068] Among them, corrosion potential is the potential of metal materials measured under specific environmental conditions in the absence of external current. It is a key indicator to characterize the corrosion state of metal materials and can be used to evaluate the corrosion tendency of metal materials in soil. The more negative the corrosion potential, the greater the tendency of metal materials to corrode.

[0069] The corrosion rate characterizes the speed of metal corrosion in soil. Online monitoring devices for grounding grid corrosion primarily measure the reduction in metal thickness per unit time. The corrosion rate is a key indicator for assessing metal corrosion, as it can be used to assess the level of corrosion occurring in metals and the age at which component protective layers become damaged.

[0070] Soil resistivity reflects the conductivity of the soil medium and is an important indicator of soil corrosivity. It is also a comprehensive factor affecting soil corrosion. Factors such as soil salt content, moisture content, and temperature all affect soil resistivity. Generally, soil with low resistivity is more corrosive. Therefore, using soil resistivity to determine the soil's corrosive conductivity and, in turn, the corrosion status of the grounding grid, can improve the accuracy of metal corrosion assessments.

[0071] The ratio between Cl ion concentration and hydroxide ion concentration is a comprehensive indicator that takes into account the effects of Cl ion concentration and soil pH on the corrosion of metal materials. Among them: (1) pH value is an indicator of the acidity and alkalinity of the soil and is a comprehensive reflection of the salt content in the soil. Generally speaking, acidic soils are more corrosive, and the lower the soil pH value, the stronger its corrosiveness. Metal materials are generally less corrosive in neutral and alkaline soils; (2) The intrusion of chlorides is one of the important reasons for the corrosion of grounding electrodes in grounding grids. Chloride ions can destroy the passivation film on the surface of the grounding electrode and cause local corrosion of the grounding electrode, which has a catalytic effect on the corrosion process. Chloride ions are extremely strong depassivating agents. It is generally believed that in heterogeneous soils, chloride ions can destroy the passivation film on the surface of metal materials, causing local corrosion of the metal. Therefore, based on the measured soil pH value and chloride ion concentration, the ratio of chloride ion concentration to hydroxide ion concentration is calculated, which can be used to comprehensively evaluate the corrosion risk of metal materials in the soil. If the pH value in the soil is lower and the chloride ion concentration is higher, the risk of corrosion of the metal material is greater. The dynamic change trend of the ratio of chloride ion concentration to hydroxide ion concentration can also be tracked and monitored to determine the corrosion development trend and corrosion risk.

[0072] The weights of A, B, C, and D are determined based on the influence of the measured parameters and the corrosion of the grounding grid, and are also determined based on engineering experience for the convenience of calculation.

[0073] The grounding grid is in normal condition, which means that the surface of the grounding electrode of the grounding grid can remain blunt, no corrosion occurs, and the corrosion resistance is good. The probability of no corrosion is greater than 90%, and it can be used normally.

[0074] The grounding grid is in a usable state, which means that the corrosion resistance of the grounding electrode of the grounding grid is general, and the probability of corrosion is about 50%, or corrosion may occur, but the corrosion rate is low. The grounding grid grounding electrode is still usable and only needs to be paid attention to.

[0075] The unusable state of the grounding grid indicates that the surface of the grounding electrode of the grounding grid has become dull, the probability of corrosion is greater than 90%, the corrosion rate is increased, the corrosion resistance is poor, and the grounding electrode is no longer usable. If necessary, cathodic protection, maintenance and replacement or other measures must be taken.

[0076] The scoring standards for A, B, C, and D are as follows:

[0077] For example, when the corrosion potential of a grounding electrode of a grounding grid in such a soil environment is maintained at -700mV to -800mV (vs. MnO2), the corrosion rate is maintained at 0.05mm / a, the soil resistivity is approximately 85kΩ·cm, the Cl chloride ion concentration is approximately 3.256×10-7mol / L, and the pH value is approximately 8.3. According to the grounding grid corrosion status evaluation method involved in this embodiment, the corresponding A score is 2, B score is 1, C score is 2, the ratio of Cl chloride ion concentration to hydroxide ion concentration is 0.1604, and the corresponding D score is 1. The total grounding grid corrosion status evaluation score E = 2×40% + 1×30% + 2×10% + 1×20% = 1.5. Therefore, according to the above evaluation rules, the surface of the grounding electrode of the grounding grid can maintain a passive state and is in a relatively stable passivation state, with a low corrosion rate and good corrosion resistance. The probability of no corrosion is greater than 90%, indicating that the grounding electrode of the grounding grid is currently in normal use.

[0078] The effectiveness and accuracy of the monitoring and evaluation method in this embodiment are demonstrated through simulation experiments, as follows:

[0079] 1. Experimental environment construction:

[0080] A test specimen simulating a metal grounding electrode in a grounding grid was constructed in the laboratory. The electrochemical monitoring sensor, part of the on-line monitoring device for the corrosion status of the grounding grid, was then buried along with the test specimen in the soil environment of the simulated grounding grid site.

[0081] During this process, an online monitoring device for grounding grid corrosion status simultaneously monitors soil resistivity, soil pH, soil Cl ion concentration, and the corrosion potential and corrosion rate of the metal grounding electrode. This is used to determine the actual corrosion state of the metal grounding electrode in the simulated grounding grid. During the experiment, a 3.5% NaCl solution is added to the soil as needed to maintain moisture and accelerate the corrosion of the test specimens.

[0082] 2. Experimental results and data evaluation and analysis:

[0083] Based on the experimental environment built in step 1, a simulation test of the corrosion state of the metal grounding electrode of the grounding grid was carried out. The specific test results are compared as follows:

[0084] (1) Initial state:

[0085] About three days after the laboratory was set up, the corrosion potential and corrosion rate of the metal grounding electrode as well as the soil resistivity, soil pH value, and soil Cl ion concentration parameters were measured using an online monitoring device for the corrosion status of the grounding grid. The typical data are shown in the following table:

[0086] According to the monitoring and evaluation method in this embodiment, according to the final evaluation score E=40%A+30%B+10%C+20%D=40%*1+30%*1+10%*1+20%*1=1<1.5 of the judgment expression for the corrosion state of the grounding grid, it is judged that the surface of the grounding electrode of the grounding grid can remain passive and is in a relatively stable passivation state, with a low corrosion rate and good corrosion resistance. The probability of no corrosion is greater than 90%, that is, the grounding electrode of the grounding grid is currently in normal use. After physical inspection, it is consistent with the actual object in the photo of the grounding electrode of the simulated grounding grid just buried in the soil at this time.

[0087] (2) Three months later:

[0088] The above experiment was continued, and during the experiment, a 3.5% NaCl solution was added to the soil regularly (about every 15 days) as needed to keep the soil moist and thus accelerate the corrosion progress of the test sample. After the third month, the corrosion potential and corrosion rate of the metal grounding electrode were measured by the online monitoring device for the corrosion status of the grounding grid, as well as the soil resistivity, soil environment pH value, and soil Cl ion concentration parameters at this time. The following table shows typical data:

[0089] According to the monitoring and evaluation method of this embodiment, the final evaluation score E = 1.6, based on the judgment expression for the grounding grid corrosion state, is greater than 1.5 and less than 2.7. This indicates that the corrosion resistance of the grounding electrodes in this grounding grid is average, with a probability of corrosion of approximately 50%. Alternatively, corrosion may occur, but at a low rate, and the grounding electrodes in the grounding grid are still usable. Inspection of the simulated grounding grid grounding electrodes in the soil at this point indicates that the metal of the grounding electrodes has corroded, consistent with the aforementioned evaluation results.

[0090] (3) Twelve months later:

[0091] The above experiment was continued, and during the experiment, a 3.5% NaCl solution was added to the soil regularly (about every 10 days) as needed to keep the soil moist and thus accelerate the corrosion progress of the test sample. After the 12th month, the corrosion potential and corrosion rate of the metal grounding electrode were measured by the online monitoring device for the corrosion status of the grounding grid, as well as the soil resistivity, soil environment pH value, and soil Cl ion concentration parameters at this time. The specific typical data are shown in the following table:

[0092] According to the monitoring and evaluation method of this embodiment, the final evaluation score E = 2.7 based on the judgment expression for the grounding grid corrosion state indicates that the grounding electrode surface of this grounding grid has become dull, with a probability of corrosion exceeding 90%. The corrosion rate has significantly increased, and the corrosion resistance has deteriorated. Inspection of the simulated grounding grid grounding electrode in the soil at this time showed that the grounding electrode metal had obvious corrosion rust, consistent with the aforementioned evaluation results.

[0093] In summary, the present embodiment provides a method for monitoring and evaluating the corrosion status of a grounding grid. By accurately measuring the pH value of the soil environment and combining parameters such as the chloride ion concentration, soil resistivity, corrosion potential, and corrosion rate of the grounding electrode in the soil environment, it is possible to achieve comprehensive, accurate, and effective corrosion monitoring of the grounding electrode structure of the grounding grid, thereby more effectively evaluating the safety and service life of the substation grounding grid operation, thereby providing technical support for power operation and maintenance personnel to take more scientific and reasonable maintenance measures.

[0094] Although the above embodiments have described in detail the concepts and embodiments of the present invention with reference to the accompanying drawings, ordinary technicians in this field can recognize that various improvements and modifications can still be made to the present invention without departing from the scope of the claims, so they are not described in detail here.

Claims

1. A method for monitoring and evaluating the corrosion state of a grounding grid, characterized in that: It includes the following steps: Obtain the soil resistivity, soil environmental pH value, soil Cl ion concentration, corrosion potential and corrosion rate of the grounding grid area; Establish a judgment expression for the corrosion state of the grounding grid regarding the soil resistivity, the soil environmental pH value, the soil chloride ion concentration, the corrosion potential and the corrosion rate. The expression is as follows: E = 40%A + 30%B + 10%C + 20%D; In the formula, E is the grounding grid corrosion state parameter used to characterize the state of the grounding grid, which is divided into an unavailable state, an available state and a normal state; A is the score value corresponding to the corrosion potential; B is the score value corresponding to the corrosion rate; C is the score value corresponding to the soil resistivity; D is the score value corresponding to the ratio between the soil chloride ion concentration and the hydroxide ion concentration calculated by combining the soil environmental pH value; Calculate the value of E according to the expression and judge the corrosion state of the grounding grid based on the value of E.

2. The monitoring and evaluation method for the corrosion state of a grounding grid according to claim 1, characterized in that: The judgment of the grounding grid corrosion state parameter E is as follows: When E is greater than or equal to 2.7, it is judged that the grounding grid is in an unavailable state; When E is greater than 1.5 and less than 2.7, it is judged that the grounding grid is in an available state; When E is less than or equal to 1.5, it is judged that the grounding grid is in a normal state.

3. The monitoring and evaluation method for the corrosion state of a grounding grid according to claim 1, characterized in that: The value-taking standards of each score value include: When the corrosion potential is greater than -500 mV, A = 1; when the corrosion potential is between -500 mV and -850 mV, A = 2; when the corrosion potential is less than -850 mV, A = 3; When the corrosion rate is less than 0.1 mm / a, B = 1; when the corrosion rate is between 0.1 mm / a and 1 mm / a, B = 2; when the corrosion rate is greater than 1 mm / a, B = 3; When the soil resistivity is greater than 100 kΩ·cm, C = 1; when the soil resistivity is between 50 kΩ·cm and 100 kΩ·cm, C = 2; when the soil resistivity is between 10 kΩ·cm and 50 kΩ·cm, C = 3; when the soil resistivity is less than 10 kΩ·cm, C = 4; When the ratio between the soil chloride ion concentration and the hydroxide ion concentration is less than 0.6, D = 1; when the ratio between the soil chloride ion concentration and the hydroxide ion concentration is greater than 0.6, D = 2.

4. The monitoring and evaluation method for the corrosion state of a grounding grid according to claim 1, wherein: The soil resistivity is calculated by measuring the soil resistance within the area of the grounding grid, and the calculation formula is: In the formula, ρ is the soil resistivity, R is the measured soil resistance, L is the distance between the resistance electrodes, and S is the cross-sectional area of the resistance electrodes.

5. The monitoring and evaluation method for the corrosion state of a grounding grid according to claim 1, characterized in that: The pH value of the soil environment is calculated by measuring the open-circuit potential of the pH of the soil within the earthing grid area, and the calculation formula is: Where η pH is the pH value of the soil environment, u pH is the open-circuit potential value of pH measured by the electrochemical corrosion probe, b pH is the intercept corresponding to the pH value of the soil environment, k pH is the slope corresponding to the pH value of the soil environment.

6. The monitoring and evaluation method for the corrosion state of a grounding grid according to claim 1, characterized in that: The soil chloride ion concentration is calculated by measuring the open-circuit potential of Cl ions in the soil within the earthing grid area, and the calculation formula is as follows: In the formula, η Cl is the Cl chloride ion concentration value of the soil environment, u Cl is the open circuit potential value of Cl chloride ions measured by the electrochemical corrosion probe, b Cl is the intercept corresponding to Cl chloride ions in the soil environment, k Cl is the slope corresponding to the Cl chloride ion concentration in the soil environment.

7. A method for monitoring and evaluating the corrosion state of a grounding grid according to claim 1, characterized in that: Based on the measured soil environmental pH value η pH and the Cl chloride ion concentration η Cl , first calculate the hydroxide ion concentration σ, and then calculate the ratio λ between the Cl chloride ion concentration η Cl and the hydroxide ion concentration σ. Among them, the calculation formula for the hydroxide ion concentration is The corresponding ratio 8. A monitoring and evaluation method for the corrosion state of a grounding grid according to claim 1, characterized in that: The corrosion rate is calculated by measuring the corrosion current of the grounding electrodes of the grounding grid, and the calculation formula is: where V is the corrosion rate of the grounding electrode of the grounding grid, i corr is the corrosion current density of the grounding electrode, A is the atomic weight of the grounding electrode material, and n is the number of electrons gained or lost by the grounding electrode material It is the density of the grounding electrode material.