Grounding grid fault diagnosis method based on earth surface potential frequency response

Abstract

The invention relates to the technical field of grounding grid fault diagnosis, and discloses a grounding grid fault diagnosis method based on earth surface potential frequency response, which comprises the following steps: S1, constructing a layered soil model, and correcting self-resistance and mutual resistance parameters of a conductor; constructing an admittance matrix containing multiple types of conductors based on the influence of self resistance, mutual resistance and leakage resistance of the conductors; s2, establishing a transient current model, and solving earth surface potential through frequency domain conversion; s3, simulating surface potential distribution in a fault-free state and a fault state, and extracting the characteristic change of the surface potential during the fault; s4, quantifying a fault characteristic value through a Manhattan distance function; the amplitude and frequency of the excitation current are optimized to amplify a fault characteristic value; and S5, diagnosing the fault type, position and degree of the grounding grid based on the characteristic value difference. According to the invention, the feature recognition precision under the uneven soil or complex grounding grid structure is effectively improved, the grounding grid fault diagnosis effect is enhanced, and the fault type, position and degree are accurately determined.

Description

Technical Field

[0001] This invention relates to the field of grounding grid fault diagnosis technology, and more specifically to a grounding grid fault diagnosis method based on the frequency response of ground surface potential. Background Technology

[0002] Grounding grids play an indispensable role in many critical sectors such as construction, communications, and power. When ground equipment is struck by lightning or a system malfunctions, high voltage can easily be generated, which not only interferes with the normal operation of the equipment but also poses a serious threat to social property safety and public safety. Currently, the grounding materials used in domestic grounding grids are mostly steel. Although this material has the advantages of high strength, high hardness, and lower cost than copper, it performs poorly in terms of conductivity, corrosion resistance, and oxidation resistance. Under the influence of external environmental factors, the grounding grid is prone to corrosion and even breakage, leading to a decline in its performance, causing power system failures, and ultimately affecting the stable power supply of the power grid.

[0003] To address the aforementioned issues, various grounding grid fault detection and diagnosis technologies have been developed. One technology uses the high-current method to study the impact of detection current frequency and lead wiring on the detection results, thus solving the problem of interference current in the grounding grid to some extent. However, this technology suffers from significant drawbacks, including high workload and construction difficulty, making it difficult to meet the practical needs of efficient detection. Another technology utilizes the potential and magnetic field characteristics of the grounding grid to achieve fault diagnosis and type identification in substation grounding grids, providing a new approach to fault investigation. Yet another technology analyzes the magnetic field distribution on the surface of large grounding grids by diagnosing magnetic induction intensity, and determines the breakpoint fault and specific location of the grounding grid conductor based on the characteristics and laws of the magnetic field distribution. However, in practical applications, the magnetic field environment around substations is extremely complex, severely affecting the accuracy of the diagnostic results of this technology. Furthermore, some technologies combine electrical network theory with specific algorithms to diagnose corroded conductor sections. However, in the theoretical model construction process, resistance is simply treated as pure resistance, without fully considering the self-inductance and mutual inductance between conductors, leading to deviations between the diagnostic results and the actual situation, making it difficult to accurately reflect the true fault state of the grounding grid.

[0004] The shortcomings of these existing technologies mean that the detection and diagnosis of grounding grid faults are always inefficient and inaccurate, making it impossible to detect potential hazards in the grounding grid in a timely and reliable manner, and thus making it difficult to effectively avoid a series of safety accidents and economic losses caused by grounding grid faults. Summary of the Invention

[0005] The present invention aims to provide a grounding grid fault diagnosis method based on the frequency response of the ground surface potential, so as to solve the problems of low efficiency and insufficient accuracy of existing grounding grid fault diagnosis methods.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: a grounding grid fault diagnosis method based on surface potential frequency response, comprising the following steps: S1. Construct a layered soil model and correct the conductor self-resistance and mutual resistance parameters; based on the influence of conductor self-resistance, mutual resistance and leakage resistance, obtain the relationship between voltage equation and leakage current, and construct an admittance matrix that includes multiple types of conductors; S2. Establish a lightning / short-circuit transient current model, solve for the ground potential through frequency domain transformation, and analyze the transient response; S3, Simulate the surface potential distribution under fault-free and fault conditions, compare and analyze the potential differences, and extract the characteristic changes of surface potential during faults; the fault conditions include fracture and corrosion. S4, quantifies fault characteristic values ​​using the Manhattan distance function; and optimizes the amplitude and frequency of the excitation current to amplify the fault characteristic values; the fault characteristic values ​​include corrosion characteristic values. and fracture characteristic values ; S5, based on eigenvalue differences, diagnoses the type, location, and extent of grounding grid faults.

[0007] The principles and advantages of this scheme are: This scheme is based on the voltage-current relationship of the grounding grid and the distribution of leakage current-surface potential. It constructs a layered soil model to correct conductor self-resistance and mutual resistance, forming a multi-type conductor admittance matrix that includes inductance parameters, adapting to non-uniform soil and complex grounding grid structures. Simultaneously, a lightning / short-circuit transient current model is established, and the surface potential is solved via frequency domain transformation, covering transient response analysis under extreme conditions. Through simulation comparison of fault and fault-free potential distributions, features are extracted and quantified using Manhattan distance. Furthermore, the fault features are amplified by optimizing the excitation current amplitude and frequency. Finally, the fault type, location, and severity are diagnosed based on the differences in feature values.

[0008] Existing technologies often assume uniform soil and neglect inductance, making them only suitable for simple mesh structures. This solution, through layered soil correction and an inductance-incorporated admittance matrix, adapts to non-uniform geology and complex topologies, effectively improving diagnostic accuracy. Furthermore, existing technologies focus on steady-state analysis and lack transient capabilities. This solution, through lightning / short-circuit transient response analysis, significantly shortens the response time and covers extreme fault scenarios. In addition, this solution, through simulation comparison and Manhattan distance quantization, balances current dissipation safety, amplifying fault characteristics while avoiding equipment damage, significantly enhancing fault characteristic identification and accurately distinguishing between fracture and corrosion degrees. Attached Figure Description

[0009] Figure 1 This is a flowchart illustrating the grounding grid fault diagnosis method based on the surface potential frequency response of the present invention. Figure 2This is a pre-defined equivalent circuit model of the grounding grid for the grounding grid fault diagnosis method based on the surface potential frequency response of the present invention. Figure 3 This is a preset grounding grid simulation calculation model for the grounding grid fault diagnosis method based on surface potential frequency response of the present invention; Figure 4 This is a comparison diagram of the surface potential distribution of a grounding grid in normal and fault states, based on the ground potential frequency response-based grounding grid fault diagnosis method of the present invention. Detailed Implementation

[0010] The following detailed description illustrates the specific implementation method: The grounding grid fault diagnosis method based on the surface potential frequency response in this embodiment quantitatively analyzes the grounding fault characteristics through the Manhattan distance function, considers the frequency characteristics of the conductor under the corresponding conditions, and amplifies the fault characteristic value by optimizing the excitation current, making the fault situation of the grounding grid more intuitive and further enhancing the diagnostic effect of grounding grid faults.

[0011] A grounding grid fault diagnosis method based on the surface potential frequency response is provided, as shown in the attached figure. Figure 1 As shown, it includes the following steps: S1. Construct a layered soil model and correct the conductor self-resistance and mutual resistance parameters. Based on the influence of conductor self-resistance, mutual resistance and leakage resistance, obtain the relationship between voltage equation and leakage current, construct an admittance matrix containing multiple types of conductors, and form an equivalent circuit model of the grounding grid.

[0012] In this embodiment, it is first assumed that the grounding grid has n branches and m nodes. For the U-shaped structure, the current... Input to the entire grounding grid system, as shown in the attached... Figure 2 As shown. Therefore, in this model, Indicates the end node of the conductor. This indicates the leakage current flowing into the soil. This indicates the center node of the conductor.

[0013] Since the grounding conductor is not a perfect conductor and has a certain resistance, a potential difference will be generated as the grounding grid current dissipates to the ground along the conductor. Assuming the leakage current flows to the ground from the center node of the conductor, and the axial impedance is twice the end impedance, current dissipation will cause changes in the voltage across all conductor surfaces. Therefore, the total voltage on the j-th conductor segment is: (1); In the formula, Mutual resistance; Let i be the leakage current flowing into the soil at point i; Let the resistance be . Then, using the Green's function of the point current source and applying the Dirac function as the solution coefficients, the relationship between the leakage current and the center potential can be obtained: (2); In the formula, , This refers to the leakage current of the conductor. It is an n×n matrix, namely the internal resistance to ground and the mutual resistance to ground.

[0014] The soil is divided into n layers, each assigned a different resistivity. and thickness A layered soil structure model was established. The self-resistance of conductors in the layered soil was calculated using the method of images. and mutual resistance To correct the resistance parameters under the original assumption of homogeneous soil, the self-resistance of stratified soil is expressed as: (3); In the formula, The resistivity of the surface soil; The conductor length; The radius of the conductor; For conductor burial depth; Let n be the soil resistivity of the k-th layer; n is the number of soil layers. Let be the thickness of the k-th soil layer.

[0015] The mutual resistance is derived based on the method of images.

[0016] Based on the relationship between the obtained voltage equation and the leakage current, the node voltage equation is established: (4); in, The node potential vector; The vector is the injected current; the admittance matrix Y contains the conductor's self-resistance, mutual resistance, and inductance parameters, replacing the assumed resistance parameters with complex admittance.

[0017] In this embodiment, the admittance matrix elements for multiple types of conductors are represented as follows: (5); In the formula, The resistance of the conductor between nodes i and j; The imaginary unit; The angular frequency of the excitation current; Let the mutual inductance between the conductors at nodes i and j be considered. Based on the corrected resistance matrix, the nodal voltage equations are re-derived to solve for the surface potential distribution under non-uniform soil.

[0018] A graph theory approach is used to describe topological relationships, and an admittance matrix containing multiple types of conductors is constructed. For complex structures such as ring and radial structures, the admittance matrix Y describes the connection relationship between nodes, constructs a topological matrix, solves the node voltage V, and forms an equivalent circuit model of grounding grids with various structural types. This covers a variety of common grounding grid structures and meets various grounding grid fault diagnosis needs.

[0019] S2. Establish a lightning / short-circuit transient current model, solve for the ground potential through frequency domain transformation, and analyze the transient response.

[0020] In this embodiment, a double exponential function is used to describe the lightning impulse current, and a transient current excitation model is established, expressed as follows: (6); By converting the transient surface potential to frequency domain components using Fourier transform and combining it with the frequency domain impedance of the grounding grid, the transient surface potential can be expressed as follows: (7); In the formula, This represents the peak value of the transient current. The attenuation coefficient is 1; The attenuation coefficient is 2; The transient current frequency domain component; This represents the frequency domain impedance of the grounding grid. The system calculates the surface potential at different times, extracts transient characteristics such as peak value and rising edge, and enables accurate diagnosis of transient faults such as lightning strikes and short circuits, thereby improving response time.

[0021] S3 simulates the surface potential distribution under fault-free and fault conditions, compares and analyzes the potential differences, and extracts the characteristic changes in surface potential during faults; fault conditions include fracture and corrosion.

[0022] In this embodiment, as shown in the appendix Figure 3 As shown, assuming the grounding grid has 6x6 mesh openings, a conductor length of 10m, a burial depth of h=0.8m, and uses 50mmx5mm flat steel with a resistivity of 1.7x10⁻⁶... 7 An excitation current with an amplitude of 20A and a frequency of 60Hz is injected into node 24 to simulate the changes in ground potential when it is faulty and without faults.

[0023] Assume the grounding grid has the following fault within conductor X=0-60m at Y=20: (1) A 0.2m break appears at the conductor segment (14.4, 14.6).

[0024] (2) Corrosion occurred in the conductor segment within the (20,30) region, and its radius changed from 9 mm to 4.5 mm.

[0025] (3) There is a 0.1m break in the conductor segment (46.5, 46.6).

[0026] Then as attached Figure 4 As shown, when a grounding grid fault occurs, the surface potential of the grounding grid decreases significantly. The current flowing into the soil from the conductor during a break, and the reduction in the conductor's cross-sectional area during corrosion, can both be equivalent to an increase in conductor resistance, thus affecting the leakage current performance at that location and leading to a decrease in leakage current, thereby lowering the surface potential. Therefore, changes in surface potential can serve as an effective basis for judging grounding grid faults. Fault characteristics can be extracted by comparing the differences.

[0027] S4, quantifies fault characteristic values ​​using the Manhattan distance function; and optimizes the amplitude and frequency of the excitation current to amplify the fault characteristic values; the fault characteristic values ​​include corrosion characteristic values. and fracture characteristic values .

[0028] The voltage change at the ground surface potential nodes above the grounding grid conductor is used as a characteristic information of the fault. The Manhattan distance function is used to define fault characteristic values, transforming discrete potential changes into quantifiable characteristic values ​​to distinguish between corrosion and fracture fault modes. Among these, the corrosion characteristic value... The cumulative effect of potential changes at both ends of the conductor segment under corrosion conditions; fracture characteristic value. The change in potential node voltage at the nearest endpoint to the break point when the conductor segment breaks; represented as follows: ; (8); In the formula, , These are the surface potential node voltage values ​​at the left and right ends of the corrosion fault in the fault-free grounding grid, respectively; , These are the surface potential node voltage values ​​at the left and right ends of the grounding grid after corrosion. This represents the surface potential node voltage value at this point when the grounding grid is intact. This represents the surface potential node voltage value at the nearest endpoint of the fault point in the grounding grid during a fault. This allows for the quantification of the fault characteristics in the grounding grid.

[0029] Based on this, the amplitude and frequency of the excitation current are increased according to the skin effect and the degree of current dissipation to amplify the fault characteristic values ​​and enhance the efficiency of fault diagnosis.

[0030] In this embodiment, the skin effect refers to the phenomenon where the current density reaches its maximum at the surface of the grounding conductor as it passes through the conductor, while the current gradually decreases inside the conductor. The skin effect concentrates the conductor current on the surface, reducing the effective conductive cross-sectional area. This leads to an increase in conductor resistance with increasing frequency, thereby altering the frequency domain impedance characteristics of the grounding grid, affecting the distribution pattern of the ground potential, and significantly increasing the non-uniformity of the current distribution. The skin effect is related to the current penetration depth. Negative correlation, represented as (9); In the formula, Resistivity; For frequency; is the magnetic permeability.

[0031] Appropriate use of the skin effect can enhance the potential difference signal at the fault location (fracture / corrosion) and optimize the excitation frequency to amplify the fault characteristic value. However, it is necessary to control the upper limit of the frequency to avoid excessive current dissipation due to the skin effect, thus ensuring equipment safety and diagnostic accuracy.

[0032] In this embodiment, when determining the skin effect under high-frequency excitation, the polarization and conductivity mechanisms within the soil change with frequency (i.e., "dispersion effect"), and the skin effect also alters the current penetration depth in the soil. At this point, the soil resistivity measured at DC / low frequency can no longer accurately reflect the actual equivalent resistivity at high frequencies and needs to be recalibrated based on the current candidate frequency. Therefore, in this embodiment, the correction value for soil resistivity is re-determined by considering the relationship between different frequencies and soil resistivity, thus correcting the soil resistivity to determine the injected current frequency. The soil resistivity correction formula is as follows: (10); In the formula, The frequency of the injected current; These are the conversion factors; This is a preset value for soil resistivity.

[0033] In this embodiment, when a high-frequency current is applied to the grounding grid, the resistivity of the grounding grid conductor increases significantly due to the skin effect; while the soil resistivity near the grounding grid conductor decreases due to the soil polarization effect. Based on the relationship between soil resistivity and frequency, a formula for calculating soil resistivity is fitted and expressed as follows: (11); Meanwhile, the soil resistivity was set to 100 Ω•m during power frequency current injection. Therefore, the soil resistivity conversion factor for power frequency injection at different injection frequencies was calculated, i.e., the conversion factor is: ; Then the soil resistivity correction formula (10) is obtained. When the frequency of the injected current is changed each time, the corresponding soil resistivity correction value is calculated according to formula (10) and then input into the calculation module to make up for the lack of soil resistivity change caused by soil polarization when applying high frequency excitation current.

[0034] Substituting the corrected soil resistivity into the skin effect formula (9), parameters such as current penetration depth and effective conductor resistance are calculated to determine whether the skin effect intensity meets the requirements. That is, the skin effect should be large enough to amplify fault characteristics (such as potential differences at fracture / corrosion sites), while avoiding excessive current runoff due to an overly strong skin effect. In this embodiment, based on the influence of the current runoff degree, the optimal injection current frequency that can effectively amplify fault characteristics while ensuring soil current runoff safety and diagnostic accuracy is selected. 3KHz is chosen as the frequency point for grounding grid fault diagnosis to amplify fault characteristic values.

[0035] S5, based on eigenvalue differences, diagnoses the type, location, and extent of grounding grid faults.

[0036] This embodiment includes the following fault determination process: S5.1 Determine whether the node potential characteristic value has changed; if it has changed, it is determined that a fault has occurred, and jump to S5.3; if it has not changed, jump to S5.2.

[0037] In this embodiment, based on the admittance matrix model corrected for layered soil, including correction for layered soil self-resistance / mutual resistance and complex structural topology connections, the corrected potential characteristic values ​​of each node under normal conditions are calculated. The potential characteristic values ​​of each node in the current grounding grid are measured, and the differences are analyzed with the reference values.

[0038] If the difference exceeds a preset threshold, i.e., the potential is significantly lower than the normal potential, it is judged as a suspected fault, and the process jumps to S5.3. If there is no difference, the process jumps to S5.2.

[0039] S5.2, appropriately increase the excitation current frequency, measure whether the characteristic value of the characteristic point potential changes, if it changes, jump to S5.3; if it does not change, it is determined that there is no fault and the diagnosis ends.

[0040] Based on current soil stratification parameters, dispersion effect correction is applied to soil resistivity at high frequencies. The corrected resistivity is then substituted into the skin effect formula to calculate current penetration depth and dispersion ratio, thus determining the upper limit of frequency adjustment.

[0041] The frequency is gradually increased from the reference frequency to candidate frequencies within the safety limit, such as from 60Hz to 3kHz. The corrected node potential characteristic value is calculated at each frequency level. If the difference in characteristic value at a certain frequency exceeds the threshold, the process jumps to S5.3; if there is no difference at all candidate frequencies, the process is determined to be fault-free, and the diagnosis ends.

[0042] S5.3, Identify the faulty segment and determine whether the difference between the two ends of the node is significantly different; if so, determine that it is in a fracture state and jump to S5.4; if not, determine that it is in a corrosion state and end the diagnosis.

[0043] In this embodiment, the conductor segment with the most significant change in potential characteristic value is located using the node connection relationship of the complex structure admittance matrix to determine the location of the fault segment. The corrected potential difference between the nodes at both ends of this segment is calculated and analyzed.

[0044] If the difference shows a steep abrupt change, it is determined to be a broken state, and the process jumps to S5.4.

[0045] If the difference shows a gradual change, it is determined to be a corrosion state. The degree of corrosion is quantified by combining the corrosion characteristic value (Formula 8) and the diagnosis ends.

[0046] S5.4, based on fracture characteristic values Determine the location of the fracture point.

[0047] In this embodiment, the fracture characteristic value is calculated according to equation (8). Input the corrected potential values ​​at both ends of the fracture segment. Analyze the potential values ​​of each sub-node within the fracture segment. Distribution gradient (near the break point) (Maximum value), combined with the node coordinates of the complex structural topology, to locate the break point.

[0048] It can also superimpose peak potential characteristics under lightning / short-circuit transient current excitation to further narrow down the range of the fault point. Output the specific coordinates of the fault point and end the diagnosis.

[0049] This embodiment integrates dynamic correction of dispersion effect of layered soil resistivity, calculation of current penetration depth and current dispersion ratio of skin effect, fault segment location of complex structure admittance matrix, quantification of corrosion / fracture characteristic value of Manhattan distance function, and supplementary analysis of transient response. It systematically solves the problems of large diagnostic errors, low fault feature identification, and insufficient diagnostic accuracy in traditional schemes under non-uniform soil or complex grounding grid structures, breaking through the limitation of single-condition adaptability of traditional schemes.

[0050] The above descriptions are merely embodiments of the present invention, and common knowledge such as specific technical solutions and / or characteristics are not described in detail here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the technical solutions of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A grounding grid fault diagnosis method based on surface potential frequency response, characterized in that, Includes the following steps: S1. Construct a layered soil model and correct the conductor self-resistance and mutual resistance parameters. Based on the influence of conductor self-resistance, mutual resistance and leakage resistance, obtain the relationship between voltage equation and leakage current, construct an admittance matrix containing multiple types of conductors, and form an equivalent circuit model of the grounding grid. S2. Establish a lightning / short-circuit transient current model, solve for the ground potential through frequency domain transformation, and analyze the transient response; S3 simulates the surface potential distribution under fault-free and fault conditions, compares and analyzes the potential differences, and extracts the characteristic changes of surface potential during faults. The fault states include fracture state and corrosion state; S4 quantifies fault characteristic values ​​using the Manhattan distance function; Furthermore, the amplitude and frequency of the excitation current are optimized to amplify the fault characteristic values; The fault characteristic values ​​include corrosion characteristic values. and fracture characteristic values ; S5, based on eigenvalue differences, diagnoses the type, location, and extent of grounding grid faults.

2. The grounding grid fault diagnosis method based on surface potential frequency response according to claim 1, characterized in that: In S1, the self-resistance of the layered soil is expressed as: ； In the formula, The resistivity of the surface soil; The conductor length; The radius of the conductor; For conductor burial depth; Let n be the soil resistivity of the k-th layer; n is the number of soil layers. Let be the thickness of the k-th soil layer.

3. The grounding grid fault diagnosis method based on surface potential frequency response according to claim 1, characterized in that: In S1, based on the relationship between the voltage equation and the leakage current, the node voltage equation is established. ； The admittance matrix Y contains the conductor's self-resistance, mutual resistance, and inductance parameters.

4. The grounding grid fault diagnosis method based on surface potential frequency response according to claim 3, characterized in that: The admittance matrix elements of multi-type conductors are then expressed as: ； In the formula, The resistance of the conductor between nodes i and j; The imaginary unit; The angular frequency of the excitation current; Let i be the mutual inductance between the conductors at nodes i and j.

5. The grounding grid fault diagnosis method based on surface potential frequency response according to claim 4, characterized in that: In S2, the transient current model is a double exponential function, expressed as: ； Transient surface potential is represented as ； In the formula, This represents the peak value of the transient current. The attenuation coefficient is 1; The attenuation coefficient is 2; The transient current frequency domain component; This is the frequency domain impedance of the grounding grid.

6. The grounding grid fault diagnosis method based on surface potential frequency response according to claim 1, characterized in that: The corrosion characteristic value The cumulative effect of potential changes at both ends of the conductor segment; the fracture characteristic value The potential change at the nearest endpoint to the breakpoint is represented as follows: ； ； In the formula, , These are the surface potential node voltage values ​​at the left and right ends of the corrosion fault in the fault-free grounding grid, respectively; , These are the surface potential node voltage values ​​at the left and right ends of the grounding grid after corrosion. This represents the surface potential node voltage value at this point when the grounding grid is intact. This represents the surface potential node voltage value at the nearest endpoint of the grounding grid fault.

7. The grounding grid fault diagnosis method based on surface potential frequency response according to claim 1, characterized in that: In S4, the amplitude and frequency of the excitation current are increased based on the skin effect and the degree of current dissipation to amplify the fault characteristic values.

8. The grounding grid fault diagnosis method based on surface potential frequency response according to claim 7, characterized in that: When determining the skin effect at high frequencies, the relationship between different frequencies and soil resistivity is also considered to redetermine the correction value of soil resistivity, thereby determining the frequency of the injected current; the correction formula for soil resistivity is as follows: ； In the formula, The frequency of the injected current; These are the conversion factors; This is a preset value for soil resistivity.

9. The grounding grid fault diagnosis method based on surface potential frequency response according to claim 7, characterized in that: Based on the influence of current dissipation, 3kHz was selected as the frequency point for grounding grid fault diagnosis to amplify the fault characteristic values.

10. The grounding grid fault diagnosis method based on surface potential frequency response according to claim 1, characterized in that: The following fault determination process is included in S5: S5.1 Determine whether the node potential characteristic value has changed; if it has changed, it is determined that a fault has occurred, and jump to S5.3; If there are no changes, proceed to S5.2; S5.2, appropriately increase the excitation current frequency and measure whether the characteristic value of the characteristic point potential changes. If it changes, jump to S5.3; if it does not change, it is determined that there is no fault and the diagnosis ends. S5.3, Identify the faulty segment and determine whether the difference between the two ends of the node is significantly different; if so, determine it as a fracture state and jump to S5.4; if not, determine it as a corrosion state and end the diagnosis. S5.4, based on fracture characteristic values Determine the location of the fracture point.

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