Non-contact measurement method for grounding resistance of power transmission tower based on electromagnetic coupling principle

Abstract

A power transmission tower grounding resistance non-contact measurement method based on the electromagnetic coupling principle comprises the following steps that transmitting and receiving electromagnetic coupling coils are arranged around an iron tower grounding body, and geometric calibration and spatial positioning of a measurement area are completed by combining grounding grid structure parameters and soil conduction characteristics; injecting a high-frequency alternating-current excitation signal into the transmitting coil, and synchronously acquiring the amplitude and phase response of the induced voltage at a receiving coil end; carrying out filtering processing on the induction signal by adopting a time-frequency analysis and phase decoupling algorithm, and solving a function relationship between electromagnetic response and grounding impedance by combining a coupling equivalent model; based on experimental calibration data and scene parameters, a nonlinear mapping model of induction response and grounding resistance is constructed, and real-time inversion calculation is carried out by combining a solving result obtained in the third step. According to the invention, the real-time accurate measurement of the grounding resistance under the conditions of no power failure and no wire breakage is realized, and the safety, the operation convenience and the anti-interference capability in a complex environment in the measurement process are obviously improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of power system grounding detection, and particularly relates to a non-contact measurement method for grounding resistance of a power transmission tower based on an electromagnetic coupling principle. BACKGROUND

[0002] As an important component of high-voltage transmission lines, the grounding system of a power transmission tower plays an important role in draining lightning current, fault current, and stabilizing the potential of equipment. Grounding resistance, as a key parameter for measuring grounding performance, directly affects the safety and reliability of the power system. In particular, in areas with frequent thunderstorms, rocky soil, or high altitudes, abnormal grounding resistance can easily cause equipment insulation breakdown, voltage counterattack, and other problems, posing a serious threat to the safe operation of the transmission line. Therefore, accurate measurement and continuous monitoring of grounding resistance have become a key technical problem in the operation and maintenance of transmission lines.

[0003] Currently, the commonly used methods for measuring grounding resistance in engineering mainly include the three-pole method, the four-pole method, and the variable frequency injection method. Although these methods have certain measurement accuracy in theory, they generally have significant limitations. First, most of these methods require disconnecting the existing grounding lead to insert test electrodes to establish a measurement path, which is not only tedious and time-consuming, but also temporarily disrupts the integrity of the grounding system during measurement, posing a safety hazard to equipment and personnel. Second, these methods generally cannot be carried out under the operating state of the equipment, and require planned power outage or manual attendance during measurement, which is not suitable for the continuous and real-time data collection requirements of modern power grids.

[0004] In addition, traditional methods have poor adaptability in complex geographical environments. Fluctuations in soil conductivity, changes in terrain, and interference from weather factors often result in unstable and poorly reproducible measurement data. At the same time, in strong electromagnetic interference environments such as around substations or transmission corridors, induced noise signals severely affect the accuracy of the measurement system, limiting the engineering applicability of these methods. More importantly, most current grounding resistance measurement devices are portable and rely on manual operation, and do not yet have the functions of automation, intelligence, and remote control, making it difficult to integrate them into the online monitoring system of the transmission line.

[0005] Although attempts have been made in recent years to introduce electromagnetic coupling and non-contact sensing technology to explore the application of non-invasive measurement methods in power systems, these methods are still in the principle verification stage in the field of grounding resistance measurement, and have not yet formed a mature and reliable technical system, particularly in terms of signal processing accuracy, electromagnetic modeling, and environmental adaptability. SUMMARY

[0006] The application aims to provide a power transmission tower grounding resistance non-contact measurement method based on the principle of electromagnetic coupling, aiming to solve the technical problems of high risk of wire breaking operation, poor real-time performance, interference sensitivity, strong dependence on manual operation and the like in the existing grounding resistance detection process. Not only the real-time and accurate measurement of the grounding resistance under the condition of no power-off and no wire breaking is realized, but also the safety, operation convenience and anti-interference ability in complex environment of the measurement process are significantly improved.

[0007] The technical solution of the application to solve the above technical problems is as follows:

[0008] A power transmission tower grounding resistance non-contact measurement method based on the principle of electromagnetic coupling, the specific steps are as follows:

[0009] S1: arranging transmitting and receiving electromagnetic coupling coils at reasonable positions around the tower grounding body, completing geometric calibration and spatial positioning of the measurement area in combination with the grounding net structure parameters and soil conductivity characteristics, and ensuring stable coupling of signals;

[0010] S2: injecting a high-frequency alternating excitation signal into the transmitting coil, synchronously collecting the amplitude and phase response of the induced voltage at the receiving coil end, realizing non-contact sensing of electromagnetic field disturbance around the grounding body, and constituting the basis of time domain response;

[0011] S3: filtering the induced signal by using time-frequency analysis and phase decoupling algorithm, eliminating external interference and background noise, and solving the functional relationship between electromagnetic response and grounding impedance in combination with the coupling equivalent model;

[0012] S4: constructing a nonlinear mapping model of induced response and grounding resistance based on experimental calibration data and scene parameters, combining the solving result of step 3 to realize real-time inversion calculation, and realizing the measurement of grounding resistance without wire breaking.

[0013] Alternatively, in step S1, the arrangement positions of the transmitting coil and the receiving coil can be obtained by calculation to ensure that they cover the entire electromagnetic disturbance area of the grounding system. Specifically, the arrangement needs to be optimized according to the conductivity distribution of the grounding net and the ground surface structure to reduce the influence of soil conductivity change on the signal. In addition, the adjustment of the distance and angle between the coils should ensure the stable coupling of the signal, and the structure of the grounding system can be dynamically optimized and adjusted.

[0014] Optionally, in step S2, the high-frequency AC excitation signal can be selected in the range of 10 kHz to 1 MHz to ensure that the signal can effectively penetrate the grounding body and reflect its electromagnetic characteristics. Sine wave excitation or frequency modulation techniques can be used to produce different amplitude induction responses at different frequency bands. In addition, lock-in amplification technology is used to synchronize the amplitude and phase of the induced voltage, ensuring that small changes in the signal can be accurately captured during measurement, improving the accuracy of the measurement results.

[0015] Optionally, in step S3, the collected induction signals are processed by short-time Fourier transform (STFT) and adaptive band-pass filtering algorithm to extract effective frequency domain features and suppress external electromagnetic interference. Time-frequency analysis can more accurately capture electromagnetic responses at different frequencies by decomposing signals into multiple frequency bands, especially for weak signals in low signal-to-noise ratio environments. In addition, by decoupling phase differences, multi-path signal interference is avoided, ensuring accurate measurement of each signal source. Then, combined with the electromagnetic coupling equivalent model, numerical calculation method is used to establish the relationship between signal and grounding impedance, further enhancing the accuracy of signal processing.

[0016] Optionally, in step S4, the nonlinear mapping model is constructed using techniques such as support vector regression (SVR). Through the collection of a large amount of experimental calibration data and on-site scene parameters in advance, the model can adapt to different terrains, soil conductivity and other factors, continuously optimizing the prediction accuracy of grounding resistance. Specifically, during real-time inversion calculation, model optimization algorithms based on training data are used, so that the parameters of the calculation model can be automatically adjusted for each measurement, ensuring accuracy and stability in various operating environments. This method allows continuous monitoring of grounding resistance without disconnecting the grounding lead and real-time feedback of measurement results.

[0017] The beneficial effects of the present application: by constructing the spatial coupling relationship between the transmitting and receiving electromagnetic coils, using high-frequency excitation signals to excite the response field in the grounding system, and then collecting the induced voltage signal by the receiving end non-contact, extracting the electromagnetic parameters related to the grounding state, combining signal processing technology and nonlinear modeling method, the high-precision real-time measurement of grounding resistance without disconnecting the grounding lead is realized. This method not only can avoid the risk of power failure and operation in the traditional measurement process, and ensure the safe operation of the equipment, but also can provide accurate and stable results in complex environment, especially in electromagnetic interference and low signal-to-noise ratio conditions. Through time-frequency analysis and phase decoupling, the background noise and external interference are effectively removed, and combined with finite element simulation and data fusion optimization algorithm, the measurement accuracy and dynamic inversion ability are further improved. The present application has the functions of real-time monitoring of grounding resistance change, automatic calibration and optimization, and is suitable for different soil conditions, humidity change and complex terrain environment, simplifies the operation and maintenance, and reduces the operation and maintenance cost. At the same time, this method has the advantages of simple deployment, safe measurement and system scalability, and can be widely applied to the online detection of transmission tower grounding resistance and the state monitoring and intelligent operation and maintenance of transmission line of smart grid, and has significant technical advantages and application value. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 The flowchart of the transmission tower grounding resistance non-contact measurement method based on electromagnetic coupling principle provided by the present application. DETAILED DESCRIPTION

[0019] As shown in Figure 1 The transmission tower grounding resistance non-contact measurement method based on electromagnetic coupling principle provided by the present application has the following steps:

[0020] S1: The transmitting and receiving electromagnetic coupling coils are reasonably arranged around the grounding body of the tower to ensure stable coupling of the signal and obtain accurate measurement results; the geometric calibration and spatial positioning of the measurement area are completed in combination with the grounding net structure parameters and the soil conductivity characteristics, to ensure stable coupling of the signal.

[0021] The specific implementation process is as follows:

[0022] 1. The position of the transmitting and receiving electromagnetic coupling coils

[0023] Firstly, the transmitting and receiving electromagnetic coupling coils should be reasonably arranged according to the grounding net structure of the transmission tower, and the arrangement position should be selected near the grounding net, which can cover the electromagnetic field disturbance area of the grounding body and can minimize the influence of external electromagnetic interference on the measurement.

[0024] For the grounding system, the positions of the transmitting coil and the receiving coil need to be optimized according to the grounding body geometry and soil conductivity distribution. Specifically, the angle and distance of the coil arrangement should meet the following conditions:

[0025] where d is the distance between the transmitting coil and the receiving coil, α is the size parameter of the grounding body, and θ is the installation angle.

[0026] 2. Geometric calibration of the measurement area

[0027] According to the structure and layout position of the grounding grid, the geometric calibration of the measurement area is carried out. This includes confirming the boundary conditions of the measurement area with the reference coordinate system, and combining the actual measurement data to position the measurement area in space. Specifically, by establishing a three-dimensional coordinate system to describe the positional relationship between the transmitting and receiving coils, and conducting electronic magnetic field simulation, the optimal coil layout angle and distance are determined. The spatial positioning formula can be expressed as:

[0028]

[0029] where, and are the coordinates of the transmitting coil and the receiving coil in three-dimensional space, respectively. By optimizing these coordinates, the signal coupling effect between the two is maximized, thereby improving the transmission efficiency of the signal.

[0030] 3. Coupling parameter optimization

[0031] The change of soil conductivity of the grounding grid will directly affect the transmission effect of electromagnetic signals, so the change of soil conductivity needs to be considered when laying the coil. By measuring the soil conductivity under different geological conditions in real time, the coupling parameters are optimized according to the following formula:

[0032]

[0033] where Z eff is the effective grounding impedance, ρ is the soil conductivity, and d is the distance between the transmitting and receiving coils. By adjusting the coil position and distance, the coupling efficiency of the electromagnetic signal can be maximized, while compensating for errors caused by changes in soil conductivity.

[0034] 4. Ensure stable signal coupling

[0035] In order to ensure the stable coupling of the signal, the angle of the transmitting and receiving coils can be fine-tuned according to the current distribution of the grounding system. Through multiple experiments and simulations, the layout angle θ and position parameters of the coil are optimized to minimize measurement errors caused by the structure of the grounding grid or external factors such as electromagnetic interference, metal obstacles, etc. Finally, the calculated optimal layout angle and position satisfy the following conditions:

[0036]

[0037] where θ is the layout angle, h is the tower height, and d is the distance between the transmitting and receiving coils. After optimization, the laid coils can ensure the best signal receiving and transmitting effect, thereby improving the measurement accuracy.

[0038] S2: Inject a high-frequency alternating excitation signal into the transmitting coil, and synchronously collect the amplitude and phase response of the induced voltage at the receiving coil end to realize non-contact sensing of the electromagnetic field disturbance around the grounding body, thereby constituting the time-domain response basis and providing time-domain response data support for subsequent signal analysis and grounding resistance calculation; specifically including:

[0039] 1. Injection and frequency selection of excitation signal

[0040] First, an AC excitation signal with adjustable frequency is injected into the transmitting coil. The frequency range of the signal is generally selected between 10 kHz and 1 MHz to adapt to different soil types and grounding system responses. The frequency selection of the excitation signal needs to be adjusted according to the soil conductivity and grounding resistance to ensure that the signal can effectively penetrate the ground and produce an induced effect on the grounding system.

[0041] Specifically, the frequency f of the excitation signal can be selected as follows:

[0042] f min = 10 kHz, f max = 1 MHz (5)

[0043] Through the sinusoidal signal in this frequency range, it can be ensured that the lower frequency signal can penetrate the denser soil, while the high-frequency signal is suitable for looser or wet soil conditions, thereby improving the quality of the induced signal.

[0044] 2. Injection and waveform control of excitation signal

[0045] The excitation signal adopts a sinusoidal wave form, which is driven by a power amplifier to radiate the transmitting coil. In order to obtain the best signal excitation effect, the amplitude A tx of the excitation signal needs to be dynamically adjusted according to the estimated value of the on-site grounding resistance to ensure that the signal is strong enough to penetrate the grounding system and be effectively captured by the receiving coil.

[0046] The expression of the injected sinusoidal excitation signal is as follows:

[0047] V tx (t) = A tx sin(2πft + φ) (6)

[0048] where V tx (t) is the voltage of the transmitting coil at time t, and A txwhere A is the amplitude of the excitation signal, f is the frequency, and φ is the phase of the signal. By adjusting the amplitude and frequency of the excitation signal, it is ensured that the signal can generate effective electromagnetic field disturbances under different geographical environments and soil conditions.

[0049] 3. Collection and synchronous measurement of induced voltage

[0050] The receiving coil is used to synchronously collect the induced voltage generated by the electromagnetic signal injected by the transmitting coil. The amplitude A rx and phase information of the induced voltage will change with the changes in the electromagnetic characteristics of the grounding system. These changes can reflect the characteristic information of the grounding resistance.

[0051] During signal collection, the sampling accuracy is improved through synchronous phase-locked amplification technology, which locks the signal at a specific frequency and eliminates interference from other frequency bands. The basic principle of synchronous phase-locked amplification is to extract the induced voltage signal in a phase-synchronous manner with the excitation signal, reducing interference from background noise or other external electromagnetic sources.

[0052] The amplitude and phase of the induced voltage signal can be represented as:

[0053]

[0054] where A rx is the amplitude of the induced voltage of the receiving coil, is the phase response of the induced voltage, and f is the signal frequency.

[0055] 4. Signal synchronous sampling and processing

[0056] The synchronously collected induced voltage signal is sampled by a high-speed data acquisition system and compared with the reference signal to ensure that the collected signal completely matches the frequency and phase characteristics of the excitation signal. The sampled signal is further processed by a digital signal processing (DSP) module to extract useful amplitude and phase information.

[0057] The selection of sampling frequency and bandwidth needs to be optimized according to the variation range of the grounding resistance to ensure the accuracy and real-time performance of signal processing. Generally, the sampling frequency f sample should satisfy the following conditions:

[0058] f sample ≥ 2f max (8)

[0059] That is, the sampling frequency is at least twice the frequency of the excitation signal, ensuring that the signal changes can be fully captured.

[0060] S3: Adopting time-frequency analysis and phase decoupling algorithm to filter the induction signal, eliminate external interference and background noise, and solve the functional relationship between electromagnetic response and grounding impedance based on the coupling equivalent model to ensure the accuracy of measurement and finally realize the real-time inversion and calculation of grounding resistance; specifically including:

[0061] 1. Time-frequency analysis and signal filtering

[0062] In order to effectively process the induction signal in complex environment, first of all, time-frequency analysis technology is adopted to filter the collected induction signal. Because in the power environment, the signal is often disturbed by noise with a wide range of frequencies, time-frequency analysis can effectively identify the useful frequency components in the signal and remove the interference. Short-time Fourier transform (STFT) is selected to decompose the signal and extract the electromagnetic characteristics of each frequency band.

[0063] The specific time-frequency analysis steps are as follows:

[0064] 1) Signal segmentation: The collected induction signal is divided into multiple time periods, each time period has a length of N, the sampling frequency is f sample , and the time resolution is:

[0065]

[0066] 2) Fourier transform: Fourier transform is performed on each signal segment to obtain the frequency domain representation:

[0067]

[0068] Where X(f, t) is the frequency domain signal, x(y) is the time domain signal, f is the frequency, and t is the time.

[0069] 3) Band-pass filtering: By designing an adaptive band-pass filter, the useful signal within the frequency range is preserved, and the low and high frequency noise is removed. Specifically, according to the frequency distribution of the signal, the appropriate frequency band is selected for filtering, so as to ensure the extraction of effective signal.

[0070] After time-frequency analysis, the main characteristics of the signal are extracted, effectively reducing the background noise and unnecessary frequency components, providing a clean signal basis for subsequent phase decoupling and grounding impedance calculation.

[0071] 2. Phase decoupling and signal demodulation

[0072] Due to the influence of multipath propagation and environmental interference, the phase of the induced signal may be offset, affecting the measurement accuracy. To solve this problem, a phase decoupling algorithm is used to eliminate the phase error caused by different signal paths. By calculating the phase difference between multiple paths, an accurate combined phase is obtained, ensuring that the phase of the signal truly reflects the electromagnetic characteristics of the grounding system.

[0073] The formula for phase decoupling is:

[0074]

[0075] where A i is the signal amplitude of the i-th path, is the signal phase of the i-th path, is the combined phase after decoupling.

[0076] Through this process, the original phase information of each path can be recovered from multiple paths, eliminating the phase error caused by multipath propagation, reflection and environmental interference, ensuring that the acquired induced signal is more accurate.

[0077] 3. Establishment and solution of coupled equivalent model

[0078] After completing the time-frequency analysis and phase decoupling, the relationship between electromagnetic response and grounding resistance needs to be derived through the coupled equivalent model. This model simulates the propagation of electromagnetic waves in the grounding body by considering factors such as the geometry of the grounding system, soil conductivity, soil humidity, etc., establishing a nonlinear relationship between electromagnetic response and grounding resistance.

[0079] The relationship between grounding resistance and induced voltage, transmitted current can be expressed as:

[0080]

[0081] where Z eff is the grounding resistance, V rx is the induced voltage measured at the receiving end, and I tx is the current intensity injected by the transmitting coil.

[0082] The calculation of grounding resistance not only depends on theoretical formulas, but also needs to be combined with finite element method (FEM) for numerical simulation to simulate the propagation and current distribution of electromagnetic waves in the grounding body. Finite element method (FEM) simulates the distribution of electric field and current by discretizing the geometric structure of the grounding system into small elements, accurately calculating the grounding resistance.

[0083] The solution process of finite element method is as follows:

[0084] 1) Grounding system discretization: Based on the information of the grounding grid's geometry, the layout of grounding electrodes, soil conductivity, etc., the physical area of the grounding system is meshed.

[0085] 2) Current distribution and electric field simulation: By solving Maxwell's equations or electrostatic field equations, the distribution of electric field and current is calculated, and the relationship between grounding resistance and electromagnetic response is obtained.

[0086] 3) Influence of soil conductivity: According to the influence of different soil conductivities on electromagnetic fields, simulation calculations are carried out. Soil conductivity is a key factor affecting electromagnetic wave propagation, and finite element method can accurately incorporate it into calculations.

[0087] 4) Setting of boundary conditions: In the external area of the grounding system, the electric field intensity is assumed to be zero or the potential tends to be constant, and the boundary conditions of the electric field are set to ensure the accuracy of the simulation results.

[0088] 4. Minimization of objective function and optimization

[0089] Based on signal processing and coupled model solving, the model calculation accuracy is further improved through optimization algorithm. In order to minimize the error between experimental data and simulation data, an objective function is designed, and gradient descent method is used to optimize the model parameters.

[0090] The expression of the objective function is:

[0091]

[0092] where, is the grounding resistance value in the experimental calibration data, Z calc (x k ) is the grounding resistance value calculated by the coupled model, x k is the input experimental parameter. Through the gradient descent method to minimize the objective function, adjust the parameters of the coupled model, so that the calculation result of each measurement can be adaptively adjusted under different environmental conditions, so as to obtain more accurate grounding resistance measurement results.

[0093] S4: Based on the experimental calibration data and scene parameters, a nonlinear mapping model of induced response and grounding resistance is constructed, and real-time inversion calculation is carried out combined with the third step solving result, realizing real-time and high-precision grounding resistance measurement without breaking the line condition.

[0094] This step uses experimental calibration data combined with optimization algorithm to realize automatic calibration and calculation, improving measurement accuracy and system adaptability.

[0095] 1. Construction of nonlinear mapping model

[0096] The nonlinear mapping model maps the signal amplitude, phase information processed from step S3, and input features such as the geometric parameters of the grounding system, soil conductivity, etc. to the grounding resistance output. This model captures the complex nonlinear relationship between input features and grounding resistance, thus achieving accurate inversion calculation.

[0097] (1) Input feature and data preprocessing

[0098] To ensure that the model training can extract the most valuable information from the data, we first need to perform data preprocessing. The input features include:

[0099] Signal amplitude: the signal amplitude after time-frequency analysis, reflecting the strength of the signal.

[0100] Signal phase: the phase information after phase decoupling processing, providing the timing characteristics of the signal.

[0101] Grounding grid structure parameters: the layout, spacing, shape, etc. of the grounding electrode, which directly affects the distribution of electromagnetic field.

[0102] Soil conductivity: the soil conductivity affects the propagation of current in the grounding body, so it needs to be considered in the model.

[0103] Data standardization: due to the different units and dimensions of each feature, standardization is performed to ensure that the model training will not be affected by the scale of some features. Each input feature will be standardized to a form with a mean of 0 and a standard deviation of 1:

[0104]

[0105] where X is the original input data, μ and σ are the mean and standard deviation of the feature, respectively.

[0106] (2) Model selection and design

[0107] To accurately reflect the complex relationship between input features and grounding resistance, we choose deep neural network (DNN) and support vector regression (SVR) as the main regression model. DNN can learn the nonlinear mapping between input data and grounding resistance through multiple hidden layers, suitable for processing complex, high-dimensional input data.

[0108] Deep neural network (DNN): this model contains multiple hidden layers, which can learn complex nonlinear relationships. Each hidden layer uses a ReLU activation function to introduce nonlinearity, enhancing the model's expressive power.

[0109] Support Vector Regression (SVR): SVR is suitable for handling smaller datasets and can effectively handle high-dimensional data. By adjusting the kernel function, SVR can capture the precise mapping between input features and grounding resistance.

[0110] Network architecture design:

[0111] 1) Input layer: receives standardized feature data. Each input feature corresponds to a node, so the number of nodes in the input layer is equal to the number of features.

[0112] 2) Hidden layer: multiple hidden layers, each using a ReLU activation function, with the number of nodes set according to the complexity of the features (e.g., 50 to 200 nodes per layer).

[0113] 3) Output layer: outputs the predicted value of grounding resistance, with one node.

[0114] The calculation form of each layer is:

[0115] h i =ReLU(W i ·h i-1 +b i ) (15)

[0116] where W i is the weight matrix of the i-th layer, b i is the bias term, and ReLU is the activation function.

[0117] (3) Model training

[0118] The training process uses Mean Squared Error (MSE) as the loss function, minimizing the error between the model's predicted value and the true value through optimization algorithms. The loss function is defined as:

[0119]

[0120] where Z calc is the grounding resistance value in the experimental calibration data, Z i (x i ) is the grounding resistance value calculated by the model, x calc is the input feature data, and N is the number of samples.

[0121] (4) Model validation and evaluation

[0122] After training is complete, cross-validation is used to evaluate the model's performance. The data set is divided into training, validation, and test sets:

[0123] Training set: used to train the model and adjust parameters.

[0124] Validation set: used to fine-tune hyperparameters and avoid overfitting.

[0125] Test Set: Used to evaluate the model's performance on unseen data.

[0126] Through cross-validation, ensure the generalization ability of the model, avoid overfitting of the model on the training data.

[0127] 2. Real-time inversion calculation and optimization

[0128] After the nonlinear mapping model is trained, it can be used for real-time inversion calculation to calculate the value of the grounding resistance. The real-time signal data is input into the trained model, and the model outputs the real-time grounding resistance value.

[0129] In order to further improve the accuracy of the inversion calculation, gradient descent method, Newton method and other optimization algorithms are used to correct the inversion results. The optimization goal is to minimize the error between the experimental data and the model prediction results, so as to improve the calculation accuracy. The optimization objective function is:

[0130]

[0131] Where, is the grounding resistance value in the experimental data, Z calc (x k ) is the grounding resistance value predicted by the model, x k is the input experimental parameter.

[0132] By minimizing this objective function, the optimized grounding resistance value can more accurately reflect the state of the grounding system.

[0133] 3. Data fusion and result optimization

[0134] In order to further improve the accuracy and stability of the grounding resistance measurement, step S4 also includes the fusion of multiple data sources. This process can reduce the error that may exist in a single measurement point and improve the stability of the final measurement result.

[0135] Weighted fusion: The grounding resistance results of multiple measurement points are weighted according to reliability to obtain the final fusion value. The weighted fusion formula is:

[0136]

[0137] Where, Z i is the grounding resistance value of the i-th measurement point, w i is the weight of the measurement point, which is determined by signal quality or measurement accuracy.

[0138] Integrated learning: Use integrated learning algorithms (such as random forest, XGBoost, etc.) to fuse the outputs of multiple models, and through the integration of multiple regression models, obtain more accurate grounding resistance measurement values.

[0139] 4. Final optimization and environmental compensation

[0140] After completing the nonlinear model inversion calculation and data fusion, the next task is to perform the final optimization and environmental compensation. Since the ground resistance measurement may be affected by environmental factors such as temperature, humidity, etc., appropriate calibration and adjustment are needed.

[0141] Environmental compensation formula:

[0142] Z comp = Z calc ×(1+α(T-T0)+β(H-H0)) (19)

[0143] where T and H are the current temperature and humidity, T0 and H0 are the temperature and humidity under standard conditions, and α and β are the temperature and humidity compensation coefficients obtained from experimental calibration.

[0144] Simulation experiment

[0145] 1. Experimental purpose

[0146] In order to verify the effectiveness and precision of the non-contact measurement method of transmission tower grounding resistance based on electromagnetic coupling principle proposed in this invention, numerical simulation and inversion experiment are carried out. Through simulation under different soil conductivities and coil layout conditions, the inversion ability of the method to the grounding resistance is analyzed, and its anti-interference and robustness are evaluated.

[0147] 2. Experimental method

[0148] A three-dimensional coupling model of the transmission tower grounding system and the transmitting / receiving coils is established using finite element software. The excitation frequency range is 20 kHz–500 kHz, and the transmitting current is 1 A. The soil conductivity σ is taken within 0.01–0.5 S / m, the coil spacing varies between 0.5–2.0 m, and the installation angle is taken between 0–90°. The amplitude and phase of the induced voltage of the receiving coil are calculated under each group of parameters, and Gaussian noise is added to simulate the measurement error in the field. The decoupling and inversion method proposed in this invention is used to estimate the grounding resistance R g , which is compared with the true value.

[0149] 3. Experimental results

[0150] The following table shows the comparison results of the true value and the inversion value of the grounding resistance of some simulation samples (10 groups of data are selected).

[0151] Table 1 Comparison of true value and predicted results of grounding resistance of simulation samples

[0152]

[0153]

[0154] As can be seen from Table 1, in the multiple sets of simulation samples, the non-contact measurement and inversion method proposed in the application can accurately estimate the grounding resistance, the average absolute error of the predicted value and the true value is about 25Ω, and the root mean square error is about 29Ω. After further introducing the multi-frequency amplitude and phase joint characteristics and combining the nonlinear method such as support vector regression, the error can be further reduced to within 10Ω, indicating that the method has good engineering application potential and popularization value.

[0155] The above only describes the preferred embodiments of the application and is not intended to limit the application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the application shall be included in the protection scope of the application.

Claims

1. A non-contact measurement method for the grounding resistance of transmission towers based on the principle of electromagnetic coupling, characterized in that, Includes the following steps: S1: Install transmitting and receiving electromagnetic coupling coils around the grounding body of the tower, and combine the grounding grid structure parameters and soil conductivity characteristics to complete the geometric calibration and spatial positioning of the measurement area to ensure stable signal coupling; S2: Inject a high-frequency AC excitation signal into the transmitting coil and simultaneously collect the amplitude and phase response of the induced voltage at the receiving coil end to realize non-contact sensing of electromagnetic field disturbances around the grounding body, forming the basis of time-domain response; S3: The inductive signal is filtered using time-frequency analysis and phase decoupling algorithm to eliminate external interference and background noise. The functional relationship between electromagnetic response signal and grounding impedance is solved by combining the coupled equivalent model. S4: Based on experimental calibration data and scenario parameters, a nonlinear mapping model between inductive response and grounding resistance is constructed. Combined with the solution results in step 3, real-time inversion calculation is performed to realize grounding resistance measurement without the need for wire disconnection.

2. The contactless measurement method for grounding resistance of transmission towers based on the principle of electromagnetic coupling according to claim 1, characterized in that, In step S1, the placement of the transmitting coil and the receiving coil is optimized based on the geometry of the grounding electrode and the distribution of soil conductivity.

3. The contactless measurement method for grounding resistance of transmission towers based on the principle of electromagnetic coupling according to claim 1, characterized in that, In step S2, the high-frequency AC excitation signal is a swept-frequency sine wave in the range of 10kHz to 1MHz, and synchronous lock-in amplification technology is used to collect the amplitude and phase of the induced voltage, and multi-frequency response sampling is performed on the induced voltage to obtain rich frequency domain information.

4. The contactless measurement method for grounding resistance of transmission towers based on the principle of electromagnetic coupling according to claim 1, characterized in that, In step S3, when performing time-frequency analysis, the acquired inductive signal is divided into multiple frequency bands. The inductive signal is processed by a combination of short-time Fourier transform (STFT) and adaptive bandpass filtering algorithm to extract effective frequency domain features. At the same time, the multipath interference effect is corrected through a decoupling phase difference compensation mechanism.

5. The contactless measurement method for grounding resistance of transmission towers based on the principle of electromagnetic coupling according to claim 1, characterized in that, In step S4, the constructed nonlinear mapping model is trained based on support vector regression (SVR) or neural network regression algorithms, and the model parameters are automatically corrected according to real-time input parameters to achieve adaptive inversion accuracy optimization.

6. The contactless measurement method for grounding resistance of transmission towers based on the principle of electromagnetic coupling according to claim 2, characterized in that, When optimizing coupling parameters, the optimization is based on the relationship between effective coupling impedance and spacing, satisfying the following: Among them, Z eff For effective grounding impedance, ρ is the soil conductivity, and d is the distance between the transmitting and receiving coils; The layout angle was optimized by combining the relationship between tower height and spacing: Where θ is the deployment angle, h is the tower height, and d is the distance between the transmitting and receiving coils.

7. The contactless measurement method for grounding resistance of transmission towers based on the principle of electromagnetic coupling according to claim 1, characterized in that, In step S2, the excitation signal is in the form of a sine wave, which drives the transmitting coil to radiate through a power amplifier; in order to obtain the best signal excitation effect, the amplitude A of the excitation signal is... tx The signal is dynamically adjusted based on the estimated grounding resistance to ensure that it is strong enough to penetrate the grounding system and be effectively captured by the receiving coil. The expression for the injected sinusoidal excitation signal is as follows: V tx (t)=A tx sin(2πft+φ) (6) Among them, V tx (t) represents the voltage of the transmitting coil at time t, A tx Let f be the amplitude of the excitation signal, φ be the frequency, and φ be the signal phase; the frequency range is 10kHz ≤ f ≤ 1MHz, and the sampling frequency satisfies the Nyquist condition f. s ≥2f.

8. The contactless measurement method for grounding resistance of transmission towers based on the principle of electromagnetic coupling according to claim 1, characterized in that, In step S3, The formula for phase decoupling is: Among them, A i Let be the signal amplitude of the i-th path. Let i be the signal phase of the i-th path. This is the synthesized phase after decoupling.

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