Resistance grounding qualification method applied to hazardous chemical vehicle

Abstract

The application relates to the technical field of resistance grounding detection, and discloses a resistance grounding qualification determination method applied to a dangerous chemical vehicle, which comprises the following steps: step S101, constructing a low-frequency impedance sequence and a high-frequency impedance sequence; step S102, calculating a steady-state baseline and a salt bridge conductive coefficient; step S103, judging whether a pulse event occurs; step S104, determining a salt bridge azimuth angle and constructing a two-dimensional pulse space matrix; step S105, calculating a pulse stress index and a steady-state direct-current resistance; and step S106, judging whether the grounding resistance is qualified. The application effectively distinguishes the instantaneous short-circuit pulse formed by salt film re-liquefaction from structural defects such as metal corrosion and loose connection through double-frequency current injection, pulse event identification and two-dimensional pulse space matrix construction, ensures that the grounding resistance meets the safety standard through the steady-state direct-current resistance, quantifies the corrosion risk through the pulse stress index, and avoids the misjudgment problem caused by a single resistance value through the joint determination of the double thresholds.

Description

Technical Field

[0001] This invention relates to the field of resistance grounding detection technology, and more specifically, to a method for determining the compliance of resistance grounding in hazardous chemical vehicles. Background Technology

[0002] Hazardous chemical vehicles require a reliable grounding system to release static electricity during transport to prevent explosions, fires, and other safety accidents caused by static buildup. Grounding resistance is a core indicator of the grounding system's effectiveness. However, their operating environments are complex, especially in cold, saline, or humid environments such as coastal areas and northern winter snowmelt zones. Salt deposits can easily form on the surface of the vehicle's metal grounding components. When ambient humidity increases (e.g., a sudden rise in humidity at dawn), the salt film absorbs moisture, changing from a solid to a liquid state, forming a highly conductive salt bridge. This can cause a momentary short-circuit pulse in the grounding loop, resulting in a sharp drop in grounding resistance. This momentary short circuit caused by salt film reliquefaction is an environmental disturbance, not a structural problem with the grounding system itself (e.g., resistance increases due to metal corrosion or loose connections).

[0003] Traditional grounding resistance testing methods often rely on single-frequency signals or static resistance value measurements, which cannot effectively distinguish between the instantaneous resistance drop caused by salt bridges and actual grounding system degradation. In high humidity conditions, low resistance caused by salt bridges is easily misjudged as grounding compliance, masking potential risks such as metal corrosion and loose connections. In dry conditions, the resistance rebound after the salt bridge disappears may be overlooked, thus failing to detect real problems and seriously affecting the accuracy of grounding safety assessment. Therefore, there is an urgent need for a grounding resistance compliance testing method that can accurately distinguish between environmental interference and structural defects. Summary of the Invention

[0004] This invention provides a method for determining the qualified grounding resistance of hazardous chemical vehicles, thereby solving the technical problems mentioned in the background section.

[0005] This invention provides a method for determining the pass / failability of grounding resistance in hazardous chemical vehicles, comprising the following steps: Step S101: Inject low-frequency current and high-frequency current into the closed grounding loop respectively, and collect the loop voltage to obtain the low-frequency impedance sequence and high-frequency impedance sequence respectively, and simultaneously collect the original resistance sequence and relative humidity sequence. Step S102: Apply medium filtering to the low-frequency impedance sequence to obtain a steady-state baseline, and apply discrete wavelet transform to the high-frequency impedance sequence to extract the salt bridge conductivity coefficient. Step S103: When the joint detection conditions are met simultaneously, it is identified as a transient short-circuit pulse event of salt film reliquefaction. Step S104: Calculate the pulse energy value for each pulse event, use the current arrival difference collected by the distributed coil to determine the salt bridge azimuth angle, and write the pulse energy value, salt bridge azimuth angle and pulse event end time into the two-dimensional pulse space matrix. Step S105: Within the preset analysis time window, the pulse stress index is obtained based on the two-dimensional pulse space matrix and combined with the azimuth weight accumulation, and the steady-state DC resistance is calculated in the pulse-free section. Step S106: If the steady-state DC resistance is less than or equal to the preset resistance threshold and the pulse stress index is less than or equal to the preset index threshold, the grounding resistance of the hazardous chemical vehicle is deemed qualified; otherwise, it is deemed unqualified, and a self-calibration strategy is executed.

[0006] Furthermore, the sliding window size and step size of the median filter are custom parameters. The median of all impedance values ​​within each sliding window is extracted and arranged in the sliding order to obtain the steady-state baseline.

[0007] Furthermore, the mean of the sequence is subtracted from each data point in the high-frequency impedance sequence, and then the sequence is decomposed into approximate coefficients and detail coefficients by a discrete wavelet transform with a custom decomposition level. The sum of the absolute values ​​of all detail coefficients is taken as the salt bridge conductivity coefficient.

[0008] Furthermore, the conditions for joint testing include: Condition 1. Extract data points from the steady-state baseline that are at the same timestamp as each impedance value in the low-frequency impedance sequence, calculate the ratio of the difference between the two data points to the former data point as the relative decrease, and determine whether the relative decrease is greater than or equal to the first preset threshold, where the first preset threshold is a user-defined parameter; Condition 2. Extract the impedance values ​​from the original impedance sequence that are at the same time stamp as each impedance value in the high-frequency resistance sequence, calculate the ratio of the difference between the two to the data point of the former as the high-frequency difference, and determine whether the high-frequency difference is greater than or equal to the second preset threshold, where the second preset threshold is a user-defined parameter; Condition 3. Determine that for each relative humidity in the relative humidity sequence, the relative humidity is greater than or equal to the third preset threshold and the relative humidity change rate is greater than or equal to the fourth preset threshold, where the third preset threshold and the fourth preset threshold are custom parameters; Condition 4. Extract the impedance values ​​from the high-frequency impedance sequence that are at the same timestamp as each impedance value in the low-frequency resistance sequence, calculate the ratio of the two as the spectrum ratio, and determine that the spectrum ratio is less than or equal to the fifth preset threshold, where the fifth preset threshold is a user-defined parameter.

[0009] Furthermore, the start and end timestamps of each pulse event are determined, and the integral of the relative decrease during this period is calculated as the pulse energy value.

[0010] Furthermore, a Rogowski coil is arranged on each side of the front and sides of the vehicle body in the closed grounding loop. The time it takes for the instantaneous short-circuit current triggered by the formation of the salt bridge to reach the coil is recorded. The time difference between the arrival times of the current on both sides of the vehicle body is calculated based on the time it takes for the current to reach the coil at the front of the vehicle body. The time difference is converted into the azimuth angle of the salt bridge relative to the coil layout through the time difference positioning algorithm. The azimuth angle of the salt bridge is the positive horizontal axis with the direction of the vehicle body as the positive horizontal axis, the direction of the front of the vehicle body as 0°, the left side of the vehicle body as +90°, and the right side of the vehicle body as -90°.

[0011] Furthermore, the two-dimensional pulse space matrix uses the pulse event end time as the vertical index and the salt bridge azimuth angle partition as the horizontal index. The matrix element value is the pulse energy value, and the 0° to 360° range is divided into 12 discrete angular regions at 30° intervals.

[0012] Furthermore, the pulse stress index (PSI) is calculated by extracting element values ​​from the two-dimensional pulse space matrix based on the start and end timestamps of the preset analysis time window. The formula for calculating the PSI is as follows: Where M represents the number of discrete azimuth angles. This represents the number of pulse events corresponding to the i-th azimuth angle. This represents the azimuth weight of the i-th discrete azimuth angle. This represents the pulse energy value of the j-th pulse event at the i-th azimuth angle.

[0013] Furthermore, based on the start and end timestamps of the preset analysis time window, the average value of the impedance values ​​without pulse events is extracted from the original resistance sequence as a temporary DC resistance, and based on the start and end timestamps of the preset analysis time window, the average value of the two ends of the steady-state baseline is extracted as the baseline drift. The difference between the temporary DC resistance and the baseline drift is taken as the steady-state DC resistance.

[0014] Furthermore, the preset resistance threshold and preset exponent threshold are both custom parameters; the self-calibration strategy is to continuously blow 50°C hot air into the underside of the vehicle and the grounding electrode for 5 minutes to remove moisture from the surface of the grounding electrode. After standing for 2 minutes, return to steps S101 to S105 to execute. If the grounding resistance is qualified, the vehicle will be automatically released and marked as self-calibration successful in the log; otherwise, the vehicle will be locked and a maintenance task will be generated.

[0015] The beneficial effects of this invention are as follows: This invention achieves accurate assessment of the safety status of the grounding system of hazardous chemical vehicles through techniques such as dual-frequency current injection, precise pulse event identification, two-dimensional pulse space matrix construction, and dual-threshold determination. It can effectively distinguish between instantaneous short-circuit pulses formed by salt film reliquefaction and structural defects such as metal corrosion and loose connections. It ensures that the static grounding resistance meets safety standards through steady-state DC resistance, quantifies dynamic corrosion risk through the pulse stress index, and avoids the problem of misjudgment due to a single resistance value in traditional methods through dual-threshold joint determination. Simultaneously, the two-dimensional pulse space matrix allows salt bridge events to be presented intuitively in the spatiotemporal dimension, facilitating rapid location of high-incidence areas. The dynamic setting of the pulse stress index threshold adapts to different environmental corrosion characteristics, and the self-calibration strategy further reduces misjudgments caused by environmental interference. This not only strictly guarantees the safety baseline of the grounding system but also reduces unnecessary maintenance interruptions, balancing safety and operational efficiency, and significantly improving the accuracy and reliability of hazardous chemical vehicle grounding safety assessment. Attached Figure Description

[0016] Figure 1 This is a flowchart of the method for determining the resistance grounding qualification of hazardous chemical vehicles according to the present invention; Figure 2 This is a schematic diagram of the closed grounding circuit for hazardous chemical vehicles according to the present invention; Figure 3 This is the equivalent circuit diagram of the closed grounding circuit for hazardous chemical vehicles of the present invention; Figure 4 This is a schematic diagram of the three-stage detection method of the present invention. Detailed Implementation

[0017] The subject matter described herein will now be discussed with reference to exemplary embodiments. It should be understood that these embodiments are discussed only to enable those skilled in the art to better understand and implement the subject matter described herein, and changes may be made to the function and arrangement of the elements discussed without departing from the scope of this specification. Various processes or components may be omitted, substituted, or added as needed in the examples. Furthermore, features described in some examples may be combined in other examples.

[0018] It should be noted that, unless otherwise defined, the technical or scientific terms used in one or more embodiments of the present invention should have the ordinary meaning understood by one of ordinary skill in the art to which this invention pertains. The terms "first," "second," and similar terms used in one or more embodiments of the present invention do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as "comprising" or "including" indicate that the element or object preceding the term encompasses the elements or objects listed following the term and their equivalents, without excluding other elements or objects. Terms such as "connected" or "linked" are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Terms such as "upper," "lower," "left," and "right" are used only to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0019] like Figures 1-4 As shown, the method for determining the pass / failability of resistance grounding applied to hazardous chemical vehicles includes the following steps: Step S101: Inject low-frequency current and high-frequency current into the closed grounding loop respectively, and collect the loop voltage to obtain the low-frequency impedance sequence and high-frequency impedance sequence respectively, and simultaneously collect the original resistance sequence and relative humidity sequence. Step S102: Apply medium filtering to the low-frequency impedance sequence to obtain a steady-state baseline, and apply discrete wavelet transform to the high-frequency impedance sequence to extract the salt bridge conductivity coefficient. Step S103: When the joint detection conditions are met simultaneously, it is identified as a transient short-circuit pulse event of salt film reliquefaction. Step S104: Calculate the pulse energy value for each pulse event, use the current arrival difference collected by the distributed coil to determine the salt bridge azimuth angle, and write the pulse energy value, salt bridge azimuth angle and pulse event end time into the two-dimensional pulse space matrix. Step S105: Within the preset analysis time window, the pulse stress index is obtained based on the two-dimensional pulse space matrix and combined with the azimuth weight accumulation, and the steady-state DC resistance is calculated in the pulse-free section. Step S106: If the steady-state DC resistance is less than or equal to the preset resistance threshold and the pulse stress index is less than or equal to the preset index threshold, the grounding resistance of the hazardous chemical vehicle is deemed qualified; otherwise, it is deemed unqualified, and a self-calibration strategy is executed.

[0020] In one embodiment of the present invention, such as Figure 2As shown, a complete conductive path for current to flow is formed by following the sequence of the grounding electrode on the left side of the vehicle body, the contact point on the left side of the vehicle body, the contact point on the right side of the vehicle body, and the grounding electrode on the right side of the vehicle body, i.e., a closed grounding loop. Single-point deterioration (such as loose grounding electrode, oxidation of contact point, etc.) is converted into an overall resistance change. Any connection or grounding resistance that does not meet the standard (for example, the grounding resistance should not exceed 10 ohms or lower) will trigger a test resistance value that is unqualified, thereby achieving a thorough foolproof monitoring effect.

[0021] In one embodiment of the present invention, the frequencies corresponding to the low-frequency current and the high-frequency current are 1Hz and 3kHz, respectively. The low-frequency current is close to the characteristics of DC and mainly reflects the actual contact resistance between metals (such as the bridging resistance between the vehicle body and the grounding electrode). The salt film has a large impedance to the low-frequency current, so the low-frequency current can reflect the deterioration of the metal body (such as metal corrosion, loose connection, etc.). The water film formed by the reliquefaction of the salt film has an extremely low impedance to the high-frequency current, so it will drop sharply when the salt bridge is formed, mainly reflecting the instantaneous short-circuit effect of the salt film.

[0022] In one embodiment of the present invention, the frequency and sampling period of the acquisition loop voltage are both custom parameters. For example, the sampling frequency is set to 50Hz, and the sampling period is generally between 3 and 8 minutes, which can completely capture the salt film pulse. That is, the lengths of the low-frequency impedance sequence and the high-frequency impedance sequence are generally between 9000 and 24000, and the continuous data of the most recent 24 hours are retained by default. The original resistance sequence is acquired in the current channel without frequency modulation, and the sampling frequency is also 50Hz. It is in the same frequency as the fundamental frequency of the power grid, so the influence of power frequency interference on the loop can be directly observed. The relative humidity sequence can be output in real time through the digital humidity module (e.g., SHT30) of the vehicle chassis. The main control MCU is aligned with the resistance sequence according to the timestamp. The timestamps of all sequences are unified through the existing GNSS module to ensure zero drift of different sequences in the same second.

[0023] In one embodiment of the present invention, the sliding window size and step size of the median filter are both user-defined parameters. The median of all impedance values ​​within each sliding window is extracted and arranged in the sliding order to obtain the steady-state baseline. For example, if the sliding window size and step size are both set to 7, and the length of the low-frequency impedance sequence is between 9000 and 24000, then the number of data points for the steady-state baseline is between 1286 and 3428. The formula for calculating the number of data points for the steady-state baseline is as follows: , where Len represents the sequence length, and Wid and Step represent the sliding window size and step size, respectively.

[0024] It should be noted that median filtering has a strong ability to suppress transient interference such as pulses and spikes. It can effectively eliminate the sudden drop in resistance pulses caused by salt film reliquefaction and retain the long-term trend of metal contact resistance (such as resistance rise caused by slow corrosion). In other words, the steady-state baseline reflects the true resistance level of the grounding system when there is no transient interference, providing a basis for subsequent pulse event detection.

[0025] In one embodiment of the present invention, the mean of the sequence is first subtracted from each data point in the high-frequency impedance sequence, and then the sequence is decomposed into approximate coefficients and detail coefficients by a discrete wavelet transform with a custom decomposition level. The sum of the absolute values ​​of all detail coefficients is taken as the salt bridge conductivity coefficient. Preferably, the decomposition level of the discrete wavelet transform is set to 4.

[0026] It should be noted that removing the DC component can eliminate the masking of high-frequency features by the overall signal offset and highlight the fluctuations caused by the transient conductivity of the salt film. The conductivity coefficient of the salt bridge directly reflects the conductivity of the salt bridge. Under normal conditions, the conductivity coefficient of the salt bridge is close to 0. During the short-circuit pulse of the salt film, it can rise to 5 to 10 times the baseline. Discrete wavelet transform can accurately separate high-frequency details from low-frequency trends. The transient conductivity characteristics of the salt film can be captured by simply summing the detail coefficients, avoiding the excessive smoothing of transient signals by traditional filtering methods, thereby improving the accuracy of salt bridge identification.

[0027] In one embodiment of the present invention, the joint detection conditions include: Condition 1. Extract data points from the steady-state baseline that are at the same timestamp as each impedance value in the low-frequency impedance sequence, calculate the ratio of the difference between the two data points to the former data point as the relative decrease, and determine that the relative decrease is greater than or equal to a first preset threshold, wherein the first preset threshold is a custom parameter, preferably set to 0.3; Condition 2. Extract the impedance values ​​from the original impedance sequence that are at the same time stamp as each impedance value in the high-frequency resistance sequence, calculate the ratio of the difference between the two to the data point of the former as the high-frequency difference, and determine that the high-frequency difference is greater than or equal to the second preset threshold, wherein the second preset threshold is a custom parameter, preferably, the first preset threshold is set to 0.2; Condition 3. Determine that each relative humidity in the relative humidity sequence is greater than or equal to a third preset threshold and the relative humidity change rate is greater than or equal to a fourth preset threshold, wherein the third preset threshold and the fourth preset threshold are custom parameters. Preferably, the third preset threshold is set to 0.9 and the fourth preset threshold is set to 0.05. Condition 4. Extract the impedance values ​​from the high-frequency impedance sequence that are at the same time stamp as each impedance value in the low-frequency resistance sequence, calculate the ratio of the two as the spectrum ratio, and determine that the spectrum ratio is less than or equal to the fifth preset threshold, where the fifth preset threshold is a custom parameter, preferably set to 0.2.

[0028] It should be noted that in condition 1, the number of data points in the steady-state baseline is the same as the number of impedance values ​​in the low-frequency impedance sequence, i.e., the step size of the sliding window for median filtering is 1. If the two numbers are different, the low-frequency impedance sequence is used as the reference, and data points at the same or previous timestamp as each impedance value in the low-frequency impedance sequence are extracted from the steady-state baseline. For condition 1, when a transient short circuit occurs during salt film reliquefaction, the ionic conductivity increases, and the impedance of the low-frequency current will decrease significantly. At this time, the actual value of the low-frequency impedance sequence will be much smaller than the steady-state baseline. For condition 2, when a transient short circuit occurs during salt film reliquefaction, the high-frequency impedance decreases significantly due to the presence of the salt bridge. For condition 3, the essence of salt film reliquefaction is that the salt film absorbs moisture and changes from a solid to a liquid state, and high humidity is a necessary environmental condition for the hygroscopic liquefaction of the salt film. For condition 4, when a transient short circuit occurs during salt film reliquefaction, the high-frequency impedance will be much smaller than the low-frequency impedance, and the ratio between the two will decrease significantly.

[0029] In one embodiment of the present invention, the start and end timestamps of each pulse event are determined, and the integral of the relative decrease during this period is calculated as the pulse energy value.

[0030] In one embodiment of the present invention, a Rogowski coil is arranged on each side of the front and sides of the vehicle body of the closed grounding loop. The time when the instantaneous short-circuit current caused by the formation of the salt bridge is recorded to reach the coil. The time difference of the current arrival on both sides of the vehicle body is calculated based on the time when the current at the front of the vehicle reaches the coil. The time difference is converted into the azimuth angle of the salt bridge relative to the coil layout by the time difference positioning algorithm as the azimuth angle of the salt bridge. The direction of the vehicle body is the positive horizontal axis, the direction of the front of the vehicle is 0°, the left side of the vehicle body is +90°, and the right side of the vehicle body is -90°.

[0031] It should be noted that the time difference positioning algorithm calculates the distance difference by multiplying the speed of light by the time difference, and then uses the trigonometric function formula for the azimuth of the salt bridge to solve for the azimuth of the salt bridge. In addition, a mapping table between the known azimuth of the salt bridge and the time difference can be established, which will not be elaborated here.

[0032] In one embodiment of the present invention, the two-dimensional pulse space matrix uses the pulse event end time as the vertical index and the salt bridge azimuth angle partition as the horizontal index, and the matrix element value is the pulse energy value, wherein 0° to 360° is divided into 12 discrete angular regions at 30° intervals.

[0033] It should be noted that the two-dimensional pulse space matrix allows salt bridge short-circuit events to be presented intuitively on a time and orientation grid, making it easy to quickly identify high-incidence areas and quantify the severity of events. The discrete angular region can also significantly reduce the amount of data, thereby accelerating the calculation speed of the pulse stress index.

[0034] In one embodiment of the present invention, the pulse stress index (PSI) is calculated by extracting element values ​​from a two-dimensional pulse space matrix based on the start and end timestamps of a preset analysis time window. The formula for calculating the PSI is as follows: Where M represents the number of discrete azimuth angles. This represents the number of pulse events corresponding to the i-th azimuth angle. This represents the azimuth weight of the i-th discrete azimuth angle. This represents the pulse energy value of the j-th pulse event at the i-th azimuth angle.

[0035] It should be noted that the preset analysis time window is a custom parameter. Preferably, the preset analysis time window is set to the most recent 3 minutes. The azimuth weights of different discrete azimuth angles are custom parameters with a total value of 1. The settings are adjusted according to the differences in the structure, corrosion risk, or maintenance priority of different vehicle locations. For example, water is more likely to accumulate at the bottom of the vehicle body, resulting in a higher risk of salt bridge corrosion. The larger the value of the pulse stress index, the greater the overall risk of salt bridge corrosion in the vehicle's grounding system.

[0036] In one embodiment of the present invention, the average value of the impedance values ​​without pulse events is extracted from the original resistance sequence according to the start and end timestamps of the preset analysis time window as a temporary DC resistance, and the average value of the two ends of the steady-state baseline is extracted from the steady-state baseline according to the start and end timestamps of the preset analysis time window as the baseline drift. The difference between the temporary DC resistance and the baseline drift is used as the steady-state DC resistance.

[0037] It should be noted that the circuit resistance of hazardous chemical vehicles drops sharply and instantaneously when a salt film short-circuit pulse occurs. If the average of the entire original resistance sequence is directly calculated, the impedance value of the pulse event will lower the average value and mask the true grounding condition. Therefore, it is necessary to first remove the impedance values ​​of all pulse events to represent the steady-state conductivity of hazardous chemical vehicles. Temperature, humidity, or thermal expansion and contraction of materials will also slowly change the metal contact resistance. Therefore, the average value of the two ends of the steady-state baseline is extracted as the baseline drift to eliminate slowly changing environmental factors and make the final steady-state DC resistance closer to the true value.

[0038] In one embodiment of the present invention, both the preset resistance threshold and the preset index threshold are custom parameters. Preferably, the preset resistance threshold is set to 10 ohms, and the pulse stress index threshold can be dynamically set according to the region. For example, based on the pulse stress index of the past 30 days, the pulse stress index threshold of the normal region is set to the sum of the mean and three times the standard deviation, and the pulse stress index threshold of the high-altitude and high-salt region is set to the sum of the mean and two times the standard deviation.

[0039] It should be noted that in conventional areas (such as dry inland areas), pulse stress mainly comes from occasional vibrations and transient poor contact. The pulse stress index fluctuation is characterized by low amplitude and low frequency. Three times the standard deviation (covering the 99.7% confidence interval) can effectively filter out normal noise and avoid misjudging slight disturbances as corrosion anomalies. In cold and saline areas (such as coastal areas and northern winter snowmelt areas), pulse stress is affected by salt spray and freeze-thaw cycles. The corrosion process is faster and the pulse signal is more complex. Using two times the standard deviation (covering the 95% confidence interval) can narrow the threshold range and make it more sensitive to small stress changes caused by early corrosion, thus providing early warning.

[0040] In one embodiment of the present invention, the self-calibration strategy is to continuously blow 50°C hot air into the underside of the vehicle and the grounding electrode for 5 minutes to remove moisture from the surface of the grounding electrode. After standing for 2 minutes, the process returns to steps S101 to S105. If the grounding resistance is qualified, the vehicle is automatically released and marked as self-calibration successful in the log. Otherwise, the vehicle is locked, a maintenance task is generated, and a prompt is made to check the grounding wire, grounding electrode backfill, frame bolts, etc.

[0041] It should be noted that the testing indicator for a grounding system is the grounding resistance value, which is typically measured using a grounding resistance tester, such as... Figure 4 As shown, a three-level detection method is used, with current electrodes (C), voltage electrodes (P), and the grounding electrode (E) arranged in a straight line, with a spacing of at least 20m. The test voltage is between 50V and 1000V. In online monitoring in hazardous chemical environments, this method cannot meet relevant explosion-proof requirements. Furthermore, the down conductor must be electrically disconnected from the protected object during testing; otherwise, online monitoring will cause damage to the protected object. In hazardous chemical fields, due to the large applied voltage and current, explosion-proof requirements cannot be met. This invention uses a double grounding stake equipotential connection and a clamp-on method for testing on the equipotential connection line. If either grounding stake is faulty, the test will fail. This not only enhances the reliability of the grounding effect but also easily meets safety and explosion-proof standards due to the extremely small test voltage and current of the clamp-on method. During online monitoring, it is not necessary to disconnect other protective equipment connected to the grounding stakes. The test circuit is formed by the natural connection between the equipotential connection line and the earth. The tested resistance value is the sum of the resistance of the two grounding points. If the grounding resistance of either grounding point exceeds the preset resistance threshold, it is considered a faulty grounding.

[0042] It should be noted that the interval and threshold sizes are set for ease of comparison. The size of the threshold depends on the amount of sample data and the base number set by those skilled in the art for each set of sample data, as long as it does not affect the proportional relationship between the parameter and the quantized value. Furthermore, the above formulas are all dimensionless calculations, and the formulas are derived from software simulations using a large amount of collected data to obtain the most recent real-world results. The preset parameters in the formulas are set by those skilled in the art according to the actual situation.

[0043] The embodiments of this example have been described above. However, this example is not limited to the specific implementation methods described above. The specific implementation methods described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms based on the guidance of this example, and all of them are within the protection scope of this example.

Claims

1. A method for determining the compliance of grounding resistance in hazardous chemical vehicles, characterized in that, Includes the following steps: Step S101: Inject low-frequency current and high-frequency current into the closed grounding loop respectively, and collect the loop voltage to obtain the low-frequency impedance sequence and high-frequency impedance sequence respectively, and simultaneously collect the original resistance sequence and relative humidity sequence. Step S102: Apply medium filtering to the low-frequency impedance sequence to obtain a steady-state baseline, and apply discrete wavelet transform to the high-frequency impedance sequence to extract the salt bridge conductivity coefficient. Step S103: When the joint detection conditions are met simultaneously, it is identified as a transient short-circuit pulse event of salt film reliquefaction. Step S104: Calculate the pulse energy value for each pulse event, use the current arrival difference collected by the distributed coil to determine the salt bridge azimuth angle, and write the pulse energy value, salt bridge azimuth angle and pulse event end time into the two-dimensional pulse space matrix. Step S105: Within the preset analysis time window, the pulse stress index is obtained based on the two-dimensional pulse space matrix and combined with the azimuth weight accumulation, and the steady-state DC resistance is calculated in the pulse-free section. Step S106: If the steady-state DC resistance is less than or equal to the preset resistance threshold and the pulse stress index is less than or equal to the preset index threshold, the grounding resistance of the hazardous chemical vehicle is deemed qualified; otherwise, it is deemed unqualified, and a self-calibration strategy is executed. Both the preset resistance threshold and the preset exponent threshold are custom parameters. The self-calibration strategy is to continuously blow 50°C hot air into the vehicle underside and the grounding electrode for 5 minutes to remove moisture from the surface of the grounding electrode. After standing for 2 minutes, return to steps S101 to S105 to execute. If the grounding resistance is qualified, the vehicle will be automatically released and marked as self-calibration successful in the log. Otherwise, the vehicle will be locked and a maintenance task will be generated.

2. The method for determining the pass / fail qualification of resistance grounding applied to hazardous chemical vehicles according to claim 1, characterized in that, The sliding window size and step size of the median filter are custom parameters. The median of all impedance values ​​within each sliding window is extracted and arranged in the sliding order to obtain the steady-state baseline.

3. The method for determining the pass / fail qualification of resistance grounding applied to hazardous chemical vehicles according to claim 1, characterized in that, First, subtract the mean of the sequence from each data point in the high-frequency impedance sequence. Then, decompose it into approximate coefficients and detail coefficients using a discrete wavelet transform with a custom decomposition level. The sum of the absolute values ​​of all detail coefficients is taken as the salt bridge conductivity coefficient.

4. The method for determining the pass / fail qualification of resistance grounding applied to hazardous chemical vehicles according to claim 1, characterized in that, The joint testing conditions include: Condition 1. Extract data points from the steady-state baseline that are at the same timestamp as each impedance value in the low-frequency impedance sequence, calculate the ratio of the difference between the two data points to the former data point as the relative decrease, and determine whether the relative decrease is greater than or equal to the first preset threshold, where the first preset threshold is a user-defined parameter; Condition 2. Extract the impedance values ​​from the original impedance sequence that are at the same time stamp as each impedance value in the high-frequency resistance sequence, calculate the ratio of the difference between the two to the data point of the former as the high-frequency difference, and determine whether the high-frequency difference is greater than or equal to the second preset threshold, where the second preset threshold is a user-defined parameter; Condition 3. Determine that for each relative humidity in the relative humidity sequence, the relative humidity is greater than or equal to the third preset threshold and the relative humidity change rate is greater than or equal to the fourth preset threshold, where the third preset threshold and the fourth preset threshold are custom parameters; Condition 4. Extract the impedance values ​​from the high-frequency impedance sequence that are at the same timestamp as each impedance value in the low-frequency resistance sequence, calculate the ratio of the two as the spectrum ratio, and determine that the spectrum ratio is less than or equal to the fifth preset threshold, where the fifth preset threshold is a user-defined parameter.

5. The method for determining the pass / fail qualification of resistance grounding applied to hazardous chemical vehicles according to claim 4, characterized in that, Determine the start and end timestamps of each pulse event, and calculate the integral of the relative decrease during this period as the pulse energy value.

6. The method for determining the pass / fail qualification of resistance grounding applied to hazardous chemical vehicles according to claim 1, characterized in that, A Rogowski coil is placed on each side of the front and sides of the vehicle body in a closed grounding loop. The time it takes for the instantaneous short-circuit current triggered by the formation of the salt bridge to reach the coil is recorded. The time difference between the arrival times of the current on both sides of the vehicle body is calculated based on the time it takes for the current to reach the coil at the front of the vehicle body. The time difference is converted into the azimuth angle of the salt bridge relative to the coil layout using a time difference positioning algorithm. The direction of the vehicle body is taken as the positive horizontal axis, with the direction of the front of the vehicle body at 0°, the left side of the vehicle body at +90°, and the right side of the vehicle body at -90°.

7. The method for determining the pass / fail qualification of resistance grounding applied to hazardous chemical vehicles according to claim 1, characterized in that, The two-dimensional pulse space matrix uses the pulse event end time as the vertical index and the salt bridge azimuth partition as the horizontal index. The matrix element value is the pulse energy value, and the 0° to 360° range is divided into 12 discrete angular regions at 30° intervals.

8. The method for determining the grounding qualification of hazardous chemical vehicles according to claim 7, characterized in that, The pulse stress index (PSI) is calculated by extracting element values ​​from the two-dimensional pulse space matrix based on the start and end timestamps of the preset analysis time window. The formula for calculating the PSI is as follows: Where M represents the number of discrete azimuth angles. This represents the number of pulse events corresponding to the i-th azimuth angle. This represents the azimuth weight of the i-th discrete azimuth angle. This represents the pulse energy value of the j-th pulse event at the i-th azimuth angle.

9. The method for determining the pass / fail qualification of resistance grounding applied to hazardous chemical vehicles according to claim 1, characterized in that, The average value of the impedance values ​​without pulse events is extracted from the original resistance sequence according to the start and end timestamps of the preset analysis time window as the temporary DC resistance. The average value of the two ends of the steady-state baseline is extracted from the steady-state baseline according to the start and end timestamps of the preset analysis time window as the baseline drift. The difference between the temporary DC resistance and the baseline drift is taken as the steady-state DC resistance.

10. The method for determining the pass / fail qualification of resistance grounding applied to hazardous chemical vehicles according to claim 1, characterized in that, The system employs a double grounding stake equipotential bonding system, using a clamp-on method for testing on the equipotential bonding line. If either grounding stake is faulty, the test will fail. Furthermore, online monitoring can be performed without disconnecting other protective devices connected to the grounding stake.

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