A method and device for automatic compensation of grounding resistance of cable branch boxes

Abstract

This invention discloses an automatic compensation method and device for grounding resistance of cable branch boxes, belonging to the technical field of power distribution equipment. The method includes: determining target resistance compensation information based on environmental data and grounding resistance detection information; and automatically compensating the grounding resistance of the cable branch box based on the target resistance compensation information to maintain the grounding resistance constant at a set value. Specifically, using resistance combination mapping information, based on soil moisture value and the current actual grounding resistance value, a parallel resistor switching scheme that makes the system's equivalent grounding resistance equal to the set value is determined as the optimal resistance combination, and a relay drive command is generated to drive a relay array to switch the parallel resistors in the adjustable resistor network. This invention also provides a corresponding compensation system, electronic device, cable branch box, and storage medium. This invention can automatically sense environmental changes and compensate for grounding resistance in real time, solving the problem that traditional fixed grounding schemes cannot adapt to dynamic changes in the soil environment.

Description

Technical Field

[0001] This application relates to the field of power distribution equipment technology, and in particular to a method and apparatus for automatic compensation of grounding resistance of cable branch boxes. Background Technology

[0002] With the rapid development of urban power distribution networks, cable distribution boxes, as important node equipment in medium and low voltage power distribution systems, are widely used in power distribution in urban residential areas, commercial areas, and industrial parks. The grounding system of cable distribution boxes is a key protective measure to ensure the safe operation of equipment and personal safety. Its grounding resistance value must meet national standards and is usually maintained below 4Ω.

[0003] In relevant cable branch box grounding technology solutions, the traditional approach mainly uses fixed grounding electrodes combined with chemical resistance-reducing agents. Once the grounding resistance is adjusted to a qualified value during equipment installation and commissioning, no further dynamic adjustments are made during subsequent operation. However, the actual value of grounding resistance is greatly affected by soil environmental factors. Soil resistivity changes significantly with seasonal fluctuations in parameters such as soil moisture content, temperature, and salinity. For example, during the rainy season in summer, soil moisture content is high, soil resistivity is low, and the grounding resistance may drop below the design value; while in the dry winter or during periods of frozen soil, the soil moisture content drops sharply or freeze-thaw cycles occur, causing the soil resistivity to rise dramatically, resulting in the grounding resistance significantly exceeding the standard limit.

[0004] The shortcomings of the existing technologies mentioned above are that fixed grounding schemes cannot adapt to dynamic changes in the soil environment. When the grounding resistance exceeds the standard due to seasonal factors, problems can only be detected through regular manual inspections, followed by passive remediation by adding grounding electrodes or resistance-reducing agents. This approach not only has a delayed response and a long window of opportunity for potential safety hazards, but also incurs high manual maintenance costs, making it difficult to guarantee the frequency and coverage of inspections in remote areas or when there are a large number of devices. Therefore, there is an urgent need for a technical solution that can automatically sense environmental changes and compensate for grounding resistance in real time. Summary of the Invention

[0005] In view of the above problems, this application provides a method and device for automatic compensation of grounding resistance of cable branch boxes, which can automatically adjust the configuration of parallel resistance network according to soil moisture and seasonal changes, maintain the grounding resistance of cable branch boxes at a constant set value, and solve the technical problem of grounding resistance getting out of control with environmental changes in the prior art.

[0006] In some embodiments, an automatic compensation method for the grounding resistance of a cable branch box is provided, comprising: determining target resistance compensation information based on environmental acquisition information and grounding resistance detection information; automatically compensating the grounding resistance of the cable branch box based on the target resistance compensation information to maintain the grounding resistance constant at a set value; wherein the environmental acquisition information includes soil moisture value, the grounding resistance detection information includes current actual grounding resistance value, and the target resistance compensation information includes optimal resistance combination of an adjustable resistance network; determining the target resistance compensation information based on the environmental acquisition information and grounding resistance detection information comprises: using resistance combination mapping information, determining a parallel resistance switching scheme that makes the system equivalent grounding resistance equal to the set value based on the soil moisture value and the current actual grounding resistance value, as the optimal resistance combination; wherein the resistance combination mapping information includes: the mapping relationship between the soil moisture value, the current actual grounding resistance value, and the optimal resistance combination; automatically compensating the grounding resistance of the cable branch box comprises: generating a relay driving command based on the optimal resistance combination, driving a relay array to switch the parallel resistance in the adjustable resistance network.

[0007] In this embodiment, by collecting two key pieces of information, soil moisture and actual grounding resistance value, the current grounding status is comprehensively judged, and the optimal compensation scheme is quickly determined by using the resistance combination mapping relationship, thus realizing closed-loop automatic control of grounding resistance. This ensures that the grounding system continuously meets safety standards without manual intervention.

[0008] In some embodiments, the environmental acquisition information and the grounding resistance detection information are obtained through periodic sampling; the periodic sampling includes: collecting the soil moisture value through a humidity sensor according to a preset sampling period; and measuring the current actual grounding resistance value through a grounding resistance testing module according to the preset sampling period.

[0009] In this embodiment, the periodic sampling strategy can ensure that the system can perceive environmental changes in a timely manner, while avoiding unnecessary energy consumption caused by continuous monitoring, thus achieving a balance between monitoring accuracy and system power consumption.

[0010] In some embodiments, the method further includes: determining a grounding resistance deviation value based on the current actual grounding resistance value and the set value; determining to perform automatic compensation of the grounding resistance of the cable branch box if the grounding resistance deviation value exceeds a preset deviation threshold; and determining to maintain the current resistance network configuration if the grounding resistance deviation value does not exceed the preset deviation threshold.

[0011] In this embodiment, by setting a deviation threshold as a trigger condition, frequent relay operation caused by minor measurement fluctuations is avoided, extending the service life of the relay and resistive elements, while ensuring timely response and compensation when the deviation is significant.

[0012] In some embodiments, determining the parallel resistor switching scheme that makes the system equivalent grounding resistance equal to the set value using resistor combination mapping information includes: traversing discrete combinations of the on / off states of each branch relay according to the resistance value parameters of each branch resistor in the adjustable resistor network, calculating the equivalent parallel resistance value of the adjustable resistor network under each combination; calculating the system equivalent grounding resistance value under each combination according to the current actual grounding resistance value and the equivalent parallel resistance value corresponding to each combination; and selecting the combination that minimizes the deviation between the system equivalent grounding resistance value and the set value as the optimal resistor combination.

[0013] In this embodiment, by traversing all discrete combinations and selecting the scheme with the smallest deviation, the globally optimal solution is ensured under the constraint of finite resistance ranges, thereby maximizing the compensation accuracy.

[0014] In some embodiments, the method further includes: determining a current soil resistivity estimate based on the soil moisture value using moisture-resistivity mapping information; predicting the trend of change of the current actual grounding resistance value based on the current soil resistivity estimate; and adjusting the sampling frequency of the periodic sampling based on the trend of change; wherein the moisture-resistivity mapping information includes the mapping relationship between the soil moisture value and the soil resistivity.

[0015] In this embodiment, the correlation between humidity and resistivity is used to predict the changing trend of grounding resistance. When the environment changes drastically, the sampling frequency is increased to speed up the response, and when the environment is stable, the sampling frequency is reduced to save power consumption, thus realizing an adaptive intelligent sampling strategy.

[0016] According to a second aspect of this application, an automatic compensation system for grounding resistance of a cable branch box is provided, comprising: a humidity sensor for collecting soil moisture values; a grounding resistance testing module for measuring the current actual grounding resistance value; an adjustable resistance network including multiple parallel resistance branches; a relay array connected to each parallel resistance branch of the adjustable resistance network for engaging or disengaging the corresponding parallel resistance branch; and a microcontroller connected to the humidity sensor, the grounding resistance testing module, and the relay array respectively, for calculating an optimal resistance combination based on the soil moisture value and the current actual grounding resistance value, and driving the relay array to engage or disengage the parallel resistance branches in the adjustable resistance network according to the optimal resistance combination, so as to maintain the system grounding resistance constant at a set value.

[0017] According to a third aspect of this application, an electronic device is provided, including a memory and a processor coupled to the memory, the processor being configured to execute the automatic compensation method for grounding resistance of cable branch boxes as described in any of the above embodiments based on instructions stored in the memory.

[0018] According to a fourth aspect of this application, a cable branch box is provided, including a box body, a cable branching device disposed in the box body, a grounding electrode connected to the grounding terminal of the cable branching device, and an automatic grounding resistance compensation system for the cable branch box, wherein an adjustable resistance network of the automatic compensation system is connected in parallel with the grounding electrode.

[0019] According to a fifth aspect of this application, a computer-readable storage medium is provided, wherein computer program instructions are stored therein, and when the computer program instructions are executed by a processor, the automatic compensation method for grounding resistance of cable branch boxes described in any of the above embodiments is implemented.

[0020] Compared with existing technologies, the beneficial effects of this application are as follows: it breaks through the inherent limitations of traditional water injection / resistance reduction liquid physical intervention schemes and distribution network neutral point fault switching schemes, and transfers the parallel resistor switching technology from the field of relay protection to the field of constant value compensation of cable branch box grounding resistance, and constructs a closed-loop control system of environmental perception, state measurement, deviation judgment, precise approximation and automatic compensation. Compared to water injection schemes, which rely on water infiltration and diffusion resulting in response delays of several hours to several days, are unavailable in arid and frozen soil regions, and cause grounding electrode corrosion due to frequent water injection, this application achieves millisecond-level response through pure electrical compensation. It is not limited by water source or climate conditions, and the compensation process is completely reversible and does not damage the grounding electrode itself. Compared to neutral point fault switching schemes, which are limited to a single transient action during a fault, this application can repeat precise adjustments infinitely over operating cycles of several months or even years. By setting deviation thresholds, it effectively avoids frequent actions caused by measurement fluctuations, significantly extending the lifespan of relays and resistors. Simultaneously, the binary weighted adjustable resistor network design allows a limited number of branches to cover a wide range of resistance adjustment needs, achieving a balance between hardware cost and compensation accuracy. Furthermore, the introduction of soil moisture sensing and adaptive sampling frequency adjustment mechanisms enables the system to predict environmental change trends, automatically increasing monitoring density during drastic environmental changes and reducing power consumption during stable environments, achieving intelligent, low-power, long-term unattended operation. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the main flow of an automatic compensation method for grounding resistance of cable branch boxes provided in some embodiments of this application.

[0022] Figure 2This is a schematic diagram of a sub-process for periodically sampling to obtain environmental information and grounding resistance detection information, provided for some embodiments of this application.

[0023] Figure 3 This is a schematic diagram illustrating the logical flow of deviation judgment and triggering compensation decision provided in some embodiments of this application.

[0024] Figure 4 This is a schematic diagram of a sub-process for calculating the optimal resistance combination provided in some embodiments of this application.

[0025] Figure 5 This is a flowchart illustrating the adaptive sampling frequency adjustment logic provided in some embodiments of this application.

[0026] Figure 6 The diagram shows the circuit topology of the adjustable resistor network and relay array provided in some embodiments of this application.

[0027] Figure 7 This is a schematic diagram of the module architecture of an automatic compensation system for grounding resistance of cable branch boxes provided in some embodiments of this application.

[0028] Figure 8 This is a schematic diagram of the hardware structure of an electronic device provided in some embodiments of this application.

[0029] Figure 9 This is a schematic diagram showing the overall structure and system installation location of a cable branch box provided in some embodiments of this application.

[0030] Figure 10 This is a schematic diagram illustrating the mapping relationship between soil moisture and soil resistivity provided for some embodiments of this application. Detailed Implementation

[0031] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings.

[0032] It should be understood that in the description of this application, terms such as "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. "And / or" means any and all combinations of one or more related listed items. Terms such as "comprising" and "including" mean that the elements or objects preceding "comprising" or "including" cover the elements or objects listed after "comprising" or "including" and their equivalents, and do not exclude other elements or objects.

[0033] It should be understood that in this application, "connection" can be a direct connection or an indirect connection through an intermediate element, and "electrical connection" can be a wired connection or a wireless connection. The directional terms such as "upper," "lower," "inner," and "outer" are relative to the placement of the components in the drawings and are used only for the convenience and simplification of description, and do not indicate or imply that the device or element referred to must have a specific orientation.

[0034] To enable those skilled in the art to better understand the present application, a brief explanation of the technical background knowledge involved in the present application will be provided below.

[0035] Cable distribution boxes are sealed switchgear used in power distribution networks to branch, converge, and transfer cable lines. They are typically installed outdoors or underground, and their metal casings must be reliably grounded to prevent electric shock hazards caused by insulation failures. Grounding systems usually consist of grounding electrodes (such as vertical grounding rods or horizontal grounding strips) buried in the soil. The grounding resistance value is determined by the geometric parameters of the grounding electrodes and the soil resistivity. Soil resistivity is a parameter measuring the conductivity of soil, and its value is affected by various factors such as soil type, moisture content, temperature, and chemical composition, typically varying between tens and thousands of Ω•m. When soil moisture content decreases or the temperature drops below freezing, soil resistivity increases significantly, causing the grounding resistance value to exceed standard limits.

[0036] An adjustable resistor network is a circuit structure in which multiple resistor branches with fixed resistance values ​​are connected in controllable parallel connection through switching elements (such as relays). When a relay in a branch is closed, the resistance of that branch is added to the parallel network; when the relay is open, that branch is disconnected. By combining different branch switching operations, various equivalent resistance values ​​can be obtained. If the resistance values ​​of each branch are set according to binary weights (such as R, 2R, 4R, 8R, etc.), then N branches can achieve 2... N A variety of equivalent resistance values ​​are available, covering a wide adjustment range.

[0037] The embodiments of this application will be described in detail below with reference to the accompanying drawings.

[0038] like Figure 1 As shown in the figure, this application provides an automatic compensation method for the grounding resistance of a cable branch box, including the following steps: Step S101: Determine the target resistance compensation information based on the environmental data and grounding resistance detection information.

[0039] Specifically, in this step, the system acquires environmental data reflecting the current environmental state and grounding resistance detection data characterizing the current grounding system state, and calculates the optimal resistance compensation scheme based on these data.

[0040] The environmental data collected includes soil moisture content. Soil moisture content reflects the water content of the soil surrounding the grounding electrode and is a key factor affecting soil resistivity. For example, in some embodiments, the moisture sensor measures the current soil volumetric moisture content to be 15%, corresponding to a relatively dry soil condition.

[0041] The grounding resistance detection information includes the current actual grounding resistance value. This value is obtained through actual measurement by the grounding resistance testing module and reflects the true resistance state of the grounding system under current conditions. For example, in some embodiments, the grounding resistance testing module uses the three-electrode method to measure the current actual grounding resistance value as 6.8Ω, which exceeds the set value of 4Ω.

[0042] The target resistance compensation information includes the optimal resistance combination for the adjustable resistor network. This combination specifies whether the relays in each branch of the adjustable resistor network should be closed or open, so that the equivalent grounding resistance of the system after the ground electrode is connected in parallel with the adjustable resistor network is equal to or closest to the set value.

[0043] In some embodiments, by utilizing resistance combination mapping information, a parallel resistor switching scheme that makes the system's equivalent grounding resistance equal to a set value is determined based on the soil moisture value and the current actual grounding resistance value, as the optimal resistance combination.

[0044] The resistance combination mapping information includes the mapping relationship between soil moisture value and current actual grounding resistance value and the optimal resistance combination. This mapping relationship can be represented as a pre-stored lookup table or as a calculation algorithm executed in real time by the microcontroller.

[0045] For example, in some embodiments, the set value is 4Ω, while the current actual grounding resistance is 6.8Ω. According to the parallel resistance formula, the equivalent resistance R of the compensation resistor network to be implemented is... p It should satisfy: 1 / 4 = 1 / 6.8 + 1 / R p R is calculated p ≈9.71Ω. Based on this, the microcontroller searches for the combination with the equivalent parallel resistance closest to 9.71Ω among all possible combinations of the adjustable resistor network, and determines it as the optimal resistor combination.

[0046] Step S102: Based on the target resistance compensation information, automatically compensate the grounding resistance of the cable branch box to maintain the grounding resistance at a constant set value.

[0047] Specifically, based on the optimal resistor combination, the microcontroller generates relay drive instructions, and outputs high-level or low-level signals to each relay in the relay array through the drive circuit, so that the corresponding relay is closed or opened, completing the connection or disconnection operation of the parallel resistor branch in the adjustable resistor network.

[0048] For example, in some embodiments, the adjustable resistor network comprises five branches with resistances of 10Ω, 20Ω, 40Ω, 80Ω, and 160Ω. The microcontroller calculates and determines that the parallel combination of the first branch (10Ω) and the third branch (40Ω) needs to be activated, with an equivalent resistance of 10×40 / (10+40)=8Ω. At this point, the system's equivalent ground resistance is 6.8×8 / (6.8+8)=3.68Ω, close to the set value of 4Ω. The microcontroller outputs a closing command to the relays corresponding to the first and third branches, and an opening command to the relays of the remaining branches.

[0049] In this embodiment, real-time compensation of grounding resistance is achieved by automatically switching parallel resistors, eliminating the need for manual inspection and operation, which significantly improves the reliability and maintenance efficiency of the grounding protection system.

[0050] like Figure 2 As shown, in some embodiments, environmental acquisition information and grounding resistance detection information are obtained through periodic sampling, specifically including the following sub-steps: Step S201: Collect soil moisture values ​​using a humidity sensor according to a preset sampling period.

[0051] In some embodiments, the preset sampling period is 4 hours, meaning the system activates the humidity sensor to collect soil moisture data every 4 hours. The humidity sensor can be a capacitive soil moisture sensor, buried in the soil near the grounding electrode, with the measurement depth consistent with the burial depth of the grounding electrode (e.g., 0.8m to 1.2m).

[0052] For example, in one sampling, the humidity sensor returned a soil volumetric moisture content reading of 22%, indicating that the soil was in a moderately moist state.

[0053] Step S202: Measure the current actual grounding resistance value using the grounding resistance test module according to the preset sampling period.

[0054] In some embodiments, the grounding resistance testing module employs a constant current injection method (frequency conversion method), injecting a small-amplitude alternating current of a specific frequency into the grounding electrode, measuring the voltage drop between the grounding electrode and the distant reference electrode, and calculating the grounding resistance value. This module is integrated into the system and operates synchronously with the humidity sensor, being woken up by the microcontroller in each sampling cycle to perform the measurement.

[0055] For example, during the same sampling period mentioned above, the grounding resistance test module measured the current actual grounding resistance value to be 5.2Ω.

[0056] In this embodiment, periodic sampling enables the system to continuously track the impact of environmental changes on grounding resistance. The selection of the sampling period needs to balance response speed and system power consumption: a period that is too short will increase power consumption and the number of relay actions, while a period that is too long may cause the grounding resistance to exceed the limit for an excessively long time. A 4-hour sampling period is suitable for general environments, and can be shortened to 1 hour in areas with frequent extreme weather.

[0057] like Figure 3 As shown, in some embodiments, a deviation determination step is included before determining the target resistance compensation information: Step S301: Determine the grounding resistance deviation value based on the current actual grounding resistance value and the set value.

[0058] Specifically, the grounding resistance deviation value = |current actual grounding resistance value - set value|. For example, if the current actual grounding resistance value is 5.2Ω and the set value is 4Ω, then the deviation value = |5.2 - 4| = 1.2Ω.

[0059] Step S302: Determine whether the grounding resistance deviation value exceeds the preset deviation threshold.

[0060] In some embodiments, the preset deviation threshold is set to 0.5Ω. This threshold setting takes into account factors such as measurement error and relay fatigue, avoiding unnecessary compensation actions triggered by minor measurement fluctuations.

[0061] Step S303: If the grounding resistance deviation value exceeds the preset deviation threshold, determine to perform automatic compensation for the grounding resistance of the cable branch box.

[0062] Continuing with the above values, the deviation value of 1.2Ω is greater than the deviation threshold of 0.5Ω. The system determines that a compensation operation needs to be performed and proceeds to the optimal resistance combination calculation process in step S101.

[0063] Step S304: If the grounding resistance deviation value does not exceed the preset deviation threshold, determine to maintain the current resistor network configuration unchanged.

[0064] For example, if the current actual grounding resistance is 4.3Ω, and the deviation value is |4.3-4|=0.3Ω<0.5Ω, the system determines that the current grounding resistance is within an acceptable range, does not perform compensation operation, and maintains the existing relay state until the next sampling period.

[0065] In this embodiment, the deviation threshold mechanism effectively avoids frequent relay operation. The mechanical lifespan of a relay is typically between 100,000 and 1 million cycles; if every small fluctuation triggers a switch, the system's lifespan will be significantly shortened. By setting a reasonable dead-zone threshold, the system only performs adjustments when the grounding resistance truly deviates from the safe range, balancing safety and durability.

[0066] like Figure 4 As shown, in some embodiments, the specific calculation process for the optimal resistor combination includes the following sub-steps: Step S401: Based on the resistance parameters of each branch resistor in the adjustable resistor network, iterate through the discrete combinations of the on / off states of each branch relay, and calculate the equivalent parallel resistance value of the adjustable resistor network under each combination.

[0067] Specifically, assume the adjustable resistor network contains N branches, with resistance values ​​of R1, R2, ..., R... N Each branch circuit's relay has two states: ON (closed, engaged) and OFF (disengaged, cut off). There are a total of 2... N -1 valid connection combination (excluding the case of all branches being disconnected, because no compensation resistor is connected when all branches are disconnected). For each combination, the system calculates the parallel equivalent resistance value of the connected branches.

[0068] For example, in some embodiments, the adjustable resistor network comprises four branches with resistance values ​​set in binary weights: R1=10Ω, R2=20Ω, R3=40Ω, and R4=80Ω. There are a total of 2... 4 -1 = 15 valid combinations. When R1 and R2 are connected, the equivalent parallel resistance = 10 × 20 / (10 + 20) ≈ 6.67 Ω; when only R3 is connected, the equivalent parallel resistance = 40 Ω; when R1, R2 and R4 are connected, the equivalent parallel resistance = 1 / (1 / 10 + 1 / 20 + 1 / 80) ≈ 6.15 Ω.

[0069] Step S402: Calculate the system equivalent grounding resistance value for each combination based on the current actual grounding resistance value and the equivalent parallel resistance value corresponding to each combination.

[0070] The system's equivalent grounding resistance is the parallel value of the grounding electrode resistance and the connected compensation resistor network, calculated using the formula: R sys =R earth ×R network / (R earth +R network ), where R earth R is the current actual grounding resistance value. network This is the equivalent parallel resistance value of the adjustable resistor network under this combination.

[0071] Continuing with the above values, let the current actual grounding resistance value R be... earth =6.8Ω: When R1 and R2 (equivalent to 6.67Ω) are applied, R sys =6.8×6.67 / (6.8+6.67)≈3.37Ω; When only R3 (equivalent to 40Ω) is used, R sys=6.8×40 / (6.8+40)≈5.81Ω; When only R2 (equivalent to 20Ω) is used, R sys =6.8×20 / (6.8+20)≈5.07Ω; When R2 and R3 are added (equivalent to 20×40 / (20+40)≈13.33Ω), R sys =6.8×13.33 / (6.8+13.33)≈4.50Ω; When only R1 (equivalent to 10Ω) is used, R sys =6.8×10 / (6.8+10)≈4.05Ω.

[0072] Step S403: The combination that minimizes the deviation between the system's equivalent grounding resistance value and the set value is taken as the optimal resistance combination.

[0073] Continuing with the above values, the set value is 4Ω. The deviations for each combination are as follows: when R1 and R2 are connected, the deviation is |3.37-4|=0.63Ω; when only R3 is connected, the deviation is |5.81-4|=1.81Ω; when only R2 is connected, the deviation is |5.07-4|=1.07Ω; when R2 and R3 are connected, the deviation is |4.50-4|=0.50Ω; when only R1 is connected, the deviation is |4.05-4|=0.05Ω. Among them, the deviation is the smallest (0.05Ω) when only R1 (10Ω) is connected. Therefore, the optimal resistor combination is determined to be: the relay in the R1 branch is closed, and the relays in the R2, R3, and R4 branches are open.

[0074] In this embodiment, by traversing all valid combinations and comparing deviations, the globally optimal compensation scheme is ensured under discrete resistance constraints. When the number of branches is large (e.g., N≥8), the computational load increases, but for embedded microcontrollers, the calculation of 15 to 255 combinations can still be completed in milliseconds without affecting the system response speed.

[0075] like Figure 5 As shown, in some embodiments, an adaptive sampling frequency adjustment step is also included: Step S501: Based on the soil moisture value, use the moisture-resistivity mapping information to determine the current soil resistivity estimate.

[0076] Moisture-resistivity mapping information includes the mapping relationship between soil moisture values ​​and soil resistivity. This mapping relationship can be obtained through experimental calibration and stored as a lookup table, or it can be calculated using empirical formulas. Figure 10 As shown, soil resistivity usually decreases nonlinearly with increasing moisture content. When the moisture content is below 10%, the resistivity increases sharply, and when the moisture content is above 25%, the resistivity tends to level off.

[0077] For example, in some embodiments, the humidity sensor measures the soil volumetric moisture content to be 8%, and the corresponding estimated soil resistivity value is 350 Ω•m, which is a high resistivity state, obtained by looking up the mapping table.

[0078] Step S502: Based on the current soil resistivity estimate, predict the trend of the current actual grounding resistance value.

[0079] In some embodiments, the system compares the current resistivity estimate with the resistivity estimate of the previous cycle to calculate the rate of change. If the rate of change exceeds a preset rate of change threshold (e.g., a change of more than 20% per cycle), the grounding resistance is determined to be in a state of rapid change.

[0080] For example, if the estimated soil resistivity in the previous period was 280 Ω•m and it is currently 350 Ω•m, the rate of change = (350-280) / 280≈25%>20%, which is judged as a rapid change trend.

[0081] Step S503: Based on the changing trend, adjust the sampling frequency of periodic sampling.

[0082] In some embodiments, when a rapid change trend is detected, the sampling period is shortened from the default 4 hours to 1 hour to monitor grounding resistance changes more intensively and compensate in a timely manner. When the rate of change is lower than a preset rate of change threshold for several consecutive periods, the default sampling period is restored to save power consumption.

[0083] In this embodiment, the adaptive sampling frequency mechanism enables the system to increase the monitoring density during periods of drastic environmental changes (such as rapid soil drying after heavy rain or sudden temperature drops in winter), ensuring that the grounding resistance does not exceed the standard for a long time between two samplings. At the same time, it reduces the sampling frequency during periods of stable environment to save system power consumption and extend the service life of sensors and test modules.

[0084] like Figure 6 As shown below, the specific circuit structure of the adjustable resistor network and relay array will be explained.

[0085] In some embodiments, the adjustable resistor network includes N parallel resistor branches (N is a positive integer, such as N=4 or N=5), each branch consisting of a fixed resistor and a normally open relay connected in series. One end of all branches is connected to the ground electrode, and the other end is connected to the auxiliary ground electrode (or directly to the grounding busbar of the cable branch box). The control terminal of each branch relay is connected to the corresponding GPIO pin of the microcontroller.

[0086] In some embodiments, the resistance values ​​of each branch are set according to a binary weighted relationship. For example, the resistance values ​​of a 4-branch system are 10Ω, 20Ω, 40Ω, and 80Ω, and the resistance values ​​of a 5-branch system are 10Ω, 20Ω, 40Ω, 80Ω, and 160Ω. This arrangement allows N branches to provide 2 N -1 different equivalent resistance values, covering a continuous range from the minimum value (equivalent value when all branches are connected in parallel) to the maximum value (value when only the branch with the maximum resistance is connected).

[0087] For example, for a 4-branch system (10Ω, 20Ω, 40Ω, 80Ω), when all branches are engaged, the equivalent resistance is approximately 5.33Ω (1 / (1 / 10+1 / 20+1 / 40+1 / 80)). When only the 80Ω branch is engaged, the equivalent resistance is 80Ω. The system can provide 15 discrete resistance levels within the range of 5.33Ω to 80Ω.

[0088] In some embodiments, high-power metal oxide film resistors or cement resistors are selected, and their rated power is determined based on the fault current that may flow, ensuring that they will not burn out due to overheating during a ground fault. Sealed power relays are selected, with contact rated current not lower than the expected peak fault current, and they possess moisture-proof and dust-proof properties to adapt to outdoor installation environments.

[0089] In this embodiment, the binary weighted resistance design allows a limited number of branches to cover a wider adjustment range and a closer adjustment step, achieving the best balance between hardware cost (number of branches) and compensation accuracy (gear density).

[0090] like Figure 7 As shown in the illustration, this application also provides a modular architecture for an automatic compensation system for the grounding resistance of a cable branch box. The system includes the following components:

[0091] A humidity sensor, buried in the soil near the grounding electrode, is used to collect soil moisture values ​​and transmit the data to a microcontroller. In some embodiments, the humidity sensor communicates with the microcontroller via an analog signal interface (such as a 4-20mA current loop) or a digital interface (such as RS485 / Modbus protocol).

[0092] A grounding resistance testing module, connected to the grounding electrode and auxiliary test electrode, is used to measure the current actual grounding resistance value. In some embodiments, this module employs a frequency conversion method, injecting a specific frequency signal (e.g., 128Hz) different from the power frequency to avoid the influence of power frequency interference on the measurement results.

[0093] An adjustable resistor network consists of multiple parallel resistor branches, each branch composed of a fixed resistor and a relay connected in series, with one end connected to the ground electrode and the other end connected to an auxiliary ground electrode.

[0094] The relay array, comprising relays corresponding one-to-one with each branch of the adjustable resistor network, is controlled by a microcontroller to enable or disable the resistors in each branch.

[0095] The microcontroller, as the core control unit of the system, is connected to the humidity sensor, the grounding resistance test module, and the relay array, respectively. The microcontroller internally runs a compensation control program to perform functions such as periodic sampling scheduling, data processing, optimal resistance combination calculation, and relay drive command output.

[0096] In some embodiments, the system further includes a communication module (such as a 4G / NB-IoT module) for remotely uploading grounding resistance monitoring data to the operation and maintenance management platform to achieve remote status monitoring and alarm notification.

[0097] In some embodiments, the system further includes a power management module that provides a stable power supply for each functional module. The power management module can draw power from the low-voltage bus inside the cable branch box and output the DC voltage (such as 3.3V or 5V) required by the microcontroller and the voltage (such as 12V or 24V) required for relay drive through a DC-DC converter.

[0098] like Figure 8 As shown in the illustration, this application also provides an electronic device. The electronic device includes a memory and a processor coupled to the memory. The memory stores computer program instructions, and the processor is configured to execute the automatic compensation method for grounding resistance of cable branch boxes described in any of the above embodiments based on the instructions stored in the memory.

[0099] In some embodiments, the electronic device is an embedded microcontroller system, the processor is an ARM Cortex-M series microcontroller or a similar low-power embedded processor, and the memory includes Flash memory for storing program code and SRAM for storing runtime data. The electronic device also includes an analog-to-digital converter (ADC) for acquiring analog signals from the humidity sensor; general-purpose input / output pins (GPIO) for outputting relay drive signals; and a communication interface (such as UART, SPI, or I2C) for communicating with the grounding resistance test module.

[0100] In some embodiments, the electronic device connects to the processor, memory, and various peripheral interfaces via a system bus, and is configured with a watchdog timer to ensure the reliability of program operation. When a program malfunctions, the watchdog timer triggers a system reset, reinitializes the modules, and restores normal compensation control.

[0101] like Figure 9As shown in the illustration, this application also provides a cable branch box. The cable branch box includes a box body, cable branching equipment disposed inside the box body, a grounding electrode connected to the grounding terminal of the cable branching equipment, and the aforementioned automatic grounding resistance compensation system for the cable branch box.

[0102] In some embodiments, the enclosure is an outdoor sealed cabinet made of stainless steel or galvanized steel sheet, possessing waterproof, dustproof, and corrosion-resistant properties. Cable branching equipment includes incoming and outgoing cable terminations, load switches, or fuse combination appliances, etc. The grounding electrode is one or more copper-plated steel rods, driven vertically into the soil surrounding the enclosure. The adjustable resistor network of the automatic compensation system is connected in parallel with the grounding electrode, and its electrical connection point is located on the grounding busbar inside the enclosure.

[0103] In some embodiments, the humidity sensor is led out from inside the enclosure via a waterproof cable and buried in the soil approximately 0.3 m away from the grounding electrode. The grounding resistance test module is installed in the control compartment inside the enclosure, with its measuring electrode leads leading out from the bottom of the enclosure and connecting to auxiliary and potential electrodes buried in the soil. The microcontroller and relay array are also installed in the control compartment and connected to an external resistor network via sealed terminals.

[0104] In some embodiments, the resistors of the adjustable resistor network are installed in a protective box outside the enclosure or buried directly in the soil (when the resistors have a sufficient protection level) to form an effective parallel grounding path with the grounding electrode.

[0105] In this embodiment, the automatic compensation system is integrated inside the cable branch box without changing the original branch box's external dimensions and installation method, which facilitates integration into new equipment and upgrades to existing equipment.

[0106] The following describes a complete execution flow of an embodiment of the method of this application.

[0107] Suppose a 10kV cable branch box is installed in the power distribution network of a residential area in a city, equipped with the automatic grounding resistance compensation system of this application. The system parameters are set as follows: the set value is 4Ω, the preset deviation threshold is 0.5Ω, the preset sampling period is 4 hours, and the adjustable resistor network contains 4 branches (with resistance values ​​of 10Ω, 20Ω, 40Ω, and 80Ω respectively). In the initial state, all relays are disconnected (no compensation resistor is engaged).

[0108] At 10:00 AM on a summer morning, the system performed a sampling operation according to the sampling cycle. The humidity sensor measured the soil volumetric moisture content to be 30% (the soil was moist after summer rainfall), and the grounding resistance test module measured the current actual grounding resistance value to be 3.5Ω. The system calculated the deviation value as |3.5-4|=0.5Ω, which is equal to the preset deviation threshold of 0.5Ω. Since the threshold is not exceeded, the current configuration remains unchanged.

[0109] As autumn transitions into early winter, the soil gradually dries out. During a sampling session at 2 PM on a November afternoon, the humidity sensor measured a soil volumetric moisture content of 12%, while the grounding resistance test module measured an actual grounding resistance value of 7.2Ω. The system calculated the deviation as |7.2 - 4| = 3.2Ω > 0.5Ω, triggering the compensation process.

[0110] The microcontroller iterates through 15 valid combinations of the four branches and calculates the equivalent grounding resistance of the system for each combination: when only R1 (10Ω) is connected, R sys =7.2×10 / (7.2+10)≈4.19Ω, deviation 0.19Ω; when only R2 (20Ω) is used, R sys =7.2×20 / (7.2+20)≈5.29Ω, deviation 1.29Ω; when R1 and R3 (10Ω parallel to 40Ω=8Ω) are connected, R sys =7.2×8 / (7.2+8)≈3.79Ω, deviation 0.21Ω; the deviation is smallest when only R1 is connected. The microcontroller determines the optimal combination to connect only the R1 branch and outputs relay drive command: K1 closes, K2, K3, and K4 open.

[0111] After compensation was performed, the system's equivalent grounding resistance was approximately 4.19Ω, with a deviation of 0.19Ω < 0.5Ω, meeting the requirements. The system entered a stable operating state.

[0112] The following day, during sampling, due to a further drop in temperature and a decrease in soil moisture content to 9%, the grounding resistance test module measured the actual grounding resistance of the system under the current condition (R1 already engaged) to be 4.8Ω. Note that this current actual grounding resistance value refers to the resistance of the grounding electrode itself after removing the compensation resistors; the system needs to be recalculated. The microcontroller first disconnected all relays, measured the bare grounding electrode resistance at 9.5Ω, and then recalculated the optimal combination. After iteration, when R1 and R2 (10Ω parallel to 20Ω ≈ 6.67Ω) were engaged, R... sys =9.5×6.67 / (9.5+6.67)≈3.92Ω, with a deviation of 0.08Ω, which is the optimal solution. The microcontroller outputs instructions to close K1 and K2 and open K3 and K4.

[0113] The above process demonstrates the entire process of the system automatically tracking and adjusting to seasonal changes.

[0114] It should be understood that the method steps in the embodiments of this application do not necessarily have to be performed in the specific order described above. For example, environmental information acquisition and grounding resistance measurement can be performed simultaneously or sequentially, and are not limited to the specific order in the above embodiments.

[0115] It should be understood that the above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any changes or substitutions within the technical scope disclosed in this application should be covered within the scope of protection of this application. For example, the specific values ​​such as the number of branches, the resistance value of each branch, the sampling period, and the deviation threshold of the adjustable resistor network can be adjusted according to the actual application scenario; the relay can be replaced with other electronic switching components such as solid-state relays or MOSFET switches; the humidity sensor can be replaced with other sensors that can reflect changes in the electrical properties of the soil (such as temperature sensors, conductivity sensors, etc.).

[0116] It should be understood that the computer program product described in this application can be implemented by computer-executable instructions stored in a non-transitory computer-readable storage medium, including but not limited to Flash memory, ROM, EEPROM, SD card, etc. When the computer-executable instructions are loaded and executed by a processor, the method flow described in the above embodiments of this application is implemented.

[0117] It should be understood that those skilled in the art can make various modifications, equivalent substitutions and improvements to the above embodiments without departing from the spirit and principles of this application, and such modifications, equivalent substitutions and improvements should all be included within the protection scope of this application.

Claims

1. A method for automatically compensating for a grounding resistance of a cable branch box, characterized by, include: Based on environmental data and grounding resistance detection data, the target resistance compensation information is determined. Based on the target resistance compensation information, the grounding resistance of the cable branch box is automatically compensated to maintain the grounding resistance at a constant set value. The environmental acquisition information includes soil moisture value, the grounding resistance detection information includes the current actual grounding resistance value, and the target resistance compensation information includes the optimal resistance combination of the adjustable resistance network. The determination of target resistance compensation information based on environmental data and grounding resistance detection information includes: Using the resistance combination mapping information, based on the soil moisture value and the current actual grounding resistance value, a parallel resistance switching scheme that makes the system's equivalent grounding resistance equal to the set value is determined as the optimal resistance combination; The resistance combination mapping information includes: the mapping relationship between the soil moisture value and the current actual grounding resistance value and the optimal resistance combination; The automatic compensation for the grounding resistance of the cable branch box includes: Based on the optimal resistor combination, a relay driving command is generated to drive the relay array to switch the parallel resistors in the adjustable resistor network. Also includes: The grounding resistance deviation value is determined based on the current actual grounding resistance value and the set value; If the grounding resistance deviation exceeds a preset deviation threshold, it is determined that automatic compensation for the grounding resistance of the cable branch box will be performed. If the grounding resistance deviation value does not exceed the preset deviation threshold, it is determined to maintain the current resistor network configuration unchanged; The method of determining the parallel resistor switching scheme that makes the system's equivalent grounding resistance equal to the set value by utilizing resistor combination mapping information includes: Based on the resistance parameters of each branch resistor in the adjustable resistor network, the discrete combinations of the on / off states of each branch relay are traversed, and the equivalent parallel resistance value of the adjustable resistor network under each combination is calculated. Based on the current actual grounding resistance value and the equivalent parallel resistance value corresponding to each combination, calculate the system equivalent grounding resistance value for each combination; The combination that minimizes the deviation between the system's equivalent grounding resistance value and the set value is taken as the optimal resistance combination.

2. The method of claim 1, wherein, The environmental data and the grounding resistance detection data are obtained through periodic sampling. The periodic sampling includes: The soil moisture value is collected by a humidity sensor according to a preset sampling period; The current actual grounding resistance value is measured by the grounding resistance test module according to the preset sampling period.

3. The method as described in claim 2, characterized in that, Also includes: Based on the soil moisture value, the current soil resistivity estimate is determined using moisture-resistivity mapping information; Based on the current estimated soil resistivity, predict the trend of change in the current actual grounding resistance value; Based on the aforementioned trend, adjust the sampling frequency of the periodic sampling. The humidity-resistivity mapping information includes the mapping relationship between the soil humidity value and the soil resistivity.

4. An automatic compensation system for grounding resistance of a cable branch box, characterized in that, The method described in any one of claims 1-3 includes: Humidity sensor, used to collect soil moisture values; The grounding resistance test module is used to measure the current actual grounding resistance value. Adjustable resistor network, including multiple parallel resistor branches; A relay array is connected to each parallel resistor branch of the adjustable resistor network to enable or disable the corresponding parallel resistor branch. The microcontroller is connected to the humidity sensor, the grounding resistance test module, and the relay array, respectively. It is used to calculate the optimal resistance combination based on the soil moisture value and the current actual grounding resistance value, and drive the relay array to switch the parallel resistance branch in the adjustable resistance network according to the optimal resistance combination, so as to maintain the system grounding resistance constant at the set value.

5. The system as described in claim 4, characterized in that, The resistance values ​​of each parallel resistor branch in the adjustable resistor network are set according to a binary weighting relationship, so that the switching combination of the multiple parallel resistor branches covers uniform discrete resistance value points within the preset resistance adjustment range. The microcontroller is also configured to: trigger a resistance compensation operation when the deviation between the current actual grounding resistance value and the set value exceeds a preset deviation threshold; and maintain the current switching state when the deviation does not exceed the preset deviation threshold.

6. An electronic device, characterized in that, include: Memory; And a processor coupled to the memory, the processor being configured to perform the method as described in any one of claims 1 to 3 based on instructions stored in the memory.

7. A cable branch box, characterized in that, include: Box; Cable branching equipment installed inside the enclosure; The grounding electrode is connected to the grounding terminal of the cable branch equipment. And the automatic compensation system for grounding resistance of cable branch box as described in claim 4 or 5, wherein the adjustable resistance network of the automatic compensation system is connected in parallel with the grounding electrode.

8. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores computer program instructions that, when executed by a processor, implement the method as described in any one of claims 1 to 3.

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