Ac low-voltage comprehensive distribution box comprehensive protection method and ac low-voltage comprehensive distribution box

Abstract

The application relates to the technical field of power distribution box protection, and discloses an alternating-current low-voltage comprehensive power distribution box comprehensive protection method and an alternating-current low-voltage comprehensive power distribution box. The method comprises the following steps: collecting transformer temperature, main loop current and each branch loop current in real time; injecting an alternating-current monitoring signal into the main loop periodically and extracting the signal to calculate the ground insulation resistance of the main loop; determining the type and severity level of overload, overheating and insulation drop faults according to operation state data and the insulation resistance; performing hierarchical protection according to the severity level, including sending a warning, starting load adjustment or cutting off the power supply of the corresponding loop; setting a main control unit and a backup control unit, the backup unit listens to communication data and takes over the control when the main unit fails. The application can quantize insulation parameters under the condition of no power outage, fuse electric heating stress evaluation faults, dynamically adjust loads according to priorities, and realize redundant switching of the control unit.

Description

Technical Field

[0001] This application relates to the field of distribution box protection technology, and in particular to a comprehensive protection method for AC low-voltage integrated distribution boxes and AC low-voltage integrated distribution boxes. Background Technology

[0002] Existing low-voltage distribution box protection systems are mostly based on overcurrent protection and fixed threshold alarms, offering limited functionality. Insulation resistance testing typically relies on manual measurement using an insulation resistance meter circuit by circuit after a power outage, which cannot meet the uninterrupted monitoring requirements of continuous production scenarios. If online measurement using the DC injection method is employed, the line-to-ground distributed capacitance will generate a polarization effect, causing the measurement results to deviate significantly from the true value. In industrial settings, high-frequency harmonics generated by numerous nonlinear loads such as frequency converters and servo drives are superimposed on the power frequency leakage current, leading to frequent malfunctions of conventional residual current protection devices. Operators find it difficult to distinguish between the resistive and capacitive components in the leakage current, making it impossible to accurately determine whether the insulation has truly deteriorated.

[0003] In terms of fault diagnosis, existing methods mostly rely on threshold comparisons of single electrical parameters. An overload is determined and the circuit breaker trips if the main circuit current exceeds the set value, failing to distinguish between inrush current during motor startup and actual heat accumulation, easily leading to unnecessary power outages. Transformer temperature rise exhibits thermal inertia; short-term overcurrent may not cause overheating, while heat accumulated from long-term low-rate overloads is often ignored because it hasn't reached the transient threshold. Protection logic only provides tripping or non-tripping options, lacking a mechanism for graded handling based on severity. Directly cutting off all power supply in case of overload or insulation degradation would cause production interruption, while continued operation might exacerbate the fault. The industrial environment where distribution boxes are located experiences strong electromagnetic interference and high temperatures. Long-term operation of a single control unit carries the risk of failure; once the control circuit fails, the entire protection system loses its monitoring capability. Currently, there is a lack of redundant takeover measures to ensure basic protection functions under extreme conditions. Therefore, a protection scheme is needed that can accurately monitor insulation online, comprehensively assess electrothermal stress levels, and has the capability to switch over in case of control unit failure.

[0004] Therefore, the present invention provides a comprehensive protection method for AC low-voltage integrated distribution boxes and an AC low-voltage integrated distribution box. Summary of the Invention

[0005] This application provides a comprehensive protection method for AC low-voltage integrated distribution boxes and an AC low-voltage integrated distribution box, which are used to improve power supply continuity and distribution box safety.

[0006] Firstly, this application provides a method for integrated protection of an AC low-voltage integrated distribution box, the method comprising: Step S1: Collect real-time operating status data inside the distribution box, including transformer temperature, main circuit current and current of each branch circuit; Step S2: Periodically inject AC monitoring signals into the main circuit of the distribution box, extract AC monitoring signals from the main circuit, and calculate the insulation resistance of the main circuit to the grounding terminal based on the extracted AC monitoring signals; Step S3: Based on the operating status data and insulation resistance, determine the fault type and fault severity level. Fault types include overload fault, overheating fault and insulation degradation fault. Step S4: Execute the corresponding graded protection actions according to the severity level of the fault. The graded protection actions include sending early warning information to the outside, activating the load regulation control strategy, and cutting off the power supply to the corresponding circuit. Step S5: Set up a main control unit and a backup control unit in the distribution box. The backup control unit monitors the communication data in real time and determines whether the main control unit has failed based on the communication data. If so, the backup control unit controls the distribution box based on the pre-stored protection control program.

[0007] Secondly, this application provides an AC low-voltage integrated distribution box, including the following modules: The status acquisition module is used to collect real-time operating status data inside the distribution box. The operating status data includes transformer temperature, main circuit current and current of each branch circuit. The collected operating status data is compared with the preset warning threshold and alarm threshold to obtain the comparison result. The insulation monitoring module is used to periodically inject AC monitoring signals into the main circuit of the distribution box, extract AC monitoring signals from the main circuit, and calculate the insulation resistance of the main circuit to the grounding terminal based on the extracted AC monitoring signals. The fault determination module is used to determine the fault type and severity level based on the comparison results and insulation resistance values. Fault types include overload fault, overheating fault and insulation degradation fault. The graded protection module is used to execute corresponding graded protection actions according to the severity level of the fault. The graded protection actions include sending early warning information to the outside, activating the load regulation control strategy, and cutting off the power supply to the corresponding circuit. The control switching module is used to set up a main control unit and a backup control unit in the distribution box. The backup control unit monitors the communication data in real time and determines whether the main control unit has failed based on the monitored data. If so, the backup control unit controls the distribution box based on the pre-stored protection control program.

[0008] Compared with the prior art, the beneficial effects of the present invention are at least as follows: The technical solution provided in this application achieves accurate online measurement of insulation resistance under grid noise and distributed capacitance interference by injecting dual-frequency AC signals and separating resistive leakage current components, combined with temperature compensation correction. It utilizes the electrothermal coupling stress index and its time integral to assess cumulative thermal fatigue and dynamically adjusts the insulation warning threshold accordingly, distinguishing between slow aging and sudden defects, reducing false alarms and missed alarms. A graded protection strategy is adopted, enabling early warning and enhanced heat dissipation during primary faults, tiered load shedding according to circuit importance to maintain core power supply during secondary overloads, and direct tripping and locking reset during secondary insulation faults, balancing safety and power supply continuity. The main and backup control units achieve seamless switching through heartbeat monitoring, avoiding single-point failure risks. Simultaneously, historical data trend analysis can generate maintenance warnings in advance, comprehensively improving the operational reliability of the distribution box under harsh conditions. Attached Figure Description

[0009] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0010] Figure 1 This is a schematic diagram of one embodiment of the integrated protection method for AC low-voltage integrated distribution box in this application. Figure 2 This is a structural diagram of the AC low-voltage integrated distribution box in the embodiments of this application. Detailed Implementation

[0011] This application provides a method for integrated protection of an AC low-voltage integrated distribution box and an AC low-voltage integrated distribution box. The terms "first," "second," "third," "fourth," etc. (if present) in the specification, claims, and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments described herein can be implemented in a sequence other than that illustrated or described herein. Furthermore, the terms "comprising" or "having" and any variations thereof are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or device that includes a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or devices.

[0012] For ease of understanding, the specific process of the embodiments of this application is described below. Please refer to [link / reference]. Figure 1 One embodiment of the integrated protection method for AC low-voltage integrated distribution boxes in this application includes: Step S1: Collect real-time operating status data inside the distribution box, including transformer temperature, main circuit current and current of each branch circuit; Specifically, existing protection methods typically only collect the main circuit current for overcurrent protection, but neglect the heat accumulation process of the equipment and the load distribution of each branch. Considering that in actual industrial sites, the transformer temperature rise is proportional to the square of the current and has a lag, monitoring only the current cannot truly reflect the thermal stress borne by the distribution box. In order to comprehensively monitor the internal state of the distribution box and provide basic data for subsequent multi-angle coupling analysis, the operating status data inside the distribution box is collected in real time. The operating status data includes transformer temperature, main circuit current and current of each branch circuit.

[0013] Step S2: Periodically inject AC monitoring signals into the main circuit of the distribution box, extract AC monitoring signals from the main circuit, and calculate the insulation resistance of the main circuit to the grounding terminal based on the extracted AC monitoring signals; Specifically, existing insulation monitoring typically involves manual measurement using equipment after a power outage, which cannot meet the needs of continuous production scenarios. If a DC injection method is used, the distributed capacitance of the line can cause polarization effects, reducing measurement accuracy. To address these issues and prevent grounding faults or electrical fires caused by insulation aging, considering that AC signals can penetrate distributed capacitance without affecting power frequency power quality, an AC monitoring signal is periodically injected into the main circuit of the distribution box. This involves using a signal generator to inject a low-frequency AC voltage (non-power frequency) into the main circuit bus via a transformer. The signal leaks to the ground through the line-to-ground insulation resistance, forming a weak leakage current. This current signal is then collected by a highly sensitive zero-sequence current transformer, and a bandpass filter is used to filter out power frequency and harmonic interference. Finally, the insulation resistance to ground is calculated using Ohm's law. This process enables real-time quantitative monitoring of insulation parameters without power outages and also avoids sudden short-circuit faults caused by insulation degradation.

[0014] Step S3: Based on the operating status data and insulation resistance, determine the fault type and fault severity level. Fault types include overload fault, overheating fault and insulation degradation fault. Specifically, existing protection systems often misjudge inrush current at the moment of equipment startup as overload tripping, or fail to report overload due to long-term low-rate overload accumulating heat that does not exceed the standard. However, actual faults often have multiple characteristics, such as overheating accompanied by overload. In order to improve the accuracy of the judgment, multi-parameter fusion judgment is performed based on operating status data and insulation resistance, and refined classification and grading are carried out to distinguish different faults. This facilitates the subsequent development of accurate protection mechanisms and avoids misoperation.

[0015] Step S4: Execute the corresponding graded protection actions according to the severity level of the fault. The graded protection actions include sending early warning information to the outside, activating the load regulation control strategy, and cutting off the power supply to the corresponding circuit. Specifically, existing protection methods have relatively simple logic, typically tripping directly after a trigger condition, which can lead to unplanned power outages. To maximize continuous power supply while ensuring equipment safety, different protection strategies should be developed based on the priority of on-site loads. For example, in the event of a minor fault such as a Level 1 fault, a warning message can be sent to relevant personnel. Upon receiving the warning message, personnel can manually adjust the on-site power consumption as needed. In the event of a more serious Level 2 fault, simply sending a warning message is insufficient. Typically, based on pre-stored importance levels, the power to be reduced can be calculated, and less important circuits can be prioritized for disconnection, thereby maximizing power supply continuity while ensuring power safety.

[0016] Step S5: Set up a main control unit and a backup control unit in the distribution box. The backup control unit monitors the communication data in real time and determines whether the main control unit has failed based on the communication data. If so, the backup control unit controls the distribution box based on the pre-stored protection control program.

[0017] Specifically, in actual industrial applications, situations such as strong electromagnetic interference and high temperatures are common. If a single control unit fails, the distribution box will become uncontrollable, posing a significant safety hazard. Considering the reliability of the distribution box protection, a main control unit and a backup control unit are installed inside the distribution box. The main control unit and the backup control unit are connected via a bus. Under normal circumstances, the backup control unit is in monitoring mode, acquiring the periodic heartbeat signals sent by the main control unit in real time, as well as the communication data between the two units. If the backup control unit does not receive a heartbeat signal from the main control unit for several consecutive cycles, it determines that the main control unit has failed. At this time, the backup control unit controls the distribution box based on a pre-stored protection control program, achieving seamless control switching and ensuring the safety of the distribution box.

[0018] In one specific embodiment, step S2 specifically includes the following steps: Step S21: Generate a first AC signal and a second AC signal. Inject the first AC signal into the main circuit during a first duration. After waiting for a first time interval, inject the second AC signal into the main circuit during a second duration. Step S22: Extract the loop current signal containing the AC monitoring signal from the main loop, and use a bandpass filter to separate the current component of the first AC signal and the current component of the second AC signal. Step S23: Calculate the resistance component of the ground drain current based on the amplitude of the two separated current components, and use the resistance component value as the insulation resistance of the main circuit. Step S24: Collect transformer temperature data, and perform temperature compensation correction on the insulation resistance according to the pre-established temperature insulation resistance correction function to obtain the corrected insulation resistance.

[0019] Specifically, in industrial applications with numerous frequency converters, the power distribution network exhibits two significant characteristics: first, the long cable lengths result in substantial natural distributed capacitance between the lines and ground; second, the extensive use of nonlinear loads such as frequency converters and servo electrodes introduces significant high-frequency harmonic noise into the power grid. Existing leakage current protection methods monitor the total leakage current at the power frequency. The normal capacitive current generated by long cables and the harmonic current generated by frequency converters mix into the total current, causing the total leakage current to exceed the tripping threshold, leading to false alarms and inaccurate tripping. Furthermore, existing methods typically cannot distinguish the source of the leakage current. To address this issue, in order to filter out harmonic interference and eliminate the influence of distributed capacitance under load conditions with uninterrupted power supply and grid noise, the insulation resistance, which indicates insulation quality, must be extracted, and measurement errors caused by ambient temperature must be eliminated, thereby preventing false tripping.

[0020] First, the main circuit voltage signal is acquired, and a fast Fourier analysis is performed to extract the background harmonic spectrum. The low-interference frequency band is identified as the target frequency band to generate the first AC signal and the second AC signal. To avoid overlap and conflict between the two signals, the first AC signal and the second AC signal are injected into the main circuit alternately. In order to obtain the small corresponding current at a specific frequency injected in the complex total leakage current, the total current signal acquired by the zero-sequence current transformer is converted by A / D conversion. Two high-order digital bandpass filters are configured in the digital signal processor to align the center frequency to the two actual injected frequency points and filter out all current components other than the center frequency to obtain the current components of the first AC signal and the second AC signal. This step can eliminate the interference of power frequency and frequency conversion harmonics on the measurement results.

[0021] The directly measured leakage current is the vector sum of resistive and capacitive currents. Considering that the impedance is formed by parallel resistance and capacitance, and based on the physical characteristic that the capacitive reactance changes with frequency under dual-frequency conditions while the insulation resistance does not change with frequency, the resistive component of the leakage current to ground is calculated based on the amplitudes of the two separated current components, and this resistive component value is used as the insulation resistance of the main circuit. The resistance of cable and transformer insulation materials has a negative temperature coefficient; the higher the temperature, the lower the resistance. During high-load operation in summer, the insulation resistance may drop by half. Traditional protection thresholds are fixed, and insulation degradation is easily judged at high temperatures. Therefore, in order to eliminate the influence of ambient temperature and equipment heating on the resistivity of insulation materials and prevent false alarms under high-temperature conditions, the resistance correction coefficient corresponding to the transformer temperature is obtained based on the real-time transformer temperature and a pre-established temperature insulation resistance correction function. The calculated insulation resistance is multiplied by the corresponding correction coefficient to obtain the corrected insulation resistance.

[0022] The temperature insulation resistance correction curve was established using an experimental method. Specifically, a reference temperature was selected, and the insulating material used in the distribution box was placed in a test chamber with precise temperature control. Several temperature points were selected within the temperature range that the equipment might encounter. After the temperature stabilized at the corresponding temperature point, the corresponding insulation resistance was measured to obtain a set of temperature resistance data. The corresponding temperature resistance data was converted into a scatter plot and fitted into an exponential function using the least squares method. This exponential function was used as the temperature insulation resistance correction function, and the temperature insulation resistance correction function was stored to facilitate the subsequent acquisition of correction coefficients at different temperatures.

[0023] Furthermore, based on the amplitudes of the two separated current components, the resistive component of the ground leakage current is calculated, specifically including: The ground leakage current is generated by both resistance and capacitance. According to complex circuit theory, the total ground admittance Y of the parallel circuit at a specific frequency is: ,in, The angular frequency is used. The measured total leakage current I is the vector sum of the resistive and capacitive components. j is a complex number whose amplitude satisfies Ohm's law in complex form. f is the frequency of the injected AC signal, which is a known value. The unknown variables are the insulation resistance R and the distributed capacitance C. A first AC signal with a first frequency and a second AC signal with a second frequency are injected into the main circuit, and the corresponding current amplitudes are measured. According to the formula for the admittance magnitude of a parallel circuit... Where U refers to the effective value of the AC voltage of a specific frequency injected into the main circuit by the signal generator, I refers to the effective value of the leakage current component of a specific frequency flowing through the parallel circuit of insulation resistance and distributed capacitance under the drive of the injected signal, and the square of the admittance magnitude is equal to the sum of the square of the resistance and the square of the capacitance. From this, we can obtain two systems of two linear equations consisting of the two injected frequencies. , among which, is , These refer to the effective voltage values ​​of the first AC signal and the second AC signal, respectively. , These refer to the effective values ​​of the leakage current components at specific frequencies flowing through the parallel circuit of insulation resistance and distributed capacitance under the drive of the first AC signal and the second AC signal, respectively. , These refer to the frequencies of the first and second injected AC signals, respectively. R can be calculated using two sets of two linear equations. This method allows us to remove capacitive interference based on the magnitude of the current and obtain the true insulation resistance.

[0024] In one specific embodiment, generating a first AC signal and a second AC signal specifically includes the following steps: The voltage signal on the main circuit is acquired, and a fast Fourier transform is performed on the voltage signal to obtain the background harmonic spectrum distribution. In the background harmonic spectrum distribution, two frequency bands with amplitudes lower than a preset interference threshold and distances greater than a preset distance threshold are identified as target frequency bands. A first AC signal with a first frequency and a second AC signal with a second frequency are generated in the target frequency bands.

[0025] Specifically, existing dual-frequency injection typically uses a fixed frequency. However, in industrial applications, the operating frequency of the frequency converter changes dynamically. If the power grid experiences strong interference at the fixed frequency, it can distort the monitoring results. To prevent the weak injected monitoring signal from being overwhelmed by noise, the main circuit voltage signal is first acquired and subjected to a fast Fourier transform to obtain the background harmonic spectrum distribution. This background harmonic spectrum distribution exposes all potential interference sources in the power grid.

[0026] In order to find stable frequency bands in a frequency band full of interference, an interference threshold is set in advance. Based on the interference threshold, two frequency bands with amplitudes lower than the interference threshold are identified. When it is found that all interference amplitudes within a certain continuous frequency range are less than the interference threshold, the corresponding frequency band is marked as a candidate frequency band. Two candidate frequency bands with a distance greater than the distance threshold are marked as target frequency bands. This step can avoid strong harmonic pollution points in the power grid and select high-quality target frequency bands.

[0027] Based on the frequency values ​​of the two selected target frequency bands, a direct digital frequency synthesizer is used to synthesize a first AC signal and a second AC signal with corresponding frequencies. The first AC signal has a first frequency, and the second AC signal has a second frequency, with the first and second frequencies corresponding to the selected target frequency bands. This step generates two AC signals, namely the first AC signal and the second AC signal, that avoid power grid harmonics.

[0028] In one specific embodiment, determining the fault type and fault severity level includes the following steps: Step S31: Obtain the effective value of the main circuit current and the real-time temperature of the transformer. Use the ratio of the square of the main circuit current to the square of the rated current as the electrical load factor, the ratio of the real-time temperature of the transformer to the preset temperature threshold as the thermal load factor, and the product of the electrical load factor and the thermal load factor as the real-time electrothermal coupling stress index. Step S32: Integrate the real-time electrothermal coupling stress index that is greater than the reference value over time to obtain the cumulative thermal fatigue value. When the cumulative thermal fatigue value is greater than the first threshold and less than the second threshold, it is determined to be a first-level overload. When the cumulative thermal fatigue value is greater than or equal to the second threshold, it is determined to be a second-level overload. Step S33: Calculate the insulation aging penalty coefficient based on the cumulative thermal fatigue value, and correct the insulation warning threshold based on the penalty coefficient to obtain the dynamic insulation warning threshold; Step S34: Calculate the slope of the insulation resistance decrease within a preset time window. When the insulation resistance is less than the dynamic insulation warning threshold and greater than the insulation alarm threshold, and the slope of the insulation resistance decrease is greater than the preset change rate, it is determined to be a first-level insulation fault. When the insulation resistance is less than the insulation alarm threshold, it is determined to be a second-level insulation fault.

[0029] Specifically, current passing through a conductor generates Joule heat, and in high-temperature environments, ambient temperature also constitutes a heat dissipation resistance. Judging solely by current or temperature cannot accurately reflect the aging rate that the insulation material is undergoing. To more scientifically assess equipment operating conditions, predict and accurately classify hidden faults in the distribution box in advance, the effective value of the main circuit current and the real-time temperature of the transformer are obtained. The square of the current is divided by the square of the rated current to obtain the electrical load rate, which represents the intensity of the heat source. The current real-time temperature is divided by the preset safe temperature threshold to obtain the thermal load rate, which represents the severity of heat dissipation. The closer the value is to 1, the closer the equipment is to the edge of thermal collapse. It reflects the combined result of external ambient temperature, ventilation conditions inside the chassis, and the heat generated in the early stages. Multiplying the electrical load rate by the thermal load rate yields the real-time electrothermal coupling stress index. The electrothermal coupling stress index represents the comprehensive physical destructive force that the equipment is currently experiencing. The larger the electrothermal coupling stress index, the greater the risk of the insulation material being damaged by heat.

[0030] A baseline value is preset for the electrothermal coupling stress index. An electrothermal coupling stress index less than or equal to the baseline value indicates that the equipment is in a relatively safe state. If the existence of overload is determined solely based on the instantaneous electrothermal coupling stress index, it is easy to cause frequent false trips. In order to obtain long-term hidden overloads and thermal damage and eliminate misjudgments caused by motor starting inrush current, the real-time electrothermal coupling stress index greater than the baseline value is continuously integrated over time to obtain the cumulative thermal fatigue value. The cumulative thermal fatigue value represents the total value of thermal damage suffered by the equipment over a period of time. When the cumulative thermal fatigue value is greater than the first threshold and less than the second threshold, it is determined to be a level one overload; when the cumulative thermal fatigue value is greater than or equal to the second threshold, it is determined to be a level two overload.

[0031] Existing methods typically determine the presence of insulation faults by using a fixed value of insulation resistance. However, older equipment has poor overvoltage resistance, and even small fluctuations can trigger insulation faults. A higher cumulative thermal fatigue value indicates more severe thermal damage to the equipment, a shorter remaining lifespan of the insulation material, and poorer overvoltage resistance. Therefore, an insulation aging penalty coefficient is calculated based on the cumulative thermal fatigue value. The calculation formula is as follows: Where P is the insulation aging penalty coefficient, Q is the cumulative thermal fatigue value, and α and β are coefficients fitted based on the aging test data of the insulation material. The dynamic insulation warning threshold is obtained by correcting the insulation warning threshold based on the penalty coefficient, achieving the purpose of determining insulation faults based on the actual aging fatigue degree of the equipment. The dynamic insulation warning threshold is then obtained by correcting the insulation warning threshold again based on the penalty coefficient. The calculation formula for the dynamic insulation warning threshold is as follows: ,in, This is a dynamic insulation warning value. This is the baseline insulation warning value. The influence weight of the penalty coefficient.

[0032] In reality, the decrease in insulation resistance mainly stems from two causes: normal long-term aging, resulting in a slow decline in resistance; and sudden defects in the insulation material, such as cracks, moisture absorption, or partial discharge, causing a rapid drop in resistance within a short period. Relying solely on insulation resistance is insufficient to distinguish between these two situations. To address this issue, multiple insulation resistance measurements are collected within a preset time window. A linear regression method is used to calculate the slope of the insulation resistance decrease over time. When the insulation resistance is less than the dynamic insulation warning threshold but greater than the insulation alarm threshold, and the slope of the insulation resistance decrease is greater than a preset abrupt change rate, it is classified as a Level 1 insulation fault. At this point, the insulation resistance is already below the dynamic insulation warning threshold and the rate of decrease is relatively rapid, requiring notification to relevant personnel to determine whether appropriate measures should be initiated. When the insulation resistance is less than the insulation alarm threshold, it is classified as a Level 2 insulation fault. This indicates severe insulation damage and a high risk of short circuit, requiring immediate action. Relying solely on sending alarm messages for staff notification may lead to delays in handling due to human error or operational delays. The insulation alarm threshold is defined as being less than the dynamic insulation warning threshold.

[0033] In one specific embodiment, the corresponding graded protection action is executed according to the severity level of the fault, specifically including the following steps: Step S41: When a Level 1 overload fault or Level 1 insulation fault is determined to occur, a warning message with the cumulative thermal fatigue value and insulation warning threshold is sent to the management terminal, and all heat dissipation equipment in the distribution box is turned on. Step S42: Upon determining that a level 2 overload fault has occurred, maintain the main circuit power supply and simultaneously activate the load regulation control strategy; Step S43: When a secondary insulation fault is detected, physical damage is determined, and the main circuit breaker is controlled to trip while the reset component is locked.

[0034] Specifically, to ensure maximum power supply continuity while maintaining safety, when a Level 1 overload fault or Level 1 insulation fault is detected, a warning message containing cumulative thermal fatigue values ​​and dynamic insulation warning thresholds is sent to the management terminal. Simultaneously, all cooling devices within the distribution box are forcibly activated. The management terminal, held by relevant personnel, allows them to take corresponding measures upon receiving the warning message. This step utilizes remaining cooling capacity to slow down the physical aging process of the equipment and quantifies equipment health status data for relevant personnel, facilitating appropriate action. When a Level 2 overload fault is detected, indicating an electrical overload in the distribution box, to avoid directly cutting off the main power supply, power to core production equipment is selectively and partially cut off, maintaining the main circuit's power supply. Simultaneously, a load regulation control strategy is activated. When a Level 2 insulation fault is detected, cable damage may exist, indicating a drop in insulation resistance to a dangerous level and a sharp decrease in compressive strength, constituting severe physical damage. To prevent accidents, the main circuit breaker is forcibly tripped, and reset components are locked, ensuring the safety of the distribution box and the site where it is used.

[0035] In one specific embodiment, activating the load regulation control strategy includes the following steps: Step S421: Set the target stress recovery value, and calculate in reverse based on the calculation method of the electric coupling stress index to obtain the main circuit current value that needs to be reduced under the current transformer real-time temperature as the target current value; Step S422: Obtain the real-time operating current of each branch circuit, read the preset circuit importance level, and define the set of branch circuits with the lowest importance level as operable circuits. Step S423: In the operable circuit, obtain the branch circuit combination whose sum of real-time operating current is greater than or equal to the target current value and whose difference from the target current value is the smallest, and control the disconnection of all branch circuits in the branch circuit combination. Step S424: Recalculate the real-time electrothermal coupling stress index. If the electrothermal coupling stress index is still greater than the target stress recovery value, update the target current value. Define the set of branch circuits with the lowest importance level among the currently uncut branch circuits as new operable circuits. Repeat step S423 until the real-time electrothermal coupling stress index drops below the target stress recovery value.

[0036] Specifically, to maintain power supply as much as possible under severe overload conditions, a target stress recovery value is first set. The electrothermal coupling stress index calculation logic is used for reverse calculation. Due to the delayed nature of heat accumulation, the target current value is the main circuit current that needs to be reduced at the current transformer real-time temperature. Existing methods typically use a fixed proportion or random disconnection of branch circuits, which can easily lead to over-disconnection or under-disconnection. This step quantifies the disconnection target. Then, the operating current of each branch circuit is acquired in real time, and the pre-configured importance level of the branch circuits is read. The set of branch circuits with the lowest importance level is first defined as operable circuits. Combinatorial optimization calculations are performed within the operable circuits to obtain the combination of branch circuits with real-time operating current greater than or equal to the target current value and the smallest difference from the target current value. All branch circuits within the corresponding combination are then disconnected. After a single disconnection, the thermal stress reduction may not meet expectations due to insufficient disconnection force or high ambient temperature. The operating parameters are then re-acquired, and the real-time electrothermal coupling stress index is calculated. If the index is still greater than the target stress recovery value, it indicates that the current disconnection force is insufficient to curb overload. Therefore, the target current value is recalculated and updated. The set of branch circuits with the lowest importance level among the currently undisconnected branch circuits is defined as the new operable circuit, and step S423 is repeated. If the electrothermal coupling stress index after another disconnection is still greater than the target stress recovery value, the set of branch circuits with the lowest importance level among the currently undisconnected branch circuits is defined as the new operable circuit, and step S423 is repeated until the real-time electrothermal coupling stress index drops below the target stress recovery value. This step, through dynamic disconnection from low to high importance level, ensures power supply continuity as much as possible while ensuring that the power distribution equipment is not damaged.

[0037] In one specific embodiment, the backup control unit controls the distribution box based on a pre-stored protection control program, specifically including the following steps: Step S51: The main control unit, the backup control unit, and multiple data acquisition units are connected through a data bus. The main control unit sends query requests to the data acquisition units and receives response data packets through the data bus. The main control unit also exchanges operating status heartbeat signals with the backup control unit through the data bus. Step S52: The backup control unit continuously monitors the communication data on the data bus and extracts the sending address and receiving address of the communication data. If the heartbeat signal of the main control unit is not received within the preset communication cycle, it is determined that the main control unit has failed. Step S53: The backup control unit reads the protection control program from the memory and loads it for operation, establishes a direct communication connection with the data acquisition unit, and performs monitoring and control functions on the distribution box.

[0038] Specifically, addressing the issue of high temperatures and strong electromagnetic interference in real-world industrial applications that can easily lead to the failure of a single control unit, a main control unit and a backup control unit are installed within the distribution box. The main control unit sends a heartbeat signal containing operational status data to the backup control unit at a preset cycle. Under normal conditions, the backup control unit is in real-time monitoring mode, listening to communication data on the data bus and extracting the sender and receiver addresses of the communication data. If the backup control unit does not receive a valid heartbeat signal within a preset number of consecutive monitoring cycles, it determines that the main control unit has failed. In industrial settings, intermittent data loss often occurs. Switching control units based on single confirmations can easily lead to frequent control switching. Therefore, this step introduces continuous cycle confirmation to effectively eliminate misjudgments caused by transient interference. After confirming the fault, the backup control unit reads the protection control program from memory, loads and runs it, and establishes a direct communication connection with the data acquisition unit. Simultaneously, combined with the previously monitored communication data, it continuously monitors and controls the distribution box, ensuring seamless takeover of control functions after the main control unit fails.

[0039] In one specific embodiment, the analysis of historical operational data includes the following steps: The collected operating status data, calculated insulation resistance, and fault type are added with time tags and stored in the database. Trend analysis is performed on the stored insulation resistance to calculate the insulation aging rate. When the insulation aging rate exceeds the preset aging threshold, maintenance early warning information is generated.

[0040] Specifically, addressing the issue that existing distribution box protection methods typically only identify instantaneous faults and lack the ability to track the long-term health status evolution of distribution boxes, this method adds time tags to collected operating status data, calculated insulation resistance, and fault types before storing them in a database to establish a reliable data foundation. This facilitates subsequent macro-analysis based on the stored historical data. During the application of distribution boxes, the degradation of the insulation layers of cables and transformers is a slow, cumulative process, and is easily accelerated by frequent overload thermal stress. To generate early maintenance warnings, trend analysis is performed on the insulation resistance data stored in the database. A data fitting algorithm is used to calculate the long-term slope of the insulation resistance decrease over time, which is the insulation aging rate. When the insulation aging rate exceeds a preset aging threshold, a maintenance warning is generated. This method, by calculating the long-term insulation aging rate, achieves a dynamic quantitative assessment of the equipment's insulation life. Before the insulation performance deteriorates to a dangerous state and triggers an actual insulation fault, it can provide accurate maintenance intervention warnings to relevant personnel, improving the overall safety of continuous power supply systems.

[0041] According to another aspect of the embodiments of the present invention, reference is made to... Figure 2As shown, an AC low-voltage integrated distribution box is also provided, comprising modules for implementing the integrated protection method for an AC low-voltage integrated distribution box as described above. The specific functions of each module are as follows: The status acquisition module is used to collect real-time operating status data inside the distribution box, including transformer temperature, main circuit current and current of each branch circuit. The insulation monitoring module is used to periodically inject AC monitoring signals into the main circuit of the distribution box, extract AC monitoring signals from the main circuit, and calculate the insulation resistance of the main circuit to the grounding terminal based on the extracted AC monitoring signals. The fault determination module is used to determine the fault type and severity level based on the comparison results and insulation resistance values. Fault types include overload fault, overheating fault and insulation degradation fault. The graded protection module is used to execute corresponding graded protection actions according to the severity level of the fault. The graded protection actions include sending early warning information to the outside, activating the load regulation control strategy, and cutting off the power supply to the corresponding circuit. The control switching module is used to set up a main control unit and a backup control unit in the distribution box. The backup control unit monitors the communication data in real time and determines whether the main control unit has failed based on the monitored data. If so, the backup control unit controls the distribution box based on the pre-stored protection control program.

[0042] The above-described embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. A comprehensive protection method for AC low-voltage integrated distribution boxes, characterized in that, The method includes: Step S1: Collect real-time operating status data inside the distribution box, including transformer temperature, main circuit current and current of each branch circuit; Step S2: Periodically inject AC monitoring signals into the main circuit of the distribution box, extract AC monitoring signals from the main circuit, and calculate the insulation resistance of the main circuit to the grounding terminal based on the extracted AC monitoring signals, including: Step S21: Generate a first AC signal and a second AC signal, inject the first AC signal into the main circuit during a first duration, wait for a first time interval, and then inject the second AC signal into the main circuit during a second duration; Step S22: Extract the loop current signal containing the AC monitoring signal from the main circuit, and separate the current components of the first AC signal and the second AC signal using a bandpass filter; Step S23: Based on the amplitude of the two separated current components; Step S24: Collect transformer temperature data, and perform temperature compensation correction on the insulation resistance according to a pre-established temperature insulation resistance correction function to obtain the corrected insulation resistance; Step S3: Based on the operating status data and insulation resistance, determine the fault type and severity level, including: Step S31: Obtain the effective value of the main circuit current and the real-time temperature of the transformer; use the ratio of the square of the main circuit current to the square of the rated current as the electrical load factor; use the ratio of the real-time temperature of the transformer to a preset temperature threshold as the thermal load factor; and use the product of the electrical load factor and the thermal load factor as the real-time electrothermal coupling stress index; Step S32: Integrate the real-time electrothermal coupling stress index greater than the benchmark value over time to obtain the cumulative thermal fatigue value; when the cumulative thermal fatigue value is greater than the first threshold and less than the second threshold, it is determined to be a fault. Level 1 overload: When the cumulative thermal fatigue value is greater than or equal to the second threshold, it is determined to be a Level 2 overload; Step S33: Calculate the insulation aging penalty coefficient based on the cumulative thermal fatigue value, and correct the insulation warning threshold based on the penalty coefficient to obtain the dynamic insulation warning threshold; Step S34: Calculate the slope of the decrease in insulation resistance within a preset time window. When the insulation resistance is less than the dynamic insulation warning threshold and greater than the insulation alarm threshold, and the slope of the decrease in insulation resistance is greater than the preset mutation rate, it is determined to be a Level 1 insulation fault. When the insulation resistance is less than the insulation alarm threshold, it is determined to be a Level 2 insulation fault. The fault types include overload fault, overheating fault and insulation degradation fault. Step S4: Execute the corresponding graded protection actions according to the severity level of the fault. The graded protection actions include sending early warning information to the outside, activating the load regulation control strategy, and cutting off the power supply to the corresponding circuit. Step S5: Set up a main control unit and a backup control unit in the distribution box. The backup control unit monitors the communication data in real time and determines whether the main control unit has failed based on the communication data. If so, the backup control unit controls the distribution box based on the pre-stored protection control program.

2. The method according to claim 1, characterized in that, Generating a first AC signal and a second AC signal includes: The voltage signal on the main circuit is acquired, and a fast Fourier transform is performed on the voltage signal to obtain the background harmonic spectrum distribution. In the background harmonic spectrum distribution, two frequency bands with amplitudes lower than a preset interference threshold and distances greater than a preset distance threshold are identified as target frequency bands. A first AC signal with a first frequency and a second AC signal with a second frequency are generated in the target frequency bands.

3. The method according to claim 1, characterized in that, Based on the severity level of the fault, corresponding graded protection actions are executed, including: Step S41: When a Level 1 overload fault or Level 1 insulation fault is determined to occur, a warning message with the cumulative thermal fatigue value and insulation warning threshold is sent to the management terminal, and all heat dissipation equipment in the distribution box is turned on. Step S42: Upon determining that a level 2 overload fault has occurred, maintain the main circuit power supply and simultaneously activate the load regulation control strategy; Step S43: When a secondary insulation fault is detected, physical damage is determined, and the main circuit breaker is controlled to trip while the reset component is locked.

4. The method according to claim 3, characterized in that, Initiate load regulation and control strategies, including: Step S421: Set the target stress recovery value, and calculate in reverse based on the calculation method of the electric coupling stress index to obtain the main circuit current value that needs to be reduced under the current transformer real-time temperature as the target current value; Step S422: Obtain the real-time operating current of each branch circuit, read the preset circuit importance level, and define the set of branch circuits with the lowest importance level as operable circuits. Step S423: In the operable circuit, obtain the branch circuit combination whose sum of real-time operating current is greater than or equal to the target current value and whose difference from the target current value is the smallest, and control the disconnection of all branch circuits in the branch circuit combination. Step S424: Recalculate the real-time electrothermal coupling stress index. If the electrothermal coupling stress index is still greater than the target stress recovery value, update the target current value. Define the set of branch circuits with the lowest importance level among the currently uncut branch circuits as new operable circuits. Repeat step S423 until the real-time electrothermal coupling stress index drops below the target stress recovery value.

5. The method according to claim 1, characterized in that, The backup control unit controls the distribution box based on a pre-stored protection control program, including: Step S51: The main control unit, the backup control unit, and multiple data acquisition units are connected through a data bus. The main control unit sends query requests to the data acquisition units and receives response data packets through the data bus. The main control unit also exchanges operating status heartbeat signals with the backup control unit through the data bus. Step S52: The backup control unit continuously monitors the communication data on the data bus and extracts the sending address and receiving address of the communication data. If the heartbeat signal of the main control unit is not received within the preset communication cycle, it is determined that the main control unit has failed. Step S53: The backup control unit reads the protection control program from the memory and loads it for operation, establishes a direct communication connection with the data acquisition unit, and performs monitoring and control functions on the distribution box.

6. The method according to claim 1, characterized in that, It also includes the step of analyzing historical operational data: The collected operating status data, calculated insulation resistance, and fault type are added with time tags and stored in the database. Trend analysis is performed on the stored insulation resistance to calculate the insulation aging rate. When the insulation aging rate exceeds the preset aging threshold, maintenance early warning information is generated.

7. An AC low-voltage integrated distribution box, used to implement the integrated protection method for AC low-voltage integrated distribution boxes as described in any one of claims 1-6, characterized in that, Includes the following modules: The status acquisition module is used to collect real-time operating status data inside the distribution box, including transformer temperature, main circuit current and current of each branch circuit. An insulation monitoring module is used to periodically inject AC monitoring signals into the main circuit of the distribution box, extract AC monitoring signals from the main circuit, and calculate the insulation resistance of the main circuit to the grounding terminal based on the extracted AC monitoring signals. The module includes: Step S21, generating a first AC signal and a second AC signal, injecting the first AC signal into the main circuit for a first duration, waiting for a first time interval, and then injecting the second AC signal into the main circuit for a second duration; Step S22, extracting the loop current signal containing the AC monitoring signal from the main circuit, and separating the current components of the first AC signal and the second AC signal using a bandpass filter; Step S23, calculating the current components based on their amplitudes; and Step S24, collecting transformer temperature data and performing temperature compensation correction on the insulation resistance according to a pre-established temperature insulation resistance correction function to obtain the corrected insulation resistance. The fault determination module is used to determine the fault type and severity level based on operating status data and insulation resistance, including: Step S31, obtaining the effective value of the main circuit current and the real-time temperature of the transformer; using the ratio of the square of the main circuit current to the square of the rated current as the electrical load rate; using the ratio of the real-time temperature of the transformer to a preset temperature threshold as the thermal load rate; and using the product of the electrical load rate and the thermal load rate as the real-time electrothermal coupling stress index; Step S32, performing time integration on the real-time electrothermal coupling stress index greater than the benchmark value to obtain the cumulative thermal fatigue value; and determining the fault type and severity level when the cumulative thermal fatigue value is greater than a first threshold and less than a second threshold. The first-level overload is determined when the cumulative thermal fatigue value is greater than or equal to the second threshold. Step S33: Calculate the insulation aging penalty coefficient based on the cumulative thermal fatigue value, and correct the insulation warning threshold based on the penalty coefficient to obtain the dynamic insulation warning threshold. Step S34: Calculate the slope of the insulation resistance decrease in the preset time window. When the insulation resistance is less than the dynamic insulation warning threshold and greater than the insulation alarm threshold, and the slope of the insulation resistance decrease is greater than the preset change rate, it is determined to be a first-level insulation fault. When the insulation resistance is less than the insulation alarm threshold, it is determined to be a second-level insulation fault. The fault types include overload fault, overheating fault and insulation degradation fault. The graded protection module is used to execute corresponding graded protection actions according to the severity level of the fault. The graded protection actions include sending early warning information to the outside, activating the load regulation control strategy, and cutting off the power supply to the corresponding circuit. The control switching module is used to set up a main control unit and a backup control unit in the distribution box. The backup control unit monitors the communication data in real time and determines whether the main control unit has failed based on the monitored data. If so, the backup control unit controls the distribution box based on the pre-stored protection control program.

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