A low-power cable sheath circulating current monitoring system

Abstract

This invention relates to the field of cable sheath circulating current monitoring technology, proposing a low-power cable sheath circulating current monitoring system. The system includes: acquiring circulating current signals from different cables at different periods; establishing a subsequence of circulating current signals for each period; constructing a periodic circulating current fluctuation index; analyzing the differences in the periodic circulating current fluctuation index between adjacent periods; switching the operating mode of the cable sheath circulating current monitoring system; and obtaining monitoring results of circulating current risk based on circulating current risk conditions. This invention can dynamically adjust the sampling frequency of cable sheath circulating current monitoring according to the stability of the circulating current signal.

Description

Technical Field

[0001] This invention relates to the field of cable sheath circulation current monitoring technology, and specifically to a low-power cable sheath circulation current monitoring system. Background Technology

[0002] The metallic sheath of high-voltage cables is a critical structure for ensuring safe operation. Its main functions are mechanical protection, corrosion prevention, and electric field shielding. During normal cable operation, the metallic sheath generates an induced voltage due to the electromagnetic induction of the current in the cable conductors. If the sheath grounding is inadequate or insulation defects exist, circulating currents can form within the sheath. These circulating currents can cause overheating, reduce the cable's current carrying capacity and lifespan, accelerate electrochemical corrosion of the metallic sheath, leading to perforation and damage, and ultimately threatening the safe and stable operation of the power grid.

[0003] When cables are in high-risk operating conditions, the sheath circulating current is prone to fluctuations or abrupt changes. Therefore, it is necessary to increase the sampling frequency of cable sheath circulating current monitoring to capture abnormal changes in the circulating current in real time and avoid missing early fault signals due to excessively long sampling intervals. When cables are in low-risk operating conditions, the circulating current signal is stable, requiring a reduction in the sampling frequency of cable sheath circulating current monitoring to meet basic monitoring needs and avoid resource waste caused by high-frequency sampling throughout the entire process. However, currently, it is not possible to dynamically adjust the sampling frequency of cable sheath circulating current monitoring based on the stability of the circulating current signal. Summary of the Invention

[0004] This invention provides a low-power cable sheath circulating current monitoring system to solve the problem of not being able to dynamically adjust the sampling frequency of cable sheath circulating current monitoring based on the stability of the circulating current signal. The specific technical solution adopted is as follows:

[0005] One embodiment of the present invention provides a low-power cable sheath circulating current monitoring system, which includes the following modules:

[0006] An integrated CT sensor module is used for synchronizing the circulating signal and power supply;

[0007] The multi-voltage domain power management module is used to store electrical energy, switch power supply modes, generate different voltages to power various components of the system, and connects to the integrated CT sensor module.

[0008] The ultra-low power main control module is used to collect circulating current signals of different cables in different cycles. Based on the differences between the circulating current signals collected by the cables in the cycle, the circulating current signal subsequences of the cables in the cycle are established in different ways. The circulating current signal subsequences collected by all cables in the same cycle are analyzed to construct the periodic circulating current fluctuation index. The periodic circulating current fluctuation index is used to quantify the discrete intensity and overall fluctuation energy of the circulating current signals of all cables in the cycle. The difference of the periodic circulating current fluctuation index between adjacent cycles is analyzed to switch the operation mode of the cable sheath circulating current monitoring system and obtain the monitoring results of circulating current risk in combination with the circulating current risk conditions.

[0009] The low-voltage communication module is used to report monitoring results and is connected to the ultra-low power main control module.

[0010] Furthermore, the integrated CT sensor module is integrated into the same magnetic core structure, which includes a power-taking coil and a sampling coil.

[0011] Furthermore, the method for establishing the periodic circulating signal subsequence of the cable is as follows:

[0012] The fluctuation intensity is determined based on the differences between the circulating current signals collected by the cable within the cycle;

[0013] When the fluctuation intensity is greater than a preset first judgment threshold, a first preset number of circulation signal subsequences are established; otherwise, a second preset number of circulation signal subsequences are established.

[0014] Furthermore, the fluctuation intensity is the coefficient of variation of the circulating signal collected by the cable within the period.

[0015] Furthermore, the method for constructing the periodic circulation fluctuation index of the aforementioned period is as follows:

[0016] The coefficient of variation of all circulating signals within a circulating signal subsequence is denoted as the characteristic difference of the circulating signal subsequence.

[0017] When the number of circulating current signal subsequences corresponding to the circulating current signals collected by all cables in the same period is not equal, the circulating current signal sequences corresponding to all cables in the same period are divided into a first preset number of circulating current signal subsequences, and the characteristic differences of the circulating current signal subsequences are recalculated.

[0018] Based on the characteristic differences, a periodic characteristic difference matrix is ​​established, and the F-norm of the characteristic difference matrix is ​​denoted as the periodic circulation fluctuation index of the period corresponding to the characteristic difference matrix.

[0019] Furthermore, the specific steps for analyzing the differences in the periodic circulation fluctuation index between adjacent periods and switching the operating mode of the cable sheath circulation monitoring system are as follows:

[0020] The absolute value of the difference between the periodic circulation fluctuation index of the previous period and the periodic circulation fluctuation index of the previous period is denoted as the periodic circulation change difference.

[0021] Let any cable be designated as the first cable. Replace the circulating current signal collected by the first cable in the previous adjacent period with the circulating current signal collected within the period. Based on the circulating current signals of the first cable and all other cables in the period and the previous adjacent period, calculate the difference in circulating current change in the period corresponding to the first cable and record it as the difference in replacement circulating current change in the period corresponding to the first cable.

[0022] The operating mode of the cable sheath circulation monitoring system is determined by comparing the differences in the replacement circulation current changes of all cables in the corresponding cycles with the numerical relationship of the preset second judgment threshold.

[0023] Furthermore, the operating modes of the cable sheath circulation monitoring system include: ultra-low frequency reconnaissance mode, first conventional monitoring mode, second conventional monitoring mode, and high frequency diagnostic mode.

[0024] Furthermore, the circulation risk conditions include:

[0025] Replace the cable whose circulating current variation is greater than the second judgment threshold and whose current during the cycle is greater than 50A;

[0026] Replace the cable whose circulating current variation is greater than the second judgment threshold if the current exceeds 20% of the load current during the cycle;

[0027] The cable whose circulating current variation is greater than the second judgment threshold is replaced by a cable whose phase-to-phase current ratio is greater than 3 within the cycle.

[0028] Furthermore, the specific steps for obtaining the monitoring results of circulation risk by combining circulation risk conditions are as follows:

[0029] If any one of the circulating current risk conditions is met, the cable is determined to have a circulating current risk; otherwise, the cable is determined not to have a circulating current risk.

[0030] Furthermore, the low-voltage communication module adopts a 4G or NB-IoT communication module with an operating voltage of 1.8V.

[0031] The beneficial effects of this invention are:

[0032] This application establishes different circulating current signal subsequences for cables within a cycle based on the differences between the circulating current signals collected during the cycle. It provides a more detailed analysis of the circulating current signals within cycles with more significant non-stationarity. Specifically, it analyzes the corresponding circulating current signal subsequences collected from all cables in the same cycle, constructing a periodic circulating current fluctuation index. This index is used to quantify the discrete intensity and overall fluctuation energy of the circulating current signals from all cables within the cycle. Then, it analyzes the differences in the periodic circulating current fluctuation indices between adjacent cycles to further evaluate whether non-stationary fluctuations have occurred in the circulating current signals collected during the cycle, and the degree of such fluctuations. This allows for switching the operating mode of the cable sheath circulating current monitoring system and obtaining monitoring results of circulating current risk based on circulating current risk conditions. When the cable is in a high-risk operating condition, it promptly captures abnormal changes in the circulating current, avoiding the omission of fault precursor signals due to excessively long sampling intervals. When the cable is in a low-risk operating condition, it avoids the waste of resources caused by high-frequency sampling, solving the problem of not being able to dynamically adjust the sampling frequency of cable sheath circulating current monitoring based on the stability of the circulating current signal. Attached Figure Description

[0033] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0034] Figure 1 This is a schematic diagram of a low-power cable sheath circulation current monitoring system provided in one embodiment of the present invention. Detailed Implementation

[0035] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] Please see Figure 1 The diagram illustrates a low-power cable sheath circulating current monitoring system according to an embodiment of the present invention. The system includes: an integrated CT sensor module, a multi-voltage domain power management module, an ultra-low power main control module, and a low-voltage communication module.

[0037] The low-power cable sheath circulation monitoring system of the present invention consists of an integrated CT sensor module, a multi-voltage domain power management module, an ultra-low power main control module, and a low-voltage communication module.

[0038] Integrated CT sensor module with synchronized circulating signal and power supply.

[0039] The integrated CT sensor module is integrated into the same magnetic core structure, which includes a power-harvesting coil and a sampling coil. The power-harvesting coil is used to obtain energy from the cable grounding wire to power the cable sheath circulating current monitoring system. The sampling coil is used to synchronously collect the circulating current signal, realizing physical synchronization between energy acquisition and signal acquisition, and reducing phase error and external interference.

[0040] The multi-voltage domain power management module is used to store electrical energy, switch power supply modes, generate different voltages to power various components of the system, and connects to the integrated CT sensor module.

[0041] The multi-voltage domain power management module is connected to the integrated CT sensor module. The multi-voltage domain power management module includes an energy acquisition and primary processing unit, a high-efficiency energy management and energy storage unit, a multi-voltage domain generation and dynamic power switching unit, and the specific functions of each unit of the multi-voltage domain power management module are as follows:

[0042] 1. Energy Acquisition and Primary Processing Unit: Rectifies and stabilizes the AC power induced by the power acquisition coil before outputting it.

[0043] 2. High-efficiency energy management and energy storage unit: It has a built-in DC-DC boost regulator chip with MPPT function to ensure that the CT power take-off coil always works at close to the maximum output power. At the same time, it outputs a stable intermediate bus voltage that can be used for charging, and adopts a composite energy storage solution that combines supercapacitors and rechargeable lithium batteries.

[0044] 3. Multi-voltage domain generation and dynamic power switching unit: Includes a priority switching circuit controlled by an ultra-low power main control module to realize the switching between CT power supply and battery power supply; designed 3-channel LDO network to supply power to some peripheral sensors and interface circuits, main control MCU and low voltage communication module respectively.

[0045] The ultra-low power main control module is used to collect circulating current signals of different cables in different cycles. Based on the differences between the circulating current signals collected by the cables within a cycle, it establishes the circulating current signal subsequences of the cables in a cycle in different ways. It analyzes the corresponding circulating current signal subsequences collected by all cables in the same cycle and constructs the periodic circulating current fluctuation index. The periodic circulating current fluctuation index is used to quantify the discrete intensity and overall fluctuation energy of the circulating current signals of all cables within a cycle. It analyzes the differences in the periodic circulating current fluctuation index of adjacent cycles, switches the operation mode of the cable sheath circulating current monitoring system, and obtains the monitoring results of circulating current risk in combination with the circulating current risk conditions.

[0046] The ultra-low power main control module includes an ultra-low power MCU and a high-precision 24-bit... The system includes an ADC, multiple ultra-low-power comparators, and a timer with a low-power RTC real-time clock. Through firmware programming, the main control module implements a power management state machine with three states: deep sleep mode, data acquisition and processing mode, and communication collaboration mode. The firmware embeds intelligent algorithms that can analyze historical data and dynamically adjust the sampling frequency to achieve the optimal balance between monitoring accuracy and system power consumption.

[0047] The workflow of the cable sheath circulating current monitoring system is as follows:

[0048] 1. System power-on and initialization: After the system is powered by the CT or battery, the main control MCU and peripheral circuits complete the initialization and the system runs in "high-frequency diagnostic mode".

[0049] 2. Dynamic Power Consumption Scheduling: When the main control MCU is not acquiring circulating current signals, it is in sleep mode, and the static current in sleep mode is less than or equal to 20μA. When acquiring circulating current signals, the MCU switches to data acquisition mode and starts the sampling coil to acquire circulating current signals. At this time, the current is less than or equal to 40mA. After the circulating current signal acquisition is completed, the MCU controls the low-voltage communication module to power on and enter the data transmission mode to package and upload the data. At this time, the peak current is less than or equal to 240mA. After the data transmission is completed, the MCU switches back to sleep mode.

[0050] 3. Intelligent sampling and data processing: The MCU adaptively selects the system's operating mode based on the processing results of the circulating current signal by the ultra-low power main control module.

[0051] The operating modes of the cable sheath circulation monitoring system include ultra-low frequency reconnaissance mode, first conventional monitoring mode, second conventional monitoring mode, and high frequency diagnostic mode.

[0052] Specifically, the ultra-low frequency reconnaissance mode has a sampling interval of 10 minutes, performing data acquisition and uploading every 10 minutes. This mode minimizes power consumption when the cable sheath circulating current monitoring system is in an absolutely stable state. The first conventional monitoring mode has a sampling interval of 5 minutes, performing data acquisition and uploading every 5 minutes. This mode provides initial conventional monitoring of the cable sheath circulating current monitoring system, balancing data continuity and power consumption, and capturing fault conditions. The second conventional monitoring mode has a sampling interval of 1 minute, performing data acquisition and uploading every 1 minute. This mode provides secondary conventional monitoring of the cable sheath circulating current monitoring system, further balancing data continuity and power consumption, and accurately capturing fault conditions. The high-frequency diagnostic mode has a sampling interval of 10 seconds, performing data acquisition and uploading every 10 seconds. This mode temporarily relaxes power consumption limits to fully capture the transient fault process. Simultaneously, it accurately captures abnormal circulating current characteristics, providing high-resolution data support for fault diagnosis.

[0053] In the integrated CT sensor module, sampling coils are used to collect the circulating current signal of the single-core cable where the sampling coil is located.

[0054] The cable consists of three cables; the sampling interval for the circulating current signal is 10 seconds, and the sampling period is 6 hours. In practical applications, as other implementation methods, the implementer can decide the sampling frequency and sampling period according to the actual situation. This invention does not impose any special restrictions.

[0055] The circulating current signals of the cable collected in the same cycle are input into the ultra-low power main control module according to the collection order, and the ultra-low power main control module completes the processing of the circulating current signals.

[0056] When processing the circulating current signal, the first step is to denoise the circulating current signal of the cable collected in the same period to eliminate interference from external factors.

[0057] In this embodiment, a moving average filtering algorithm is used to denoise the circulating current signal. The moving average window parameter is set to 7. The use of a moving average filtering algorithm for denoising is a well-known technique and will not be elaborated further. As other embodiments, while achieving the goal of denoising the circulating current signal, implementers may use other methods in the prior art for denoising the circulating current signal; this invention does not impose any special limitations.

[0058] When there is no circulating current risk in the cable sheath, the circulating current signal acquisition frequency can be appropriately reduced to lower system power consumption. Specifically, when the circulating current signal fluctuates smoothly without obvious abnormalities, it indicates that the circulating current state is stable, and energy consumption can be saved by reducing the sampling frequency. Conversely, if the circulating current signal shows abnormalities such as sudden increases or violent fluctuations, it indicates that the circulating current risk may be increased. In this case, the sampling frequency should be increased to monitor the signal dynamics more intensively, identify potential faults in a timely manner, and take countermeasures.

[0059] The core cause of circulating current is the uneven distribution of current and voltage in cable lines, leading to a potential difference between cable cores. Specifically, when multiple cables are running in parallel, the current in each cable conductor will exhibit uneven distribution, resulting in randomness in the current and voltage distribution among the multiple cables. Consequently, the degree to which each cable is affected by circulating current varies. In contrast, the current and voltage distribution of a single cable is relatively stable, and its circulating current signal changes more smoothly.

[0060] This means that when there is no risk of circulating current in the cable sheath circulation monitoring system, the changes in the circulating current signals among the three cables will show a stable relationship. If one or more of the cables experience a risk of circulating current, this stable relationship will be broken.

[0061] The sequence of circulating current signals collected from any cable in any cycle is denoted as the target circulating current signal sequence. The circulating current signals are arranged in the order they were collected within the sequence.

[0062] When abnormal fluctuations occur in the circulation signal within the target circulation signal sequence, the circulation signal within the target circulation signal sequence will exhibit non-stationary changes over time.

[0063] The coefficient of variation of all circulating signals within the target circulating signal sequence is denoted as the fluctuation intensity of the target circulating signal sequence. When the fluctuation intensity of the target circulating signal sequence is greater than a first judgment threshold, the target circulating signal sequence is divided into a first preset number of circulating signal subsequences; when the fluctuation intensity of the target circulating signal sequence is less than or equal to the first judgment threshold, the target circulating signal sequence is divided into a second preset number of circulating signal subsequences.

[0064] The method for setting the first judgment threshold is as follows: when the cable is working normally, the average value of the fluctuation intensity of the circulating current signal sequence of the cable in 100 cycles is used as the first judgment threshold; in this embodiment, the first preset number is 12 and the second preset number is 3.

[0065] Based on the numerical relationship between the fluctuation intensity of the target circulation signal sequence and the first judgment threshold, the target circulation signal sequence is divided into different numbers of circulation signal subsequences, which allows for more detailed analysis of circulation signals within periods with more significant non-stationarity.

[0066] The coefficient of variation of all circulating signals within the circulating signal subsequences divided from the target circulating signal sequence is denoted as the characteristic difference of the circulating signal subsequences.

[0067] The same method can be used to obtain the characteristic differences of each circulating signal subsequence composed of the circulating signals collected by each cable in each cycle.

[0068] The number of circulating signal subsequences corresponding to the circulating signals collected by the three cables in the same period is compared. When the number is not equal, the division of the circulating signal subsequences is updated. Specifically, the circulating signal sequences corresponding to the three cables in the same period are divided into a first preset number of circulating signal subsequences, and the characteristic differences of each circulating signal subsequence are recalculated.

[0069] Based on the characteristic differences of all circulating signal subsequences composed of circulating signals collected from the three cables in the same period, a characteristic difference matrix for the same period is established. Using the singular value decomposition algorithm, singular values ​​are calculated based on the characteristic difference matrix of the period, and the F-norm (Frobenius Norm) of the characteristic difference matrix is ​​calculated based on the singular values. The F-norm of the characteristic difference matrix is ​​denoted as the periodic circulating fluctuation index of the period corresponding to the characteristic difference matrix.

[0070] The periodic circulation fluctuation index is used to evaluate the degree of non-stationary variation of all circulating current signals of all cables within a period. The larger the periodic circulation fluctuation index, the more severe the overall fluctuation of the cable sheath circulation and the more significant the non-stationary characteristics within that period.

[0071] The specific method for establishing the periodic feature difference matrix is ​​as follows: the feature differences of the circulating signal subsequences of the three cables in the same period corresponding to the same time period are taken as the same column of the feature difference matrix. According to the order of the corresponding time periods from early to late, the different columns are arranged from left to right. The values ​​of the same row of the feature difference matrix are the feature differences of the circulating signal subsequences of the same cable in the same period.

[0072] Among them, the singular value decomposition algorithm and the calculation of the F-norm of the matrix are well-known techniques and will not be described in detail.

[0073] The singular values ​​of the characteristic difference matrix are used to represent the energy intensity of the characteristic difference matrix in the main direction. When the difference between the different singular values ​​of the three cables in the same period is smaller, the circulation signal of the three cables in the same period is more stable, and the probability of circulation risk of the three cables in the same period is smaller. At this time, the periodic circulation fluctuation index of the period corresponding to the characteristic difference matrix is ​​smaller.

[0074] When the circulating current signal collected by the cable in a certain period shows non-stationary fluctuations, the periodic circulating current fluctuation index of the cable in that period is larger than that of the previous adjacent period. Therefore, the periodic circulating current fluctuation index of adjacent periods can be compared to evaluate whether the circulating current signal collected in the period has shown non-stationary fluctuations and the degree of fluctuation of the non-stationary fluctuations.

[0075] The absolute value of the difference between the periodic circulation fluctuation index of the current period and the previous adjacent period is denoted as the periodic circulation change difference. Taking any cable as the first cable, the circulation signal collected by the first cable in the previous adjacent period is replaced with the circulation signal collected within the current period. Following the same method, based on the circulation signals of the first cable and all other cables in the current period and the previous adjacent period, the periodic circulation change difference corresponding to the first cable is calculated and denoted as the replacement circulation change difference corresponding to the first cable.

[0076] Specifically, before replacement, the signal data length of the first cable in the current cycle can be adjusted to be consistent with the previous cycle through linear interpolation or downsampling, or both can be unified to the standard length.

[0077] The same method can be used to obtain the difference in replacement circulating current for each cable in the corresponding cycle.

[0078] Compare the numerical relationship between the differences in replacement circulation current changes for all cables in the corresponding cycles and the second judgment threshold, and determine the operating mode of the cable sheath circulation current monitoring system based on the numerical relationship.

[0079] Specifically, when the difference in replacement circulating current variation for all cables within a given period is less than or equal to the second judgment threshold, the operating mode of the cable sheath circulating current monitoring system is switched to ultra-low frequency detection mode. In this mode, the local non-stationary fluctuations in the circulating current signals collected by all cables within a given period are within acceptable limits. When the difference in replacement circulating current variation for only one cable within a given period is less than or equal to the second judgment threshold, and the differences in replacement circulating current variation for the other cables within a given period are greater than the second judgment threshold, the operating mode of the cable sheath circulating current monitoring system is switched to the second conventional monitoring mode. In this mode, the circulating current signals collected by the cable with a replacement circulating current variation less than or equal to the second judgment threshold within a given period exhibit local non-stationary fluctuations, while the local non-stationary fluctuations in the circulating current signals collected by the other cables within a given period are within acceptable limits. Within acceptable limits; when the difference in replacement circulating current change between two cables corresponding to the same period is less than or equal to the second judgment threshold, and the difference in replacement circulating current change between the other cables corresponding to the same period is greater than the second judgment threshold, the operating mode of the cable sheath circulating current monitoring system is switched to the first conventional monitoring mode. At this time, the circulating current signal collected within the period of the cable with a replacement circulating current change difference less than or equal to the second judgment threshold shows local non-stationary fluctuations, while the local non-stationary fluctuations of the circulating current signal collected within the period of the other cables are all within acceptable limits; when the difference in replacement circulating current change between the periods of all cables is greater than the second judgment threshold, the operating mode of the cable sheath circulating current monitoring system is switched to the high-frequency diagnostic mode. At this time, the circulating current signal collected within the period of all cables shows local non-stationary fluctuations.

[0080] The method for setting the second judgment threshold is as follows: when the cable is working normally, the difference in the circulating current change of the cable in 100 consecutive adjacent cycles is obtained, and the average value of all the differences in the circulating current change is used as the second judgment threshold.

[0081] After determining the operating mode of the cable sheath circulating current monitoring system, it is judged whether the circulating current risk conditions are met. When any one of the circulating current risk conditions is met, it is determined that the cable has a circulating current risk, and the monitoring result of "cable has a circulating current risk" is reported to the monitoring center through the low-voltage communication module; when none of the circulating current risk conditions are met, it is determined that the cable has no circulating current risk, and the monitoring result of "cable has no circulating current risk" is reported to the monitoring center through the low-voltage communication module. At the same time, the operating mode of the cable sheath circulating current monitoring system is switched to the ultra-low frequency reconnaissance mode.

[0082] The specific conditions for circulating current risk include: (1) the current of the cable whose circulating current variation is greater than the second judgment threshold is greater than 50A during the cycle; (2) the current of the cable whose circulating current variation is greater than the second judgment threshold is greater than 20% of the load current during the cycle; and (3) the ratio of the maximum to the minimum amplitude of the three-phase current of the cable whose circulating current variation is greater than the second judgment threshold is greater than 3 during the cycle. The current of the cable during the cycle can be collected by a sampling coil. During the ratio calculation, to avoid the denominator being zero, a preset value needs to be added to the denominator. In this embodiment, the preset value is 0.01.

[0083] When there is no circulating current risk in the cable sheath, the system power consumption can be reduced by lowering the circulating current signal acquisition frequency. Specifically, when the circulating current signal fluctuates smoothly and without obvious abnormalities, it indicates that the circulating current state is stable, and the sampling frequency can be reduced to save energy. Conversely, if the circulating current signal shows a sudden increase or violent fluctuations, it indicates that the circulating current risk may be increased, and the sampling frequency needs to be increased to identify potential faults and take countermeasures in a timely manner through intensive monitoring of signal dynamics. The core reason for the generation of circulating current is the uneven distribution of current and voltage in the cable line, resulting in a potential difference between the cable cores. Specifically, when multiple cables are running in parallel, the current in each cable conductor will exhibit uneven distribution, making the current and voltage distribution among multiple cables random, thus leading to differences in the degree to which each cable is affected by circulating current. In contrast, the current and voltage distribution of a single cable is relatively stable, and its circulating current signal changes more smoothly. This means that when there is no circulating current risk in the cable, the circulating current signal changes among the three cables will show a stable relationship; if one or two cables experience circulating current risk, this stable relationship will be broken.

[0084] To achieve early warning of circulating current risks, the system can enter a higher frequency monitoring state in advance. Specifically, using the analog comparator built into the MCU, the cable voltage is compared with the safety threshold voltage set by the DAC. The analog comparator can operate independently when the MCU is in deep sleep mode. Regardless of the operating mode of the cable sheath circulating current monitoring system, once the instantaneous current value exceeds the limit, the analog comparator will immediately generate an interrupt signal, forcibly waking up the sleeping MCU and switching the operating mode of the cable sheath circulating current monitoring system to high-frequency diagnostic mode to complete the instantaneous over-limit judgment. This mechanism, known as the rapid early warning mechanism for circulating current risks, has a response speed of microseconds and can effectively capture sudden instantaneous faults that may be missed by software polling.

[0085] All threshold parameters and the current state of the state machine are stored in the MCU's EEPROM or Flash, ensuring that the cable sheath circulating current monitoring system can restore the previous monitoring context after a reset or power failure restart, rather than directly returning to the initial state. The power management module is simultaneously notified each time the algorithm completes a state transition. For example, when returning from "high-frequency diagnostic mode" to "second normal monitoring mode," the algorithm triggers an instruction for the power management module to check the energy storage unit's power level. If the power is sufficient, the CT is used to draw power and charge the battery.

[0086] The low-voltage communication module is used to report monitoring results and is connected to the ultra-low power main control module.

[0087] The low-voltage communication module uses a 4G or NB-IoT communication module with a working voltage of 1.8V, which is connected to the ultra-low power main control module. It is responsible for remotely uploading the processed circulating current signal to the monitoring center and receiving remote commands issued by the monitoring center.

[0088] This completes the circulation monitoring of the cable sheath circulation monitoring system.

[0089] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A low-power cable sheath circulating current monitoring system, characterized in that, The system includes the following modules: An integrated CT sensor module is used for synchronizing the circulating signal and power supply; The multi-voltage domain power management module is used to store electrical energy, switch power supply modes, generate different voltages to power various components of the system, and connects to the integrated CT sensor module. The ultra-low power main control module is used to collect circulating current signals of different cables in different cycles. Based on the differences between the circulating current signals collected by the cables in the cycle, the circulating current signal subsequences of the cables in the cycle are established in different ways. The circulating current signal subsequences collected by all cables in the same cycle are analyzed to construct the periodic circulating current fluctuation index. The periodic circulating current fluctuation index is used to quantify the discrete intensity and overall fluctuation energy of the circulating current signals of all cables in the cycle. The difference of the periodic circulating current fluctuation index between adjacent cycles is analyzed to switch the operation mode of the cable sheath circulating current monitoring system and obtain the monitoring results of circulating current risk in combination with the circulating current risk conditions. The low-voltage communication module is used to report monitoring results and is connected to the ultra-low power main control module. The method for establishing the periodic circulating signal subsequence of the cable is as follows: The fluctuation intensity is determined based on the differences between the circulating current signals collected by the cable within the cycle; When the fluctuation intensity is greater than a preset first judgment threshold, a first preset number of circulation signal subsequences are established; otherwise, a second preset number of circulation signal subsequences are established. The method for constructing the periodic circulation fluctuation index of the aforementioned period is as follows: The coefficient of variation of all circulating signals within a circulating signal subsequence is denoted as the characteristic difference of the circulating signal subsequence. When the number of circulating current signal subsequences corresponding to the circulating current signals collected by all cables in the same period is not equal, the circulating current signal sequences corresponding to all cables in the same period are divided into a first preset number of circulating current signal subsequences, and the characteristic differences of the circulating current signal subsequences are recalculated. Based on the characteristic differences, a periodic characteristic difference matrix is ​​established, and the F-norm of the characteristic difference matrix is ​​denoted as the periodic circulation fluctuation index of the period corresponding to the characteristic difference matrix. The specific steps for analyzing the differences in the periodic circulation fluctuation index between adjacent periods and switching the operating mode of the cable sheath circulation monitoring system are as follows: The absolute value of the difference between the periodic circulation fluctuation index of the previous period and the periodic circulation fluctuation index of the previous period is denoted as the periodic circulation change difference. Let any cable be designated as the first cable. Replace the circulating current signal collected by the first cable in the previous adjacent period with the circulating current signal collected within the period. Based on the circulating current signals of the first cable and all other cables in the period and the previous adjacent period, calculate the difference in circulating current change in the period corresponding to the first cable and record it as the difference in replacement circulating current change in the period corresponding to the first cable. The operating mode of the cable sheath circulation monitoring system is determined by comparing the differences in the replacement circulation current changes of all cables in the corresponding cycles with the numerical relationship of the preset second judgment threshold.

2. The low-power cable sheath circulating current monitoring system according to claim 1, characterized in that, The integrated CT sensor module is integrated into the same magnetic core structure, which includes a power-taking coil and a sampling coil.

3. The low-power cable sheath circulating current monitoring system according to claim 1, characterized in that, The fluctuation intensity is the coefficient of variation of the circulating signal collected by the cable within a period.

4. The low-power cable sheath circulating current monitoring system according to claim 1, characterized in that, The operating modes of the cable sheath circulation monitoring system include: ultra-low frequency reconnaissance mode, first conventional monitoring mode, second conventional monitoring mode, and high frequency diagnostic mode.

5. A low-power cable sheath circulating current monitoring system according to claim 1, characterized in that, The circulation risk conditions include: Replace the cable whose circulating current variation is greater than the second judgment threshold and whose current during the cycle is greater than 50A; Replace the cable whose circulating current variation is greater than the second judgment threshold if the current exceeds 20% of the load current during the cycle; The cable whose circulating current variation is greater than the second judgment threshold is replaced by a cable whose phase-to-phase current ratio is greater than 3 within the cycle.

6. The low-power cable sheath circulating current monitoring system according to claim 1, characterized in that, The specific steps for obtaining the monitoring results of circulation risk by combining circulation risk conditions are as follows: If any one of the circulating current risk conditions is met, the cable is determined to have a circulating current risk; otherwise, the cable is determined not to have a circulating current risk.

7. A low-power cable sheath circulating current monitoring system according to claim 1, characterized in that, The low-voltage communication module uses a 4G or NB-IoT communication module with an operating voltage of 1.8V.

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