Passive wireless sensing monitoring method for distribution cable

Abstract

The invention discloses a passive and wireless sensing monitoring method for a distribution cable, which comprises the following steps of: describing a special process structure of a cable laid in a distribution cable trench, determining a current-electromagnetic field mathematical model, constructing a current-electromagnetic simulation model, and analyzing two leakage current distributions with or without a metal sheath layer based on the simulation model. And determining the incidence relation between the cable leakage current and the aging problem. A current on-line monitoring system based on subG wireless communication is designed to solve the problem of real-time monitoring of cable leakage current. A high-precision current sensor is adopted to measure electromagnetic field information, and remote transmission of monitoring data is realized through a wireless communication module; and the field passive problem is solved by adopting a three-core cable electromagnetic field self-power-taking mode. And the Internet of Things cloud platform is developed to complete interconnection between the terminal equipment and the cloud platform, and equipment management and data flow visual display functions are realized. A passive wireless leakage current monitoring system realizes on-line monitoring of insulation aging of a cable and a joint, solves the practical problem of on-line monitoring of insulation aging, and has certain engineering application value.

Description

Technical Field

[0001] The invention relates to cable technology, in particular to an online passive wireless monitoring method for cable insulation aging. Background Art

[0002] With the transformation and upgrade of urban power grids, power cables are widely used in urban distribution systems, placing higher demands on the safe operation of cable lines. Cable joints, as crucial accessories for distribution cables, are susceptible to accelerated insulation aging during operation due to elevated cable or ambient temperatures, which can lead to fires in severe cases. For cable joints installed in cable trenches within urban distribution networks, manual temperature inspections are time-consuming and labor-intensive due to the unique operating environment, and real-time monitoring is difficult. Online temperature monitoring is the most intuitive way to identify cable fires. By monitoring the temperature of cable intermediate joints in real time, early warning can be issued before a fault occurs, enabling timely troubleshooting or replacement of the intermediate joints, thereby preventing further damage. Power cable lines are a critical component of the national power grid, with 1.76 million kilometers of power lines nationwide. With an intermediate joint located every 300-500 meters, there are approximately 6 million intermediate joints nationwide. Distribution cable trenches operate in a relatively closed environment and lack a direct power supply. Placing monitoring equipment at the joints presents significant challenges in both power supply and data transmission. Furthermore, ensuring accurate and cost-effective cable leakage current monitoring requires careful consideration of the appropriate placement of sensing devices and energy supply. Therefore, based on the above problems, the present invention develops a cable leakage current monitoring and self-energy collection system suitable for the cable trench operating environment. Through electromagnetic field analysis, a reasonable solution for the layout of measuring equipment is provided, the reasonable layout of sensing equipment is realized, and the power supply problem of the collection device is solved by self-energy collection through the induced magnetic field. To a certain extent, it solves the practical problems of cable current monitoring and has certain engineering application value.

[0003] At present, cable insulation aging detection mostly adopts offline methods, but the efficiency is too low, and the coupling relationship between the sensing device and the cable magnetic field is uncertain. Secondly, in terms of energy supply, the mode of direct optical fiber supply or lithium battery power supply is adopted, which brings great safety hazards to the underground operating environment and the overall cost is high. Compared with the current monitoring means, the method and system designed in the present invention are more in line with the requirements of the underground operating environment of distribution cables. Summary of the Invention

[0004] The existing technology has the problem that cable insulation aging detection mostly adopts offline methods, but the efficiency is too low, and the coupling relationship between the sensing device and the cable magnetic field is uncertain. Secondly, in terms of energy supply, the mode of direct optical fiber supply or lithium battery power supply is adopted, which brings great safety hazards to the underground operating environment and the overall cost is high.

[0005] In order to solve the above problems, the present invention provides a passive wireless sensing monitoring method for distribution cables, which is characterized by a designed electromagnetic field-based self-energy current monitoring terminal device, and the specific steps are as follows:

[0006] The modeling scale is a 1:1 replica of the real three-phase cable;

[0007] The cross-sectional area of ​​the conductive core is 3*95 mm2, the thickness of the insulation layer is 1.1 mm, the outer diameter of the cable is 33.4 mm, and the thickness of the outer protective layer is 2.5 mm. P is an arbitrary point outside the cable, and the angle between the displacement vector at point P and the field vector at point P is α.

[0008] For the ideal two-dimensional modeling of a three-phase cable, the cable usually satisfies the requirement of length L > diameter D, so it can be approximately considered as an infinitely long straight conductor. For transient analysis of the cable current, a very short time period is taken, during which the cable current is assumed to be constant. According to the Biot-Savart law, it can be seen that:

[0009]

[0010] Where μ0 is the vacuum permeability, μ0=4π×10 -7 Tm / A, I is the current size, L is the integral path, dl is the infinitesimal length of the current, It is the unit vector of the current source pointing to the point to be determined. On any ray starting from the center of the cable, the farther the point on the ray is from the cable, the smaller the magnetic induction intensity. If you want to improve the power extraction efficiency, you need to make full use of the area with large magnetic induction intensity close to the outer protective layer of the cable. The value of the magnetic induction intensity in the direction of the x and y axes at every 1° on the outer circumference of the three-phase cable at each moment is derived as B x ,B y , and at the same time derive the normalized values ​​of the displacement vector of the point in the x and y axis directions as X,Y;

[0011] The normal magnetic induction intensity of each point on the outer circumference is calculated as follows:

[0012]

[0013] The maximum normal magnetic induction intensity on the outer circumference at each moment is subtracted from the minimum value to obtain the value of the maximum normal magnetic induction intensity difference at that moment. The values ​​of this value at each moment in a power system cycle are compared. It can be found that the maximum normal magnetic induction intensity difference occurs at 1.7, 5.0, 8.3, 11.7, 15, and 18.3 ms.

[0014] Based on the above principles, the magnetic field energy acquisition module of the sensor is designed;

[0015] The DC power is converted into microwave energy by a microwave source and then transmitted through the transmitting antenna and transmitted through free space. The receiving antenna is responsible for receiving the radio frequency energy and then converting the radio frequency energy into DC energy for use through the rectifier circuit.

[0016] The wireless sensor node captures the special electromagnetic wave energy in the environment through the receiving antenna, and then converts it into DC energy storage and management through the matching network and rectification circuit, and then provides the energy to the wireless temperature sensor system;

[0017] Since the impedance and matching of the receiving antenna will affect the effective energy entering the rectifier circuit, and the design optimization of the rectifier circuit also depends on the receiving frequency and impedance, it is necessary to consider the receiving antenna and the rectifier circuit together. The rectifier antenna model part, which includes the receiving antenna and the rectifier circuit, is replaced by a resonant unit composed of inductor L and capacitor C. The resonant frequency of LC is the operating frequency of the antenna. The input power source composed of the source resistor Z represents the input power received in the air. This power can be adjusted according to the electromagnetic field power of the actual environment. The rectifier circuit part consists of a voltage doubling topology, a filter capacitor, and a load. The electromagnetic energy harvesting wireless sensor node will rectify, boost, and store the wireless energy obtained for the collection of different sensing quantities and wireless transmission of information. Due to the large energy transmission loss of the electromagnetic field in space, the utilization rate is lower than that of other direct energy sources. Improving the conversion efficiency of electromagnetic energy harvesting to obtain higher instantaneous energy is the key to improving the working performance of the entire system. The power finally converted by the rectifier and filter circuit can be calculated using the circuit rectification efficiency calculation formula:

[0018]

[0019] This formula considers the conversion power under ideal impedance matching conditions. In actual development and design, circuit losses should be considered to optimize impedance matching as much as possible.

[0020] Under the optimal approach, we gain a deep understanding of the coupling mechanism of cable insulation aging variables. Through simulation, we find that common-mode leakage current is proportional to the insulation capacitance, the injected monitoring voltage amplitude, and the cable length. During cable aging, the insulation capacitive leakage current increases significantly. By monitoring the leakage current, we can identify cable aging defects and fault characteristics.

[0021] Determine the coupling relationship between the distribution of multi-mode leakage current changes and the early aging position; when it is very difficult to measure the voltage distribution on the entire cable, the early aging is initially located by measuring the common-mode leakage current at the cable end. The common-mode leakage current I CM Produced by the common-mode voltage applied to the cable insulation, it is expressed as follows:

[0022]

[0023] Where C(x) represents the insulation capacitance at position x on the cable. For cables that have aged early, the increase in insulation capacitance in the aging section will cause a change in the common-mode leakage current. The change in common-mode leakage current can be expressed as follows:

[0024] dI CM =I CM -I CM0

[0025] Where, I CM is the measured common-mode leakage current amplitude, I CM0 It is the common-mode leakage current amplitude when the cable is intact, which can be measured when the new cable is put into operation. The first parameter is the increase in common-mode leakage current caused by the increase in capacitance in the early aging section; the second parameter is the leakage current change caused by the change in voltage distribution on the entire cable due to early aging. The second part is the main factor causing the change in common-mode leakage current. For different degrees of early aging occurring at the same position, the change in common-mode leakage current will also show a similar distribution in the frequency domain, but the amplitude will be different. For different degrees of early aging occurring at the same position, the change in common-mode leakage current will also show a similar distribution in the frequency domain, but the amplitude will be different.

[0026] In the preferred mode, a method of self-energy extraction using cable electromagnetic fields is proposed. Energy is obtained through electromagnetic field modeling. The wireless sensor nodes rectify, boost and store the obtained wireless energy for the collection of different sensing quantities and wireless transmission of information.

[0027] In the preferred mode, a regional distributed wireless radio frequency communication system is designed to maximize space utilization. In the case of limited resources, the use of a distributed antenna system can maximize the utilization of space resources. The distributed antenna system can cover a wider range, and the resources within the range can be used in a polarized manner, providing faster transmission rates. The distributed antenna system uses distributed optical fiber technology.

[0028] The data transmission link between the sensor and the sideband device is established using a SubG low-power communication chip. The wireless communication mode should comprehensively consider parameters such as transmission distance, transmit power, power consumption, and air interface transmission rate. Low-rate mode can achieve a longer wireless transmission distance. While meeting the required communication distance, higher transmission rates can effectively save communication time and optimize the device's RF power consumption. The microprocessor configures and drives each sensor chip, as well as implements the communication protocol. Key considerations include device packaging, operating current, and standby power consumption. The communication module should provide multiple external interfaces to accommodate different sensor module access requirements. An ultra-low current load switch is used to switch the RF power amplifier chip on and off to reduce system standby power consumption. The antenna uses a PATCH end-loading scheme, which enables the antenna to form multiple resonances at adjacent frequency points, thereby increasing bandwidth and improving antenna robustness. When the target tunnel section is long and the communication network cost is low, antenna telemetry technology is required to achieve RF power amplification and long-distance transmission. Antenna telemetry converts baseband signals into optical signals for transmission, and performs RF processing and power amplification at the remote end.

[0029] Beneficial effects of the present invention: The present invention first describes the special process structure of cables laid in distribution cable trenches, determines the mathematical model of the current-electromagnetic field formed during the operation and defects of distribution cables, and based on this, uses the finite element analysis method to perform numerical simulation calculations on the current field, constructs a current-electromagnetic simulation model, analyzes the leakage current distribution of two types with and without metal sheath layers based on the simulation model, and deeply analyzes the leakage current variation law under different influencing factors, and finally determines the correlation between cable leakage current and aging problems. In order to solve the problem of real-time monitoring of cable leakage current, combined with the specific application scenarios of cable trenches, a current online monitoring system based on subG wireless communication is designed. The system terminal equipment uses a low-power communication chip as the control core to control data acquisition and operating frequency, selects a suitable power supply and designs a power management circuit; uses a high-precision current sensor to measure electromagnetic field information, and realizes remote transmission of monitoring data through a wireless communication module; the present invention also takes into account the problem of limited power supply in underground space and adopts a three-core cable electromagnetic field self-powering mode to supply power to wireless communication and signal processing units, solving the problem of on-site passivity. The software for the terminal device was designed, and an IoT cloud platform was developed. This system establishes a connection with the cloud platform via the LwM2M protocol, interconnecting the terminal device and the cloud platform, enabling device management and data flow visualization. The passive wireless leakage current monitoring system developed by this invention can perform online monitoring of cable and connector insulation aging. By using electromagnetic field analysis, it provides a rational solution for monitoring equipment layout, addressing the practical problem of online insulation aging monitoring to a certain extent and possessing considerable engineering application value.

[0030] To address the sensor power supply issue, an electromagnetically coupled power line energy harvesting system was designed. This system maximizes energy harvesting by operating in the soft saturation region or near the magnetic saturation region of the magnetic core. To address the complex nonlinear issues caused by the magnetic saturation effect and accurately model and simulate the energy harvesting system, the authors proposed a circuit simulation model of the core that accounts for magnetic saturation, using the inverse tangent function to fit the magnetization curve of the core material based on Maxwell's equations. Lumped parameter nonlinear inductors were used to simulate the coil core. The core model was applied in circuit simulation software to study the relationship between system power output and loss, core parameters, and coil turns. A complete energy harvesting system parameter design process was established to meet application design requirements. By optimizing the core simulation model and the power line energy harvesting system, and designing the energy management circuit and control strategy for the power line energy harvesting system based on the magnetic saturation effect, a self-powered technology based on power cable magnetic field energy harvesting was realized. This effectively solves the energy supply problem of wireless temperature sensor terminal monitoring devices around power cables, optimizes the energy harvesting system circuit design, and promotes the development and application of wireless sensor and cable detection technologies. The application scenario of the present invention is designed as a 10kV transmission line. The power transmission at this voltage level is generally 200-2000kW. Therefore, the primary side current input range is designed to be 0-200A, and the typical working state is 100A.

[0031] The present invention integrates the self-energy extraction device with a new type of current sensor to form an integrated device, which is deployed and installed on the distribution cable or accessories, and can solve the problem of passive and accurate measurement of the cable. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 The present invention provides a passive wireless monitoring system architecture for cable insulation aging;

[0033] Figure 2 The hardware structure of a passive wireless monitoring system for cable insulation aging provided in this application;

[0034] Figure 3 A low-power wireless communication transmission principle diagram provided by this application;

[0035] Figure 4 This application provides a hardware structure of a cable self-energy measurement device. DETAILED DESCRIPTION

[0036] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0037] The following specific embodiments are used to describe the technical solution of the present invention in detail. The following specific embodiments can be combined with each other, and the same or similar concepts or processes may not be described in detail in some embodiments.

[0038] The present invention designs a method for designing a distributed insulation aging monitoring and self-energy extraction integrated device for distribution cables. The specific implementation methods and steps are described as follows:

[0039] When the cable conductor passes through the alternating current, the energy loss of the cable insulation layer under the action of the AC voltage is called the insulation dielectric loss. The specific calculation formula is:

[0040]

[0041] Where c represents the cable capacitance per unit length, F / m; is the angular frequency, is the AC frequency; U0 is the phase voltage applied to the cable; tanδ is the dielectric loss factor of the specific material; δ is the dielectric loss angle.

[0042] Cable insulation aging is often accompanied by changes in relative dielectric constant, which makes the insulation electrical parameter G in and C inChanges occur. Relevant literature points out that for cables with polymer insulation, the rapid cooling process during the production process will leave many gaps in the insulation. During the operation of the cable, the number of gaps in the insulation will continue to increase, and moisture and impurities in the environment will easily enter the gaps, causing the relative dielectric constant of the cable insulation to increase. By measuring the cable insulation leakage current, the cable insulation capacitance and resistance can be monitored, thereby estimating the degree of insulation aging. The present invention mainly monitors the insulation capacitance. As the degree of aging increases, the rising trend of the insulation capacitance remains consistent over a wider frequency band, which brings great flexibility to the monitoring; secondly, at the power frequency or higher frequency, the capacitive part of the insulation leakage current is much larger than its resistive part, making the monitoring accuracy and sensitivity of the insulation capacitance higher. Both the insulation capacitive leakage current and the resistive leakage current gradually increase with the increase in the degree of cable aging. And throughout the entire process of cable aging, the insulation capacitive leakage current is much larger than the resistive leakage current. In the early aging process of the cable, the insulation capacitive leakage current increases significantly, while the resistive leakage current changes little. When aging is severe, although the insulation resistive leakage current increases rapidly, it is still an order of magnitude lower than the capacitive leakage current. Therefore, at power frequency, the capacitive leakage current accounts for the vast majority of the insulation leakage current. By measuring the insulation leakage current, the insulation capacitance can be effectively monitored.

[0043] The common-mode leakage current is proportional to the insulation capacitance, the injected monitoring voltage amplitude, and the cable length. Therefore, the TMR technology can be used to measure the magnetic field size generated by the injected current of the cable. Since the magnetic field of the leakage current belongs to the current in the micro range, TMR technology is selected for measurement. TMR is a new magnetoresistance effect measurement technology that uses the tunnel magnetoresistance effect of magnetic multilayer film materials to sense the magnetic field. The leakage current information is extracted by the electromagnetic sensor, so that the aging of the cable insulation can be known. However, the monitored measurement data cannot be transmitted out in the tunnel, and the power supply problem of the data processing and transmission unit cannot be solved. The data in the distribution cable channel cannot be transmitted to the background. Therefore, the present invention designs a passive wireless sensing monitoring method for distribution cables. Based on the distributed characteristics of distribution cables, low-power SubG wireless communication technology is used as a solution for remote data transmission, and the comprehensive management of monitoring terminal equipment is realized through the Internet of Things cloud platform. By installing monitoring equipment on site, real-time monitoring of the insulation aging characteristics of the cable operation can be achieved.

[0044] The distribution cable has a large number of joints and long segments, resulting in a large amount of monitoring data, which requires analysis and processing. Furthermore, the joints are relatively scattered, and there is no stable power supply. Therefore, the leakage current monitoring system should have good data processing and analysis, self-power supply, and remote equipment management capabilities. The monitoring system terminal equipment is arranged in the cable trench, which is inconvenient to operate and communication is blocked. The remote communication and operating power consumption performance of the monitoring system should be optimized. In view of the above situation, the designed cable joint leakage current monitoring system should have the following functions:

[0045] (1) Real-time data collection: The leakage current monitoring system needs to obtain real-time insulation data of cable joints and the entire line to ensure the accuracy and reliability of the data and truly reflect the aging status of the cable insulation. In the context of high informationization, data collection should meet the characteristics of automation and intelligence. Through the monitoring terminal equipment deployed on site, unmanned data automatic collection can be achieved. According to management needs, the data can be further processed and analyzed to facilitate management by operation and maintenance personnel.

[0046] (2) Self-energy collection to ensure stable operation time: The operation time of the temperature monitoring system depends on the power supply of the terminal equipment. The equipment adopts the electromagnetic energy collection mode to directly collect micro energy on the distribution cable to power the sensing device. However, since the collected energy is limited, the monitoring terminal should have low power consumption performance to ensure the system operation time.

[0047] (3) Remote and reliable communication: Cable connectors are dispersed and distributed over long distances. Remote and reliable transmission of monitoring data is key to ensuring stable system operation. Communication methods are primarily wired and wireless, ensuring real-time link connectivity.

[0048] (4) Equipment control and management: Centralized management of monitoring terminal equipment can greatly improve the intelligence level of the leakage current monitoring system. Relying on the Internet of Things cloud platform, it provides friendly human-computer interaction functions. Not only can the application center remotely obtain terminal equipment information and realize data viewing and analysis functions, but it can also realize remote control and management of terminal equipment by issuing commands, comprehensively grasp the operating status of terminal equipment, and improve the level of intelligent management.

[0049] The architecture of the passive wireless sensing and monitoring system for distribution cables developed by the present invention can be summarized as a self-powered terminal device, a wireless network, and a sensing device. The overall system architecture is as follows: Figure 1 The terminal device is the most basic part of the monitoring system. It consists of multiple data acquisition nodes distributed at the cable joint operation site. Through the rational arrangement of current sensors, it completes the leakage current data collection and upload, and can also execute the control commands issued by the cloud platform.

[0050] The self-powered current monitoring terminal device is the core of the entire system, with the goal of achieving energy supply, temperature data collection, long-range and short-range communication, and low-power operation. Its hardware design and implementation are crucial to ensure the reliable and stable operation of the leakage current monitoring system. The overall hardware framework of the device is as follows: Figure 2 As shown, the system primarily consists of a current sensor, a self-powered energy module, a main control chip, a SubG wireless communication module, and related peripheral circuits. The current sensor measures the leakage current along the entire cable in real time and transmits it to the main control chip. The self-powered energy chip provides energy to the entire terminal node, maintaining its normal operation. The main control chip, using a high-performance STM32 microprocessor, further packages and processes temperature data and controls the coordinated operation of the terminal's various hardware modules. The SubG module, using a low-power communication chip, enables data hopping within the current sensor channel and can connect to long-distance optical fiber and 4G transmission. It serves as a data transfer bridge between the terminal device and the cloud platform, enabling network access and data forwarding.

[0051] (1) Leakage current acquisition module

[0052] In the leakage current simulation module, the TMR magnetic sensor converts the magnetic field generated by the current to be measured into a voltage signal after analog signal processing; the voltage signal output by the analog front end is converted into a digital signal by the ADC; the digital signal is sent to the digital signal processing unit for digital filtering, digital conditioning and other processing. The digital conditioning module compensates the voltage signal according to the ambient temperature value measured by the built-in temperature sensor to ensure the measurement accuracy of the current sensor in the entire temperature range; after the signal is processed by the digital signal control unit, one path is converted into an analog voltage signal output through the DAC, and the other path is output as a digital voltage signal through the PWM controller.

[0053] (2) Self-energy module

[0054] For energy extraction from three-core three-phase cables, it is difficult to achieve energy extraction using traditional methods due to the complex magnetic flux lines after the superposition of the magnetic induction intensity generated by the three phases. The modeling scale is a 1:1 scale reproduction of the actual three-phase cable. Among them, the cross-sectional area of ​​the conductive core is 3*95mm2, the thickness of the insulation layer is 1.1mm, the outer diameter of the cable is 33.4mm, and the thickness of the outer protective layer is 2.5mm. The ideal two-dimensional modeling of the three-phase cable is as follows: Figure 3 As shown, P is an arbitrary point outside the cable, and the angle between the displacement vector at point P and the field vector at point P is α.

[0055] For ideal two-dimensional modeling of a three-phase cable, the cable typically satisfies the requirement of length L > diameter D, so it can be approximately considered an infinitely long straight conductor. Transient analysis of the cable current involves taking a very short time period and assuming that the cable current remains constant during this time period. According to the Biot-Savart law:

[0056]

[0057] Where μ0 is the vacuum permeability, μ0=4π×10 -7 Tm / A, I is the current size, L is the integral path, dl is the infinitesimal length of the current, is the unit vector from the current source to the point to be determined. On any ray starting from the cable center, the farther the point on the ray is from the cable, the smaller the magnetic induction intensity. To improve the power extraction efficiency, it is necessary to make full use of the area with high magnetic induction intensity close to the outer protective layer of the cable. The value of the magnetic induction intensity in the x and y axes at every 1° on the outer circumference of the three-phase cable at each moment is derived as B x ,B y At the same time, the normalized values ​​of the displacement vector of the point in the x and y axis directions are derived as X, Y. The normal magnetic induction intensity of each point on the outer circumference is calculated as follows:

[0058]

[0059] Subtracting the minimum value from the maximum value of the normal magnetic flux density on the outer circumference at each moment yields the maximum normal magnetic flux density difference at that moment. By comparing this value at each moment within a power system cycle, it can be found that the maximum normal magnetic flux density difference occurs at 1.7, 5.0, 8.3, 11.7, 15, and 18.3 ms.

[0060] Based on the above principles, the sensor's magnetic field energy harvesting module is designed to provide energy to the wireless sensor in the electromagnetic field of the energy supply node in a targeted manner. The wireless sensor can flexibly configure sensing parameters and wireless protocols. The structure of the electromagnetic energy harvesting module is as follows: Figure 4 As shown:

[0061] DC power is converted into microwave energy by a microwave source and then transmitted through a transmitting antenna for free-space transmission. The receiving antenna receives the RF energy and converts it into DC energy for use via a rectifier circuit. The wireless sensor node captures specific electromagnetic wave energy in the environment through the receiving antenna. This energy is then converted into DC energy for storage and management via a matching network and rectifier circuit, which then provides the energy to the wireless temperature sensor system. Because the impedance and matching of the receiving antenna affect the effective energy entering the rectifier circuit, and the design optimization of the rectifier circuit also depends on the receiving frequency and impedance, it is necessary to consider both the receiving antenna and the rectifier circuit together. The rectifier antenna model, which includes the receiving antenna and rectifier circuit, is replaced by a resonant unit consisting of an inductor L and a capacitor C. The resonant frequency of LC is the same as the antenna's operating frequency. The input power source, formed by the source resistor Z, represents the input power received from the air. This power can be adjusted based on the actual electromagnetic field power in the environment. The rectifier circuit consists of a voltage-doubling topology, a filter capacitor, and a load. Electromagnetic energy harvesting wireless sensor nodes rectify, boost, and store the wireless energy they receive for the collection of various sensing quantities and wireless transmission of information. Due to the high energy transmission loss in the electromagnetic field, the utilization rate is lower than that of other direct energy sources. Improving the conversion efficiency of electromagnetic energy harvesting to obtain higher instantaneous energy is the key to improving the performance of the entire system. The power ultimately converted by the rectifier and filter circuit can be calculated using the circuit rectification efficiency calculation formula:

[0062]

[0063] This formula considers the conversion power under ideal impedance matching conditions. In actual development and design, circuit losses should be considered to optimize impedance matching as much as possible.

[0064] (3) Communication module

[0065] Antennas are key components in wireless communications and are crucial for enhancing node coverage and improving network flexibility. The unique transmission environment of pipe corridors necessitates a variety of antenna technologies to support low-power transmission in communication networks. This invention combines multi-beam switching antenna technology, adaptive antenna technology, and antenna telemetry technology with novel SubG technology to achieve a flexible networking solution. SubG low-power communication chips establish data transmission links between sensors and sideband devices. Wireless communication modes should comprehensively consider parameters such as transmission distance, transmit power, power consumption, and air interface transmission rate. Low-rate modes offer longer wireless transmission ranges. While meeting communication distance requirements, higher transmission rates can effectively save communication time and optimize device RF power consumption. The microprocessor configures and drives the sensor chips, implementing the communication protocol. Key considerations include device packaging, operating current, and standby power consumption. The communication module provides multiple external interfaces to accommodate different sensor module access requirements. An ultra-low current load switch switches the RF power amplifier chip on and off, reducing system standby power consumption. The antenna uses a PATCH end-loading solution, which allows the antenna to form multiple resonances at adjacent frequency points, thereby increasing the bandwidth and making the antenna robust. When the target tunnel section is long and the communication network cost is low, it is necessary to use antenna telemetry technology to achieve RF power amplification and long-distance transmission. Antenna telemetry is a technology that converts baseband signals into optical signals for transmission and performs RF processing and power amplification at the remote end. The present invention proposes a regional distributed antenna system in which each node has a separate branch connected to the resource processing unit.

[0066] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A passive wireless sensing monitoring method for distribution cables, characterized in that: The designed electromagnetic field-based self-energy current monitoring terminal device has the following specific steps: The modeling scale is a 1:1 replica of the real three-phase cable; The cross-sectional area of ​​the conductive core is 3*95 mm2, the thickness of the insulation layer is 1.1 mm, the outer diameter of the cable is 33.4 mm, and the thickness of the outer protective layer is 2.5 mm. P is an arbitrary point outside the cable, and the angle between the displacement vector at point P and the field vector at point P is α. For the ideal two-dimensional modeling of a three-phase cable, the cable usually satisfies the requirement of length L > diameter D, so it can be approximately considered as an infinitely long straight conductor. For transient analysis of the cable current, a very short time period is taken, during which the cable current is assumed to be constant. According to the Biot-Savart law, it can be seen that: Where μ0 is the vacuum permeability, μ0=4π×10 -7 Tm / A, I is the current size, L is the integral path, dl is the infinitesimal length of the current, It is the unit vector of the current source pointing to the point to be determined. On any ray starting from the center of the cable, the farther the point on the ray is from the cable, the smaller the magnetic induction intensity. If you want to improve the power extraction efficiency, you need to make full use of the area with large magnetic induction intensity close to the outer protective layer of the cable. The value of the magnetic induction intensity in the direction of the x and y axes at every 1° on the outer circumference of the three-phase cable at each moment is derived as B x ,B y , and at the same time derive the normalized values ​​of the displacement vector of the point in the x and y axis directions as X,Y; The normal magnetic induction intensity of each point on the outer circumference is calculated as follows: The maximum normal magnetic induction intensity on the outer circumference at each moment is subtracted from the minimum value to obtain the value of the maximum normal magnetic induction intensity difference at that moment. The values ​​of this value at each moment in a power system cycle are compared. It can be found that the maximum normal magnetic induction intensity difference occurs at 1.7, 5.0, 8.3, 11.7, 15, and 18.3 ms. Based on the above principles, the magnetic field energy acquisition module of the sensor is designed; The DC power is converted into microwave energy by a microwave source and then transmitted through the transmitting antenna and transmitted through free space. The receiving antenna is responsible for receiving the radio frequency energy and then converting the radio frequency energy into DC energy for use through the rectifier circuit. The wireless sensor node captures the special electromagnetic wave energy in the environment through the receiving antenna, and then converts it into DC energy storage and management through the matching network and rectification circuit, and then provides the energy to the wireless temperature sensor system; Since the impedance and matching of the receiving antenna will affect the effective energy entering the rectifier circuit, and the design optimization of the rectifier circuit also depends on the receiving frequency and impedance, it is necessary to consider the receiving antenna and the rectifier circuit together. The rectifier antenna model part including the receiving antenna and the rectifier circuit is replaced by a resonant unit composed of inductor L and capacitor C. The resonant frequency of LC is the operating frequency of the antenna. The input power source composed of the source resistor Z represents the input power received in the air. This power can be adjusted according to the electromagnetic field power of the actual environment. The rectifier circuit part consists of a voltage doubling topology, filter capacitors and loads. The electromagnetic energy harvesting wireless sensor node rectifies, boosts and stores the obtained wireless energy for the collection of different sensing quantities and wireless transmission of information. Due to the large energy transmission loss of the electromagnetic field in space, the utilization rate is lower than that of other direct energy sources. Improving the conversion efficiency of electromagnetic energy harvesting to obtain higher instantaneous energy is the key to improving the working performance of the entire system. The power finally converted by the rectifier and filter circuit can be calculated by the circuit rectification efficiency calculation formula: This formula considers the conversion power under ideal impedance matching conditions. In actual development and design, circuit losses should be considered to optimize impedance matching as much as possible.

2. The method according to claim 1, characterized in that We have a deep understanding of the coupling mechanism of cable insulation aging variables. Through simulation, we found that common-mode leakage current is proportional to the insulation capacitance, the injected monitoring voltage amplitude, and the cable length. During cable aging, the insulation capacitive leakage current increases significantly. By monitoring the leakage current, we can identify cable aging defects and fault characteristics. Determine the coupling relationship between the distribution of multi-mode leakage current changes and the early aging position; when it is very difficult to measure the voltage distribution on the entire cable, the early aging is initially located by measuring the common-mode leakage current at the cable end. The common-mode leakage current I CM Produced by the common-mode voltage applied to the cable insulation, it is expressed as follows: Where C(x) represents the insulation capacitance at position x on the cable. For cables that have aged early, the increase in insulation capacitance in the aging section will cause a change in the common-mode leakage current. The change in common-mode leakage current can be expressed as follows: of CM =I CM -I CM0 Where, I CM is the measured common-mode leakage current amplitude, I CM0 It is the common-mode leakage current amplitude when the cable is intact, which can be measured when the new cable is put into operation. The first parameter is the increase in common-mode leakage current caused by the increase in capacitance in the early aging section; the second parameter is the leakage current change caused by the change in voltage distribution on the entire cable due to early aging. The second part is the main factor causing the change in common-mode leakage current. For different degrees of early aging occurring at the same position, the change in common-mode leakage current will also show a similar distribution in the frequency domain, but the amplitude will be different. For different degrees of early aging occurring at the same position, the change in common-mode leakage current will also show a similar distribution in the frequency domain, but the amplitude will be different.

3. The method according to claim 1, characterized in that A method of self-harvesting energy using cable electromagnetic fields is proposed. Energy is obtained through electromagnetic field modeling. The wireless sensor nodes rectify, boost and store the obtained wireless energy for the collection of different sensing quantities and wireless transmission of information.

4. The method according to claim 3, characterized in that A regional distributed wireless radio frequency communication system is designed to maximize spatial utilization. When resources are limited, a distributed antenna system can maximize spatial resource utilization. The distributed antenna system can cover a wide range, and the resources within the range can be used in a polarized manner, providing faster transmission rates. The distributed antenna system uses distributed optical fiber technology. The data transmission link between the sensor and the sideband device is established through the SubG low-power communication chip. The wireless communication mode should comprehensively consider parameters such as transmission distance, transmission power, power consumption, and air interface transmission rate. The low-rate mode can bring a longer wireless transmission distance. Under the premise of meeting the communication distance requirements, a higher transmission rate can more effectively save communication time and is more conducive to optimizing the device's RF power consumption. The microprocessor completes the configuration and driving of each sensor chip and the specific implementation of the communication protocol. It should also mainly consider device packaging, operating current, standby power consumption, etc. The communication module can provide multiple external interfaces to adapt to the access requirements of different types of sensor modules. The ultra-low current load switch is used to switch the RF power amplifier chip on and off to reduce the system's standby power consumption. The antenna adopts a PATCH end-loading solution, which enables the antenna to form multiple resonances at adjacent frequency points, thereby increasing the bandwidth and making the antenna robust. When the target tunnel section is long and the communication network cost is low, it is necessary to use antenna telemetry technology to achieve RF power amplification and long-distance transmission. Antenna telemetry is a technology that converts baseband signals into optical signals for transmission and performs RF processing and power amplification at the remote end.

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