Ground wire energy pickup system based on flexible CT (Computed Tomography)

Abstract

A ground wire energy-collecting system based on a flexible CT comprises a flexible current transformer and a resonance compensation unit. The flexible current transformer comprises a flexible magnetic core and a flexible conductive coil, the flexible magnetic core is made of a flexible high-permeability material, the flexible conductive coil is wound on the flexible magnetic core, and the flexible magnetic core and the flexible conductive coil are used for being continuously wound on a ground wire of an overhead transmission line, so that the flexible magnetic core forms a closed magnetic circuit without an air gap; and the resonance compensation unit is electrically connected with the flexible conductive coil and forms series resonance with an equivalent inductor of the flexible current transformer at a working frequency so as to suppress reactive power loss and improve energy taking efficiency. The invention has the advantages of light structure, continuous magnetic circuit, capability of realizing efficient and stable energy taking under a low-current working condition and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of smart grid, in particular to an induction power supply system and method for power transmission line online monitoring equipment, and particularly to a ground wire energy harvesting system based on flexible CT. BACKGROUND

[0002] With the rapid development of smart grid, the demand for online devices such as state monitoring devices, sensors and communication terminals of power transmission lines is rapidly growing. These devices need stable and reliable long-term power supply. At present, the traditional way (chemical battery, solar energy, etc.) to supply power to these line devices has problems such as high maintenance cost, great influence of environmental factors (such as light, weather), great construction difficulty or limited life, which is difficult to meet the actual needs of smart grid online monitoring.

[0003] In order to solve the above power supply problem, the ground wire induction power supply technology has gradually become a research hotspot. This technology uses the induced current existing in the overhead ground wire such as OPGW (Optical Fiber Composite Overhead Ground Wire) to couple the magnetic field through CT (Current Transformer), and induces electromotive force in the secondary coil of the transformer, thereby harvesting power. This method has the advantages of no external power supply, easy installation and reliable operation.

[0004] However, the existing ground wire induction power supply technology still has many defects and challenges in practical application: first, the traditional CT power supply device usually adopts rigid core and winding structure. This structure is large in size and high in weight, which not only makes the installation and transportation on the ground wire inconvenient, but also causes a large mechanical load to the overhead ground wire. Second, in order to facilitate installation, the traditional rigid CT is often designed as an open-close structure, but this inevitably introduces air gap at the joint of the magnetic core. The existence of air gap will significantly increase the magnetic resistance of the magnetic circuit, reduce the equivalent permeability, and cause the electromagnetic conversion efficiency to decrease. More seriously, the error, vibration or thermal expansion and contraction during field installation may cause the air gap to change, and thus cause the fluctuation of the key parameters such as CT excitation inductance. The instability of excitation parameters makes it difficult for the system to accurately compensate reactive power, which seriously limits the further improvement of power supply efficiency. SUMMARY

[0005] In view of the above problems of the prior art, the technical problem to be solved by the present application is how to provide a ground wire energy harvesting system based on flexible CT, which is light in structure, continuous in magnetic circuit and can realize efficient and stable power supply under low current working condition.

[0006] In order to solve the above technical problems, the present application adopts the following technical scheme: The ground wire energy harvesting system based on flexible CT comprises a flexible current transformer and a resonance compensation unit; the flexible current transformer comprises a flexible magnetic core composed of a flexible high magnetic permeability material and a flexible conductive coil wound on the flexible magnetic core, the flexible magnetic core and the flexible conductive coil are used for being continuously wrapped on the ground wire of an overhead transmission line, so that the flexible magnetic core forms a closed magnetic circuit without air gap; the resonance compensation unit is electrically connected with the flexible conductive coil and forms series resonance with the equivalent inductance of the flexible current transformer at the working frequency to realize ground wire de-energization.

[0007] The flexible magnetic core composed of the flexible high magnetic permeability material and the flexible conductive coil have high flexibility and lightweight characteristics. This is very important for the application scene of overhead ground wire, because the ground wire itself has strict load limitation, and the lightweight design effectively solves the mechanical load problem caused by the bulkiness of the traditional rigid CT. At the same time, in its installation mode, for the working condition that the ground wire cannot be moved or cut off on site, the flexible magnetic core can be "wound" on site, so that the flexible magnetic core is tightly fitted to form a closed magnetic circuit without air gap. The problem of excitation inductance fluctuation caused by air gap change of the traditional open-close CT is fundamentally overcome, and the continuity of the magnetic circuit and the stability of the parameters are ensured. In addition, the introduction of the resonance compensation unit causes resonance with the inductance of the flexible CT itself at the working frequency, so that the secondary side loop is in a low equivalent impedance or purely resistive state, effectively compensating the inductive reactive of the system and suppressing the reactive loss, thereby greatly improving the transmission capacity of active power and realizing stable and efficient energy harvesting in low current working condition.

[0008] Further, the flexible high magnetic permeability material is nanocrystalline ribbon material.

[0009] Compared with the silicon steel or alloy strip used in the traditional transformer, the nanocrystalline ribbon material has higher initial magnetic permeability and magnetic permeability, which helps to generate higher secondary side induced voltage in the case of weak ground wire current. At the same time, it has lower coercive force and loss characteristics, and the material form is an extremely thin foil or ribbon, which is an ideal flexible soft magnetic material for on-site "winding" to adjust inductance.

[0010] Further, the flexible conductive coil is made of FPC (Flexible Printed Circuit, flexible printed circuit board).

[0011] FPC itself has the characteristics of bendability and thinness, and can better realize winding installation in cooperation with the flexible magnetic core. In addition, the FPC process adopts photoetching and etching technology, the number of turns, wire width and spacing of the coil can be accurately controlled, has extremely high manufacturing consistency and repeatability, and can reduce additional resistance and distributed capacitance, and reduce loss.

[0012] Further, the coil wire of the flexible conductive coil is parallel to the axis of the flexible current transformer on the FPC flexible printed circuit board.

[0013] The magnetic field direction generated by the current in the ground wire follows the right-hand screw rule, and the magnetic field lines around the ground wire are distributed in concentric circles. Arranging the FPC circuit plane parallel to the ground wire axis, i.e. arranging the coil wire parallel to the winding axis, can effectively cut more magnetic lines on the FPC, maximize the magnetic flux capture capability, and significantly enhance the induced voltage and power.

[0014] Further, the FPC flexible printed circuit board adopts a laminated structure to realize multi-layer winding.

[0015] The laminated structure design of the FPC allows multiple layers of flexible CT units to be wound outside the same ground wire. By increasing the number of FPC layers in a limited space and using reasonable wiring design, the equivalent total number of turns of the induction coil can be significantly improved, thereby doubling the induced voltage output and power.

[0016] As a preferred embodiment, the ground wire power supply system comprises a plurality of flexible current transformers.

[0017] Further, a plurality of flexible current transformers are sequentially wrapped around the same ground wire in the axial direction.

[0018] Further, the flexible conductive coils of a plurality of flexible current transformers are connected in series.

[0019] By physically connecting a plurality of lightweight flexible CT units in series along the axis of the same ground wire, and electrically connecting the flexible conductive coils on the secondary side in series, the series structure can realize the mutual superposition of the secondary induction voltages of each CT, making the total output voltage approximately n times that of a single unit, thereby greatly improving the total output power of the system and the utilization rate of the voltage in the later stage.

[0020] As a preferred embodiment, the resonance compensation unit is a compensation capacitor connected in series to the flexible conductive coil, and the compensation capacitor and the equivalent inductance of the flexible current transformer form a series resonance circuit at power frequency.

[0021] By connecting the compensation capacitor in series to the secondary side of the power supply transformer, i.e. the flexible conductive coil, an LC series resonance can be formed at power frequency. At the series resonance point, the equivalent impedance of the receiving side is significantly reduced, maximizing the loop current. This method can effectively offset the inductive reactive component of the system, making the secondary loop purely resistive, thereby significantly improving the active power output.

[0022] Further, a rectification and voltage stabilization module is connected to the output end of the flexible conductive coil.

[0023] The power output from the flexible CT sensor is in AC form. To ensure reliable power supply for the online monitoring equipment, a subsequent rectification and voltage regulation module is required. This module includes rectification, filtering, and voltage regulation circuits to convert the acquired AC power into a stable and reliable DC power supply for the load.

[0024] Compared with the prior art, the present invention has the following beneficial effects: 1. Optimized structure, convenient installation, and lightweight: This invention adopts a structure combining a flexible magnetic core (including but not limited to nanocrystalline thin strips) with a flexible conductive coil (including but not limited to), completely revolutionizing the problems of bulky and difficult installation of traditional rigid CT scanners. The system is flexible and lightweight, and can be directly and conveniently wrapped around the overhead ground wire without power interruption, with minimal mechanical load on the ground wire.

[0025] 2. Gapless magnetic circuit with stable parameters and high efficiency: Through continuous wrapping of flexible material, the flexible magnetic core forms a gapless closed magnetic circuit, fundamentally eliminating the problems of high magnetic reluctance and excitation inductance fluctuations caused by air gap changes in traditional open-close CT scanners. This gapless structure significantly improves magnetic permeability and electromagnetic conversion efficiency, and ensures the stability of the excitation inductance, providing a reliable prerequisite for subsequent precise resonance compensation.

[0026] 3. Resonance compensation significantly improves energy harvesting power: By setting a resonance compensation unit, this invention enables the system to resonate at the power frequency, effectively suppressing inductive reactive power loss and making the circuit purely resistive, thus greatly improving the system's active power output and energy harvesting efficiency. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of induction energy harvesting; Figure 2 Equivalent calculation circuit for electromagnetic induction energy extraction from the ground wire; Figure 3 The spatial geometric layout of the power transmission busbar and ground wire; Figure 4 A circuit for calculating the equivalent energy extraction value from the ground wire; Figure 5 To simplify the equivalent circuit; Figure 6 This is a flexible CT structure diagram; Figure 7 This is a structural diagram of a two-layer flexible CT scanner. Figure 8 For electromagnetic simulation model; Figure 9 The change in magnetizing inductance under different primary side current excitations; Figure 10 This is a diagram showing the magnetic flux density distribution of a closed, gapless magnetic ring. Figure 11The magnetic flux density distribution diagram for a 0.1mm air gap magnetic ring; Figure 12 It is a single-layer FPC magnetic core; Figure 13 It is a double-layer FPC magnetic core; Figure 14 Physical model for energy harvesting by ground-line CT; Figure 15 Model of the grounding CT power extraction circuit; Figure 16 Model of the resonant compensation CT energy harvesting circuit; Figure 17 Schematic diagram of a multi-stage current transformer group energy harvesting system for resonance compensation; Figure 18 This is a structural diagram of the energy harvesting system; Figure 19 The system input current and voltage waveforms are shown below. Figure 20 The output current and voltage waveforms of the energy harvesting transformer are shown below. Figure 21 This is an exploded structural diagram of the flexible current transformer in Example 2; Figure 22 This is a schematic diagram of the flexible current transformer in the winding state in Example 2; Figure 23 This is a schematic diagram of the structure of the first flexible substrate in Example 2; Figure 24 This is a schematic diagram of the structure of the second flexible substrate in Example 2; Figure 25 This is an exploded structural diagram of another multilayer flexible substrate in Example 2; Figure 26 This is a schematic diagram of a flexible current transformer application in Example 2; Figure 27 This is a schematic diagram of another flexible current transformer application in Example 2. Detailed Implementation

[0028] The technical solutions in the embodiments of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are merely some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0029] Example 1: This Example 1 provides a ground wire energy pickup system based on flexible CT. The system is used to pick up energy from the ground wire wrapped around the overhead transmission line, including but not limited to OPGW optical cable.

[0030] Energy harvesting principle and circuit model: such asFigure 1 As shown, when an alternating current flows through an overhead transmission line, it generates an alternating electromagnetic field in the surrounding space. When this electromagnetic field couples with any closed loop in space, it induces a voltage and a current in the loop. Based on Faraday's law of electromagnetic induction, if a current transformer (CT) is placed around the ground wire, an electromotive force can be induced in its secondary coil through magnetic field coupling, thus achieving energy harvesting.

[0031] In this embodiment, the energy harvesting transformer is directly mounted on the outside of the OPGW optical cable. It utilizes the alternating magnetic flux generated in the magnetic core by the ground wire current to induce a voltage on the secondary side. This scheme is easy to install, has almost no impact on the grounding impedance, and effectively extracts electrical energy from the ground wire. During the ground wire induction energy harvesting process, the overhead ground wire acts as the primary coil of the transformer; its current magnitude determines the system's input energy and is also a crucial constraint in the transformer design.

[0032] Based on the structural characteristics of overhead transmission lines, a corresponding equivalent circuit model is established to reflect the distribution of induced current and energy transmission characteristics in the ground wire. Figure 2 The equivalent calculation circuit for electromagnetic induction energy extraction from the ground wire is shown in this model. In this model, the overhead ground wire and the OPGW optical cable are grounded tower by tower. E 1(m) For OPGW in the m The induced electromotive force of the gear, Z 1(m) For OPGW in the m The self-impedance of the range, E 2(m) For ordinary ground wire in the first m The induced electromotive force of the gear, Z 2(m) For ordinary ground wire in the first m The self-impedance of the gate. R m express m Tower grounding resistance, R m+1 express m +1 tower grounding resistance, R n This represents the grounding resistance of the nth tower. m The meaning of file is m ~( m +1) For convenience, the line between the towers is denoted as... S m Each ground wire can be considered as an interconnected electrical unit, and each tower grounding point has a certain grounding resistance. The OPGW and ordinary ground wire form multiple segments of induced coupling between different towers, each segment possessing induced potential, self-impedance, and mutual impedance. These parameters allow for analysis of the current distribution between segments and the energy harvesting at the energy extraction points.

[0033] Figure 3This is a spatial geometric layout diagram of the transmission busbar and ground wire. In the diagram, 1 and 2 represent the OPGW optical cable and the ordinary ground wire, respectively, and a, b, and c represent the three-phase transmission conductors. d a1 represents the straight-line distance from the No. 1 overhead ground wire to the a-phase conductor in the transmission line. d b1 represents the straight-line distance from the No. 1 overhead ground wire to the b-phase conductor in the transmission line. d c1 represents the straight-line distance from the No. 1 overhead ground wire to the c-phase conductor in the transmission line. d c2 represents the straight-line distance from the No. 2 ordinary ground wire to the c-phase conductor in the transmission line. d bc represents the straight-line distance between phase b and phase c conductors in the transmission line. d g represents the depth of the equivalent conductor of the earth, R d This represents the equivalent resistance of the ground wire.

[0034] For ease of analysis, the energy harvesting transformer is installed between the m-th and (m+1)-th towers, such as... Figure 4 As shown. The secondary load of the current transformer is represented by a resistive element RL. By equivalence processing of the lines on both sides, the entire multi-tower ground wire network can be simplified into a loop composed of an equivalent voltage source, equivalent impedance, and energy extraction load, where R1 represents the grounding resistance of the first tower and R2 represents the grounding resistance of the second tower. The simplified result is... Figure 5 The equivalent model shown represents the lines at both ends of the ground wire as equivalent branches, thus simplifying the complex transmission network into a single energy extraction branch. This branch extracts energy from the ground wire current through mutual inductance coupling, achieving inductive energy extraction. Here, Ue(m) is the equivalent voltage viewed from the left of node m, Ze(m) is the equivalent impedance viewed from the left of node m, Ue(m+1) is the equivalent voltage viewed from the right of node m, and Ze(m+1) is the impedance viewed from the right of node m.

[0035] When the number of transmission towers is large, the ground wire induction parameters tend to stabilize, and the system enters the quasi-steady-state operating region. Furthermore, the ground wire current exhibits a linear relationship with the load power, and the energy harvesting performance is proportional to the transmission conductor current. Adopting an OPGW tower-by-tower grounding structure and a single-point grounding structure with ordinary ground wires ensures lightning protection safety while significantly improving the stability of induced energy harvesting. The established equivalent circuit model for energy harvesting effectively describes the electrical characteristics of the system, providing a theoretical basis for the design of flexible current transformers (CTs) and subsequent resonant compensation structures.

[0036] Flexible Current Transformer: Based on the above principle, this embodiment provides a ground wire energy harvesting system based on a flexible current transformer (CT), including a flexible current transformer and a resonant compensation unit. The flexible current transformer includes a flexible magnetic core made of a flexible high-permeability material and a flexible conductive coil wound on the flexible magnetic core. The flexible magnetic core and the flexible conductive coil are used to continuously wrap around the ground wire of the overhead transmission line, so that the flexible magnetic core forms a gapless closed magnetic circuit. The resonant compensation unit is electrically connected to the flexible conductive coil and forms a series resonance with the equivalent inductance of the flexible current transformer at the operating frequency to suppress reactive power loss and improve energy harvesting efficiency.

[0037] This embodiment employs a fully flexible thin-film magnetic core material, which can be completely wrapped around the ground wire during use, achieving a gapless closed magnetic circuit and significantly improving permeability and energy harvesting efficiency. Because nanocrystalline thin-film materials have higher initial permeability and permeability compared to silicon steel or alloy strips used in traditional current transformers, they help generate higher secondary-side induced voltage even with weak ground current. Simultaneously, they exhibit low coercivity and loss characteristics, and their extremely thin foil or strip form makes them ideal flexible soft magnetic materials for on-site "winding" to adjust inductance. The flexible high-permeability material in this embodiment is a nanocrystalline thin-film material.

[0038] Meanwhile, the flexible conductive coil is made using a flexible printed circuit board (FPC). Since the magnetic field generated by the current in the ground wire follows the right-hand screw rule, and the magnetic field lines are distributed concentrically around the ground wire, to allow the coil wires on the FPC to effectively cut more magnetic field lines, the coil wires of the flexible conductive coil are arranged parallel to the axis formed by the flexible current transformer on the FPC flexible printed circuit board, i.e., parallel to the ground wire axis. This significantly improves the magnetic flux capture capability and enhances the induced voltage and energy harvesting power. Therefore, the FPC circuit board is arranged parallel to the ground wire, such as... Figure 6 As shown, this maximizes the magnetic field coupling effect.

[0039] The flexible CT proposed in this embodiment demonstrates significant advantages in structural design, material selection, and manufacturing process. In particular, the use of a layered flexible structure greatly improves the system's adaptability and reliability while maintaining magnetic properties. Its main advantages are as follows: 1. Layered Structure Design Enables Multi-Layer Winding: Both the FPC circuit board and flexible magnetic core of the flexible CT can be designed with multi-layer stacking, meaning multiple flexible CT units are wound around the same ground wire to form a stacked structure. This structure can significantly increase the total number of induction turns and magnetic coupling area, thereby multiplying the induction voltage output and energy harvesting power. Furthermore, multi-layer stacking allows for flexible adjustment of single-layer thickness and interlayer spacing to optimize high-frequency response characteristics and magnetic field distribution. Through reasonable interlayer insulation and shielding design, electromagnetic interference between adjacent layers can be effectively reduced, achieving a high-efficiency, low-loss multi-layer magnetic coupling system, such as...Figure 7 As shown.

[0040] 2. High flexibility and adaptability: Thanks to the combination of a flexible FPC substrate and a flexible nanocrystalline magnetic core, the entire CT can be freely bent and rolled, and can be tightly fitted to ground wires, conductors, or irregular surfaces. Compared with traditional rigid CTs, its installation is not limited by spatial shape and can be used in confined, irregular, or high-density wiring environments. It is particularly suitable for smart cables, power transmission conductor monitoring, and substation busbar power extraction.

[0041] 3. Lightweight and compact: The thickness of the flexible FPC and thin strip magnetic core is typically only 0.05–0.2 mm, resulting in an extremely thin and lightweight overall structure. Compared to traditional iron core and winding structures, the weight can be reduced by more than 70%, and the volume by nearly half. This makes flexible CT not only easy to carry and install, but also suitable for space- and weight-sensitive applications, such as power distribution automation equipment and portable testing terminals.

[0042] 4. High Manufacturing Consistency and Repeatability: Traditional wire-wound CTs are prone to uneven turn spacing and coil shape deviations during manual or mechanical winding, resulting in large output errors. In contrast, the FPC process uses photolithography and etching technology, allowing for precise control of linewidth, spacing, and number of turns down to the micrometer level, achieving high consistency and repeatability. In mass production, the electromagnetic parameters of each flexible CT unit exhibit excellent consistency, which is beneficial for system calibration and subsequent maintenance.

[0043] 5. Enables multi-functional integration: In addition to functioning as a secondary induction coil, the FPC substrate can integrate signal conditioning circuits, temperature sensing elements, current detection chips, and other modules, achieving an integrated design of sensing, monitoring, and signal output. Through multi-layered wiring, a power extraction layer, a signal transmission layer, and a shielding layer can be formed, thereby achieving electromagnetic isolation and system integration within a limited space.

[0044] 6. Excellent frequency response and low loss characteristics: The flexible nanocrystalline magnetic core has high initial permeability and low loss characteristics. Combined with the precise turns design of the FPC, the flexible CT maintains stable voltage response characteristics over a wide frequency range. Especially under high-frequency conditions, the thin strip magnetic core can effectively suppress eddy current losses, and the stacked multi-coil wiring structure can further balance parasitic capacitance effects, achieving a smoother frequency response curve.

[0045] 7. Convenient Maintenance and Replacement: The flexible CT adopts an encapsulated structure, allowing for quick replacement or maintenance through simple disassembly and assembly. Its layered modular design allows for adjustment of the number of layers and sensing capabilities according to site requirements, eliminating the need for complete replacement and significantly reducing maintenance costs and construction complexity.

[0046] Simulation verification of magnetic core parameters: In flexible CT, the magnetic core adopts a gapless closed-loop wrapping design, fundamentally eliminating the excitation inductance fluctuation problem caused by air gap changes in traditional open-loop magnetic cores. This structure achieves highly consistent magnetic circuit characteristics through the tight winding of nanocrystalline thin strips around the ground wire and the symmetrical bonding of the FPC, keeping the excitation inductance stable and thus ensuring the reliable maintenance of the resonant state with the fixed compensation capacitor.

[0047] To verify the electromagnetic performance of the flexible CT, this embodiment established an electromagnetic simulation model of the CT based on Ansys-Maxwell finite element simulation software, such as... Figure 8 As shown in the figure, the model focuses on evaluating the effects of different primary currents, permeability of nanocrystalline materials, and equivalent number of turns of the FPC on the magnetic flux distribution, excitation inductance, and induced output voltage of the magnetic core in a gapless structure.

[0048] Simulation results show that the excitation inductance stability of the flexible CT under a closed magnetic circuit structure is significantly better than that of the traditional CT with an air gap, and no significant deviation is observed during current fluctuations. Figure 9 As shown.

[0049] The high permeability and low loss characteristics of nanocrystalline materials ensure uniform magnetic flux distribution in the magnetic core under normal operating conditions, without local saturation. By running a Maxwell electromagnetic simulation model, the magnetic flux density distribution of the magnetic core under conditions of no air gap and 0.1 mm air gap was obtained. The simulation results show that the magnetic flux density distribution of the core is uniform. Further comparison... Figure 10 , Figure 11 It can be observed that the overall magnetic flux density of the core decreases after the air gap is introduced, where B[tesla] represents the magnetic flux. The only difference between the two models is whether or not an air gap is introduced, and the main reason for this change is obviously the effect of the air gap on the magnetic circuit. Since the core with an air gap has a C-shaped structure, the air gap at the joint reduces the equivalent permeability of the core and increases the magnetic reluctance of the magnetic circuit, thereby enhancing the core's resistance to saturation.

[0050] Figure 12 and Figure 13 The diagram shows the single-layer and double-layer FPC winding structures. Finite element simulation results show that the inductance of the single-layer FPC core is 104.12mH and the inductance of the double-layer FPC core is 168.68mH. The effect of the change in the number of FPC winding layers on the excitation inductance is consistent with the theoretical design. The multi-layer design can effectively improve the output without damaging the core performance.

[0051] Energy harvesting via current transformers: In high-voltage AC transmission systems, the alternating current in the conductors generates a time-varying magnetic field around them. According to Maxwell's equations, this time-varying magnetic field excites eddy electric fields, which induce currents in the OPGW (Optical Power Transformer) and the closed loop it forms. By installing current transformers (CTs) on the OPGW, the magnetic lines of force of the alternating magnetic field generated by the induced current intersect with the secondary coil of the CT core, thereby generating an induced electromotive force in the secondary coil. Connecting the load to the CT secondary coil enables energy harvesting.

[0052] In overhead power transmission environments, although some overhead conductor currents also generate magnetic fields in space, the linkage between their magnetic field lines and the secondary coil of the CT core is far weaker than the influence of the ground wire current. Therefore, the impact of conductor current on energy harvesting efficiency can be ignored. The physical model of CT energy harvesting is as follows: Figure 14 As shown.

[0053] The CT and grounding system essentially constitute a transformer system. The closed loop formed by the OPGW between adjacent towers and the grounding wires on both sides can be regarded as the primary coil, i.e., with 1 turn, while the multi-turn coil wound on the CT core is the secondary side. The actual energy harvesting device also needs to be combined with rectification and voltage regulation circuits for energy conversion and storage, ultimately supplying power to the monitoring equipment.

[0054] Considering factors such as iron loss, leakage flux, and line loss, the grounding current transformer (CT) power extraction system can be equivalently represented as a transformer circuit model including excitation resistance, excitation inductance, and load impedance, such as... Figure 15 As shown, the power processing section and the power extraction load are equivalent to Z. L R m L is the excitation resistor of the CT. m R1 is the magnetizing inductance of the CT, R1 is the internal resistance of the primary coil (OPGW), and L is the magnetizing inductance of the CT. σ1 R2 is the leakage inductance of the primary coil, and L is the internal resistance of the secondary coil. σ2 Let N1 be the leakage inductance of the secondary coil, N2 be the number of turns in the primary coil, and N1 be the number of turns in the secondary coil, where N1 = 1. To further simplify the analysis and calculation, since Z... L The leakage reactance is usually much greater than that of the primary and secondary sides, so the leakage inductance and loss of the primary and secondary sides are ignored, and the primary side parameters of the CT of the energy harvesting system are attributed to the secondary side.

[0055] To simplify the analysis, the circuit model consisting of the magnetizing resistor, magnetizing inductor, and load impedance is typically used as the equivalent model of the CT power harvesting system. The presence of the magnetizing inductor reduces the current flowing to the load, thus affecting the output power. When the CT parameters and primary side current are fixed, the power obtained by the load depends on the load impedance. If a resistive load is directly connected, the system's output power will reach its maximum value under certain load matching conditions, but the overall power harvesting efficiency will be limited.

[0056] By connecting a compensation capacitor C in parallel across the secondary circuit of the FPC in a flexible CT, a resonant compensation-type ground wire energy harvesting circuit model can be constructed, such as... Figure 16 As shown, L, L1, and L2 represent the excitation inductance of the flexible CT, and C, C1, and C2 represent the compensation capacitors of the corresponding flexible CT.

[0057] Thanks to the high and stable excitation inductance brought by the gapless magnetic core structure of the flexible CT, combined with the precisely selected compensation capacitor, the system can achieve a near-resonant state at the operating frequency of 50 Hz, thereby significantly improving the system's power transmission capability and energy extraction efficiency. The role of resonant compensation is to make the secondary circuit present a low equivalent impedance state, reduce reactive power loss, improve the power factor, and enable the system to achieve stable power supply with a low ground current.

[0058] Series-connected flexible CTs for power extraction: The induced current in overhead ground wires is typically small, resulting in limited power extraction from a single flexible CT, which is insufficient to meet the power supply requirements of high-power online monitoring equipment. Therefore, multiple flexible CTs can be connected in series for power extraction to increase the system output power.

[0059] Multiple flexible CTs of the same model are sequentially and tightly wrapped around the same OPGW ground wire, sharing the same primary conductor. The FPC secondary circuits of each CT are then connected in series to supply power to the load.

[0060] The series structure significantly improves the total induced electromotive force and output power of the system. The secondary voltages of n current transformers are superimposed, making the output voltage approximately n times that of a single transformer, greatly improving the energy harvesting power and the utilization rate of the subsequent voltage stage. At the same time, the series structure facilitates impedance matching in the downstream voltage regulation circuit, improving energy conversion efficiency.

[0061] The lightweight and flexible nature of flexible CT scanners allows for a compact structure even when installed in multiple series configurations, minimizing the impact on the mechanical load on the ground wire and simplifying installation. Multi-CT systems also offer redundancy; the failure of a single CT scanner will not cause the entire system to shut down, thus improving the reliability of the power harvesting system.

[0062] Simulation and experimental results both show that, under the same ground current conditions, the CT series scheme can significantly expand the output power range and is an effective way to improve the power supply capability of online ground monitoring equipment.

[0063] Resonant compensation multi-stage instrument transformer group energy harvesting: Multiple energy-harvesting instrument transformers simultaneously harvest energy from the ground wire, collecting the induced electrical energy to the primary side of the energy-collecting transformer. Compensation capacitors are introduced into each energy-harvesting branch and the input side to achieve graded reactive power compensation. After output from the secondary side of the energy-collecting transformer, a stable power supply can be provided to the online monitoring terminal through a downstream rectification and voltage regulation circuit. The schematic diagram of the resonant compensation multi-stage instrument transformer group energy harvesting system is shown below. Figure 17 As shown.

[0064] The overhead ground wire current fluctuates with changes in transmission load, typically ranging from a few amperes to over ten amperes. To achieve stable output over a wide current range, this embodiment designs a multi-stage current transformer group energy harvesting system with resonant compensation, as shown in the structural diagram below. Figure 18 As shown.

[0065] The system consists of multiple energy harvesting transformer units, each employing a flexible current transformer (CT) structure with a compensation capacitor introduced on the secondary side. In the energy harvesting circuit, the compensated electrical energy is induced into the magnetic core through the overhead ground wire and then transmitted to the secondary winding via electromagnetic induction. By rationally designing the compensation capacitor and the winding self-inductance, the secondary side of the energy harvesting transformer and the primary side of the energy collecting transformer form a series resonance, thereby canceling the reactive power component of the system and significantly improving the active power output.

[0066] This multi-stage system combines the three major characteristics of power superposition, resonance compensation, and energy concentration. It can achieve efficient, stable, and scalable ground wire induction energy harvesting without significantly increasing the size and weight, providing reliable power support for online monitoring equipment of transmission lines.

[0067] An energy harvesting model was established in finite element magnetic field simulation software to simulate and analyze the parameter characteristics of the current transformer group, thereby verifying the correctness of the aforementioned theoretical derivation of the current transformer parameters. Then, using the magnetic field simulation results, the corresponding parameters were substituted into the circuit model, and the compensation capacitor values ​​of each loop were solved by combining the aforementioned capacitor matching function expression. Next, using Simulink simulation software, the waveform characteristics of the current and voltage of each loop in the system with and without compensation were compared, which also verified the aforementioned theoretical derivation of the loop current amplitude. Simultaneously, to verify the power characteristics of different energy harvesting systems, a simulation analysis of a conventional single-stage current transformer energy harvesting system was also performed. Comparing the power output of each energy harvesting system further demonstrates that the energy harvesting system designed in this embodiment has a significantly higher output power than the conventional single-stage current transformer energy harvesting system.

[0068] The input current and voltage waveforms of the energy harvesting system are as follows: Figure 19 As shown in the figure, it can be clearly observed that the voltage and current waveforms of the system input are in phase, meaning that the line impedance characteristics of the overhead ground wire are purely resistive. This is because the compensation capacitor of the tuning circuit is referred to its primary side through the tuning transformer. Under the action of the power frequency, the compensation capacitor and the inductive impedance of the line resonate in series, which compensates for the reactive power on the input side of the energy harvesting system, thereby increasing the power input of the system.

[0069] The output current and voltage waveforms of the energy harvesting transformer group are as follows: Figure 20As shown in the figure, it is clear from the figure that after capacitor compensation is implemented in the energy harvesting circuit, the current and voltage waveforms at both the energy harvesting circuit and the load are in phase. At this time, the inductor and the matching capacitor in the circuit resonate in series, making the circuit purely resistive, thus completing the reactive power compensation of each circuit and improving the output power of the energy harvesting system.

[0070] Furthermore, it is clearly shown in the figure that as the ground induced current increases, the output power of both the compensated multi-stage transformer group energy harvesting system and the conventional single-stage transformer energy harvesting system increases, with the power change being more significant in the energy harvesting method proposed in this paper. The multi-stage transformer group energy harvesting method without resonant compensation has poor pickup capability, with an output power only in the milliwatt range under the maximum ground induced current. Therefore, it can be seen that the reactive power loss in the system is relatively large when using transformers for ground induction energy harvesting; without resonant capacitor compensation, the final output power of the system will be greatly reduced.

[0071] Meanwhile, the output power of a compensated multi-stage instrument transformer group energy harvesting system is significantly improved after resonant compensation compared to a conventional single-stage instrument transformer energy harvesting system. The output power of the former is generally more than six times that of the conventional single-stage instrument transformer energy harvesting system. This is especially evident when the ground wire induced current is weak, where the conventional single-stage instrument transformer energy harvesting system can hardly harvest any energy, while the resonant-compensated multi-stage instrument transformer group energy harvesting system greatly improves the output power of the ground wire induced current energy harvesting system.

[0072] Example 2: Based on Example 1, this example provides a flexible current transformer, such as... Figure 21 and Figure 22 As shown, it includes a sheet-shaped flexible magnetic core 1, which is made of a flexible high-permeability material. The flexible magnetic core 1 has two sides with stacked and opposite flexible substrates 2. The flexible magnetic core 1 is disposed between the two flexible substrates 2 and can be rolled up at least one turn in the width direction of the flexible substrate 2 together with the flexible substrate 2. The flexible substrate 2 has coil wires 3 extending along the length direction. Multiple coil wires 3 are evenly distributed along the width direction of the flexible substrate 2, and the coil wires on the two flexible substrates 2 are connected in series to form a flexible conductive coil.

[0073] By combining a sheet-like flexible magnetic core with a flexible substrate, the material and structure themselves possess lightweight and flexible characteristics, directly overcoming the rigidity and bulkiness of traditional CT scanners. Simultaneously, the sheet-like flexible magnetic core is a continuous, seamless component. When the current transformer is rolled up along the width of the flexible substrate to wrap around the ground wire, its continuous flexible magnetic core naturally forms a gapless closed magnetic circuit. This structure fundamentally eliminates the problems of high magnetic reluctance caused by air gaps in traditional CT scanners, as well as unstable excitation inductance and low efficiency caused by air gap variations. Furthermore, the coil wires extend along the length direction, while the entire current transformer can be rolled up along the width direction. This ensures that when the current transformer is rolled into a cylindrical shape, its coil wires are parallel to the axis formed by the roll, thereby correctly and maximally cutting the annular magnetic lines of force generated by the measured conductor, i.e., the ground wire, achieving efficient induction.

[0074] In this embodiment, the flexible high magnetic permeability material is a nanocrystalline thin strip material, the flexible substrate 2 is an FPC (Flexible Printed Circuit) flexible printed circuit board, and the thickness of the flexible magnetic core 1 and the flexible substrate 2 is 0.05-0.2 mm.

[0075] Figure 23 and Figure 24 As shown, the flexible substrate 2 includes a first flexible substrate 21 and a second flexible substrate 22 located on both sides of the flexible magnetic core 1. The coil wires on the first flexible substrate 21 and the coil wires on the second flexible substrate 22 are arranged parallel to each other in the thickness direction, and one end of each of the two corresponding coil wires 3 is connected. One end of all the coil wires 3 on the second flexible substrate 22 is deflected to the same side, and a connection is formed at the location of adjacent coil wires, such as... Figure 4 As shown, the connecting portion is connected to the end of the coil wire facing the first flexible substrate 21.

[0076] By aligning the coil wires on both flexible substrates strictly parallel and stacked in the thickness direction, a structure similar to a parallel-plate capacitor is formed between the two wires, maximizing the overlap area between the coil wires. This structure results in a significant parasitic capacitance within the flexible current transformer itself. This parasitic capacitance can serve as part of a resonant circuit. When applied to ground-based power harvesting systems, it can significantly reduce the capacity or volume of the external "resonance compensation unit" (i.e., the compensation capacitor) required to achieve resonance, thus further reducing the overall weight, volume, and cost of the entire power harvesting system.

[0077] Specifically, both ends of the coil wire 3 have exposed conductive discs 4, which are correspondingly disposed on opposite sides of the first flexible substrate 21 and the second flexible substrate 22. The two conductive discs 4 facing each other can be bonded and connected when the first flexible substrate 21 and the second flexible substrate 22 are rolled up together.

[0078] When the flexible current transformer is rolled up for installation, the outer flexible substrate applies a rolling force inward, while the inner flexible substrate applies a tension outward, causing the two opposing conductive discs to fit tightly together and conduct electricity. This structure utilizes the mechanical pressing generated by its own rolling up to replace the traditional soldering process, which not only greatly simplifies the installation process on-site, especially for high-altitude operations, but also avoids the additional weight introduced by soldering, contributing to the ultimate lightweighting of the component.

[0079] Simply relying on the pressure generated by curling force may lead to poor contact due to vibration or loosening. To make the contact of the conductive disc more reliable, such as Figure 21 As shown, the first flexible substrate 21 and the second flexible substrate 22 also have detachable locking strips 5 on both sides of their length direction. One side of the locking strip 5 has a locking groove that runs through the side edge. The width of the locking groove matches the thickness of the first flexible substrate 21 and the second flexible substrate 22 and is locked onto the first flexible substrate 21 and the second flexible substrate 22.

[0080] By adding detachable clips to the short sides of the flexible substrate along its length, i.e. the short sides where the conductive disks are located, and using the clip slots to hold the edges of the flexible substrate, a continuous, stable, and independent mechanical clamping force is provided to ensure that the first and second flexible substrates are firmly pressed together. This allows the conductive disks between the two substrates to maintain a more reliable fit, thereby ensuring the long-term stability of the electrical connection and low contact resistance.

[0081] Considering the difficulties of working at heights, the clamping strip is made of a flexible, bendable material to simplify installation, and its length matches the width of the flexible substrate 2. During installation, the strip can be inserted from one end and pushed along the edge, making on-site installation more convenient. Simultaneously, the flexible material ensures that the strip provides clamping force without hindering the flexible current transformer's ability to bend in the width direction, allowing it to bend along with the main body. Furthermore, by matching the strip's length to the width (short side) of the flexible substrate, it ensures that the strip covers the entire edge of the substrate, allowing the clamping force to be evenly distributed across all conductive pads, resulting in more reliable pressing.

[0082] Specifically, in the width direction of the flexible substrate 2, one side of the flexible magnetic core 1 is adapted to the edge of the flexible substrate 2, and the other side extends to the outside of the flexible substrate 2 to form a strip structure 11 that can be wound around the outermost layer. The extension length of the strip structure 11 is greater than the width of the flexible substrate 2.

[0083] During installation, by winding the strip structure of the flexible magnetic core onto the outermost layer, operators can flexibly adjust the number of layers of the outer flexible magnetic core according to the ground current conditions on site, cutting off excess flexible magnetic core and thus changing the total effective number of layers of the flexible magnetic core. This allows direct adjustment of the total inductance and magnetic saturation characteristics of the transformer, enabling the same product to adapt to different operating conditions and achieve optimal energy harvesting efficiency. Furthermore, during installation, wrapping the flexible magnetic core around the outermost layer of the flexible substrate utilizes the high permeability of the flexible magnetic core to form a magnetic shield for the internal coils. This effectively confines the electromagnetic field within the magnetic core, preventing energy loss and improving the stability and efficiency of energy transmission. Moreover, due to the magnetic shielding, there is no need to consider electromagnetic compatibility and magnetic saturation issues in practical engineering applications, further improving energy harvesting efficiency.

[0084] The width of the strip structure matches the length of the flexible substrate, and it can completely cover the flexible substrate when wound. This ensures that when the strip structure is wound as the outermost layer, its width is sufficient and just right to completely cover the inner flexible substrate from one end to the other, thereby achieving complete electromagnetic shielding, confining all electromagnetic fields inside the magnetic core, and maximizing the prevention of energy loss and external interference. Additionally, it also forms a protective enclosure around the flexible substrate.

[0085] Considering the difficulty of working at heights, self-adhesive is provided on one side of the strip structure to simplify the final fixation. The self-adhesive allows the strip structure to be easily and firmly fixed to the underlying magnetic core layer without any additional tools or clips, avoiding welding and greatly simplifying the installation process for working at heights. It also ensures that the number of magnetic core layers after winding will not loosen due to vibration or external force, thus guaranteeing the long-term stability of the adjusted inductance parameters.

[0086] In specific implementation, it can also be done according to Figure 25 The structure shown is such that the first flexible substrate 21 and the second flexible substrate 22 are both stacked with at least two layers, and the coil wires facing each other on any two adjacent layers of the first flexible substrate 21 or the second flexible substrate 22 are connected in parallel.

[0087] By connecting opposing coil wires on adjacent layers in parallel, the total cross-sectional area of ​​the wires is effectively increased. According to the law of resistance, this can significantly reduce the equivalent internal resistance of the flexible conductive coil, thereby reducing power loss and improving energy harvesting efficiency. Furthermore, multiple parallel, opposing coil wires further increase their parasitic capacitance, helping to reduce reliance on external compensation capacitors in system applications.

[0088] The preferred construction operation process for using the flexible current transformer of this embodiment during high-altitude operations is as follows: 1. Preparation and positioning: The operator first takes out the sheet-like flexible current transformer. At this time, the flexible current transformer is in the shape of a thin sheet of paper, and confirms that its structure is intact.

[0089] 2. Main Body Curling: The flexible current transformer, with its flexible substrate on one side, is attached to the target overhead ground wire (i.e., the conductor being measured) along the axial direction of the target overhead ground wire. The coil conductor 3 is parallel to the ground wire, and the flexible substrate 2 is curled along its width direction—that is, wrapped around the target overhead ground wire. The area containing the flexible substrate 2 is wrapped around the target overhead ground wire at least one turn. Figure 26 As shown, the main body of the current transformer is wrapped around the ground wire.

[0090] 3. Solderless Automatic Conductivity: During the winding process, the first flexible substrate 21 and the second flexible substrate 22 will naturally stack and face each other. Due to the elastic force generated by the winding, the exposed conductive pads 4 located on the opposite sides (inner sides) of the two substrates will automatically adhere to each other, achieving preliminary electrical conduction. This process does not require soldering.

[0091] 4. Mechanical locking and fixing: To ensure more reliable contact of the conductive disk 4, the operator takes a detachable locking strip 5 made of flexible material. The operator aligns the slot on one side of the locking strip 5 with the two short edges along the length of the flexible substrate 2, i.e., the short side where the conductive disk 4 is located. The operator inserts the locking strip 5 from one end and pushes it along the edge until the locking strip 5, whose length matches the width of the substrate, is fully engaged on the two flexible substrates 2, thus firmly locking the conductive disk 4.

[0092] 5. Next, the operator continues to wind the strip structure 11 of the flexible magnetic core 1, ensuring that the strip structure 11 is wrapped around the outer layer at least once, such as... Figure 27 As shown, the output value of the flexible current transformer is measured simultaneously. Once it is within the set range, the excess strip structure 11 is cut off, and the strip structure 11 is fixed to the lower surface using the self-adhesive on one side, thus completing the installation.

[0093] 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, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A ground wire energy pickup system based on flexible CT, characterized in that, The system includes a flexible current transformer and a resonant compensation unit. The flexible current transformer comprises a flexible magnetic core made of a flexible high-permeability material and a flexible conductive coil wound on the flexible magnetic core. The flexible magnetic core and the flexible conductive coil are used to continuously wrap around the ground wire of the overhead transmission line, so that the flexible magnetic core forms a closed magnetic circuit without air gap. The resonant compensation unit is electrically connected to the flexible conductive coil and forms a series resonance with the equivalent inductance of the flexible current transformer at the operating frequency to realize energy extraction from the ground wire.

2. The ground wire energy pickup system based on flexible CT as described in claim 1, characterized in that, The flexible high magnetic permeability material is a nanocrystalline thin strip material.

3. The ground wire energy pickup system based on flexible CT as described in claim 1, characterized in that, The flexible conductive coil is made of FPC flexible printed circuit board.

4. The ground wire energy pickup system based on flexible CT as described in claim 3, characterized in that, On the FPC flexible printed circuit board, the coil wires of the flexible conductive coil are parallel to the axis formed by the flexible current transformer.

5. The ground wire energy pickup system based on flexible CT as described in claim 3, characterized in that, The FPC flexible printed circuit board adopts a stacked structure to achieve multi-layer winding.

6. The ground wire energy pickup system based on flexible CT as described in claim 1, characterized in that, The ground wire energy harvesting system includes multiple flexible current transformers.

7. The ground wire energy pickup system based on flexible CT as described in claim 6, characterized in that, Multiple flexible current transformers are sequentially connected along the axial direction and wrapped around the same ground wire.

8. The ground wire energy pickup system based on flexible CT as described in claim 6 or 7, characterized in that, The flexible conductive coils of multiple flexible current transformers are connected in series in sequence.

9. The ground wire energy pickup system based on flexible CT as described in claim 1, characterized in that, The resonant compensation unit is a compensation capacitor connected in series on the flexible conductive coil. The compensation capacitor and the equivalent inductance of the flexible current transformer form a series resonant circuit at the power frequency.

10. The ground wire energy pickup system based on flexible CT as described in claim 1, characterized in that, It also includes a rectification and voltage regulation module, which is connected to the output terminal of the flexible conductive coil.

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