Cable discharge optical fiber detection sensor

Abstract

A cable discharge optical fiber detection sensor belongs to the technical field of optical fiber sensing and comprises a light source, a single-mode optical fiber, an acoustic optical modulator, an erbium-doped optical fiber amplifier, a beam splitter, a circulator, a beam combiner, a photodiode, a data processor and an optical fiber cable. The positive magnetostriction annular optical fiber and the negative magnetostriction annular optical fiber are arranged on the two sides of the high-voltage cable respectively, and the cable sheath is arranged outside the high-voltage cable. The technical scheme of the invention not only overcomes the limitation of the traditional discharge detection method, but also provides a novel sensor which is high in sensitivity, strong in anti-interference capability and easy to deploy in a distributed manner for the safety monitoring of the high-voltage cable, and has important engineering application value.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical fiber sensing, and particularly relates to an optical fiber detection sensor for cable discharge. Background Art

[0002] In the field of electromagnetic sensing research, as an important medium for the interaction of substances, the detection technology of magnetic fields has experienced a leap from macroscopic magnetometers to micro-nano magnetoelectric coupling devices. Typical engineering applications show (IEEE Trans. Magn., 2020) that when high-voltage cables operate under conditions of ≥110 kV, the partial discharge current caused by the polarization loss of dielectric materials can reach the pC level, and the accompanying transient magnetic field has characteristics of a steep front (<10 μs) and a wide frequency spectrum (DC - 1 MHz), which poses severe requirements on the dynamic response characteristics of the sensing system. Taking the measured data of a ±800 kV UHV converter station as an example (CIGRE TB 785), when the converter valve triggers abnormally, the transient magnetic field intensity of the grounding wire can jump to 2.3 mT within 50 ns, and the spectral energy is mainly distributed in the range of 300 kHz - 800 kHz.

[0003] With the rapid development of the power system, the safe operation of high-voltage transmission cables has become the key to ensuring the stable power supply. During the long-term operation of high-voltage cables, local discharge phenomena may be caused by insulation aging, mechanical damage, or environmental factors (such as lightning strikes, pollution, etc.). Local discharge not only accelerates the deterioration of insulating materials but may also lead to serious power accidents such as short circuits and fires. Therefore, real-time monitoring of the discharge phenomena of high-voltage cables is of great significance for preventing power system failures.

[0004] Domestically, for the detection of the fixed magnetic field and induced magnetic field of high-voltage cable discharges, weak magnetic detection devices for cable defects have been developed successively. This technology uses a non-contact detection method to detect weak magnetic field signals around the cable through a magnetic concentrating ring and a magnetic-sensitive chip to determine whether there are defects inside the cable. The device includes a magnetic shielding housing, a power supply, a control circuit board, etc. Subsequently, a magnetic field ranging device for high-voltage wires has also been developed. This device includes a three-axis magnetic field detection module, a signal amplification module, and a main control module, and realizes distance measurement by detecting the magnetic field signals around the high-voltage wires. Currently, there are also weak magnetic detection devices for wires and cables, which collect weak magnetic field signals near the wires and cables through magnetic field sensors, and after A / D conversion and single-chip microcomputer processing, output the magnetic field intensity value and the cable existence status.

[0005] In the field of electromagnetic sensing, existing technologies face multiple performance bottlenecks. Traditional electromagnetic sensing technologies rely on Rogowski coils and capacitive coupling methods (IEC 60270 standard). Based on the principle of Faraday electromagnetic induction, the signal-to-noise ratio deteriorates to less than 15 dB in a strong electromagnetic environment (>50 kV / m), making it difficult to capture the weak magnetic field signals of less than 100 pT generated by early partial discharges in high-voltage cables. Taking the actual measurement of a ±800 kV converter station as an example, the positioning error of traditional sensors for local defects less than 10 cm exceeds ±2 m, and the average annual power outage for maintenance reaches 37 minutes per 100 km of cable (EPRI 2022), severely restricting power supply reliability. Although Hall effect sensors have relatively high sensitivity, their temperature drift coefficient of 0.05% / °C results in an error exceeding ±1% when the environmental temperature difference is 20°C, and their linear range of ±200 mT cannot handle the 10 T-level magnetic field during lightning transients.

[0006] The evolution of magnetostrictive fiber optic sensing technology presents new challenges. The FBG magnetostrictive coating solution achieves a theoretical sensitivity of 3.2 pm / mT through Terfenol-D materials, but the insufficient interfacial bonding strength leads to a time delay jitter exceeding 500 μs under transient magnetic fields, and the temperature drift coefficient of 0.35 nm / °C results in a measurement error of 12.6% in actual measurements at offshore wind farms. Although the Fabry-Perot cavity interference solution improves the detection accuracy, it is limited by the 5% openness of the hysteresis loop and the coercive force of 200 A / m (Patent CN201910235642.8), resulting in measurement hysteresis errors. The emerging photonic crystal fiber technology uses magnetorheological fluid to fill the microporous structure, achieving a sensitivity of 0.1 nT level (J. Lightwave Technol., 2023), but the microfluidic system is sensitive to 5 Hz vibrations with a displacement of 50 μm, and there is a 23% sensitivity attenuation after 3000 hours of accelerated aging, unable to meet the requirement of ten-year maintenance-free for power equipment.

[0007] Technology comparison reveals key performance gaps: The sensitivity of traditional Rogowski coils remains stagnant at the 1 mT level, while the FBG solution, although improved to 0.5 nT, still cannot detect the 80 pT signals of early cable partial discharges (CIGRE TB 758). The lack of multi-dimensional sensing capabilities leads to a misjudgment rate of up to 63% for common-mode interference between adjacent cables (simulation data), and the ±200 mT range of commercial sensors is severely mismatched with the 8.7 T magnetic field during lightning transients (actual measurements in ±1100 kV projects). Industry data shows (IEEE PES2023) that 68% of high-voltage cable failures globally are due to missed detection of partial discharges, with an annual loss exceeding $1.2 billion, highlighting the urgent need for new technologies with a sensitivity of 10 pT, a positioning accuracy of 0.2 m, and a dynamic range of ±10 T. These bottlenecks drive the invention to break through in the innovative direction of enhanced magneto-optical coupling and temperature self-compensation to achieve a detection coverage rate of 98% of the IEC 62478 standard.

[0008] First, the sensitivity of the transmission and scattering sensor is relatively low, making it difficult to detect weak discharge signals. During the operation of the cable, the early discharge signals are usually very weak. If the sensor fails to capture these signals in a timely manner, potential faults may be overlooked, increasing the risk of cable operation. For example, in high-voltage transmission lines, partial discharge is often an early sign of cable insulation aging. If these signals cannot be detected in a timely manner, it may lead to insulation breakdown and even cause serious safety accidents. Therefore, improving the sensitivity of the sensor is the key to solving this problem.

[0009] Secondly, the limited spatial resolution is another significant drawback. Existing scattering sensors have difficulty in precisely locating the position where the discharge occurs during long-distance cable monitoring. For example, in transmission lines dozens or even hundreds of kilometers long, the spatial resolution of the sensor may only reach a few meters or even more than ten meters, which is far from sufficient in actual fault troubleshooting. Precise location of the fault point is crucial for quickly repairing the cable and reducing power outage time. However, the large positioning error of the existing technology affects the efficiency of fault troubleshooting. Therefore, how to improve the spatial resolution, especially in the application effect of long-distance monitoring, is one of the key points that current technology needs to break through. Summary of the Invention

[0010] The technical problem to be solved by the present invention is to provide a fiber optic detection sensor for cable discharge. This sensor utilizes the transient strong magnetic field generated by high-voltage discharge, and through the magnetostrictive effect, causes deformation of the cladding of the fiber optic loop, thereby changing the scattering characteristics of the light transmitted in the optical fiber. By detecting the change in frequency shift, sensitive detection and precise positioning of the discharge signal can be achieved. In addition, combined with coherent detection technology, it can effectively suppress environmental noise and improve the detection signal-to-noise ratio. The technical solution of the present invention not only overcomes the limitations of traditional discharge detection methods, but also provides a new type of sensor with high sensitivity, strong anti-interference ability and easy distributed deployment for the safety monitoring of high-voltage cables, having important engineering application value.

[0011] A fiber optic detection sensor for cable discharge includes a light source, a single-mode optical fiber, an acousto-optic modulator, an erbium-doped fiber amplifier, a beam splitter, a circulator, a combiner, a photodiode, a data processor, and an optical fiber cable. The center of the optical fiber cable is a high-voltage cable, and a positive magnetostrictive ring-shaped optical fiber and a negative magnetostrictive ring-shaped optical fiber are respectively arranged on both sides of the high-voltage cable, and a cable sheath is arranged outside the high-voltage cable;

[0012] The light source is split into two paths through the single-mode optical fiber, successively passing through the acousto-optic modulator, the erbium-doped fiber amplifier, and the beam splitter. One path is the reference arm, and the other path is the sensing arm;

[0013] The sensing arm light after beam splitting enters the circulator, which guides the light to the positive magnetostrictive ring-shaped optical fiber and the negative magnetostrictive ring-shaped optical fiber on the high-voltage cable. They are wound around the surface of the high-voltage cable with opposite magnetostrictive coefficients to form a differential sensing structure. The sensing light is reflected at the end of the optical fiber cable, returns along the original path to the circulator, and enters the beam combiner together with the reference arm light. After the two beams of light interfere, the phase difference is converted into an optical intensity fluctuation, which is converted into an electrical signal by a photodiode and transmitted to the data processor.

[0014] The core of the positive magnetostrictive ring-shaped optical fiber is the fiber core, the outside of the fiber core is the optical fiber cladding, and the outside of the optical fiber cladding is coated with a positive magnetostrictive material.

[0015] The core of the negative magnetostrictive ring-shaped optical fiber is the fiber core, the outside of the fiber core is the optical fiber cladding, and the outside of the optical fiber cladding is coated with a negative magnetostrictive material.

[0016] The center of the high-voltage cable is a copper conductor, and a cable insulation layer is arranged outside the copper conductor.

[0017] Through the above design scheme, the present invention can bring the following beneficial effects: The present invention provides a cable discharge optical fiber detection sensor, which can detect weak internal discharge signals of the cable by utilizing the characteristic that scattering is very sensitive to the change of the refractive index of the optical fiber, and improves the detection sensitivity. By utilizing the characteristic that the optical fiber sensing technology itself has strong anti-electromagnetic interference ability, it is used for monitoring the complex electromagnetic environment of high-voltage cables, and improves the anti-interference ability. The structure of coating the positive and negative magnetostrictive materials in a ring shape on the optical fiber cladding solves the problems of limited magnetic field detection direction and limited accuracy. The invention can not only accurately locate the subtle changes of the magnetic field, but also solve the problem that it is difficult to monitor the omnidirectional magnetic field change by using magnetostrictive materials at present.

[0018] Furthermore, compared with the traditional Hall effect sensor, the present invention integrates the dual advantages of photonic crystal fiber technology and magnetoelectric coupling effect: First, the multi-layer heterojunction cladding structure realizes the spatial decoupling of the magnetic field vector through the difference in magnetostrictive coefficients, and can synchronously obtain the magnetic field strength, gradient and azimuth information in cooperation with the phase-sensitive optical time domain reflectometry technology; Second, the Fe-Ga / PDMS composite cladding prepared by plasma-enhanced chemical vapor deposition process has a 42% higher magnetomechanical response sensitivity than the traditional Terfenol-D material, and at the same time has a temperature self-compensation characteristic; In addition, the combination of the microstructured grating array and the DSPGD demodulation algorithm enables the system to achieve a spatial resolution of 20 cm while maintaining a linearity of 0.05% FS.

[0019] The sensor proposes a magneto-opto-mechanical multi-physical field coupling model, and realizes broadband magnetic field detection (DC - 1kHz) through the non-linear change of the equivalent elastic modulus of the cladding; develops a gradient refractive index compensation technology to effectively suppress the signal crosstalk caused by multi-mode coupling, and the signal-to-noise ratio is increased to 68dB; adopts a microwave photonics frequency division multiplexing scheme, and 120 independent sensing units can be integrated in a single optical fiber to construct a distributed intelligent monitoring network. Experiments show that the device has significant response characteristics to the transient magnetic field generated by the corona discharge of a 500kV high-voltage cable, and the phase noise is lower than 0.8μrad / √Hz, which is particularly suitable for strong electromagnetic interference scenarios such as the state monitoring of smart grids and high-voltage cables. Description of the Drawings

[0020] The present invention will be further described below in conjunction with the drawings and specific embodiments:

[0021] Figure 1 Schematic structural diagram of a fiber optic cable discharge detection sensor of the present invention.

[0022] Figure 2 Schematic structural diagram of a negative magnetostrictive ring-shaped optical fiber of a fiber optic cable discharge detection sensor of the present invention.

[0023] Figure 3 Schematic structural diagram of a positive magnetostrictive ring-shaped optical fiber of a fiber optic cable discharge detection sensor of the present invention.

[0024] Figure 4 Schematic cross-sectional diagram of an optical fiber cable of a fiber optic cable discharge detection sensor of the present invention.

[0025] Figure 5 Schematic diagram showing the force generated on the magnetostrictive material due to the magnetic field generated during the creepage of the cable in the specific embodiment of a fiber optic cable discharge detection sensor of the present invention.

[0026] Figure 6 Schematic diagram showing the force generated on the magnetostrictive material due to the magnetic field generated during the leakage of the cable in the specific embodiment of a fiber optic cable discharge detection sensor of the present invention.

[0027] In the figure, 1 - core, 2 - optical fiber cladding, 3 - negative magnetostrictive material, 4 - positive magnetostrictive material, 5 - light source, 6 - single-mode optical fiber, 7 - acousto-optic modulator, 8 - erbium-doped fiber amplifier, 9 - beam splitter, 10 - circulator, 11 - high-voltage cable, 12 - positive magnetostrictive ring-shaped optical fiber, 13 - negative magnetostrictive ring-shaped optical fiber, 14 - high-voltage cable, 15 - photodiode, 16 - data processor, 17 - optical fiber cable, 18 - copper conductor, 19 - cable sheath, 20 - cable insulation layer. Specific Embodiments

[0028] A fiber optic cable discharge detection sensor, as Figures 1-4As shown in the figure, it includes a light source 5, a single-mode optical fiber 6, an acousto-optic modulator 7, an erbium-doped fiber amplifier 8, a beam splitter 9, a circulator 10, a combiner 14, a photodiode 15, a data processor 16, and an optical fiber cable 17. The center of the optical fiber cable 17 is a high-voltage cable 11. On both sides of the high-voltage cable 11, a positive magnetostrictive ring-shaped optical fiber 12 and a negative magnetostrictive ring-shaped optical fiber 13 are respectively arranged. A cable sheath 19 is arranged outside the high-voltage cable 11.

[0029] The light from the light source 5 passes through the acousto-optic modulator 7, the erbium-doped fiber amplifier 8, and the beam splitter 9 in sequence through the single-mode optical fiber 6 and is split into two paths. One path is the reference arm, and the other path is the sensing arm.

[0030] The light of the split sensing arm enters the circulator 10, and the light is guided to the positive magnetostrictive ring-shaped optical fiber 12 and the negative magnetostrictive ring-shaped optical fiber 13 on the high-voltage cable 11, which are wound around the surface of the high-voltage cable 11 with opposite magnetostrictive coefficients to form a differential sensing structure. The sensing light is reflected at the end of the optical fiber cable 17, returns along the original path to the circulator 10, and enters the combiner 14 together with the reference arm light. After the two beams of light interfere, the phase difference is converted into an optical intensity fluctuation, which is converted into an electrical signal by the photodiode 15 and transmitted to the data processor 16.

[0031] The center of the positive magnetostrictive ring-shaped optical fiber 12 is a fiber core 1. Outside the fiber core 1 is an optical fiber cladding 2, and a positive magnetostrictive material 4 is coated outside the optical fiber cladding 2.

[0032] The center of the negative magnetostrictive ring-shaped optical fiber 13 is a fiber core 1. Outside the fiber core 1 is an optical fiber cladding 2, and a negative magnetostrictive material 3 is coated outside the optical fiber cladding 2.

[0033] And the positive magnetostrictive ring-shaped optical fiber 12 and the negative magnetostrictive ring-shaped optical fiber 13 are parallel.

[0034] The center of the high-voltage cable 11 is a copper conductor 18, and a cable insulation layer 20 is arranged outside the copper conductor 18.

[0035] In the present invention, a magnetostrictive deformation medium layer and a buffer protection layer are alternately deposited on the surface of a standard single-mode optical fiber substrate to form a composite cladding system with stress-sensitive characteristics. At the same time, a microstructured Bragg grating array is implanted at specific phase points along the axis of the fiber core 1, and a low-interference grating group with a reflectivity lower than 5% is realized by femtosecond laser direct writing technology. This sensor exhibits a magnetic field resolution of 1.2 pm / mT in the range of 0 - 500 mT and has a dynamic response characteristic of <100 ms.

[0036] The laser light source 5 emits continuous laser light, which is transmitted through a single-mode optical fiber 6 to an acousto-optic modulator 7. The laser light is frequency-modulated by a high-frequency electrical signal to provide a heterodyne reference for subsequent interference detection. The modulated light enters an erbium-doped fiber amplifier 8 to increase the power, and then is split into two paths by a beam splitter 9: one path is the reference arm, and the other path is the sensing arm. The split light enters a circulator 10, which guides the light to a positive magnetostrictive ring-shaped optical fiber 12 and a negative magnetostrictive ring-shaped optical fiber 13 on a high-voltage cable 11. The two fibers are wound around the cable surface with opposite magnetostriction coefficients to form a differential sensing structure. When the cable discharges, a transient current generates an alternating magnetic field, which causes the magnetostrictive material to deform: the positive magnetostrictive optical fiber 12 elongates in the magnetic field, resulting in an increase in the optical propagation path (phase delay). The negative magnetostrictive optical fiber 13 contracts in the magnetic field, resulting in a shortening of the optical propagation path (phase advance). The phase changes of the two paths are in opposite directions, and the sensitivity of the interference signal is amplified through the differential effect. The sensing light is reflected at the end of the optical fiber and returns along the original path to the circulator, and enters a beam combiner 14 together with the reference arm light. The two beams of light interfere, and the phase difference is converted into an optical intensity fluctuation. The change in the interference optical intensity is converted into an electrical signal and transmitted to a data processor 16 to extract the phase change amount by demodulating the heterodyne signal. Combining the differential responses of the positive / negative optical fibers, environmental noises such as temperature are eliminated, and the discharge event is accurately located.

[0037] Combined with Figure 5 and Figure 6 , where B is the magnetic field generated during the discharge (creepage or leakage) in the cable, which is caused by the fault current.

[0038] F1 / F1' is the main force (appearing in pairs and in opposite directions) generated by the magnetostrictive material under the action of the magnetic field B.

[0039] F2 / F2' is the reverse force of the main force generated by the magnetostrictive material under the action of the magnetic field B (appearing in pairs and in opposite directions).

[0040] Arrow direction in the figure: The arrow of B represents the magnetic field direction (determined by the current direction and following the right-hand screw rule).

[0041] The arrows of F1 / F1' and F2 / F2' represent the force directions, and the paired arrows reflect the mechanical balance (F1 is to the left and F1' is to the right).

[0042] Effect: The deformation of the magnetostrictive material is transmitted to the optical fiber core through F1 / F1', changing the refractive index or the phase of the optical signal, and thus being detected by the sensor.

[0043] The existence of F2 / F2' prevents the optical fiber from being damaged due to excessive unilateral force, ensuring the stability of the sensing structure.

[0044] Figure 5The application scenario can detect early insulation degradation, such as partial discharge caused by surface contamination. Source of magnetic field (B): When there is creepage (surface partial discharge), a microcurrent is formed on the surface of the cable insulation layer, generating a local non-uniform magnetic field (the direction of B is determined by the direction of the current, conforming to the right-hand rule).

[0045] Acting force (F1 / F1'): Positive and negative magnetostrictive materials are affected by the magnetic field B and produce tensile or compressive deformation due to the magnetostrictive effect.

[0046] F1 and F1' are the main acting forces exerted on the optical fiber when the magnetostrictive material deforms, with opposite directions (F1 is the tensile force and F1' is the thrust force).

[0047] Reaction force (F2 / F2'): When the magnetostrictive material deforms, the optical fiber generates reaction forces F2 and F2' due to the reaction of the material, which are used to balance the main acting forces.

[0048] For example: If F1 pulls the optical fiber to the left, F2 will push the optical fiber to the right to maintain the mechanical balance of the system.

[0049] Figure 6 The application scenario can identify severe insulation faults, such as current leakage caused by insulation breakdown. Change in magnetic field (B): When there is leakage (the current forms a large leakage path through the insulation defect), the fault current is stronger, and the intensity of the magnetic field B is higher and the distribution is wider.

[0050] Enhancement of acting force (F1 / F1'): A stronger magnetic field B causes more significant deformation of the magnetostrictive material, increasing the amplitude of the main acting force F1 / F1'. When the direction of the leakage path changes (the direction of the current flow reverses), the direction of F1 / F1' is opposite to Figure 5 the opposite.

[0051] Adjustment of reaction force (F2 / F2'): The reaction force increases synchronously with the main acting force to ensure the stability of the optical fiber sensor under a strong magnetic field.

Claims

1. A cable discharge optical fiber detection sensor, characterized in that: The invention comprises a light source (5), a single-mode optical fiber (6), an acousto-optic modulator (7), an erbium-doped optical fiber amplifier (8), a beam splitter (9), a circulator (10), a beam combiner (14), a photodiode (15), a data processor (16), and an optical fiber cable (17). The center of the optical fiber cable (17) is a high-voltage cable (11). A positive magnetostrictive annular optical fiber (12) and a negative magnetostrictive annular optical fiber (13) are respectively arranged on both sides of the high-voltage cable (11). A cable sheath (19) is arranged outside the high-voltage cable (11). The light source (5) passes through a single-mode optical fiber (6) and sequentially passes through an acousto-optic modulator (7), an erbium-doped optical fiber amplifier (8) and a beam splitter (9) to be split into two paths, one being a reference arm and the other being a sensor arm; The split sensing arm light enters the circulator (10), and the light is guided to the positive magnetostrictive ring optical fiber (12) and the negative magnetostrictive ring optical fiber (13) on the high-voltage cable (11), which are wound around the surface of the high-voltage cable (11) with opposite magnetostrictive coefficients, forming a differential sensing structure; the sensing light is reflected at the end of the optical fiber cable (17), returns to the circulator (10) along the original path, and enters the beam combiner (14) together with the reference arm light; after the two beams interfere, the phase difference is converted into light intensity fluctuation, which is converted into an electrical signal through a photodiode (15) and transmitted to a data processor (16).

2. A cable discharge optical fiber detection sensor according to claim 1, characterized in that: The center of the positive magnetostrictive annular optical fiber (12) is a fiber core (1), the outside of the fiber core (1) is an optical fiber cladding (2), and the outside of the optical fiber cladding (2) is coated with a positive magnetostrictive material (4).

3. A cable discharge optical fiber detection sensor according to claim 1, characterized in that: The center of the negative magnetostrictive annular optical fiber (13) is a fiber core (1), the outside of the fiber core (1) is an optical fiber cladding (2), and the outside of the optical fiber cladding (2) is coated with a negative magnetostrictive material (3).

4. A cable discharge optical fiber detection sensor according to claim 1, characterized in that: The center of the high-voltage cable (11) is a copper conductor (18), and the outside of the copper conductor (18) is provided with a cable insulation layer (20).

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