Optical fiber intensity modulation-based ADSS optical cable leakage current optical fiber sensor

Abstract

The invention discloses an optical fiber intensity modulation-based ADSS optical cable leakage current optical fiber sensor. The optical fiber sensor comprises a first optical fiber, a second optical fiber, a U-shaped groove body and a light intensity detection device, the light intensity detection device adopts a dual-channel ratio demodulation structure and comprises two PIN receivers and a hardware ratio device, the second optical fiber adopts a dual-core optical fiber, double fiber cores of the second optical fiber are respectively aligned with the two independent PIN receivers, the rear end calculates the ratio output of two paths of light currents in real time through the hardware ratio device, and common-mode drift is eliminated. According to the sensor, the coupling loss change caused by micro displacement of the permanent magnet alloy coating optical fiber in an alternating magnetic field is utilized, temperature drift is eliminated through the optical fiber ratio demodulation technology, 0.2-level precision current measurement is achieved, and the sensor has the advantages of being simple in structure, low in cost, high in anti-interference capacity and the like and is suitable for monitoring the electro-corrosion leakage current of the ADSS optical cable.

Description

Technical Field

[0001] This invention relates to the field of power system distribution network technology, and in particular to a fiber optic sensor for leakage current of ADSS optical cable based on fiber intensity modulation, which can achieve high-precision measurement of leakage current of ADSS optical cable electrical corrosion. Background Technology

[0002] ADSS (All-Dielectric Self-Supporting Cable) is a special type of optical cable designed for overhead installation and is widely used in power communication systems, long-distance trunk communication, intelligent transportation and other fields.

[0003] ADSS optical cable uses all-dielectric materials, with both the internal fiber core and outer sheath made of insulating materials and containing no metal components. Therefore, it has extremely strong resistance to electromagnetic interference and can operate stably near high-voltage power lines or in strong electromagnetic field environments. No additional support structure is required; the cable itself has sufficient strength to be directly suspended from power poles or communication lines, saving installation costs and time. High-strength aramid fiber is used as reinforcement, enabling it to withstand significant tensile force and external impact, making it suitable for long-distance overhead laying in harsh weather conditions. The outer sheath uses highly weather-resistant polyethylene (PE) or electro-erosion resistant (AT) materials, allowing stable operation in harsh conditions such as temperatures ranging from -40℃ to 70℃, high humidity, and strong electric fields. Weighing only one-third of traditional optical cables, it reduces the difficulty of transportation and installation, and decreases the load requirements on support structures.

[0004] ADSS optical cables are used for real-time data transmission in high-voltage transmission networks, such as power dispatching and fault monitoring. They also support intelligent distribution networks, enabling functions like distribution automation and remote meter reading. Furthermore, they are used for long-distance trunk communication, suitable for backbone network construction across mountainous areas, rivers, and other complex terrains, reducing the need for repeater equipment.

[0005] The advantages of ADSS optical cable are:

[0006] Easy to install: The installation process is simple and quick, requiring no power outages, which effectively reduces the difficulty and cost of construction.

[0007] High reliability: The all-dielectric design eliminates the risk of electro-corrosion and has a lifespan of over 30 years; the aramid reinforcement layer ensures mechanical strength in large-span scenarios.

[0008] Economic benefits: Lightweight, reducing tower load; supports co-pole installation with power lines, reducing land occupation and construction costs.

[0009] Compatibility: It can be used as a supplement to OPGW optical cable to solve the power isolation problem and is compatible with multiple communication protocols such as FTTX and CATV.

[0010] Selection and maintenance points

[0011] Voltage level matching: Select the appropriate sheath material according to the application scenario. For example, use PE sheath for scenarios below 110kV and AT sheath for high voltage environments.

[0012] Span calculation: The amount of aramid used needs to be customized according to parameters such as tower spacing and ice load to avoid overload.

[0013] Operation and maintenance strategy: Regularly inspect the electrolytic corrosion of the outer sheath and use OTDR technology to monitor fiber optic attenuation.

[0014] With its unique structure and excellent performance, ADSS optical cable has demonstrated strong competitiveness in fields such as power communication, long-distance transmission, and intelligent transportation, and can effectively meet the requirements of modern communication networks for high reliability, resistance to electromagnetic interference, and economy.

[0015] With the rapid development of power communication networks, ADSS optical cables, with their advantages of good insulation performance and light weight, have become a key facility for communication transmission in high-voltage transmission lines. However, in actual operation, electro-corrosion has gradually become an "invisible killer" threatening its safe and stable operation, making research on leakage current detection technology urgent.

[0016] ADSS optical cables are exposed to high-voltage, high-electric-field environments for extended periods. Due to capacitive coupling with high-voltage conductors, induced AC potentials can form on their surface under humid or polluted conditions, leading to grounding leakage current. The heat generated by this leakage current causes a dry band to form on the cable surface. Accumulated voltage on this dry band triggers an electric arc discharge. The continued action of the arc can cause carbonization of the cable sheath, forming dendritic discharge channels. In severe cases, this can even lead to cable breakage, resulting in communication outages and loss of control over power system dispatch.

[0017] Currently, traditional ADSS fiber optic cable leakage current detection relies on manual inspection and simple sensor monitoring. Manual inspection is limited by environmental factors and personnel experience, resulting in low efficiency and a high risk of missed detections; conventional sensor monitoring is susceptible to electromagnetic interference, leading to insufficient data accuracy.

[0018] Therefore, in order to better ensure the safe and stable operation of power communication systems and improve the accuracy and reliability of ADSS optical cable leakage current detection, it is of great significance to carry out research on ADSS optical cable passive leakage current detection technology. Summary of the Invention

[0019] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a fiber optic leakage current sensor based on fiber intensity modulation (ADSS) optical cable. This invention employs the principle of fiber coupling loss modulation, effectively overcoming the deficiencies of traditional current sensors and existing fiber optic current sensors, achieving high-precision, low-cost, and high-stability current measurement, and can also be used for partial discharge detection.

[0020] This invention is achieved through the following technical solution:

[0021] A fiber optic leakage current sensor based on fiber intensity modulation type ADSS optical cable includes a first optical fiber, a second optical fiber, a U-shaped groove body, and a light intensity detection device.

[0022] A U-shaped groove 1 is formed on the U-shaped groove body. A U-shaped groove 2 and a U-shaped groove 3 are formed on the left and right sides of the U-shaped groove 1, respectively. Both U-shaped groove 2 and U-shaped groove 3 are connected to U-shaped groove 1. There is a micron-level misalignment between the central axes of U-shaped groove 2 and U-shaped groove 3. A first optical fiber and a second optical fiber are installed in U-shaped groove 2 and U-shaped groove 3, respectively. There is a micron-level misalignment between the central axes of the first optical fiber and the second optical fiber. The first optical fiber is fixed. A permanent magnet alloy layer is plated on the end of the second optical fiber near the first optical fiber. The end of the second optical fiber with the permanent magnet alloy layer is suspended and extends into U-shaped groove 1, so that the end of the second optical fiber with the permanent magnet alloy layer vibrates slightly in the magnetic field. The unplated end of the second optical fiber is fixed.

[0023] The light intensity detection device adopts a dual-channel ratio demodulation structure, including two PIN receivers and a hardware ratio converter. The second optical fiber is a dual-core optical fiber, with each core aligned with one of the two independent PIN receivers. The light source enters the first optical fiber from one end, and the first optical fiber transmits the optical signal to the second optical fiber. The second optical fiber then transmits the optical signal to the two independent PIN receivers. The PIN receivers convert the optical signal into an electrical signal, and the back-end uses the hardware ratio converter to calculate the ratio of the two photocurrents in real time and output the result to eliminate common-mode drift.

[0024] The U-shaped groove body is integrally mounted on a rigid metal or ceramic chassis, and the chassis material has a high elastic modulus.

[0025] The U-shaped groove body is made of quartz glass. The first U-shaped groove is located in the middle of the U-shaped groove body. The second and third U-shaped grooves, which have a micron-level misalignment of the central axis, are integrally processed on the quartz glass.

[0026] It also includes a magnetic collecting ring, which is sleeved on the outside of one end of the second optical fiber coated with a permanent magnet alloy layer and indirectly fixed by the rigid chassis.

[0027] The permanent magnet alloy layer is a nickel-iron alloy or an aluminum-nickel-cobalt alloy.

[0028] The extension length of the second optical fiber is 1-2 mm.

[0029] When the grounding leakage current of the ADSS optical cable generates an alternating magnetic field, the magnetic dipole inside the permanent magnet alloy layer in the magnetic field will be subjected to the magnetic force, resulting in a Lorentz force. This causes the permanent magnet alloy layer to move along the direction of the magnetic field, which in turn causes a slight vibration at one end of the second optical fiber coated with the permanent magnet alloy layer. This changes the micron-level interaxial misalignment between the first and second optical fibers. The change in the relative position of the first and second optical fibers causes a change in the coupling loss between the optical fibers. The displacement is converted into an optical intensity modulation signal through the exponential change in coupling loss, thereby modulating the optical intensity.

[0030] The formula for calculating the Lorentz force on the magnetic dipole within the permanent magnet alloy layer is as follows:

[0031]

[0032] Where F is the Lorentz force on the magnetic dipole within the permanent magnet alloy layer, and q is the charge of the charged particle. It is the particle's velocity. It is the alternating magnetic induction intensity generated by the leakage current;

[0033] The vibration displacement at one end of the second optical fiber coated with the permanent magnet alloy layer after being subjected to the Lorentz force is as follows:

[0034] Δx=k·F·L 3 / (E·I)

[0035] Where Δx is the vibration displacement generated at one end of the second optical fiber coated with a permanent magnet alloy layer, k is the structurally related proportionality coefficient, L is the cantilever length of the second optical fiber, E is the elastic modulus of the permanent magnet alloy layer, and I is the moment of inertia of the cross section.

[0036] The modulation function of the light intensity modulation signal is:

[0037] I out =I o ·exp(-α·(Δx) 2 )

[0038] Among them, I out It is the output light intensity of the second optical fiber, I o α is the initial coupled light intensity, and α is the fiber coupling attenuation coefficient.

[0039] The light intensity detection device achieves current measurement by detecting the change in coupling efficiency corresponding to the axis offset of the first and second optical fibers, as detailed below:

[0040] The light intensity ratio is: I1 and I2 are the received light intensities of the second fiber optic dual core, respectively.

[0041] Coupling efficiency: I in It is the input light intensity of the first fiber, I out It is the total light intensity output from the second optical fiber;

[0042] Leakage current: β is the system calibration coefficient. It is the rate of change of coupling efficiency.

[0043] The coefficient of thermal expansion of the U-shaped grooves two and three of the quartz glass is 10. -7 Magnitude.

[0044] The light intensity received by the second optical fiber is expressed as follows:

[0045]

[0046] In the formula, I0 represents the light intensity coupled from the light source into the first optical fiber, σ is a parameter characterizing the refractive index distribution of the optical fiber, and a0 is the core radius of the first optical fiber. The modulation parameters are related to the type of light source and the coupling between the light source and the first optical fiber; θ c denoted as the maximum emission angle of the first optical fiber; S is the core area of ​​the second optical fiber; x, y, and z are the lateral coordinates and axial distances on the end face of the second optical fiber, respectively; x and y are the lateral coordinates of the end face of the second optical fiber, and z is the axial distance between the two optical fibers.

[0047] From the above formula, we can see that the intensity of light incident on the second fiber is related to its core area. When there is no relative positional deviation between the first and second fibers, the coupling loss is minimal and the intensity of light entering the second fiber from the first fiber is maximum. As the interaxial deviation between the first and second fibers increases, the intensity of light entering the second fiber decreases accordingly.

[0048] The advantages of this invention are: by changing the interaxial deviation at the micrometer level, the coupling loss between optical fibers can sensitively reflect the change in magnetic field, thereby achieving high-sensitivity detection of leakage current.

[0049] The vibration of the second optical fiber in this invention can precisely modulate the light intensity, enabling the light intensity detection device to detect minute changes in the magnetic field.

[0050] The light intensity detection device of this invention adopts a dual-channel ratio demodulation structure. Through two PIN receivers and a hardware ratio converter, it can calculate the ratio of the two photocurrents in real time, eliminate the influence of common-mode drift, and improve measurement accuracy. The use of the hardware ratio converter can effectively reduce the impact of environmental interference and system noise on the measurement results.

[0051] The sensor of this invention utilizes the change in coupling loss caused by the micro-displacement of permanent magnet alloy coated optical fiber in an alternating magnetic field. Temperature drift is eliminated through optical fiber ratio demodulation technology, achieving current measurement with an accuracy of 0.2%. This invention has the advantages of simple structure, low cost, and strong anti-interference ability, and is suitable for monitoring leakage current of ADSS optical cable electrical corrosion. Attached Figure Description

[0052] Figure 1 This is a schematic diagram of the structure of the present invention;

[0053] Figure 2 This is a cross-sectional view of the present invention;

[0054] Figure 3 This is a side view of the U-shaped channel body;

[0055] Figure 4 This is a curve showing how light intensity changes as the optical fiber's axis deflects. Detailed Implementation

[0056] like Figure 1 , 2 As shown in Figures 1 and 3, a fiber optic leakage current sensor based on fiber intensity modulation ADSS optical cable includes a first optical fiber 1, a second optical fiber 2, a U-shaped groove body 3, and a light intensity detection device.

[0057] A U-shaped groove 4 is formed on the U-shaped groove body 3. A second U-shaped groove 5 and a third U-shaped groove 6 are formed on the left and right sides of the first U-shaped groove 4, respectively. Both the second U-shaped groove 5 and the third U-shaped groove 6 are connected to the first U-shaped groove 4. The second U-shaped groove 5 and the third U-shaped groove 6 have a micron-level misalignment of their central axes. A first optical fiber 1 and a second optical fiber 2 are installed in the second U-shaped groove 5 and the third U-shaped groove 6, respectively. The first optical fiber 1 and the second optical fiber 2 have a micron-level misalignment of their central axes, which forms an initial coupling loss. The first optical fiber 1 is fixed. A permanent magnet alloy layer 7 is coated on the end of the second optical fiber 2 near the first optical fiber 1. The end of the second optical fiber 2 coated with the permanent magnet alloy layer 7 is suspended and extends into the first U-shaped groove 4, so that the end of the second optical fiber 2 coated with the permanent magnet alloy layer 7 vibrates slightly in the magnetic field. The non-coated end of the second optical fiber 2 is fixed.

[0058] The light intensity detection device employs a dual-channel ratio demodulation structure, including two PIN receivers 8 and a hardware ratio converter. The second optical fiber 2 is a dual-core fiber, used for more complex optical signal processing and anti-interference functions. The two cores of the second optical fiber 2 are respectively aligned with the two independent PIN receivers 8. The light source 9 enters the first optical fiber 1 from one end. The first optical fiber 1 transmits the optical signal to the second optical fiber 2, and the second optical fiber 2 transmits the optical signal to the two independent PIN receivers 8. The PIN receivers 8 convert the optical signal into an electrical signal. The back-end uses the hardware ratio converter to calculate the ratio of the two optical currents in real time and outputs it to eliminate common-mode drift. The second optical fiber can also be a multi-core fiber, with the number of PIN receivers being exactly the same as the number of fiber cores; and the output optical current ratio is the real-time ratio of the dual-channel differential optical currents, used to eliminate common-mode drift.

[0059] The U-shaped groove body 3 is mounted on a rigid metal or ceramic chassis. The chassis material has a high elastic modulus to suppress the transmission of external vibrations.

[0060] The U-shaped groove body is made of quartz glass. The first U-shaped groove 4 is located in the middle of the U-shaped groove body 3. The second U-shaped groove 5 and the third U-shaped groove 6, which have micron-level central axis misalignment, are integrally processed on the quartz glass.

[0061] It also includes a magnetic collecting ring 10, which is sleeved on the outside of one end of the second optical fiber 2 coated with a permanent magnet alloy layer 7 and indirectly fixed by the rigid chassis, in order to enhance the local magnetic field strength.

[0062] The permanent magnet alloy layer 7 is a nickel-iron alloy or an aluminum-nickel-cobalt alloy.

[0063] The second optical fiber 2 has an extension length of 1-2 mm to reduce inertial effects. The extension length refers to the end plated with permanent magnet alloy.

[0064] When the grounding leakage current of ADSS optical cable 11 generates an alternating magnetic field, the magnetic dipole inside the permanent magnet alloy layer 7 in the magnetic field will be subjected to the magnetic field force, causing it to be subjected to the Lorentz force, which makes the permanent magnet alloy layer 7 move along the direction of the magnetic field. This causes one end of the second optical fiber 2 coated with the permanent magnet alloy layer 7 to vibrate slightly, thereby changing the micron-level interaxial deviation between the first optical fiber 1 and the second optical fiber 2. The change in the relative position of the first optical fiber 1 and the second optical fiber 2 causes the coupling loss between the optical fibers to change. The displacement is converted into an optical intensity modulation signal through the exponential change of the coupling loss, thereby modulating the optical intensity.

[0065] The formula for calculating the Lorentz force on the magnetic dipole within the permanent magnet alloy layer is as follows:

[0066]

[0067] Where F is the Lorentz force on the magnetic dipole within the permanent magnet alloy layer, and q is the charge of the charged particle. It is the particle's velocity. It is the alternating magnetic induction intensity generated by the leakage current;

[0068] The vibration displacement at one end of the second optical fiber coated with the permanent magnet alloy layer after being subjected to the Lorentz force is as follows:

[0069] Δx=k·F·L 3 / (E·I)

[0070] Where Δx is the vibration displacement generated at one end of the second optical fiber coated with a permanent magnet alloy layer, k is the structurally related proportionality coefficient, L is the cantilever length of the second optical fiber, E is the elastic modulus of the permanent magnet alloy layer, and I is the moment of inertia of the cross section.

[0071] The modulation function of the light intensity modulation signal is:

[0072] I out =I o ·exp(-α·(Δx) 2 )

[0073] Among them, I out It is the output light intensity of the second optical fiber, I o α is the initial coupled light intensity, and α is the fiber coupling attenuation coefficient.

[0074] The light intensity detection device measures the current by detecting the change in coupling efficiency corresponding to the axial offset of the first optical fiber 1 and the second optical fiber 2, as detailed below:

[0075] The light intensity ratio is: I1 and I2 are the received light intensities of the second fiber optic dual core, respectively.

[0076] Coupling efficiency: I in It is the input light intensity of the first fiber, I out It is the total light intensity output from the second optical fiber;

[0077] Leakage current: β is the system calibration coefficient. It is the rate of change of coupling efficiency.

[0078] The coefficient of thermal expansion of the U-shaped groove 2.5 and U-shaped groove 3.6 of the quartz glass is 10. -7 The scale ensures the stability of the sensor under different temperature conditions.

[0079] The light intensity received by the second optical fiber 2 is expressed as follows:

[0080]

[0081] In the formula, I0 represents the light intensity coupled from the light source into the first optical fiber 1, σ represents a parameter characterizing the refractive index distribution of the optical fiber, and a0 represents the core radius of the first optical fiber 1. The modulation parameters are related to the type of light source and the coupling between the light source and the first optical fiber 1; θ c S is the maximum emission angle of the first optical fiber 1; S is the core area of ​​the second optical fiber 2; x, y, z are the transverse coordinates and axial distances on the end face of the second optical fiber 2, respectively; x, y are the transverse coordinates of the end face of the second optical fiber, and z is the axial distance between the two optical fibers.

[0082] From the above formula, it can be seen that the intensity of light incident on the second optical fiber 2 is related to its core area. When there is no relative positional deviation between the first optical fiber 1 and the second optical fiber 2, the coupling loss is minimal, and the light intensity entering the second optical fiber 2 from the first optical fiber 1 is maximum. As the interaxial deviation between the first optical fiber 1 and the second optical fiber 2 increases, the light intensity entering the second optical fiber 2 decreases accordingly. Figure 4 As shown.

[0083] The second optical fiber 2 is a dual-core optical fiber, so the light intensity received by its two cores has opposite trends. Subtracting the light intensity received by the two optical fiber cores can double the sensitivity of the system detection.

[0084] To enhance the local magnetic field strength, a magnetic collecting ring 10 is also included, which is sleeved on the outside of the permanent magnet alloy layer 7. Its function is as follows:

[0085] ① Concentrate the dispersed magnetic field into a specific area to increase the strength and concentration of the magnetic field.

[0086] ② The magnetic ring 10 can guide the direction of the magnetic field lines, making the magnetic circuit smoother and more controllable.

[0087] ③ It can shield and confine the magnetic field, reduce the leakage of the magnetic field into the surrounding environment, and also avoid interference from external magnetic fields to the sensor, thereby improving the sensor's anti-interference ability.

[0088] The working principle of this invention is as follows:

[0089] Magnetic field induction and fiber optic vibration:

[0090] When the ground leakage current of ADSS optical cable 11 generates an alternating magnetic field, the permanent magnet alloy layer 7 at the end of the second optical fiber 2 is subjected to the magnetic force and generates a slight vibration.

[0091] The magnetic dipole inside the permanent magnet alloy layer 7 (such as nickel-iron alloy or aluminum-nickel-cobalt alloy) is subjected to Lorentz force in the magnetic field, causing the permanent magnet alloy layer 7 to move along the direction of the magnetic field, which in turn drives one end of the second optical fiber 2 coated with the permanent magnet alloy layer 7 to vibrate.

[0092] This vibration alters the micron-level interaxial misalignment between the first optical fiber 1 and the second optical fiber 2.

[0093] Light intensity control:

[0094] The light source enters from one end of the first optical fiber 1, and the optical signal is transmitted to the second optical fiber 2 through the first optical fiber 1.

[0095] As the interaxial misalignment between the first optical fiber 1 and the second optical fiber 2 changes, the coupling loss between the optical fibers also changes accordingly.

[0096] Changes in coupling loss lead to changes in light intensity, and these changes are converted into light intensity modulation signals through the exponential relationship of coupling loss.

[0097] Light intensity detection and ratio demodulation:

[0098] The two cores of the second optical fiber 2 are respectively aligned with two independent PIN receivers 8, which convert the received optical signals into electrical signals.

[0099] The hardware ratior calculates the ratio of the two photocurrents in real time, eliminating the influence of common-mode drift, thereby accurately measuring the change in light intensity.

[0100] Structural stability:

[0101] The U-shaped channel body 3 is made of quartz glass, which has a low coefficient of expansion (10). -7 (on a scale of magnitude) to ensure the stability of the structure when the temperature changes.

[0102] The U-shaped channel body 3 is mounted on a rigid metal or ceramic chassis with a high elastic modulus, further enhancing the stability of the structure.

[0103] This invention has high sensitivity:

[0104] By varying the interaxial misalignment at the micrometer level, the coupling loss between optical fibers can sensitively reflect changes in the magnetic field, thereby enabling highly sensitive detection of leakage current.

[0105] The vibration of the second optical fiber 2 can precisely modulate the light intensity, enabling the light intensity detection device to detect minute changes in the magnetic field.

[0106] This invention achieves high-precision measurement:

[0107] The light intensity detection device adopts a dual-channel ratio demodulation structure. Through two PIN receivers 8 and a hardware ratioor, it can calculate the ratio of the two photocurrents in real time, eliminate the influence of common-mode drift, and improve measurement accuracy.

[0108] The use of hardware ratiors can effectively reduce the impact of environmental interference and system noise on measurement results.

[0109] The invention has a stable structure:

[0110] The U-shaped groove body 3 is made of quartz glass, which has a low coefficient of expansion and can resist the effects of temperature changes, ensuring the long-term stability of the sensor.

[0111] The use of a rigid chassis further enhances the stability of the structure, enabling the sensor to function normally even in complex environments.

[0112] This invention has strong anti-interference capabilities:

[0113] Ratio demodulation technology can effectively eliminate common-mode interference caused by changes in light source intensity and fiber loss, thereby improving the system's anti-interference capability.

[0114] The hardware ratior design makes the system highly tolerant of environmental noise and power fluctuations.

[0115] Non-contact measurement:

[0116] The sensor indirectly measures leakage current by detecting changes in the magnetic field, eliminating the need for direct contact with the ADSS optical cable 11, thus avoiding physical damage to the cable and improving measurement safety.

[0117] Non-contact measurement methods allow sensors to be installed in areas where direct contact is inconvenient, increasing application flexibility.

[0118] This invention has real-time monitoring capabilities:

[0119] The sensor can monitor the leakage current changes of ADSS optical cable 11 in real time, promptly detect potential safety hazards, and provide a guarantee for the safe operation of the power system.

[0120] Real-time monitoring enables the system to respond quickly to changes in leakage current and take timely measures to reduce the probability of failure.

[0121] This invention achieves highly sensitive and accurate measurement of leakage current in ADSS optical cable 11 through ingenious structural design and advanced light intensity detection technology. Its strong structural stability and high anti-interference capability make it suitable for long-term monitoring in complex environments, providing strong technical support for the safe operation of power systems.

Claims

1. A fiber optic leakage current sensor based on fiber intensity modulation type ADSS optical cable, characterized in that: It includes a first optical fiber, a second optical fiber, a U-shaped groove body, and a light intensity detection device; A U-shaped groove 1 is formed on the U-shaped groove body. A U-shaped groove 2 and a U-shaped groove 3 are formed on the left and right sides of the U-shaped groove 1, respectively. Both U-shaped groove 2 and U-shaped groove 3 are connected to U-shaped groove 1. There is a micron-level misalignment between the central axes of U-shaped groove 2 and U-shaped groove 3. A first optical fiber and a second optical fiber are installed in U-shaped groove 2 and U-shaped groove 3, respectively. There is a micron-level misalignment between the central axes of the first optical fiber and the second optical fiber. The first optical fiber is fixed. A permanent magnet alloy layer is plated on the end of the second optical fiber near the first optical fiber. The end of the second optical fiber with the permanent magnet alloy layer is suspended and extends into U-shaped groove 1, so that the end of the second optical fiber with the permanent magnet alloy layer vibrates slightly in the magnetic field. The unplated end of the second optical fiber is fixed. The light intensity detection device adopts a dual-channel ratio demodulation structure, including two PIN receivers and a hardware ratio converter. The second optical fiber is a dual-core optical fiber, with each core aligned with one of the two independent PIN receivers. The light source enters the first optical fiber from one end, and the first optical fiber transmits the optical signal to the second optical fiber. The second optical fiber then transmits the optical signal to the two independent PIN receivers. The PIN receivers convert the optical signal into an electrical signal, and the back-end uses the hardware ratio converter to calculate the ratio of the two photocurrents in real time and output the result to eliminate common-mode drift.

2. The fiber optic leakage current sensor based on fiber intensity modulation type ADSS optical cable according to claim 1, characterized in that: The U-shaped groove body is integrally mounted on a rigid metal or ceramic chassis, and the chassis material has a high elastic modulus.

3. The fiber optic leakage current sensor based on fiber intensity modulation type ADSS optical cable according to claim 1, characterized in that: The U-shaped groove body is made of quartz glass. The first U-shaped groove is located in the middle of the U-shaped groove body. The second and third U-shaped grooves, which have a micron-level misalignment of the central axis, are integrally processed on the quartz glass.

4. The fiber optic leakage current sensor based on fiber intensity modulation type ADSS optical cable according to claim 2, characterized in that: It also includes a magnetic collecting ring, which is sleeved on the outside of one end of the second optical fiber coated with a permanent magnet alloy layer and indirectly fixed by the rigid chassis.

5. The fiber optic leakage current sensor based on fiber intensity modulation type ADSS optical cable according to claim 1, characterized in that: The permanent magnet alloy layer is a nickel-iron alloy or an aluminum-nickel-cobalt alloy.

6. The fiber optic leakage current sensor based on fiber intensity modulation type ADSS optical cable according to claim 1, characterized in that: The extension length of the second optical fiber is 1-2 mm.

7. The fiber optic leakage current sensor based on fiber intensity modulation type ADSS optical cable according to claim 1, characterized in that: When the grounding leakage current of the ADSS optical cable generates an alternating magnetic field, the magnetic dipole inside the permanent magnet alloy layer in the magnetic field will be subjected to the magnetic force, causing it to be subjected to the Lorentz force. This causes the permanent magnet alloy layer to move along the direction of the magnetic field, which in turn causes one end of the second optical fiber coated with the permanent magnet alloy layer to vibrate slightly. This changes the micron-level interaxial misalignment between the first and second optical fibers. The change in the relative position of the first and second optical fibers causes a change in the coupling loss between the optical fibers. The displacement is converted into an optical intensity modulation signal through the exponential change of the coupling loss, thereby modulating the optical intensity. The formula for calculating the Lorentz force on the magnetic dipole within the permanent magnet alloy layer is as follows: Where F is the Lorentz force on the magnetic dipole within the permanent magnet alloy layer, and q is the charge of the charged particle. It is the particle's velocity. It is the alternating magnetic induction intensity generated by the leakage current; The vibration displacement at one end of the second optical fiber coated with the permanent magnet alloy layer after being subjected to the Lorentz force is as follows: Δx=k·F·L 3 / (E·I) Where Δx is the vibration displacement generated at one end of the second optical fiber coated with a permanent magnet alloy layer, k is the structurally related proportionality coefficient, L is the cantilever length of the second optical fiber, E is the elastic modulus of the permanent magnet alloy layer, and I is the moment of inertia of the cross section. The modulation function of the light intensity modulation signal is: I out =I o ·exp(-α·(Δx) 2 ) Among them, I out It is the output light intensity of the second optical fiber, I o α is the initial coupled light intensity, and α is the fiber coupling attenuation coefficient.

8. The fiber optic leakage current sensor based on fiber intensity modulation type ADSS optical cable according to claim 1, characterized in that: The light intensity detection device achieves current measurement by detecting the change in coupling efficiency corresponding to the axis offset of the first and second optical fibers, as detailed below: The light intensity ratio is: I1 and I2 are the received light intensities of the second fiber optic dual core, respectively. Coupling efficiency: I in It is the input light intensity of the first fiber, I out It is the total light intensity output from the second optical fiber; Leakage current: β is the system calibration coefficient. It is the rate of change of coupling efficiency.

9. A fiber optic leakage current sensor based on fiber intensity modulation type ADSS optical cable according to claim 3, characterized in that: The coefficient of thermal expansion of the U-shaped grooves two and three of the quartz glass is 10. -7 Magnitude.

10. A fiber optic leakage current sensor based on fiber intensity modulation type ADSS optical cable according to claim 1, characterized in that: The light intensity received by the second optical fiber is expressed as follows: In the formula, I0 is the light intensity coupled from the light source into the first optical fiber, σ is a parameter characterizing the refractive index distribution of the optical fiber, a0 is the core radius of the first optical fiber, and ζ is a modulation parameter related to the type of light source and the coupling between the light source and the first optical fiber; θ c The maximum emission angle of the first optical fiber is S; the core area of ​​the second optical fiber is S; x, y, z are the transverse coordinates and axial distances on the end face of the second optical fiber, respectively; x and y are the transverse coordinates on the end face of the second optical fiber, and z is the axial distance between the two optical fibers. From the above formula, we can see that the intensity of light incident on the second fiber is related to its core area. When there is no relative positional deviation between the first and second fibers, the coupling loss is minimal and the intensity of light entering the second fiber from the first fiber is maximum. As the interaxial deviation between the first and second fibers increases, the intensity of light entering the second fiber decreases accordingly.

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