An ultrahigh voltage fiber-optic current transformer fiber-optic abnormality monitoring device and method

Abstract

This invention discloses a fiber optic anomaly monitoring device and method for ultra-high voltage fiber optic current transformers. The device includes a fiber optic sensing module, a diagnostic optical path input module, a diagnostic optical path output module, and a signal processing module. The diagnostic optical path input module injects diagnostic light with wavelengths distinct from the probe light into the delay loop of the fiber optic sensing module and monitors the optical power of the two orthogonally polarized components at the injection end to obtain the angle between the transmission axis of the polarizer and the main axis of the delay loop fiber. The diagnostic optical path output module receives the diagnostic light after passing through the delay loop, decomposes it into two orthogonally polarized components, monitors their optical power, and obtains the total output optical power and the angle between the transmission axis of the polarizer at the output end and the main axis of the delay loop fiber. The signal processing module establishes a mathematical model based on the Jones matrix method to solve the linear birefringence of the delay loop and locates the anomaly position of the delay loop using an OTDR. This allows for online monitoring of delay loop anomalies in the fiber optic current transformer without shutdown, simultaneously completing anomaly location and anomaly degree quantification.

Description

Technical Field

[0001] This invention belongs to the field of optical fiber sensing technology, and particularly relates to an optical fiber anomaly monitoring device and method for ultra-high voltage optical fiber current transformers. Background Technology

[0002] Fiber optic current transformers have been widely used in key scenarios such as UHVDC converter stations and new energy power plants due to their outstanding advantages such as strong anti-electromagnetic interference capability, high measurement accuracy, large dynamic range, no risk of magnetic saturation, and passive primary side.

[0003] As a key component in fiber optic current transformers, the fiber optic delay loop's internal fiber bending, twisting, and compression directly affect the transformer's measurement accuracy and operational reliability. Therefore, monitoring the fiber optic delay loop for anomalies is crucial for ensuring the transformer's normal operation. However, current technologies typically rely on manual offline disassembly and shutdown for anomaly monitoring. This method not only affects the transformer's normal operation but is also inefficient and cannot meet the requirements of long-term continuous operation in power grid and industrial applications.

[0004] Furthermore, existing technologies lack comprehensive diagnostic capabilities for abnormal states of fiber delay loops. On the one hand, it is difficult to determine whether there is an open circuit fault in the delay loop without shutting down the system. On the other hand, it is difficult to further determine whether there are potential abnormalities such as minor bending or twisting of the internal fiber when the delay loop is not open. Moreover, it is impossible to accurately locate the abnormal position. Summary of the Invention

[0005] To address the shortcomings of existing technologies in monitoring fiber optic anomalies in ultra-high voltage fiber optic current transformers, which requires offline disassembly and cannot fully diagnose delay loop anomalies, this invention provides a device and method for monitoring fiber optic anomalies in ultra-high voltage fiber optic current transformers.

[0006] In a first aspect, the present invention provides an optical fiber anomaly monitoring device for ultra-high voltage optical fiber current transformers, comprising: The fiber optic sensing module includes a light source A, a coupler A, a polarizer, a first 45° fusion splice, a phase modulator, a wavelength division multiplexer A, a delay loop, a wavelength division multiplexer B, a second 45° fusion splice, a λ / 4 waveplate, a current-carrying conductor, a sensing fiber, and a reflector. The probe light emitted by the light source A passes through the coupler A, polarizer, first 45° fusion splice, phase modulator, wavelength division multiplexer A, delay loop, wavelength division multiplexer B, second 45° fusion splice, λ / 4 waveplate, current-carrying conductor, and sensing fiber to the reflector and then returns along the original optical path, carrying current and phase information based on the Faraday effect. The diagnostic optical path input module includes a light source B, a collimating lens A, a polarizer A, a collimating lens B, an OTDR, a coupler B, a wavelength division multiplexer A, a polarization beam splitter B, a spatial optical power meter C, and a spatial optical power meter D. The light source B emits continuous laser light, which is converted from divergent light to parallel light after passing through the collimating lens A. The polarizer A converts the parallel light into parallel linearly polarized light, which then passes through the collimating lens B, the second port of the coupler B, and the wavelength division multiplexer A before entering the fiber optic current transformer. At the fourth port of the coupler B, it passes through the polarization beam splitter B and enters the spatial optical power meters C and D, respectively. The spatial optical power meters C and D are used to monitor the optical power of two orthogonal polarization components. The diagnostic optical path output module includes a wavelength division multiplexer B, a collimating lens C, a polarizer B, a collimating lens D, a polarization beam splitter A, a spatial optical power meter A, and a spatial optical power meter B. The wavelength division multiplexer B separates the light waves from the delay ring and converts them into parallel polarized light by the collimating lens C. The light output by the polarizer B is decomposed into two orthogonal polarization components by the polarization beam splitter A, which respectively enter the spatial optical power meter A and the spatial optical power meter B. The spatial optical power meter A and the spatial optical power meter B are used to monitor the optical power of the two orthogonal polarization components respectively. The signal processing module includes a photodetector, an information processing unit, and a phase modulator. The optical signal received by the photodetector is amplified, converted, and its information is read by the information processing unit. The information processing unit controls the phase modulator to apply phase modulation based on the information.

[0007] Furthermore, the coupler A is a 2×2 coupler with a coupling ratio of 50:50. The first port of the coupler A is the input port, and the second and third ports of the coupler A are the output ports. The optical power ratio of the two output ports is 50:50. The coupler B is a 2×2 coupler with a coupling ratio of 50:50. The first port of the coupler B is the input port, and the second and fourth ports of the coupler B are the output ports. The optical power ratio of the two output ports is 50:50.

[0008] Secondly, this invention provides a method for monitoring fiber optic anomalies in ultra-high voltage fiber optic current transformers, comprising the following steps: S1: The light emitted from light source A is split into two paths by coupler A. One path is converted into linearly polarized light by a polarizer, then passes through the first 45° fusion splice, phase modulator, wavelength division multiplexer A, delay loop, wavelength division multiplexer B, second 45° fusion splice, and λ / 4 waveplate, and is converted into circularly polarized light before entering the sensing fiber. It is subjected to the magnetic field of the current in the current-carrying conductor, which generates a Faraday phase shift. After being reflected by the mirror, it generates another Faraday phase shift and returns. The returned light is converted into linearly polarized light by the λ / 4 waveplate and returns to coupler A along the original path. The other path directly enters the photodetector for optical power monitoring. The returned light enters the photodetector through coupler A and is then processed by the signal processing unit for current calculation. S2: Light source B emits continuous laser light with wavelengths distinct from those of light source A. This light is converted into parallel light by collimating lens A, then into parallel linearly polarized light by polarizer A, and finally enters the delay loop via collimating lens B, coupler B, and wavelength division multiplexer A. Simultaneously, the light output from the fourth port of coupler B is decomposed into two orthogonal polarization components by polarization beam splitter B, which enter spatial optical power meter C and spatial optical power meter D, respectively. By dividing and converting the measurement results of spatial optical power meter C and spatial optical power meter D, the angle between the transmission axis of polarizer A and the main axis of the delay loop fiber is obtained. S3: The polarized light after passing through the delay loop is emitted from the second port of wavelength division multiplexer B, converted into parallel polarized light by collimating lens C, and then enters polarization beam splitter A after passing through polarizer B and collimating lens D. It is decomposed into two orthogonal polarization components, which are received by spatial optical power meter A and spatial optical power meter B respectively. The measurement results of spatial optical power meter A and spatial optical power meter B are summed to obtain output result I. The measurement results of spatial optical power meter A and spatial optical power meter B are divided to obtain the angle between the transmission axis of polarizer B and the main axis of delay loop fiber. S4: A mathematical model for the diagnostic optical path is established based on the Jones matrix method. The mathematical model takes the output optical power of the light source B, the output result I, the angle between the transmission axis of polarizer A and the main axis of the delay ring fiber, and the angle between the transmission axis of polarizer B and the main axis of the delay ring fiber as known quantities, and takes the linear birefringence of the delay ring caused by the abnormal state as the only unknown quantity. The linear birefringence information of the delay ring is obtained in real time by solving the mathematical model. S5: The laser pulse emitted by the OTDR enters the coupler B through the third port of the coupler B, and after being output through the second port of the coupler B, it passes through the wavelength division multiplexer A, the delay loop, the wavelength division multiplexer B, the second 45° fusion splice, the λ / 4 waveplate, and the sensing fiber to reach the reflector and is reflected back. The returned light returns to the OTDR along the original path. The OTDR calculates the distance from the abnormal change point of optical power to the OTDR based on the intensity of the reflected light signal, and generates an OTDR optical power attenuation trace, marking the abnormal time point and its location.

[0009] Furthermore, the light source A uses light with a wavelength of 1310nm, while the light source B and the OTDR use light with a wavelength of 1550nm. The wavelength division multiplexer A and the wavelength division multiplexer B are used to separate and recombine light of different wavelengths.

[0010] Furthermore, the method also includes a three-level judgment step for delay loop disconnection: When light source A and light source B are operating normally, and spatial optical power meter A, spatial optical power meter B and photodetector all detect optical power, it is determined that the delay loop is not open-circuited. When light source A and light source B are operating normally, if spatial optical power meter A, spatial optical power meter B and photodetector do not detect optical power, it is determined that the delay loop is open. When light source A and light source B are operating normally, if spatial optical power meter A and spatial optical power meter B detect optical power but photodetector does not detect optical power, it is determined that the delay loop is not open-circuited and there is an abnormality in the optical path of the fiber optic sensing module other than the delay loop.

[0011] Furthermore, in step S4, the linear birefringence of the delay ring is measured using the polarizer rotation method, specifically as follows: By adjusting the rotating base to make the transmission axes of polarizer A and polarizer B parallel to each other, and setting the reference angle α, the optical power received by spatial optical power meter A and spatial optical power meter B after being split by polarization beam splitter A is measured at positions where the angle between the transmission axes of polarizer A and polarizer B and the main axis of delay ring fiber is α, 4α and 8α, respectively, and three optical power measurement values ​​are obtained. Based on the three optical power measurements, a system of three equations is established, and the unique solution for linear birefringence is obtained by solving the system of equations.

[0012] Furthermore, after step S5, the method further includes: When an abnormal abrupt change occurs in the optical power attenuation trace of the OTDR, the abnormal position on the delay ring that is twisted, bent or squeezed is located based on the distance from the abnormal abrupt change to the OTDR. The calculated linear birefringence information is compared with a preset linear birefringence threshold. When the linear birefringence information exceeds the linear birefringence threshold, it is determined that the delay ring has abnormally bent and an alarm signal is output.

[0013] The fiber optic anomaly monitoring device and method for ultra-high voltage fiber optic current transformer disclosed in this application have the following beneficial effects: By integrating diagnostic optical input and output modules into the fiber optic current transformer, the transformer can be monitored online without being shut down or disassembled offline. The injection and extraction of diagnostic light are completed under normal operating conditions of the transformer, without affecting its normal current measurement function. This enables uninterrupted online monitoring of the fiber optic current transformer, improves monitoring efficiency, and ensures the continuous operation of the power system.

[0014] By setting up dual light sources with distinct wavelengths (light source A uses 1310nm, and light source B and OTDR use 1550nm), and using a wavelength division multiplexer to separate and recombine different wavelengths of light, the diagnostic optical path and the original sensing optical path of the current transformer can share the same delay ring and the same transmission fiber. This eliminates the need to lay a separate fiber for the diagnostic optical path, simplifying the device structure and reducing implementation costs.

[0015] In the diagnostic optical path input module, by setting a polarization beam splitter B and two spatial optical power meters at the fourth port of coupler B, the angle between the transmission axis of polarizer A and the main axis of the delay ring fiber can be monitored and calibrated in real time during the diagnostic optical injection stage. This provides accurate initial parameters for subsequent precise linear birefringence calculations and avoids measurement errors caused by uncertain initial angles.

[0016] In the diagnostic optical output module, by setting up a polarization beam splitter A and two spatial optical power meters after polarizer B, independent monitoring of the two orthogonal polarization components after passing through the delay loop is realized. The total output optical power and the angle between the transmission axis of polarizer B and the main axis of the delay loop fiber can be obtained simultaneously, providing a complete set of input parameters for the mathematical model based on the Jones matrix method.

[0017] By establishing a diagnostic optical path mathematical model based on the Jones matrix method, and solving for linear birefringence as the only unknown, accurate quantitative measurement of linear birefringence caused by fiber torsion, bending, and compression within the delay ring was achieved. Combined with the polarizer rotation method, a system of three equations was established through three optical power measurements at different angles, yielding a unique solution for linear birefringence and eliminating ambiguity due to multiple solutions.

[0018] By using OTDR based on the principle of optical backscattering, fault location of the delay ring can be achieved. When an abnormal abrupt change occurs in the optical power attenuation trace of the OTDR, the abnormal position on the delay ring can be accurately located according to the distance from the abrupt change to the OTDR, thus realizing the spatial location of the abnormal point.

[0019] By employing a three-level delay loop disconnection judgment mechanism, and utilizing the combined judgment of optical power monitoring results from spatial optical power meter A, spatial optical power meter B, and photodetector, the mechanism accurately distinguishes between three states: "delay loop not disconnected," "delay loop disconnected," and "disconnection of all optical fibers except the delay loop," providing clear direction for fault diagnosis.

[0020] By combining the linear birefringence calculation results with the OTDR positioning results, a complete diagnostic system of "anomaly location + anomaly severity quantification" is formed. The OTDR is responsible for discovering the anomaly location, while the polarization rotation method is responsible for quantifying the anomaly severity (bending radius). The two work together to enable maintenance personnel to know not only where the anomaly occurred but also how serious it is, providing a complete basis for subsequent maintenance decisions. Attached Figure Description

[0021] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is a schematic diagram illustrating the structural principle of an ultra-high voltage fiber optic current transformer fiber optic anomaly monitoring device according to the present invention.

[0023] Figure 1 The specific optical components and their designations are as follows: 1. Light source A; 2. Coupler A; 3. Polarizer; 4. First 45° fusion splice; 5. Phase modulator; 6. Light source B; 7. Collimating lens A; 8. Polarizer A; 9. Collimating lens B; 10. OTDR; 11. Coupler B; 12. Wavelength division multiplexer A; 13. Delay loop; 14. Wavelength division multiplexer B; 15. Collimating lens C; 16. Polarizer B; 17. Collimating lens D; 18. Polarization beam splitter A; 19. Second 45° fusion splice; 20. λ / 4 waveplate; 21. Current-carrying conductor; 22. Sensing fiber; 23. Mirror; 24. Photodetector; 25. Spatial optical power meter A; 26. Spatial optical power meter B; 27. Polarization beam splitter B; 28. Spatial optical power meter C; 29. ​​Spatial optical power meter D. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] like Figure 1As shown in the figure, an ultra-high voltage fiber optic current transformer fiber optic anomaly monitoring device provided by an embodiment of the present invention includes a fiber optic sensing module, a diagnostic optical path input module, a diagnostic optical path output module, and a signal processing module.

[0026] The fiber optic sensing module includes a light source A, a coupler A, a polarizer, a first 45° fusion splice, a phase modulator, a wavelength division multiplexer A, a delay loop, a wavelength division multiplexer B, a second 45° fusion splice, a λ / 4 waveplate, a current-carrying conductor, a sensing fiber, and a reflector. The probe light emitted by the light source A passes through the coupler A, polarizer, first 45° fusion splice, phase modulator, wavelength division multiplexer A, delay loop, wavelength division multiplexer B, second 45° fusion splice, λ / 4 waveplate, current-carrying conductor, and sensing fiber to the reflector and then returns along the original optical path, carrying current and phase information based on the Faraday effect. The diagnostic optical path input module includes a light source B, a collimating lens A, a polarizer A, a collimating lens B, an OTDR, a coupler B, a wavelength division multiplexer A, a polarization beam splitter B, a spatial optical power meter C, and a spatial optical power meter D. The light source B emits continuous laser light, which is converted from divergent light to parallel light after passing through the collimating lens A. The polarizer A converts the parallel light into parallel linearly polarized light, which then passes through the collimating lens B, the second port of the coupler B, and the wavelength division multiplexer A before entering the fiber optic current transformer. At the fourth port of the coupler B, it passes through the polarization beam splitter B and enters the spatial optical power meters C and D, respectively. The spatial optical power meters C and D are used to monitor the optical power of two orthogonal polarization components. The diagnostic optical path output module includes a wavelength division multiplexer B, a collimating lens C, a polarizer B, a collimating lens D, a polarization beam splitter A, a spatial optical power meter A, and a spatial optical power meter B. The wavelength division multiplexer B separates the light waves from the delay ring and converts them into parallel polarized light by the collimating lens C. The light output by the polarizer B is decomposed into two orthogonal polarization components by the polarization beam splitter A, which respectively enter the spatial optical power meter A and the spatial optical power meter B. The spatial optical power meter A and the spatial optical power meter B are used to monitor the optical power of the two orthogonal polarization components respectively. The signal processing module includes a photodetector, an information processing unit, and a phase modulator. The optical signal received by the photodetector is amplified, converted, and its information is read by the information processing unit. The information processing unit controls the phase modulator to apply phase modulation based on the information.

[0027] Specifically, the coupler A is a 2×2 coupler with a coupling ratio of 50:50. The first port of the coupler A is the input port, and the second and third ports of the coupler A are the output ports. The optical power ratio of the two output ports is 50:50. The coupler B is a 2×2 coupler with a coupling ratio of 50:50. The first port of the coupler B is the input port, and the second and fourth ports of the coupler B are the output ports. The optical power ratio of the two output ports is 50:50.

[0028] The present invention also provides a method for fiber optic anomaly monitoring using the above-mentioned device, comprising the following steps: Step S1: Normal optical path propagation steps of fiber optic current transformer.

[0029] Light emitted from light source A enters coupler A through the first port of coupler A. 50% of the light is transmitted to the polarizer through the second port of coupler A, and the other 50% of the light enters the photodetector through the first port of the photodetector through the third port of coupler A. The light signal is converted into a voltage signal and output from the second port of the photodetector. This voltage signal enters the signal processing unit for optical power monitoring.

[0030] As light travels from the first port of the polarizer to the second port, it becomes linearly polarized. This linearly polarized light exits from the second port of the polarizer, passes through the first 45° fusion point, enters the phase modulator from the first port, is modulated by the phase modulator, and exits from the second port. The output linearly polarized light enters from the first port of wavelength division multiplexer A, exits from the second port of wavelength division multiplexer A, passes through a delay loop, enters wavelength division multiplexer B from the first port, and exits from the second port of wavelength division multiplexer B.

[0031] Linearly polarized light output from the second port of wavelength division multiplexer B is transmitted to the second 45° fusion splice. Light output from the second 45° fusion splice enters the λ / 4 waveplate from the first port. When it exits from the second port of the λ / 4 waveplate, the linearly polarized light is converted into left-handed and right-handed circularly polarized light. The circularly polarized light enters the sensing fiber and is subjected to the magnetic field of the current in the current-carrying conductor, generating a Faraday phase shift F. The circularly polarized light carrying the Faraday phase shift F is transmitted to the reflector and reflected back to the sensing fiber, generating another Faraday phase shift F.

[0032] The circularly polarized light carrying the Faraday phase shift F is transmitted to the λ / 4 waveplate and becomes linearly polarized again. After passing through the second 45° fusion point, it enters the second port of the wavelength division multiplexer B and is output from the first port of the wavelength division multiplexer B. After passing through the delay loop, it enters the second port of the wavelength division multiplexer A and is output from the first port of the wavelength division multiplexer A.

[0033] Linearly polarized light output from the first port of wavelength division multiplexer A enters the phase modulator through the second port of the phase modulator, and again receives the modulation voltage applied to the third port of the phase modulator by the signal processing unit to generate a modulation phase. The linearly polarized light carrying the modulation phase is output from the first port of the phase modulator, passes through the first 45° fusion point, and is transmitted from the second port of the polarizer back to the first port of the polarizer.

[0034] The light output from the first port of the polarizer enters the coupler A from the second port of the coupler A. 50% of the light is output from the third port of the coupler A and enters the photodetector from the first port of the photodetector. The light signal is converted into a voltage signal and output from the second port of the photodetector to the signal processing unit for current calculation.

[0035] During the normal optical path propagation process described above, the probe light emitted by light source A carries a Faraday phase shift of 2 times after traveling back and forth along the optical path once. This phase shift is proportional to the magnitude of the current in the current-carrying conductor. The signal processing unit can calculate the measured current value by detecting this phase shift.

[0036] Step S2: Diagnostic optical path input step.

[0037] Light source B emits continuous laser light with wavelengths distinct from those of light source A. To avoid interference between the light emitted by light source B and light source A, light source A is selected to have a wavelength of 1310 nm, while light source B and the OTDR use light with a wavelength of 1550 nm. Through wavelength division multiplexers A and B, the two different wavelengths of light can be transmitted in the same optical fiber without interference—a wavelength division multiplexer can combine different wavelengths of light into the same optical fiber for transmission, or it can separate different wavelengths of light transmitted in the same optical fiber to different ports.

[0038] The continuous laser emitted from source B is converted from divergent light to parallel light by collimating lens A. The parallel light then passes through polarizer A to form parallel linearly polarized light, which is then coupled by collimating lens B into the first port of coupler B. After being split by coupler B, 50% of the optical signal is output from the second port of coupler B and enters the delay loop via wavelength division multiplexer A; the other 50% of the optical signal is output from the fourth port of coupler B and decomposed into two orthogonally polarized components by polarization beam splitter B, which then enter spatial optical power meters C and D, respectively.

[0039] Spatial optical power meters C and D measure the optical power of the two orthogonal polarization components respectively. By dividing and converting the two measurement results, the angle α0 between the transmission axis of polarizer A and the principal axis of the delay ring fiber can be obtained. This angle α0 serves as a known input parameter for the mathematical model in the subsequent step S4.

[0040] Step S3: Diagnostic optical path output steps.

[0041] The polarized light, after passing through the delay loop, exits from the second port of wavelength division multiplexer B. During transmission, this polarized light carries information about the linear birefringence caused by the torsion, bending, and compression of the delay loop.

[0042] The outgoing light is converted into parallel polarized light by collimating lens C, and then enters polarization beam splitter A after passing through polarizer B and collimating lens D. Polarization beam splitter A decomposes the input light into two orthogonally polarized components, which are received by spatial optical power meter A and spatial optical power meter B, respectively.

[0043] The total output optical power is obtained by adding the measurement results of spatial optical power meter A and spatial optical power meter B, and is denoted as the current calculation result. The value of the current calculation result is directly related to the magnitude of the linear birefringence of the delay ring—the larger the linear birefringence, the larger the phase difference between the two orthogonal polarization components, and the smaller the output optical power after interference by polarizer B.

[0044] The measurement results of spatial optical power meter A and spatial optical power meter B are divided and converted to obtain the angle β0 between the transmission axis of polarizer B and the principal axis of the delay loop fiber. This angle β0 is also used as a known input parameter for the mathematical model in the subsequent step S4.

[0045] Step S4: Solving the linear birefringence of the delay ring.

[0046] A mathematical model of the diagnostic optical path is established based on the Jones matrix method. The Jones matrix method is a mathematical method used to describe the propagation of polarized light in an optical system. By representing each optical device as a corresponding Jones matrix, and multiplying the Jones matrices of each device sequentially according to the light propagation path, the Jones matrix of the entire optical system is obtained, thereby establishing the mathematical relationship between the input polarization state and the output polarization state.

[0047] In this embodiment, the optical components of the diagnostic optical path include, in sequence: polarizer A, delay ring, and polarizer B. Polarizer A converts the input light into linearly polarized light, the delay ring introduces linear birefringence δ, and polarizer B performs polarization analysis on the output light. The Jones matrix of each component is represented as follows: The Jones matrix of polarizer A is The angle between its transmission axis and the main axis of the delay ring fiber is α0; The Jones matrix of the delay loop is The introduced linear birefringence is δ, which is generated by factors such as twisting, bending, and squeezing of the fiber inside the delay ring. It is the only unknown parameter in the diagnostic optical path mathematical model. The Jones matrix of polarizer B is The angle between its transmission axis and the main axis of the delay ring fiber is β0.

[0048] The total Jones matrix of the entire diagnostic optical path is The incident light becomes linearly polarized light after passing through polarizer A, and its Jones vector is... After passing through the delay ring and polarizer B, the Jones vector of the outgoing light is: .

[0049] The emitted light is decomposed into two orthogonally polarized components by polarization beam splitter A. Spatial optical power meters A and B measure the optical power of the two components respectively, and the sum of the two is the output result I. Therefore, the relationship between the current calculation result and the incident light power P0, the angle α0 between the transmission axis of polarizer A and the principal axis of the delay ring fiber, the angle β0 between the transmission axis of polarizer B and the principal axis of the delay ring fiber, and the linear birefringence δ is as follows: , Where f is a functional relationship derived using the Jones matrix method.

[0050] In this mathematical model, P0 is a known quantity (output optical power of light source B), α0 is a known quantity measured in step S2, and β0 is a known quantity measured in step S3. For the output result I measured in step S3, only the linear birefringence δ is the unique unknown. Therefore, by solving this mathematical model, the linear birefringence information of the retardation ring can be obtained in real time.

[0051] To further improve the accuracy of linear birefringence measurement and eliminate ambiguity, this embodiment employs a polarizer rotation method. Specifically, by adjusting the rotating base to make the transmission axes of polarizers A and B parallel to each other, and setting a reference angle α, the optical power received by spatial optical power meters A and B after beam splitting by polarizer A is measured at angles α, 4α, and 8α between the transmission axes of polarizers A and B and the principal axis of the delay loop fiber. Three optical power measurements, P1, P2, and P3, are recorded. The relationship between the three optical power measurements, the incident optical power P0, and the linear birefringence δ satisfies the following three equations: P1 = P0·cos²(2α+δ), P2 = P0·cos²(8α+δ), P3 = P0·cos²(16α+δ), Solving the three equations simultaneously yields a unique solution for the linear birefringence δ. By measuring at three different included angles, the potential for multiple solutions when solving a single equation is effectively eliminated, ensuring the uniqueness and accuracy of the linear birefringence measurement results.

[0052] Step S5: OTDR fault location steps.

[0053] The laser pulse emitted by the OTDR (Optical Time Domain Reflectometer) enters coupler B through the third port of coupler B, exits from the second port of coupler B, and then passes through wavelength division multiplexer A, delay loop, wavelength division multiplexer B, second 45° fusion splice, λ / 4 waveplate, and sensing fiber to reach the reflector. After being reflected by the reflector, it returns along the original path. The returned light again passes through the sensing fiber, λ / 4 waveplate, second 45° fusion splice, wavelength division multiplexer B, and delay loop, then enters wavelength division multiplexer A through the second port of wavelength division multiplexer A. After exiting from the first port of wavelength division multiplexer A, it enters coupler B through the second port of coupler B, and finally exits from the third port of coupler B back to the OTDR.

[0054] OTDR calculates the distance from the reflection point to the OTDR based on the intensity of the reflected light signal, using a built-in photoelectric conversion device and signal analysis system. The working principle of OTDR is based on backscattering and Fresnel reflection of light—when a light pulse propagates in an optical fiber, encountering defects in the fiber (such as break points, bends, abnormal fusion splices, etc.) will cause a sudden change in the intensity of backscattered light. OTDR can determine the location of the abnormal point by detecting this sudden change.

[0055] The OTDR generates an OTDR optical power attenuation trace and marks anomalous time points and their locations. The OTDR optical power attenuation trace is a curve with distance on the x-axis and backscattered optical power on the y-axis, reflecting the optical power loss at various points along the fiber length. When a twist, bend, or compression occurs at a certain location on the delay loop, the optical power loss at that location will increase significantly, appearing as an anomalous abrupt change in optical power on the OTDR optical power attenuation trace. The x-axis position corresponding to this abrupt change is the distance from the anomalous point to the OTDR.

[0056] The 1550nm wavelength light from the OTDR and the 1550nm wavelength light from source B have the same wavelength. They can share the same optical path in the device via time-division multiplexing—the OTDR emits pulsed light only during diagnostic testing, while source B operates during continuous light measurement. They operate in different time intervals and do not interfere with each other. Simultaneously, the 1550nm wavelength light from the OTDR and the 1310nm wavelength light from source A are separated and combined using wavelength division multiplexers A and B, without interfering with the normal operating optical path of the fiber optic current transformer.

[0057] Based on completing the above steps S1 to S5, this method also includes a three-level judgment step for delayed loop disconnection and an abnormal diagnosis output step.

[0058] The specific steps for determining the third level of delay loop disconnection are as follows: When light source A and light source B are operating normally, and spatial optical power meter A, spatial optical power meter B, and photodetector all detect optical power, it is determined that the delay loop is not broken and the complete optical path of the fiber optic sensing module remains unobstructed.

[0059] When light sources A and B are operating normally, if spatial optical power meter A, spatial optical power meter B, and the photodetector fail to detect optical power, it is determined that the delay loop is open. In this case, since the delay loop is a shared part of the fiber optic sensing module and the diagnostic optical path, an open delay loop will simultaneously interrupt the optical transmission of both the sensing and diagnostic optical paths, thus preventing any monitoring points from detecting optical power.

[0060] When light sources A and B are operating normally, if spatial optical power meters A and B detect optical power while the photodetector does not, it is determined that the delay loop is normal, and the problem lies with the remaining optical fibers in the fiber optic sensing module (excluding the delay loop) being broken. In this case, the diagnostic optical path can still pass through the delay loop and reach the diagnostic optical path output module, so spatial optical power meters A and B can still detect optical power; however, the sensing optical path cannot return to the photodetector due to the broken fibers in other parts, therefore the photodetector cannot detect optical power.

[0061] The specific steps for abnormal diagnosis output are as follows: When an abnormal abrupt change occurs in the optical power attenuation trace of the OTDR, the abnormal location on the delay ring that has been twisted, bent, or squeezed can be located based on the distance from the abnormal abrupt change to the OTDR.

[0062] The linear birefringence information obtained in step S4 is compared with the preset linear birefringence threshold. When the linear birefringence information exceeds the preset linear birefringence threshold, it is determined that the delay ring has abnormally bent and an alarm signal is output.

[0063] Through the above steps, this invention achieves comprehensive anomaly monitoring of the delay loop of the fiber optic current transformer—locating the anomaly position using an OTDR, quantifying the anomaly degree (the magnitude of linear birefringence) using the polarization rotation method, and distinguishing the type of circuit break by a three-level circuit breaker judgment, providing maintenance personnel with complete diagnostic information on "absence of anomaly → location of anomaly → degree of anomaly".

[0064] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A fiber optic anomaly monitoring device for ultra-high voltage fiber optic current transformers, characterized in that, include: The fiber optic sensing module includes a light source A (1), a coupler A (2), a polarizer (3), a first 45° fusion splice (4), a phase modulator (5), a wavelength division multiplexer A (12), a delay loop (13), a wavelength division multiplexer B (14), a second 45° fusion splice (19), a λ / 4 waveplate (20), a current-carrying conductor (21), a sensing fiber (22), and a reflector (23). The probe light emitted by the light source A (1) passes through the coupler A (2), the polarizer (3), the first 45° fusion splice (4), the phase modulator (5), the wavelength division multiplexer A (12), the delay loop (13), the wavelength division multiplexer B (14), the second 45° fusion splice (19), the λ / 4 waveplate (20), the current-carrying conductor (21), and the sensing fiber (22) to reach the reflector (23) and then returns along the original optical path, carrying current and phase information based on the Faraday effect. The diagnostic optical path input module includes a light source B (6), a collimating lens A (7), a polarizer A (8), a collimating lens B (9), an OTDR (10), a coupler B (11), a wavelength division multiplexer A (12), a polarization beam splitter B (27), a spatial optical power meter C (28), and a spatial optical power meter D (29). The light source B (6) emits continuous laser light, which is converted from divergent light to parallel light after passing through the collimating lens A (7). The polarizer A (8) is used to convert the parallel light into parallel linearly polarized light, which then passes through the collimating lens B (9), the second port of the coupler B (11), and the wavelength division multiplexer A (12) into the fiber optic current transformer. At the fourth port of the coupler B (11), it passes through the polarization beam splitter B (27) into the spatial optical power meter C (28) and the spatial optical power meter D (29). The spatial optical power meter C (28) and the spatial optical power meter D (29) are used to monitor the optical power of two orthogonal polarization components respectively. The diagnostic optical output module includes a wavelength division multiplexer B (14), a collimating lens C (15), a polarizer B (16), a collimating lens D (17), a polarization beam splitter A (18), a spatial optical power meter A (25), and a spatial optical power meter B (26). The wavelength division multiplexer B (14) separates the light waves from the delay ring (13) and converts them into parallel polarized light through the collimating lens C (15). The light output by the polarizer B (16) is decomposed into two orthogonal polarization components by the polarization beam splitter A (18), which enter the spatial optical power meter A (25) and the spatial optical power meter B (26) respectively. The spatial optical power meter A (25) and the spatial optical power meter B (26) are used to monitor the optical power of the two orthogonal polarization components respectively. The signal processing module includes a photodetector (24), an information processing unit, and a phase modulator (5). The optical signal received by the photodetector (24) is amplified, converted, and the information carried is read by the information processing unit. The information processing unit controls the phase modulator (5) to apply phase modulation according to the information.

2. The fiber optic anomaly monitoring device for ultra-high voltage fiber optic current transformers according to claim 1, characterized in that, The coupler A (2) is a 2×2 coupler with a coupling ratio of 50:

50. The first port of the coupler A (2) is the input port, and the second and third ports of the coupler A (2) are the output ports. The optical power ratio of the two output ports is 50:

50. The coupler B (11) is a 2×2 coupler with a coupling ratio of 50:

50. The first port of the coupler B (11) is the input port, and the second and fourth ports of the coupler B (11) are the output ports. The optical power ratio of the two output ports is 50:

50.

3. A method for monitoring fiber optic anomalies in ultra-high voltage fiber optic current transformers, characterized in that, Monitoring using the apparatus described in any one of claims 1-2 includes the following steps: S1: The light emitted by the light source A (1) is split into two paths by the coupler A (2). One path is converted into linearly polarized light by the polarizer (3), and then passes through the first 45° fusion splice (4), phase modulator (5), wavelength division multiplexer A (12), delay ring (13), wavelength division multiplexer B (14), second 45° fusion splice (19), and λ / 4 waveplate (20) to be converted into circularly polarized light and enters the sensing fiber (22). It is subjected to the magnetic field of the current on the current-carrying conductor (21) and generates a Faraday phase shift. After being reflected by the mirror (23), it generates a Faraday phase shift again and returns. The returned light is converted into linearly polarized light by the λ / 4 waveplate (20) and returns to the coupler A (2) along the original path. The other path directly enters the photodetector (24) for optical power monitoring. The returned light enters the photodetector (24) through the coupler A (2) and is then used by the signal processing unit for current calculation. S2: Light source B (6) emits continuous laser light with wavelengths distinct from those of light source A (1). This light is converted into parallel light by collimating lens A (7), then into parallel linearly polarized light by polarizer A (8), and finally enters delay ring (13) via collimating lens B (9), coupler B (11), and wavelength division multiplexer A (12). Simultaneously, the light output from the fourth port of coupler B (11) is decomposed into two orthogonal polarization components by polarization beam splitter B (27), which enter spatial optical power meter C (28) and spatial optical power meter D (29) respectively. By dividing and converting the measurement results of spatial optical power meter C (28) and spatial optical power meter D (29), the angle between the transmission axis of polarizer A (8) and the main axis of the fiber of delay ring (13) is obtained. S3: The polarized light passing through the delay ring (13) is emitted from the second port of the wavelength division multiplexer B (14), converted into parallel polarized light by the collimating lens C (15), and then enters the polarization beam splitter A (18) after passing through the polarizer B (16) and the collimating lens D (17) to be decomposed into two orthogonal polarization components, which are received by the spatial optical power meter A (25) and the spatial optical power meter B (26) respectively. The measurement results of the spatial optical power meter A (25) and the spatial optical power meter B (26) are summed to obtain the output result I. The measurement results of the spatial optical power meter A (25) and the spatial optical power meter B (26) are divided to obtain the angle between the transmission axis of the polarizer B (16) and the main axis of the fiber of the delay ring (13). S4: A mathematical model for the diagnostic optical path is established based on the Jones matrix method. The mathematical model takes the output optical power of the light source B (6), the output result I, the angle between the transmission axis of polarizer A (8) and the main axis of the delay ring (13) fiber, and the angle between the transmission axis of polarizer B (16) and the main axis of the delay ring (13) fiber as known quantities, and takes the linear birefringence of the delay ring (13) caused by the abnormal state as the only unknown quantity. The linear birefringence information of the delay ring (13) is obtained in real time by solving the mathematical model. S5: The laser pulse emitted by OTDR (10) enters coupler B (11) through the third port of coupler B (11), and after being output through the second port of coupler B (11), it passes through wavelength division multiplexer A (12), delay loop (13), wavelength division multiplexer B (14), second 45° fusion splice (19), λ / 4 waveplate (20), and sensing fiber (22) to reach mirror (23) and is reflected back. The returned light returns to OTDR (10) along the original path. OTDR (10) calculates the distance from the abnormal change point of optical power to OTDR based on the intensity of the reflected light signal, and generates OTDR optical power attenuation trace, marking the abnormal time point and its location.

4. The method for monitoring fiber optic anomalies in an ultra-high voltage fiber optic current transformer according to claim 3, characterized in that, The light source A (1) uses light with a wavelength of 1310nm, and the light source B (6) and the OTDR (10) use light with a wavelength of 1550nm. The wavelength division multiplexer A (12) and the wavelength division multiplexer B (14) realize the separation and recombination of light with different wavelengths.

5. The method for monitoring fiber optic anomalies in an ultra-high voltage fiber optic current transformer according to claim 3, characterized in that, The method also includes a three-level judgment step for delay loop disconnection: When light source A (1) and light source B (6) are working normally, and spatial optical power meter A (25), spatial optical power meter B (26) and photodetector (24) all detect optical power, it is determined that the delay loop (13) is not open circuit; When light source A (1) and light source B (6) are working normally, if space optical power meter A (25), space optical power meter B (26) and photodetector (24) do not detect optical power, it is determined that the delay loop (13) is open circuit. When light source A (1) and light source B (6) are working normally, if space optical power meter A (25) and space optical power meter B (26) detect optical power but photodetector (24) does not detect optical power, it is determined that the delay loop (13) is not open-circuited and there is an abnormality in the optical path of the fiber optic sensing module other than the delay loop (13).

6. The method for monitoring fiber optic anomalies in an ultra-high voltage fiber optic current transformer according to claim 3, characterized in that, In step S4, the linear birefringence of the delay ring (13) is measured using the polarizer rotation method, specifically as follows: By adjusting the rotating seat to make the transmission axes of polarizer A (8) and polarizer B (16) parallel to each other, and setting the reference angle α, the optical power received by spatial optical power meter A (25) and spatial optical power meter B (26) after beam splitting by polarizer A (18) is measured at positions where the angle between the transmission axes of polarizer A (8) and polarizer B (16) and the main axis of the delay ring (13) fiber is α, 4α and 8α, respectively, and three optical power measurement values ​​are obtained; Based on the three optical power measurements, a system of three equations is established, and the unique solution for linear birefringence is obtained by solving the system of equations.

7. The method for monitoring fiber optic anomalies in an ultra-high voltage fiber optic current transformer according to claim 3, characterized in that, Following step S5, the following is also included: When an abnormal abrupt change occurs in the optical power attenuation trace of the OTDR (10), the abnormal position of the delay ring (13) that is twisted, bent or squeezed is located according to the distance from the abnormal abrupt change to the OTDR (10). The calculated linear birefringence information is compared with the preset linear birefringence threshold. When the linear birefringence information exceeds the linear birefringence threshold, it is determined that the delay ring (13) has abnormally bent and an alarm signal is output.

Images