A valve-side outlet device electric field measurement system for a flexible polarization-maintaining optical fiber

Abstract

The present application relates to the technical field of spatial electric field measurement, and discloses a valve-side outlet device electric field measurement system introduced by flexible polarization maintaining optical fiber, which comprises: a flexible polarization maintaining optical fiber, which introduces external detection laser into the interior of the valve-side outlet device; an integrated exit head, which converts the detection laser introduced by the flexible polarization maintaining optical fiber from linearly polarized light into circularly polarized light, and the circularly polarized light vertically penetrates the oil passage; the insulating oil in the oil passage produces Kerr effect under the action of the spatial electric field of the valve-side outlet device, so that the two orthogonal polarization components parallel and perpendicular to the spatial electric field direction in the circularly polarized light produce phase delay; a plane mirror, which reflects the circularly polarized light passing through the oil passage and then outputs the circularly polarized light from the quartz observation window on the lower end side wall of the valve-side outlet device; and a photoelectric detection receiving unit, which receives the output light beam of the quartz observation window, and measures the spatial electric field of the valve-side outlet device according to the two orthogonal polarization components with phase delay in the output light beam, so as to improve the electric field measurement precision.

Description

Technical Field

[0001] This invention relates to the field of space electric field measurement technology, and in particular to an electric field measurement system for a valve-side output device using a flexible polarization-maintaining optical fiber. Background Technology

[0002] As a key hub in high-voltage direct current (HVDC) transmission systems, the valve-side outgoing line unit of a converter transformer is a crucial component with a highly compact and complex insulation structure, dense distribution of high and low potentials, and relatively concentrated electric field stress. Real-time, in-situ, multi-point measurements of the actual electric field distribution characteristics within its intricate internal oil channels are of significant engineering application value and scientific importance for verifying the insulation design margin of ultra-high-voltage equipment, assessing the insulation condition during long-term operation, and assisting in the analysis of fault mechanisms such as dielectric breakdown.

[0003] Currently, there are two main measurement schemes for the spatial electric field distribution of the valve-side output device of the converter transformer: Interventional internal space electric field measurement technology based on metallic electrical sensing probes aims to directly obtain the actual spatial electric field distribution at a specific location within an insulating medium. This technology employs a miniature field strength probe as the spatial sensing unit. This probe inevitably includes metal plates, a metal casing, or conductive leads. When this probe, containing these metallic materials, is implanted into the complex oil gap environment of ultra-high voltage AC / DC superposition, the high conductivity of the metal conductor itself severely disrupts and distorts the original spatial electric field distribution of the measured area, posing insulation safety hazards to high-voltage electrical equipment.

[0004] Electro-optical measurement technology employs an all-dielectric optical measurement architecture, utilizing the inherent birefringence of matter under an electric field as a sensing mechanism. In practical implementation, to balance high-voltage insulation safety and sensing accuracy, existing technologies typically use a hardware architecture combining optical fibers with independent electro-optical components. This additional, physically implanted independent electro-optical component inevitably distorts the original spatial electric field at the measurement point, posing insulation safety hazards to high-voltage electrical equipment. Summary of the Invention

[0005] The purpose of this invention is to provide an electric field measurement system for a valve-side output device using a flexible polarization-maintaining optical fiber, which can solve the problem of distortion and interference caused by the measurement device on the original electric field distribution, affecting the insulation safety of high-voltage electrical equipment.

[0006] To address the aforementioned technical problems, embodiments of the present invention provide an electric field measurement system for a valve-side output device using a flexible polarization-maintaining optical fiber, comprising: a flexible polarization-maintaining optical fiber, an integrated emitter head disposed on the side wall of an insulating cardboard plate at the edge of the oil passage within the valve-side output device, a plane mirror disposed at the bottom of the valve-side output device, and a photoelectric detection unit disposed outside the valve-side output device; wherein, one end of the flexible polarization-maintaining optical fiber is connected to the integrated emitter head, and the other end is connected to an external light source; Flexible polarization-maintaining optical fiber is used to introduce external probe lasers into the valve-side output device. The light-emitting surface of the integrated emitter head faces the oil channel below, which is used to convert the probe laser introduced by the flexible polarization-maintaining fiber from linearly polarized light into circularly polarized light, and make the circularly polarized light penetrate the oil channel perpendicularly; wherein, the insulating oil in the oil channel generates the Kerr effect under the action of the spatial electric field of the valve side outlet device, causing the two orthogonal polarization components in the circularly polarized light that are parallel to the spatial electric field direction and perpendicular to the spatial electric field direction to produce a phase delay. The plane mirror is located directly below the output light path of the integrated output head. It is used to reflect the circularly polarized light passing through the oil passage so that it can be output from the quartz observation window on the lower side wall of the valve side output device. The photoelectric detection and receiving unit faces the quartz observation window of the valve-side output device to receive the output beam from the quartz observation window. Based on the two orthogonal polarization components with phase delay in the output beam, it measures the spatial electric field of the valve-side output device. Furthermore, the valve-side outlet device has multiple oil channels of different levels, the integrated outlet head has multiple corresponding types, and the flexible polarization-maintaining optical fiber has multiple optical fiber branches. The system also includes a flange plate fixed to the housing of the valve-side outlet device, and the flange plate contains multiple optical fiber physical interfaces. The output pigtail of the external light source is selectively connected to the beginning of the fiber optic branch through a physical fiber optic interface to measure the spatial electric field of the oil channel.

[0007] Furthermore, the outer ring of the flange disc is evenly distributed with multiple mounting bolt holes, so as to fix it to the valve side outlet device housing through the multiple mounting bolt holes; The multiple fiber optic physical interfaces are evenly distributed on the inner ring of the flange disc, and all adopt a high-pressure oil-proof sealing through-hole design.

[0008] Furthermore, each of the integrated ejector heads is fixed to the insulating cardboard sidewall of the corresponding level of the oil passage edge within the valve-side cable outlet device; Each of the optical fiber branches is made of germanium-doped quartz glass, an insulating optical material, and is coated with an oil-resistant insulating coating.

[0009] Furthermore, the integrated output head includes an optical fiber collimator, a polarizer, and a quarter-wave plate; Fiber optic collimators are used to shape the probe laser into a parallel, narrow beam with a diameter within a preset range; The transmission axis of the polarizer and the fast axis of the quarter-wave plate are fixed at a spatial angle of 45°, which is used to modulate the parallel narrow beam into circularly polarized light with two orthogonal polarization components having corresponding phase delays.

[0010] Furthermore, the substrate of the planar reflector is made of polytetrafluoroethylene material, and its surface is coated with a high-reflectivity all-dielectric polarization-maintaining film corresponding to the working wavelength of the external light source.

[0011] Furthermore, both the external light source and the photoelectric detection and receiving unit are located in a low-potential safety area outside the valve-side outgoing device.

[0012] Furthermore, the planar reflector is fixed to a support tray at the bottom of the valve-side outlet device.

[0013] Furthermore, the photoelectric detection and receiving unit is connected to an external light source to spatially separate the output beam into two orthogonally linearly polarized beams with mutually perpendicular polarization directions, and to convert the orthogonally linearly polarized beams into two light intensity voltages containing information on the strength of the DC electric field. The two light intensity voltages are sampled several times at high frequency, and the mathematical variance of the light intensity voltages sampled at high frequency is calculated in real time. The random fluctuations and dispersion of light intensity voltage are assessed based on mathematical variance to determine whether the quality of light intensity voltage meets the standard; if the mathematical variance exceeds the preset confidence level safety threshold, the quality of light intensity voltage is determined to be substandard. If the quality of the light intensity voltage does not meet the standard, the electrical gain of the transimpedance amplifier inside the photoelectric detection and receiving unit is adjusted, and a control command is issued to the external light source. Within the preset safe physical threshold range, the output light power of the external light source is adjusted until the mathematical variance of the light intensity voltage tends to converge smoothly, so as to measure the spatial electric field of the valve side output device through the corresponding output beam.

[0014] Furthermore, the photoelectric detection and receiving unit is used to normalize the two beams of orthogonally linearly polarized light, establish an analytical relationship between the spatial electric field and the output intensity of the orthogonally linearly polarized light based on the optical transfer function constructed by the Jones matrix, and solve for the absolute amplitude and direction angle of the spatial electric field according to the analytical relationship.

[0015] The electric field measurement system for the valve-side output device introduced by the flexible polarization-maintaining optical fiber provided by the present invention has at least the following beneficial effects: This invention utilizes the naturally continuous insulating oil channel inside the valve-side outlet device of a converter transformer as the primary sensing medium. When circularly polarized light penetrates this oil channel, which is under strong DC electric field polarization, the orthogonal polarization components parallel to and perpendicular to the electric field direction will produce a refractive index difference, causing a phase delay between the two orthogonal polarization components. Therefore, the light beam that ultimately penetrates the oil channel carries real spatial electric field information, thereby realizing the spatial electric field measurement of the converter transformer valve-side outlet device. This sensing process relies entirely on the pure oil channel, without introducing any metal parts or independent electro-optical elements, truly achieving lossless sensing and modulation of the native DC electric field, and avoiding equipment insulation safety hazards caused by spatial electric field distortion.

[0016] Furthermore, the probe laser is introduced into the device through flexible polarization-maintaining fiber. Utilizing its flexible physical characteristics, the fiber can shuttle and run along the insulating support inside the device, flexibly bypassing complex high-voltage metal leads, and extending and accurately delivering to different depth measurement points in the core insulating area. At the same time, the strong inherent stress birefringence of the flexible polarization-maintaining fiber can force the probe beam to propagate along a specific polarization axis, thereby effectively suppressing the random depolarization and signal crosstalk effects caused by long-distance mechanical winding bending and electromechanical vibration, further improving the accuracy of space electric field measurement.

[0017] In addition, considering that the DC space electric field lines inside the converter transformer are complex and their direction is difficult to predict, this invention converts the probe beam into circularly polarized light through an integrated emitter head. The introduction of this circularly polarized light gives the system good spatial isotropy in cross-section, successfully avoiding the optical measurement blind zone caused by the deflection of the unknown electric field direction, and can effectively ensure the accuracy of space electric field measurement. Attached Figure Description

[0018] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this invention, illustrate exemplary embodiments of the invention and are used to explain the invention, but do not constitute an undue limitation of the invention. In the drawings:

[0019] Figure 1 A schematic diagram of the structure of an electric field measurement system for a valve-side output device using a flexible polarization-maintaining optical fiber, provided by the present invention. Figure 2 A schematic diagram illustrating the positional relationship between an integrated ejector head and an oil passage provided by the present invention; Figure 3 A schematic diagram of the structure of a flange disc provided by the present invention; Figure 4 This is a schematic diagram of the structure of a photoelectric detection and receiving unit provided by the present invention; Figure 5This invention provides a schematic diagram of the spatial electric field measurement process for a converter transformer valve-side output device. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with specific embodiments and corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0021] In recent years, with the in-depth development of ultra-high voltage direct current (UHVDC) transmission technology, fiber optic sensing technology, due to its inherent advantages such as intrinsic safety, excellent electrical insulation performance, good anti-electromagnetic interference capability, small size, and extremely flexible wiring, is being increasingly widely introduced into complex engineering environments with high voltage, strong magnetic fields, and confined spaces. Distributed fiber optic sensing technology has made a breakthrough by utilizing the physical characteristics of sensing optical fibers, which integrate sensing and transmission. This not only effectively eliminates the risk of foreign object discharge caused by traditional metallic electrical sensors, but also enables long-distance, large-scale networking and blind-spot-free continuous monitoring. It can perceive and acquire the spatial distribution and dynamic changes of physical parameters at every point along the fiber optic transmission path with high fidelity.

[0022] Currently, in the field of multi-physical parameter monitoring within transformers, distributed fiber optic sensing technology has achieved extremely rich research results and a solid foundation for engineering applications. Specifically, in the spatial monitoring of temperature fields, one approach discloses a time-domain and frequency-domain reflection technique based on fiber backscattering, as well as a fiber optic grating sensor that deeply integrates optical multiplexing technology. This technique can overcome the complex electromagnetic environment inside transformers and has been maturely applied to accurately map and acquire real-time temperature distribution patterns inside transformer windings and narrow oil channels. In the measurement of mechanical vibration and acoustic parameters, in addition to the widespread use of Rayleigh backscattering-based sensing technology, various high-sensitivity interferometric sensing structures have been developed in depth. For example, one approach discloses a Mach-Zehnder-Sagnak hybrid interferometric distributed fiber optic vibration sensing technology, which combines advantages such as high stability, wide frequency response range, good versatility, simple structure, and extremely convenient deployment. It can generate highly sensitive interferometric responses to weak sound waves and strain signals.

[0023] Given the all-dielectric properties, excellent electrical insulation performance, and superior flexible signal transmission capabilities exhibited by distributed optical fiber sensing technology in monitoring multiple physical parameters such as temperature and vibration, related fields have begun to explore its application in the spatial electric field measurement of high-voltage insulating oil. In complex high-electric-field measurement systems, optical fiber is not only a passive device but also a crucial optical signal transmission carrier and waveguide medium. Leveraging its extremely small geometric size and arbitrarily bendable physical properties, optical fiber can freely traverse and cross the extremely complex oil-paper composite insulation barrier inside converter transformers, precisely and safely guiding the probe beam emitted by the light source system located on the external low-potential side to the core sensing area deep within the high-voltage region with extremely low loss. After completing the electric field sensing, the optical fiber can stably transmit the weak signal light carrying local electric field information back to the external photoelectric receiving unit for decoding and inversion calculations. This transmission mode based on a purely optical medium completely isolates the ultra-high-voltage end and the low-voltage control end in physical space, greatly improving the insulation safety margin of the monitoring system.

[0024] Based on the above analysis, if the low-loss flexible guiding capability and spatial addressing advantage of optical fiber in transmitting optical signals, as well as its ability to penetrate narrow and hidden areas, can be organically combined with the secondary electro-optic effect of transformer oil in response to high-voltage electric fields, it is expected to provide a new and effective means for the existing insulation diagnosis system, thereby overcoming the limitation of the internal insulation structure of the UHV valve side outlet device on the blocking of the measured polarized light.

[0025] Currently, there are three main representative monitoring and measurement technologies for the internal insulation status and spatial electric field distribution of large oil-filled electrical equipment such as converter transformers: The first type is traditional macroscopic monitoring technology based on port electrical parameters and partial discharge. This type of solution mainly relies on existing ports or flange interfaces of electrical equipment to extract high-frequency signals of partial discharge, thereby achieving macroscopic monitoring of the overall operating status of the electrical equipment. For example, one solution discloses a transformer partial discharge detection device based on a built-in UHF sensor. This solution fixes the sensor inside the transformer tank through a flange interface, thereby receiving the overall discharge electromagnetic wave signal inside the transformer at a fixed access point. Another solution discloses a transformer UHF partial discharge detection device, which directly uses the transformer's original external electrical port as a UHF sensor to lead the UHF electromagnetic wave signal to the outside for detection, avoiding the implantation of additional physical probes. Although this type of technology can effectively capture partial discharge electromagnetic waves caused by insulation degradation, it is essentially still a macroscopic state assessment based on port signals, and it is difficult to directly and accurately reflect the true distribution of the electric field inside the equipment.

[0026] The second existing technology is an interventional internal space electric field measurement technology based on a metallic electrical sensing probe. To directly obtain the actual spatial electric field distribution at a specific location within the insulating medium, this type of solution uses a miniature field strength probe as the spatial sensing unit. For example, one solution discloses an interference optimization method and system for internal electric field probes, which details how a measuring device containing a sensing probe is physically implanted into the casing of ultra-high voltage GIS equipment using customized mechanical fasteners for direct measurement. However, this type of interventional metallic probe technology has inherent limitations: due to the direct introduction of the metallic material and fasteners, it inevitably distorts and interferes with the original extremely strong enclosed electric field inside the equipment, which can easily lead to a shift in probe measurement sensitivity and may seriously threaten the insulation safety of the high-voltage equipment itself.

[0027] The third approach is based on electro-optical effect optical measurement technology. This approach employs an all-dielectric optical measurement architecture, utilizing the inherent birefringence of matter under an electric field as a sensing mechanism. In practical implementation, to balance high-voltage insulation safety and sensing accuracy, existing technologies typically use a hardware architecture combining optical fibers and independent electro-optical components. However, the sensing medium and internal optical path design mainly exhibit two typical forms. An earlier approach, such as one that discloses a system for measuring electrical parameters using an optical converter, specifically describes a hardware implementation where an input optical fiber guides a beam emitted from an external laser to an independent solid-state optical effect element located within the measurement area. After the beam undergoes a polarization state change due to local electric field modulation, it is then directly transmitted back to the receiving end via another output optical fiber. Building upon this, another approach discloses an integrated electric field measurement probe combining optical fiber guidance technology and the Kerr effect. This approach uses a transmission optical fiber to guide the measurement beam to an integrated probe unit placed inside a liquid dielectric, and uses non-metallic materials as the overall structural support to reduce the alteration of the measured electric field introduced by the physical probe.

[0028] 1) Traditional macroscopic monitoring technologies have low sensitivity and cannot identify early fault characteristics. They can only detect accompanying electromagnetic waves or acoustic signals after the internal insulation of the equipment has deteriorated or partial discharge has occurred. This method can only reflect the overall macroscopic operating status of the equipment and cannot obtain the three-dimensional electric field distribution inside the high-voltage equipment, thus failing to provide early warning of insulation hazards.

[0029] 2) The shortcoming of interventional electrical probe measurement technology lies in the fact that its probes inevitably contain metal plates, metal shells, or conductive leads. When these metal probes are implanted into the complex oil gap environment of ultra-high voltage AC and DC superposition, on the one hand, the high conductivity of the metal conductor itself will seriously disrupt and distort the original spatial electric field distribution of the measured area (such as the probe intervention interference in the above scheme); on the other hand, the suspended metal parts are very likely to become discharge burrs under extremely high field strength, causing serious partial discharge or even overall insulation breakdown, posing a safety hazard to the equipment.

[0030] 3) While optical measurement technology based on the electro-optic effect solves the problem of physical obstruction of straight optical paths in space by utilizing fiber optic transmission, it still faces insurmountable practical engineering measurement problems in UHV converter valves when applied to valve-side outgoing devices with complex internal structures. Because independent sensing elements with a certain physical volume must be implanted at the measurement point, these additional physical probes are difficult to penetrate and install in the narrow, complex oil channels formed by the interlacing of high-density insulating components (such as insulating paper tubes, support strips, etc.), resulting in measurement blind zones still existing in critical areas with high field strength. Furthermore, although the dielectric constant of the materials used in the probe equipment disclosed in the above schemes is close to that of insulating oil, under actual operating conditions, the outgoing device experiences complex voltage and current superimposed with DC pulsations, and the conductivity of the insulating oil is also dynamically affected by this complex operating condition. These additional independent sensing elements, after physical implantation, inevitably cause distortion of the original spatial electric field at the measurement point, introducing additional insulation safety hazards to UHV electrical equipment.

[0031] To address the technical problems of electric field distortion and insulation safety hazards easily caused by existing interventional measurement technologies, this invention aims to provide a spatial electric field optical measurement system based on a combination of flexible optical fiber and insulating reflector. Flexible polarization-maintaining optical fiber is used for optical signal transmission, enabling flexible wiring to resist electromagnetic interference and effectively avoiding complex physical obstructions within electrical equipment. Simultaneously, no metal components or external independent solid-state sensing crystals are introduced into the measurement area; the inherent Kerr effect of transformer insulating oil is directly used as the sensing medium. This system can achieve high-resolution measurement of the internal spatial electric field while avoiding distortion interference to the original electric field distribution caused by the measuring device, thereby effectively ensuring the insulation safety of ultra-high voltage electrical equipment.

[0032] The technical solutions provided by the various embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0033] One embodiment of the present invention relates to an electric field measurement system for a valve-side output device using a flexible polarization-maintaining optical fiber. The specific structure of this embodiment's electric field measurement system using a flexible polarization-maintaining optical fiber for the valve-side output device can be as follows: Figures 1 to 3As shown, it includes: a flexible polarization-maintaining optical fiber 1, an integrated emitter 2 located on the side wall of the insulating cardboard at the edge of the oil passage inside the valve-side output device, a plane reflector 3 located at the bottom inside the valve-side output device, and a photoelectric detection unit 4 located outside the valve-side output device; wherein, one end of the flexible polarization-maintaining optical fiber is connected to the integrated emitter, and the other end is connected to an external light source 5. Flexible polarization-maintaining optical fiber is used to introduce external probe lasers into the valve-side output device. The light-emitting surface of the integrated emitter head faces the oil channel below, which is used to convert the probe laser introduced by the flexible polarization-maintaining fiber from linearly polarized light into circularly polarized light, and make the circularly polarized light penetrate the oil channel perpendicularly; wherein, the insulating oil in the oil channel generates the Kerr effect under the action of the spatial electric field of the valve side outlet device, causing the two orthogonal polarization components in the circularly polarized light that are parallel to the spatial electric field direction and perpendicular to the spatial electric field direction to produce a phase delay. The plane mirror is located directly below the output light path of the integrated output head. It is used to reflect the circularly polarized light passing through the oil passage so that it can be output from the quartz observation window on the lower side wall of the valve side output device. The photoelectric detection receiving unit faces the quartz observation window of the valve-side outlet device to receive the output beam of the quartz observation window and measure the spatial electric field of the valve-side outlet device based on the two orthogonal polarization components with phase delay in the output beam.

[0034] The following is a detailed description of the implementation details of the electric field measurement system of the valve-side output device introduced by the flexible polarization-maintaining optical fiber in this embodiment. The following content is only for the convenience of understanding and is not necessary for implementing this solution.

[0035] First, it should be noted that the electric field measurement system of this embodiment can realize the electric field measurement of any large oil-filled electrical equipment, such as the valve side output device of a converter transformer.

[0036] In practice, both the external light source and the photoelectric detection and receiving unit are located in a low-potential safety area outside the high-voltage electrical equipment. The external light source incorporates a highly stable semiconductor laser, capable of outputting continuous detection laser light of a specific wavelength. The photoelectric detection and receiving unit is primarily used to receive and demodulate the reflected light signal carrying electric field information after it has undergone spatial transmission.

[0037] In one example, the valve-side outlet device has multiple oil passages 6 at different levels, for example... Figure 2 The first oil passage 61 and the second oil passage 62 shown correspond to multiple integrated ejector heads, for example... Figure 2 The first integrated emitter 21 and the second integrated emitter 22 are shown. At the same time, the flexible polarization-maintaining fiber also includes multiple fiber branches.

[0038] The operation of the electric field measurement system of the valve-side output device introduced by the flexible polarization-maintaining optical fiber in this embodiment relies not only on the above-mentioned components, but also on the original structure of the converter transformer valve-side output device, such as the external metal shell and the quartz observation window on the lower side wall.

[0039] Specifically, the electric field measurement system of this embodiment also includes a flange 7 fixed to the housing of the valve-side outlet device, and the flange 71 includes multiple optical fiber physical interfaces. The output pigtail of the external light source is selectively connected to the beginning of the optical fiber branch through the optical fiber physical interface to selectively measure the spatial electric field of the oil passage.

[0040] Among them, such as Figure 3 As shown, the flange is mounted on the upper part of the valve-side output device, serving as a passive junction for the internal and external optical paths of the space electric field measurement. Multiple mounting bolt holes 72 are evenly distributed on the outer ring of the flange, allowing the entire flange tray to be securely and sealingly fastened to the external metal housing of the valve-side output device. The inner ring of the flange compactly incorporates multiple smaller, independent fiber optic physical interfaces. These fiber optic physical interfaces all employ a high-pressure, leak-proof, oil-sealed through-hole design, providing a low-loss optical signal connection channel while ensuring the oil and gas tightness of the device body.

[0041] The flexible polarization-maintaining optical fiber consists of multiple independent fiber branches inside the valve-side output device. These branches are made of insulating optical materials such as germanium-doped quartz glass and are coated with an oil-resistant insulating coating. The input ends of these internal fiber branches are anchored internally to the back of different fiber physical interfaces on the flange tray. Utilizing their flexible physical characteristics, the optical fibers can shuttle and run along the insulating support inside the equipment, flexibly bypassing complex high-voltage metal leads, and extending and precisely delivering to different depth measurement points (i.e., arbitrary oil channels) in the core insulating area.

[0042] In one specific embodiment, for a detection wavelength of 638nm, commercially available panda-type flexible polarization-maintaining fiber can be selected in actual engineering to effectively adapt to the polarization-maintaining transmission requirements of the detection laser.

[0043] The first and second integrated emitters are respectively fixed on the sidewalls of the oil-paper composite insulating cardboard at the edges of different levels of the oil channels within the valve-side output device, and are respectively connected to different fiber branches of the flexible polarization-maintaining fiber. Each integrated emitter contains a fiber collimator, a polarizer, and a quarter-wave plate, which are sequentially and compactly encapsulated inside. To obtain high-purity circularly polarized light, the spatial electric field measurement system of this embodiment strictly controls the assembly angle of the optical components. The collimator shapes the diverging beam emitted from the fiber end face into a parallel narrow beam with a diameter within a preset range (e.g., 1 mm to 5 mm), and the transmission axis of the polarizer and the fast axis of the quarter-wave plate are fixed at a 45° spatial angle to modulate the parallel narrow beam into circularly polarized light with corresponding phase delays between the two orthogonal polarization components.

[0044] The first and second oil channels are the original pure liquid insulating oil channels inside the valve-side output device. The first oil channel is directly opposite the light-emitting surface of the first integrated emitter head, and the second oil channel is directly opposite the light-emitting surface of the second integrated emitter head.

[0045] The bottom planar reflector is fixed to a support tray at the bottom of the valve-side outlet device, located below the vertical outgoing light path of the first and second oil channels. The substrate of the planar reflector is made of polytetrafluoroethylene (PTFE), a high-molecular insulating material with good compatibility with the insulating oil of the valve-side outlet device and excellent electrical properties. Its surface is coated with a high-reflectivity, all-dielectric polarization-maintaining film for the operating wavelength. This structural design effectively avoids the risk of partial discharge caused by traditional metal reflectors or metal films under high voltage and strong electric fields, while ensuring high optical reflection efficiency and polarization state maintenance.

[0046] Specifically, the photoelectric detection and receiving unit is a dual-channel photoelectric detection and receiving unit, such as... Figure 4 The non-polarized beam splitting and dual-path orthogonal detection architecture shown is designed to simultaneously decouple the intensity and direction of the electric field. The measurement beam carrying Kerr effect information, reflected from the interior, first enters a non-polarized beam splitting prism (NPBS) 41, which splits the beam into transmission and reflection paths at a 1:1 intensity ratio, while strictly maintaining the polarization state of the beam. The transmission path contains a first analyzer 42 with a transmission axis fixed at -45° and a photodetector 43; the reflection path (second branch) contains a second analyzer 44 with a transmission axis fixed at 0° and a photodetector 45. The two detectors convert the optical signals into electrical signals, which are then sent to a multi-channel lock-in amplifier 46. By jointly calculating the polarization components in two independent dimensions, independent measurements of the electric field vector amplitude and direction can be achieved.

[0047] In the actual measurement process of this embodiment, the operator manually connects the output fiber of the external light source to the corresponding external physical interface on the flange tray according to the target insulation area (first oil channel or second oil channel) to be measured, thereby realizing the electric field measurement of different measurement channels. For example, the 638nm laser is introduced through the selected flexible polarization-maintaining fiber branch, emitted by the corresponding integrated emitter and converted into circularly polarized light. This polarized light penetrates the corresponding oil channel perpendicularly. Under the action of the DC electric field, the insulating oil undergoes the Kerr effect, and a small phase delay is generated between the orthogonal polarization components of the beam. Subsequently, the beam hits the polytetrafluoroethylene bottom plane reflector at the bottom and is laterally deflected, smoothly passing through the observation window of the lower side wall and entering the photoelectric detection and receiving unit for signal evaluation and demodulation, so as to infer the true three-dimensional absolute electric field of the oil channel at that location. When it is necessary to measure another oil channel, the operator only needs to manually switch the external laser source to another corresponding interface on the flange tray.

[0048] Figure 5 A schematic flowchart of a method for measuring the multi-layer spatial electric field inside a valve-side outlet device using the spatial electric field measurement system of this embodiment is provided. The spatial electric field measurement method involved in this embodiment mainly covers core processes such as optical path gating and optical sensing, signal closed-loop evaluation and demodulation inversion, including measurement channel selection 501, polarization state modulation 502, optical path oil gap sensing 503, internal optical path folding and emission 504, photoelectric reception and signal evaluation 505, adjustment of laser power and detection gain 506, normalized signal demodulation and inversion 507, switching of flange tray fiber optic interface 508, and finally generating an oil channel electric field distribution map 509.

[0049] During the selection of the measurement channel, based on the on-site insulation health diagnosis requirements of the valve-side outgoing line device, the testers first manually identified the target measurement point of the current valve-side outgoing line, such as locking the observation target point to the first oil passage in the high potential gradient region. Then, the optical fiber output end of the external light source was physically inserted and tightly locked to the corresponding external optical physical interface at the upper flange tray of the valve-side outgoing line device. After ensuring the safe closure of the physical optical path, the testers controlled the external light source to output a high-purity continuous probe laser with a wavelength stabilized at 638 nanometers. This optical path selection mechanism endows a single core optoelectronic measurement and control instrument with the ability to perform multi-node, full-domain monitoring of massive high-voltage equipment. After successfully crossing the physical interface and entering the system, the laser steadily propagates along the flexible polarization-maintaining fiber deep into the valve-side outgoing line device. The extremely strong inherent stress birefringence characteristics of the polarization-maintaining fiber force the probe light wave to propagate along a specific polarization axis, thereby effectively suppressing the random depolarization and signal crosstalk effects caused by long-distance mechanical winding bending and electromechanical vibration.

[0050] After the laser beam is successfully introduced into the internal target region, the system immediately enters the polarization modulation stage. The original divergent beam emitted from the end of the flexible polarization-maintaining fiber smoothly enters the first integrated output head fixed on the insulating cardboard. The beam is first shaped into a collimated parallel beam with a low divergence angle by the built-in micro collimating lens. Subsequently, this parallel beam passes through a combination of a polarizer and a quarter-wave plate, whose transmission axis and fast axis are strictly fixed at a 45-degree spatial angle by the process. Through the forced physical modulation of this optical component, the two orthogonal components of the linearly polarized light are precisely introduced with a fixed phase delay difference, thereby accurately converting it into standard circularly polarized light in which the electric vector rotates uniformly in space. Considering the complex distribution and unpredictable direction of the DC spatial electric field lines inside the valve-side output device, the introduction of circularly polarized light endows the sensing system with good spatial isotropy in the cross-section, successfully avoiding the optical measurement blind zone caused by the deflection of the unknown electric field direction.

[0051] After completing the aforementioned polarization modulation, the light beam formally enters the core optical path gap sensing process. Circularly polarized light is emitted perpendicularly from the end face of the first integrated emitter, penetrating the valve-side outlet pure liquid insulating oil channel (i.e., the first oil channel). Under the continuous polarization effect of the strong DC spatial electric field inside the valve-side outlet device, the isotropic insulating oil molecules undergo microscopic dipole orientation, thus exhibiting optical birefringence characteristics similar to a uniaxial crystal on a macroscopic scale. This measurement stage cleverly utilizes the naturally continuous insulating oil channel inside the outlet device as the primary sensing medium. When circularly polarized light penetrates this oil gap under strong DC electric field polarization, its orthogonal polarization components parallel and perpendicular to the electric field direction experience a slight difference in refractive index. Relying on the effective accumulation of this free-space optical path, this originally weak phase difference is physically amplified in spatial distance, ultimately producing a macroscopically measurable phase delay physical quantity that is strictly proportional to the square of the DC electric field intensity. The light beam thus becomes elliptically polarized light carrying information about the true electric field amplitude. This sensing process relies entirely on the pure oil gap, without introducing any solid electrodes or external sensing crystals, thus truly achieving lossless sensing and modulation of the native DC electric field.

[0052] After undergoing long-path physical sensing, the light beam follows a predetermined optical path, undergoing internal optical path reflection and emission. This elliptically polarized light, carrying an electric field signal, precisely strikes the surface of a planar reflector located on the bottom support tray directly below the optical path after passing through the oil channel. At this point, a lateral optical path reversal occurs, and the beam then smoothly and straightens through a quartz glass observation window pre-installed on the lower side wall of the output device, safely exiting into a low-potential safe area for testing personnel. This bottom reflector design not only effectively guides the signal light path but also prevents the freely traveling beam from directly illuminating the physical structure at the bottom of the transformer due to uncontrolled divergence or slight deflection, thus avoiding unintended dissipation of the optical signal.

[0053] After the beam is safely emitted outside the equipment, the system enters the photoelectric reception and signal evaluation process. The emitted beam enters the photoelectric detection and receiving unit, first passing through its internally integrated polarization beam splitter. Utilizing the principle of polarization beam splitting, it is spatially separated into two orthogonally linearly polarized beams with mutually perpendicular polarization directions. These beams are then converted into two initial light intensity voltage signals containing information about the strength of the DC electric field by a high-frequency photodetector with highly matched parameters. Considering the unavoidable presence of oil thermal convection, tiny suspended particles, and random disturbances in the optical path caused by weak vibrations of the transformer body within the internal oil channels, the system control microprocessor does not rely on single snapshot sampling. Instead, it performs hundreds or thousands of uninterrupted high-frequency samples of these two original voltage signals within a very short observation window, and calculates the mathematical variance or standard deviation sequence of these multiple sampled voltage values ​​in real time. The system uses this mathematical variance to objectively assess the degree of random fluctuation and dispersion of the currently received light intensity, using this as the core data criterion for determining whether the current optical signal quality meets the standards.

[0054] If the signal variance calculated by the underlying algorithm exceeds the preset confidence level safety threshold, the system determines that the current optical signal quality is substandard. The control logic will then automatically enter the step of adjusting the laser power and detection gain along the feedback link. The microprocessor will first moderately increase the electrical gain of the transimpedance amplifier inside the detection receiver unit to improve the amplitude response of the weak electrical signal. More importantly, the system simultaneously sends a control command to the remote external light source module through the feedback control line, actively and steadily increasing the output optical power of the 638 nm continuous laser within the safe physical threshold allowed by nonlinear optical effects. The substantial increase in optical power can bring a higher spatial photon flux density, forcibly penetrating the transformer insulating oil channel where particle scattering may occur, reducing the adverse effects of oil turbidity on the attenuation of the effective optical signal. After completing the dual dynamic adjustment of external optical power and electrical gain, since the physical optical path is continuously operating, the physically enhanced detection beam will continue to undergo the sensing and emission process. The control logic will then automatically return to the photoelectric reception and signal variance evaluation stage, repeating this cycle until the variance of multiple high-frequency samples tends to converge smoothly.

[0055] Once the signal quality assessment confirms compliance and the variance has fully converged, the system formally enters the normalized signal demodulation and inversion stage. For the DC-level signal acquired by the dual channels and modulated by the polarization beam splitter intensity, in this stage, the system establishes a rigorous analytical relationship between the two-dimensional spatial electric field vector and the dual-channel optical output intensity based on the dual-path optical transfer function derived from Jones matrix theory.

[0056] Specifically, the angle between the polarizer and the horizontal reference axis is set to... The angle between the fast and slow axes of the quarter-wave plate is Under the reference state without an electric field, the output reference light intensity of the analyzer is calibrated as follows: The high-voltage DC electric field (amplitude) at the actual valve side outlet. The unknown direction angle is Under the action of ) the analyzer 1 (offset angle) The analyzer 2 outputs two Kerr effect-modulated light intensity components synchronously, denoted as follows: and The digital signal processing unit first calculates the normalized ratio factor. and To filter out long-path common-mode attenuation interference, the underlying software then calls the following set of electro-optic transfer nonlinear equations to simultaneously inversely derive the absolute amplitude of the two-dimensional electric field vector. and direction angle :

[0057] ; ; In the formula, This represents the pre-calibrated Kerr constant of the transformer insulating oil; This represents the effective optical equivalent path length through which the probe beam actually traverses a purely insulating oil gap under polarization. By simultaneously solving the above core algorithm model, the system can decouple and output the two-dimensional vector physical quantity of the absolute spatial electric field in real time and with high precision under complex transformer oil gap conditions with unknown electric field direction.

[0058] After the data inversion calculation at the current depth measurement point is successfully completed, the system's internal logic will assess whether all target oil channels have been traversed and measured. If not, the on-site testing personnel will perform the switch of the flange tray fiber optic interface according to the procedure. The operator manually and smoothly pulls the laser pigtail of the external light source module from the current physical interface and plugs it in and locks it to the specific fiber optic interface associated with the next insulation target measurement point. This simple physical switching action instantly triggers the peripheral measurement loop, and the system naturally returns to the initial measurement channel selection step, using the same set of high-precision external photoelectric instruments to carry out a new round of precise polarization modulation, sensing sampling, and inversion demodulation at the depth of the next layer of insulation of the transformer. After the operator has traversed and confirmed that all the predetermined multiple depth oil channels have been measured, the system exits the entire measurement loop and executes the final step of generating the oil channel electric field distribution map. The system's host computer processing software seamlessly stitches and performs high-order interpolation calculations on multiple sets of multi-dimensional spatial electric field inversion data extracted from the long oil channels at each level, ultimately automatically rendering a complete, three-dimensional, and intuitive equipotential line map of the DC electric field gradient distribution inside the outgoing line device. This visualized digital map, as a core diagnostic asset for assessing the health status of high-voltage insulation, is permanently stored and archived by the system. Subsequently, the testing personnel sequentially disconnected the power supply to each external instrument, safely and systematically concluding the entire high-precision multi-point distributed spatial electric field measurement task.

[0059] This invention designs an optical path folding structure using a flexible optical fiber and a bottom reflector. By utilizing the flexible optical fiber to bypass the complex internal insulation structure, the probe light is vertically introduced into the target oil channel. Combined with the reflector on the bottom support tray, the long-path transmitted beam is laterally folded and exited through the window. This structure overcomes the engineering challenge of the narrow internal space of the transformer, which makes the straight-through optical path susceptible to physical obstruction. It also reduces beam deflection caused by equipment vibration and improves the stability of the optical signal at the receiving end.

[0060] Simultaneously, a multi-point measurement selection mechanism with manual plug-and-play flange interfaces is proposed. Multiple polarization-maintaining fiber optic branches corresponding to different depth measurement points are arranged inside the equipment, and the interfaces are uniformly led to an external flange tray. During measurement, different fiber optic branches are connected by manually plugging and unplugging the light source pigtail externally. This mechanism effectively solves the problem of high cost in scanning and measuring the electric field of the multi-layer oil passage inside the UHV converter valve outlet device, enabling online monitoring of the electric field of the multi-layer oil passage inside the UHV converter valve outlet while controlling hardware costs.

[0061] Those skilled in the art will understand that the above embodiments are specific embodiments for implementing the present invention, and in practical applications, various changes in form and detail can be made without departing from the spirit and scope of the embodiments of the present invention. Any person skilled in the art can make various modifications and alterations without departing from the spirit and scope of the embodiments of the present invention; therefore, the scope of protection of the embodiments of the present invention should be determined by the scope defined in the claims.

Claims

1. An electric field measurement system for a valve-side output device using a flexible polarization-maintaining optical fiber, characterized in that, The system includes: a flexible polarization-maintaining optical fiber, an integrated emitter head disposed on the side wall of the insulating cardboard at the edge of the oil passage inside the valve-side output device, a plane reflector disposed at the bottom inside the valve-side output device, and a photoelectric detection unit disposed outside the valve-side output device; wherein, one end of the flexible polarization-maintaining optical fiber is connected to the integrated emitter head, and the other end is connected to an external light source. Flexible polarization-maintaining optical fiber is used to introduce external probe lasers into the valve-side output device. The light-emitting surface of the integrated emitter head faces the oil channel below, which is used to convert the probe laser introduced by the flexible polarization-maintaining fiber from linearly polarized light into circularly polarized light, and make the circularly polarized light penetrate the oil channel perpendicularly; wherein, the insulating oil in the oil channel generates the Kerr effect under the action of the spatial electric field of the valve side outlet device, causing the two orthogonal polarization components in the circularly polarized light that are parallel to the spatial electric field direction and perpendicular to the spatial electric field direction to produce a phase delay. The plane mirror is located directly below the output light path of the integrated output head. It is used to reflect the circularly polarized light passing through the oil passage so that it can be output from the quartz observation window on the lower side wall of the valve side output device. The photoelectric detection receiving unit faces the quartz observation window of the valve-side outlet device to receive the output beam of the quartz observation window and measure the spatial electric field of the valve-side outlet device based on the two orthogonal polarization components with phase delay in the output beam.

2. The electric field measurement system for the valve-side output device introduced by the flexible polarization-maintaining optical fiber according to claim 1, characterized in that, The valve-side outlet device has multiple oil channels of different levels, the integrated outlet head has multiple corresponding types, and the flexible polarization-maintaining optical fiber has multiple optical fiber branches. The system also includes a flange plate fixed to the housing of the valve-side outlet device, and the flange plate contains multiple optical fiber physical interfaces. The output pigtail of the external light source is selectively connected to the beginning of the fiber optic branch through a physical fiber optic interface to measure the spatial electric field of the oil channel.

3. The electric field measurement system for the valve-side output device introduced by the flexible polarization-maintaining optical fiber according to claim 2, characterized in that, The flange has multiple mounting bolt holes evenly distributed on its outer ring to be fixed to the valve side outlet device housing through the multiple mounting bolt holes. The multiple fiber optic physical interfaces are evenly distributed on the inner ring of the flange disc, and all adopt a high-pressure oil-proof sealing through-hole design.

4. The electric field measurement system for the valve-side output device introduced by the flexible polarization-maintaining optical fiber according to claim 2, characterized in that, Each of the integrated ejector heads is fixed to the insulating cardboard sidewall of the oil passage edge of the corresponding level within the valve-side outlet device; Each of the optical fiber branches is made of germanium-doped quartz glass, an insulating optical material, and is coated with an oil-resistant insulating coating.

5. The electric field measurement system for the valve-side output device introduced by the flexible polarization-maintaining optical fiber according to claim 1, characterized in that, The integrated output head includes an optical fiber collimator, a polarizer, and a quarter-wave plate. Fiber optic collimators are used to shape the probe laser into a parallel, narrow beam with a diameter within a preset range; The transmission axis of the polarizer and the fast axis of the quarter-wave plate are fixed at a spatial angle of 45°, which is used to modulate the parallel narrow beam into circularly polarized light with two orthogonal polarization components having corresponding phase delays.

6. The electric field measurement system for the valve-side output device introduced by the flexible polarization-maintaining optical fiber according to claim 1, characterized in that, The substrate of the planar reflector is made of polytetrafluoroethylene and the surface is coated with a high-reflectivity, all-dielectric polarization-maintaining film corresponding to the working wavelength of the external light source.

7. The electric field measurement system for the valve-side output device introduced by the flexible polarization-maintaining optical fiber according to claim 1, characterized in that, Both the external light source and the photoelectric detection and receiving unit are located in a low-potential safety area outside the valve-side outgoing device.

8. The electric field measurement system for the valve-side output device introduced by the flexible polarization-maintaining optical fiber according to claim 1, characterized in that, The planar reflector is fixed on the support tray at the bottom of the valve-side outlet device.

9. The electric field measurement system for the valve-side output device introduced by the flexible polarization-maintaining optical fiber according to claim 1, characterized in that, The photoelectric detection and receiving unit is connected to an external light source and is used to spatially separate the output beam into two orthogonally linearly polarized beams with mutually perpendicular polarization directions, and to convert the orthogonally linearly polarized beams into two light intensity voltages containing information on the strength of the DC electric field. The two light intensity voltages are sampled several times at high frequency, and the mathematical variance of the light intensity voltages sampled at high frequency is calculated in real time. The random fluctuations and dispersion of light intensity voltage are assessed based on mathematical variance to determine whether the quality of light intensity voltage meets the standard; if the mathematical variance exceeds the preset confidence level safety threshold, the quality of light intensity voltage is determined to be substandard. If the quality of the light intensity voltage does not meet the standard, the electrical gain of the transimpedance amplifier inside the photoelectric detection and receiving unit is adjusted, and a control command is issued to the external light source. Within the preset safe physical threshold range, the output light power of the external light source is adjusted until the mathematical variance of the light intensity voltage tends to converge smoothly, so as to measure the spatial electric field of the valve side output device through the corresponding output beam.

10. The electric field measurement system for the valve-side output device introduced by the flexible polarization-maintaining optical fiber according to claim 9, characterized in that, The photoelectric detection and receiving unit is used to normalize two beams of orthogonally linearly polarized light, establish an analytical relationship between the spatial electric field and the output intensity of the orthogonally linearly polarized light based on the optical transfer function constructed by the Jones matrix, and solve for the absolute amplitude and direction angle of the spatial electric field according to the analytical relationship.

Images