A transformer outgoing line device oil electric field measurement system based on a discrete optical path

Abstract

The application relates to the technical field of electric field measurement, and discloses a transformer outgoing device oil electric field measurement system based on a discrete light path, which comprises the following: a light source module arranged outside the device and a first reflector arranged opposite to the light source module and arranged directly above an oil channel in the device; a detection light beam emitted by the light source module is horizontally incident to the first reflector; the reflecting surface of the first reflector is at an angle of 45 degrees with the detection light beam; the detection light beam vertically penetrates through the oil channel after being reflected by the first reflector, thereby forming a measurement light beam carrying oil electric field information; the measurement light beam is reflected by a second reflector arranged directly below the oil channel to a photoelectric detection receiving unit arranged outside the device, thereby performing oil electric field measurement of the device; the light source module is fixed to a lifting platform; the light source module is driven by the lifting platform to move in the vertical direction; the detection light beam is reflected by different positions of the reflecting surface of the first reflector to different oil channels arranged in parallel in the vertical direction in the device, thereby performing electric field measurement of the different oil channels.

Description

Technical Field

[0001] This invention relates to the field of electric field measurement technology, and in particular to an oil electric field measurement system for transformer outlet devices based on discrete optical paths. Background Technology

[0002] Converter transformers are core equipment in high-voltage direct current (HVDC) transmission systems, and their operational reliability is crucial to the safety and stability of the entire power grid. Within the overall structure of a converter transformer, the valve-side outlet device plays a vital role in connecting the transformer body to the bushings, and is a key component with complex insulation structures and concentrated electric field stress. This device is filled with flowing transformer oil and houses high-voltage conductors and multiple layers of insulation barriers. Under actual operating conditions, it must simultaneously withstand the impact of combined voltages, including AC, DC, and polarity reversal voltages. Because the electrical characteristics of the transformer oil-paper composite insulation system are easily affected by temperature gradients, fluid flow rates, and operating time, especially under the influence of a DC electric field, the accumulation of space charge in the oil and interface polarization can lead to discrepancies between the actual electric field distribution and numerical simulation results based on ideal constants. This field distortion is often the root cause of partial discharge and even insulation breakdown. Therefore, overcoming the limitations of theoretical calculations and seeking a technical means to perform in-situ, real-time, and non-contact measurement of the electric field in the oil under the complex environment inside the valve-side outlet device has significant engineering value for verifying insulation design margins, analyzing fault mechanisms, and improving equipment manufacturing processes.

[0003] Currently, transmission measurement techniques based on the Kerr electro-optic effect have become the mainstream method for studying the electric field distribution characteristics of liquid dielectrics in laboratory environments. This scheme utilizes the Kerr effect inherent in transformer oil, inferring electric field information by observing the change in light intensity after the beam penetrates the entire electric field region. However, this conventional direct-through transmission measurement scheme, based on an ideal laboratory model, is mainly conducted in the laboratory, and its optical path design relies entirely on unobstructed open or regular spaces. The internal structure of the device on the valve side of the converter transformer is complex, with the structure consisting of insulating barriers, support bars, and metal shielding covers resulting in an extremely narrow permissible optical path. This high-density solid insulation layout often physically obstructs the straight optical path, creating a difficult-to-reach measurement blind zone. Simultaneously, the measurement beam must be precisely transmitted within the narrow insulating oil gap channel, placing extremely high demands on the collimation and stability of the optical path. In non-ideal engineering environments, even a small optical path offset or beam divergence can cause the laser beam to graze onto the insulating cardboard or metal surface, inducing severe interface diffuse reflection and stray light interference. This not only leads to a sharp decrease in the energy of the effective measurement spot and distortion of the polarization state, but also makes it difficult to build a robust measurement system under strong geometric constraints.

[0004] Therefore, directly applying the aforementioned transmission measurement technology based on the Kerr electro-optic effect to the actual valve-side output device of a converter transformer faces severe physical structural bottlenecks. Summary of the Invention

[0005] The purpose of this invention is to provide an oil electric field measurement system for transformer outlet devices based on discrete optical paths, which can solve the problem that existing transmission measurement technology based on Kerr electro-optic effect cannot be directly applied to the valve side outlet devices of real converter transformers for electric field measurement.

[0006] To address the aforementioned technical problems, embodiments of the present invention provide a transformer outgoing line device oil electric field measurement system based on discrete optical paths, comprising: An electro-optical measurement system located outside the device, and a first reflector and a second reflector located directly above and below multiple oil passages inside the device; wherein the electro-optical measurement system includes a lifting platform, a light source module, and a photoelectric detection and receiving unit; The light source module and the first reflector are positioned opposite each other. After the light source module emits a detection beam, the detection beam is incident horizontally on the first reflector. The reflector surface of the first reflector is at a 45° angle to the detection beam, so that the detection beam is reflected by the first reflector and passes vertically downward through the oil passage to form a measurement beam carrying the electric field information in the oil. The measurement beam is then reflected by the second reflector to the photoelectric detection receiving unit to measure the electric field in the oil of the device. The light source module is fixed on the lifting platform. The lifting platform drives the light source module to move in the vertical direction so that the detection beam is reflected by different positions of the reflector surface of the first reflector to different oil channels that are distributed in parallel in the vertical direction inside the device, so as to measure the electric field of different oil channels inside the device.

[0007] Furthermore, the photoelectric detection and receiving unit is positioned directly opposite the second reflector, with the reflective surface of the second reflector at a 45° angle to the measurement beam, so that the measurement beam is reflected by the second reflector and then incident horizontally onto the photoelectric detection and receiving unit.

[0008] Furthermore, flange interfaces are provided on the side wall of the device housing, opposite the light source module and the photoelectric detection and receiving unit. Each flange interface is provided with a circular optical observation window to allow the detection beam to enter and the measurement beam to exit, respectively.

[0009] Furthermore, a non-polarizing beam splitter is provided on the horizontal incident light path of the detection beam from the light source module to the first reflector, and the photoelectric detection receiving unit is located at the reflection port of the non-polarizing beam splitter. The second reflector is a retroreflector. After the measurement beam is reflected by the retroreflector, it undergoes a 180° reverse reflection and passes through the same oil channel again vertically upward along a path parallel to the detection beam passing through the oil channel. After being reflected by the first reflector, it exits from the device in a discrete free space optical path that is collinear with and opposite to the horizontal incident light path, and is reflected by a non-polarizing beam splitter to the photoelectric detection and receiving unit.

[0010] Furthermore, a flange interface is provided on the side wall of the device housing, directly opposite the light source module. A circular optical observation window is provided on the flange interface to allow the detection beam to enter and the measurement beam to exit.

[0011] Furthermore, the electro-optic measurement system is mounted on an attitude adaptive optics platform. The base of the attitude adaptive optics platform is equipped with an angle locking mechanism or a precision ball joint structure, which is used to drive the electro-optic measurement system to adjust the tilt angle so that the emission optical axis of the light source module of the electro-optic measurement system is parallel to the central axis of the device and perpendicular to the flange interface surface on the device that is directly opposite the light source module.

[0012] Furthermore, the light source module includes a helium-neon laser, a polarizer, and a quarter-wave plate; A helium-neon laser is used to emit a laser beam, while a polarizer and a quarter-wave plate are used together to shape the laser beam into circularly polarized light, which is then used as a probe beam.

[0013] Furthermore, the first and second reflectors are housed within the device, using an internal insulating barrier or support structure as a carrier.

[0014] Furthermore, the non-polarizing beam splitter splits the beam reflected back from the first mirror into two beams, a transmitted beam and a reflected beam, in a 1:1 ratio of light intensity, before they enter the photoelectric detection and receiving unit. The photoelectric detection and receiving unit detects the light intensity signals of the two beams in the transmitted and reflected light paths respectively through two analyzers with the transmission axes fixed at -45° and 0°. Based on the optical transfer function constructed by the Jones matrix theory, the amplitude and direction of the electric field are measured using the light intensity signals of the two beams.

[0015] Furthermore, the photoelectric detection and receiving unit, based on the optical transfer function, determines the correction coefficients for amplitude and direction according to the transmission coefficients of the optical devices in the entire measurement loop from emitting the detection beam to obtaining the measurement beam to the two orthogonal components in the measurement beam, as well as the initial phase delay introduced by the optical devices, and obtains the target amplitude and target direction of the electric field according to the determined correction coefficients.

[0016] The transformer outlet device oil electric field measurement system based on discrete optical path provided by the present invention has at least the following beneficial effects: By installing a liftable electro-optic measurement system outside the valve-side outlet device of the converter transformer, and pre-installing discrete reflectors (first and second reflectors) inside the device, the liftable electro-optic measurement system emits a probe beam that enters the device horizontally from the side. The beam is deflected by the discrete reflectors within the device, navigating the extremely narrow oil gap channel and bypassing all solid insulation obstructions, thus eliminating measurement blind spots. This overcomes the physical structural bottleneck of the converter transformer valve-side outlet device and directly incorporates transmission measurement technology based on the Kerr electro-optic effect, enabling electric field measurement of the device. The electro-optic measurement system, vertically displaced outside the device via a lifting platform, combined with the internal discrete reflectors, allows for automated switching and continuous scanning measurement of different oil channels. Attached Figure Description

[0017] 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:

[0018] Figure 1 A schematic diagram of the structure of an oil electric field measurement system based on a discrete optical path for transformer output devices provided by this invention. Figure 1 ; Figure 2 A schematic diagram of the structure of an oil electric field measurement system based on a discrete optical path for transformer output devices provided by this invention. Figure 2 ; Figure 3 A schematic diagram of the structure of an oil electric field measurement system based on a discrete optical path for transformer output devices provided by this invention. Figure 3 ; Figure 4 This is a schematic diagram of the structure of a photoelectric detection and receiving unit provided by the present invention; Figure 5 This is a flowchart illustrating a method for measuring the electric field in oil of a converter transformer valve-side outlet device, provided by the present invention. Detailed Implementation

[0019] 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.

[0020] The technical solutions provided by the various embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0021] One embodiment of the present invention relates to an oil electric field measurement system for a transformer outlet device based on a discrete optical path. The implementation details of the oil electric field measurement system for a transformer outlet device based on a discrete optical path in this embodiment are described in detail below. The following implementation details are provided for ease of understanding and are not necessary for implementing this solution.

[0022] The transformer outlet device oil electric field measurement system based on discrete optical path in this embodiment includes: an electro-optic measurement system located outside the device and a first reflector and a second reflector located directly above and below multiple oil channels inside the device; wherein, the electro-optic measurement system includes a lifting platform, a light source module, and a photoelectric detection and receiving unit; The light source module and the first reflector are positioned opposite each other. After the light source module emits a detection beam, the detection beam is incident horizontally on the first reflector. The reflector surface of the first reflector is at a 45° angle to the detection beam, so that the detection beam is reflected by the first reflector and passes vertically downward through the oil passage to form a measurement beam carrying the electric field information in the oil. The measurement beam is then reflected by the second reflector to the photoelectric detection receiving unit to measure the electric field in the oil of the device. The light source module is fixed on the lifting platform. The lifting platform drives the light source module to move in the vertical direction so that the detection beam is reflected by different positions of the reflector surface of the first reflector to different oil channels that are distributed in parallel in the vertical direction inside the device, so as to measure the electric field of different oil channels inside the device.

[0023] In some embodiments, the photoelectric detection and receiving unit is positioned opposite the second reflector, with the reflective surface of the second reflector at a 45° angle to the measurement beam, so that the measurement beam is reflected by the second reflector and then horizontally incident on the photoelectric detection and receiving unit. Flange interfaces are provided on the side wall of the device housing, opposite the light source module and the photoelectric detection and receiving unit. Each flange interface has a circular optical observation window to allow the detection beam to enter and the measurement beam to exit, respectively.

[0024] like Figure 1 The structure shown comprises a liftable external electro-optic measurement system 100, a valve-side output device 109, an optical observation window 106, and a first discrete reflector 107 and a second discrete reflector 108 working in close cooperation. The liftable external electro-optic measurement system is located outside the output device and internally includes a vertical precision lifting platform 101, a helium-neon laser 102, a polarizer 103, a quarter-wave plate 104, and a dual-channel photoelectric detection and receiving unit 105.

[0025] The entire optical transceiver system is mounted on a vertical precision lifting platform, which is fixed to a bracket on the outer wall of the output device. Driven by a stepper motor, it can move the laser and detector vertically in millimeter-level reciprocating motion. The core purpose of this design is to directly and precisely change the height of the incident laser beam through the physical lifting of an external system, thereby using it as a driving source to switch the internal measurement optical path.

[0026] To accommodate the vertical movement of the external system, the interface flange 106 installed on the side wall of the outgoing line device is specially designed. This flange features a circular optical observation window 106. The vertical length of the window covers the distribution range of all the internal insulating oil channels to be tested, ensuring that the probe beam from the vertically moving external system can pass through the transparent window and reflect into the first and second insulating oil channels 110 and 111 to be tested inside the device. Within the high-voltage oil immersion environment inside the outgoing line device, a first discrete reflector 107 and a second discrete reflector 108 are arranged, utilizing existing insulation barriers or support structures within the device as carriers. The two discrete reflectors 107 and 108 are arranged according to the location of the oil channels to be tested. The substrate of the reflectors is made of polytetrafluoroethylene (PTFE), an insulating material with good compatibility with transformer oil and excellent electrical properties. The surface is coated with a high-reflectivity, all-dielectric polarization-maintaining film for the operating wavelength, ensuring optical reflection efficiency while avoiding the discharge risk introduced by metallic materials.

[0027] In some embodiments, the electro-optic measurement system is mounted on an attitude adaptive optics platform. The base of the attitude adaptive optics platform is provided with an angle locking mechanism or a precision ball joint structure to drive the electro-optic measurement system to adjust the tilt angle so that the emission optical axis of the light source module of the electro-optic measurement system is parallel to the central axis of the device and perpendicular to the flange interface surface on the device that is directly opposite the light source module.

[0028] like Figure 2The structure shown addresses the oblique insertion installation structure commonly used in converter transformer valve-side outgoing line devices in practical engineering. This invention further provides an adaptive measurement implementation method with spatial attitude adjustment capabilities. Given the fixed process tilt angle between the outgoing line device body and the ground plane, traditional vertical or horizontal measurement platforms cannot meet the requirements of coaxial coupling of the optical axis. Therefore, this embodiment introduces a multi-degree-of-freedom attitude adjustment mechanism into the mechanical support structure of the external measurement system, constructing a measurement architecture with oblique incidence and coaxial return transmission. The external electro-optical measurement system is mounted on an attitude adaptive optics platform with pitch angle adjustment capabilities. The platform base is equipped with an angle locking mechanism or a precision ball joint structure, which can drive the upper linear guide rail and optical components (including laser 102, polarizer 103, quarter-wave plate 104, and dual-channel detection unit 105) to adjust their overall tilt angle. Before measurement, by adjusting the platform tilt angle, the emission optical axis of the external optical system is made strictly parallel to the central axis of the output device and perpendicular to the window surface of the single-sided sealed light-transmitting flange 106. This design ensures that the laser beam can pass through the flange window with zero incident angle, avoiding refraction offset and Fresnel reflection loss caused by tilted incident light, and achieving a perfect geometric match between the external measurement reference and the internal tilted structure.

[0029] This implementation significantly expands the engineering applicability of the invention. Through adaptive attitude adjustment of the external platform, a single measurement device can be adapted to converter transformers of different voltage levels and installation tilt angles, eliminating the need for customized optical interfaces for each device. Simultaneously, in conjunction with the retroreflection technology described in the preceding embodiments, the returned beam can accurately return to the external detector along the tilted axis, solving the challenges of optical path calibration and signal stability in non-orthogonal systems.

[0030] In some embodiments, a non-polarizing beam splitter is provided on the horizontal incident optical path of the probe beam from the light source module to the first reflector, and the photoelectric detection receiving unit is located at the reflection port of the non-polarizing beam splitter. The second reflector is a retroreflector. After the measurement beam is reflected by the retroreflector, it undergoes a 180° reverse reflection, passes vertically upward along a path parallel to the probe beam passing through the oil channel, passes through the same oil channel again, and is reflected by the first reflector before exiting from the device in a discrete free space optical path that is collinear with and opposite to the horizontal incident optical path, so as to be reflected by the non-polarizing beam splitter to the photoelectric detection receiving unit. A flange interface is provided on the side wall of the device housing, opposite to the light source module, and a circular optical observation window is provided on the flange interface to allow the probe beam to enter and the measurement beam to exit.

[0031] like Figure 3To further reduce the modification requirements of the measuring device on the converter transformer's main structure, a single-sided opening measurement implementation method based on retroreflector technology is also provided. The measuring device in this embodiment mainly consists of three parts: an external vertical lifting optical platform, a single-sided sealed light-transmitting flange, and a folded retroreflective sensing component located inside the output device. The external vertical lifting optical platform is independently located outside the output device, and its precision lifting frame integrates a laser emitting unit and a dual-channel signal receiving unit. In the emitting optical path, the laser beam is modulated sequentially by a polarizer 103 and a quarter-wave plate 104 before horizontally entering a non-polarizing beam splitter prism. In the receiving optical path, the dual-channel photoelectric detection receiving unit is placed at a specific port of the beam splitter prism, specifically for receiving the signal beam returned via the coaxial optical path. Unlike the double-sided transmission scheme, the sealed light-transmitting flange in this embodiment is only installed at the opening on one side of the output device, eliminating the need for a side-mounted light outlet. This single-end measurement design reduces the amount of machining required on the transformer's main structure and the risk of sealing issues.

[0032] An anti-reflective optical component is installed within the oil-paper insulation structure inside the output device. A 45° all-dielectric folding mirror 107 is positioned at the optical path entrance of this component. Its function is to deflect the horizontally incident laser beam from the flange window by 90°, transforming it into a vertically downward probe beam. The deflected beam will then pass vertically through the longitudinal oil channel formed between the paperboards; this area is the electric field sensitive region where the Kerr effect occurs. An all-dielectric retroreflector 118 is fixedly installed at the bottom of the measuring oil channel. This component is crucial for achieving coaxial backlighting, responsible for ensuring that the downward probe beam is reflected back along its original parallel path.

[0033] The measurement principle of this embodiment mainly relies on the optical phase conjugate characteristics of the retroreflector and the superposition effect of the coaxial two-way optical path. During the measurement process, the polarized light emitted by the laser is transmitted through the beam splitter and reflected by the upper folding mirror, then transmitted vertically downwards and induces the electric field distribution in the longitudinal oil channel. When the beam reaches the bottom retroreflector, it undergoes a 180° reverse reflection. Regardless of any slight tilting or mechanical vibration of the retroreflector with the transformer body, the reflected beam always remains strictly parallel to the incident beam. The returning beam is transmitted upwards along the original path or a slightly displaced parallel path, passes through the upper folding mirror again to return to the horizontal direction, and finally exits through the single flange window. After being reflected by the non-polarizing beam splitter 115, it enters the dual-channel photoelectric detection and receiving unit.

[0034] In its specific implementation, this embodiment employs the following for the photoelectric detection and receiving unit: Figure 4The 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) 115, which splits the beam into transmission and reflection paths at a 1:1 intensity ratio, while strictly maintaining the polarization state of the beam. In the transmission path, an analyzer 116 with a fixed transmission axis of -45° and a photodetector 117 are sequentially arranged; in the reflection path (second branch), an analyzer 114 with a fixed transmission axis of 0° and a photodetector 113 are sequentially arranged. The two detectors convert the optical signals into electrical signals, which are then sent to a multi-channel lock-in amplifier 112. By jointly calculating the polarization components in two independent dimensions, independent measurements of the electric field vector amplitude and direction can be achieved.

[0035] In some embodiments, the transformer outlet device oil electric field measurement system based on discrete optical paths of the present invention measures the electric field in the oil through, as shown in... Figure 5 The execution process shown mainly includes two stages: system preparation and scanning measurement. The system preparation stage includes system initialization and parameter setting 501, and vertical positioning of the external platform 502; the scanning measurement stage includes beam reflection through the measurement area 503, synchronous acquisition of dual-channel signals 504, electric field vector inversion calculation 505, repeated acquisition and averaging 507, adjusting the lifting platform to the next height 508, and generating the oil passage electric field distribution map 506.

[0036] The system preparation has two purposes: one is to ensure that the frequency-stabilized laser and lock-in amplifier reach thermal equilibrium and eliminate the influence of temperature drift noise on the measurement of weak Kerr signals; the other is to establish an initial optical path reference so that the external measurement system can achieve precise optical coupling with the discrete reflector of the first oil channel to be measured inside, thus preparing for subsequent scanning measurements.

[0037] During system initialization and parameter setting (501), the frequency-stabilized helium-neon laser is first turned on and preheated for 15-30 minutes until its power stability is better than 1% before proceeding with subsequent operations. Simultaneously, the reference frequency (corresponding to the modulation signal frequency) and integration time constant of the multi-channel lock-in amplifier are set. A reasonable integration time constant can effectively suppress power frequency interference and random noise, improving the signal-to-noise ratio. After initialization, the external precision lifting platform is zeroed, and according to the preset oil passage position coordinates, the external platform is vertically positioned (502), moving the optical transceiver system to the first measurement height, ensuring that the incident beam can pass through the circular window and be horizontally directed towards the internal reflector.

[0038] In the scanning measurement phase, the light beam is first reflected through the measurement area 503. The horizontally incident beam is deflected by the upper reflector inside and then passes perpendicularly through the insulating oil gap to be measured. The Kerr effect occurs in the transformer oil, and the beam polarization state changes with the electric field strength. It is then deflected again by the lower reflector and returns to the outside along the same path or parallel to the outside. Next, dual-channel signal synchronous acquisition 504 is performed. The external receiving system uses a non-polarizing beam splitter to split the returning beam into two paths, which pass through -45° and 0° analyzers respectively. A lock-in amplifier synchronously acquires the light intensity signals from both detectors, extracting the fundamental and harmonic components carrying electric field information.

[0039] During data processing, the electric field vector inversion calculation is performed using the acquired light intensity components. Specifically, based on the dual-path optical transfer function derived from Jones matrix theory, the system normalizes the modulated light intensity signals acquired from both channels and extracts the characteristic light intensity ratio parameters corresponding to the 0° and -45° polarization detection directions (denoted as...). and ,in (This is the reference output light intensity under no electric field). The computer system internally calls the following set of analytical equations to simultaneously calculate the amplitude of the electric field vector at the current measurement point. and direction angle :

[0040] ; ; In the formula, I x and I x 45 These represent the light intensity parameters at the corresponding 0° and -45° polarization directions, which were simultaneously acquired by the dual channels under the action of the DC electric field to be measured. I 1 B represents the corresponding channel output light intensity of the system under the reference state without electric field; B represents the inherent Kerr constant of the transformer insulating oil pre-calibrated; L represents the effective optical equivalent path length of the probe beam actually traversing the insulating oil gap region under the polarization of the electric field. θ 2 This represents the set spatial offset angle of the analyzer in the measurement optical path (in this embodiment, the value is -45°).

[0041] Furthermore, considering that optical elements (such as the quartz observation window on the lower sidewall and a quarter-wave plate) are not absolutely ideal devices in actual engineering measurement environments, the difference in transmission coefficients for the two orthogonal polarization components in the beam, as well as the inherent phase delay error caused by defects in the device's own materials, will introduce non-negligible systematic errors. Therefore, this invention specifically introduces an optical error compensation mechanism for the two-dimensional electric field vector in the underlying calculation model of the digital signal processing unit.

[0042] Specifically, based on the Jones matrix theory, the optical transfer function is derived. Based on the transmission coefficients of the optical devices in the entire measurement loop from the emission of the probe beam to the acquisition of the measurement beam to the two orthogonal components in the measurement beam, as well as the initial phase delay introduced by the optical devices, the correction coefficients for amplitude and direction are determined respectively. Based on the determined correction coefficients, the target amplitude and target direction of the electric field are obtained.

[0043] For example, the total transmission coefficients of the X and Y components of the light beam to non-ideal devices such as the quartz window (i.e., the optical observation window) on the flange interface in the measurement optical path are denoted as follows: and The total initial phase delay error caused by the combination of the quarter-wave plate and the window plate on the flange interface is denoted as . Based on the Jones matrix, the transmission reference and interference terms of DC orthogonal light intensity are decoupled to derive the comprehensive correction coefficient for the DC electric field vector amplitude. And the orientation angle correction coefficient caused by the imbalance of the dual-channel reference light intensity. Their analytical expressions are as follows:

[0044] ; ; After rigorous physical calibration, the actual two-dimensional DC electric field amplitude at the current measuring point With direction angle The following modified system of equations can be used to solve the problem simultaneously: ; ; In the formula, I x and I x 45 These represent the modulated characteristic light intensity parameters corresponding to the 0° and -45° polarization directions, which were synchronously acquired by the dual channels under the action of the DC electric field to be measured. I 1 The output reference light intensity of the corresponding detection channel is pre-calibrated under the condition of no electric field reference. θ 2This represents the set spatial offset angle of the corresponding analyzer in the measurement optical path.

[0045] During the initial calibration phase of the system, the correction coefficient can be fixed by measuring the transmission coefficient deviation and phase accuracy of the relevant optical components. This algorithm effectively filters out the DC inversion drift caused by the optical hardware from a physical derivation perspective, further improving the accuracy of electric field measurement.

[0046] To improve the confidence of the measurement data, a repeated acquisition and averaging judgment mechanism 507 is introduced into the process. If the current oil passage measurement has not been completed (for example, the data fluctuation exceeds the threshold), the system will automatically repeat step 504 to perform weighted averaging on the data collected multiple times in order to filter out measurement errors caused by occasional environmental vibrations.

[0047] After completing the measurement of the current oil channel, the system will determine whether all preset oil channels have been traversed. If there are any unmeasured oil channels, the system will proceed to step 508, which involves adjusting the lifting platform to the next height. At this point, the stepper motor drives the external platform to move vertically to the next preset height, driving the incident beam to translate and align with the reflector group corresponding to the next layer of insulating oil channel, repeating the beam traversal, signal acquisition, and calculation process. Once all preset oil channels have been traversed, the system integrates the data from each discrete measurement point, generates the oil channel electric field distribution map 506, and then shuts down the system, ending the measurement process.

[0048] This invention provides a transformer outgoing line device oil electric field measurement system based on discrete optical path. The core components of the system include an external vertical displacement scanning frame and two internal discrete reflectors. The external precision lifting platform drives the measurement optical path to translate in the vertical direction. With the help of two sets of internal pre-set reflectors, online monitoring of the electric field distribution in multi-layer oil channels can be achieved without damaging the complex internal oil-paper insulation structure.

[0049] This invention also proposes a polarization switching method for a dual-aperture measurement optical path. By adjusting the vertical height of the external optical system, the mirror pairs at different internal positions are precisely coupled, thereby changing the oil channel area through which the measurement beam passes. This solves the engineering problem of multi-point, multi-depth electric field scanning measurement inside a closed high-pressure vessel.

[0050] This invention also proposes a single-sided aperture measurement scheme based on retroreflection technology. Utilizing the unique self-collimation and phase conjugation characteristics of retroreflectors, the probe beam undergoes back reflection at the end of the longitudinal oil channel and returns parallel to its original path. Measurement can be completed by opening an optical window on only one side of the transformer. This scheme solves the engineering difficulty of opening dual windows on the same side in converter transformers due to their narrow space and complex structure. Furthermore, the double-path optical design effectively doubles the measurement optical path, improving measurement sensitivity in liquid media with weak Kerr constants and effectively enhancing measurement accuracy.

[0051] This invention also designs a method for electric field vector calculation, demodulation, and error compensation based on unpolarized beam splitting and dual-channel orthogonal polarization analysis. A beam splitter is used to split the return beam carrying electric field information into two paths, each configured with a polarizer at a specific angle for synchronous detection. Simultaneously, a comprehensive error compensation coefficient for transmittance differences and initial phase delays in non-ideal optical devices is embedded in the underlying Jones matrix calculation model. An algorithm is used to achieve real-time, high-precision decoupling of the real DC electric field magnitude and orientation angle. This method overcomes the technical limitation of existing measurement methods that require frequent manual rotation of optical components, making it impossible to measure transient changes in the electric field. The introduced error compensation mechanism can, to a certain extent, suppress the two-dimensional vector calculation deviation caused by the non-ideal characteristics of the hardware.

[0052] 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. A transformer outlet device oil electric field measurement system based on discrete optical path, characterized in that, The system includes: an electro-optic measurement system located outside the device, and a first reflector and a second reflector located directly above and below multiple oil passages inside the device; wherein, the electro-optic measurement system includes a lifting platform, a light source module, and a photoelectric detection and receiving unit; The light source module and the first reflector are positioned opposite each other. After the light source module emits a detection beam, the detection beam is incident horizontally on the first reflector. The reflector surface of the first reflector is at a 45° angle to the detection beam, so that the detection beam is reflected by the first reflector and passes vertically downward through the oil passage to form a measurement beam carrying the electric field information in the oil. The measurement beam is then reflected by the second reflector to the photoelectric detection receiving unit to measure the electric field in the oil of the device. The light source module is fixed on the lifting platform. The lifting platform drives the light source module to move in the vertical direction so that the detection beam is reflected by different positions of the reflector surface of the first reflector to different oil channels that are distributed in parallel in the vertical direction inside the device, so as to measure the electric field of different oil channels inside the device.

2. The transformer outlet device oil electric field measurement system based on discrete optical path according to claim 1, characterized in that, The photoelectric detection and receiving unit is positioned directly opposite the second reflector. The reflector surface of the second reflector is at a 45° angle to the measurement beam, so that the measurement beam is reflected by the second reflector and then incident horizontally onto the photoelectric detection and receiving unit.

3. The transformer output device oil electric field measurement system based on discrete optical path according to claim 2, characterized in that, The device housing has flange interfaces on its side walls, opposite the light source module and the photoelectric detection and receiving unit. Each flange interface has a circular optical observation window to allow the detection beam to enter and the measurement beam to exit, respectively.

4. The transformer outlet device oil electric field measurement system based on discrete optical path according to claim 1, characterized in that, The detection beam is provided with a non-polarizing beam splitter on the horizontal incident optical path from the light source module to the first reflector, and the photoelectric detection receiving unit is located at the reflection port of the non-polarizing beam splitter. The second reflector is a retroreflector. After the measurement beam is reflected by the retroreflector, it undergoes a 180° reverse reflection and passes through the same oil channel again vertically upward along a path parallel to the detection beam passing through the oil channel. After being reflected by the first reflector, it exits from the device in a discrete free space optical path that is collinear with and opposite to the horizontal incident light path, and is reflected by a non-polarizing beam splitter to the photoelectric detection and receiving unit.

5. The transformer outlet device oil electric field measurement system based on discrete optical path according to claim 4, characterized in that, The device housing has a flange interface on its side wall, directly opposite the light source module. The flange interface has a circular optical observation window to allow the probe beam to enter and the measurement beam to exit.

6. The transformer outlet device oil electric field measurement system based on discrete optical path according to claim 3 or 5, characterized in that, The electro-optic measurement system is mounted on an attitude adaptive optics platform. The base of the attitude adaptive optics platform is equipped with an angle locking mechanism or a precision ball joint structure, which is used to drive the electro-optic measurement system to adjust the tilt angle so that the emission optical axis of the light source module of the electro-optic measurement system is parallel to the central axis of the device and perpendicular to the flange interface surface on the device that is directly opposite the light source module.

7. The transformer outlet device oil electric field measurement system based on discrete optical path according to claim 1, characterized in that, The light source module includes a helium-neon laser, a polarizer, and a quarter-wave plate; A helium-neon laser is used to emit a laser beam, while a polarizer and a quarter-wave plate are used together to shape the laser beam into circularly polarized light, which is then used as a probe beam.

8. The transformer outlet device oil electric field measurement system based on discrete optical path according to claim 1, characterized in that, The first and second reflectors are housed within the device, using an internal insulating barrier or support structure as a carrier.

9. The transformer outlet device oil electric field measurement system based on discrete optical path according to claim 5, characterized in that, The non-polarizing beam splitter splits the beam reflected back from the first reflecting mirror into two beams, a transmitted beam and a reflected beam, in a 1:1 ratio of light intensity, which then enter the photoelectric detection and receiving unit. The photoelectric detection and receiving unit detects the light intensity signals of the two beams in the transmitted and reflected light paths respectively through two analyzers with the transmission axes fixed at -45° and 0°. Based on the optical transfer function constructed by the Jones matrix theory, the amplitude and direction of the electric field are measured using the light intensity signals of the two beams.

10. The transformer outlet device oil electric field measurement system based on discrete optical path according to claim 9, characterized in that, The photoelectric detection and receiving unit, based on the optical transfer function, determines the correction coefficients for amplitude and direction according to the transmission coefficients of the optical devices in the entire measurement loop from the emission of the detection beam to the acquisition of the measurement beam to the two orthogonal components in the measurement beam, as well as the initial phase delay introduced by the optical devices. Based on the determined correction coefficients, the target amplitude and target direction of the electric field are obtained.

Images