On-line monitoring system and method for complex wide-frequency-domain overvoltage of high-voltage power equipment

Abstract

The invention relates to the technical field of overvoltage monitoring, in particular to a wide-frequency-domain overvoltage online monitoring system and method for electric power high-voltage equipment. Comprising an electric field sensor array, an acquisition unit, a calculation unit and an output unit, the electric field sensor array comprises a plurality of sensors which are radially distributed on the same circumferential plane and have different measuring ranges and sensitivities, and sensors which are axially distributed; the electric field sensor comprises a sensing unit and a fiber bragg grating temperature measuring unit; the fiber bragg grating temperature measuring unit is suitable for measuring the temperature of the sensing unit; the acquisition unit is suitable for synchronously acquiring the emergent light intensity of the sensing unit and the temperature data of the fiber grating temperature measurement unit. The multi-range sensors distributed in the radial direction achieve wide-range and high-sensitivity voltage sensing through differential design, the intrusion direction of overvoltage can be determined through cooperation of the axial sensors and the radial sensors, and the problem that the range and sensitivity of a single electric field sensor are mutually restricted is solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of overvoltage monitoring, and particularly relates to a wide frequency domain overvoltage online monitoring system and method for power high-voltage equipment. BACKGROUND

[0002] With the further improvement of the new energy penetration rate, the power high-voltage equipment will face more severe complex overvoltage threats. The overvoltage measurement of the non-contact optical method can be realized by the electric field sensor based on the photoelectric effect. However, the measurement sensitivity and the measurement range of a single electric field sensor are mutually restricted, and it is difficult to consider the real-time sensing of high sensitivity and large range. In addition, the temperature of the power high-voltage equipment changes greatly in different seasons and operating conditions, and the measurement accuracy of the electric field sensor is greatly affected by the environmental temperature, which further restricts the improvement of the measurement accuracy of the existing electric field sensor. SUMMARY

[0003] Therefore, the present application provides a wide frequency domain overvoltage online monitoring system and method for power high-voltage equipment to solve the problems of range, accuracy and sensitivity when measuring overvoltage by using an electric field sensor.

[0004] In a first aspect, the present application provides a wide frequency domain overvoltage online monitoring system for power high-voltage equipment, comprising an electric field sensor array, an acquisition unit, a calculation unit and an output unit.

[0005] The electric field sensor array comprises a plurality of sensors radially distributed on the same circumferential plane and having different ranges and sensitivities, and an axially distributed sensor.

[0006] The electric field sensor comprises a sensing unit and a fiber grating temperature measurement unit, and the fiber grating temperature measurement unit is suitable for measuring the temperature of the sensing unit.

[0007] The acquisition unit is suitable for synchronously acquiring the exit light intensity of the sensing unit and the temperature data of the fiber grating temperature measurement unit.

[0008] The calculation unit is used for obtaining the phase difference according to the exit light intensity, compensating the photoelectric coefficient based on the temperature data, and calculating the overvoltage of each electric field sensor based on the phase difference and the photoelectric coefficient. The overvoltage intrusion direction is obtained based on the overvoltages of all electric field sensors, and the overvoltage waveform is obtained by data fitting of the circumferential plane electric field sensor. The range of the overvoltage waveform is the total range of the circumferential plane electric field sensor, and the sensitivity of the overvoltage waveform is consistent with the highest sensitivity in the circumferential plane electric field sensor.

[0009] The output unit is suitable for outputting the overvoltage waveform and the overvoltage intrusion direction.

[0010] The application builds an overvoltage monitoring system with wide range and high sensitivity through the cooperative design of the electric field sensor array, the acquisition unit, the calculation unit and the output unit. The multi-range radial sensors realize wide range and high sensitivity voltage sensing through differential design, and the axial sensor cooperates with the radial sensor to determine the invasion direction of the overvoltage, solving the problem of mutual restriction of the range and sensitivity of a single electric field sensor, and realizing the decoupling of the range and sensitivity. The fiber grating temperature measurement unit measures the temperature of the sensing unit, realizes real-time monitoring of the temperature of the photoelectric crystal and compensation of the photoelectric coefficient, effectively overcomes the influence of temperature change on the measurement accuracy, enables the system to work stably in a wide temperature environment, adapts to the monitoring needs of power equipment in different seasons and different operating conditions, and greatly improves the reliability of engineering application. Through the cooperative work of the multi-sensor array, different types of overvoltage such as lightning overvoltage, operating overvoltage, power frequency overvoltage and resonance overvoltage can be monitored in real time, and the amplitude, frequency and time characteristics can be captured completely, providing comprehensive basic data for power system overvoltage protection, supporting equipment insulation state evaluation and optimization design of protection strategy.

[0011] In an optional implementation, the electric field sensors on the circumferential plane are at least 4, uniformly distributed along the radial direction;

[0012] The axial distribution of the electric field sensor is at least 1, perpendicular to the circumferential plane.

[0013] The application adopts the spatial layout of "at least four radial sensors + at least one axial sensor" to provide structural support for three-dimensional sensing and direction judgment of overvoltage. The uniformly distributed radial sensors can effectively capture the plane component of the electric field, and the axial distribution of the sensors is responsible for sensing the vertical component of the electric field, and the combination of the two realizes the complete inversion of the spatial electric field vector, so that the system can accurately describe the electric field distribution characteristics when the overvoltage invades, and is more consistent with the actual spatial electric field distribution law of the power equipment than the traditional point measurement method, providing more real data for the research of overvoltage propagation characteristics. By analyzing the signal differences of different sensors, the system can quickly judge the invasion direction of the overvoltage, such as distinguishing whether the overvoltage comes from the line side or the high-voltage power equipment side, providing key basis for fault tracing, shortening the power equipment fault troubleshooting time, improving the operation and maintenance efficiency, and providing clear direction guidance for targeted protection measures. The multi-sensor array layout can obtain multiple detection data, making the fitted data more accurate.

[0014] In an optional implementation, the electric field sensor array is time-synchronized.

[0015] In the present application, the time-domain synchronization of the electric field sensor array ensures the synchronous sampling of each sensor to the high-frequency overvoltage signal, avoids the waveform distortion caused by the time sequence deviation, enables the system to accurately restore the front characteristics of the lightning overvoltage and other transient processes, provides an accurate time reference for the rapid action of the overvoltage protection device, and improves the safety protection response speed of the power system in the face of sudden overvoltage. For various overvoltages with different durations, the time-domain synchronization ensures the time consistency of the multi-sensor sampling data, enabling the system to completely capture the full process waveform of the overvoltage from occurrence to decay, and providing reliable data for the amplitude, frequency and energy analysis of the overvoltage. Synchronous sampling enables each sensor signal to have high consistency in phase difference calculation, combined with subsequent Jones matrix operation and photoelectric coefficient compensation, significantly improving the sensitivity of electric field strength inversion, making the measurement results of the system closer to the actual value, and providing a reliable quantitative basis for the overvoltage tolerance evaluation of power equipment.

[0016] In an optional embodiment, the sensing unit comprises a photoelectric crystal, and a reflective film is arranged on the opposite surface of the photoelectric crystal for reflecting incident light in the photoelectric crystal.

[0017] In the present application, by adjusting the reflection times of incident light in the photoelectric crystal, the propagation path length of light in the crystal can be effectively changed, and the response sensitivity of the sensor to the electric field strength can be adjusted.

[0018] In an optional embodiment, the sensing unit is provided with an incident polarizer, a quarter-wave plate and an exit polarizer, the polarization direction of the incident polarizer is orthogonal to the polarization direction of the exit polarizer, and the optical path of the sensing unit passes through the incident polarizer, the quarter-wave plate, the photoelectric crystal and the exit polarizer in sequence.

[0019] In the present application, the orthogonal layout of the incident polarizer, the quarter-wave plate and the exit polarizer in the sensing unit optimizes the modulation and detection process of the optical signal. By converting linearly polarized light into circularly polarized light and cooperating with orthogonal polarizer detection, the system is more sensitive to the phase change caused by the electric field, can capture weak electric field fluctuations, and improves the monitoring capability of low-amplitude overvoltage. Circularly polarized light is less affected by the birefringence of the photoelectric crystal and external vibration during propagation, combined with the detection method of the orthogonal polarizer, effectively suppresses the influence of environmental interference on the optical signal, improves the anti-interference ability, enables the system to maintain stable measurement performance in the strong electromagnetic interference environment of the substation, improves the reliability of the monitoring data, and ensures the authenticity of the data in the complex electromagnetic environment.

[0020] In an optional embodiment, the acquisition unit is communicatively connected to the electric field sensor through an optical fiber.

[0021] In the present application, the optical fiber transmission is not affected by electromagnetic interference, and the acquisition unit is connected with the electric field sensor through the optical fiber, so that the acquisition unit, the calculation unit connected with the acquisition unit, and the output unit connected with the calculation unit are away from the over-voltage field area, and the acquisition unit, the calculation unit, and the output unit are protected from the interference of the over-voltage field.

[0022] In an optional embodiment, the fiber grating temperature measurement unit is integrated with the photoelectric crystal, and is suitable for measuring the temperature of the photoelectric crystal.

[0023] In the present application, the fiber grating temperature measurement unit is integrated with the photoelectric crystal, and the real-time and accuracy of temperature compensation are realized. The integrated design enables the temperature measurement unit to quickly respond to the temperature change of the photoelectric crystal, avoids the response delay of the traditional separate temperature measurement scheme, ensures the timeliness of the photoelectric coefficient compensation, makes the system still maintain the measurement accuracy under the condition of rapid temperature change, adapts to the dynamic operation demand of the power equipment, and improves the environmental adaptability of the monitoring system. Through real-time temperature compensation, the influence of temperature change on the photoelectric effect is effectively eliminated, the measurement accuracy of the sensor is not disturbed by the environmental temperature fluctuation, the stability is maintained in a wide temperature range, the measurement error caused by temperature drift is reduced, and reliable data support is provided for the long-term reliability evaluation of the power equipment.

[0024] In an optional embodiment, the electric field sensors on the same circumferential plane realize the differentiation of the range and sensitivity through different reflection times of the incident light.

[0025] In the present application, the electric field sensors with different reflection times are respectively responsible for the over-voltage monitoring of different range, and through the cooperative work, the full range coverage from low amplitude to high amplitude over-voltage is realized, the measurement saturation or sensitivity reduction problem of the single range sensor when facing extreme over-voltage is avoided, the monitoring range of the system is expanded, and it is ensured that various over-voltages can be accurately captured. The sensor array with differentiated range and sensitivity provides multi-dimensional measurement data, and through the synchronous fitting of the calculation unit, the total range waveform containing the over-voltage waveforms of the electric field sensors on each circumferential plane can be effectively obtained. The electric field sensor with the highest sensitivity can also be determined based on the reflection times of the incident light, and the over-voltage waveform sensitivity of other electric field sensors is unified based on the over-voltage waveform sensitivity of the electric field sensor with the highest sensitivity, and then the over-voltage waveform with the full range and the same sensitivity as the highest one is obtained.

[0026] In a second aspect, a wide frequency domain over-voltage online monitoring method for power high-voltage equipment is suitable for the wide frequency domain over-voltage online monitoring system for power high-voltage equipment as described above, and includes the following steps:

[0027] Collecting the outgoing light intensity and temperature data;

[0028] The phase difference is obtained according to the light intensity, and the photoelectric coefficient is compensated based on the temperature data;

[0029] The overvoltage of each electric field sensor is calculated based on the phase difference and the photoelectric coefficient;

[0030] The overvoltage intrusion direction is obtained based on the overvoltage of all electric field sensors;

[0031] The overvoltage waveform is obtained by data fitting of the circumferential planar electric field sensor, wherein the range of the overvoltage waveform is the total range of the circumferential planar electric field sensor, and the sensitivity of the overvoltage waveform is consistent with the highest sensitivity in the circumferential planar electric field sensor;

[0032] The overvoltage waveform and the overvoltage intrusion direction are output.

[0033] In the present application, from the collection of light intensity and temperature data to the calculation of phase difference, compensation of photoelectric coefficient, overvoltage inversion, direction judgment and waveform fitting, a complete data processing chain is formed, each step has clear algorithm support, avoiding the randomness of data processing, ensuring the repeatability and reliability of overvoltage monitoring results, and providing a unified standard for overvoltage data analysis of power system. By using the cooperative measurement advantage of electric field sensor array and through comprehensive analysis and fitting of sensor data, not only the accurate measurement of overvoltage amplitude is realized, but also the intrusion direction of overvoltage is judged, providing multi-dimensional information for overvoltage tracing and protection, and improving the fault diagnosis ability of the system.

[0034] In an optional embodiment, it further comprises:

[0035] A standard overvoltage waveform model database is established, and the overvoltage waveform is corrected based on the standard overvoltage waveform model.

[0036] In the present application, the standard overvoltage waveform model database contains typical characteristics of various overvoltages, and by comparing the measured waveform with the standard model, the waveform distortion caused by environmental interference, sensor error and other factors can be effectively corrected, the restoration sensitivity of the overvoltage waveform is improved, the uncertainty of the overvoltage is eliminated, and the monitoring data is closer to the actual overvoltage characteristics, providing a more reliable basis for the insulation evaluation of power equipment.

[0037] Based on the waveform correction of the standard model, the type and characteristic parameters of the overvoltage can be quickly identified, combined with the overvoltage intrusion direction judgment, the precise positioning of the fault source and the accurate diagnosis of the fault type are realized, providing more targeted guidance for the maintenance and maintenance of power equipment, shortening the fault processing time and improving the operation and maintenance efficiency.

[0038] The standardized waveform model provides a basis for statistical analysis and law research of overvoltage, and through comparison and analysis of long-term monitoring data and the standard model, the maintenance strategy of power equipment can be optimized, preventive maintenance can be realized, equipment failure rate can be reduced, and operation reliability and economy of the power system can be improved. BRIEF DESCRIPTION OF DRAWINGS

[0039] In order to more clearly illustrate the specific embodiments of the present application or the technical solutions in the prior art, the drawings needed to be used in the specific embodiments or prior art description will be briefly introduced as follows. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor on the basis of these drawings.

[0040] Fig. 1 The figure is a schematic diagram of an electric field sensor structure of an embodiment of the present application.

[0041] Fig. 2 The figure is a schematic diagram of an electric field sensor array distribution of an embodiment of the present application.

[0042] Explanation of reference signs:

[0043] 1, electric field sensor; 2, fiber grating temperature measurement unit; 3, photoelectric crystal; 4, reflective film; 5, incident polarizer; 6, quarter-wave plate; 7, exit polarizer; 8, optical fiber. DETAILED DESCRIPTION

[0044] In order to make the purpose, technical scheme and advantages of the embodiments of the present application more clear, the technical scheme in the embodiments of the present application will be described clearly and completely in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are some of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0045] With the further improvement of new energy penetration rate, power high-voltage equipment will face more serious complex overvoltage (lightning overvoltage, operating overvoltage, power frequency overvoltage and resonance overvoltage, etc.) threat, temporary overvoltage includes: power frequency overvoltage and resonance overvoltage, the frequency is in 10Hz~500Hz, the time is in 0.03s~3600s. Transient overvoltage includes: operating overvoltage and lightning overvoltage, the frequency change range is wide, the highest can reach 100MHz, the time change range is as small as 3ns. The traditional contact type voltage detection technology: mainly through the electromagnetic voltage transformer or the capacitive voltage transformer is directly connected to the measured main circuit to capture the voltage characteristics; the electromagnetic voltage transformer can only effectively capture the power frequency steady-state signal, if measuring higher frequency or lower frequency voltage, there will be obvious error; the capacitive voltage transformer has the disadvantages of weak anti-interference ability, insufficient load capacity, poor linearity under high voltage, etc., and it is difficult to adapt to the requirements of intelligent operation and maintenance. The existing new non-contact voltage measurement technology includes electrical method and optical method, the existing non-contact electrical method is based on induction charge, inverse piezoelectric effect, electrostatic force and other principles, because it introduces a parasitic capacitance depending on the induction principle of the metal electrode, which causes the distortion of the measured electric field distribution, and it is difficult to meet the high sensitivity monitoring requirements of transient voltage in complex electromagnetic environment. The existing non-contact optical method realizes voltage measurement based on photoelectric effect, but the measurement sensitivity and measurement range of a single electric field sensor are mutually restricted, it is difficult to balance high sensitivity and large range real-time sensing, in addition, the temperature change range of power high-voltage equipment in different seasons and operation conditions is large, the measurement accuracy of the electric field sensor is greatly affected by the environmental temperature, which further restricts the improvement of the measurement accuracy of the existing electric field sensor.

[0046] The embodiments of the present application will be described below in combination with Figs. 1-2

[0047] Embodiment 1

[0048] The present application provides a power high-voltage equipment wide frequency domain overvoltage online monitoring system, comprising an electric field sensor array, an acquisition unit, a calculation unit and an output unit.

[0049] The electric field sensor array comprises a plurality of sensors radially distributed on the same circumferential plane and having different ranges and sensitivities, and an axially distributed sensor; the electric field sensor is based on photoelectric effect.

[0050] The electric field sensor 1 comprises a sensing unit and a fiber grating temperature measurement unit 2, and the fiber grating temperature measurement unit 2 is suitable for measuring the temperature of the sensing unit.

[0051] The acquisition unit is suitable for synchronously acquiring the exit light intensity of the sensing unit and the temperature data of the fiber grating temperature measurement unit 2.

[0052] ​The computing unit is configured to obtain a phase difference according to the outgoing light intensity, compensate a photoelectric coefficient based on the temperature data, and calculate an overvoltage of each electric field sensor 1 based on the phase difference and the photoelectric coefficient, obtain an overvoltage intrusion direction based on overvoltages of all electric field sensors 1, and perform data fitting on the circumferential plane electric field sensor 1 to obtain an overvoltage waveform, wherein a range of the overvoltage waveform is a total range of the circumferential plane electric field sensor 1, and a sensitivity of the overvoltage waveform is consistent with a highest sensitivity in the circumferential plane electric field sensor 1.

[0053] The output unit is adapted to output the overvoltage waveform and the overvoltage intrusion direction.

[0054] The application builds an overvoltage monitoring system with wide range and high sensitivity through the cooperative design of the electric field sensor array, the acquisition unit, the computing unit and the output unit. The multi-range sensors distributed in the radial direction realize wide-range and high-sensitivity voltage sensing through differential design, and the axial sensors and the radial sensors cooperate to determine the intrusion direction of the overvoltage, thereby solving the problem of mutual restriction between the range and the sensitivity of a single electric field sensor 1. The fiber grating temperature measurement unit 2 measures the temperature of the sensing unit, realizes real-time monitoring of the temperature of the photoelectric crystal 3 and compensation of the photoelectric coefficient, effectively overcomes the influence of temperature change on the measurement accuracy, and enables the system to work stably in a wide temperature environment, thereby adapting to the monitoring needs of power equipment in different seasons and different operating conditions, and greatly improving the reliability of engineering application. Through the cooperative work of the multi-sensor array, different types of overvoltage such as lightning overvoltage, operating overvoltage, power frequency overvoltage and resonance overvoltage can be monitored in real time, and the amplitude, frequency and time characteristics thereof can be captured completely, thereby providing comprehensive basic data for overvoltage protection of the power system, and supporting the optimization design of equipment insulation state evaluation and protection strategy.

[0055] In an optional embodiment, the electric field sensors 1 on the circumferential plane are at least 4 and are uniformly distributed in the radial direction.

[0056] The electric field sensors 1 distributed in the axial direction are at least 1 and are perpendicular to the circumferential plane.

[0057] The application adopts a spatial layout of "at least four radial sensors + at least one axial sensor", which provides structural support for three-dimensional perception and direction judgment of overvoltage. The radially uniformly distributed sensors can effectively capture the planar component of the electric field, and the axially distributed sensors are responsible for perceiving the vertical component of the electric field, and the combination of the two realizes the complete inversion of the spatial electric field vector, so that the system can accurately describe the electric field distribution characteristics when the overvoltage invades, and is more consistent with the actual spatial electric field distribution law of the power equipment than the traditional point measurement method, and provides more real data for the research on the propagation characteristics of overvoltage. By analyzing the signal differences of different sensors, the system can quickly judge the invasion direction of the overvoltage, such as distinguishing whether the overvoltage comes from the line side or the high-voltage power equipment side, providing a key basis for fault tracing, shortening the troubleshooting time of power equipment, improving the operation and maintenance efficiency, and providing a clear direction for the development of targeted protection measures. The waveform fitting in the four directions of the multi-sensor array layout can improve the sensitivity of the system.

[0058] In an optional embodiment, the time domain synchronization of the electric field sensor array.

[0059] In the application, the time domain synchronization of the electric field sensor array ensures the synchronous sampling of high-frequency overvoltage signals by each sensor, avoids waveform distortion caused by time sequence deviation, and enables the system to accurately restore the front characteristics of lightning overvoltage and other transient processes, thereby providing an accurate time reference for the rapid action of overvoltage protection devices and improving the safety protection response speed of the power system when facing sudden overvoltage. For various overvoltages with different durations, time domain synchronization ensures the time consistency of the sampling data of the multi-sensor, so that the system can completely capture the whole process waveform of the overvoltage from occurrence to attenuation, and provide reliable data for the amplitude, frequency and energy analysis of the overvoltage. Synchronous sampling makes the signals of each sensor have high consistency in phase difference calculation, and combined with subsequent Jones matrix operation and photoelectric coefficient compensation, the sensitivity of electric field strength inversion is significantly improved, so that the measurement result of the system on the overvoltage is closer to the actual value, and a reliable quantitative basis is provided for the overvoltage withstand capability evaluation of the power equipment.

[0060] In an optional embodiment, the sensing unit comprises a photoelectric crystal 3, and a reflective film 4 is arranged on the opposite surface of the photoelectric crystal 3, for reflecting the incident light in the photoelectric crystal 3, so that the incident light is reflected in the photoelectric crystal 3. The reflective film 4 is provided with an incident channel and an exit channel for the incident light to enter the photoelectric crystal and the exit light to leave the photoelectric crystal.

[0061] In the application, by adjusting the number of reflections of the incident light in the photoelectric crystal 3, the propagation path length of the light in the crystal can be effectively changed, and then the response sensitivity of the sensor to the electric field strength can be adjusted.

[0062] In an alternative embodiment, the sensing unit is provided with an incident polarizer 5, a quarter-wave plate 6 and an exit polarizer 7, the polarization direction of the incident polarizer 5 is orthogonal to that of the exit polarizer 7, and the light path of the sensing unit passes through the incident polarizer 5, the quarter-wave plate 6, the photoelectric crystal 3 and the exit polarizer 7 in sequence. Among them, the incident polarizer 5 can be considered as a polarizer, which changes the incident natural light into linearly polarized light. The polarization direction of the linearly polarized light is usually at an angle of 45° with the o-axis or e-axis of the crystal. The exit polarizer 7 can be considered as an analyzer, which is placed at the exit end of the crystal, and the transmission axis direction of the analyzer is usually perpendicular to the transmission axis direction of the polarizer (crossed polarizer). The analyzer forces the o light and e light components to project in the transmission axis direction and interfere and superimpose.

[0063] In this application, the orthogonal layout of the incident polarizer 5, the quarter-wave plate 6 and the exit polarizer 7 in the sensing unit optimizes the modulation and detection process of the optical signal. By converting linearly polarized light into circularly polarized light and cooperating with orthogonal polarizer detection, the system is more sensitive to the phase change caused by the electric field, can capture weak electric field fluctuations, and improves the monitoring ability of low amplitude overvoltage. Circularly polarized light is less affected by the birefringence of the photoelectric crystal 3 and external vibration during propagation, combined with the detection method of orthogonal polarizers, effectively suppresses the influence of environmental interference on the optical signal, improves the anti-interference ability, makes the system still maintain stable measurement performance in the substation environment with strong electromagnetic interference, improves the reliability of the monitoring data, and ensures the authenticity of the data in the complex electromagnetic environment.

[0064] Electro-optic crystal is a crystal (such as lithium niobate LiNbO3, potassium dihydrogen phosphate KDP, etc.) with electro-optic effect (such as Pockels effect or Kerr effect). When an external electric field is applied to it, its refractive index will change. Electro-optic crystal is also usually an optically anisotropic crystal with birefringence characteristics. When a beam of light is incident on the crystal, it will be decomposed into two beams of linearly polarized light with perpendicular vibration directions:

[0065] Ordinary light (o light): follows the refraction law, refractive index is constant n0.

[0066] Extraordinary light (e light): does not strictly follow the refraction law, refractive index changes with the direction of propagation n e .

[0067] When a voltage is applied to the photoelectric crystal 3, the electric field changes the refractive index of the crystal. The electric field usually changes the refractive index of o light and e light differently (Δn0≠Δn e ). This makes the o light and e light produce different phase delays after passing through the crystal with a light path length L, thereby introducing an additional phase difference δ(V) between them, which is controlled by the overvoltage:

[0068] δ(V)=(2π / λ)·(Δn e (V)-Δn0(V))·L=(2π / λ)Δ(Δn(V))·L Formula 1

[0069] Where λ is the wavelength of light. This phase difference δ(V) is directly controlled by the overvoltage V.

[0070] After the two orthogonal polarization components of o light and e light pass through the electro-optical crystal, due to the phase difference δ(V), when they are combined again (projected onto the analyzer), coherent superposition (interference) will occur.

[0071] The interference results in a change in the polarization state and / or intensity of the outgoing light. This change is dynamic, real-time, and precisely corresponds to the overvoltage V.

[0072] The intensities of the o-light and e-light are I1 and I2 respectively. The total light intensity I after interference satisfies:

[0073]

[0074] in, is the phase difference between the two beams of light, and the total light intensity I can be considered as the output light intensity.

[0075] when When (phase difference 0, 2π, ...), the light intensity is maximum:

[0076]

[0077] when When (phase difference π, 3π, ...), the light intensity is minimum:

[0078]

[0079] Among them, I max It can be obtained through experiments. The specific method is to input an incident light with an intensity of I0, add a controllable electric field, and gradually adjust the intensity of the electric field to obtain the maximum output light intensity, and the minimum output light intensity is 0. The incident light intensity in this application is the same as the incident light intensity in the experiment, so the I involved is max consistent.

[0080] Light intensity ratio conversion: From formula 3 and formula 4, we can get:

[0081]

[0082] Substituting into formula 2, we can get:

[0083]

[0084] Phase difference inversion: Arrange formula 5 to get:

[0085]

[0086] When I min = 0 (double-beam equal light intensity interference), the formula is simplified as:

[0087]

[0088] The phase difference generated by the photoelectric crystal 3 under the action of the overvoltage E is:

[0089]

[0090] Where λ is the wavelength of the laser, γ is the photoelectric coefficient, and L is the optical path (related to the number of reflections).

[0091] The overvoltage E can be obtained by formula 8, and formula 7 and formula 8 can be solved together:

[0092]

[0093] Based on the calibration data, the compensation formula is established:

[0094] γ(T) = γ0[1 + α(T-T0) + β(T-T0) 2 ] Formula 10

[0095] Where γ0 is the reference photoelectric coefficient at reference temperature T0, and α and β are temperature coefficients. The real-time temperature data is used to correct γ, eliminating the influence of temperature on measurement accuracy.

[0096] Substituting formula 10 into formula 9, the electric field strength considering the influence of temperature is obtained:

[0097]

[0098] The size of the overvoltage U i of each electric field sensor can be calculated:

[0099]

[0100] Where P0 is the reference point where the electric field sensor is located, P is the surface point of the power equipment, and the integral path is along the electric field line direction.

[0101] It should be noted that the transformation of linearly polarized light and circularly polarized light can be described by a 2x2 complex matrix of Jones matrix. The polarization state of incident light is expressed by Jones vector , and the exit state after the optical element is , where J is the Jones matrix of the element.

[0102] The polarizer is only allowed to pass through a specific direction of polarized light, such as the Jones matrix of the x-direction polarizer:

[0103]

[0104] The quarter-wave plate 6 introduces a phase difference of π / 2, and the Jones matrix is:

[0105]

[0106] The photoelectric crystal 3 introduces a phase difference to the orthogonal polarization components under the action of an overvoltage field The Jones matrix is:

[0107]

[0108] The exit light intensity And The Jones matrix needs to be operated on each element in cascade to obtain. Taking the light path of "incident polarizer 5→ quarter-wave plate 6→ photoelectric crystal 3→ exit polarizer 7" as an example:

[0109]

[0110] After unfolding and calculating the modulus square, the relationship between the light intensity I and the phase difference is obtained. The formula 5 is the theoretical source.

[0111] The light intensity superposition model of double-beam interference It is essentially a simplified representation of the Jones matrix operation. When the two beams are orthogonal polarization components, the Jones matrix can prove that only the same direction polarization component can produce interference, and the orthogonal component does not interfere, thereby strictly limiting the condition of light intensity superposition, and providing a theoretical basis for the previous assumption "the minimum exit light intensity is 0" (only when the two beams are the same polarization and the phase difference is π, the light intensity is completely cancelled).

[0112] The electro-optic effect (Pockels effect) of the photoelectric crystal 3 is related to the electric field E through the phase difference parameter in the Jones matrix, and the formula is one of the core inputs of the Jones matrix operation. The polarization state analysis of the Jones matrix can establish a quantitative relationship between the electric field and the light intensity modulation, and provide theoretical support for formula 8 and formula 9.

[0113] In an alternative embodiment, the acquisition unit is communicatively connected to the electric field sensor 1 through the optical fiber 8.

[0114] In the present application, the optical fiber 8 transmission is not affected by electromagnetic interference, and the acquisition unit is communicatively connected to the electric field sensor 1 through the optical fiber 8, so that the acquisition unit, the calculation unit connected to the acquisition unit, and the output unit connected to the calculation unit are away from the overvoltage field area, and the acquisition unit, the calculation unit, and the output unit are protected from the interference of the overvoltage field.

[0115] In an alternative embodiment, the fiber grating temperature measurement unit 2 is integrated with the photoelectric crystal 3, and is suitable for measuring the temperature of the photoelectric crystal 3.

[0116] In this application, the fiber grating temperature measurement unit 2 is integrated with the photoelectric crystal 3, and realizes the real-time and accuracy of temperature compensation. The integrated design enables the temperature measurement unit to quickly respond to the temperature change of the photoelectric crystal 3, avoids the response delay of the traditional separate temperature measurement scheme, ensures the timeliness of the photoelectric coefficient compensation, makes the system still maintain the measurement accuracy under the condition of rapid temperature change, adapts to the dynamic operation demand of the power equipment, and improves the environmental adaptability of the monitoring system. Through real-time temperature compensation, the influence of temperature change on the photoelectric effect is effectively eliminated, the measurement accuracy of the sensor is not disturbed by the environmental temperature fluctuation, the stability is maintained in a wide temperature range, the measurement error caused by temperature drift is reduced, and reliable data support is provided for long-term reliability evaluation of the power equipment.

[0117] In an alternative embodiment, the electric field sensors 1 on the same circumferential plane realize the differentiation of range and sensitivity through different reflection times of incident light. By adjusting the crystal thickness, the incident angle of laser entering the crystal and the position of passing out of the crystal, the reflection times of the incident laser are modulated. The more the reflection times, the higher the sensitivity and the smaller the range.

[0118] In this application, the electric field sensors 1 with different reflection times are respectively responsible for overvoltage monitoring in different range ranges, and through cooperative work, the full range coverage from low amplitude to high amplitude overvoltage is realized, avoiding the measurement saturation or sensitivity decline problem of single range sensor when facing extreme overvoltage, expanding the monitoring range of the system, and ensuring that various overvoltages can be accurately captured. The sensor array with differentiated range and sensitivity provides multi-dimensional measurement data, and through the synchronous fitting of the calculation unit, the total range waveform containing the overvoltage waveforms of each circumferential plane electric field sensor 1 can be effectively obtained. The highest sensitivity electric field sensor 1 can also be determined based on the reflection times of the incident light, and the overvoltage waveform sensitivity of other electric field sensors 1 is unified based on the overvoltage waveform sensitivity of the highest electric field sensor 1, and then the overvoltage waveform with full range and the same sensitivity as the highest one is obtained. The sensitivity of the electric field sensor 1 with the most reflection times of incident light is the highest, which can be based on the waveform trend of the remaining electric field sensors 1, and the waveforms are differentiated by interpolation method, so that the sensitivity is consistent with the highest one.

[0119] Embodiment 2

[0120] A power high-voltage equipment wide frequency domain overvoltage online monitoring method is suitable for the power high-voltage equipment wide frequency domain overvoltage online monitoring system as described above, and includes the following steps:

[0121] Collecting the outgoing light intensity and temperature data;

[0122] The phase difference is obtained according to the light intensity, and the photoelectric coefficient is compensated based on the temperature data;

[0123] The overvoltage of each electric field sensor 1 is calculated based on the phase difference and the photoelectric coefficient;

[0124] The overvoltage intrusion direction is obtained based on the overvoltages of all electric field sensors 1;

[0125] The overvoltage waveform is obtained by data fitting of the circumferential planar electric field sensor 1, wherein the range of the overvoltage waveform is the total range of the circumferential planar electric field sensor 1, and the sensitivity of the overvoltage waveform is consistent with the highest sensitivity in the circumferential planar electric field sensor 1;

[0126] The overvoltage waveform and the overvoltage intrusion direction are output.

[0127] In the present application, from the collection of light intensity and temperature data to the calculation of phase difference, compensation of photoelectric coefficient, overvoltage inversion, direction judgment and waveform fitting, a complete data processing chain is formed, each step has clear algorithm support, avoiding the randomness of data processing, ensuring the repeatability and reliability of the overvoltage monitoring results, and providing a unified standard for overvoltage data analysis of power system. By using the cooperative measurement advantage of the electric field sensor array and through comprehensive analysis and fitting of the data of each sensor, not only the accurate measurement of overvoltage amplitude is realized, but also the intrusion direction of overvoltage is judged, providing multi-dimensional information for the tracing and protection of overvoltage, and improving the fault diagnosis ability of the system.

[0128] In an optional embodiment, the method further comprises:

[0129] A standard overvoltage waveform model database is established, and the overvoltage waveform is corrected based on the standard overvoltage waveform model.

[0130] The present application can also include offline data training for the precision and sensitivity of the monitoring system to realize offline calibration, for example, using standard instruments or power frequency to correct the precision and sensitivity. In the present application, the measurement precision can be improved and corrected through the spatial arrangement of the electric field sensor array, data fitting of the electric field sensor array and offline data training. The sensitivity can be corrected through offline data training. The sensitivity and range can be decoupled through data fitting of the electric field sensor array.

[0131] The present application can also include a standard overvoltage waveform model database establishment unit for establishing a standard overvoltage waveform model database.

[0132] In the present application, the standard overvoltage waveform model database contains typical characteristics of various overvoltages. By comparing the measured waveform with the standard model, the waveform distortion caused by environmental interference, sensor error and other factors can be effectively corrected, the restoration sensitivity of the overvoltage waveform is improved, the uncertainty of the overvoltage is eliminated, the monitoring data is closer to the actual overvoltage characteristics, and a more reliable basis is provided for the insulation evaluation of power equipment.

[0133] Based on the waveform correction of the standard model, the type and characteristic parameters of the overvoltage can be quickly identified, combined with the judgment of the overvoltage intrusion direction, the auxiliary fault type judgment is realized, more targeted guidance is provided for the maintenance and maintenance of power equipment, the fault processing time is shortened, and the operation and maintenance efficiency is improved.

[0134] The standardized waveform model provides a basis for statistical analysis and rule research of overvoltage. Through comparison and analysis of long-term monitoring data and standard model, the maintenance strategy of power equipment can be optimized, preventive maintenance can be realized, equipment failure rate can be reduced, and operation reliability and economy of power system can be improved.

[0135] In an optional implementation, it further comprises:

[0136] A three-dimensional electric field model is established to visualize the three-dimensional fluctuation of the electric field when the overvoltage intrudes in real time.

[0137] The present application can also include a three-dimensional electric field model establishing unit for establishing a three-dimensional electric field model. A denoising unit can be arranged between the acquisition unit and the calculation unit, and noise points can be removed through time-frequency decomposition.

[0138] The three-dimensional visualization model converts abstract electric field data into intuitive spatial field strength distribution images, enabling operation and maintenance personnel to clearly observe the spatial propagation path and intensity change of the electric field when the overvoltage intrudes, which helps to deeply understand the propagation law of overvoltage in power equipment and provides a visual basis for equipment insulation design and optimization.

[0139] Although the embodiments of the present application are described in conjunction with the drawings, various modifications and variations can be made by those skilled in the art without departing from the spirit and scope of the present application, and such modifications and variations all fall within the scope defined by the appended claims.

Claims

1. A wide-band overvoltage online monitoring system for electric high-voltage equipment, characterized in that: It includes an electric field sensor array, an acquisition unit, a calculation unit and an output unit; The electric field sensor array includes a plurality of sensors radially distributed on the same circumferential plane and having different ranges and sensitivities, and sensors distributed axially; The electric field sensor (1) comprises a sensing unit and a fiber Bragg grating temperature measurement unit (2), wherein the fiber Bragg grating temperature measurement unit (2) is suitable for measuring the temperature of the sensing unit; The acquisition unit is suitable for synchronously acquiring the output light intensity of the sensing unit and the temperature data of the fiber grating temperature measurement unit (2); The calculation unit is used to obtain a phase difference according to the intensity of the emitted light, and to compensate the photoelectric coefficient based on temperature data, and to calculate the overvoltage of each electric field sensor (1) based on the phase difference and the photoelectric coefficient, to obtain the overvoltage intrusion direction based on the overvoltage of all electric field sensors (1), and to perform data fitting on the circular plane electric field sensor (1) to obtain an overvoltage waveform, wherein the range of the overvoltage waveform is the total range of the circular plane electric field sensor (1), and the sensitivity of the overvoltage waveform is consistent with the highest sensitivity of the circular plane electric field sensor (1). The output unit is suitable for outputting an overvoltage waveform and an overvoltage intrusion direction.

2. The wide-band overvoltage online monitoring system for electric high-voltage equipment according to claim 1 is characterized in that: There are at least four electric field sensors (1) on the circumferential plane, which are evenly distributed along the radial direction; There is at least one axially distributed electric field sensor (1) perpendicular to the circumferential plane.

3. The wide-band overvoltage online monitoring system for electric high-voltage equipment according to claim 1 is characterized in that: Time domain synchronization of the electric field sensor array.

4. The wide-band overvoltage online monitoring system for electric high-voltage equipment according to claim 1 is characterized in that: The sensing unit comprises a photoelectric crystal (3), the opposite surface of which is provided with a reflection film (4) for reflecting incident light in the photoelectric crystal (3).

5. The wide-band overvoltage online monitoring system for electric high-voltage equipment according to claim 4 is characterized in that: The sensing unit is provided with an incident polarizer (5), a quarter-wave plate (6), and an exit polarizer (7); the polarization direction of the incident polarizer (5) is orthogonal to the polarization direction of the exit polarizer (7); and the optical path of the sensing unit passes through the incident polarizer (5), the quarter-wave plate (6), the photoelectric crystal (3), and the exit polarizer (7) in sequence.

6. The wide-band overvoltage online monitoring system for electric high-voltage equipment according to claim 1 is characterized in that: The acquisition unit is communicatively connected to the electric field sensor (1) via an optical fiber (8).

7. The wide-band overvoltage online monitoring system for electric high-voltage equipment according to claim 1 is characterized in that: The fiber grating temperature measurement unit (2) is integrated with the photoelectric crystal (3) and is suitable for measuring the temperature of the photoelectric crystal (3).

8. The wide-band overvoltage online monitoring system for electric high-voltage equipment according to claim 1 is characterized in that: The electric field sensor (1) on the same circular plane achieves differentiation of measurement range and sensitivity by different reflection times of incident light.

9. A method for online monitoring of overvoltage in a wide frequency domain of electric high-voltage equipment, applicable to the online monitoring system for overvoltage in a wide frequency domain of electric high-voltage equipment according to any one of claims 1 to 8, characterized in that: The following steps are involved: Collect output light intensity and temperature data; The phase difference is obtained according to the outgoing light intensity, and the photoelectric coefficient is compensated based on the temperature data; calculating an overvoltage of each electric field sensor (1) based on the phase difference and the photoelectric coefficient; Obtaining an overvoltage intrusion direction based on overvoltages of all electric field sensors (1); Performing data fitting on the circular plane electric field sensor (1) to obtain an overvoltage waveform, wherein the range of the overvoltage waveform is the total range of the circular plane electric field sensor (1), and the sensitivity of the overvoltage waveform is consistent with the highest sensitivity of the circular plane electric field sensor (1); Output overvoltage waveform and overvoltage intrusion direction.

10. The method for online monitoring of wide-band overvoltage of electric high-voltage equipment according to claim 9, characterized in that: Also includes: A standard overvoltage waveform model database is established, and the overvoltage waveform is corrected based on the standard overvoltage waveform model.

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