Optical fiber magnetic field detection system based on feedback interference effect and application of optical fiber magnetic field detection system in power equipment partial discharge electromagnetic wave signal detection

Abstract

The invention discloses an optical fiber magnetic field detection system based on a feedback interference effect and application of the optical fiber magnetic field detection system in partial discharge electromagnetic wave signal detection of power equipment, and belongs to the technical field of partial discharge detection. According to the invention, problems existing in a partial discharge detection method of power equipment are solved. An optical fiber Fabry-Perot (F-P) laser coated with a magnetic fluid film is used as a sensor probe, the sensitivity of the F-P laser is enhanced through a feedback interference system, and the reflectivity and phase conditions of the magnetic fluid are changed through the action of a partial discharge electromagnetic wave signal on the magnetic fluid. The total optical path difference of the self-mixing interference signals output by the feedback interference system is changed, and then the phase of feedback light is changed, so that the change of the output light intensity is caused, the detection of electromagnetic wave signals is realized, and higher sensitivity, wider detection range, larger multiplexing capacity and more excellent anti-electromagnetic interference capability are realized.

Description

Technical Field

[0001] The present invention relates to an optical fiber magnetic field detection system based on a feedback interference effect and its application in detecting partial discharge electromagnetic wave signals of power equipment, belonging to the technical field of partial discharge detection. Background Art

[0002] High-voltage electrical equipment such as power transformers, transmission lines, and gas-insulated switches are key components of the power system, and their reliable operation is extremely crucial for the stability of the power grid system. Faults caused by the reduction of the insulation level of electrical equipment account for a relatively large proportion in electrical faults. Approximately 10% of electrical equipment will cause serious consequences such as explosions after insulation defects occur, which pose a serious threat to the personal safety of power grid maintenance personnel. Partial discharge is the main precursor of insulation faults in electrical equipment. When partial discharge occurs, physical characteristics such as pulse current, electromagnetic wave, ultrasonic wave, and discharge products often appear. By detecting these physical quantities and timely discovering the partial discharge defects existing inside the equipment, fault early warning can be realized to ensure the safety of the equipment and the reliability of power supply. In recent years, with the cross-development of various disciplines, the research on using optical fiber ultrasonic sensors for ultrasonic detection of partial discharge in power equipment has received extensive attention. However, due to the high viscoelasticity of insulating materials, the acoustic wave absorption attenuation is serious, and acoustic sensors are generally less sensitive than electrical sensors in the partial discharge detection environment. Therefore, the detection range of a single optical fiber ultrasonic sensor is severely limited at present, the number of sensors required for network operation is large, and the pressure on the upper computer for data acquisition and processing is high. For ultra-high frequency sensors, although they have high sensitivity, they face problems such as rapid signal attenuation and severe electromagnetic interference. Although other chemical detection methods have high accuracy, they have a long detection time and poor real-time performance. To sum up, there is still a need for a sensing system with high sensitivity, long transmission distance, and strong real-time performance to meet the current partial discharge detection requirements of power equipment. Summary of the Invention

[0003] The present invention aims at the problems existing in the existing partial discharge detection methods for power equipment, and provides an optical fiber magnetic field detection system based on a feedback interference effect and its application in detecting partial discharge electromagnetic wave signals of power equipment.

[0004] The technical solution of the present invention:

[0005] One of the purposes of the present invention is to provide an F-P cavity sensor, which includes an optical fiber collimator, a resonant cavity, a magnetic fluid thin film, and a gain medium;

[0006] The magnetic fluid thin film is coated on the end face of the optical fiber collimator, the gain medium is parallel to the magnetic fluid thin film on the end face of the optical fiber collimator and forms an F-P cavity through the resonant cavity, and the F-P cavity is filled with air.

[0007] Further defined, the thickness of the magnetic fluid thin film is 400 μm.

[0008] Further defined, the material for preparing the magnetic fluid thin film is oil-based magnetic fluid, with a concentration of 4%, a saturation magnetization value of 11 mT, and a viscosity of 60 mPa·s.

[0009] Further defined, the oil-based magnetic fluid is produced by Ferrotec Corporation.

[0010] Further defined, the preparation method of the magnetic fluid thin film is: coating the oil-based magnetic fluid on the end face of the fiber collimator and fixing it with ultraviolet curing glue.

[0011] Even further defined, the ultraviolet curing glue is purchased from Norland Corporation in the United States, and the model is NOA83H.

[0012] Even further defined, the method of fixing with ultraviolet curing glue is irradiating with an ultraviolet lamp for 120 s.

[0013] Further defined, the material of the gain medium is erbium-ytterbium co-doped glass.

[0014] Even further defined, the erbium-ytterbium co-doped glass is purchased from Optogama in Lithuania, and the model is 7823.

[0015] The second object of the present invention is to provide a fiber optic magnetic field detection system based on the feedback interference effect, including a pump light source, a wavelength division multiplexer, an F-P cavity sensor, a coupler, an attenuator, a mirror, an isolator, a polarization controller, a polarization analyzer, and an optical converter;

[0016] The pump light source and the F-P cavity sensor are respectively connected to the wavelength division multiplexer, and the output end of the wavelength division multiplexer is connected to the input end of the coupler; one output end of the coupler is sequentially connected to the attenuator and the mirror, and the other output end is sequentially connected to the isolator, the polarization controller, the polarization analyzer, and the optical converter.

[0017] Further defined, the central wavelength of the pump light source is 980 nm.

[0018] Further defined, the coupler is a 1×2 fiber optic coupler.

[0019] The second object of the present invention is to provide an application of the above-mentioned fiber optic magnetic field detection system based on the feedback interference effect, specifically for detecting the partial discharge electromagnetic wave signal of power equipment.

[0020] The third object of the present invention is to provide a method for detecting the above-mentioned partial discharge electromagnetic wave signal, specifically placing the F-P cavity sensor in the fiber optic magnetic field detection system based on the feedback interference effect in the environment where the power equipment is located.

[0021] Further defined, after the light emitted by the pump light source is injected into the F-P cavity sensor through the wavelength division multiplexer, it exits through the port of the wavelength division multiplexer. The emitted light passes through a coupler, and then part of it returns to the F-P cavity sensor through an attenuator and a mirror. After being reflected by the magnetic fluid thin film, the feedback light passes through a polarization controller and an analyzer in sequence and is detected by a photodetector. When partial discharge occurs in the power equipment, the electromagnetic wave signal of the partial discharge acts on the magnetic fluid thin film of the F-P cavity sensor, causing the reflectivity of the magnetic fluid thin film to change, and then changing the light intensity of the feedback light signal. At the same time, the feedback interference effect realized by the three-mirror cavity model composed of the gain medium, the magnetic fluid thin film and the mirror in the F-P cavity sensor is used to enhance the change in the light intensity of the feedback light signal formed due to the change in the reflectivity of the magnetic fluid thin film, so that the light intensity and light phase of the feedback light signal change further, realizing the sensitive detection of the electromagnetic wave signal.

[0022] Further defined, when the central wavelength of the pump light source is 980 nm, the laser wavelength emitted from the port of the wavelength division multiplexer is 1550 nm.

[0023] Beneficial effects:

[0024] The present invention provides a fiber optic Fabry-Perot (F-P) laser coated with a magnetic fluid thin film as a sensor probe, and uses a feedback interference system to enhance the sensitivity of the F-P laser. The action of the partial discharge electromagnetic wave signal on the magnetic fluid changes its reflectivity and phase conditions, causing the total optical path difference of the self-mixing interference signal output by the feedback interference system to change, and then changing the phase of the feedback light, thereby causing a change in the output light intensity, realizing the detection of the electromagnetic wave signal.

[0025] The fiber optic magnetic field detection system based on the feedback interference effect provided by the present invention determines the occurrence of partial discharge by detecting the electromagnetic wave signal generated by the discharge. Compared with the fiber optic acoustic wave sensor, it has higher sensitivity and a wider detection range. Compared with the traditional electrical measurement method, it has a longer detection distance, a larger multiplexing capacity and better electromagnetic interference resistance. Compared with the chemical detection method, it has stronger real-time performance. Description of the drawings

[0026] Figure 1 It is a schematic structural diagram of the F-P cavity sensor;

[0027] Figure 2 It is a fiber optic magnetic field detection system based on the feedback interference effect;

[0028] Figure 3 It is a spectrogram of the laser emitted from the port of the wavelength division multiplexer;

[0029] Figure 4 It is a schematic diagram of the principle of the three-mirror cavity model;

[0030] Figure 5 is a partial discharge signal detection platform;

[0031] Figure 6 is a diagram of the partial discharge signal detection result;

[0032] In the figure, 1 - optical fiber collimator, 1-1 - collimator pigtail, 2 - resonant cavity, 3 - magnetorheological fluid thin film, 4 - gain medium, 5 - F-P cavity sensor, 6 - wavelength division multiplexer, 7 - pump light source, 8 - coupler, 9 - attenuator, 10 - mirror, 11 - isolator, 12 - polarization controller, 13 - analyzer, 14 - photodetector. Specific embodiments

[0033] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention; obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0034] In the description of the present invention, it should be noted that the orientation or positional relationship indicated by the terms "upper", "lower", "inner", "outer", "top / bottom end", etc. is based on the orientation or positional relationship shown in the accompanying drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation of the present invention.

[0035] In the description of the present invention, it should be noted that unless otherwise clearly specified and limited, the terms "installed", "provided with", "sheathed / connected", "connected", etc. should be understood in a broad sense. For example, "connected" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the internal communication of two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0036] Such as Figure 1As shown in the figure, the present invention provides an F-P cavity sensor, which includes an optical fiber collimator 1, a resonant cavity 2, a magnetic fluid film 3, and a gain medium 4. Among them, the magnetic fluid film 3 is coated on the end face of the optical fiber collimator 1, and the gain medium 4 is parallel to the magnetic fluid film 3 on the end face of the optical fiber collimator 1 and forms an F-P cavity through the resonant cavity 2, and the F-P cavity is filled with air. Specifically, the thickness of the magnetic fluid film is 400 μm, the material for preparing the magnetic fluid film is an oil-based magnetic fluid with a concentration of 4% produced by Ferrotec Corporation, its carrier liquid is synthetic esters, the saturation magnetization value is 11 mT, and the viscosity is 60 mPa·s. The method for preparing the magnetic fluid film is as follows: coat the magnetic fluid on the end face of the optical fiber collimator 1, and then fix it with an ultraviolet curing adhesive. The ultraviolet adhesive cures to form a protective film on the outer surface of the magnetic fluid film. The method for fixing with the ultraviolet curing adhesive is ultraviolet lamp irradiation for 120 s. The ultraviolet curing adhesive is purchased from Norland Corporation of the United States, and the model is NOA83H. The gain medium is purchased from Optogama Corporation of Lithuania, and the model is 7823 erbium-ytterbium co-doped glass.

[0037] As Figure 2 shown in the figure, the present invention provides an optical fiber magnetic field detection system based on the feedback interference effect. The system includes a pump light source 7, a wavelength division multiplexer 6, the above-mentioned F-P cavity sensor 5, a coupler 8, an attenuator 9, a mirror 10, an isolator 11, a polarization controller 12, an analyzer 13, and an optical converter 14. Among them, the pump light source 7 and the F-P cavity sensor 5 are respectively connected to the wavelength division multiplexer 6, and the output end of the wavelength division multiplexer 6 is connected to the input end of the coupler 8. One output end of the coupler 8 is sequentially connected to the attenuator 9 and the mirror 10, and the other output end is sequentially connected to the isolator 11, the polarization controller 12, the analyzer, and the optical converter 14. Specifically, the central wavelength of the pump light source 7 is 980 nm, and the coupler 8 is a 1×2 optical fiber coupler.

[0038] The method for detecting the partial discharge electromagnetic wave signal of a power equipment by using the above-mentioned optical fiber magnetic field detection system based on the feedback interference effect is as follows:

[0039] The pump light source 7 emits a laser with a central wavelength of 980 nm, which is injected into the F-P cavity sensor 5 through the wavelength division multiplexer 6, and vertically enters the resonant cavity 2 through the optical fiber collimator 1. The resonant cavity 2 is filled with air. The light reflects back and forth between the two reflective end faces of the magnetic fluid film 3 and the gain medium 4 in the F-P cavity sensor 5 to form a multi-beam interference effect, and finally a laser with an extremely narrow line width of 1550 nm is emitted through the wavelength division multiplexer 6. The specific spectrum is as Figure 3 shown in the figure.

[0040] The reason for selecting the 1550nm laser with an extremely narrow emission linewidth in this application is that the light in the 1550nm band has the lowest attenuation in optical fibers. Specifically, it is achieved by using an erbium-ytterbium co-doped glass as the gain medium. Among different gain materials, rare-earth ions have become commonly used doping materials in solid-state lasers due to their high efficiency, long high-energy-level lifetimes, ability to generate short pulses, and wide emission spectra. Since the light in the 1550nm band has the lowest attenuation in optical fibers, the radiation wavelength of erbium ions meets the requirements. However, due to its small absorption transition cross-section, it is difficult to achieve high-efficiency pump absorption transitions in erbium-doped gain media. To avoid quenching effects, ytterbium ions are generally doped as sensitizers to solve this problem. Ytterbium ions can effectively absorb 980nm pump light and then transfer the energy to erbium ions in the ground state and excite them to high energy levels. Finally, erbium ions transition from high energy levels to the ground state energy level and radiate 1550nm wavelength laser light.

[0041] The extremely narrow linewidth 1550nm laser emitted through the wavelength division multiplexer 6 is coupled by the coupler 8 (a one-to-two fiber coupler), and a part of the light returns to the F-P sensor 5 through the attenuator 9 and the mirror 10. After being reflected by the magnetic fluid film, the feedback light is detected by the photodetector 14 after passing through the polarization controller and the analyzer in sequence. At the same time, the light intensity of the feedback light is adjusted using the attenuator, and the polarization angle of the polarizer of the analyzer is rotated to the horizontal direction to obtain the feedback interference signal of horizontally polarized light.

[0042] Magnetic fluid is also known as magnetic liquid. Its appearance is a brownish colloidal solution with high stability. Usually, it is in a stable liquid state, and its basic composition includes magnetic nanoparticles, surfactants, and base liquid. When there is no external magnetic field, the magnetic fluid particles are evenly distributed in the base liquid, presenting a liquid state as a whole. However, after applying a magnetic field, the nano-magnetic particles respond rapidly, and the microstructure of the magnetic fluid generates a clustering phenomenon to form magnetic flocs. The magnetic flocs form magnetic chains in the direction of the magnetic field during the continuous application of the magnetic field. The magnetic chains are arranged along the direction of the external magnetic field, and fluid regions are formed between the magnetic chains. Light can only pass through the fluid regions, so the effective density and area ratio of the magnetic fluid determine the light transmission ability of the magnetic body. Under the action of an external magnetic field, the effective density of the liquid phase is:

[0043]

[0044] In the formula, M s is the saturation magnetization intensity per gram of magnetic fluid, M c is the saturation magnetization intensity per gram of magnetic chain, ρ is the density of the magnetic fluid, ρ s is the density of the formed magnetic chain, A refers to the cross-sectional area of the magnetic fluid thin sheet, A c is the cross-sectional area occupied by magnetic chains in A.

[0045] Magnetic fluid has superparamagnetism. According to the dichroism of magnetic fluid, the attenuation degree of linearly polarized light parallel to the magnetic field is greater than that perpendicular to the magnetic field.

[0046] When the light beam is incident perpendicularly to the surface of the magnetic liquid, the magnetic field direction is parallel to the light-transmitting surface, and the light transmittance is the ratio of the interference signal amplitudes before and after the action of the magnetic field. The average amplitudes before and after applying the magnetic field are H 0 and H respectively. The reflectivity expression of the magnetic fluid is

[0047]

[0048] That is, after being affected by the external magnetic field, the light intensity changes after the laser passes through the magnetic fluid. At this time, the amplitude of the laser self-mixing interference signal under weak feedback also changes, and finally the signal to be measured is demodulated by optoelectronics. Therefore, the partial discharge signal will directly affect the reflectivity of the magnetic fluid film and the attenuation coefficient of the linearly polarized light in the horizontal direction. When the magnetic fluid film is used as the cavity composition condition of the F-P sensor 5 in this application, as long as there is a slight interference, it will bring a drastic light intensity fluctuation. The linearly polarized light in the horizontal direction can be detected through the polarization controller and the analyzer, and the signal is transmitted to the upper computer through the optoelectronic detector 14.

[0049] However, the sensitivity of the light intensity attenuation generated by the magnetic fluid alone is not sufficient to meet the requirements of partial discharge detection. Therefore, this application uses a feedback interference system to enhance the detection sensitivity of the system. As Figure 4 shown, in this application, a three-mirror cavity model is constructed using the gain medium 4, the magnetic fluid film 3, and the mirror 10. The resonant cavity 2 between the gain medium 4 and the magnetic fluid film 3 constitutes the inner cavity of the laser, and the magnetic fluid film 3 and the mirror 10 constitute the outer cavity of the laser. l is a fixed value representing the length of the inner cavity of the laser, and L changes according to the change of the external mirror 10, representing the outer cavity length. The intensity and optical path of the feedback light are actively adjusted by adjusting the mirror 10. The intensity and phase of the feedback light can change, causing changes in the spectrum and total light intensity of the feedback light. The light intensity and light phase changes of the feedback light are detected by the optoelectronic detector.

[0050] The phase change of the specific feedback interference system is expressed as:

[0051]

[0052] where ω represents the angular frequency of the light wave; c is the speed of light in vacuum; n is the refractive index of the fiber core.

[0053] When the electromagnetic wave of partial discharge acts on the magnetic fluid film 3, it will change the reflectivity and phase conditions of the magnetic fluid film 3, change the total optical path difference, and then change the phase of the feedback light, and further cause a change in the output light intensity. Therefore, the output optical power of the laser self-mixing magnetic field detection system is:

[0054]

[0055] wherein, m is the fringe contrast of the self-mixing interference signal, also known as the modulation coefficient; P 0 is the initial optical power of the system.

[0056] Furthermore, in order to verify the detection effect of the above-mentioned fiber optic magnetic field detection system based on the feedback interference effect, as Figure 5 shown, a partial discharge signal detection platform is built, and an experimental transformer model is used to simulate the actual detection environment to simulate the real propagation process of the partial discharge signal. The partial discharge source is a standard needle-plate electrode, and a high-frequency CT sensor used in engineering practical applications is used as a comparison sensor. The detection results of the sensors of this system are as Figure 6 shown. As can be seen from Figure 6 this, the fiber optic magnetic field detection system based on the feedback interference effect provided by this application can effectively detect partial discharge signals, and at the same time its detection signal-to-noise ratio is significantly higher than that of the high-frequency CT sensor.

[0057] Although the present invention has been disclosed above with preferred embodiments, it is not intended to limit the present invention. Anyone familiar with this technology can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention should be defined by the claims.

Claims

1. A FP cavity sensor, characterized in that: It includes a fiber collimator, a resonant cavity, a magnetic fluid film and a gain medium; The magnetic fluid film is coated on the end face of the optical fiber collimator, the gain medium is parallel to the magnetic fluid film on the end face of the optical fiber collimator and forms an FP cavity through the resonant cavity, and the FP cavity is filled with air.

2. The FP cavity sensor according to claim 1, characterized in that: The thickness of the magnetic fluid film is 400 μm. The material used to prepare the magnetic fluid film is an oil-based magnetic fluid with a concentration of 4%, a saturation magnetization value of 11 mT, and a viscosity of 60 mPa·s.

3. The FP cavity sensor according to claim 1, characterized in that: The material of the gain medium is erbium-ytterbium co-doped glass.

4. An optical fiber magnetic field detection system based on feedback interference effect, characterized in that: It comprises a pump light source, a wavelength division multiplexer, the FP cavity sensor according to any one of claims 1 to 3, a coupler, an attenuator, a reflector, an isolator, a bias controller, an analyzer and an optical converter; The pump light source and the FP cavity sensor are connected to the wavelength division multiplexer respectively, and the output end of the wavelength division multiplexer is connected to the input end of the coupler; one output end of the coupler is connected to the attenuator and the reflector in sequence, and the other output end is connected to the isolator, the polarization controller, the analyzer and the optical converter in sequence.

5. The optical fiber magnetic field detection system based on feedback interference effect according to claim 4, characterized in that: The central wavelength of the pump light source is 980nm.

6. The optical fiber magnetic field detection system based on feedback interference effect according to claim 4, characterized in that: The coupler is a one-to-two optical fiber coupler.

7. An application of the optical fiber magnetic field detection system based on feedback interference effect according to any one of claims 4 to 6, characterized in that: Used for detection of partial discharge electromagnetic wave signals from power equipment.

8. A method for detecting partial discharge electromagnetic wave signals, characterized in that: The FP cavity sensor in the optical fiber magnetic field detection system based on feedback interference effect as described in any one of claims 4 to 6 is placed in the environment where the power equipment is located.

9. The detection method according to claim 8, characterized in that: The light emitted by the pump light source is injected into the FP cavity sensor through the wavelength division multiplexer and then emitted through the port of the wavelength division multiplexer. The emitted light passes through the coupler and then passes through the attenuator and the reflector to return to the FP cavity sensor. After being reflected by the magnetic fluid film, the feedback light passes through the polarization controller and the analyzer in sequence and is detected by the photodetector. When partial discharge occurs in the power equipment, the electromagnetic wave signal of the partial discharge acts on the magnetic fluid film of the FP cavity sensor, causing the reflectivity of the magnetic fluid film to change, thereby changing the light intensity of the feedback light signal. At the same time, the feedback interference effect realized by the three-mirror cavity model composed of the gain medium, the magnetic fluid film and the reflector in the FP cavity sensor is used to enhance the light intensity change of the feedback light signal formed by the change of the reflectivity of the magnetic fluid film, so that the light intensity and light phase of the feedback light signal are further changed, thereby realizing sensitive detection of the electromagnetic wave signal.

10. The detection method according to claim 8, characterized in that: When the central wavelength of the pump light source is 980 nm, the wavelength of the laser emitted from the port of the wavelength division multiplexer is 1550 nm.

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