A dual mach-zehnder fiber sensing optical path, discharge positioning method and device

Abstract

The application relates to the technical field of optical fiber sensing, and particularly relates to a double Mach-Zehnder optical fiber sensing optical path, a discharge positioning method and a device. The optical path comprises: a first optical coupler; a second optical coupler, which is used for splitting a first light beam into a first reference light beam and a first sensing light beam; a third optical coupler, which is used for splitting a second light beam into a second reference light beam and a second sensing light beam; a first acousto-optic modulator, which is used for applying a first offset frequency to the first reference light beam and the second reference light beam respectively to obtain a first offset reference light beam and a second offset reference light beam; a second acousto-optic modulator, which is used for applying a second offset frequency to the first sensing light beam and the second sensing light beam respectively to obtain a first offset sensing light beam and a second offset sensing light beam; and the first offset frequency is not equal to the second offset frequency. The application effectively improves the detection capability of a distributed optical fiber sensing system on a weak signal and the signal demodulation quality.

Description

Technical Field

[0001] This invention relates to the field of fiber optic sensing technology, specifically to a dual Mach-Zehnder fiber optic sensing optical path, a discharge positioning method, and a device. Background Technology

[0002] During the production, installation, and long-term operation of electrical equipment such as gas-insulated switchgear (GIS), transformers, and power cables, conductive impurities such as metal particles inevitably arise or become mixed in. These impurities are prone to tripping and inducing partial discharge under a high electric field. Continuous discharge gradually degrades the internal insulation performance of the equipment, and in severe cases, can lead to major accidents such as insulation breakdown. Therefore, effective monitoring of internal partial discharge signals is a crucial maintenance task for preventing faults and ensuring the safe and stable operation of the system.

[0003] Acoustic emission sensing technology based on fiber optic interferometry is often used for partial discharge monitoring due to its advantages such as insulation, strong resistance to electromagnetic interference, and ease of networking. Among them, the dual Mach-Zehnder (MZ) fiber optic interferometer, with its fewer optical components and multi-point detection capabilities, is currently a popular solution for distributed fiber optic sensing. However, existing dual Mach-Zehnder fiber optic interferometer optical paths are susceptible to the influence of stray light backscattered from the fiber optic link, resulting in increased background noise. Since the acoustic emission signal corresponding to partial discharge is weak in amplitude and has low characteristic signal intensity, the high background noise will completely cover the effective characteristic signal, making it impossible to accurately extract partial discharge information and significantly reducing detection sensitivity and positioning accuracy. Summary of the Invention

[0004] This invention provides a dual Mach-Zehnder fiber sensing optical path, a discharge localization method, and a device to solve the problem of high background noise in dual Mach-Zehnder fiber interferometric optical paths, thereby improving the sensitivity and localization accuracy of partial discharge detection.

[0005] According to one aspect of the present invention, a dual Mach-Zehnder fiber optic sensing optical path is provided, comprising:

[0006] The first optical coupler is used to split the original beam into a first beam and a second beam;

[0007] A second optical coupler, wherein the first end of the second optical coupler is connected to the first end of the first optical coupler, is used to split the first beam into a first reference beam and a first sensing beam.

[0008] A third optical coupler, wherein a first end of the third optical coupler is connected to a second end of the first optical coupler, is used to split the second beam into a second reference beam and a second sensing beam.

[0009] A first acousto-optic modulator is connected between the second end of the second optical coupler and the second end of the third optical coupler, and is used to apply a first offset frequency to the first reference beam and the second reference beam respectively to obtain a first offset reference beam and a second offset reference beam.

[0010] The second acousto-optic modulator is connected between the third end of the second optical coupler and the third end of the third optical coupler, and is used to apply a second offset frequency to the first sensing beam and the second sensing beam respectively to obtain the first offset sensing beam and the second offset sensing beam.

[0011] The first offset frequency is not equal to the second offset frequency;

[0012] A first photodetector is connected to the fourth end of the second optical coupler and is used to receive the first interference beam obtained after the second offset reference beam and the second offset sensing beam interfere in the second optical coupler, and to convert the first interference beam into a first interference signal.

[0013] The second photodetector is connected to the fourth end of the third optical coupler and is used to receive the second interference beam obtained after the first offset reference beam and the first offset sensing beam interfere in the third optical coupler, and to convert the second interference beam into a second interference signal.

[0014] According to another aspect of the present invention, a partial discharge localization method is provided, applied to the dual Mach-Zehnder fiber optic sensing optical path described in any embodiment of the present invention, the partial discharge localization method comprising:

[0015] The signals output by the first photodetector and the second photodetector are filtered according to the first offset frequency and the second offset frequency to obtain the first interference signal and the second interference signal;

[0016] A first orthogonal reference signal and a second orthogonal reference signal with the same frequency as the first interference signal and the second interference signal are generated respectively;

[0017] The first interference signal is multiplied by the first orthogonal reference signal and the second orthogonal reference signal respectively and filtered to obtain a first set of baseband signals. The second interference signal is multiplied by the first orthogonal reference signal and the second orthogonal reference signal respectively and filtered to obtain a second set of baseband signals. The first set of baseband signals includes a first in-phase component and a first quadrature component, and the second set of baseband signals includes a second in-phase component and a second quadrature component.

[0018] Differential-cross multiplication operations are performed on the first in-phase component and the first quadrature component, as well as on the second in-phase component and the second quadrature component, respectively. The difference is then calculated and normalized to obtain the first phase change signal and the second phase change signal.

[0019] The first phase change signal and the second phase change signal are integrated respectively to obtain the first phase change amount and the second phase change amount;

[0020] The time delay between the first interference signal and the second interference signal is determined based on the first phase change and the second phase change, and the location of the partial discharge is determined based on the time delay.

[0021] According to another aspect of the present invention, a partial discharge location device is provided, comprising the dual Mach-Zehnder fiber optic sensing optical path described in any embodiment of the present invention.

[0022] The technical solution of this invention modulates the optical frequencies of the first and second sensing beams on the sensing fiber and the first and second reference beams on the reference fiber, respectively, by setting two first and second acousto-optic modulators with different frequencies. Then, the photoelectric signals are converted using first and second photodetectors, resulting in a significant difference between the frequencies of the first and second interference signals and the frequencies of the noise interference signals formed by backscattered light. This allows for effective suppression and filtering of noise interference. Therefore, the solution of this invention weakens the submergence effect of backscattered light on weak sensing signals, significantly reduces the background noise caused by backscattered light, ensures the integrity and identifiability of weak acoustic-vibration sensing signals of partial discharge, and effectively improves the detection capability and signal demodulation quality of the distributed fiber optic sensing system for weak signals.

[0023] It should be understood that the description in this section is not intended to identify key or essential features of the embodiments of the present invention, nor is it intended to limit the scope of the invention. Other features of the invention will become readily apparent from the following description. Attached Figure Description

[0024] To more clearly illustrate the technical solutions of the embodiments of this disclosure, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this disclosure. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 This is a schematic diagram of a dual Mach-Zehnder fiber optic sensing optical path provided in an embodiment of the present invention;

[0026] Figure 2 A flowchart of a partial discharge localization method provided in an embodiment of the present invention;

[0027] Figure 3 A comparison diagram of phase noise density spectrum after IQ demodulation of a dual Mach-Zehnder fiber sensing optical path provided in an embodiment of the present invention;

[0028] Figure 4 A phase noise time-domain comparison curve is provided for an embodiment of the present invention. Detailed Implementation

[0029] The embodiments of this disclosure will now be described in detail with reference to the accompanying drawings.

[0030] The following specific examples illustrate the implementation of this disclosure. Those skilled in the art can easily understand other advantages and effects of this disclosure from the content disclosed in this specification. Obviously, the described embodiments are only a part of the embodiments of this disclosure, and not all of them. This disclosure can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of this disclosure. It should be noted that, in the absence of conflict, the following embodiments and features in the embodiments can be combined with each other. Based on the embodiments in this disclosure, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this disclosure.

[0031] It should be noted that various aspects of embodiments within the scope of the appended claims are described below. It will be apparent that the aspects described herein can be embodied in a wide variety of forms, and any particular structure and / or function described herein is merely illustrative. Based on this disclosure, those skilled in the art will understand that one aspect described herein can be implemented independently of any other aspect, and two or more of these aspects can be combined in various ways. For example, any number of aspects set forth herein can be used to implement the device and / or practice the method. Additionally, this device and / or method can be implemented using structures and / or functionalities other than one or more of the aspects set forth herein.

[0032] It should also be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of this disclosure. The drawings only show the components related to this disclosure and are not drawn according to the number, shape and size of the components in actual implementation. In actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0033] Furthermore, specific details are provided in the following description to facilitate a thorough understanding of the examples. However, those skilled in the art will understand that the described aspects can be practiced without these specific details.

[0034] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of protection of the present invention.

[0035] Figure 1 This is a schematic diagram of a dual Mach-Zehnder fiber optic sensing optical path provided in an embodiment of the present invention. This embodiment is applicable to the partial discharge detection of power equipment such as GIS, transformers, and power cables. This dual Mach-Zehnder fiber optic sensing optical path can be configured in a dual Mach-Zehnder fiber optic sensor. Figure 1 As shown, the dual Mach-Zehnder fiber optic sensing path includes:

[0036] A first optical coupler C1 is used to split the original light beam into a first beam and a second beam. A second optical coupler C2, with its first end connected to the first end of the first optical coupler C1, is used to split the first beam into a first reference beam and a first sensing beam. A third optical coupler C3, with its first end connected to the second end of the first optical coupler C1, is used to split the second beam into a second reference beam and a second sensing beam. A first acousto-optic modulator AOM1, connected between the second ends of the second optical coupler C2 and the third optical coupler C3, is used to apply a first offset frequency to the first and second reference beams respectively, obtaining a first offset reference beam and a second offset reference beam. A second acousto-optic modulator AOM2, connected between the third ends of the second optical coupler C2 and the third optical coupler C3, is used to apply a second offset frequency to the first and second sensing beams respectively, obtaining a first offset sensing beam and a second offset sensing beam. The first offset frequency and the second offset frequency are not equal. The first photodetector PD1 is connected to the fourth end of the second optical coupler C2. It is used to receive the first interference beam obtained after the second offset reference beam and the second offset sensing beam interfere in the second optical coupler C2, and to convert the first interference beam into a first interference signal. The second photodetector PD2 is connected to the fourth end of the third optical coupler C3. It is used to receive the second interference beam obtained after the first offset reference beam and the first offset sensing beam interfere in the third optical coupler C3, and to convert the second interference beam into a second interference signal.

[0037] Specifically, an optical coupler is a passive optical device capable of splitting, combining, interfering with, and switching optical signals. A reference beam refers to a beam that propagates along a fixed optical path in a reference fiber, unaffected by external acoustic vibrations or deformations. As a reference beam, it is used to compare with the sensing beam, providing a stable phase reference unaffected by external measured signals. The sensing beam refers to a beam that propagates along a sensing fiber and is positioned close to the device under test. The sensing beam undergoes phase changes due to external partial discharges, acoustic vibrations, and micro-deformations, carrying information about the measured physical quantity; it is used as a probe light to acquire the measured signal. An acousto-optic modulator is an active optical modulator that utilizes the principle of acousto-optic interaction to frequency-shift and intensity-modulate the incident beam. An acousto-optic modulator can apply a fixed offset frequency to the transmitted beam, causing a stable frequency shift in the output beam relative to the incident beam, providing a controllable frequency reference for the fiber optic interferometer system. An offset reference beam is the reference beam after a fixed offset frequency has been applied by the acousto-optic modulator. In this embodiment of the invention, the offset reference beam generates a first offset frequency shift based on the original reference beam. The offset sensing beam is a sensing beam after a fixed offset frequency is applied by an acousto-optic modulator. In this embodiment of the invention, the offset sensing beam generates a second offset frequency shift based on the original sensing beam. A photodetector is a photoelectric conversion device capable of receiving optical signals in an optical path and linearly converting interference beams with varying intensity and amplitude into processable voltage and current signals. An interference beam refers to a composite beam with periodically changing amplitude formed by combining two coherent offset reference beams and offset sensing beams through an optical coupler, resulting in phase-construction and destructive phase interactions. The intensity variation of the interference beam carries external disturbances and phase. An interference signal refers to the analog electrical signal output after the interference beam undergoes photoelectric conversion by the photodetector. The amplitude of the interference signal changes periodically with the intensity of the interference light, carrying the phase distortion, acoustic disturbances, and frequency shift characteristics of the sensing optical path.

[0038] In this embodiment of the invention, the first optical coupler C1 splits the original light beam equally, obtaining a first beam and a second beam with consistent light intensity amplitude. The first beam is split into a first reference beam and a first sensing beam by the second optical coupler C2. The first reference beam is modulated by the first acousto-optic modulator AOM1, generating a frequency shift of the first offset frequency to obtain the first offset reference beam. The first sensing beam is modulated by the second acousto-optic modulator AOM2, generating a frequency shift of the second offset frequency to obtain the first offset sensing beam. The first offset sensing beam and the first offset reference beam interfere at the third optical coupler C3 to obtain the second interference beam. The second photodetector PD2 converts the second interference beam into an electrical signal, i.e., the second interference signal. The second beam is split into a second reference beam and a second sensing beam by the third optical coupler C3. The second reference beam is modulated by the first acousto-optic modulator AOM1, generating a frequency shift of the first offset frequency to obtain the second offset reference beam. The second sensing beam is modulated by the second acousto-optic modulator AOM2, generating a frequency shift of the second offset frequency to obtain the second offset sensing beam. The second offset sensing beam and the second offset reference beam interfere at the second optical coupler C2 to obtain the first interference beam. The first photodetector PD1 converts the first interference beam into an electrical signal, namely the first interference signal.

[0039] Furthermore, a first acousto-optic modulator AOM1 and a second acousto-optic modulator AOM2 with different frequency shifts are used to modulate the optical frequencies of the first and second reference beams passing through the reference fiber, and the first and second sensing beams passing through the sensing fiber, respectively. Taking the first reference beam and the first sensing beam as examples, the specific process is as follows: Define the frequency shifts of the first acousto-optic modulator AOM1 and the second acousto-optic modulator AOM2, i.e., the first offset frequency and the second offset frequency are f0 and f0', respectively; the signal beams of the first sensing beam and the first reference beam are respectively I... s and I r The backscattered light from the reference fiber that has not undergone the second frequency shift of the first acousto-optic modulator AOM1 is I. rb1 The backscattered light of the sensing fiber without undergoing the second acousto-optic modulator AOM2 (double frequency shift) is I. sb1 The backscattered light from the reference fiber after a second frequency shift by the first acousto-optic modulator AOM1 is I. rb2 The backscattered light of the sensing fiber after being frequency-shifted twice by the second acousto-optic modulator AOM2 is I. sb2 Because acousto-optic modulators suffer from significant light transmission losses, I sb2 I rb2 Negligible, the frequency components of the interference beam combination output from the third optical coupler C3 are shown in the table below: Table 1. Frequency components of the interference beam combination output from the third optical coupler C3

[0040] <![CDATA[I s with I r Interference <![CDATA[f0- f0’]]> <![CDATA[I r with I rb1 Interference <![CDATA[f0]]> <![CDATA[I s with I sb1 Interference <![CDATA[f0’]]> <![CDATA[I sb1 with I sb1 Interference 0 <![CDATA[I s with I rb1 Interference <![CDATA[f0’]]> <![CDATA[I sb1 with I rb1 Interference 0 <![CDATA[I r with I sb1 Interference <![CDATA[f0]]> <![CDATA[I rb1 with I rb1 Interference 0

[0041] As can be seen from the table above, by modulating the optical frequencies of the first reference beam and the first sensing beam respectively using the first acousto-optic modulator AOM1 and the second acousto-optic modulator AOM2 with different frequency shifts, the target interference beam, i.e., I... s with I r The frequency of the second interference beam obtained by interference differs significantly from the frequency of the noise interference beam formed by the backscattered light. For example, setting f0' = 80MHz and f0 = 100MHz, the target interference beam frequency should be 20MHz, while the noise beam frequencies are 80MHz and 100MHz. Based on this, the optical signal can be converted to an electrical signal using the second photodetector PD2, that is, the second interference beam is converted into a second interference signal, and the noise beam is converted into noise signals respectively. Then, the noise signals are removed by bandpass filtering, retaining only the second interference signal. The process of obtaining the first interference signal by modulating the second reference beam and the second sensing beam through the first acousto-optic modulator AOM1 and the second acousto-optic modulator AOM2, converting them into electrical signals by the first photodetector PD1, and then filtering them is similar.

[0042] The technical solution of this invention uses two acousto-optic modulators, AOM1 and AOM2, with different frequencies to modulate the optical frequencies of the first and second sensing beams on the sensing fiber and the first and second reference beams on the reference fiber, respectively. Then, photoelectric signal conversion is achieved through first photodetector PD1 and second photodetector PD2. This results in a significant difference between the frequencies of the first and second interference signals and the frequencies of the noise interference signals formed by backscattered light, allowing for effective suppression and filtering of noise interference. Therefore, the technical solution of this invention weakens the submergence effect of backscattered light on weak sensing signals, significantly reduces the background noise caused by backscattered light, ensures the integrity and identifiability of weak acoustic-vibration sensing signals of partial discharge, and effectively improves the detection capability and signal demodulation quality of the distributed fiber optic sensing system for weak signals.

[0043] Based on the above embodiments, continue to refer to Figure 1Optionally, the dual Mach-Zehnder fiber optic sensing optical path further includes: a fourth optical coupler C4, the first end of which is connected to the second end of the second optical coupler C2, and the second end of which is connected to the second end of the third optical coupler C3, for separating a first information beam from a first offset reference beam; a fifth optical coupler C5, the first end of which is connected to the third end of the second optical coupler C2, and the second end of which is connected to the third end of the third optical coupler C3, for separating a second information beam from the first offset sensing beam; and a sixth optical coupler C6, the first end of which is connected to the third end of the fourth optical coupler C4, and the second end of which is connected to the third end of the fifth optical coupler C5. The third photodetector PD3 is connected to the third end of the sixth optical coupler C6. It is used to receive the self-interference beam obtained after the first information beam and the second information beam interfere in the sixth optical coupler C6, and convert the self-interference beam into a self-interference signal. The self-interference signal is used as the demodulation reference signal of the dual Mach-Zehnder fiber optic sensing optical path.

[0044] Specifically, the information beam refers to a portion of the beam coupled and split from the offset reference beam and the offset sensing beam. It does not participate in external sensing interference and is specifically used for monitoring the optical path's own state, reserving a dedicated optical path beam for subsequent generation of reference interference and demodulation reference. The self-interference beam refers to the composite beam formed by the coherent superposition and mutual interference of the first information beam split from the fourth optical coupler C4 and the second information beam split from the fifth optical coupler C5 within the sixth optical coupler C6. The self-interference beam only reflects the inherent disturbances of the optical path itself and does not contain external measured acoustic and vibration sensing information. The self-interference signal refers to the electrical signal output after photoelectric conversion by the third photodetector PD3. The self-interference signal only carries information about the optical path's inherent disturbances such as light source fluctuations, polarization drift, device temperature drift, and fiber backscattering, and does not contain external partial discharge measured signal components. The demodulation reference signal uses the self-interference signal as a reference signal to characterize the inherent noise and phase drift of the dual Mach-Zehnder fiber sensing optical path. The demodulation reference signal performs baseline calibration, error compensation, and background noise cancellation on the two sensing interference signals during the signal demodulation process, thereby eliminating the interference of the optical path itself and improving the demodulation accuracy and detection precision of weak partial discharge signals.

[0045] In this embodiment of the invention, at the ends of the sensing fiber and the reference fiber, i.e., before the third coupler, a first information beam and a second information beam are respectively drawn out using a fourth optical coupler C4 and a fifth optical coupler C5. These first and second information beams are then guided into a sixth optical coupler C6 to interfere, resulting in a self-interference beam. This self-interference beam is converted into an electrical signal, i.e., a self-interference signal, by a third photodetector PD3. Since the self-interference signal originates directly from the main interference optical path, it can track in real time the frequency drift caused by environmental influences on the first acousto-optic modulator AOM1 and the second acousto-optic modulator AOM2.

[0046] The technical solution of this invention, by adding a fourth optical coupler C4, a fifth optical coupler C5, and a sixth optical coupler C6, extracts the first and second information beams from the ends of the sensing and reference optical fibers and interferes with them to generate a self-interference beam that follows the frequency shift drift frequency changes of the first acousto-optic modulator AOM1 and the second acousto-optic modulator AOM2 in real time. The self-interference beam is then converted into a self-interference signal using a third photodetector PD3. This self-interference signal is used as a demodulation reference signal in the demodulation algorithm, which can eliminate frequency shift deviation noise and further reduce the inherent noise of the optical path.

[0047] Based on the above embodiments, optionally, the dual Mach-Zehnder fiber sensing optical path further includes: a narrow linewidth laser L1, the output end of which is connected to the incident end of the first optical coupler C1 for outputting the original beam.

[0048] Specifically, the narrow linewidth laser L1 is a laser emission source with extremely narrow output spectral linewidth and excellent coherence, capable of outputting a continuous original beam with stable frequency, low phase noise, and good monochromaticity.

[0049] In this embodiment of the invention, the output end of the narrow linewidth laser L1 is connected to the incident end of the first optical coupler C1 to output a stable frequency and excellent coherence original beam, providing a reference light source that meets the coherent interference conditions for the dual Mach-Zehnder fiber interferometer sensing optical path.

[0050] Based on the above embodiments, optionally, the first optical coupler C1 and the second optical coupler C2, the first optical coupler C1 and the third optical coupler C3, the second optical coupler C2 and the first acousto-optic modulator AOM1, the first acousto-optic modulator AOM1 and the third optical coupler C3, the second optical coupler C2 and the second acousto-optic modulator AOM2, and the second acousto-optic modulator AOM2 and the third optical coupler C3 are all connected by single-mode optical fiber, and two beams of light with opposite directions can be transmitted simultaneously and independently within the single-mode optical fiber.

[0051] Specifically, single-mode fiber is a special optical fiber transmission medium that allows only the fundamental mode light wave to propagate within the fiber core. It can constrain a light beam to propagate directionally along the optical path in a single transmission mode, and is the basic transmission carrier used for optical path interconnection between various optical devices in fiber optic interferometric sensing systems. Single-mode fiber has bidirectional independent transmission capability; two beams with opposite propagation directions can be carried simultaneously within the same single-mode fiber. The two beams do not interfere with each other and propagate independently, making it suitable for working scenarios such as beam splitting, backhauling, and backscattered light transmission in optical paths.

[0052] Based on the above embodiments, optionally, the first optical coupler C1, the second optical coupler C2 and the third optical coupler C3 are all single-mode fiber directional optical couplers.

[0053] Specifically, a single-mode fiber directional optical coupler is a passive optical device designed based on the transmission principle of single-mode fiber. It can realize the splitting, combining and directional transmission of single-mode beams. It can split the input single-mode beam according to a preset ratio, or make multiple single-mode beams merge and generate interference. At the same time, it has directional transmission characteristics, allowing the beam to be transmitted only in a specific direction, effectively reducing the scattering loss of optical signals.

[0054] In this embodiment of the invention, the first optical coupler C1, the second optical coupler C2, and the third optical coupler C3 are all single-mode fiber directional optical couplers, which can realize precise beam splitting, beam combining, and directional transmission of single-mode beams, ensuring the stability of the interference process, while reducing noise interference caused by beam scattering.

[0055] Based on the above embodiments, optionally, the fourth optical coupler C4 and the fifth optical coupler C5 are both weak beam splitting optical couplers.

[0056] Specifically, a weak beam splitter is a passive optical device that can couple a small amount of optical signal from the main optical path with an extremely low beam splitting ratio without affecting the normal transmission of the main optical path, while preserving the optical power of the main optical path to the maximum extent, ensuring that the signal transmission and interference function of the main optical path are not affected.

[0057] Figure 2 This is a flowchart of a partial discharge localization method provided by an embodiment of the present invention. This embodiment is applicable to the partial discharge detection of power equipment such as GIS, transformers, and power cables. This method is applied to the dual Mach-Zehnder fiber optic sensing optical path provided in any embodiment of the present invention, such as... Figure 2 As shown, the method includes:

[0058] S210. Filter the signals output by the first photodetector PD1 and the second photodetector PD2 according to the first offset frequency and the second offset frequency to obtain the first interference signal and the second interference signal.

[0059] For example, taking the signal output from the second photodetector PD2 as an example, assuming the frequency shifts of the first acousto-optic modulator AOM1 and the second acousto-optic modulator AOM2, i.e., the first offset frequency and the second offset frequency, are 100MHz and 80MHz respectively, then the frequency of the target interference beam should be 20MHz, meaning the frequency of the second interference signal should be 20MHz. The frequency of the noise signal is 100MHz or 80MHz. Therefore, a bandpass filter can be used to filter out the noise signal, retaining only the 20MHz signal as the second interference signal. Similarly, the signal output from the first photodetector PD1 can be filtered to obtain the first interference signal.

[0060] S220. Generate a first orthogonal reference signal and a second orthogonal reference signal that have the same frequency as the first interference signal and the second interference signal, respectively.

[0061] Specifically, the phase of the first and second interference signals is demodulated using the in-phase and quadrature (IQ) demodulation method. Assuming the intensities of the first and second interference signals are the same, let the first interference signal be... Second interference signal They are respectively:

[0062]

[0063] Wherein, U0 is the amplitude of the AC component of the interference optical signal, and f0 and f0' are the first offset frequency and the second offset frequency, respectively; The change in phase of the interference light caused by the external acoustic signal acting on the sensing optical fiber; and τ represents the initial phases of the first and second interference signals, respectively; τ is the time delay between the first and second interference signals. For acoustic emission detection, the phase change of the interference light is mainly caused by the change in fiber length due to mechanical acoustic waves. It can be represented as:

[0064]

[0065] Where λ represents the wavelength of light, and ΔL represents the change in length difference between the sensing fiber and the reference fiber. Since the length of the reference fiber remains constant, ΔL can also be expressed as the change in length of the sensing fiber.

[0066] Based on this, a first orthogonal reference signal R(t) and a second orthogonal reference signal R(t)′ with the same frequency as the AC components of the first and second interference signals are generated:

[0067]

[0068] In the formula, R0 is the amplitude of the reference signal quantity. In this embodiment of the invention, R0 = 1V is taken.

[0069] S230. The first interference signal is multiplied by the first orthogonal reference signal and the second orthogonal reference signal respectively, and then filtered to obtain a first set of baseband signals. The second interference signal is multiplied by the first orthogonal reference signal and the second orthogonal reference signal respectively, and then filtered to obtain a second set of baseband signals. The first set of baseband signals includes a first in-phase component and a first quadrature component, and the second set of baseband signals includes a second in-phase component and a second quadrature component.

[0070] Specifically, taking the first interference signal as an example,

[0071]

[0072]

[0073] The obtained signal is then passed through a low-pass filter with a cutoff frequency much smaller than f0-f0' to filter out high-frequency components, resulting in the first set of baseband signals. This first set of baseband signals includes a first in-phase component. and the first orthogonal component :

[0074]

[0075] S240. Perform differential-cross multiplication operations on the first in-phase component and the first quadrature component, as well as the second in-phase component and the second quadrature component, respectively, calculate the difference, and normalize to obtain the first phase change signal and the second phase change signal.

[0076] For example, the intermediate signal can be obtained by performing differentiation-cross multiplication on the first in-phase component and the first quadrature component and then taking the difference. :

[0077]

[0078] To eliminate the influence of signal amplitude, the intermediate signal M(t) is divided by and Normalizing the sum of squares yields the first phase change signal. :

[0079]

[0080] S250. Integrate the first phase change signal and the second phase change signal respectively to obtain the first phase change amount and the second phase change amount.

[0081] For example, with the first phase change signal For example, the first phase change It can be represented as:

[0082]

[0083] Similarly, the second phase change can be calculated. (t + τ).

[0084] S260. Determine the time delay between the first interference signal and the second interference signal based on the first phase change and the second phase change, and determine the location of the partial discharge based on the time delay.

[0085] Specifically, the time delay τ can be obtained by cross-correlation calculation of the first and second phase changes after demodulation. Then, the location of partial discharge can be determined according to the following formula:

[0086]

[0087] Where L is the total length of the sensing fiber or reference fiber, that is, the length of any fiber between the second optical coupler C2 and the third optical coupler C3; L0 is the length of the guiding fiber, that is, the length of the fiber between the first optical coupler C1 and the third optical coupler C3; x is the distance from the partial discharge point to the second optical coupler C2; and v is the speed of light in the fiber.

[0088] Based on the above embodiments, optionally, a first orthogonal reference signal and a second orthogonal reference signal with the same frequency as the first interference signal and the second interference signal are generated, including: demodulating the self-interference signal to obtain the first orthogonal reference signal and the second orthogonal reference signal.

[0089] In this embodiment of the invention, since the self-interference signal is directly taken from the dual Mach-Zehnder fiber sensing optical path, it can reflect and follow the frequency drift and phase disturbance caused by environmental disturbances such as temperature fluctuations and power supply drift of the first acousto-optic modulator AOM1 and the second acousto-optic modulator AOM2 in real time, providing a dynamic reference for the demodulation of the subsequent sensing interference signal, thereby achieving accurate calibration and compensation of the optical path background noise.

[0090] Figure 3 A comparison of the phase noise density spectrum after IQ demodulation of a dual Mach-Zehnder fiber sensing optical path provided in an embodiment of the present invention. Figure 3As shown, the dark blue curve represents the phase noise density spectrum of the existing dual Mach-Zehnder fiber sensing optical path after IQ demodulation, denoted as Initial PND; the red curve represents the phase noise density spectrum of the dual Mach-Zehnder fiber sensing optical path using the self-interference signal as the demodulation reference signal after IQ demodulation, denoted as PND with syncsignal; the light blue curve represents the phase noise density spectrum of the dual Mach-Zehnder fiber sensing optical path modulated by dual acousto-optic modulators and using the self-interference signal as the demodulation reference signal after IQ demodulation, denoted as PND with sync signal and dual AOM; the horizontal axis represents frequency in kHz; the vertical axis represents noise level in dB. Figure 3 It can be seen that the phase noise of the dual Mach-Zehnder fiber optic sensing path, which uses a frequency-synchronized self-interference signal as the demodulation reference signal, is significantly reduced, with a phase noise reduction of approximately 25 dB in the 20 kHz–200 kHz frequency band. It can also be seen that after using frequency differences to eliminate the interference signal formed by backscattered light, the phase noise of the dual Mach-Zehnder fiber optic sensing path is further reduced. Compared to the system phase noise of only performing reference signal synchronization, the introduction of two acousto-optic modulators reduces the phase noise in the 20 kHz–200 kHz frequency band by 11 dB. In summary, for the dual Mach-Zehnder fiber optic sensing path, the self-interference signal can be used as the adjustment reference signal, and the backscattered light interference can be separated by dual acousto-optic modulators, thereby reducing the phase noise in the 20 kHz–200 kHz frequency band by 34 dB.

[0091] Figure 4 This is a phase noise time-domain comparison curve provided for an embodiment of the present invention. For example... Figure 4 As shown, the red curve is the noise time-domain plot of the dual Mach-Zehnder fiber optic sensing optical path with the self-interference signal as the demodulation reference signal and synchronous noise reduction using dual acousto-optic modulators, denoted as Suppressed phase noise; the blue curve is the noise time-domain plot of the traditional dual Mach-Zehnder fiber optic sensing optical path, denoted as Initial phase noise; the horizontal axis represents time, denoted as Time, in ms; the first vertical axis represents the initial phase amplitude, denoted as Initial phase amplitude, in rad; the second vertical axis represents the phase amplitude after noise reduction, denoted as Suppressed phase amplitude, in rad. It can be seen that the phase noise of the dual Mach-Zehnder fiber optic sensing optical path after adopting dual noise suppression measures is approximately -100dB in the frequency range of 20kHz to 200kHz. Integrating the phase noise density in this frequency band, the root mean square value of the phase noise of the dual Mach-Zehnder fiber optic sensing optical path is calculated to be 0.0036rad. The average signal strength of the dual Mach-Zehnder fiber optic sensing path is approximately 6.09 × 10⁻ 6The signal strength is rad, and the standard deviation is 0.0035 rad. Using the signal mean superimposed with three times the standard deviation as the system detection lower limit criterion, calculations show that the phase detection lower limit for a dual Mach-Zehnder fiber optic sensing path with self-interference signal as demodulation reference signal synchronous correction and a dual acousto-optic modulator architecture is approximately 0.0105 rad. Figure 4 The detection limit is marked as 0.0105 rad. That is, when performing partial discharge acoustic emission detection using this embodiment of the invention, as long as the phase amplitude of the signal under test exceeds 0.0105 rad, it can be determined as a valid partial discharge signal. In contrast, the traditional dual Mach-Zehnder fiber optic sensing path, which does not employ this noise suppression scheme, has a phase detection limit of approximately 0.6615 rad. Figure 4 The detection limit is marked as 0.6615 rad. This demonstrates that by using the self-interference signal as the demodulation reference signal and the dual acousto-optic modulator frequency division noise reduction design in this embodiment of the invention, the lower limit of phase detection in the dual Mach-Zehnder fiber optic sensing path is significantly reduced, and the detection performance is improved by 98.4%.

[0092] The technical solution provided in this invention relies on a dual Mach-Zehnder fiber sensing optical path architecture. Frequency division filtering is performed based on the first and second offset frequencies to accurately separate the first and second interference signals. The self-interference signal is then demodulated to generate a first orthogonal reference signal and a second orthogonal reference signal synchronized with the actual carrier frequency. Then, through orthogonal demodulation processing, differential cross-multiplication, and integration, the two phase changes are extracted. The partial discharge location is determined based on the time delay of the two phase changes. On one hand, this invention, through a dual acousto-optic modulator frequency division design, creates a significant frequency difference between the effective interference signal and the noise interference signal generated by backscattered light. By using filtering methods, multi-beam coherent crosstalk caused by fiber backscattering can be effectively suppressed, preventing weak partial discharge acoustic vibration signals from being submerged by noise, and significantly improving the signal-to-noise ratio and weak signal demodulation capability of the optical path. On the other hand, this invention abandons the traditional method of using a fixed ideal reference signal for orthogonal demodulation. Instead, it uses the self-interference signal of the optical path itself as a dynamic demodulation reference. This allows it to follow the actual frequency shift of the first acousto-optic modulator AOM1 and the second acousto-optic modulator AOM2 caused by environmental disturbances in real time, keeping the reference signal synchronized with the carrier frequency of the interference signal. This suppresses the phase noise caused by the frequency shift deviation of the acousto-optic modulator at its source. In summary, the solution provided by this invention can effectively reduce the background noise of the dual Mach-Zehnder fiber optic sensing optical path architecture, thereby achieving accurate localization of partial discharge.

[0093] This invention also provides a partial discharge location device, which includes the dual Mach-Zehnder fiber optic sensing optical path provided in any embodiment of the invention, and has the corresponding functional modules and beneficial effects of the dual Mach-Zehnder fiber optic sensing optical path.

[0094] It should be understood that the various forms of processes shown above can be used, with steps reordered, added, or deleted. For example, the steps described in this invention can be executed in parallel, sequentially, or in different orders, as long as the desired result of the technical solution of this invention can be achieved, and this is not limited herein.

[0095] The specific embodiments described above do not constitute a limitation on the scope of protection of this invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A dual Mach-Zehnder fiber optic sensing optical path, characterized in that, include: The first optical coupler is used to split the original beam into a first beam and a second beam; A second optical coupler, wherein the first end of the second optical coupler is connected to the first end of the first optical coupler, is used to split the first beam into a first reference beam and a first sensing beam. A third optical coupler, wherein a first end of the third optical coupler is connected to a second end of the first optical coupler, is used to split the second beam into a second reference beam and a second sensing beam. A first acousto-optic modulator is connected between the second end of the second optical coupler and the second end of the third optical coupler, and is used to apply a first offset frequency to the first reference beam and the second reference beam respectively to obtain a first offset reference beam and a second offset reference beam. The second acousto-optic modulator is connected between the third end of the second optical coupler and the third end of the third optical coupler, and is used to apply a second offset frequency to the first sensing beam and the second sensing beam respectively to obtain the first offset sensing beam and the second offset sensing beam. The first offset frequency is not equal to the second offset frequency; A first photodetector is connected to the fourth end of the second optical coupler and is used to receive the first interference beam obtained after the second offset reference beam and the second offset sensing beam interfere in the second optical coupler, and to convert the first interference beam into a first interference signal. The second photodetector is connected to the fourth end of the third optical coupler and is used to receive the second interference beam obtained after the first offset reference beam and the first offset sensing beam interfere in the third optical coupler, and to convert the second interference beam into a second interference signal. The dual Mach-Zehnder fiber sensing optical path further includes: a fourth optical coupler, the first end of which is connected to the second end of the second optical coupler, and the second end of which is connected to the second end of the third optical coupler, for separating the first information beam from the first offset reference beam; A fifth optical coupler, wherein the first end of the fifth optical coupler is connected to the third end of the second optical coupler, and the second end of the fourth optical coupler is connected to the third end of the third optical coupler, is used to separate the second information beam from the first offset sensing beam; A sixth optical coupler, wherein the first end of the sixth optical coupler is connected to the third end of the fourth optical coupler, and the second end of the sixth optical coupler is connected to the third end of the fifth optical coupler; The third photodetector is connected to the third end of the sixth optical coupler and is used to receive the self-interference beam obtained after the first information beam and the second information beam interfere in the sixth optical coupler, and convert the self-interference beam into a self-interference signal; the self-interference signal is used as the demodulation reference signal of the dual Mach-Zehnder fiber sensing optical path; the self-interference signal follows the frequency shift change of the first acousto-optic modulator and the second acousto-optic modulator.

2. The dual Mach-Zehnder fiber optic sensing optical path according to claim 1, characterized in that, Also includes: A narrow linewidth laser, the output end of which is connected to the incident end of the first optical coupler, is used to output the original beam.

3. The dual Mach-Zehnder fiber optic sensing optical path according to claim 1, characterized in that, The first optical coupler is connected to the second optical coupler, the first optical coupler is connected to the third optical coupler, the second optical coupler is connected to the first acousto-optic modulator, the first acousto-optic modulator is connected to the third optical coupler, the second optical coupler is connected to the second acousto-optic modulator, and the second acousto-optic modulator is connected to the third optical coupler through single-mode optical fiber. Two beams of light with opposite directions can be transmitted simultaneously and independently in the single-mode optical fiber.

4. The dual Mach-Zehnder fiber optic sensing optical path according to claim 1, characterized in that, The first optical coupler, the second optical coupler, and the third optical coupler are all single-mode fiber directional optical couplers.

5. The dual Mach-Zehnder fiber optic sensing optical path according to claim 1, characterized in that, Both the fourth and fifth optical couplers are weak beam splitting optical couplers.

6. A method for locating partial discharge, characterized in that, Applied to the dual Mach-Zehnder fiber optic sensing optical path according to any one of claims 1-5, the partial discharge localization method includes: The signals output by the first photodetector and the second photodetector are filtered according to the first offset frequency and the second offset frequency to obtain the first interference signal and the second interference signal; A first orthogonal reference signal and a second orthogonal reference signal with the same frequency as the first interference signal and the second interference signal are generated respectively; The first interference signal is multiplied by the first orthogonal reference signal and the second orthogonal reference signal respectively and filtered to obtain a first set of baseband signals. The second interference signal is multiplied by the first orthogonal reference signal and the second orthogonal reference signal respectively and filtered to obtain a second set of baseband signals. The first set of baseband signals includes a first in-phase component and a first quadrature component, and the second set of baseband signals includes a second in-phase component and a second quadrature component. Differential-cross multiplication operations are performed on the first in-phase component and the first quadrature component, as well as on the second in-phase component and the second quadrature component, respectively. The difference is then calculated and normalized to obtain the first phase change signal and the second phase change signal. The first phase change signal and the second phase change signal are integrated respectively to obtain the first phase change amount and the second phase change amount; The time delay between the first interference signal and the second interference signal is determined based on the first phase change and the second phase change, and the location of the partial discharge is determined based on the time delay.

7. The partial discharge localization method according to claim 6, characterized in that, The step of generating a first orthogonal reference signal and a second orthogonal reference signal with the same frequency as the first interference signal and the second interference signal, respectively, includes: The self-interference signal is demodulated to obtain the first orthogonal reference signal and the second orthogonal reference signal.

8. A partial discharge locating device, characterized in that, Includes the dual Mach-Zehnder fiber optic sensing optical path as described in any one of claims 1-6.

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