A flexible multi-fiber loop series-connected acoustic sensor based on a Sagnac interferometer and its detection method

Abstract

The present invention discloses a flexible multi-fiber loop series acoustic sensor based on a Sagnac interferometer and its detection method, belonging to the technical field of partial discharge detection. The present invention solves the key problems existing in the electrical and optical ultrasonic sensors widely used in the detection of partial discharge ultrasonic signals, such as low detection sensitivity, poor anti-interference ability, limited application scenarios, poor multi-point detection ability, and high manufacturing cost of the complete set of systems. The present invention designs multiple planar flexible fiber loop sensing probes with different resonant frequencies, and connects the sensing probes in series. The sensing probes with different resonant frequencies are distributed at different detection points, and the detection points are marked through the resonant frequencies, thereby completing the photoelectric conversion and signal acquisition of single-channel fiber sensing.

Description

Technical Field

[0001] The present invention relates to a flexible multi-fiber loop series acoustic sensor based on a Sagnac interferometer and its application in the localization detection of partial discharge ultrasonic signals in power equipment, belonging to the technical field of partial discharge detection. Background Art

[0002] Partial discharge in power equipment is the main factor endangering insulation safety, which is extremely likely to cause operation accidents and result in huge economic losses. Therefore, the detection of partial discharge phenomena is particularly important. Usually, the occurrence of partial discharge phenomena is accompanied by phenomena such as sound, light, electricity, and chemical reactions. Among them, the detection of partial discharge ultrasonic signals has high real-time performance and anti-interference ability, and can quickly locate the partial discharge point through the output signal of the acoustic sensor. However, existing electrical ultrasonic sensors and fiber optic ultrasonic sensors both face key problems in the detection of partial discharge ultrasonic signals, such as low detection sensitivity, poor quasi-distributed ability, and extremely high costs for multi-point detection systems. Among them, electrical ultrasonic sensors are mainly piezoelectric ceramic sensors (PZT). Although this type of sensor has mature technology and a complete supporting demodulation and acquisition system, when applied to the detection of partial discharge ultrasonic signals in power equipment, it has key problems faced at the detection end, such as poor anti-electromagnetic interference ability, low detection sensitivity, and poor applicability of the installation coupling method (the sensing probe is a cylindrical rigid solid structure and can only be installed on the flat position of power equipment, and is limited in installation on the surface of power equipment with characteristics such as GIS and GIL with a tank structure). At the same time, because this type of sensor cannot be interconnected in series and has a short signal transmission distance, its quasi-distributed detection ability is poor, and each sensing probe needs to be equipped with a separate acquisition channel, resulting in a significant increase in the manufacturing cost of the detection system as the number of detection points increases.

[0003] In recent years, in view of the many problems existing in PZT sensors, more practitioners and researchers related to partial discharge detection of power equipment have turned their research efforts to fiber optic ultrasonic sensing technology. This technology has unique advantages of strong anti-electromagnetic interference ability and the ability to achieve a fully insulated structure in the detection of partial discharge ultrasonic signals. Among many fiber optic ultrasonic sensors, fiber Bragg grating ultrasonic sensors are rarely used for partial discharge ultrasonic signal detection due to their low detection sensitivity. Fiber optic ultrasonic sensors such as Fabry-Perot, Mach-Zehnder, Michelson, and Sagnac have been widely studied in the detection of partial discharge ultrasonic signals. Among them, the Fabry-Perot fiber optic ultrasonic sensor based on the multi-beam interference principle is only applicable to the detection of partial discharge ultrasonic signals in transformer oil insulation, and the sensor is greatly affected by environmental factors, with poor detection stability, and there is also the problem that the cost of the complete set of systems increases significantly as the number of detection points of the PZT sensor increases. For the main Mach-Zehnder, Michelson, and Sagnac fiber optic ultrasonic sensors that detect partial discharge ultrasonic signals based on the double-beam interference principle, the Mach-Zehnder and Michelson fiber optic ultrasonic sensors require the lengths of the measurement arm and the reference arm to be kept consistent, and phase adjustment is required to ensure high-sensitivity detection of partial discharge ultrasonic signals. The detection system is complex and has poor stability. At the same time, due to the use of phase demodulation, each sensing probe needs to be equipped with a photoelectric converter and a data acquisition channel. Therefore, an increase in the number of detection points will lead to a significant increase in the cost of the detection system. The Sagnac fiber optic ultrasonic sensor forms interference between the measurement and reference beams in a single closed-loop optical path, and does not need to consider the problems of optical path length matching and phase modulation. However, it needs to be driven by a low-coherence light source, resulting in low detection sensitivity, and each of its sensing probes also needs to be equipped with a photoelectric converter and a data acquisition channel, and there is still the key problem of high manufacturing cost of the sensing system. At the same time, the sensing probes of the above-mentioned several double-beam interference ultrasonic sensors are all solidified multi-fiber wound ring structures, resulting in limited application scenarios for partial discharge ultrasonic signal detection. Summary of the Invention

[0004] Aiming at the key problems existing in the electrical and optical ultrasonic sensors widely used in the detection of partial discharge ultrasonic signals, such as low detection sensitivity, poor anti-interference ability, limited application scenarios, poor multi-point detection ability, and high manufacturing cost of the complete set of systems, the present invention provides a flexible multi-fiber ring series acoustic sensor based on a Sagnac interferometer and its application in the localization detection of partial discharge ultrasonic signals of power equipment.

[0005] Technical solution of the present invention:

[0006] One of the purposes of the present invention is to provide a flexible multi-fiber ring series acoustic sensor based on a Sagnac interferometer, which is characterized by comprising a driving light source 1, a 2*2 coupler 2, a plurality of sensing probes 3, a delay fiber 4, a photoelectric converter 5, a data acquisition module 6, and a data analysis and processing module 7;

[0007] The multiple sensing probes 3 are planar flexible optical fiber loops with different resonant frequencies;

[0008] The driving light source 1 is connected to a 2×2 coupler. The multiple sensing probes 3 and the delay optical fiber 4 are connected in series in sequence and then connected to the 2×2 coupler 2. And the 2×2 coupler 2 is further connected to a photoelectric converter 5, a data acquisition module 6 and a data analysis and processing module 7 in sequence.

[0009] Further defined, the driving light source 1 is a C-band broadband light source.

[0010] Further defined, the sensing probe 3 is formed by winding an optical fiber along a plane and curing it with epoxy resin.

[0011] Further defined, the resonant frequency of the sensing probe 3 is selected within the range of 20 - 200 kHz.

[0012] Further defined, the number of the sensing probes 3 is more than 2.

[0013] The second object of the present invention is to provide an application of the above-mentioned flexible multi-fiber-loop series-connected acoustic sensor based on a Sagnac interferometer, specifically for the positioning detection of partial discharge ultrasonic signals in power equipment.

[0014] The third object of the present invention is to provide a method for positioning and detecting partial discharge ultrasonic signals. Specifically, the multiple sensing probes 3 with different resonant frequencies in the above-mentioned flexible multi-fiber-loop series-connected acoustic sensor based on a Sagnac interferometer are respectively installed at positions far away from each other on the same power equipment or at different positions of non-same power equipment with spatial isolation.

[0015] Further defined, the optical signal emitted by the driving light source 1 is divided into two paths by the 2×2 coupler 2. One path passes through the multiple sensing probes 3 in sequence and then returns to the 2×2 coupler 2 through the delay optical fiber 4. The other path first passes through the delay optical fiber 4 and then passes through the multiple sensing probes 3 and returns to the 2×2 coupler 2. The two paths of light interfere in the 2×2 coupler and are received by the photoelectric converter 5 and then enter the data acquisition module 6. When partial discharge occurs at the position where a certain sensing probe 3 of the power equipment is located or at the positions where multiple sensing probes 3 are located, after the sensing probe 3 detects the partial discharge ultrasonic signal, the data acquisition module 6 outputs a time-domain waveform signal. The data analysis and processing module 7 performs Fourier analysis on this signal to obtain the frequency-domain information of the time-domain signal. By comparing whether the characteristic frequency of the frequency-domain information overlaps with the resonant characteristic peaks of one or more sensing probes 3, the partial discharge position is determined.

[0016] A fourth object of the present invention is to provide a method for local discharge ultrasonic signal positioning detection for ABC three-phase lines in GIS. Specifically, the three sensing probes 3 in the flexible multi-fiber loop series acoustic sensor based on the Sagnac interferometer described above are respectively installed on the ABC three-phase lines.

[0017] Further limited, the resonance frequencies of the three sensing probes 3 are 25 kHz, 60 kHz, and 115 kHz respectively.

[0018] Beneficial effects:

[0019] According to the characteristics that the intrinsic broadband characteristics of the local discharge ultrasonic signal are basically in the range of 20 kHz - 200 kHz (although the standard ranges given by IEC, IEEE, CIGRE, etc. are different, they are basically in the range of 20 kHz - 200 kHz), the present invention adopts the Sagnac interference principle, designs multiple planar flexible fiber loop sensing probes with different resonance frequencies, and connects the sensing probes in series. The sensing probes with different resonance frequencies are distributed at different detection points, and the detection points are marked through the resonance frequencies, thereby completing the photoelectric conversion and signal acquisition of single-channel fiber sensing, and solving the problems of poor multi-point detection ability of sensors widely used in local discharge ultrasonic signal detection and high manufacturing cost of complete sets of systems. Compared with the prior art, it also has the following advantages:

[0020] (1) The sensing probe used in the present invention is made by winding an optical fiber into a planar flexible fiber loop along the plane, and then solidifying and encapsulating it with a low Young's modulus elastic epoxy resin. By increasing the sound signal receiving area, the sensitivity of the sensing probe is greatly improved, and the applicability of the sensing probe for detecting local discharge ultrasonic signals in multiple scenarios is improved through the design of the planar flexible solidification and encapsulation structure (such as it can be installed and used in the internal oil area of the transformer and on the outer surface of the transformer oil tank wall without additional operations, and can be directly used on the curved walls of power equipment with tank-type structures such as GIS and GIL), solving the key problems of low detection sensitivity and poor applicability of local discharge ultrasonic sensors.

[0021] (2) The present invention adopts all-fiber Sagnac interference sensing with extremely strong anti-electromagnetic interference ability, and the sensing and measurement optical paths share one optical fiber. The system structure is simple and the anti-environmental interference ability is strong.

[0022] (3) The present invention adopts the form of connecting flexible planar fiber loop sensing probes in series. While detecting local discharge ultrasonic signals, it can judge the sensing probe that detects local discharge through the peak value of the frequency domain information characteristics of the system output signal, and at the same time, the location where the local discharge occurs can be determined according to the position of the sensing probe, so as to realize the marking of the detection position through the resonance frequency of the sensing probe. Description of the drawings

[0023] Figure 1 Schematic diagram of the flexible multi - fiber - loop - series acoustic sensor based on Sagnac interferometer provided by this application;

[0024] Figure 2 Physical photo of the sensing probe;

[0025] Figure 3 Partial discharge ultrasonic signal positioning and detection system of the flexible multi - fiber - loop - series acoustic sensor based on Sagnac interferometer built for Example 1;

[0026] Figure 4 Time - domain signal waveform obtained when partial discharge occurs at the position of isolation space 3 in Example 1;

[0027] Figure 5 Frequency - domain signal waveform obtained when partial discharge occurs at the position of isolation space 3 in Example 1;

[0028] Figure 6 Time - domain signal waveform obtained when partial discharges occur at the positions of isolation spaces 1 - 3 in Example 1;

[0029] Figure 7 Frequency - domain signal waveform obtained when partial discharges occur at the positions of isolation spaces 1 - 3 in Example 1;

[0030] In the figure, 1 - driving light source, 2 - 2 * 2 coupler, 3 - sensing probe, 4 - delay fiber, 5 - photoelectric converter, 6 - data acquisition module, 7 - data analysis and processing module, 8 - first isolation space, 9 - second isolation space, 10 - third isolation space. Detailed implementation manners

[0031] 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 making creative efforts belong to the scope of protection of the present invention.

[0032] In the description of the present invention, it should be noted that the orientation or positional relationship indicated by terms such as "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 to the present invention.

[0033] In the description of the present invention, it should be noted that unless otherwise clearly defined and limited, terms such as "installation", "equipped with", "sheathed / connected", "connection", etc. should be understood in a broad sense. For example, "connection" 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 communication inside two components. 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.

[0034] Such as Figure 1As shown in the figure, the present invention provides a flexible multi-fiber loop series acoustic sensor based on a Sagnac interferometer. The sensor includes a driving light source 1, a 2×2 coupler 2, a plurality of sensing probes 3, a delay fiber 4, a photoelectric converter 5, a data acquisition module 6, and a data analysis and processing module 7. Specifically, the driving light source 1 is connected to the 2×2 coupler. The plurality of sensing probes 3 and the delay fiber 4 are connected to the 2×2 coupler in series in sequence. Moreover, the 2×2 coupler is also connected to the photoelectric converter 5, the data acquisition module 6, and the data analysis and processing module 7 in sequence. Among them, the plurality of sensing probes 3 are formed by winding an optical fiber along a plane and curing with epoxy resin, and are planar flexible optical fiber loops with different resonant frequencies. The driving light source 1 is a C-band broadband light source. With such a setting, by respectively installing the plurality of sensing probes 3 at positions that are far away from the same power equipment and where ultrasonic signals cannot propagate, or at different positions of non-same power equipment with spatial isolation (for example, the ABC three-phase lines in GIS have clear spatial isolation characteristics). Using the C-band broadband light source as the driving light source 1, the optical signal emitted by the driving light source 1 is split into two paths by the 2×2 coupler 2. One path first passes through the plurality of sensing probes 3 and then continues to propagate through the delay fiber 4 and returns to the 2×2 coupler 2. The other path first passes through the delay fiber 4 and then passes through the plurality of sensing probes 3 and continues to propagate back to the 2×2 coupler 2. The two paths of light interfere at the 2×2 coupler 2 and are received by the photoelectric converter 5 and then enter the data acquisition module 6.When partial discharge occurs at a certain position where the sensing probe 3 is located, the ultrasonic signal generated by the partial discharge acts on the sensing probe 3 at this position in the form of a mechanical wave. Since the sensing probe 3 is made of fiber winding, the acoustic signal causes the fiber to vibrate, and the optical signal passing through the fiber loop changes, resulting in a change in the interference optical signal in the 2×2 coupler 2 (assuming that there is no partial discharge, then the interference optical signal incident on the photoelectric converter after output from this 2×2 coupler 2 should remain constant, and the electrical signal output by the photoelectric conversion also remains constant). This changing interference optical signal becomes a changing electrical signal after passing through the photoelectric converter. At this time, a high level with a rising edge appears, and the data acquisition module 6 outputs a time-domain waveform signal, triggering the data analysis module 7 to perform data acquisition, processing, and analysis. Through the data analysis and processing module 7, Fourier analysis is performed on this signal to obtain the frequency-domain information of the time-domain signal. Since all the used sensing probes 3 detect with narrowband resonance characteristics, the sensing probe 3 naturally outputs frequency-domain information with resonance frequency characteristic values. At this time, by comparing the characteristic frequencies of the frequency-domain information of the output signal of the detection system, it can be determined which sensing probe 3 detects the partial discharge ultrasonic signal. For example, if the frequency-domain characteristic peak of the output signal of the detection system overlaps with the resonance characteristic peak of the sensing probe 3 at the first installation position, it can be judged that partial discharge occurs in the area range of position 1. If there are two frequency-domain characteristic peaks in the output signal of the detection system, and they overlap with the resonance frequency peaks of the sensing probe 3 at the first installation position and the second installation position respectively, it can be judged that partial discharge occurs at both the first installation position and the second installation position.

[0035] The sensing probe 3 designed in the present invention is as Figure 2 shown, which is made by winding the optical fiber along a plane and cured with a low Young's modulus epoxy resin, having good flexibility, and can be closely attached to the surface of the non-planar power equipment housing to detect partial discharge ultrasonic signals. Since the sensing probe 3 is in a planar unfolded shape, its acoustic receiving area is greatly improved compared with the traditional fiber loops used in EFPI sensors and double-beam interferometers, thereby improving its detection sensitivity. And the inherent resonance frequency of this sensing probe can be changed by adjusting the planar structure size and the winding layer number.

[0036] Preparation of the sensing probe: The sensing probe consists of two parts. One part is made of fiber winding, and the other part is a coupling substrate for modulating the resonance frequency of the sensing probe. The fiber loop is a planar single-layer fiber winding, as Figure 2As shown in the figure, the inner diameter of the fiber optic loop is 20 mm, the outer diameter is 60 mm, and it is wound by a single-mode optical fiber with a length of 10 m and is quickly cured and shaped by ultraviolet curing glue. The base structure for modulating the resonant frequency is cast from flexible epoxy resin. The inner and outer diameters of this structure are the same as those of the fiber optic loop, and the resonant frequency is modulated by changing the thickness. The thickness of the resonant frequency modulation base of the sensing probe 3 with a resonant frequency of 25 kHz is 1 mm, the thickness of the resonant frequency modulation base of the sensing probe 3 with a resonant frequency of 60 kHz is 5 mm, and the thickness of the resonant frequency modulation base of the sensing probe 3 with a resonant frequency of 115 kHz is 12 mm. During the preparation process, first, the preparation of the fiber optic loop is completed. Subsequently, a mold with a matching size is fixed on the fiber optic loop, and epoxy resin is poured onto the mold for curing, so that the flexible epoxy resin and the fiber optic loop become an integrated structure.

[0037] Using the above flexible multi-fiber optic loop series acoustic sensor based on the Sagnac interferometer to build a partial discharge ultrasonic signal positioning detection system, as Figure 3 shown, three sensing probes 3 with resonant frequencies of 25 kHz, 60 kHz, and 115 kHz are respectively placed in the first isolation space 8, the second isolation space 9, and the third isolation space 10, and high-voltage pulse signal generators are also respectively placed in the first isolation space 8, the second isolation space 9, and the third isolation space 10.

[0038] First, use the high-voltage pulse signal generator in the third isolation space 10 to generate a partial discharge ultrasonic signal. The time-domain signal waveform and its frequency-domain signal captured by the detection system are as Figure 4 and Figure 5 shown. It can be clearly seen from the frequency-domain signal that the frequency-domain signal collected by the detection system has a 115 kHz resonant characteristic peak. Subsequently, the high-voltage pulse generators in the first isolation space 8, the second isolation space 9, and the third isolation space 10 are discharged simultaneously. The time-domain signal waveform and its frequency-domain signal captured by the detection system are as Figure 6 and Figure 7 shown. The frequency domain collected by the detection system has obvious 25 kHz, 60 kHz, and 115 kHz resonant characteristic peaks. It can be seen from this that the above form of connecting the flexible planar fiber optic loop sensing probes in series can simultaneously detect partial discharge ultrasonic signals, and the sensing probe that detects partial discharge can be judged through the characteristic peak value of the frequency-domain information of the system output signal. At the same time, the location where partial discharge occurs can be determined according to the position of the sensing probe to realize the marking of detection through the resonant frequency of the sensing probe.

[0039] 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 flexible multi-fiber loop series-connected acoustic sensor based on a Sagnac interferometer, characterized in that It includes a driving light source, a 2×2 coupler, multiple sensing probes, a delay optical fiber, a photoelectric converter, a data acquisition module, and a data analysis and processing module; The multiple sensing probes are planar flexible optical fiber loops with different resonant frequencies; The driving light source is connected to the 2×2 coupler. The multiple sensing probes and the delay optical fiber are connected in series in sequence and then connected to the 2×2 coupler. Moreover, the 2×2 coupler is also connected to the photoelectric converter, the data acquisition module, and the data analysis and processing module in sequence; The flexible multi-fiber-loop series acoustic sensor based on the Sagnac interferometer is used for partial discharge ultrasonic signal positioning detection. Specifically, the multiple sensing probes with different resonant frequencies in the flexible multi-fiber-loop series acoustic sensor based on the Sagnac interferometer are respectively installed at positions far away from each other on the same power equipment or at different positions of non-same power equipment with spatial isolation; The optical signal emitted by the driving light source is divided into two paths by the 2×2 coupler. One path passes through multiple sensing probes in sequence and then returns to the 2×2 coupler through the delay optical fiber. The other path first passes through the delay optical fiber and then passes through multiple sensing probes and returns to the 2×2 coupler. The two paths of light interfere in the 2×2 coupler and are received by the photoelectric converter and then enter the data acquisition module. When partial discharge occurs at the position where a certain sensing probe of the power equipment is located or at the positions where multiple sensing probes are located, after the sensing probe detects the partial discharge ultrasonic signal, the data acquisition module outputs a time-domain waveform signal, and the data analysis and processing module performs Fourier analysis on this signal to obtain the frequency-domain information of the time-domain signal. By comparing whether the characteristic frequency of the frequency-domain information overlaps with the resonant characteristic peak of one or more sensing probes, the partial discharge position is determined; The sensing probe consists of two parts. One part is wound by an optical fiber, and the other part is a coupling substrate for modulating the resonant frequency of the sensing probe. The optical fiber loop is wound by a planar single-layer optical fiber, and the resonant frequency is modulated by changing the thickness of the coupling substrate.

2. The flexible multi-fiber loop series-connected acoustic sensor based on the Sagnac interferometer according to claim 1, characterized in that, The driving light source is a C-band broadband light source.

3. The flexible multi-fiber loop series-connected acoustic sensor based on a Sagnac interferometer according to claim 1, characterized in that, The sensing probe is formed by winding an optical fiber along a plane and curing it with epoxy resin.

4. The flexible multi-fiber loop series-connected acoustic sensor based on a Sagnac interferometer according to claim 1, characterized in that, The resonant frequency of the sensing probe is selected within the range of 20 - 200 kHz.

5. The flexible multi-fiber loop series-connected acoustic sensor based on a Sagnac interferometer according to claim 1, characterized in that, The number of sensing probes is more than 2.

6. A positioning detection method for partial discharge ultrasonic signals of power equipment, characterized in that, Use the flexible multi-fiber-loop series acoustic sensor based on the Sagnac interferometer described in any one of claims 1 to 5 for detection.

7. A method for local discharge ultrasonic signal positioning and detection, characterized in that, Respectively install the multiple sensing probes with different resonant frequencies in the flexible multi-fiber-loop series acoustic sensor based on the Sagnac interferometer described in any one of claims 1 to 5 at positions far away from each other on the same power equipment or at different positions of non-same power equipment with spatial isolation.

8. The partial discharge ultrasonic signal positioning and detection method according to claim 7, characterized in that The optical signal emitted by the driving light source is divided into two paths by a 2×2 coupler. One path sequentially passes through multiple sensing probes and then returns to the 2×2 coupler through a delay optical fiber. The other path first passes through the delay optical fiber and then passes through multiple sensing probes to return to the 2×2 coupler. The two paths of light interfere in the 2×2 coupler and are received by a photoelectric converter and then enter the data acquisition module. When partial discharge occurs at the position of a certain sensing probe or the positions of multiple sensing probes of the power equipment, after the sensing probe detects the partial discharge ultrasonic signal, the data acquisition module outputs a time-domain waveform signal. The data analysis and processing module performs Fourier analysis on this signal to obtain the frequency-domain information of the time-domain signal. By comparing whether the characteristic frequency of the frequency-domain information overlaps with the resonance characteristic peaks of one or more sensing probes, the partial discharge position is determined.

9. A method for localizing and detecting partial discharge ultrasonic signals of ABC three-phase lines in GIS, characterized in that, Three sensing probes with different resonance frequencies in the flexible multi-fiber loop series acoustic sensor based on the Sagnac interferometer according to any one of claims 1 to 5 are respectively installed on the ABC three-phase lines.

10. The detection method according to claim 9, wherein The resonance frequencies of the three sensing probes are 25 kHz, 60 kHz, and 115 kHz respectively.

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