Broadband EFPI sensor constructed by multi-resonance characteristics and application thereof in partial discharge detection

Abstract

The invention discloses a broadband EFPI sensor constructed by multi-resonance characteristics and application thereof in partial discharge detection, and belongs to the technical field of partial discharge detection. The problem that an existing narrow-band ultrasonic sensor is unstable in detection sensitivity when facing broadband partial discharge ultrasonic signals with randomly distributed sound energy spectrums is solved. An EFPI sensor front-end sound sensitive diaphragm is constructed by adopting a mode of laminating multiple layers of cavities, each layer of cavity is formed by separating multiple layers of diaphragms, each layer of diaphragm has different resonant frequencies, the cavity adjacent to the tail end of an EFPI sensor optical fiber is filled with an air medium, and the other cavities are filled with transformer oil, so that the EFPI sensor front-end sound sensitive diaphragm is formed. The mechanical vibration and sound pressure waves of the diaphragm are transmitted by using the low compression characteristic of the liquid, a strong effect on the cavity length change of the Fabry-Perot cavity is formed, the detection sensitivity of the EFPI sensor in more frequency band ranges is improved, and the stability of the partial discharge ultrasonic sensor on the detection sensitivity of partial discharge ultrasonic signals is improved.

Description

Technical Field

[0001] The present invention relates to a wide-band EFPI sensor constructed with multi-resonant characteristics and its application in partial discharge detection, belonging to the technical field of partial discharge detection. Background Art

[0002] Partial discharge is an early manifestation of the insulation deterioration of high-voltage power equipment. Detecting it can effectively evaluate the insulation status of the equipment, timely eliminate potential risks, and thus improve the safety and stability of equipment operation. Therefore, the detection of partial discharge is crucial. When partial discharge occurs, it is accompanied by various physical phenomena such as sound, light, electricity, heat, and chemistry. Among them, the ultrasonic signal has become an important means for partial discharge detection because of its strong anti-interference ability, ability to quickly locate the discharge source, and high real-time performance.

[0003] For the detection of partial discharge ultrasonic signals, the commonly used sensors mainly include optical acoustic sensors and piezoelectric ceramic (PZT) sensors. Among them, optical sensors have received extensive attention and research because of their excellent anti-electromagnetic interference ability, high sensitivity, and long-distance transmission ability. Among many optical ultrasonic sensors, the extrinsic Fabry-Perot (EFPI) sensor has become a research hotspot due to its advantages of high detection sensitivity, simple structure, small volume, and the characteristic that it can be designed as a fully insulated structure for internal installation.

[0004] However, for the typical narrow-band detection method of using a single characteristic resonance frequency by the EFPI sensor to detect partial discharge ultrasonic signals, for partial discharge ultrasonic signals with a broadband signal output characteristic and a certain randomness in the spectral energy distribution, the improvement of the sensor detection sensitivity only means the improvement of the detection sensitivity for a certain part of specific partial discharge ultrasonic signals, rather than the improvement of the detection sensitivity for all partial discharge ultrasonic signals. When the acoustic energy of partial discharge ultrasonic signals is less or not distributed in the detection frequency band of the narrow-band detection EFPI sensor, it is very difficult for the EFPI sensor to detect partial discharge ultrasonic signals, and even unable to detect any ultrasonic signals. This problem is also a key problem encountered by PZT sensors that also work with narrow-band detection characteristics in practical applications, and it is also a key problem that restricts the large-scale popularization and application of the acoustic detection method in the insulation detection of power equipment. Therefore, there is an urgent need for ultrasonic sensors with high detection sensitivity and a wider detection frequency band in engineering practice. Summary of the Invention

[0005] Aiming at the problem of unstable detection sensitivity of narrow-band ultrasonic sensors (such as PZT, EFPI, etc.) widely used in the existing power equipment insulation detection engineering applications when facing wide-band partial discharge ultrasonic signals with a random acoustic energy spectrum distribution, the present invention provides a wide-band EFPI sensor constructed with multi-resonant characteristics and its application in partial discharge detection.

[0006] Technical solution of the present invention:

[0007] One of the objectives of the present invention is to provide a wide-band EFPI sensor constructed with multi-resonant characteristics, including an EFPI sensor and a plurality of diaphragms located in the Fabry-Perot cavity of the EFPI sensor. The plurality of diaphragms divide the Fabry-Perot cavity into a plurality of cavities, and reflective films are coated on both the upper and lower surfaces of the cavity adjacent to the fiber end of the EFPI sensor.

[0008] Further defined, the plurality of diaphragms respectively have different resonant frequencies.

[0009] Further defined, starting from the fiber end of the EFPI sensor, the resonant frequencies of the diaphragms decrease in sequence.

[0010] Further defined, the reflectivity of the reflective film is 90%.

[0011] Further defined, the cavity adjacent to the fiber end of the EFPI sensor is filled with air medium, and the remaining cavities are filled with transformer oil.

[0012] Further defined, the number of diaphragms is 3.

[0013] Even further defined, starting from the fiber end of the EFPI sensor, the diaphragms are sequentially named the first diaphragm, the second diaphragm, and the third diaphragm. The resonant frequency of the first diaphragm is 100 kHz, the resonant frequency of the second diaphragm is 70 kHz, and the resonant frequency of the third diaphragm is 30 kHz.

[0014] Another objective of the present invention is to provide an application of the above wide-band EFPI sensor constructed with multi-resonant characteristics, specifically for partial discharge detection.

[0015] Further defined, for the detection of partial discharge ultrasonic signals

[0016] Further defined, the wide-band EFPI sensor constructed with multi-resonant characteristics is completely immersed in transformer oil for partial discharge detection.

[0017] Beneficial effects:

[0018] The present invention constructs the acoustic sensitive diaphragm at the front end of the EFPI sensor by means of multi-layer cavity layer stacking. Each cavity layer is separated by multiple diaphragms, and each diaphragm has a different resonance frequency. The cavity adjacent to the fiber end of the EFPI sensor is filled with air medium, and the remaining cavities are filled with transformer oil. The air cavity constitutes the Fabry-Perot cavity of the EFPI sensor. According to the basic detection principle of the EFPI sensor, the change in the length of the Fabry-Perot cavity determines the intensity of the output signal of the EFPI sensor, that is, the detection sensitivity. Therefore, in order to efficiently transfer the high-response output of each cavity diaphragm at its respective resonance frequency to the last cavity layer, the present invention fills transformer oil in each cavity except the Fabry-Perot cavity, and uses the low compressibility of the liquid to transfer the mechanical vibration of the diaphragm and the acoustic pressure wave. Especially when each diaphragm resonates, the amplitude increases significantly, and the pressure transfer is more obvious. And because the Fabry-Perot cavity is filled with air medium, it also has excellent compressibility, that is, at this time, a strong effect of the high-response output of each cavity diaphragm resonance on the change in the length of the Fabry-Perot cavity is formed, thereby improving the detection sensitivity of the EFPI sensor in a wider frequency band range and enhancing the stability of the detection sensitivity of the partial discharge ultrasonic sensor to partial discharge ultrasonic signals. Description of the Drawings

[0019] Figure 1 Schematic diagram of the structure of the wide-band EFPI sensor with multi-resonant characteristics provided by the present invention;

[0020] Figure 2 Schematic diagram of the partial discharge signal monitoring system of the wide-band EFPI sensor with multi-resonant characteristics provided by the present invention;

[0021] Figure 3 Comparison diagram of the first group of detected time-domain signals between the wide-band EFPI sensor with multi-resonant characteristics provided by the present invention and the traditional PET sensor;

[0022] Figure 4 First group of detected frequency-domain signal diagrams of the traditional PET sensor;

[0023] Figure 5 First group of detected frequency-domain signal diagrams of the wide-band EFPI sensor with multi-resonant characteristics provided by the present invention;

[0024] Figure 6 Comparison diagram of the second group of detected time-domain signals between the wide-band EFPI sensor with multi-resonant characteristics provided by the present invention and the traditional PET sensor;

[0025] Figure 7 Second group of detected frequency-domain signal diagrams of the traditional PET sensor;

[0026] Figure 8The second set of detected frequency-domain signal diagrams of the broadband EFPI sensor constructed with the multi-resonant characteristics provided by the present invention.

[0027] In the figure, 1 - optical fiber, 2 - capillary glass, 3 - first diaphragm, 4 - second diaphragm, 5 - third diaphragm, 6 - reflective film. Specific implementation manners

[0028] 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.

[0029] 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, and 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 construed as a limitation of the present invention.

[0030] In the description of the present invention, it should be noted that unless otherwise clearly specified and defined, 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 communication inside 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.

[0031] Such as Figure 1As shown in the figure, the present invention provides a broadband EFPI sensor constructed with multi-resonant characteristics, including an EFPI sensor and multiple diaphragms located in the Fabry-Perot cavity of the EFPI sensor. The multiple diaphragms divide the Fabry-Perot cavity of the EFPI sensor into multiple cavities, and reflective films 6 with a reflectivity of 90% are coated on the upper and lower surfaces of the cavity adjacent to the end of optical fiber 1, forming an interference spectrum. The optical fiber 1 of the EFPI sensor is sleeved in a capillary glass 2, and the diaphragms are sequentially named the first diaphragm 3, the second diaphragm 4, and the third diaphragm 5 starting from the end of the optical fiber 1. The multiple diaphragms have different resonant frequencies. Specifically, the resonant frequency of the first diaphragm is 100 kHz, the resonant frequency of the second diaphragm is 70 kHz, and the resonant frequency of the third diaphragm is 30 kHz. The cavity adjacent to the end of optical fiber 1 is filled with air medium, and the remaining cavities are filled with transformer oil. When performing partial discharge detection, the broadband EFPI sensor constructed with multi-resonant characteristics is completely immersed in transformer oil. At this time, the outer surface of the third diaphragm 5 is in the transformer oil, and the inner surface is in contact with the transformer oil in the cavity; the inner and outer surfaces of the second diaphragm 4 are both in contact with the transformer oil; the outer surface of the first diaphragm 3 is in contact with the transformer oil, and the inner surface is in contact with the air medium. With such a setting, the front-end acoustic sensitive diaphragms of the EFPI sensor are constructed in a three-layer and three-cavity superposition manner. The cavities filled with transformer oil are the fluid transfer channels for acoustic mechanical pressure waves. At the same time, the cavity support structure also serves as the transfer medium for acoustic mechanical waves, transmitting the partial discharge ultrasonic signal to each layer of diaphragm. Thus, through these two key energy transfer channels, the partial discharge ultrasonic signal is transmitted to the first diaphragm 3 in the form of broadband energy delivery, causing the cavity length of the air cavity (the Fabry-Perot cavity of the reconstructed EFPI sensor) to change along with the partial discharge ultrasonic signal. Moreover, the resonant high-response frequency bands of the first diaphragm 3, the second diaphragm 4, and the third diaphragm 5, through the form of a large increase in the resonant state amplitude of the diaphragm, act on the air cavity with an ultra-high response at the respective resonant frequencies of the first diaphragm 3, the second diaphragm 4, and the third diaphragm 5, forming the detection characteristics of multi-resonant broadband high sensitivity.

[0032] As Figure 2 shown in the figure, a comparison of partial discharge detection of partial discharge ultrasonic signals was carried out between the broadband EFPI sensor constructed with the above multi-resonant characteristics and a traditional piezoelectric ceramic sensor (PZT) of model SR150. The partial discharge source was a plate-plate electrode in transformer oil. The broadband EFPI sensor constructed with the above multi-resonant characteristics was completely immersed in transformer oil, and the PZT sensor was externally attached to the oil tank wall. High voltage electricity was provided by a power frequency high voltage step-up transformer. An intensity demodulation system was used to demodulate the above EFPI sensor, and an oscilloscope was used to collect the partial discharge ultrasonic signals of the above EFPI sensor and the PZT sensor.

[0033] Under the condition that the test conditions remain unchanged, multiple measurements are carried out. Due to the random distribution of the sound energy spectrum of the partial discharge ultrasonic signal, the detection results of the above-mentioned EFPI sensor and PZT sensor can be classified into the following two groups of detection results. The first group of detection results is as shown in Figures 3 - 5 shown. It can be seen from Figure 3 that the peak-to-peak value of the output signal of the above-mentioned EFPI sensor is basically the same as that of the output signal of the PZT sensor. It can be seen from Figure 4 that the PZT sensor has typical narrow-band detection characteristics, and the center resonance frequency is 150 kHz, which is consistent with the 150 kHz resonance characteristics of the PZT sensor of model SR150. It can be seen from Figure 5 that the frequency domains of the output signals of the above-mentioned EFPI sensor are 30 kHz, 70 kHz, and 100 kHz respectively, which are consistent with the respective resonance frequencies of the three diaphragm sheets of the EFPI sensor. Thus, it also shows the multi-resonance wide-band detection characteristics of the EFPI sensor.

[0034] The second group of experimental detection results is as shown in Figures 6 - 8 shown. It can be seen from Figure 6 that the peak-to-peak value of the output signal of the EFPI sensor is significantly higher than that of the PZT sensor. The characteristic information of Figure 7 and Figure 8 is consistent with that of Figure 4 and Figure 5 in the first group of experimental detection results. Since the PZT of model SR150 is only sensitive to the sound signal near the 150 kHz frequency, when the energy of the partial discharge ultrasonic signal is high near the 150 kHz frequency, the PZT shows high sensitivity. However, when the energy of the partial discharge ultrasonic signal is low near the 150 kHz frequency, then the PZT shows low sensitivity. For the same set of detection systems, when the peak-to-peak value of the output signal of the above-mentioned EFPI sensor is significantly higher than that of the PZT sensor, it reflects the characteristic that the above-mentioned EFPI sensor has a wide-band energy spectrum random distribution for the partial discharge source itself. At this time, it also shows that the partial discharge ultrasonic signal in the second group of experiments has a stronger energy spectrum distribution within the detection frequency band of the EFPI sensor, while the detection frequency band of the PZT just happens not to be in this range. This also shows the advantage of the EFPI sensor with a wider frequency band designed by the present invention in the detection of partial discharge ultrasonic signals.

[0035] 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 modifications and decorations 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 wideband EFPI sensor constructed with multi-resonant characteristics, characterized in that, It includes an EFPI sensor and a plurality of diaphragms located in the Fabry-Perot cavity of the EFPI sensor. The plurality of diaphragms divide the Fabry-Perot cavity into a plurality of cavities, and reflective films are coated on both the upper and lower surfaces of the cavity adjacent to the fiber end of the EFPI sensor.

2. The sensor according to claim 1, wherein The plurality of diaphragms respectively have different resonance frequencies.

3. The sensor according to claim 1, wherein Starting from the fiber end of the EFPI sensor, the resonance frequencies of the diaphragms decrease in sequence.

4. The sensor according to claim 1, characterized in that, The reflectivity of the reflective film is 90%.

5. The sensor according to claim 1, characterized in that, The cavity adjacent to the fiber end of the EFPI sensor is filled with air medium, and the remaining cavities are filled with transformer oil.

6. The sensor according to claim 1, characterized in that The number of diaphragms is 3.

7. The sensor according to claim 6, wherein Starting from the fiber end of the EFPI sensor, the diaphragms are sequentially named the first diaphragm, the second diaphragm, and the third diaphragm; the resonance frequency of the first diaphragm is 100 kHz, the resonance frequency of the second diaphragm is 70 kHz, and the resonance frequency of the third diaphragm is 30 kHz.

8. Application of a broadband EFPI sensor constructed with multi-resonant characteristics according to any one of claims 1 to 7, characterized in that, It is used for partial discharge detection.

9. The application according to claim 8, wherein It is used for the detection of partial discharge ultrasonic signals.

10. The application according to claim 8, characterized in that, The broadband EFPI sensor constructed with multi-resonance characteristics is completely immersed in transformer oil for partial discharge detection.

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