A multi-resonance characteristic constructed wideband EFPI sensor and its application in partial discharge detection

Abstract

This invention discloses a broadband EFPI sensor constructed with multi-resonance characteristics and its application in partial discharge detection, belonging to the field of partial discharge detection technology. This invention solves the problem of unstable sensitivity in existing narrow-band ultrasonic sensors when facing wide-band partial discharge ultrasonic signals with randomly distributed acoustic energy spectra. This invention employs a multi-layered, stacked cavity structure to construct the acoustically sensitive diaphragm at the front end of the EFPI sensor. Each cavity layer is composed of multiple diaphragms with different resonant frequencies. The cavity adjacent to the fiber optic tail of the EFPI sensor is filled with air, while the remaining cavities are filled with transformer oil. The low compressibility of the liquid transmits the mechanical vibration of the diaphragms and the acoustic pressure waves, creating a strong effect on the changes in the Fabry-Perot cavity length. This improves the detection sensitivity of the EFPI sensor across a wider frequency range and enhances the stability of the partial discharge ultrasonic sensor's detection sensitivity for partial discharge ultrasonic signals.

Description

Technical Field

[0001] This invention relates to a wideband EFPI sensor constructed with multi-resonance characteristics and its application in partial discharge detection, belonging to the field of partial discharge detection technology. Background Technology

[0002] Partial discharge is an early sign of insulation degradation in high-voltage power equipment. Detecting it can effectively assess the insulation status of the equipment, eliminate potential risks in a timely manner, and thus improve the safety and stability of equipment operation. Therefore, partial discharge detection is crucial. Partial discharge is accompanied by various physical phenomena such as sound, light, electricity, heat, and chemicals. Among these, ultrasonic signals have become an important means of partial discharge detection due to their strong anti-interference ability, ability to quickly locate the discharge source, and high real-time performance.

[0003] For the detection of ultrasonic signals from partial discharge, commonly used sensors mainly include optical acoustic sensors and piezoelectric ceramic (PZT) sensors. Among them, optical sensors have received widespread attention and research due to their excellent electromagnetic interference resistance, high sensitivity, and long-distance transmission capabilities. Among numerous optical ultrasonic sensors, the intrinsic Fabry-Perot (EFPI) sensor has become a research hotspot due to its advantages of high detection sensitivity, simple structure, small size, and the ability to be designed as a fully insulated structure for internal mounting.

[0004] However, the typical narrowband detection method of EFPI sensors, which uses a single characteristic resonant frequency for partial discharge ultrasonic signal detection, only improves the detection sensitivity of a specific portion of partial discharge ultrasonic signals, rather than all partial discharge ultrasonic signals, given that the signal output characteristics are broadband and the spectral energy distribution has a certain degree of randomness. When the acoustic energy of the partial discharge ultrasonic signal is less or non-existent within the detection frequency band of the narrowband detection EFPI sensor, the EFPI sensor has difficulty detecting the partial discharge ultrasonic signal, or even cannot detect any ultrasonic signal at all. This problem is also a key issue encountered by PZT sensors, which operate with narrowband detection characteristics, in practical applications. This is also a key reason why partial discharge acoustic measurement methods cannot be widely applied in the insulation testing of power equipment. Therefore, it is evident that 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] This invention addresses the problem of unstable sensitivity in detecting wide-band partial discharge ultrasonic signals with randomly distributed acoustic energy spectra using narrow-band ultrasonic sensors (PZT, EFPI, etc.) widely used in existing power equipment insulation testing engineering applications. It provides a wide-band EFPI sensor constructed with multi-resonance characteristics and its application in partial discharge detection.

[0006] The technical solution of this invention:

[0007] One of the objectives of this invention is to provide a broadband EFPI sensor constructed with multi-resonance characteristics, including an EFPI sensor and multiple diaphragms located within the Fabry-Perot cavity of the EFPI sensor. The multiple diaphragms divide the Fabry-Perot cavity into multiple chambers, and the upper and lower surfaces of the chambers adjacent to the fiber tail of the EFPI sensor are coated with reflective films.

[0008] Furthermore, each of the multiple diaphragms has a different resonant frequency.

[0009] Further specifying, the resonant frequency of the diaphragm decreases sequentially starting from the end of the optical fiber in the EFPI sensor.

[0010] Furthermore, the reflective film has a reflectivity of 90%.

[0011] Further specifying, the cavity adjacent to the fiber optic tail of the EFPI sensor is filled with air, while the remaining cavities are filled with transformer oil.

[0012] Further specifying, the number of membranes is 3.

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

[0014] The second objective of this invention is to provide an application of the broadband EFPI sensor constructed using the above-mentioned multi-resonance characteristics, specifically for partial discharge detection.

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

[0016] To further limit this, the wideband EFPI sensor, constructed with multi-resonance characteristics, was completely immersed in transformer oil for partial discharge detection.

[0017] Beneficial effects:

[0018] This invention employs a multi-layered, stacked cavity structure to construct the acoustically sensitive diaphragm at the front end of the EFPI sensor. Each cavity layer is composed of multiple diaphragms, each with a different resonant frequency. The cavity adjacent to the fiber optic tail of the EFPI sensor is filled with air, while 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 output signal strength, i.e., the detection sensitivity. Therefore, to ensure high response output at each cavity diaphragm's respective resonant frequency, [further details are needed]. The pressure is effectively transmitted to the last cavity. In this invention, each cavity except the previous Fapper cavity is filled with transformer oil. The low compressibility of the liquid is used to transmit the mechanical vibration of the diaphragm and the acoustic pressure wave. In particular, the amplitude of each diaphragm increases significantly when it resonates, and the pressure transmission is more obvious. Since the Fapper cavity is an air medium, it also has excellent compressibility. At this time, the high response output of the diaphragm resonance of each cavity layer has a strong effect on the change of the Fapper cavity length. This improves the detection sensitivity of the EFPI sensor in a wider frequency range and enhances the stability of the partial discharge ultrasonic sensor's detection sensitivity for partial discharge ultrasonic signals. Attached Figure Description

[0019] Figure 1 A schematic diagram of the structure of the broadband EFPI sensor constructed based on the multi-resonance characteristics provided by the present invention;

[0020] Figure 2 A schematic diagram of a partial discharge signal monitoring system for a broadband EFPI sensor constructed based on the multi-resonance characteristics provided by this invention;

[0021] Figure 3 A comparison of the first set of detection time-domain signals between the broadband EFPI sensor constructed based on the multi-resonance characteristics provided by this invention and a traditional PET sensor;

[0022] Figure 4 This is the first set of detection frequency domain signal diagrams for a traditional PET sensor;

[0023] Figure 5 The first set of detection frequency domain signal diagrams of the broadband EFPI sensor constructed based on the multi-resonance characteristics provided by the present invention;

[0024] Figure 6 A comparison of the second set of detection time-domain signals between the broadband EFPI sensor constructed based on the multi-resonance characteristics provided by this invention and a traditional PET sensor;

[0025] Figure 7 This is the second set of detection frequency domain signal diagrams for a traditional PET sensor;

[0026] Figure 8The second set of detection frequency domain signal diagrams for the broadband EFPI sensor constructed based on the multi-resonance characteristics provided by the present invention.

[0027] In the diagram, 1-optical fiber, 2-capillary glass, 3-first membrane, 4-second membrane, 5-third membrane, and 6-reflective film. Detailed Implementation

[0028] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0029] In the description of this invention, it should be noted that the terms "upper", "lower", "inner", "outer", "top / bottom", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0030] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installed," "equipped with," "sleeved / connected," "connected," etc., should be interpreted broadly. 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 a direct connection or an indirect connection through an intermediate medium; it can be a connection within two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0031] like Figure 1As shown, this invention provides a broadband EFPI sensor constructed with multi-resonance characteristics, including an EFPI sensor and multiple diaphragms located within the EFPI sensor's Fabry-Perot cavity. The multiple diaphragms divide the EFPI sensor's Fabry-Perot cavity into multiple chambers, and the upper and lower surfaces of the chambers adjacent to the tail end of optical fiber 1 are coated with a reflective film 6 with a reflectivity of 90%, forming an interference spectrum. The optical fiber 1 of the EFPI sensor is housed within a capillary glass 2. Starting from the tail end of optical fiber 1, the diaphragms are sequentially named first diaphragm 3, second diaphragm 4, and third diaphragm 5. Each diaphragm has a different resonant frequency; specifically, the resonant frequency of the first diaphragm is 100kHz, the resonant frequency of the second diaphragm is 70kHz, and the resonant frequency of the third diaphragm is 30kHz. The chamber adjacent to the tail end of optical fiber 1 is filled with air, while the remaining chambers are filled with transformer oil. When performing partial discharge detection, the broadband EFPI sensor constructed with multi-resonance 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 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. This configuration employs a three-layer, three-cavity stacked structure to construct the acoustically sensitive diaphragm at the front end of the EFPI sensor. The cavity filled with transformer oil serves as the fluid transmission channel for the acoustic-mechanical pressure wave, while the cavity support structure also acts as the transmission medium for the acoustic-mechanical wave, transmitting the partial discharge ultrasonic signal to each diaphragm layer. Thus, the partial discharge ultrasonic signal is transmitted to the first diaphragm 3 via these two key energy transmission channels in a broadband energy delivery manner. This causes the length of the air cavity (the Fabry-Perot cavity of the reconstructed EFPI sensor) to change along with the partial discharge ultrasonic signal. Furthermore, the high-response frequency bands of the first diaphragm 3, the second diaphragm 4, and the third diaphragm 5 are amplified through a significant increase in the amplitude of the diaphragm resonant states, resulting in the ultra-high response of the partial discharge ultrasonic signal at the respective resonant frequencies of the first diaphragm 3, the second diaphragm 4, and the third diaphragm 5 to the air cavity, forming a multi-resonant, broadband, and high-sensitivity detection characteristic.

[0032] like Figure 2 As shown, the wideband EFPI sensor constructed with the above-mentioned multi-resonance characteristics is compared with the conventional piezoelectric ceramic sensor (PZT) of model SR150 in terms of partial discharge detection of ultrasonic signals. The partial discharge source is a plate electrode in transformer oil. The wideband EFPI sensor constructed with the above-mentioned multi-resonance characteristics is completely immersed in transformer oil. The PZT sensor is externally attached to the oil tank wall. High voltage is provided by the power frequency high voltage step-up transformer. The EFPI sensor is demodulated using an intensity demodulation system, and the partial discharge ultrasonic signals of the EFPI sensor and the PZT sensor are acquired using an oscilloscope.

[0033] Under unchanged test conditions, multiple measurements were performed. Due to the random distribution of the acoustic energy spectrum of the partial discharge ultrasonic signal, the detection results of the EFPI sensor and PZT sensor can be classified into the following two groups of results. The first group of detection results is as follows: Figure 3-5 As shown. By Figure 3 It can be seen that the peak-to-peak value of the output signal of the EFPI sensor is basically the same as that of the PZT sensor. Figure 4 It can be seen that the PZT sensor exhibits typical narrowband detection characteristics, with a center resonant frequency of 150kHz, consistent with the 150kHz resonant characteristic of the SR150 PZT sensor. Figure 5 It can be seen that the frequency domains of the output signals of the above EFPI sensor are 30kHz, 70kHz and 100kHz, which are consistent with the resonant frequencies of the three diaphragms of the EFPI sensor, thus demonstrating the multi-resonance wideband detection characteristics of the EFPI sensor.

[0034] The results of the second set of experiments, such as Figure 6-8 As shown, by Figure 6 It can be seen that the peak-to-peak value of the output signal of the EFPI sensor is significantly higher than that of the PZT sensor. Figure 7 and Figure 8 Feature information and the results of the first set of experiments Figure 4 and Figure 5 Consistent. Since the SR150 PZT is only sensitive to acoustic signals around 150kHz, it exhibits high sensitivity when the partial discharge ultrasonic signal has high energy around 150kHz. However, when the partial discharge ultrasonic signal has low energy around 150kHz, the PZT exhibits low sensitivity. In the case where the peak-to-peak value of the EFPI sensor output signal is significantly higher than that of the PZT sensor in the same detection system, it demonstrates that the EFPI sensor has a wide-bandwidth random energy spectrum distribution characteristic for the partial discharge source itself. This also indicates that the partial discharge ultrasonic signal in the second set 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 happens to be outside this range. This also demonstrates the advantage of the wider-bandwidth EFPI sensor designed in this invention in the detection of partial discharge ultrasonic signals.

[0035] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Anyone skilled in the art can make various modifications and alterations without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be determined by the claims.

Claims

1. A broadband EFPI sensor constructed using multi-resonance characteristics, characterized in that, It includes an EFPI sensor and multiple diaphragms located within the EFPI sensor's Fabry-Perot cavity. The multiple diaphragms divide the Fabry-Perot cavity into multiple chambers, and the upper and lower surfaces of the chambers adjacent to the fiber optic tail of the EFPI sensor are coated with reflective films.

2. The sensor according to claim 1, characterized in that, Multiple diaphragms each have a different resonant frequency.

3. The sensor according to claim 1, characterized in that, The resonant frequencies of the diaphragm decrease sequentially starting from the fiber optic tail end of the EFPI sensor.

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

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

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

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

8. An application of a broadband EFPI sensor constructed using the multi-resonance characteristics described in any one of claims 1 to 7, characterized in that, Used for partial discharge detection.

9. The application according to claim 8, characterized in that, Used for the detection of ultrasonic signals of partial discharge.

10. The application according to claim 8, characterized in that, A wideband EFPI sensor with multi-resonance characteristics was fully immersed in transformer oil for partial discharge detection.

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