Passive wireless underground cable partial discharge sensing system and method

Abstract

The application discloses a passive wireless underground cable partial discharge sensing system and method, relates to the technical field of underground cable partial discharge measurement, and can realize passive wireless communication of underground cable partial discharge signals by adopting the principle of external sensor disturbance sensing tag impedance. The system comprises a sensing tag module, a partial discharge sensor module and a reader module. The sensing tag module is used for receiving incident radio frequency signals emitted by the reader module, and modulating echo radio frequency signals by impedance mismatch when receiving alternating voltage signals applied by the partial discharge sensor module, and reflecting the modulated echo radio frequency signals to the reader module. The partial discharge sensor module is used for acquiring ultrasonic signals generated by underground cable partial discharge, and converting the ultrasonic signals into alternating voltage signals, and applying the alternating voltage signals to the sensing tag module. The reader module is used for emitting incident radio frequency signals, and receiving echo radio frequency signals reflected by the sensing tag module, demodulating the echo radio frequency signals, and obtaining partial discharge signals.

Description

Technical Field

[0001] This application relates to the field of partial discharge measurement technology for underground cables, and in particular to a passive wireless partial discharge sensing system and method for underground cables. Background Technology

[0002] With the continuous development of society, underground cables are currently used for power transmission. During long-term operation, defects may appear in the cable insulation layer due to factors such as on-site manufacturing processes, environmental corrosion, and aging of electrical materials. These defects can lead to electric field distortion, resulting in partial discharge. Prolonged discharge accelerates the aging of the insulation layer, ultimately causing the power cable to fail.

[0003] Currently, relevant technicians utilize the characteristics of UHF electromagnetic waves and ultrasonic waves generated during partial discharge of cables. They employ detection methods such as UHF and ultrasonic methods, using sensors to acquire these two signals separately to detect partial discharge signals, or simultaneously acquire the two signals and fuse them at the data terminal to achieve the detection and location of partial discharge.

[0004] In the process of developing this application, the applicant discovered that the relevant technology has at least the following problems:

[0005] Current sensors for acquiring signals all require battery power, long signal transmission lines, and expensive data acquisition cards to acquire high-frequency signals. This makes them unsuitable for large-scale deployment in confined underground high-voltage power corridors. Furthermore, the messy transmission lines can interfere with normal maintenance processes. Therefore, there is an urgent need for a passive wireless underground cable partial discharge sensing system and method to improve cable detection efficiency. Summary of the Invention

[0006] In view of this, this application provides a passive wireless underground cable partial discharge sensing system and method. The main purpose is to solve the problems that current sensors for acquiring signals all need to be powered by batteries, use long signal transmission lines and high-cost data acquisition cards to acquire high-frequency signals, which are not suitable for large-scale deployment in narrow underground high-voltage power corridors, and the messy transmission lines will affect the normal maintenance process of the staff.

[0007] According to a first aspect of this application, a passive wireless underground cable partial discharge sensing system is provided, the method comprising: a sensing tag module, a partial discharge sensor module, and a reader module;

[0008] The sensor tag module is used to receive the incident radio frequency signal emitted by the reader module, and when it receives the AC voltage applied by the partial discharge sensor module, it modulates the amplitude, resonant frequency and phase of the echo radio frequency signal by using impedance mismatch, and reflects the modulated echo radio frequency signal back to the reader module.

[0009] The partial discharge sensor module is a sensor that can convert ultrasonic signals into AC voltage signals. It is used to acquire ultrasonic signals generated by partial discharge of underground cables, convert the ultrasonic signals into AC voltage signals, and apply the AC voltage signals to the sensor tag module.

[0010] The reader module is used to transmit the incident radio frequency signal of 433MHz continuous sinusoidal frequency and receive the echo radio frequency signal reflected by the sensor tag module, and demodulate the echo radio frequency signal to obtain a partial discharge signal.

[0011] Optionally, the sensing tag module includes: a surface acoustic wave unit, an impedance matching network unit, and a tag antenna unit;

[0012] The surface acoustic wave unit is used to receive the incident radio frequency signal transmitted by the tag antenna unit, convert the incident radio frequency signal into an acoustic wave signal, generate an echo radio frequency signal, and transmit the echo radio frequency signal to the tag antenna unit.

[0013] The impedance matching network unit is used to be electrically connected to the surface acoustic wave unit and the tag antenna unit respectively, so that the sensing tag module is in an impedance matching state. When it receives the AC voltage applied by the partial discharge sensor module, it generates impedance mismatch and changes the antenna reflection coefficient.

[0014] The tag antenna unit is used to receive the incident radio frequency signal emitted by the reader module, transmit the incident radio frequency signal to the surface acoustic wave unit, receive the echo radio frequency signal transmitted by the surface acoustic wave unit, and reflect the echo radio frequency signal back to the reader module.

[0015] Optionally, the surface acoustic wave unit includes: a piezoelectric substrate, an interdigital transducer, and a reflective grating;

[0016] The interdigital transducer is disposed on the piezoelectric substrate. The piezoelectric substrate and the interdigital transducer convert the incident radio frequency signal into an acoustic wave signal based on the inverse piezoelectric effect, and the acoustic wave signal is transmitted to the reflective grating along the surface of the surface acoustic wave device.

[0017] The interdigital transducer receives the acoustic wave signal reflected by the reflective grating;

[0018] The piezoelectric substrate and the interdigital transducer convert the acoustic wave signal into the echo radio frequency signal based on the positive piezoelectric effect, and transmit the echo radio frequency signal to the tag antenna unit;

[0019] The reflective grating is used to receive the acoustic signal and reflect it back to the interdigital transducer according to the antenna reflection coefficient.

[0020] Optionally, the impedance matching network unit is a T-type or Pi-type network composed of a variable capacitor, an inductor, a resistor, and a capacitor, including: a variable capacitor;

[0021] The variable capacitor is used to receive the AC voltage applied by the partial discharge sensor module, and to change the capacitance value of the variable capacitor according to the voltage across its terminals.

[0022] Optionally, the reader module includes: a reader antenna unit and a reader control unit;

[0023] The reader antenna unit is used to transmit the incident radio frequency signal of 433MHz continuous sinusoidal frequency and receive the echo radio frequency signal reflected by the sensor tag module, and transmit the echo radio frequency signal to the reader control unit.

[0024] The reader control unit is electrically connected to the reader antenna unit and is used to generate the incident radio frequency signal and receive the echo radio frequency signal transmitted by the reader antenna unit, demodulate the echo radio frequency signal to obtain the partial discharge signal.

[0025] According to a second aspect of this application, a passive wireless method for sensing partial discharge in underground cables based on a passive wireless underground cable partial discharge sensing system is provided, the method comprising:

[0026] The partial discharge sensor module acquires the ultrasonic signal generated by the partial discharge of the underground cable, converts the ultrasonic signal into an AC voltage signal, and applies the AC voltage signal to the variable capacitor of the impedance matching network unit in the sensor tag module, so as to cause the sensor tag module to produce impedance mismatch and change the antenna reflection coefficient.

[0027] The reader module transmits a continuous sinusoidal incident radio frequency signal of 433MHz to the sensor tag module;

[0028] The sensor tag module receives the incident radio frequency signal emitted by the reader module, modulates the echo radio frequency signal based on the incident radio frequency signal and the antenna reflection coefficient, and reflects the echo radio frequency signal back to the reader module.

[0029] The reader module receives the echo radio frequency signal reflected by the sensor tag module, demodulates the echo radio frequency signal, and obtains a partial discharge signal.

[0030] Optionally, the sensing tag module receives the incident radio frequency signal emitted by the reader module, including:

[0031] The impedance matching network unit in the sensing tag module is electrically connected to the surface acoustic wave unit and the tag antenna unit in the sensing tag module, respectively, so that the sensing tag module is in an impedance matching state.

[0032] The tag antenna unit receives the incident radio frequency signal sent by the reader antenna unit of the reader module and transmits the incident radio frequency signal to the surface acoustic wave unit.

[0033] Optionally, the step of modulating the echo radio frequency signal based on the incident radio frequency signal and the antenna reflection coefficient, and reflecting the echo radio frequency signal to the reader module, includes:

[0034] The piezoelectric substrate and interdigital transducer of the surface acoustic wave unit of the sensing tag module receive the incident radio frequency signal, convert the incident radio frequency signal into an acoustic wave signal based on the inverse piezoelectric effect, and transmit the acoustic wave signal along the surface of the surface acoustic wave device to the reflection grating in the surface acoustic wave unit.

[0035] The reflective grating modulates the echo radio frequency signal based on the antenna reflection coefficient;

[0036] The interdigital transducer transmits the echo radio frequency signal to the tag antenna unit;

[0037] The tag antenna unit receives the echo radio frequency signal transmitted by the surface acoustic wave unit and reflects the echo radio frequency signal to the reader module.

[0038] Optionally, the reflective grating modulates the echo radio frequency signal based on the antenna reflection coefficient, including:

[0039] The reflective grating reflects the acoustic signal back to the interdigital transducer according to the antenna reflection coefficient;

[0040] The interdigital transducer and the piezoelectric substrate convert the acoustic wave signal into the echo radio frequency signal based on the positive piezoelectric effect.

[0041] Optionally, the reader module receives the echo radio frequency signal reflected by the sensor tag module, demodulates the echo radio frequency signal to obtain a partial discharge signal, including:

[0042] The reader antenna unit in the reader module receives the echo radio frequency signal reflected by the sensor tag module and transmits the echo radio frequency signal to the reader control unit in the reader module.

[0043] The reader control unit receives the echo radio frequency signal transmitted by the reader antenna unit, demodulates the echo radio frequency signal, and obtains the partial discharge signal.

[0044] Using the above technical solution, this application provides a passive wireless underground cable partial discharge sensing system and method. First, a partial discharge sensor module acquires the ultrasonic signal generated by partial discharge in the underground cable and converts it into an AC voltage signal. This AC voltage signal is applied to the variable capacitor in the impedance matching network unit of the sensing tag module, causing impedance mismatch and changing the antenna reflection coefficient. Subsequently, a reader module transmits a continuous sinusoidal incident radio frequency (RF) signal of 433MHz to the sensing tag module. Next, the sensing tag module receives the incident RF signal transmitted by the reader module, modulates the echo RF signal based on the incident RF signal and the antenna reflection coefficient, and reflects the echo RF signal back to the reader module. Finally, the reader module receives the echo RF signal reflected by the sensing tag module, demodulates the echo RF signal, and obtains the partial discharge signal. In this application, the partial discharge sensor senses the ultrasonic waves generated by partial discharge and converts them into an AC voltage signal. The AC voltage signal causes impedance mismatch in the sensing tag module, and the reader module receives the mismatched tag echo RF signal and demodulates the partial discharge signal. The sensor tag module is ready to use immediately upon attachment, requiring no battery power and operating wirelessly continuously solely based on the radio frequency signals transmitted by the reader module. It utilizes the principle of external sensor perturbing the impedance of the sensor tag to achieve passive wireless communication of partial discharge signals from underground cables. This allows for high-rate sampling of partial discharge signals and offers advantages such as small size, long lifespan, and passive operation.

[0045] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0046] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0047] Figure 1AA schematic diagram of a passive wireless underground cable partial discharge sensing system provided in an embodiment of this application is shown.

[0048] Figure 1B A schematic diagram of a passive wireless underground cable partial discharge sensing system provided in an embodiment of this application is shown.

[0049] Figure 1C A schematic diagram of a passive wireless underground cable partial discharge sensing system provided in an embodiment of this application is shown.

[0050] Figure 2 A flowchart illustrating a method for a passive wireless underground cable partial discharge sensing system according to an embodiment of this application is shown. Detailed Implementation

[0051] Exemplary embodiments of the present application will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present application are shown in the drawings, it should be understood that the present application may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this application will be thorough and complete, and will fully convey the scope of the present application to those skilled in the art.

[0052] This application provides a passive wireless partial discharge sensing system for underground cables. First, a partial discharge sensor module acquires ultrasonic signals generated by partial discharge in the underground cable and converts these signals into AC voltage signals. These AC voltage signals are then applied to the variable capacitor in the impedance matching network unit of the sensing tag module, causing impedance mismatch and altering the antenna reflection coefficient. Next, a reader module transmits a continuous sinusoidal incident radio frequency (RF) signal at 433MHz to the sensing tag module. The sensing tag module then receives the RF signal transmitted by the reader module, modulates the echo RF signal based on the incident RF signal and the antenna reflection coefficient, and reflects the echo RF signal back to the reader module. Finally, the reader module receives the reflected echo RF signal from the sensing tag module, demodulates it, and obtains the partial discharge signal. In this application, the partial discharge sensor detects the ultrasonic waves generated by partial discharge and converts them into AC voltage signals. The AC voltage signal causes impedance mismatch in the sensing tag module, and the reader module receives the mismatched tag echo RF signal and demodulates the partial discharge signal. The sensor tag module is ready to use immediately upon attachment, requiring no battery power and operating wirelessly continuously solely based on the radio frequency signals transmitted by the reader module. It utilizes the principle of external sensor perturbing the impedance of the sensor tag to achieve passive wireless communication of partial discharge signals from underground cables. This allows for high-rate sampling of partial discharge signals and offers advantages such as small size, long lifespan, and passive operation. Figure 1AAs shown, the passive wireless underground cable partial discharge sensing system includes: a sensing tag module 10, a partial discharge sensor module 20, and a reader module 30.

[0053] In the embodiments of this application, such as Figure 1B As shown, the sensor tag module 10 includes a surface acoustic wave unit 11, an impedance matching network unit 12, and a tag antenna unit 13; a partial discharge sensor module 20; a reader module 30 includes a reader antenna unit 31 and a reader control unit 32; an incident radio frequency signal 40; and an echo radio frequency signal 50.

[0054] Specifically, the impedance matching network unit 12 of the sensing tag module 10 is a T-type or Pi-type network composed of variable capacitors, inductors, resistors and capacitors, which is electrically connected to the surface acoustic wave unit 11 and the tag antenna unit 13 respectively to form a high impedance matching of the sensing tag module 10.

[0055] The partial discharge sensor module 20 is a sensor that can convert ultrasonic signals into AC voltage signals, such as a piezoelectric ultrasonic sensor based on the electromechanical coupling principle or an ultrasonic triboelectric nanomotor based on the charge transfer principle. It is used to sense ultrasonic signals generated by partial discharge in underground cables in real time and convert the ultrasonic signals into AC voltage. In an optional implementation, the partial discharge sensor module 20 is a piezoelectric ultrasonic sensor. When the ultrasonic wave causes the piezoelectric film to vibrate, the piezoelectric film generates an AC voltage signal output according to the piezoelectric effect, thereby converting the ultrasonic signal into an AC voltage signal. After calibration, the AC voltage information can be correlated with the ultrasonic amplitude. The AC voltage is then applied to the variable capacitor 121 of the impedance matching network unit 12 in the sensor tag module 10. The capacitance of the variable capacitor 121 changes with the voltage across its terminals, causing impedance mismatch in the sensor tag module 10.

[0056] Furthermore, impedance mismatch in the sensor tag module 10 can cause changes in the antenna reflection coefficient, resulting in variations in the amplitude, resonant frequency, phase, and power of the echo RF signal 50. Specifically, for example... Figure 1CAs shown, in an optional implementation, the surface acoustic wave unit can be a resonant surface acoustic wave unit. The resonant surface acoustic wave unit includes: a piezoelectric substrate 111, an interdigital transducer 112, and a reflector grating 113. The piezoelectric substrate 111 and the interdigital transducer 112 convert the incident radio frequency signal 40 emitted from the reader module 30 into an acoustic wave through the inverse piezoelectric effect. This acoustic wave is transmitted along the surface of the surface acoustic wave device to the reflector grating 113. The reflector grating 113 reflects the acoustic wave signal back to the interdigital transducer 112 according to the antenna reflection coefficient. The interdigital transducer 112 and the piezoelectric substrate 111 then convert the acoustic wave signal into an echo radio frequency signal 50 through the direct piezoelectric effect, and the echo radio frequency signal 50 is reflected back to the reader module 30 through the tag antenna unit 13.

[0057] The reader module 30 includes a reader antenna unit 31 and a reader control unit 32. The reader antenna unit 31 is electrically connected to the reader control unit 32. The reader antenna unit 31 transmits the incident radio frequency signal 40 generated by the reader control unit 32 to the sensor tag module 10, and receives the echo radio frequency signal 50 reflected by the sensor tag module 10. The echo radio frequency signal 50 is then transmitted to the reader control unit 32, where it is demodulated using demodulation technology to obtain a partial discharge signal.

[0058] This application provides a passive wireless method for detecting partial discharge in underground cables, based on a passive wireless underground cable partial discharge sensing system. Figure 2 As shown, the method includes:

[0059] 201. The partial discharge sensor module acquires the ultrasonic signal generated by the partial discharge of the underground cable and converts the ultrasonic signal into an AC voltage signal. The AC voltage signal is applied to the variable capacitor of the impedance matching network unit in the sensor tag module to cause impedance mismatch in the sensor tag module and change the antenna reflection coefficient.

[0060] In this embodiment, the partial discharge sensor module can be a piezoelectric ultrasonic sensor. When the ultrasonic wave causes the piezoelectric film to vibrate, the piezoelectric film generates an AC voltage signal output according to the piezoelectric effect, thereby converting the ultrasonic signal into an AC voltage signal. After calibration, the AC voltage information can be correlated with the ultrasonic amplitude. The AC voltage is then applied to the variable capacitor of the impedance matching network unit in the sensor tag module, causing the capacitance of the variable capacitor to change with the voltage across the capacitor. This results in impedance mismatch in the sensor tag module 10, changing the antenna reflection coefficient, and consequently altering the amplitude, resonant frequency, phase, and power of the echo radio frequency signal.

[0061] 202. The reader module transmits a continuous sinusoidal incident radio frequency signal of 433MHz to the sensor tag module.

[0062] In this embodiment, the reader antenna unit in the reader module continuously transmits a continuous 433MHz sinusoidal incident radio frequency signal generated by the reader control unit to the sensor tag module, so that the sensor tag module can operate wirelessly continuously without the need for a battery to provide power, relying only on the incident radio frequency signal transmitted by the reader.

[0063] 203. The sensor tag module receives the incident radio frequency signal emitted by the reader module, modulates the echo radio frequency signal based on the incident radio frequency signal and the antenna reflection coefficient, and reflects the echo radio frequency signal back to the reader module.

[0064] In this embodiment, the impedance matching network unit in the sensing tag module is electrically connected to the surface acoustic wave unit and the tag antenna unit in the sensing tag module, respectively, so that the sensing tag module is in an impedance matching state.

[0065] Furthermore, the tag antenna unit receives the incident radio frequency (RF) signal transmitted by the reader antenna unit of the reader module and transmits it to the surface acoustic wave (SAW) unit. Subsequently, the piezoelectric substrate and interdigital transducer of the SAW unit receive the incident RF signal and convert it into an acoustic signal based on the inverse piezoelectric effect. This acoustic signal is then transmitted along the surface of the SAW device to a reflection grating in the SAW unit. Next, the reflection grating reflects the acoustic signal back to the interdigital transducer based on the antenna reflection coefficient. The interdigital transducer and piezoelectric substrate convert the acoustic signal into an echo RF signal based on the direct piezoelectric effect. Finally, the interdigital transducer transmits the echo RF signal to the tag antenna unit, which receives the echo RF signal transmitted by the SAW unit and reflects it back to the reader module.

[0066] 204. The reader module receives the echo radio frequency signal reflected by the sensor tag module, demodulates the echo radio frequency signal, and obtains the partial discharge signal.

[0067] In this embodiment, the reader antenna unit in the reader module is electrically connected to the reader control unit. The reader antenna unit receives the echo radio frequency signal reflected by the sensor tag module and transmits the echo radio frequency signal to the reader control unit so that the reader control unit can demodulate it using demodulation technology to obtain the partial discharge signal.

[0068] The method provided in this application first uses a partial discharge sensor module to acquire ultrasonic signals generated by partial discharge in underground cables, and converts the ultrasonic signals into AC voltage signals. These AC voltage signals are then applied to the variable capacitor in the impedance matching network unit of the sensor tag module, causing impedance mismatch and altering the antenna reflection coefficient. Subsequently, a reader module transmits a continuous sinusoidal incident radio frequency (RF) signal of 433MHz to the sensor tag module. Next, the sensor tag module receives the incident RF signal transmitted by the reader module, modulates the echo RF signal based on the incident RF signal and the antenna reflection coefficient, and reflects the echo RF signal back to the reader module. Finally, the reader module receives the echo RF signal reflected by the sensor tag module, demodulates the echo RF signal, and obtains the partial discharge signal. In this application, the partial discharge sensor detects the ultrasonic waves generated by partial discharge and converts them into AC voltage signals. The AC voltage signal causes impedance mismatch in the sensor tag module, and the reader module receives the mismatched tag echo RF signal and demodulates the partial discharge signal. The sensor tag module is plug-and-play, requires no battery power, and can operate continuously wirelessly solely based on the RF signals transmitted by the reader module. The passive wireless communication of partial discharge signals from underground cables is achieved by using the principle of external sensor perturbation of the sensing tag impedance. It can perform high-speed sampling of partial discharge signals and has the advantages of small size, long life and passive operation.

[0069] In an exemplary embodiment, a computer-readable storage medium is also provided, on which a computer program is stored, which, when executed by a processor, implements the steps of the passive wireless underground cable partial discharge sensing system method based on the passive wireless underground cable partial discharge sensing system.

[0070] Through the above description of the embodiments, those skilled in the art can clearly understand that this application can be implemented in hardware or by using software plus necessary general-purpose hardware platforms. Based on this understanding, the technical solution of this application can be embodied in the form of a software product, which can be stored in a non-volatile storage medium (such as a CD-ROM, USB flash drive, external hard drive, etc.) and includes several instructions to cause a computer device (such as a personal computer, server, or network device, etc.) to execute the methods described in the various embodiments of this application.

[0071] Those skilled in the art will understand that the accompanying drawings are merely schematic diagrams of a preferred embodiment, and the modules or processes shown in the drawings are not necessarily essential for implementing this application.

[0072] Those skilled in the art will understand that the modules in the apparatus of the implementation scenario can be distributed within the apparatus of the implementation scenario as described, or they can be located in one or more apparatuses different from this implementation scenario, with corresponding changes. The modules of the above-described implementation scenario can be combined into one module, or they can be further divided into multiple sub-modules.

[0073] The serial numbers in this application are for descriptive purposes only and do not represent the superiority or inferiority of the implementation scenario.

[0074] The above disclosures are only a few specific implementation scenarios of this application. However, this application is not limited to these. Any variations that can be conceived by those skilled in the art should fall within the protection scope of this application.

Claims

1. A passive wireless partial discharge sensing system for underground cables, characterized in that, The sensor tag module, the partial discharge sensor module and the reader module are connected to each other. The sensor tag module is configured to receive an incident radio frequency signal emitted by the reader module, convert the incident radio frequency signal into an acoustic wave signal, generate a return radio frequency signal, and change an antenna reflection coefficient by impedance mismatch when an alternating voltage applied by the partial discharge sensor module is received, so as to modulate the amplitude, resonance frequency and phase of the return radio frequency signal, and reflect the modulated return radio frequency signal to the reader module. The partial discharge sensor module is a piezoelectric ultrasonic sensor capable of converting an ultrasonic signal into an alternating voltage signal, and is configured to acquire an ultrasonic signal generated by partial discharge of an underground cable. The reader module is configured to emit the incident radio frequency signal of a continuous sine wave at 433 MHz, receive the return radio frequency signal reflected by the sensor tag module, demodulate the return radio frequency signal, and obtain a partial discharge signal.

2. The passive wireless partial discharge sensing system for underground cables according to claim 1, wherein, The sensor tag module comprises a surface acoustic wave unit, an impedance matching network unit and a tag antenna unit. The surface acoustic wave unit is configured to receive the incident radio frequency signal transmitted by the tag antenna unit, convert the incident radio frequency signal into an acoustic wave signal, generate a return radio frequency signal, and transmit the return radio frequency signal to the tag antenna unit. The impedance matching network unit is electrically connected to the surface acoustic wave unit and the tag antenna unit, so that the sensor tag module is in an impedance matching state. The tag antenna unit is configured to receive the incident radio frequency signal emitted by the reader module, transmit the incident radio frequency signal to the surface acoustic wave unit, receive the return radio frequency signal transmitted by the surface acoustic wave unit, and reflect the return radio frequency signal to the reader module.

3. The passive wireless partial discharge sensing system for underground cables of claim 2, wherein, The surface acoustic wave unit comprises a piezoelectric substrate, an interdigital transducer and a reflection grating. The interdigital transducer is arranged on the piezoelectric substrate. The piezoelectric substrate and the interdigital transducer convert the acoustic wave signal into the return radio frequency signal based on the positive piezoelectric effect, and transmit the return radio frequency signal to the tag antenna unit. The reflection grating is configured to receive the acoustic wave signal and reflect the acoustic wave signal back to the interdigital transducer according to the antenna reflection coefficient. The impedance matching network unit comprises a variable capacitor, an inductor, a resistor and a capacitor, and is a T-type or Pi-type network.

4. The passive wireless partial discharge sensing system for underground cables of claim 2, wherein, ​ The variable capacitor is used for receiving the AC voltage applied by the partial discharge sensor module, and changes the capacitance of the variable capacitor according to the voltage across the variable capacitor.

5. The passive wireless partial discharge sensing system for underground cables of claim 1, wherein, The reader module comprises a reader antenna unit and a reader control unit. The reader antenna unit is used for transmitting the incident radio frequency signal of 433 MHz continuous sine and receiving the echo radio frequency signal reflected by the sensing tag module, and transmitting the echo radio frequency signal to the reader control unit. The reader control unit is electrically connected with the reader antenna unit, and is used for generating the incident radio frequency signal and receiving the echo radio frequency signal transmitted by the reader antenna unit, demodulating the echo radio frequency signal to obtain the partial discharge signal.

6. A passive wireless underground cable partial discharge sensing method based on the passive wireless underground cable partial discharge sensing system of any one of claims 1-5, characterized in that, It comprises: The partial discharge sensor module acquires the ultrasonic signal generated by the partial discharge of the underground cable. When the ultrasonic wave causes the piezoelectric film to vibrate, the piezoelectric film will generate an alternating voltage signal output according to the piezoelectric effect, thereby converting the ultrasonic signal into an alternating voltage signal. The alternating voltage signal is applied to the variable capacitor of the impedance matching network unit in the sensing tag module, so that the sensing tag module generates impedance mismatch and changes the antenna reflection coefficient. The partial discharge sensor module is a piezoelectric ultrasonic sensor that can convert ultrasonic signals into alternating voltage signals. The reader module transmits an incident radio frequency signal of 433 MHz continuous sine to the sensing tag module. The sensing tag module receives the incident radio frequency signal transmitted by the reader module, converts the incident radio frequency signal into an acoustic signal, generates an echo radio frequency signal, and when receiving the alternating voltage applied by the partial discharge sensor module, modulates the echo radio frequency signal based on the incident radio frequency signal and the antenna reflection coefficient by using impedance mismatch, and reflects the echo radio frequency signal to the reader module. The reader module receives the echo radio frequency signal reflected by the sensing tag module, demodulates the echo radio frequency signal to obtain the partial discharge signal.

7. The method of claim 6, wherein, The sensing tag module receives the incident radio frequency signal transmitted by the reader module, which comprises: The impedance matching network unit in the sensing tag module is electrically connected with the surface acoustic wave unit in the sensing tag module and the tag antenna unit in the sensing tag module, so that the sensing tag module is in an impedance matching state. The tag antenna unit receives the incident radio frequency signal transmitted by the reader antenna unit of the reader module, and transmits the incident radio frequency signal to the surface acoustic wave unit.

8. The method of claim 6, wherein, The modulation of the echo radio frequency signal based on the incident radio frequency signal and the antenna reflection coefficient, and the reflection of the echo radio frequency signal to the reader module, comprises: The piezoelectric substrate and the interdigital transducer of the surface acoustic wave unit of the sensing tag module receive the incident radio frequency signal, convert the incident radio frequency signal into an acoustic signal based on the inverse piezoelectric effect, and transmit the acoustic signal along the surface of the surface acoustic wave device to the reflection grating in the surface acoustic wave unit. The reflection grating modulates the echo radio frequency signal based on the antenna reflection coefficient; The interdigital transducer transmits the echo radio frequency signal to the tag antenna unit; The tag antenna unit receives the echo radio frequency signal transmitted by the surface acoustic wave unit, and reflects the echo radio frequency signal to the reader module.

9. The method of claim 8, wherein, The reflection grating modulates the echo radio frequency signal based on the antenna reflection coefficient, including: The reflection grating reflects the acoustic wave signal back to the interdigital transducer according to the antenna reflection coefficient; The interdigital transducer and the piezoelectric substrate convert the acoustic wave signal into the echo radio frequency signal based on the positive piezoelectric effect.

10. The method of claim 6, wherein, The reader module receives the echo radio frequency signal reflected by the sensing tag module, demodulates the echo radio frequency signal to obtain a partial discharge signal, including: The reader antenna unit in the reader module receives the echo radio frequency signal reflected by the sensing tag module, and transmits the echo radio frequency signal to the reader control unit in the reader module; The reader control unit receives the echo radio frequency signal transmitted by the reader antenna unit, demodulates the echo radio frequency signal to obtain the partial discharge signal.

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