Cable joint partial discharge monitoring system and method
By wrapping the fiber ring on the cable connector and combining the fiber interferometer and defect diagnosis system based on 3×3 phase demodulation, the problem of difficulty in accurately monitoring the local discharge of the cable connector in the prior art is solved, real-time monitoring and accurate diagnosis of the local discharge of the cable connector is achieved, and the safety and reliability of the power system are improved.
Patent Information
- Application Number
- CN202510187984.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-02-20
- Publication Date
- 2025-06-10
AI Technical Summary
The prior art is difficult to accurately and in real time to monitor the local discharge conditions of cable connectors, which poses threat to the safety and reliability of the power system.
The fiber ring wound around the cold shrink tube of the cable connector, an optical fiber interferometer based on 3×3 phase demodulation, and a defect diagnosis system are used to monitor and diagnose local discharges in real time through fiber sensing technology.
Real-time monitoring and accurate diagnosis of local discharge of cable connectors is realized, and the safety and reliability of the power system is improved.
Smart Images
Figure CN120121944A_ABST
Abstract
Description
Technical Field
[0001] This application belongs to the field of cable joint detection, and particularly relates to a cable joint partial discharge monitoring system and method. Background Art
[0002] In the power system, the cable joint is an important component for connecting cables, and the stability and safety of its operating state are directly related to the reliability of the entire power system. However, due to various factors that may affect the cable joint during installation and operation, such as environmental factors, material aging, manufacturing process defects, etc., local discharge phenomena may occur inside the joint. Local discharge not only causes a decrease in the insulation performance of the cable joint but may also trigger serious accidents such as short circuits and fires, posing a serious threat to the safe operation of the power system.
[0003] Most traditional cable joint partial discharge monitoring methods rely on electrical quantity measurements, such as measuring parameters like leakage current and dielectric loss to indirectly judge the partial discharge situation. However, these methods often have limitations such as low sensitivity and susceptibility to interference, and it is difficult to accurately and real - time reflect the partial discharge condition of the cable joint. Summary of the Invention
[0004] The purpose of this application is to overcome the defects existing in the above - mentioned prior art and provide a cable joint partial discharge monitoring system and method.
[0005] A cable joint partial discharge monitoring system provided by this application includes: an optical fiber loop wound around the cold - shrinkable tube of the cable joint, an optical fiber interferometer based on 3×3 phase demodulation, and a defect diagnosis system;
[0006] The optical fiber interferometer includes a narrow - line - width laser, an isolator, a circulator, a 3×3 coupler, a sensing optical fiber, a reference optical fiber, a Faraday rotator, and a photoelectric converter;
[0007] The optical fiber loop includes the sensing optical fiber wound in multiple turns at a 45° angle on the cold - shrinkable tube;
[0008] The laser emitted by the narrow - line - width laser enters the circulator after passing through the isolator, and then enters the 3×3 coupler. The 3×3 coupler divides the laser into two beams;
[0009] The two beams of laser respectively enter the sensing optical fiber and the reference optical fiber, are reflected by the Faraday rotators at the ends of the sensing optical fiber and the reference optical fiber, return along the original laser path, and interfere after entering the 3×3 coupler;
[0010] The interfering laser is divided into three beams of laser with a 120° phase difference and output to the photoelectric converter to be converted into a voltage signal;
[0011] The voltage signal is input into the defect diagnosis system for diagnosing the partial discharge defect of the cable joint.
[0012] Optionally, the optical-electric converter includes PD1, PD2, and PD3;
[0013] PD2 and PD3 receive two of the three laser beams with a phase difference of 120° from each other, and PD1 receives the other one of the three laser beams with a phase difference of 120° from each other that returns in the direction of the narrow linewidth laser.
[0014] Optionally, a tight sheath made of polycarbonate is provided outside the sensing optical fiber.
[0015] Optionally, the coupling agent between the sensing optical fiber and the cold-shrinkable tube is a polyurethane coupling agent.
[0016] Optionally, a digital oscilloscope and a computer are further included;
[0017] After the optical-electric converter converts the optical signal into a voltage signal, it is collected by the digital oscilloscope and recorded and analyzed by the computer to reflect the ultrasonic signal.
[0018] Optionally, the sensing optical fiber is wound around the cold-shrinkable tube for a total of ten turns at an angle of 45° with the vertical direction.
[0019] Optionally, the defect diagnosis system includes a data acquisition module, an equivalent bandwidth extraction module, a signal length extraction module, a discharge type training module, and a discharge type recognition module;
[0020] The equivalent bandwidth extraction module extracts the spectral range from the peak frequency point to its 5 dB attenuation from the ultrasonic spectrum as the equivalent bandwidth of the ultrasonic data;
[0021] The signal length extraction module extracts the time length from the start to 15% of the signal peak of the original ultrasonic signal data as the signal length of the ultrasonic signal waveform data;
[0022] The discharge type training module is based on a convolutional neural network and receives the equivalent bandwidth and signal length of the ultrasonic signal obtained by feature extraction for cumulative training;
[0023] The discharge type recognition module performs discharge type classification and recognition.
[0024] This application also provides a method for monitoring partial discharge of a cable joint, including: monitoring the partial discharge of the cable joint by using the above-mentioned partial discharge monitoring system for a cable joint;
[0025] The described partial discharge monitoring system for a cable joint includes: an optical fiber loop wound around the cold-shrinkable tube of the cable joint, an optical fiber interferometer based on 3×3 phase demodulation, and a defect diagnosis system; the optical fiber interferometer includes a narrow-linewidth laser, an isolator, a circulator, a 3×3 coupler, a sensing optical fiber, a reference optical fiber, a Faraday rotator mirror, and a photoelectric converter; the optical fiber loop includes the sensing optical fiber wound in multiple turns at a 45° angle on the cold-shrinkable tube; the laser emitted by the narrow-linewidth laser enters the circulator after passing through the isolator, and then enters the 3×3 coupler, and the 3×3 coupler divides the laser into two beams; the two beams of laser respectively enter the sensing optical fiber and the reference optical fiber, and after being reflected by the Faraday rotator mirrors at the ends of the sensing optical fiber and the reference optical fiber, return along the original laser path, enter the 3×3 coupler and interfere; the interfering laser is divided into three beams of laser with a 120° phase difference and output to the photoelectric converter to be converted into a voltage signal; the voltage signal is input to the defect diagnosis system for defect diagnosis of the partial discharge of the cable joint.
[0026] Optionally, a tight sheath is provided outside the sensing optical fiber.
[0027] Optionally, the defect diagnosis system includes a data acquisition module, an equivalent bandwidth extraction module, a signal length extraction module, a discharge type training module, and a discharge type identification module;
[0028] The equivalent bandwidth extraction module extracts the spectral range from the peak frequency point to its 5 dB attenuation in the ultrasonic spectrum as the equivalent bandwidth of the ultrasonic data.
[0029] The signal length extraction module extracts the time length from the start to 15% of the signal peak of the original ultrasonic signal data as the signal length of the ultrasonic signal waveform data.
[0030] The discharge type training module is based on a convolutional neural network and receives the equivalent bandwidth and signal length of the ultrasonic signal obtained by feature extraction for cumulative training.
[0031] The discharge type identification module performs discharge type classification and identification.
[0032] The beneficial effects of this application are:
[0033] A partial discharge monitoring system for cable joints provided by the present application includes: an optical fiber loop wound around the cold shrinkable tube of the cable joint, an optical fiber interferometer based on 3×3 phase demodulation, and a defect diagnosis system; the optical fiber interferometer includes a narrow linewidth laser, an isolator, a circulator, a 3×3 coupler, a sensing optical fiber, a reference optical fiber, a Faraday mirror, and a photoelectric converter; the optical fiber loop includes the sensing optical fiber wound around the cold shrinkable tube at a 45° angle for multiple turns; the laser emitted by the narrow linewidth laser enters the circulator after passing through the isolator, and then enters the 3×3 coupler, and the 3×3 coupler divides the laser into two beams; the two beams of laser respectively enter the sensing optical fiber and the reference optical fiber, and are reflected by the Faraday mirrors at the ends of the sensing optical fiber and the reference optical fiber and return along the original laser path, and interfere after entering the 3×3 coupler; the interfering laser is divided into three beams of laser with a phase difference of 120° and output to the photoelectric converter to be converted into a voltage signal; the voltage signal is input to the defect diagnosis system for diagnosing the partial discharge defect of the cable joint. The present application realizes the real-time monitoring and accurate diagnosis of the partial discharge of the cable joint through the advantages of optical fiber sensing technology, and improves the safety and reliability of the power system. Description of the Drawings
[0034] Figure 1 is a schematic diagram of the partial discharge monitoring system for cable joints in the present application;
[0035] Figure 2 is a schematic diagram of the structure of the built-in optical fiber loop in the present application. Detailed Description of the Embodiments
[0036] The exemplary embodiments of the present disclosure will be described in more detail below with reference to the drawings. Although the exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided so that the present disclosure can be more thoroughly understood and the scope of the present disclosure can be fully conveyed to those skilled in the art.
[0037] A partial discharge monitoring system for a cable joint 202 provided by the present application includes: an optical fiber loop wound around the cold shrinkable tube of the cable joint 202, an optical fiber interferometer based on 3×3 phase demodulation, and a defect diagnosis system.
[0038] The optical fiber interferometer based on 3×3 phase demodulation proposed by the present application is used to realize the high-sensitivity detection of the weak ultrasonic signals generated by the partial discharge of the cable joint 202.
[0039] Such as Figure 1As shown in the figure, the core components of the fiber optic interferometer based on 3×3 phase demodulation include a narrow linewidth laser 101, a laser isolator 102, a circulator 103, a 3×3 coupler 104, a sensing fiber 108, a reference fiber 109, a Faraday rotation mirror, and a photoelectric converter (PD). The entire system measures and analyzes ultrasonic signals by controlling the laser transmission path and phase change.
[0040] The narrow linewidth laser 101 serves as a laser source, emitting laser light with good monochromaticity and strong coherence. This laser has a relatively narrow linewidth, which helps improve the accuracy of interference measurement.
[0041] The laser first passes through a laser isolator 102. The function of the laser isolator 102 is to prevent the reflected laser from damaging the laser and ensure the stable operation of the laser.
[0042] Further, the laser passing through the laser isolator 102 enters the circulator 103. The circulator 103 is a special optical device that allows the laser to enter from one port and output from another port, while preventing the laser from flowing back from the output port to the input port. In this way, the laser is guided to the 3×3 coupler 104.
[0043] The 3×3 coupler 104 is a key component in the interferometer. It divides the input laser into two laser beams with equal intensity, which enter the sensing fiber 108 and the reference fiber 109 respectively. When these two laser beams are transmitted in the fiber, they will be affected by different disturbances (such as the phase change caused by ultrasonic signals), thus forming a phase difference.
[0044] Among them, the fiber loop includes the sensing fiber 108 wound around the cold shrinkable tube at a 45° angle for multiple turns.
[0045] Faraday rotation mirrors are connected to the ends of both the sensing fiber 108 and the reference fiber 109. The Faraday rotation mirror can not only reflect the laser signal back along the original path but also ensure that the reflected laser maintains its original polarization state unchanged, thus avoiding the influence of polarization state change on interference measurement.
[0046] When the two reflected laser beams enter the 3×3 coupler 104 again, an interference phenomenon will occur. Since the two laser beams are affected by different disturbances during transmission, their phases will be different. This phase difference will cause the intensity of the interfering laser to change.
[0047] The interfered laser is divided into three laser beams with a phase difference of 120° by the 3×3 coupler 104 and output. This phase distribution makes the interference signal have unique waveform characteristics, which is convenient for subsequent signal processing and analysis.
[0048] Two of the interfering laser beams directly enter the photoelectric converters PD2106 and PD3107, converting the laser signals into voltage signals. The other laser beam returns towards the laser. After passing through the circulator 103 midway, it is guided to the photoelectric converter PD1105. In this way, the three photoelectric converters respectively record the interference signals of three different phases.
[0049] These voltage signals are collected by a digital oscilloscope and then recorded and analyzed by a computer. Through algorithm processing, the phase information of the ultrasonic signal can be extracted, thereby realizing the monitoring and diagnosis of partial discharge in the cable joint 202.
[0050] In order to significantly improve the effect and accuracy of the sensing system in monitoring partial discharge in the cable joint 202, this application designs an innovative sensing structure, namely the fiber optic loop. The core of the fiber optic loop is to tightly wind the sensing optical fiber 108 around the cold shrink tube of the cable joint 202 in a specific manner. The following is a detailed description of this sensing structure and its key parameters:
[0051] In view of the possible adverse effects that the beloved sensing optical fiber 108 may have during the winding process due to excessive bending, this application specifically selects the B115-60-U10 bend-insensitive single-mode optical fiber. This optical fiber has excellent anti-bending performance and can adapt to the complex shape of the cold shrink tube surface while ensuring the signal transmission quality.
[0052] To prevent the sensing optical fiber 108 from being damaged during the subsequent fabrication, installation, and operation of the cable joint 202, this application sleevs the sensing optical fiber 108 with a tight sheath. This design not only improves the durability of the optical fiber but also ensures its stability during long-term monitoring.
[0053] When selecting the sheath material, this application fully considers the action mechanism of ultrasonic signals on the optical fiber. To ensure that the sensing optical fiber 108 can generate sufficient deformation under the action of ultrasonic signals and then be converted into measurable signals, this application selects polycarbonate with a relatively large elastic modulus as the sheath material. This material not only has excellent elastic properties but also can effectively transmit ultrasonic signals.
[0054] As Figure 2 shown, in order to enhance the strain effect of the sensing optical fiber 108 under the action of ultrasonic signals, this application adopts a specific winding method. The optical fiber is tightly wound around the cold shrink tube at an angle of 45° with the vertical direction. This winding method not only optimizes the strain distribution of the optical fiber but also improves its sensitivity to ultrasonic signals.
[0055] In view of the fact that the difference in acoustic impedance between the sensing optical fiber 108 and the cold-shrinkable tube may affect the propagation effect of the ultrasonic signal, this application selects a polyurethane couplant to weaken this effect. The polyurethane couplant has excellent acoustic impedance matching performance, which can ensure the efficient transmission of ultrasonic signals between the optical fiber and the cold-shrinkable tube.
[0056] To further enhance the detection performance of the sensor, this application winds the sensing optical fiber 108 around the cold-shrinkable tube for a total of ten turns. This design not only improves the signal strength but also increases the monitoring redundancy, thereby improving the reliability of the system.
[0057] To facilitate the access of the sensing optical fiber 108 to the monitoring system, this application selects an LC-type fiber optic connector. This connector not only has excellent connection performance but also ensures the stable transmission of optical fiber signals, providing strong support for subsequent monitoring and analysis.
[0058] The voltage signal is input into the defect diagnosis system for diagnosing partial discharge defects of the cable joint 202.
[0059] The defect type diagnosis system is a comprehensive system integrating multiple links such as data acquisition, signal processing, feature extraction, machine learning, and classification, aiming to efficiently and accurately identify different types of partial discharge defects in the cable joint 202.
[0060] This system mainly includes three core stages: data acquisition and storage, signal preprocessing and feature extraction, and discharge type recognition based on convolutional neural network, mainly including:
[0061] Data acquisition module: Capture the ultrasonic signals generated by partial discharge of the cable joint 202 through specially designed sensors. These sensors are usually arranged at key positions of the cable joint 202 to ensure that the weakest discharge signals can be captured.
[0062] The collected raw ultrasonic data will be transmitted to the prototype of the system in real time and stored.
[0063] Equivalent bandwidth extraction module: To extract key information from ultrasonic signals, this application designs an equivalent bandwidth extraction module. This module first analyzes the spectrum of the ultrasonic signal to find the peak frequency point, and then determines the range where the spectrum decays by 5 dB starting from the peak frequency point. This range is defined as the equivalent bandwidth of the ultrasonic data, which reflects the main frequency components of the signal and their distribution.
[0064] Signal length extraction module: In addition to the equivalent bandwidth, the signal length is also an important parameter characterizing the ultrasonic signal characteristics. The signal length extraction module of this application measures the time length of the original ultrasonic signal data from the starting point to 15% of the signal peak, and this length is used as the signal length of the ultrasonic signal waveform data for subsequent feature analysis.
[0065] Discharge type training module: After preprocessing and feature extraction, the equivalent bandwidth and signal length of the obtained ultrasonic signal are used as feature inputs and fed into the discharge type training module based on a convolutional neural network.
[0066] The discharge type training module uses these features for deep learning training. To ensure the stability and accuracy of the model, the system sets a sample accumulation mechanism. When the discharge type training module accumulates 1000 samples, further sample collection stops.
[0067] Discharge type recognition module: After completion of training, the discharge type recognition module uses the trained model to classify and recognize the discharge type of a new ultrasonic signal. This module can automatically analyze the features of the input signal and classify it into one of the predefined discharge types.
[0068] Recognition result output: Finally, the system gives the current recognition result, including information such as the discharge type and its corresponding confidence level. This information is of great significance for the fault diagnosis, maintenance decision-making, and safe operation of the cable joint 202.
[0069] This application also provides a method for monitoring partial discharge of a cable joint 202, including: using the above-mentioned partial discharge monitoring system for a cable joint 202 to monitor the partial discharge of the cable joint 202;
[0070] The local discharge monitoring system for a cable joint 202 includes: an optical fiber loop wound around the cold shrinkable tube of the cable joint 202, an optical fiber interferometer based on 3×3 phase demodulation, and a defect diagnosis system; the optical fiber interferometer includes a narrow linewidth laser 101, a laser isolator 102, a circulator 103, a 3×3 coupler 104, a sensing optical fiber 108, a reference optical fiber 109, a Faraday rotator mirror 110, and a photoelectric converter; the optical fiber loop includes the sensing optical fiber 108 wound around the cold shrinkable tube at a 45° angle for multiple turns; the laser emitted by the narrow linewidth laser 101 enters the circulator 103 after passing through the laser isolator 102, and then enters the 3×3 coupler 104, and the 3×3 coupler 104 divides the laser into two beams; the two beams of laser respectively enter the sensing optical fiber 108 and the reference optical fiber 109, and after being reflected by the Faraday rotator mirror 110 at the ends of the sensing optical fiber 108 and the reference optical fiber 109, they return along the original laser path, enter the 3×3 coupler 104 and interfere; the interfering laser is divided into three beams of laser with a 120° phase difference and output to the photoelectric converter to be converted into a voltage signal; the voltage signal is input to the defect diagnosis system for local discharge defect diagnosis of the cable joint 202.
[0071] Further, a tight sheath is provided outside the sensing optical fiber 108.
[0072] Further, the defect diagnosis system includes a data acquisition module, an equivalent bandwidth extraction module, a signal length extraction module, a discharge type training module, and a discharge type recognition module;
[0073] The equivalent bandwidth extraction module extracts the spectral range from the peak frequency point to its 5 dB attenuation in the ultrasonic spectrum as the equivalent bandwidth of the ultrasonic data.
[0074] The signal length extraction module extracts the time length from the start to 15% of the signal peak of the original ultrasonic signal data as the signal length of the ultrasonic signal waveform data.
[0075] The discharge type training module is based on a convolutional neural network and receives the equivalent bandwidth and signal length of the ultrasonic signal obtained by feature extraction for cumulative training.
[0076] The discharge type recognition module performs discharge type classification and recognition.
Claims
1. A cable joint partial discharge monitoring system, characterized in that: include: An optical fiber ring arranged on the cable joint cold shrink tube, an optical fiber interferometer based on 3×3 phase demodulation, and a defect diagnosis system; The fiber interferometer comprises a narrow line width laser, an isolator, a circulator, a 3×3 coupler, a sensing fiber, a reference fiber, a Faraday rotator and a photoelectric converter; The optical fiber ring includes the sensing optical fiber wound multiple times at an angle of 45° on the cold shrink tube; The laser light emitted by the narrow line width laser enters the circulator after passing through the isolator, and then enters the 3×3 coupler. The 3×3 coupler divides the laser light emitted by the narrow line width laser into two laser beams. The two laser beams emitted by the narrow linewidth laser enter the sensing fiber and the reference fiber respectively, are reflected by the Faraday rotator mirrors at the ends of the sensing fiber and the reference fiber, and then return along the original laser path, and interfere after entering the 3×3 coupler; The two interfering laser beams are divided into three laser beams with a phase difference of 120° and output to the photoelectric converter to convert into voltage signals; The voltage signal is input into the defect diagnosis system to perform partial discharge defect diagnosis on the cable joint.
2. The cable joint partial discharge monitoring system according to claim 1, characterized in that: The photoelectric converter includes PD1, PD2, and PD3; The PD2 and PD3 receive two laser beams among the three laser beams with a phase difference of 120°, and the PD1 receives another laser beam among the three laser beams with a phase difference of 120° that are returned toward the narrow linewidth laser.
3. The cable joint partial discharge monitoring system according to claim 1, characterized in that: The sensing optical fiber is provided with a tight sheath made of polycarbonate.
4. The cable joint partial discharge monitoring system according to claim 1, characterized in that: The coupling agent between the sensing optical fiber and the cold shrink tube is a polyurethane coupling agent.
5. The cable joint partial discharge monitoring system according to claim 1, characterized in that: Also included are a digital oscilloscope and computer; The photoelectric converter converts the optical signal into a voltage signal, which is then collected by a digital oscilloscope and recorded and analyzed by a computer to reflect the ultrasonic signal.
6. The cable joint partial discharge monitoring system according to claim 1, characterized in that: The sensing optical fiber is wound around the cold shrink tube at an angle of 45° to the vertical direction for a total of ten turns.
7. The cable joint partial discharge monitoring system according to claim 1, characterized in that: The defect diagnosis system includes a data acquisition module, an equivalent bandwidth extraction module, a signal length extraction module, a discharge type training module and a discharge type identification module; The equivalent bandwidth extraction module extracts the spectrum range from the peak frequency point to its attenuation of 5 dB from the ultrasonic spectrum as the equivalent bandwidth of the ultrasonic data; The signal length extraction module extracts the time length from the start of the ultrasonic signal raw data to 15% of the signal peak value as the signal length of the ultrasonic signal waveform data; The discharge type training module is based on a convolutional neural network and receives the ultrasonic signal equivalent bandwidth and the signal length for accumulation training; The discharge type identification module performs discharge type classification and identification.
8. A method for monitoring partial discharge of a cable joint, characterized in that: include: Using the cable joint partial discharge monitoring system according to any one of claims 1 to 7 to perform partial discharge monitoring on the cable joint; The cable joint partial discharge monitoring system comprises: an optical fiber ring wound on a cable joint cold shrink tube, an optical fiber interferometer based on 3×3 phase demodulation, and a defect diagnosis system; The fiber interferometer includes a narrow linewidth laser, an isolator, a circulator, a 3×3 coupler, a sensing fiber, a reference fiber, a Faraday rotator and a photoelectric converter; the fiber ring includes the sensing fiber wound multiple times at an angle of 45° on the shrink tube; the laser light emitted by the narrow linewidth laser enters the circulator after passing through the isolator, and then enters the 3×3 coupler, and the 3×3 coupler divides the laser light into two beams; the two beams of laser light enter the sensing fiber and the reference fiber respectively, and return along the original laser path after being reflected by the Faraday rotator at the end of the sensing fiber and the reference fiber, and interfere after entering the 3×3 coupler; the interfered laser light is divided into three beams of laser light with a phase difference of 120°, which are output to the photoelectric converter and converted into voltage signals; the voltage signal is input to the defect diagnosis system for partial discharge defect diagnosis of cable joints.
9. The cable joint partial discharge monitoring method according to claim 8, characterized in that: The sensing optical fiber is provided with a tight sheath outside.
10. The cable joint partial discharge monitoring system according to claim 8, characterized in that: The defect diagnosis system includes a data acquisition module, an equivalent bandwidth extraction module, a signal length extraction module, a discharge type training module and a discharge type identification module; The equivalent bandwidth extraction module extracts the spectrum range from the peak frequency point to its attenuation of 5 dB from the ultrasonic spectrum as the equivalent bandwidth of the ultrasonic data; The signal length extraction module extracts the time length from the start of the ultrasonic signal raw data to 15% of the signal peak value as the signal length of the ultrasonic signal waveform data; The discharge type training module is based on a convolutional neural network, and receives the ultrasonic signal equivalent bandwidth and signal length obtained by feature extraction for accumulation training; The discharge type identification module performs discharge type classification and identification.