A generator stator winding partial discharge monitoring system and method based on optical fiber sensing

Abstract

This invention discloses a generator stator winding partial discharge monitoring system and method based on fiber optic sensing, relating to the field of partial discharge monitoring technology for large generators. The system includes fiber optic sensors, a fiber optic sensing module, a data acquisition module, and a host computer. The fiber optic sensors are arranged at the stator bar slots, with one sensor at each slot. The fiber optic sensors are connected to the data acquisition module via the fiber optic sensing module, which in turn is connected to the host computer via a coaxial cable. The fiber optic sensing module employs a phase-sensitive optical time-domain reflectometer (OTDR) to collect and analyze signals in the fiber optic cable for acoustic signal measurement. The host computer records partial discharge measurement data, performs noise reduction, plots time-frequency diagrams, and extracts time-domain and frequency-domain characteristic values ​​of the partial discharge to assess the discharge frequency and intensity. This monitoring system and method effectively improve equipment operational safety and extend the generator's service life.

Description

Technical Field

[0001] This invention relates to the field of partial discharge monitoring technology for large generators, and specifically to a generator stator winding partial discharge monitoring system and method based on fiber optic sensing. Background Technology

[0002] With the rapid development of my country's social economy, electricity demand has continued to grow, and electricity load has been rising year by year. The safe and stable operation of the power system has become a core support for ensuring the normal operation of social production and life. As the core power generation equipment of the power system, the reliability of generator operation directly determines the stability of power supply, and the stable operation of generator stator windings is a key prerequisite for ensuring the safe operation of generators and even the entire power system.

[0003] Partial discharge is a common phenomenon in generator stator windings during actual operation. If this phenomenon persists or continues to develop, it can cause a series of serious hazards, directly threatening the safe operation of the generator and shortening its service life. Firstly, the high-energy electrons, ions, and ozone generated by partial discharge continuously corrode the insulation material of the stator windings, leading to a gradual decrease in insulation strength and ultimately causing serious faults such as inter-turn short circuits, phase-to-phase short circuits, or grounding breakdowns, resulting in sudden generator shutdowns. Secondly, partial discharge can also directly cause short circuits in the stator windings. Furthermore, after insulation deterioration, the high-voltage windings may discharge to the core or casing, triggering protection devices to trip, further expanding the scope of the fault and causing significant economic losses and safety hazards to the power system. Therefore, effectively monitoring the partial discharge of generator stator windings and promptly detecting potential internal defects is a crucial measure to prevent faults and ensure the stable operation of the power system.

[0004] Currently, various technical approaches have been developed for detecting partial discharge in generator stator windings, mainly categorized into electrical and non-electrical methods. Electrical methods include pulse current methods and ultra-high frequency methods. These electrical detection techniques possess high detection sensitivity and have certain advantages in capturing partial discharge signals, but they generally suffer from poor electromagnetic compatibility, making them susceptible to interference in the complex electromagnetic environment of generator operation sites, affecting the accuracy of the detection results. Non-electrical methods achieve fault diagnosis by capturing physical or chemical signals such as acoustic emission, optical radiation, thermal effects, and chemical products generated during partial discharge. These methods include chemical detection, optical detection, and acoustic detection, among which acoustic detection has been widely used in equipment inspection due to its ease of operation.

[0005] Traditional acoustic testing methods mainly use piezoelectric ceramic transducers (PZTs) for auscultatory testing. However, this testing method has significant limitations in practical applications: on the one hand, there is strong electromagnetic interference at the generator operating site, and piezoelectric ceramic transducers are easily affected by electromagnetic signals, resulting in distorted detection signals; on the other hand, its signal transmission distance is limited, making it difficult to meet the long-distance monitoring needs of large generator equipment and complex power stations.

[0006] In summary, existing partial discharge detection methods all have varying degrees of shortcomings, making it difficult to simultaneously meet the requirements of generator operating environments for electromagnetic interference resistance, signal transmission distance, ease of operation, and measurement accuracy. Therefore, developing an online monitoring method for partial discharge in generator stator windings that possesses strong electromagnetic interference resistance, long transmission distance, ease of operation, and accurate measurement has become an urgent technical problem to be solved in the field of power equipment monitoring, and is of great significance for improving the reliability of power system operation. Summary of the Invention

[0007] The purpose of this invention is to propose a generator stator winding partial discharge monitoring system and method based on fiber optic sensing, which realizes real-time and accurate online monitoring of generator stator winding partial discharge, effectively improving equipment operation safety and extending generator service life.

[0008] This invention is achieved through the following technical solution: A generator stator winding partial discharge monitoring system based on fiber optic sensing includes a fiber optic sensor, a fiber optic sensing module, a data acquisition module, and a host computer. The fiber optic sensors are arranged at the slot outlets of the generator stator bars. Each stator bar slot outlet is equipped with a fiber optic sensor. The fiber optic sensors are connected to the fiber optic sensing module, the fiber optic sensing module is connected to the data acquisition module, and the data acquisition module is connected to the host computer via a coaxial cable. The fiber optic sensing module employs a phase-sensitive optical time-domain reflectometer to acquire and analyze signals in the optical fiber to achieve acoustic signal measurement. The host computer is used to record partial discharge measurement data, perform noise reduction processing, draw time-frequency diagrams, and extract time-domain and frequency-domain feature values ​​of partial discharge to evaluate the frequency and intensity of discharge occurrence.

[0009] Furthermore, the fiber optic sensor is a spindle-type cylindrical fiber optic sensor. The spindle material is selected from epoxy board or laminated glass cloth board that matches the acoustic impedance of the main insulation of the stator winding. A sensing fiber of a preset length is wound on the spindle, and the frequency response range of the fiber optic sensor is 15kHz~40kHz.

[0010] Furthermore, the fiber optic sensors at the slots of each stator bar are connected in series to form a distributed fiber optic sensing link with multiple sensing points.

[0011] Furthermore, the fiber optic sensor and the stator bar are filled with epoxy resin and fixed by epoxy-impregnated binding rope.

[0012] Furthermore, the fiber optic sensing module includes a laser, an acousto-optic modulator, a fiber optic amplifier, a circulator, a photodetector, and an arbitrary waveform generator; The continuous light output from the laser is split into a probe optical path and a reference optical path by a 1×2 optical coupler. The acousto-optic modulator modulates the light in the probe optical path into pulsed light under the control of an arbitrary waveform generator. The pulsed light is amplified by an optical fiber amplifier to form a probe pulse. The probe pulse is input into the optical fiber under test through a circulator. Its backscattered signal is returned by the circulator and converted from optical signal to electrical signal by a photodetector. The phase of the optical pulse is then obtained by demodulation through a 2×2 coupler.

[0013] Furthermore, the output of the fiber optic amplifier is also connected to a filter to remove amplified spontaneous emission noise.

[0014] Furthermore, the radio frequency signal of the acousto-optic modulator, the probe pulse repetition frequency, and the trigger period of the data acquisition module are controlled by the data processing system of the host computer to achieve time-synchronized operation.

[0015] Furthermore, the time-domain feature values ​​include peak-to-peak values. PP , Rectified average value ARV Root mean square RMS Waveform factor FF Pulse factor IF Margin factor CF ; The frequency domain characteristic values ​​include the centroid frequency. FC Frequency variance FV Power spectral entropy PSE .

[0016] A method for monitoring partial discharge in generator stator windings based on fiber optic sensing includes the following steps: S1. The acoustic signal generated by the partial discharge of the generator stator winding disturbs the fiber optic sensor arranged at the slot of the stator bar. The scattered signal under the disturbance is transmitted along the fiber optic to the fiber optic sensing module for phase demodulation. S2. The data acquisition module digitizes the demodulated signal phase information and sends it to the host computer. S3. The host computer records partial discharge measurement data at different times; S4. The host computer performs noise reduction processing on the measurement data in step S3 and plots a partial discharge time-frequency diagram. S5. The host computer extracts the time-domain and frequency-domain feature values ​​of partial discharge based on the time-frequency diagram in step S4, and evaluates the occurrence frequency and intensity information of partial discharge based on the feature values.

[0017] Furthermore, in step S1, the optical fiber sensor is a mandrel-type cylindrical structure. The mandrel material is matched with the acoustic impedance of the main insulation of the stator winding, and each optical fiber sensor is connected in series to form a distributed sensing link. The acoustic signal is transmitted to the sensing optical fiber through the mandrel and causes the optical fiber to strain, thereby realizing the phase change of the scattered signal.

[0018] Furthermore, in step S1, the fiber optic sensing module outputs continuous light through a laser, which is then split by an optical coupler, pulse-modulated by an acousto-optic modulator, and amplified by an optical fiber amplifier to form a detection pulse. After the detection pulse is input into the optical fiber through a circulator, its backscattered signal is converted by a photodetector and demodulated by a coupler to complete phase demodulation.

[0019] Furthermore, in step S5, the time-domain feature value is calculated using the maximum value, minimum value, and number of sampling points of the sample sequence, and the frequency-domain feature value is extracted by performing a fast Fourier transform and power spectral density conversion on the partial discharge signal.

[0020] Compared with the prior art, the present invention has the following advantages and beneficial effects: This invention proposes a generator stator winding partial discharge monitoring system based on fiber optic sensing. Addressing the specific monitoring needs of the stator bar slot outlets (areas of concentrated electrical and mechanical stress), the system employs point-by-point deployment of fiber optic sensors combined with a φ-OTDR sensing module, and utilizes multi-dimensional feature values ​​to assess the frequency and intensity of discharge. This overcomes the limitations of existing single-point monitoring technologies, which lack comprehensive coverage, and solves the problem of traditional monitoring methods that can only qualitatively determine the frequency and intensity of discharge. It achieves precise and comprehensive monitoring of stator winding partial discharge. Furthermore, fiber optic sensing is resistant to electromagnetic interference and adaptable to the complex electromagnetic environment of generators, filling a technological gap in generator stator slot outlet monitoring.

[0021] II. In this invention, a mandrel-type cylindrical fiber optic sensor is used, with a frequency response range of 15kHz~40kHz. The mandrel material is matched with the acoustic impedance of the main insulation of the stator winding, significantly reducing reflection and attenuation during acoustic signal transmission; it precisely matches the main frequency band of partial discharge ultrasonic signals. Compared with existing sensors without a mandrel design or without frequency optimization, the sensing sensitivity is significantly improved, capable of capturing weak discharge signals ≤200pC, solving the problems of low acoustic coupling efficiency and response mismatch between the sensor and the generator stator insulation structure.

[0022] Third, in this invention, the fiber optic sensors at each slot are connected in series to form a distributed link, enabling multi-point synchronous monitoring through a single fiber. This avoids the drawbacks of complex wiring and high costs associated with existing distributed arrays, while also overcoming the limitation of limited monitoring range of single-point sensors. The series design eliminates the need for additional transmission links, simplifying the system architecture. Simultaneously, it ensures independent signal transmission from each measuring point without interference, reducing equipment investment costs, providing broad coverage, and improving system reliability.

[0023] IV. In this invention, a fixing method of "epoxy resin filling + adhesive-impregnated binding rope" is adopted. The epoxy resin filling eliminates the air gap between the sensor and the stator conductor, improving the acoustic signal transmission efficiency; the adhesive-impregnated binding rope is suitable for the vibration environment during generator operation, ensuring the long-term stability of the installation structure. This solves the problems of easy aging of coupling agent filling and easy loosening of simple binding in the prior art. This design not only ensures the stability of signal transmission but also extends the service life of the sensor, resolving the contradiction between sensor installation reliability and acoustic coupling efficiency under generator vibration conditions.

[0024] V. This invention proposes a complete φ-OTDR sensing link, which forms a closed-loop signal processing flow through 1×2 coupler splitting, acousto-optic modulator pulsed processing, and 2×2 coupler phase demodulation. Compared with existing Sagnac interferometers or simple intensity demodulation schemes, this architecture can accurately capture the phase changes of light pulses, effectively restore weak ultrasonic signals, improve the demodulation accuracy of partial discharge signals, and provide high-quality data support for subsequent feature value extraction.

[0025] VI. In this invention, a filter is added after the fiber optic amplifier to remove spontaneous emission noise generated during amplification, thus resolving the inherent contradiction of "signal amplification and noise superposition" in existing fiber optic amplification technology. After noise suppression, the signal-to-noise ratio is significantly improved, avoiding noise interference with phase demodulation and feature extraction, ensuring accurate identification of effective signals even in low-discharge scenarios, and expanding the system's weak signal detection capability.

[0026] VII. In this invention, the timing synchronization of the acousto-optic modulator radio frequency signal, the probe pulse repetition frequency, and the data acquisition module trigger cycle is achieved through a host computer data processing system, avoiding signal distortion and acquisition misalignment problems caused by asynchronous timing of various components in the prior art. Synchronous control ensures the coordination of probe pulse generation, signal transmission, and data acquisition, significantly improving the time accuracy of phase demodulation and digital processing, and guaranteeing the accuracy and consistency of monitoring data.

[0027] 8. In this invention, time-domain feature values ​​are integrated ( PP , ARV etc.) and frequency domain eigenvalues ​​( FC , FV , PSE This system, along with other technologies, forms a multi-dimensional evaluation system. Time-domain features comprehensively reflect signal amplitude and energy characteristics, while frequency-domain features accurately characterize energy distribution and dispersion. In particular, power spectral entropy can directly correlate with the severity of the discharge. Compared to existing technologies that rely on single-feature value evaluation or simple comparative evaluation, this combination achieves quantitative and refined judgment of the discharge state, solving the technical bottleneck of accurately locating the intensity level and development trend of partial discharge.

[0028] IX. This invention proposes a method for monitoring partial discharge in generator stator windings based on fiber optic sensing. Each step of the complete monitoring process is optimized for the monitoring scenario of the generator stator slot outlet. Noise reduction in step S4 improves data quality, and multi-feature extraction in step S5 enables quantitative evaluation, overcoming the limitations of existing methods such as fragmented processes and poor adaptability. The entire process, from signal acquisition to result output, forms a closed loop, ensuring both monitoring efficiency and evaluation accuracy, creatively achieving precise full-process monitoring of partial discharge in generator stator windings.

[0029] 10. In this invention, "mandrel acoustic impedance matching" and "series distributed link" are combined at the methodological level. The acoustic signal is efficiently transmitted to the sensing optical fiber through the matching mandrel and induces strain, ensuring significant phase change; the series link enables synchronous acquisition of signals from multiple points. This design not only solves the problems of low acoustic coupling efficiency and difficulty in capturing weak signals in existing sensors, but also overcomes the limitations of complex wiring for multi-point monitoring, achieving a synergy of "high sensitivity and wide coverage," and is suitable for monitoring the multi-strand bar outlets of generator stators.

[0030] XI. In this invention, the phase demodulation steps of the fiber optic sensing module, from continuous light output and split modulation to amplification detection and scattering signal demodulation, each step forms a standardized operating logic, ensuring the consistency and accuracy of phase demodulation. It can effectively capture minute phase changes caused by partial discharge, improve the reliability of signal demodulation, and provide a high-quality foundation for subsequent data processing.

[0031] 12. In this invention, the specific calculation logic for time-domain and frequency-domain feature values ​​is clearly defined. Time-domain feature values ​​are directly calculated based on extreme values ​​and the number of points in the sample sequence, while frequency-domain feature values ​​are extracted through Fourier transform and power spectral density conversion, ensuring the standardization and repeatability of feature value extraction. This method enables discharge assessment to have a unified standard, improves the comparability of monitoring results between different operating conditions and different equipment, and solves the technical problems of strong subjectivity and lack of quantitative basis in partial discharge assessment. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the stator bar partial discharge fiber optic monitoring test platform of the generator stator winding partial discharge monitoring system based on fiber optic sensing of the present invention.

[0033] Figure 2 This is a schematic diagram of the fiber optic sensing module of the monitoring system of the present invention.

[0034] Figure 3 This is a schematic diagram of the fiber optic sensor and its arrangement in the monitoring system of the present invention.

[0035] Figure 4 This is a schematic diagram of the on-site layout of the monitoring system of the present invention.

[0036] Figure 5 This is a diagram illustrating the discharge initiation signal detected by the fiber optic sensing module of the monitoring system of the present invention.

[0037] Figure 6 This is a diagram illustrating the detection signals of the partial discharge fiber optic sensing module at 10kV, 15kV, and 20kV in the monitoring system of the present invention (I).

[0038] Figure 7 This is a diagram (II) illustrating the detection signals of the partial discharge fiber optic sensing module at 10kV, 15kV, and 20kV in the monitoring system of the present invention.

[0039] Figure 8 This is a PRPD diagram of internal defects in the bar of the monitoring system of the present invention. Detailed Implementation

[0040] The present invention will be further described in detail below with reference to embodiments, but the implementation of the present invention is not limited thereto.

[0041] Example 1 This embodiment is one of the basic implementation methods, a generator stator winding partial discharge monitoring system based on fiber optic sensing, including a fiber optic sensor, a fiber optic sensing module, a data acquisition module, and a host computer. The fiber optic sensors are arranged at the slot outlets of the generator stator bars. Each stator bar slot outlet is equipped with a fiber optic sensor. The fiber optic sensors are connected to the fiber optic sensing module, the fiber optic sensing module is connected to the data acquisition module, and the data acquisition module is connected to the host computer via a coaxial cable. The fiber optic sensing module employs a phase-sensitive optical time-domain reflectometer to acquire and analyze signals in the optical fiber to achieve acoustic signal measurement. The host computer is used to record partial discharge measurement data, perform noise reduction processing, draw time-frequency diagrams, and extract time-domain and frequency-domain feature values ​​of partial discharge to evaluate the frequency and intensity of discharge occurrence.

[0042] refer to Figures 1-4 The specific operation procedure of this stator winding defect partial discharge monitoring system based on fiber optic sensing is as follows: I. Establish a testing platform.

[0043] A stator winding partial discharge detection platform based on fiber optic sensing was constructed. The core components of the platform include the stator winding to be tested, a fiber optic sensor, a fiber optic sensing module, a data acquisition module, and a host computer. The component connection method is as follows: the fiber optic sensor is deployed at a designated position at the stator slot outlet; the fiber optic sensor establishes a signal transmission link with the data acquisition module through the fiber optic sensing module; and the data acquisition module communicates with the host computer via a coaxial cable.

[0044] II. Signal perception and demodulation.

[0045] When a partial discharge occurs in the stator winding of a hydro generator, the resulting acoustic signal will disturb the fiber optic sensor. The scattered signal caused by the disturbance is transmitted along the fiber optic cable to the circulator. After phase demodulation by the photodetector, the signal phase information is converted into a digital signal by the data acquisition module and transmitted to the host computer.

[0046] III. Data Recording and Processing.

[0047] The measurement data of the fiber optic sensing module under different test voltage conditions is recorded by the host computer, and the raw data is preprocessed to remove noise. Based on the processed data, the time-frequency spectrum of the measurement data of the fiber optic sensing module under different voltage conditions within a single power frequency cycle is plotted.

[0048] IV. Feature Extraction and State Assessment.

[0049] The time-domain and frequency characteristic parameters of partial discharge are extracted from the discharge signal. Based on the characteristic parameters, the occurrence frequency and discharge intensity of partial discharge are analyzed and evaluated to determine the partial discharge state of the stator winding.

[0050] Example 2 This embodiment is a further optimization of embodiment 1. The difference is that the fiber optic sensor is a spindle-type cylindrical fiber optic sensor. The spindle material is selected from epoxy board or laminated glass cloth board that matches the acoustic impedance of the main insulation of the stator winding. A sensing fiber of a preset length is wound on the spindle, and the frequency response range of the fiber optic sensor is 15kHz~40kHz.

[0051] Example 3 Compared with Examples 1 and 2, the difference in this embodiment is that the fiber optic sensors at the slots of each stator bar are connected in series to form a distributed fiber optic sensing link with multiple sensing points.

[0052] Example 4 The difference between this embodiment and embodiments 1-3 is that the fiber optic sensor and the stator bar are filled with epoxy resin and fixed by adhesive-impregnated binding rope.

[0053] Example 5 Compared with embodiments 1-4, the difference in this embodiment is that the fiber optic sensing module includes a laser, an acousto-optic modulator, a fiber optic amplifier, a circulator, a photodetector, and an arbitrary waveform generator. The continuous light output from the laser is split into a probe optical path and a reference optical path by a 1×2 optical coupler. The acousto-optic modulator modulates the light in the probe optical path into pulsed light under the control of an arbitrary waveform generator. The pulsed light is amplified by an optical fiber amplifier to form a probe pulse. The probe pulse is input into the optical fiber under test through a circulator. Its backscattered signal is returned by the circulator and converted from optical signal to electrical signal by a photodetector. The phase of the optical pulse is then obtained by demodulation through a 2×2 coupler.

[0054] Example 6 The difference between this embodiment and embodiments 1-5 is that the output end of the fiber optic amplifier is also connected to a filter to remove amplified spontaneous emission noise.

[0055] Example 7 Compared with Examples 1-6, the difference in this embodiment is that the radio frequency signal of the acousto-optic modulator, the probe pulse repetition frequency, and the triggering period of the data acquisition module are controlled by the data processing system of the host computer to achieve time-synchronized operation.

[0056] Example 8 The difference between this embodiment and embodiments 1-7 is that the time-domain feature values ​​include peak-to-peak values. PP , Rectified average value ARV Root mean square RMS Waveform factor FF Pulse factor IF Margin factor CF The frequency domain eigenvalues ​​include the centroid frequency. FC Frequency variance FV Power spectral entropy PSE .

[0057] Example 9 This embodiment proposes a superior method for monitoring partial discharge in generator stator windings based on fiber optic sensing, comprising the following steps: S1. The acoustic signal generated by the partial discharge of the generator stator winding disturbs the fiber optic sensor arranged at the slot of the stator bar. The scattered signal under the disturbance is transmitted along the fiber optic to the fiber optic sensing module for phase demodulation. S2. The data acquisition module digitizes the demodulated signal phase information and sends it to the host computer. S3. The host computer records partial discharge measurement data at different times; S4. The host computer performs noise reduction processing on the measurement data in step S3 and plots a partial discharge time-frequency diagram. S5. The host computer extracts the time-domain and frequency-domain feature values ​​of partial discharge based on the time-frequency diagram in step S4, and evaluates the occurrence frequency and intensity information of partial discharge based on the feature values.

[0058] In step S1 of this embodiment, the optical fiber sensor is a mandrel-type cylindrical structure. The mandrel material is matched with the acoustic impedance of the main insulation of the stator winding, and each optical fiber sensor is connected in series to form a distributed sensing link. The acoustic signal is transmitted to the sensing optical fiber through the mandrel and causes the optical fiber to strain, thereby realizing the phase change of the scattered signal.

[0059] The fiber optic sensing module outputs continuous light from a laser, which is then split by an optical coupler, pulse-modulated by an acousto-optic modulator, and amplified by an optical fiber amplifier to form a detection pulse. After the detection pulse is input into the optical fiber via a circulator, its backscattered signal is converted by a photodetector and demodulated by a coupler to complete phase demodulation.

[0060] In step S5 of this embodiment, the time-domain feature value is calculated using the maximum value, minimum value, and number of sampling points of the sample sequence, and the frequency-domain feature value is extracted by performing a fast Fourier transform and power spectral density conversion on the partial discharge signal.

[0061] Example 10 To facilitate public understanding of the present invention, this embodiment uses a preferred fiber optic sensing-based generator stator winding partial discharge monitoring system as an example for further explanation. The monitoring system includes a fiber optic sensor, a fiber optic sensing module, a data acquisition module, and a host computer.

[0062] The fiber optic sensors are arranged at the slot outlets of the generator stator bars. Each stator bar slot outlet is equipped with a fiber optic sensor. The fiber optic sensors are connected to the fiber optic sensing module, the fiber optic sensing module is connected to the data acquisition module, and the data acquisition module is connected to the host computer via a coaxial cable. The fiber optic sensing module employs a phase-sensitive optical time-domain reflectometer to acquire and analyze signals in the optical fiber to achieve acoustic signal measurement. The host computer is used to record partial discharge measurement data, perform noise reduction processing, draw time-frequency diagrams, and extract time-domain and frequency-domain feature values ​​of partial discharge to evaluate the frequency and intensity of discharge occurrence.

[0063] In this embodiment, the fiber optic sensor is a spindle-type cylindrical fiber optic sensor. The spindle material is selected from epoxy board or laminated glass cloth board that matches the acoustic impedance of the main insulation of the stator winding. A sensing fiber of a preset length is wound on the spindle, and the center frequency of the spindle is 25kHz.

[0064] In this embodiment, the fiber optic sensors at the slots of each stator bar are connected in series to form a distributed fiber optic sensing link with multiple sensing points.

[0065] In this embodiment, the fiber optic sensor and the stator bar are filled with epoxy resin and fixed by epoxy-impregnated binding rope.

[0066] In this embodiment, the fiber optic sensor at the stator bar slot of the generator stator winding is installed in the manner described above, which ensures that the installation structure is firm and reliable. At the same time, multiple fiber optic ultrasonic sensors are connected in series to form a distributed fiber optic sensing link with multiple sensing points. This measurement method is a distributed measurement, which realizes multi-point partial discharge measurement of the stator winding through a single optical fiber.

[0067] In this embodiment, the detection principle of the fiber optic sensor is as follows: When width W ,power P When a pulse of light is incident on an optical fiber, the power of the resulting backscattered Rayleigh (RBS) signal can be expressed as: , in, γ and S These are all scattering coefficients determined by the incident light wavelength and the fiber type. v The speed of light in an optical fiber.

[0068] Because the power of RBS is very low, the external sound field is generally sensed by detecting its phase change. External disturbances cause the optical fiber to strain. By analyzing the phase change at that position before and after the disturbance, it can be quantitatively measured.

[0069] For the mandrel structure, the optical fiber is wound around the outer surface of the mandrel. When the mandrel is strained under the action of acoustic waves, the outer wound optical fiber will be subjected to a large strain, thereby achieving optical fiber sensitization.

[0070] Assuming the fiber layer is tightly wound on the core, the sound pressure P Acting on the bottom of the mandrel, the axial displacement of the sensing fiber can be obtained according to the elastic body stress equation and boundary conditions: , in, R The mandrel radius is... E and μ These are Young's modulus and Poisson's ratio of the mandrel material, respectively.

[0071] σ RE The reaction force of the mandrel under pressure can be expressed as: , in, E f and S f Here are the elastic modulus and area of ​​the quartz portion of the optical fiber. N Δ is the number of turns of the sensing fiber. r This refers to the axial displacement of the sensing fiber.

[0072] Combined with Δ r and σ RE The calculation formula can be used to obtain the axial displacement per unit sound pressure: , The total change Δ in the length of the sensing fiber L : , Ignoring inter-turn gaps and with a small number of fiber layers, the number of fiber turns wound on the core shaft is... N ≈ L / 2 πR Combined with Δ L The calculation formula can be obtained as follows: , Where n is the effective refractive index of the optical fiber.

[0073] In this embodiment, the fiber optic sensing module uses a phase-sensitive optical time-domain reflectometer to collect and analyze signals in the optical fiber, thereby measuring acoustic signals.

[0074] The fiber optic sensing module includes a laser, an acousto-optic modulator, an optical fiber amplifier (EDFA), a circulator, a photodetector (BPD), and an arbitrary waveform generator (AWG). The laser outputs continuous light, which is split into a probe path and a reference path by a 1×2 optical coupler. Under the control of the arbitrary waveform generator, the acousto-optic modulator modulates the input of the probe path into pulsed light. This pulsed light is amplified by the optical fiber amplifier to obtain a probe pulse. After the probe pulse is input into the fiber under test through the circulator, its backscattered signal returns through the circulator. The photodetector performs the optical signal to electrical signal conversion, and a 2×2 coupler demodulates the phase of the optical pulse.

[0075] Specifically, a filter can be connected after the fiber amplifier to remove the amplified spontaneous emission noise.

[0076] Specifically, the data acquisition module digitizes the output of the fiber optic sensing module and transmits it to the data processing system of the host computer for data analysis.

[0077] Specifically, the radio frequency signal of the acousto-optic modulator, the probe pulse repetition frequency, and the trigger period of the DAQ are controlled by the data processing system to achieve synchronous operation of the timing.

[0078] In this embodiment, the photodetector demodulation method is as follows: The photocurrent output of the photodetector is: , in, , These are the phases of the signal light and the local oscillator light, respectively. It is the amplitude of the signal light. It is the frequency shift introduced by the system.

[0079] Construct a pair of orthogonal reference signals with the same frequency as I_s(t) in the digital domain: I r1 = A r sin(Δωt), I r2 = A r cos ( Δ ωt ), Will I s ( t Multiplying these terms by the aforementioned reference signal yields the second harmonic and fundamental frequency terms, respectively. Passing these terms through a low-pass filter yields: , , The phase value can be obtained from the above formula: .

[0080] In this embodiment, the time-domain characteristic values ​​include peak-to-peak value (PP) and rectified average value. ARV Root mean square RMS Waveform factor FF Pulse factor IF Margin factor CF Frequency domain eigenvalues ​​include the centroid frequency. FC Frequency variance FV Power spectral entropy PSE .

[0081] The methods for obtaining time-domain feature values ​​are as follows: (1) The formula for calculating the peak-to-peak value PP is: , in, P max ( X i ) represents the maximum value of the sample sequence.P min ( X i ) represents the minimum value of the sample sequence, while the peak-to-peak value reflects the range of signal amplitude variation.

[0082] (2) The rectified average value ARV The calculation formula is: , in, N The number of sampling points for the partial discharge signal is represented by the rectified average value, which characterizes the average amplitude of the partial discharge sample.

[0083] (3) The root mean square RMS The calculation formula is: , From an energy perspective, the root mean square (RMS) can effectively characterize the effective value of the partial discharge signal.

[0084] (4) The waveform factor FF The calculation formula is: FF = RMS / ARV , The waveform factor is the ratio of the root mean square of the sample to the rectified average value, which can characterize the degree of deviation of the waveform from the sine wave.

[0085] (6) The pulse factor IF The calculation formula is: IF = PP / ARV , The impulse factor is the ratio of the peak-to-peak value of a sample to the rectified average value, reflecting the relative magnitude of the impulse signal in the sample.

[0086] (7) The margin factor CF The calculation formula is: , The margin factor is the ratio of the peak-to-peak value of a sample to its root square amplitude, which characterizes the relative intensity of the impulse component in the signal.

[0087] The method for obtaining frequency domain eigenvalues ​​is as follows: For partial discharge input sequence X i First, it is converted into a spectral sequence. X ( f ): , in, N The length of the sequence. X( f The amplitude of the partial discharge signal in the frequency domain after fast Fourier transform is given. The spectrum is then converted into power spectral density. , Extract the centroid frequency and frequency variance of the power spectrum respectively.

[0088] (1) Centroid frequency FC The calculation formula is: , The centroid frequency characterizes the concentration trend of the main energy components in the power spectrum, and its value will shift towards the peak region of the power spectrum.

[0089] (2) Frequency variance FV The calculation formula is: , Frequency variance reflects the dispersion of energy in the frequency domain. The more concentrated the energy is in the centroid frequency region, the smaller the frequency variance; the more dispersed the energy distribution, the larger the frequency variance value.

[0090] (3) Power spectral entropy PSE The calculation formula is: , in, P ( x ) is the probability density function of the power spectral density, which is the proportion of the energy of each sub-band to the total energy of the entire frequency band. After obtaining it, substitute it into the above formula.

[0091] Power spectral entropy reflects the dispersion characteristics of signal energy in the frequency domain. A lower entropy value indicates a more stable power spectral state, with energy mainly distributed in a few characteristic frequency bands. In this case, the degree of partial discharge is often more severe.

[0092] Based on the above monitoring system, it was validated in the laboratory. The specific process is as follows: (1) A stator winding partial discharge detection platform based on fiber optic sensing technology was constructed. This platform includes core components such as the stator winding to be tested, an AC power supply, a fiber optic sensor, a fiber optic sensing module, and a host computer. The functions and connections of each component are as follows: the AC power supply powers the stator winding to be tested to induce obvious partial discharge phenomena; the fiber optic sensor is positioned at the stator slot outlet; the fiber optic sensor is connected to the oscilloscope input via the fiber optic sensing module, and the host computer is connected to the oscilloscope input via a coaxial cable.

[0093] (2) Use AC power to perform a step-by-step pressure application operation on the stator bar to be tested; (3) During the pressurization process, if a partial discharge occurs in the stator winding to be tested, the resulting acoustic signal will disturb the fiber optic sensor. The scattered signal caused by this disturbance is transmitted along the optical fiber to the circulator. After phase demodulation by the photodetector, the data acquisition module digitizes the phase information of the demodulated signal and finally transmits the digitized data to the host computer.

[0094] refer to Figure 5 , Figure 5 The display shows the discharge initiation signal detected by the stator winding defect partial discharge monitoring system. When the applied voltage is 10kV, a signal stronger than the noise floor can be observed from the time-domain measurement results. At this time, the partial discharge quantity does not exceed 200 pC, and peak values ​​of the acoustic signal can be seen in multiple cycles.

[0095] refer to Figure 6 , Figure 7 Continue to increase the voltage and record the measurement data of the monitoring system under different test voltages. Select the measurement data within a single power frequency cycle at 15kV, 20kV and 25kV for plotting.

[0096] The measurement signal of this monitoring system can characterize the change law of discharge intensity: as the applied voltage increases, the discharge quantity shows an increasing trend, the measurement signal intensity of the fiber optic sensor system increases synchronously, the oscillation amplitude of the time-domain waveform increases accordingly, and the proportion of signal components in the characteristic frequency band of the spectrum increases significantly; the frequency distribution of the measurement signal is concentrated in the range of 15~40kHz, and the peak point of the spectrum is located near 25kHz.

[0097] (4) The host computer records and preprocesses the measurement data collected by the stator winding defect partial discharge monitoring system based on fiber optic sensing technology under each test voltage condition; and simultaneously plots the time-frequency characteristic spectrum of the measurement data in a single power frequency cycle under different voltage conditions, as well as the partial discharge phase resolution spectrum (PRPD) corresponding to the internal defects of the stator bar.

[0098] Pulse current data from 100 power frequency cycles were collected to plot the PRPD (Pressure Producer Detection Map) of internal defects in the stator bars, with reference to... Figure 8 .Depend on Figure 8 It can be seen that the discharge quantity of internal defects in the stator bars is at a high level, and the discharge intensity of the negative half-wave is significantly higher than that of the positive half-wave; the discharge phase of the positive half-wave is mainly distributed in the voltage rise stage, and the corresponding phase range is 0°~90°; the distribution range of the discharge phase of the negative half-wave is 135°~270°.

[0099] (5) Based on Figures 5-8 The experimental spectrum shown can be used to calculate the aforementioned multi-dimensional partial discharge time-domain and frequency-domain characteristic parameters. These characteristic parameters can comprehensively characterize various effective information about the partial discharge of the stator winding.

[0100] This embodiment proposes a generator stator winding partial discharge monitoring system based on fiber optic sensing. The system comprises fiber optic sensors, a fiber optic sensing module, a data acquisition module, and a host computer. It employs a design where fiber optic sensors are positioned at the slot openings of each stator bar. When partial discharge occurs in the turbine generator stator winding, the resulting acoustic signal disturbs the fiber optic sensors. By monitoring this disturbance signal, the system can accurately capture the partial discharge signal of the stator winding, thereby achieving real-time and accurate online monitoring of the generator stator winding partial discharge. This monitoring system and method effectively improve the safety of equipment operation and extend the service life of the generator.

[0101] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications or equivalent changes made to the above embodiments based on the technical essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A generator stator winding partial discharge monitoring system based on fiber optic sensing, characterized in that, Includes fiber optic sensors, fiber optic sensing modules, data acquisition modules, and host computers; The fiber optic sensors are arranged at the slot outlets of the generator stator bars. Each stator bar slot outlet is equipped with a fiber optic sensor. The fiber optic sensors are connected to the fiber optic sensing module, the fiber optic sensing module is connected to the data acquisition module, and the data acquisition module is connected to the host computer via a coaxial cable. The fiber optic sensing module employs a phase-sensitive optical time-domain reflectometer to acquire and analyze signals in the optical fiber to achieve acoustic signal measurement. The host computer is used to record partial discharge measurement data, perform noise reduction processing, draw time-frequency diagrams, and extract time-domain and frequency-domain feature values ​​of partial discharge to evaluate the frequency and intensity of discharge occurrence.

2. The monitoring system according to claim 1, characterized in that: The fiber optic sensor is a spindle-type cylindrical fiber optic sensor. The spindle material is selected from epoxy board or laminated glass cloth board that matches the acoustic impedance of the main insulation of the stator winding. A sensing fiber of a preset length is wound on the spindle, and the frequency response range of the fiber optic sensor is 15kHz~40kHz.

3. The monitoring system according to claim 1, characterized in that: The fiber optic sensors at the slots of each stator bar are connected in series to form a distributed fiber optic sensing link with multiple sensing points.

4. The monitoring system according to claim 1, characterized in that: The fiber optic sensor is filled with epoxy resin and fixed by epoxy-impregnated binding rope.

5. The monitoring system according to claim 1, characterized in that: The fiber optic sensing module includes a laser, an acousto-optic modulator, a fiber optic amplifier, a circulator, a photodetector, and an arbitrary waveform generator. The continuous light output from the laser is split into a probe optical path and a reference optical path by an optical coupler. The acousto-optic modulator modulates the light in the probe optical path into pulsed light under the control of an arbitrary waveform generator. The pulsed light is amplified by an optical fiber amplifier to form a probe pulse. The probe pulse is input into the optical fiber under test through a circulator. Its backscattered signal is returned by the circulator and converted from optical signal to electrical signal by a photodetector. The phase of the optical pulse is then obtained by demodulation through a coupler.

6. The monitoring system according to claim 5, characterized in that: The output of the fiber optic amplifier is also connected to a filter to remove amplified spontaneous emission noise.

7. The monitoring system according to claim 5, characterized in that: The radio frequency signal of the acousto-optic modulator, the probe pulse repetition frequency, and the trigger period of the data acquisition module are controlled by the data processing system of the host computer to achieve time-synchronized operation.

8. The monitoring system according to claim 1, characterized in that, The time-domain feature values ​​include peak-to-peak values. PP , Rectified average value ARV Root mean square RMS Waveform factor FF Pulse factor IF Margin factor CF ; The frequency domain characteristic values ​​include the centroid frequency. FC Frequency variance FV Power spectral entropy PSE .

9. A method for monitoring partial discharge in generator stator windings based on fiber optic sensing, characterized in that, Includes the following steps: S1. The acoustic signal generated by the partial discharge of the generator stator winding disturbs the fiber optic sensor arranged at the slot of the stator bar. The scattered signal under the disturbance is transmitted along the fiber optic to the fiber optic sensing module for phase demodulation. S2. The data acquisition module digitizes the demodulated signal phase information and sends it to the host computer. S3. The host computer records partial discharge measurement data at different times; S4. The host computer performs noise reduction processing on the measurement data in step S3 and plots a partial discharge time-frequency diagram. S5. The host computer extracts the time-domain and frequency-domain feature values ​​of partial discharge based on the time-frequency diagram in step S4, and evaluates the occurrence frequency and intensity information of partial discharge based on the feature values.

10. The monitoring method according to claim 9, characterized in that: In step S1, the fiber optic sensor is a mandrel-type cylindrical structure. The mandrel material is matched with the acoustic impedance of the main insulation of the stator winding, and each fiber optic sensor is connected in series to form a distributed sensing link. The acoustic signal is transmitted to the sensing fiber through the mandrel and causes fiber strain, thereby realizing the phase change of the scattered signal.

11. The monitoring method according to claim 9, characterized in that: In step S1, the fiber optic sensing module outputs continuous light through a laser, which is then split by an optical coupler, pulse-modulated by an acousto-optic modulator, and amplified by an optical fiber amplifier to form a detection pulse. After the detection pulse is input into the optical fiber through a circulator, its backscattered signal is converted by a photodetector and demodulated by a coupler to complete phase demodulation.

12. The monitoring method according to claim 9, characterized in that: In step S5, the time-domain feature value is calculated using the maximum value, minimum value, and number of sampling points of the sample sequence, and the frequency-domain feature value is extracted by performing a fast Fourier transform and power spectral density conversion on the partial discharge signal.

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