| Fiber-optic sensing partial discharge detection has become one of the important means of electrical equipment state detection;as the main method of unconventional partial discharge ultrasonic detection at present,extrinsic fiber-optic F-P sensor has a compact structure,strong anti-electromagnetic interference ability,and excellent directionality,good reusability,and it can be built into power equipment.The current solutions for improving the ultrasonic detection performance of optical fiber F-P sensors mainly focus on the optimization of the sensor diaphragm material,size parameters,and structure.While the lack of research on the correlation between the characteristics of typical oil-paper insulation partial discharge ultrasonic signals and the optical fiber F-P sensor limits the use of optical fiber F-P ultrasonic detection.The thesis carried out research on the characteristics of partial discharge ultrasonic signals of typical oil-paper insulation and multi-frequency optical fiber F-P ultrasonic sensing detection.The main work includes:(1)The test platform for the research of oil-paper insulation partial discharge ultrasonic signal and its propagation was built first,and then the spectrum of typical oil-paper-insulation partial discharge ultrasonic signals and their attenuation characteristics in the propagation process were studied.The experimental results showed that there are big differences in the frequency spectrum of the ultrasonic signal of the three typical oil-paper-insulation discharge models.The frequency spectrum of partial discharge in air cavity is relatively narrow,mainly concentrated in the 20 k Hz～40 k Hz frequency band,but the amplitude is higher.The surface discharge on pressboard has a wider spectrum distribution,and the voltage amplitudes in multiple frequency bands are relatively obvious.The metal tip discharge model in oil has relatively uniformly distributed and high-amplitude voltages in the 20 k Hz～160 k Hz frequency band;and the frequency signals are more likely to be attenuated due to propagation distance,insulating cardboard and winding barriers.(2)The working characteristics of the extrinsic optical fiber F-P sensor are analyzed from the perspectives of optics and mechanics.Aiming at the fluid-solid coupling problem involved in the vibration of the F-P sensor diaphragm in transformer oil,a correction coefficient related to the transformer oil density is introduced to establish the diaphragm vibration model of the optical fiber F-P sensor in the liquid phase environment,which can better guide the design of the F-P sensor diaphragm for the detection of the specific frequency ultrasonic signal in the transformer oil;three types of F-P sensors with measured center frequencies of 32 k Hz,121 k Hz and 153 k Hz were developed to meet the requirements of the multi-frequency F-P sensor array for differential detection of typical oil-paper insulation partial discharges.(3)Multi-frequency optical fiber F-P sensor arrays based on independent photodetector and a multiplexed photodetector are constructed separately.The experimental results show that the multi-frequency optical fiber F-P sensing array can effectively improve the sensitivity and accuracy of the overall detection of partial discharges,and has the ability to locate the discharge.At the same time,it can avoid the lack of detection or detection errors caused by the use of any sensor alone.In addition,different sensors in the multi-frequency optical fiber F-P sensor array have different responses to different types of partial discharge ultrasonic signals,which can provide a basis for partial discharge pattern recognition.The research of the thesis lays the foundation for the good application of extrinsic optical fiber F-P sensor in the on-line monitoring and identification of partial discharge of oil-paper insulation electrical equipment. |
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