Study On Detection Of PD-induced Acoustic Emission In Liquid Dielectrics Based On Extrinsic Optical Fiber Fabry-perot Sensor

The acoustic emission detection method of partial discharge is an effectivemethod to measure partial discharge in liquid dielectrics. Compared withpiezoelectric ceramics sensor, the advantage of extrinsic fiber Fabry-Perot(FP)sensor is that it can be implanted in liquid dielectric for measurement. The signalis free from electromagnetic interference in the process of sensing andtransmission. Extrinsic fiber FP sensor which includes acousto-optic couplingquartz diaphragm, fiber and manganese steel cavity. The extrinsic fiber FP sensorhas exquisite and agile structure and has unique advantages in the field of liquidmedium partial discharge detection. This paper studies the structure design of thesensor, parameter selection, processing preparation, characterization, simulationanalysis and experimental measurement.On the basis of theoretical calculation and software simulation, this paperproposes the methods of structure design of the sensor and parameter selection,analyses quartz membrane structure parameters, FP sensor sensitivity and therelationship of the first-order natural frequency. This paper made the FP sensorusing coating quartz diaphragm and coating tail fiber end as optical flat,constructs the forced demodulation system, and studies the meaning of FP sensorworking point to intensity demodulation. Aiming at the problems of sensorworking point drift and characteristic curve distortion which are caused by thechanges of temperature and the pressure of liquid medium, and according to theworking principle of FP sensor, this paper trims light source center wavelength by voltage-temperature-center wavelength control mode to adjust thecharacteristic curve of FP sensor and ensures the working point Q can be testedunder the ideal condition. Using digital signal generator as excitation source, thispaper detects measured performance of optical fiber sensor system andpiezoelectric sensor system by simulation experiment.This paper sets up partial discharge joint detection system and detectsultrasonic signal which is send out from needle-plate PD in liquid dielectric.Experimental results prove that the optical fiber sensing system based onextrinsic FP sensor and piezoelectric ceramic sensor system has good detectionperformance, the FP sensor which is made by quartz diaphragm can complete thetest of ultrasonic signal induced by PD. Although the sensitivity has been unable tofully achieve the sensitivity of PZT, the experimental results show that it ispossible to beyond the PZT through further optimization design. In the final,analyses the influence factors of ultrasonic signal detection of partial dischargeand the improvement measures are proposed.