Acoustic Propagation On PD In Insulating Oil With Solid Medium And Optimization Design Of F-P Acoustic Structure

Insulation failure of electrical equipment poses a major threat to the normal operation of the power system,and Partial Discharge(PD)is the initial performance of insulation damage.If the partial discharge exists for a long time,it will cause insulation degradation,affect the safe operation of electrical equipment,and even cause equipment failure,resulting in huge economic losses.The extrinsic fiber-optic Fabry-Perot(F-P)sensor can effectively detect partial discharge acoustic emission signals and is used to discover latent faults in power equipment.However,it is still facing the problem for F-P sensor of low detection sensitivity when it is used for power equipment testing.There are two main reasons for this problem: one is the sensitivity of the sensor itself;the other is due to the influence of liquid-solid composite insulation on sound wave propagation.Based on the basic principle of acoustic wave propagation,the acoustic wave coupling characteristics of liquid-solid composite insulation are analyzed,and the influence of solid medium on ultrasonic propagation in liquid insulation is calculated by sound field finite element analysis,then the transient sound energy transfer process of sound wave through liquid-solid-liquid composite medium is analyzed.To investigate the relationship between the sound pressure intensity in liquid medium after ultrasonic-liquid-solidliquid coupling and the sound pressure intensity transmitted through a single liquid medium,and the influence of physical properties of solid medium on the variation of coupled sound pressure intensity.The response of Fabry-Perot sensor in different media is compared by using PZT continuous ultrasonic source and plate-plate electrode partial discharge acoustic source.At the same time,the method of reflecting the acoustic energy of the concentrated space to the F-P sensitive diaphragm by the parabolic lens structure is proposed,and the acoustic response amplitude of the F-P sensor is improved to improve the sensitivity.The results show that the F-P sensor in the liquid-solid-liquid acoustic propagation medium responds more to the same intensity acoustic signal than the pure liquid medium.The sound pressure enhancement effect is related to the distance between the sensor and the solid medium and the characteristics of the solid medium material.The sound pressure intensity in the liquid medium after the solid medium increases first and then decreases with the increase of the distance.And the sound pressure intensity transmitted through the liquid-solid-liquid medium is proportional to the density and Young's modulus of the solid medium.The F-P sensor with acoustic focusing structure can significantly improve the sensitivity of the PD detection,and its partial response amplitude is about 3 times that of the bare sensor.