Joint Measurement Method And System Design Based On PEA And Laser Detection Principles

The distribution of space charge is crucial for the evaluation of the performance and state of insulating materials.Given the significant differences in the distribution of space charge in insulating materials under different operating environments,the development of corresponding charge measurement techniques for different insulation environments has become an important means of reliably evaluating the insulation performance and operating status of electrical equipment.In current research,although existing charge measurement methods can achieve testing under power frequency and DC conditions,it is difficult to detect charges under high frequency and transient pulse stress conditions.The main reason is that the measurement resolution and speed are insufficient.The development of optoelectronic space charge measurement methods with high spatial resolution and high measurement speed potential has become an important means of studying the evolution of space charge under complex stress conditions.Therefore,this paper proposes an optoelectronic space charge measurement method with high measurement speed and high spatial resolution potential,and verifies its feasibility from theoretical and experimental levels.Firstly,the joint test principle and structural design method of PEA(pulsed electro-acoustic,PEA)and laser detection are proposed,and a mathematical transformation model of the whole process of space charge-optical signal is constructed to verify the feasibility of the method from a theoretical level.Combining traditional electroacoustic pulse method with optoelectronic detection technology,a space charge optoelectronic measurement method based on photoelastic effect is proposed.Based on photoelastic effect,a mathematical model of refractive index ellipsoid change of sensing material under stress loading is established.Through Stokes vector,mathematical description of different state polarized light is realized.Combined with Mueller matrix of optical elements,a characterization model of polarization state change when laser passes through multiple optical elements is established.By analyzing the generation and propagation attenuation process of sound waves disturbed by charges,the transmission mechanism of space charge conversion elastic wave in joint test system is clarified,and a mathematical model of multi-state signal transmission in whole process of charge measurement is established.Further,a mathematical characterization model for spatial resolution and sensitivity suitable for optoelectronic measurement methods is proposed,and the influencing factors and characteristics of sensitivity for transmission and reflection ellipsometry are analyzed.Combined with sensor characteristics,laser parameters and photoelastic effect path,a spatial resolution mathematical model suitable for optoelectronic measurement methods is proposed.Based on the influence of stress change on detector output signal change,a sensitivity mathematical model for measuring system is established.Based on two indicators,transmission and reflection ellipsometry are studied and analyzed.Ellipsometric stress measurement experiments were carried out at different incident angles,sensor thicknesses and laser diameters.Eight cases where detection light undergoes photoelastic effect in sensor were analyzed along with corresponding constraint conditions and photoelastic effect range.It was pointed out that reflection ellipsometry has nanometer-level spatial resolution at the expense of certain sensitivity conditions.When sensor thickness is 0.1 μm and laser diameter is 81 μm,spatial resolution of reflection ellipsometry can reach 50 nm.Based on equivalent characterization model of sound wave propagation and molecular dynamics simulation of photoelastic materials,design of high-reliability high-photoelastic coefficient sensing module for joint measurement system was completed.On one hand,based on similarity between elastic wave propagation in joint test system and voltage wave propagation in basic transmission line model,equivalent characterization model for sound wave propagation part in system was proposed.Based on simulation results of charge under different structural characteristics of sensing module,optimal design scheme for sensing module suitable for joint test method was proposed.On other hand,combined with molecular dynamics simulation,a sensor material modification design idea based on SU-8 glue as matrix and different types of nanotubes as doping molecules was proposed.Mechanical properties of 5 groups SU-8 glue/carbon nanotube composite systems at different temperatures were studied.High-reliability high-photoelastic coefficient sensor was developed based on photolithography process.Further,using built reflection ellipsometry detection system to evaluate measurement performance of developed sensor.Finally,femtosecond laser irradiation target material replaces piezoelectric actuator to generate weaker elastic wave to compare elastic response between PEA piezoelectric sensor and new photoelastic sensor in ellipsometry measurement system.It was pointed out that photoelastic sensor has smooth waveform without distortion and high measurement reliability.Feasibility of joint test system based on PEA and laser detection was verified from experimental level.In summary,this paper proposes a space charge measurement method with high measurement speed potential and high spatial resolution potential.A mathematical characterization model for whole process signal transformation is established.Influencing factors and characteristics of sensitivity for transmission and reflection ellipsometry are analyzed.Optimal structure design core sensing module completed development high-reliability high-photoelastic coefficient sensor based on comparative study PEA piezoelectric sensing module feasibility joint test system was verified.The research results of this paper can lay theoretical model and sensing foundation for implementation of high time-space resolution space charge measurement method in future.