Development Of Elastic Wave Ellipsometry Measurement System And Sampling Sensor For High-speed Detection Of Space Charge

The space charge distribution is an important indicator of the expiration of the operational aging and deterioration state of the insulating material.It is to effectively evaluate the dielectric performance of insulation in the internal space charge of the insulation,and it is a key basis for ensuring the normal operation of power electronics.The non-destructive measurement method of insulating space charge,including electroacoustic pulse(PEA)method,have been widely used in DC and power frequency AC test environments,but the space charge high speed measurement under high frequency transients and pulse stress is basically blank.The spatial resolution of optoelectronics principles using pulsed laser as excitation in the measurement method can reach the nanometer level,but the existing detection means is limited to the measurement speed.The development of high-speed space charge detection method under terahertz excitation has important theoretical significance and application value.In this paper,a high-speed measurement method of space charge optoelectronics based on elastic-optical effect(stress birefringence effect)is proposed.The terahertz wave generated by the interaction of femtosecond laser and electro-optic crystal acts on the space charge inside the sample as the excitation,and the charge elastic wave is detected using an elastic-optical sampling sensor having elastic-optical effect.Based on the working principle of PEA test system,the physical process of terahertz excitation and space charge interaction is described in detail without considering the attenuation and dispersion of elastic wave in the process of propagation.In the measurement scheme,fused silica glass is selected as the material base of the sensor.Based on the refractive index ellipsoid equation,the principle of elastic-optical effect is analyzed,and the relationship between the refractive index change and the stress in the three principal directions of the material is analyzed.The system detection portion uses a He-Ne laser,and the polarization state of the detection light is analyzed by Stokes vector and Mueller matrix.The mathematical models of the above three parts of space charge measurement are established to verify the feasibility of the optoelectronics scheme from the theoretical level.The specific working process of the high-speed space charge measurement system in the scheme is described,and its advantages and disadvantages are discussed.The elliptical polarization measuring system for elastic wave detection is built,which proves the feasibility of the detection part of Optoelectronics scheme.The detection system uses a He-Ne laser,a polarizing plate,a quarter-wave plate,a Wollaston prism,a balanced photodetector,etc.,and a piezoelectric actuator is selected for achieving the elastic stress effect of space charge.In the system construction process,in order to reduce the system vibration and improve stability,the RTV silicone rubber is used between the moving end of the piezoelectric actuator and the material.Different in the way the polarization detecting light passes through the sensor,the elliptical method is divided into transmissive elliptical measurement and reflective elliptical elliptical measurement.The two systems are tested respectively.It is found that the voltage output and stress input of the balance detector are approximately linear,and they can respond well to different types of elastic waves.Therefore,the measurement system can be used for high-speed space charge detection.The material selection and structure design of the elastic-optical sampling sensor are carried out,and the optical properties of the material and sensor are preliminarily analyzed.The ellipsometry measurement system was used to test the polycarbonate and fused silica glass purchased.It was found that fused silica glass had better mechanical stability,so quartz glass was selected as the sensor material.For the transmission sensor structure,the relationship between the incident distance and the output of the probe light was not constant,so it was difficult to be used for the subsequent stable and repetitive space charge measurement,so the sensor was stable The structure should be reflective and the thickness should be less than 1 mm.Through the performance test and error analysis of the physical model of the reflective sensor,it is found that when the sinusoidal elastic wave of different frequencies is applied,the DC component will appear in the output of the detector in the high frequency excitation section,and the peak amplitude of the output is also different,which provides a reference for the subsequent charge information inversion.In summary,this paper proposes a high-speed measurement method of space charge optoelectronics based on the elastic-optical effect using terahertz wave as excitation,and the production of the detection portion of the program and the production of the sensor are carried out.The experimental research and theoretical analysis of this paper can provide an important basis for the subsequent optoelectronic measurements.