Research On Space Charge Measurement Of LDPE Based On The Optical Method

In recent decades, polymer insulating dielectrics have been more and morewidely used in the field of electric power. With the rapid development ofelectrical industry, the demands for electrical properties of solid dielectrics haveincreased. The problem of space charge in solid dielectrics is a constraint to theimprovement of electrical properties of dielectric materials. At present, thedevelopment of nondestructive testing methods and technology has beenrelatively mature, and these methods have been applied to the research oninsulating materials. Due to the bandwidth of the measurement system, its spatialresolution can only reach the micron scale. Therefore, in order to study thebehavior of space charge at a smaller scale, it is particularly important to putforward a new method of space charge measurement.In this thesis, a research program of all-optical space charge measurement inlow density polyethylene (LDPE) is proposed. In the program, the pulsedphotoelectric field is used to have an interaction with LDPE, and the stressbirefringence effect is used to test the elastic wave. The principle of theinteraction between photoelectric field and the material is briefly introduced, sois the stress birefringence effect. The testing system is also built according to theexperimental scheme. In addition, the sample structure of LDPE with electro-optic polymer on its surface is designed, and the existing problems of theproposed scheme are analyzed.Whether the pulsed photoelectric field can cause a perturbation of spacecharge in dielectrics is the foundation of space charge measurement in soliddielectrics based on the optical method. In order to verify this hypothesis, avalidation testing system is set up, the pulse laser is used as the exciting light,and the detection part of pulsed electro-acoustic (PEA) testing system is used formeasuring. The results of the validation experiment and the PEA testing system are compared. The results indicate that the photoelectric field can generate theelastic wave by causing a perturbation of space charge in LDPE.In this dissertation, the wavelength of exciting light and angle of incidenceon the surface of LDPE is changed by using the validation testing system. Theoutput voltage waveforms at different photoelectric fields are obtained, theinfluence of wavelength of laser and incident angle is analyzed, and the signalthat reflects the space charge is extracted.