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Research on New Photo Stimulated Discharge Spectrometer and PSD Spectral of Typical Polymers

Author: HeLiJuan
Tutor: LeiQingQuan
School: Harbin University of Science and Technology
Course: High Voltage and Insulation Technology
Keywords: polymer dielectric material space charge photo-stimulated discharge Optical Parametric Oscillator
CLC: TM215
Type: PhD thesis
Year: 2010
Downloads: 62
Quote: 1
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Abstract

Space charge plays an important role in electrical aging and breakdown of engineering dielectrics, and it has becoming an important factor for restricting the development of high electric field of power cable. Meanwhile, with the rapid development of electromechanical sensing applications, the long-term charge-storage mechanisms urgently need to be researched clearly because of the importance of space charge storage stability in polymer electret of electromechanical sensors. In recent years, space charge effects mentioned above in polymer are always the focus problems that are concerned by relevant researchers. Space charge is often captured by the trap, and the trap characteristics decide charge storage and transport. Therefore it has important scientific meaning and practical value to accurately characterize energy distribution of charge trap in polymer dielectric materials in order to improve their properties and application.In this dissertation, we measure the energy distribution of trap in polymer materials by photo-stimulated discharge (PSD), and finish the work as follows: Design and set up the first PSD measuring spectrum analyzer based on optical parametric oscillator (OPO) as exciting light source at home and abroad. The range of output wavelength is 2300-210nm. The range of trap energy measurement is about 0.50-5.90eV and an accuracy is of±0.01eV. At the same time the output photon flux density is up to 3.0×10 24 cm ? 2 s?1 or more in the whole band. The PSD spectrum is better able to meet the measurement requirements from respect of exciting light intensity, output wavelength range, output wavelength tunable properties and the measurement accuracy.Because the light source of new PSD spectrum analyzer is laser, the output light may damage the chemical structures of polymer materials. In view of such a problem, we prove the new PSD spectrum analyzer dose not has any the destructive action on chemical structures of tested materials by using Fourier infrared and Raman spectroscopy. The molecular chain structures of samples are not broken and they do not generate new free radicals. Therefore the laser irradiation does not generate additional charge trap and not cause either light erosion or photodegradation.Using the new PSD spectrum analyzer, PSD method is studied in detail. This includes the study of trap distribution in different experimental conditions for the same tested sample, such as no charge injection, different charge injection methods, different charge injection doses, different number of scans and so on. Put forward energy calibration method of PSD spectra. Through the analysis of the original PSD spectra, we identify the original PSD spectra contain the information of not only trap charge release but also exciting light energy change. In order to eliminate the influence of exciting light energy change, we propose energy normalized PSD spectra, which can really give the informations of the distribution of charge trap in dielectric. Based on the Labview, we develop control software, which can combine with the hardware system and achieve energy normalization of the PSD spectra.PSD spectra of typical polymer materials of polyester, polyimide, polypropylene, and cross-linked polyethylene were tested by the new PSD spectrometer. It was found that the charge traps in polyester is mainly in the range of 4.10-5.20eV, meanwhile 3.10-4.10 eV traps distribution in polyimide. The traps of these two materials are related with the carbonyl. There is a trap distribution of 4.80-5.90eV in polypropylene and trap more than 4.80eV in crosslinked polyethylene, which most likely come from residual catalyst during the polymerization process.Combine new PSD spectrum analyzer with TSC and PEA to study the distribution of charge trap in PE in detail. Generally speaking, TSC can only measure shallow trap because of the limit to heat-resistance temperature of material itself, while PSD is fit for measuring deep trap. Through our research we find the measurement result of TSC is only the apparent trap depth. In fact, the trap charges by the thermal and the optical excitation are from the same trap. Thermal stimulated method not only stimulates trap charges, but also makes trap depth become shallow due to thermal erosion. Therefore PSD really reflects the intrinsic properties of trap in polymer materials.

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CLC: > Industrial Technology > Electrotechnical > Electrical materials > Insulating materials,dielectric,and its products > Solid dielectric
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