Space charge distribution measurements in polymers by an improved pulsed electro-acoustic method.

摘要

This study presents a novel method of processing measured signals from the Pulsed Electro-Acoustic (PEA) method in order to obtain space charge distributions with improved resolution and accuracy. The proposed method (i.e. the simulation model method) enables surface charges to be distinguished from space charge distributions. Therefore, space charge distributions can be processed separately from surface charges without surface charges being mixed into the obtained space charge distributions. In addition, a nonlinear detection and optimization process in the simulation model is proposed as an option for even better charge distribution results. A brief review of solid breakdown mechanisms and space charge effects illustrates the importance of space charge distribution measurements. A literature review of the available space charge distribution measuring techniques shows the advantages of the PEA method for space charge distribution measurements. Furthermore, the deconvolution procedure (DCON) and the direct method (DM), the two previous methods used to obtain space charge distributions from the PEA measured signals, are critically reviewed and re-analyzed in order to gain a better appreciation of the proposed simulation model method. The obtained results of four sets of synthetic signals by the DM, the DCON, and the point matching simulation model (PMSM) methods; and the obtained results of two sets of experimental signals by the PMSM method demonstrate the advantages associated with the use of the simulation model method. Also presented are experimental studies designed and conducted to determine the dynamic changes of space charge distributions under HVDC uniform field voltage applications for sheet specimens made of LDPE, HDPE, UHMWPE, PP and PMMA. The experimental results are then summarized and discussed. Moreover, in this thesis, the PEA method principle is further extended to nonuniform fields (i.e. needle-plane electrode configurations), where space charge effects are considered crucial.