03_chargmotion_insu - 826 Wintle: Charge Motion in...

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Wintle: Charge Motion in Technical Insulators: Facts, Fancies 826 Charge Motion in Technical Insulators: Facts, Fancies and Simulations H. J. Wintle Department of Physics Queen’s University Kingston K7L 3N6, Canada ABSTRACT Technical insulators, whether gas, liquid or solid, are largely characterized by unipolor ionic flow. The carriers are supplied by injection, or by bulk ionization, and the charge transport is space charge perturbed. I shall discuss theoretical modeling of steady state, time dependent, and oscillatory conditions. Continuum equations have provided the basis for early models of corona currents. First I show the validity of the Deutsch assumption in gases, and then extend the calculation to describe the situation far downwind. These equations also account for many effects in solids such as injection transients and open circuit decay. We discuss their ap - plication to electrode blocking capacitance, and to discharge currents in shorted samples. We note that even the simplest bipolar flows require many parameters to describe them. Next, we consider the problem of reconstructing distributions from acoustic pulse and similar measurements that necessarily contain instrumental broadening of the signals. It is then necessary to attempt to explain the observed evolution of the charge density by simulations. We discuss some of the problems associated with the algorithms, and with modeling the microscopic details of the carrier motion when the numerical approximation is necessarily mesoscopic. We mention some applications of the theory to approximation is necessarily meso - scopic. We mention some applications of the theory to measurements made with AFM probes, with the SEM mirror method, and with a Faraday cage. We mention the difficulties in accounting for low frequency oscillations in cables. Finally, we () outline the materials problems identity of carriers and traps , the numerical ( problems reconstruction, discrimination between the effects of various carrier )( types and dipoles, and deduction of parameters , and the logical problems dis - ) tinction between simulation and accurate modeling which need our future atten - tion. Index Terms — Space charge, insulators, conduction, modeling, simulation, oscillations, surface conduction. 1 INTRODUCTION HE flow of current in insulators and the associated T space charge effects are topics of considerable techni- cal interest. To the materials scientist, they show that there is no such thing as a perfect insulator. For the high volt- age engineer, this imperfection leads to leakage and even- tually breakdown in solids, in liquids and in gases. From the commercial point of view, they give rise to a variety of useful devices, such as electrostatic precipitators, photo- copiers, organic light emitting diodes, and so on. Scientific Manuscript recei ® ed on 30 April 2003, in final form 14 July 2003.
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This note was uploaded on 06/08/2011 for the course ELECTRICAL 124 taught by Professor Ghjk during the Spring '11 term at Institute of Technology.

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03_chargmotion_insu - 826 Wintle: Charge Motion in...

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