03_pd_tree_g - IEEE Transactions on Dielectrics and...

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IEEE Transactions on Dielectrics and Electrical Insulation Vol. 10, No. 3; June 2003 425 Modelling of Partial Discharge Development in Electrical Tree Channels M. D. Noskov, A. S. Malinovski M. Sack and A. J. Schwab Institute of Electric Ener~ Systems and High-Voltage Technology (EH) University of Karlsmhe Kaiser str. 12, D-76128 Karlsruhe, Germany ABSTRACT A model of partial discharge development in electrical tree strnctures is presented. The model considers channel conductivity, charge transport, and electric field re- distribution during propagation the discharge along the channels. It has been used for numerical investigation temporal-spatial and electric characteristics of the partial discharges in capillaries and electrical trees exposed to ac voltage in a needle-plane geometry. The simulation results have been compared with experi- mental data given in the literature. Index Terms - Electrical treeing, partial discharges, mathematical modelling. 1 INTRODUCTION LECTRICAL treeing is one of the main causes for cal fields [l]. The electrical tree growth results from par- tial discharges (PD) within gas-filled tree channels. The PD behavior depends on the electrical tree shape and growth mode. Therefore, the analysis of the PD activity can he useful for diagnostics of the insulation degrada- tion. In order to understand PD behaviour it is important to clarify the dynamics discharge development in elec- trical tree structures. The PD development is a complex process involving transitions of tree channels into con- ducting and non-conducting states, charge transport along the channels and electric field redistribution within the insulation. A quantitative description of these interrelated processes can be achieved by mathematical modeling. Until now, various models have been proposed to de- scribe PD behavior in electrical treeing, e.g. [Z-71. These models allow simulation of the main features of PD activ- ity observed in experiments, but they do not consider the temporal dynamics of the PD development along the tree channels. The proposed PD model describes the self-con- sistent dynamics of the electric field, charge and conduc- tivity distributions along the tree channels. The model is E. failure of polymeric insulation in alternating electri- used in computer investigation of the spatial-temporal and electric characteristics of the PD development in a capil- lary cavity and an electrical tree structure. 2 MODEL OF PD DEVELOPMENT 2.1 PHYSICAL BACKGROUND AND BASIC ASSUMPTIONS The new model of PD development includes the propa- gation of the discharge along the channels, charge trans- port, and electric field redistribution. The development of a discharge within a narrow tubular channel involves many ,different processes such as collision and photo ionization, electron-ion recombination, electron and ion drift, elec- tron attachment to the channel surface and gas molecules, etc. [1,8-121. Moreover, changes of temperature and pres- sure within the channels can result in ablation and defor- mation of the dielectric material. The system of basic
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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_pd_tree_g - IEEE Transactions on Dielectrics and...

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