04_aged_ldp_xlpe - 2004 Inrernarional Conference on Solid...

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2004 Inrernarional Conference on Solid Dielectrics. Toulouse, France, Ju!v 5-9, 2004 Comparative Study of Space Charge in Aged Low-Density Polyethylene and Crosslinked Polyethylene M. Carmo Lanp I*, E.R. Neagu I.' and J.N. Marat-Mendes ' I Departamento de Ciincias dos Materiais, (CENIMAT), Faculdade de Cisncias e Tecnologia, Universidade Nova de Lisboa, 2829-5 16 Caparica, Portugal 'Dept. of Physics, Technical University of lasi, Str. D. Mangeron N. 67, Iasi-6600, Romania * E-mail: canno~dcm.fct.iinl.pi Abstract: Polyethylene is one of the most widely used polymeric insulators in medium and high voltage power cables. However the importance of space charge distribution and its influence on the electrical aging in this polymer is not fully understood. The very good insulating properties of the material implying very long relaxation times (few days and even longer are usual) and low currents (few pA or below) make individual measurements of isothermal chargeidischarge currents and thermostimulated currents difficult to analyze and reproduce. A single type of measurements does not take into account the space charge that remains trapped for long times. A combined procedure of isothermal and non-isothermal current measurements developed for high insulating polymers was used for low density polyethylene (LDPE) and crosslinked polyethylene (XLPE) films electrically aged. The press-molded LDPE and XLPE films were electrically aged under similar conditions using an AC electric field while immersed in a sodium chloride aqueous solution at constant temperature (electro-thermal aging). The use of the combined procedure for current measurement allowed obtaining information about space charge traps, activation energies and relaxation times for both LDPE and XLPE. This data was used to compare electrical aging under similar conditions for the two types of polyethylene. INTRODUCTION The study of space charge (de)trapping and transport in high insulating polymers is difficult and time consuming because of the traps long relaxation times. Single isothermal charging/discharging currents can some times give reproducible results while other times reproducibility is not encountered. But when non-isothermal measurements are performed (such as TSDC) it is even more difficult to have reproducibility Therefore the analysis of the traps characteristics is also affected [I]. This is a consequence of a residual charge that remains in the sample (trapped in traps with long relaxation times). So it is necessary to use a combined procedure of isothermal chargingldischarging measurements together with non-isothermal experiments with special attention to the control of the remaining space charge after each run of the experiment. This procedure was developed by Neagu et al.
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This note was uploaded on 06/11/2011 for the course ELECTRICAL 124 taught by Professor Ghjk during the Spring '11 term at Institute of Technology.

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04_aged_ldp_xlpe - 2004 Inrernarional Conference on Solid...

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