05_efield_wetcable - IEEE Transactions on Dielectrics and...

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IEEE Transactions on Dielectrics and Electrical Insulation Vol. 12, No. 6; December 2005 1125 Electric Field Computation in Wet Cable Insulation Using Finite Element Approach H. S. B. Elayyan and M. H. Abderrazzaq Electric Power Engineering Division Hijjawi Faculty for Engineering Technology Yarmouk University, Irbid 21163, Jordan ABSTRACT Accurate assessment of cable insulation conditions can be achieved by implement - ing advanced diagnostic and simulation techniques that assist the measurement and monitoring of the properties related to aging and failure of the insulation sys - tem. It is well recognized that the electric field distribution is the dominant factor in the initiation of degradation process in the insulation system. In such a system, and due to the presence of pollutants such as water or moisture, local field en - hancement occurs resulting in field stress values enough to cause local breakdown of the insulation. The finite element simulation technique is used to evaluate the electric field inside the power cable. A model that illustrates the water-dielectric interface within the cable insulation system is proposed. The difficulties associated with the building of such a model, which contains elliptically shaped water parti - cles and unusually configured insulation areas, are illustrated. Finally, the link be - tween the local field concentration in the vicinity of water particles and the possi - bility of insulation failure, which can be developed to a complete breakdown, is dis - cussed. Index Terms — Power cables, finite element, electrical insulation, electric field, water absorption. 1 INTRODUCTION HE cable industry in general, and the insulation T technology in particular, has benefited greatly from the revolution in material engineering. This is evident by the wide range of modern cables of improved design and performance. Electrical insulation is the backbone of the power cable, and its state is usually used to reflect the real age of this cable. The dielectric response of the insu- lation system has always been a subject of interest due to the variety of stresses, which the cable insulation has to be continuously exposed to. The growth in the class of volt- age of power cables is accompanied by the increase in the insulation thickness. This is depicted in Figure 1 for a se- ries of power cables having the same design and similar wx working environment 1 . One of the major problems, which shorten the life of high voltage cables, is the presence of water inside the insulation material of the cables. This simply explains the fact that, after some years of introducing polyethylene ca- Ž. bles PE , electric breakdown due to ‘‘water trees’’ ap- peared. Aging due to water treeing significantly reduces w the electrical breakdown strength of the insulation 2, 3, Manuscript recei ® ed on 28 June 2004, in final form 18 April 2005.
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05_efield_wetcable - IEEE Transactions on Dielectrics and...

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