The danger of water trees in polymer insulated power cables evaluated from calculations of electric field in the presence of water trees of different shapes and permittivity distributions

Journal of Electrostatics (Impact Factor: 1.27). 06/1997; DOI: 10.1016/S0304-3886(97)00066-1

ABSTRACT From the assumption that water trees influence the AC electric field distribution in the insulation due to their permittivity higher than that of the surrounding medium, calculations of electric field in the vicinity of model water trees are presented. The electric field is locally amplified and reaches values high enough to be considered as a danger for the cables.

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    ABSTRACT: During the growth of water trees in the XLPE cable insulation, the distribution of the electric field is modified because of the local change of the dielectric properties of the material. A better knowledge of the comparative danger for the different kinds of water trees could lead to a way of improving the quality of cable insulation. Numerical analysis results show that the dielectric permittivity of a water tree itself and its distribution inside it are so influential to the electric field intensity both in the tip and on the surface of the water tree that they may play important roles both in water tree inception and growth and in the morphology of water treeing.
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    ABSTRACT: A three-dimensional computation of the electric field and breakdown voltage in power cable insulation containing water trees and space charges is presented. The breakdown voltage and the conductivity of cylindrical samples of cable insulation containing water trees were measured. The samples have been aged in wet environment under ac voltages of frequencies comprised between 1 and 5 kHz. Exponential and parabolic spatial variations of permittivity and space charge density and the electrostatic, electro-kinetic and quasi-stationary regimes of the electric field were considered. The best correlation between the experimental breakdown voltage and the calculated one has been obtained in quasi-stationary regime.
    Journal of Electrostatics 04/2013; 71(2):145–154. DOI:10.1016/j.elstat.2012.12.041 · 1.27 Impact Factor
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    ABSTRACT: In this paper, the distribution of the electric field in the polyethylene insulation of a medium voltage power cable is computed in the absence and in the presence of water trees and space charge. The computations are made in variable regime, from the voltage switch-on up to one hour of application of the electrical stress. The water trees are considered of semi spherical shape and of known permittivity and conductivity. The conductivity and the characteristics of the water trees are determined experimentally. The influence of the dimensions of water trees and of the associated space charge layers (length and charge density) are analyzed in terms of local values of the electric field and of reduction of the cable breakdown voltage. It is shown that, for a water tree of given length, the probability of insulation breakdown reaches its maximum for a given ratio between space charge density and length of the space charge area.
    IEEE Transactions on Dielectrics and Electrical Insulation 10/2013; 20(5):1530-1539. DOI:10.1109/TDEI.2013.6633680 · 1.23 Impact Factor