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). 01/1997; 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: This paper presents an experimental study regarding the variation of permittivity and loss factor of power cables polyethylene insulation, due to the change of the frequency (f<sub>a</sub>) and the duration (τ) of the applied electrical field. The experiments were performed on XLPE flat disc samples from a medium voltage cable insulation. The samples were aged in an electric field of E = 4 kV/mm and f<sub>a</sub> = 3-5 kHz in the presence of a NaCl solution (0.1 mole/l) for a period τ = 24-96 hours. After ageing, water trees density and dimensions (lengths and diameters), the real and imaginary parts of the permittivity and loss factor were measured. The results show that the all quantities increase with f<sub>a</sub> and τ and the permittivity and loss factor increase with the decrease of the measurement frequency.
    Solid Dielectrics (ICSD), 2010 10th IEEE International Conference on; 08/2010
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    ABSTRACT: Under the action of an electric field and in the presence of water, water trees develop inside power cables insulations. Regardless of their type, shape or dimension, water trees contribute to the worsening of electrical properties, especially lowering the inception voltages of partial discharges and electrical trees leading to breakdown [1]. In this paper an experimental study regarding the variation of permittivity and loss factor of the polyethylene with the frequency (f<sub>a</sub>) and the duration (τ) of applied electrical field is presented. The experiments were made on flat XLPE samples sliced from a power cables insulation. The samples were subjected to an electrical field with the intensity E = 4 kV/mm and frequencies f<sub>a</sub> = 3 and 5 kHz for τ = 48, 72 and 96 hours. After ageing the water trees dimensions (length l<sub>wt</sub> and diameter D) and concentration c<sub>wt</sub> were measured. The permittivity (ε<sub>r</sub>) and the loss factor (tgδ) were measured (using a NOVOCONTROL dielectric spectrometer) at the temperature T = 30°C and frequency f<sub>m</sub> = 10<sup>3-</sup>-10<sup>6</sup> Hz. The results show that with the increase of ageing time or the ageing frequency all the quantities c<sub>wt</sub> l<sub>wt</sub> D, ε<sub>r</sub> and tgδ increase, too.
    Advanced Topics in Electrical Engineering (ATEE), 2011 7th International Symposium on; 06/2011
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    ABSTRACT: A study on the influence of water trees in polymeric insulations for a point–point geometry is presented. Using an adequate numerical method we were able to calculate the electric field distribution: the variation of the maximum electric field is considered as a function of the water tree length and permittivity. In laboratory, we obtained the partial-discharge inception voltage (PDIV) as well as the pre-breakdown voltage (PV) and we observed the alteration of the breakdown paths induced by the PE degradation. We also found a good correlation between these experimental results and the calculated distribution of electric field. Both experimental and computational results provide interesting knowledge about the effect of water treeing in polymeric insulations.
    Journal of Electrostatics 01/2000; · 1.00 Impact Factor