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Öğe Calculation of electrical field of spherical and cylindrical gas voids in dielectrics by taking surface conductivity into consideration(Emerald Group Publishing Ltd, 2005) Alisoy, GT; Alisoy, HZ; Koseoglu, MPurpose - To determine the electrical field E-1(t) in spherical and cylindrical gas voids existing in an insulator by considering surface conductivity of gas voids having an electrical permittivity of epsilon(1) and conductivity of gamma(1) for DC and AC situations. Design/methodology/approach - Analytical expressions satisfying Laplace equation for inside and outside of the cylindrical and spherical gas voids in an insulator located in an external electrical field having a definite time dependent character, have been derived by considering the surface conductivity of the gas void. The coefficients included by these analytical expressions have been determined by utilizing the continuity equation of the current on the surface of the voids. Findings - It has been demonstrated that the electrical field remains uniform in spherical and cylindrical gas voids when the surface conductivity of gas void has been considered. It has been determined that the contact charging process of different shaped particles has an exponential characteristic, and some expressions have been derived to determine the time constants of this process for practical purposes. Practical implications - The results have been applied to the problems about contact charging of semi-spherical and semi-cylindrical insulated particles located at a charged surface and problems about the calculation of onset discharging voltage of ionization process in dielectric including gas voids. Originality/value - For spherical and cylindrical gas voids, the onset discharging voltage corresponding to the ionization process occurring in gas voids has increased by increasing the surface conductivity of the void. For the limit value of the surface conductivity, the voids in the insulator behaves like metal particles distributed into the insulator, for this reason, at the outside of the void, especially in the regions where the voids are close to the electrodes and each other, the electrical field will be non-uniform and will increase. This situation will cause the ignition of the partial discharge and destroy to the insulator.Öğe Charging kinetics of spherical dielectric particles in a unipolar corona field(Elsevier Science Bv, 2005) Alisoy, HZ; Alisoy, GT; Koseoglu, MIn this paper, we investigate the charging of spherical dielectric particles in an electric field and unipolar volume charge. A differential equation expressing the charging process is derived and solved numerically using a modified Euler method. The results obtained allow one to determine the charge on the particle for arbitrary values of the particle's radius and permittivity as well as the electric field intensity and surrounding volume charge density. These parameters all influence the charging process considerably. We demonstrate that a stationary particle acquires less charge than a rotating particle. (c) 2005 Elsevier B.V. All rights reserved.Öğe Combined kinetic charging of particles on the precipitating electrode in a corona field(Iop Publishing Ltd, 2004) Alisoy, HZ; Alisoy, GT; Hamamci, SE; Koseoglu, MIn this paper, we give the results of the theoretical study concerning the combined kinetic charging of the particles on the precipitating electrode in a corona field by taking into account contact charging. We derive some mathematical equations that allow us to determine the limit charge values on the particles and the charging kinetics of the particles. It has been demonstrated that the limit charge value on the particle can be less than the value calculated using the Pauthenier theory. In the case when the time constant ratio of contact and field charging mechanisms is equal to the ratio of the maximum charges of these charging mechanisms, we find that the sign of the limit charge on the particle has changed.Öğe Internal ionization process in polymer dielectrics in strong electrical field(Elsevier Science Bv, 2004) Alisoy, GT; Alisoy, HZ; Rustamov, SA; Arkan, MIn this paper, the effects of internal ionization process, which occur in the voids under strong electrical field, on the polymer dielectrics degradation with time are analyzed. Theoretical equations have been derived for partial discharge V-I characteristic, voltage and discharge current variation with time in the discharge channel, discharge channel cross-section area variation with time and voltage, and channel expansion. The results have shown that approximately 21% of released energy is used for channel expansion and similar to3% of released energy is used for atom ionization when resonant emission and heat transfer are ignored. Effect of discharge impulses on the surface of dielectric for different pi values has been compared. (C) 2003 Elsevier B.V. All rights reserved.Öğe Physicomathematical analysis of surface modification of polymers by glow discharge in SF6+N2 medium(Elsevier, 2005) Alisoy, HZ; Baysar, A; Alisoy, GTIn this paper, surface modification of dielectric polymers, having different physical and chemical properties (polyimide-PI, polystyrene-PS, Polyethylene terephthalate-PET), treated in contourized glow discharge in SF6 + N-2 gas medium near cathode was studied. The electret state, formed as a result of modification, caused an increase in the surface energy. Surface charge densities and contact angles of dielectric polymers whose surfaces were activated under identical conditions, were measured. Upon activation, formation of electret state on the dielectrics strained the sessile drop and consequently the contact angle changed. A mathematical model relating the contact angle and the surface charge density was derived. Experimental results agreed well with the theoretical model. (c) 2005 Published by Elsevier B.V.
