Physical Background Of Space Charge

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Overview This chapter is divided in to two parts; the first part is reviewing the physical background of space charge, while the second part is reviewing some previous models that were proposed to calculate space charge under HVDC. Space charge One of the properties of insulation material under HVDC is their tendency to accumulate space charge; this is due to allowing weak electrical conduction by these materials [18]. The charges which are flow within insulation may be non-uniform due to non-homogeneity of the material [12]. Therefore, based on continuity equation, when the flow of charge particles into a region is different with the charge particles out of that region, charge would be accumulated with duration of time [1, 12]. ∇.J=(-∂ρ)/∂t (2.1) Where: J= Current density (A/m2) ρ = Electric charge density (C/m3) Furthermore, according to the Gauss’ Law, electric field distribution is highly affected by space charge which is clear in equation 2.2 [19]: ∇.E=ρ/(ε_0 ε_r ) (2.2) Where ε_"0" is the vacuum permittivity and εr is the relative permittivity of the material. Therefore, when the space charge present in insulation material, the value of electric field would be equal to summation of two contribution fields which are space charge field and external applied field (Laplacian field) [19, 20]. E ⃗=(E_0 ) ⃗+ (E_ρ ) ⃗ (2.3) ... ... middle of paper ... ...MW theories, the dynamic model (DM) has been proposed by Leroy [27] which is a computer simulation for calculating the interfacial charge for XLPE/EPR sandwich system. Oppositely with NMW, the DM model focused on microscopic approach to reproduce the charge transport in XLPE/EPR sandwich system. After comparing the results of NMW and DM, they found that accumulated charge at the interface which calculated by DM is higher compared to NMW and it is better reproduced with the experimental result [27]. Furthermore, in [28], the estimation of electric field distribution and interfacial charge between XLPE and rubber has been described at different value of temperature using COMSOL software. They found that, the interfacial charge between these two dielectrics changes between positive and negative, due to the variation of field and temperature dependencies on conductivity.
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