Current flow at the interface of copper and polyethylene in high-voltage apparatus / Mohammed Ahmed Elshahat Abosaleh ; Supervised Hussein I. Anis , Ahmed A. Huzayyin

Thesis (Ph.D.) - Cairo University - Faculty of Engineering - Department of Electrical Power and Machines

Computational quantum mechanics in the framework of density functional theory (DFT) is used to develop the interface model between Cu (111) and PE (001). The 2bulk plus band line up3 method and the projected density of states (PDOS) analysis are combined to calculate the actual barrier to charge injection. This combination of methods lead to finding new states appearing between the Fermi level of Cu and the conduction band of PE, which lowered the barrier to electrons injection. These states are due to morphological deformation that takes place in both the metal and the polymer at the interface. The most common chemical impurities that are normally found in PE are studied in this thesis to understand their impact on conduction mechanism. These impurities, such as carbonyl, vinyl, and conjugated double bond, produce trap states between the conduction and valence bands of PE, which reduce the barrier height to around the experimental value of 1 eV. The lowered barrier height increases the charge injection, which then facilitates the conduction mechanism. Variations in the dielectric constant at the interface are also a significant factor. The present study investigates the change in dielectric constant of PE at the interface with Cu using the microscopic polarization theory. It is concluded that the calculated current density using Schottky injection mechanism under a certain electric field and temperature does not only depend on the barrier height, but also on the relative dielectric constant at the interface, which in turn changed the current density and the conduction process

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