الفهرس 
Chapter 1 IntroductionOnly 14 pages are availabe for public view
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Abstract
A severe short circuit between two different voltage transmission lines may have occurred when two or more overhead transmission circuits having different voltages exist in the same area and intersect with each other. This may cause enormous failure to the utility equipment on the lower voltage circuits due to the resulting transient overvoltage. In the Egyptian electric network, the intersections of (220 kV and 66 kV) and (500 kV and 220 kV) transmission lines have happened many times in different power plants. So, it is important to study the impact of this new transient overvoltage effect on the power system. The study is to analyze and evaluate the impact of this overvoltage on the transmission lines, low voltage side power transformers, and other system components, system voltage and monitor the effect of the resulting current on all protection devices. This study is implemented via a real power system which is the DAMEITTA power plant and introduces an electrical analysis via various simulations, first the system is simulated in the normal condition and the results had been compared with the real results to be verified. Secondly, the fault is applied and analyzed via voltage and current waveform amplitudes for each system component which gives important information about the excessive overvoltage behavior effect on the system and the lower voltage side power transformer. The study is carried out using PSCAD/EMTDC.A proposed methodology is introduced to protect the power transformer on the lower voltage side from this kind of transient overvoltage conducive to full damage to the transformer. The proposed methodology relies on the combination of the sequence components of the currents from both sides of the transformer to detect the flow direction of the current to identify the status form of the transformer. Moreover, it uses the voltage measurements of the lower voltage side to detect the resulting overvoltage. The magnitude and phase angle of current measurements are computed using Fast Fourier Transform (FFT). from the principle of reliability, the proposed methodology had been tested for security and dependability in more different cases of the power transformer such as inrush current phenomena, overexcitation, CT saturation, and internal faults. Also, for the system disturbance cases such as overvoltage conditions, different types of external faults, and overvoltage which leads to an internal fault because of transformer insulation.