<span>The use of solar energy may replace the present fossil fuel or gas to produce electricity. The goal of this study is to set up a simulation model to survey the performance of a photovoltaic thermal system (PV/T) based on the computational fluid dynamics (CFD) method. Ansys fluent software has been used for the simulation procedure. The electrical panel output and its efficiency were investigated numerically. In addition, the effect of variations in absorbed radiation on inlet fluid and absorber panel temperature on the system performance was investigated. The study was conducted for three cases, in a first case, where there is no refrigerant in the system and in the latter case, at constant fluid rate of the pump, whereas the third case with optimal pump operation. The numerical findings obtained from CFD simulators have been compared with the test records of the experimental results of the literature. The two results have a good agreement. From the obtained results, it can be noted that the system shows a good improvement for the electric net efficiency level of 3.52% with a lower reduction of the thermal system efficiency of 1.96% in comparison to the system when using the constantly high flow rate.</span>

With the wide spread of transmission lines and distribution networks, there is a higher exposure to magnetic fields generated by those lines, leading to more cases of human health impacts. The aim of this paper is to conduct a comparative analysis of magnetic field levels in the vicinity of a three-phase overhead line, which mounted on a steel lattice and a reinforced concrete columns. The analysis includes the influence of the change in phase position of all currents, both in low and medium voltage system of the considered mixed lines. Emphasis have been consented on investigate the influence on distribution of magnetic fields of the currents induced in the ferromagnetic and conductive parts of the columns. The mathematical calculations were conducted numerically by using "COMSOL"Multiphysics software package, which is based on application of the finite element method, on twodimensional mixed lines model. The obtained results indicate that the intensity of magnetic induction vector decreases in the area around the columns due to the induced currents in ferromagnetic conductive parts of columns. This phenomenon is more pronounced in steel lattice columns, while it is less pronounced in the reinforced concrete columns.

The aim of this paper is to conduct a mutual comparison of switching energy losses in cascade gallium nitride (GaN) and silicon "super junction" MOSFET” transistor, in both cases designed for a maximum operating voltage of (650 V). For the analysis of switching characteristics of transistors used double pulse test method by using detailed SPICE simulation model. Data on transient on and off processes were generated using the “LTspice” simulation package in a wide range of drain currents with two different gate resistance values of the tested transistors. The total energy losses in the GaN have been simulated during one transistor at (on and off cycle). The obtained results indicate that the superior switching characteristics of GaN devices for a drain current of (30 A) is five to eight times less than the switching characteristics of silicon “MOSFET” transistor when compared to silicon components, especially during operation of transistors with high drain currents.

A B S T R A C TThe electric power transformers are very important part of the modern electric power and transmission line network systems. They are a high level source of the electromagnetic fields which can effect the workers health in the station. In this research, an electric and magnetic fields are generated due to the operation of the substation power distribution of 132/33 kV that investigated in order to avoid the workers overexposure these fields workers. This research has two phases a mathematical calculations and practical measurements. The intensities of the electric and magnetic fields have been measured at a substation using EMF tester device. The safe zones around the dangerous equipment have been determined. A comparison between the obtained results and the standard safety guideline limits has been done and the comparison results shows that they are within the acceptable limits.

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