In this study, the improvement of the turbine performance of Savonius, one of the vertical axis wind turbines, was carried out numerically. The numerical approach used in the improvement studies was supported by experimental results and was confirmed. Within the scope of this improvement, a wind collector was placed in the turbine front zone to decrease the negative moment on the counter-rotating blade of the Savonius turbine. To obtain the highest turbine performance, all of the changes in the design parameters of this wind collector, such as the wind inlet width, wind outlet width, collector length, and collector height, were examined, and ideal design parameters of the collector were specified. The geometric parameters of the investigated wind collector were taken depending on the circular dimension of the Savonius turbine used. Unsteady simulations for different geometric parameters using the sliding mesh approach were performed in the CFD program. According to the numerical analysis results, the power-coefficient of the conventional turbine was increased to 0.23 levels by using the wind collector with the ideal geometric parameters. Thus, with the use of a wind collector, the power coefficient of a conventional Savonius wind turbine was improved by about 54%.

Wind farms are often located in regions with high keraunic levels. The high rate of lightning occurrence together with the high resistance of the soil can negatively affect wind farms or individual wind turbines. Therefore, a proper protection system against direct lightning strokes is essential for wind farms. In this paper, by modeling the wind farm in EMTP software, the protection of the collector cable network of wind farms against direct lightning strokes is investigated. To do that, the metallic sheath of the Collector cable and sheath bonding are modeled in the EMTP environment, and the overvoltages on the collector cable caused by direct lightning strokes to wind turbines are calculated. Also, different topologies of wind farms are considered to determine the effect of wind turbine arrangements on lightning protection of collector cables. To this aim, the best method to protect against direct lightning strokes is selected by implementing different sheath bonding methods in collector cables. Then, various sheath grounding methods and grounding systems are examined. Finally, the proper protection scheme to protect the wind farm collector cable against direct lightning strokes is proposed owing to the wind turbine topology.

In an effort to boost the aerodynamic performance of vertical axis wind turbines (VAWT), a half-airfoil wind collector structure is proposed, inspired by the contour shape of NACA airfoils. To explore the influence of the half-airfoil wind collector on the performance of VAWTs, an optimization design of the half-airfoil wind collector structure is conducted using the Design of Experiments (DOE) method. Based on the NACA0021 airfoil, simulations of computational fluid dynamics (CFD) are used to examine the instantaneous torque, power coefficient, overall torque, and dynamic flow field of the VAWT blades under the influence of the half-airfoil wind collector. The findings reveal that the half-airfoil wind collector has a good wind-collecting effect, effectively guiding the airflow to concentrate on the blades, increasing the local airflow velocity over the blades, and strengthening the differential in pressure between the blades' inner and outer surfaces. This results in an increased torque on the blades and lessens losses related to the enlargement and detachment of dynamic stall vortices. Consequently, the power coefficient of the VAWT is augmented within the scope of high tip-speed ratio. Specifically, When the tip-speed ratio is 3. 08, with geometric parameters of x = 0, d = 29c, α = 5°, and the NACA0021 contour, the highest power coefficient reaches 0. 59, showing an improvement of 55. 8% over the standard VAWT. When the tip-speed ratio rises, the half-airfoil wind collector maintains a high power coefficient and torque coefficient, demonstrating that it enables the VAWT to operate more efficiently at higher rotational speeds, thus expanding the operational range.

Considering problems associated with nonrenewable fuels such as pollution and high cost, efforts are being made to develop use of renewable energy sources like solar energy. Solar collectors could often be employed as important devices for thermal applications. Unglazed Transpired Collector (UTC) is a modern preheating and heating equipment used for ventilating air or drying crops. Heat transfer in the UTC is accomplished by passing air through holes of the unglazed collector. In this study, the effect of wind stream parallel to the collector surface on its performance is investigated using numerical techniques. The study is based on total energy balance where new equations are incorporated in order to consider the wind effect. The results show that increasing the wind velocity may decrease or increase the collector efficiency depending on the incoming air approach velocity. This is due to opposite effects of wind and radiation heat losses with convection heat transfer from collector surface to inlet air. Moreover, the heat exchange effectiveness increases with increasing the wind velocity for any approach velocity.

In this study, the effect of wind speed on the energy and exergy efficiencies of the LS-2 parabolic trough solar collector have been studied. The wind speed on the reflector and receiver has been considered between zero and 27 m/s. Three working fluids of Therminol VP-1, Syltherm 800 and Dowtherm A have been used. The inlet temperature of the working fluid and volumetric flow rate are assumed to be in the range of 300-650 K and 50-600 L/min, respectively. In order to solve the governing equations, a developed thermal model in the engineering equation solver has been used. The results showed that at the inlet fluid temperature of 650 K and volumetric flow rate of 50 L/min, if the wind speed increases to 27 m/s, the energy efficiency decreases using Therminol VP-1, Syltherm 800 and Dowtherm A are 0. 87%, 1. 16% and 0. 85%, respectively and the exergy efficiency decreases are 0. 88%, 1. 18% and 0. 86%, respectively. Also the results showed that the variations of energy and exergy efficiencies for wind speeds greater than 10 m/s are negligible. The results indicated that although wind speed increase has little effect on the energy and exergy efficiencies of the collector, but the rate of these decreases are comparable with the rate of efficiency increases observed in previous studies using different efficiency enhancement strategies such as turbulators and nanofluids, so wind speed is important. The performance evaluation study revealed that using Therminol VP-1 and Dowtherm A are more suitable than Syltherm 800 to be used as working fluids in parabolic trough solar collectors

Distance relays calculate the path impedance between the fault point and the relay location by sampling the voltage and current at the relay location. By using the ratio of the impedance estimated by the relay to the impedance of the line where the relay is installed, the location of the fault can be estimated by a distance relay. However, several factors influence the estimated impedance and proper operation of distance relays. The most important of these factors is the resistive fault occurrence, which results in an increase in the impedance and deviation of the impedance estimated by the relay as well as causes relay under-reach. Therefore, in the present study, an adaptive method is proposed to modify the protection zones of distance relays settings under different operating conditions and resistive single-line-to-ground (SLG) fault occurrence. Furthermore, the adaptive distance protection of transmission lines, wind farm collector lines and the protection coordination of the relays in these lines are investigated. In this method, an adaptive coefficient is added to the conventional characteristics of distance relays to improve the accuracy and coordination. The proposed adaptive method can also maintain the coordination of different protection zones of primary and backup relay pairs. In addition to analytical verification, the numerical results obtained from simulation show the efficiency of the proposed method. The proposed method is implemented on a power system with transmission lines and wind farms and simulated in MATLAB/Simulink environment.

This paper deals with the performance of a heat pipe solar collector. The solar collector consisted of an interconnected heat pipe so as to reduce the production cost by using an interconnected heat pipe because all the heat pipes can be evacuated, sealed and tested at once. Performance of a prototype of the heat pipe solar collector was experimentally examined, and the results were compared with those obtained through theoretical analysis. The results shown in this paper seem feasible.

In this paper, a novel risk-based, two-objective (technical and economical) optimal reactive power dispatch method in a wind-integrated power system is proposed which is more consistent with operational criteria.  The technical objective includes the minimization of the new voltage instability risk index. The economical objective includes cost minimization of reactive power generation and active power loss. The proposed voltage instability risk employs a hybrid possibilistic (Delphi-Fuzzy)-probabilistic approach that takes into consideration the operator’s experience, the wind speed and demand forecast uncertainties when quantifying the risk index. The decision variables are the reactive power resources of the system. To solve the problem, the modified multi-objective particle swarm optimization algorithm with sine and cosine acceleration coefficients is utilized. The method is implemented on the modified IEEE 30-bus system. The proposed method is compared with those in the previously published literature, and the results confirm that the proposed risk index is better at estimating the voltage instability risk of the system, especially in cases with severe impact and low probability. In addition, according to the simulation results compared to typical security-based planning, the proposed risk-based planning may increase the security and economy of the system due to better utilization of system resources.