فصلنامه مهندسی و مدیریت انرژی
سال نهم شماره 4 (پیاپی 34، زمستان 1398)

Low-impedance transformer ground differential relay is a part of power transformer protection system employed for detecting the internal earth faults. This is a fast and sensitive relay, but in some situations such as external faults and inrush current conditions, it may be exposed to maloperation due to current transformer (CT) saturation. In this paper, a new intelligent transformer ground differential relay based on probabilistic neural network (PNN) is presented. To do so, a real power transformer is simulated under a large number of different operating conditions, including internal fault, external fault, and inrush current by using PSCAD/EMTDC software. Then, one cycle data of differential current obtained from each simulation case of mentioned operation conditions is used to provide exemplar patterns. Then, a probabilistic neural network is trained using them. Finally, the trained network is employed as a detection core of the new relay. A comparative evaluation proves the absolute superiority of the proposed method in comparison with some other methods regarding its immunity against maloperation.

In this paper, a new structure of axial flux switched reluctance motors (AFSRMs) is proposed. Different combinations of rotors and stators affect motor torque and its performance. In this regard, changing the stator structure of the AFSRM leads to better results for torque and magnetic flux. The advantages of the proposed structure are short flux path, segmental rotor with improved flux density. The main geometrical, electrical, and physical characteristics of the proposed structure are presented. Then, the proposed structure is modified by using a higher number of rotor segments than the reshaped stator modules. The proposed structure can be an appropriate candidate for electric vehicles (EVs) and hybrid electric vehicles (HEVs). The results reveal that the proposed and the modified motors deliver the same torque with 36.5% and 46.7% lower active material mass, respectively in comparison of the reference motor. The performance comparison of the selected motors has been investigated by using Quasi-3D analysis.

Nowadays, there has been an increasing interest in transformerless inverter for grid-connected photovoltaic (PV) systems due to low cost, high efficiency, and light weight. One of the factors in describing a grid’s behaviors is the capability of reactive power control by the inverter. According to the standard VDE-AR-N 4105, the grid-tied PV inverters of power rating below 3.68KVA should attain power factor (PF) from 0.95 up to 0.95 lagging. Thus this paper presents a new topology with the ability to eliminate common mode leakage, to control reactive power, and to correct power factor. The generation and extinction of this current is analyzed. It is worth saying that none of the open loop structures presented so far can control the reactive power individually without any controllers. Therefore, here a new approach based on proportional – resonant controller with fast response-- is described. Simulations, done with the active load and RL load, show the excellent performance of the proposed algorithm. Then, a proposed inverter with 98 % efficiency is compared with H5, H6 and HERIC inverters.

This paper addresses the improvement of active and reactive power control in a multi-machine system using battery energy storage system, frequency control, and voltage regulation simultaneously. In the proposed method, each wind unit is equipped with an exclusive storage unit with a control system. This method for battery energy storage system includes two decoupled control loops-- one loop for active power control and the other loop for the reactivation of power control. In addition, there are two supplementary control loops for frequency control and voltage regulation in the rotor side converter of each generator. Besides, the proposed control strategy, here, optimally tunes all the parameters of controllers have been optimized simultaneously by utilizing a mixed integer nonlinear optimization programming by ICA and GA algorithm. The simulation results carried out from MATLAB software show the effectiveness not only of the proposed control scheme in utilizing battery energy storage system in the control of the active and reactive power of the wind assortment but also of the strategy in balanced and unbalanced conditions of the networks.

One of the barriers in implementing energy efficiency projects in residential buildings is financing limitation. Financing of such projects requires more complex financial structures due to their multilateral nature, and it can be realized through capital market. In this study we introduce some financial instruments for financing of energy efficiency projects in the context of Iran capital market by thematic analysis. The statistical population of the study consists of literature about financing in energy efficiency market. After examination of literature, 41 resources were selected as samples. The reliability of the results is 0.903 according to Holsti' POA. The results show that the related contents of financing of energy efficiency can be themed in four categories: institutional structures, role of public sector, contractual structures, and financing models. Finally, the financing model of energy efficiency projects in residential buildings is extracted based on obtained thematic networks and result deduction.

This paper proposes a novel method for site selection of large-scale photovoltaic (PV) power plants using the geographic information system (GIS) and multiple criteria decision making (MCDM). In the proposed method, by consideration of the different constraints and limits such as natural and artificial barriers, the feasible area is decreased in comparison to the whole area. The several important criteria and indices, including solar irradiance, apparent dip, and electrical characteristics are introduced to site selection of PV power plants. The priority and importance of any introduced indices are determined based on experts’ opinions and through using the analytic hierarchy process (AHP). Finally, through the use of techniques for order of preference by similarity to ideal solution (TOPSIS) and the GIS weighed overlay technique, the suitability, and the priority of the different sites regarding PV power plant capabilities are evaluated. Karbala province in Iraq has been selected as an actual cases study. Although, Iraq has a significant capability for PV power plants, but the technical and economic feasibility studies and site selection have not been performed yet. Hence, applying the proposed method to this case study would be interesting and useful based on practical purposes.

The environmental pollution crisis caused by the excessive use of fossil fuels and the risk of the destruction of natural resources and reserves, as well as the excessive production of greenhouse gases and, consequently, global warming, led many energy researchers to use renewable energy As a fossil fuel alternative. Solar chimneys are one of the types of renewable energies that have been taken into consideration by researchers over the past decade. Solar chimney power plants are such plants which include solar collectors, chimney and turbines that are placed at the entrance of the chimney. The aim of this study is numerical modeling of a solar chimney power plant prototype model built in Tehran University and investigation of the affecting parameters on enhancement the air velocity within it. The two dimensional numerical modeling based on finite volume method is conducted using  standard wall function turbulence modeling through an optimum mesh. The numerical results show good agreement with experimental data with maximum 6 percent difference in magnitude. Comparing with similar studies, modeling the power plant without using the energy storage properties of the earth by using constant heat flux on the collector regardless of the environmental radiation conditions has been conducted in the present research. The results show that increasing the chimney height, collector radius and collector height and decreasing the radius of the  chimney would result in increasing 76 percent in air velocity through the chimney (from 1.7 m/s in the experimental model to 3m/s) and consequently improving the model efficiency. Furthermore, among the effective parameters, collector and chimney radius play greater roll on increasing the air velocity through the chimney. The results of this research may play significant role on optimizing the constructed solar chimney power plant model.

The water consumption of steam power plants is one of the big challenges in the world. One of the suggested methods for reducing water in these power plants is the utilization of forced dry cooling tower. However, these types of cooling towers are dependent on weather conditions and reduced power plant efficiency. One way to solve this problem is to downfall water on it during hot hours. In this article, the forced dry and cooling towers are studied analytically. Then, with the consideration of characteristics of a power plant, the size and characteristics of dry and wet cooling towers are computed according to design temperature. These results are compared with experimental data and wet cooling towers of a power plant, and their accuracy has been verified. Only at temperatures higher than the design temperature is water falling on the tubes and fins of cooling tower. Using data from the weather station of power plant location, the numbers of hours when the ambient temperature has been higher than the design temperature are calculated and water consumption is computed. Calculations show that for a power plant of 320 MW at design temperature of 30°C, ninety seven percent (97%) of the water consumption can be saved. The loss of power output due to the use of dry cooling tower electric fans and pumps is 3.93 percent of output power.

In this study, a new configuration of heat pipes as Heat Pipe Network is introduced. Here, the heat pipe network is designed, constructed, and put under the performance assessment. This heat pipe network consists of 4 vertical heat pipes connected to evaporator collector from bottom and condenser collector from top. In order to investigate the effect of nano-fluids on the thermal efficiency and thermal resistance of heat pipes network, copper oxide nano-fluids were prepared using a two-step method. Heat pipe network with 50% filling ratio water and copper oxide nano-fluid as working fluid was tested under different heat loads. It is found that the total resistance of heat pipe network using copper oxide nano-fluid with volumetric concentrations of 1%, 3%, and 5% --mixed with water as working fluid-- is reduced to 0.95, 0.84, and 0.75, respectively in comparison with dionized water. Moreover, for 5% volumetric concentration of nano-fluid, thermal efficiency exceed to 80%.

The aim of this study is to investigate the performance of a gas turbine cycle equipped with a Stirling engine from the thermodynamic point of view. In this system, a part of the heat loss from the gas turbine is transmitted to a Stirling engine to generate more power. In the analysis of the proposed system, the governing equations of the hybrid cycles are modeled in MATLAB software and Schmidt, and ideal adiabatic models are used to solve the Stirling engine. In the analysis of the hybrid cycle, the compressor pressure ratio and turbine inlet temperature are considered as two Important and effective parameters. The results show that reducing the compressor pressure ratio and increasing the turbine inlet temperature improve the performance of the Stirling engine. The results indicate that the use of the hybrid gas turbine cycle and the Stirling engine will increase the power of the gas turbine from 268 kW to 468/6 kW, based on the Schmidt model, and 457/3 kW, based on the ideal adiabatic model. Also, the electrical efficiency of the system increases by 18/1%, based on the Schmidt model, and about 17/1%, based on the ideal adiabatic model.