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Directional overcurrent relays utilize the voltage phasor as a reference for determining the direction of the fault. This requires measuring both current and voltage and makes the directional overcurrent relays more costly than the non-directional type. In this paper, a new method for detection the fault occurrence and fault direction is proposed, that is based on Teager energy operator. Teager energy operator is a simple algorithm that is used to signal processing and extraction of instantaneous changes in amplitude and frequency of a signal. To this end, the proposed algorithm uses only three consecutive samples of measured current signal for detection of fault and its direction. This method does not require phasor estimation and complex calculations. In addition, the method is very fast. This Algorithm is implemented and verified for different types of fault and several conditions using Matlab/Simulink. The simulation results show that the proposed method is fast and has acceptable accuracy. [ABSTRACT FROM AUTHOR]

In this paper, a new single-stage power factor correction (PFC) converter is presented. In the input stage of this structure, a buck converter is used to correct the power factor. So, the voltage stress of bulk capacitor reduced, and one of the main problems in the single stage PFC converters is solved. Moreover, by employing a compensator circuit, the input current dead angle which is the main drawback of the existing buck type PFCs is obviated, thus the total harmonic distortion is very low. In converters with buck PFC, input current dead angle results in high THD. In the proposed converter, using an inductor coupled with the main transformer, this problem is solved. A part of input power is transmitted directly to the output that helps to improve efficiency. The proposed converter is analyzed and the validity of the proposed solution is proven in the form of theoretical analysis, simulation and practical results. [ABSTRACT FROM AUTHOR]

With the Penetration of renewable energies into power system, the influence of uncertainties in solving various problems in the field of power system operation has increased. One of the most important concepts in this field is optimal power flow, which, with the presence of uncertainties, cannot be modeled by definite methods, and should be revised based on applying the probabilistic approaches. In this paper, numerical methods including the Monte Carlo Simulation method and analytical methods including point estimation methods, internal point method and unscented transformation method are used to solve the POPF in an IEEE-118 bus system. The obtained results indicate that the methods based on point estimation are able to find the optimal points in less computational time than other techniques. This is mainly due to the limited points, which these methods need as the starting points. From another perspective, the magnitude changes in the voltage profile of the generation units are also more stable in the internal point method. Furthermore, in terms of the convergence rate, the internal point method is much faster than the Monte Carlo Simulation method. [ABSTRACT FROM AUTHOR]

In this paper, the effect of surface charges and pollution on flashover voltage of polymeric insulators under DC voltage have been investigated and analyzed. For this purpose, four types of polymeric insulators with different profiles have been selected and then experimental tests of DC flashover voltage have been performed. According to the obtained results, with increasing pollution in presence of positive surface charges flashover voltage reduce, but negative charges increase it. Also in this paper, a model based on geometric parameters including specific leakage distance, shed spacing to shed depth ratio, amount of surface charges and pollution is proposed using an artificial neural network. The comparison of the obtained results from experimental tests and ANN model show that the results of ANN are consistent with experimental tests. [ABSTRACT FROM AUTHOR]

In this paper, a multi-objective function is proposed for optimal placement of the capacitors in radial distribution networks considering the effect of harmonics. In addition to the voltage profile, active losses and installation cost, the resonant phenomenon caused by the harmonics is also included in proposed objective function. The PSO meta-initiative method has been employed in order to optimize the function. A novel approach has been introduced to analyze the harmonic load flow in distribution networks. The proposed method is based on four matrices that are constant during the load flow. Therefore, in this method, the repeater counters and the harmonic frequencies are the only variables. Due to the elimination of backward-forward sweeps in this approach, the calculations are fast and accurate. This method has been implemented on a standard 14-bus system and a real power distribution network in Lorestan province, Iran. Simulation results confirm the accuracy and speed of the proposed load flow method as well as the effectiveness of the proposed method for optimal placement of the capacitors in the harmonic polluted networks. [ABSTRACT FROM AUTHOR]

Nowadays distributed generation has been given considerable attention due to the increase in energy consumption and the need for using renewable energies. So, the concept of the micro grids for connecting and coordinating different distributed resources via the local power control systems has been introduced. A micro grid connects to the network at normal condition of the operation but in order to increase the system reliability and to promote the generated power quality to feed the sensitive loads, they can operate in the islanding mode too. In the islanding mode of operation in order to supply the whole load and to maintain the balance between the supply and demand, these resources use the conventional droop methods. Generally, using the conventional voltage droop control due to the difference in the impedance of the feeder connect to the resources and also the asymmetrical nature of the network, dose not lead to an appropriate reactive power sharing between the resources. In fact, using conventional droop control creates an intrinsic compromise between the accuracy of reactive power sharing and voltage regulation of micro grid buses. Therefore, in the proposed method of this paper, the coefficients of the voltage droops characteristics of the grid resources are determined by solving an optimization problem using the genetic algorithm (GA). Also in order to improve the reactive power sharing, a novel control strategy based on the adaptive virtual impedance is presented. In this method the ideal reactive power sharing is achieved by using the virtual impedance and compensating the voltage drop of the lines. The virtual impedance setting is done through the data of the voltage of PCC bus in microgrid and sending via a low bandwidth communicational link to the local controller of each resource. The proposed method is robust against the network structure changes, presence of local loads, and interruption in the communication link. Simulation results show the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

This paper presents a new approach for islanding detection based on fast STransform, in distribution networks with distributed generators. In this method, at first, S-Transform of voltage and current at point of common coupling are calculated; then, features of normal and islanding operation are extracted using S matrix and frequency contours. The features are extracted using several simulations; considering load switching, motor load switching, transient faults, and islanding conditions with different power mismatches for local load. Finally, support vector machine has been proposed for classifying the extracted features to detect the islanding. For more studies, a distribution system is simulated using PSCAD/EMTDC and feature vectors corresponding to different situations of islanding and normal operation are extracted and used for training and test of support vector machine classifier. To evaluate the performance of proposed scheme, the obtained results are compared with results of other methods. Comparison of the results shows that the proposed method has higher accuracy and speed in islanding detection. Also, the proposed approach is effective, fast and would not be affected by noise during classifying of conditions. [ABSTRACT FROM AUTHOR]

In this paper, a single solid oxide fuel cell with internal reforming and parallel flow is modeled and optimized. The single fuel cell is a part of a stack of fuel cell system used for cogeneration of heat and work. The governing equations including the conservation equations of mass, momentum, energy and electrochemistry relations are solved by gPROMS software and validated using the data available in literature. The effect of quantities such as the rate of fuel consumption, amount of excess air and the percentage of pre reforming of fuel on the power and the efficiency of the fuel cell were evaluated. The results show that the percentage of the fuel pre reforming on the performance of fuel cell is more effective than other parameters and the power output and energy efficiency increase with it as well. Optimal working point of fuel cell with three objective functions (output power, the product of output voltage in voltage efficiency and output power in energy efficiency) has been obtained. The optimal current density is less than the current density of maximum power output. The optimal power output and energy efficiency taking minimum energy dissipation into account are 1.11W/cm² and 42%o respectively and by considering minimum exergy are 1.46 W/cm² and 24%, respectively. [ABSTRACT FROM AUTHOR]

In this paper, dry electro-discharge machining (Dry EDM), one of the newest machining processes which differs mainly from conventional EDM in using gaseous dielectric along with tool electrode rotation, has been studied. Gap voltage, discharge current, pulse-on-time, pulse-off time, dielectric gas pressure, and electrode rotational speed have been considered as effective input parameters. Response surface methodology (RSM) has been used to optimize the machining performance with respect to material removal rate (MRR). Base on the results and analysis of running experiments, it can be concluded that MRR increases by increasing gap voltage, discharge current, the ratio of pulse-on time over pulse-off time, input gas pressure, and electrode rotational speed. There also exists an optimum amount of pulse-on time determined according to the machining circumstances. Also the material removal rate in dry EDM has been improved compared with that in conventional EDM in identical conditions. [ABSTRACT FROM AUTHOR]

Eccentricity fault is one of the prevalent faults in rotating machines which can cause other mechanical and electrical faults. This paper focuses on detecting the static and dynamic eccentricity faults in the squirrel-cage induction motors. The induction motor is modeled by the finite element method (FEM), a powerful and accurate method, using FLUX 2D software. The current signal cannot be used to detect the static and dynamic eccentricity faults especially when their severity is small. Therefore, the search-coil based method is employed and the voltage of two symmetrical search-coils is analyzed to detect and diagnose the static and dynamic faults. Since two search-coils are open-circuit, they do not affect the behavior of the induction motor. The analysis based on the principal component analysis (PCA) method shows that there exists an intelligent pattern that, firstly, is sensitive to the occurrence of eccentricity faults, even to a low degree, and secondly, has the ability to distinguish the type of fault (static or dynamic). [ABSTRACT FROM AUTHOR]

Nowadays, determining the contribution of the individual consumers to the harmonic contamination is required for improving power quality. Due to changes occurred in lines, transformers, loads and generators over time, network operating conditions and impedance of different sectors are frequently varied resulting in the change in the contribution of harmonic sources. In this paper, an intelligent-based three-step method is developed to continuously determine the contribution of each harmonic source to the harmonic voltage of different buses without any access to the voltage phase data at different buses in the network. In this algorithm, firstly, the K-means clustering method is used for pre-processing of the measured data in order to reduce the background harmonic destructive effect on accuracy of the harmonic contribution determination. After calculating the harmonic contribution, the K-nearest neighbor method is used to generalize the results, and subsequently to create a continuous harmonic contribution matrix (HCM). Finally, the method is applied to a standard power network-based calculation example. The results demonstrate the capability of the proposed algorithm to evaluate the effects of harmonic sources in power networks. [ABSTRACT FROM AUTHOR]