نشریه مهندسی برق و مهندسی کامپیوتر ایران
سال نوزدهم شماره 3 (پیاپی 64، پاییز 1400)

Over current relays that are used commonly in distribution system can't detect high impedance fault. Therefore for that purpose it is necessary to design special algorithms. In this paper, a method based on harmonic analysis is presented. In this technique, the proposed relay, after fault occurs, extracts the required harmonic and according designed algorithm, occurrence of fault is reported. Software of this relay for different scenarios of high impedance faults was tested; also its hardware of relay in laboratory tests could correctly identify events.

Nowadays, with the increasing share of wind power in electrical energy sector, performance evaluation indices are of great importance. Such indices can lead to optimal utilization of invested capital and effective development of existing wind farms. Despite having some of the required characteristics, the capacity factor based on traditional definition has some limitation. This study aims to extend the concept of capacity factor and presents a comprehensive formulation in order to calculate this index using measured and simulated data for one turbine, all turbines connected to a feeder or a busbar, and all turbines of a wind farm. This formulation also provides a framework for calculating the capacity factor in various time periods (annual, seasonal, monthly, etc.) and different time slots (all hours, special hours, hourly, etc.). As a case study, performance of the installed wind turbines in Manjil wind farm is investigated over an operation period using both measured and simulated data. Performance evaluation of the farm is also carried out with a newer variable speed type. Moreover, capacity factors of the feeders, busbars, and the entire farm are calculated using the turbines simulated data as well as measured data of the feeders over an operation period, and various results of exploring the obtained capacity factors are presented. Numerical results demonstrate the effectiveness of newly presented method for the performance evaluation of wind turbines and wind farms based on extended concept of capacity factor.

As moisture condenses on the surface of the contaminated insulators, the electrical conductivity of the insulator surface increases, resulting in a leakage current on the surface and causing the insulators to fail. Condensation of moisture on the insulator surface occurs due to the mechanism of radiation cooling, mainly in the early mornings of winters. In this case, the temperature of the insulator surface is lower than the dew point. In this paper, a sample of real fine dust collected from the dust center and chemical analysis and measurement of electrical conductivity in the wet state were performed. By simulating a 230-kV contaminated composite insulator in COMSOL Multiphysics software, the magnitude of leakage current was obtained and verified by an experimental test. Also, using heat transfer governing relations, the temperature of the insulator surface during the leakage current flow, was determined and compared with the images captured by the thermo-vision camera during the test. The results show that the leakage current and the surface temperature of the insulator increase with increasing the conduction and thickness of the contamination layer and consequently the probability of insulator failure also increases. Experimental testing shows that simulation of insulators with finite elements-based commercial software can be a reliable method for pre-analysis of insulators.

Transition metal dichalcogenides FETs (TMDFETs) are among the emerging devices that have been considered by researchers in recent years. In this paper, the effect of parameter variations, temperature and power supply on the performance of TMDFET transistors has been investigated in comparison with Si-MOSFET technology. The results indicate that TMDFET is less sensitive to these variations compared to Si-MOSFET devices. By selecting the appropriate transistors size ratios, the performance of the TMDFET-based conventional 6-transistor static random access memory cell is evaluated in comparison with the Si-MOSFET in 16nm technology. Simulations are performed at room temperature, 0.7 V supply voltage and the same conditions for both TMDFET and Si-MOSFET devices. The results of the simulations show that TMDFET-based SRAM cell has 29.44% more WTP, corresponding to more writing ability, 49.49% more WTI×WTV, corresponding to higher writing noise margin, and 29.48% lower read delay. In other words, a TMDFET-based SRAM cell performs better than Si-MOS-SRAM in terms of write ability, static read margin, and read delay.

One of the main goals of distribution network operators is to reduce the cost of operating the network and improve profit. In this paper, the problem of siting and determining the size of energy storage batteries are studied. The constituent components of the objective function of the placement problem include the profit from the operation of the distributed generation unit, the profit from the reduction of grid power losses, the cost of installing an energy storage system, and the profit from the reduction of energy purchased from the upstream network. The model used for positioning is based on the probabilistic behavior of solar radiation, energy consumers, and electricity market operators. To model the stochastic nature of the output power of solar power plants, the probability density function has been used, and to model the load and price of electricity, the scenario method has been used. The simulations were performed using MATLAB software. The proposed method can manage the generation of solar power plants using the siting and management of charge and discharge of batteries.

In this paper, a new algorithm of Gaussian sum filters for state estimation of nonlinear systems is presented. The proposed method consists of several parallel Cubature Kalman filters each of which is implemented according to the simplex spherical-radial rule. In this method, the probability density function is the sum of the weights of several Gaussian functions. The mean value, covariance, and weight coefficients of these Gaussian functions are calculated recursively over time, and each of the Cubature Kalman filters are responsible for updating one of these functions. Finally, the performance of the proposed filter is investigated using two nonlinear state estimation problems and the results are compared with conventional nonlinear filters. The simulation results show the appropriate accuracy of the proposed algorithm in state estimation of nonlinear systems.

In this paper a novel compact microstrip coupler using T-shaped and stepped impedance resonators is proposed, simulated and fabricated. In the proposed structure long quadrature wavelength lines are replaced with small resonators, which results in size reduction and harmonics suppression. The proposed coupler correctly works at 1 GHz and suppresses 2nd up to 7th unwanted harmonics. Moreover the designed coupler reduces the circuit size more than 65% compared to the conventional coupler.