مجله مهندسی برق و الکترونیک ایران
سال سیزدهم شماره 1 (بهار 1395)

In recent years¡ due to environmental concerns together with rising costs of the fossil fuels¡ the wind energy usage in electricity generation of various countries has experienced a growing trend. Owing to inherent characteristics of wind turbines output generation¡ i.e. uncertainty in their output level as well as being undispatchable¡ the rapid growth of installed wind farms¡ however¡ has caused some new challenges in operation and planning studies of power systems. Among the major challenges in operation of high wind penetrated power systems¡ wind energy curtailment has been considered as an attractive ongoing area of research which can significantly determine the capacity credit of wind farms. In this regard¡ this paper at first tries to model the uncertainty in wind farms output level exploiting an analytical method and then it proposes an innovative fossil units redispatch algorithm as a short term solution in wind energy curtailment issues. The wind energy maximization is introduced as the objective function of the redipatch problem. In order to investigate the abilities of the proposed method in reducing the curtailment level of wind farms¡ various cases are applied to the modified IEEE 24 bus Reliability Test System (IEEE-RTS) and the obtained results confirms its applicability.

Electric distribution companies regulation has important effect on power system. Distribution services costing are done by two method¡ price base and performance base. Distribution company cost include operational and investment. Services quality¡ productivity improvement and etc are applied by benchmarking. With regard to different condition of companies¡ it is important that regulator benchmarks similar of them. In this paper¡ comprehensive algorithm is proposed to distribution companies clustering in operation expenditure (Opex) determination process. Three method and different cluster validation indexes is used in clustering that increase accuracy. Subsequently¡ clustering methods effects analyses in opex by standard deviation index. Finally proposed method is applied to UK electric distribution companies.

This paper is introducing a new controlling scheme with second generation wavelet transform and sandia frequency shift (SFS) for islanding detection of inverter-based distributed generation. This new hybrid method combines two active and passive methods through two performance zones. The new hybrid method calculates energy entropy of wavelet coefficients in its passive zone and if it increases from a predefined threshold¡ the method goes into its active performance zone which is implemented by SFS method. In the active performance zone if the frequency of PCC is beyond the range which is defined in the standards¡ islanding condition can be detected by frequency relays otherwise the hybrid method will back to its passive performance zone. The new hybrid islanding detection method uses second generation wavelet transform (lifting scheme) which allows faster implementation of wavelet calculations. The advantage of the new method compared to passive methods is reduction of non-detection zone and also compared to active methods is reducing injection of disturbances into the system. All simulation results have been done in MATLAB/Simulink software. The results confirm the idea which is presented in this paper.

Individual Distributed Energy Resources (DERs) do not have sufficient capacity¡ flexibility or controllability to participate in the electricity markets. By aggregation of some individual DERs into a Virtual Power Plant (VPP)¡ this problem may be resolved. Under this concept¡ individual DERs would be able to gain access and visibility across the electricity markets. The aim of this paper is planning a Commercial VVP (CVPP) for participating in simultaneous energy and spinning reserve markets for a pool framework. Several Distributed Generation (DG) units and storages are included in the CVPP portfolio. The presented model of the CVPP is a mixed-integer linear programming (MILP). In this Paper the DER units included in the CVPP portfolio are not located in one geographical area. Therefore the CVPP takes only the operational constraints of DER units into account. It is proposed that each TVPP would then run a linear algorithm based on sensitivity analysis in which the distribution system constraints are met while aiming at minimizing the violations from the CVVPs scheduling. The presented model is a constrained linear least-squares problem which takes the operational constraints of DER units into account. The results show the effectiveness of this proposed approach.

Optimal bidding strategy of power generation companies is one of the most important problems of the restructured power systems. This problem must maximize generation companies’ profit in a competitive electricity market environment. The concept of Fuzzy Expectation Value (FEV) is proposed in this paper for building of optimal bidding strategies. Based on historical data¡ the production cost and the experts'' knowledge¡ the well-known fuzzy set theory is employed to represent the bidding behaviors of rival generation companies. Then a fuzzy programming model is developed and a solution method is proposed. A numerical example with six suppliers and two large consumers is performed to and the results are compared with the Particle Swarm Optimization (PSO)¡ Genetic Algorithm (GA)¡ and Monte Carlo method. The obtained results show the capability and the viability of the proposed method.

In this paper¡ Generation Companies (GENCOs) bidding in wholesale electricity market is explained with considering the effect of transmission network and uncertainty about bidding strategy adopted by rival GENCOs. Due to oligopolistic restructured electricity market¡ economic model of supply function equilibrium is used for modeling GENCOs competing. In this competition¡ each GENCO is in search of maximum profit while generation scheduling and price which paid to each GENCO is determined by Independent System Operator (ISO). Thus¡ the problem of determining optimal bidding strategy for desired GENCO is modeling by bi-level programming method. So that¡ in upper level the profit of each GENCO has been maximized and in lower level ISO with the aim of minimizing the amount of electrical energy consumers’ payment subject to secured operation of power system¡ will be clear the market. In addition¡ since each GENCO is faced with uncertainty about the strategies of rival GENCOs¡ in this paper the mentioned bi-level programming is treated as a stochastic programming and to simulate uncertainty the Monte Carlo method is used. GENCOs competition in the presence of uncertainty has been studied in the context of incomplete information game. Also by measurement of value at Risk (VaR)¡ according risk level of each GENCO bidding strategy has been adopted. The proposed methodology in this paper is implemented on a 30-bus IEEE test system¡ and the results showed a significant effect of risk level on bidding strategy adopted by each GENCO.

In this paper¡ a new model has been introduced for scheduling of a multi-microgrid consisting of low voltage microgrids¡ distributed generation resources and interruptible loads. In this model¡ system operator runs its internal market¡ then by using the results and modeling the upstream market¡ the internal market is finally cleared based on nodal prices and considering network losses. Furthermore¡ the model has been extended by introducing the multimicrogrid reactive power market and simultaneous running of active and reactive power markets¡ to maximize social welfare. Finally¡ the proposed model has been applied on a test network as a case study in order to evaluate the proposed algorithm.

This paper presents a new method¡ based on analytical relations and Monte Carlo simulation for calculating the lightning performance of overhead lines caused by direct strokes. The aim of the work is to reduce the computing time together with retaining enough accuracy to estimate the line lightning performance and performing the risk analysis of power networks. In the proposed method¡ some modified equations based on the calculation methods have been derived. Thereafter¡ to calculate the lightning overvoltages and lightning performance¡ Monte Carlo simulation has been applied to the derived equations. Considering the results of ATP simulation¡ in addition to significantly high speed calculation¡ the insulation risk of failure calculated by the proposed method is acceptable and valid for risk analysis of overhead lines. Also¡ the lightning performance can be predicted with good accuracy. However¡ all the stages of the proposed method are coded in MATLAB and no software simulating is required

In this paper, pattern recognition algorithms are employed to detect and classify the type of high impedance faults (broken and unbroken) and in case of broken ones to determine the surface (gravel, asphalt and concrete) which the conductor has become in contact with it in power distribution networks. These methods are multilayer SVM and Fuzzy ART classifiers on the bases of features extracted by S-transform and TTtransform from feeder one cycle post-fault current waveforms. These features include energy, standard deviation and median absolute deviation. The proposed algorithms have been tested on different data set, obtained from field tests and simulated data for events with similar characteristics. The results have shown that the features which are extracted by applying TT-transform contain more information and separability characteristics than those extracted by S-transform and also Fuzzy ART classifier has more accuracy in comparison with multilayer SVM.

Due to both safety and economic issues¡ exhaustive and optimal design of the grounding system of high voltage substations is one of the most important¡ expensive¡ sensitive¡ and complicated problems of the high voltage substations. In this paper¡ a novel designing method is proposed which consist of seven fundamental steps. The method is based on the ANSI/IEEE Std. 80-2000 standard. Most of the parameters affecting the safety and economic costs are considered as the optimization variables which are set by using smart method. The grounding system is designed by defining an appropriate objective function which contains the essential parameters that affects the relevant cost. Moreover¡ an optimization technique known as random search algorithm is suggested in order to solve the associated nonlinear problems with nonlinear boundary conditions. As a practical case study¡ we implemented the proposed method for designing of the grounding system of a high voltage substation in Taft city and a 230/63 kV high voltage substation. The system was also designed using a usual approach which is based on the ANSI/IEEE Std. 80-2000 standard along with the trial and error method. Our comparison study¡ confirm the superiority of the proposed method from both safety and economic points of view.

Distribution transformers with OVAL windings introduces as optimal Optimums transformers in the lowest power. Because consumption of Iron and copper decrease in these transformers¡ it decreases Loss of power transformers than cylindertransformers. Pay attention to the level of deformation transformers in OVAL¡ its electromagnetic forces will be reduced. All Articles have given different methods of calculation for electromagnetic forces of cylinder transformers. But¡ now¡ electromagnetic forces of OVAL transformers have never decreased. Therefore¡ this article has considered Transformer Forces Analysis 200kVA. Moreover¡ it compares this kind of transformer with cylinder transformers 200kVA. These forces are analyzed in two states: normal and Three-phase short circuit. So we can use FINIT ELEMENT METHOD (FEM) in 3D environment. In this method¡electromagnetic vector potential¡flux density and electromagnetic forces will be calculated. In this method¡ software MAXWELL V.13 has been used.

One of the important power quality issues is voltage sag. The voltage sag can generate many undesirable effects on electrical equipment. The major effect of voltage sag on electrical machine is torque pulsations after and during voltage sag. In this paper¡ using a simple theoretical analysis called stator flux trajectory method¡ producing manner of the torque pulsations and the impact of sag characteristics on the pulsations severity are investigated. Also¡ the critical characteristics that have the worst effects on machine behavior are identified. sag magnitude and duration and initial point-on-wave are the major characteristics that can influence the motor behavior. To justify the theoretical analysis¡ a typical synchronous motor simulated by applying different sag types and the results compared with the theoretical analysis. The results of the simulation confirm the validity of the proposed analysis.