Environment and Electrical Engineering (EEEIC), 2011 10th International Conference on

This paper, investigates the effect of High Impedance Fault (HIF) on wind turbine equipped with Doubly Fed Induction Generator (DFIG) operation. Consequently, a new proposed method is used to HIF detecting in power system connected to wind farm equipped with DFIGs means of harmonic component analyzing of DFIG rotor current. The simulation has been done with PSCAD/EMTDC software. View full abstract»

Recently big fault currents flow in a network. The fault current will exceed capacity of circuit breakers soon and all the various rational solutions to solve this problem are taken into account. Under these circumstances, superconducting fault current limiter(SFCL) is a new alternative in the viewpoint of technical and economic aspects. This study presents operation processes for a resistive-type of SFCL, and it proposes reliability model for the SFCL. When a SFCL is installed into a network, the contribution of decreased fault currents to failure for distribution equipments can be quantified. As a result, it is expected that a SFCL makes the reliability of adjacent equipments on existing network improve and these changes are analyzed. We propose a methodology to evaluate the reliability in the distribution network where a SFCL is installed considering a reliability model for SFCL and reliability changes for adjacent equipments which are proposed in this paper. View full abstract»

This paper presents an approach using a high-performance feedback neural network optimizer based on a new idea of successive approximation, for the control of interconnected multi-reservoir systems. The main advantages of the proposed neural network optimizer over the existing neural network optimization models are that no dual variables, penalty parameters, or Lagrange multipliers are required. It is very simple in structure and has the least number of state variables. In particular, the projected optimization network has better asymptotic stability. For an arbitrarily given initial point, the trajectory of the network converges to an optimal solution of the convex nonlinear programming problem. The proposed neural network optimizer has been tested on a practical system consisting of a set of ten linked reservoirs where the objective is to find out the optimal amounts of water releases from each hydro-plant during each interval in the interconnected system. Also to minimize and distribute uniformly the energy deficit if any, subject to a number of governing constraints such as demand-supply balance, flow balance equation, bounds on reservoir storage, bounds on water releases and coupling constraints. View full abstract»

Specificity of residential area transmission system is a highly meshed network with combined overhead and cable sections. In center of Zagreb town, control of transmission system is additionally complicated by a special operation of the 110 kV cable link between two power plants important for town's heat and electricity supply. Cable link has to be opened in order to control the power flows and to reduce short circuit current level. The consequence is a radial supply of two major substations in central Zagreb. The paper proposes an implementation of System Integrity Protection Scheme for automated control of Transmission System of central Zagreb. Proposed solution provides closed cable loop and possibility of island operating state of central Zagreb power system according to specific disturbances in bulk power system. View full abstract»

The paper presents the two-stages adaptive approach for short-term forecast of parameters of expected operating conditions. The first stage involves decomposition of the time series into intrinsic modal functions and subsequent application of the Hilbert transform. During the second stage the computed modal functions and amplitudes are employed as input functions for artificial neural networks. Their optimal combinations is constructed using methods of simulated annealing and neural-genetic input selection approach. The efficiency of developed approach is demonstrated on real time the problem of forecasting power flow and voltage level. View full abstract»

The paper presents an intelligent approach to monitoring of the expected operating conditions on the basis of the self-organizing Kohonen maps and k-means method. The suggested approach makes it possible to effectively follow changes in the current and expected operating conditions and predict heavy load conditions and/or development of emergency conditions almost in real time. View full abstract»

Large deployments of Distributed Generators (DGs) have substantial impacts on the structure of existing networks. In order to tackle these issues, it has been proposed to divide the network into smaller manageable sets which can be more effectively and efficiently operated. This very concept is called the `Microgrid'. However, due to their unprecedented structure, these smaller grids experience very significant protection issues. Conventional fault current protection schemes cannot be used and should be modified due to the existence of generators at all levels of the distribution system. Furthermore, two distinct operating modes (grid connected and islanded modes) exist in microgrids causing the fault currents in a system to vary substantially. It is also a challenge to operate Inverter Interfaced DGs (IIDGs) and estimate their fault currents. Fault current limiters have thus been proposed for proper operation of DGs in a network. This paper presents a conceptual design of a microgrid protection system which makes use of current limiters in fault current estimation. It utilizes extensive communication to monitor the microgrid and update relay fault currents according to the variations in the system. The proposed system is designed so that it can respond to dynamic changes in the system such as the connection/disconnection of DGs. View full abstract»

The modeling of heat diffusion phenomena is important to develop optimal control strategies for ground coupled heat pump systems. This paper will discuss different model extraction techniques for such heat diffusion problems, namely using rational transfer function models in both the Laplace and the Warburg domain. The experimental verification is done using measurements on the heat diffusion problem in an isolated bar. The best rational transfer function models in the Laplace variable s and in the Warburg variable √s are compared, demonstrating that the Warburg domain has better predicting capabilities when it comes to predicting the lower frequency behavior of the system. View full abstract»

DC microgrids are gaining popularity over ac microgrids, because of high efficiency and reliability with low installation cost. To achieve equal load sharing (in per unit) among sources, droop based controllers are used. However, equal sharing of load is achieved in ideal system. This paper investigates the deviation in load currents from their ideal values. Steady state mathematical model of the system is developed. This model is applicable to any interconnecting structure of sources and loads. Deviation of source currents from their ideal values is expressed in terms of load distribution pattern and differences in nominal voltages. Sensitivity of source currents to load currents and nominal voltages is derived. Effects of branch resistances and droop constants on the sensitivity of source currents are examined. Results obtained by analysis are verified by detailed simulation study. Viability of the model is confirmed by experimental results from a scaled-down laboratory prototype of dc microgrid. View full abstract»

The paper deals with the partial results of the project specialized in innovation of research in magnetic lenses and chambers of electron microscopes. The paper is aimed at the simulation of magnetic field distribution of some types of magnetic lenses in software Ansys with the employment of results of magnetic measurements. View full abstract»

The paper deals with the basic goals and partial results of the project, which focuses on innovative research of the magnetic lenses and chambers of electron microscopes. The paper is divided into two parts. This first part contains the analyses of magnetic properties of the steels which are designed for construction of lenses and chambers. View full abstract»

This paper describes constitution and design characteristics of a passive unbalance compensator for variable loads in three-phase four-wire industrial installations. Unbalance compensator is integrated by three-phase connections of variable coils and capacitors. Inductance and capacitance values of those elements and unbalance power supplied by the compensator can be changed by switches commanded by an electronic control circuit. The minimum unbalance power supplied by the compensator is the “power of the unbalance step”. This quantity defines composition and values of the elements of the “unbalance step”, which is the basic three-phase connection of coils and capacitors in the compensator. Since unbalances in power systems are caused by active and reactive loads, two unbalance steps have been defined: active and reactive. Finally, unbalance compensator operation has been tested for an industrial installation. View full abstract»

PLL principles system and its applications in harmonic analysis are firstly discussed and then integrated presenting methods to increase the PLL-based instrumentation efficiency. A comparison between the performance of systems before and after the application of these methods are shown to validate the efficiency o f the proposed methods. View full abstract»

Our study present a study of the wind layer in seven Algerian sites "Saharan sites" (In Amenas, In Salah, Tindouf, Adrar, Béchar, Ghardaïa and Tamanrasset). This study is based on data and statistics published in the atlas wind of Algeria established by the National office of the Meteorology, which had 37 stations of measures. The annual average wind speed for the selected sites ranged from 4.00 m/s to 7.20 m/s and a mean wind power density from 82.51 W/m² to 283.12 W/m² at standard height of 10m. The wind speed and the Weibull parameters were extrapolated standard height 10m with 30 and 50m by using vertical extrapolation laws. The Weibull parameters k and c are determined and used for estimate the annual average wind speed and the power density for each site. View full abstract»

For accurate location of a partial discharge source in the power cables, exact determination of time of arrival of initiated waves by PD source, is very important. The proposed method in this paper is based on applying mathematical morphology operators to perform this task. In this method the Opening-Closing filter of mathematical morphology is used for noise reduction of signal and gradient operator is used for edge detection. The proposed method does not need to have any information about the load and the cable. Comparison with the published methods has shown higher accuracy of the proposed method. Moreover the effect of noise level, noise spectrum, pulse shape and load impedance on PD location accuracy are investigated. View full abstract»

In this paper, the effect of the reactive power deviation (ΔQ) auxiliary signal on the classic power system stabilizers (PSS) with ΔP+ Δω inputs is studied and then the multi-input power system stabilizer (MPSS) with ΔW+ΔQ+ΔP inputs is investigated. Then, the effect of communication lines active power variance signal between two ΔP_Tie-line regions, as one of the inputs of fuzzy multi-input power system stabilizer (FMPSS), on the increase of low frequency oscillation damping is examined. The efficiency of the proposed model is examined by simulating a four-machine power system. Results show the model reduces the cost of system. View full abstract»

A realistic simulation of fault arc is required in proper design of transmission system equipment such as fault locators. Usually, in the travelling wave-based fault location algorithms, the effect of the arc of the fault is neglected. The influence of fault arc characteristics on the accuracy of fault locator which is based on the travelling wave theorem, is studied in this paper. Proposed algorithm uses samples taken from two terminals and shows that it is possible to calculate the accurate location of fault by measuring voltage transients caused by the fault. The travelling wave-based algorithm does not use the line parameters. Therefore, the accuracy of algorithm is not affected by aging, change of climate and temperature, which change wave speed. In addition, the effect of fault conditions such as arcing fault resistance, fault inception angle and fault distance are studied on the accuracy of the proposed algorithm. Simulations carried out by SimPowerSystem toolbox of MATLAB software confirm that mentioned parameters do not affect the accuracy of the method. View full abstract»

Harmonic currents, generated by non-linear loads, produce `penalty losses' in every element of an electrical distribution system. These harmonic-related losses reduce system efficiency, cause apparatus overheating, and increase power and air conditioning costs. In this paper, evaluation of transformer losses under non-linear load conditions will be discussed. In addition, the results of practical measurements of full filled on 7 units of distribution transformers in Tabriz Power Electric Distribution network are evaluated and some suggestions to improve the situation are presented. View full abstract»

Distance relay is the main protection of power transmission lines and make an important role in power system stabilization if it operates selective and instantaneous. In this paper, the trajectory of the fault impedance is determined. It is shown that in the end of the first zone or in the middle of the second zone, distance relay could not make a correct decision for operating if the fault occurs with arc. So to overcome this problem, in this paper a novel technique using total harmonic distortion (THD) is proposed. The proposed method makes the distance relay more selective and instantaneous. View full abstract»

As a renewable, clean energy, wind energy has attract more and more attention. It has become a common understanding of the world to vigorously develop wind energy. In order to guarantee the safety and reliability for wind power integration operation, it is of great significance to establish an appropriate wind power generator system model and analyze its electromagnetic transient characteristics. This paper analyzes the control strategy of doubly-fed induction generator (DFIG) based wind generator. Vector decoupling control technology has been adopted to establish the mathematical model of DFIG based wind generator. Furthermore, an electromagnetic dynamic simulation model of DFIG based wind generator is established based on the platform of PSCAD/EMTDC. A short circuit fault is simulated to study the dynamic response of DFIG based wind generator. Finally, transient characteristic of DFIG is analyzed by this paper. View full abstract»