فهرست مطالب

Majlesi Journal of Energy Management
Volume:4 Issue: 1, Mar 2015

  • تاریخ انتشار: 1394/02/15
  • تعداد عناوین: 8
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  • Perfect Modelling of Grounding Systems to Study Electromagnetic Transients via Vector Fitting Method
    Mehrdad Mahmoudian Page 1
    As wind farms grow rapidly throughout the world, the grounding system and ground impedance of wind turbine towers under transients have got more important. As a matter of fact, an exact model to testify dynamic properties of grounding system should represent nonlinear effects of soil ionization and be frequency dependent. Some new researches conducted in this issue, all are based circuit theory which does not allow for accurate analysis of aforementioned behaviors. This paper has come to express a new approach to model any grounding system only by few RLC branches in wide frequency range. A new model and some simple formula that is recommended in this paper, represent all effects of transient phenomena of lightning strikes and all analysis have got more easier than other approach. By using this method, there’s no difference between those grounding system buried in cylindrical soils or conical one, multi-layer oil or not, humid soil or not and so on, they all are available for transient analysis. Then the outputs or the RLC branches are implemented in EMTP and get analyzed. So it’s possible to evaluate power systems under lightning strikes with presence of precise behavior of grounding systems.
  • Sarwan Yousefi Page 9
    Electric trains inject a large amount of harmonics to the power network and consume high reactive power which makes them one of the worst loads kinds to be used in the power systems. These loads have non-linear characteristics and cause harmonic distortion. Filtering is one of the common ways utilized to eliminate harmonics and compensate reactive power. Filters are categorized in three types: passive, active and hybrid. Both passive and active filters have their own deficiencies while hybrid filters benefit from advantages of both former filters while overcoming their deficiencies. In this paper, active, passive and hybrid filters are discussed and then a suitable hybrid structure is introduced. Thereupon a harmonic model of an intercity electric train is presented and application of the proposed hybrid filter structure to the train is simulated using MATLAB/SIMULINK. The obtained results demonstrate the effectiveness of utilization of such hybrid filter structure in elimination of harmonic components and reactive power compensation.
  • Hatef Farshi Page 15
    Design of Automatic Generation Control (AGC) plays a vital role in automation of power system. In this paper, determination of the Proportional-Integral-Derivate (PID) controller parameters with three optimization algorithms such as Particle Swarm Optimization (PSO), Genetic Algorithm (GA) and Imperialist Competitive Algorithm (ICA) for AGC of two-area interconnected hydro thermal power system is investigated. The hydro and thermal areas are comprised with an electric governor and reheat turbine, respectively. The designed PID controller with the proposed approaches is simulated in MATLAB/SIMULINK and their results compared with each other and some previous studies.
  • Amireh Nourbakhsh Page 21
    Cavitation bubbles are produced in a liquid flow when the static pressure is below the saturated vapor pressure. These bubbles move with liquid flow and violently collapse in high pressure regions. Violent collapse of the bubbles is believed to be one of the most important parameters in mechanical damage of hydraulic machineries and structures. They have also beneficial effects in medicine and Lithotripsy surgery. Experimental and numerical results show that during the collapse phase of a cavitation bubble near a rigid boundary a liquid jet is developed on the side of bubble far from the rigid boundary and directed towards the boundary. This liquid jet threads the collapsing bubble, creating a toroidal bubble. Cavitation bubbles behavior near various boundaries depends on material, dimension and shape of the surface and the bubble distance from the nearby boundary.In this paper, growth and collapse of a cavitation bubble inside a rigid cylinder with a compliant coating (a model of human’s vessels) are studied using Boundary Integral Equation and Finite Difference Methods. The fluid flow is treated as a potential flow and Boundary Integral Equation Method is used to solve Laplace’s equation for velocity potential. The compliant coating is modeled as a membrane with a spring foundation. At the interface between the fluid and the membrane, the pressure and normal velocity in the flow are matched to the pressure and normal velocity of the membrane using linearized condition.The effects of the parameters describing the flow (the fluid density, the initial cavity size and its position) and the parameters describing the compliant coating (the mass per unit area and spring constant) on the interaction between the fluid and the cylindrical compliant coating are shown throughout the numerical results. It is shown that by increasing the compliancy of the coating, the bubble life time decreases and the mass per unit area has an important role in bubble behavior.
  • Amir Naebi Toutounchi Page 41
    Yearly maintenance scheduling of power generating units is an important scheduling problem that has to be solved within a restructured power system. Solving period of this problem usually is a one year basis. In this paper, a bi-level approach is used to solve maintenance scheduling problem. The upper level of this bi-level problem represents the profit maximization of power units owned by a generation company (GENCO) while the lower level problem represents the market clearing process. This means that a GENCO wants to maximize its own profit in a market and due to the participation of other producers in it, the market should be cleared and the independent system operator (ISO) establishes the desired security level. The bi-level problem is formulated as a mathematical program with equilibrium constraints (MPEC) using the primal-dual formulation. Various case studies are conducted using the IEEE reliability test system (RTS) and the obtained results are compared.
  • Mahmoud Torabi Page 51
    In this work, a tesla transformer with a resonant air core is designed and fabricated. For design and simulation Tesla Coil Cad and Microcap software are used. It is show that in contrast to usual transformer, voltage conversion ratio is depended on resonant ratio. Also tesla transformer works in high frequency effectively.
  • Mehdi Esmaeilzadeh, Iraj Ahmadi, Nabiollah Ramezani Page 55
    The use of Distributed Generation (DG) units as small power generation units in distribution networks has received increasing attention during recent years. Distributed generation applications are growing due to environmental and economic issues, technological improvements, and privatization of power systems. Distributed generation application, however, has negative effects in protection coordination. Due to penetration of DG disturbs the radial nature of conventional distribution networks. Therefore, protection coordination will be changed in some cases, and in some other cases it will be lost. This paper proposes a Genetic Algorithm (GA) technique for the optimal placement of DG units in the distribution systems with considering protection coordination limits.
  • Navid Keliddar, Seyed Saeed Allah Mortazavi, Hasan Barati, Abbas Moosavi Dehsheikh Page 65
    In restructured power systems environment, one important principle for survival in transactions is success in market competition. Success in competition may only be achieved through optimal use of available facilities. This point of view may be considered in optimal operation of Distribution Company (DISCO). Considering Interruptible Loads (ILs), is one of DISCO options in the market competition. This paper shows how using various IL contracts alongside with utilizing Distributed Generations (DGs) and power exchange with grid may lead to more profits of DISCO. The expressed scenarios shows proficiency of the proposed method. The suggested model is evaluated by an 18 buses test system. Results show the advantages of using various IL contracts in DISCO operation.