Sharif Digital Repository

With new progresses in technology, a growing need to power energy has emerged. In Iran most of power plants are far from cities and therefore expansion of power network will cause long transmission lines with high capacities which connect power plants to cities. There are three solutions for these kinds of lines: 1) two-circuit transmission lines 2) higher voltages 3) new forms of transmission lines (HVDC and compact). In this thesis some of these suggestions have been analyzed to find the best solution for a 560 Km transmission line in Iran.
Designing transmission lines has a lot of steps which all are related to each other. In this project a comprehensive algorithm has been utilized to... 

Nowadays, multilevel converters are significantly developed in industrial applications as well as energy transmission systems regarding proper quality of output waveforms and fault tolerant operation ability. Among the different topologies of multilevel converters, modular multilevel converter (MMC) due to its modularity feature it more accepted in high voltage direct current (HVDC) transmission systems. Fast fault detection in power electronics converters is necessary to bypass the defected part in order to prevent failure propagation to other Submodules and to provide continues servicing. On this basis, different researches are reported in literature for MMCs fault tolerant operation. In... 

The increase in the amount of groundwater exploitation and climate changes has made land subsidence into one of the environmental problems and has caused many problems in various infrastructures such as urban areas, residential buildings, and vital arteries such as power transmission lines. Many areas of the country, especially areas with smooth topography such as plains where alluvium accumulates, due to excessive exploitation of groundwater resources and climate changes, are facing a decrease in the level of groundwater, an increase in the thickness of the unsaturated layer, and as a result, progressive subsidence. In particular, the destructive effects of land subsidence on power... 

One of the main and challenging stages in the development of hybrid vehicles (HEVs) is the conceptual design of its powertrain, which includes two parts: architecture design and sizing. This research aims to introduce a novel framework for conceptual design of HEV powertrains. By using this framework, not only the sizing of components is optimized but also the optimal architecture of powertrain is selected. In the proposed framework, by finding the optimal values of the powertrain design variables, including type of architecture and sizing variables (such as nominal powers, nominal torques, conversion ratios, etc.), the performance and the cost of hybrid vehicle is optimized in three layers... 

The current restructuring trend in power industry emplaces the owners and managers under a great pressure to not only reduce the associated investment costs, but also reasonably cut the operation and maintenance expenses as much as possible, while keeping both the power quality and reliability requirements met. Reliability-Centered Maintenance (RCM) has been proved to be in response to this dilemma in power systems since it has been yet successfully applied in various engineering contexts worldwide. This process is more challenging when it comes to the power transmission systems because of its bulkiness and complex structure. On the other hand, market involvement and its intricate behavior... 

Renewable energy resources, e.g. wind, solar and geothermal, experience rapid progresses in electric power industry all over the world. So, it becomes essential that these free-emission electrical energy resources be integrated in the existing generating capacity planning procedures. On the other hand, the uncertain and intermittent nature of these energies has led to some problems in their integration in power systems. The reserve requirement in a renewable-based power system is a main challenge, which has to be addressed properly. In this way, this research presents an analytical approach, based on the modified PJM method, to quantify the risk of renewable energies commitment during the... 

In recent years passenger cars have been known as the main source of air pollution in urban areas. Despite all the research and efforts in minimizing the fuel consumption and emissions of internal combustion engines (ICE), this is merely a temporary solution. The permanent solution to overcome these disavantages is the use of electric vehicles (EV). The main downside of using electric vehicles is their short driving range. Multi-speed transmissions can be adopted to overcome this problem. Continuously variable transmissions (CVT) and infinitely variable transmissions (IVT) have been proven to enhance fuel economy in ICE vehicles and a great deal of research is being conducted to maximize... 

The current state of restructuring in the electric power industry has forced power companies to maintain and enhance service reliability and quality while controlling associated costs. Therefore these companies often seek to improve operational performance, increase productivity and promote management of their assets to restrain production costs while satisfying customers’ needs. Maintenance of system components has great impacts on both service quality and also system costs. However, it has been proved that traditional maintenance strategies which have been implemented in electrical companies are inefficient. Thus, Managing maintenance procedures would help companies to reduce their costs... 

In this thesis, DC transmission of offshore wind farms is studied thoroughly. Various system configurations that are introduced in the literatures are discussed and their control scheme for normal conditions and grid faults are studied. Then, the HVDC transmission based on voltage source converter, located between a local offshore ac grid and the onshore ac system is investigated as the most practical choice. The HVDC linke circuit elements are calculated and the control strategies of the offshore and onshore converters are introduced. DFIGs are considered to be the best choice for the offshore wind turbine generators. Then, the system is simulated and the frequency of the offshore grid is... 

Ilam refinery has three synchronous generator units each with a capacity of 26.5 MVA and two six-phase LCI-fed synchronous compressors, each with a capacity of 8 MW. Generators of Ilam gas refinery have instability issue in case of island operation. With launching one generator unit and then connecting two compressors the instability problem and tripping of the generators appear. Given the importance of this issue, various tests and corresponding measurements in both electrical and mechanical aspects were carried out at the plant in on-grid and island operations to analyze the cause of instability phenomena. The mechanical part of tests analyses the frequency of oscillations and vibration in... 

Electrical power is an inseparable part of human life. Therefore, design and analysis of electrical transmission towers have always been important for scientists. In common design methods due to the lightness of these structures only the wind load is considered and earthquake effects are neglected. On the other hand, regarding regulation No.2800 a lot of areas of Iran are located in earthquake zones. Therefore, it is necessary to evaluate the performance of these structures against earthquakes. In this research, regarding conducted studies, we decided to use incremental dynamic analysis method (IDA) in order to evaluate seismic performance of the tower. In sake of thoroughness of the... 

Power transmission lines, which are responsible for the distribution and transmission of electrical energy from the power plant to the consumer areas, due to their characteristics such as long length and flexibility with low structural damping, face environmental irritations, especially the galloping phenomenon, causing many damages annually. In this study, it has been attempted to reduce the vibrations of power transmission lines by designing a robust active control and by using intermediate actuators in such a way that the failures of these lines can be prevented. For this purpose, linear modeling of the system and designing the controller using the pole replacement method have been done.... 

Nowadays, industrial companies deal with a wide range of serious problems in the field of power transmission maintenance and also fault detection. A large amount of money and time is spent on these issues in order to solve them; consequently, there is an essential need for this subject. In this thesis, in order to tackle those major issues which were referred above, an artificial neural network is trained with only one hidden layer. Also, a suitable database for training an efficient neural network is needed. Thus, a one-stage gearbox system with appropriate degrees of freedom is used to set up referred database. In this system, a crack is imposed to a tooth of spur gear with different sizes... 

The purpose of this study is to establish a lateral-torsional-axial dynamic model for spur and helical geared rotor systems subject to shaft bow manufacturing error. Timoshinko shaft element, elastic bearings and rigid disks used to simulate different element in the model. Tooth contacts is modeled with linear spring and damper along the pressure line.Results show that the vibration pattern of the unbalanced load and shaft bow effect is different. These obtained patterns might help with the fault diagnostics of rotating machinery. The vibration will be lowest if the unbalanced load and the shaft bow amplitude locates out of phase. The previous researches show that different pattern of the... 

In this thesis an approximate method is proposed for analysis of two dimensional photonic crystal waveguides. In this method an equivalent impedance is assigned to photonic crystal regions and the waveguide region is modeled with a transmission line. Waveguide’s loss is also analysed and computed by this method. In other words the proposed method is able to determine the complex propagation constant of guided modes without computing any complex roots for dispersion equation. Although like any other approximate method, the accuracy of this method is dependent to some special conditions but it’s advantage over other numerical methods is its simplicity and its capability for waveguide designs.... 

Due to pollution and destructive effects on the environment, while consuming a large amount of fossil fuels that can be converted into high value-added products, gasoline cars are gradually replaced by electric cars. Modern electric vehicles are generally designed and manufactured on the platform of gasoline vehicles. In the present study, it is tried to design three models of electric vehicles based on the SAINA vehicle. Initially, for the first model, an electric motor instead of the SAINA gasoline engine is employed to provide the power required for the vehicle. Then, for the second model, two electric motors are used namely one in the rear axle and one in the front. The third model uses...