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Total 131 records

    Fault Diagnosis of Crack Growth in Power Transmission Systems, using Neural Network

    , M.Sc. Thesis Sharif University of Technology Delavari, Mohammad Mohsen (Author) ; Selk Ghafari, Ali (Supervisor) ; Khayyat, Amir Ali Akbar ($item.subfieldsMap.e)
    Abstract
    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... 

    Crack Detection in a Rotor using Traditional Mode Shape Based Modal Analysis Methods and Experimental Evaluation

    , M.Sc. Thesis Sharif University of Technology Ashtiani, Mohammad Reza (Author) ; Mohammad Navazi, Hossein (Supervisor)
    Abstract
    Fatigue crack growth can have harmful effects on the reliability rotary machine. While an early warning to crack, can be used to extend the life of these expensive machines and increase reliability.Structural Vibration Condition Monitoring as a primary fault detection method, achieved to a lot amazing result and for this reason studies vibration behavior of cracked rotational shaft is a big issue for engineers of dynamic machine.In this research, first check the fault detection methods based on structural vibration condition monitoring, mode shape methods were extracted. Then by modeling rotational shaft in computer and creation of crack on it, fault detection quality of these methods have... 

    Identification and Attractiveness Assessment of Technologies Used in Aging Aircraft Life Extension

    , M.Sc. Thesis Sharif University of Technology Mohammadi, Morteza (Author) ; Abedian, Ali (Supervisor)
    Abstract
    Lifetime extension would be a necessary preventive action to halt micro cracks expansion on the airplane external surface. To decide about whether to perform this operation, one should examine technological maturity, costs and technical parameters. Technical status in lifetime extension is one of the major drivers of this decision which should be considered in the first step of technology management process which is known as the technology attractiveness step. In this research, major technologies of rejuvenation is examined and categorized by the technology mapping. Also, key processes of rejuvenation and technological fields ranking has been determined by the procedural view tools of the... 

    Energy Efficient Concurrent Test of Switches and Links for Networks-On-Chip

    , M.Sc. Thesis Sharif University of Technology Alamian, Sanaz (Author) ; Hessabi, Shahin (Supervisor)
    Abstract
    Nowadays by increasing the number of processing cores in system-on-chip, using networks-on-chip, as an optimized interconnection foundation for transferring data between processing cores is inevitable .Based on this, the necessity of designing and implementing an optimized structure for testing network-on-chip, considering various overheads such as power consumption, latency, bandwidth and area, becomes an important issue in designing network-on-chip. The purpose of this project is to design an optimized structure for testing routers and connecting links in network, which considers power consumption overhead, latency and area overhead on one hand, and fault coverage on the other hand.... 

    Reducing the Energy Overhead of Replication Mechanisms in Distributed Embedded Systems

    , M.Sc. Thesis Sharif University of Technology Salehi Khanghahbar, Mohammad (Author) ; Ejlali, Alireza (Supervisor)
    Abstract
    Distributed embedded systems are widely used in safety-critical applications, such as avionics platform and flight control system. Faults in such applications may cause catastrophic effect. Therefore, these systems must be fault-tolerant and must be designed not only to detect faults but also to recover from faults. Fault tolerance is normally realized on multi-processor system via temporal duplication (time-redundancy) or spatial duplication (hardware-redundancy) depending on the availability of the slack time. Slack time is defined as the difference between the deadline and execution time. Duplication is a common technique to achieve fault tolerance in safety-critical applications, but may... 

    Fault Detection in Robotic Swarm

    , M.Sc. Thesis Sharif University of Technology Mollahossein, Mojtaba (Author) ; Alasti, Aria (Supervisor) ; Salarieh, Hassan (Co-Supervisor)
    Abstract
    Fault detection in swarm robots is one of the most important issues that has drawn a lot of scientists’ attention. Previous studies have shown a lot of problems regarding this issue, such as dependency of data-based methods to mission and high complexity of model-based methods on the condition that nonlinear models are used. Extended information filter is an applicable method for fault detection because it could turn the inverse of a big matrix to a simple summation of information that is so desired in terms of calculations. The goal of this study is to identify the agents with fault in swarm robots online by modifying the extended information filter. In this study, it has been attempted to... 

    Application of SPM for Fault Detection and RUL Estimation; Comparison with Vibration Analysis

    , M.Sc. Thesis Sharif University of Technology Davoodabadi, Ali (Author) ; Behzad, Mehdi (Supervisor)
    Abstract
    Rolling element bearings (REBs) are one of the most critical components in rotating ma-chines. Failure of these components may lead to fatal and costly breakdowns in rotating machinery. Therefore, it is significant to detect faults at early stage accurately. The pur-pose of this study is to compare vibration analysis and shock pulse method (SPM) in early detection of fault and remaining useful life prediction of REBs. To the aim, a set of ac-celerated life tests on REBs was planned. Vibration and shock pulse values accelerated life tests of the REBs were simultaneously measured from the moment of start to the end of the failure by two vibration and shock pulse sensors and their changes were... 

    Fault Detection of Rotary System with Signal Processing and Intelligent Systems

    , M.Sc. Thesis Sharif University of Technology Tebyanian, Afshin (Author) ; Behzad, Mehdi (Supervisor)
    Abstract
    Condition monitoring and fault detection is an important way to provide economy in both time and costs. Many methods are developed for this purpose. Vibration analysis is one of the most important ways in this field. In this thesis, fault detection of mechanical rotary systems with nonlinear and non-stationary nature has been developed by use of empirical mode decomposition (EMD) and Hilbert transform. Firstly the measured signal is transformed into some intrinsic mode functions (IMF’s) by EMD, and then the Hilbert transform is implemented on each IMF. With Hilbert transform, the instantaneous frequency of system and then the mean frequency are obtained. Mean frequency is a key definition... 

    Criteria for Evaluating Bogie Performance For Sustaining Ride Quality

    , Ph.D. Dissertation Sharif University of Technology Shokouhi Dolat Abadi, Nader (Author) ; Sayyadi, Hassan (Supervisor)
    Abstract
    This thesis proposes a dynamic model for studding influences of suspension components behavior on rail vehicle dynamics. As the air springs are very important isolating component in rail vehicles, a new complete nonlinear air spring model, with taking into consideration of thermo–dynamical effects, is developed. The model coefficients are tuned based on the real test data and it can be easily used in dynamic modeling of air springs. The new proposed vehicle model is a complete track–vehicle model with 70 degree of freedoms which is addressed as a modular type. Experimental results from complete rail–vehicle field test, showed remarkable agreement between proposed model and test results.... 

    Fault Detection in Plant Wide

    , Ph.D. Dissertation Sharif University of Technology Tayyebi, Shokoufe (Author) ; Bozorgmehry, Ramin (Supervisor) ; Shahrokhi, Mohammad (Supervisor)
    Abstract
    The accurate fault diagnosing system design helps the process safety and also helps increasing the products quality of the process. In this project, the fuzzy system and neural network have been used for fault detection and diagnosis of a yeast fermentation bioreactor. In one case, parameters of membership functions are selected in a conventional manner. In second case, the optimal values of these parameters have been obtained using the genetic algorithm. In another case, the neural network system is used for fault detection. These three cases are compared based on their performances in fault diagnosis of a yeast fermentation bioreactor for three different conditions. The results indicate... 

    Turn-to-Turn Fault Detection in Power Transformers in the Presence of Inrush Current

    , M.Sc. Thesis Sharif University of Technology Fallah Mollamahmod, Mahdi (Author) ; Hajipour, Ehsan (Supervisor)
    Abstract
    One of the most critical equipments in power grids are power transformers, which are vulnerable to damage due to the possibility of faults in its various components. A very common category of such faults is turn-to-turn fault in its winding. This fault initiates by the aging of the winding insulation with a short circuit of several adjacent loops to each other and if it is not detected quickly by the transformer protection, it will spread rapidly and can lead to irreparable failure in the transformer. Traditionally, turn-to-turn fault should be detected by mechanical pressure relays, however, due to the poor performance of these relays in the rapid detection of this type of fault, in the... 

    Design and Implementation of a Fault Detecting Algorithm for a High Voltage Underground Cable Using UHF Wireless Measuring Method

    , M.Sc. Thesis Sharif University of Technology Vasighzadeh Ansari, Arman (Author) ; Vakilian, Mehdi (Supervisor)
    Abstract
    One of the common problems in using high voltage network is the occurrence of partial electrical discharge in high voltage equipment such as cables. This problem may not be serious at first, but over time it can cause wear, corrosion, or reduction of equipment life, and eventually, if not prevented in a timely manner, can cause electrical sparks, larger problems, and possibly equipment and network become irreparable. On the one hand, due to very clear reasons, we need the voltage level to be high, and on the other hand, due to the application of high voltage level and the need to optimally design the insulation system to reduce their dimensions and construction costs, there will be the... 

    Geometric-Based Fault Diagnosis in a Grid-Connected Inverter

    , Ph.D. Dissertation Sharif University of Technology Mashreghi, Ali (Author) ; Namvar, Mehrzad (Supervisor)
    Abstract
    Inverters are the main utility in transmitting power from distributed generation (DG) systems toward grid and their safe and immune performance has become a major concern among the system designers. In addition to poor power transmittance, faults in inverter can harm other equipment such as DG and local load. Consequently different protections has been considered to increase the reliability of these systems. Some of these protections like fuses and varistors are implemented in the hardware while others are considered in the processor. In the later class of protections, fault detection and isolation (FDI) system has been the subject of intense investigation in inverters over the past two... 

    An Accurate Algorithm for Power Transformer Turn to Turn Fault Detection to Enhance the Performance of Differential Relay

    , Ph.D. Dissertation Sharif University of Technology Farzin, Nima (Author) ; Vakilian, Mehdi (Supervisor) ; Hajipour, Ehsan (Co-Supervisor)
    Abstract
    Power transformer is one of the most important equipment in the power system which plays a key role in the reliability and quality of power delivery. Among numerous failure modes of a typical power transformer, the turn-to-turn fault (TTF) is one of the most prominent reasons for its unplanned outage. A turn-to-turn fault quite often begins with the degradation of the winding insulation between two adjacent turns, then in a short time, this low-level fault can progress to a large number of turns and results in the transformer costly damages. Therefore, it is vital to detect TTF at an early stage and prevent its progression to a catastrophic disaster. The conventional percentage differential... 

    Improvement of Inverter-based AC Microgrids Protection Against Short Circuit

    , Ph.D. Dissertation Sharif University of Technology Zarei, Fariborz (Author) ; Mokhtari, Hossein (Supervisor) ; Blaabjerg, Frede (Co-Supervisor)
    Abstract
    Inverter-based distributed generations (IBDGs) have gained special interest in the electricity supply chain due to the advancements in power electronics technology. Power electronic inverters provide high-efficiency energy conversion with full controllability over a wide operating range, and ancillary services such as reactive power support and active filtering. Considering the voltage and frequency control capability of power inverters, supplying inverter-based micro-grid (IBMG) loads is now pissible. Despite the significant opportunities associated with such sources, they introduce new challenges that should be addressed properly. Reliable and accurate protection against short circuit... 

    Fault-Tolerant Operation of Three-Phase Dual Active Bridge Converter Against Semiconductor Power Switches Fault

    , M.Sc. Thesis Sharif University of Technology Davoodi Moghadam, Amirali (Author) ; Zolghadri, Mohammad Reza (Supervisor)
    Abstract
    The three-phase Dual Active Bridge DC-DC converter, by virtue of its various advantages, has been widely used in numerous industrial and sensitive applications. However, this converter includes a large number of power switching devices, which are the most fragile components in Power Electronics, and therefore, can pose a threat to appropriateness of the converter for such applications. Accordingly, introducing a fault-tolerant scheme for this converter is necessary, in order to meet the demands of high reliability and service continuity in aforementioned applications. In this thesis, firstly, the converter is studied during normal operation as well as under switch open-circuit fault, and the... 

    Applying of Data Fusion Method for Improving the Protection System of the High Voltage DC Power Supply

    , M.Sc. Thesis Sharif University of Technology Ayoubi, Ramin (Author) ; Kaboli, Shahriyar (Supervisor)
    Abstract
    Short-circuit fault detection is mandatory in a high voltage DC power supply to prevent fatal damage. The majority of converters employ a single sensor to detect the short-circuit fault. This attribute increases the interference vulnerability of the fault detection system in the presence of noise. Therefore, miss detections and false alarms are possible to occur. Miss detections and false alarms are harmful catastrophes in most applications. A commonly used method to suppress the noise impacts is using a low-bandwidth low-pass filter. However, the use of the low-bandwidth low-pass filter reduces the speed of fault detection due to the filter delay. This paper proposes a fast fault detection... 

    Performance Improvement of Cascaded H-bridge Multilevel Inverter under Faulty Conditions

    , Ph.D. Dissertation Sharif University of Technology Ouni, Saeed (Author) ; Zolghadri, Mohammad Reza (Supervisor) ; Oraee Mirzamani, Hashem (Supervisor) ; Rodriguez, Jose (Co-Advisor)
    Abstract
    Fault-tolerant ability is more subjected in Cascaded H-Bridge Multilevel Inverter due to its high-power medium-voltage applications and large number of semiconductors switches used in its structure. In this thesis, the goal is performance improvement of Cascaded H-bridge Multilevel Inverter under faulty conditions. Since to achieve the post-fault ability two steps; fault detection and post-fault control are required, both steps are considered in the improving process. In this dissertation, first operation of Cascaded H-Bridge Multilevel Inverter in normal and faulty condition is surveyed. Then, the conventional fault detection methods are mentioned and post-fault control methods are... 

    Leak Detection and Location in Oil Transmission Lines by Closed Form Solution and Linear Observer

    , M.Sc. Thesis Sharif University of Technology Derakhshan, Masoud (Author) ; Haeri, Mohammad (Supervisor)
    Abstract
    In this paper, an approach is proposed to estimate the location of the leaks in oil pipelines. The pipeline possesses a system of Partial Differential Equations (PDE). First, a closed-form solution is applied to the pipeline equations and the leakage location is found solving the steady-state equations. To tackle the case where the pressure and flowrate do not reach constant values, the initial estimations are provided by the closed-form solution. Then, the pressures, flow rates, and leakage coefficient are estimated by solving the system of differential equations. This system is then discretized with respect to the location variable to yield the system state equations which, in turn, are... 

    Open-Circuit Fault Detection and Localization in Five-Level Active Neutral Point Clamped Converter

    , M.Sc. Thesis Sharif University of Technology Montazeri Hedesh, Hamid (Author) ; Zolghadri, Mohammad Reza (Supervisor)
    Abstract
    Five-Level Active-Neutral-Point -Clamped (5L-ANPC) converter is used for medium-voltage and high-power applications. In many of these applications, availability and robustness against fault are the most important issues. On the other hand, this converter is made of a large number of power semiconductor switches, diodes and capacitors which could increase the failure probability. Thus, fault detection of power circuit elements is necessary for fault tolerant operation of the converter. In this thesis, following an introduction to the topology and operation principles of Five-Level Active Neutral point clamped converter, a novel open-circuit fault detection and localization method is...