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    Theoretical and experimental investigation of transformer winding fault detection using comparison of transfer function coefficients

    , Article Transactions on Electrical Engineering, Electronics, and Communications ; Volume 10, Issue 1 , 2012 , Pages 10-16 ; 16859545 (ISSN) Bigdeli, M ; Vakilian, M ; Rahimpour, E ; Azizian, D ; Sharif University of Technology
    2012
    Abstract
    In this work, a new model of transformer winding is developed. The components in the model are determined by the geometric and electric data of the winding (detailed model) and using experimental data based on genetic algorithm. Under different degrees of axial displacement and radial deformation in the winding, the circuit parameters of the model will change and thus the equivalent circuit characteristics will be influenced. After acquiring the model parameters in the intact and faulted cases, transfer function coefficients are derived in model using nodal analysis. Subsequently, introducing a new index based on these coefficients, the type and extent of penetration of the fault in the... 

    A probabilistic neural network classifier-based method for transformer winding fault identification through its transfer function measurement

    , Article International Transactions on Electrical Energy Systems ; Volume 23, Issue 3 , 2013 , Pages 392-404 ; 20507038 (ISSN) Bigdeli, M ; Vakilian, M ; Rahimpour, E ; Sharif University of Technology
    2013
    Abstract
    In this paper, a new method is introduced for identification of transformer winding fault through transfer function analysis. For this analysis, vector fitting and probabilistic neural network are used. The results of transfer functions estimation through vector fitting are employed for training of neural network, and consequently, probabilistic neural network is used for classification of faults. The required data for fault type identification are obtained by measurements on two groups of transformers (one is a classic 20 kV transformer, and the other is a model transformer) under intact condition and under different fault conditions (axial displacement, radial deformation, disc space... 

    A new method for detection and evaluation of winding mechanical faults in transformer through transfer function measurements

    , Article Advances in Electrical and Computer Engineering ; Volume 11, Issue 2 , 2011 , Pages 23-30 ; 15827445 (ISSN) Bigdeli, M ; Vakilian, M ; Rahimpour, E ; Sharif University of Technology
    2011
    Abstract
    Transfer function (TF) is an acknowledged method for power transformer mechanical faults detection. However the past published works mostly discovered how to specify the faults levels and paid less attention to detection of the type of faults using comparison of TFs. whereas, it seems important for most of the applications to specify the type of fault without opening the unit. This paper presents a new method based on vector fitting (VF) to compare the TFs and specify the type, level and location of the fault. For development of the method, and its verification the required measurements are carried out on four model transformers; under intact condition, and under different fault conditions... 

    CDM-based closed-loop transfer function design for ramp input

    , Article Transactions of the Institute of Measurement and Control ; Volume 33, Issue 5 , 2011 , Pages 558-572 ; 01423312 (ISSN) Haeri, M ; Tavazoei, M. S ; Sharif University of Technology
    2011
    Abstract
    This paper presents a method to determine the denominator and numerator polynomials of a closed-loop transfer function in order to obtain desired transient and steady-state responses in terms of the overshoot, speed (time needed for the relative error to become less than a specific amount) and the steady-state error when the desired output is a ramp signal. Meanwhile, a controller is designed with the same characteristic equation for the closed-loop system to eliminate step and ramp disturbances  

    Notes on the state space realizations of rational order transfer functions

    , Article IEEE Transactions on Circuits and Systems I: Regular Papers ; Volume 58, Issue 5 , 2011 , Pages 1099-1108 ; 15498328 (ISSN) Tavakoli-Kakhki, M ; Haeri, M ; Tavazoei, M. S ; Sharif University of Technology
    2011
    Abstract
    In this paper, the concept of minimal state space realization for a fractional order system is defined from the inner dimension point of view. Some basic differences of the minimal realization concept in the fractional and integer order systems are discussed. Five lower bounds are obtained for the inner dimension of a minimal state space realization of a fractional order transfer function. Also, the concept of optimal realization, which can be a helpful concept in practice, is introduced for transfer functions having rational orders. An algorithm is suggested to obtain the optimal realizations of rational order transfer functions. The introduced concept might be used to get minimal... 

    Transformer winding faults classification based on transfer function analysis by support vector machine

    , Article IET Electric Power Applications ; Volume 6, Issue 5 , 2012 , Pages 268-276 ; 17518660 (ISSN) Bigdeli, M ; Vakilian, M ; Rahimpour, E ; Sharif University of Technology
    Abstract
    This study presents an intelligent fault classification method for identification of transformer winding fault through transfer function (TF) analysis. For this analysis support vector machine (SVM) is used. The required data for training and testing of SVM are obtained by measurement on two groups of transformers (one is a classic 20 kV transformer and the other is a model transformer) under intact condition and under different fault conditions (axial displacement, radial deformation, disc space variation and short circuit of winding). Two different features extracted from the measured TFs are then used as the inputs to SVM classifier for fault classification. The accuracy of proposed... 

    Comparison of transfer functions using estimated rational functions to detect winding mechanical faults in transformers

    , Article Archives of Electrical Engineering ; Volume 61, Issue 1 , 2012 , Pages 85-99 ; 00040746 (ISSN) Bigdeli, M ; Vakilian, M ; Rahimpour, E ; Sharif University of Technology
    2012
    Abstract
    As it is found in the related published literatures, the transfer function (TF) evaluation method is the most feasible method for detection of winding mechanical faults in transformers. Therefore, investigation of an accurate method for evaluation of the TFs is very important. This paper presents three new indices to compare the transformer TFs and consequently to detect the winding mechanical faults. These indices are based on estimated rational functions. To develop the method, the necessary measurements are carried out on a 1.3 MVA transformer winding, under intact condition, as well as different fault conditions (axial displacement of winding). The obtained results demonstrate the high... 

    The minimal state space realization for a class of fractional order transfer functions

    , Article SIAM Journal on Control and Optimization ; Volume 48, Issue 7 , 2010 , Pages 4317-4326 ; 03630129 (ISSN) Tavakoli Kakhki, M ; Haeri, M ; Sharif University of Technology
    2010
    Abstract
    In this paper, the minimal state space realization of a fractional order transfer function is investigated in the sense of inner dimension both for commensurate and incommensurate cases. It is shown that while the traditional tools are applicable to check the minimality of a commensurate realization, there is no specific procedure to be certain about the minimality of incommensurate realizations. In this regard, the necessary and sufficient conditions are obtained for a specific class of fractional order transfer functions by which one can verify the existence of minimal realizations with inner dimension 2. Furthermore, a transformation is introduced through which all these realizations can... 

    An improvement of the matrix-fracture transfer function in free fall gravity drainage

    , Article Petroleum Science and Technology ; Vol. 31, issue. 24 , Apr , 2011 , Pages. 2612-2620 ; 10916466 (ISSN) Samimi, S. E ; Masihi, M ; Sharif University of Technology
    Abstract
    The simulation of fractured reservoir is conventionally performed by using dual porosity formulation in which the type of transfer function may be critical. Over the past few years, various models with their strength and weakness have been developed to account for matrix-fracture interporosity flow. However, some of them are unable to simulate some mechanisms like gravity drainage. In this work, the most well-known transfer functions have been examined for simulation of the gravity drainage in a single block model and an improvement has been introduced to modify them. The validation of the developed approach have been done by using fine grid simulation  

    Effect of rf pumping frequency and RF input power on the flux to voltage transfer function of rf-SQUIDs

    , Article IEEE Transactions on Applied Superconductivity ; Volume 17, Issue 2 , 2007 , Pages 676-679 ; 10518223 (ISSN) Akram, R ; Eker, T ; Bozbey, A ; Fardmanesh, M ; Schubert, J ; Banzet, M ; Sharif University of Technology
    2007
    Abstract
    We present the results on the correlation between the flux to voltage transfer function, Vspp, of the rf-SQUID and the rf-bias frequency as well as rf-bias power. Measurements were performed for different SQUID gradiometer samples chosen from the same batch or different batches. In order to have full control on the electronics parameters, an experimental rf-SQUID circuit was designed and implemented with an operation frequency of 600 MHz to 900 MHz. According to our findings, It has been observed that at any particular rf-bias power, Vspp vs. rf-bias frequency shows Sine-like behavior. We observed that the main lobe maxima exist close to the resonance frequency of the LC tank circuit and by... 

    Investigation of Premixed V-shaped Flame Response to Acoustic Oscillations

    , M.Sc. Thesis Sharif University of Technology Nabatian, Negar (Author) ; Farshchi, Mohammad (Supervisor)
    Abstract
    Low emissions combustion V-flame combustors are exceptionally prone to combustion instabilities. These systems for land based gas turbines rely on a premixed or partially premixed combustion process. As V-flames do not anchored on the lip of combustor, an experimental study of the transfer function of these flames shows that they are more sensitive to fuel oscillations and in the range of frequencies, they behave like an amplifier. This paper presents an experimental study of the transfer function of a ducted, laminar, premixed V and M-flames. V-flame, laminar, propane/air premixed flame stabilised at the rim of the burner. The limit of M and V-flame are identified without excitation, then... 

    On the essential instabilities caused by fractional-order transfer functions

    , Article Mathematical Problems in Engineering ; Volume 2008 , 2008 ; 1024123X (ISSN) Merrikh Bayat, F ; Karimi Ghartemani, M ; Sharif University of Technology
    2008
    Abstract
    The exact stability condition for certain class of fractional-order (multivalued) transfer functions is presented. Unlike the conventional case that the stability is directly studied by investigating the poles of the transfer function, in the systems under consideration, the branch points must also come into account as another kind of singularities. It is shown that a multivalued transfer function can behave unstably because of the numerator term while it has no unstable poles. So, in this case, not only the characteristic equation but the numerator term is of significant importance. In this manner, a family of unstable fractional-order transfer functions is introduced which exhibit... 

    Fractional/distributed-order systems and irrational transfer functions with monotonic step responses

    , Article JVC/Journal of Vibration and Control ; Vol. 20, issue. 11 , 2014 , pp. 1697-1706 Tavazoei, M. S ; Sharif University of Technology
    Abstract
    This paper deals with irrational transfer functions having monotonic nondecreasing step responses. Firstly, some results on the monotonicity of step responses in irrational transfer functions describing fractional- or distributed-order systems are presented. Then, some conditions guaranteeing the existence of monotonic nondecreasing step responses in more general forms of irrational transfer functions are found. Various examples are brought to show the usefulness of the obtained results in time response analysis of fractional/distributed-order systems. The achievements of the paper can be used in the design of control systems having monotonic step responses  

    Laser diode modulation under large signal conditions

    , Article 2013 21st Iranian Conference on Electrical Engineering ; May , 2013 , Page(s): 1 - 5 ; 9781467356343 (ISBN) Ahmadian, A ; Sharif University of Technology
    2013
    Abstract
    Large signal behavior of the Laser Diode is analyzed with the aim of finding a qualitative relationship between modulation amplitude and the change in the shape of its transfer function. It is found that, at quasi-static conditions, increasing the amplitude of the modulating signal smoothes out the original piecewise-linear transfer function of the diode. It further shifts the now smoothed knee point to lower DC currents. As the frequency increases, however, these effects become less and less pronounced. In addition, the transfer function becomes rather wavy due to the failure of current density to reach the saturation level necessary for adequate stimulated emission. At even higher... 

    Minimal realizations for some classes of fractional order transfer functions

    , Article IEEE Journal on Emerging and Selected Topics in Circuits and Systems ; Volume 3, Issue 3 , 2013 , Pages 313-321 ; 21563357 (ISSN) Tavazoei, M. S ; Tavakoli Kakhki, M ; Sharif University of Technology
    2013
    Abstract
    It has been known that finding a minimal pseudo state space realization for a fractional order transfer function is helpful in circuitry implementation of such a transfer function with the minimum number of fractional capacitors. Considering this importance, the present paper deals with finding minimal realizations for some classes of fractional order transfer functions. To this end, at first some upper bounds are obtained for the minimal inner dimension of a fractional order transfer function. By considering these upper bounds and also the lower bounds, previously presented in literature, the minimal inner dimension is exactly found for some classes of fractional order transfer functions.... 

    Characteristic ratio assignment in fractional order systems (case 0 < v ≤ 0.5)

    , Article Transactions of the Institute of Measurement and Control ; Volume 35, Issue 3 , 2013 , Pages 360-374 ; 01423312 (ISSN) Tabatabaei, M ; Haeri, M ; Sharif University of Technology
    2013
    Abstract
    Five different approaches are presented to assign characteristic ratios for commensurate fractional order systems having order in (0,0.5]. Through the indirect methods, a closed-loop or plant transfer function is converted to a commensurate order one with an order greater than 0.5 so that the previously designed CRA method by the authors is applicable. The first method among the proposed direct ones is based on increasing the order of the desired closed-loop transfer function that allows the employment of positive characteristic ratios. In the second method the closed-loop response is sped up by augmenting an appropriate zero. The final method uses negative characteristic ratios to reach the... 

    Transformer winding diagnosis using comparison of transfer function coefficients

    , Article ECTI-CON 2011 - 8th Electrical Engineering/ Electronics, Computer, Telecommunications and Information Technology (ECTI) Association of Thailand - Conference 2011, 17 May 2011 through 19 May 2011, Khon Kaen ; 2011 , Pages 681-683 ; 9781457704246 (ISBN) Bigdeli, M ; Vakilian, M ; Rahimpour, E ; Azizian, D ; Sharif University of Technology
    2011
    Abstract
    In this work, a new model of transformer winding is developed. The components in the model are determined by the geometric and electric data of the winding. Under different degrees of axial displacement and radial deformation in the winding, circuit parameters in the model will be changed and thus the character of the circuit will be influenced. After acquiring the model parameters in the intact and faulted cases, transfer function coefficients derived in model from nodal analysis. Then using introduce the new index based on coefficients we can specify the type and extent of penetration of the fault in the winding. Results presented demonstrate the potential of this method  

    Stability preservation analysis in direct discretization of fractional order transfer functions

    , Article Signal Processing ; Volume 91, Issue 3 , 2011 , Pages 508-512 ; 01651684 (ISSN) Siami, M ; Saleh Tavazoei, M ; Haeri, M ; Sharif University of Technology
    Abstract
    In this paper, a class of the direct methods for discretization of fractional order transfer functions is studied in the sense of stability preservation. The stability boundary curve is exactly determined for these discretization methods. Having this boundary helps us to recognize whether the original system and its discretized model are the same in the sense of stability. Finally, some illustrative examples are presented to evaluate achievements of the paper  

    Realizability of fractional-order impedances by passive electrical networks composed of a fractional capacitor and RLC components

    , Article IEEE Transactions on Circuits and Systems I: Regular Papers ; Volume 62, Issue 12 , 2015 , Pages 2829-2835 ; 15498328 (ISSN) Sarafraz, M. S ; Tavazoei, M. S ; Sharif University of Technology
    Abstract
    This paper deals with realization of fractional-order impedance functions by passive electrical networks composed of a fractional capacitor and some RLC components. The necessary and sufficient conditions for the existence of such a realization are found in a general case. Also for impedance functions described by a class of fractional-order transfer functions, the realizability conditions are stated as some algebraic conditions on the parameters of the transfer function. Moreover, a procedure is proposed for implementation of such impedance functions by passive electrical networks composed of a fractional capacitor and some RLC components. Numerical examples are presented to show the... 

    Frequency domain identification of a tapered beam embedded by piezoelectric layer

    , Article 2016 International Conference on Advanced Mechatronic Systems, ICAMechS 2016, 30 November 2016 through 3 December 2016 ; 2017 , Pages 312-317 ; 23250682 (ISSN); 9781509053469 (ISBN) Banazadeh, A ; Ahranjani, F. F ; Kamankesh, Z ; Sharif University of Technology
    IEEE Computer Society  2017
    Abstract
    This study is conducted aiming to identify the dynamics of a tapered beam, embedded by piezoelectric layer. Narrowing the tip of the beam equipped with piezoelectric patches leads to optimize the output power after excitation by the frequency sweep input. An accelerometer is installed on the beam base, which measures the acceleration that is applied to the system. Piezoelectric sensors also measure the generated voltage. The experimental test data is handled through CIFER software, using Fourier transform and Bode plot in the frequency domain, to obtain appropriate transfer functions. MATLAB is used for nonlinear simulation and validation of discrete transfer functions by a set of data that...