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    Parameters calculation of transformer winding detailed model based on finite element method to study partial discharge

    , Article International Review on Modelling and Simulations ; Volume 5, Issue 5 , October , 2012 , Pages 1995-2000 ; 19749821 (ISSN) Hosseini, S. M. H ; Vakilian, M ; Enjavimadar, S. M ; Sharif University of Technology
    Praise Worthy Prize  2012
    The first step to locate Partial Discharge in power transformers is to find a model that can clearly explain the behavior of the winding in high-frequency. The detailed model is one of the models used for the study of PD. One of the fundamental problems of the described model is to find its parameters. And the accuracy in calculating these parameters has significant impact on reducing the simulation error and PD locating. The current paper seeks to calculate the parameters of the detailed model 20kv distribution transformer winding by using the finite element method (FEM). Comparing the results of this model with pulse waveforms obtained from the PD to the winding in the laboratory... 

    Determination of Eddy Current Losses in Power Transformer Tank and Analysis of Methods for Reduction of These Losses

    , M.Sc. Thesis Sharif University of Technology Motalleb, Mehdi (Author) ; Abbaspour Tehranifard, Ali (Supervisor) ; Vakilian, Mehdi (Supervisor)
    The leads with heavy current passing through the covering plates, and the winding in a transformer, are sources of eddy current losses. Due to this loss some regions of tank wall are subject to serious local overheating. It affects the safety and reliability of this expensive bject and power delivery.Heavy current in large power transformers and special type transformers give rise to a concentrated passage of eddy currents which in turn cause high local losses and overheating in the metallic parts especially in the steel tank walls of transformer.This local overheating is dangerous for transformer oil and the solid insulations. Therefore the calculation of losses and proper design of... 

    Modeling the Hysteresis Characteristic of Power Transformer Core for the Assessment of Inrush Current and Providing a Method to Reduce this Current

    , M.Sc. Thesis Sharif University of Technology Hassani Kaboutarkhani, Reza (Author) ; Vakilian, Mehdi (Supervisor)
    Inrush current as an inherent phenomena in transformer energizing cause to dramatic increase in current which flow through windings of transformer in first periods of energizing. first peak of inrush current can exceed even to several orders of nominal current but it decrease with time and at last after damping process it reaches to nominal currents. In large transformer this time can exceed to several minutes and cause damage to winding insulation, mechanical defects, wrong response of protection system and interrupting loads. Magnitude of this current has a close relation with residual flux. In this thesis a method for calculation of inrush current in single phase and three phase... 

    Time-Variant evaluation of electromagnetic forces on transformer windings during inrush current and short-circuit by FEM

    , Article Arabian Journal for Science and Engineering ; Volume 38, Issue 4 , 2013 , Pages 883-893 ; 13198025 (ISSN) Eslami, A ; Vakilian, M ; Sharif University of Technology
    Time-variant axial and radial electromagnetic for ces under inrush current and short-circuit current are calculated (by finite element method; FEM) and compared. A simplified analytic method is presented for computation of inrush current in transformer. The simulation results obtained by this method are compared with the measured values. A compact three-phase, core-type 132/20 KV, 30 MVA, power transformer is modeled, employing two-dimensional (2D) FEM, the different forces under short-circuit and inrush current conditions are evaluated as a function of time. The simulation results for this sample transformer show that the inrush current axial force is larger than clamping force (which is... 

    Power transformers internal insulation design improvements using electric field analysis through finite-element methods

    , Article IEEE Transactions on Magnetics ; Volume 44, Issue 2 , 2008 , Pages 273-278 ; 00189464 (ISSN) Khaligh, A ; Vakilian, M ; Sharif University of Technology
    Understanding the potential and electric field distribution in the insulation system of a transformer during transients is vital to its construction. Therefore, we have developed a method for electric field analysis inside a power transformer. The method consists of the following steps. 1) A lumped parameter equivalent model is constructed by dividing transformer windings into several blocks. 2) The electric circuit parameters of this model are calculated. 3) Employing the results of the transformer transient model analysis as boundary conditions, a 2-D asymmetrical electric field finite-element analysis is performed to determine electric fields through the windings. The method has been... 

    An extended Markov model to determine the reliability of protective system

    , Article 2006 IEEE Power India Conference, New Delhi, 10 April 2006 through 12 April 2006 ; Volume 2005 , 2005 , Pages 428-432 ; 0780395255 (ISBN); 9780780395251 (ISBN) Seyedi, H ; Fotuhi, M ; Sanaye Pasand, M ; Sharif University of Technology
    In this paper a reliability model for power transformer protection is proposed. The model is an extension of a previously proposed Markov model for transmission line protection. Optimum routine test and self checking intervals of the power transformer protection system are determined using the extended Markov model. © 2006 IEEE  

    Power transformers internal insulation design improvements through finite element methods

    , Article IEEE TENCON 2004 - 2004 IEEE Region 10 Conference: Analog and Digital Techniques in Electrical Engineering, Chiang Mai, 21 November 2004 through 24 November 2004 ; Volume C , 2004 , Pages C440-C443 Khaligh, A ; Vakilian, M ; IEEE Region 10 ; Sharif University of Technology
    The knowledge of the potential and field distribution in the insulation system of a transformer, during transient excitation is vital to its construction. This paper deals with insulation design improvements of power transformers using electric field analysis. The calculation methods for electric field analysis inside a power transformer impressed with impulse voltage is presented. Initially, a lumped parameter equivalent model is constructed by dividing transformer windings into several blocks and by computing the electric circuit parameters of this model. Next, the electric field is determined employing the results of the transformer transient model circuit analysis as boundary conditions;... 

    A method for modeling power transformer tap winding for transient studies

    , Article Conference Record of IEEE International Symposium on Electrical Insulation, Indianapolis, IN, 19 September 2004 through 22 September 2004 ; 2004 , Pages 34-37 ; 01642006 (ISSN) Naderi, M. S ; Vakilian, M ; Sharif University of Technology
    One of the challenges a transformer designer is faced with is to correctly model the different types of transformer windings for transient study. For a precise insulation design, determination of transformer transient responses is unavoidable. The basis of these studies is calculation of transient responses due to application of standard switching and lightning impulse wave to the transformer winding. In a previous work, a computer program was developed for determination of the layer and disk type windings transient model parameters based on design data. This program has all of the necessary capabilities for a detailed transient study. As a continuation of that work, in this paper a method... 

    Data mining on partial discharge signals of power transformer's defect models

    , Article 2010 45th International Universities' Power Engineering Conference, UPEC 2010, Cardiff, 31 August 2010 through 3 September 2010 ; 2010 ; 9780956557025 (ISBN) Darabad, V. P ; Vakilian, M ; Sharif University of Technology
    Partial discharge (PD) is a common phenomenon which occurs in insulation of high voltage equipments, such as; transformers and has a damaging effect on the insulation. If data mining techniques be used to find specifications and features of different types of partial discharges in power transformers, one can monitor the insulation condition of such equipment online and continuously. Those results can be employed to develop preventive measures more exactly and consequently the maintenance would require less time and cost for electric utility and improve the life time expectancy of the transformers. In this paper experiments are set up to create models for some types of PD that occurs in Power... 

    A Hybrid transformer pd monitoring method using simultaneous iec60270 and rf data

    , Article IEEE Transactions on Power Delivery ; Volume 34, Issue 4 , 2019 , Pages 1374-1382 ; 08858977 (ISSN) Firuzi, K ; Vakilian, M ; Phung, B. T ; Blackburn, T. R ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2019
    Transformers are the key component in power system transmission and distribution networks. Condition-based maintenance will increase their expected life, and online monitoring is essential to ensure operation reliability. In this paper, a new approach to transformer online monitoring is provided based on partial discharge (PD) measurement. Simultaneous measurements of PD using IEC60270 and radio frequency (RF) techniques are employed to explore new features that can be used to distinguish between internal PDs and external interference, as well as among different internal PD sources. Stream clustering based on the density grid method with only a few features required is used to categorize... 

    Inductance calculation of HTS transformers with multi-segment windings considering insulation constraints

    , Article Journal of Superconductivity and Novel Magnetism ; Volume 34, Issue 5 , 2021 , Pages 1329-1339 ; 15571939 (ISSN) Moradnouri, A ; Vakilian, M ; Hekmati, A ; Fardmanesh, M ; Sharif University of Technology
    Springer  2021
    High-temperature superconducting (HTS) transformers with multi-segment windings have been proposed in earlier literatures for the hysteresis loss reduction and short circuit electromagnetic force mitigation. The optimum distributive ratios for these multi-segment windings have been determined in earlier literatures. Asymmetrical seven segment winding with its optimum distributive ratio (k = 1/12) results in minimization of short circuit electromagnetic forces under normal tap and any adjusted tap. However, insulation design and leakage inductance calculation for the multi-segment winding of an HTS transformer have not been addressed in past literatures. Insulation design is one of the most... 

    Data Mining on Partial Discharge Signals of Power Transformer’s Defect Models

    , Ph.D. Dissertation Sharif University of Technology Parvin Darabad, Vahid (Author) ; Vakilian, Mehdi (Supervisor) ; Phung, Bao Toan (Co-Advisor) ; Blackburn, Trevor (Co-Advisor)
    In this thesis the goal is to use data Mining techniques for finding features of different Partial discharges happen in power transformer insulation defect models in order to monitor the insulation condition of in-service power transformers continuously and on-line and to identify any type of insulation defect in power transformers at the early stage of formation.For this purpose, power transformer Insulation defects are modeled physically and partial discharge current pulses are recorded as Partial discharge data.Tow format of data are investigated, in first one, recorded data in one power frequency cycle are explored and in second one, individual PD pulses are considered for study.In... 

    Optimizing the operation of current differential protection by power differential relay for three phase transformer

    , Article 2006 IEEE GCC Conference, GCC 2006, Manama, 20 March 2006 through 22 March 2006 ; 2006 ; 9780780395909 (ISBN) Bahmani, B ; Esmi Jahromi, M ; Ranjbar, A. M ; Sharif University of Technology
    To avoid the needless trip by magnetizing inrush current, the second harmonic component is commonly used for blocking differential relay in power transformers. However, the main problems of the current comparison method are in the very high inrush currents and relatively small fault currents regarding winding short circuits. Also The second harmonic component in fault current is increased in long lines which may blocks the relay operation. This paper describes a method to discriminate internal fault from inrush current and faults with a high second harmonic component by the sum of active power flowing into the transformer from each terminal. The average power is almost negligible for... 

    Investigation of partial discharge propagation and location in multiple-α and single- α transformer windings using optimized wavelet analysis

    , Article Iranian Journal of Science and Technology, Transaction B: Engineering ; Volume 30, Issue 6 , 2006 , Pages 655-666 ; 03601307 (ISSN) Salay Naderi, M ; Vakilian, M ; Blackburn, T. R ; Phung, T. B ; Salay Naderi, M ; Sharif University of Technology
    Partial discharges (PD) are recognized as the main cause of the inner insulation deterioration process in power transformers. Therefore, the optimum inner insulation design is one of the challenges a transformer designer is faced with. Transformer strength, especially during transient conditions, is a criterion for transformer insulation designers. This challenge has made designers initiate and employ other types of winding, for example, rather than ordinary layer and disc windings employ the multiple-α windings. Multiple-α windings have a more complicated structure and are comprised of various parts with different physical structures and electrical characteristics. Typical partial discharge... 

    Modeling and Data Mining of Partial Discharge in Power Transformer Solid Insulation

    , M.Sc. Thesis Sharif University of Technology Jahangir, Hamid (Author) ; Vakilian, Mehdi (Supervisor)
    Transformers are one of the most important equipments in transmission and distribution networks. Transformer unplanned outages have severe impacts on the continuity of power system operation. To improve the reliability of transformers and to achieve an optimum operation cost, online condition monitoring of transformers is inevitable. Information about the quality of the transformers insulation system is known as the best parameter to be monitored in a transformer. Since partial discharge signals are initiated long before the beginning of a severe damage, partial discharge monitoring and its evaluation canbe employed to warn the operator.Data mining on the partial discharge signals extracts... 

    Online Monitoring of PD in Power Transformers

    , M.Sc. Thesis Sharif University of Technology Ghaffarian Niasar, Mohamad (Author) ; Vakilian, Mehdi (Supervisor)
    PD detection can be done using on-line or off-line methods. Online PD detection methods have several advantages; such as: increasing system reliability, outage time reduction and higher safety. This method doesn’t need any special high voltage source. When on line monitoring is carried out for PD measurement, the noises in the environment and the electromagnetic interference (EMI) make it difficult to detect the PD signal. Therefore de-noising should be employed to filter out the interferences involved in the detected signal. In this thesis wavelet transform is introduced for this purpose. In this method, the background noise in the site of measurement is recorded as a reference noise to be... 

    Evaluation of Electromagnetic Forces on three-phase Core-Type Power Transformer Windings during Inrush Current by FEM

    , M.Sc. Thesis Sharif University of Technology Eslami, Ali (Author) ; Vakilian, Mehdi (Supervisor)
    Inrush Current is a form of over-current that occurs during energization of a transformer. For power transformers, the magnitude of the first peak of inrush current is initially several times the rated load current but slowly decreases until it finally reaches the normal exciting current value. This process typically takes several minutes. Time-variant axial and radial electromagnetic forces under inrush current and short-circuit current are calculated (by finite element method; FEM), and compared. An analytic method is presented for computation of inrush current in transformer. The simulation results obtained by this proposed method are compared with the measured values. A compact... 

    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)
    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... 

    Step change-point estimation of multivariate binomial processes

    , Article International Journal of Quality and Reliability Management ; Vol. 31, Issue 5 , April , 2014 , pp. 566-587 ; ISSN: 0265-671X Niaki, S. T. A ; Khedmati, M ; Sharif University of Technology
    Purpose: The purpose of this paper is to propose two control charts to monitor multi-attribute processes and then a maximum likelihood estimator for the change point of the parameter vector (process fraction non-conforming) of multivariate binomial processes. Design/methodology/approach: The performance of the proposed estimator is evaluated for both control charts using some simulation experiments. At the end, the applicability of the proposed method is illustrated using a real case. Findings: The proposed estimator provides accurate and useful estimation of the change point for almost all of the shift magnitudes, regardless of the process dimension. Moreover, based on the results obtained... 

    TANK shielding contribution on reduction of eddy current losses in power transformers

    , Article PPC2009 - 17th IEEE International Pulsed Power Conference, 28 June 2009 through 2 July 2009, Washington, DC ; 2009 , Pages 641-645 ; 9781424440658 (ISBN) Motalleb, M ; Vakilian, M ; Abbaspour, A ; Sharif University of Technology
    The current sources in power transformers such as leads and windings are also sources of Eddy current losses. Due to these losses some parts of tank wall are subject to serious local overheating. It affects the safety and reliability of these expensive objects and their power delivery. There are various methods for reduction of these eddy current losses. One of them is the internal shielding of transformer tank wall. In this paper the tank eddy current losses reduction, through its shielding is determined. ©2009 IEEE