ترانسفورماتور

Open Access Article

1 - Determination of Control Variables in Power Systems to Maximum Load Restoration
H. Afrakhte A. Yazdian Varjani

20.1001.1.16823745.1386.5.10.4.1

This paper presents a new method to maximize load restoration in faulted condition in power systems. Control variables which are used to restore maximum load include tap of power transformers, generation rescheduling, and load shedding in the worst case. Modeling is don More

This paper presents a new method to maximize load restoration in faulted condition in power systems. Control variables which are used to restore maximum load include tap of power transformers, generation rescheduling, and load shedding in the worst case. Modeling is done in three stages with various control variables arrangements. In the first stage of modeling, power transformer tap is used as a control variable. In the second stage, power transformers taps and generations rescheduling are considered. In the last stage, load shedding as another variable is added to decision variable spaces. Since the number of variables is high and final solution space can be nonlinear, genetic algorithm is used in the optimization process. The capabilities of the proposed method were assessed using IEEE-RTS test system with satisfactory results. Manuscript profile

Open Access Article

2 - Transformers Oil Static Electrification Analysis by Using Open Cycle System
B. vahidi Gh. Rasuli Hashemabad

20.1001.1.16823745.1387.6.14.8.0

Static electrification due to oil flow is the main reason for several electrical breakdown in large transformers. In the present paper this phenomenon has been investigated by the aid of open cycle system. Finally from tests results obtained by authors, the effects of a More

Static electrification due to oil flow is the main reason for several electrical breakdown in large transformers. In the present paper this phenomenon has been investigated by the aid of open cycle system. Finally from tests results obtained by authors, the effects of applied electric field, temperature and oil flow velocity on static electrification have been investigated. Manuscript profile

Open Access Article

3 - A Novel Wavelet Based Method for Improvement of Power Transformer Differential Relay against Magnetizing Inrush Current and CT Saturation
A. Rahmati M. Sanaye-Pasand

20.1001.1.16823745.1388.7.18.4.1

Differential protective relay serves as the main protection of transformers against faults in the windings for many years. Unremitting tries for more smart of this protection relay have been done by different creative manufactures and up to now different methods and inv More

Differential protective relay serves as the main protection of transformers against faults in the windings for many years. Unremitting tries for more smart of this protection relay have been done by different creative manufactures and up to now different methods and inventions have been proposed for better operational of the differential relay. However, a differential protection for differential currents would be handicapped by difficulties due to several natural phenomena which are the cause of false differential currents and misoperate of the relay. Some of these phenomena, such as the inrush current and saturation of instrument current transformers, are the main concern in designing an efficient differential protection algorithm. This paper at first, proposes a new algorithm based on the Wavelet Transform (WT) to identify internal fault from magnetizing inrush in three phase power transformers. The internal faults can be accurately discriminated from inrush current less than a quarter a cycle after the disturbance. At following with definition of an index which it is extracted from the high frequencies by WT, the restrain current in bias-current characteristic of differential relay has been improved. Obtained results demonstrate that the proposed algorithm can provide the desired response and can be used as a very fast and accurate method. Manuscript profile

Open Access Article

4 - Determination of a New Model for Investigating Ultra-Saturation Phenomenon during the Enegization of the Loaded Three-Phase Power Transformer and Its Effect on Differential Protection
B. Noshad M. Razaz S. Gh. Seifossadat

20.1001.1.16823745.1392.11.3.4.9

One of the mal-operation of the power transformer differential protection that may occur during the energization of a loaded power transformer is the ultra-saturation phenomenon. In this paper, a new model to study the ultra-saturation phenomenon during the energizaton More

One of the mal-operation of the power transformer differential protection that may occur during the energization of a loaded power transformer is the ultra-saturation phenomenon. In this paper, a new model to study the ultra-saturation phenomenon during the energizaton of a loaded three-phase power transformer is presented and its effect on the differential protection of the power transformer is considered. For modeling of the ultra-saturation phenomenon, the nonlinear characteristic of the transformer core and the saturation effect of current transformers are considered. It is assumed that the load of the power transformer is a resistive and an inductive load. The mal-operation of the differential protection depends on a variety of factors the most important parameters of which are inception angle and residual flux. In this paper the parameters mentioned will study in different cases. In this paper, simulation is done by MATLAB program. Manuscript profile

Open Access Article

5 - A New Unified Power Quality Conditioner based on Trans-Z-Source Inverter
M. Siahi Mohammad Davoodi

20.1001.1.16823745.1395.14.1.6.8

Unified Power quality conditioner (UPQC) consists of back to back voltage source inverters. In UPQC combination of parallel and series active power filters are used to compensate for the nonlinear load current harmonics and voltage distortions, simultaneously. For appro More

Unified Power quality conditioner (UPQC) consists of back to back voltage source inverters. In UPQC combination of parallel and series active power filters are used to compensate for the nonlinear load current harmonics and voltage distortions, simultaneously. For appropriate performance of both converters and bidirectional power flow, the DC link voltage should be at least 1.41 times larger than the line to line voltage in the high voltage part of the system; i.e. the parallel active filter. One of the determining factors for the cost of semiconductors is the maximum tolerable voltage stress. The voltage stress of the series converter increases when the DC link voltage is high. In order to overcome this deficiency, a Z-source network is added to the common structure of back to back invertors in the UPQC. It will reduce the applied DC voltage to the series active power filters significantly and decrease the cost of manufacturing. In this structure, an impedance source network is used in an AC/DC inverter to produce a buck-boost effect. Additionally, dead time has been eliminated through the use of a Z source network in the parallel active filter and thus its performance and reliability has increased impressively. In this paper, a comparison study has been conducted through necessary simulations for the performance evaluation of the common and proposed structures. The total switching device power has been used as a criteria to confirm the manufacturing cost reduction in the proposed structure. Manuscript profile

Open Access Article

6 - 3D Finite Element Analysis of MV Three-Phase Transformer Mechanical Forces Effected by Inrush Current Based on a Novel Winding Structure
A. Nasiri A. Ranjbar F. Faghihi S. Soleymani

20.1001.1.16823745.1395.14.2.3.7

Transient mechanical force in transformer induced critical mechanical stress on windings and transformers in radial and axial directions. In this paper, impact of force’s within transient inrush current duration on MV three phase transformer with propose novelty windin More

Transient mechanical force in transformer induced critical mechanical stress on windings and transformers in radial and axial directions. In this paper, impact of force’s within transient inrush current duration on MV three phase transformer with propose novelty winding configuration (S-P-S) to considered. In order to forces analysis, a 3-D model of three phase transformer developed by use Ansoft Maxwell V15.0. Magnetic vector potential, Magnetic flux density and electro-mechanical force’s of SPS-type and conventional-type of configuration windings and transformer calculated from a 3D finite element model. Based on the comparison and result analysis, proposed an optimal configuration for transformer winding in order to trade-off and minimization of electromechanical force’s in the transient inrush current state. Manuscript profile

Open Access Article

7 - An Improved Grid Connected Transformerless Inverter with Proportional Resonant Controller
J. Fallah Ardashir M. Sabahi S. H. Hosseini E. Babaei G. Gharehpetian

20.1001.1.16823745.1396.15.1.4.3

The grid tied PV systems without transformer have some benefits such as low cost, weight and size and also increases the overall efficiency. The galvanic connection between the grid and PV system causes leakage current in the transformerless inverter to flow through pa More

The grid tied PV systems without transformer have some benefits such as low cost, weight and size and also increases the overall efficiency. The galvanic connection between the grid and PV system causes leakage current in the transformerless inverter to flow through parasitic capacitors between the PV system and ground and causes personal safety problems, increases the output harmonic spectrum, and system losses. This paper introduces a modified single phase two stage transformerless inverter for grid connected photovoltaic systems with low leakage current. The neutral of the grid is directly connected to the negative terminal of PV panel that eliminates leakage current without complex control strategy. In this paper, a Proportional Resonant (PR) control strategy is used to control the injected current. The performance of the transformerless inverter is analyzed and its structure has been simulated in PSCAD/EMTDC and the obtained results tested experimentally. Manuscript profile

Open Access Article

8 - Operational Analysis of the Buck Boost DC–DC Converter with High Step-Up Voltage Gain
M. R. Banaei H. A. Faeghi Bonab

20.1001.1.16823745.1396.15.3.3.6

In some applications that we need a high voltage gain such as the photovoltaic cell and fuel cell, high step up dc-dc converters must be used, but conventional boost converter cannot provide the high voltage gain. For this reason, in this paper, a single switch transfor More

In some applications that we need a high voltage gain such as the photovoltaic cell and fuel cell, high step up dc-dc converters must be used, but conventional boost converter cannot provide the high voltage gain. For this reason, in this paper, a single switch transformerless high step-up buck boost dc-dc converter with reduced voltage stress on the semiconductors is proposed. The proposed converter has higher voltage gain in step-up mode in comparison with conventional boost and buck-boost converters. Reduced voltage stress on the active switch allows to choose lower voltage rating MOSFETs to reduce both switching and conduction losses. Low voltage stress on the diodes allows the use of Schottky rectifiers for alleviating the reverse-recovery current. The proposed converter can be operated in the continuous conduction mode (CCM) and the discontinuous conduction mode (DCM). In this paper, different operation modes of the proposed converter, calculation of the voltage gain, the currents that flow through the components, efficiency and capacitors voltage ripple are presented. To verify the operation of the proposed converter, simulation results via PSCAD software and experimental results are provided. Manuscript profile

Open Access Article

9 - Investigation of Fundamental Mode of Ferroresonance for Transformer considering the Inverse JA Hysteresis Model
B. Rezaeealam M. Mikhak Beyranvand

20.1001.1.16823745.1397.16.1.9.5

Severe saturation of the magnetic core is the most influential factor in ferroresonance that leads to distorted currents and voltages. , modeling the nonlinear behavior of the magnetic core is the most important challenge in ferroresonance study. In this paper, finite e More

Severe saturation of the magnetic core is the most influential factor in ferroresonance that leads to distorted currents and voltages. , modeling the nonlinear behavior of the magnetic core is the most important challenge in ferroresonance study. In this paper, finite element method in conjunction with the inverse Jiles-Atherton (JA) hysteresis model of the steel core, is employed for modeling of a single-phase transformer accurately. Then, ferroresonance is studied by inserting different capacitors in series with the unloaded transformer, and the corresponding variation of copper losses and iron losses are obtained and discussed. Ferroresonance affects the shape of the hysteresis loop that necessitates the retuning of the parameters of the JA hysteresis model. The numerical results agree well with the experimental ones. Manuscript profile

Open Access Article

10 - Winding Losses Calculation in Multi-Winding Traction Transformer Using a Semi-Numerical Method
D. Azizian G. Gharehpetian

20.1001.1.16823745.1397.16.4.4.6

Nowadays, multi-winding transformers are widely used in power systems, especially in traction networks and steel producing companies. The multi-winding transformers have special geometry. They encounter with serious problems and difficulties in design procedure in compa More

Nowadays, multi-winding transformers are widely used in power systems, especially in traction networks and steel producing companies. The multi-winding transformers have special geometry. They encounter with serious problems and difficulties in design procedure in comparison with conventional two-winding transformers. Considering the importance of windings losses (and the generated heat), the current research firstly focuses on thermal calculations in this type of transformers, also introduces a semi-numerical technique for electromagnetic analysis of split-winding traction system transformer. Combining finite element and analytical methods, the windings losses distribution due to eddy currents is calculated and the modeling results are validated using the experimental results. As shown, the introduced semi-numerical method is a powerful technique for electromagnetic modeling and winding losses calculations in split-winding transformers. Also, the winding losses of the split-winding transformer are discussed and compared to the conventional two-winding transformer results. Finally, the relation between the winding losses and frequency is studied in this paper. Manuscript profile

Open Access Article

11 - A Model-Based Approach for Improving Power Transformer Differential Protection
Zahra Kazemi Mohammad Mohammadpour E. Farjah

20.1001.1.16823745.1398.17.3.6.3

In this paper, a new algorithm based on Kalman Filter (KF) is proposed for improving the reliability of power transformer differential protection. The three-phase currents of the transformer at the energization side are first estimated by KF. Three residual signals whic More

In this paper, a new algorithm based on Kalman Filter (KF) is proposed for improving the reliability of power transformer differential protection. The three-phase currents of the transformer at the energization side are first estimated by KF. Three residual signals which are the differences between the measured (by current transformers) and estimated (by KF) are defined and considered as the decision criteria to discriminate the fault and inrush conditions. During the transformer energization, the residual signals are almost zero. However, in fault conditions, the residual signals exceed a determined threshold value and a trip command will be subsequently issued. The performance of the proposed method is verified using simulations in MATLAB and PSCAD software. Manuscript profile

Open Access Article

12 - A Thermal Equivalent Circuit for Thermal Analysis of Power Transformers under Harmonic Loads
m. mikhak B. Rezaeealam m. jafarboland v. ebrahimian m. asgari

20.1001.1.16823745.1398.17.4.1.0

The majority of the power transformers failures are caused by the thermal stresses under abnormal operating conditions, such as harmonic loads. Therefore, it is of great interest to determine the temperature distribution inside the power transformers. In this paper, a n More

The majority of the power transformers failures are caused by the thermal stresses under abnormal operating conditions, such as harmonic loads. Therefore, it is of great interest to determine the temperature distribution inside the power transformers. In this paper, a new thermal equivalent circuit is presented by which the temperature in different regions of the transformer is estimated under harmonic loads. Also, the three-dimensional Finite Element (FE) Model of the power transformer is developed to calculate the power losses in each part of the transformer that are considered as the heat sources in the proposed equivalent circuit. The computed hotspot and average oil temperatures are compared with those obtained from IEEE Std C57.91 method, thereby the accuracy of the proposed method for calculating the temperature rise due to harmonic loads, is investigated. Finally, derating of the power transformer is discussed under harmonic loads. Manuscript profile

Open Access Article

13 - Evaluation of the Effect of Transformer Oil Parameters on the Transformer Health Index Using Curve Estimation Method
Morteza Saeid Hamed Zeinoddini-Meymand

Transformers are one of the most expensive and important equipment in power systems that are under the influence of electrical, thermal and chemical reactions The transformer health index is a standard that is used to evaluate the condition and determine the remaining l More

Transformers are one of the most expensive and important equipment in power systems that are under the influence of electrical, thermal and chemical reactions The transformer health index is a standard that is used to evaluate the condition and determine the remaining life of the transformer by using laboratory data and field inspections. The purpose of this article is to determine the relationships between electrical, physical, chemical parameters of oil, dissolved gases in oil and transformer health index. One of the advantages of using the regression method in the analysis of transformer data compared to other methods for determining the transformer health index is determining the influence of the parameters that have the greatest impact on each other. In this article, Curve Estimation Regression method is used and the results are drawn by drawing graphs by SPSS statistical software to analyze the parameters. To carry out the simulations, the laboratory data of some transformers have been considered. Manuscript profile

Open Access Article

14 - Integrated Modeling of Bidirectional Solid-State Transformers: Rectifier, DC to DC Converter and Inverter Stages
hamed molla-ahmadian morteza shafiei javid khorasani

20.1001.1.16823745.1401.20.3.13.1

: One of the new and growing equipment in modern power networks is solid state or power electronic transformer. These types of transformers are based on power semiconductor switches and high frequency transformers. Compared to traditional transformers, it has several ca More

: One of the new and growing equipment in modern power networks is solid state or power electronic transformer. These types of transformers are based on power semiconductor switches and high frequency transformers. Compared to traditional transformers, it has several capabilities such as the ability to operate with input voltage variations in amplitude and frequency, automatic regulation of output voltage and input power factor correction. The investigated transformer has the ability to transfer power in both directions and has three stages, including the rectifier, the middle stage and the inverter stage. This transformer has a large number of semiconductor switches and its modeling, analysis, design and simulation is difficult and complex. In particular, real-time simulation of these transformers with conventional models is not possible. In these cases, the use of averaging theory seems to be the appropriate solution. In this paper, the averaging theory is applied to a solid-state transformer and its modeling is done in a simple and powerful way with the ability to study real-time, transient and steady states performance. The proposed modeling includes differential equations and equivalent circuits and offers an integrated transformer model with the ability to study the interaction between stages as a part of power system. The presented models are used in simulation of smart grids, DC microgrids and connection of distributed generation sources to the grid, as well as analysis and design of solid-state transformer behavior in areas such as renewable energies and electrical transportation. In addition to the proposed modeling, the closed-loop control structure has been implemented for all three stages. Transformer simulation is performed by implementing differential equations in SIMULINK/MATLAB software and verified the proposed model. Manuscript profile

Open Access Article

15 - Performance Improvement of High Voltage Transformer in Klystron Amplifier Power Supply by Magnetizing Current Balancing
Abolfazl Nasiri mohsen ganji seed mohamad Alavi

In this research, the structure of a Full-bridge converter has been used to feed the klystron amplifier. Three Full-bridge transducer modules with high voltage transformers are used to supply the power of klystron (100 kW, 4 kV, 25 kV). The output of More

In this research, the structure of a Full-bridge converter has been used to feed the klystron amplifier. Three Full-bridge transducer modules with high voltage transformers are used to supply the power of klystron (100 kW, 4 kV, 25 kV). The output of the transformers is rectifier in a star structure and after passing through a π filter, the circuit of the klystron lamp is supplied. The output of the power supply is 1 ms width and frequency of repetition is 50 Hz. The input voltage of the converter is 500 VDC, which is supplied by a three-phase feed. In this research, by balancing the magnetizing current of high frequency transformers, the maximum magnetization current of transformers decreases and decreases the maximum current of transistors. In addition, the core dimensions of the transformer decrease by reducing the maximum magnetization current. As a result, the dimensions, volume, and weight of the klystron drive circuit are reduced. Also, by using leakage inductance of high frequency transformer, series resonance circuit has been created and soft switching conditions have been provided. In this way, it improves the performance of the klystron driven circuit. Modulator performance has been simulated and approved using PSCAD software and resistive load. Manuscript profile

Open Access Article

16 - Detection and Analysis of Acoustic Signals of Power Transformers On-Load Tap Changers for Assessment of Their Faults
adel younesi Abbas Ghayebloo Hasanreza Mirzaei

On load tap changers are very important equipment of the power transfor More

On load tap changers are very important equipment of the power transformers. Due to the strongly mechanical movements and high-energy arcs, this equipment has a much higher failure rate with respect to other internal transformer equipment. Online and accurate evaluation of well operation of these equipment by indicators with no interfere on the normal operation of the transformer, is very important issue. In this paper, various faults detecting methods in the tap changer have been discussed an investigated by some extracted features of acoustic signals. These signals have been captured experimentally in various tap changing periods by an accelerometer sensor mounted on a power transformer body. In this paper, in addition to common features, two new feathers entitled time and frequency indicators have been introduced. Finally, for selecting the proper features to faults detection and proposing an effective classification method, some available experimental data were randomly defected by results in the references, and classified successfully as healthy and defective data by support vector machine (SVM) method. Manuscript profile

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