M. Jamali, M. Mirzaie, S. A. Gholamian,
Volume 7, Issue 3 (9-2011)
Abstract
The phenomenon of magnetizing inrush is a transient condition, which occurs primarily when a transformer is energized. The magnitude of inrush current may be as high as ten times or more times of transformer rated current that causes malfunction of protection system. So, for safe running of a transformer, it is necessary to distinguish inrush current from fault currents. In this paper, an equivalent instantaneous inductance (EII) technique is used to discriminate inrush current from fault currents. For this purpose, a three-phase power transformer has been simulated in Maxwell software that is based on finite elements. This three-phase power transformer has been used to simulate different conditions. Then, the results have been used as inputs in MATLAB program to implement the equivalent instantaneous inductance technique. The results show that in the case of inrush current, the equivalent instantaneous inductance has a drastic variation, while it is almost constant in the cases of fault conditions.
M. Heidarzadeh, M. R. Besmi,
Volume 10, Issue 2 (6-2014)
Abstract
Overvoltage distribution along the transformer winding must be uniform to certify the safety of the operation of the power transformer. Influence of the parameters variation on the impulse voltage distribution (IVD) in disk winding transformer is going to be analyzed which hasn’t been analyzed on this type of winding in the previous papers. In this research, a transformer with disk winding and rectangular cross-section is analyzed. Equations for capacitances between winding turns and also equations for capacitances between turns and core are deduced. Noting that the relationships presented are dependent on the parameters of the transformer winding, so with changing these parameters, the capacitances of turn –turn and turn – core and finally the capacitances of total series and parallel of the winding will be changed. The purpose of this paper is to show the effect of the variations of these parameters on the IVD in disk winding of transformer. This paper, will assess how to change the parameters of disk winding in order to achieve a uniform initial IVD along the winding and to reduce the amplitude of impulse voltage fluctuations (AIVF) in winding and which parameters have more effect in making uniform the IVD on the disk winding.
A. Vahedi, A. Baktash,
Volume 11, Issue 1 (3-2015)
Abstract
Recently, tape wound cores due to their excellent magnetic properties, are widely used in different types of transformers. Performance prediction of these transformers needs an accurate model with ability to determine flux distribution within the core and magnetic loss. Spiral structure of tape wound cores affects the flux distribution and always cause complication of analysis. In this paper, a model based on reluctance networks method is presented for analysis of magnetic flux in wound cores. Using this model, distribution of longitudinal and transverse fluxes within the core can be determined. To consider the nonlinearity of the core, a dynamic hysteresis model is included in the presented model. Having flux density in different points of the core, magnetic losses can be calculated. To evaluate the validity of the model, results are compared with 2-D FEM simulations. In addition, a transformer designed for series-resonant converter and simulation results are compared with experimental measurements. Comparisons show accuracy of the model besides simplicity and fast convergence
M. A. Taghikhani, A. Sheikholeslami, Z. Taghikhani,
Volume 11, Issue 2 (6-2015)
Abstract
This paper presents a new method for evaluation and simulation of inrush current in various transformers using operational matrices and Hartley transform. Unlike most of the previous works, time and frequency domain calculations are conducted simultaneously. Mathematical equations are first represented to compute the inrush current based on reiteration and then Hartley transform is used to study harmonic effects in the frequency domain. Being a real valued function and accordingly giving results with the higher speed of calculations are the main features of Hartley transform. The inrush problem is initially solved for single-phase transformers for switching at different angles of the voltage waveform using this method and then the results of harmonic domain are compared with that of Fourier transform. The methodology is also applied to three-phase three-limb transformers since the analysis of their transient behavior is significant owing to the flux coupling interactions in multi-leg core structures. The feasibility and efficacy of the method is illustrated with appropriate circuits and MATLAB code is developed to get the time and frequency domain waveforms with high accuracy. The results are helpful to identify and evaluate inrush current harmonic effects in various transformers and hence the efficiency of the method is verified.
S. Hajiaghasi, K. Abbaszadeh, A. Salemnia,
Volume 15, Issue 1 (3-2019)
Abstract
Interturn fault detection is a challenging issue in power transformer protection. In this paper, interturn faults of distribution transformer are studied and a new online detection method based on vibration analysis is proposed. Transformer electromagnetic forces are analyzed by time stepping finite element (TSFE) modeling of interturn fault. Since the vibration associated with inter-turn faults is caused by electromagnetic forces, axial and radial electromagnetic forces for various interturn faults are studied. Transformer winding vibration under interturn faults is studied through an equivalent mathematical model combined with electromagnetic force analysis. The results show that it is feasible to predict the interturn winding faults of transformer windings with the transformer vibration analysis method. Simulation and experimentation studies are carried out on 20/0.4 kV, 50 kVA distribution transformer. The results confirm the effectiveness of the proposed method.
