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The transformers are an integral part of the power system. In transformers, the main consequence of harmonic currents is an increase in losses, mainly in windings, because of the deformation of the leakage fields. Higher losses mean that more heat is generated in the transformer so that the operating temperature increases, leading to deterioration of the insulation and a potential reduction in lifetime. Due to the non-linear loads, the transformers are much affected by the distorted currents and supply voltages which largely reduce its efficiency due to overheating. Nonlinear loads cause harmonics to flow in the power lines which can overload wiring and many desktops, personal computers present nonlinear loads to the AC supply because of their power supplies design (capacitor input power supply). In power transformers, the main consequence of harmonic currents is an increase in losses, mainly in windings, because of the deformation of the leakage fields. Higher losses mean that more heat is generated in the transformer so that the operating temperature increases, leading to deterioration of the insulation and a potential reduction in lifetime. As a result, it is necessary to reduce the maximum power load on the transformer, a practice referred to as de-rating, or to take extra care in the design of the transformer to reduce these losses. To estimate the de-rating of the transformer, the load's K Factor may be used. Thus analysing this problem and reducing the losses of the transformer has become a major area of research in today's scenario. This report includes the effects of non-sinusoidal supply voltage on the transformer excitation current and the core losses which includes eddy current and hysteresis losses. INTRODUCTION Events over the last several years have focused attention on certain types of loads on the electrical system that results in power quality problems for the user and utility alike. Equipment which has become common place in most facilities including computer power supplies, solid state lighting ballasts, adjustable speed drives (ASDs), and uninterruptible power supplies (UPSs) are examples of non-linear loads. It is forecast that before the end of the century, half of all electrical devices will operate with a nonlinear current draw. These nonlinear loads are the cause of current harmonics. Non-linear loads are loads in which the current waveform does not have a linear relationship with the voltage waveform. Non-linear loads generate voltage and current harmonics which can have adverse effects on equipment that are used to deliver electrical energy such as transformers, feeders, circuit breakers, which are subjected to higher heating losses due to harmonic currents consumed by non-linear loads. The discontinuous, Harmonic currents cause overheating of electrical distribution system wiring, transformer overheating and shortened transformer service life. Electrical fires resulting from distribution system wiring and transformer overheating were rare occurrences until harmonic currents became a problem. Transformers which provide power into an industrial environment are subject to higher heating losses due to harmonic generating sources (non-linear loads) to which they are connected. The major source of harmonic currents is the switch mode power supply found in most desktop computers, terminals, data processors and other office equipment is a good example of a non-linear load. The switching action of the computer power supply results in distortion of the current waveform [2]. Harmonics are produced by the diode-capacitor input section of power supplies. The diode-capacitor section rectifies the AC input power into the DC voltage used by the internal circuits. The personal computer uses DC voltage internally to power the various circuits and boards that make up the computer. The circuit of the power supply only draws current from the AC line during the peaks of the voltage waveform, thereby charging a capacitor to the Peak of the line voltage. The DC equipment requirements are fed from this capacitor and, as a result, the current waveform becomes distorted. The increasing usage of non-linear loads on electrical power systems is causing greater concern for the possible loss of transformer life. So, Manufacturers of distribution transformers have developed a rating system called K Factor, a design which is capable of withstanding the effects of harmonic load currents. The amount of harmonics produced by a given load is represented by the term "K" factor. The larger the "K" factor, the more harmonics are present [3].
Master of Engineering Thesis GTU India, 2013
Transformers are most essential and consequential elements in electricity transmission and distribution. Therefore, in order to have a transformer working at optimum level, many researches and tests have been being performed. The goal of these tests and researches is reducing the amount of losses and extends lifetime of a transformer. During the conversion of the electricity in a transformer, some losses occur. These losses occur at windings and core of the transformer and they turn into heat. Transformers are widely used in almost all industrial application and is must for any basic industrial setup. As every machine, when running under normal condition is subjected to different kind of faults, the solution of which has to be carried out in advance to achieve best possible efficiency before actual use of the transformer. In the initial step, we go through the numerous papers which has worked on different parameters of transformer using FEM analysis. And the results of the same will be used in determining modelling of a transformer in the software using Finite Element approach. This method helps to develop accurate models of the machine under both healthy and faulty conditions. It also accurately calculates magnetic fields and related transformer design parameters for different types of transformers with completed geometry, which increases possibilities of improving the design during the planning stage (Before actual use of transformer). Using this method, analysis of Internal Insulation Design Improvements, Accurate Prediction and Minimization of No Load Loss, Internal Stresses at high frequency and faults like leakage reactance, internal winding stress etc. will be carried out. The analysis with the fault condition listed above will be simulated in FEM based software and the result will be compared with that of the transformer under healthy condition, which helps a great in knowing the worst possible condition under which transformer can be used. The design of the transformer carried out by the above method will be helpful to the industry in the sense that maximum possible efficiency and accurate calculation of magnetic field and stresses on windings can be achieved under worst possible conditions.
This paper briefly describe the design of the transformer with the given KVA rating, the frequency at which it is working, magnetic flux density and the current density. The analysis of the transformer of the transformer was performed and the characteristic plot of efficiency, core losses, ohmic losses and core losses are analyzed how the transformer works with vary in frequency, primary voltage and KVA rating of the transformer. This has been generated using the matlab.
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Accurate simulation and loss estimation in power transformers are crucial for both the design phase and useful life of the transformer. In this study, core losses and magnetic flux densities of a power transformer for different frequency values are calculated. For this, ANSYS @ MAXWELL software based on the Finite Elements Method (SEY) and the 3D simulation model of the transformer were examined. The results obtained from simulations performed at 50 Hz and 60 Hz frequencies were compared with theoretical and experimental results. It has been observed that increasing the frequency causes increased heat and loss in the core of the transformer.
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