Güç sistemi harmoniklerinin bilgisayarlı simülasyonu ve ölçümü

Abstract

Güç sisteminde çalışan mühendisler için bilgisayar ile analiz önemli bir araç olarak kullanılmak tadır. Güç sistemindeki bozulmalar ve sorunların değerlendirilmesinde, güç sistemlerinin benzetişimi ve modellenmesi gerekli olur. Devredeki bozulmalar çok kez sistemdeki Uç faz akım ve gerilim dalga çeki 11 erindeki bozulmalar olarak ortaya çıkar. Uluslar arası düzeyde çalışma konusu olan bir bozulma şekli ise, günümüz modern güç sistemlerini olumsuz olarak etkileyen, " Güç Sistemi Harmonikleri " dir. Bu konuda çeşitli ülkelerde belirlenmiş olan uluslar arası sınır değerler Tablo 1.1* de sunulmuştur. Güç sistemindeki AA harmonikleri, sistemi artan bir oranda etkilemekte, tesislerde zarara ve güç kesintilerine neden olmaktadır. Her ne kadar süzgeç devreleri yaygın bir şekilde kullanılmaya başlanmışsada süzgeci eme tesislerinin toplam maliyeti artırması. Statik Var sistemi yada Ark Fırını gibi tesislerde kullanılan süzgeçlerde, maliyet optimizasyonunu gerekli hale getirmiştir. Sorunun en önemli kısmının ise güç sistemindeki harmoni ki er in kuramsal olarak hesaplanmasında bulunduğu görülmektedir. Bu çalışma, zamanla değişen yüklerin ve bunların meydana getirdiği harmoni ki er in incelenmesi amacı ile geliştirilen, bilgisayarlı ölçüm ve benzetişim yöntemlerini içermektedir. Benzetişim sonunda hesaplanan kuramsal sonuçlarla ölçüm sonuçları karşılaştırılmıştır. Ölçüm amacı ile gidilen Mahmut Bey'de Orpaş Ark Fırını Tesislerinde bazı datalar alınmıştır. Hesaplamalarda zaman domeni ve " Hızİı Fourier Dönüşümü " CFFTD bağıntıları kullanılmıştır.

Computer analysis is an important tool for power system engineers. The simulation and modeling of the various power system networks is necessary to help evalute problems and disturbances through practical solutions. An increase in the number, and influences, of nonlinear harmonic producing devices connected to the power system has increased significantly during the past decade. Industrial installations utilizing modern arc furnace technology, power electronic systems have been studied in this thesis. These applications cause non- linearities to appear at the AC terminals of the high power transformers located at the power network sub stations. Due to the duty cycles and load profiles of these applications, the voltage and current wave forms are becoming distorted and more nonsinusoi- dal. Through this thesis work a versatile and high speed computerized measrementand simulation technique has been formulated and implemented. Its capabilities demonstrated for the data acquisition of time-varying, nonlinear loads. A simulation technique based upon frequency and time domain modelling of the network components and harmonik producing devices has been developed for this thesis study. Voltage and Current AC harmonics are penetrating todays power systems at an increaseing rate. The propagation of AC harmonics throughout the power networks produce undesired voltage voltage distrubances, causing damage to equipment and power outages. Computerized measurement and simulation techniquis for the study of power system harmonics are becoming very important analysis tools. Both the suppliers and consumers of electrical energy must improve their understanding of the causes and utilize better analytical techniques for the prediction and solution of harmonic problems. The power system network is primarily described and studied as a complex circuit with linear elements and sources with sinusoidal functions. Usual y the performance conditions of the system define the applicable network model. - vi - The study of harmonic penetration into the power system network, which involves computer analysis and simulation techniques, is one of the main objectives of this work. The prediction and estimation of voltage harmonics, propagation of current harmonics, and waveform distortionCs!» caused by the various categories of nonlinear loads will be addressed. In addition, a new analytical approach and measurement results will be presented. It is the objective of this study to develop alternate analytical and measurement approaches for the determination of AC harmonic penetration into the power system network. As mentioned earlier, distortions in the power system are primarily due to the nonlinear V-I characteristics at the terminals of elements, loads, and sources in the network. Nonlinear loads are classified as devices which produce nonsinusoidal currents at the input side of its terminals. These types of devices are : * Power Electronic switching devices Devi c e Con ver si on Rectifier AC » DC DC Linked Inverter AC » DC - ? AC Cycl ©converter and AC choppers AC ? AC * Magnetic circuits acting in their saturation region > transformers, motors * Arcing elements and systems > mechanical rectifiers C commutator -type motor sD > Arc Furnaces - vii - > gas-type fl orescent lighting systems. Since nonlinear loads and sources are the primary causes for harmonics in the power system, further explanations and accepted interpretations have been identified. The V-I characteristics of passive elements Crezistors, inductors, capasitors? define the classifica tion of whether or not these are linear or nonlinear components in the network. Nonlinear components which have nonlinear V-I characteristics are identified according to the distortions upon the input AC voltage and current waveforms. The following cases that one may come across are listed. Input Waveforms Loads, El ements Harmonic Source Case I : The incoming input waveforms are sinusoidal and later transfer into a non-sinusoidal waveform due to the 1 oads. el ements, or devices connection combination. Case II: The incoming input waveformCs^ are originally non-si nusoi dal. The propagation of harmonic signals throughout a network are dependent upon how the admittances and impedances are effected by the harmonic currents flowing. The equivalent, lumped parameter circuit representation of a power system, therefore, can be modelled by using the YBUS Matrix or ZBUS Matrix approaches. The advantages and/or disadvantages between these two models are not addressed by this research effort. The utilization and., benefits seen by using the YBUS Matrix approach for modelling the systems components and predicting voltage - viii - and current harmonic distortion levels are documented here. Frequency-domain harmonic studies require that the components be modelled as a function of the fundamental frequency and variations in the components characteristics based upon harmonic orders. The YBUS Matrix is used for determining the network admittance values. The constr action of the YBUS and formation of the injected harmonic current vector values form the algorithm to determine the voltage harmonics in the network. Presented here, since -1 C1D bus I I bus I I bus I both balanced and unbalanced case conditions can be analyzed. In the balanced case, the Ybus matrix is simply and the I bus vector is mostly zeroes except at the bus locations where harmonic disturbances are specified. In Chapter 1, harmonic sources, nonliner loads are presented. Chapter 2 included harmonic resonance conditions C serial and parallel resonances). Chapter 3 deals with the modelling and simulation approaches used in this study. Power system component harmonic models, and several types of nonlinear load models have been described. Chapter 4 is mainly concerned with the harmonic measurement system specifications and the requirements considered to be important aspects for taking harmonic measurements of time-varying loads. In Chapter 5, two case studies are presented. An Arc Furnace CORPAŞ A. S. 3 in Istanbul. V-I waveforms are masured and FFT Analysis are studied. Figure S. 1 shows current waveform and FFT Analysis. Figure S. 2 shows voltage waveform and FFT Analysis. The second case studies PETLAS Rubber factory in Kırşehir. To estimate harmonic numder and magnetuid, we modelled the system. On the other hand, for V-I waveforms are data aquired and FFT Analysis are made.