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World Academy of Science, Engineering and Technology 55 2009

Determination of the Characteristics for Ferroresonance Phenomenon in Electric Power Systems
Sezen Yildirim, Tahir Çetin Akinci, Serhat Şeker, and Nazmi Ekren described as the jump to a higher fundamental frequency state, but also it is given with bifurcations to the sub-harmonic, quasi-periodic, and chaotic oscillations in anycircuit containing a nonlinear inductor [4]. This term was first time used by P. Boucherot in 1920 to appellation of oscillations in circuits with nonlinear inductance and capacitance [5]-[8]. In this paper, West Anatolian Electric Power Network of 380kV is modeled and the characteristics due to the ferroresonance behavior are extracted. In this manner, spectral analysis techniques are applied to oneof the phase (phase-R) voltages of the sample power network and satisfied results are obtained to denote the frequency properties. II. SPECTRAL ANALYSIS METHODS Spectral Analysis methods include Short Time Fourier Transform (STFT) and Power Spectral Density (PSD) techniques. A. Short Time Fourier Transform and Spectrogram The short time Fourier transform introduced by Gabor in 1946 is useful inpresenting the time localization of frequency components of signals. The STFT spectrum is obtained by windowing the signal through a fixed dimension window. The signal may be considered approximately stationary in this window. The window dimension is fixed both time and frequency resolutions. To define the STFT, let us consider a signal x(t) with assumption that it is stationary when it is windowedthrough a fixed dimension window g(t), centered at time location τ. The Fourier transform of the windowed signal yields the STFT [9]. +∞ (1) STFT {x(t )} ≡ X (τ , f ) = ∫ x(t ) g (t − τ ) exp[− j 2πft ]dt
−∞

Abstract—Ferroresonance is an electrical phenomenon in
nonlinear character, which frequently occurs in power system due to transmission line faults and single or more-phase switching onthe lines as well as usage of the saturable transformers. In this study, the ferroresonance phenomena are investigated under the modeling of the West Anatolian Electric Power Network of 380 kV in Turkey. The ferroresonance event is observed as a result of removing the loads at the end of the lines. In this sense, two different cases are considered. At first, the switching is applied at 2nd secondand the ferroresonance affects are observed between 2nd and 4th seconds in the voltage variations of the phase-R. Hence the ferroresonance and nonferroresonance parts of the overall data are compared with each others using the Fourier transform techniques to show the ferroresonance affects.

Keywords—Ferroresonance, West Anatolian Electric Power System, Power System Modeling, Switching, SpectralAnalysis. I. INTRODUCTION

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NE of the most serious problems in electrical power systems is related to the existence of over-voltages resulting under a ferroresonant condition. It generally occurs when the system is unbalanced, like switching or the series connections of the capacitors with transformer magnetizing impedance. This situation can result in over-voltages that can cause failuresin transformers, cables, and arresters. The Ferroresonance phenomenon composes to the high voltage levels because of the relative ratios of losses, magnetizing impedance and cable capacitance fall into its more favorable range. Also, the abnormal rates of harmonics and transient or steady-state over-voltages (can often be dangerous )dangerously for most electrical equipments in the power systems.Therefore, in the related literature, the ferroresonance is defined as a general term applied to a wide variety of interactions between capacitors and iron-core inductors that result in unusual voltages and/or currents [1]-[3]. In this sense, the ferroresonance phenomenon is known as a nonlinear phenomenon that cause to over voltages in power systems. The affect of the ferroresonance can not be...