On the Empirical Estimation of Utility Distribution Damping Parameters Using Power Quality Waveform Data
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Research Article On the Empirical Estimation of Utility Distribution Damping Parameters Using Power Quality Waveform Data Kyeon Hur,1 Surya Santoso,1 and Irene Y. H. Gu2 1 Department 2 Department
of Electrical and Computer Engineering, The University of Texas at Austin, Austin, TX 78712, USA of Signals and Systems, Chalmers University of Technology, 412 96 Gothenburg, Sweden
Received 30 April 2006; Revised 18 December 2006; Accepted 24 December 2006 Recommended by M. Reza Iravani This paper describes an efficient yet accurate methodology for estimating system damping. The proposed technique is based on linear dynamic system theory and the Hilbert damping analysis. The proposed technique requires capacitor switching waveforms only. The detected envelope of the intrinsic transient portion of the voltage waveform after capacitor bank energizing and its decay rate along with the damped resonant frequency are used to quantify effective X/R ratio of a system. Thus, the proposed method provides complete knowledge of system impedance characteristics. The estimated system damping can also be used to evaluate the system vulnerability to various PQ disturbances, particularly resonance phenomena, so that a utility may take preventive measures and improve PQ of the system. Copyright © 2007 Kyeon Hur et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
1.
INTRODUCTION
Harmonic resonance in a utility distribution system can occur when the system natural resonant frequency—formed by the overall system inductance and the capacitance of a capacitor bank—is excited by relatively small harmonic currents from nonlinear loads [1]. The system voltage and current may be amplified and highly distorted during the resonance encounter. This scenario is more likely to occur when a capacitor bank is energized in a weak system with little or negligible resistive damping. During a resonance, the voltage drop across the substation transformer and current flowing in the capacitor bank is magnified by Q times. Q is the quality factor of a resonant circuit and is generally represented by XL /R, where XL and R are the reactance and resistance of the distribution system Thevenin equivalent source and substation transformer at the resonant frequency. Note that during a resonance, the magnitude of XL is equal to but opposite in sign to that of XC , the reactance of a capacitor bank. In addition, during a resonance, XL and XC reactances are h and 1/h multiple of their respective fundamental frequency reactance, where h is the harmonic order of the resonant frequency. Due to the highly distorted voltage and current, the impacts of harmonic resonance can be wide ranging, from louder noise to overheating and failure of capacitors and transformers [1, 2].
Based on this background, it is desirable to predict the likelihood of harmonic resonance using system damping parameters such as the Q f
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