Wavelet Transform for Processing Power Quality Disturbances
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Research Article Wavelet Transform for Processing Power Quality Disturbances S. Chen and H. Y. Zhu School of Electrical and Electronic Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798 Received 29 April 2006; Revised 25 January 2007; Accepted 17 February 2007 Recommended by Irene Y. H. Gu The emergence of power quality as a topical issue in power systems in the 1990s largely coincides with the huge advancements achieved in the computing technology and information theory. This unsurprisingly has spurred the development of more sophisticated instruments for measuring power quality disturbances and the use of new methods in processing and analyzing the measurements. Fourier theory was the core of many traditional techniques and it is still widely used today. However, it is increasingly being replaced by newer approaches notably wavelet transform and especially in the post-event processing of the time-varying phenomena. This paper reviews the use of wavelet transform approach in processing power quality data. The strengths, limitations, and challenges in employing the methods are discussed with consideration of the needs and expectations when analyzing power quality disturbances. Several examples are given and discussions are made on the various design issues and considerations, which would be useful to those contemplating adopting wavelet transform in power quality applications. A new approach of combining wavelet transform and rank correlation is introduced as an alternative method for identifying capacitor-switching transients. Copyright © 2007 S. Chen and H. Y. Zhu. 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.
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INTRODUCTION
Power quality is an umbrella terminology covering a multitude of voltage disturbances and distortions in power systems [1, 2]. It is often taken as synonymous to voltage quality as electrical equipment is generally designed to operate on voltage supply of certain “quality.” However, “quality” is a subjective matter as it depends very much on the individual requirements and circumstances. Voltage that is considered good for operating water heater may not be adequate for powering computers. In essence, power quality is a compatibility issue between the supply systems and loads [3]. As long as both can coexist without causing any ill effects on each other, the quality can be regarded as good or adequate. Hence, the scope of power quality is often extended to include imperfections in the design of supply system such as unbalanced transmission/distribution lines, poor connections, and inapt groundings. Nonetheless, the majority of disruptions recognized as power quality problems involve electromagnetic phenomena that cause the supply voltage to deviate from its ideal characteristics of constant frequency (50/60 Hz), constant voltage magnitude (nominal values), and completely sinusoidal [1]. These
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