Journal Volume 17 Issue 2

Application of Two Dimensional Wavelet Transform for Classification of Power Quality Disturbances

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Nader Mollayi, Hossein Mokhtari

 Identification of voltage and current disturbances is an important task in power system monitoring and protection. In this paper, the application of two-dimensional wavelet transform for characterization of a wide variety range of power quality disturbances is discussed, and a new algo­rithm, based on image processing techniques is proposed for this purpose. A matrix is formed based on a specified number of cycles in such a way that the samples of voltage signal in each cycle form one row of that matrix. This matrix can be regarded as a two dimensional image. A two-dimensional wavelet transform is used to decompose the image into approximation and details, which contain low frequency and high frequency components along the rows and columns, respectively...

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Study on the Low Frequency Transients in Power Transformers and Some Protection-Related Issues

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Mohamed M. Saied

 This paper presents typical results for the non-linear low frequency transients following the energization of power transformers. The three operating conditions of no-load, full-load and internal faults are considered. A direct analytical procedure is applied for solving the corresponding set of differential equations describing the transformers equivalent circuit. The core representation is based on the use of curve fitting applied to their magnetization curves. The results include plots versus time for the supply current, the core flux, the magnetizing current as well as the internal induced voltage. Moreover, graphs for the hysteresis loops relating the instantaneous values of both the excitation current and the core flux are given. An approach is also presented for the numerical determination of the amplitudes of the different harmonics existing in any of these signals utilizing the corresponding equidistant samples...

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