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A phase angle comparison method for detection of current-transformer (CT) saturation and stability against mis-operation on heavy external faults in numerical current differential relay is presented in this paper. The proposed directional criterion is based on comparison of line currents phase angle of two sides of the power transformer. Defined criterion can differentiate saturation condition from...
Differential protection relays may false tripping for external faults due to current transformer saturation (CT). This paper presents an adaptive technique for transformer differential protection against saturation of current transformers, based on differential currents. A Wavelet Index (WI) by wavelet Transform has been devised using extracted feature from differential currents due to saturation...
To avoid the needless trip by magnetizing inrush current, the second harmonic component is commonly used for blocking differential relay in power transformers. However, the main problems of the current comparison method are in the very high inrush currents and relatively small fault currents regarding winding short circuits. Also The second harmonic component in fault current is increased in long...
Summary form only given, as follows. This paper presents the development of a wavelet-based scheme, for distinguishing between transformer inrush currents and power system fault currents, which proved to provide a reliable, fast and computationally efficient tool. The operating time of the scheme is less than half power frequency cycle (based on 5 kHz sampling rate). In this work, a wavelet transform...
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