Application of Wavelet Packet and S Transforms for Differential Protection of Power Transformer

Noori Taboor, Waad; Ahmed Obed, Adel; Abdul Nabi Alwan, Majed

	Application of Wavelet Packet and S Transforms for Differential Protection of Power Transformer
Journal of Engineering
Article 1, Volume 19, Issue 2, 2013, Pages 264-279
Authors
Waad Noori Taboor; Adel Ahmed Obed; Majed Abdul Nabi Alwan
Abstract
The differential protection of power transformers appears to be more difficult than any type of protection for any other part or element in a power system. Such difficulties arise from the existence of the magnetizing inrush phenomenon. Therefore, it is necessary to recognize between inrush current and the current arise from internal faults. In this paper, two approaches based on wavelet packet transform (WPT) and S-transform (ST) are applied to recognize different types of currents following in the transformer. In WPT approach, the selection of optimal mother wavelet and the optimal number of resolution is carried out using minimum description length (MDL) criteria before taking the decision for the extraction features from the WPT tree. In ST approach, the spectral energy index and the standard deviation (STD) are calculated from the S-matrix obtained by discrete S-transform. The two approaches are tested for generating a trip signal and disconnecting the transformer supply experimentally using 1KVA, 220/110V, 50Hz, three-phase transformer. The experimental results show that the trip signal is initiated faster in WPT approach while the transformer is disconnected from the supply after a delay of 10-15msec in the two approaches due to computer interface and the relay circuit used.
Keywords
differential protection; wavelet packet transform; transform; inrush and fault Currents recognition

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