Transformer Protection

Abstract

This chapter presents two MM-based schemes for the identification of transformer magnetising inrush. The first scheme detects the inrush current using a morphological decomposition scheme (MDS) to extract the singularity peculiar to the asymmetric inrush waveform, while attenuating other irrelevant features [135]. By quantifying the extracted features, the inrush current is then identified using a set of simple criteria. The second is a multi-resolution decomposition scheme (MRDS), which is developed based on MDS but performs faster than MDS [93]. It decomposes a current signal into multi-resolution levels using synthesis and analysis operators of MM. MRDS is able to discriminate between inrush and internal fault currents even in the case of an inrush that contains a low second harmonic component and an internal fault current that has a high second harmonic component. Simulation studies have been undertaken to evaluate the two schemes based on a three-phase high voltage power transformer operating under different conditions. The test results show that the schemes are able to identify inrush currents reliably and provide an alternative solution for transformer differential protection.