Mathematical morphology based inrush blocking scheme in transformer protection

摘要

Transformer inrush currents during energization result in maloperation of transformer differential protection, due to the flow of magnetizing current only on the primary or the source side of the transformer. Presence of dead angles i.e. dead period in magnetizing inrush, is one of the classic characteristics of inrush current, resulting in an asymmetric peaky nonsinusoidal waveform. This paper presents a method of identifying this distortion in waveform using a mathematical morphological scheme, which is a signal and image processing technique. The weighted mathematical morphological (WMM) gradient operator is applied to the current signal and waveform correlation analysis have been performed on the resultant waveforms. This data is assessed using certain criteria to detect inrush and fault currents. The propositioned algorithm was simulated and tested under different test scenarios using MATLAB. Moreover, a comparative analysis was carried out with a conventional relay. This method is not reliant on the transformer models and is precise and swift in its output.