A morphological scheme for the correction of CT saturation waveforms
Tangyu Ji, Qinghua Wu, Wenhu Tang, Lin Jiang · 2011
The saturation of a current transformer (CT) will cause severe distortion in the secondary current. Each fundamental cycle of the secondary current consists of two portions, the unsaturated portion and the saturation. This paper proposes a morphological scheme for the detection of the saturations and an embedding and optimization scheme for the removal of the exponential decaying DC offset and the compensation of the saturations. Two multi-scale morphological filters are designed to detect the occurrence of the fault and the beginnings and ends of the saturations. In order to compensate the saturations, the DC offset needs to be removed first. The removal is performed in the phase space, where the unsaturated portions have a spectacular geometry feature that can instruct the estimation of the parameters of the DC offset. After the offset is removed from the secondary current, the resulting offset-free signal is embedded to the phase space, so that the geometry feature of the unsaturated portions is used to instruct the compensation. This paper presents two simulation cases to demonstrate the performance of the proposed schemes, which show that it is possible to accurately detect the saturations, estimate the DC offset component and reconstruct the secondary current.