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Current transformers (CTs) may saturate during internal fault, external fault, over excitation, exciting inrush current and other phenomena, which would cause protection relay malfunction or even tripping. As a result, it is vital to mitigate the adverse effects of CT saturation. By analyzing the secondary current waveform, which has abrupt changes where saturation begins and ends, the paper proposes...
The harmonic elements of stator current in induction motors will change under the condition of stator inter-turn short circuit. According to this characteristic, in this paper, a novel technique based on discrete wavelet transform (DWT) is proposed for the identification of induction motor stator inter-turn short circuit. The power systems computer aided design (PSCAD) is employed to simulate the...
This paper presents a novel algorithm for secondary current signal segmentation of saturated current transformer (CT) using three morphological gradient-based detectors. The saturation onset detector is used to monitor the occurrence of saturation and then trigger the positive/negative segmentation detector, which are designed to locate the starting point and the ending point of CT saturation. The...
Sympathetic interaction between transformers would lead to mal-operation of transformer differential protection. Based on the fact that the waveform of internal fault current has the sinusoidal features while the sympathetic inrush has not, a weighted mathematical morphological method is proposed for the identification of sympathetic inrush. In the simulation studies, the identification results have...
This paper presents a directional protection scheme for transmission lines based on directional comparison of the non-period current, which is estimated by a second-order differential algorithm. When the directions of non-periodic current at both sides are the same, the fault is discriminated as internal fault. When the directions are opposite, the fault is discriminated as external fault. A variety...
This paper proposes a novel method to detect the saturation intervals of current transformer (CT) secondary current. The method features the waveform properties of the distorted secondary current, which has abrupt changes where saturation begins and ends. Two algorithms, the improved morphological gradient and the morphological decomposition, are designed to extract the saturation intervals, respectively,...
This paper proposes an approach using weighted mathematical morphology (WMM) to effectively identify inrush current. The identification is based on the feature that the waveform of inrush current is quite different from sinusoid whereas internal fault current is nearly sinusoidal. Compared with the traditional method based on the second harmonic, the proposed approach reduces the data window from...
This paper proposes a novel scheme to detect the saturation of current transformers (CTs) for protection blocking. The scheme modifies the morphological skeleton method and applies it to analyze the shape information of CT secondary current. Afterwards, two indices are introduced to determine the existence of saturation. Simulation studies under a variety of fault conditions have been conducted using...
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