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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...
Transformer electromagnetic design closely related to leakage magnetic field[1][2]. Increasing with the capacity of transformer, the rise of temperature will affect the normal operation of the transformer. This paper will use the existing commercial software and instrument to leakage magnetic field simulation, calculation of temperature rise and the corresponding experiment. In order to better optimize...
This paper proposes an application framework to reinforce the existing process for ontology-based transformer fault diagnosis with formal probabilistic semantics using the Bayesian Network. This framework allows users to quantify a certain fault with Bayesian Network, based on the knowledge embedded in a transformer ontology regarding relationships of faults and their features such as causes, symptoms...
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...
Dissolved gas analysis (DGA) has proved to be one of the most useful techniques to detect the incipient faults of power transformers. This paper presents a novel method named multi-kernel support vector classifier (MKSVC), to analyze the DGA for fault diagnosis of transformers. Different from the conventional support vector machine (SVM), MKSVC uses a combined kernel formed through a linear combination...
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...
This paper presents a novel method for current transformer (CT) saturation detection and compensation. In the method, CT saturation characteristics are represented by a partial nonlinear regression model. The parameters of this model can be estimated rapidly and accurately using both unsaturated and saturated sections of the waveform of a secondary fault current, even in a heavy saturation scenario,...
This paper presents a simplified distributed parameter model for minor winding deformation fault analysis of power transformers on the basis of frequency response analysis (FRA). The FRA data of an experimental transformer is employed as a reference trace, which are compared with the simulations of the simplified distributed parameter model concerning minor winding deformation faults. In order to...
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