The paper deals with experimental identification of transformer internal faults, an important factor in reliability and sustainability of power supply systems. Task of identification of transformer internal faults requires increasing sensitivity of relay protection by calculation of components most sensitive to interwire faults from transformer current. In order to study internal faults in transformer, the model in Simulink MATLAB was developed on the basis of transformer constitutive equations. Transformer with short circuited wires was simulated as a multiwinding transformer. We provide the calculation of transformer parameters. Model was applied for analysis of transients in power transformers, such as interwire fault, transformer inrush, and fault in transformer connections. Analysis of power transformer internal faults by means of time-dependent symmetrical components of currents is provided. These symmetrical components were calculated for the first harmonic of current by means of discrimination of firs harmonic by low-pass filter and compensating elements implementing phase shift. Described method allows calculation of symmetrical components during transient and under non-sinusoidal conditions. Simulation results showed the advantage of instantaneous symmetrical components of other direct values. Those components were implemented in relay protection algorithms for identification of internal faults in transformers.
A stator malfunction occurs due to insulation damage, which means that the stator is directly connected to the power supply, and a direct connection is the direct cause of a major accident. For this reason, a lot of research is being done to identify faults. In recent years, studies on Motor Electrical Signature Analysis are being performed, sensorless methods for fault diagnosis of the stator of an induction motor. However, it has problems with it, it has the difficulty in interpreting multi-faults and in detecting an inter-turn short circuit of a stator. This paper suggested a tool that can diagnose 2-turn short circuit, through the relationship between self-inductance and mutual inductance in the synchronous reference frame of a D-Q transformation.
The article considers electrical complexes with power plants of small capacity. The influence of power generation sources on short-circuit current distribution has been investigated. Reduced sensitivity of back-up current protection and dependence of current distribution on power plant capacity are revealed. Recommendations for minimizing false operation of short-circuit protection in networks with distributed power generation are proposed. An algorithm for adaptive current protection, which uses graph theory to determine the stages of selectivity of relay protection based on finding the shortest Dijkstra path and calculation of equivalent resistance in networks with multiple sources of power generation, which provides selec-tivity and sensitivity of current protection when changing the generated power of generators and the structure of the distribution network is pre-sented. The algorithm uses communication lines with a central control unit to monitor the distribution network and update the current triggering of the relay protection in accordance with changes in the structure of the power grid. The proposed system is designed so that it can respond to dynamic changes in the structure of the network and the state of operation of power plants. Simulation modeling in the Matlab/Simulink software package was performed and the results of the algorithm are presented.
This article focuses on studying the influence of additional sources of electricity generation on the traditional distribution grid, which leads to a change in the direction of the power flow in the grid. Consequently, the sensitivity and speed of current protection are not provided due to the dynamic operation of distributed generation sources. This paper considers the effect of distributed generation on the protection of the power grid. A special emphasis is on problems which may occur in the power grid in the presence of distributed generation. The theoretical background of blinding and calculation of the effect is also presented. The studies presented are made by computer modelling in Matlab/Simulink.
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