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Modeling of incomplete-phase operating modes of power autotransformers

V.A. Martynov, A.N. Golubev

Vestnik IGEU, 2017 issue 3, pp. 40—47

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Abstract in English: 

Background: When operating power autotransformers that have become widely used in 110 kV and higher voltage networks, it is often necessary to deal with incomplete-phase modes caused by disconnections of one or two phases in case of short circuits or phase-by-phase repairs. This leads to asymmetry of the voltage of autotransformers, which affects the quality of power supply to consumers, and it is dangerous for the autotransformer itself as incomplete-phase operation may lead to overloading of individual windings. The presence of an electrical connection between high and medium voltages determines the approach to analyzing their operating modes. The theoretical analysis and the general approach to the calculation of asymmetric modes of two-winding transformers have been studied in detail but the asymmetric operating modes of three-winding autotransformers have not been analyzed well yet. Thus, it is quite urgent now to find theoretical approaches to the calculation of asymmetric operating modes of power autotransformers.

Materials and methods: The study is based on the method of symmetric components, as well as the substitution circuit of three-winding autotransformers for currents of different sequences.

Results: An approach has been developed to calculating autotransformer and combined asymmetric operating modes of power autotransformers based on the method of symmetrical components. New mathematical models of the main incomplete-phase modes have been proposed. An example has been given of calculating the combined incomplete-phase mode according to the autotransformer rated values for the next disconnection of the line wires of the middle, lower and higher voltages components.

Conclusion: The proposed model and obtained analytical expressions allow us to determine the currents and voltages of the phase windings of the autotransformer in a variety of asymmetric modes of operation based on a unified approach.

Key words: autotransformer, symmetric component method, design substitution circuit, asymmetric mode, incomplete-phase mode.

References in English: 
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Ключевые слова на русском языке: 
автотрансформатор, метод симметричных составляющих, расчетная схема замещения, несимметричный режим, неполнофазный режим
Ключевые слова на английском языке: 
autotransformer, symmetric component method, design substitution circuit, asymmetric mode, incomplete-phase mode
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