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Home / 2018 issue 5 / Operational analysis of distance protection on single power supply lines in case of unbalanced short-circuits in the secondary winding of the «wye-delta» phase displacement group transformer

Operational analysis of distance protection on single power supply lines in case of unbalanced short-circuits in the secondary winding of the «wye-delta» phase displacement group transformer

V.A. Shuin, M.S. Al-Homidi, V.V. Mozhzhukhina, T.S. Frolova

Vestnik IGEU, 2018 issue 5, pp. 39—45

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Abstract in English: 

Background. Distance protection is normally used to increase the efficiency of distant backup protection in case of phase-to-phase short circuits in 110–220 kV transmission lines. A host of factors influence the sensitivity of distance protection backup stage in case of unbalanced phase-to-phase short-circuits in the secondary winding of step-down and branch stations, the main ones being the «star-delta» transformation and the transient resistance at the fault site. The currently used methods of estimating the actuation setpoints of distance protection backup stages do not take into account the complex effect of these factors on the resistance value and angle at the protection terminals, which can lead to unintended failures of protection equipment to operate. Therefore, an analysis of the performance features of distance protection backup stages for phase-to-phase unbalanced short-circuits in the secondary winding of «star-delta» transformers is an urgent problem aimed at making the actuation setpoint selection methods more exact.

Materials and methods. To analyze the influence of the «star-triangle» transformation and transient resistance at the fault site in case of unbalanced two-phase and three-phase short circuits, we used simulation by analytical and simulation mathematical models.

Results. An analytical solution has been obtained for the reactive and active components of primary resistance at distance protection terminals in case of unbalanced two-phase and three-phase resistive short circuits in the secondary winding of transformers with the most common «star-delta» winding group. The reliability of this solution was verified on a simulation model in the Simulink simulation system.

Conclusions. The obtained analytical expressions for the active and reactive components of resistance relay measurement in case of unbalanced resistive short-circuits in the secondary winding of «star-delta» transformers allows us to increase the accuracy and sensitivity of the methods of selecting the actuation setpoint of distance protection backup stages with different operating characteristics in single-side power supply transmission lines.

References in English: 

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Key words in Russian: 
ЛЭП высокого напряжения, междуфазные короткие замыкания, дальнее резервирование, дистанционные защиты, трансформация «звезда-треугольник», несимметричные короткие замыкания
Key words in English: 
high-voltage power lines, phase-to-phase short circuits, distant backup protection, distance protection, «wye-delta» transformation, unbalanced short-circuits
The DOI index: 
10.17588/2072-2672.2018.5.039-045
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