Widerstandsverteilung in Schaltlichtbögen von Selbstblasleistungsschaltern während der Stromnulldurchgangsphase

  • Resistance distribution in switching arcs of self-blast circuit breakers at the current zero phase

Tang, Ming-Chark; Schnettler, Armin (Thesis advisor)

Aachen : Mainz (2010)
Dissertation / PhD Thesis

In: Aachener Beiträge zur Hochspannungstechnik 13
Page(s)/Article-Nr.: III, 109 S. : Ill., graph. Darst.

Zugl.: Aachen, Techn. Hochsch., Diss., 2010

Abstract

SF6 self-blast circuit breakers are widely used as switching elements in electrical power systems. In case of a short-circuit fault the breaker contacts are separated leading to an ignition of an electric arc. Hence, the current flow is carried by the electric arc itself. Due to a cooling of the arc at the current zero phase, the arc can be successfully extinguished. The switching gap is converted from a conductive state to an insulating one. Thus, the development of the gap resistance over time is a measure of this switching process. Up to now, the total resistance value of the switching arc is used for the assessment of the switching performance without considering the spatial distribution of the resistance. In this thesis a measuring arrangement is developed to determine the partial resistance distribution of the switching arc during the current zero phase. This arrangement is adapted to a self-blast circuit breaker model. The physical cooling mechanisms can be evaluated by using an Computational Fluid Dynamics simulation of this process. Due to the high global warming potential of SF6, the replacement by alternative gases in self-blast circuit breakers is gaining importance. Hence, the promising substitute gas CO2 is analysed using this investigation concept and discussed in reference to SF6. Due to the measurements of the spatial distribution of the resistance of the switching arc a more detailed insight into the current zero phase is achieved. In addition, the simulated cooling behaviour can be considered to identify the important physical processes for the arc quenching. Two characteristic areas can be identified. The resistance of the first area is generated by a convective cooling process , while the cooling of the second area is evolved due to a turbulent process. Both are the main cooling processes of the self-blast circuit breaker model using SF6. By using CO2, however, the convective effect becomes the dominating arc quenching process. The total cooling performance of the SF6 circuit breaker is superior to the CO2 circuit breaker leading to a higher total resistance and thereby a better interruption capability. Detailed knowledge of the resistance distribution leads to a better understanding of the processes during the current zero phase. This enables further optimisation of gas circuit breakers.

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