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Keywords: self-blast, series puffer (double volume), short line fault interruption, thermal interruption, optimized procedure Current zero measurements are performed for 245 kV-50 kA-60 Hz short line fault (L90) interruption tests with a self-blast interrupting chamber (double volume system; see Fig. 1) which has the interrupting capability up to 245 kV-50 kA-50 Hz L90. Lower L90 interruption capability is observed for longer arcing time although very high pressure rise is obtained. It may be caused by higher blowing temperature and lower blowing density for longer arcing time. New interruption criteria and a optimization method of the chamber design are necessary for the self-blast interrupting chamber to improve L90 interruption capability with it. Blowing pressure is obviously important for L90 interruption capability. In addtion, lower blowing gas density and higher temperature around the current zero may be critical for the self-blast chamber than conventional puffer type chamber. In this paper, average gas density and temperature are optimized in thermal volume to improve L90 capability as a primary stage although direct criterion for L90 should be arc conductance around current zero in the post-arc region. The optimization process for the interrupting chamber is performed with the computing cord which includes one-dimensional fluid dyanamics, arc modeling and kinematic equations. The new chambers are designed at 245 kV-50 kA-60 Hz to improve pressure rise and average gas density in thermal volume for long arcing time. After that, the chamber geometry is modified through two-dimensional fluid dynamics simulation because all parameters of the chambers are not able to decided through only the one-dimensional optimization. 245 kV-50 kA-60 Hz L90 interruptions are performed with the new chamber (model 60). Improvement of L90 interruption capability for model 60 is obviously observed comparing with model50 in Fig. 2. Arc conductace at 200 ns before current zero is distributed Fig. 1. Self-blast chamber configuration (double volume system) from 0.8 upto 1.1 mS in successful cases with model 60 in Fig. 2(a). The suggested optimization method is an efficient tool for the self-blast interrupting chamber design. The criteria for 60 Hz L90 are the pressure rise of 1.81 PU (1.0 PU for 50 Hz L90) and the average temperature of 1100 K in the thermal volume around current zero. Arc conductane around current zero should be the criteion for L90 interruption essentially. However, very sophsticated computing method is neccesary to calculate of it because temperature gradient and time variation in the post arc region around current zero are very steep and electric conductivity is very sensitive to temperature in the post arc. The study of computing methods is required to calculate arc conductance around current zero as a direct criterion for L90 interruption capability with higher accuracy. (a) Arc conductance at 200 ns before current zero (b) Pressure rise in thermal room at current zero Fig. 2. Experimental results for curr...
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