In this paper, we propose a new method for the detection of high impedance faults, which uses the incremental variance of normalized even order ratio measure. Staged fault tests are extensively carried in Korean electric power systems. From the analysis of the staged fault test data, it was found that there exists an intermittent arcing phenomenon in most high impedance faults and the waveformsof this arcing fault current has an unsymmetrical shape in each cycle. From these facts, we present three criteria of an even order power, an even order ratio, and an even order incremental variance criterion for fault detection, all of which are based on the changes of normalized even order harmonic power in fault current. These criteria are compared with each other through the analysis of staged fault data and normal switching event data. By this comparison, it will be shown that the even order incremental variance criterion is superior to the other two criteria and that, with this proposed criterions, high impedance faults can be distinguished from normal switching events including special loads such as electric furnaces and subways. Microprocessor based protective relays, which can detect high impedance faults by using the proposed methods, have been constructed and installed on KEPCO substations and tested during last two years.
The aim of this study is to improve mixing rate of dry sorbent injection technology (DSI). A CFD (Computational Fluid Dynamics) code is used to predict the sorbent dispersion rate, pressure drop and turbulent kinetic energy of mixing particles and gas flow for three different vortex generators, which have been designed for the inside of the duct. After analyzing simulated results, it was shown that a similar trend of change in the dispersion rate in three different vortex generators had taken place and that the dispersion rate curve could reach over 80% by applying the lobed-plate and guide-vane(B) vortex generators. The lowest pressure drop was obtained when a lobed-plate was installed, whereas the highest pressure drop occurred when a guide-vane(A) was installed. The turbulent kinetic energy is nearly always stable when a lobed-plate is applied, but increases very quickly after passing through a guide-vane and then slowly decreases when a guide-vane(B) is applied. The situation for in the case of guide-vane(A) is somewhat more complicated.
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