HIGH IMPEDANCE FAULT-DETECTION UTILIZING INCREMENTAL VARIANCE OF NORMALIZED EVEN ORDER HARMONIC POWER

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 waveforms of 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.