A NEW CRITERION FOR EARTH FAULT LINE SELECTION BASED ON WAVELET PACKETS IN SMALL CURRENT NEUTRAL GROUNDING SYSTEM

This paper analyses the development of fault line selection, the deficiencies and the advantages of the methods based on wavelet packets and presents a new criterion for earth fault line selection based on wavelet packets. Based on the principle of maximum energy,it selects the special frequency band that has the major characteristics of transient capacitance current.Comparing the polarity of the special frequency band of each line with the polarity of the zero sequence voltage's first half wave,it can detect the fault line. The detecting process with this new criterion is simple and more able to decrease the affects of disturbances. Further more, this new criterion is still effective in the case of two lines in power system. Simulation indicates that on condition of various earth faults, the fault line can be selected based on the criterion more reliably.