New method for fault components extraction and fault phases selection

This paper proposes a new method to extract fault components in small current neutral grounding system. Both short-time fault components and long-time ones can be gotten by this method. Fault components are firstly introduced into definite time and over-current protective relays and it can significantly improve the performance of time-delay protection. Based on this method a scheme to accurately calculate system impedance is put forward. In order to overcome the low sensitivity of the fault phase selection method adopting fault components of phase current difference, a high sensitivity phase selection method based on the fault components of phase current sum is presented.