A three-stage configuration is commonly used: Stage I: Instantaneous zero-sequence current protection, covering 70%–80% of the line length. So, in this case, to protect the whole line, the setting has to be able to detect fault current above 150 A. This document gives the model setting calculations, line protection r other power system elements like transformer, shunt reactor and bus bar. Protective relays and devices have been developed over 100 years ago to provide “lastline”of defense for the electrical systems. They are intended to quickly identify a fault and isolate it so the balance of the system continue to run under normal conditions.