The final part of the circuit is the tripping circuit which may be either AC/DC. They act as the first line of defense by detecting and isolating faults or abnormal conditions on power lines to prevent damage to equipment and ensure the safe and reliable operation of the network. In this guide, we will explore the different types of line protection relays commonly used in. The protected zone is the part of the network in which faults cause the protection function to operate. Definite time delay means that the protection operate time dose not change or depend on the. With line differential protection, the zone of protection is defined by the location of the current transformers (CTs) monitoring the currents at each end of the line.