Adaptive Setting of Digital Relay for Transmission Line Protection

Distance relay is the most widely used in transmission line protection because it is useful not only as main protection but also as back-up protection. However, the protection range of the distance relay is always fixed in the unchangeable operating range while the power system varies, and therefore, the distance relay is the most highly influenced by power system changes. In this regard, this paper describes an approach to minimize the mal-operation of the distance relay due to the power system changes through changing the protection range of the distance relay into an optimal condition in response to load variation and power system conditions. Also mal-function of the distance relay in case of high resistance ground faults can be minimized through modeling the protection range into quadratic function.