Adaptive setting of digital relay for transmission line protection

The distance relay is the most widely relay used in transmission line protection because it is applicable 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 one that is the most highly influenced by the power system changes. In this regard, this paper describes an approach to minimize the maloperation of the distance relay due to the power system changes through changing protection range of the distance relay into optimal condition in response to the load variation and power system condition. Also malfunction of the distance relay in case of high resistance ground faults could be minimized through modeling the protection range into a quadratic function.