Fundamentals of Distance Protection

In this paper we have reviewed some basic principles of distance protection. This includes fundamentals of measuring distance to fault based on electrical signals from one end of the circuit; the principles of amplitude and phase comparators to implement a distance relay; and various technologies used to build distance relays. A number of application aspects have been discussed including shaping of the impedance characteristic, the impact of fault resistance, different methods of polarizing distance functions, the need for phase selection, switchable vs. non-switchable schemes, distance function looking through power transformers or series compensated lines.