Abstract: The distance protection has advantageous of flexible operation mode, reliable action and stable performance due to the performance of distance protection is influenced by electric system operation mode slightly, so distance protection is applied in lines of various voltage classes. But there are some problems needing attention in distance protection, and several malfunction faults are the problems occurred frequently. The several malfunction faults were analyzed, and the concrete measures to prevent malfunction were given in this paper.

Key words: microcomputer protection, distance protection, impedance characteristic, overreach, late-reshutting acceleration, inrush current