Abstract: When the high resistance ground fault occurs in the line, the fault characteristics are not obvious. At present, it is difficult for the protection device with single terminal electric quantity to realize the reliable and quick operation of the wholeline, and identify the fault.This paper introduces a single-phase high resistance grounding fault of 110 kV transmission line, analyzes the protection action of relevant lines and main transformer after the fault, points out the fault cause. It draws a conclusion that when the high resistance grounding fault is unstable and stable, protection devices may be refused to move, and its selectivity and sensitivity is difficult to meet the requirements.

Key words: high resistance grounding, distance protection, zero sequence protection, override trip