The electrical characteristics of a homogeneous phase and non-grounding short-circuit of double-circuit lines on the same tower in a high voltage power grid are analyzed, and the behavior of the current differential protection is verified through simulation. The possibility that the homogeneous phase and non-grounding short-circuit across the lines are converted to ground faults and phase-to-phase faults is highlighted. Based on the field case, this paper analyzes the risks caused by the homogeneous phase and non-grounding faults to the normal operation of the power grid and the switching operation of maintenance personnel when the operation mode of the 220 kV power system changes. Corresponding preventive measures such as the establishment of a line inspection plan and the promotion of intelligent operation inspection are put forward, and the necessity of improving the quality of transmission line patrols to eliminate, in time, hidden dangers is emphasized. This work is supported by the Natural Science Foundation of Jiangsu Province (No. BK20170672).