The ice-shedding may induce isolated ground wires temporary grounding during de-icing, which can cause the protective relay of direct current de-icing devices triggered frequently and unnecessarily. After analyzing the circuit of the grounding isolated ground wire, the conclusion can be obtained that the temporary grounding of isolated ground wires leads to the fluctuation of electric quantities. On the basis of above analysis, the permutation entropy is applied to describe the trend of the voltage waveform, which is able to overcome the influence of high frequency harmonics caused by converters. Based on the voltage trend acquired by the permutation entropy, the variance is employed to determine the fault and the disturbance. Then, parameters of the de-icing device in Kunbei substation is utilized for simulation. The simulation results verify the effectiveness of the proposed method, which can be performed to identify the disturbance induced by de-icing and the permanent fault.