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A novel line non-unit protection principle based on traveling wave is proposed in the paper, it measures the instantaneous frequency of traveling wave crest at the point of transmission line near the line trap. If the frequency is large than the lower cut off frequency of line trap, internal fault is thus detected. The influence of line trap for the instantaneous frequency is also investigated. Hilbert-Huang Transform (HHT) is used in extracting the special frequency signals. Theoretical analysis and EMTP simulation results show the protection is correction.