Based on the dynamic model of the Doubly-Fed Induction Generator (DFIG) under double dq synchronous reference frames, the analytical expressions of equivalent positive and negative sequence superimposed impedances of the DFIG are derived, and their phase angle characteristics are studied. With the variable impedance angles of DFIG, the sequence currents angle difference between fault location and measurement location is described when a line to ground fault occurs, thus the phase angles of the fault voltage and the compensation voltage referred to the measured voltage are derived. Based on the phase difference between fault voltage and the compensation voltage during internal and external fault, a distance protection scheme based on voltage phase comparison is proposed for the transmission line connecting wind farm with DFIGs. The proposed scheme is validated by the simulation results, which show that it is insensitive to the grounding resistance, the fault location and the operation conditions of the wind farm, and can distinguish the internal and external fault accurately. This work is supported by National Natural Science Foundation of China (No. 51637004).