This paper analyzes the impact of the transient response characteristics of double-fed induction generators on power-frequency protection from the perspective of phasor extraction. Firstly, it examines the relationship between the transient response of the double-fed induction generator and the rotor-side converter as well as the Crowbar circuit under different fault depths, obtaining the transient response characteristics under various levels of voltage sag. Then, based on the conclusions of the transient response analysis, the paper analyzes the impact of the transient response on AC line differential protection and distance protection under different fault depths from the phasor extraction viewpoint. Scenarios where the protection misoperates are presented, and the reasons for incorrect operations are explained in conjunction with the fault analysis conclusions.