Small-signal stability analysis of power system oscillations is a well-established field within power system analysis, but not much attention has yet been paid to systems with a high penetration of wind turbines (WTs) and with large wind power plants (WPPs). A comprehensive analysis is presented, which assesses the impact of full-load converter interfaced WTs on power system small-signal stability. The study is based on a seven-generator network with lightly damped inter-area modes. A detailed WT model with all grid relevant control functions is used in the study. The WT is, furthermore, equipped with a park-level WPP voltage controller and comparisons are presented. The WT model for this work is a validated dynamic model of the 3.6 MW Siemens wind power WT. The study is based on modal analysis which is complemented with the time-domain simulations on the non-linear system.