Wind turbine power is a vital source of renewable energy and accounts for major plants in generating electricity in various countries. The aim of this paper is to develop the physical model of three types of wind-turbine induction generators and to investigate their impacts on the frequency in a single-area power system. The generator types are as follows: (i) squirrel cage induction generator (SCIG); (ii) doublyfed induction generator (DFIG) and (iii) brushless doubly-fed induction generator (BDFIG). The analysis scenario is demonstrating the effect of variable wind speeds on the grid frequency under load variations. The simulation results show that BDFIG achieves better performance in comparison with DFIG and SCIG in terms of maintaining the grid frequency.