Transient stability of wind generation system is evaluated in terms of critical clearing time (CCT) of fault. CCT of a wind generation systemconnected to grid is calculated based on the maximum amount of time that thewind generation system remains connected to grid, without becoming unstable, when the grid is subjected to a fault. In the literature, the wind turbine model has been used for steady state analysis alone, that is, it is used for finding the initial operating mechanical torque output of the turbine. The turbine model is then completely neglected in case of transient stability analysis by assuming constant mechanical torque output for a particular wind speed. This may not be true, as the mechanical torque-speed characteristic of a wind turbine depends not only on the wind speed but also on the slip of the induction generator connected to the wind turbine. This paper explains the necessity of considering the wind turbine model for the transient stability and steady state analysis of grid connected induction generator based wind generation system. A detailed analysis has been done on the effect of various electrical and mechanical factors on CCT determination and the simulation results are presented. © 2013 IEEE.