Energy generation is stepping on to the integration of more renewable sources as it is environment friendly and poses less ecological impact. Practical feasibility of such technologies has to be studied well before it is implemented on a system. Large scale integration of Renewable Energy Sources (RES) will reduce the total system inertia and can have adverse effects on power system transient stability. The objective of this paper is to find the impact of renewable energy penetration on one of the power system stability indicators called critical clearing time (CCT). The study is carried out on the well known IEEE 9 bus system considering different penetration of type-IV wind turbine generators (WTG). CCT is calculated for different fault locations using Dynamic Security Assessment Tools (DSA Tools) software of Powertech Labs. Furthermore, the correlation between inertia distribution index (IDI) and CCT is also explored. The results shows that the RES can have positive as well as negative impact on CCT. © 2023 IEEE.