In this paper, a transient stability analysis of an 18205 bus Western Electricity Coordinating Council (WECC) system has been carried out when all conventional sources have been replaced with converter interfaced generation (CIG). In this 100% CIG system, the only rotating machines directly connected to the network are wound rotor induction generator wind turbines and induction motor loads. The inertia contribution of these rotating devices is small. With close to zero inertia in the system, the dynamic performance of the system under different contingencies is examined and discussed. The analysis conducted demonstrates that while such a futuristic system can survive certain contingencies, well designed coordinated wide-area converter control action may have to be incorporated to enhance the reliability of the system.