Micro-grid is a new concept gained significant attentions due to the increasing distributed energy sources. Several micro-grid test beds in the forms of either hardware or software simulation have been developed around the world. In Taiwan, one 20KVA 3W3Ø micro-grid test bed has been conducted in National Tsing Hua University (NTHU). This micro-grid consists of various fundamental power system components, including two synchronous generators (SG), one fixed speed induction generator (FSIG), and one doubly-fed induction generator (DFIG). In this paper, simulation results on two different scenarios: (a) transition from the grid-connected mode to the islanding mode, and (b) load variation in the islanding mode of the NTHU micro-grid system in distributed real-time simulation platform OPAL-RT are reported. Also, on-site development of the micro-grid system is illustrated.