Successful operation of a power system depends largely on the engineer's ability to provide safe, reliable and economic service to the customer. Advanced simulation technologies provide useful means to the engineer for the design and analysis of the power system, and assisting them in making reasonable decisions. Due to powerful software and advanced real-time simulators, it became possible to simulate the dynamic behavior of very large power systems including HVDC and FACTS, and to verify the performance of these complex systems with the original control and protection equipment in a fast and accurate manner. The simulation covers all stages of development and operation of a power system, such as planning, design, test and also during operation. In this paper, advanced software and real-time power system simulation technologies are presented. With practical examples benefits of the simulation for large power systems are also demonstrated.