RTDS (Real Time Digital Simulator) has several benefits. First, current power system simulation tool dose not simulate electromagnetic transient phenomenon, but it is possible using RTDS. Second, off-line electromagnetic transient simulation tools (EMTDC, PS-CAD, etc.) do not simulate real-time analysis, but RTDS is able to do real-time analysis. Third, RTDS is able to simulate related external devices those are protection relays, new developed control devices and power system devices. So many engineers use RTDS in power industry using these advantages of RTDS. KEPCO (Korea Electric Power Corporation) also use RTDS for developing new special protection scheme that is a new developed protection scheme for maintaining voltage stability in metropolitan area using real time synchro phasor data. Voltage stability phenomena of power system are divided three parts by time period. Those are transient, short term and long term voltage stability phenomena. Almost critical voltage stability problems happen in long term time period. Because power system devices and loads those influence voltage stability have long term dynamic characteristic. So if we want correct results of voltage stability analysis, then we have to analyze long term dynamic about voltage stability. Long term dynamic characteristic of voltage stability that is influenced by under voltage tap changer, over excite limiter, dynamic loads and so on. Unfortunately, we had not an analysis environment about long term dynamics for validating new control system. So this paper discusses about modeling and simulation of long term dynamics using RTDS. First, we build well known test system that consists of 2 generators and 11 buses using RTDS. Second, we model dynamic controllers and devices those are under load tap changer, over exciting limiter and dynamic load and we validate those dynamic characteristics. Those influence to long term voltage stability. Lastly, we simulate voltage collapse phenomena during long term time period using test-system include built long term dynamic models when occurring line fault.