The paper presents the simulation results and the feedbacks from users of a real-time simulator coupled to the clone of an actual UNICOS based control system. This simulator have been developed for the large scale cryogenic systems of LHC. In order to respect the real system architecture, the simulator is composed of different simulation tools sharing data through a standard protocol. The modeling of the process makes use of EcosimPro, a commercial simulation software for industrial systems. Within the model each cryogenic component is represented by a set of differential and algebraic equations and the helium properties are taken from a specialized helium library. The control system is simulated with a PLC-simulator running the actual process control logic. These simulation tools are connected to the SCADA system used to operate the cryogenic plant. Thus, the existing control policy and supervision systems can be reused identically in simulation. The work objectives were threefold: first, to provide tools for operators training, second, to check new control strategies before their implementation and third, to improve our knowledge of the behavior of the cryogenic systems.