Due to the increasing penetration of distributed generation, storage, electric vehicles and new ICT technologies, distribution networks are evolving towards the Smart Grid paradigm. For this reason, new control strategies, algorithms and technologies need to be tested and validated before their actual field implementation. In this paper we present a novel modular distributed infrastructure, based on real-time simulation, for multi-purpose Smart Grid studies. The different components of the infrastructure are described and the system is applied to a case study based on a real urban district located in northern Italy. The presented infrastructure is shown to be flexible and useful for different and multi-disciplinary Smart Grid studies.