The integration of variable uncertain renewable generation, together with the increased consumers active role and energy-constraint resources (energy efficiency, demand response and energy storage), result in the need for a more flexible grid infrastructure with adequate ramping capability. In particular, the Italian power system is characterized by a large amount of renewable generation localized in the South, while the major load centers are in North and Center-North market zones: in this context, a key role is played by an efficient generation portfolio and a strong grid infrastructure, in order to guarantee flexibility and stability of the system. In this paper, the flexibility assessment is performed by evaluating a set of indicators related to system and network performances, for the Centre South - Centre North section. The aim is to assess the ability of the transmission system in keeping up the desired standard of security and reliability in the two different conditions, in the presence and in the absence of the planned HVDC link Villanova-Fano.