Abstract
This paper presents a new methodology for long-term transmission planning over large systems. The developed approach aims at finding the optimal design of a large grid including its modular development plan over a long time horizon. Advanced optimization and simulation methods have been investigated to tackle this very large and complex problem, which includes highly combinatorial aspects and stochastic behaviours of system components, while ensuring some control over the system. Some tools have been implemented and tested on a case study based on the French and Spanish systems. The preliminary results of this study give an estimation of the resources that would be needed for a real study over a system of the size of the whole pan-European network for the period 2020 to 2050. © 2015 IEEE.