In Brazil, the planning of the energy operation of the National Interconnected Power System is currently done through a chain of mathematical models designed to optimise the planning according to criterion of minimisation of the expected value of the total operation`s cost. However, since the 2001-2002 energy supply crisis, there was an intensification in the search for methods of optimization allowing explicit consideration of additional criteria, such as the operative security. In this context, this work proposes a modelling using genetic algorithms that makes possible the consideration of multiple objectives in the optimisation process without compromising the physical representation of the system and its uncertainties. A multicriteria approach to the problem allows that various indicators, like, for instance, annual deficit, which currently are only results of the optimisation, become controllable from its consideration in the optimisation process. The modelling proposal was computationally implemented in language C# using the GAcom library developed by the ICA/PUC-Rio. The performance of the proposed methodology was evaluated through potential National Inter- connected Power System case studies. The results, as well as the benefits seen when using the multicriteria optimisation, are discussed throughout the text.