Abstract The expected increase of intermittent electricity production imposed by renewable energy sources in Northern Europe poses rising challenges to the operation of the power system. The Nordic hydro based power system, particularly the Norwegian, is in a favourable position to provide necessary production flexibility to the Continental European power system. For this provision sufficient transfer capacity is required. In order to assess the provision of power production flexibility, a detailed operation optimisation model is necessary. Moreover, investments in the power system have to be set in relation to the economic outcome of the system operation. As a simultaneous system optimisation is not possible due to the size of the operation optimisation model, a two-step investment algorithm containing an iteration loop is proposed in this paper. The proposed investment algorithm identifies profitable investments based on the results of the operation optimisation model, where the effect of the investments on the power market outcome is taken into account through the iterative process. The presented investment algorithm is used for a transmission expansion analysis for a 2030 scenario of the Northern European power system. The results for the simulation of the scenario and the transmission expansion analysis are presented as well.