An efficient approach for the numerical integration of a European power system network model is described. The time evolution of the power system is modeled by a system of differential and algebraic equations. In standard numerical time integration methods the most active variables impose the time step for the whole system. We describe an approach, which allows the use of different, local time steps over the variables. The partitioning of the components of the system in different classes of activity is based on the topology of the power system.