A power system is composed of various components such as generators, transformers, transmission lines, switching devices and loads. They have their mathematical model and graphical representation. Sometimes, a power system’s change of topology occurs due to events like short circuits, lightning striking a transformer, or a reconfiguration of the transmission system. In this thesis, a new way of simulating large scale power systems is presented from the modeling point of view. In the literature, a lot of modeling methods and mathematical tools are available to tackle this subject. However, this thesis mainly focuses on the time domain simulation of large scale power systems - and in particular, transients which appear after a change of topology. A change of topology in electrical networks impact time domain simulations on two levels. The first impact is that it is necessary to update or re-compute the set of equations. The computation time of this action on the topology can be significant - especially for large scale power systems. The second impact of this change of topology is the transient that will occur. Usually, this change will impose to numerically compute fast oscillations in currents and voltages until they reach a new steady state...@en