I. Introduction
The changes in the grid structure can be described as a transition from the proven vertical structure of generation to consumption with a few, but powerful generators (figure 1, left), to a distributed, increasingly amorphous and strongly meshed structure with numerous renewable energy generators which have very different feed-in characteristics (fig. 1 right). Consequently, depending on the local distribution of generators and local grid capacity, there can be an increased line impedance and reduction in short circuit power, which may cause or promote the appearance and mitigation of various disturbances.