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Abstract: Overhead lines, high voltage cable systems and substations are important elements of the high voltage network. More and more close combinations of these elements are used in urban networks. This leads to new transient situations and a more complex transient behaviour in case of lightning or switching events. Additionally the requirements of a constant power supply ask for new efforts to predict impacts caused by interruptions. Based on this fact this paper deals with investigations to evaluate the transient behaviour of a close combined 400kV urban system. Numerical tools are basically a modern method to estimate transient stresses, help to optimize the insulation coordination and can simulate various circuit states. Thus, temporary faults can be reduced or avoided at all. One of the major aspect of this work is the close connection of an overhead line, a cable section and a substation related to the 400kV system. Additionally attention was paid to the transformers and the secondary side of the system, a 110-kV urban distribution network. A number of calculations were carried out to get an overview of the transient stress caused by lightning or switching in numerous network nodes of the substation. Of additional interest have been different circuit states at the 400kV gas insulated substations (GIS) and the transient behaviour at the arrestors. Amplitudes and the energy consumption at the arrestors were taken into account. These actual investigations were carried out to get useful information''s about the transient stress in this important Viennese 400kV substation, which was officially put into operation in May 2006. As an output of these investigations the results influence the strategy in running the network. [Copyright &y& Elsevier]