This thesis deals with the electromagnetic compatibility (EMC) problems of distributed electrical networks, especially that caused by lightning to electrified railway. Lightning transients were found to damage important devices that control train movements, causing traffic stoppage and delays. This thesis attempts to develop computational models for identification of parameters influencing the coupling phenomena between those devices and lightning. Some supporting experimental investigations are also carried out. This thesis forms the groundwork on the subject of lightning interaction with the electrified railway networks. Lightning induces transient overvoltages in railway conductor systems such as tracks, overhead wires, and underground cables, either due to direct lightning strike to the system or due to the coupling of electromagnetic fields from remote strikes. Models based on multiconductor transmission line theory were developed for calculating the induced voltages and currents. A transmission line return stroke model, that can predict the remote electromagnetic fields comparable to experimental observations, is also developed. Earlier works on modeling earth return impedances for transient studies in power distribution systems are not readily applicable for railways for lightning transients, in cases of low earth conductivities found in Sweden and for large variation in conductor heights. For the wires above ground, the ground impedance models were modified for wide range of frequencies, soil conductivities and wide spread of conductor heights. Influences of pole insulator flashovers, pole-footing soil ionizations and interconnections between the conductors on the lightning surge propagation are studied. Wave propagation in buried shielded and unshielded cables with ground return is studied. Simplified, valid and computationally efficient ground impedance expressions for buried and on-ground wires are proposed. A model for the coupling phenomena (transfer impedance) through multiple cable shields with multiconductor core is also proposed. Besides, experimental studies on lightning induced transients entering a railway technical house, failure modes of relay and rectifier units used in the train position/signaling applications for lightning transients are performed. A high frequency circuit model for the booster transformer for lightning interaction studies is developed. The simulation models are being converted to user-friendly software for the practicing engineers of the railway industry.

Im Rahmen der Arbeit wird der Begriff Sicherheit aus verschiedenen Blickwinkeln beleuchtet, Randbedingungen aus Theorie und Praxis zielorientiert strukturiert und ein Vorschlag für eine Integration betrieblicher Aspekte in Sicherheitsanalysen dargelegt. Dazu werden zunächst die normativ verankerten Lebenszyklusphasen des Bahnsystems und die darin festgelegten Verantwortlichkeiten vorgestellt. Darauf aufbauend erfolgt die beispielhafte Beschreibung einer neuen Analysemethode in Verfügbarkeits-Sicherheits-Diagrammen für betriebliche Szenarien des Bahnsystems. Die Arbeit endet mit der Vorstellung des Modells zur ganzheitlichen Sicherheitsbetrachtung des Bahnsystems, welches die zuvor gewonnenen Erkenntnisse integriert und die Grundlage für das Zulassungsverfahren von Bahnanlagen mit betrieblichem Sicherheitsnachweis legt. / This thesis deals with the detailed analysis of the term safety from different points of view. The main target of the document is the integration of operational aspects within technical solutions for railway systems. Operational use-cases have been analyzed using the availability-safety-diagram. The document concludes with the introduction of a model for holistic safety-related consideration of railway systems.