In this work a simplified analysis of electrically large multi-room systems using simulations is shown. It is an estimative method which is based on the description of complex systems using electromagnetic topology. An extension to the topology approach made here enables the physical segmentation of electrically large multi-room systems for high frequency estimations by neglecting late time components.Starting from the topology of a multi-room system, the coupling paths from the disturbance source to the room of interest are identified. The classification of the coupling between the different rooms of the system as weak or strong allows its segmentation in electrically smaller subsystems. These subsystems are analyzed independently and the system level estimation is achieved using currents in fictitious dipole antennas or electric fields as calibrating values.The simplified analysis has been applied to several examples and an error evaluation shows a good agreement between results from the simplified analysis and results obtained with full scale analysis. A flow chart is presented which gives guidance in the decision whether to use simplified analysis or full scale analysis on the multi-room system.Advantages in using a simplified analysis include a modular approach as well as a fast estimation of quantities in lower shielding levels. The modular approach allows the reuse of simulation results and the derivation of topology based hardening solutions.This work can be used to achieve a faster vulnerability analysis of complex systems against IEMI threats and parametric analysis of multi-room systems in the design phase.Key points of the doctor's thesis:- Multi-room systems- Electromagnetic topology- Early and late time components of electromagnetic fields- Estimative approach for the analysis of complex systems- Simplified analysis of electrically large systems- Protection against EMC and IEMI threats- Use of numerical field computation- Hardening of complex infrastructures- Reuse of simulation results