As well as other products, „electricity“ has to fulfil certain quality criteria. A degradation of power quality can be a consequence of network disturbances caused by customer installations (harmonics from power electronics, voltage fluctuations from fluctuating loads). Faults (short circuits) in the transmission or distribution grid lead to voltage dips or interruptions (reliability). Research activities of the Institute for Electrical Power Systems include amongst others the measurement and simulation of power quality phenomena. This is for instance the calculation of harmonic grid impedance, the transfer of disturbances through the grid and probabilistic reliability analysis. A further key aspect is the calculation and evaluation of ohmic, inductive and capacitive interference.