In this thesis a modelling approach for transformer topology models based on special measurements is presented. The special measurements are used for the parameterisation of the hysteresis model. The special AC saturation test or the DC hysteresis measurement is carried out via the transformer terminals. The DC hysteresis measurement can also be performed on already installed transformers in the field using a portable transformer tester. The measurement data from the special measurements are used in the following for the parameterisation of the hysteresis model within the framework of parameter optimisation. The Jiles-Atherton (JA) or a non-linear capacitor is used as the hysteresis model. The presented approach was tested with two transformer topology models using the inductance-reluctance and capacitance-permeance analogy. The parameterised models were validated with the open circuit test.In addition to the presented power transformer modelling approach, a transformer neutral point measurement system was further developed to measure and observe GICs in the transmission system. The existing five measurement systems were updated and an additional three measurement systems were installed in the transmission grid.weiterlesen