Simulative Investigation of Saturation in Distribution Transformers at Underfrequency

One potential approach to deal with low-inertia related frequency control problems in the Continental Europe synchronous area could be to follow the example of smaller iso-lated power systems, i.e. to permit greater temporary frequency fluctuations. To evaluate this idea, we must assess the impacts on currently installed grid equipment. In this paper, a distribution transformer model is implemented in the COMSOL Multiphysics simulation environment, based on real data provided by a German manufacturer. In addition to the data sheet information, we consider three alternative common design scenarios. By observing the hysteresis loops and the differential permeability curves derived from them, we investigate if magnetic saturation can occur in the frequency range 40–50 Hz. Furthermore, we determine the frequency-dependent parameters for the single-phase equivalent circuit by performing short-circuit and open-circuit tests. The results show that transformers designed to operate close to the saturation flux density at rated frequency are more likely to become magnetically saturated in the range 40–50 Hz. No influence on the short-circuit parameters is ob-served. The greatest impact is found for the main inductance in the shunt impedance branch. Measurements at real transformers are required to verify the simulation-based results.