The computation of the effects of harmonic currents on transformers using a coupled electromagnetic-thermal FEM approach

The use of coupled electromagnetic-thermal finite element methods to estimate the thermal impact of power system harmonics on transformers is illustrated. At first, the magnetic modelling of transformers is outlined with attention for the core, windings and the external source or loads. Particular attention is paid to the foil windings. The loss computation and the thermal modelling is discussed. The calculation of the global coupled problem using a mixed frequency and time domain approach, for the steady-state as well as for a long-term transient evolution, is treated. These methods are applied to a 30 kVA distribution transformer. The results are compared with measurements. A derating procedure based on the simulated hot spot temperature is presented