Finite element models for the computation of the transient potential and field distribution in the winding system of high voltage power transformers

The knowledge of the potential and field distribution in the winding system of a transformer, during transient excitation is vital to its construction. In this paper the problem of modeling large numbers of winding turns is solved with detailed finite element models. Frequency-dependent phenomena such as skin and proximity effects in the conductors, tan δ losses in the insulation, or the displacement of the magnetic flux in the iron core are considered. The two methods are applied to investigate the transient behavior of a 66 kV distribution transformer and a 420 kV generator transformer using both direct transient analysis and with AC analysis and the application of the FFT. The computed results are compared with measurements to verify the developed methods. AC analyses are performed to obtain the frequencies at which the winding system is most endangered